FR3060558A1 - PROCESS FOR PRODUCING BUTADIENE COMPRISING IMPROVED SEPARATION STEPS - Google Patents

Abstract

The invention relates to the use of a bulkhead column for separating a feedstock comprising ethanol, acetaldehyde, butadiene and water and a process for the production of butadiene from ethanol implementing separation steps comprising partition columns.

Description

Holder (s): IFP ENERGIES NOUVELLES Public establishment, COMPAGNIE GENERALE DES ETABLISSEMENTS MICHELIN Limited partnership with shares, MICHELIN RECHERCHE ET TECHNIQUE S.A. Société anonyme.

Agent (s): IFP ENERGIES NOUVELLES.

Pty PROCESS FOR PRODUCING BUTADIENE COMPRISING IMPROVED SEPARATION STEPS.

The invention relates to the use of a partition column for separating a feed comprising ethanol, acetaldehyde, butadiene and water as well as a process for producing butadiene from ethanol using implementing separation steps comprising partition columns.

FR 3 060 558 - A1

TECHNICAL FIELD OF THE INVENTION

The invention relates to a process for the production of butadiene from ethanol, operating in two reaction stages: a first reaction stage producing acetaldehyde, and a second stage producing butadiene from a mixture of ethanol and acetaldehyde.

PRIOR ART

The process for producing 1,3-butadiene from ethanol has a limited pass conversion rate. The unconsumed reagent (s) must therefore pass several times in a sequence of unitary separation operations as well as in the reactor (s) before being converted into 1,3butadiene. Each loss in unit operations results in an overall loss within the process which quickly becomes unacceptable from an economic point of view.

In addition, the catalyst used to produce 1,3-butadiene generates numerous by-products in small quantities:

• hydrocarbons comprising from 1 to 16 carbon atoms, saturated or unsaturated, or even aromatic, • oxygenated products (such as alcohols, phenols, aldehydes, eetones, acids, esters, ethers, acetals, ...), saturated or unsaturated, even aromatic.

Some of these by-products are generated in significant quantities, in particular diethyl ether or ethyl acetate.

Furthermore, the reaction for converting ethanol or an ethanol / acetaldehyde mixture to 1,3butadiene produces water (approximately 2 moles of water per mole of 1,3-butadiene), which must be eliminated from the process.

Finally, hydrogen is produced in large quantities in the first reaction zone for converting ethanol into acetaldehyde (approximately 1 mole of hydrogen per mole of acetaldehyde) as well as, in a weaker manner, in the second reaction zone of conversion of the ethanol / acetaldehyde mixture to 1.3 butadiene. This hydrogen can be burned to be used as thermal energy, or purified to be sold.

Part of these by-products are gaseous under the operating conditions of the process downstream of the reactors at the level of the separators and are problematic for the purification of 1,3-butadiene. Another part of these by-products is liquid under the operating conditions of the process downstream of the reactors at the level of the separators. It is not easy to remove these liquid by-products from ethanol and unconverted acetaldehyde before recycling them to the catalytic reactor producing 1,3-butadiene. In particular, a large proportion (around 70% by weight) of liquid by-products have an intermediate volatility between that of ethanol and acetaldehyde. A fraction of these liquid by-products with volatility intermediate between that of ethanol and acetaldehyde can be eliminated by simple distillation, but with a loss of ethanol and acetaldehyde. This loss of reagents makes the process unattractive from an economic point of view.

Other byproducts are generated in minute quantities. These thousands of hydrocarbon and oxygenated compounds produced in the reaction sections are called "brown oils". These "brown oils" have the particularity of being soluble in ethanol, but insoluble in water. They can clog and clog equipment wherever they are not diluted with a large amount of ethanol.

In addition, ethanol and acetaldehyde can react together to form diethylacetal and water. The reaction for the formation of diethylacetal is balanced: the reaction towards diethylacetal is favored by a low temperature, and the reverse reaction by a high temperature. The kinetics are obviously favored by a high temperature, but also by the presence of acid, in particular acetic acid which is one of the impurities produced in the second reactor. This is why the diethylacetal returning to the reactor will be transformed again into acetaldehyde and ethanol. On the other hand, the production of diethylacetal can occur within unitary separation operations which are used to purify and recycle ethanol and acetaldehyde. Depending on the sequence of unit operations that is implemented, this diethylacetal can be eliminated with the by-products, which then represents an indirect loss in ethanol and acetaldehyde. This loss of reagents, if it occurred, would decrease the economic benefit of the process.

Finally, a significant part of the liquid by-products is unstable (olefins, aldehydes, ...), and reacts under the conditions of temperature and pressure of the unitary separation operations which are used to purify and recycle ethanol and l acetaldehyde. These reactions generate heavier byproducts which can precipitate and thus foul the various equipment.

In the CARBIDE process for the production of 1,3-butadiene in two stages, presented in the book "Synthetic rubber", chapter 4 (WJ Toussaint and J. Lee Marah), a liquid effluent containing ethanol and acetaldehyde not converted , the water produced by the reaction and introduced into the process to purify the gaseous effluents, as well as the numerous liquid by-products, is treated by a sequence of three columns to be distilled. Lateral racking, followed by partial washing and recycling were planned, and even under these conditions, the operation was often interrupted to wash the unit before restarting.

French patent FR 3,026,100 presents a solution by washing with hydrocarbons and backwashing with water to remove a large part of the impurities before distilling the residual mixture in two columns for recycling to the two reactors. A disadvantage of this method is that during the washing / backwashing operation precipitation can occur, which would then lead to the formation of a deposit on the washing column, which can be troublesome for the operation. The residual distillation water, normally used for backwashing, would also keep part of this deposit. By using a solvent other than hydrocarbons, this deposit could be avoided, but this solvent is more viscous, and would require a higher operating temperature which makes the presence of acetaldehyde, very volatile, annoying.

In addition, the presence of diethylacetal formed by the reaction of ethanol with acetaldehyde causes losses, because this compound is partially extracted by hydrocarbons.

Another problem with the process is the very large number of columns, which does not facilitate operation and start-up, and the large amount of energy required, both in the reaction sections and in the separation sections, resulting in a high processing cost.

The object of this patent is to overcome these drawbacks by an arrangement of the different process, reducing the risk of product loss and fouling, reducing the number of separation steps, and reducing the energy required for the purification of different compounds.

OBJECT AND INTEREST OF THE INVENTION

An advantage of the process according to the invention, or of the use of a partition column according to the invention, is to prevent, or at least greatly limit the formation of diethylacetal, by effectively separating the acetaldehyde from ethanol, so that the joint residence time of these two compounds is as short as possible.

The Applicant has also identified an arrangement of unit operations making it possible to separate ethanol and acetaldehyde very early on, which makes it possible to treat separately and in a specific manner the sections comprising these compounds.

In particular, the Applicant has discovered that judicious use of partition columns in steps D2) of first purification of butadiene and E3) of ethanol treatment not only makes it possible to improve the overall yield of the process, in particular by reducing the loss of reagents, but also to reduce its energy consumption while reducing the number of necessary equipment and the operational problems linked to fouling.

Dividing wall columns are described in many patents such as US patent 5,914,012.

DETAILED DESCRIPTION OF THE INVENTION

The invention relates to the use of a partition column for separating a feed comprising butadiene, ethanol, acetaldehyde and water into a raw butadiene effluent at the top comprising more than 90% by weight of butadiene, a raw acetaldehyde effluent as a side draw-off and a raw ethanol effluent at the bottom, said column also being supplied by a flow of water, said partition of the partition column partitioning a central section of the column into two compartments, the central compartment in which the supply is carried out being called the inlet compartment, the central compartment from which the raw acetaldehyde effluent is withdrawn being called the withdrawal compartment and the upper and lower parts of the column not comprising a partition being called respectively compartment head and bottom compartment, said inlet compartment comprising between 8 and 15 theo trays risks, advantageously between 10 and 12, said withdrawal compartment comprises between 8 and 15 theoretical plates, advantageously between 10 and 12, said head compartment comprising from 5 to 20 theoretical plates, advantageously from 10 to 15 and said bottom compartment comprising between 5 and 10 theoretical platforms, advantageously between 6 and 10.

The supply to said partition column advantageously comprises from 20 to 30% of butadiene, from 50 to 60% of ethanol, from 3 to 8% of acetaldehyde and of water, the percentages being molar percentages.

A special device known to those skilled in the art distributes the liquid from the head compartment between the inlet and withdrawal compartments. Advantageously, between 40 and 70 mol% of the liquid coming from the head compartment is directed towards the inlet compartment, preferably between 50 and 60% and very preferentially between 55 and 60%, the residual fraction feeding the racking compartment.

A special device known to those skilled in the art distributes the gas from the bottom compartment between the inlet and withdrawal compartments. Advantageously, between 50 and 80 mol% of the gas coming from the bottom compartment is directed towards the inlet compartment, preferably between 60 and 70%, and very preferably between 65 and 70%, the residual fraction feeding the withdrawal compartment.

Said supply to said partition column is supplied to a tray located in the central third of said inlet compartment. Thus, if for example the entry compartment comprises 9 theoretical stages, said mixture is supplied between the plates 4 and 6.

Said flow of water supplying said partition column is supplied to a tray located in the upper third of said inlet compartment.

The head compartment receives the gas phases from the inlet and withdrawal compartments, which are mixed and brought into contact with the liquid in the head compartment tray located immediately above the partition.

