System and method for separating DMAC (dimethylacetamide) from benzene hydrogenation circulating benzene

Abstract

The invention belongs to the technical field of partial hydrogenation reaction production of benzene, and particularly relates to a system and a method for separating DMAC (dimethylacetamide) from benzene hydrogenation circulating benzene. The system for separating DMAC from benzene hydrogenation circulating benzene comprises a benzene hydrogenation reactor, an extractive distillation tower and a water scrubber, a benzene feeding hole and a hydrogen inlet are formed in one side of the benzene hydrogenation reactor, and the benzene feeding hole is connected with a benzene feeding pipeline; a reactant outlet is formed in the other side of the benzene hydrogenation reactor, the reactant outlet is communicated with a material inlet of the extractive distillation tower, a circulating benzene outlet is formed above the extractive distillation tower, and the circulating benzene outlet is communicated with a feeding hole below the water washing tower. The system and the method can replace the traditional benzene hydrogenation rectification separation process; after separation, the content of DMAC in the circulating benzene is zero, DMAC in the circulating benzene is completely removed, and the poisoning phenomenon of the benzene hydrogenation ruthenium-zinc catalyst caused by nitrides is prevented.

Description

Technical Field

[0001] The invention belongs to the technical field of benzene partial hydrogenation reaction production, and particularly relates to a system and method for separating DMAC from benzene hydrogenation cycle benzene. Background Art

[0002] At present, the partial hydrogenation reaction of benzene in the cyclohexanone unit uses desulfurized benzene and hydrogen for partial hydrogenation of benzene (the hydrogenation catalyst is a ruthenium-based catalyst, which is expensive). The sulfides and nitrides (easily soluble in water) carried by the reactants may cause poisoning and deactivation of the hydrogenation catalyst, so the quality requirements for the raw materials benzene and hydrogen are relatively high.

[0003] The benzene in the hydrogenation reaction comes from two sources: fresh benzene, which enters the benzene feed tank after desulfurization; and recycled benzene, which is the unreacted benzene in the hydrogenation reaction. Recycled benzene is the benzene that returns to the benzene feed tank after being purified by extractive distillation (using N,N-dimethylacetamide, DMAC, as the extractant) after the hydrogenation reaction. Current distillation technology cannot completely separate the extractant from the recycled benzene, resulting in a DMAC content of approximately 2 ppm in the recycled benzene. This DMAC enters the benzene hydrogenation reactor and, upon heating with water, hydrolyzes into nitrides, poisoning the hydrogenation catalyst and reducing its service life.

[0004] The shortcomings of traditional benzene hydrogenation and distillation separation technology are as follows: ① Current distillation technology cannot completely separate the unreacted benzene and DMAC in the hydrogenation reaction. As a result, under normal circumstances, the circulating benzene will carry a small amount of DMAC into the hydrogenation reactor, where it will be hydrolyzed into nitride and poison the ruthenium zinc catalyst; ② Acetic acid, another hydrolysis product of DMAC, will also increase the heavy component content of the product, affecting the extraction effect and increasing separation energy consumption.

[0005] In view of this, the present invention is proposed. Summary of the Invention

[0006] The object of the present invention is to provide a system and method for separating DMAC from circulating benzene in benzene hydrogenation; the system and method solve the problems of difficult separation of DMAC from circulating benzene and high catalyst consumption in traditional benzene hydrogenation refining.

[0007] In order to achieve the above object, the present invention provides the following technical solutions:

[0008] A system for separating DMAC from recycled benzene during benzene hydrogenation comprises a benzene hydrogenation reactor, an extractive distillation column, and a water scrubber. A benzene feed port and a hydrogen inlet are provided on one side of the benzene hydrogenation reactor, and the benzene feed port is connected to a benzene feed pipeline. A reactant outlet is provided on the other side of the benzene hydrogenation reactor, and the reactant outlet is connected to a material inlet of the extractive distillation column. A recycled benzene outlet is provided above the extractive distillation column, and the recycled benzene outlet is connected to a feed port below the water scrubber.

[0009] Furthermore, a desalted water inlet is provided on one side of the water washing tower, and the desalted water inlet is connected to a desalted water pipeline; a recovered benzene outlet is provided above the other side of the water washing tower, and the recovered benzene outlet is connected to a benzene feed tank through a recovery pipeline.

