MXPA98002515A - Process of production of ether and olefin from a hydrocarbon cutting containing at least one tertiary olefin by synthesis after decomposition of eter that includes a first phase of olefin purification by fractionamy - Google Patents

Abstract

A process for the production of ether and olefin, from a hydrocarbon section containing at least one tertiary olefin, by synthesis of at least tertiary alkyl ether after fractionation to recover an organic fraction containing the ether which decomposes in a product (P1) containing at least one alcohol and at least one tertiary olefin, which is fractionated, then the tertiary olefin is purified in an extraction zone (L1) by washing with water from which a fraction is recovered containing the tertiary olefin that is sent to a separation zone (Co) from which an aqueous liquid fraction and a liquid fraction of hydrocarbons containing most of the tertiary olefin are recovered

Description

PROCESS OF PRODUCTION OF ETHER AND OF OLEFIN FROM A HYDROCARBON CUTTING CONTAINING AT LEAST ONE TERTIARY OLEFIN BY SYNTHESIS AFTER THE DECOMPOSITION OF ETHER INCLUDING A FIRST PHASE OF OLEFIN PURIFICATION BY FRACTIONATION FIELD OF THE INVENTION The invention relates to an integrated process for the synthesis of pure tertiary olefins, from cuts containing hydrocarbons, comprising an etherification step of said hydrocarbon cutting by at least one alcohol in which a product comprising at least one alcohol is formed. minus one tertiary alkyl ether which is sent to a decomposition zone of tertiary alkyl ether (s) from which a product comprising at least one tertiary olefin of high purity is recovered. This refers in particular to a production process of high purity isobutene, from a cut containing G4 hydrocarbons comprising the formation, from this cut and of methanol, the methyl ether of tertiary butyl alcohol (MTBE initials English of methyl-third- REF: 027023. butyl ether), then the decomposition of MTBE and the fractionation of the decomposition product into methyl alcohol and the purified isobutene. The process according to the present invention is applied regularly to the synthesis of any tertiary olefin from tertiary alkyl ether [for example ETBE (tert-butyl alcohol ethyl ether of the English initials ethyl-tert-butyl-ether), ETAE (ethyl ether of tertioamyl alcohol of the English initials ethyl-tertio-amyl-ether), TAME (tertioamyl alcohol methyl ether of the English initials tertio-amyl-methyl-ether), isopropyl-tert-butyl-ether]. The following description of the present invention, and more particularly the operating conditions, are given by way of indication for the synthesis of isobutene from hydrocarbon cuts which essentially contain the hydrocarbons of 4 carbon atoms (such as isobutene) by synthesis and decomposition of MTBE.

BACKGROUND OF THE INVENTION There are several production routes of high purity isobutene industrially exploited. The oldest is the extraction process with sulfuric acid, but it is expensive and obsolete; it is a pollutant famous for the rejection of the acid used.

In addition, the yield of isobutene does not exceed 90%. The ARCO firm uses the dehydration route for tert-butyl alcohol (ABT), the latter is the by-product obtained with the production process of propylene oxide. The process for the dehydrogenation of isobutane is being developed in the course of the last years due to the important and growing demand of MTBE. However, this process has not been operated profitably more than for very large production capacities. The production of high purity isobutene by cracking MTBE is better suited for small capacities than for large capacities.

In addition, this route benefits all the infrastructure related to the increasing importance of ethers in gasolines reformulated. The numerous refineries in all parts of the world have MTBE production facilities, for example. Another part of the plan also has an MTBE change plan worldwide. This means that the production of high purity isobutene via, the formation and decomposition of MTBE, which can be started, easily all over the world, even outside the refineries. The idea of producing isobutene by the decomposition of ether, and more particularly MTBE, has been known for some time, but the processes of Procurement proposed by the prior art or art present certain drawbacks.

DESCRIPTION OF THE INVENTION Thus, in the process developed by SUMITOMO, described by the example in the patent application EP-A-68 785, the decomposition reaction of MTBE is carried out in the liquid phase, in the presence of an acid-type solid resin catalyst of ion exchange. . Product flows are obtained: isobutene and methanol. As the scheme describes it, isobutene It is directly obtained in the dome of a distillation column without another purification step. The isobutene thus obtained contains a certain number of impurities, to start with a small fraction of methanol that is distilled by azeotropy, of dimethylether (DME) the volatile compound formed by condensation of methanol in the presence of an acid catalyst. It is likely that the purity of the isobutene is then insufficient for a use such as the manufacture of polyisobutene or other copolymers. In addition, it does not seem possible to avoid the accumulation of heavy impurities, such as the dimers of isobutene or of the methyl butyl ether of secondary butyl alcohol (MSBE), which in the end inevitably results in a reduction in the purity of the products. In the process developed by ERDOLCHEMIE, described for example in US-A-4 409 421, the purification of the isobutene formed comprises the removal of residual alcohol carried with the tertiary olefin by adsorption. This method has the disadvantage of having to regenerate the adsorbent regularly. In addition, the recovery of most of the Alcohol resulting from decomposition is not solved. More recently, the same company described, in US-A-5 095 164, employ the same decomposition reaction in a distillation equipment. The catalyst is then placed at the bottom of the column at the level of the reboiler. This particular operation is limiting from the point of view of the reaction temperature, directly imposed by the nature of the ether and the operating pressure. In addition, this actually favors the formation of reaction by-products such as the formation of isobutene dimers and / or the formation of dimethylether. In this regard, the quality and / or conversion of the products are not clearly explained. On the other hand, the company BASF describes, in the patent US-A-4 287 379, a scheme that integrates at the same time the synthesis stage of the ether, its separation, then the decomposition step of the ether to produce the isobutene. However, to avoid certain stages of purification, the etherification is made with a C3 or C4 alcohol, which is a major drawback compared to the international MTBE market.

