MXPA97005620A - Procedure for the obtaining of alquil-ter.butileteres and di-n-buteno de cabutanos de ca - Google Patents

Abstract

The present invention relates to: The invention relates to a process for the preparation of alkyl-tert.-butyl ethers and di-n-butene in a production coupled from field butanes, where (a) the dehydrogen -butane and iso-butane contained in the field butanes 1, in a dehydrogenation step 2, obtaining a dehydrogenation mixture 3 containing n-butene or iso-butene, (b) the dehydrogenation mixture 3 is brought to the stage of etherification 4 and there, selectively, the iso-butene is transformed with an alkanol 5 into an alkyl tert-butyl ether 6, and (c) the remainder of the dehydrogenation mixture 7 is taken to the oligomerization step. 8 and n-butene is catalytically oligomerized. In a preferred embodiment, to the field butanes 1, before entering the dehydrogenation step 2, in the hydrogenation step 9 they are subjected to hydrogenation conditions, they are taken to a separation step 10, which is subordinated to a isomerization stage 11, by means of which the n- / iso can be adjusted according to the proportion of desired amounts of di-n-butene to methyl tertiary butyl ether, and which has changed field-1 -butanol in its n- / proportion iso- to the dehydrogenation stage

Description

PROCEDURE FOR THE OBTAINING OF RENT-TER.BUTILÉTERES AND DI-N-BUTENO FROM FIELD BUTANES The invention relates to a process for the preparation of alkyl tertiary butyl ether (hereinafter abbreviated RTBE, where R represents alkyl) and di-n-butene in a production coupled from field butanes, transforming the iso -butane in alkyl tertiary butyl ether and n-butane in di-n-butene and being able to regulate the proportion of quantities of these two products, adjusting correspondingly the amount ratio of n-butane to iso-butane by isomerization. The RTBE are used as an additive for gasoline to increase the octane rating. They are obtained by the addition of alkanols in iso-butene, which is also called etherification. Iso-butene can come from four different sources: thermal vapor decomposers, propylene oxide installations, petroleum refineries (ie FC decomposers) and facilities for the dehydrogenation of iso-butane (see RA Pogliano et al., Dehydrogenation -Based Ether Production Adding Valué to LPG and Gas Condensate, 1996 Petrochemical Review, De itt &Company, Houston Texas). In the case of the first three sources, iso-butene is produced as a component of section C, that is, as a direct secondary product. In the case of the dehydrogenation of iso-butane, iso-butene is often an indirect by-product of such facilities, since the starting material, iso-butane, is also obtained as a direct by-product in thermal steam decomposers and refineries of petroleum or by the isomerization of n-butane, which, on the other hand, is a secondary product in steam thermal decomposers and oil refineries. The current global production of RTBE is approximately 25 million t / year, with an upward trend. The production of butanes and butenes as by-products in a given decomposer or a certain oil refinery is too small to fully take advantage of the "Economies of Scale" that exist in the RTBE procedure. Isobutene and / or iso-butane (for dehydrogenated) of the decomposers and / or refineries would have to be collected in order to operate an RTBE installation with optimum capacity. Alternatively, a sufficient cut of C4 could be collected from these facilities and processed at the site to obtain iso-butene and iso-butane. Both variants, and particularly the second, have the objection that the transport of liquefied gases is very expensive, not ultimately due to the expensive security measures. The isomeric mixture which is formed, in addition to higher oligomers of butene, by the dimerization and / or co-dimerization of butenes, that is, of n-butene and / or iso-butene, in the oligomerization of butenes is referred to as dibutene. Di-n-butene is referred to as the product of the dimerization of n-butene, ie, 1-butene and / or 2-butene. The basic components of di-n-butene are 3-methyl-2-heptene, 3,4-dimethyl-2-hexene and, to a lesser extent, n-octenes. Di-iso-butene is the isomeric mixture obtained by the dimerization of iso-butene. Di-iso-butene is more branched than dibutene, and this, in turn, is more branched than di-n-butene. Dibutene, di-n-butene and di-isobutene are starting materials for the preparation of isomeric nonanols by hydroformylation and hydrogenation of the Cg aldehydes obtained in this way. The esters of these nonanoles, particularly the phthalic acid ester, are softeners that are produced in significant volumes and are used mainly for polyvinyl chloride. The di-n-butene nonanoles are, to a greater extent, straight chain than the nanoanes of dibutene, which, in turn, are less branched than the nonanoles of di-iso-butene. The esters of the di-n-butene nonanoles have advantages of technical application with respect to the esters of other nonanoles and, for that reason, they are particularly demanded. N-butene is obtained for the dimerization, as well as iso-butene, for example from cuts of C4, as they are produced in steam thermal decomposers or FC decomposers. Cuts of C4 are usually processed by first dissociating 1,3-butadiene by selective washing, for example with N-methylpyrrolidone. Iso-butene is a desired and particularly valuable component of the C cutoff, because, alone or mixed with other C4 hydrocarbons, it can be chemically transformed to desired products, for example with iso-butane to high-octane iso-octane or with an alcohol to an RTBE, particularly with methanol to methyl tertiary butyl ether (MTBE). After the reaction of the iso-butene, the n-butenes and n-butane remain. The part of n-butene in the products of the dissociation of the steam thermal decomposer, or else of the oil refinery, is, however, proportionally low. In the steam thermal decomposers it is around 10% by weight, based on the main target product, ethylene. A steam thermal decomposer with the respectable capacity of 600,000 t / year of ethylene therefore provides only about 60,000 t / year