System and method for increasing yield of p-xylene through combination of toluene methylation and heavy aromatic hydrocarbon lightening
阅读说明：本技术 一种甲苯甲基化联合重芳烃轻质化增产对二甲苯的系统及方法 (System and method for increasing yield of p-xylene through combination of toluene methylation and heavy aromatic hydrocarbon lightening ) 是由 王江涛 曲顺利 鹿晓斌 贺同强 郭雷 徐国峰 王芳 吴桐 李飞飞 于 2020-05-29 设计创作，主要内容包括：本发明提供一种甲苯甲基化联合重芳烃轻质化增产对二甲苯的系统及方法,所述系统及方法通过甲苯的择形烷基化技术以及C10+重芳烃轻质化技术实现增产对二甲苯,解决了现有芳烃技术中对二甲苯选择性低、芳烃原料苯环利用率低、C10+重芳烃低成本利用等问题。(The invention provides a system and a method for increasing yield of p-xylene by combining toluene methylation with heavy aromatics in a light state, wherein the system and the method realize the yield increase of p-xylene by using a shape-selective alkylation technology of toluene and a C10+ heavy aromatics light state technology, and solve the problems of low p-xylene selectivity, low utilization rate of aromatic raw material benzene rings, low cost utilization of C10+ heavy aromatics and the like in the prior aromatic technology.)
1. The system is characterized by comprising a toluene methanol alkylation system and a heavy aromatic light conversion system which are connected, wherein the toluene methanol alkylation system comprises an aromatic extraction unit, a benzene tower unit, a toluene methanol alkylation reaction unit, a toluene circulating tower unit, a xylene tower unit and a crystallization separation unit which are sequentially connected;
the xylene tower unit is provided with a C8+ A mixed aromatic hydrocarbon outlet and a mixed xylene outlet, the mixed xylene outlet is connected with the crystallization separation unit, and the C8+ A mixed aromatic hydrocarbon outlet is connected with the heavy aromatic hydrocarbon conversion system;
the heavy aromatic hydrocarbon conversion system comprises a heavy aromatic hydrocarbon conversion unit, a low-carbon aromatic hydrocarbon tower unit, a carbon nonaromatic hydrocarbon tower unit and a benzene and carbon nonaromatic hydrocarbon alkylation transfer unit which are sequentially connected, wherein a product outlet of the carbon nonaromatic hydrocarbon alkylation transfer unit is connected with the benzene tower unit, the benzene tower unit is provided with a benzene outlet and a C7+ A mixed aromatic hydrocarbon outlet, the benzene outlet is connected with the benzene and carbon nonaromatic hydrocarbon alkylation transfer unit, and the C7+ A mixed aromatic hydrocarbon outlet is connected with an outlet of the toluene tower unit.
2. The system of claim 1, wherein the aromatic extraction unit is provided with a raw material inlet, a mixed aromatic outlet and a non-aromatic outlet, the raw material inlet is connected with a feed pipeline, and the mixed aromatic outlet is connected with the benzene tower unit;
preferably, the toluene tower unit is provided with a toluene outlet and a C8+ a mixed aromatic hydrocarbon outlet, the toluene outlet is connected with the toluene methanol alkylation reaction unit, and the C8+ a mixed aromatic hydrocarbon outlet is connected with the xylene tower unit.
3. The system of claim 1 or 2, wherein the toluene methanol alkylation reaction unit is provided with a mixed aromatic hydrocarbon product outlet and a non-aromatic hydrocarbon product outlet, and the mixed aromatic hydrocarbon product outlet is connected with the toluene circulating tower unit;
preferably, toluene circulating tower unit is provided with toluene outlet, benzene export, mixed xylene export and the mixed aromatics export of C9+ A, the toluene export with toluene methanol alkylation reaction unit links to each other, the benzene export with feed line links to each other, mixed xylene export with crystallization separation unit links to each other, the mixed aromatics export of C9+ A with xylene tower unit links to each other.
4. The system of any one of claims 1-3, wherein the crystallization separation unit is provided with a para-xylene outlet and a mixed carbon and eight aromatic hydrocarbon outlet, the mixed carbon and eight aromatic hydrocarbon outlet is connected with a mixed xylene isomerization unit, and the mixed xylene isomerization unit is connected with the xylene tower unit.