This company has also described in the text of US-A-4 320 232 a process for the preparation of the MTBE and isobutene conjugate comprising the formation of ether from a cut of C4 containing isobutene by reaction of this cut into a mixture of alcohol containing methanol and alcohols with 3 carbon atoms or with four carbon atoms, in the transcruso from which is formed a mixture containing MTBE (tertiobutyl alcohol methyl ether and tertiary alkyl esters of alcohols with C4 and C4 which is sent to an area of decomposition in which isobutene is formed The use of a mixture of alcohol uniquely complicates the process in particular at the level of separation and purification of products, on the other hand this process involves more frequently the use of two stages of etherification Finally, we can also cite the two phases of the SNAMPROGETTI process presented in the Chemical Economy &Engineering Review, vol.14 No. 6 january 1982, which includes at the same time the synthesis of MTBE and the stage of decomposition of MTBE for the Isobutene production. It seems that the schemes that a certain loss of water by carrying and / or saturation of flux or isobutene, at the level of washing of isobutene to remove alcohol, is not taken into account. This is translated or converted to final 1 either in a reduction of the wash water flow rate, or in a loss of efficiency of this washing section. This can then impair the quality of the isobutene produced. On the other hand, according to these schemes, the fraction of hydrocarbons leaving the extraction column of water containing a relatively large amount of free water is sent completely to the fractionation column that allows the recovery of purified isobutene which implies that this column must treat a important product quantity and thus must have important sizing characteristics, which makes the process particularly costly and delicate in its operation. The process according to the invention makes it possible to remedy the aforementioned drawbacks. It relates to a production process of tertiary olefin (s) characterized by (very) high purity, from a hydrocarbon cut that contains them, by a method comprising the formation then the decomposition of at least one tertiary alkyl ether. This process is likewise a process adapted to evaluate the tertiary olefins contained in the hydrocarbon cuts in the form of pure tertiary olefins, usable in particular in the formation of polymers and / or copolymers and / or in the form of alkyl ethers tertiary, which can be used in particular as additives in motor fuels in combustion. The invention relates to a process comprising the formation, then the decomposition of tertiary alkyl ether as defined above, in particular of MTBE or ETBE, for the production of tertiary olefin (s), of isobutene in particular, of high purity. In the case of the decomposition of other ethers, a mixture containing a plurality of tertiary olefins can be obtained. Thus, in the case of the decomposition of TAME, a mixture is obtained which contains methyl-2-butene-1 and methyl-2-butene-2. In addition to the reaction zones themselves, the process according to the invention comprises the zones of purification or recovery or recycling of different products in such a way that optimizes the valuation of the products or b t en s and minimizes the losses. The present invention relates to a process for the production of pure tertiary olefin and / or tertiary alkyl ether from a hydrocarbon section containing at least one ether ether tertiary ether, said process comprises: a) a step of forming at least one tertiary alkyl ether by contacting it with a reaction zone, generally comprising at least one reactor (Rl), and containing an etherification catalyst, of at least one cut-off hydrocarbons containing at least one tertiary olefin ether with at least one primary or secondary alcohol generally, preferably primary, which is in general 1 to 6, preferably 1 to 4 carbon atoms per molecule, preferably methyl alcohol or of ethyl alcohol or isopropanol, more preferably methyl alcohol or ethyl alcohol, b) a step of separating most of the product from step a) into an organic fraction (01) depleted in tertiary alkyl ether, and preferably does not contain substantially tertiary alkyl ether, and an organic fraction (El) , enriched in tertiary alkyl ether, and preferably containing substantially all of the tertiary alkyl ether formed in the course of step a), c) a step of decomposition of at least a portion of the tertiary alkyl ether contained in the organic fraction (El) of step b), in a reaction zone generally comprised of at least one reactor (R2) containing a catalyst of ether decomposition, in a product (Pl) containing at least one alcohol and at least one tertiary olefin, d) a stage of fractionation of at least a part of the product (Pl), and possibly of the entire product, in a fractionation zone (Cl) that allows obtaining a part of fraction (A) containing the most of the tertiary olefin and optionally a minimum fraction of alcohol and of the possible light compounds initially contained in the part of said product (Pl), and on the other hand a fraction (B) containing the greater part of alcohol formed in stage -c) and optionally of the non-decomposed ether in step c), e) a purification step of at least a part of the fraction (A) in which said part is sent to an extraction zone (Ll) for washing in water from which an aqueous fraction is obtained (C) which contains most of the alcohol initially present in said part and a fraction (D) that contains most of the tertiary olefin initially present in said part, said fraction (D) contains said tertiary olefin, water, optionally light compounds and is substantially free of alcohol, Said process is characterized in that it comprises a step f) in which at least a part of the fraction (D) is sent to a separation zone (Co) to from which an aqueous liquid fraction (Le) and a liquid organic fraction (Ohpl) containing the greater part of tertiary olefin initially present in said part of fraction (D) is recovered, said fraction (Ohpl) containing said tertiary olefin , a small amount of water and eventually light compounds. In a particular form the embodiment of the process according to the invention, a part of the organic fraction (El) containing the tertiary alkyl ether is sent to the motor fuel fractions and the other part is sent to step c) of the decomposition of the tertiary alkyl ether. According to another particular form of the embodiment, the process according to the invention comprises a step b) in which at least a part of the organic fraction (El) resulting from step b) containing the tertiary alkyl ether is sent to an area of purification (C4), for example by distillation, from which a heavy fraction (Ll) depleted in tertiary alkyl ether containing, for example, the oligomers and MSBE (methyl ether of secondary butyl alcohol) is obtained, which can be least in part sent to the torch and / or at least a part to the motor fuel fractions, and a lighter fraction (E2) enriched in tertiary alkyl ether which is mostly sent to step c) of ether decomposition. According to this form of use another part of the organic fraction (El) containing the tertiary alkyl ether can be sent directly to the motor fuel fractions and still another part can be sent directly to stage c). It is also possible to send the entire organic fraction (El) containing tertiary alkyl ether to the zone (C4) of step b). It is also possible to send only part of the organic fraction (El) to step b) and all the rest directly to step c). In a particular embodiment of the process according to the invention, which also makes it possible to obtain a tertiary olefin of high purity, at least a part of the liquid fraction (Ohpl) recovered in step f) is sent to a step g) in a step fractionation zone (C2) in which said part of the liquid fraction (Ohpl) is fractionated on the one hand into a fraction (0hp2) containing the tertiary olefin and on the other hand into a fraction (F) containing the largest fraction part of the possible light compounds and possibly a reduced amount of residual water. The fraction (F) can be separated into a gaseous fraction which is evacuated for example to the torch and a liquid fraction that is at least partly forwarded to the fractionation zone (C2) of step g) (line (20b) output from line (20) or line (22) in Figures 1 and 2. According to this particular form, it is usually preferred that the fractionation zone of step g) comprises at least one permanent means of recovery from of the fraction (F) of a light fraction that is substantially anhydrous. Very often this medium allows to separate at least a part of the fraction (F) in a light fraction that is substantially anhydrous and in an aqueous fraction. This means is for example a separating balloon provided with at least one medium, for example a branch, which allows the decanting and transfer of an aqueous fraction. In this case, at least a part of the aqueous fraction obtained in step g) is preferably recycled to step e) in the extraction zone (Ll) for washing in water. Then, the anhydrous sensitive light fraction is usually separated into a gas fraction that is evacuates for example towards the torch and a liquid fraction in general sensibly anhydrous which is at least a part forwarded to the fractionation zone (C2) of step g). According to another mode of use,? a fraction (F) (or the light fraction obtained from said fraction (F), leaving step g), is at least partly sent to a catalytic cracking zone. According to another variant, the fraction (F) (or the light fraction obtained from said fraction (F)) leaving the stage g) is at least partly sent to an ether synthesis reaction zone, preferably the ether synthesis reaction zone of step a). According to another variant, the fraction (F) (or the light fraction obtained from said fraction (F)), which leaves the stage g), is at least partly sent to the torch. The most frequent process of the present invention comprises a step h) in which at least a part of the aqueous fraction (C) leaving the stage e) is sent to a fractionation zone (C3) from which recover a fraction (G) that contains most of the alcohol initially present in said part and an aqueous fraction (H) liberated from most of the initial alcohol present in said part. According to this mode of operation, at least a part of said fraction (G) can be sent to an ether synthesis zone, preferably the ether synthesis reaction zone of step a).

