WO2013149823A1

WO2013149823A1 - Method for producing vinyl acetate

Info

Publication number: WO2013149823A1
Application number: PCT/EP2013/055705
Authority: WO
Inventors: Johann Wagner; Heribert Westermayer
Original assignee: Wacker Chemie Ag
Priority date: 2012-04-03
Filing date: 2013-03-19
Publication date: 2013-10-10
Also published as: DE102012205444A1

Abstract

The invention relates to a method for producing vinyl acetate in a heterogeneously catalyzed, continuous gas-phase reaction by reacting ethylene with acetic acid and oxygen, and separating the product gas mixture essentially containing ethylene, vinyl acetate, acetic acid, water, carbon dioxide, and other inert gases, and returning a circulating gas flow containing ethylene, after recharging the circulating gas flow with ethylene, acetic acid, and oxygen, characterized in that the gas-phase reaction is performed in a reactor cascade comprising at least two reactors arranged one following the other. The circulating gas flow is returned to a first reactor, the product gas mixture leaving the first reactor is charged with oxygen, and optionally with acetic acid and/or with ethylene, and is fed to a second reactor. If additional reactors are arranged following the second reactor, the product gas mixture is also charged with oxygen, and optionally with acetic acid and/or with ethylene, before the product gas mixture is transferred from each preceding reactor to the next reactor, and the product gas mixture leaving the last reactor of the reactor cascade is fed to the separation process of the product gas mixture.

Description

Process for the preparation of vinyl acetate

The invention relates to a process for the preparation of vinyl acetate in a heterogeneously catalyzed, continuous gas phase process by reacting ethylene with acetic acid and oxygen in at least two reactors arranged one behind the other.

Vinyl acetate (VAM) is produced in a continuous process with recycling of the purified product stream (recycle gas system). In a heterogeneously catalyzed gas phase process, ethylene reacts with acetic acid and oxygen on fixed-bed catalysts which generally contain palladium and alkali metal salts on a support material and may additionally be doped with gold, rhodium or cadmium.

The educts ethylene, oxygen and acetic acid are in an exothermic reaction (VAM: Δ _Β Η ° ₂ 99 = - 176 kJ / mol), generally at a pressure of 1 to 30 bar and a temperature of 130 ° C to 200 ° C, converted in a gas phase oxidation reactor to vinyl acetate:

C ₂ H ₄ + CH ₃ COOH + Ji Oj -> CH ₃ COOCH = CH ₂ + H ₂ O

The major secondary reaction is the total ethylene oxidation to C0 ₂ :

C ₂ H ₄ + 3 0 ₂ -> 2 C0 ₂ + 2 H ₂ 0

The reaction is incomplete: the ethylene conversion is about 5 to 20%, the acetic acid conversion at 20 to 60% and the oxygen conversion up to 90%.

Therefore, in the production of vinyl acetate, a gas mixture consisting predominantly of ethylene, carbon dioxide, ethane, nitrogen and oxygen is circulated. The gas stream is generally mixed with the reactants acetic acid, ethylene and oxygen before the gas phase oxidation reactor and with Heating steam operated heat exchangers brought to reaction temperature.

Due to the incomplete conversion of the educts, the unreacted acetic acid is also removed from the gaseous reaction product which leaves the reactor after leaving the gas phase oxidation reactor in addition to the reaction product vinyl acetate. Since the proportion of ethylene contained therein is recirculated back into the reactor as so-called recycle gas, disruptive by-products such as water, CO ₂ , acetaldehyde and acetic acid esters, such as methyl or ethyl acetate, are removed as completely as possible from the recycle gas. Similarly, the content of introduced via the oxygen inert, such as nitrogen and argon, should be kept as low as possible. The same applies to the inert methane and ethane.

