RU2449978C1 - Method of aromatising non-aromatic hydrocarbons - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to a method of aromatising non-aromatic hydrocarbons contained in a hydrogenated fraction of a C₆-C₈ pyrolysis condensate. The method involves reaction of starting material with a metal-containing zeolite aromatisation catalyst at high temperature, and is characterised by that the starting material is a hydrogenated fraction of a C₆-C₈ pyrolysis condensate containing not less than 70 wt % aromatic hydrocarbons and 8-30 wt % non-aromatic hydrocarbons. The aromatisation catalyst used is a zeolite having entrance window diameter 5.1-7.3Ǻ, having molar ratio of silicon to aluminium equal to 25-140, modified with metals selected from: zinc, gallium, silver, rhodium, platinum, rare-earth elements, as well as combinations thereof.

EFFECT: invention increases output of the end product - benzene and reduces output of light hydrocarbon fractions when processing pyrolysis condensate.

7 cl, 42 ex, 4 tbl

Description

The invention relates to the field of organic chemistry and can be used to process pyrolysis condensate (pyrocondensate), a by-product of ethylene production, with the aim of converting paraffins and naphthenes contained in pyrocondensate into aromatic hydrocarbons.

(As used herein, the “term” pyrocondensate refers to by-products of ethylene production). Used in the present invention, the term "pyrolysis condensate" is a fraction of the liquid pyrolysis products with a boiling point less than 200 ° C. One of the sources of pyrocondensate are industrial ethylene furnaces. Depending on the type of feedstock, the amount of pyrocondensate is from 2 to 20% of the feed supplied to the pyrolysis. In the process of condensate processing, a C ₆ -C ₈ fraction is usually isolated having a boiling point of 70-150 ° C. The mentioned fraction is 65-75% of the total mass of pyrocondensate and is characterized by the fact that it contains mainly aromatic hydrocarbons: benzene, toluene, xylenes (BTK), as well as olefins, dienes, naphthenes.

In world practice, the C ₆ -C ₈ pyrocondensate fraction is usually hydrotreated, on which the olefins and dienes are hydrogenated and desulfurized. After hydrotreating, it is possible to carry out extraction-distillation separation of the fraction into commercial products, or hydrodealkylation can be carried out, in which alkyl aromatic hydrocarbons are converted to the target product - benzene, and non-aromatic hydrocarbons are cracked to produce light hydrocarbons.

A known method of producing benzene from benzene-containing hydrocarbon mixtures of various origins, which combines rectification with two-stage catalytic hydrogenation to produce a C ₆ -C ₈ hydrocarbon fraction and hydrodealkylation of the obtained fraction. At the same time, part of the C ₆ -C ₈ hydrocarbon fraction after further hydrogenation is subjected to additional rectification with selection from the top of the column of a product containing 30 to 95 wt.% Benzene from its content in the initial C ₆ -C ₈ hydrocarbon fraction and the bottom residue containing the rest the amount of benzene and aromatic and non-aromatic hydrocarbons C ₇ -C ₈ , which is directed to hydrodealkylation. A product containing from 30 to 95 wt.% Benzene from its content in the C ₆ -C ₈ hydrocarbon fraction is subjected to extractive distillation with a selective solvent (RU 2291892, 01.20.2007).

A known method of producing benzene from mixtures containing benzene and / or alkylbenzenes with a high content of sulfur-containing substances. The method consists in hydrodealkylation of these compounds with a partial return of the undealkylated component to the hydrodealkylation stage as a recycle, and feeding into the indicated recycle highly aromatic fraction with a high content of sulfur-containing substances, mainly not more than 1.5 wt.% Sulfur, and with the content of aromatic compounds C _{6 -15} not less than 60%. According to this method, the technological scheme for processing into benzene aromatic fractions of liquid pyrolysis and / or coking coal products with boiling points from 60 to 340 ° C provides for their two-stage hydrogenation on palladium-sulfide and alumina-cobaltomolybdenum catalysts followed by hydrocracking of paraffin compounds and thermal hydrodealkylation of aromatic compounds (toluene , o-, m-, p-xylenes, ethylbenzene) to benzene. Then the product is sequentially fed into a stabilization column, a preliminary rectification column, a catalytic purification reactor and a benzene column (RU 2193548, 11.27.2002).