5. The system of any one of claims 1 to 4, wherein the low carbon aromatic hydrocarbon tower unit is provided with a C9+ A mixed aromatic hydrocarbon outlet and a low carbon aromatic hydrocarbon outlet, the C9+ A mixed aromatic hydrocarbon outlet is connected with the carbon nonaromatic hydrocarbon tower unit, and the low carbon aromatic hydrocarbon outlet is connected with the feed pipeline;
preferably, the carbon nonaromatic hydrocarbon tower unit is provided with a heavy aromatic hydrocarbon outlet and a carbon nonaromatic hydrocarbon outlet, the heavy aromatic hydrocarbon outlet is connected with the heavy aromatic hydrocarbon removing tower unit, and the carbon nonaromatic hydrocarbon outlet is connected with the benzene and carbon nonaromatic hydrocarbon alkylation transfer unit;
preferably, the heavy aromatic hydrocarbon removing tower unit is provided with a carbon decaaromatic hydrocarbon outlet and a heavy oil outlet, and the carbon decaaromatic hydrocarbon outlet is connected with the heavy aromatic hydrocarbon lightening unit.
6. A method for increasing yield of p-xylene by toluene methylation in combination with heavy aromatics upgrading, the method being performed in the system of any one of claims 1-5, the method comprising the steps of:
(1) the raw materials enter the toluene methanol alkylation system, the raw materials sequentially pass through an aromatic hydrocarbon extraction unit, a benzene tower unit, a toluene methanol alkylation reaction unit, a toluene circulating tower unit, a xylene tower unit and a crystallization separation unit to obtain pure p-xylene products, and C8+ A mixed aromatic hydrocarbon obtained by the separation of the xylene unit enters the heavy aromatic hydrocarbon conversion system;
(2) the C8+ A mixed aromatic hydrocarbon enters the heavy aromatic hydrocarbon conversion system and then sequentially enters a heavy aromatic hydrocarbon conversion unit, a low-carbon aromatic hydrocarbon tower unit, a carbon nonaromatic hydrocarbon tower unit and a benzene and carbon nonaaromatic hydrocarbon alkylation transfer unit, benzene in the benzene and carbon nonaaromatic hydrocarbon alkylation transfer unit comes from the benzene tower unit, and a product of the carbon nonaaromatic hydrocarbon alkylation transfer unit returns to the benzene tower unit.
7. The method of claim 6, wherein the feedstock of step (1) comprises non-aromatics, benzene, toluene C-eight aromatics, and C-nine and above aromatics;
preferably, the raw material in the step (1) is a mixed pentane-removed aromatic hydrocarbon of a reforming device;
preferably, the raw material in the step (1) is subjected to non-aromatic hydrocarbon separation by the aromatic hydrocarbon extraction unit to obtain mixed aromatic hydrocarbon, and the mixed aromatic hydrocarbon enters the benzene tower unit;
preferably, the mixed aromatic hydrocarbon is separated by the benzene tower unit in the step (1) to obtain benzene and a C7+ A mixed aromatic hydrocarbon, and the C7+ A mixed aromatic hydrocarbon enters the toluene tower unit;
preferably, the C7+ a mixed aromatic hydrocarbon is separated by the toluene tower unit in step (1) to obtain toluene and C8+ a mixed aromatic hydrocarbon, the toluene enters the toluene methanol alkylation reaction unit, and the C8+ a mixed aromatic hydrocarbon enters the xylene tower unit;
preferably, the toluene methanol alkylation reaction unit in the step (1) reacts to obtain a mixed aromatic hydrocarbon product and a non-aromatic hydrocarbon product, and the mixed aromatic hydrocarbon product enters a basic circulation tower unit;
preferably, the toluene methanol alkylation reaction unit adopts a multi-section methanol solution liquid-phase feeding fixed bed reactor;
preferably, the toluene methanol alkylation reactionThe pressure of the reaction is 0.2-0.4 Mpag, the reaction temperature is 350-500 ℃, the hydrogen partial pressure is more than 0.07-0.30 Mpag, and the mass space velocity of the toluene is 1.0-2.0 h-1The hydrogen-hydrocarbon molar ratio is 1.5-4, the total molar ratio of the alcohol to the benzene is 0.65-0.96, and the volume concentration of the methanol solution fed into the side line is 80-100%;
preferably, the toluene methanol alkylation reaction is carried out under catalytic conditions of a catalyst comprising platinum and/or an oxide of platinum;
preferably, the selectivity of mixed xylene in the product of the toluene methanol alkylation reaction is more than 95 percent, the selectivity of p-xylene in the mixed xylene is more than 92 percent, the methanol conversion rate is more than 99.5 percent, and the selectivity of product benzene is less than 1.5 percent;
preferably, in the step (1), the toluene circulation tower unit separates to obtain toluene, benzene, mixed xylene and C9+ a mixed aromatic hydrocarbon, the toluene returns to the toluene methanol alkylation reaction unit, the benzene returns to the aromatic hydrocarbon extraction unit, the mixed xylene enters the crystallization separation unit, and the C9+ a mixed aromatic hydrocarbon enters the xylene unit.