Therefore, the reactor leaving the gaseous reaction mixture in a relatively complex, multi-stage, usually operated with heating steam and cooling water, thermal see separation process, before it can be recycled as cycle gas to the reactor. The unreacted acetic acid is returned to the reactor after the separation from the cycle gas as back acetic acid (acetic acid cycle). For example, it is possible to proceed as follows: In general, the gaseous reaction mixture (circulating gas) is freed from vinyl acetate, acetic acid and water after leaving the reactor in a pre-dewatering column. The gaseous phase obtained from the pre-dewatering is freed from residual vinyl acetate in the cycle gas scrubber. After that is from a

Partial stream of the circulating gas in a C0 ₂ -Wäscher C0 ₂ separated. This partial stream is recombined with the remaining cycle gas, and the recycle gas is returned to the gas phase oxidation reactor.

The obtained in the process just described from the pre-dewatering column and the recycle gas scrubber liquid phases, which predominantly vinyl acetate, acetic acid and water are generally separated by distillation in an azeotropic column, a dewatering column and a pure vinyl acetate column and pure vinyl acetate monomer (VAM) won. Such a work-up process is described, for example, in WO 2011/089070 Al.

To increase the capacity of a plant is proposed in WO 2008/071610 A2 to use catalysts with increased activity and selectivity. In DE 10 2011 081 786 Al it is proposed to line up catalyst layers of different activities in order to increase the space-time yield. DE 10 2004 050 585 A1 recommends microreactors based on wall reactors, in which the catalytic synthesis takes place in a large number of reaction spaces, in order to improve the space-yield and the selectivity. US 4,654,801 employs an integrated control system for improving the yield and selectivity in vinyl acetate monomer preparation. However, these measures are often not sufficient to achieve a significant increase in capacity, for example greater than 20%. In order to achieve a significant increase in the production capacity of a VAM system, it would be conceivable simply to increase the volume of the reactor. However, due to the incomplete reaction in the oxidation reaction between acetic acid, ethylene and oxygen, such a measure would also significantly increase the amount of recycle gas, which in turn would necessitate corresponding capacity expansions in the cycle gas system and in the distillation units for treating the recycle gas.

The patent literature discloses a number of integrated processes in which uniform products are obtained by connecting several reactors in series, for example, from different starting materials. EP 0 877 727 B1 describes an integrated process for the preparation of acetic acid and / or vinyl acetate, in a first stage ethane and / or ethylene in the presence of a catalyst be converted to acetic acid, and this reaction product is reacted in a second stage in the presence of a VAM catalyst to vinyl acetate. EP 1 201 631 A2 describes a process with two reactors arranged one behind the other, wherein in the first reactor two catalysts with different selectivities catalyze the conversion of ethane to acetic acid and ethylene, and at least part of the reaction product from the first reactor is reacted in a second reactor in the presence of a VAM catalyst to vinyl acetate. From WO 2005/092829 Al an arrangement of two reactors is known in which methanol and carbon monoxide are converted to acetic acid in the first reactor, and in a second reactor, this acetic acid is reacted with ethylene and oxygen to vinyl acetate. EP 1 180 092 B1 describes a process for the preparation of vinyl acetate in which in a first reactor, in the presence of a first catalyst, ethane and / or ethylene are oxidized to acetic acid, and in a second reactor, in the presence of a second catalyst, the reaction product from the first reactor is converted to vinyl acetate.

The invention was based on the object, the capacity of a plant for the production of vinyl acetate in a catalyzed gas phase process, in which in a gas phase oxidation reactor ethylene with acetic acid and oxygen on a fixed bed catalyst is converted to vinyl acetate, without increasing the amount of cycle gas accordingly enlarge. Another task was to reduce the specific energy consumption per ton of vinyl acetate monomer.

The invention relates to a process for the preparation of vinyl acetate in a supported catalyst with heterogeneously catalyzed, continuous gas phase reaction by reaction of ethylene with acetic acid and oxygen, and

Separating the product gas mixture containing essentially ethylene, vinyl acetate, acetic acid, water, carbon dioxide and other inert gases, and recycling an ethylene-containing circulating gas stream, after recharging the circulating gas stream with ethylene, acetic acid and oxygen,

characterized in that

the gas phase reaction is carried out in a reactor cascade from at least two reactors arranged one behind the other, the cycle gas stream being returned to a first reactor,

the product gas mixture leaving the first reactor is loaded with oxygen, and optionally with acetic acid and / or with ethylene,

and fed to a second reactor,

wherein, if further reactors are arranged behind the second reactor, prior to the transfer of the product gas mixture from the preceding to the next reactor this also each with oxygen, and optionally charged with acetic acid and / or with ethylene,

and in each case the product gas mixture leaving the last reactor of the reactor cascade is fed to the separation of the product gas mixture.