[0010] Furthermore, an automatic regulating valve is provided on the pipeline connecting the circulating benzene outlet and the feed inlet below the water washing tower.

[0011] Furthermore, an automatic regulating valve is provided on the desalted water pipeline.

[0012] Furthermore, a wastewater outlet is provided at the bottom of the water washing tower, the wastewater outlet is connected to a wastewater pipeline, and an automatic regulating valve is provided on the wastewater pipeline.

[0013] Furthermore, a remote liquid level gauge is provided in the water washing tower; the remote liquid level gauge and the automatic regulating valve on the wastewater pipeline are controlled by an automatic control loop to adjust the liquid level in the water washing tower to ensure the extraction effect.

[0014] In addition, the present invention also provides a method for separating DMAC from benzene in a benzene hydrogenation cycle, using the above-mentioned system, comprising the following steps:

[0015] S1, the raw material benzene is fed into the benzene hydrogenation reactor through the benzene feed pipeline, and reacts with hydrogen under the action of catalyst to produce cyclohexene and cyclohexane;

[0016] S2, cyclohexene, cyclohexane and unreacted benzene are sent to the extractive distillation tower together, and the extractant DMAC is added for extractive distillation. The recycled benzene carrying DMAC is extracted from the top of the extractive distillation tower and sent to the bottom of the water washing tower;

[0017] S3. After washing with high brine in the water scrubber, the DMAC in the circulating benzene is transferred to the water phase and discharged from the wastewater outlet of the water scrubber. The washed benzene is taken out from the top of the water scrubber and returned to the benzene feed tank for reuse.

[0018] Furthermore, in step S1, the reaction conditions are: reaction temperature 140-150° C., reaction pressure 4.5-5.5 MPa.

[0019] Compared with the closest existing technology, the technical solution provided by the present invention has the following excellent effects:

[0020] (1) The system and method of the present invention for separating DMAC from recycled benzene in benzene hydrogenation can replace the traditional benzene hydrogenation distillation separation process; after separation, the DMAC content in the recycled benzene is zero, completely removing DMAC from the recycled benzene, and preventing poisoning of the benzene hydrogenation ruthenium zinc catalyst caused by nitrides;

[0021] (2) The process flow is simple, the equipment failure rate is low, and it is easy to maintain; the energy consumption is low and the service life of the catalyst can be extended, thereby reducing the system operating cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The drawings and the accompanying drawings, which constitute part of this application, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. Among them:

[0023] Figure 1 Schematic diagram of a system for separating DMAC from benzene in a benzene hydrogenation cycle according to the present invention.

[0024] In the figure: 1-benzene hydrogenation reactor; 2-extractive distillation tower; 3-water scrubber; 11-benzene feed inlet; 12-hydrogen inlet; 10-benzene feed pipeline; 13-reactant outlet; 21-circulating benzene outlet; 31-desalted water inlet; 30-desalted water pipeline; 32-recovered benzene outlet; 40-recovery pipeline; 33-wastewater outlet; 50-wastewater pipeline. DETAILED DESCRIPTION

[0025] The present invention will be described in detail below with reference to the accompanying drawings and in combination with embodiments. It should be noted that, in the absence of conflict, the embodiments and features of the embodiments of the present invention can be combined with each other.

[0026] In the description of the present invention, the terms "longitudinal", "transverse", "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the present invention and do not require that the present invention must be constructed and operated in a specific orientation. Therefore, they should not be understood as limitations on the present invention. The terms "connected" and "connected" used in the present invention should be understood in a broad sense. For example, it can be a fixed connection or a detachable connection; it can be a direct connection or an indirect connection through an intermediate component. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to the specific circumstances.

[0027] According to a first aspect of the present invention, a system for separating DMAC from benzene hydrogenation cycle benzene is provided, such as Figure 1 As shown, it includes a benzene hydrogenation reactor 1, an extractive distillation tower 2 and a water scrubber 3; a benzene feed port 11 and a hydrogen inlet 12 are provided on one side of the benzene hydrogenation reactor 1, and the benzene feed port 11 is connected to a benzene feed pipeline 10; a reactant outlet 13 is provided on the other side of the benzene hydrogenation reactor 1, and the reactant outlet 13 is connected to the material inlet of the extractive distillation tower 2; a circulating benzene outlet 21 is provided above the extractive distillation tower 2, and the circulating benzene outlet 21 is connected to the feed port at the bottom of the water scrubber 3.