It is also possible to send all of this alcohol to said ether synthesis zone. It is also possible to partially or completely recover this alcohol for other uses. According to this mode of operation, at least a part of the aqueous fraction (H) obtained in step h) can also be at least a part recycled to stage e) in the area (Ll) of extraction by washing in water . According to this mode of operation, at least a part of the aqueous fraction (H) obtained in step f) can also be at least a part sent to a water treatment area. In a preferred form of use of the process of the present invention, at least a part of the fraction (B) obtained in step d), which contains most of the alcohol formed in step c) and eventually the ether does not decomposed in step c), it is sent to an ether synthesis zone, preference in the ether synthesis zone of step a). It is also possible to send all of this fraction to said ether synthesis zone. It is also possible to partially or totally recover this fraction for other uses. In a preferred form of use of the. In the process of the present invention, at least a part of the aqueous fraction (Le) obtained in step f) is recycled to step e) in the extraction zone (Ll) for washing with water. These various water recycles are independent of each other and can be carried out together or separately. Water that is not recycled is usually purged after it is usually sent to a water treatment area for use. This purge is the most frequently present at least in the aqueous fraction (H) obtained in step h) due to the presence of an area (C3). In particular, this purge makes it possible to prevent the accumulation of heavy compounds, for example heavy alcohols.