8. The method of claim 7, wherein the crystallization separation unit of step (1) separates a pure xylene product and mixed carbon and eight aromatic hydrocarbons, and the mixed carbon and eight aromatic hydrocarbons enter the mixed xylene isomerization unit;
preferably, the product of the mixed xylene isomerization unit enters the xylene column unit;
preferably, the xylene unit in the step (1) separates mixed xylene and C8+ A mixed aromatic hydrocarbon, and the mixed xylene enters the crystallization separation unit.
9. The method of claim 6, wherein the products of the heavy aromatics conversion unit of step (2) enter a low carbon aromatics column unit;
preferably, the heavy aromatics light ends unit comprises a pre-hydrogenation section and a light ends reforming section;
preferably, the reaction temperature of the pre-hydrogenation section is 160-200 ℃ and 200-250 ℃, and the reaction pressure is 2.0-5.5 Mpag;
preferably, the reaction temperature of the light reforming process is 280-300 ℃, 300-340 ℃ and 340-360 ℃, and the reaction pressure is 2.0-5.5 Mpag;
preferably, the low-carbon aromatic hydrocarbon tower unit in the step (2) separates to obtain C9+ a mixed aromatic hydrocarbon and low-carbon aromatic hydrocarbon, the low-carbon aromatic hydrocarbon includes benzene, toluene and carbon octa-aromatic hydrocarbon, the C9+ a mixed aromatic hydrocarbon enters a carbon nonaromatic hydrocarbon tower unit, and the low-carbon aromatic hydrocarbon returns to the aromatic hydrocarbon extraction unit;
preferably, the carbon nonaromatic hydrocarbon tower unit separates to obtain heavy aromatic hydrocarbon and carbon nonaromatic hydrocarbon, the carbon nonaromatic hydrocarbon enters the benzene and carbon nonaromatic hydrocarbon alkylation transfer unit, and the heavy aromatic hydrocarbon enters the heavy aromatic hydrocarbon removal tower unit.
10. The method of claim 9, wherein the heavy aromatics removal unit separates heavy oil and carbon deca-aromatics, the carbon deca-aromatics return to the heavy aromatics conversion unit, and the heavy oil is recovered as a product.
Technical Field
The invention belongs to the field of petrochemical industry. Relates to equipment and a method for producing paraxylene, in particular to a system and a method for increasing the yield of paraxylene by combining toluene methylation with heavy aromatics light conversion.
Background
Aromatic hydrocarbon is an important raw material for producing synthetic fibers, the core of an industrial chain of the aromatic hydrocarbon is mainly Paraxylene (PX), typical PX at present mainly comes from naphtha which is an intermediate product in a petroleum refining process, reformed gasoline and pyrolysis gasoline are obtained after catalytic reforming or ethylene pyrolysis, mixed xylene is obtained after an aromatic hydrocarbon extraction process, a disproportionation reaction, an alkylation transfer reaction and the like, and then the mixed xylene is obtained through adsorption separation or crystallization separation. At present, international PX production processes mainly comprise production processes developed by American UOP company and French IFP company, and domestic Chinese petrifaction overcomes the difficulty of the whole-process of PX in 2011, so that the international PX production process becomes one of main PX technical patent merchants.
At present, the traditional process of a refinery mainly comprises toluene disproportionation reaction and alkylation transfer to generate carbon-eight mixed aromatic hydrocarbon, so that the yield of p-xylene is increased, byproducts of benzene, carbon-nine aromatic hydrocarbon and heavy aromatic hydrocarbon with carbon ten or more are generated, carbon-nine aromatic hydrocarbon (a small amount of carbon-ten aromatic hydrocarbon) can be used for alkylation transfer reaction to prepare mixed xylene, most of the carbon-ten or more heavy aromatic hydrocarbon is used as fuel to be wasted, and the value utilization rate is only about 8%. The main mode is that products such as durene, naphthalene and the like with higher separation bid value are separated by a rectifying device, or a small part of the products is used for producing solvent naphtha or gasoline blending, and most of the products are treated by the lowest price fuel oil and are converted into oil residue. According to the prior production process, the utilization rate of benzene rings in mixed aromatic hydrocarbon is low, one part of the benzene rings is removed to a target product xylene, the other part of the benzene rings is removed to a benzene product and heavy aromatic hydrocarbon, and the selectivity of the p-xylene is low; in addition, the utilization rate of the existing heavy aromatics with carbon ten or more is low, which wastes resources and seriously pollutes the environment, and the economic effect of the heavy aromatics is difficult to be exerted.
Disclosure of Invention
Aiming at the technical problems in the prior art, the invention provides a system and a method for increasing the yield of p-xylene by combining toluene methylation with heavy aromatics in a light conversion mode.
