Extraction-membrane coupling process and device for cyclohexane / KA oil separation

Abstract

The invention belongs to the technical field of chemical engineering, and mainly relates to an extraction-membrane coupling process for cyclohexane / KA oil separation. Comprising the following steps: step 1, extracting and separating a cyclohexane / KA oil mixture by using sulfolane as an extracting agent to obtain an extract phase containing sulfolane / KA oil and a raffinate phase mainly containing cyclohexane and sulfolane; step 2, sequentially carrying out reduced pressure rectification and normal pressure rectification on the extract phase, and separating cyclohexane from KA oil; step 3, adding water into the raffinate phase for back extraction to obtain a cyclohexane stream and a mixed stream of sulfolane / water; the mixed stream of sulfolane / water is separated through a dehydration separation membrane. Compared with the traditional cyclohexane / KA oil separation process, the method has the advantages that the energy consumption in the separation process can be greatly reduced, the extraction agent in the raffinate phase is recovered by adopting the membrane separation technology, and meanwhile, the environmental pollution caused by the extraction agent is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical engineering, and mainly relates to an extraction-membrane coupling process for cyclohexane / KA oil separation. Background Art

[0002] KA oil is a product obtained by cyclohexane oxidation-alkali decomposition, including cyclohexanol, cyclohexanone and impurities, and is an important intermediate product in the cyclohexane oxidation process. Cyclohexanone is an important organic chemical raw material, mainly used as an intermediate for the manufacture of caprolactam and adipic acid in industry, and is also an important industrial solvent. It can be used in industries such as medicine, paint, coating, rubber and pesticides, and is also used in printing and plastic recycling.

[0003] Due to the low conversion rate of cyclohexane, the material after alkali decomposition contains only about 5% KA oil, and the rest is unconverted cyclohexane. The traditional process uses distillation to separate cyclohexane / KA oil, that is, cyclohexane is evaporated to the top of the tower through a distillation tower, and then condensed and recycled to the oxidation unit to continue the reaction; KA oil is obtained in the tower kettle, and caustic soda is added for saponification to remove impurities such as acids and esters, and finally the cyclohexanol in the KA oil is dehydrogenated and distilled to obtain cyclohexanone products. In the traditional process, the energy consumption of the alkane distillation process is high, the caustic soda added in the saponification process will cause cyclohexanol and cyclohexanone to condense, and the discharge of waste alkali liquid will cause cyclohexanol and cyclohexanone to be lost. In addition, the incineration of waste alkali will also bring about problems such as three waste emissions and environmental pollution. There is no effective solution to the industry pain points of high energy consumption, low yield, and high three wastes so far. Therefore, there is an urgent need for a green and environmentally friendly process for the separation of cyclohexane / KA oil to meet the growing market demand. Summary of the invention

[0004] The object of the present invention is to provide an extraction-membrane coupling process for cyclohexane / KA oil separation to solve the problems of high investment cost, high energy consumption and poor separation effect of double-effect distillation equipment.

[0005] As a pressure-based separation technology, membrane separation is not limited by thermodynamic equilibrium, has the advantages of high flux, low energy consumption, and low pollution, and is suitable for the separation of near-boiling and azeotropic systems. Therefore, the present invention couples extraction separation with membrane separation technology to produce a certain synergistic effect between the two. By utilizing the high-efficiency separation effect of membrane separation, the amount of extractant used is reduced, and the equipment investment cost and operating cost are reduced. Compared with the original double-effect distillation process, the economic benefit of the process is greatly improved, and the process is more environmentally friendly, which is in line with the background of the development of green chemical industry.

