CN108997077B - Composite solvent and method for extracting and rectifying aromatic hydrocarbons from hydrocarbon mixture - Google Patents

Abstract

式(Ⅰ)中，R₁和R₂分别选自C₁～C₄的烷基、环烷基或芳基。所述的复合溶剂性质稳定，无腐蚀性，对芳烃具有较高的选择性，并且在使用过程中易于调控，可降低萃取精馏操作的物耗和能耗。A composite solvent for extracting, rectifying and separating aromatic hydrocarbons from a hydrocarbon mixture, comprising 40-80 mass % sulfolane and 20-60 mass % co-solvent, wherein the co-solvent is a sulfone derivative having the structure of formula (I) things,

In formula (I), R ₁ and R ₂ are independently selected from C ₁ -C ₄ alkyl, cycloalkyl or aryl. The composite solvent has stable properties, is non-corrosive, has high selectivity to aromatic hydrocarbons, is easy to control during use, and can reduce material consumption and energy consumption of extractive distillation operations.

Description

Composite solvent and method for extracting and rectifying aromatic hydrocarbons from hydrocarbon mixture

technical field

The invention relates to a composite solvent for separating aromatic hydrocarbons from petroleum fluids, specifically, a composite solvent for separating high-purity aromatic hydrocarbons from petroleum hydrocarbon raw materials by extractive rectification and an application method thereof.

Background technique

There are two main processes for the separation of aromatics from hydrocarbon mixtures such as catalytic reformed gasoline and hydrocracking gasoline. One is liquid-liquid extraction, which is essentially a combined process of liquid-liquid extraction and extractive rectification. It is suitable for separating aromatic hydrocarbons from wide-cut raw materials. The solvents used are glycol solvents, sulfolane, etc. The liquid-liquid extraction process can obtain high-purity benzene, toluene, xylene (BTX) products with high yields, but the content of aromatic hydrocarbons in the raw materials should not be too high, otherwise the extraction tower will not be easy to operate. The other is the Extractive Distillation (ED) process, which is a method of separating aromatic hydrocarbons from raw materials by utilizing the different effects of solvents on the relative volatility of each component of hydrocarbons. In contrast, the extractive distillation process has low energy consumption and simple process, and is more suitable for processing raw materials with high aromatic content and narrow fractions. The solvents used are generally glycols, sulfolane, N-methylpyrrolidone, N-formyl Morpholine, etc., the resulting product is benzene, or benzene and toluene.

The reason why benzene, toluene and xylene cannot be separated and purified by ED process is that it is difficult to balance the selectivity and solubility of the currently used solvents. In the C ₆ -C ₈ fraction of cracked hydrogenated gasoline, the aromatic hydrocarbon with the lowest boiling point was benzene (80.1°C), and the cycloalkane with the highest boiling point was ethylcyclohexane (131.8°C). In the ED tower, to realize that benzene exists in the rich solvent of the tower kettle, and ethyl cyclohexane is distilled to the top of the tower, the interaction between the solvent and benzene is required to be strong, and the non-aromatic substances such as p-ethyl cyclohexane are more exclusive. However, solvents with high selectivity tend to have poor solubility for non-aromatic hydrocarbons, and are prone to phase separation in the upper part of the tower, especially between the solvent feeding position and the raw material feeding position, which makes the ED tower difficult to operate.

The addition of at least one co-solvent to the highly selective solvent has the potential to increase the selectivity of the solvent and increase the overall efficiency of the primary solvent.

CN1430660A discloses a method for purifying aromatic hydrocarbons from petroleum liquid. The main solvent is sulfolane, and the cosolvent is selected from 3-methylsulfolane, N-methyl-2-pyrrolidone (NMP), acetophenone, isophorone and A kind of morpholine, the composite solvent is used in the system of separating benzene/n-heptane, and the effect is better than that of pure sulfolane.