of n-butene. It could increase its amount (and that of the iso-butenes), dehydrogenating about 15'000 t / year of n- and iso-butane, which are produced in addition to the n-butenes. However, it is not recommended, since dehydrogenation facilities require high investment costs and, for such a small capacity, they are not profitable. As it was said, iso-butene is a product of decomposition with great demand and, for this reason, it is usually not available for isomerization to n-butene. The amount of n-butenes produced directly by a steam thermal decomposer or an oil refinery is not enough to produce enough di-n-butene for a nonanol facility, whose capacity is so large that it could compete economically with the large existing facilities for the production of important softening alcohols, such as 2-ethylhexanol. As already mentioned, propylene oxide installations are less productive. Therefore, n-butenes should be collected from various steam thermal decomposers, refineries or propylene oxide installations (or process the cutting of C4 from various sources to n-butene) and oligomerize the pooled n-butene, to cover the need to draw us from a sufficiently large industrial nonanol facility. The transport of liquefied gases, however, is expensive, as already mentioned. Therefore, it would be desirable to be able to make n-butene and iso-butene available in one place without transport over long distances, in the quantities required in a coupled production for the operation of a large, economically advantageous facility, for the production of di-n-butene, for example with a capacity of 200'000 to 800'000 t / year, and another equal facility for the production of RTBE, for example with a capacity of 300'000 to 800'000 t / year. It would also be desirable to configure the mixture of these facilities so that the ratio of amounts of n-butene to iso-butene can be adjusted correspondingly to the desired amounts of di-n-butene and RTBE. An installation that meets these requirements is represented with its basic and optional features as a block diagram in the attached figure. The invention is a process for obtaining alkyl-ter. butyl ether and di-n-butene in a production coupled from field butanes, in which (a) the n-butane and iso-butane contained in the field butanes 1 are dehydrogenated together in a dehydrogenation step. , obtaining a dehydrogenation mixture 3 containing n-butene and iso-butene, (b) the dehydrogenation mixture 3 is guided to the etherification step 4 and there, selectively, the iso-butene is transformed with an alkanol 5 into an alkyl-ter. butyl ether 6, and (c) the rest of the dehydrogenation mixture 7 is guided to the oligomerization step 8 and there n-butene is catalytically oligomerized. A preferred embodiment of the process is characterized in that the field butanes 1, before entering the dehydrogenation step 2, in the hydrogenation step 9 are subjected to hydrogenation conditions, are carried to a separation step 10, which is subordinate to an isomerization stage 11, by which the amount ratio of n-butane to iso-butane (ratio n- / iso-) can be adjusted according to the desired amount ratio of di-n-butene to alkyl- terbether, and thus carrying field butane modified in its n- / iso- ratio to the dehydrogenation step 2. This preferred embodiment of the invention is characterized by a high flexibility, therefore, within the limits set by the With the capabilities of the di-n-butene installation and the installation of RTBE, the quantities of di-n-butene and RTBE can be varied according to market needs. As field butanes, it is called the C fraction of the "wet" parts of the natural gas as well as the gases that accompany the oil, which are separated from the gases in liquid form by drying and cooling to approx. -302C. By distillation at low temperatures, butanes are obtained from them, whose composition varies depending on the place, but which, in general, contain approx. 30% iso-butane and approx. 65% n-butane. Other components are, usually, approx. 2% hydrocarbons with less than 4 carbon atoms and approx. 3% hydrocarbons with more than 4 carbon atoms. The field butanes, without dissociation, can be used as a material in steam thermal decomposers or as additives for gasoline. They can be dissociated by fractional distillation in n-butane and iso-butane. Iso-butane is used, for example, in important amounts for the production of propylene oxide by co-oxidation of propylene and iso-butane, and as an alkylating agent, with which n-butene is alkylated, or else, iso- butene to iso-octane, which, due to its high octane rating, can be seen as an additive for gasoline. In contrast, n-butane found less significant applications. It serves, for example, as butane gas for heating purposes or, in comparatively small quantities, it is used for the preparation of polymers or copolymers or of anhydrous maleic acid by atmospheric oxidation. Before, n-butane, through the n-butene stage, is also dehydrogenated to 1,3-butadiene, but now this process is no longer profitable. As iso-butane is the desired component of field butane, n-butane is isomerized on a large scale to iso-butane (see, for example, RA Pogliano et al., Dehydrogenation-Based Ether Production, 1996 Petrochemical Review, De itt &; Company, Houston Texas, Butamer procedure * page 6, as well as ST Bakas, F. Nierlich et al, Production of Ethers from Field Butans and Refinery Streams, AIChE Su mer Meeting, 1990, San Diego, California, page 11). Therefore, it was not part of the technique's tendency to develop a process that takes advantage of n-butane as such or, even, transforms isobutane into n-butane, to obtain more di-n-butene from them. The process according to the invention is carried out in two consecutive partial stages, (A) obtaining RTBE and (B) obtaining di-n-butene. In principle, the order of these partial steps can be any, but it is advantageous to first obtain RTBE and then di-n-butene, since iso-butene is also active as regards oligomerization. The di-iso-butene obtained is, as already mentioned, more branched and thus leads to iso-nonanols with less good technical application characteristics.

