Method for simultaneous receipt of di-n-butene and alkyl tert-butyl ethers from natural butane

 

(57) Abstract:

Usage: petrochemistry. Essence: natural butane divided into n-butane and isobutane, n-butane is subjected to dehydrogenation and subsequent oligomerization of the obtained n-butene to a mixture of oligomers and the release of the last di-n-butene. Isobutane is subjected to dehydrogenation to mixtures containing isobutene that at the stage of esterification is subjected to interaction with alkanols to the alkyl tert-butyl ether. The technical result - increase in the efficiency of the process. 6 C. p. F.-ly, 1 Il.

The invention relates to the processing of natural butane, and more particularly to a method for simultaneous obtaining di-n-butene from natural alkyl tert-butyl ethers.

Alkyl tert-butyl ethers (hereinafter: ALBA) is used as an additive to motor gasoline to increase its octane number. Get them by joining alkanols to isobutene; this process is also called esterification.

Isobutene can have four different stocknike: he may be a product of the cracking unit with water vapor, plant for producing propylene oxide, oil plants (plants for catalytic cracking in to the ate, 1996 Petrochemical Review, publisher DeWitt & Company, Houston, Texas, USA). In the first three of these sources isobutene is obtained as a component of the fraction4that is , as directly obtained by-product. When the dehydrogenation of isobutane isobutene often represents an indirect by-product obtained in such installations, as its original connection, isobutane, also obtained as a direct by-product in the cracking plants with steam or refineries, or by isomerization of n-butane, which on its part is a by-product in the cracking plants with water vapor and at refineries. Currently, the world production of ETBE is about 25 million tons per year, with a tendency to increase. The amount of butane and butenes obtained as by-products in only one cracking unit or only one refinery, is too small to fully enjoy the economical production by extending it, in General available in the case of the process of obtaining ATBA. That is, you would subitem, to operate the installation for ETBE at optimal capacity. An alternative could be to collect a sufficient number of fraction C4of units of the specified type and to process it with getting isobutene and isobutane. However, the problem with both possibilities is that the transportation of liquid gases is expensive, not least because of the expensive security measures.

Debuted is a mixture of isomers, which is obtained by oligomerization of butenes along with higher butenova the oligomers resulting from the dimerization and/or codimerization of butenes, i.e., n-butene and/or isobutene. Under di-n-butene understand the product of the dimerization of n-butene, i.e., 1-butene and/or 2-butene. Important components of di-n-butene are 3-methyl-2-hepten, 3,4-dimethyl-2-hexene and secondary value n-oceny. Diisobutyl represents a mixture of isomers, which is obtained in the dimerization of isobutene. Diisobutyl is more extensive than debuted, which, in turn, is more extensive than di-n-butene.

Debuted, di-n-butene and Diisobutyl are the starting compounds to obtain isomeric nonanols by Hydra the x nonanalog, in particular esters of phthalic acid, are plasticizers produced in large scale and is used primarily in PVC. Nonanol of di-n-butene are much more straightforward than nonanol from dibucaine, which, however, with his hand less extensive than nonanol from Diisobutylene. Esters of nonanalog of di-n-butene have the technical advantages compared with esters of other nonanalog and therefore are in great demand.

N-butene to dimerization, as well as isobutene, can be obtained, for example, of the fraction4cracking unit with water vapor or installation for catalytic cracking in a fluidized bed. Fractions WITH4processed, usually by separating 1,3-butadiene using selective leaching, for example, using N-methylpyrrolidone. Isobutene is a desirable and is particularly valuable component fraction4because it can separately or in mixture with other hydrocarbons with 4 carbon atoms subjected to chemical interaction with the receipt of the products, high demand, for example, isobutane to high-octane isooctane, or with methanol to Metka get n-butenes, n-butane and isobutane. However, the share of n-butene among the cleavage products of the cracking unit with water vapor or oil refinery is relatively small, namely in the cracking plants with water vapor, it amounts to about 10 weight. % in terms of the main target product, i.e., ethylene. This means that using the cracking unit with water vapor, with an impressive capacity of 600,000 tons of ethylene per year, receive only about 60 000 tonnes of n-butene in the year. You could increase the amounts of n-butenes (and Isobutanol) by dehydrogenation of n - and isobutane obtained with n-butenes in a quantity of approximately 15,000 tons per year. However, this is not recommended because plants for the dehydrogenation require high capital investment and are uneconomical with such a small capacity.