No feeding is carried out in the racking compartment. The configuration of the partition column according to the invention makes it possible to form a stomach for the concentration of acetaldehyde in the withdrawal compartment, so that the raw acetaldehyde effluent withdrawn comprises more than 70 mol% of acetaldehyde.

In addition, the configuration according to the invention makes it possible to considerably reduce the concentration of acetaldehyde in the bottom compartment of said column and to have only traces of this compound in the reboiler. In the configuration according to the invention, the small amount of diethylacetal produced upstream of the process by reaction of ethanol and acetaldehyde in the various separation operations at low temperature is found in the bottom of the column compartment and in the reboiler, with a residence time of 8 to 10 minutes, at a higher temperature, and without acetaldehyde. It will therefore be able to redecompose into ethanol and acetaldehyde. The latter, lighter, then rises in the column to be withdrawn in the raw acetaldehyde effluent.

Advantageously, a water flow corresponding to 15 to 20 mol% of the flow of butadiene withdrawn at the head of said column is injected at the head of said partition column. This flow of water reduces the amount of acetaldehyde present in the crude butadiene effluent.

The invention also relates to a process for the production of butadiene from an ethanol feedstock comprising at least 80% by weight of ethanol comprising at least:

A) a step for converting ethanol into acetaldehyde comprising at least:

a reaction section fed at least with a fraction of the ethanol-rich effluent from step E3), operated at a pressure between 0.1 and 1.0 MPa and at a temperature between 200 and 500 ° C. presence of a catalyst, and a separation section making it possible to separate the effluent from said reaction section into at least one hydrogen effluent and one ethanol / acetaldehyde effluent;

B) a butadiene conversion stage comprising at least:

a reaction section fed at least with a fraction of said ethanol / acetaldehyde effluent from step A), with a washing effluent from step C1), with a fraction of the acetaldehyde-rich effluent from step E1), operated in the presence of a catalyst, at a temperature between 300 and 400 ° C, and at a pressure between 0.1 and 1.0 MPa, the feed rates being adjusted so that the ratio ethanol / acetaldehyde molar at the inlet of said reaction section is between 1 and 5, and a separation section for separating the effluent from said reaction section into at least one gaseous effluent and one liquid effluent;

C1) a hydrogen treatment step comprising at least:

a compression section compressing said hydrogen effluent from step A) at a pressure between 0.1 and 1.0 MPa, and a gas-liquid washing section supplied at a temperature between 25 and 60 ° C by said hydrogen effluent from the compression section, at a temperature between 15 ° C and -30 ° C by a fraction of said ethanol effluentrich from step E3), and by a fraction of said ethanol / acetaldehyde effluent from step A), and producing at least one washing effluent and one purified hydrogen effluent;

D1) a butadiene extraction step comprising at least:

a compression section compressing said gaseous effluent from step B) at a pressure between 0.1 and 1.0 MPa, a gas-liquid washing section comprising a washing column supplied at the head at a temperature between 20 and -20 ° C. with an ethanol lux consisting of said ethanol feedstock of the process and / or of a fraction of the effluent rich in ethanol coming from step E3) and at the bottom by said gaseous effluent coming from step B ) compressed and cooled, and producing at least one effluent by-product gas and one butadiene washing effluent;

D2) a step of first purification of butadiene comprising at least:

a distillation section comprising a partition column supplied at least with the liquid effluent from said step B) mixed with the butadiene washing effluent from step D1) and by the backwashing water effluent from from step E1) and producing a crude butadiene effluent, a crude acetaldehyde effluent and a crude ethanol effluent; a gas-liquid washing section fed at the bottom with said raw butadiene effluent and at the head with a flow of water, and producing at the head a pre-purified butadiene effluent and at the bottom with a waste water effluent;

D3) a subsequent butadiene purification step, fed at least with said pre-purified butadiene effluent from said step D2), and producing at least one purified butadiene effluent;

E1) a step of washing the acetaldehyde supplied by the raw acetaldehyde effluent from step D2) and by a fraction of the wastewater effluent from step D2), and producing a counter-water effluent washing, an effluent rich in acetaldehyde and a diethyl ether effluent;

E2) an effluent treatment step, fed at least with the raw ethanol effluent from step D2), and with a fraction of the water-rich effluent from step E3), and producing at least one ethanol raffinate, a light brown oil effluent and a heavy brown oil effluent;

E3) a step for separating the ethanol comprising a distillation section comprising a partition column supplied at least with the ethanol raffinate from step E2), and producing at least one effluent rich in ethanol, an effluent rich in water and a dirty water effluent;

F) a step of washing with water, supplied with the gaseous by-product effluent from step D1), as well as by a fraction of the water-rich effluent from said step E3) and producing at least an alcoholic water effluent.

Charge

The ethanol feedstock used in the process according to the invention can come from any origin, fossil, plant or animal, and in particular from processes for the production of ethanol from plant resources. Said charge comprises at least 80% by weight of ethanol, preferably at least 90% by weight, and preferably at least 93% by weight. Very preferably, said ethanol charge meets the specifications for fuel ethanol EN 15376.

Step A) of converting ethanol to acetaldehyde

The process according to the invention comprises a step A) of converting ethanol into acetaldehyde comprising at least:

a reaction section fed at least with a fraction of the ethanol-rich effluent from step E3), said fraction preferably constituting at least 10% of the flow rate of said ethanol-rich effluent from step E3), and advantageously with at least a fraction of said ethanol feed, operated at a pressure between 0.1 and 1.0 MPa and at a temperature between 200 and 500 ° C in the presence of a catalyst, and

- A separation section for separating the effluent from said reaction section into at least one hydrogen effluent and one ethanol / acetaldehyde effluent.

Under operating conditions, said hydrogen effluent is in gaseous form and said ethanol / acetaldehyde effluent is in liquid form.

Said reaction section makes it possible to convert ethanol into acetaldehyde in the presence of a catalyst preferably consisting of a mixture of chromium oxide and copper oxide, or of any other suitable catalyst. These catalysts are well known to those skilled in the art.

Said reaction section is operated at a pressure between 0.1 and 1.0 MPa, preferably between 0.1 and 0.5 MPa, preferably between 0.1 and 0.3 MPa, and at a temperature between 200 and 500 ° C, preferably between 250 and 300 ° C.

The conversion of ethanol is between 20 and 40%, with a selectivity between 85 and 100% towards acetaldehyde, preferably between 90 and 95% towards acetaldehyde.

The effluent from said reaction section also includes by-products such as crotonaldehyde, butyraldehyde, diethylacetal, ethyl acetate and acetic acid.

Said separation section implements gas-liquid separation means known to those skilled in the art. Preferably, a gas-liquid separator operated at a pressure between 0.1 and 0.3 MPa and a temperature between 25 and 60 ° C. will be used.

Step B) conversion to butadiene

The method according to the invention comprises a step B) of conversion to butadiene comprising at least:

a reaction section fed at least with a fraction of said ethanol / acetaldehyde effluent from step A), with a washing effluent from step C1), and with a fraction of the acetaldehyde-rich effluent from l 'step E1), operated in the presence of a catalyst, at a temperature between 300 and 400 ° C, and at a complete pressure between 0.1 and 1.0 MPa, the feed rates being adjusted so that the ethanol / acetaldehyde molar ratio at the inlet of said reaction section is between 1 and 5, and

- A separation section for separating the effluent from said reaction section into at least one gaseous effluent and one liquid effluent.

The flow rate of the various feeds to the reaction section of said step B) is adjusted so that the ethanol to acetaldehyde molar ratio at the inlet of said reaction section is between 1 and 5, preferably between 2 and 4 so again more preferred between 2.3 and 3.6.

Said reaction section makes it possible to convert part of the ethanol / acetaldehyde mixture into at least butadiene. The selectivity of the transformation of the ethanol / acetaldehyde mixture is preferably greater than 60%, preferably more than 70%, very preferably more than 80%. By selectivity is meant the molar ratio of the flow of butadiene in the effluent from said reaction section to the flow of ethanol and acetaldehyde consumed in said reaction section. The conversion of the conversion of the ethanol / acetaldehyde mixture is preferably greater than 20%, preferably more than 30%, more preferably more than 40%. By conversion is meant the molar ratio of the flow rate of ethanol and acetaldehyde in the effluent from said reaction section to the flow rate of ethanol and acetaldehyde in the feed to said reaction section. Said reaction section is operated in the presence of a catalyst, advantageously a catalyst supported on silica chosen from the group consisting of catalysts comprising tantalum, zirconium or columbium oxide, preferably comprising 2% of tantalum oxide ( see for example Corson, Jones, Welling, Hincbley, Stahly, Ind. Eng Chem. 1950, 42, 2, 359373). Said reaction section is operated at a temperature between 300 and 400 ° C, preferably between 320 and 370 ° C and at a pressure between 0.1 and 1.0 MPa, preferably between 0.1 and 0.5 MPa, preferably between 0.1 and 0.3 MPa.

Preferably, approximately 65 to 90% of the acetaldehyde is converted in said reaction section as well as approximately 20 to 60% of the ethanol. The effluent from said reaction section therefore also comprises ethanol and acetaldehyde. Many impurities can be produced with butadiene, including ethylene, propylene, diethyl ether (DEE), ethyl acetate, butanol, hexanol, butenes, pentenes, pentadienes, hexènes, et hexadiènes.