CN104058916A discloses a kind of morpholine mixed solvent for extracting and rectifying aromatic hydrocarbons and its use method, the mixed solvent is N-formyl morpholine and N-acetylmorpholine, and the separation object is petroleum benzene C ₆ -C ₈ fraction , the obtained aromatic hydrocarbon product still contains a solvent with a concentration of more than 1 mg/L, and subsequent denitrification treatment is still required in practical application.

CN1272408C discloses a composite solvent for extracting and rectifying aromatic hydrocarbons. The main solvent is sulfone compounds, glycol compounds, N-formyl morpholine or N-methylpyrrolidone; the auxiliary solvent is hydrocarbons with two benzene rings compound. By using the composite solvent to separate and reform the C ₆ -C ₇ fractions of the depentanized oil, a high-purity benzene/toluene mixed aromatic product can be obtained with a high yield.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a composite solvent and method for extracting and rectifying aromatic hydrocarbons from hydrocarbon mixtures. It is easy to control and can reduce the material consumption and energy consumption of extractive distillation operation.

The composite solvent for extracting and rectifying aromatic hydrocarbons from hydrocarbon mixtures provided by the present invention comprises 40-80 mass % of sulfolane and 20-60 mass % of co-solvent, and the co-solvent is a sulfone having the structure of formula (I). derivative,

In formula (I), R ₁ and R ₂ are independently selected from C ₁ -C ₄ alkyl, cycloalkyl or aryl.

The method of the invention adds an appropriate amount of sulfone derivatives represented by formula (I) into the sulfolane solvent as a co-solvent, and can effectively reduce the solvent ratio when extracting and rectifying the aromatic hydrocarbons in the raw material containing naphthenes. Energy consumption is saved, and the separated product does not contain nitrogen, the sulfur content is less than 1mg/L, and no subsequent refining treatment is required.

Description of drawings

FIG. 1 is a schematic flow diagram of the present invention using a composite solvent for extractive distillation.

Detailed ways

The composite solvent provided by the invention includes a main solvent—sulfolane and a cosolvent—a sulfone derivative with two substituents. The main solvent determines the main properties of the composite solvent, and the cosolvent and the main solvent act synergistically to improve the selectivity of the solvent to aromatic hydrocarbons. , and increase the solubility of non-aromatic hydrocarbons and improve gas-liquid mass transfer performance. The composite solvent of the invention has high boiling point, stable properties, and good solubility for raw materials. On the basis of ensuring high selectivity, the overall efficiency of extractive distillation is better than that of a single solvent, which can improve the quality of aromatic hydrocarbons obtained by separation, and improve the Aromatic yield.

The composite solvent of the present invention preferably comprises 45-78 mass % of sulfolane and 22-55 mass % of cosolvent.

The co-solvent is a sulfone derivative with two substituents described in formula (I), wherein the substituents R ₁ and R ₂ may be the same or different, and are respectively selected from C ₁ -C ₄ alkanes radical, cycloalkyl or aryl. The cycloalkyl group is preferably a C ₄ -C ₆ cycloalkyl group, and the aryl group is preferably a phenyl group.

Preferably, R ₁ and R ₂ in the co-solvent are different, R ₁ and R ₂ are respectively selected from C ₁ -C ₄ alkyl groups, and the C ₁ -C ₄ alkyl groups may be methyl, Ethyl, propyl, isopropyl, butyl, isobutyl.

In the case where R ₁ and R ₂ in the co-solvent are different, R ₁ can also be selected from C ₁ -C ₄ alkyl groups, and R ₂ is selected from cyclohexyl or phenyl.

The auxiliary solvent of the present invention can be: methyl ethyl sulfone, methyl isopropyl sulfone, ethyl isopropyl sulfone, methyl cyclopentyl sulfone, methyl phenyl sulfone, ethyl phenyl sulfone, Diphenylsulfone.