As above indicated, isobutene is a valuable product of cracking and, therefore, generally not available for the isomerization of n-butene. However, the number of n-butenes directly obtained in the cracking unit with water vapor or oil refinery is not enough to obtain sufficient quantities of di-n-butene to set the ability to compete with existing large plants for important alcohols, employees as plasticizers, for example, 2-ethylhexanol. As above indicated, install to obtain propylene oxide are even less productive, as to obtain n-butenes. This means that it would be necessary to collect n-butenes from different cracking plants with water vapor, oil refineries or plants for propylene oxide (or process fraction WITH4from different sources to obtain n-butene) and together expose their oligomerization in order to achieve full boot install to get nonanol large enough for economical working. However, as already mentioned, the transportation of liquid gases the road.

Therefore, the object of the invention is to develop a method that allows obtaining n-butene and isobutene in one place, i.e. without the need to transport over long distances, namely in the quantity demanded for the joint production of di-n-butene, ATBA on the device for producing di-n-butene, having a capacity, for example, 200 000 - 800 000 t/year, and at the same installation for ETBE, in particular, methyl tert-butyl ether, having a capacity, for example, 300 000 to 800 000 tons/year in Addition, would be a desirable development of the way, what icestone di-n-butene and methyl tert-butyl ether.

The problem is solved by the proposed method for simultaneous obtaining di-n-butene and alkyl tert-butyl ethers from natural butane due to the fact that

(a) natural butane divided into n-butane and isobutane at the stage of separation,

(b) n-butane is subjected to dehydration under dehydrogenation to containing n-butene mixture, followed by oligomerization of the obtained n-butene at the stage of oligomerization to a mixture of oligomers and the release of the last di-n-butene,

(C) isobutane is subjected to dehydration under dehydrogenation to mixtures containing isobutene that at the stage of esterification is subjected to interaction with alkanols to the alkyl tert-butyl ether.

Before stage separation of natural butane can be subjected to hydrogenation under hydrogenation, while the separation stage is associated with the stage isomerization intended to establish the quantitative relationships of n-butane and isobutane in accordance with the desired quantitative ratio of alkyl tert-butyl ether and di-n-butene.

Between the stage dehydrogenation and stage by oligomerization in any sequence can be realized a stage of selective hydrogenation and/or stage clear is positive cleaning, recycle on stage dehydrogenation.

Between the stage dehydrogenation and stage of esterification can be accomplished a stage of selective hydrogenation. The residual gases from the stage of esterification through the purification step can be recycled to the stage of dehydrogenation. As alkanol preferably using ethanol, isopropanol, Isobe-canal or, in particular, methanol.

The proposed method is highly flexible, as within the capacity of the installation to obtain di-n-butene and installation for ATBA number di-n-butene, ETBE can be adjusted depending on market requirements.

Under natural butane understand a fraction WITH4"wet" natural gas components and accompanying oil gas emitted from these gases in liquid form by cooling to about -30oC. By low-temperature distillation of them receive butane, the composition of which varies depending on the field. However, in General natural butane contain about 30% of isobutane and 65% n-butane and, as a rule, as further components for approximately 2% of hydrocarbons with 1 to 3 carbon atoms and about 3% of hydrocarbons having a number of carbon atoms greater than four.

the m or as an additive to motor gasoline. They can be divided into n-butane and isobutane by fractional distillation. Isobutane is used on a large scale, for example, to obtain propylene oxide by sookielee propylene and isobutane, and also as agent for alkylation of n-butene, respectively isobutene to isooctane, which because of its high octane value as an additive to motor gasoline. In contrast, there are only less important area of application of n-butane. The latter, such as butane gas for heating purposes or it is used in relatively small quantities for polymers or copolymers or maleic anhydride by oxidation with air.

Implementation of the proposed method is illustrated by the processing scheme shown in the drawing.

A) Obtaining di-n-butene

First division stage 1 natural butane gas supplied through the line 2, is divided into n-butane, taken on the line 3, and isobutane, is withdrawn through line 4. The division is advisable carried out in a high column, in which n-butane using fractional distillation at low temperature or preferably at elevated pressure, a - 20oC below. At the same time as the cubic product receive hydrocarbons with the number of atoms above four, n-butane assign as a side stream, and isobutane assign as the major product together with lighter components.