Said reaction section being supplied with a fraction of the effluent rich in acetaldehyde from step E1), the ethanol to acetaldehyde ratio at the inlet to this section is adjusted by controlling the fraction of the effluent rich in ethanol coming from said step E3) feeding step A), and therefore producing acetaldehyde. Indeed, the remaining fraction of the ethanol-rich effluent from said step E3) feeds step C1) of hydrogen treatment and forms, after washing the hydrogen effluent, said washing effluent from said step C1) which feeds said step B). However, this washing effluent from said step C1) contains very little acetaldehyde. The control of the ethanol to acetaldehyde ratio at the inlet of said reaction section is therefore easy with the process according to the invention.

The butadiene conversion reaction being carried out at high temperature, a practice known to a person skilled in the art consists in heating the feed to said reaction section with the effluent from this section. However, such an exchange, commonly called charge / effluent exchange, does not allow the feed to said reaction section to be preheated to a temperature above about 100 ° C. Indeed, the condensate temperature of the effluent from said reaction section is between 90 and 110 ° C. The greater part of the heat necessary for heating said supply must therefore be supplied by utilities external to the process.

It is therefore particularly advantageous to set up a heat pump between the effluent and the supply to said reaction section. In this particular arrangement, a refrigerant is vaporized by exchange with the effluent from said reaction section, compressed and then at least partially condensed by heat exchange with the supply to said reaction section. The at least partially condensed refrigerant is then completely condensed and then expanded before being vaporized again during the exchange with the effluent from said reaction section. Said refrigerant is advantageously a mixture of hydrocarbons, very advantageously at least a mixture of hydrocarbons with 3, 4 or 5 carbon atoms, and very preferably a mixture of 40 to 50 mol% of n-butane, of 40 at 50 mol% of i-butane, and from 0 to 20 mol% of npentene or pentane.

Said separation section implements gas-liquid separation means known to those skilled in the art. Preferably, a gas-liquid separator operated at a pressure between 0.1 and 0.3 MPa and a temperature between 25 and 60 ° C. will be used.

Step C1) of hydrogen treatment

The method according to the invention comprises a step C1) of hydrogen treatment comprising at least:

a compression section compressing said hydrogen effluent from step A) at a pressure of between 0.1 and 1.0 MPa, and

a gas-liquid washing section supplied at a temperature between 25 and 60 ° C with said hydrogen effluent from the compression section, at a temperature between 15 ° C and -30 ° C with a fraction of said effluent rich in âhanol from step E3), and by a fraction of said ethanol / acetaldehyde effluent from step A), and producing at least one washing effluent and one purified hydrogen effluent.

Preferably, said step C1) is not fed by any other flow.

Said fraction of said ethanol / acetaldehyde effluent from step A) is between 0 and 100%. The use of a fraction of said ethanol / acetaldehyde effluent makes it possible to reduce the flow rate of the fraction of said ethanol-rich effluent obtained from said step E3).

Said step C1) makes it possible to obtain a very pure purified hydrogen effluent, that is to say comprising at least 90 mol% of hydrogen, preferably 99 mol% of hydrogen, preferably 99.8 mol% of hydrogen. This purity is adjusted by the flow rates of the fractions of the ethanol-rich effluent and of the ethanol / acetaldehyde effluent. The purified hydrogen effluent also includes traces of water and ethanol. This step also makes it possible to recover the ethanol and acetaldehyde included in the hydrogen effluent obtained from said step A), thus allowing their recycling and maximizing the overall yield of the process.

The hydrogen effluent from step A) is compressed in a compression section at a pressure between 0.1 and 1.0 MPa, advantageously between 0.1 and 0.7 MPa, and preferably between 0, 4 and 0.68 MPa. The effect of this compression is on the one hand to decrease the volume flow of gas, and on the other hand to improve the efficiency of the downstream washing.

The compressed hydrogen effluent is then cooled to a temperature between 25 and 60 ° C, preferably between 30 ° C and 40 ° C, then fed into the washing column of the washing section in which it is brought into contact with said fraction of the ethanol effluent from step E3) and said fraction of the ethanol / acetaldehyde effluent from step A), said fractions being fed respectively at the top and at an intermediate point of said washing column. These two fractions are each cooled to a temperature between 15 ° C and -30 ° C, preferably between 0 ° C and -15 ° C before being fed into the said washing column. Advantageously, the ethanol-rich effluent from step E3) will be supplied at a temperature lower than that of said fraction of the ethanol / acetaldehyde effluent from step A), thus creating a thermal gradient between the head and the bottom and limiting solvent losses in the purified hydrogen effluent. The gas-liquid washing column of the washing section is provided with trays or loose or structured packing.

The presence of a large amount of ethanol relative to the water in said washing section makes it possible to operate at low temperatures without the risk of forming hydrates in this column. The low temperature of the washing liquids and the temperature gradient between the head and the bottom make it possible to obtain a very good recovery of the acetaldehyde present in the compressed hydrogen effluent, and a very good purity of the purified hydrogen effluent, withdrawn at the head of said washing section. Thus, the loss of acetaldehyde in the purified hydrogen effluent is zero. In addition, the loss of ethanol in purified hydrogen is very low due to the low temperature of the ethanol introduced at the top of the washing section, which is authorized by the absence of formation of hydrates.

Step D1) extraction of butadiene

The method according to the invention comprises a step D1) of extraction of butadiene comprising at least:

a compression section compressing said gaseous effluent from step B) at a pressure between 0.1 and 1.0 MPa;

a gas-liquid washing section comprising a washing column supplied at the head at a temperature between 20 and -20 ° C. by an ethanol stream consisting of said ethanol feedstock of the process and / or of a fraction of the effluent rich in ethanol from step E3) and at the bottom with said gaseous effluent from step B) compressed and cooled, and producing at least one gaseous byproduct effluent and one butadiene washing effluent.

The gaseous effluent from step B) is compressed in said compression section at a pressure between 0.1 and 1.0 MPa, preferably between 0.1 and 0.7 MPa, and preferably between 0, 2 and 0.5 MPa. The effect of this compression is on the one hand to decrease the volume flow of gas, and on the other hand to improve the efficiency of the downstream washing. Preferably, the compressed gaseous effluent is then cooled to a temperature between 25 and 60 ° C, preferably between 30 ° C and 40 ° C.

Said ethanol stream supplying the gas-liquid washing section of step D1) preferably comprises at least 80% by weight of ethanol, preferably at least 90% by weight, and preferably at least 93% by weight. Said ethanol stream feeding step D1) may contain methanol, water, ethyl acetate, butanol and hexanol. Preferably, said ethanol stream supplying step D1) comprises less than 10% by weight of acetaldehyde, preferably less than 5% by weight, and preferably less than 1% by weight. Preferably, said ethanol stream supplying step D1) comprises less than 20% by weight of water, preferably less than 5% by weight, preferably less than 1% by weight.

In a preferred arrangement, said ethanol stream supplying step D1) consists of said ethanol feedstock of the process. An advantage of this arrangement is that said charge is free from the reaction byproducts formed in steps A) and B) and which can be concentrated by recycling. In particular, this ethanol charge does not contain acetaldehyde, or only in trace amounts.

In another preferred arrangement, said ethanol stream consists of a fraction of the ethanol effluent from step E3) of separation of ethanol.

The use of an ethanol stream containing little or no acetaldehyde minimizes the entrainment of acetaldehyde in said effluent by-product gas withdrawn at the top of said gas-liquid washing section reducing the losses in overall process yield, thus than the wash water flow required in step F).

Said ethanol stream supplying step D1) is cooled before being fed to the head of said gas-liquid washing column of the washing section at a temperature between 20 and -20 ° C, preferably between 15 ° C and 5 ° C. The advantage of cooling said ethanol stream is to improve the performance of the washing operation by minimizing the entrainment of ethanol and acetaldehyde in said effluent by-product gas. Thus, all of the butadiene present in the gaseous effluent from step B) compressed and cooled is slaughtered, and the gaseous by-product effluent withdrawn at the top of said gas-liquid washing section is free of butadiene.

The minimization of the entrainment of acetaldehyde in said effluent by-product gas makes it possible, incidentally, to significantly reduce the water flow rate required in step F) of washing with water the by-product gases, including the objective is to recover the ethanol and any traces of acetaldehyde entrained in the effluent by-product gas withdrawn at the head of the ethanol washing section of step D1).

The butadiene washing effluent withdrawn from the bottom of said gas-liquid washing section of step D1) as well as the liquid effluent from step B) feed the step of first purification of butadiene D2).

Step D2) of first purification of butadiene

The method according to the invention comprises a step D2) of first purification of the butadiene comprising at least:

a distillation section comprising a partition column supplied at least with the liquid effluent from said step B) mixed with the butadiene washing effluent from step D1) and by the backwashing water effluent from from step E1) and producing a crude butadiene effluent, a crude acetaldehyde effluent and a crude ethanol effluent;

a gas-liquid washing section fed at the bottom with said raw butadiene effluent and at the head with a flow of water, and producing at the head a pre-purified butadiene effluent and at the bottom with a waste water effluent;

Preferably, said water flow is a flow of water of external origin to the process.

Said distillation section comprises a partition column fed at least by the liquid effluent from said step B) and by the washing butadiene effluent from step D1) and producing a raw butadiene effluent at the head comprising more than 90 % by weight of butadiene, a crude acetaldehyde effluent as lateral withdrawal and a crude ethanol effluent at the bottom.

