RU2026851C1 - Method of synthesis of benzene, toluene, ortho- and para-xylene - Google Patents

Abstract

FIELD: chemical technology. SUBSTANCE: products: benzene, empirical formula is C₆H₆, yield is 14.2-14.6%; toluene, empirical formula is C₇H₈, yield is 22.2-23.3%; o- and p-xylenes, empirical formula is C₈H₁₀, yield is 6.0-8.9% . Reagent 1: C₃-C₄-alkanes. Catalyst: Zn- or Ga-containing zeolite type ZSM-8. Process conditions: reactor block consisting of cascade of consecutive connected 3-4 reactors, at 400-600 C. Recycle of m-xylene fraction isolated from products contacting to the last by course reaction reactor, time contacting in the last reactor is 0.3-1.8 s. EFFECT: improved method of synthesis. 2 cl, 2 dwg, 8 tbl

Description

 The invention relates to the field of petrochemical synthesis, more specifically to the production of benzene, toluene, o- and p-xylenes.

The main method of industrial production of these hydrocarbons is currently the catalytic reforming of gasolines. The process is carried out at a temperature of 480-520 ^about With a hydrogen pressure of 7-25 at. In this process, m-, o- and p-xylenes are obtained in equilibrium. To obtain o- and p-xylenes, the process of isomerization of the m-xylene fraction on a platinum-mordenite-containing catalyst is used. The disadvantages of the process are the scarcity and high cost of raw materials, the need to circulate large volumes of hydrogen, extractive methods for the separation of aromatic hydrocarbons due to the presence of paraffin hydrocarbons with close boiling points, the use of different catalysts in the processes of catalytic reforming and isomerization of the m-xylene fraction.

An alternative method for producing aromatic hydrocarbons may be the production of gaseous C ₃ -C ₄ hydrocarbons, the resources of which are large and the use of insufficiently qualified.

Known is a method of synthesis of benzene, toluene, o- and p-xylene from the hydrocarbons C ₃ -C ₄ at a temperature of 482-537 ^C, 9˙10 minimum working pressure ^{of 5} Pa and a space velocity of 2hr ^-1 feed (contact time with ≈5) using as catalysts various high-silicon zeolites of the ZSM type promoted by various metals (zinc, gallium). The process is carried out in a cascade of series-connected reactors with heating of the reaction products between reactors with continuous catalyst regeneration. The main disadvantage of this method is the relatively low yields of benzene, toluene, o- and p-xylenes due to the formation of m-xylene, ethylbenzene and C ₉₊ aromatics.

The closest in technical essence is an improved method for producing aromatics from C ₃ -C ₄ hydrocarbons with benzene or toluene recycle.

As a catalyst, zeolite of the ZSM-5 type with deposited gallium (0.1-10%) is used. The process is as follows (see figure 1). Propane (stream 1) together with a portion of the isolated benzene or toluene up to 8 mol.% For hydrocarbon feed (stream 2), as well as hydrogen (stream 4) enters the reactor block 6 at 487-565 ^о С and a pressure of 5-7 at. The total residence time of the raw material mixture in the reaction zone is 6-7 s. As a result of the dehydrocyclodimerization reaction, a mixture of products and unreacted propane (stream 7) are obtained, which, passing through the refrigerator 8 and the separator 9, are separated. light gases and H ₂ in accordance with the balance are returned to recycling (stream 4), and the liquid phase is separated in the system of fractional columns according to figure 1. Part of the released benzene or toluene (up to 8 mol.% For hydrocarbons) is recycled. The conversion of propane to aromatics during recycling of 6 wt.% Benzene was 66%. Without benzene recycling, propane conversion was 60%. Due to the fact that the material balance for the products is not presented in EP N 0230655, the authors reproduced this patent in the reaction of high-purity propane dehydrocyclodimerization with 6 mol% toluene recycle on a ZSM-5 catalyst with module 60 and supported Ga in an amount of 3% at 560 ^{° C} and the total residence time in the reaction zone from 6-7. The conversion of propane to aromatics was 66 wt.%, And the selectivity of the formation of o- and p-xylenes was 3.73 wt.%. The main disadvantage of this method is the low yield of o- and p-xylenes.

 The aim of the present invention is to increase the yield of o- and p-xylenes.

This goal is achieved through an improved method for producing aromatic hydrocarbons from C ₃ -C ₄ hydrocarbons using Zn or Ga-containing high-silicon zeolite catalysts of the ZSM-5 type as a catalyst in a reactor block consisting of a cascade of series-connected reactors at 400-600 ^о C. The reaction products obtained are separated into the recycle fraction of the starting alkanes, the benzene, toluene, xylene and C ₉₊ aromatics. The isolated xylene fraction is subjected to separation by distillation and adsorption methods or using a cryogenic technique. The isolated m-xylene fraction (all or part of it) is recycled to the last reactor unit along the contact time of the stream containing the methaxyl fraction with the catalyst of 0.3-1.8 s.