The conditions that can be employed in step a) of the present invention are the well-known classical conditions of the man skilled in the art for the synthesis of tertiary alkyl ether from a hydrocarbon cut-off containing at least one tertiary olefin and can be less an alcohol, in particular an alcohol having 1 to 6 carbon atoms per molecule and more often methanol or ethanol. The hydrocarbon cuts which are used in the context of the present invention contain at least one tertiary olefin and in general other saturated or unsaturated hydrocarbon compounds such as, for example, other olefins, paraffins, optionally a reduced proportion of water, and / or of carbon oxides. The pure tertiary olefins contemplated to be prepared according to the present invention are the compounds whose olefinic carbon atom is branched. These compounds are usually from 4 to 10 carbon atoms per molecule, preferably from 4 to 8 carbon atoms per molecule and more frequently from 4 to 6 carbon atoms per molecule. It is possible to quote isobutene, methyl-2-butene-1, methyl-2-butene-2, tertiary hexanes, tertiary octenes and tertiary decades. C4 and / or C5 cuts resulting from refining or petrochemicals, such as C4 and / or C5 cuts of steam cracking, usually after extraction of dienes, cuts of C5 and / or catalytic cracking, can be cited. the resulting cuts of isomerization (hydroisomerization or skeletal isomerization) and the cuts obtained by dehydrogenation of paraffins. The synthesis of ether is most frequently carried out in the presence of an acid catalyst and more often of a solid acid catalyst selected from the group consisting of organic acid resins (for example sulphonic resins) and solid mineral acid resins under the conditions of the ether synthesis reaction (for example grafted mineral solids carrying at least one sulfonic organic group for example alkyl sulfonic, aryl sulphonic, alkylaryl sulfonic and in particular grafted polysiloxanes and more particularly those grafted with at least one alkyl sulfonic group). Said catalyst may be a commercial resin such as the resin Amberlyst 15 or 35 or the resin M 31 of the company DOW-CHEMICAL, or a commercial grafted polysiloxane. In this step a) the amount of alcohol employed is usually such that the molar ratio of alcohol / tertiary olefin present in the charge is almost 0.5: about 8: 1, often about 0.8: 1 to about 5: 1, more often from about 0.9: 1 to about 4: 1. The reaction temperature is usually around 20C to about 120C, often around 30C to about 100C, most often around 40C to around 90C. The WH (volumetric velocity per hour) in volume of charge per volume of the catalyst per hour is usually around 0.005 to about 100, often about 0.01 to about 50, and more often about 0.1. to about 10. The pressure is usually chosen so that the constituents present in the solid reaction zone are in the liquid state. Usually the absolute pressure in this etherification zone is from about 1 bar to about 40 bar, frequently from about 1 bar to about 25 bar (l bar is equal to 0.1 Mpa).

The conditions of use of step b) of separation of the product resulting from stage a) in an organic fraction (01) that practically does not contain the tertiary alkyl ether and an organic fraction (El) enriched in tertiary alkyl ether, preferably containing practically all of the tertiary alkyl ether formed during step a), are the classical conditions that depend on the compounds present in the product resulting from step a). This separation can be carried out in the more or less severe conditions that allow obtaining a fraction (01) which still contains a reduced proportion of ether.

The man of office can also choose the operating conditions in order to obtain the desired separation. The conditions are more frequently chosen so that a fraction (El) containing almost the total of the ether formed during step a) is obtained. In the context of the invention, the etherification reaction zone of step a) may be different from the separation or fractionation zone of step b), or a device comprising a mixed reaction and fractionation zone may be used. (distillation column catalytic) as already described for example in numerous patents and other publications of the prior art. In the case of a process in which the MTBE is manufactured in step a), the distillation separation column usually works at an absolute pressure of about 1 to about 30 bar, identical or different from that prevailing in the area of etherification. This column usually takes from 3 to 80 theoretical plates and frequently from 10 to 50 theoretical plates. The conditions of use of step c) of the present invention are the classical conditions of decomposition of tertiary alkyl ether well common to man by trade. In a preferred embodiment, this step c) can be used without adding fractionated water in the product introduced in the decomposition zone. However, it will be possible to add a certain amount of water, for example, up to the limit of the solubility of the water in the ether to be decomposed. Usually the conditions of use of this step c) are chosen so that most of the tertiary alkyl ether decomposes giving an alcohol and an olefin tertiary In this decomposition zone the absolute pressure is usually from about 1 to about 30 bar, preferably from about 1 to about 12 bar, the temperature is usually between 50C and 300C and preferably between 100C and 250C, the WH (space velocity per hour) is usually between 0.1 and 200 hl and more frequently between 0.5 and 100h-1. In this area, the acid catalysts, which are common to man by trade, can be used. It is usually preferred to use solid acid catalysts. Thus the catalyst can be chosen from the group consisting of the organic acid resins and the solid mineral acid resins under the conditions of the decomposition reaction of the ether. Among these compounds, those chosen from the group consisting of grafted mineral solids carrying at least one organic group of the alkyl sulfonic type are most frequently used., aryl-sulfonic or alkylaryl-sulfonic. One of the preferred forms of use of this step c) uses a catalyst chosen from the group consisting of the polysiloxanes grafted with at least one alkyl sulfonic group.

The general conditions of use of step d) of fractionation of the product (Pl) resulting from step c) of decomposition of the ether, is a stage where conditions are chosen in particular depending on the characteristics of the alcohol and the tertiary olefin formed . The skilled man can also choose these conditions to obtain the desired separation between a fraction containing the greater part of alcohol and a fraction containing the greater part of olefin. For example, in the case of the decomposition of MTBE and the formation of methanol and isobutene, the absolute pressure in the distillation column is from about 1 to about 15 bar, preferably from about 1 to about 10 bar. , identical or different from the one in the decomposition zone. The bottom temperature of the column depends in turn on the pressure prevailing in said column and on the composition of the bottom product, in particular the molar ratio between methanol and MTBE possibly present as a result of a partial decomposition of this ether in step c). In the case of a unit treating 1 kg / h of MTBE, the distillation column usually takes between 3 and 80 theoretical plates and more frequently between 10 and 50 theoretical plates. In step e) of purification at least a part of the fraction (A) which contains most of the tertiary olefin obtained in step c) is sent to an extraction zone (Ll) for washing with water. The amount of water used for this washing is usually such that the volumetric ratio between the volume of said amount of water introduced in said extraction zone and said fraction part (A) introduced into said extraction zone (Vagua / VA) is about 0.005 to about 20. Most often this amount of water is such that the ratio of Vagua / A is about 0.005 to about 10, of preference of about 0.01 to about 5 and even more preferably about 0.02 of about 1. The flow rate of water in this wash zone (Ll) is regulated many times depending on the level maintenance of funds in the fractionation zone (C3) of water and alcohol, in the event of the presence of such zone (C3). This background level can be defined as the minimum level necessary for the proper functioning of said area.