Preferably, the process is carried out in a reactor cascade of two reactors connected in series. In general, as gas-phase oxidation reactors, stainless steel reactors with a volume of several cubic meters are used. Preferably, the heterogeneously catalyzed, continuous gas-phase reaction is carried out in ^"tubular reactors, which are loaded with a fixed bed catalyst. In general, this fixed-bed tube-bundle reactors with several thousand vertically arranged usually 2,000 to 20,000, densely packed and in general, equipped cylindrical tubes. For large-scale applications, pipes with a length of 4 m to 10 m and an internal diameter of generally 20 mm to 50 mm are generally used.The tubes of the tube bundle are generally made of stainless steel and are made of a cylindrical container The spaces between the tubes themselves, and the Tubes and the container, for example, flows through a water / steam mixture for cooling (boiling water cooling). In general, the tube reactors connected in series in the reactor cascade are approximately the same size. Optionally, to control reactivity, the dimensions (dimensions) of the tube reactors in the reactor cascade may be different. That is, the design of the tube reactors in the reactor cascade may differ with respect to the number of tubes, the diameter of the tubes, and / or the tube length. For example, the number of tubes of the reactors connected downstream of the first reactor can be increased in relation to that of the respective preceding reactor, in order to increase the reactor volume to the volume of the reactor after the reloading process

To adjust the cycle gas. In general, the cycle gas quantity in the process according to the invention only increases by up to 20%, based on the mass flow, and only by up to 15%, based on the operating volume flow. Accordingly, the number of tubes in the tube reactors can be increased.

The tubes of the tube reactors are filled with commercially available supported catalysts as fixed bed catalysts. These supported catalysts are generally doped with precious metals (salts) and with activators. Commercially available are supported catalysts based on an inorganic support material such as titanium oxide, silica or alumina, which are generally coated with a palladium compound in combination with an activator component. The activator compound is usually an alkali metal compound, preferably its carboxylates, such as potassium acetate. In addition, gold, rhodium or cadmium is often doped. These supported catalysts can be present in different shapes, for example as spheres, cylinders or rings, the dimensions of which are adapted to the tubes used and generally have lengths or widths of 3 mm to 10 mm or diameter of 3 mm to 6 mm. In general, the individual tube reactors of the reactor cascade are charged with the same catalyst. However, it is also possible to proceed in such a way that supported catalysts of different doping and thus different activity are used in the respective tube reactors. For example, in the reactors following the first reactor, the decreasing activity can be compensated with a more active catalyst. Optionally, the bed height can be varied, that is, the reactors can be filled with the same bed height or in different bed height with supported catalyst. For example, in order to reduce pressure losses, the dumping height of the first reactor (compared with the operation with only one reactor) can be reduced, or the dumping height of the second or further downstream reactors can be reduced compared to the respective preceding reactor.

In the process according to the invention, the first reactor of the reactor cascade is charged with ethylene, oxygen and acetic acid for start-up, or charged in continuous operation with the circulating gas charged with ethylene, oxygen and acetic acid. As a rule, the first reactor is also charged with an activator compound, for example potassium acetate. The amounts of educts to be used are known per se to those skilled in the art. Ethylene is generally used in excess of the stoichiometric ratio to acetic acid. The amount of oxygen is limited upwards by the ignition limit in the recycle gas. The gas phase reaction is abs in the reactors of the reactor cascade at a pressure of preferably 8 to 14 bar. and at a temperature of preferably 130 ° C to 200 ° C performed.

