A complex solvent and method for separating styrene from a hydrocarbon mixture

Abstract

A composite solvent for separating styrene from a hydrocarbon mixture, comprising 35-80 mass% of a main solvent and 20-65 mass% of a cosolvent, wherein the main solvent is sulfolane, and the cosolvent is 1,3-dimethyl-2-imidazolidinone and / or gamma-butyrolactone. The composite solvent can be used as an extractant to separate styrene from a hydrocarbon mixture by extractive distillation, which can effectively reduce the operating temperature of the extractive distillation column, reduce the polymerization of styrene, reduce energy consumption, and obtain high yield and purity of styrene.

Description

TECHNICAL FIELD

[0001] The present application relates to a complex solvent and method for separating styrene from a hydrocarbon mixture, in particular, a complex solvent and method for extractive distillation recovery of styrene from a hydrocarbon mixture. BACKGROUND

[0002] Extractive distillation is a well-known technique for separating components of a mixture by adding a third component (called an extractive agent or solvent) to the feed liquid to change the relative volatility of the components. The extractive agent has a much higher boiling point than the components of the feed liquid and does not form azeotropes with the components. Extractive distillation is often used to separate mixtures in which the components have very similar boiling points (volatilities). Normal distillation cannot separate such mixtures, but with the use of a solvent, the relative volatilities can be changed to allow separation.

[0003] Styrene monomer is an important basic organic chemical raw material, and also has a wide range of applications in coatings, pesticides, pharmaceuticals and other aspects. According to statistics, the cracking gasoline produced by ethylene cracking device contains 3-5% of styrene. A million tons of ethylene device, the cracking gasoline contains about 20-30 thousand tons of styrene per year. In the existing process of treating cracking gasoline, this part of the styrene is hydrogenated into ethylbenzene and exists in xylene. This hydrocarbon mixture rich in ethylbenzene is not ideal for feeding to the downstream p-xylene device as a raw material. If super distillation is used to separate ethylbenzene and then dehydrogenated to styrene, the process is long, energy consumption is high, and it is also unreasonable.

[0004] The more difficult to separate from styrene in cracking gasoline is o-xylene, and the difference between their boiling points is only 0.8°C, and the relative volatility is only 1.04. Ordinary distillation requires thousands of theoretical plates. The use of extractive distillation technology to recover styrene from cracking gasoline is a mature technology. The key to the extractive distillation process is the performance of the solvent, mainly including selectivity, boiling point and control of the operating temperature of the extractive distillation process, which has a crucial influence on the technical and economic indicators of the separation process, and also relates to whether the device can be operated stably for a long period. The excellent selectivity of the solvent can greatly change the relative volatility of styrene / o-xylene, which determines whether high-purity styrene can be obtained; controlling a lower operating temperature can reduce some factors that are not conducive to the long-term operation of the device caused by the polymerization of styrene and increase the yield of styrene product.

[0005] USP3763015 discloses a method for separating styrene from steam cracking gasoline using a polymerization inhibitor and extractive distillation, which is carried out in the presence of a polar solvent and a nitrogen-containing polymerization inhibitor, then recovering styrene from the solvent, and then reacting the recovered styrene with sufficient nitric acid to remove impurities in the styrene, and then distilling again to remove impurities to obtain substantially colorless pure styrene. The polar solvent is selected from dimethylacetamide, dimethylformamide, N-methylpyrrolidone and dimethyl sulfoxide, and the polymerization inhibitor is hydroquinone or p-tert-butyl hydroquinone. However, the preferred dimethylacetamide solvent has a low boiling point (165°C) and a small difference between the boiling points of o-xylene and styrene, resulting in high energy consumption.

[0006] CN1225081A discloses a method for separating styrene from cracking gasoline by extractive distillation, in which the solvent for extractive distillation is divided into two parts, the first part of the solvent is mainly composed of propylene carbonate, sulfolane, methyl carbitol, 1-methyl-2-pyrrolidone or a mixture thereof, but not water, and the second part of the solvent is composed of water. The first part of the solvent is introduced from the upper part of the extractive distillation column, and the second part of the solvent is introduced from the bottom of the extractive distillation column.