This parameter is a classic parameter well known to the man by trade. This regulation is often done in the manual mode by the operators, because it is possible that this regulation is carried out by an automatic regulation loop of said LCR of the Anglo-Saxon initials of the Level Control Regulation. Whichever mode of regulation is chosen, the amount of water can generally be adjusted with the help of a means of introducing additional water into the zone (Ll). This water supply makes it possible in particular to compensate for water losses due to the water drag and / or the saturation of the flow of the treated hydrocarbon, as well as the replacement of the water eventually purged. This extraction zone (Ll) is usually a column of dishes operating at a temperature of about l-100C, preferably from about 10 to about 60C. The absolute pressure in this zone is from about 1 to about 20 bar, more frequently from about 1 to about 15 bar, identical or different from that prevailing in the fractionation zone of step d). Step f) comprises a separation zone of at least a part of the fraction (D) resulting from the zone (Ll) of step e) in an aqueous liquid fraction (Le) and in a liquid hydrocarbon fraction (Ohpl), to an area (Co), is a classic stage well-known to the expert. This step is usually employed in a coalescence apparatus, in which the water is grouped in the lower part of the apparatus by coalescence. The conditions of temperature and of the prevailing pressure in this zone are of the same ranges that reign in the zone (Ll). The pressure (respectively the temperature) can be identical or different in said zone (Ll). In the area (Co), thus separates the free water contained in the product (D) resulting from step e). In addition, said zone (Co) is the same, it also very frequently has a zone function or loading flask for the purification zone (C2) of the tertiary olefin, in the case of the presence of such a zone (C2) . Any other common means of the ex-officio man may be employed within the framework of the present invention. By way of example, the use of an absorbent having a selectivity preferably of one of the aqueous or organic fractions can be mentioned.

The optional step g) of fractionation of at least a part of the fraction (Ohpl) resulting from the zone (Co) of stage f), towards a zone (C2), in a fraction (0hp2) containing the tertiary olefin and in a fraction (F) containing most of the possible light compounds present in said fraction (Ohpl) and eventually the waste water contained in said part of the liquid fraction (Ohpl), is usually effected in a distillation column that works at an absolute pressure of from about 1 to about 15 bar, more frequently from about 3 to about 10 bar, identical or different from that prevailing in the separation zone of step f). For a unit that produces 0.6 kg / h of isobutene, this column is usually from about 3 to about 80 theoretical plates and more frequently from about 5 to about 50 theoretical plates. The background temperature of the column depends in particular on the prevailing pressure of said column. The optional step h) of fractionation in a zone (C3), of at least a part of the aqueous fraction (C), which contains most of the alcohol initially present in fraction (A) in a fraction (G) which contains most of the alcohol initially present in said fraction part (C) and in an aqueous fraction (H) released from most of the alcohol initially present in said fraction part (C), is usually carried out in a distillation column (C3) under absolute pressure of about 1 to about 12 bar, preferably about 1 to about 8 bar, identical or different to that prevailing in the area (Ll) of water extraction from the stage e). The background temperature of the column depends in particular on the pressure prevailing in said column; it is usually around 50 to about 300C and more often around 65 to about 200C. The column 1 usually ranges from about 2 to about 80 plates and more frequently from about 3 to about 60 theoretical plates. Figures 1 and 2 are the schemes illustrated at the beginning of each preferred variant that may be employed in the present invention. The dotted line strokes show the various possible options. In the first variant illustrated in Figure 1, the hydrocarbon charge containing at least one olefin Tertiary is introduced by line 1 in the etherification and fractionation zone (Rl). In this zone (Rl) a supply of alcohol is regularly introduced via line 2 and line 3a through the eventual recycled alcohol. Said zone (Rl) contains an etherification acid catalyst. The product obtained by etherification of the hydrocarbon cutting is divided in said zone (Rl) into a hydrocarbon organic fraction (01) leaving line 4 and into an organic fraction (El) containing the formed ether leaving line 5 A part of this organic fraction (El) is sent via line 5a to the motor fuel fractions and the other part is sent via line 5c to the ether decomposition zone (R2). Line 6 retrieves a product (Pl) containing a tertiary olefin and alcohol that is sent to the fractionation column (Cl). The product containing the alcohol leaving the column (Cl) by line 3 for example may be sent partly by lines 3,3c then 3a to the area (Rl). Another part of this product can be evacuated through lines 3 and 3b. The product that contains the tertiary definition is introduced by line 7 in an area (Ll) of water extraction in the which water is introduced through line 11 and from which a fraction (D) impoverished in alcohol is recovered by line 9 that is sent to separation zone Co from which a fraction is recovered through line 23 aqueous liquid (Le) and by line 24 a liquid fraction of hydrocarbons (Ohpl) containing the majority of tertiary olefin initially present in fraction (D). Said fraction (Ohpl), said tertiary olefin contains a reduced amount of water and optionally the light compounds, is sent via line 24 to a fractionation zone (C2). On line 8, it recovers at the exit of. the zone (Ll) an aqueous product (2) containing the alcohol that is introduced into the fractionation zone (C3). From the fractionation zone (C2), the ultra-pure tertiary olefin (Ohp2) is recovered via line 28 and light products are recovered from line 27. These light products are, for example, partly sent to the torch by lines 27 and 27a, but can be sent to a catalytic cracking zone or to an ether synthesis zone, which is preferably the zone (Rl), and against recycled part reflux by lines 19, 20 and 20b to the fractionation zone (C2). It is thus possible and it is a preferred embodiment to send at least a part of these light products through lines 19 and 21 to a separation zone (DI), from which a fraction formed in line 13 is recovered through line 13. most of water, by line 22 a liquid fraction of light products that are reflowed as a reflux to column (C2) by line 20b, and by line 12 at least a part of gaseous light products is recovered which are for example at least one part sent to the torch, but can also be sent to a catalytic cracking zone or to an area, preferably the zone (Rl), of ether synthesis. It is also possible to combine the two embodiments described above. The aqueous fraction recovered by line 13 may for example be returned partly by lines 14a, 14, 15 and 11 to zone (Ll) or partly recovered by line 13a. From the fractionation zone (C3), line 10 is recovered by alcohol which can, for example, be partly sent by lines 16 and 3a to the zone (R1) or recovered by line 10a. From this zone (C3), an aqueous fraction is also recovered by line 39 which can be sent at least in the part to a water treatment zone on line 39a or is recycled by lines 17, 15 and 11 at least in the part to zone (Ll). The aqueous liquid fraction (Le) recovered by line 23 from the separation zone (Co) can be sent at least partly to the water treatment zone via line 26 or is recycled via lines 25, 14 , 15 and 11 at least in part to the area (Ll), in addition to an eventual supply of water outside line 15b. The second variant illustrated in figure 2 differs from that described in relation to figure 1 in that the product (El) leaving the etherification zone and (Rl) is at least partly sent by lines 5 and 50 to a zone of purification (C4), the other part, if it exists, is sent directly by lines 5, 5b and 5c to the zone (R2) of decomposition of the ether. From the purification zone (C4) a heavy, ether-poor fraction is recovered via line 52 and an ether-enriched fraction is sent via line 5c to zone (R2) via line 51. The other schematic elements in Figure 2 are similar to those described in relation to Figure 1.

