Heavy desorption agent ethylbenzene adsorption separation process

Abstract

The invention discloses a heavy desorption agent ethylbenzene adsorption separation process. The method comprises the following steps: introducing a C8 isomer raw material into a four-zone simulated moving bed adsorption tower, carrying out adsorption separation on ethylbenzene and other C8 aromatic isomers, respectively introducing an extract and a raffinate into a first rectifying tower and a second rectifying tower, fractionating and separating a desorption agent for recycling, and obtaining a high-purity ethylbenzene product at the top of the first rectifying tower. Compared with a traditional light desorption agent ethylbenzene adsorption separation system, the separation energy consumption is reduced to a certain extent by adopting a heavy desorption agent system and matching with a small-grain low-metal exchange rate adsorbent, and the method is more environmentally friendly and economical.

Description

Technical Field

[0001] The present application relates to the field of adsorption separation technology, and in particular to an adsorption separation process of heavy desorbent ethylbenzene. Background Art

[0002] Ethylbenzene is an important basic chemical raw material, which can be used to produce styrene, and further produce styrene homopolymer and copolymer with styrene as the main component. In industry, reforming oil, ethylene cracking gasoline, and xylene isomerization products are rich in ethylbenzene. If the ethylbenzene in them can be separated and recycled, it will create huge economic benefits. At present, the research on recovering ethylbenzene from mixed C8 aromatics mainly focuses on pressure swing adsorption separation technology, crystallization technology, and simulated moving bed adsorption separation technology.

[0003] Patent US6573418B2 uses a pressure swing adsorption-simulated moving bed combined process to recover ethylbenzene and paraxylene from mixed C8 aromatics. The mixed C8 raw material enters the pressure swing adsorption unit through heating and gasification, and the adsorbent selectively adsorbs ethylbenzene and paraxylene. This stream is passed into the simulated moving bed for further adsorption and separation. After selective adsorption, paraxylene and ethylbenzene products rich in desorbent can be obtained, and ethylbenzene can be obtained after fractionation. This process verifies the feasibility of recovering ethylbenzene from mixed C8 aromatics, but the process flow is too long and the energy consumption is too high.

[0004] Patent CN104513124 uses pressure swing adsorption technology to obtain high-purity ethylbenzene products and a mixture of meta-xylene and ortho-xylene using a C8 aromatic mixture that does not contain para-xylene as raw material. This process uses multiple adsorption beds, and each cycle includes eight steps: adsorption, equalization and pressure reduction, forward pressure release, displacement, reverse pressure release, purge, homogeneous pressure increase, and final pressure increase. The process is relatively complex and the raw material adaptability is insufficient.

[0005] Patent USP3729523 discloses a method for recovering isomers in C8 aromatics, in which the C8 aromatics are separated into a first stream containing p-xylene and ethylbenzene and a second stream containing m-xylene and o-xylene in an adsorption separation section. The p-xylene in the first stream is then crystallized and recovered, and the crystallization mother liquor is distilled to obtain ethylbenzene. The second stream is distilled to remove the solvent and separate a portion of m-xylene and o-xylene. The process flow is relatively cumbersome and highly complex.

[0006] Therefore, the current use of gas phase pressure swing adsorption technology to separate ethylbenzene requires vaporization of the components, which consumes a lot of energy. In addition, the traditional simulated moving bed process uses a light desorbent, has a high desorption ratio, high energy consumption in the distillation process, and requires a large investment, which cannot meet industrial needs well. Summary of the invention

[0007] In order to solve the technical problem of high energy consumption in the prior art, the present application provides a heavy desorbent ethylbenzene adsorption separation process. The method adopts a heavy desorbent system in the traditional ethylbenzene adsorption separation process, which greatly reduces process energy consumption, reduces environmental pollution and increases economic benefits while obtaining a high-purity ethylbenzene product.

[0008] The present application provides a heavy desorbent ethylbenzene adsorption separation process, which is achieved by adopting the following technical solution.