The reaction temperature in the reactors of the reactor cascade of preferably 130 ° C. to 200 ° C. is set, for example, by boiling water cooling at a pressure of 1 to 30 bar abs., Preferably 8 to 14 bar abs. In this case, water vapor, the so-called self-vapor, with a temperature of 120 ° C to 185 ° C at a pressure of 1 to 10 bar abs. preferably 2.5 to 7 bar abs. , educated. In a preferred embodiment, each reactor of the reactor cascade has its own boiling water cooling circuit. When passing the product gas mixture through a reactor, pressure losses of 0.5 to 2 bar generally occur. It prevail so in addition to other pressure conditions and other temperature conditions in the downstream reactor. With separate boiling water cooling circuit, the temperature control in each reactor can be adapted to the respective prevailing conditions. This gives an approximately isothermal reaction procedure with corresponding improvement in the selectivity of the gas phase reaction. Another advantage is that the capillary condensation of the acetic acid can be prevented with an adapted temperature control.

Essentially, the product gas stream leaving the first reactor contains vinyl acetate, ethylene, acetic acid, water, oxygen, CO ₂ and the inert nitrogen, argon, methane and ethane. As mentioned above, the gas phase oxidation is incomplete: The ethylene conversion is about 5 to 20%, the acetic acid conversion at 20 to 60% and the SauerstoffUmsatz up to 90%.

The product gas stream leaving the first reactor is therefore recharged with oxygen before the second reactor. The amount is calculated so that the ignition limit (LEL = lower explosion limit) of the cycle gas is not exceeded. The addition of the oxygen to the product gas stream of the first reactor can preferably be effected by means of a static mixer or with a mixing nozzle.

If more than two reactors are arranged one behind the other in the reactor cascade, the addition of oxygen in the same manner can be used, in each case when the product gas stream leaving the preceding reactor is transferred to the next reactor, as in the transfer of the product gas stream from the first reactor the second reactor of the reactor cascade. In a further preferred embodiment, the product gas mixture leaving the first reactor before the second reactor is additionally charged with acetic acid in addition to oxygen. The supply of acetic acid, for example, analogous to

Essigsäuresättigung before the first reactor with a Essigsäu- saturates take place. The acetic acid saturator is preferably in the form of a column, for example as a packed column or, preferably, as a tray column with a number of rectification trays. The leaving the first reactor gaseous product mixture is introduced together with liquid, optionally preheated acetic acid in the Essigsäuresättiger, wherein the acetic acid at the prevailing at this point

Circulating gas pressure evaporates.

In this embodiment, due to the strong overheating of the recycle gas, more acetic acid may vaporize than is stoichiometrically necessary, and the liquid phase withdrawn in the bottom of the acetic acid ester contains water and VAM which can polymerize.

The acetic acid evaporation can therefore also be carried out in a heated heat exchanger at circulating gas pressure after the first reactor. Note that in this embodiment, at the pressure level of the circulating gas, preferably 8 to 14 bar abs., The boiling temperature of acetic acid is generally from 200 to 230 ° C. The heat exchanger is therefore generally abs with high pressure steam of 19 to 28 bar. heated or with a fired heater. These high vapor pressure levels are usually not readily available. In addition, deposits and fouling due to partial decomposition of acetic acid are possible at this temperature level.

The acetic acid evaporation is therefore in a preferred embodiment at low pressure, preferably from 3 to 6 bar abs. followed by the acetic acid vapor, preferably with a mechanical compressor, is compressed to the pressure level of the circulating gas and in which from the ers- th reactor emerging circulating gas, before its transfer into the second reactor, is initiated.

The acetic acid can also be injected into the hot product gas mixture emerging from the first reactor, for example via a spray or mixing nozzle. Preferably, fresh acetic acid is injected. The stoichiometric nachzuladende acetic acid evaporates completely, with the recycle gas cools. If necessary, the cycle gas can be reheated with steam upstream of the second reactor.

If ethylene is to be added after the first reactor, the ethylene may be added prior to acetic acid addition or thereafter.