In order to achieve the purpose, the invention adopts the following technical scheme:
one of the purposes of the invention is to provide a system for increasing the yield of p-xylene by combining toluene methylation with heavy aromatics in light conversion, which is characterized by comprising a toluene methanol alkylation system and a heavy aromatics light conversion system which are connected with each other, wherein the toluene methanol alkylation system comprises an aromatic hydrocarbon extraction unit, a benzene tower unit, a toluene methanol alkylation reaction unit, a toluene circulating tower unit, a xylene tower unit and a crystallization separation unit which are sequentially connected with each other;
the xylene tower unit is provided with a C8+ A mixed aromatic hydrocarbon outlet and a mixed xylene outlet, the mixed xylene outlet is connected with the crystallization separation unit, and the C8+ A mixed aromatic hydrocarbon outlet is connected with the heavy aromatic hydrocarbon conversion system;
the heavy aromatic hydrocarbon conversion system comprises a heavy aromatic hydrocarbon conversion unit, a low-carbon aromatic hydrocarbon tower unit, a carbon nonaromatic hydrocarbon tower unit and a benzene and carbon nonaromatic hydrocarbon alkylation transfer unit which are sequentially connected, wherein a product outlet of the carbon nonaromatic hydrocarbon alkylation transfer unit is connected with the benzene tower unit, the benzene tower unit is provided with a benzene outlet and a C7+ A mixed aromatic hydrocarbon outlet, the benzene outlet is connected with the benzene and carbon nonaromatic hydrocarbon alkylation transfer unit, and the C7+ A mixed aromatic hydrocarbon outlet is connected with an outlet of the toluene tower unit.
As a preferred technical scheme of the invention, the aromatic hydrocarbon extraction unit is provided with a raw material inlet, a mixed aromatic hydrocarbon outlet and a non-aromatic hydrocarbon outlet, wherein the raw material inlet is connected with a feeding pipeline, and the mixed aromatic hydrocarbon outlet is connected with the benzene tower unit.
Preferably, the toluene tower unit is provided with a toluene outlet and a C8+ a mixed aromatic hydrocarbon outlet, the toluene outlet is connected with the toluene methanol alkylation reaction unit, and the C8+ a mixed aromatic hydrocarbon outlet is connected with the xylene tower unit.
As a preferred technical scheme of the invention, the toluene methanol alkylation reaction unit is provided with a mixed aromatic hydrocarbon product outlet and a non-aromatic hydrocarbon product outlet, and the mixed aromatic hydrocarbon product outlet is connected with the toluene circulating tower unit.
Preferably, toluene circulating tower unit is provided with toluene outlet, benzene export, mixed xylene export and the mixed aromatics export of C9+ A, the toluene export with toluene methanol alkylation reaction unit links to each other, the benzene export with feed line links to each other, mixed xylene export with crystallization separation unit links to each other, the mixed aromatics export of C9+ A with xylene tower unit links to each other.
As a preferable technical scheme of the invention, the crystallization separation unit is provided with a paraxylene outlet and a mixed carbon and octaene outlet, the mixed carbon and octaene outlet is connected with a mixed xylene isomerization unit, and the mixed xylene isomerization unit is connected with the xylene tower unit.
As a preferable technical scheme of the invention, the low-carbon aromatic hydrocarbon tower unit is provided with a C9+ A mixed aromatic hydrocarbon outlet and a low-carbon aromatic hydrocarbon outlet, the C9+ A mixed aromatic hydrocarbon outlet is connected with the carbon nonaromatic hydrocarbon tower unit, and the low-carbon aromatic hydrocarbon outlet is connected with the feeding pipeline.
Preferably, the carbon nonaromatic hydrocarbon tower unit is provided with a heavy aromatic hydrocarbon outlet and a carbon nonaromatic hydrocarbon outlet, the heavy aromatic hydrocarbon outlet is connected with the heavy aromatic hydrocarbon removing tower unit, and the carbon nonaromatic hydrocarbon outlet is connected with the benzene and carbon nonaromatic hydrocarbon alkylation transfer unit.
Preferably, the heavy aromatic hydrocarbon removing tower unit is provided with a carbon decaaromatic hydrocarbon outlet and a heavy oil outlet, and the carbon decaaromatic hydrocarbon outlet is connected with the heavy aromatic hydrocarbon lightening unit.