[0009] A heavy desorbent ethylbenzene adsorption separation process comprises the following steps:

[0010] S1. A raw material containing C8 aromatic isomers and a heavy desorbent of monosubstituted aromatics having a boiling point greater than 150° C. are introduced into a simulated moving bed adsorption tower for adsorption separation to obtain an ethylbenzene-rich extract and an ethylbenzene-poor raffinate, wherein the adsorbent is a small-grained low-exchange molecular sieve;

[0011] S2. The extracted liquid and the residual liquid enter the first distillation tower and the second distillation tower respectively for fractionation and separation of the desorbent for recycling, the by-product is taken out from the top of the second distillation tower, and the ethylbenzene product is taken out from the top of the first distillation tower.

[0012] Furthermore, in step S1, the monosubstituted aromatic heavy desorbent with a boiling point greater than 150° C. is one or more combinations of n-propylbenzene, isopropylbenzene, n-butylbenzene, isobutylbenzene, tert-butylbenzene, and sec-butylbenzene.

[0013] Furthermore, the adsorbent is a metal-modified molecular sieve with a specific surface area of ​​≥400m 2 / g; the molecular sieve particle size range is 0.3-1.5 microns, preferably 0.5-1.0 microns; the metal content is 0.1%-1.5%, preferably 0.2%-1.0%; the molecular sieve type is one or a combination of X, Y, ZSM-5, A; the metal ion is one or a combination of Ca, Cs, Ba, K, Na, Ni, Ru.

[0014] Furthermore, the raw material containing C8 aromatic isomers is one or more combinations of catalytic reforming product oil or ethylene cracking gasoline, wherein the mass fraction of ethylbenzene is 15% to 50%.

[0015] Furthermore, the adsorbent bed temperature in the simulated moving bed adsorption tower is 100-250° C., preferably 120-180° C.; the adsorption pressure is 0.1-1.8 MPa, preferably 0.2-1.4 MPa; the number of adsorption tower bed layers is 8-24, preferably 8-16.

[0016] Furthermore, the volume flow rate ratio of the raw material to the desorbent in the simulated moving bed adsorption tower (1) is 1:(1-5), preferably 1:(1.5-3.5).

[0017] Furthermore, the step time in the simulated moving bed adsorption tower is 70 to 800 s, preferably 100 to 1000 s.

[0018] Furthermore, in step S2, the number of plates of the distillation tower is 50-100, preferably 60-80; the operating pressure of the distillation tower is 0.03-0.15 MPa, preferably 0.025-0.1 MPa; and the reflux ratio of the distillation tower is 0.5-3.0, preferably 1.0-2.5.

[0019] This application has the following beneficial effects.

[0020] The present invention significantly reduces the energy consumption of the distillation process while efficiently separating ethylbenzene by innovating the desorbent system and matching it with a small-grain low-metal exchange rate adsorbent. When the extract does not include the desorbent, the ethylbenzene purity mass fraction is ≥99.8%, the yield is ≥95%, and the heavy desorbent ethylbenzene separation process reduces the energy consumption by more than 40% compared with the traditional simulated moving bed ethylbenzene separation process. The method of the present invention has a simple process flow, low energy consumption, and obtains a high-purity ethylbenzene product, which has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The present invention is a flow chart of the heavy desorbent ethylbenzene separation process.

[0022] Among them, 1. simulated moving bed adsorption tower; 2. first distillation tower; 3. second distillation tower; 4. desorbent storage tank. DETAILED DESCRIPTION

[0023] The present patent application is further described below in conjunction with embodiments.

[0024] Unless otherwise specified, the experimental methods used in the following examples are all conventional methods; the materials, reagents, etc. used in the following preparation examples and examples, unless otherwise specified, can be obtained from commercial channels.

