MX2008006359A - Process for the separation of c5 hydrocarbons present in streams prevalently containing c4 products used for the production of high-octane hydrocarbon compounds by the se- lective dimerization of isobutene - Google Patents

Abstract

A process is described for the separation of C5hydrocarbons present, in a quantity ranging from 0.2 to 20%by weight, in streams prevalently containing C4products used for the production of high-octane hydrocarbon compounds, by the selective dimerization of isobutene, characterized in that the dimerization reactionis carried out in the presence of linear and branched alcohols and alkyl ethers in a quantity which is such as to have a molar ratio alcohols/alkyl ethers/isobutene in the feeding higher than 0.01. The present invention relates to a novel process for the preparation of a compound of formula (I):which comprises reacting a compound of formula (II):with a compound of general formula (III):wherein R1and R2are H or C1-4alkyl or R1and R2join together to form a C2-3alkylene group, which is optionally substituted by from 1 to 4 methyl or ethyl groups, or an anhydride of the compound (III), in the presence of a base and of a palladium catalyst which is (a) a palladium (0)- or palladium (IÎ)-triarylphosphine complex optionally in the presence of additional amounts of a triarylphoshine ligand, or (b) a palladium (II) salt in the presence of a triarylphosphine ligand, or (c) metallic palladium, optionally deposited on a support, in the presence of triarylphosphine;there being used from 0.9 to 2 moles of compound (III) for each mole of compound (II). A process is described for the separation of C5hydrocarbons present, in a quantity ranging from 0.2 to 20%by weight, in streams prevalently containing C4products used for the production of high-octane hydrocarbon compounds, by the selective dimerization of isobutene, characterized in that the dimerization reaction is carried out in the presence of linear and branched alcohols and alkyl ethers in a quantity which is such as to have a molar ratio alcohols/alkyl ethers/isobutene in the feeding higher than 0.01.

Description

PROCESS FOR THE SEPARATION OF C5 HYDROCARBONS PRESENT IN CURRENTS CONTAINING PREDOMINANTLY PRODUCTS OF C4 USED FOR THE PRODUCTION OF HIGH-OCTOPAN HYDROCARBON COMPOUNDS BY THE SELECTIVE DIMERIZATION OF ISOBUTENUM Field of the Invention The present invention relates to a process for the separation of C5 hydrocarbons present in the C fillers used for the production of high octane hydrocarbon compounds by the selective dimerization reaction of isobutene and to a lesser extent possible linear olefins, in the presence of linear and branched alcohols and alkyl ethers, which favor the production of high selectivities in the catalyst part. The obtained mixture can then be hydrogenated with conventional methods to obtain a product with improved octane characteristics, additional.

