Composite adsorbent for separation of ethylbenzene by adsorptive distillation and its application

Abstract

A composite adsorbent for separating ethylbenzene from C8 aromatic hydrocarbons by adsorption and distillation, comprising 1 to 50% by mass of a xylene adsorbent and 50 to 99% by mass of a carrier liquid, wherein the carrier liquid is selected from one or two of alkanes, aryl-substituted alkanes, decahydronaphthalene and alkyl-substituted decahydronaphthalene, wherein the alkane is C8 aromatic hydrocarbons. 10 ~C 26 The alkane, wherein the aryl-substituted alkane is C 13 ~C 16 The composite adsorbent can increase the volatility of ethylbenzene relative to other C8 aromatic hydrocarbons, so that high-purity ethylbenzene can be separated from C8 aromatic hydrocarbons by adsorption distillation.

Description

Technical Field

[0001] The present invention relates to a composite adsorbent for adsorption distillation separation and its application, and in particular to a composite adsorbent for adsorption distillation separation of C 8 Method for ethylbenzene in aromatics. Background Art

[0002] Ethylbenzene is an important chemical raw material, mainly used to produce styrene. Currently, ethylbenzene is mainly produced by alkylation of benzene and ethylene. In the petroleum refining and chemical industry, ethylbenzene resources are abundant, and reforming C 8 Ethylbenzene accounts for about 18% by mass in the fraction, and ethylene cracking C 8 Ethylbenzene accounts for about 50% by mass in the fraction. If this part of ethylbenzene can be directly separated, the consumption of ethylene and benzene can be saved and the allocation of chemical resources can be optimized. 8 After the ethylbenzene in the fraction is separated, the xylene without ethylbenzene or with greatly reduced ethylbenzene content can be used as the feedstock of the aromatics complex, which will significantly improve the efficiency of the aromatics complex. 8 A new process for efficiently separating ethylbenzene from aromatics is very necessary.

[0003] Currently, from C 8 There are three methods for separating ethylbenzene from aromatic hydrocarbons: super fractionation, adsorption and extraction. 8 Separation of ethylbenzene from distillates is a traditional process because mixed C 8 The four isomers of aromatic hydrocarbons have similar boiling points, among which ethylbenzene and p-xylene have a boiling point difference of only 2.2°C, making them difficult to separate using distillation methods.

[0004] GB1198592 describes the use of a single or multiple distillation columns to separate C 8 The aromatics method requires at least 250 plates, preferably 365 plates, and a reflux ratio of 100 to 250: 1. This method can separate ethylbenzene, o-xylene, and a mixture of p-xylene and m-xylene by distillation, and the mixture of p-xylene and m-xylene is then crystallized to separate p-xylene, and the remaining components are isomerized. It has high energy consumption and no economic advantage.

[0005] The separation of ethylbenzene by adsorption can be divided into two categories: one is the preferential adsorption of C 8 The non-ethylbenzene components in the aromatics are obtained from the raffinate to obtain ethylbenzene products. For example, US3917734, US4079094 and US4108915 use Ca-X / Y, Sr-KX or Sr-X zeolites respectively to preferentially adsorb C 8Xylene isomers in aromatics, ethylbenzene products are obtained from the raffinate, but it is difficult to obtain high-purity ethylbenzene products using this type of adsorbent, and its purity is easily affected by the composition of the raw materials. Another type is to preferentially adsorb ethylbenzene. CN100577617C discloses a method for separating mixed C 8 A method for separating ethylbenzene and p-xylene from aromatic hydrocarbons, wherein a purge gas is used to purge the adsorption bed during the pressure swing adsorption separation process, and the adsorbent used is a ZSM-5 molecular sieve. This adsorbent can only absorb p-xylene and ethylbenzene together but cannot separate them, and the adsorbent has low selectivity for the target products p-xylene and ethylbenzene.

[0006] The extractive distillation process is a method that uses an extractant to increase the relative volatility of the components to be separated to improve the separation efficiency. Currently, the solvents reported for the extraction distillation separation of ethylbenzene are difficult to provide ideal selectivity and have low separation efficiency.