A known method for producing benzene, according to which alkylaromatic compounds (BTX fraction of pyrocondensate, or aromatic concentrate of the process of aromatization of liquefied gases, or pure toluene), hydrogen, phenolic fraction (or other oxygen-containing aromatic fraction) and recycling of unreacted compounds is heated to the temperature of the beginning of the hydrodealkylation process (580 -620 ° C) and sent to reactors, where the temperature is 620-740 ° C. The effluent from the reactor is separated, separating the hydrogen-containing gas from liquid hydrocarbons and water. Liquid hydrocarbons are fed for distillation. Resin compounds are removed from the bottom of the column, and the distillate is fed to a post-treatment reactor. The purified stream is fed to a commercial benzene recovery column. Benzene is removed from one of the upper plates of the column, and the upper and still flows are recycled to the process (RU 2290393, 12/27/2006).

The methods described above are quite complex. In addition, in the above-described methods for producing benzene, the paraffins and naphthenes contained in the hydrogenated pyrocondensate fraction are cracked to form light hydrocarbons during hydrodealkylation, which leads to the loss of valuable hydrocarbon feedstocks.

A known method of producing aromatic hydrocarbons and lower olefins, in which the catalytic dehydrocyclization of hydrocarbons (C ₂ -C ₆ paraffins) in the presence of a zinc-containing zeolite catalyst is carried out, the products of dehydrocyclization are separated by gas-liquid separation into product A — C ₆₊ aromatic hydrocarbons, and product B - a mixture of non-aromatic hydrocarbons C ₁ -C ₆ with hydrogen, hydrodealkylation of product A is carried out to obtain commercial benzene and pyrolysis of product B to produce lower olefins. Commodity benzene, methane and ethane fractions are isolated from hydrodealkylation products. Commodity ethylene and propylene are isolated from gaseous pyrolysis products, liquid pyrolysis products - pyrolysis condensate containing aromatic hydrocarbons are subjected to hydrogenation and hydrodesulfurization and subsequent hydrodealkylation to produce commercial benzene, methane and ethane fractions, the latter is recycled to pyrolysis (RU 2370482, 10.20.2009).

Light hydrocarbons obtained in the described and similar methods are used as fuel gas, while the yield of valuable aromatic hydrocarbons (benzene) by this technology is not high enough.

Thus, it seems appropriate to increase the yield of aromatic hydrocarbons from secondary raw materials by aromatizing them.

Many aromatization catalysts are known, among which metal zeolites should be distinguished, described, for example, in SU 1608920, 10.20.1995, RU 2098455, 10.12.1997, RU 2092240, 10.10.1997, RU 2367643, 10.04.2008.

The closest in technical essence and the achieved result is a method of aromatization of non-aromatic hydrocarbons, according to which the hydrocarbon stream containing a hydrogenated fraction of C ₆ -C ₈ pyrocondensate is fed to a metal-containing zeolite aromatization catalyst, which is a preliminary dealuminated zeolite ZSM-5 with a molar ratio silicon to aluminum 2-200, modified with metals selected from the series: nickel, palladium, molybdenum, gallium, platinum, while the feedstock e contains about 30% paraffins, about 8% naphthenes, about 23% olefins and 32-33% aromatic compounds (benzene, toluene, xylenes). The interaction is carried out at 450-650 ° C, with a molar ratio of hydrogen to hydrocarbons of raw materials equal to 2: 1 (US 6593503, July 15, 2003, example 4 of table 4).

The disadvantage of this method is that it is not effective in aromatizing a raw material that contains a significant amount of aromatic compounds, including when a hydrogenated C ₆ -C ₈ pyrocondensate fraction containing about 80 wt.% Aromatic hydrocarbons is used as a raw material. The processing of just such a fraction of pyrocondensate is required at Russian plants.

The objective of the present invention is to increase the growth of aromatic compounds in catalysis during the processing of pyrocondensate, the composition of which is characterized by a high content of aromatic compounds and a low content of paraffins and naphthenes.

The problem is solved by the described method of aromatization of non-aromatic hydrocarbons contained in a hydrogenated fraction of C ₆ -C ₈ pyrocondensate, which includes the interaction at elevated temperature of the feedstock - a hydrogenated fraction of C ₆ -C ₈ pyrocondensate containing at least 70 wt.% Aromatic hydrocarbons and 8- 30 wt.% Non-aromatic hydrocarbons, with an aromatization catalyst — zeolite with an inlet diameter of 5.1-7.3 Å, having a molar ratio of silicon to aluminum equal to 25-140, modified metals, selected bubbled from the group of zinc, gallium, copper, silver, rhodium, platinum, rare earths, and combinations thereof.

