JPS5877828A - Conversion of xylene containing ethylbenzene - Google Patents

Abstract

PURPOSE:To recover high purity benzene in the isomerization of xylenes containing ethylbenzene and the simultaneous conversion of the ethylbenzene to benzene, by recycling a part of the recovered benzene to the isomerization process, and decomposing the by-product to a low-boiling substance. CONSTITUTION:At least a part of ethylbenzene contained in xylene is dealkylated and at the same time, xylene is isomerized by treating the xylene containing ethylbenzene in the presence of hydrogen using a binary catalyst composed of a hydrogenation active component and a solid acid component. In the above process, a part of the recovered benzene is recycled to the reaction step to effect the recovery of high purity benzene. The amount of benzene fraction recycled to the reactor is usually 0.5-20 times, especially 1-10 times of benzene produced by the dealkylation reaction. The hydrogenation active component is e.g. preferably rhenium, etc., and the solid acid component is preferably mordenite, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of isomerizing xylenes containing ethylbenzene in the presence of hydrogen and converting at least a portion of the ethylbenzene into benzene.

More specifically, the present invention relates to a method of reducing the amount of non-aromatic components having a boiling point similar to that of benzene mixed into the benzene fraction obtained by this reaction, thereby obtaining benzene with higher usefulness.

Demand for paraxylene has increased significantly as a raw material for synthetic fiber polyester. On the other hand, the demand for ortho-xylene and meta-xylene is smaller than that for para-xylene, and the xylene isomerization reaction that converts these xylenes to para-xylene is industrially important.

In general, industrially used xylene raw materials are obtained by aromatic extraction and fractional distillation of reaction products from naphtha reforming or cracking, and both contain ethylbenzene. In this way, ethylbenzene is removed from the xylene raw material by some means, and para-xylene is produced by combining the separation step and the isomerization step.

Methods for removing ethylbenzene include a method of separating ethylbenzene as it is, and a method of converting it into other more useful compounds by reaction. An example of the former is a distillation method. In this case, since the boiling point difference between ethylbenzene and xylenes is small, it is necessary to carry out ultra-precision distillation, which is an economically disadvantageous method with high equipment and utility costs. An example of the latter is a method in which ethylbenzene is converted into xylenes using a binary catalyst consisting of a platinum component and a solid acid component, and the xylenes are isomerized at the same time. The method of removing diethylbenzene by reaction does not require any special equipment, so it can be said to be an economically advantageous method. However, in the above-mentioned method using a binary catalyst, platinum, which is an extremely expensive noble metal, is used, or there is a limit to the conversion rate of diethylbenzene due to the thermodynamic equilibrium relationship between ethylbenzene and xylene isomers. The problem with this.

Further improvements are desired.

As a solution to the above problems, a method of converting ethylbenzene into benzene and ethane using a catalyst consisting of a solid acid component and a hydrogenation component has recently attracted attention. That is,
The reaction of hydrogenation dealkylation of ethylbenzene to benzene and ethane is hardly subject to thermodynamic constraints, so it is relatively easy to improve the conversion rate, and the benzene obtained by this reaction is similar to xylenes. The present inventors proposed a mordenite catalyst containing rhenium and/or phosphorus, or a catalyst further containing molybdenum, tungsten, and vanadium, as a catalyst that has a large boiling point difference, can be easily separated by distillation, and can be used for synthesis. -83952.55
-140408, 56-18092, etc., proposed this earlier. However, in order to further improve the efficiency of this reaction, it is desirable to improve the following points. One is the selectivity of the reaction, which involves the transalkylation of ethyl groups to ethylbenzene and xylene, and the disproportionation reaction of xylenes, minimizing the loss of xylene. The other is to increase the purity of the benzene that is recovered. One of the advantages of this reaction is that the recovered benzene can be used as a raw material for styrene, lactam, etc., but with the catalysts known so far, non-aromatic The amount of group hydrocarbon by-products is large, and in order to increase the effectiveness of benzene, it is necessary to reduce the amount of these by-products. Regarding the former, it is possible to increase the selectivity by manipulating the reaction conditions by taking advantage of the difference in reaction order and activation energy between trans-alkylation, unrestricted reaction, and dealkylation, but essentially it is possible to improve the catalyst. Must be based on Regarding the latter, C! It is conceivable that the decomposition activity may be decomposed to ~C4 components, but it is difficult to suppress the decomposition activity without decreasing the deethylation activity because both reactions proceed on the same acidic point, and increasing the decomposition activity will cause the decomposition of xylene. etc. are also decomposed, and in any case, it is difficult to solve the problem with a catalyst.