In the invention, in a toluene methanol alkylation reaction unit, a ZSM molecular sieve containing platinum and other metals is used as a catalyst, and under the hydrogen environment, toluene effectively undergoes shape selective alkylation reaction by adopting a fixed bed multi-section catalyst to generate mixed xylene, so that the benzene ring of the raw material is utilized in a hundred percent; the entered methanol and toluene are subjected to shape-selective alkylation reaction, the selectivity of the generated mixed xylene is more than 94 percent, the selectivity of the p-xylene in the mixed xylene is more than 94 percent, the mixed xylene is preferentially separated by a crystallization separation process to obtain high-purity p-xylene, and the residual mixed xylene enters an isomerization unit; the heavy aromatic hydrocarbon lightening unit obtains low-carbon aromatic hydrocarbons with high added value and gasoline blending components with high octane number from cheap heavy aromatic hydrocarbons with more than ten carbon atoms under the action of catalysts such as palladium and the like, the conversion rate of the heavy aromatic hydrocarbons with more than ten carbon atoms is more than 65%, main products comprise C6-C8 low-carbon aromatic hydrocarbons and C9 heavy aromatic hydrocarbons, the C6-C8 low-carbon aromatic hydrocarbons enter the aromatic hydrocarbon separation unit, and the C9 heavy aromatic hydrocarbons enter the benzene and C9 alkylation transfer reaction unit; the benzene and C9 alkylation transfer reaction unit adopts bismuth-containing zeolite catalyst, and the alkylation transfer reaction is carried out in the presence of hydrogen, so that the benzene and C9 in the reaction system are effectively digested and converted into dimethylbenzene, the benzene ring of aromatic hydrocarbon is further utilized, and the generated methylbenzene and dimethylbenzene enter the separation unit.
In the present invention, C7+ a represents an aromatic hydrocarbon having seven or more carbon atoms, C8+ a represents an aromatic hydrocarbon having eight or more carbon atoms, and C9+ a represents an aromatic hydrocarbon having nine or more carbon atoms.
The invention also aims to provide a method for increasing yield of p-xylene by combining toluene methylation with heavy aromatics in light conversion, which uses the system for increasing yield of p-xylene by combining toluene methylation with heavy aromatics in light conversion, and comprises the following steps:
(1) the raw materials enter the toluene methanol alkylation system, the raw materials sequentially pass through an aromatic hydrocarbon extraction unit, a benzene tower unit, a toluene methanol alkylation reaction unit, a toluene circulating tower unit, a xylene tower unit and a crystallization separation unit to obtain pure p-xylene products, and C8+ A mixed aromatic hydrocarbon obtained by the separation of the xylene unit enters the heavy aromatic hydrocarbon conversion system;
(2) the C8+ A mixed aromatic hydrocarbon enters the heavy aromatic hydrocarbon conversion system and then sequentially enters a heavy aromatic hydrocarbon conversion unit, a low-carbon aromatic hydrocarbon tower unit, a carbon nonaromatic hydrocarbon tower unit and a benzene and carbon nonaaromatic hydrocarbon alkylation transfer unit, benzene in the benzene and carbon nonaaromatic hydrocarbon alkylation transfer unit comes from the benzene tower unit, and a product of the carbon nonaaromatic hydrocarbon alkylation transfer unit returns to the benzene tower unit.
As a preferable technical scheme of the invention, the raw materials in the step (1) comprise non-aromatic hydrocarbon, benzene, toluene carbon octa-aromatic hydrocarbon and carbon nine or more aromatic hydrocarbon.
Preferably, the raw material in the step (1) is depentanized mixed aromatic hydrocarbon of a reforming device.
Preferably, the raw material in the step (1) is subjected to non-aromatic hydrocarbon separation by the aromatic hydrocarbon extraction unit to obtain mixed aromatic hydrocarbon, and the mixed aromatic hydrocarbon enters the benzene tower unit.
Preferably, the mixed aromatic hydrocarbon is separated by the benzene tower unit in the step (1) to obtain benzene and a C7+ A mixed aromatic hydrocarbon, and the C7+ A mixed aromatic hydrocarbon enters the toluene tower unit.
Preferably, the C7+ a mixed aromatic hydrocarbon is separated by the toluene tower unit in step (1) to obtain toluene and C8+ a mixed aromatic hydrocarbon, the toluene enters the toluene methanol alkylation reaction unit, and the C8+ a mixed aromatic hydrocarbon enters the xylene tower unit.
Preferably, the toluene methanol alkylation reaction unit in the step (1) reacts to obtain a mixed aromatic hydrocarbon product and a non-aromatic hydrocarbon product, and the mixed aromatic hydrocarbon product enters a basic circulation tower unit.
Preferably, the toluene methanol alkylation reaction unit adopts a multi-section methanol solution liquid phase feeding fixed bed reactor.