(A) Obtaining RTBE Field butans 1or alternatively, the field butanes modified in their composition by isomerization (see section (C)) are brought to the dehydrogenation step 2, which is an essential characteristic of the process according to the invention. There the field butanes are dehydrogenated to a dehydrogenation mixture 3 containing n-butene and iso-butene. Dehydrogenation is a co-dehydrogenation of n-butane and iso-butane. It is noteworthy that the dehydrogenation of field butanes, which are a mixture of components with different dehydrogenation behavior, is achieved so well. The process conditions correspond to a large extent to those known for n-butane and iso-butane. So, S.T. Bakas, F.

Nierlich et al., Loe. cit. , pages 12 et seq., describe the Oleflex process, which is generally suitable for the production of light olefins and with which, for example, isobutane with a selectivity of 91 to 93% can be dehydrogenated to iso-butene. Other related publications are those of G.C. Sturtevant et al., Oleflex - Selective Production of Light Olefins, 1988 UOP Technology Conference, as well as EP 0 149 698. Conveniently, dehydrogenation is carried out in the gas phase in solidified or fluidized catalysts, for example chromium oxide (III) ) or, advantageously, in platinum catalysts with aluminum oxide or zeolites as carriers. The dehydrogenation generally takes place at temperatures of 400 to 800 ° C., advantageously 550 to 650 seconds. Work is usually carried out at atmospheric pressure or at slightly elevated pressure up to 3 bar. The residence time in the catalytic layer is, depending on the catalyst, the temperature and degree of reaction desired, in general between 1 and 60 minutes. The flow is correspondingly, usually, between 0.6 and 36 kg of n-butane and io-butane (as a mixture) per m of catalyst and hour. It is convenient to carry out the dehydrogenation only until the dehydrogenation mixture 3 remains unchanged approx. 50% of n-butane and iso-butane. At higher temperatures higher degrees of reaction could be achieved. However, decomposition reactions that lower the yield and, due to the deposit of coke, reduce the life of the dehydrogenation catalyst take place to a greater extent. The optimum combination of the reaction conditions leading to the desired degree of reaction, such as catalyst type, temperature and residence time, can be easily determined by orientation tests. The dehydrogenation mixture 3 usually contains 90 to 95% by weight of C4 hydrocarbons and furthermore hydrogen, as well as low and high boiling portions. Before the oligomerization, it is conveniently cleaned beforehand in a first cleaning step (not shown in the figure) and in a selective hydrogenation stage 14. In the first cleaning stage, the C4 fraction and the parts condensed out of the gas phase of highest boiling. The condensate is distilled under pressure, with the hydrocarbons having less than 4 dissolved carbon atoms coming first. From the higher boiling portions, the saturated and unsaturated C4 hydrocarbons are obtained as the main product in another distillation, which goes to the other process, and as a residue the comparatively small amount of hydrocarbons with more than 4 carbon atoms. The hydrocarbons C generally contain small amounts, for example 0.01 to 5% by volume, of dienes, such as propadiene and, in particular, 1,3-butadiene. It is advisable to remove these dienes, because even in clearly smaller amounts they can subsequently damage the catalyst in the oligomerization step 8. A suitable process is the selective hydrogenation 14, which, in addition, raises the part of the desired n-butene. Selective hydrogenation has been described, for example, by F. Nierlich et