The addition levels of acetic acid and / or ethylene are generally sized to replace that consumed in the gas phase oxidation in the previous reactor. Preference is also given to an embodiment in which acetic acid is evaporated or evaporated together with ethylene injected in a heat exchanger at the pressure level of the circulating gas (circulating gas pressure) and is added to the product gas stream emerging from the first reactor. The mass ratio of ethylene to acetic acid is preferably 1/3 to 2/3. Due to the simultaneous addition of ethylene and acetic acid in the heat exchanger, the partial pressure of acetic acid is reduced, and the acetic acid evaporates at circulating gas pressure even at temperatures below 200 ° C. Thus, the above-mentioned problem of the decomposition of acetic acid with the risk of deposits in the apparatus is prevented. In addition, the heat exchanger with steam of a much lower pressure level, generally with steam at a pressure of 12 to 20 bar abs. to be heated.

Preferred heat exchanger constructions are shell-and-tube heat exchangers with product on the tube side and shell-side steam heating. Also swapped pages (product on the Shell side) are possible. In a heat exchanger with several heating zones, it might be possible to use gradually separate steam. The heat exchangers mentioned can be designed with or without natural circulation (thermosiphon). Preference is given to adding fresh acetic acid with complete evaporation; However, it is also possible, at least in part, to add back-acetic acid and, if appropriate, to remove the high-boiling components contained therein by partial discharge of a liquid stream.

Another way to evaporate the acetic acid at the recycle gas pressure by means of the partial pressure-lowering effect of ethylene is to use the "saturator", but not with recycle gas, but only with the nachzuladenden ethylene, and the vaporized ethylene / acetic acid mixture emerging from the first reactor The charged ethylene is passed through a column, preferably with random packings, packings or trays, and acetic acid is added, preferably fresh acetic acid The column is heated by heated pump flow and / or heated feed streams (ethylene / acetic acid) at recycle gas pressure ,

In a further preferred embodiment, the activator component of the catalyst can be added to the product gas stream leaving the first reactor. For this purpose, an aerosol of a solution of the activator, generally an alkali metal carboxylate such as potassium acetate, is added. The amounts added can be determined by analyzing a small partial flow of the circulating gas leaving the first and the preceding reactor, respectively. For this purpose, for example, the small partial flow can be partially condensed or washed and the condensate analyzed. If more than two reactors are arranged one behind the other in the reactor cascade, it is possible, for the addition of acetic acid, of ethylene, in each case when the product gas stream leaving the preceding reactor is transferred to the next reactor. for the addition of acetic acid in combination with ethylene, and for the addition of the activator component of the catalyst, preferably proceed in the same manner as in the transfer of the product gas stream from the first reactor into the second reactor of the reactor cascade.

The workup of the product gas mixture, which is obtained after the second reactor or after the last reactor of the reactor cascade, and the recycling of the cycle gas to the first reactor is known and can be carried out, for example, analogously to the method already described above in the prior art:

In general, the gaseous reaction mixture (circulating gas) is freed after leaving the last reactor of the reactor cascade in a pre-dewatering column of vinyl acetate, acetic acid and water. The gaseous phase obtained from the pre-dewatering is generally freed from residual vinyl acetate in the cycle gas scrubber. Thereafter, can be separated from a partial stream of the circulating gas, in a C0 ₂ scrubber, C0 ₂ . The partial stream is combined with the remaining cycle gas and the recycle gas, after reloading with ethylene, acetic acid and oxygen, recycled to the gas phase oxidation reactor.

The liquid phases obtained from the pre-dewatering column and the recycle gas scrubber, which predominantly contain vinyl acetate, acetic acid and water, are generally separated by distillation in an azeotropic column, a dewatering column and a pure vinyl acetate column, and pure vinyl acetate monomer (VAM) is recovered. Such a processing process is described, for example, in WO 2011/089070 Al.

The inventive method has the advantage that with relatively low, specific investment costs, a significant increase in capacity of a plant for VAM production is obtained. Compared to a single reactor, a reactor cascade of two or more reactors can generally increase VAM production capacity by 50% to 100%. The amount of circulating gas to be worked up after the last reactor increases only at the pre-drainage and its condensation, generally by up to 15%. In the cycle gas scrubbing, at the cycle gas compressor and the acetic acid saturation, increases in relation to the increased VAM production capacity, the amount of cycle gas to be processed only insignificantly, with the result that no other capacity expansion in the cycle gas system is required. Only the cycle gas compressor must compensate if necessary additional pressure loss of the reactors following the first reactor. This unchanged load state from the recycle gas scrubber to the first reactor is due to the fact that the vinyl acetate and water additionally formed in the reactor cascade almost completely accumulates as a sump in the first workup step after the reactor cascade, generally in the pre-dewatering column, and Therefore, the Grundkreisgasmenge not we considerably increased.