The heavy fraction recovered by line 52 is, for example, at least in the part sent to the fuel fractions. Suitable examples illustrate the invention without limiting the annotation.

EXAMPLE 1 A pilot-type equipment is used comprising the tubular reactors (Rl) and (R2) of respective volume of 20 milliliters and 10 milliliters. The first reactor (Rl) contains 6 grams of Amberlyst resin of 15, sold by the company ROHM ET HAAS and operates at a relative pressure of 10 bar, at an average temperature of 50C. It is fed by a cut of C4 resulting from catalytic cracking containing 20% by weight of isobutene and pure methanol sold by the company ALDRICH as a product with a purity greater than 99% by weight. The amount of methanol is adjusted so that the molar ratio of methanol / isobutene introduced to the reactor (RI) is 1.2. The reactor works with a WH of 0.5 h-l. In the conditions chosen the conversion of isobutene to MTBE is generally 97.5%. The second reactor (R2) contains 3 grams of the commercial catalyst based on polysiloxanes grafted with at least one alkyl sulfonic group. The reactor R2 is fed with a load containing 100% by weight of MTBE, at a VHL of 15 h-1, the relative pressure in the reactor is 7 bar and the average temperature is 160 ° C. Table 1 shows the composition of the charge introduced into the reactor R2 for the decomposition of MTBE and the composition of the product collected at the reactor outlet R2.

TABLE 1 load (% by weight) effluent R2 (% by weight) MTBE 100 10 Isobutene 56.1 Methanol 32.1 DME 0.5 Dimer 1.1 H20 0.2 With the help of the software sold by the American company SIMSCI (Simulation Science INC.) Under the commercial name Pro II, the various purification sections are calculated. A distillation column (Col), operating under a relative pressure of 7 bar, consisting of 10 theoretical plates, is used to step b) of the process of the invention to obtain a bottom product (El) and a dome product (01) (The fractionation of the product resulting from step a) of etherification of the isobutene contained in the section of (C4)) is simulated here. A distillation column (Cl), which operates with a relative pressure of 7 bar, formed by 10 theoretical plates, is used in step c) of the process of the invention to obtain a bottom product (B) and a dome product. (TO) . (The fractionation of the product resulting from step c) of MTBE decomposition is simulated here).

An extraction column for washing in water (Ll), which is a column of dishes operating at a temperature of 30C at a relative pressure of 12 bar, is used in step e) of the process of the invention to obtain an aqueous fraction ( C) and an organic fraction (D). A system for extracting the free water drawn to stage e) in fraction (D), of coalescence type (Co), allows to obtain an aqueous fraction (Le) and an organic fraction (Ohpl). It works under a relative pressure of 12 bar at a temperature of 30C. A distillation column (C2), the last isobutene purification step, operating under a relative pressure of 7 bar, and consisting of 10 theoretical plates, is used in step g) of the process of the invention to obtain a bottom product (Ohpl) which is of purified isobutene and a dome product (F) containing the light compounds. The column (Col) is fed with the product resulting from the etherification reactor. The product (El) recovered at the bottom of the column (Col) is used to feed the reactor (R2). The column (Cl) is fed by the effluent of (R2). The product (A) collected in the dome of (Cl) is sent to the column of extraction (Ll) or washed with an amount of water whose volumetric flow is equal to one tenth of the flow of (A). An aqueous fraction (C) is collected containing most of the methanol contained in (A), and a hydrocarbon fraction (D) containing a small amount of free water entrained. This fraction of free water is finally eliminated after decanting in the decantation system (Co) in the form of a fraction (Le) and an organic fraction of hydrocarbon (Ohpl) is recovered. Finally, the hydrocarbon fraction (Ohpl) is treated in column (C2) in order to produce at the bottom of the column a fraction (Ohpl) which is of high purity isobutene and in the dome, a light fraction (F). ) containing, in particular, dimethyl ether (DME). The obtained material balances are given in tables 2,3 and 4 afterwards.