al. In Erdol & Kohle, Erdgas, Petrochemie, 1986, pages 73 et seq. It is carried out in the liquid phase with hydrogen completely dissolved in stoichiometric amounts. Suitable hydrogenation catalysts are, for example, nickel and particularly palladium on a carrier, for example 0.3% by weight of palladium on activated carbon or, preferably, on aluminum oxide. A small amount of carbon monoxide in the ppm range promotes the selectivity of the hydrogenation of 1,3-butadiene to monoolefin and causes the formation of polymers, contrary to the so-called "green oil", which deactivates the catalyst. The process works in general at room temperature or at an elevated temperature up to 60 seconds and under high pressures, suitably up to 20 bar. The content in 1, 3-butadiene in the dehydrogenation mixture is thus reduced to values of less than 1 ppm. Advantageously, selective hydrogenation is carried out under hydroisomerizing conditions. Thus 1-butene is isomerized at the same time to 2-butene, which, unlike 1-butene, in the separation step 16 to be described later, can be separated by distillation of n-butane / iso-butane. For more details on the selective hydrogenation under hydroisomerizing conditions, see for example F. Nierlich, Integrated Tert. Butyl Alcohol / Di-n-Butene Production from FCC C4's, Erdol, Erdgas, Kohle 103 (11), pages 486 et seq., 1989. As dienes are a problem for subsequent oligomerization, but less so for etherification, the Selective hydrogenation 14 can also be arranged after the etherification step 4 in the flow of the rest of the dehydrogenation mixture 7, before or preferably after the cleaning step 15 to be described later. This arrangement allows, if necessary, that the reactor of the selective hydrogenation step 14 be smaller, since the volume of the remainder of the dehydrogenation mixture 7, after the separation of the iso-butene in the etherification stage 4, by Of course, it is smaller than that of the dehydrogenation mixture 3. The dehydrogenation mixture 3, optionally after the preliminary cleaning and the selective hydrogenation, is carried to the etherification stage 4, which is an essential characteristic of the process according to the invention. The iso-butene contained with an alkanol 5 is reacted in a manner known per se (see, for example, Methyl-Tert-Butyl Ether, Ullmanns Enzyclopedia of Industrial Chemistry, Volume A 16, pages 543 et seq., VCH Verlagsgesellschaft, Weinheim ). Preferred alkanols are those with 1 to 6 carbon atoms, such as ethanol, isopropanol, isobutanol and, particularly, methanol. As n-butene is much less reactive, a selective etherification takes place which practically only consumes iso-butene. The reaction takes place in the liquid phase or in the liquid-gas phase, generally at a temperature of 50 to 90sc and under a pressure that is adjusted to the corresponding temperature. It is expedient to work with a slight excess of ethanol stequium in methanol, whereby the selectivity of the isobutene reaction is increased and its dimerization is reduced. As the catalyst, for example, an acid betonite or, advantageously, an acid ion exchanger with large pores is used. From the reaction mixture of the etherification step 4, the remaining dehydrogenation mixture 7 and the excessive alkanol of the RTBE 6 which formed was distilled off. In the case of MTBE the rest of the dehydrogenation mixture 7 and methanol form an azeotrope. This is washed with water and dissociates to an aqueous phase and a dehydrogenation mixture residue 7. The aqueous phase is processed in methanol, which is fed back to the etherification, and in water, which is used again for washing. The rest of the dehydrogenation mixture 7 goes to obtain di-n-butene.