[0006] The process scheme of the invention is:

[0007] An extraction-membrane coupling process for cyclohexane / KA oil separation comprises the following steps:

[0008] Step 1, extracting and separating the cyclohexane / KA oil mixture, using sulfolane as the extractant, to obtain an extract phase containing sulfolane / KA oil and a raffinate phase mainly containing cyclohexane and sulfolane;

[0009] Step 2, the extract phase is subjected to vacuum distillation and atmospheric distillation in sequence to separate cyclohexane and KA oil;

[0010] Step 3, the raffinate phase is subjected to back extraction by adding water to obtain a cyclohexane stream and a mixed stream of sulfolane / water; the mixed stream of sulfolane / water is separated by a dehydration separation membrane.

[0011] The temperature range of the extraction separation is 10-60°C.

[0012] During the vacuum distillation process, the number of tower plates is 5-20, the feed position is at 2-8 plates, the tower top temperature is 20-40°C, and the tower bottom temperature is 150-200°C.

[0013] During the atmospheric distillation process, the number of tower plates is 5-20, the feed position is at 2-8 plates, the top temperature is 60-90°C, and the bottom temperature is 150-180°C.

[0014] The shell side temperature range for water stripping is 10-50℃.

[0015] The dehydration separation membrane adopts a pervaporation membrane, and the permeation side thereof is under negative pressure conditions, and the negative pressure is a gauge pressure, which is less than 200Pa.

[0016] The cyclohexane / KA oil mixture contains 80-98% cyclohexane and 2-20% KA oil.

[0017] The weight ratio of cyclohexanol to cyclohexanone in KA oil ranges from 0.5 to 1.5:1.

[0018] An extraction-membrane coupling device for cyclohexane / KA oil separation, comprising:

[0019] The extraction tower is provided with an extractant addition port, and is used for extracting and separating the cyclohexane / KA oil mixture, and the extractant used is sulfolane;

[0020] A vacuum distillation tower, the feed port of which is connected to the bottom of the extraction tower, and is used for vacuum distillation of the extraction phase containing sulfolane / KA oil;

[0021] The atmospheric distillation tower has a feed port connected to the top of the vacuum distillation tower, and is used to separate cyclohexane and KA oil from the distillate;

[0022] A stripping tower connected to the top of the extraction tower is used to strip the raffinate phase by adding water to obtain a sulfolane / water solution and cyclohexane;

[0023] The dehydration separation membrane is connected to the bottom of the stripping tower and is used for dehydrating the sulfolane / water solution.

[0024] The dehydration separation membrane is selected from NaA molecular sieve membrane, zeolite membrane, sodium alginate membrane or PVA membrane.

[0025] The stripping tower has one stage or more than two stages.

[0026] The interception side of the dehydration separation membrane is connected to the extractant addition port on the extraction tower.

[0027] Beneficial Effects

[0028] The process of the invention has the following characteristics:

[0029] (1) Compared with the traditional cyclohexane / KA oil separation process, the energy consumption of the separation process can be greatly reduced. The membrane separation technology is used to recover the extractant in the raffinate phase, while reducing the environmental pollution caused by the extractant.

[0030] (2) The process has a low operating temperature and will not cause the extractant sulfolane to decompose due to excessively high temperature, resulting in problems such as low recovery rate, and can effectively reduce the loss of the extractant.

[0031] (3) The membrane separation technology with high separation efficiency, simple operation process and low environmental pollution is used to remove the residual water after back extraction, which can effectively reduce the cost of process and environmental pollution treatment.

[0032] (4) The molecular sieve membrane dehydration process operates under normal pressure conditions, which facilitates equipment maintenance and reduces equipment investment and operating costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 :Separation of cyclohexane / KA oil by extraction-membrane coupling process

[0034] Explanation of the reference numerals: P1, P2, P3, P4, P5 - DC pumps; EXTRACT1, EXTRACT2, EXTRACT3, EXTRACT4 - extraction towers; F1, F2, F3 - splitters; E1 - heat exchanger; H1 - preheater; T1 - vacuum distillation tower; T2 - atmospheric pressure tower; V1 - cyclohexane storage tank; V2 - KA storage tank; M1 - membrane unit (including pervaporation). DETAILED DESCRIPTION