Said partition partitions a central section of the column into two compartments. The central compartment in which the power is supplied is called the entry compartment. The central compartment from which the raw acetaldehyde effluent is withdrawn is called the withdrawal compartment. The upper and lower parts of the column not comprising a partition are called respectively the head compartment and the bottom compartment.

A special device known to those skilled in the art distributes the liquid from the head compartment between the inlet and withdrawal compartments. Advantageously, between 40 and 70 mol% of the liquid coming from the head compartment is directed towards the inlet compartment, preferably between 50 and 60% and very preferentially between 55 and 60%, the residual fraction feeding the racking compartment.

A special device known to those skilled in the art distributes the gas from the bottom compartment between the inlet and withdrawal compartments. Advantageously, between 50 and 80 mol% of the gas coming from the bottom compartment is directed towards the inlet compartment, preferably between 60 and 70%, and very preferably between 65 and 70%, the residual fraction feeding the withdrawal compartment.

The entry compartment comprises between 8 and 15 theoretical plates, advantageously between 10 and 12. The racking compartment comprises between 8 and 15 theoretical plates, advantageously between 10 and 12. The bottom compartment comprises between 5 and 10 theoretical plates, advantageously between 6 and 10.

The mixture of the liquid effluent from said step B) and the butadiene washing effluent from step D1) is fed to a tray located in the central third of said inlet compartment. Thus, if for example the entry compartment comprises 9 theoretical stages, said mixture is supplied between the plates 4 and 6.

The backwashing water effluent is fed to a tray located in the upper third of said inlet compartment.

The head compartment comprises from 5 to 20 theoretical plates, advantageously from 10 to 15. This compartment receives the gas phases from the inlet and withdrawal compartments, which are mixed and brought into contact with the liquid in the tray of the compartment. head located immediately above the partition.

No feeding is carried out in the racking compartment. The configuration of the partition column according to the invention makes it possible to form an acetaldehyde concentration stomach in the withdrawal compartment, such that the raw acetaldehyde effluent withdrawn comprises more than 70 mol% of acetaldehyde.

In addition, the configuration according to the invention makes it possible to considerably reduce the concentration of acetaldehyde in the bottom compartment of said column and to have only traces of this compound in the reboiler. In the configuration according to the invention, the small amount of diethylacetal produced upstream of the process by reaction of ethanol and acetaldehyde in the various separation operations at low temperature is found in the bottom of the column compartment and in the reboiler, with a residence time of 8 to 10 minutes, at a higher temperature, and without acetaldehyde. It will therefore be able to redecompose into ethanol and acetaldehyde. The latter, lighter, then rises in the column to be withdrawn in the raw acetaldehyde effluent.

Advantageously, a water flow corresponding to 15 to 20 mol% of the flow of butadiene withdrawn at the head of said column is injected at the head of said partition column. This water flow makes it possible to reduce the amount of acetaldehyde present in the crude butadiene effluent and therefore to relieve the gas-liquid washing section of said step D2).

The crude butadiene effluent from the distillation section comprises the majority of the butadiene, but still contains many impurities, including a large amount of acetaldehyde which forms an azeotrope with butadiene and therefore cannot be completely removed by distillation. Thus, the flow rate of said water flow in the gas-liquid washing section is adjusted to obtain the desired specification for acetaldehyde in the pre-purified butadiene effluent.

Said water stream is cooled to a temperature below 25 ° C, preferably below 20 ° C had to feed the gas-liquid washing section so as to wash with a reduced amount of water. The supply temperature of said water flow is chosen so as not to form hydrates with butadiene and the light hydrocarbons still present in the crude butadiene effluent. Said gas-liquid washing section is operated at a pressure making it possible to ensure that there is no condensation of the butadiene and that it remains in the gas form. The operating pressure of this section is between 0.1 and 1 MPa, and preferably between 0.2 and 0.3 MPa. The gaseous effluent from said gas-liquid washing section constitutes the pre-purified butadiene effluent while the water effluent from said gas-liquid washing section constitutes the waste water effluent.

The wastewater effluent contains acetaldehyde and a little butadiene, and can be sent to the bulkhead column in section D2) at the head compartment, at step E2) for effluent treatment, or towards step E1) of washing the acetaldehyde.

Step D3) subsequent purification of butadiene

The method according to the invention comprises a step D3) subsequent purification of the butadiene fed at least by said pre-purified butadiene effluent from said step D2), and producing at least one purified butadiene effluent.

Step D3) makes it possible to purify the butadiene at a very high level of purity (more than 99.5% by weight, preferably more than 99.8% by weight, and very preferably more than 99.9% by weight), while limiting the losses of product by separating the impurities which have not or partially been removed during step D1), and D2).

Said pre-purified butadiene effluent comprises at least 70% by weight, preferably at least 80% by weight of butadiene as well as impurities, due in particular to the degradation of the selectivity to butadiene in the reaction section, among which there are traces of oxygenated impurities such as acetaldehyde, diethyl ether and water, and at most 15% by weight of C ₄ impurities of the butene and butane type, hydrocarbons comprising at least 5 carbon atoms (C5 + hydrocarbons) as well as light gases, in particular hydrogen, ethane, ethylene, propane, propylene.

Said step D3) can be carried out by any means known to the skilled person. It advantageously comprises a separation section by extractive distillation in the presence of a polar solvent, miscible in the liquid phase with said effluent butadiene pre-purified under the operating conditions of said separation section, having a lower volatility than the 1,3butadiene compounds , butene-2 and butynes, so as to remain in the liquid phase in said separation section, but which can be separated from these compounds by distillation. Said solvent is advantageously chosen from the group consisting of dimethylformamide (DMF), Nmethylpyrrolidone, acetonitrile and their mixtures. Said extractive distillation separation section produces a light distillate and a butadiene residue.

Said extractive distillation separation section is operated such that said butadiene residue comprises at least 95% by weight, advantageously at least 98% by weight and preferably at least 99% by weight of the butadiene included in said effluent butadiene pre-purified. Said section is also operated such that the amount of butene-1 in said butadiene residue represents at most 0.5% of the weight of butadiene included in said residue. The operation is carried out by adjusting the ratio of solvent flow rate to flow rate of pre-purified butadiene effluent, as well as the reflux rate of extractive distillation, as known to those skilled in the art.

In the particular arrangement where step D3) comprises a section for separation by extractive distillation, said step D3) comprises a section for separation of the solvent by distillation fed by said butadiene residue from said section for separation by extractive distillation and separating into head a toad butadiene distillate and at the bottom a solvent residue.

The distillation is advantageously a conventional distillation known to those skilled in the art, operated in such a way that said solvent residue comprises less than 1% by weight of butadiene, advantageously no longer comprises butadiene, and that said topped butadiene distillate comprises less than 0, 5% by weight of solvent, advantageously no longer comprises solvent.

Said distillation is advantageously carried out at the lowest possible pressure to limit the exposure of the butadiene-rich streams to high temperatures where polymerization or decomposition could take place. Said distillation is advantageously carried out at a head temperature of less than 60 ° C, preferably less than 50 ° C, and at a head pressure of less than 0.5 MPa, preferably less than 0.4 MPa.

Said solvent residue then advantageously feeds said separation section by extractive distillation as a stream comprising a solvent, advantageously in admixture with a make-up of solvent.

Said step D3) advantageously comprises a final distillation section supplied with the topped butadiene distillate from the solvent separation section, separating at the head a purified butadiene effluent and at the bottom a butene residue.

This section eliminates heavy impurities, and in particular traces of cis-2-butenes, as well as residual butynes-1 and 1,2-butadiene and diethyl ether possibly present in the topped butadiene distillate.

Said purified butadiene effluent comprises at least 99.5% by weight of butadiene. The yield of stage D3), defined as the flow of butadiene in the purified butadiene effluent over the flow of butadiene in the pre-purified butadiene effluent supplying stage D3) is at least equal to 95% by weight, of preferably 98%, preferably greater than 99% by weight

Step E1) washing the acetaldehyde

The method according to the invention comprises a step E1) of washing the acetaldehyde supplied with the raw acetaldehyde effluent from step D2) and by a fraction of the waste water effluent from step D2), and producing a backwashing water effluent, an acetaldehyde-rich effluent and a diethyl ether effluent.

Said step advantageously comprises a washing section and a backwashing section.

Said washing section is supplied with said crude acetaldehyde effluent and with an effluent comprising a solvent, advantageously an petroleum cut comprising no sulfur. Said solvent makes it possible to capture the least hydrophilic elements, such as diethyl ether, ethyl acetate, hexene and other hydrocarbons present in said effluent acetaldehyde.

The washed raw acetaldehyde effluent constitutes the effluent rich in acetaldehyde. Said effluent rich in acetaldehyde from step E1) is then recycled in the rest of the process according to the invention.

The effluent comprising a solvent charged with impurities then feeds the backwashing section in which it is brought into contact with a fraction of the wastewater effluent from step D2). This backwashing section makes it possible to recover from the aqueous phase the most water-soluble products such as acetaldehyde entrained with the solvent. The water from the backwashing constitutes the backwashing water effluent and feeds step D2) while the effluent comprising a solvent, washed in the backwashing section, feeds a solvent regeneration section.

Said solvent regeneration section, supplied with the effluent comprising a solvent, washed in the backwashing section, makes it possible, on the one hand, to separate an effluent comprising a recycled solvent towards the washing section of said step E1) and d on the other hand, an impurity effluent comprising in particular diethyl ether, ethyl acetate, hexene and other light impurities constituting the diethyl ether effluent. This section can be implemented by distillation or by any other means known to those skilled in the art.