(B) Obtaining di-n-butene The starting material for this is the n-butene contained in the rest of the dehydrogenation mixture 7. If a selective hydrogenation 14 was not provided before the etherification stage 4, it must have place now, sooner or later, and advantageously after the cleaning step 15. Its basic component is a molecular sieve, in which other substances harmful to the oligomerization catalyst are removed, thereby further increasing its life. Among these harmful substances are compounds of oxygen and sulfur. Molecular sieve cleaning has been described, for example, by F. Nierlich et al. In EP-B1 0 395 857. A molecular sieve with a pore diameter of 4 to 15 Angstroms is advantageously used, advantageously from 7 to 13 Angstrom. . In some cases it is convenient for industrial reasons to pass the rest of the dehydrogenation mixture 7 consecutively through molecular sieves of various pore sizes. The process can be carried out in the gaseous, liquid or liquid-gas phase. According to the above, the pressure is generally 1 to 200 bar. It is conveniently worked at room temperature or at elevated temperatures up to 200SC.

The chemical nature of molecular sieves is less important than their physical constitution, that is, in particular the size of the pores. It is therefore possible to use the most diverse molecular sieves, both crystalline and synthetic aluminum silicates, for example sheet silicates in layers, as well as synthetic molecular sieves, for example those with zeolite structure. Zeolites of type A, X and Y can be obtained, inter alia, from Bayer AG, Dow Chemical Co., Union Carbide Corporation, Laporte Industries Ltd. and Mobil Oil Co. For the process, those molecular sieves are also suitable. they contain in addition to aluminum and silicon also other atoms incorporated by exchange of cations, such as gallium, indium or lanthanum, as well as nickel, cobalt, copper, zinc or silver. Also suitable are zeolites in which, in addition to aluminum and silicon, other atoms, such as boron or phosphorus, were incorporated into the grid by mixed precipitation. In the remainder of the dehydrogenation mixture 7, optionally cleaned by selective hydrogenation 14 and / or treatment with a molecular sieve 15, n-butene is advantageously separated from the other gaseous components in the separation stage 16 (waste gas I 17), such as isobutane and the unbuffered iso-butene in the etherification step 4, and is carried to the oligomerization step 8, which is an essential part of the process according to the invention. This separation of the rest of the dehydrogenation mixture 7 before the oligomerization is convenient, since otherwise the oligomerization step 8 would be charged with unnecessarily large amounts of materials and, in addition, unwanted cooligomers would be formed from n-butene and iso -buteno. The oligomerization is carried out in a manner known per se, for example, F. Nierlich has described in Oligomerization for Better Gasoline, Hydrocarbon Processing, 1992 (2), pages 45 et seq., Or F. Nierlich et al. In the document already EP-B1 0 395 857. In general, the liquid phase is used and a homogeneous catalyst is used, for example, a system composed of octoate (II) of nickel, ethylaluminum chloride and a free fatty acid (DE-PS 28 55 423), or one of the many known catalysts, fixed or suspended in the oligomerization mixture, based on nickel and silicon, is preferably used. The catalysts often contain additional aluminum. Thus, DD-PS 160 037 discloses obtaining a precipitation catalyst containing nickel and aluminum on silicon oxide as a carrier material. Other usable catalysts are obtained by exchanging the positively charged particles located on the surface of the carrier materials, such as protons or sodium ions, by nickel ions. The above is achieved with the most diverse carrier materials, such as aluminum amorphous silicate (R. Espinoza et al., Appl. Kat., 31 (1987), pages 259-266.; crystalline aluminum silicate (DE-PS 20 29 624); zeolites of the type ZSM (NL-PS 8 500 459); a zeolite X (DE-PS 23 47 235); X and Y zeolites (A. Barth et al., Z. Anorg, Allg. Chem. 521, (1985), pages 207-214); and an orderly (EP-A 0 233 302). The oligomerization is conveniently carried out, according to the catalyst, at 20 to 200 ° C and under pressures of 1 to 100 bar. The reaction time (or contact time) is generally 5 to 60 minutes. The parameters of the process, in particular the type of catalyst, the temperature and the contact time, are coordinated in such a way that the desired degree of oligomerization is achieved, that is, mainly a dimerization. For this, of course, the reaction can not be carried out in its entire volume, but convenient transformations of 30 to 70% per shift are sought. Optimal combinations of the process parameters can be determined without difficulty by orientation tests. From the oligomerization mixture 19, the waste gas II 21 is distilled off in the separation stage 20. It can be fed back to the dehydrogenation stage 2 or carried to the isomerization stage 11, if it exists and is operating. Finally, the waste gas II 21 can also be taken to the hydrogenation step 18, whose function is illustrated below. The alternatives for the treatment of residual gas II 21 are indicated in the figure by dotted lines. If a catalyst of the type of the aforementioned liquid catalysts was used in the oligomerization step 8, the waste gases II 21 must be cleaned beforehand to protect the dehydrogenation catalyst or the isomerization catalyst. The oligomerization mixture 19 is first treated with water to extract the catalyst components. The separated waste gas II 21 is then dried with a suitable molecular sieve, other secondary components also being separated. The variously unsaturated compounds, such as butins, are then removed by hydrogenation, for example with palladium catalysts, and, finally, the waste gas II 21 thus cleaned is brought to the dehydrogenation stage 2 or to the isomerization stage 11. These measures Cleaning for residual gas II 21 are not necessary if a solid oligomerization catalyst is used. From the remaining liquid phase of the oligomerization mixture 19, di-n-butene 22 and n-butene-23 are separated in the separation step 20 by fractional distillation, ie isomeric isdecenes. The main di-n-butene product is directly suitable for obtaining nonanoles. Dodecenes 23 are a desired by-product. They can be hydroformylated, the hydroformylation products can be hydrogenated and the tridecanols thus obtained can be oxidylated, thereby obtaining valuable washing raw materials. The waste gas I 17 that is produced in the separation step 16 can be fed back to the dehydrogenation step 2, if the field butanes 1 are hydrogenated directly without modifying the n- / iso- ratio by isomerization. If there is an isomerization stage 11 and it operates, then the waste gas I 17 can be carried directly or through the hydrogenation step 18 to the isomerization stage 11. The alternatives for the treatment of the waste gas I 17 are shown in the figure again with dotted lines.