[0025] like Figure 1 As shown, a heavy desorbent ethylbenzene adsorption separation process includes a simulated moving bed adsorption tower 1, the extracted liquid outlet and the residual liquid outlet of the simulated moving bed adsorption tower 1 are respectively connected to the first distillation tower 2 and the second distillation tower 3, the desorbent outlets of the first distillation tower 2 and the second distillation tower 3 are both connected to the desorbent storage tank 4, and the discharge port of the desorbent storage tank 4 is connected to the desorbent inlet of the simulated moving bed adsorption tower 1.

[0026] The C8 aromatic isomer raw material is passed into the simulated moving bed adsorption tower 1, and after the simulated moving bed adsorption separation, the ethylbenzene-poor raffinate and ethylbenzene-rich extract are obtained, both of which contain desorbent and need to be further separated. The extract and the raffinate enter the first distillation tower 2 and the second distillation tower 3 respectively, and the desorbent is recycled by fractionation. The second distillation tower 3 obtains C8 aromatic isomer byproducts other than ethylbenzene and exits the device, and the high-purity ethylbenzene product is obtained at the top of the first distillation tower 2.

[0027] Example 1

[0028] A heavy desorbent ethylbenzene adsorption separation process, specifically as follows:

[0029] (1) The ethylbenzene feedstock is catalytically reformed to produce oil, the ethylbenzene content of which is 19.8% by mass. The main composition is shown in Table 1. The desorbent used is 70% by mass of propylbenzene and 30% by mass of butylbenzene.

[0030] (2) The adsorbent used in the simulated moving bed is K and Ba modified ZSM-5 molecular sieve. 150g potassium chloride and 220g barium chloride are dissolved in 4L deionized water to prepare an exchange solution. 400g ZSM-5 molecular sieve balls are placed in the exchange kettle, and the prepared exchange solution is added. Ion exchange is carried out at 95°C for 4 hours. After the exchange is completed, the exchanged molecular sieve is rinsed with a large amount of deionized water. Then, the rinsed molecular sieve is dried at 200°C for 10 hours to obtain the modified ZSM-5 molecular sieve. The purity of the ZSM-5 molecular sieve is 99.9% by mass, the content of K2O is 0.8% by mass, the content of BaCl2 is 0.42% by mass, the adsorbent particle size is 1.0 micron, and the specific surface area is 430m 2 / g.

[0031] (3) Simulated moving bed process conditions: Ethylbenzene raw material is introduced into a four-zone simulated moving bed device, and the simulated moving bed contains 12 adsorption beds, including adsorption zone (I), refining zone (II), desorption zone (III) and isolation zone (IV), wherein the number of beds in zone I-zone II-zone III-zone IV is 5-3-3-1, and each bed contains five material pipelines, corresponding to ethylbenzene raw material, desorbent, extract, residual liquid and flushing liquid, respectively. Each pipeline is provided with a programmable valve, and the four zones are switched one by one along the material flow direction. Periodic switching of the inlet and outlet valves can realize continuous adsorption separation. In this embodiment, the step time is set to 150s, the adsorption cycle is 1800s, the adsorbent bed temperature is 120°C, the adsorption pressure is 0.7MPa, and the volume flow rate ratio of ethylbenzene raw material to desorbent is 1:2.5.

[0032] (4) The number of plates of the first distillation tower 2 is 55; the operating pressure is 0.1 MPa; the reflux ratio of the distillation tower is 1.8; the number of plates of the second distillation tower 3 is 60, the operating pressure is 0.1 MPa; the reflux ratio of the distillation tower is 1.7.

[0033] When the extract does not contain desorbent, the purity of ethylbenzene is 99.8% and the yield is 96.2%. The energy consumption analysis is shown in Table 2.

[0034] Example 2

[0035] A heavy desorbent ethylbenzene adsorption separation process, specifically as follows:

[0036] (1) The ethylbenzene raw material is ethylene cracking gasoline, the ethylbenzene content is 31.3% by mass, the main composition is shown in Table 1, and the desorbent is isobutylene.