The diethylacetal present in the raw acetaldehyde effluent is partially extracted in the washing section, and recovered in the aqueous phase in the backwashing section, isolated from ethanol and acetaldehyde. It will therefore decompose again into ethanol and acetaldehyde, which are returned to the partition column via the backwashing water effluent, thus greatly minimizing the yield losses due to the formation of diethylacetal compared to the prior art. .

Effluent treatment step E2)

The method according to the invention comprises a step E2) for treating the effluents, supplied at least with the raw ethanol effluent from step D2) and by a fraction of the water-rich effluent from step E3 ), and producing at least one ethanol raffinate, one light brown oil effluent and one heavy brown oil effluent;

The crude ethanol effluent from step D2) mainly comprises ethanol, water but also impurities such as ethyl acetate and brown oils as defined above. These impurities can accumulate if they are sent back to reaction stages A) and B) within the ethanol-rich effluent from stage E3) and if they are only partially converted in the reaction sections of the stages A) and B). Step E2) makes it possible to recover part of these impurities before step E3) of separation of the ethanol, which makes it possible to avoid the demixing of the brown oils within the columns to be distilled, to simplify the distillation scheme , and to obtain at the end of step E3) an effluent rich in ethanol and an effluent rich in water of greater purity compared to the prior art.

Preferably, said step E2) comprises at least one washing / backwashing section, a distillation section for light brown oils, and a distillation section for heavy brown oils.

Said preferential washing / backwashing section is supplied at an intermediate point by said raw ethanol effluent from step D2).

Said preferred washing / backwashing section is supplied at the bottom with a hydrocarbon effluent and at the head with a fraction of the water-rich effluent from step E3), which does not include ethanol and acetaldehyde and by a fraction of the wastewater effluent from step D2) which contains traces of acetaldehyde. The hydrocarbon effluent and the fraction of the water-rich effluent from step E3) are supplied at a temperature preferably between 10 and 70 ° C, preferably between 45 and 55 ° C. Said washing / backwashing section produces, at the top, a washing hydrocarbon extract charged with a fraction of impurities and brown oils, and at the bottom said ethanol raffinate.

Said washing / backwashing section is preferably operated at a pressure between 0.1 and 0.5 MPa, preferably between 0.2 and 0.4 MPa. Preferably, the fraction of the water-rich effluent from step E3) and the wastewater effluent from step D2) to perform the backwashing is adjusted so that the water content in the ethanol raffinate is greater than 30% by weight, preferably greater than 40% by weight.

Washing the raw ethanol effluent from step D2) with a hydrocarbon effluent causes certain impurities such as brown oils.

The backwash column section with the water-rich effluent from step E3) and from step D2) collects ethanol which could have been lost by entrainment in the solvent.

Said hydrocarbon effluent may contain saturated and / or unsaturated and / or aromatic hydrocarbons, preferably saturated hydrocarbons. Said hydrocarbon effluent advantageously consists of a mixture of hydrocarbons having between 6 and 40 carbon atoms, preferably between 10 and 20 carbon atoms. In a nonlimiting manner, said hydrocarbon effluent can be a diesel or desulphurized kerosene cut or else a cut of hydrocarbons produced by a Fischer-Tropsh type unit.

In one embodiment, the contact between the two liquid phases in said washing / backwashing section is carried out in a liquid-liquid extractor. Different modes of contact can be considered. Mention may be made, without limitation, of a packed column, a pulsed column, or else a stirred compartmentalized column. In another embodiment, the contact between the two liquid phases in said washing / backwashing section is made within a membrane contactor, or a cascade of membrane contactors. This method of contact is particularly well suited to the system implemented. Indeed, water-ethanolhydrocarbon mixtures are known to form stable emulsions, which can be problematic in a liquid-liquid extractor. The membrane contactor generates a large contact area, promoting the transfer of impurities and oils to the hydrocarbon phase, without generating an emulsion.

Said hydrocarbon wash extract feeds said light brown oil distillation section, which produces as distillate said light brown oil effluent, and a hydrocarbon residue comprising the heavy fraction of brown oils.

Said light brown oil effluent is composed of impurities produced by reaction step B), mainly ethyl acetate and traces of crotonaldehyde and butanal, but also of the light fraction of brown oils, composed of impurities in smaller quantities. This effluent can be burned to provide part of the heat required for the hot oil circuit or the process steam boilers.

Said hydrocarbon residue contains mainly the hydrocarbons used for washing, but also the heaviest fraction of brown oils. To avoid the accumulation of brown oils by recycling the hydrocarbon effluent to the liquid-liquid extractor, a fraction of said hydrocarbon residue is treated in said heavy oil distillation section, consisting of a distillation column, which produces a hydrocarbon distillate composed mainly of hydrocarbons with still some traces of brown oils and, as a residue, said effluent heavy brown oils comprising more than 80%, preferably more than 85% of hydrocarbons as well as the brown oils heavier. The fraction of said hydrocarbon effluent sent to said oil distillation section is between 5 and 30% of the total flow rate of said hydrocarbon residue, and preferably between 10 and 20%. The hydrocarbon distillate is mixed with the fraction of the hydrocarbon residue which has not been treated in said heavy oil distillation section in order to form the hydrocarbon effluent feeding said washing / backwashing section.

The heavy brown oil effluent, which preferably represents between 0.1 and 20% of the charge of said heavy oil distillation section, preferably between 0.3 and 5%, can be burnt to provide part of the heat required to the hot oil circuit or to the process steam boilers. An addition of hydrocarbons equivalent to the losses at the bottom of said heavy oil distillation section is necessary to keep the washing rate constant. The heavy brown oil distillation section is operated so as to maintain the concentration of brown oils in the hydrocarbon recycling loop (hydrocarbon effluent / washing oil effluent loop) constant.

Light and heavy brown oil effluents are eliminated from the process.

The addition of water within the washing / backwashing section allows a better functioning of the process for removing impurities and brown oils according to the invention.

The process according to the invention thus avoids regular purging of ethanol in order to avoid the accumulation of brown oils, which makes it possible to improve the overall performance of the process.

Step E3) of ethanol separation

The process according to the invention comprises a step E3) comprising a distillation section comprising a partition column supplied at least with the ethanol raffinate resulting from step E2), and producing at least one effluent rich in ethanol, an effluent rich in water and an effluent dirty water.

Said distillation section comprises a partition column supplied at least with the ethanol raffinate from step E2) and producing at the bottom an effluent rich in water and an effluent dirty water, and at the top an effluent rich in ethanol.

Said partition partitions the lower two thirds of the column into two compartments. The compartment in which the supply is made is called the entry compartment, the second compartment being called the lower compartment. The top of the column with no bulkhead is called the head compartment.

A special device known to those skilled in the art distributes the liquid from the head compartment between the inlet and lower compartments. Advantageously, between 25 and 60 mol% of the liquid coming from the head compartment is directed towards the inlet compartment, preferably between 35 and 55% and very preferably between 35 and 45%, the residual fraction feeding the lower compartment.

The entry compartment comprises between 8 and 25 theoretical plates, advantageously between 12 and 20. The lower compartment comprises between 8 and 25 theoretical plates, advantageously between 12 and 20.

The ethanol raffinate from E2), advantageously mixed with the alcoholic water effluent from step F), is fed to a tray located in the upper half of said inlet compartment. Thus, if for example the entry compartment comprises 14 theoretical stages, said mixture is supplied between the trays 1 and 7, the trays being numbered in the direction of flow of the liquid.

Water and acetic acid, which are less volatile, preferentially go to the bottom of the column, while the azeotropes butanol / water and ethanol / water go to the head.

The entry and lower compartments each have their reboiler.

The inlet compartment reboiler completely eliminates ethanol at the bottom of the column. From the bottom of this compartment is extracted the dirty water effluent, charged with acetic acid and “brown oils” possibly still present, said dirty water effluent being eliminated from the process to be optionally treated in a process for reprocessing of waste water.

The head compartment comprises from 3 to 10 theoretical plates, advantageously from 4 to 6. This compartment receives the gas phases coming from the inlet and lower compartments, which are mixed and brought into contact with the liquid in the tray of the head compartment located immediately above the partition.

Only the liquid from the head compartment descends into the lower compartment, which is therefore freed from most of the acetic acid and the residual "brown oils". The reboiler at the bottom of the lower compartment eliminates all traces of ethanol. Thus, the water-rich effluent produced at the bottom of the lower compartment contains little acetic acid (less than 0.5 mol%, even less than 0.25 mol%), and no other impurity other than in the state traces, that is to say present less than 0.1% by weight, advantageously less than 0.01% by weight.

In a particular arrangement of the distillation section of said step E3), said bulkhead column of said distillation section comprises a heat pump comprising a round-trip operation of refrigerant between the condenser and the reboilers of said column.

Said refrigerant, advantageously a mixture of hydrocarbons, very advantageously a mixture of hydrocarbons comprising from 3 to 5 carbon atoms, and very preferably an equimolar mixture n-butane / isobutane, is compressed to a pressure between 2 and 3 MPa, advantageously between 2.3 and 2.8 MPa. The compressed fluid is separated into two fractions sent respectively to the reboilers of the inlet compartment and the lower compartment, these fractions then being completely condensed. These fractions, separately or as a mixture, then preheat the feed to said wall column and are then expanded to a pressure between 0.5 and 1.5 MPa, advantageously between 0.8 and 1.4 MPa. If this has not been done after exchange in the reboilers, the two fractions are then mixed, the mixture being completely vaporized by heat exchange with the vapor drawn off at the head of said wall column in the condenser of said column before be compressed again, thereby closing the refrigerant circulation loop.