(C) Variation of the amounts of di-n-butne and RTBE As mentioned above, it is convenient to attach to the process an isomerization step 11, since in this way the proportion of the di-n-butene amounts can be varied and RTBE (product ratio). The possibilities of variation are limited only by the capacities of the di-n-butene installation and that of RTBE. Considering investment costs, both facilities will rarely be so large that the total field butane flow available can only be processed in one facility while the other does not ote. Even so, the isomerization stage 11 brings the possibility of reacting flexibly within the limits given, to the requirements of the market. If it is desired to modify the n- / isopredated ratio of the field butanes 1, they are conveniently passed through a hydrogenation step 9 first, if they contain unsaturated compounds. These are hydrogenated there and then can no longer damage the catalyst of the isomerization stage 11. The hydrogenation is carried out in a manner known se (see, for example, KH Walter et al. In The Hüls Process for Selective Hydrogenation of Butadiene in Crude C4's , Development and Technical Application, DGKM-Tagung, Kassel, November 1993). Therefore, the liquid phase and, depending on the catalyst, are conveniently worked at room temture or at an elevated temture up to 90 seconds and under a pressure of 4 to 20 bar, the partial pressure of the hydrogen being from 1 to 15 bar. The usual catalysts are used for the hydrogenation of olefins, for example, 0.3% palladium on aluminum oxide. The hydrogenated field butanes 1 are brought to separation stage 10, whose basic component is an active column, oted at low temture and / or high pressure. If more alkyl tertiary butyl ether should be produced than that corresponding to the iso-butane portion of field butane 1, an amount corresponding to the desired product ratio of n-butane 12 in the side stream is sucked (as waste). in the background, hydrocarbons with more than 4 carbon atoms are produced) and carried to the stage of isomerization 11. The optional character of this measurement is indicated in the figure with a dotted line. In the isomerization stage 11, n-butane is converted into maximum iso-butane until equilibrium, which, depending on the temture, is between 40 to 55% of n-butane and 60 to 45% of iso-butane. The isomerization mixture 13 returns to the separation stage 10. Therefore, in the result to the dehydrogenation step 2, a field butane is fed, whose iso-butane portion is increased with respect to the butane of field 1. If more di-n-butene must be produced than that corresponding to the n-butane portion of field butane 1, suitably the iso-butane-rich waste gas I 17 is carried out from the separation stage 16, completely or partially, and either directly or through the hydrogenation step 18, to the isomerization step 11. In this case, the waste gas II 21 is brought directly to the dehydrogenation step. Then, in the result, to the dehydrogenation step 2 a field butane is fed, whose n-butane portion is increased with respect to the field butane 1. The isomerization of n- and iso-butane is a known reaction. In general, the gas phase is oted at a temture of 150 to 230 ° C under a pressure of 14 to 30 bar and with a platinum catalyst on aluminum oxide as a carrier, whose selectivity can be further improved by providing it with a chlorine compounds, such as hydrocarbon tetrachlor. Advantageously, a small amount of hydrogen is added to counteract a dehydrogenation. The selectivity of the isomerization is high, the decomposition into smaller fractions only takes place in insignificant amounts (about 2%) (see, for example, HW Grote, Oil and Gas Journal, 56 (13), pages 573 et seq. (1958)). The yields in the desired isomers are correspondingly high. The isomerization mixture 13 is fed back to the separation step 10, from which a field butane with an n- / iso-modified proportion proceeds correspondingly to the end, with respect to the original field 1 butane, to reach the dehydrogenation step 2.