[0028] Specifically, a desalted water inlet 31 is located on one side of the water scrubber 3, connected to a desalted water pipeline 30. A recovered benzene outlet 32 ​​is located above the other side of the water scrubber 3, connected to the benzene feed pipeline 10 via a recovery pipeline 40. A wastewater outlet 33 is located at the bottom of the water scrubber 3, connected to a wastewater pipeline 50. An automatic regulating valve is installed on the wastewater pipeline 50, and a remote level gauge is installed within the water scrubber. Both the remote level gauge and the automatic regulating valve on the wastewater pipeline 50 are controlled by an automatic control circuit to adjust the liquid level within the water scrubber to ensure extraction efficiency. Furthermore, an automatic regulating valve is installed on the pipeline connecting the recycled benzene outlet 21 to the feed port at the bottom of the water scrubber 3, and an automatic regulating valve is installed on the desalted water pipeline 30 to adjust the amount of desalted water used based on the flow rate of recycled benzene.

[0029] The method for separating DMAC from benzene hydrogenation cycle benzene using the system of the present invention is as follows:

[0030] Raw benzene is fed into a benzene hydrogenation reactor 1 via a benzene feed line 10. Raw hydrogen is pressurized by a compressor and fed into the benzene hydrogenation reactor 1. Under the action of a ruthenium-zinc catalyst, the benzene and hydrogen react with sufficient stirring to produce cyclohexene and cyclohexane. The reaction temperature is 140-150°C, the pressure is 4.5-5.5 MPa, the benzene conversion rate is approximately 40%, and the selectivity for cyclohexene is approximately 80%.

[0031] Cyclohexene, cyclohexane, and unreacted benzene are fed together into extractive distillation column 2. Because benzene, cyclohexene, and cyclohexane have similar boiling points, traditional distillation cannot completely separate them. Therefore, extractive distillation using the extractant DMAC (N,N-dimethylacetamide) is required. This distillation method results in approximately 2 ppm of DMAC being carried over into the separated benzene (recycled benzene). After extractive distillation, the circulating benzene carrying DMAC is withdrawn from the top of the extractive distillation column and fed to the bottom of the water scrubber 3. Desalted water is added from the top of the water scrubber 3 and the circulating benzene carrying DMAC is washed with high-salt water. On the packing of the water scrubber 3, the two are broken down into small droplets, allowing them to fully contact each other due to the density difference. Due to the hydrolysis reaction between DMAC and water to produce dimethylamine and acetic acid, both of which are highly soluble in water, the DMAC in the benzene is transferred to the aqueous phase and discharged through the wastewater outlet 33 at the bottom of the water scrubber 3. The washed benzene is withdrawn from the top of the water scrubber 3 and returned by gravity to the benzene feed line 10, where it is mixed with fresh benzene and reused.

[0032] According to the material properties of benzene, DMAC and hydrophilicity of the hydrolyzed nitride, a water scrubber is added after the traditional benzene and DMAC separation tower. Unreacted recycled benzene from the hydrogenation unit is fed from the bottom of the water scrubber, and high-purity water is fed from the top of the tower. The two materials are exchanged in the tower, and trace amounts of DMAC in the recycled benzene are transferred to the aqueous phase, thereby completing the purification of the recycled benzene.

[0033] Experimental Example 1

[0034] This embodiment provides a system for separating DMAC from recycled benzene during benzene hydrogenation, comprising a benzene hydrogenation reactor, an extractive distillation column, and a water scrubber. A benzene feed inlet and a hydrogen inlet are provided on one side of the benzene hydrogenation reactor, and the benzene feed inlet is connected to a benzene feed pipeline. A reactant outlet is provided on the other side of the benzene hydrogenation reactor, and the reactant outlet is connected to the material inlet of the extractive distillation column. A recycled benzene outlet is provided above the extractive distillation column, and the recycled benzene outlet is connected to the feed inlet below the water scrubber.