Of course, other heat pumps similar to those described in step B) or in step E3) can be installed in order to further reduce the energy consumption, in particular around the reaction section of the step. A), or from the distillation section of step D2) for example.

The low content of acetic acid in the effluent rich in water makes it possible to limit the formation of diethylacetal, favored by the presence of acetic acid in the stages where this effluent is recycled. In addition, the use of the configuration according to the invention makes it possible to rid the water-rich effluent of any residues of brown oils which would not have been extracted in step E2).

Said ethanol-rich and water-rich effluents from step E3) are then recycled in the rest of the process according to the invention. The fraction of said ethanol-rich effluent feeding step A) and that feeding step C1) are adjusted so as to adjust the ethanol / acetaldehyde ratio at the input of the reaction section of step B).

The fraction of said water-rich effluent feeding said step F) is adjusted so as to recover the ethanol from the combustible gas. Likewise, the fraction of said effluent rich in water feeding said step E2) is adjusted so as to recover the ethanol.

In another embodiment of the invention, said ethanol-rich and water-rich effluents undergo a purification step separately before being recycled in the rest of the process. By purification is meant to bring said effluents into contact with adsorbents such as, for example, activated carbon, silica, alumina or even a functionalized polymeric resin. For example, an activated carbon eliminates the traces of butanol and hexanol included in the stream rich in ethanol. For example, a basic resin eliminates the acetic acid present in the water-rich effluent. When the adsorbents are saturated, and do not guarantee the purity of the effluents rich in acetaldehyde, rich in ethanol and rich in water, they are either eliminated or regenerated to be reused.

Step F) washing gaseous by-products with water

The method according to the invention comprises a step F) of washing with water supplied with the gaseous by-product effluent from step D1), as well as by a fraction of the water-rich effluent from said step E3) and produces at least one alcoholic water effluent.

The objective of said step F) is to recover the small fraction of ethanol entrained in said effluent by-product gas from step D1) in order to improve the overall yield of the process.

The fraction of the water-rich effluent from said step E3) required in said step F) according to the invention is very small, since the gaseous effluent from step B) was washed in step D1) with an ethanol stream containing little or no acetaldehyde. There remains in this stream only a small fraction of ethanol, easily recovered with a small amount of water compared to the amount of water that would have been necessary if there were traces of acetaldehyde in the effluent by-product gas from step D1).

The water loaded with ethanol after washing is withdrawn from said step F) and constitutes the alcoholic water effluent. It advantageously feeds step E3).

The method according to the invention therefore makes it possible to minimize the flow rate of the effluents to be treated in the effluent treatment step. It also makes it possible to minimize the losses of butadiene, by making it possible to recover more than 98%, preferably more than 99% of the butadiene produced at the end of the reaction stages in said purified butadiene effluent.

DESCRIPTION OF THE FIGURES

FIG. 1 shows a particular arrangement of the steps of the method according to the invention.

A fraction of the ethanol-rich effluent (1) from step E3) feeds a step A) of conversion of ethanol into acetaldehyde producing a hydrogen effluent (5) and an ethanol / acetaldehyde effluent, part of which (50 ) feeds step C1) of hydrogen treatment, the other part (52) feeding step B) of conversion to butadiene.

Step C1) is also fed with a fraction of the ethanol-rich effluent (49) from step E3) and the hydrogen effluent (5) and produces a washing effluent (51) and a purified hydrogen effluent (10).

Step B) of conversion to butadiene is fed with a fraction (52) of said ethanol / acetaldehyde effluent from step A), with a washing effluent (51) from step C1) and with a fraction of the effluent rich in acetaldehyde (17) from step E1). This step produces a gaseous effluent (21) and a liquid effluent (31).

The gaseous effluent (21) feeds a step D1) of extraction of the butadiene. This step is also fed by a stream of ethanol (15) which washes the gaseous effluent (21) so as to produce a butadiene washing effluent (25). The gas washed with ethanol feeds the stage F) of washing with water as an effluent by-product gas (26) in which it is again washed with a fraction of the effluent rich in water (53 ) from step E3) to produce, on the one hand, a combustible gas effluent (28) and an alcoholic water effluent (30).

The liquid effluent (31) from B) and the butadiene washing effluent (25) from D1) feed step D2) of first purification of the butadiene in which it is separated into a prepurified butadiene effluent (38), a wastewater effluent, part of which (37-2) feeds step E1) and another part (37-3) feeds step E2), a raw acetaldehyde effluent (73) and a raw ethanol effluent (34).

This step D2) is also supplied with a flow of water (36) and an effluent of backwashing water (75) from step E1) of washing the acetaldehyde. This step makes it possible to wash the raw acetaldehyde effluent (73) in order to ultimately produce an effluent rich in acetaldehyde (17), the impurities being removed by the diethyl ether effluent (83).

The purification of the pre-purified butadiene effluent (38) is completed in step D3), which produces a purified butadiene effluent (62).

The raw ethanol effluent (34) from step D2) feeds the step E2) of effluent treatment. This step makes it possible to separate an ethanol raffinate (70), an effluent from light brown oils (67) and an effluent from heavy brown oils (68).

The ethanol raffinate is purified in the ethanol separation step E3) to produce an ethanol-rich effluent (724), a water-rich effluent (725) and a dirty water effluent (72).

Figure 2 shows an arrangement of the process according to the invention.

An ethanol-rich effluent (1) from a distillation section 71 is sent to the reaction section 2, or part of the ethanol is mainly converted into acetaldehyde and hydrogen, the product of the reaction (3) being sent to the separation section 4.

The separation section 4 makes it possible to separate a gas phase (5), compressed in section 6, and a liquid phase which is separated into two parts, one (52) feeding the reaction section 18, the other (50) sent to the washing section 8. The separation step (8) is also supplied with a fraction of the ethanol-rich effluent (49) to wash the compressed gas (7) and produce purified hydrogen with traces water and ethanol (10).

The reaction section 18 is supplied with an effluent rich in acetaldehyde (17) coming from the washing section 74, by the ethanol / acetaldehyde mixture (51) coming from the hydrogen washing section 8 and by part of the liquid phase (52 ) from the separation section 4.

The effluent (19) from the reaction section 18 is sent to the gas-liquid separation section 20. The vapor phase (21) is compressed in section 22. The compressed gas (23) is washed in section 24 by the ethanol charge (15) to recover the butadiene, which avoids bringing back into the butadiene impurities which could have been concentrated by recycling. The gas (26) from this ethanol wash is washed in the wash section 27 with a fraction of the water-rich effluent (53) from the distillation 71. The water loaded with ethanol (30) after washing is returned to the distillation section 71, to the water-ethanol separation column. The gas (28) is removed from the process.

The liquid phase (31) of the separator 20 is mixed with the liquid (25) from the washing 24. The mixture is sent to distillation comprising a partition column 32, which will separate a crude butadiene effluent (33) at the head, an effluent crude acetaldehyde (73) in a lateral racking, and a crude ethanol effluent (34) at the bottom. The crude butadiene effluent (33) is sent to a water wash 35 intended to remove polar impurities and in particular acetaldehyde, which must not be present above a few ppm in the final butadiene. The water (36) used for this washing is clean water, not recycled, so as not to risk introducing impurities into the final product. The amount of water used is adjusted to obtain the acetaldehyde specification.

The wastewater effluent (37) is returned partly (37-1) to the distillation comprising a partition column 32, partly (37-2) to the section 74 for washing / backwashing the raw acetaldehyde effluent, and partly (37-3) to section 63 for solvent washing.

The raw acetaldehyde effluent (73) is sent to section 74 to be washed with an effluent comprising heavy hydrocarbons (78). The heavy hydrocarbons loaded with diethyl ether and other impurities are backwashed with the fraction of the wastewater effluent (37-2) to recover the acetaldehyde which would have been entrained. The washed heavy hydrocarbons (76), loaded with impurities, feed the regeneration section 77, from which the regenerated hydrocarbons (78) returning to the washing, and a light fraction (83), containing in particular diethyl ether, ethyl acetate, pentene, hexene and other light impurities. Another solvent than hydrocarbons could be used as well.

The washed butadiene (38) is separated from the butenes in an extractive distillation section 79. The butadiene (62) resulting from extraction 79 leaves with a purity satisfactory for the current specifications (more than 99.5%), the residual impurities being mainly butenes (61) and a butyne / butene mixture (58). A section for purifying the extraction solvent 81 is supplied with the solvent (80) from the extractive distillation section 79, making it possible to withdraw the impurities accumulated in the solvent (55). The regenerated solvent (82) is returned to section 79.

The bottom product (34) from the distillation 32 is sent to the effluent treatment section 63. The heavy washing hydrocarbons, loaded with impurities (65) feed the regeneration section 66, from which the regenerated hydrocarbons (69) returning to washing, a light fraction (67), containing in particular ethyl acetate and some Light "brown oils". A heavy cup (68) is also produced, containing heavy "brown oils" and a small part of the washing hydrocarbons. Another heavier, more viscous solvent than hydrocarbons could advantageously be used, taking advantage of the fact that the acetaldehyde and the light impurities are left in the bulkhead column 32 and that the temperature of the washing operation can be increased. .