[0007] CN1962013A discloses a solvent for extractive distillation for recovering styrene from a steam cracking hydrocarbon mixture, which comprises 15-60% by mass of a sulfone compound and 40-45% by mass of a nitrogen-containing compound. The sulfone compound is selected from dimethyl sulfoxide or sulfolane, and the nitrogen-containing compound is selected from at least one of malononitrile, dimethylacetamide, N-methyl-2-pyrrolidone, 2-pyrrolidone, ethylpiperazine or N-formylmorpholine. The solvent can make the pH value of the solvent about 7, and improve the relative volatility of o-xylene to styrene. When used for recovering styrene in the C8 fraction of cracking gasoline, the solvent has the advantages of convenient separation and inhibition of styrene polymerization.

[0008] CN101468938A discloses a composite solvent for extractive distillation for separating styrene, which comprises 62-90% by mass of a main solvent and 10-38% by mass of a cosolvent. The main solvent is selected from a sulfone compound, a pyrrolidone compound, a glycol compound or a mixture of any two or three thereof, and the cosolvent is selected from a C9-C12 aromatic compound, an amide containing 2-6 carbon atoms or a mixture thereof.

[0009] CN103360200A discloses a composite solvent for extractive distillation for recovering styrene from a hydrocarbon mixture, which comprises 80-99% by mass of a main solvent, 0.01-19% by mass of a cosolvent and 0.1-2.0% by mass of water. The main solvent is a sulfone compound, and the cosolvent is methoxyphenol. The composite solvent is used in combination with a polymerization inhibitor, which can reduce the amount of the polymerization inhibitor and the polymerization rate of styrene.

[0010] CN102452891A discloses a method for separating styrene from a hydrocarbon mixture by extractive distillation, which comprises introducing the hydrocarbon mixture from the middle of an extractive distillation column, introducing a solvent from the upper part of the extractive distillation column, and adding pure styrene at the bottom of the extractive distillation column. After extractive distillation, the raffinate is discharged from the top of the extractive distillation column, and the solvent rich in styrene is discharged from the bottom of the extractive distillation column and introduced into a solvent recovery column. The styrene is discharged from the top of the recovery column, and the solvent poor in styrene is discharged from the bottom of the recovery column and recycled to the upper part of the extractive distillation column for reuse. The solvent is one or more of sulfolane, diethylene glycol, triethylene glycol, tetraethylene glycol, N,N-dimethylacetamide and N-formylmorpholine. The method can effectively reduce the temperature at the bottom of the extractive distillation column, significantly reduce the polymerization of styrene, and prolong the operation period of the device. However, the addition of pure styrene at the bottom of the extractive distillation column reduces the processing capacity and increases the energy consumption.

[0011] The above prior art all uses composite solvents to try to maintain the high selectivity of the solvent system, but the effect is generally poor in actual tests. For example, sulfolane is used as the main solvent, and dimethylacetamide, N-methyl-2-pyrrolidone or N-formylmorpholine is used as the cosolvent. Compared with pure sulfolane, the selectivity is decreased. Some single solvents such as tetraethylene glycol have a higher boiling point, resulting in a higher operating temperature. It is well known that the temperature has a great influence on the polymerization rate of styrene. When the temperature exceeds 130℃, the polymerization of styrene is significantly accelerated, and when the temperature exceeds 140℃, the addition of a polymerization inhibitor cannot effectively reduce the polymerization. In the extractive distillation process, the content of styrene at the bottom of the extractive distillation column is high, and the operating temperature is high, so the polymerization is most likely to occur. Therefore, selecting a suitable solvent to reduce the bubble point temperature of the low styrene solvent system in the extractive distillation column is the most fundamental means to solve the polymerization of styrene. SUMMARY

[0012] The purpose of the present application is to provide a composite solvent for recovering styrene from a hydrocarbon mixture and a method thereof. The composite solvent is used as an extractant to separate styrene from a hydrocarbon mixture by extractive distillation, which can effectively reduce the operating temperature of the extractive distillation column, reduce the polymerization of styrene, reduce the energy consumption, and has a higher yield and purity of styrene.