[0007] US4292142 discloses a method for separating ethylbenzene from p-xylene and m-xylene by extractive distillation, using maleic anhydride and phthalic anhydride as extractive distillation composite solvents, and oxygen-containing compounds can be added to reduce the freezing point of maleic anhydride and phthalic anhydride. Under the condition of a solvent ratio of 1.5, the relative volatility of ethylbenzene and p-xylene can reach 1.22.

[0008] US5135620 discloses extractive distillation from C 8 A method for separating ethylbenzene from aromatic hydrocarbons, using monovalent copper hydrocarbon sulfonate as an entrainer, extractive distillation to separate C 8 Ethylbenzene in aromatic hydrocarbons, the sulfonic acid includes p-toluenesulfonic acid, p-dodecylbenzenesulfonic acid, p-hexadecylbenzenesulfonic acid, naphthalenesulfonic acid, phenolsulfonic acid, naphtholsulfonic acid or halogenated benzenesulfonic acid. The entrainer is firstly introduced into an extractive distillation tower, the component rich in ethylbenzene is discharged from the top of the tower, and the entrainer dissolved in xylene is discharged from the bottom of the tower, and the xylene and the entrainer can be separated by a distillation tower, the xylene is discharged from the top of the tower, and the entrainer dissolved in xylene is discharged from the bottom of the tower and returned to the extractive distillation tower. Under the condition of a solvent ratio of 2, the relative volatility of ethylbenzene and xylene reaches 1.16. Summary of the invention

[0009] The object of the present invention is to provide a 8 Composite adsorbent for separation of ethylbenzene from aromatic hydrocarbons by adsorption and distillation and its application, the composite adsorbent can improve the relative efficiency of ethylbenzene to other C 8 The volatility of aromatic hydrocarbons can be adjusted by adsorption distillation from C 8 Separation of high purity ethylbenzene from aromatics.

[0010] The present invention provides a 8A composite adsorbent for separating ethylbenzene from aromatic hydrocarbons by adsorption and distillation, comprising 1 to 50% by mass of a xylene adsorbent and 50 to 99% by mass of a carrier liquid, wherein the carrier liquid is selected from one or two of alkanes, aryl-substituted alkanes, decahydronaphthalene and alkyl-substituted decahydronaphthalene, wherein the alkane is C 10 ~C 26 The alkane, wherein the aryl-substituted alkane is C 13 ~C 16 Aryl substituted alkanes.

[0011] The composite adsorbent provided by the present invention is obtained by mixing a xylene adsorbent and an appropriate amount of a carrier liquid, and can be used to separate C 8 The method can separate ethylbenzene and xylene from aromatic hydrocarbons and obtain a high-purity ethylbenzene product. The method can reduce fixed investment and energy consumption for separating ethylbenzene. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 The invention provides a method for 8 Schematic diagram of a process for separating ethylbenzene from aromatic hydrocarbons by adsorptive distillation. DETAILED DESCRIPTION

[0013] The composite adsorbent provided by the present invention comprises a xylene adsorbent and a carrier liquid, wherein the xylene adsorbent adsorbs xylene during the adsorption distillation process, thereby easily allowing ethylbenzene to react with C 8 The xylene separation in aromatics, the carrier liquid is used to carry the xylene adsorbent flow, which does not interact with C 8 Aromatic hydrocarbons react, and the boiling point is preferably greater than 180°C. In this way, the carrier liquid does not volatilize to the top of the adsorption distillation tower during the adsorption distillation process, and carries the adsorbent for adsorbing xylene into the distillation desorption tower. In the distillation desorption tower, the xylene in the adsorbent is desorbed, and the carrier liquid carries the regenerated xylene adsorbent back to the adsorption distillation tower for reuse. The composite adsorbent can significantly increase the relative volatility of ethylbenzene to each isomer of xylene, so that it can be adsorbed from C 8 Separation of high purity ethylbenzene from aromatics.

[0014] The xylene adsorbent in the composite adsorbent of the present invention is used to increase the relative volatility of ethylbenzene to the xylene isomers, and the carrier liquid is used to carry the xylene adsorbent to flow. The composite adsorbent preferably includes 5-35 mass % of the xylene adsorbent and 65-95 mass % of the carrier liquid.

[0015] The xylene adsorbent is preferably a Y molecular sieve with a metal ion of group IA and / or group IIA occupying the cation position, and the group IA metal ion is preferably Li + Or Na + , Group IIA metal ions are preferably Sr 2+ Or Ba 2+, more preferably NaY molecular sieve.