In view of the above points, the present inventors conducted a reaction in which xylenes containing ethylbenzene are isomerized in the presence of hydrogen, and at least a portion of the ethylbenzene is converted into benzene. An investigation into an improvement method revealed that if a portion of the recovered benzene is recycled to the isomerization process, non-aromatic hydrocarbons with a boiling point similar to that of benzene will be decomposed into hydrocarbons with a lower boiling point. We have discovered this and arrived at the present invention.

The method according to the invention will be explained with reference to the flow sheet of FIG.

Xylenes containing ethylbenzene (1) C, recirculating liquid (
2, 3) (4) and supplied to the reactor (5). The reactor effluent (6) is sent to a distillation column (7) and separated into a top fraction (8) and a bottom fraction 00). Top fraction (8)
consists mainly of benzene, part (3) of which is recycled to the reactor (5) and the remainder (9) recovered. The column bottom fraction 00) is sent to the xylene separation step (2), where the free xylene 0◇ is separated and recovered, and the raffinate component (2) from which free xylene has been removed is recycled to the reactor (5). In this figure, other by-products such as light-boiling components, toluene, and high-boiling components with carbon atoms of 9 or more are classified or xylene is classified. The separation of ortho-xylene in step is omitted.

The raw material to be numbed in the present invention is a xylene mixture containing ethylbenzene, but there are no particular limitations on the concentrations of these components and P. In addition, feedstocks containing other aromatic components such as benzene, tolutrimethylbenzene, ethyltoluene, diethylbenzene 1, ethylxylene, etc., containing small amounts of non-aromatic hydrocarbons with a boiling point similar to that of alkylxylene are also used. can do.

Note that the reaction step and xylene separation step are appropriately selected at one feeding position of the raw material depending on its composition.

The catalyst used in the present invention is not particularly limited as long as it has the activity of converting at least a part of ethylbenzene into benzene and isomerizing xylenes, A binary catalyst consisting of: As a hydrogenated active ingredient, rhenium s
■Group b metals or group VIII metals are preferable, and as the solid acid component, acid type zeolites, especially mordenite, or ZSM type zeolites having the X-ray diffraction pattern shown in Table 1 are preferable, and still improve the selectivity of the catalyst. It is also possible to add phosphorus or the like as a substance.

Table 1 X-ray diffraction pattern 1α1 ±[1,2' S 3.8S±o,o
s” vs9B ±0.2, M3.
82±o, os vs6.37±0.1W
3.75±0.08. 56, DO±0.1
W”3.72±0.08 55.71±0.1
W Lo, 66±0.05 M5.58±0.1
W 3.00±0.05 M4, s7±o
, os v2. [lO:l:0.05' W - However, relative intensity (100I/io) vs - very strong,
S=Strong, M=Intermediate Strength, W=Weak The reactor may be a fixed bed, moving bed, or fluidized bed, but a fixed bed system is preferred because it is simple and easy to operate. Although the reaction conditions are not particularly limited, the reaction temperature is 600℃.
~600℃, reaction pressure is 50 Kl/c from atmospheric pressure
rA G , contact time;
Is the factor W/F 1-200? -cat・hr/l
-mols Hydrogen to aromatic hydrocarbon tongue ratio I (2/F is preferably 1 to 5D) In the method of the present invention, the amount of benzene fraction recycled to the reactor is determined by catalyst activity, raw material Although it may vary depending on the non-aromatic hydrocarbon content in the benzene fraction, the desired benzene fraction, etc. 1 Usually, a is preferably 5 to 20 times the amount of benzene produced in the dealkylation reaction, and particularly preferably 1 to 10 times the amount of benzene produced in the dealkylation reaction. The method of the present invention treats the recovered benzene fraction with a xylene isomerization catalyst having dealkylation activity to decompose and reduce non-aromatic hydrocarbons in the benzene fraction,
If the circulating amount of benzene fraction is less than 15 times the amount of benzene produced, the decomposition effect is insufficient, and if it is more than 20 times, the increase in cost for cyclic reprocessing is , the decomposition and reduction effect of the non-aromatic hydrocarbons is insufficient, and this method becomes less advantageous. In this type of circulating treatment of benzene fraction, the entire amount of benzene fraction is circulated to the reactor without taking it out of the process at the beginning of the reaction, and when the circulating amount of benzene reaches a standard value, the amount produced by the reaction is reduced. The corresponding benzene fraction may be separated and recovered. It is also possible to separate the toluene produced in this reaction from the reactor effluent together with the Sakanzene fraction, recirculate a portion to the reactor, and take the remaining second out of the process to separate it into benzene and toluene. be.