H-butane serves on stage dehydrogenation 5, which line 6 assign the mixture containing n-butene. The dehydrogenation carried out by known techniques. It is advisable to carry out dehydrogenation in the gas phase in the presence of the solid catalyst or catalyst present in the form of a fluidized bed, for example, in the presence of chromium oxide (III) or, preferably, platinum on alumina, or zeolite as a carrier. In General, the dehydrogenation is carried out at 400 - 800oWith, preferably 550 to 650oC. the process is Typically carried out at atmospheric pressure or slightly increased up to 3 bar pressure. The residence time in the catalyst layer in General is depending on the catalyst, temperature and the desired degree of conversion 1-60 minutes Thus, performance is usually 0.6 to 36 kg n-butane 1 m3catalyst 1 h

Suitable dehydrogenation carried out only to a residual content of n-butane in the exhaust on the line is, however, in this increasingly occur the cracking reaction, reducing output due to the formation of coke deposits lifetime of the dehydrogenation catalyst. Optimal reaction conditions leading to the attainment of the desired degree of conversion, such as type of catalyst, temperature and time can easily be determined by preliminary experiments.

As a rule, after the dehydrogenation mixture contains 90 to 95 % of hydrocarbons with 4 carbon atoms and, in addition, hydrogen and lower and higher volatile components. It is advisable to mix purify prior to oligomerization. In the first stage of purification (not shown) by condensation of the separated fraction WITH4and wysokiej components. The condensate is subjected to distillation under pressure, and too condensed, dissolved hydrocarbons with 1 to 3 carbon atoms emerge from the upper part of the column. From the cubic product by further distillation as the main product is produced hydrocarbons with 4 carbon atoms, and the remainder is a relatively small amount of hydrocarbons having a number of carbon atoms greater than four.

Hydrocarbons with 4 carbon atoms in total contain small amounts, for example from 0.01 to about 5. % of 1,3-butadiene. It is recommended to remove this component, because even on a much smaller number is darovanie 7, which, in addition, increase in the percentage of the desired n-butene. It can be done, for example, in the liquid phase with a fully dissolved hydrogen in stoichiometric quantities. As catalysts for selective hydrogenation is suitable, for example, Nickel and, in particular, palladium on a carrier, e.g. 0.3 weight. % palladium on active coal or preferably aluminum oxide. A small amount of carbon monoxide of the order of parts per million encourages the selective hydrogenation of 1,3-butadiene to monoolefins and inhibits the formation of polymers (so-called "green oil"), deactivating the catalyst. In General the method is carried out at room temperature or at elevated temperature up to about 60oC and at high pressure, suitable up to 20 bar. Thus, the content of 1,3-butadiene in the fraction4a mixture of the dehydrogenation is reduced to values less than 1 part in 1 million.

In addition, it is advisable before oligomerization stage 8 to apply the obtained fraction WITH4a mixture of the dehydrogenation, almost completely exempt from 1,3-butadiene, purification step 9 using a molecular sieve, and further removed substances as detrimental substances are compounds of oxygen and sulphur. It is advisable to use a molecular sieve with pore size of 4 to 15 angstroms, preferably 7 to 13 angstroms. In some cases, for economic reasons it is advisable to skip the dehydrogenation mixture sequentially through molecular sieves with different size of pores. This method can be performed in a gas, liquid or mixed gas-liquid phase. Depending on this pressure in General is 1 to 200 bar. It is advisable to work at room temperature or at temperatures up to 200oC.

The chemical nature of molecular sieves plays a smaller role than their physical structure, that is, in particular, the pore size. This means that you can use a variety of molecular sieves, crystalline, natural aluminum silicates, for example layered lattice silicates, as well as synthetic molecular sieves, for example, zeolite structure. There are trade zeolites of type a, X and Y, among other companies Bayer AG, Dow Chemicals To. , Union Carbide Corporation, Laporte Industries Ltd. and Mobil Oil Co. For implementing the method is also suitable synthetic molecular sieves, which along with aluminum and silicon contain other atoms, introduced by cation exchange, the synthetic zeolites, in which in addition to aluminum and silicon by coprecipitation in the lattice is built even further atoms, for example, boron or phosphorus.

As already mentioned, the stage of selective hydrogenation of 7 and a cleaning stage 9 with molekularno sieves are optional, the preferred measures in the framework of the proposed method. Their sequence in principle plays no role, however, preferred is shown in the drawing sequence.