The method for extracting and rectifying aromatic hydrocarbons from a hydrocarbon mixture provided by the present invention includes introducing the hydrocarbon mixture into the middle of the extractive rectification column, introducing the composite solvent of the present invention into the upper part of the extractive rectification column, and after extractive rectification, Non-aromatic hydrocarbons are discharged from the top of the tower, part of which is returned to the extractive rectification tower as a reflux at the top of the tower, and the other part is discharged from the system. The rich solvent rich in aromatic hydrocarbons is discharged from the bottom of the extractive rectification tower and enters the middle of the solvent recovery tower. The solvent is discharged from the bottom of the column and returned to the extractive distillation column for recycling.

In the above-mentioned method, the mass ratio of the composite solvent entering the extractive distillation column and the hydrocarbon mixture raw material, i.e. the solvent ratio is preferably 1-20, more preferably 3-10, the theoretical plate number of the extractive distillation column is 30-80, and the reflux ratio is 30-80. is 0.2-5, the temperature of the composite solvent entering the tower is preferably 70-90°C, the temperature at the bottom of the tower is preferably 120-150°C, and the pressure at the top of the tower is preferably 0.1-0.3MPa.

The number of theoretical plates of the solvent recovery column is preferably 5-30, the reflux ratio is preferably 0.5-2.0, the pressure at the top of the column is preferably 0.01-0.05MPa, and the temperature at the bottom of the column is preferably 155-190°C.

The hydrocarbon mixture described in the present invention is a C ₆ -C ₈ fraction of cracked hydrogenated gasoline, condensate, a C ₆ -C ₈ fraction of reformed oil or a C ₆ fraction of coal tar, wherein the aromatic content is preferably 20-88 quality%.

The composite solvent and the extractive distillation method provided by the invention are especially suitable for separating and recovering benzene, toluene and xylene from the C ₆ -C ₈ fraction of cracked hydrogenated gasoline.

In the present invention, the selectivity of a solvent to the two components to be separated is characterized by relative volatility (α), which is defined as:

α=(Y ₂ /X ₂ )/(Y ₁ /X ₁ ) (1)

In formula (1), X ₁ and X ₂ represent the mass fractions of component 1 and component 2 in the liquid phase, respectively, and Y ₁ and Y ₂ represent the mass fractions of component 1 and component 2 in the gas phase, respectively. The larger the value of α, the easier the extractive distillation process is, and the product with higher purity can be obtained with less distillation steps and less reflux.

The present invention will be further described below in conjunction with the accompanying drawings.

In FIG. 1 , the hydrocarbon mixture enters the heat exchanger 101 through line 1, and enters the middle of the extractive rectification column 102 after heat exchange with the lean solvent, and the composite solvent enters the extractive rectification column 102 from the upper part of the line 2. The two are in countercurrent contact for extractive rectification, the non-aromatic hydrocarbons are discharged from the top of the extractive rectification tower, enter the condenser 103 for condensation, a part is refluxed to the extractive rectification tower 102 by pipeline 4, and the rest are discharged from the pipeline 3 as non-aromatic products. The rich solvent rich in aromatic hydrocarbons is discharged from the bottom of the extractive rectification tower, and enters the solvent recovery tower 104 through pipeline 5. After distillation under reduced pressure, the aromatic hydrocarbons are discharged from the top of the tower, enter the condenser 105 for condensation, and a part is returned to the solvent by pipeline 6. Column 104 is recovered, and the rest is recovered via line 7 as an aromatic product. The lean solvent is discharged from the bottom of the solvent recovery tower, a small part of which is sent to the regeneration device through the pipeline 8, and the rest is returned to the extractive distillation column 102 through the pipeline 9 for recycling. The heating source at the bottom of the extractive rectification column and the solvent recovery column is the reboiler, that is, a part of the effluent at the bottom of the column is heated to the required temperature by the reboiler, and then sent to the bottom of the column.

The present invention is further illustrated by examples below, but the present invention is not limited thereto.