BACKGROUND OF THE INVENTION Primarily for environmental reasons, the composition of gasolines are being reformulated and the general trend is towards the production of fuels that burn better and have less evaporative emissions. The main measures to achieve this objective are listed continued (D. Sanfilippo, F. Ancillotti, M. Marchionna, Chi &Ind., 76, (1994), 32): reduction in the content of aromatic compounds and elimination of benzene; - reduction in gasoline volatility to minimize evaporative losses; - reduction in the content of light olefins, photochemically extreme reactive; - reduction in the sulfur content and the final boiling point of the gasolines. All these measures consequently create the need to project new production processes of purely hydrocarbon compounds capable of contributing positively to the previous demands. Among these, the alkylated products are extremely important since they have a high octane number, a low volatility and are practically free of olefins and aromatics. The alkylation process in the liquid phase is a reaction between isoparaffinic hydrocarbons, such as isobutene, and olefins, for example propylene, butenes, pentenes and relative mixtures thereof, in the presence of an acid catalyst for the production of C7 hydrocarbons. -C9 with a high octane number to be used in gasoline (A. Corma, A. Martinez, Catal.Rev.-Sci. Eng., 35, (1993), The main problem of the alkylation processes is due to the fact that, with the increasing environmental regulations, both of the traditional processes (with hydrofluoric and sulfuric acid) are considerable difficulties, which create uncertainties for the future; the process with hydrofluoric acid due to the toxicity of this acid, especially in populated areas, and that which uses sulfuric acid, as a result of the greater production of acidic sediment as well as the considerably corrosive nature of the catalyst. Alternative processes with solid acid catalysts are being developed but their industrial applicability still needs to be demonstrated. A hydrocarbon product of this type, on the other hand, is becoming increasingly required due to its octane characteristics (both the Research Octane Number (RON) and the Motor Octane Number (MON) are high) and those in relation to the boiling point (limited volatility but low equivalence point) that places it in the group of compositions of great interest to obtain gasolines that are more compatible with current environmental requirements. An alternative refinery process to obtain Products with characteristics similar to those of the rented products can be offered by the hydrogenation of so-called "polymer" gasoline. In the 1930s and 40s oligomerization processes (often inaccurately called polymerization in the refining industry) were widely used to convert low-boiling C3-C4 olefins into gasoline. The process leads to the production of a gasoline with a high octane number (RON of approximately 97) but with a high sensitivity (different between RON and MON) due to the purely olefinic nature of the product (J. H. Gary, G. E. Handwerk, "Petroleum Refining: Technology and Economics", 3rd Ed., M. Dekker, New York, (1994), 250). Typical olefins that are oligomerized are mainly propylene, which gives slightly higher dimers or oligomers depending on the process used, and isobutene which gives mainly dimers but is always accompanied by a considerable amount of higher oligomers. With particular attention to the oligomerization of isobutene, it is known that this reaction can be carried out either batchwise, semi-batches or continuously, either in liquid or gaseous phase, generally at temperatures ranging from 50 to 50%. 300 ° C and at atmospheric pressure or pressures such as to keep the reagents in liquid phase, if necessary. Typical catalysts for the industrial oligomerization process of isobutene are represented by phosphoric acid, generally supported in a solid (for example, kieselguhr), or acid cation exchange resins. The latter allow more insipid conditions to be used compared to phosphoric acid supported both in terms of temperature and pressure (50-100 ° C and 0.2-3 MPa with respect to 200-220 ° C and 3-10 MPa). Other catalysts are also claimed in the literature, both liquid acids such as H2S04 and sulfonic acid derivatives, and solids such as silico-aluminas, mixed oxides, zeolites, fluorinated or chlorinated aluminas, etc .; none of these catalysts however has been enabled to an industrial process to establish it, as in the case of supported phosphoric acid (F. Asinger, "Mono-olefins: chemistry and technology", Pergamon Press, Oxford, pages 435-456) and that of cationic resins (G. Scharfe, Hydrocarbon Proc, April 1973, 171). From the point of view of the product, the main problem of this process is the fact that excessive percentages of heavy oligomers such as trimers (selectivity of 20-40%) and tetramers (selectivity of 1-5) occur in the oligomerization phase. %) of isobutene. The tetramers are completely outside the gasoline fraction since they are boiling point too high and therefore represent a net loss in gasoline production; with respect to what refers to the trimers, their concentration should be reduced for the most part since they have a boiling point (170-180 ° C) in the limit of future specifications at the final point of reformulated gasolines. The problem of reducing the formation of oligomers greater than the dimers at percentages below 15% is, on the other hand, a typical problem of the oligomerization of isobutene, as is also indicated in the literature (CTO'Connor, M. Kojima , K. Shcumann, Appl. Catal., 16, (1985), 193). This level of heavy compounds is slightly higher than that of a rented product and is still tolerated in the gasoline mixture. From what is specified above, the interest in obtaining a new dimerization process of isobutene that allows the synthesis of a higher quality product, through reaching higher selectivities is evidently great. By carrying out the selective dimerization reaction of isobutene in the presence of moderate amounts of linear and branched alcohols and alkyl ethers, the production of a fraction of oligomers, which is particularly rich in dimers (> 85%) and practically free of tetramers and higher oligomers (< 0.5%). The reaction product is then hydrogenated preferentially to give a fully saturated final product with a high octane number and low sensitivity. The hydrogenation can be carried out with conventional methods as described, for example, in F. Asinger, "Mono-olefins: Chemistry and Technology", Pergamon Press, Oxford, page 455.

Description of the Invention For illustrative purposes, Table 1 indicates the octane number and the relative boiling points of some of the products obtained, by means of the process, object of the present invention.