[0035] The present invention relates to an extraction-membrane coupling process for separating cyclohexane / KA oil (cyclohexanol, cyclohexanone mixture). The technical route includes the following processes: sulfolane and cyclohexane / KA oil mixture are respectively transported to an extraction tower through a DC pump, wherein the KA oil content is 5.0wt.%. The KA oil in the raw material is extracted by sulfolane, and the extract phase is transported to a vacuum tower through a horizontal flow pump to separate the sulfolane / KA oil. The sulfolane extractant with a purity greater than 99.9wt.% is obtained in the vacuum tower kettle and circulated to the extraction tower. The discharge stream from the top of the vacuum tower is composed of cyclohexane and KA oil, wherein the cyclohexane content is 10.0wt.%, and is transported to an atmospheric tower for distillation separation of cyclohexane / KA oil through a DC pump. Cyclohexane with a purity greater than 99.6wt.% is obtained at the top of the atmospheric tower, and KA oil with a purity greater than 99.8wt.% is obtained at the bottom of the tower. The raffinate phase in the extraction tower is subjected to three-stage water-addition back extraction to obtain cyclohexane with a purity greater than 98.0wt.% and a sulfolane aqueous solution with a water content of about 50wt.%. The sulfolane aqueous solution is transported to the membrane unit for pervaporation operation. The membrane assembly is connected to a vacuum pump, and the driving force is formed by the pressure difference between the inside and outside of the membrane to remove the water in the feed liquid. In order to reduce the influence of concentration polarization, a T-type molecular sieve membrane is used for dehydration when the water content is higher than 20wt.%, and a NaA molecular sieve membrane is used for dehydration when the water content is lower than 20wt.%. Finally, the water on the permeate side of the membrane assembly will be condensed and collected into the permeate collection tank, while the sulfolane left on the retentate side is sulfolane. The sulfolane obtained by membrane separation is circulated to the extraction tower through a DC pump. Compared with the existing cyclohexane / KA oil separation process, this process can greatly reduce energy consumption, reduce equipment investment costs, improve process economic benefits, and conform to the development of green chemical industry.

[0036] Combined with Figure 1 , the raw material and the extractant enter the extraction tower through DC pumps P2 and P3 respectively for extraction and separation. The bottom of the tower is the extraction phase cyclohexane and KA oil, and the top of the tower is the residual phase cyclohexane. The extraction phase is preheated by a heat exchanger and sent to a vacuum distillation tower. The vacuum distillation tower bottom flows out sulfolane, and KA oil and a small amount of cyclohexane are distilled from the top of the tower. The overhead distillate of the vacuum distillation tower is transported to the atmospheric pressure tower through a DC pump P5 to separate cyclohexane and KA oil. The overhead distillate is cyclohexane, and the bottom distillate is KA oil. The residual phase in the extraction operation is subjected to three-stage water back extraction to obtain a cyclohexane stream and a mixed stream of cyclohexane / water. The sulfolane / water solution obtained after back extraction has a water content of about 50wt.%, which is transported to the membrane assembly through a DC pump for dehydration operation. The permeate is measured as the water phase, and the residual side obtains a logistics with a sulfolane content greater than 99.6wt.%.

[0037] In some specific implementations, the following technical solutions are included:

[0038] The extraction-membrane coupling process used for cyclohexane / KA oil separation includes an extraction tower, a vacuum distillation tower, an atmospheric distillation tower, a DC pump, a permeate collection tank, a product tank, a heat exchanger, a vacuum pump, and a membrane assembly. The raw liquid and the extractant are transported to the extraction tower through a DC pump, and the bottom effluent of the extraction tower is the extraction phase transported to the vacuum distillation tower. The bottom effluent of the vacuum distillation separation tower is sulfolane, which is circulated to the extraction tower through a DC pump. The top effluent of the vacuum distillation tower is KA oil and a small amount of cyclohexane. Cyclohexane and KA oil are separated by atmospheric distillation. The top effluent of the atmospheric tower is cyclohexane, and the bottom effluent is KA oil and is transported to the KA oil storage tank. The extraction tower obtains the raffinate phase cyclohexane, which is subjected to three-stage stripping with water. During the stripping process, the raffinate phase is cyclohexane, and the extraction phase is a mixed solution of sulfolane / water. The sulfolane / water solution enters the membrane assembly after heat exchange, and the permeate enters the permeate tank after condensation. The dehydrated sulfolane is transported to the extraction tower for recycling.