It is advantageous to use a solvent which does not produce precipitation or fouling.

The liquid (70) at the bottom of the extraction 63, containing both the liquid (34) freed of its impurities having strong affinities with hydrocarbons, and the washing water (64) is sent to the distillation section 71 comprising a partition column which makes it possible to separate an effluent rich in ethanol returned in part (1) to the reaction section 2 and in part (49) to washing 8, an effluent rich in water containing very little acetic acid and partly recycled (53) to washing 27 and partly (64) to washing 63, and a dirty water effluent (72), purged from the unit.

FIG. 3 presents a schematic view of the partition column used in the distillation section of step D2) of the process according to the invention.

The liquid effluent from step B) (31) is mixed with the butadiene washing effluent from step D1) (25) and fed into the inlet compartment of the column (320).

In the head compartment of the column (320), above the partition (321), the vapors coming from the inlet and withdrawal compartments are mixed and brought into contact with the liquid of the last tray of this section. The overhead vapor (322) from this section feeds the partial condenser (323), which cools and partially condenses the overhead product, the cooled product (324) being discharged to the reflux flask (325). The condensed part (326) is returned to the pump (327) and returned to the column (320) as reflux (328), the non-condensed part (33) constituting the crude butadiene effluent. A crude acetaldehyde effluent (73) is withdrawn from the withdrawal compartment. At the bottom of the column, a raw ethanol effluent (34) is withdrawn, a fraction being returned to the column after reheating by the reboiler (329).

FIG. 4 presents a schematic view of the partition column used in the distillation section of step E3) of the process according to the invention.

The ethanol raffinate (70) from step E2) is mixed with the alcoholic water effluent (30) from step F and fed into the inlet compartment of the bulkhead column (710). The partition wall (711) goes to the bottom of the column, but not to the head.

The bottom of the inlet compartment is reboiled by the reboiler (720), which makes it possible to completely eliminate the ethanol at the bottom of the column. From this compartment is withdrawn, via the pump (722), the effluent dirty water (72), charged with acetic acid and "brown oils" escaped from washing.

In the head compartment of the column, above the partition (711), the vapors from the inlet and lower compartments are mixed and brought into contact with the liquid of the last tray of this section. The overhead vapor from this section (712) is completely condensed in the condenser (713), then this cooled effluent (714) is fed into the reflux tank (715). The condensed liquid (716) is partly sent to the pump (717) to serve as reflux (718), the ethanol-rich effluent (724) being recycled by the pump (719) to the rest of the process.

At the bottom of the lower compartment, reboiled by the exchanger (721), a water-rich effluent (725) is withdrawn via the pump (723) which is recycled to the rest of the process.

FIG. 5 represents a thermal integration around the reaction section for conversion to butadiene as commonly adopted by a person skilled in the art and usable in the process according to the invention.

A fraction of the ethanol / acetaldehyde effluent (52) from step A) of conversion is mixed with a fraction of the acetaldehyde-rich effluent (17) from step E1) and the washing effluent ( 51) from step C1). This mixture (181) is preheated in the charge-effluent exchanger 182 and then heated to the inlet temperature in the reactor 186 by the exchanger 184 which can be, for example, an oven.

The reactor effluent (187) is first cooled in the charge-effluent exchanger 182 before being cooled in the exchanger 189 and separated between a gaseous effluent (21) and a liquid effluent (31).

FIG. 6 represents a variant according to the invention of thermal integration around the reaction section for conversion to butadiene.

A fraction of the ethanol / acetaldehyde effluent (52) from step A) of conversion is mixed with a fraction of the acetaldehyde-rich effluent (17) from step E1) and the washing effluent ( 51) from step C1). This mixture (181) is preheated in the exchanger 182-1 then heated through the charge-effluent exchanger 182-1 and finally heated to the inlet temperature in the reactor 186 by the exchanger 184 which can be, by example, an oven.

The reactor effluent (187) is first cooled in the charge-effluent exchanger 182-2 before being cooled in the exchanger 182-3 and is separated between a gaseous effluent (21) and a liquid effluent ( 31).

The heat pump uses a refrigerant which is vaporized in the exchanger 182-3, compressed in the compressor 1803, condensed at least partially in the exchanger 182-1 then completely condensed in the exchanger 189-1 before d '' be relaxed in valve 1807 and return to the exchanger 182-3.

FIG. 7 represents a variant according to the invention of thermal integration around the distillation section comprising a partition column from step E3) according to the invention.

The numbering is identical to that of figure 4. Only the additional elements are described here. They constitute the heat pump used in this variant of the method according to the invention.

The refrigerant is compressed by the compressor 7100 to a pressure of 2.5 Mpa. The temperature at the outlet of the compressor is 123 ° C. The compressed fluid is separated into two fractions (7101) and (7102) sent respectively to the heat exchangers (720) and (721) making it possible to reboil the two compartments of the column, and is completely condensed in these exchangers at a temperature of 118 ° C. At the outlet of the exchange (720), the fluid (7103) is sent to the heat exchanger (7104), which will preheat a fraction of the charge of the column and vaporize it to about 11% mol. The mixture cooled to 98 ° C is sent to the heat exchanger (7106), where it is cooled to 95.5 ° C, then sent to the valve (7108), where it is expanded to

1.1 MPa, partially vaporizing and cooling to 75 ° C.

At the outlet of the exchanger (721), the fluid (7113) is sent to the heat exchanger (7114), which will preheat the residual fraction of the charge of the column and vaporize it to approximately 11% mol . The mixture cooled to 98 ° C will be sent to the heat exchanger (7116), where it is cooled to 95.5 ° C, then sent to the valve (7118), or it is expanded to 1.1 MPa, partially vaporizing and cooling to 75 ° C.

The output of the valves (7108) and (7118) is mixed and sent to the heat exchanger (713) which is the column head condenser. The vaporized and slightly overheated mixture (7120) is sent to the compressor (7100) at a temperature of 81 ° C.

EXAMPLES

The following examples are based on process simulations taking into account the recycling of flows, and integrating thermodynamic data calibrated on experimental points (binary liquid-vapor equilibrium data and liquid-liquid partition coefficient).

In each of the examples, the feed rate is adjusted so as to obtain an annual production of approximately 150 kt / year of a butadiene having a purity of between 99.5 and 100% by weight (in line with the current use of product), with an annual operating time of the process of 8000 h.

In the following examples, in order to facilitate the comparison, it is estimated that 1 MW of electricity is equivalent to 3 MW of heat from the observation that a single gas turbine has an efficiency of 30 to 35%.

Example 1 - non-compliant

A process as described in patent FR 3,026,100 is supplied with 48,670 kg / h of a load comprising 93.3% by weight of ethanol, the remainder being water.

18850 kg / h of purified butadiene effluent are produced, ie 150.8 kt / year, comprising 99.8% by weight of butadiene. The overall consumption in utilities is:

• 201.3 t / h of steam (117.4 MW) • 86.8 MW of furnace heating • 8.4 MW of electricity • 21 t / h of process water • 25120 m ³ / h of water cooling

Or an equivalent consumption of 117.4 + 86.8 + 8.4x3 = 229.4 MW equivalent.

Example 2 - compliant

The process according to the invention is supplied with 48,670 kg / h of a charge comprising 93.3% by weight of ethanol, the remainder being water.

18820 kg / h of purified butadiene effluent are produced, ie 150.5 kt / year, comprising 99.8% by weight of butadiene. The overall consumption in utilities is:

• 178.1 t / h of steam (104 MW) • 86.7 MW of furnace heating • 9.4 MW of electricity • 21 t / h of process water • 22560 m ³ / h of cooling water

Or an equivalent consumption of 104 + 86.7 + 9.4x3 = 218.9 MW equivalent.

We see that overall consumption in utilities is down for a sustained production of butadiene.

Example 3 - Integration around the reaction section for conversion to butadiene

3.1 - Thermal integration as commonly adopted

Figure 5 shows the thermal integration commonly carried out around a reactor implementing an exothermic reaction.

When this thermal integration is implemented in the process according to the invention, the power exchanged in the charge-effluent exchanger 182 under the conditions of example 2 is 23.1 MW. The mixture (181) is thus heated to a temperature of 101 ° C.

35.9 MW are then exchanged in exchanger 184 to bring the fluid to the conditions of entry into reactor 186.

The reactor effluent is cooled first in the charge-effluent exchanger, then in exchanger 189. The power exchanged in exchanger 189 is 35.3 MW.

35.9 MW thermal is consumed for heating, and 35.3 MW must be evacuated by the cooling water.

3.2 - Implementation of a heat pump in the reaction section for conversion to butadiene

Reference is made to FIG. 6 which shows the integration of a heat pump according to a variant of the method according to the invention.

Under the conditions of Example 2, the mixture (181) is heated to 110 ° C and vaporized to 90% in the heat exchanger 182-1 by exchange against a refrigerant, which is here a mixture of hydrocarbons of molar composition 45% of n-butane, 45% of i-butane, and 10% of n-pentene. The refrigerant is completely condensed in this exchanger. The power exchanged in the 182-1 exchanger is 37.4 MW. It is 14.6 MW in the 182-2 interchange.