Preferably, a zeolite selected from MFI, BEA, MWW, FAU, MOR types is used, and more preferably an MFI zeolite with a molar ratio of silicon to aluminum of 25-40.

The zeolite used mainly has the following metal contents: zinc and / or gallium 0.5-6 wt.%, Silver 0.5-3 wt.%, Copper and / or rhodium and / or rare earth element 0.5-1 wt.% , platinum 0.3-1 wt.%.

The interaction is usually carried out in a flow reactor with a fixed catalyst bed at 360-520 ° C, a pressure of 1-50 atm, a feed rate of 0.3-12 h ^-1 and with a molar ratio of hydrogen to hydrocarbon feedstock equal to (0.3-12 ):one.

We found that not every zeolite aromatization catalyst is suitable for increasing the degree of aromatization of raw materials having an increased (more than 70%) content of aromatic compounds in the composition and reduced (less than 30%) content of paraffins and naphthenes. The catalyst we selected with the characteristics indicated in the formula has acid sites with an activation energy of 115–180 kJ / mol. The claimed technical result is achieved in the amount of the set of features set forth in claim 1 of the formula, and is not achieved outside of it. The method of aromatization of hydrocarbons of the claimed composition that we developed allows us to introduce this process into the general technological scheme for the processing of pyrocondensate after the hydrotreatment stage, while paraffins and naphthenes will be directly converted to aromatic hydrocarbons without additional steps, which will lead to an overall increase in benzene yield and a decrease in the formation of fuel gases.

The following are specific examples of the invention, while the results of the invention are summarized in table 4.

Example 1

To prepare the Zn (3) MFI (40) catalyst, we took the ammonium form of the zeolite of the MFI structure with a molar ratio of silicon to aluminum 40, which was then impregnated with an aqueous solution of Zn (NO ₃ ) ₂ * 6H ₂ O salt at the rate of 3 weight percent zinc in the catalyst and calcined at 500 ° C.

In the designations of the samples in table 4, after the metal, its mass content is indicated in parentheses; after the structural type of zeolite, the molar ratio of silicon to aluminum in it is indicated in parentheses.

Example 2

Catalytic tests were carried out in a flowing steel reactor with a fixed catalyst bed, the reaction products were separated and analyzed by gas chromatography. The catalyst described in example 1 was pre-treated in a stream of hydrogen at a temperature of 400 ° C, then the temperature was increased to 500 ° C and at a pressure of 0.1 MPa with a ratio of hydrogen to feed 1.5: 1 feed was supplied with a mass speed of 3 g / g * h A model mixture with a composition (table 1) close in distribution of hydrocarbons to the hydrogenated pyrocondensate fraction was used as raw material.

Table 1 The composition of the model mixture Hydrocarbons wt.% Hexane 3.4 Cyclohexane 4.2 Heptane 3.3 Octane 4.2 Benzene 34.1 Toluene 50.7

The model mixture contained both aromatic hydrocarbons in an amount of 85 wt.%, And paraffins and naphthenes in an amount of 15 wt.%.

The experimental results are presented in table 4, the following calculated values are presented as reaction indicators:

The conversion of paraffins and naphthenes:

where m _{alk. initial} - the mass of paraffins and naphthenes supplied with the initial mixture to the reactor in units time, m _{alk. products} - the mass of paraffins and naphthenes of the C6-C8 interval in the reaction products obtained in units time.

The increase in aromatic hydrocarbons:

,

,

where m _{arom. ref.} - the mass of aromatic substances in the initial mixture supplied to units time, m _input is the total mass of hydrocarbons at the inlet to the reactor in units time. The increase in benzene rings:

where m _{i-aroma product} is the mass i of aromatic substance from the series benzene, toluene, xylene, ethylbenzene, as well as C ₉ and C ₁₀₊ formed in units time; M _i is the molecular weight i of the aromatic substance.

,

,

where the _initial benzene rings are the number of benzene rings in the feed.

Examples 3-10.

Similar to example 2, the difference is that the reaction conditions change:

feed rate, molar ratio of hydrogen to feed, temperature and pressure.

Example 11

The catalyst was obtained analogously to example 1, the difference is that the starting zeolite is the ammonium form of the BEA zeolite with a silicon to aluminum ratio of 33, which was then impregnated with an aqueous solution of the Ga (NO ₃ ) ₂ * 8H ₂ O salt at the rate of 3 wt. % gallium per weight of calcined catalyst.