[0037] (2) The adsorbent used in the simulated moving bed is K and Cs modified Y type molecular sieve. 150g potassium chloride and 170g cesium chloride are dissolved in 4L deionized water to prepare an exchange solution. 400g Y molecular sieve balls are placed in the exchange kettle, and the prepared exchange solution is added. Ion exchange is carried out at 95°C for 4 hours. After the exchange is completed, the exchanged molecular sieve is rinsed with a large amount of deionized water. Then, the rinsed molecular sieve is dried at 200°C for 10 hours to obtain the modified Y molecular sieve. The purity of the Y type molecular sieve is 99.9% by mass, the content of K2O is 0.75% by mass, and the content of CsCl is 0.3% by mass. The adsorbent particle size is 0.8 microns and the specific surface area is 450m 2 / g.

[0038] (3) Simulated moving bed process conditions: Ethylbenzene feedstock was introduced into a four-zone simulated moving bed device. The simulated moving bed contained 16 adsorption beds, of which the number of beds in zone I-zone II-zone III-zone IV was 7-4-4-1. The step time was 200 s, the adsorption cycle was 3200 s, the adsorbent bed temperature was 140 °C, the adsorption pressure was 0.8 MPa, and the volume flow rate ratio of ethylbenzene feedstock to desorbent was 1:3.5.

[0039] (4) The number of plates of the first distillation tower 2 is 65; the operating pressure is 0.08 MPa; the reflux ratio of the distillation tower is 2.2; the number of plates of the second distillation tower 3 is 75, the operating pressure is 0.07 MPa; the reflux ratio of the distillation tower is 2.0.

[0040] When the extract does not contain desorbent, the purity of ethylbenzene is 99.5% and the yield is 98.1%. The energy consumption analysis of the process is shown in Table 2.

[0041] Comparative Example 1

[0042] A method for separating ethylbenzene is as follows:

[0043] (1) The ethylbenzene feedstock, step time, adsorption temperature and pressure were kept the same as in Example 1.

[0044] (2) The desorbent is a combination of 70% benzene and 30% toluene by mass, and the volume flow rate ratio of ethylbenzene raw material to desorbent is 1:2.1.

[0045] (3) The adsorbent is a K and Ba modified ZSM-5 molecular sieve. 260g of potassium chloride and 440g of barium chloride are dissolved in 4L of deionized water to prepare an exchange solution. 400g of ZSM-5 molecular sieve balls are placed in an exchange kettle, and the prepared exchange solution is added. Ion exchange is carried out at 95°C for 4 hours. After the exchange is completed, the exchanged molecular sieve is rinsed with a large amount of deionized water. Then, the rinsed molecular sieve is dried at 200°C for 10 hours to obtain the modified ZSM-5 molecular sieve. The purity of the ZSM-5 molecular sieve is 99.9% by mass, the content of K2O is 1.9% by mass, the content of BaCl2 is 0.8% by mass, the adsorbent particle size is 3.0 microns, and the specific surface area is 370m 2 / g.

[0046] (4) The number of plates of the first distillation tower 2 is 55; the operating pressure is 0.1 MPa; the reflux ratio of the distillation tower is 2.1; the number of plates of the second distillation tower 3 is 60, the operating pressure is 0.1 MPa; the reflux ratio of the distillation tower is 2.05.

[0047] The purity of ethylbenzene was 99.8% and the yield was 96.2%. The energy consumption analysis is shown in Table 2.

[0048] Comparative Example 2

[0049] A method for separating ethylbenzene is as follows:

[0050] (1) The ethylbenzene feedstock, step time, adsorption temperature and pressure were kept the same as in Example 2.

[0051] (2) The adsorbent is K and Cs modified Y type molecular sieve, the purity of Y type molecular sieve is 99.9% by mass. 300g potassium chloride and 3500g cesium chloride are dissolved in 4L deionized water to prepare the exchange solution. 400g Y molecular sieve balls are placed in the exchange kettle, and the prepared exchange solution is added. Ion exchange is carried out at 95°C for 4h. After the exchange is completed, the exchanged molecular sieve is rinsed with a large amount of deionized water. Then, the rinsed molecular sieve is dried at 200°C for 10 hours to obtain the modified Y molecular sieve. The content of K2O is 2.0% by mass, and the content of CsCl is 1.1% by mass. The adsorbent particle size is 2.2 microns and the specific surface area is 400m 2 / g.