[0013] The composite solvent for separating styrene from a hydrocarbon mixture provided by the present application comprises 35-80% by mass of a main solvent and 20-65% by mass of a cosolvent. The main solvent is sulfolane, and the cosolvent is 1,3-dimethyl-2-imidazolidinone and / or γ-butyrolactone.

[0014] The application uses sulfolane as the main solvent, 1,3-dimethyl-2-imidazolidinone and / or gamma-butyrolactone as the auxiliary solvent to extract and rectify styrene from a hydrocarbon mixture, which can effectively reduce the bubble point temperature of the system, thereby reducing the operating temperature at the bottom of the extractive rectification tower in the extractive rectification process, reducing the polymerization of styrene, reducing energy consumption, and the yield and purity of styrene are relatively high. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 The process flow diagram of the method for separating styrene from a hydrocarbon mixture according to the application. DETAILED DESCRIPTION

[0016] The polymerization test results of the 15% styrene content sulfolane solution show that when the temperature is 130℃, the styrene loss rate is about 1 mass%, when the temperature exceeds 140℃, the styrene loss rate reaches more than 3 mass%, and the styrene loss rate increases rapidly with the increase of the polymerization test temperature, so lower temperature can reduce the loss of styrene due to polymerization, improve the yield of styrene, and is beneficial to long-period operation of the device. The inventors of the application found that compared with the mixture of styrene and pure sulfolane, the bubble point temperature of the mixture of styrene and sulfolane as the main solvent, 1,3-dimethyl-2-imidazolidinone and / or gamma-butyrolactone as the auxiliary solvent is lower, that is, when using the composite solvent of sulfolane as the main solvent and 1,3-dimethyl-2-imidazolidinone and / or gamma-butyrolactone as the auxiliary solvent to extract and rectify styrene from a hydrocarbon mixture, the operating temperature at the bottom of the extractive rectification tower can be reduced, the polymerization of styrene can be significantly reduced, thereby improving the yield of styrene, and reducing the energy consumption of the device. The inventors of the application also found that in the system of the composite solvent of styrene, o-xylene and sulfolane as the main solvent, 1,3-dimethyl-2-imidazolidinone and / or gamma-butyrolactone as the auxiliary solvent as the extractant, the relative volatility of styrene to o-xylene is close to the system of sulfolane as the extractant, which indicates that the separation effect of the composite solvent as the extractant on styrene and o-xylene is not significantly reduced compared with sulfolane as the extractant.

[0017] The composite solvent for separating styrene from a hydrocarbon mixture comprises 35-80% by mass of a main solvent and 20-65% by mass of a cosolvent, wherein the main solvent is sulfolane, and the cosolvent is 1,3-dimethyl-2-imidazolidinone and / or gamma-butyrolactone. Preferably, when the cosolvent is 1,3-dimethyl-2-imidazolidinone, the composite solvent comprises 55-80% by mass of the main solvent and 20-45% by mass of the cosolvent; when the cosolvent is gamma-butyrolactone, the composite solvent comprises 60-80% by mass of the main solvent and 20-40% by mass of the cosolvent; and when the cosolvent is 1,3-dimethyl-2-imidazolidinone and gamma-butyrolactone, the mass ratio of 1,3-dimethyl-2-imidazolidinone to gamma-butyrolactone is 0.8-2:1.

[0018] The hydrocarbon mixture is preferably a C8 fraction of pyrolysis gasoline, which contains 5-75% by mass of styrene and 25-95% by mass of C8 aromatic hydrocarbons and non-aromatic hydrocarbons.

[0019] The method for separating styrene from a hydrocarbon mixture comprises introducing a hydrocarbon mixture containing styrene into the middle of an extractive distillation column, introducing the composite solvent into the top of the extractive distillation column, performing extractive distillation, discharging the raffinate from the top of the extractive distillation column, discharging the styrene-containing rich solvent from the bottom of the extractive distillation column into a solvent recovery column, performing distillation separation in the solvent recovery column, discharging styrene from the top of the solvent recovery column, and discharging the composite solvent from the bottom of the solvent recovery column and returning it to the extractive distillation column for recycling.

[0020] The extractive distillation column has 30-70 theoretical plates, a reflux ratio of 1-4 at the top, a bottom temperature of 120-135°C, and a top pressure of 8-20 kPa.