Example 12

Similar to example 2, the difference is that they used the catalyst described in example 11. The result of the catalytic experiment is presented in table 4.

Example 13

The catalyst was obtained analogously to example 1, the difference is that the initial zeolite is the hydrogen form of zeolite MWW, with a silicon to aluminum ratio of 30, which was then impregnated with an aqueous solution of the salt ((NH ₃ ) ₄ Pt) Cl ₂ * 4H ₂ O based on 1 wt.% platinum per mass of calcined catalyst.

Example 14

Similar to example 2, the difference is that they used the catalyst described in example 13. The result of the catalytic experiment is presented in table 4.

Example 15

The catalyst was obtained analogously to example 13, the difference is that the amount of salt ((NH ₃ ) ₄ Pt) Cl ₂ * 4H ₂ O was taken from the calculation of 0.3 wt.% Platinum per weight of calcined catalyst.

Example 16

Similar to example 2, the difference is that they used the catalyst described in example 15. The result is presented in table 4.

Example 17

The catalyst was obtained analogously to example 1, the difference is that the ammonium form of the MFI zeolite with a silicon to aluminum ratio of 25 was taken as the initial zeolite, which was then impregnated with an aqueous solution of the Ga (NO ₃ ) ₂ * 8Н ₂ O salt at the rate of 1.5 wt.% gallium per mass of calcined catalyst.

Example 18

Similar to example 2, the difference is that they used the catalyst described in example 17. The result of the catalytic experiment is presented in table 4.

Example 19

Similar to example 17, the difference is that the amount of Ga (NO ₃ ) ₂ * 8H ₂ O salt was taken from the calculation of 6 wt.% Gallium per weight of calcined catalyst.

Example 20

Similar to example 2, the difference is that they used the catalyst described in example 19. The result of the catalytic experiment is presented in table 4.

Example 21

Similar to example 1, the difference is that the molar ratio of silicon to aluminum in the initial zeolite is 140.

Example 22

Similar to example 2, the difference is that they used the catalyst described in example 21. The result of the catalytic experiment is presented in table 4.

Example 23

Similar to example 1, the difference is that the molar ratio of silicon to aluminum in the initial zeolite is 25, and the amount of Zn (NO ₃ ) ₂ * 6H ₂ O salt was taken from the calculation of 0.5 wt.% Per weight of calcined catalyst.

Example 24

Similar to example 2, the difference is that they used the catalyst described in example 23. The result of the catalytic experiment is presented in table 4.

Example 25

Similar to example 23, the difference is that the amount of Zn (NO ₃ ) ₂ * 6H ₂ O salt was taken from the calculation of 6 wt.% Per weight of calcined catalyst.

Example 26

Similar to example 2, the difference is that they used the catalyst described in example 25. The result of the catalytic experiment is presented in table 4.

Example 27

To prepare the bimetallic catalyst Zn (2) Ga (3) MFI (40), we took the ammonium form of the zeolite MFI with a ratio of silicon to aluminum 40, which was then impregnated with an aqueous solution of the salt Ga (NO ₃ ) ₂ * 8Н ₂ О at the rate of 3 weight percent Gaul. The impregnated zeolite was subsequently calcined in a stream of air at 500 ° C and in a stream of hydrogen at 400 ° C. The catalyst thus obtained was then modified with a second metal zinc by impregnating the catalyst with a solution of Zn (NO ₃ ) ₂ * 6H ₂ O salt at the rate of 2 wt.% Zinc, followed by calcination in an air stream at 500 ° C.

Example 28

Similar to example 2, the difference is that they used the catalyst described in example 27. The result of the catalytic experiment is presented in table 4.

Example 29

Similar to example 27, the difference is that silver was used as the second metal of the modifier. The amount of AgNO ₃ salt was taken from the calculation of 0.5 wt.% Silver per weight of calcined catalyst.

Example 30

Similar to example 2, the difference is that they used the catalyst described in example 29. The result of the catalytic experiment is presented in table 4.

Example 31

Similar to example 29, the difference is that the amount of salt of AgNO ₃ for modification was taken at the rate of 3 wt.% Silver per weight of calcined catalyst.

Example 32

Similar to example 2, the difference is that they used the catalyst described in example 31. The result of the catalytic experiment is presented in table 4.