Preferably, the pressure of the toluene methanol alkylation reaction is 0.2-0.4 Mpag, the reaction temperature is 350-500 ℃, the hydrogen partial pressure is greater than 0.07-0.30 Mpag, and the mass space velocity of toluene is 1.0-2.0 h-1The hydrogen-hydrocarbon molar ratio is 1.5-4, the total molar ratio of the alcohol to the benzene is 0.65-0.96, and the volume concentration of the methanol solution fed into the side line is 80-100%;
wherein the reaction pressure may be 0.22Mpag, 0.25Mpag, 0.28Mpag, 0.30Mpag, 0.32Mpag, 0.35Mpag, 0.38Mpag, etc., the reaction temperature may be 360 ℃, 380 ℃, 400 ℃, 420 ℃, 450 ℃, 480 ℃, etc., the hydrogen partial pressure may be 0.08Mpag, 0.10Mpag, 0.12Mpag, 0.15Mpag, 0.18Mpag, 0.20Mpag, 0.22Mpag, 0.25Mpag, 0.28Mpag, etc., and the toluene mass space velocity may be 1.1 hr-1、1.2h-1、1.3h-1、1.4h-1、1.5h-1、1.6h-1、1.7h-1、1.8h-1Or 1.9h-1For example, the hydrogen-to-hydrocarbon molar ratio may be 2.0, 2.5, 3.0, 3.5, etc., the total molar ratio of alkylbenzenes may be 0.70, 0.75, 0.80, 0.85, 0.90, 0.95, etc., and the volumetric concentration of the sidefed methanol solution may be 82%, 85%, 88%, 90%, 92%, 95%, 98%, etc., but is not limited to the recited values, and other values not recited in the above-mentioned ranges of values are also applicable.
Preferably, the toluene methanol alkylation reaction is carried out under catalytic conditions with a catalyst comprising platinum and/or an oxide of platinum.
Preferably, the selectivity of mixed xylene in the product of the toluene methanol alkylation reaction is more than 95%, the selectivity of p-xylene in the mixed xylene is more than 92%, the methanol conversion rate is more than 99.5%, and the selectivity of product benzene is less than 1.5%.
The mixed xylene selectivity in the product may be 95.5%, 96%, 96.5%, 97%, 97.5%, 98%, 98.5%, 99% or the like, the content of p-xylene in the mixed xylene may be 93%, 94%, 95%, 96%, 97%, 98%, 99% or the like, the methanol conversion rate may be 99.6%, 99.7%, 99.8%, 99.9% or the like, and the product benzene selectivity may be 1.4%, 1.3%, 1.2%, 1.1%, 1.0%, 0.8%, 0.5%, 0.2% or the like, but is not limited to the values listed, and other values not listed in the above numerical ranges are also applicable.
Preferably, in the step (1), the toluene circulation tower unit separates to obtain toluene, benzene, mixed xylene and C9+ a mixed aromatic hydrocarbon, the toluene returns to the toluene methanol alkylation reaction unit, the benzene returns to the aromatic hydrocarbon extraction unit, the mixed xylene enters the crystallization separation unit, and the C9+ a mixed aromatic hydrocarbon enters the xylene unit.
As a preferable technical scheme of the invention, the crystallization separation unit in the step (1) separates to obtain a pure xylene product and mixed carbon-eight aromatic hydrocarbons, and the mixed carbon-eight aromatic hydrocarbons enter the mixed xylene isomerization unit.
Preferably, the product of the mixed xylene isomerization unit enters the xylene column unit.
Preferably, the xylene unit in the step (1) separates mixed xylene and C8+ A mixed aromatic hydrocarbon, and the mixed xylene enters the crystallization separation unit.
In the present invention, the crystallization separation unit preferably performs a suspension melt crystallization separation at a temperature of-25 to 10 ℃, for example, -22 ℃, -20 ℃, -18 ℃, -15 ℃, -12 ℃, -10 ℃, -8 ℃, -5 ℃, -2 ℃, 1 ℃, 3 ℃, 6 ℃ or 8 ℃, but is not limited to the recited values, and other values not recited in the range of the values are also applicable.
As a preferable technical scheme of the invention, the product of the heavy aromatics conversion unit in the step (2) enters a low-carbon aromatics tower unit.
Preferably, the heavy aromatics upgrading unit comprises a pre-hydrogenation section and an upgrading reforming section.
Preferably, the reaction temperature of the pre-hydrogenation section is 160-200 ℃ and 200-250 ℃, and the reaction pressure is 2.0-5.5 Mpag.