The process according to the invention thus reduces the specific operating costs. It must be heated relative to the VAM output less cycle gas before the reactor cascade, and less acidic acid vaporized before the reactor cascade and be condensed after the reactor cascade, resulting in steam and cooling water savings. The energy efficiency of the process is improved because in the process according to the invention acetic acid is merely recharged depending on consumption, and in the reactors following the first reactor the unreacted base charge of the recycle gas is further used with acetic acid. In the prior art processes with a single reactor, the acetic acid remaining in the recycle gas after the reactor is first completely condensed and then completely evaporated again to be recycled to the reactor as the back acetic acid. By far the most energy-consuming and cost-intensive step in the processing and recycling of the recycle gas is, both in the conventional method with a single reactor and in the inventive method, the recycle gas compression, after separation of products and by-products and before return guide the circulating gas in the (first) reactor. Because of the higher VAM production capacity, the specific power consumption per tonne of vinyl acetate monomer produced is drastically reduced in the process according to the invention since the circulating gas quantity to be compressed hardly increases and only the pressure loss of the downstream reactors has to be compensated if necessary.

In FIGS. 1 and 2, the method according to the invention is shown in simplified form by way of example.

In Figure 1, the inventive method is sketched using the example of a reactor cascade with two reactors. The circulating gas (dashed line) is fed into the first reactor (1) and from there into the second reactor (2). Before being fed to the second reactor (2), it is charged with oxygen (3c) and optionally with ethylene (3a), acetic acid (3b) and / or the activator component (3d), here potassium acetate. After the second reactor (2), the cycle gas is generally passed into a pre-dewatering column (4), from the bottom of which most of the vinyl acetate (VAM) and also acetic acid and water are separated off. The gaseous mixture leaving the top of the pre-treatment column (4) is generally passed into a recycle gas scrubber (5) operated with acetic acid. At the bottom of the cycle gas scrubber (5) a VAM-containing acetic acid solution is separated off. The at the head of the cycle gas scrubber (5) removed circulating gas is compressed with the cycle gas compressor (6), wherein a partial stream, preferably on the pressure side, is removed, in the C0 ₂ scrubber (7) is passed, and is returned to the circulating gas stream. Before returning the recycle gas to the first reactor (1), the recycle gas is charged with ethylene, loaded with acetic acid in the acetic acid saturator (8) and, after supplying oxygen, passed into the reactor (1).

FIG. 2 shows a preferred embodiment in which the circulating gas stream (dashed line) emerging from the first reactor (not shown) enters into the second Actuator (2) is performed, wherein the supply of acetic acid and ethylene via a steam-heated heat exchanger (9). The heat exchanger (9) is for example a tube bundle heat exchanger with product on the tube side. Acetic acid and ethylene are simultaneously injected into the heat exchanger (9). The oxygen and the activator potassium acetate are added separately before the second reactor (2). The cycle gas leaving the second reactor (2) is passed into the pre-dewatering column (4).

Examples:

Comparative Example 1

A 2201 tubular reactor loaded with a supported Pd / Au catalyst was abs bar under a pressure of 10 bar. and a temperature of 165 ° C with a gas mixture with 56% by volume of ethylene, 13% by volume of acetic acid and 8% by volume of oxygen. The gas mixture leaving the reactor was passed through a pre-dewatering column and an acetic acid scrubber and compressed in a cycle gas compressor at 3 bar. Before returning the cycle gas to the reactor, it was charged with 87 kg / h of ethylene, 350 kg / h of acetic acid and 70 kg / h of oxygen

The volume of circulating gas circulating in front of the acetic acid saturator and the ethylene addition was about 710 Nm ³ / After a period of 1 year, the VAM yield was approx.