After the benzene fraction is removed from the reactor effluent as described above, toluene and ortho-xylene are separated by distillation as required, further separating and recovering the distal xylene, and the remaining components are recycled to the reactor. The present invention will be explained below with reference to examples.0 Example Note Synthetic sodium type mordenite 11 zeolon-10 DNA'' powder manufactured by y company was mixed with a 0.169 normal calcium nitrate aqueous solution at a solid-liquid ratio of 5C1/Ni) to 80 to 90% ℃ and subjected to batchwise ion exchange treatment for 60 minutes.Then, it was washed once with distilled water, and calcium ion exchange treatment was performed again, and this operation was repeated 5 times.After that, distilled water was used thoroughly. ' Washed with water and dried overnight at 110°C. This calcium ion-exchanged "Zeolon-10 DNA" was then mixed with a 0.18'7N ammonium chloride aqueous solution at a solid-liquid ratio of 5 (i/l1p). Heat to 80-90℃, 3
Batch dealkalization treatment was carried out for 0 minutes. Thereafter, it was thoroughly washed with distilled water and dried at 110°C overnight. In this case, alumina sol was added as a binder to Rudenite powder, 15% by weight in terms of alumina (At203), perrhenic acid aqueous solution as Re, 11% by weight, phosphoric acid as Phosphorus CP, 5% by weight. After adding 1% by weight of vanadium (V) to an ammonium metavanadate aqueous solution and thoroughly kneading the mixture, it was formed into particles of 10 to 24 meshes, dried at 110°C overnight, and then calcined at 500°C in air for 2 hours. .

Using this catalyst, the feedstock xylene containing ethylbenzene was reacted at a reaction temperature of 4.50°C and a reaction pressure of 10”l/a.
d G N・Hz F 12moν'rnO1%w/
F80 iP-cat-hr/? -mot was reacted. The compositions of the feedstock xylene and the reaction product were as follows.

The reaction product liquid was distilled in a rectification column to obtain benzene and toluene fractions. This fraction was analyzed for non-aromatic components using gas chromatography equipped with a hydrogen flame detector.
Calculated as 00.

The results are shown in Table 1.

Next, in addition to the distilled benzene and toluene fraction, which is equivalent to about twice the amount of benzene produced in the reaction based on benzene standards, in addition to Kishilene, W/F7J No.
t, ・hr/? −mol 0 reacted in the same way
Analysis of the composition of the supplied Mt material and the reaction product revealed the following.

The reaction product liquid was similarly distilled using a rectification column to obtain a benzene-toluene fraction. This fraction was analyzed for non-aromatic components using gas chromatography, and calculations were made with benzene as 100. The results are shown in Table 1. Furthermore, benzene and toluene fractions were added to the raw material xylene in an amount equivalent to about 6 times the amount of benzene produced in the reaction based on benzene standards, and used as a feedstock W/
F 667-cat-hr/! ? -mot was reacted in the same manner. The reaction product liquid was distilled in a rectification column, and non-aromatic components were similarly analyzed.

Table 1. By circulating more benzene and reacting,
Non-aromatic components with boiling points near benzene are reduced,
It can be seen that the benzene purity improves.

Note that in this experiment, the reaction was carried out in one pass, but in the actual flow, benzene is circulated through the reaction process, and some benzene is extracted, so the purity of benzene is further improved.

Table 1 Non-aromatic component concentration Calculated with benzene as 100

[Brief explanation of drawings]

FIG. 1 is a flowchart showing one embodiment of the method of the present invention. 1--Feedstock, 5--Reactor, 7--Distillation column, 1
2...-separation device

Claims (1)

[Claims] (1) Dealkylating xylenes containing -thi'-benzene to at least a portion of ethylbenzene in the presence of hydrogen
, A method for simultaneously isomerizing xylene 11 A method for converting xylenes containing ethylbenzene characterized by recycling a part of the recovered benzene to the reaction process 0