[0035] A desalted water inlet is located on one side of the water scrubber, connected to the desalted water pipeline. A recycled benzene outlet is located above the other side of the scrubber, connected to the benzene feed pipeline via a recycling pipeline. A wastewater outlet is located at the bottom of the scrubber, connected to the wastewater pipeline. The wastewater pipeline is equipped with an automatic regulating valve, and a remote level gauge is installed within the scrubber. Both the remote level gauge and the automatic regulating valve on the wastewater pipeline are controlled by an automatic control circuit to adjust the liquid level within the scrubber to ensure extraction efficiency. Additionally, an automatic regulating valve is installed on the pipeline connecting the recycled benzene outlet to the feed inlet below the scrubber, and an automatic regulating valve is installed on the desalted water pipeline to adjust the amount of desalted water used based on the circulating benzene flow rate.

[0036] Test Example 1

[0037] The cyclohexanone workshop of a chemical enterprise adopted the system for separating DMAC from benzene in the benzene hydrogenation cycle of Example 1. The DMAC content in the benzene before and after water washing was monitored at different times. The comparative data results are shown in Table 1:

[0038] Table 1

[0039]

[0040] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A system for separating DMAC from benzene hydrogenation cycle benzene, characterized in that: The invention comprises a benzene hydrogenation reactor, an extractive distillation tower and a water scrubber; a benzene feed port and a hydrogen inlet are provided on one side of the benzene hydrogenation reactor, and the benzene feed port is connected to a benzene feed pipeline; a reactant outlet is provided on the other side of the benzene hydrogenation reactor, and the reactant outlet is connected to the material inlet of the extractive distillation tower; a circulating benzene outlet is provided above the extractive distillation tower, and the circulating benzene outlet is connected to the feed port below the water scrubber.

2. The system for separating DMAC from benzene hydrogenation cycle benzene according to claim 1, characterized in that: A desalted water inlet is provided on one side of the water scrubber, and the desalted water inlet is connected to a desalted water pipeline; a recovered benzene outlet is provided above the other side of the water scrubber, and the recovered benzene outlet is connected to a benzene feed tank through a recovery pipeline.

3. The system for separating DMAC from benzene hydrogenation cycle benzene according to claim 2, characterized in that: An automatic regulating valve is provided on the pipeline connecting the circulating benzene outlet and the feed inlet below the water washing tower.

4. The system for separating DMAC from benzene hydrogenation cycle benzene according to claim 2, characterized in that: An automatic regulating valve is provided on the desalted water pipeline.

5. The system for separating DMAC from benzene hydrogenation cycle benzene according to claim 1, characterized in that: A wastewater outlet is provided at the bottom of the water washing tower, and the wastewater outlet is connected to a wastewater pipeline, and an automatic regulating valve is provided on the wastewater pipeline.

6. The system for separating DMAC from benzene hydrogenation cycle benzene according to claim 5, characterized in that: A remote level gauge is provided in the water washing tower; the remote level gauge and the automatic regulating valve on the wastewater pipeline are controlled by an automatic control loop to adjust the liquid level in the water washing tower to ensure the extraction effect.

7. A method for separating DMAC from benzene hydrogenation cycle benzene, characterized in that, The system according to any one of claims 1 to 6 comprises the following steps: S1, the raw material benzene is fed into the benzene hydrogenation reactor through the benzene feed pipeline, and reacts with hydrogen under the action of catalyst to produce cyclohexene and cyclohexane; S2, cyclohexene, cyclohexane and unreacted benzene are sent to the extractive distillation tower together, and the extractant DMAC is added for extractive distillation. The recycled benzene carrying DMAC is extracted from the top of the extractive distillation tower and sent to the bottom of the water washing tower; S3. After washing with high brine in the water scrubber, the DMAC in the circulating benzene is transferred to the water phase and discharged from the wastewater outlet of the water scrubber. The washed benzene is taken out from the top of the water scrubber and returned to the benzene feed tank for reuse.

8. The method for separating DMAC from benzene hydrogenation cycle benzene according to claim 7, characterized in that: In step S1, the reaction conditions are: reaction temperature 140-150° C., reaction pressure 4.5-5.5 MPa.

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