Example 33

Similar to example 27, the difference is that copper was used as the second metal of the modifier. The amount of Cu (NO ₃ ) ₂ * 3H ₂ O salt was taken from the calculation of 0.5 wt.% Copper per mass of calcined catalyst.

Example 34

Similar to example 2, the difference is that they used the catalyst described in example 33. The result of the catalytic experiment is presented in table 4.

Example 35

Similar to example 33, the difference is that the amount of salt Cu (NO ₃ ) ₂ * 3H ₂ O for promotion was taken at the rate of 1 wt.% Copper per mass of calcined catalyst.

Example 36

Similar to example 2, the difference is that they used the catalyst described in example 35. The result of the catalytic experiment is presented in table 4.

Example 37

Similar to example 27, the difference is that rhodium was used as the second metal of the modifier. The amount of salt RhCl ₃ * 4H ₂ O was taken from the calculation of 1 wt.% Rhodium per weight of calcined catalyst.

Example 38

Similar to example 2, the difference is that they used the catalyst described in example 37. The result of the catalytic experiment is presented in table 4.

Example 39

Similar to example 27, the difference is that cerium was used as the second metal of the modifier. The amount of salt Ce (NO ₃ ) ₂ * 6H ₂ O was taken from the calculation of 1 wt.% Cerium per weight of calcined catalyst.

Example 40

Similar to example 2, the difference is that they used the catalyst described in example 39. The result of the catalytic experiment is presented in table 4.

Example 41

Similar to example 2, the difference is that the hydrogenated fraction of C ₆ -C ₈ pyrocondensate, the composition of which is shown in table 2, was used as raw material.

table 2 The composition of the hydrogenated fraction of C ₆ -C ₈ pyrocondensate Hydrocarbons wt.% C ₅ 0.2 C ₆ 6.9 Cyclohexane 0.8 C ₇ 1,0 C ₈ 1,5 From ₉ 0.5 paraffins C ₁₀₊ 0.6 Benzene 53.6 Toluene 20,2 Xylenes 13.0 Aromatic C ₉ 1.3 aromatic C ₁₀₊ 0.5

The result of the catalytic experiment is presented in table 4.

Example 42

Similar to example 2, the difference is that the raw material used was a model mixture with an aromatic hydrocarbon content of 70 mass percent, the composition of which is shown in table 3.

Table 3 The composition of the model mixture Hydrocarbons wt.% Hexane 6.0 Cyclohexane 8.0 Heptane 7.0 Octane 9.0 Benzene 27.5 Toluene 42.1

The result of the catalytic experiment is presented in table 4.

Thus, from table 4 it is seen that the claimed technical result is obtained in the amount of the claimed combination of features. We have for the first time developed a method for aromatizing the C ₆ -C ₈ pyro-condensate fraction, which is characterized by a high content of aromatic compounds, without carrying out additional steps and introducing additional compounds.

Claims (7)

1. A method of aromatizing non-aromatic hydrocarbons contained in a hydrogenated C ₆ -C ₈ pyrocondensate fraction, comprising reacting the feed with a metal-containing zeolite aromatization catalyst at elevated temperature, characterized in that the hydrogenated C ₆ -C ₈ pyrocondensate fraction containing not less than 70 wt.% aromatic hydrocarbons and 8-30 wt.% non-aromatic hydrocarbons, and a zeolite with an inlet diameter of 5.1-7.3 Å having the molar ratio of silicon to aluminum, equal to 25-140, modified by metals selected from the series: zinc, gallium, copper, silver, rhodium, platinum, rare earth elements, as well as their combination. 2. The method according to claim 1, characterized in that they use a zeolite selected from MFI, BEA, MWW, FAU, MOR types, more preferably an MFI zeolite with a molar ratio of silicon to aluminum of 25-40. 3. The method according to claim 1, characterized in that the content of zinc and / or gallium in the zeolite is 0.5-6 wt.%. 4. The method according to claim 3, characterized in that the silver content in the zeolite is 0.5-3 wt.%. 5. The method according to claim 3, characterized in that the content of copper and / or rhodium and / or rare earth element in the zeolite is 0.5-1 wt.%. 6. The method according to claim 1, characterized in that the platinum content in the zeolite is 0.3-1 wt.%. 7. The method according to claim 1, characterized in that the interaction is carried out in a flow reactor with a fixed catalyst bed at 360-520 ° C, a pressure of 1-50 atm, a mass feed rate of 0.3-12 h ^-1 and with a molar ratio hydrogen to hydrocarbons, equal (0.3-12): 1.