[0021] The solvent recovery column has 20-50 theoretical plates, a reflux ratio of 1-4 at the top, a bottom temperature of 125-140°C, and a top pressure of 8-20 kPa.

[0022] The method of the present application is further described below with reference to the accompanying drawings. Figure 1In the process, the hydrocarbon mixture exchanges heat with the complex solvent and then enters the middle of the extractive distillation column 101 through pipeline 1, the complex solvent enters the upper part of the column 101 through pipeline 2, and after extractive distillation, the raffinate is discharged from the top of the column 101 through pipeline 3, and after condensation and cooling, it enters the reflux tank 102, part of the raffinate returns to the column 101 through pipeline 4, and the rest is discharged from the device through pipeline 5; the rich solvent containing styrene is discharged from the bottom of the column 101, enters the upper part of the solvent recovery column 103 through pipeline 6, and the stripping water is injected into the lower part of the recovery column 103 through pipeline 11, and the styrene is discharged from the top of the column 103 through pipeline 7, and after condensation and cooling, it enters the reflux tank 104, part of the styrene returns to the column 103 through pipeline 8, and the rest is discharged from the device through pipeline 9, and the lean solvent at the bottom of the column 103 returns to the column 101 through pipeline 10.

[0023] The application will be further described below by examples, but the application is not limited thereto.

[0024] In the examples, the relative volatility of o-xylene and styrene is measured by headspace gas chromatography. The sample to be measured is added to an Agilent 7694 headspace sampler, and when the gas-liquid equilibrium is reached, the composition of the gas phase and the liquid phase in the sampler is measured by 7890 chromatographic analysis, and the relative volatility of the components is calculated by formula (1).

[0025] α ij =(yi / y j ) / (x i / x j ) Formula (1)

[0026] In formula (1), α is the relative volatility of styrene relative to o-xylene when the gas-liquid equilibrium is reached, y is the gas phase composition, x is the liquid phase composition, i represents the light component, i.e. styrene, and j represents the heavy component, i.e. o-xylene.

[0027] Example 1

[0028] A hydrocarbon mixture raw material A containing 50% by mass of styrene and 50% by mass of o-xylene is mixed, and a complex solvent composed of 50% by mass of main solvent sulfolane and 50% by mass of cosolvent 1,3-dimethyl-2-imidazolidinone is prepared. The complex solvent and the hydrocarbon mixture raw material are mixed at a mass ratio of 4:1 (i.e. solvent ratio) to obtain a mixed solution, and the gas phase and liquid phase compositions at the gas-liquid equilibrium at 80°C are measured. The relative volatility of styrene relative to o-xylene is calculated according to formula (1), and the results are shown in Table 1. The bubble point temperature of the mixed solution of the complex solvent containing 10% styrene at 20kPa is measured, and the results are shown in Table 1.

[0029] Example 2

[0030] Example 1 was repeated with the exception that the complex solvent consisted of 75 mass% of the main solvent sulfolane and 25 mass% of the cosolvent 1,3-dimethyl-2-imidazolidinone. The results are shown in Table 1.

[0031] Example 3

[0032] Example 1 was repeated with the exception that the complex solvent consisted of 75 mass% of the main solvent sulfolane and 25 mass% of the cosolvent 1,3-dimethyl-2-imidazolidinone. The results are shown in Table 1.

[0033] Example 4

[0034] Example 1 was repeated with the exception that the complex solvent consisted of 50 mass% of the main solvent sulfolane and 50 mass% of the cosolvents 1,3-dimethyl-2-imidazolidinone and γ-butyrolactone in a mass ratio of 1 : 1. The results are shown in Table 1.

[0035] Example 5

[0036] Example 1 was repeated with the exception that the complex solvent consisted of 50 mass% of the main solvent sulfolane and 50 mass% of the cosolvent γ-butyrolactone. The results are shown in Table 1.

[0037] Comparative Example 1

[0038] Example 1 was repeated with the exception that the complex solvent consisted of 50 mass% of the main solvent sulfolane and 50 mass% of the cosolvent γ-butyrolactone. The results are shown in Table 1.

[0039] Comparative Example 2

[0040] Example 1 was repeated with the exception that the complex solvent consisted of 50 mass% of the main solvent sulfolane and 50 mass% of the cosolvent triethylene glycol monomethyl ether. The results are shown in Table 1.