[0016] The crystal particle size of the Y molecular sieve is preferably 0.1 to 2 microns, more preferably 0.2 to 1.5 microns.

[0017] The carrier liquid is selected from one or any two of alkanes, aryl-substituted alkanes, decahydronaphthalene or alkyl-substituted decahydronaphthalene, wherein the alkane can be a normal alkane or an isoalkane, preferably C 10 ~C 24 n-alkanes, more preferably C 11 ~C 20 of normal alkanes.

[0018] The aryl-substituted alkane is preferably C 13 ~C 16 of diphenylalkanes.

[0019] The alkyl group of the alkyl-substituted decalin can be C 1 ~C 12 Alkyl, preferably C 3 ~C 10 Alkyl, more preferably C 2 ~C 6 The number of substituted alkyl groups may be 1 to 4, preferably 1 to 2.

[0020] The method for separating ethylbenzene by adsorption distillation provided by the present invention comprises: 8 The aromatic hydrocarbon mixture is introduced into the middle part of the adsorption distillation tower, and the composite adsorbent of the present invention is introduced into the upper part of the adsorption distillation tower. After adsorption distillation, ethylbenzene is discharged from the top of the adsorption distillation tower, and the composite adsorbent enriched with xylene is discharged from the bottom of the tower and enters the middle part of the distillation and desorption tower. After distillation and desorption, the mixed xylene is discharged from the top of the tower, and the regenerated composite adsorbent is obtained at the bottom of the tower and returned to the upper part of the adsorption distillation tower for reuse.

[0021] In the above method, the top pressure of the adsorption distillation tower is preferably 0.01-0.2 MPa, the theoretical plate number is preferably 30-100, more preferably 30-80, the inlet temperature of the composite adsorbent is preferably 90-130°C, the bottom temperature is preferably 140-250°C, and the top temperature is preferably 70-100°C.

[0022] The composite adsorbent entering the adsorption distillation tower and C 8 The mass ratio of the aromatic hydrocarbon mixture is preferably 5 to 30, more preferably 8 to 23, and the xylene adsorbent and C in the composite adsorbent are preferably 5 to 30, more preferably 8 to 23. 8 The mass ratio of the aromatic hydrocarbon mixture is preferably 1.5-6, more preferably 2-5, and the mass ratio of the carrier liquid to the xylene adsorbent is preferably 1.5-20, more preferably 2-10. The reflux ratio at the top of the tower is preferably 1-15, more preferably 1-8.

[0023] The top pressure of the distillation desorption tower is preferably 0.01 to 0.15 MPa, more preferably 0.01 to 0.06 MPa, the number of theoretical plates is preferably 20 to 50, more preferably 25 to 45, the bottom temperature is preferably 160 to 280° C., and the top temperature is preferably 60 to 90° C. The reflux ratio at the top of the distillation desorption tower is preferably 0.3 to 3, more preferably 0.5 to 2.

[0024] In the above method, the reflux ratio is the mass ratio of the material refluxed into the tower from the upper part of the tower to the material discharged from the top of the tower.

[0025] The adsorption and distillation tower and the distillation and desorption tower may be packed towers or plate towers.

[0026] In the method of the present invention, the C 8 The ethylbenzene content in the aromatic hydrocarbon mixture is preferably 10 to 85% by mass, more preferably 15 to 60% by mass.

[0027] In adsorption distillation, relative volatility is used to measure the separation effect of the solvent. Relative volatility (α) refers to the ratio of the volatility of the volatile component i to the volatility of the non-volatile component j in the separated solution, which can reflect the difficulty of separating the two components during the distillation process. The relative volatility of the two components i and j to be separated when they reach gas-liquid equilibrium is calculated using formula (1):

[0028]

[0029] In formula (1), x is the liquid phase mole fraction of the component at equilibrium, and y is the gas phase mole fraction of the component at equilibrium. When α is 1, the volatility of the two components is equal, indicating that the two components cannot be separated by adsorption distillation. When α is greater than 1, and the larger the α value, the easier it is to separate the two components by adsorption distillation.

[0030] The present invention is further described below by means of the accompanying drawings.