 The proposed process can be carried out both in the reactor unit with a fixed catalyst bed, and with a moving catalyst bed and with continuous regeneration.

The process of aromatization of hydrocarbons With ₃ -C ₄ according to the proposed option is carried out as follows (see figure 2). A mixture of C ₃ -C ₄ hydrocarbons (stream 1) is fed into a reactor block consisting of 3-4 successive reactors (stream 1) into the first reactor along the way. C ₃ -C ₄ hydrocarbons with products are sequentially fed to the second 3, third 4 and fourth 5 reactors. The process is carried out on a silica type zeolite ZSM-5 modified with gallium or zinc, at 400-600 ^{° C} and the total contact time 5-7 seconds. The catalyst is distributed among the reactors in such a way (with a fixed catalyst bed) so that the contact time in the last reactor of the reactor unit is varied in the range of 0.3-1.8 s. In the reactor block with a moving catalyst bed, the required contact time of the stream containing the m-xylene fraction is achieved by changing the input location of the m-xylene fraction. The m-xylene fraction obtained by separation of the xylene fraction in the xylene separation unit 24 by rectification, extraction or cryogenic methods is heated and fed to the last reactor of the reactor unit (stream 6). The reaction products and unreacted C ₃ -C ₄ (stream 7) through the refrigerator-condenser 8 enter the separator 9, where there is a separation of H ₂ , C ₁ and C ₂ . Then the reaction products and unreacted C ₃ -C ₄ (stream 11) are separated in the column 12 stabilization of liquid products. Fraction C ₃ -C ₄ shown at the top of the column at ⁶⁰ ° C, a pressure of 12 atm and a reflux ratio of 3. The unreacted C ₃ -C ₄ (stream 13) is returned to the process, and liquid products (stream 14) is separated by rectification in the column system : in the column 15 at 80-81 ^{° C} and a reflux ratio of 10 at the top shown in benzene (stream 16); in the column 18 to the top of the column shown in the toluene at ¹¹⁰ ° C and a reflux ratio of 3 (stream 19); in the column 21 from the bottom of product column 18 at ^about 138-142 C and a reflux ratio of 5 allocated xylenes (stream 22), and from the bottom of the column is derived fraction C ₉₊ aromatic hydrocarbons (stream 23). Xylenes (stream 22) are fed in xylenes separation unit (24) which consists of a distillation column, wherein at the top at 139 ° ^C at a reflux ratio of 5.10 is isolated isomer mixture of m- and p-xylenes, and the cube outputted o- xylene. The mixture of m- and p-xylenes is then divided in an adsorption unit using zeolites or in a cryogenic unit due to the significant difference in their melting points. The meta-xylene fraction (stream 6) is recycled and has the following composition,%: ethylbenzene 8, p-xylene 10, o-xylene 10, m-xylene 72.

In contrast to the method described in [2], in the proposed method, the target products are benzene, toluene, o- and p-xylenes. In addition, the xylene fraction is further separated into isomers. The o- and p- isomers are currently in qualified use, and the m-xylene fraction, if necessary, is completely recycled, but not at the beginning of the process, as in [2], but in the last reactor along the way, in order to ensure the required residence time of the stream containing the m-xylene fraction is 0.3-1.8 s. An increase in the residence time above 1.8 s leads to a decrease in the yield of total aromatics, increased gas formation, and an increase in the specific gravity of C ₉₊ aromatics.

An unexpected effect in the recycling of the m-xylene fraction to the last reactor was the disproportionation of m-xylene under the indicated conditions with 100% selectivity without increasing the content of C ₉₊ aromatics. In addition, the yield and selectivity (excluding the recycle m-xylene fraction) of the formation of o- and p-xylenes under the proposed conditions is 1.6–2.4 times higher than in [2].

 The effectiveness of the proposed method is illustrated by the following examples. For the convenience of comparing process indicators, 100% propane conversion is carried out.

PRI me R 1 (prototype). In the reactor unit 6 (see FIG. 1) at 560 ^C and a pressure of 5 atm fed 100 kg / h of propane of high purity (stream 1), here also enters the column 21, stream 2, is toluene in an amount of 12.55 kg / h, which corresponds to 6 mol.% toluene. The total residence time of the raw material mixture in the reaction zone is 6-7 s. As a catalyst, zeolite of the ZSM-5 type with a module of 60 and deposited gallium in an amount of 3% is used. As a result of the dehydrocyclodimerization reaction, a mixture of reaction products is obtained (stream 7), which is sent for separation according to FIG. Part of the toluene released is recycled.

 Table 1 shows the material flow balance. The conversion of propane to aromatics is 66%.

 Aromatics yield excluding recycle stream 66 kg / h. The yield and selectivity of the formation of o- and p-xylenes 3.73 kg / h wt.%. The yield of benzene, o- and p-xylenes was 21.22 kg / h.