Example 1

In this example, the separation performance of aromatic hydrocarbons/non-aromatic hydrocarbons by a composite solvent with methyl ethyl sulfone as a co-solvent was investigated.

90 mass % of benzene and 10 mass % of ethylcyclohexane were mixed as raw materials, and added to the mixed solvent with different contents of methyl ethyl sulfone. The mass ratio of the composite solvent to the raw material, i.e., the solvent ratio, was 3.3.

The whole mixture was shaken and shaken, heated to 100° C., allowed to stand for 30 min, and its gas phase composition was analyzed by gas chromatography, and the relative volatility α of ethylcyclohexane to benzene was calculated by formula (1), where ethylcyclohexane was Component 2, benzene is the component 1, and the results are shown in Table 1.

Table 1

It can be seen from Table 1 that the relative volatility of ethylcyclohexane to benzene is only 0.14 when no solvent is added, which is far less than 1. This is because the boiling point of ethylcyclohexane is 131.8 °C, which is much higher than that of benzene. The relative volatility of pure sulfolane can be increased to 1.426 when the solvent ratio is 3.3, and the two can be separated by extractive distillation. The relative volatility of the composite solvent containing 10% by mass of methyl ethyl sulfone is slightly lower than that of sulfolane, but with the increase of the content of methyl ethyl sulfone in the composite solvent, the relative volatility increases, up to 1.565, which is about 10% higher than that of pure sulfolane .

Example 2

This example investigates the separation performance of a complex solvent with methyl isopropyl sulfone as a co-solvent for aromatics/non-aromatics.

The relative volatility of the composite solvent was measured according to the method of Example 1, except that the co-solvent in the composite solvent was methyl isopropyl sulfone. The relative volatility α of ethylcyclohexane to benzene of each solvent calculated by formula (1) is shown in Table 2.

Table 2

It can be seen from Table 2 that adding methyl isopropyl sulfone to sulfolane as a cosolvent can also effectively improve the relative volatility α of ethylcyclohexane to benzene.

Example 3

This example investigates the separation performance of the complex solvent using methyl phenyl sulfone as a co-solvent for aromatics/non-aromatics.

The relative volatility of the composite solvent was determined according to the method of Example 1, except that the co-solvent in the composite solvent was methyl phenyl sulfone. The relative volatility α of ethylcyclohexane to benzene of each solvent calculated by formula (1) is shown in Table 3.

table 3

It can be seen from Table 3 that adding methyl phenyl sulfone as a co-solvent to sulfolane can also effectively improve the relative volatility α of ethyl cyclohexane to benzene.

Comparative Example 1

This comparative example examines the effect of the disclosed co-solvents on the relative volatility of the benzene/ethylcyclohexane system.

According to the method of Example 1, using 90 mass% benzene and 10 mass% ethylcyclohexane mixture as raw materials, when evaluating different solvent ratios, adding different cosolvents and cosolvent content p-ethylcyclohexane/ The effect of the relative volatility of benzene, the results are shown in Table 4, wherein NMP is N-methylpyrrolidone.

Table 4

As can be seen from Table 4, in the process of separating the benzene/ethylcyclohexane system, adding 3-methyl sulfolane or NMP to sulfolane as a co-solvent, under the conditions of the same solvent ratio, the selectivity of the composite solvent is not higher than that of the composite solvent. pure sulfolane; and with the increase of the amount of co-solvent added, the selectivity of the composite solvent decreases.