[0031] Figure 1 In the process, C from pipeline 1 8 The aromatic mixture is introduced into the middle of the adsorption distillation tower 3, and the composite adsorbent is introduced into the upper part of the adsorption distillation tower through pipeline 2. 8 Aromatic hydrocarbons are adsorbed and distilled in the tower in countercurrent contact with the composite adsorbent. 8Xylene in the aromatics is adsorbed by the xylene adsorbent, and ethylbenzene is distilled to the top of the tower and discharged from the top pipeline 7, and ethylbenzene product is obtained after condensation. The composite adsorbent adsorbed with xylene is discharged from the bottom of the adsorption distillation tower, and enters the middle part of the distillation desorption tower 4 through pipeline 5. The xylene is desorbed from the composite adsorbent by distillation to achieve desorption and regeneration of the xylene adsorbent. The desorbed xylene is discharged from the top pipeline 8 of the distillation desorption tower, and xylene is obtained after condensation. The regenerated composite adsorbent is discharged from the bottom of the distillation desorption tower, and returns to the adsorption distillation tower through pipeline 6 and pipeline 2 for reuse. The xylene substantially does not contain ethylbenzene and can be used as an isomerization raw material to produce paraxylene.

[0032] The present invention is further described in detail below by examples, but the present invention is not limited thereto.

[0033] In the examples and comparative examples, the C 8 The method for determining the relative volatility of each aromatic component is as follows: the sample to be tested is added to an Agilent 7694 headspace injector, left for a certain period of time, and when gas-liquid equilibrium is reached, the gas phase and liquid phase composition in the injector are determined by an Agilent 7890 chromatographic analyzer, and the relative volatility of the component is calculated by formula (1).

[0034] Example 1

[0035] Ethylbenzene, p-xylene, o-xylene and m-xylene are mixed in equal proportions to form C 8 Aromatic hydrocarbon mixture is used as raw oil, and the ethylbenzene content in the raw oil is 25% by mass. NaY molecular sieve powder with a crystal size of 0.2 to 1 micron is used as xylene adsorbent, and n-tetradecane is used as carrier liquid. The xylene adsorbent and the carrier liquid are mixed to prepare a composite adsorbent, and the xylene adsorbent content in the composite adsorbent is 20% by mass, and the carrier liquid content is 80% by mass.

[0036] The composite adsorbent and feedstock oil were added into a headspace sampler, wherein the mass ratio of carrier liquid / xylene adsorbent / feedstock oil was 8:2:1, and the mass ratio of composite adsorbent to feedstock oil was 10:1. They were placed at 80°C for 45 minutes to achieve gas-liquid equilibrium, and the gas and liquid phases were taken for composition analysis. The relative volatility of ethylbenzene to each xylene isomer in the feedstock oil after adding the composite adsorbent is shown in Table 1.

[0037] Example 2

[0038] The relative volatility of ethylbenzene to xylene isomers in the feed oil after adding the composite adsorbent was determined according to the method of Example 1, except that the mass ratio of carrier liquid / xylene adsorbent / feed oil was 8:3:1, and the mass ratio of composite adsorbent to feed oil was 11:1. The results are shown in Table 1.

[0039] Example 3

[0040] The relative volatility of ethylbenzene to xylene isomers in the feed oil after adding the composite adsorbent was determined according to the method of Example 1, except that the mass ratio of carrier liquid / xylene adsorbent / feed oil was 8:4:1, and the mass ratio of composite adsorbent to feed oil was 12:1. The results are shown in Table 1.

[0041] Example 4

[0042] The relative volatility of ethylbenzene to xylene isomers in the feed oil after adding the composite adsorbent was determined according to the method of Example 1, except that the mass ratio of carrier liquid / xylene adsorbent / feed oil was 13:2:1, and the mass ratio of composite adsorbent to feed oil was 15:1. The results are shown in Table 1.

[0043] Example 5

[0044] The relative volatility of ethylbenzene to xylene isomers in the feed oil after adding the composite adsorbent was determined according to the method of Example 1, except that the mass ratio of carrier liquid / xylene adsorbent / feed oil was 18:2:1, and the mass ratio of composite adsorbent to feed oil was 20:1. The results are shown in Table 1.