Claims (9)

NOVELTY OF THE INVENTION Having described the foregoing invention, the content of the following is claimed as property: CLAIMS

1. A process for obtaining alkyl-ter. butyl ethers and di-n-butene in a coupled production from field butanes, characterized in that (a) the n-butane and iso-butane contained in the field butanes are dehydrogenated together in a dehydrogenation step, obtaining a mixture of dehydrogenation containing n-butene and iso-butene, (b) the dehydrogenation mixture is brought to the etherification step and there, selectively, the iso-butene is transformed with an alkanol in an alkyl-tert.butyl ether. ether, and (c) the rest of the dehydrogenation mixture is brought to the oligomerization step and n-butene is catalytically oligomerized therein.

2. A process according to claim 1, characterized in that the field butanes, before entering the dehydrogenation stage, in the hydrogenation stage are subjected to hydrogenation conditions, are carried to a separation stage, which is subordinated to an isomerization stage, by which the n- / iso- ratio can be adjusted according to the desired proportion of di-n-butene to methyl tert-butyl ether, and thus carries modified field butane in its n- / iso- ratio to the dehydrogenation step. A process according to one of claims 1 or 2, characterized in that between the dehydrogenation step and the etherification step or between the etherification step and the oligomerization step, a selective hydrogenation step and / or a step of cleaning with molecular sieve. A process according to one of claims 1 to 3, characterized in that, after the etherification step, the rest of the dehydrogenation mixture, in a separation step, n-butene is separated from the waste gas I and it leads to the dehydrogenation stage or, optionally, through a hydrogenation step, to the isomerization stage. A process according to one of claims 1 to 6, characterized in that, from the oligomerization mixture, in a separating step, the waste gas II is separated and taken to the dehydrogenation step or, optionally, to the dehydrogenation step. a hydrogenation step, to the isomerization stage. 6. A process according to claim 1, characterized in that ethanol, isopropanol, isobutanol or, particularly, methanol are used as the alcohol. 7. The use of the alkyl tertiary butyl ether obtained by a process according to one of claims 1 to 6, as a gasoline additive. 8. The use of di-n-butene obtained by a process according to one of claims 1 to 5, for the production of nonanoles by hydroformylation and hydrogenation of the hydroformylation product. 9. The use of the tri-n-butene obtained from the oligomerization mixture in a process according to one of claims 1 to 5, for the production by hydroformylation, hydrogenation of the product of the hydroformylation and hydroxyethylation of the product of hydrogenation, washing raw materials.