Example 4

The C ₆ -C ₈ fraction of cracked hydrogenated gasoline is used as the raw material, and its composition is shown in Table 5. The alkanes and aromatic hydrocarbons are separated by extraction and rectification according to the process shown in Figure 1. The composite solvent used contains 50% by mass of methyl ethyl sulfone, 50% by mass % sulfolane, the operating conditions of the extractive distillation tower and the solvent recovery tower are shown in Table 6, and the separation results are shown in Table 7.

table 5

Table 6

Table 7

project Example 4 Comparative Example 2 Mixed Aromatic Products Purity, mass % 99.90 99.65 Yield, mass % 99.9 99.5 non-aromatic hydrocarbons Cosolvent content, ppm 25 30 Aromatic content, mass % 0.7 2.5

Comparative Example 2

The composite solvent composed of 90% by mass of sulfolane and 10% by mass of 3-methylsulfolane was used as extractive distillation solvent, and the aromatic hydrocarbons and non-aromatic hydrocarbons in the C ₆ -C ₈ fractions of cracked hydrogenated gasoline were separated by extractive distillation according to the method of Example 4. , the operating conditions of the extractive rectification tower and the solvent recovery tower are shown in Table 6, and the results are shown in Table 7.

The results show that, compared with the composite solvent of Comparative Example 2, the composite solvent of the present invention has higher purity and yield of the separated mixed aromatic products under the condition that the solvent is relatively small and other operating conditions are basically the same.

Claims (8)

1. a composite solvent for extracting and rectifying aromatic hydrocarbons from a hydrocarbon mixture, consisting of 40-50 mass % sulfolane and 50-60 mass % co-solvent, and described co-solvent has the structure of formula (I) sulfone derivatives,

In formula (I), R ₁ and R ₂ are different, and are respectively selected from C ₁ -C ₄ alkyl, C ₄ -C ₆ cycloalkyl or phenyl, and the hydrocarbon mixture is cracked hydrogenated gasoline C ₆ - _C8 fraction, condensate or reformed oil _C6 - _C8 fraction. 2 . The composite solvent according to claim 1 , wherein the composite solvent is composed of 45-50 mass % sulfolane and 50-55 mass % cosolvent. 3 . 3 . The composite solvent according to claim 1 or 2 , wherein R ₁ and R ₂ in the co-solvent are respectively selected from C ₁ -C ₄ alkyl groups. 4 . 4 . The composite solvent according to claim 1 or 2 , wherein R ₁ in the co-solvent is selected from C ₁ -C ₄ alkyl groups, and R ₂ is selected from cyclohexane or phenyl. 5 . 5. a method for extracting and rectifying and separating aromatic hydrocarbons from hydrocarbon mixture, comprising introducing the hydrocarbon mixture into the middle of the extractive rectification tower, the composite solvent of claim 1 being introduced into the top of the extractive rectification tower, and through the extractive rectification column. , the non-aromatic hydrocarbons are discharged from the top of the tower, a part is returned to the extractive rectification tower as the top of the tower, and the other part is discharged from the system. The rich solvent rich in aromatics is discharged from the bottom of the extractive rectification tower and enters the middle of the solvent recovery tower, and the aromatics are discharged from the top of the tower. The lean solvent is discharged from the bottom of the tower and returned to the extractive distillation tower for recycling, and the hydrocarbon mixture is a C ₆ -C ₈ fraction of cracked hydrogenated gasoline, a condensate or a C ₆ -C ₈ fraction of reformed oil. 6. according to the described method of claim 5, it is characterized in that the mass ratio of the composite solvent entering the extractive distillation column and the hydrocarbon mixture raw material is 1-20, and the theoretical plate number of the extractive distillation column is 30-80, and the reflux ratio is 0.2-5, the temperature of the composite solvent entering the tower is 70-90°C, the temperature at the bottom of the tower is 120-150°C, and the pressure at the top of the tower is 0.1-0.3MPa. 7. according to the method described in claim 5, it is characterized in that the theoretical plate number of solvent recovery tower is 20-50, and reflux ratio is 0.5-2.0, tower top pressure is 0.01-0.05MPa, and tower bottom temperature is 155-190 °C. 8. The method according to claim 5, wherein the content of aromatic hydrocarbons in the hydrocarbon mixture is 20-88% by mass.

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