[0045] Example 6

[0046] The relative volatility of ethylbenzene to xylene isomers in the feed oil after adding the composite adsorbent was determined according to the method of Example 1, except that the carrier liquid used was n-undecane. The results are shown in Table 1.

[0047] Example 7

[0048] The relative volatility of ethylbenzene to xylene isomers in the feed oil after adding the composite adsorbent was determined according to the method of Example 1, except that the carrier liquid used was n-hexadecane. The results are shown in Table 1.

[0049] Example 8

[0050] The relative volatility of ethylbenzene to xylene isomers in the feed oil after adding the composite adsorbent was determined according to the method of Example 1, except that the carrier liquid used was diphenylmethane. The results are shown in Table 1.

[0051] Examples 9-10

[0052] The relative volatility of ethylbenzene to xylene isomers in the feed oil after adding the composite adsorbent was determined according to the method of Example 1, except that the carrier liquids used were butyldecalin and decalin, respectively. The results are shown in Table 1.

[0053] Example 11

[0054] The relative volatility of ethylbenzene to xylene isomers in the feed oil after adding the composite adsorbent was determined according to the method of Example 1, except that the mass ratio of ethylbenzene: p-xylene: o-xylene: m-xylene in the feed oil used was 1:2:1:1, and the ethylbenzene content in the feed oil was 20% by mass. The results are shown in Table 1.

[0055] Example 12

[0056] The relative volatility of ethylbenzene to xylene isomers in the feed oil after adding the composite adsorbent was determined according to the method of Example 1, except that the mass ratio of ethylbenzene: p-xylene: o-xylene: m-xylene in the feed oil used was 2:1:1:1, and the ethylbenzene content in the feed oil was 40% by mass. The results are shown in Table 1.

[0057] Table 1

[0058]

[0059] Comparative Example 1

[0060] The relative volatility of ethylbenzene to xylene isomers in the crude oil was determined according to the method of Example 1, except that no composite adsorbent was used. The results are shown in Table 1.

[0061] Comparative Example 2

[0062] The relative volatility of ethylbenzene to xylene isomers in the feed oil was determined according to the method of Example 1, except that no composite adsorbent was used. The mass ratio of ethylbenzene: p-xylene: o-xylene: m-xylene in the feed oil used was 1:2:1:1. The results are shown in Table 1.

[0063] Comparative Example 3

[0064] The relative volatility of ethylbenzene to xylene isomers in the feed oil was determined according to the method of Example 1, except that no composite adsorbent was used. The mass ratio of ethylbenzene: p-xylene: o-xylene: m-xylene in the feed oil used was 2:1:1:1. The results are shown in Table 1.

[0065] Comparative Example 4

[0066] The relative volatility of ethylbenzene to xylene isomers in the feed oil was determined according to the method of Example 1, except that only n-tetradecane was added to the feed oil, and the mass ratio of n-tetradecane to feed oil was 8:1. The results are shown in Table 1.

[0067] As shown in Table 1, the use of the composite adsorbent of the present invention can significantly increase the relative volatility of ethylbenzene to each isomer of xylene compared with the method without using the composite adsorbent or using only the carrier liquid, indicating that the use of the composite adsorbent of the present invention can separate C 8 Ethylbenzene among aromatic hydrocarbons.

[0068] Example 13

[0069] Using the composite adsorbent and crude oil described in Example 1, Figure 1 The process shown separates C 8 For ethylbenzene and xylene in aromatics, the operating conditions of the adsorption distillation tower and the distillation desorption tower and the purity of the obtained products are shown in Table 2.

[0070] Comparative Example 5

[0071] A common distillation tower was used to separate ethylbenzene and xylene from the feed oil described in Example 1. The operating conditions of the distillation tower and the purity of the obtained products are shown in Table 2.

[0072] Comparative Example 6

[0073] The extractive distillation method was used to separate C 8 Ethylbenzene in aromatics, C 8 Aromatic hydrocarbons are introduced into the middle of the extractive distillation tower, and the extractive solvent is introduced into the upper part of the tower. After extractive distillation, ethylbenzene is discharged from the top of the tower, and the rich solvent rich in xylene is discharged from the bottom of the tower and enters the solvent recovery tower. After distillation, xylene is discharged from the top of the tower, and the lean solvent is discharged from the bottom of the tower and returned to the extractive distillation tower. Using 1,2,4-trichlorobenzene as the extraction solvent, C 8 The aromatic hydrocarbon feedstock was prepared according to the method of Example 1. The operating conditions of the extractive distillation tower and the solvent recovery tower and the purity of the obtained product are shown in Table 2.