TABLE 2 load Rl (weight) Effluent Rl (weight) dome Col (weight) Bottom Col (weight) Isobutene 20 0.6 0.6 c out of isobutene 80 80 80 Methanol 13.7 2.7 2.7 MTBE 0 30.4 0 30.4 total 113.7 113.7 83.3 30.4 TABLE 3 Effluent R2 product B Product A Fraction water C Fraction D (% by weight) column Cl column Cl wash column Ll column Ll (g / h) (g / h) column Ll MTBE 10 10 Isobutene 56.1 56.1 56.1 Methanol 32.1 30.4 1.7 1.7 DME 0.5 0.5 0.5 Dimeros 1.1 1.1 H20 0.2 0.2 10 9.2 Flow (g / h) 100 41.5 58.5 10 10.9 57.6 TABLE 4 Aqueous fraction Fraction organic Fraction F Fraction Ohpl extracted by Co Ohpl output of Co column C2 column C2 Isobutene 56.1 1.72 54.38 SMD 0.5 0.49 0.01 H20 0, 99 0, 01 0, 01 Flow rate (g / h) '0, 99 56, 61 2, 22 54, 39 Purity of isobutene (%) 99, 98% This example shows that carrying out the process according to the invention makes it possible to obtain from a cut of C4 containing an isobutene, an isobutene with a purity of 99.98%, with an overall conversion of 82.6%. The conversion can be improved for the use of various recycles, as well as for alcohol / non-converted and for the purging of the gasoline fractions of a part of the ether formed in the course of the etherification. This conversion can thus go from 94%.

EXAMPLE 2 A pilot-type equipment is used, which comprises in the first instance a tubular reactor Rl and R2 to carry out the two stages of reaction, synthesis and decomposition of the TAME ether. The stages of separation by distillation and sections of purification are calculated with the help of the Pro II software. In the pilot unit, the synthesis of the TAME ether is carried out at a first temperature by reaction of the isoamilenes with methanol in the presence of resin Amberlyst 15 (manufactured by Rohm% Haas). For this a cut of C5 type FCC containing 22% by weight of isoamilenes (methyl-2-butene-1 and methyl-2-butene-2) with added methanol (original of Aldrich, purity> 99% by weight) is used, so that a stoichiometry load of methanol / isoamilenes of 1 is used. The unit equipped with the Rl reactor is operated at 10 bar (relative pressure) and 60C, under a VHV of 0.5hl. In the course of this step, the conversion of the isoamylenes to TAME is raised to 67%. Next, the pilot unit is operated under the different operating conditions to perform the reverse reaction of decomposition of TAME, reactor R2 contains the Deloxan ASP catalyst (manufactured by Degussa). The unit is operated under a relative pressure of 7 bar, at an average temperature of 140C. The reactor R2 is fed by a charge containing 100% by weight of TAME, under a WH of 6 h-1. He product collected at the reactor outlet R2 has the composition given in table 5: TABLE 5: TAME decomposition reaction section.

Loading (% by weight) effluent R2 (% by weight) TAME 100 15 Isoamylenes 58.2 Metanol 26.45 DME 0.25 Dimer 0.1 With the help of the Pro LT software, the various purification sections are calculated as in the previous example.

TABLE 6: The material balance refers to the synthesis of TAME.

Load Rl (weight) Effluent Rl (weight) Dome Cl (weight) Fund Cl (weight) Isoamylene 22 7.26 7.26 cs outside isoamilenes; 78 78 78 Methanol 10.1 3.36 3.36 TAME 0 21.48 21.48 TOTAL 110.1 110.1 88.62 21.48 this includes met? i-3 butene-i, olefin classified as "non-etherifiable" TABLE 7: The material balance refers to the decomposition of TAME and the purification of high purity isoamylene.

Effluent R2 Background C2 Dome C2 or Water of Fraction C Fraction D (% by weight) (g / h) product A washing TAME 15 15 Isoamylenes 58.2.2.2.2.2.2 Metaliul 26.45 24.45 2 DME 0.25 0.25 0.25 DlHieloa 0.1 0.1 H20 12 11.5 0.5 Flow rate (g / h) 100 39.55 60.45 12 13.5 58.95 The integration of the two processes (synthesis of TAME after decomposition of TAME) allows isoamilenes (methyl-2-butene-1 and methyl-2-butene-2) to be extracted from a cut of C5 with a minimum yield of 56% (The yield can be improved by diverting the recycling of the unconverted ether) and with a purity higher than 98%.

It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Having described the invention as above, the content of the following is claimed as property.