Received under degidrirovaniya 5 mixture, if necessary after the described pre-treatment, serves on stage oligomerization 8, which represents a significant admission of the proposed method. Oligomerization carried out with known methods. In General operate in the liquid phase, in the presence of, for example, a system consisting of octoate Nickel(11) chloride ethylaluminum and free fatty acid as homogeneous catalyst, or preferably, one of the many known, permanently installed or suspended in a mixture of oligomerization catalysts based on Nickel and silicon, which may be supported on a carrier. Often the catalysts additionally contain aluminum. Other prigoginian, protons or sodium ions, Nickel ions. This may be the case different media, for example, amorphous aluminium silicate, crystalline aluminium silicate, zeolites of type X, Y and ZSM.

Depending on the used catalyst for the oligomerization exercise reasonable at 20 to 200oAnd 1-100 bar. The reaction time (or contact) in General is 5-60 minutes the Parameters of the method, in particular the type of catalyst, temperature and time of contact will coordinate with each other so as to achieve the desired degree of oligomerization, i.e. mainly dimerization. Needless to say that it is impossible to achieve complete conversion of the reaction, and it is advisable to achieve 30-70% conversion for each cycle of the reaction. The optimal combination of parameters of the method can easily be installed through preliminary experiments.

The mixture oligomerization 8 serves on the stage of processing 10, which allocate the residual gases, which give on line 11 and recycled to the stage of dehydrogenation 5. In that case, if at the stage of oligomerization 8 use a catalyst of the type described liquid catalysts, it is desirable. prior to recirculation of the residual gases were purified in order Obi for the extraction of the catalyst. Then the selected residual gas is dried using a suitable molecular sieve, and separate other side components. After that, by selective hydrogenation, for example in the presence of a palladium catalyst, removing the multiply unsaturated compounds, for example, the butins, and at the end of the thus purified residual gas recycle on stage dehydrogenation 5. These techniques for cleaning the residual gas disappear when using a solid catalyst for oligomerization.

From the liquid phase of the mixture oligomerization 8 on stadii 10 by fractional distillation distinguish di-n-butene, taken along the line 12, and the trimeric n-butene, i.e., the isomer dodecene, taken along the line 13, and di-n-butene as a main product directly available for nonanalog. Dodecene are a desired by-product. They can be hydroformylating, then the product of hydroformylation subjected to hydrogenation, and the resulting tridecanol are subject oxidi-place, resulting in gain valuable raw materials detergents.

B) Receiving ALBA

Isobutane with division stage 1 serves on stage dehydrogenation 14 where it is subjected to the tion is not significantly different from dehydrogenation of n-butane on stage 5. Isobutane is subjected to dehydrogenation easier than n-butane, so within specified for stage 5 dehydrogenation limits of operation can be selected in General somewhat more moderate conditions. In the case of this process of dehydrogenation is appropriate to achieve only a conversion of about 50%.

As described above for the mixture obtained in stage dehydrogenation 5, the mixture obtained in stage dehydrogenation 14, in addition to hydrocarbons with 4 carbon atoms contains hydrogen and volatile components (which are partly contained in the natural butane and partly formed by the dehydration), as well as components with a higher boiling point. Before esterification get on stage dehydrogenation 14 a mixture of suitable clear at first (not shown in the drawing) cleanup phase, which corresponds to the stage, which is described above in connection with the purification of the mixture obtained in stage dehydrogenation 5.

Thus obtained fraction WITH4in the exhaust line 15 mixture expediently serves on the stage of selective hydrogenation of 16, on which dieny as PROPADIENE and 1,3-butadiene, are subjected to selective hydrogenation to monoolefins. Dieny are formed, for example, from about the SJ from isobutane, or they are formed in the conditions of dehydrogenation by isomerization and/or cracking reactions. At least when recirculation line 17 residual gases these diene interfere with the reaction at the stage of dehydrogenation 14 and, although to a lesser extent, at the stage of esterification 18. Therefore, phase selective hydrogenation of 16 can be placed after the stage of esterification 18 in the flow of exhaust through line 17 residual gas before the stage of purification 19 or after it. This setup allows, if necessary, to reduce the size of the reactor due to the fact that, naturally, the volume of the residual gas stream is less than the volume of the mixture, the exhaust line 15. Regarding the process conditions indicated on the explanation in connection with the stage of selective hydrogenation of 7.

Get on stage dehydrogenation 14 mixture, if necessary after preliminary selective hydrogenation, serves on the stage of esterification 18, where the contained isobutene in General known method is subjected to interaction with alkanols supplied through line 20 to ALBA, in particular to methyl tert-butyl ether. In addition to methanol as alkanol still prefer ethanol, isopropanol, Isobutanol. Interaction provide frature. It is advisable to work with a small excess of alkanol that increases the selectivity of the reaction of isobutene and inhibits dimerization. As the catalyst used, for example, acidic bentonite or, preferably, an acidic ion exchanger with a large amount of pores.