Table 1 The process, object of the present invention, for the separation of C5 hydrocarbons present, in an amount ranging from 0.2 to 20% by weight, in streams predominantly containing C4 products used for the production of high octane hydrocarbons, by the selective dimerization reaction of isobutene, it is characterized in that the reaction is carried out in the presence of linear and branched alcohols and ethers in an amount which is such as to have a molar ratio of alcohols + ethers / isobutene in the feed of 0.01 and preferably less than 0.7. It should also be noted that in the case of hydrocarbon streams that also include olefins of C4 and C5, it has been observed that at least a part of the latter can be converted by reaction with isobutene into the hydrocarbon product without altering the octane value. Therefore, it is preferred to carry out an enrichment treatment, by means of pre-isomerization, of the internal linear olefins, in order to favor the total octane number of the mixture. The process claimed herein can be applied for cuts containing mainly isobutane, isobutene, n-butane, n-butenes and saturated and olefinic C5 hydrocarbons. Although a wide variety of sources are available for the supply of these currents, the most common are those that derive from dehydrogenation processes of iso-paraffins, FCC units, steam pyrrolysis or processes for the production of pure isobutene such as dehydration of tert-butyl alcohol (TBA) or MTBE pyrrolysis and / or ETBE; these currents differ among themselves in the content of isobutene and linear butenes, as shown in Table 2.

Table 2 If the Steam Pyrrolysis currents contain diolefins in addition to the desired mono-olefins, they should be removed by means of a typical removal treatment (eg, solvent extraction or selective hydrogenation). The saturated and olefinic C5 hydrocarbons may be present in these streams, in various amounts (0.2-20% by weight), depending on the efficiency of the separation step of C4-C5. The C5 olefins present may possibly be included in the dimerization reactions.

The stream sent to the reaction steps may contain branched alcohols or a mixture of alcohols and alkyl ethers, in addition to the hydrocarbon components. The alcohols used are linear, preferably containing a number of carbon atoms ranging from 1 to 6, preferably from 4 to 7 carbon atoms; the preferred linear alcohols are methanol and / or ethanol, while the preferred branched alcohols are tert-butyl alcohol (TBA) and / or ter-amyl alcohol (TAA). The alkyl ether used can be selected from those containing a number of carbon atoms ranging from 5 to 10; preferred are MTBE (methyl tert-butyl ether, ETBE (ethyl tert-butyl ether), MSBE (methyl sec-butyl ether), ESBE (ethyl butyl ether), TAME (methyl tert-amyl ether) , TAEE (ethyl tertiary amyl ether) or mixtures thereof Isobutene is sent, together with the hydrocarbon stream in which it is contained, with the mixture of alcohols and alkyl ethers, in stoichiometric defect, in contact with the catalyst acid where the dimerization takes place The linear primary alcohol, in addition to interacting with the catalyst, also helps to limit the possible pyrrolysis of the alkyl ether and can react possibly with linear C4 dimers and olefins, while branched (tertiary) alcohol does not react with olefins due to its spherical hindrance. In order to obtain the dimerization product with the desired selectivity to dimers, it is essential to maintain a constant level of oxygenated products in the reaction environment but above all the contemporary presence of the three oxygenates (linear alcohol, branched alcohol and ether) alkyl) which, due to a synergistic effect, are capable of forming the catalytic species with the correct activity and stability. The optimum level of the sum of alcohols and alkyl ethers that must be present in the reaction environment to obtain selectivities to dimers close to 85% by weight, depends on the composition of the hydrocarbon charge. The higher the olefin content in the charge, the lower the amount of oxygenated products used. A wide variety of acid catalysts can be used for this process, but those preferred are styrene-divinyl-benzene polymer resins having sulfonic groups as catalytic centers. A wide variety of operating conditions can be used to produce high octane hydrocarbons from isobutene at the desired selectivities. It is possible to operate in vapor or liquid-vapor phase, but prefer operating conditions in liquid phase. The pressure is preferably higher than the atmospheric value, in order to keep the reactants in liquid phase, generally below 5 MPa, more preferably between 0.2-2.5 MPa. The reaction temperature preferably varies from 30 to 120 ° C. The space velocities for feeding the oxygenated hydrocarbon stream are preferably less than 30 h "1, more preferably ranging from 1 to 15 h" 1. Mainly, isobutene is converted to the reaction zone, however, part of the C4-Cs olefins present can also be converted to the useful product; in principle, there are no limits to the concentration of iso-olefins in the hydrocarbon fraction; concentrations ranging from 2 to 60% are still preferred; in the case of currents that have a high concentration of isobutene (dehydration or pyrrolysis) it is therefore advisable to dilute the charge with C4-C7 hydrocarbons. There are no limits, on the contrary, for the relationship between isobutene and linear olefins. The process, object of the present invention, can be carried out in batches or continuously, keeping in mind however that the latter is much more advantageous in industrial practice. The selected configuration of The reactor in general is a double reaction passage comprising one or more fixed-bed reactors that can be optionally selected from a tubular and adiabatic reactor. The presence of C5 hydrocarbons in the feed, however, complicates the process schemes, since these compounds have intermediate temperatures of boiling between C4 and oxygenated products, and also form azeotropic mixtures with the branched alcohols as shown in Table 3 , which indicates the boiling points of the most representative components of low boiling present in the currents.