[0052] (3) Benzene is used as the desorbent, and the volume flow rate ratio of ethylbenzene raw material to desorbent is 1:3.1.

[0053] (4) The number of plates of the first distillation tower 2 is 65; the operating pressure is 0.08 MPa; the reflux ratio of the distillation tower is 3.0; the number of plates of the second distillation tower 3 is 75, the operating pressure is 0.07 MPa; the reflux ratio of the distillation tower is 3.2.

[0054] The purity of ethylbenzene was 99.8% and the yield was 98.1%. The energy consumption analysis is shown in Table 2.

[0055] Table 1 Raw material composition

[0056]

[0057] Table 2 Comparison of results of different embodiments

[0058]

[0059] Note: Ethylbenzene yield = ethylbenzene product mass flow rate / raw material ethylbenzene flow rate × 100%.

[0060] The embodiments of this specific implementation method are all preferred embodiments of the present application, and are not intended to limit the protection scope of the present application. Therefore, all equivalent changes made based on the structure, shape, and principle of the present application should be included in the protection scope of the present application.

Claims

1. A heavy desorbent ethylbenzene adsorption separation process, characterized in that: The following steps are involved: S1. A raw material containing C8 aromatic isomers and a heavy monosubstituted aromatic desorbent having a boiling point greater than 150° C. are introduced into a simulated moving bed adsorption tower (1) for adsorption separation to obtain an ethylbenzene-rich extract and an ethylbenzene-poor raffinate, wherein the adsorbent is a small-grained low-exchange molecular sieve; S2. The extracted liquid and the residual liquid enter the first distillation tower (2) and the second distillation tower (3) respectively for fractionation and separation of the desorbent for recycling, the by-product is taken out from the top of the second distillation tower (3), and the ethylbenzene product is taken out from the top of the first distillation tower (2).

2. A heavy desorbent ethylbenzene adsorption separation process according to claim 1, characterized in that: The monosubstituted aromatic heavy desorbent with a boiling point greater than 150° C. is one or more combinations of n-propylbenzene, isopropylbenzene, n-butylbenzene, isobutylbenzene, tert-butylbenzene and sec-butylbenzene.

3. A heavy desorbent ethylbenzene adsorption separation process according to claim 1, characterized in that: The adsorbent is a metal-modified molecular sieve with a specific surface area of ​​≥400m 2 / g; molecular sieve particle size range 0.3 ~ 1.5 microns; The metal content is 0.1% to 1.5%; the molecular sieve type is one or a combination of X, Y, ZSM-5, and A; the metal ion is one or a combination of Ca, Cs, Ba, K, Na, Ni, and Ru.

4. A heavy desorbent ethylbenzene adsorption separation process according to claim 1, characterized in that: The raw material containing C8 aromatic isomers is one or more combinations of catalytic reforming oil or ethylene cracking gasoline, wherein the mass fraction of ethylbenzene is 15% to 50%.

5. A heavy desorbent ethylbenzene adsorption separation process according to claim 1, characterized in that: The adsorbent bed temperature in the simulated moving bed adsorption tower (1) is 80-250°C, the adsorption pressure is 0.1-1.8 MPa, and the number of adsorption tower bed layers is 8-24.

6. A heavy desorbent ethylbenzene adsorption separation process according to claim 1, characterized in that: The volume flow rate ratio of the raw material to the desorbent in the simulated moving bed adsorption tower (1) is 1:(1-5).

7. A heavy desorbent ethylbenzene adsorption separation process according to claim 1, characterized in that: The step time in the simulated moving bed adsorption tower (1) is 70 to 800 seconds.

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