The mixture is then heated to 285 ° C by exchange in the charge-effluent exchanger 182-2. In this exchanger, the effluent is cooled to a temperature of 172 ° C and is still completely in the vapor phase. The mixture is finally heated to the inlet conditions of reactor 186 by exchanger 184 in which 7 MW are exchanged.

The refrigerant enters the exchanger 182-3 at 35 ° C and 0.8 MPa. It is completely vaporized in this exchanger then compressed to 2.2 MPa in the compressor 1803. It is then condensed in the exchanger 182-1, then sub-cooled to 35 ° C in [exchanger 189-1 before being expanded in valve 1807.

In this particular arrangement according to the invention, 7 MW thermal, 12.4 MW of cooling water, and 5.5 MW electric for the compressor are consumed, equivalent consumption of 7 + 5.5 × 3 = 23.5 MW equivalent.

Thus, the equivalent power required for the variant implementing a heat pump is 23.5 MW, while the equivalent power required for "conventional" integration is 35.9 MW, a reduction of 35%.

The reduction on cooling water is 65%.

Example 4 - Thermal integration around the distillation section including a bulkhead column from step E3)

The distillation section comprising a bulkhead column from step E3) operated according to a first variant of the invention, that is to say in which the reboilers are supplied with steam and the condenser with water cooling, consumes 56 MW of steam and 55 MW of cooling water under the operating conditions of Example 2.

The implementation of the variant according to the invention in which a thermal integration with heat pump as described in FIG. 7 is carried out leads to a consumption of 10.2 MW of electricity for the compressor (ie an equivalent power of 10, 2x3 = 30.6 MW) and 2 MW of cooling water.

Thus, thermal integration according to this variant of the method according to the invention makes it possible to reduce the thermal power required by 45%, and the consumption of cooling water by 96%.

Using the figures from example 2 and integrating the heat pumps from examples 3.2 and 4 (around the reaction section for conversion to butadiene and around the column in section E3), the overall consumption in utilities of this variant of the process according to the invention are:

• 82.2 t / h of steam (48 MW) • 57.8 MW of furnace heating • 25.1 MW of electricity • 21 t / h of process water • 13750 m ³ / h of cooling water

Or an equivalent consumption of 48 + 57.8 + 25.1x3 = 181.1 MW equivalent.

The energy consumption of the process according to the invention is therefore further reduced by about 20% with the improvements proposed. In addition, the consumption of cooling water decreases by about 40%.

Claims (16)

1. Process for the production of butadiene from an ethanol feedstock comprising at least 80% by weight of ethanol comprising at least: A) a step for converting ethanol into acetaldehyde comprising at least: - A reaction section fed at least with a fraction of the ethanol-rich effluent from step E3), operated at a pressure between 0.1 and 1.0 MPa and at a temperature between 200 and 500 ° C. in the presence of a catalyst, and - A separation section for separating the effluent from said reaction section into at least one hydrogen effluent and one ethanol / acetaldehyde effluent; B) a butadiene conversion stage comprising at least: a reaction section fed at least with a fraction of said ethanol / acetaldehyde effluent from step A), with a washing effluent from step C1), with a fraction of the acetaldehyde-rich effluent from step E1), operated in the presence of a catalyst, at a temperature between 300 and 400 ° C, and at a pressure between 0.1 and 1.0 MPa, the feed rates being adjusted so that the ethanol / acetaldehyde molar ratio at the inlet of said reaction section is between 1 and 5, and - A separation section for separating the effluent from said reaction section into at least one gaseous effluent and one liquid effluent; C1) a hydrogen treatment step comprising at least: a compression section compressing said hydrogen effluent from step A) at a pressure of between 0.1 and 1.0 MPa, and a gas-liquid washing section supplied at a temperature between 25 and 60 ° C with said hydrogen effluent from the compression section, at a temperature between 15 ° C and -30 ° C with a fraction of said effluent rich in ethanol from step E3), and by a fraction of said ethanol / acetaldehyde effluent from step A), and producing at least one washing effluent and one purified hydrogen effluent; D1) a butadiene extraction step comprising at least: - a compression section compressing said gaseous effluent from step B) at a pressure between 0.1 and 1.0 MPa, a gas-liquid washing section comprising a washing column supplied at the head at a temperature of between 20 and -20 ° C. by an ethanol stream consisting of said ethanol feedstock from the process and / or a fraction of the rich effluent in ethanol from step E3) and at the bottom with said gaseous effluent from step B) compressed and cooled, and producing at least one effluent by-product gas and one butadiene washing effluent; D2) a step of first purification of butadiene comprising at least: a distillation section comprising a partition column supplied at least with the liquid effluent from said step B) mixed with the butadiene washing effluent from step D1) and with the backwashing water effluent from step E1) and producing a crude butadiene effluent, a crude acetaldehyde effluent and a crude ethanol effluent; a gas-liquid washing section fed at the bottom with said raw butadiene effluent and at the head with a flow of water, and producing at the head a pre-purified butadiene effluent and at the bottom with a waste water effluent; D3) a subsequent butadiene purification step, fed at least with said pre-purified butadiene effluent from said step D2), and producing at least one purified butadiene effluent; E1) a step of washing the acetaldehyde supplied by the raw acetaldehyde effluent from step D2) and by a fraction of the wastewater effluent from step D2), and producing a counter-water effluent washing, an effluent rich in acetaldehyde and a diethyl ether effluent; E2) an effluent treatment step, fed at least with the raw ethanol effluent from step D2), and with a fraction of the water-rich effluent from step E3), and producing at least one ethanol raffinate, a light brown oil effluent and a heavy brown oil effluent; E3) a step for separating the ethanol comprising a distillation section comprising a partition column supplied at least with the ethanol raffinate from step E2), and producing at least one effluent rich in ethanol, an effluent rich in water and a dirty water effluent; F) a step of washing with water, supplied with the gaseous by-product effluent from step D1), as well as by a fraction of the water-rich effluent from said step E3) and producing at least an alcoholic water effluent. 2. Method according to the preceding claim wherein said partition column of said step D2) comprises an inlet compartment comprising between 8 and 15 theoretical plates, a racking compartment comprising between 8 and 15 theoretical plates, a head compartment comprising between 5 and 20 theoretical platforms and a bottom compartment comprising between 5 and 10 theoretical platforms. 3. Method according to one of the preceding claims wherein said partition column of said step E3) comprises an inlet compartment comprising between 8 and 25 theoretical plates, a lower compartment comprising between 8 and 25 theoretical plates, and a compartment head comprising between 3 and 10 theoretical plates. 4. Method according to one of the preceding claims wherein step B) comprises a heat pump between the effluent and the supply of the reaction section of said step in which a refrigerant is vaporized by exchange with the effluent of said reaction section, compressed then at least partially condensed by heat exchange with the feed to said reaction section, then fully condensed and expanded before being vaporized again during the exchange with the effluent from said reaction section. 5. Method according to the preceding claim wherein said refrigerant is at least a mixture of hydrocarbons with 3, 4 or 5 carbon atoms. 6. Method according to one of the preceding claims in which said ethanol stream supplying step D1) consists of said ethanol feedstock of the process. 7. Method according to one of the preceding claims wherein said flow of water supplying the washing section of step D2) is a flow of water of external origin to said process for producing butadiene. 8. Method according to one of the preceding claims wherein 40 to 70 mol% of the liquid from the head compartment of the bulkhead column of the distillation section of said step D2) is directed to the inlet compartment of said column with partition. 9. Method according to one of the preceding claims wherein 50 to 80 mol% of the gas from the bottom compartment of the bulkhead column of the distillation section of said step D2) is directed to the inlet compartment of said column with partition. 10. Method according to one of the preceding claims wherein is injected at the top of the partition column of the distillation section of said step D2) a water flow corresponding to 15 to 20 mol% of the flow of butadiene withdrawn at the head of said column. 11. Method according to one of the preceding claims wherein said step D3) comprises a separation section by extractive distillation in the presence of a polar solvent. 12. The method of claim 11 wherein said polar solvent is selected from the group consisting of dimethylformamide (DMF), N-methylpyrrolidone, acetonitrile and mixtures thereof. 13. Method according to one of the preceding claims wherein the bulkhead column of said distillation section of said step E3) comprises a heat pump comprising a round-trip of refrigerant between the condenser and the reboilers of said column . 5 14. Method according to the preceding claim wherein said refrigerant is a mixture of hydrocarbons comprising from 3 to 5 carbon atoms. 15. Use of a bulkhead column to separate a feed comprising butadiene, ethanol, acetaldehyde and water into a crude butadiene overhead effluent comprising more than 10 90% by weight of butadiene, a crude acetaldehyde effluent as lateral withdrawal and a crude ethanol effluent at the bottom, said column also being supplied with a flow of water, said partition of the column to partition partitioning a central section of the column in two compartments, the central compartment in which the feeding is carried out being called the inlet compartment, the central compartment from which the raw acetaldehyde effluent is drawn off being called 15 draw-off compartment and the upper and lower parts of the column not comprising a partition being called respectively the head and bottom compartments, said inlet compartment comprising between 8 and 15 theoretical plates, said draw-off compartment comprising between 8 and 15 theoretical plates, said head compartment comprising from 5 to 20 theoretical plates, said bottom compartment comprising from 5 to 10 plates 20 theoretical. 16. Use according to the preceding claim wherein said feed comprises 20 to 30% butadiene, 50 to 60% ethanol, 3 to 8% acetaldehyde and water. 1/7