Table 3 Therefore, C5 products can not be removed from the plant along with the C products, since they will introduce oxygenated products (branched alcohols and ethers) into the stream, which are difficult to remove by means of the traditional techniques used for remove methanol (washed with water) and that are toxic for the subsequent processes of currents treatment (polymerization, alkylation and metathesis). The C5 products, on the other hand, can not be maintained in the oxygenated stream since they will accumulate rapidly. With respect to the schemes shown in the literature (US 6,011,191), it is therefore necessary to introduce an azeotropic separation step of C5 / branched alcohol, which can be inserted in different positions of the plant in relation to the C5 content in the charge and also the relative concentration of the C5 products present. The separation of the azeotropic product from C5 / branched alcohol can be done using traditional fractionation columns in which the mixture Azeotropic can be recovered at the top, bottom or as a lateral cut. The process, object of the present invention, can be carried out, in particular, by means of the following essential steps: a) feed a stream containing isobutene and C5 hydrocarbons, together with one or more streams containing oxygenated products ( linear or branched alcohols), ethers and water), at one or more reaction steps (consisting of one or more reactors); b) separating the azeotropic product of C4 / linear alcohol and possibly the C4 products of the C5 hydrocarbons, the remaining oxygenates and the hydrocarbon product, in one or more distillation columns; c) recovering the linear alcohol from the azeotropic mixture with the C4 products by means of conventional processes such as washing with water or absorption in inorganic solids; d) separating the products of C5 (as an azeotropic compound with the branched alcohol) from the remaining oxygenates and the reaction product, in one or more distillation columns, in order to obtain three streams with the desired purity; e) recycle the stream that contains the remaining oxygenated products and that containing the recovered linear alcohol, at the two reaction steps; f) feeding linear alcohol and water (which forms the branched alcohol in the reactors by reaction with the tertiary olefin) to the reaction steps to compensate for the losses of linear alcohol, which can react with the linear C4 dimers and olefins, and the branched alcohol which, on the contrary, leaves the plant together with the C5 products; g) recycle part of the C products, with or without linear alcohol, to the reaction steps in order to maximize the conversion of isobutene. For the process comprising the essential steps indicated above, the C5 products are present in the streams which predominantly contain C4 products in an amount varying preferably from 0.5 to 10% by weight. The separation of the azeotropic product from Cs / branched alcohol is preferably carried out by initiating mixtures of: a) C5-oxygenated products (ethers and branched alcohols), reaction product, wherein two hydrocarbons of C5 are recovered as a azeotropic compound with branched alcohol as head effluent using a column-based scheme, with recovery of the remaining oxygenated products as a side cut, or two fractionation columns; b) Cs-oxygenated products (ethers and branched alcohols), dimers, wherein the C5 hydrocarbons are recovered as an azeotropic compound with the branched alcohol as head effluent from a fractionation column; c) C4-C5-oxygenated products (ethers and branched alcohols), reaction product, effluent from a reaction step, where the C5 hydrocarbons are recovered as an azeotropic compound with the branched alcohol as a side cut, from a column of fractionation of whose head the azeotropic product of C4 / linear alcohol and possibly the products of C are recovered, while a mixture containing the oxygenates and the reaction product is recovered in the bottom; d) C4-C5-oxygenated products (linear and branched alcohols), where the C5 hydrocarbons are recovered as an azeotropic compound with the branched alcohol as the bottom effluent of a fractionation column from whose head the azeotropic product is recovered of C4 / linear alcohol and possibly C products. In the figures 1-6 six schemes of process, in order to clearly illustrate the present invention. Figure 1 shows a process scheme in which no C5 hydrocarbons are present in the charge and the oxygenated products are methanol (linear alcohol), TBA (branched alcohol) and MTBE (alkyl ether). The stream (1) containing isobutene, together with the reintegration feed of methanol and water (2) and recycled streams of oxygenated products (MTBE and TBA) (15) and methanol (18), is sent to a first reaction step Rl, which may consist of one or more reactors, in which the iso-olefin of C4 is selectively converted to dimers. The effluent (4) of the first reaction step is sent to a first separation column Cl in which a stream (5) containing essentially C4 hydrocarbons and methanol moves from the head, while it is collected in the bottom. a stream (6) containing essentially the reaction product and the remaining oxygenates. The head stream (5) is then fed, along with the recycled streams of oxygenated products (16) and methanol (17) to a second reaction step R2, which may consist of one or more reactors, wherein the isobutene present is selectively converted to dimers.