[0039] The extraction tower EXTRACT1 uses sulfolane as the extractant to extract a small amount of KA oil from cyclohexane / KA oil, saving the energy consumption of distilling and separating a large amount of cyclohexane.

[0040] The raw material is fed from the bottom of the extraction tower, and the extractant is fed from the top of the tower.

[0041] The first liquid phase of the extraction is KA oil flowing out from the bottom of the tower, and cyclohexane flows out from the top of the tower as the second liquid phase, and the extractant is preferably sulfolane.

[0042] During the distillation process, sulfolane is first separated by distillation, and then KA oil and a small amount of cyclohexane are separated.

[0043] The second liquid phase in the EXTRACT1 tower is separated from cyclohexane and sulfolane by three-stage water stripping, thereby effectively recovering sulfolane.

[0044] The steps include:

[0045] (1) Using sulfolane as the extractant, sulfolane and the raw material cyclohexane / KA oil are respectively transported to the extraction tower EXTRACT1. After extraction and purification, the first liquid phase is KA oil, and the second liquid phase is cyclohexane.

[0046] (2) The purified extract phase is distilled from the bottom of the extraction tower EXTRACT1 and transported to the vacuum distillation tower through a DC pump. After vacuum distillation separation, the bottom distillate is sulfolane, which is circulated by a DC pump and condensed to the extraction tower through a heat exchanger. The top of the tower is KA oil and a small amount of cyclohexane, which are transported to the atmospheric pressure tower for distillation separation through a horizontal flow pump. The top distillate of the atmospheric distillation tower is cyclohexane, and the bottom distillate is the product KA oil.

[0047] (3) The top discharge stream of the extraction tower EXTRACT1 is the raffinate phase, which is subjected to three-stage water-addition back extraction to separate cyclohexane and sulfolane. The first liquid phase is sulfolane, and the second liquid phase is cyclohexane.

[0048] (4) The sulfolane aqueous solution separated in the stripping process is heated by a preheater and then enters the membrane module. The water in the solution is separated from the sulfolane by a pervaporation membrane, and the permeate is collected from the permeate outlet by condensation and enters the permeate tank. After the membrane module is dehydrated, the retentate is transported to the extraction tower for recycling by a DC pump.

[0049] In the step (1), the extractant is preferably sulfolane, and the extraction temperature is 30°C.

[0050] The operating pressure of the recovery tower T1 for sulfolane in the extract phase in step (2) is preferably a vacuum distillation tower.

[0051] The operating pressure of the separation tower T2 for separating KA from cyclohexane in step (2) is preferably atmospheric pressure.

[0052] The extraction temperature for the tertiary water stripping to separate cyclohexane and sulfolane in step (3.) is preferably 20°C.

[0053] In step (4), the permeate side pressure of the pervaporation membrane is negative pressure, and the operating pressure range is preferably below 200 Pa.

[0054] Comparative Example 1

[0055] This example is used to illustrate the process flow of separating cyclohexane / KA oil by a double-effect distillation tower and the energy consumption analysis in the process. Take the feed of 1000kg per hour and the feed composition of 95wt.% (cyclohexane) and 5wt.% (KA oil, cyclohexanol and cyclohexanone content 1:1) as an example. Process flow: The raw material is transported to the atmospheric tower through a direct current pump, and part of the cyclohexane is distilled from the top of the tower into the cyclohexane storage tank. The bottom stream of the tower is divided into two streams by a splitter. One stream is refluxed into the T1 tower kettle after completing heat exchange with the top steam of the high-pressure tower in the heat exchanger, and the other stream is transported to the high-pressure tower through a horizontal flow pump. KA oil with a purity greater than 99.9wt.% is obtained at the bottom of the tower. After heat exchange and cooling in the heat exchanger, the top steam is divided into two parts by a splitter, one part is used as reflux, and the other part enters the cyclohexane storage tank. In this process flow, there is no bottom reboiler and no top condenser. According to Aspen calculation, the total heat load required for double-effect distillation to process 1 ton of cyclohexane / KA oil feedstock is 122kW.