2,000 t. The energy consumption for the recycle gas compression over the runtime was approx. 106 MWh. The steam consumption in circulating gas was about 1,200 t. Example 2:

The procedure was analogous to Comparative Example 1, with the difference that between the 2201 tubular reactor and the pre-dewatering column, a second 2501-tube reactor was arranged. Both reactors were charged with the supported catalyst from Comparative Example 1. The reactor 1 was charged as in Comparative Example 1 with a gas mixture with 56% by volume of ethylene, 13% by volume of acetic acid and 8% by volume of oxygen and at operated at a pressure of 10 bar abs. and a temperature of 165 ° C.

The product gas mixture leaving the reactor 1 was charged with ethylene and acetic acid. 169 kg / h of acetic acid and 87 kg / h of ethylene were fed via a heat exchanger. About a mixing nozzle 70 kg / h of oxygen was supplied. Subsequently, the recycle gas was transferred to the second reactor and the product gas mixture leaving the second reactor was worked up as described in Comparative Example 1 and returned to the first reactor after addition of acetic acid, ethylene and oxygen.

The volume of the recirculated circulating gas volume before the saturator and the ethylene addition was 710 Nm ³ / h. After a period of 1 year, the VAM yield was approximately 4,000 t. The energy consumption for the recycle gas compression over the runtime was approx. 150 MWh and thus decreased by approx. 30% in relation to VAM. The steam consumption in circulating gas was approx. 1,800 t, which was about 25% lower in relation to VAM.

Claims

Claims:

A process for the preparation of vinyl acetate in a heterogeneously catalyzed, continuous gas phase reaction by reacting ethylene with acetic acid and oxygen, and

Separating the product gas mixture containing essentially ethylene, vinyl acetate, acetic acid, water, carbon dioxide and other inert gases,

and recycling an ethylene-containing circulating gas stream, after recharging the circulating gas stream with ethylene, acetic acid and oxygen,

characterized in that

the product gas mixture leaving the first reactor is charged with oxygen, and optionally with acetic acid and / or with ethylene,

and fed to a second reactor,

2. The method according to claim 1, characterized in that the dimensions of the reactors in the reactor cascade are the same or different.

3. The method according to claim 1 or 2, characterized in that are used in the reactors supported catalysts with the same or different activity.

4. The method according to claim 1 to 3, characterized in that the reactors in the same bed height or in different bed height filled with supported catalyst who the.

5. The method according to claim 1 to 4, characterized in that each reactor of the reactor cascade is equipped with its own boiling water cooling circuit.

6. The method according to claim 1 to 5, characterized in that the from the first reactor or a cascade in the reactor preceding each reactor exiting product gas mixture before being transferred to the second or ever Weil a next reactor, in addition to oxygen additionally loaded with acetic acid becomes.

7. The method according to claim 6, characterized in that the acetic acid is added to the product from the first reactor or from a reactor in each preceding reactor exiting product gas mixture, wherein the acetic acid in each case at the prevailing at this point cycle gas pressure in a Essigsäuresättiger or in a heat exchanger is evaporated.

8. The method according to claim 6, characterized in that the acetic acid is added to the product from the first reactor or from a reactor in the preceding each reactor exiting product gas mixture, wherein the acetic acid is evaporated at a lower pressure than at the prevailing at this point cycle gas pressure and is then compressed to the pressure level of the cycle gas

9. The method according to claim 6, characterized in that the acetic acid is injected into the product gas mixture exiting from the first reactor or from a reactor which precedes in each case in the reactor cascade. A method according to claim 1 to 9, characterized in that the from the first reactor or in the reactor cascade each preceding reactor exiting product gas mixture before being transferred to the second or each next reactor, in addition to oxygen and acetic acid is additionally loaded with ethylene.

A method according to claim 10, characterized in that the acetic acid is evaporated together with ethylene in a heat exchanger at circulating gas pressure and the product from the first reactor or in the reactor cascade preceding each reactor exiting product gas mixture, before its transfer to the second or each a next reactor, is added.

A method according to claim 10, characterized in that the acetic acid is vaporized together with ethylene in a column at circulating gas pressure and the product from the first reactor or in the reactor cascade preceding each product gaseous mixture, before its transfer to the second or each a next reactor, is added.