The effluent (8) of the second reaction step is separated on a C2 column from whose bottom a stream (10) containing essentially MTBE, TBA, the dimerization product and part of the C4 products is removed and sent to the column Cl for the recovery of the product and oxygenated products. The head stream (9), consisting of C4 products and the azeotropic mixture of C / methanol, is sent, on the other hand, to a MR unit for the recovery of the alcohol, which may consist, for example, of a absorption in molecular sieves or a column washed with water. In both cases, the recovered alcohol (14) can be sent back to the two reaction steps (streams 17 and 18) while the hydrocarbon stream (13) can be used in subsequent operations. The bottom stream (6) of column Cl is sent to a further separation column C3 where a stream (11) containing essentially MTBE, TBA and dimers is removed at the head and recycled to the two reaction steps ( streams 15 and 16), whereas the reaction product (12) consisting essentially of dimers, trimers and small amounts of dimer oligomers and ethers is recovered in the background. When C5 hydrocarbons are present in the charge, on the contrary, according to the present invention, different plant configurations, schematized in the following figures 2 to 6, can be used to recover the azeotropic product of C5 / TBA, depending on the amount of C5 product present and the purity required of the currents. Therefore, Figure 2 shows a possible process scheme that differs from the previous scheme, since the stream containing oxygenated products that are to be recycled (11) (ethers and TBA) is removed from the C3 column as a side cut, while the azeotropic product (19) of C5 / TBA is recovered from the head of the column and can be optionally bound with the reaction product. The process scheme becomes more complex when a more efficient separation of the mixture of C5 products / oxygenates / reaction product is to be carried out, since a new fractionation column C4 must be inserted, as shown in the Figure 3. In this new scheme, the head stream of column C3 (11) is sent to a new column C4 where the azeotropic mixture (20) of C5 / TBA is separated at the head and the stream of oxygenated products (19). ) is separated at the bottom and recycled to the two reaction steps. Alternatively, C5 hydrocarbons can be recovered using the two fractionation columns of the products of C wherein the azeotropic mixture of C5 / TBA in this way can be recovered as side cut (19) both in the Cl column (figure 4) and in the C2 column (figure 5). However, an additional option consists in effecting the separation of the C-C5 products into a new C5 last column, as shown in Figure 6, in which it is recovered as the bottom stream (19) of the azeotropic product of C5 / TBA.