[0056] Example 1

[0057] This example is used to illustrate the process flow of cyclohexane / KA oil separation by extraction-membrane coupling method and the energy consumption analysis in the process. Take 1000 kg per hour, feed composition of 95wt.% (cyclohexane), 5wt.% (KA oil, cyclohexanol and cyclohexanone content 1:1) as an example. Figure 1As shown, the cyclohexane / KA oil raw material is transported to the extraction tower EXTRACT1 through the DC pump P3; the sulfolane extractant is transported to the extraction tower EXTRACT1 through the DC pump P2, and the KA oil-containing extract phase flows out from the bottom of the tower and enters the distillation tower T1 after being preheated by the heat exchanger E1. The distillation tower T1 uses vacuum distillation to separate sulfolane and KA oil, wherein the processing capacity of the T1 tower is 1993kg / h, the sulfolane content is 97.6wt.%, the cyclohexanone content is 1.0wt.%, the cyclohexanol content is 1.1wt.%, and the cyclohexane content is about 0.3wt.%, the operating pressure is about 5-8kPa, the number of tower plates is 9, the feed position is at the 5th plate, the tower top temperature is 30℃, and the tower bottom temperature is 176℃. The sulfolane with a purity greater than 99.9wt.% obtained at the bottom of the tower is transported to the heat exchanger E1 by a horizontal flow pump for condensation and cooling, and then sent to the extraction tower EXTRACT1 for recycling. The top distillate of the distillation tower T1 is a cyclohexane / KA oil mixture, in which the cyclohexane content is about 10wt.%, and is sent to the distillation tower T2 through the horizontal flow pump P5 to separate the cyclohexane / KA oil. The processing capacity of the distillation tower T2 is 45kg / h, in which the cyclohexane content is 11.0wt.%, the cyclohexanol content is 44.7wt.%, and the cyclohexanone content is about 44.3wt.%. The operating pressure is about 1.2-1.5kPa, the number of plates is 10, the feed position is the 6th plate, the top temperature is 87℃, and the bottom temperature is about 163℃. Finally, the bottom of the tower obtains KA oil with a purity of 99.8wt.%, and the top of the tower obtains cyclohexane with a purity greater than 99.6wt.%. The raffinate phase obtained by extraction in the extraction tower EXTRACT1 flows out from the top of the tower, and is successively extracted by water addition in EXTRACT2, EXTRACT3, and EXTRACT4. The raffinate phase obtains cyclohexane with a purity greater than 98.0wt.% and enters the cyclohexane storage tank V1. The extract phases obtained by the three-stage back extraction converge into a sulfolane aqueous solution containing about 50wt.% of water. The sulfolane aqueous solution is heated by the preheater H1 and enters the membrane unit M1. The permeate is measured as water and collected by the cold trap. The sulfolane with a purity greater than 99.6wt.% is obtained on the retentate side and circulated to the extraction tower EXTRACT1 for recycling.