[0041] Comparative Example 3

[0042] The relative volatility of styrene to o-xylene, the bubble point temperature of a mixture of the complex solvent containing 10% styrene at 20 kPa, of raw material A in a complex solvent were tested according to the method of Example 1, except that the complex solvent consisted of 50 mass% of the main solvent sulfolane and 50 mass% of the cosolvent diethylene glycol monomethyl ether, and the results are shown in Table 1.

[0043] Comparative Example 4

[0044] The relative volatility of styrene to o-xylene, the bubble point temperature of a mixture of the complex solvent containing 10% styrene at 20 kPa, of raw material A in a complex solvent were tested according to the method of Example 1, except that the complex solvent consisted of 75 mass% of the main solvent sulfolane and 25 mass% of the cosolvent diethylene glycol monomethyl ether, and the results are shown in Table 1.

[0045] Comparative Example 5

[0046] The relative volatility of styrene to o-xylene, the bubble point temperature of a mixture of the complex solvent containing 10% styrene at 20 kPa, of raw material A in a complex solvent were tested according to the method of Example 1, except that the complex solvent consisted of 50 mass% of the main solvent sulfolane and 50 mass% of the cosolvent diethylene glycol monoethyl ether, and the results are shown in Table 1.

[0047] Comparative Example 6

[0048] The relative volatility of styrene to o-xylene, the bubble point temperature of a mixture of the complex solvent containing 10% styrene at 20 kPa, of raw material A in a complex solvent were tested according to the method of Example 1, except that the complex solvent consisted of 50 mass% of the main solvent sulfolane and 50 mass% of the cosolvent N-methylpyrrolidone, and the results are shown in Table 1.

[0049] Comparative Example 7

[0050] The relative volatility of styrene to o-xylene, the bubble point temperature of a mixture of the complex solvent containing 10% styrene at 20 kPa, of raw material A in a complex solvent were tested according to the method of Example 1, except that the complex solvent consisted of 75 mass% of the main solvent sulfolane and 25 mass% of the cosolvent diethylene glycol, and the results are shown in Table 1.

[0051] Comparative Example 8

[0052] The relative volatility of styrene to o-xylene, the bubble point temperature of a mixture of the complex solvent containing 10% styrene at 20 kPa, of raw material A in a complex solvent were tested according to the method of Example 1, except that the complex solvent consisted of 75 mass% of the main solvent sulfolane and 25 mass% of the cosolvent p-diethylbenzene, and the results are shown in Table 1.

[0053] Table 1

[0054]

[0055]

[0056] From Table 1, it can be seen that the composite solvents of Examples 1-5 of the present application have higher relative volatility of styrene to o-xylene, i.e. higher selectivity of styrene, and lower bubble point temperature of the mixture of styrene and composite solvent, compared with the comparative example.

[0057] Example 6

[0058] This example separates styrene from a hydrocarbon mixture according to the process of Figure 1 , with the raw material 1 having a styrene content of 35 mass%, C8aromatics 63 mass%, and non-aromatics content of 2 mass%, and the specific composition shown in Table 2. The composite solvent comprises 50 mass% main solvent sulfolane and 50 mass% 1,3-dimethyl-2-imidazolidinone, and the extractive distillation column bottom temperature is 131°C, the yield of styrene is 99%, and the purity of styrene reaches 99.8%, with the main operating conditions shown in Table 3 and the results shown in Table 4.

[0059] Example 7

[0060] This example separates styrene from a hydrocarbon mixture according to the process of Figure 1 , with the raw material 1 having a styrene content of 35 mass%, C8aromatics 63 mass%, and non-aromatics content of 2 mass%, and the specific composition shown in Table 2. The composite solvent comprises 65 mass% main solvent sulfolane and 35 mass% cosolvent 1,3-dimethyl-2-imidazolidinone, and the extractive distillation column bottom temperature is 132°C, the yield of styrene is 99%, and the purity of styrene reaches 99.8%, with the main operating conditions shown in Table 3 and the results shown in Table 4.