Claims (17)

1. CLAIMS 1. Process for the separation of C5 hydrocarbons present, in an amount varying from 0.2 to 20% by weight, in hydrocarbon streams that predominantly contain C4 products used for the production of high octane hydrocarbon compounds, by the selective dimerization of isobutene, characterized in that the dimerization reaction is carried out in the presence of linear and branched alcohols and alkyl ethers in an amount such as to have a molar ratio of alcohols + alkyl ethers / isobutene in the higher feed 0.01, which is the separation of the azeotropic product from Cs / branched alcohol effected using traditional fractionation columns.
2. 2. Process according to claim 1, wherein the molar ratio of alcohols + alkyl ethers / isobutene is less than 0.7.
3. 3. Process according to claim 1, wherein the reaction is carried out at a temperature ranging from 30 to 120 ° C, at a pressure of less than 5 MPa and at space velocities of feeding less than 30 h "1. according to claim 1, wherein the spatial feed rates vary from 1 to 15 h "1. Process according to claim 1, wherein the linear alcohol has a number of carbon atoms that it varies from 1 to 6. The process according to claim 5, wherein the linear alcohol is selected from methanol and / or ethanol. The process according to claim 1, wherein the branched alcohol has a number of carbon atoms ranging from 4 to 7. Process according to claim 7, wherein the branched alcohol is selected from tert-butyl alcohol or tertiary alcohol. -amilico. The process according to claim 1, wherein the alkyl ether has a number of carbon atoms ranging from 5 to 10. Process according to claim 9, wherein the alkyl ether is selected from MTBE, ETBE, MSBE, ESBE , TAME, TAEE or mixtures thereof. 11. Process according to claim 1, wherein other possible olefins present in the charge react to form high octane products. 12. Process according to claim 1, wherein the isobutene content in the filler is modified by dilution with currents of C-C7. Process according to at least one of the preceding claims, comprising the following essential steps: a) feeding the hydrocarbon cutting of C4-C5 containing isobutene, together with one or more streams containing oxygenates, linear and branched alcohols, ethers and water, at one or more reaction steps, consisting of one or more reactors; b) separating the azeotropic product of C4 / linear alcohol and possibly the C4 products of the C5 hydrocarbons, the remaining oxygenates and the hydrocarbon product, in one or more distillation columns; c) recovering the linear alcohol from the azeotropic mixture with the C4 products by means of conventional processes such as washing with water or absorption in inorganic solids; d) separating the C5 hydrocarbons, such as an azeotropic compound with the branched alcohol, from the remaining oxygenates and the reaction product, in one or more fractionation columns, in order to obtain three streams with the desired purity; e) recycle the streams containing the oxygenated products, branched alcohol and ether, and the linear alcohol recovered, to the two reaction steps; f) feeding linear alcohol and water, which forms the branched alcohol in the reactors by reaction with the tertiary olefin, to the reaction steps to compensate for the losses of linear alcohol, which can react with linear C4 dimer and olefins, and alcohol branched which, on the contrary, leaves the plant together with the C5 products; g) recycle part of the C4 products, with or without linear alcohol, to the reaction steps in order to increase the maximum conversion of isobutene. Process according to claims 1 and 13, wherein the separation of the azeotropic product from Cs / branched alcohol is carried out by initiating mixtures of: a) products of Cs-oxygenates, ethers and branched alcohols, reaction products, wherein C5 hydrocarbons are recovered as an azeotropic compound with the branched alcohol as head effluent using a column-based scheme, with recovery of the remaining oxygenated products as a side cut, or two fractionation columns; b) C5-oxygenated products, ethers and branched alcohols, dimers, wherein the C5 hydrocarbons are recovered as an azeotropic compound with the branched alcohol as head effluent from a fractionating column; c) C4-Cs-oxygenated products, branched alcohols and ethers, reaction products, effluent from a reaction step, wherein the C5 hydrocarbons are recovered as an azeotropic compound with the branched alcohol as side cut from a fractionation column from which head the azeotropic product of C4 / linear alcohol and possibly the C products are recovered, while a mixture containing the oxygenates and the reaction product is recovered at the bottom; d) products of C -Cs-oxygenates, linear and branched alcohols, where the hydrocarbons of C5 are recover as an azeotropic compound with the branched alcohol as the bottom effluent of a fractionation column from whose head the azeotropic product of C4 / linear alcohol and possibly C products are recovered. 15. Process according to claims 1, 13 and 14, wherein the azeotropic mixture of C5 / branched alcohol is bound to the reaction product. 16. Process according to claims 1 and 13, wherein the dimerization reaction is carried out in one or more reactors of fixed, tubular and / or adiabatic beds. 17. Process according to claim 13, wherein the C5 hydrocarbons are present in streams containing predominantly C4 products in an amount ranging from 0.5 to 10% by weight.