From the reaction mixture stage of esterification 18 by distillation allocate the residual gas withdrawn through line 17, and possible excess alkanol separated from the produced ATBA and brought on line 21. In the case of methyl tert-butyl ether residual gas with methanol forms an azeotrope. The latter is washed with water and separated into an aqueous phase and a residual gas is recycled to the stage of dehydrogenation 14, if necessary through a stage of selective hydrogenation of 16 (which is then appropriately included in the installation) and/or purification step 19, the latter expedient process using molecular sieves, to remove, in particular, oxygen - or sulfur-containing impurities that interfere with the dehydrogenation catalyst. At least part of the residual gas can also be recycled to the stage of division 1 (not shown) in order to avoid the accumulation of n-butane vsledstvii, into methanol, which is recycled to the stage of esterification, and water, which again is used for washing.

C) regulation of the amounts of di-n-butene, ALBA

It is after division stage 1 exercise stage isomerization 22, because it allows you to change the proportion of di-n-butene, ATBA. Possible changes is limited only by the capacity of plants to obtain di-n-butene, ATBA. With regard to the necessary investments rarely both installations will build size, allowing processing of the whole flow field Bhutan only in one of the units, and the other option does not work. All stage isomerization 22 gives the flexibility to respond to market demand.

In the case of natural butane 1 contain unsaturated compounds, is suitable in addition to stage isomerization 22 to provide another stage hydrogenation 23, on which data is unsaturated compounds undergo hydrogenation, because they interfere with the isomerization. The hydrogenation carried out by a known method. It is advisable to work in the liquid phase and, depending on the catalyst, at room temperature or at elevated temperatures up to 90oAnd when damifino catalysts, for example 0,3% palladium on aluminium oxide.

Hydrogenated natural butane serves on the stage of division 1 where they are divided by the method described above for n-butane, taken on the line 3, and isobutane, is withdrawn through line 4. If the ratio of n-butane and isobutane wish to change in accordance with the requirements of both systems, a part of abundant isomer away and serves on stage isomerization 22. In the diagram alternatives shown in phantom lines. On stage isomerization 22 individual isomer transferred to another isomer up to a maximum of equilibrium depending on the temperature is 40-55% n-butane and 45-60 % of isobutane. Isomerisation of n-butane and isobutane is a known reaction. In General operate in the gas phase at 150-230oAnd 14-30 bar, and as a catalyst using platinum on alumina as the carrier, the selectivity of which can still be improved by adding chlorine compounds, for example carbon tetrachloride. To prevent the dehydrogenation is preferably add a small amount of hydrogen. The isomerization selectivity is high, the cracking up of smaller pieces is only a small part (approximately 2%).

1. Method for simultaneous receipt of di-n-butene and alkyl tert-butyl ethers from natural butane, characterized in that (a) natural butane divided into n-butane and isobutane under division (b) n-butane is subjected to dehydration under dehydrogenation to containing n-butene mixture, followed by oligomerization of the obtained n-butene at the stage of oligomerization to a mixture of oligomers and the release of the last di-n-butene, (b) isobutane is subjected to dehydration under dehydrogenation to mixtures containing isobutene, which stage of esterification is subjected to interaction with alkanols to the alkyl tert-butyl ether.

2. The method according to p. 1, characterized in that before the phase separation of natural butane is subjected to hydrogenation under hydrogenation, while the separation stage is associated with the stage isomerization intended to establish the quantitative relationships of n-butane and isobutane in accordance with the desired quantitative ratio of alkyl tert-butyl ether and di-n-butene.

3. The method according to p. 1 or 2, characterized in that between stage dehydrogenation and stage of oligomerization in any sequence carry out a stage of selective hydrogenation and/or a hundred is enough gases, which, if necessary after pre-cleaning of recycle on stage dehydrogenation.

5. The method according to one of paragraphs. 1-4, characterized in that between stage dehydrogenation and stage carry out the esterification stage of selective hydrogenation.

6. The method according to one of paragraphs. 1-5, characterized in that the residual gases from the stage of esterification through purification stage recycle on stage dehydrogenation.

7. The method according to one of paragraphs. 1-6, characterized in that as alkanol use ethanol, isopropanol, Isobutanol or, in particular, methanol.

 

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