PRI me R 2. In the reactor block, consisting of three successive reactors (see figure 2) serves 100 kg / h of propane. The process is carried out on a silica type zeolite ZSM-5 with silicate module 60 containing 1.5% of zinc, at 570 ^C and a bulk supply of liquid propane 2 h ^-1. The reaction products leaving the last reactor are cooled in a refrigerator 8 and fed to a separator 9, where hydrogen and C ₁ -C ₂ hydrocarbons are separated. Liquid products are sent to the stabilization column of liquid products 12, where C ₃ -C ₄ hydrocarbons are selected at the top. The bottoms product is sent to the benzene recovery column 15. The bottoms product of column 15 is fed for separation to column 18, where toluene is recovered at the top, and bottoms are fed to column 21. In column 21, xylenes are recovered at the top, and C ₉₊ aromatics are obtained from the column. Xylenes are divided in xylene separation unit 24; the obtained m-xylene fraction in the amount of 12 kg / h is fed into the last (third) reactor of the reactor block. The volumetric feed rate of liquid raw materials is 2 h ^-1 . The contact time in the last reactor is 1.8 s. The composition of the streams of the source and obtained products according to figure 2 are presented in table 2. The yield of benzene, o- and p-xylene (without recycle, m-xylene fraction) was 23.1 kg / h. The yield and selectivity of the formation of o- and p-xylenes is 8.9 kg / h (wt.%), Which is 2.4 times higher than in the prototype.

EXAMPLE EXAMPLE 3 The process is carried out in the same manner as in Example 2, but the reactor unit consists of 4 reactors in series, and serves fraction aromatization of C ₃ -C ₄ ratio of 50/50 at ⁶⁰⁰ ° C, the catalyst is zinc (3%) -containing zeolite type ZSM-5 with a module equal to 60. The m-xylene fraction is fed to the fourth reactor in an amount of 12 kg / h. The residence time of the stream containing the m-xylene fraction in the last reactor is 0.3 s.

 The results are presented in table.3. The yield of benzene, o- and p-xylenes was 23.3 kg / h, and the yield and selectivity of the formation of o- and p-xylenes was 8.8 kg / h (wt.%), Which is 2.35 times higher than in prototype.

 PRI me R 4. The process is carried out as in example 3, on gallium-containing (0.5%) zeolite type ZSM-5 with module 90. But the m-xylene fraction is supplied in an amount of 6 kg / h. The remainder of the m-xylene fraction is removed from the process.

 The results are presented in table. 4. The yield of benzene, o- and p-xylenes (streams 16, 25 and 26) was 20.6 kg / h, and the yield and selectivity of the formation of o- and p-xylenes was 6.0 kg / h (wt.%) , which is 1.6 times higher than in example 1.

PRI me R 5. The process is carried out in the same way as in example 2, but at a temperature of 400 ^about With gallium-containing zeolite (3.0% Ga).

 The results are presented in table.5. The yield of benzene, o- and p-xylenes was 23.1 kg / h, and the yield and selectivity of the formation of o- and p-xylenes were the same as in example 2.

EXAMPLE EXAMPLE 6 The process is carried out in the same manner as in Example 2, but the temperature in the reactor was 600 ^{° C} and contact time of m-xylene fraction with the catalyst in the last reactor - 0.1 s. The results are presented in table.6. The yield of benzene, o- and p-xylenes is 18.8 kg / h, and the yield and selectivity of o- and p-xylenes is 8.3 kg / h (wt.%), Which is higher than in the prototype, in 1, 4 times, but significantly less than in examples 2-4, due to the low conversion of m-xylene due to insufficient contact time.

 PRI me R 7. The process is carried out as in example 6, but the contact time of the stream containing the m-xylene fraction with the catalyst in the last reactor is 2.5 s.

 The results are presented in table.7. The yield of benzene, o- and p-xylenes was 21.9 kg / h. The output and selectivity of o- and p-xylene 6.4 kg / h (wt.%), Which is 1.7 times higher than in the prototype (example 1), but less than in examples 2, 3 and 5, which due to a decrease in the degree of xylene conservation (up to ≈60%) when the contact time exceeds 1.8 s.

 Comparative data of the processes of the prototype and the proposed methods are presented in table.8.

Claims (2)

1. METHOD FOR PRODUCING BENZENE, TOLUENE, ORTHO AND PARAXYLENES by contacting C ₃ - C ₄ alkanes at elevated temperature with a highly siliceous zinc or gallium-containing zeolite catalyst of the ZSM-5 type in a reactor block consisting of a cascade of reactors connected in series with the subsequent reactions to the recycle fraction of the starting alkanes, benzene, toluene, xylene and the fraction of C ₉ + aromatics, including recycling the fraction of aromatic hydrocarbon to the contacting stage, characterized in that, with the aim of to increase the yield of ortho- and paraxylene, the xylene fraction is subjected to separation and the methaxyl fraction isolated in this case is recycled as an aromatic hydrocarbon fraction to the last reactor, the process in this reactor being carried out at a contact time of 0.3-1.8 s. 2. The method according to claim 1, characterized in that the contacting process is carried out at a temperature of 400-600 ^o C.

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