Claims (21)

1. - A production process of the pure tertiary olefin and / or the tertiary alkyl ether from a hydrocarbon cut, comprising or containing at least one tertiary ether ether, the process is characterized in that it comprises: a) a step of forming at least one tertiary alkyl ether by contacting in a reaction zone, containing an etherification catalyst, with at least one hydrocarbon cut-off containing at least one tertiary olefin with etherification at least one alcohol, b) a step of separating most of the product resulting from stage a) in an organic fraction, depleted in tertiary alkyl ether, and in an organic fraction, enriched in tertiary alkyl ether formed in the course of step a), c) a step of decomposition of at least one tertiary alkyl ether contained in the organic fraction of step b), in a reaction zone containing an ether decomposition catalyst, in a product containing at least one alcohol and at least one tertiary olefin, d) a step of fractionating at least a part of the product in a fractionation zone that allows obtaining on the one hand a fraction (A) that contains most of the tertiary olefin and optionally a minimum fraction of alcohol and the compounds light optionally contained initially in the part of the product, and on the other hand a fraction (B) containing most of the alcohol formed in step c) and eventually ether not decomposed in step c), e) a purification step of at least a part of the fraction (A) in which said part is sent to an extraction zone by washing with water to From which is obtained an aqueous fraction (C) containing the most alcohol initially present in said part and a fraction (D) containing most of the tertiary olefin initially present in said part, said fraction (D) contains said tertiary olefin, water, optionally light compounds and is substantially free of alcohol, * said process is characterized in that it comprises a step f) in which at least a part of the fraction (D) is sent to an area of separation from which an aqueous liquid fraction and a liquid organic fraction containing most of the tertiary olefin initially present in said part of fraction (D) is recovered, said fraction contains said tertiary effine, a reduced amount of water and eventually of the light compounds.

2. - The process according to claim 1, characterized in that a part of the organic fraction containing the alkyl ether tertiary is sent to the fuel fractions of the engine and the other part is sent to stage c) of decomposition of the tertiary alkyl ether.

3. - The process according to claim 1 or 2, characterized in that it comprises a step b1) in which at least a part of the organic fraction resulting from step b) containing the tertiary alkyl ether is sent to a purification zone from which a heavy fraction depleted in tertiary alkyl ether is obtained and a lighter fraction enriched in tertiary alkyl ether is sent to stage c) of ether decomposition.

4. - The process according to any of claims 1 to 3, characterized in that at least a part of the liquid fraction recovered in step f) is sent to a step g) in a fractionation zone in which said part of the The liquid fraction is fractionated into a fraction containing the tertiary olefin and into a fraction (F) that contains most of the possible light compounds and eventually a smaller amount of residual water.

5. - The process according to claim 4, characterized in that the fractionation zone of step g) carries at least one medium that allows recovery from the fraction (F) of a light fraction that is substantially anhydrous.

6. - The process according to claim 5, characterized in that said means comprises a separating flask providing at least one permanent means of decanting and a liquid of an aqueous fraction.

7. - The process according to claim 6, characterized in that the aqueous fraction obtained in stage g) is at least partly recycled to stage e) in the extraction zone by washing with water.

8. - The process according to any of claims 4 to 7, characterized in that less a part of the fraction (F) or of the substantially anhydrous light fraction obtained in step g) from said fraction (F) is at least in part sent to a catalytic cracking zone.

9. - The process according to any of claims 4 to 8, characterized in that at least a part of the fraction (F) or of the substantially anhydrous light fraction obtained in step g) from said fraction (F) is at least in part sent to the ether synthesis zone of stage a).

10. - The process according to any of claims 1 to 9, characterized in that it comprises a step h) in which at least a part of the fraction (C) resulting from step e) is sent to a fractionation zone starting from from which a fraction (G) containing most of the alcohol initially present in said part and an aqueous fraction (H) free of most of the alcohol initially present in said part is recovered.

11. - The process according to claim 10, characterized in that at least a part of the fraction (G) obtained in step h) containing the alcohol is sent to the synthesis zone (Rl) of the ether of stage a) .

12. - The process according to any of claims 10 or 11, characterized in that at least a part of the aqueous fraction (H) obtained in step h) is sent at least in part to a water treatment area.

13. - The process according to any of claims 10 to 12, characterized in that at least a part of the aqueous fraction (H) obtained in stage h) is at least partly recycled to stage e) in the zone of extraction by washing with water.

14. - The process according to any of claims 1 to 13, characterized in that at least a part of the fraction (B) obtained in the step d) containing the alcohol is sent to the ether synthesis zone (Rl) of step a).

15. - The process according to any of claims 1 to 14, characterized in that at least a part of the aqueous fraction obtained in step f) is at least a part recycled to stage e) in the area of extraction by washing with water.

16. - The process according to any of claims 1 to 15, characterized in that in the step e) purification of at least a part of the fraction (A) is introduced into the extraction zone by washing with water a quantity of water such as the volumetric ratio between the volume of said water quantity introduced in said extraction zone and that of the part of the fraction (A) introduced in said extraction zone (Vagua / VA) is from 0.005 to 20.

17. - The process according to any of claims 1 to 16, characterized in that the extraction zone by washing with water of the stage e) At least one additional water introduction means is provided.

18. - The process according to any of claims 1 to 17, characterized in that the catalyst for the synthesis of the tertiary alkyl ether, is selected from the group consisting of organic acid * resins and mineral acid resins.

19. - The process according to any of claims 1 to 18, characterized in that the decomposition catalyst of the tertiary alkyl ether is selected from the group consisting of organic acid resins and mineral acid resins.

20. - The process according to any of claims 1 to 19, characterized in that the decomposition catalyst of the tertiary alkyl ether is selected from the group consisting of grafted mineral solids which contain at least one organic group of the alkyl sulfonic type, sulphonic or alkylaryl-sulfonic.

21. - The process according to any of claims 1 to 20, characterized in that the decomposition catalyst of the tertiary alkyl ether is chosen from the group formed by the polysiloxanes grafted with at least one alkyl sulfonic group.