[0074] Table 2

[0075]

[0076] *Extraction solvent / raw oil mass ratio

[0077] Example 14

[0078] Using the composite adsorbent described in Example 1, the raw oil is reforming oil C 8 fraction, wherein the mass ratio of ethylbenzene: p-xylene: m-xylene: o-xylene is 18:19:39:24, according to Figure 1 The process shown is to separate the C 8 The operating conditions of the adsorption distillation tower and the distillation desorption tower as well as the purity of the obtained products of ethylbenzene and xylene in the fractions are shown in Table 3.

[0079] Comparative Example 7

[0080] A common distillation tower was used to separate ethylbenzene and xylene from the feed oil described in Example 14. The operating conditions of the distillation tower and the purity of the obtained products are shown in Table 3.

[0081] Table 3

[0082]

[0083] Example 15

[0084] Using the composite adsorbent described in Example 1, the raw oil is ethylene cracking gasoline C 8 fraction, wherein the mass ratio of ethylbenzene: p-xylene: m-xylene: o-xylene is 52:10:23:15, according to Figure 1 The process shown is to separate the C 8 The operating conditions of the adsorption distillation tower and the distillation desorption tower as well as the purity of the obtained products of ethylbenzene and xylene in the fractions are shown in Table 4.

[0085] Comparative Example 8

[0086] A common distillation tower was used to separate ethylbenzene and xylene from the feed oil described in Example 15. The operating conditions of the distillation tower and the purity of the obtained products are shown in Table 4.

[0087] Table 4

[0088]

[0089] It can be seen from Tables 2 to 4 that the adsorption distillation of the present invention from C 8 Separating ethylbenzene from an aromatic mixture can significantly reduce energy consumption and improve the separation efficiency of ethylbenzene and xylene compared to using a common distillation tower or extractive distillation to separate ethylbenzene.

Claims

1. A method for separating ethylbenzene by adsorption distillation, comprising introducing a C8 aromatic hydrocarbon mixture into the middle of an adsorption distillation tower (3), introducing a composite adsorbent into the upper part of the adsorption distillation tower (3), and after adsorption distillation, ethylbenzene is discharged from the top of the adsorption distillation tower, and the composite adsorbent enriched with xylene is discharged from the bottom of the tower, and enters the middle of a distillation and desorption tower (4), after distillation and desorption, mixed xylene is discharged from the top of the tower, and the regenerated composite adsorbent is obtained at the bottom of the tower and returned to the upper part of the adsorption distillation tower for reuse, wherein the composite adsorbent is composed of a xylene adsorbent and a carrier liquid, wherein the xylene adsorbent is a NaY molecular sieve, and the crystal particle size of the molecular sieve is 0.1-2 μm, and the carrier liquid is selected from C 10 ~C 24 n-alkanes, C 13 ~C 16 The invention discloses a method for preparing a xylene adsorbent comprising: preparing a xylene adsorbent comprising: preparing a xylene adsorbent comprising: a diphenylalkane, decalin, or a C2-C6 alkyl-substituted decalin; a mass ratio of the carrier liquid to the xylene adsorbent is 2-4; and a reflux ratio is 1-8.

2. The method according to claim 1, characterized in that The top pressure of the adsorption distillation tower is 0.01~0.2MPa, the theoretical plate number is 30~100, the inlet temperature of the composite adsorbent is 90~130℃, and the bottom temperature is 140~250℃.

3. The method according to claim 2, characterized in that The mass ratio of the xylene adsorbent to the C8 aromatic hydrocarbon mixture in the composite adsorbent entering the adsorption distillation tower is 1.5-6.

4. The method according to claim 1, characterized in that The top pressure of the distillation desorption tower is 0.01~0.15MPa, the theoretical plate number is 20~50, and the bottom temperature is 160~280℃.

5. The method according to claim 4, characterized in that The reflux ratio of the distillation desorption tower is 0.3~3.

6. The method according to claim 1, characterized in that The ethylbenzene content in the C8 aromatic hydrocarbon mixture is 10-85% by mass.

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