The reaction temperature in the pre-hydrogenation section may be 165 ℃, 170 ℃, 175 ℃, 180 ℃, 185 ℃, 190 ℃ or 195 ℃, or 205 ℃, 210 ℃, 215 ℃, 220 ℃, 225 ℃, 230 ℃, 235 ℃, 240 ℃ or 245 ℃, and the reaction pressure may be 2.5Mpag, 3.0Mpag, 3.5Mpag, 4.0Mpag, 4.5Mpag or 5.0Mpag, but is not limited to the recited values, and other values not recited in the above-mentioned ranges of values are also applicable.
Preferably, the reaction temperature of the light reforming section is 280-300 ℃, 300-340 ℃ and 340-360 ℃, and the reaction pressure is 2.0-5.5 Mpag.
The reaction temperature in the light-ends reforming section is 282 ℃, 285 ℃, 288 ℃, 290 ℃, 292 ℃, 295 ℃, 298 ℃, 305 ℃, 310 ℃, 315 ℃, 320 ℃, 325 ℃, 330 ℃, 335 ℃, 342 ℃, 345 ℃, 348 ℃, 350 ℃, 352 ℃, 355 ℃ or 358 ℃, and the like, and the reaction pressure may be 2.5Mpag, 3.0Mpag, 3.5Mpag, 4.0Mpag, 4.5Mpag, or 5.0Mpag, but is not limited to the recited values, and other values not recited in the above-mentioned ranges of values are also applicable.
In the invention, the heavy aromatic hydrocarbon conversion unit preferably adopts a fixed bed multi-section heat transfer type reactor, and each section of reaction product heats the last section of feed gas through an external heat exchanger to maintain the mild fluctuation of the reaction temperature; the heavy aromatics light unit catalyst is divided into two parts, wherein the first part is a pre-hydrogenation section and preferably at least contains nickel, chromium, molybdenum, tungsten and other metals, alumina is used as a carrier, the second part is a light reforming section and preferably at least contains platinum, palladium and other noble metals, and the carrier adopts mordenite, a molecular sieve and the like.
Preferably, the low-carbon aromatic hydrocarbon tower unit in the step (2) separates to obtain C9+ a mixed aromatic hydrocarbon and low-carbon aromatic hydrocarbon, the low-carbon aromatic hydrocarbon includes benzene, toluene and carbon octa-aromatic hydrocarbon, the C9+ a mixed aromatic hydrocarbon enters a carbon nonaromatic hydrocarbon tower unit, and the low-carbon aromatic hydrocarbon returns to the aromatic hydrocarbon extraction unit.
Preferably, the carbon nonaromatic hydrocarbon tower unit separates to obtain heavy aromatic hydrocarbon and carbon nonaromatic hydrocarbon, the carbon nonaromatic hydrocarbon enters the benzene and carbon nonaromatic hydrocarbon alkylation transfer unit, and the heavy aromatic hydrocarbon enters the heavy aromatic hydrocarbon removal tower unit.
In the invention, the benzene and carbon nonaaromatics alkylation transfer reaction in the benzene and carbon nonaaromatics alkylation transfer unit is carried out under the catalytic condition of the catalyst.
Wherein the temperature of the benzene and the carbon nonaaromatics alkylation transfer reaction is 200-500 ℃, the reaction pressure is 1.5-4.5 Mpag, and the mass space velocity is 1-5 h-1The hydrogen-hydrocarbon molar ratio is 1 to 6.
The reaction temperature can be 250 ℃, 300 ℃, 350 ℃, 400 ℃ or 450 ℃, the reaction pressure can be 2.0Mpag, 2.5Mpag, 3.0Mpag, 3.5Mpag or 4.0Mpag, and the mass space velocity can be 1.5h-1、2h-1、2.5h-1、3h-1、3.5h-1、4h-1Or 4.5h-1For example, the hydrogen-hydrocarbon molar ratio may be 2, 3, 4 or 5, but the hydrogen-hydrocarbon molar ratio is not limited to the above-mentioned values, and other values not shown in the above-mentioned numerical ranges are also applicable.
Wherein the catalyst takes beta-zeolite, mordenite, molecular sieve or the like as a carrier to load bismuth and/or bismuth metal oxide.
As a preferable technical scheme of the invention, the heavy aromatics removal unit separates heavy oil and carbon deca-aromatics, the carbon deca-aromatics return to the heavy aromatics lightening unit, and the heavy oil is extracted as a product.