[0061] Example 8

[0062] This example separates styrene from a hydrocarbon mixture according to the process of Figure 1 , with the raw material 2 having a styrene content of 53 mass%, C8aromatics 45 mass%, and non-aromatics content of 2 mass%, and the specific composition shown in Table 2. The composite solvent comprises 75 mass% main solvent sulfolane and 25 mass% cosolvent γ-butyrolactone, and the extractive distillation column bottom temperature is 132°C, the yield of styrene is 98.5%, and the purity of styrene reaches 99.8%, with the main operating conditions shown in Table 3 and the results shown in Table 4.

[0063] Comparative Example 9

[0064] This example separates styrene from a hydrocarbon mixture according to the process of Figure 1The process of separating styrene from a hydrocarbon mixture according to the process of the present application, the raw material 1 styrene content of 35 mass%, C8aromatic hydrocarbon 63 mass%, non-aromatic hydrocarbon content of 2 mass%, see Table 2 for specific composition. The solvent is sulfolane, the extractive distillation column bottom temperature is 140°C, the yield of styrene is 96%, the purity of styrene reaches 99.8%, the styrene polymerization is intensified, and the long-period operation cannot be carried out, see Table 3 for main operating conditions, and see Table 4 for results.

[0065] Comparative Example 10

[0066] The present example is according to the process of the present application Figure 1 The process of separating styrene from a hydrocarbon mixture according to the process of the present application, the raw material 1 styrene content of 35 mass%, C8aromatic hydrocarbon 63 mass%, non-aromatic hydrocarbon content of 2 mass%, see Table 2 for specific composition. The solvent is sulfolane, the extractive distillation column bottom temperature is 140°C, the yield of styrene is 96%, the purity of styrene reaches 99.8%, the styrene polymerization is intensified, and the long-period operation cannot be carried out, see Table 3 for main operating conditions, and see Table 4 for results.

[0067] Comparative Example 10 and Example 6, the purity and yield of styrene change little, but the energy consumption increases.

[0068] Table 2

[0069]

[0070] Table 3

[0071]

[0072] Table 4

[0073]

Claims

1. A method for separating styrene from a hydrocarbon mixture, comprising introducing a styrene-containing hydrocarbon mixture from the middle of an extractive distillation column, introducing a complex solvent from the top of the extractive distillation column, performing extractive distillation, discharging the raffinate from the top of the extractive distillation column, discharging the styrene-rich solvent from the bottom of the extractive distillation column, and entering a solvent recovery column, whereby, after distillation separation, styrene is discharged from the top of the solvent recovery column, and the complex solvent is discharged from the bottom of the solvent recovery column and returned to the extractive distillation column for recycling, wherein the complex solvent comprises 35-80% by mass of a main solvent and 20-65% by mass of a co-solvent, wherein the main solvent is sulfolane and the co-solvent is 1,3-dimethyl-2-imidazolinone and / or γ-butyrolactone.

2. The method according to claim 1, characterized in that, The composite solvent comprises 55-80% by mass of a main solvent and 20-45% by mass of a co-solvent, wherein the co-solvent is 1,3-dimethyl-2-imidazolinone.

3. The method according to claim 1, characterized in that, The composite solvent comprises 60-80% by mass of a main solvent and 20-40% by mass of a co-solvent, wherein the co-solvent is γ-butyrolactone.

4. The method according to claim 1, characterized in that, When the cosolvent is 1,3-dimethyl-2-imidazolinone and γ-butyrolactone, the mass ratio of 1,3-dimethyl-2-imidazolinone to γ-butyrolactone is 0.8~2:

1.

5. The method according to claim 1, characterized in that, The mass ratio of the composite solvent to the styrene-containing hydrocarbon mixture is 3 to 6.

6. The method according to claim 1, characterized in that, The extractive distillation column has a theoretical plate number of 30-70, a top reflux ratio of 1-4, a bottom temperature of 120-135℃, and a top pressure of 8-20 kPa.

7. The method according to claim 1, characterized in that, The solvent recovery tower has a theoretical plate number of 20-50, a top reflux ratio of 1-4, a bottom temperature of 125-140℃, and a top pressure of 8-20 kPa.

8. The method according to claim 1, characterized in that, The styrene content in the hydrocarbon mixture containing styrene is 5-75% by mass.

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