[0058] In order to verify the reliability of the simulation results, the simulation data results in the extraction and stripping processes were experimentally verified. GCMS was used to quantitatively analyze the sulfolane in the extraction phase, the cyclohexane in the raffinate phase, and the cyclohexane in the raffinate phase during the stripping process. The experimental measurement showed that the sulfolane content in the extraction phase during the extraction process was about 97.0wt.%, the cyclohexane content in the raffinate phase was about 96.0wt.%, and the cyclohexane content in the raffinate phase during the stripping process was about 98.0wt.%, which was within 2% of the simulation calculation results in Aspen, proving the reliability of the simulation calculation results. According to Aspen research and calculation, the total heat load required for processing 1 ton of cyclohexane / KA oil raw materials using this process is 72kW. Compared with the original double-effect distillation process, the energy consumption of the extraction-membrane coupling separation process is saved by 41.67%, which effectively reduces the separation energy consumption and reduces the equipment investment cost, which is in line with the current era of green chemical development.

Claims

1. An extraction-membrane coupling process for cyclohexane / KA oil separation, characterized in that: The steps include: Step 1, extracting and separating the cyclohexane / KA oil mixture, using sulfolane as the extractant, to obtain an extract phase containing sulfolane / KA oil and a raffinate phase mainly containing cyclohexane and sulfolane; Step 2, the extract phase is subjected to vacuum distillation and atmospheric distillation in sequence to separate cyclohexane and KA oil; Step 3, the raffinate phase is subjected to back extraction by adding water to obtain a cyclohexane stream and a mixed stream of sulfolane / water; the mixed stream of sulfolane / water is separated by a dehydration separation membrane.

2. The extraction-membrane coupling process for cyclohexane / KA oil separation according to claim 1, characterized in that: The temperature range of extraction separation is 10-60℃; the temperature range of shell side of water stripping is 10-50℃.

3. The extraction-membrane coupling process for cyclohexane / KA oil separation according to claim 1, characterized in that: During the vacuum distillation process, the number of tower plates is 5-20, the feed position is 2-8 plates, the top temperature is 20-40°C, and the bottom temperature is 150-200°C; during the atmospheric distillation process, the number of tower plates is 5-20, the feed position is 2-8 plates, the top temperature is 60-90°C, and the bottom temperature is 150-180°C.

4. The extraction-membrane coupling process for cyclohexane / KA oil separation according to claim 1, characterized in that: The dehydration separation membrane adopts a pervaporation membrane, and the permeation side thereof is under negative pressure conditions, and the negative pressure is a gauge pressure, which is less than 200Pa.

5. The extraction-membrane coupling process for cyclohexane / KA oil separation according to claim 1, characterized in that: The cyclohexane / KA oil mixture contains 80-98% cyclohexane and 2-20% KA oil.

6. The extraction-membrane coupled process for cyclohexane / KA oil separation according to claim 1, characterized in that: The weight ratio of cyclohexanol to cyclohexanone in KA oil ranges from 0.5 to 1.5:

1.

7. An extraction-membrane coupling device for cyclohexane / KA oil separation, characterized in that: include: The extraction tower is provided with an extractant addition port, and is used for extracting and separating the cyclohexane / KA oil mixture, and the extractant used is sulfolane; A vacuum distillation tower, the feed port of which is connected to the bottom of the extraction tower, and is used for vacuum distillation of the extraction phase containing sulfolane / KA oil; An atmospheric distillation tower, the feed port of which is connected to the top of the vacuum distillation tower, for separating cyclohexane and KA oil from the distillate; a stripping tower, connected to the top of the extraction tower, for stripping the raffinate phase by adding water to obtain a sulfolane / water solution and cyclohexane; The dehydration separation membrane is connected to the bottom of the stripping tower and is used for dehydrating the sulfolane / water solution.

8. The extraction-membrane coupling device for cyclohexane / KA oil separation according to claim 7, characterized in that: The dehydration separation membrane is selected from NaA molecular sieve membrane, zeolite membrane, sodium alginate membrane or PVA membrane.

9. The extraction-membrane coupling device for cyclohexane / KA oil separation according to claim 7, characterized in that: The stripping tower has one stage or more than two stages.

10. The extraction-membrane coupling device for cyclohexane / KA oil separation according to claim 7, characterized in that: The interception side of the dehydration separation membrane is connected to the extractant addition port on the extraction tower.

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