In the invention, the method takes a typical reforming device to remove pentane mixed aromatic hydrocarbon as a raw material; benzene, toluene, mixed xylene and heavy aromatics with nine and more than nine carbons are obtained by a separation unit; the toluene and methanol obtained by separation enter a toluene and methanol alkylation reaction unit to carry out toluene shape-selective alkylation reaction to generate mixed xylene of high-concentration p-xylene, a small amount of benzene and C9+ heavy aromatics; the benzene and the carbon nonaromatic hydrocarbon obtained by separation enter a benzene and carbon nonaromatic hydrocarbon alkylation transfer unit to carry out transalkylation reaction to obtain aromatic hydrocarbon material flows such as benzene, toluene, mixed xylene and the like; the separated heavy aromatics with nine carbon atoms and more than nine carbon atoms enter a heavy aromatic hydrocarbon conversion unit to generate non-aromatic hydrocarbons, benzene, toluene, carbon octa-aromatic hydrocarbons and carbon nine-aromatic hydrocarbons, and the unreacted heavy aromatics return to the heavy aromatic hydrocarbon conversion unit; the obtained mixed xylene enters a low-temperature crystallization separation unit to obtain pure para-xylene and other mixed carbon eight aromatic hydrocarbons, and the other mixed carbon eight aromatic hydrocarbons enter an isomerization unit.
Compared with the prior art, the invention at least has the following beneficial effects:
the system and the method fully utilize benzene and heavy aromatics such as carbon nine and carbon ten to improve the utilization rate of converting benzene rings of aromatic hydrocarbon raw materials into p-xylene, simultaneously utilize a toluene shape-selecting technology to realize the improvement of the concentration of the p-xylene in mixed xylene and reduce the scale of isomerization treatment, so that the product mass concentration of the p-xylene is more than or equal to 99.8 percent; the method can obtain the p-xylene product with high added value while efficiently utilizing the heavy aromatic hydrocarbon resources, and obtains good technical effect.
Drawings
FIG. 1 is a schematic diagram of a system for increasing yield of p-xylene by toluene methylation combined with heavy aromatics upgrading provided in example 1 of the present invention;
in the figure: i is an aromatic hydrocarbon extraction unit; II is a benzene tower unit; III is a toluene column unit; IV is a toluene methanol alkylation reaction unit; v is a toluene circulating tower unit; VI is a xylene column unit; VII is a crystallization separation unit; VIII is a heavy aromatic hydrocarbon lightening unit; IX is a mixed xylene isomerization unit; x is a low carbon aromatics column unit; XI is a carbon nonaarene tower unit; XII is a heavy aromatics removal tower unit; XIII is a benzene and carbon nonalkylation transfer unit.
Stream description in fig. 1: 1 is reforming depentane mixed aromatic hydrocarbon; 2 is a mixed aromatic mixture after non-aromatic hydrocarbon is removed; 3 is separated non-aromatic hydrocarbon; 4 is C7+ A (aromatic hydrocarbon with seven or more carbon atoms, the same expression below) in the bottom of the benzene tower; 5 is benzene extracted from the top of the benzene tower; 6 is toluene extracted from the top of the toluene tower; 7 is C8+ A of the toluene tower kettle; 8 is C8+ A of the xylene column kettle; 9 is mixed xylene extracted from the side line of the xylene column; 10 is mixed aromatic hydrocarbon such as benzene, toluene and the like extracted from the top of the xylene tower; 11 is a mixed aromatic product generated by a toluene methanol alkylation reaction; 12 is non-aromatic hydrocarbon generated by toluene methanol alkylation reaction; 13 is pure toluene extracted from the side line of the toluene circulating tower; 14 is a small amount of benzene extracted from the top of the toluene circulating tower; 15 is mixed xylene extracted from the side line of the toluene circulating tower; 16 is C9+ A mixed aromatic hydrocarbon generated at the bottom of the toluene circulating tower; 17 is mixed carbon-eight aromatic hydrocarbon after para-xylene is separated by a crystallization separation unit; 18 is pure para-xylene produced by the crystallization separation unit; 19 is an isomerization unit reaction product; 20 is the product of heavy aromatic hydrocarbon unit after being lightened; 21 is C9+ A generated by the tower bottom of the low-carbon aromatic hydrocarbon tower; 22 is low-carbon aromatic hydrocarbon generated at the top of the low-carbon aromatic hydrocarbon tower, and mainly comprises benzene, toluene, carbon octa-aromatic hydrocarbon and the like; 23 is heavy aromatic hydrocarbon at the bottom of the carbon nine tower; 24 is carbon nine extracted from the top of the carbon nine tower; 25 is the carbon ten extracted from the top of the heavy aromatics removal unit; 26 is heavy oil at the bottom of a heavy aromatics removal unit tower; 27 is a mixed aromatic product of benzene and carbon nine reaction units.
The present invention is described in further detail below. The following examples are merely illustrative of the present invention and do not represent or limit the scope of the claims, which are defined by the claims.
Detailed Description
The technical scheme of the invention is further explained by the specific implementation mode in combination with the attached drawings.
To better illustrate the invention and to facilitate the understanding of the technical solutions thereof, typical but non-limiting examples of the invention are as follows: