System and process for treating wastewater of waste catalyst for producing methyl ethyl carbonate and dimethyl carbonate

Abstract

The application discloses a wastewater treatment system and process for producing waste methyl ethyl carbonate catalyst and dimethyl carbonate, which comprises a rectifying tower, the bottom of the rectifying tower is connected with the side of an evaporation tower through a pipeline, the bottom of the evaporation tower is connected with the side of a quenching kettle through a pipeline, the bottom of a nitric acid reduction tower is connected with the side of the quenching kettle through a pipeline, the bottom of the quenching kettle is connected with the side of a boundary position tank through a pipeline, and the bottom of the boundary position tank is connected with the side of a methanol recovery tower through a pipeline. The auxiliary filtering assembly is arranged, solid-liquid separation is realized through simple operation, and dry slag with extremely low moisture content is generated. In the operation process, the operation is closed, there is no risk of organic medium volatilization contacting air, the safety is high, and the environment and human health are friendly.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of chemical production, in particular to a wastewater treatment system and process for producing waste catalyst of methyl ethyl carbonate and dimethyl carbonate. BACKGROUND

[0002] The production of dimethyl carbonate by carbon monoxide carbonylation method is a relatively advanced process for producing dimethyl carbonate. The production of methyl ethyl carbonate by ester exchange of dimethyl carbonate and ethanol under the catalytic action of sodium methoxide is also the mainstream process for producing methyl ethyl carbonate. The catalyst sodium methoxide needs to be removed from the system when its activity decreases, resulting in liquid waste. Dimethyl carbonate and methyl ethyl carbonate are main raw materials for electrolyte, and under the background of the recent new energy boom, the demand for dimethyl carbonate and methyl ethyl carbonate is booming, which has given birth to a large number of devices for producing dimethyl carbonate by carbon monoxide carbonylation method and producing methyl ethyl carbonate by ester exchange. In the process of producing dimethyl carbonate by carbon monoxide carbonylation method, the unit for generating methyl nitrite will generate wastewater containing nitric acid. The two processes are related to the upstream and downstream of the same industrial chain, and the waste liquid generated in each process needs to be treated separately by adding additional carbon dioxide or sodium hydroxide, which increases the complexity of the process and the amount of wastewater. SUMMARY

[0003] The purpose of the present application is to make up for the shortcomings of the prior art, and to provide a wastewater treatment system and process for producing waste catalyst of methyl ethyl carbonate and dimethyl carbonate.

[0004] The technical scheme of the present application is as follows:

[0005] A wastewater treatment system for producing waste catalyst of methyl ethyl carbonate and dimethyl carbonate, comprising a rectifying tower, the bottom of the rectifying tower is connected to the side of an evaporation tower by a pipeline; the bottom of the evaporation tower is connected to the side of a quenching kettle by a pipeline; the bottom of a nitric acid reduction tower is connected to the side of the quenching kettle by a pipeline; the bottom of the quenching kettle is connected to the side of a boundary tank by a pipeline; and the bottom of the boundary tank is connected to the side of a methanol recovery tower by a pipeline.

[0006] Preferably, the upper part of the quenching kettle is connected to the upper part of the boundary tank by a pipeline, forming a gas phase balance.

[0007] Preferably, the side of the boundary tank is connected to the bottom of the rectifying tower and the side of the evaporation tower by a pipeline, forming a loop.

[0008] Preferably, an online pH meter is arranged on the pipeline connecting the bottom of the quenching kettle and the side of the boundary tank; and an adjusting valve is arranged on the pipeline connecting the bottom of the nitric acid reduction tower and the side of the quenching kettle.

[0009] Preferably, the quenching kettle is provided with a stirring device and a cooling water jacket.

[0010] Preferably, the interface tank is provided with an interface meter, through which the light component of the interface tank returning to the evaporation tower and the heavy component of the interface tank entering the methanol recovery tower are controlled to ensure the stability of the interface of the interface tank.

[0011] The treatment method of the waste catalyst and nitric acid wastewater treatment system for producing methyl ethyl carbonate, the treatment method comprising the following steps:

[0012] S1: The sodium methoxide catalyst and the reaction liquid are introduced into the evaporation tower from the bottom of the reaction rectifying column of the ester exchange methyl ethyl carbonate production process;

[0013] S2: The evaporation tower separates the sodium methoxide from the reaction liquid, and the unreacted dimethyl carbonate and the product methyl ethyl carbonate are collected from the upper part of the tower, and the main components in the tower kettle are waste sodium methoxide, dimethyl carbonate and methyl ethyl carbonate; then the waste sodium methoxide, dimethyl carbonate and methyl ethyl carbonate enter the quenching kettle;

[0014] S3: The nitric acid wastewater from the nitric acid reduction tower of the carbon monoxide carbonylation method for producing dimethyl carbonate enters the quenching kettle, the sodium methoxide and the water in the nitric acid wastewater are hydrolyzed to produce sodium hydroxide and methanol, and heat is released; then the sodium hydroxide reacts with the nitric acid to produce sodium nitrate and water;

[0015] S4: Then the mixture of dimethyl carbonate, methyl ethyl carbonate, methanol and sodium nitrate aqueous solution in the quenching kettle is separated by static separation in the interface kettle, and the pH of the quenching kettle is controlled at 7-8;

[0016] S5: The upper organic phase of the interface tank mainly contains dimethyl carbonate and methyl ethyl carbonate, which is returned to the evaporation tower and collected from the upper part; the lower salt water phase of the interface tank contains methanol, water and sodium nitrate, which enters the methanol recovery tower, and the methanol is collected from the upper part, and the water and sodium nitrate solution in the tower kettle enter the compound fertilizer production device;

[0017] The waste catalyst and nitric acid wastewater are harmlessly treated.

[0018] Preferably, in the step S2, the main components entering the quenching kettle from the lower part of the evaporation tower include the following components by volume percentage: dimethyl carbonate 30-40%, methyl ethyl carbonate 52-58% and sodium methoxide 8-12%; in the step S3, the main components entering the quenching kettle from the lower part of the nitric acid reduction tower include water 45-55%, methanol 40-52% and nitric acid 1.5-5.5%; water and dimethyl carbonate and methyl ethyl carbonate are immiscible.

[0019] Preferably, in the step S2, in the quenching kettle, the main components are a mixture of sodium nitrate brine and methanol, and the upper layer is a mixture of dimethyl carbonate and methyl ethyl carbonate; by controlling the amount of liquid entering the methanol recovery tower from the lower part of the quenching kettle and the amount of liquid entering the evaporation tower from the upper part of the quenching kettle, the stability of the interface of the quenching kettle is controlled.

[0020] Preferably, the medium in the pipeline connecting the bottom of the quenching kettle and the side of the boundary tank is controlled at a pH of 7-8.

[0021] The process medium entering the quenching kettle is ensured to be weakly alkaline, sodium methoxide is easy to react with water to produce methanol and sodium hydroxide, the nitric acid at the bottom of the nitric acid reduction tower is completely neutralized and reacted under weakly alkaline conditions, maintaining weak alkalinity is harmless to subsequent process equipment, if the state is acidic, nitric acid enters the subsequent process, which may corrode the equipment.

[0022] Dimethyl carbonate and methyl ethyl carbonate are easy to undergo hydrolysis reaction under the action of a catalyst at a certain temperature.

[0023] CH3OC(O)OCH3+ H20→CO2+ 2CH3OH (dimethyl carbonate hydrolysis).

[0024] The catalyst is mainly an inorganic base, such as sodium hydroxide. The mechanism of the alkaline catalyst is to deprotonate water molecules to make them become stronger nucleophiles, thereby promoting the hydrolysis reaction. After the hydrolysis of sodium methoxide, sodium hydroxide is produced, if the sodium hydroxide is not neutralized in time, under strong alkaline conditions, dimethyl carbonate and methyl ethyl carbonate will undergo hydrolysis reaction. This increases the consumption of raw materials and reduces the yield of products.

[0025] In the step S3, the temperature of the quenching kettle is controlled to be not more than 50-60 DEG C.

[0026] In the step S4, the pH of the medium in the pipeline connecting the bottom of the quenching kettle and the side of the boundary tank is controlled to be 7-8.

[0027] The process can avoid increasing the consumption of raw material DMC and reducing the yield of product methyl ethyl carbonate by controlling the pH of the quenching kettle to be 7-8.

[0028] The present application has the following beneficial effects:

[0029] 1. The waste catalyst for producing methyl ethyl carbonate by ester exchange and the waste water for producing dimethyl carbonate by carbonylation can be harmlessly treated.

[0030] 2. No additional process materials such as sodium hydroxide are consumed, and the economic effect is obvious.

[0031] 3. Because liquid sodium hydroxide is not needed, the total amount of waste water is reduced.

[0032] 4. The methanol produced by the hydrolysis of sodium methoxide can be recovered.

[0033] 5,300,000 tons of ester exchange production of methyl ethyl carbonate, carbonic acid diethyl ester. The treatment of waste catalysts need to pass into the waste methanol sodium, dimethyl carbonate and methyl ethyl carbonate mixed liquid carbon dioxide, produce sodium carbonate, methanol. Then through the solid-liquid separation will be separated, sodium carbonate, produce hazardous waste (about 2400 tons per year). The process is complex, and the cost is high. 30 million tons of gas phase carbonylation method for producing dimethyl carbonate, the generated nitric acid wastewater, conventional treatment directly added sodium hydroxide for neutralization, produce sodium nitrate wastewater into sewage treatment. Consumption of 2000 tons of sodium hydroxide, material cost 3 million yuan. Using the invention, no hazardous waste, no further treatment of nitric acid wastewater, no consumption of sodium hydroxide or other materials, greatly reducing the cost. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 The structural diagram of the present application is shown in the figure;

[0035] In the figure: rectifying column 1, evaporation tower 2, nitric acid reduction tower 3, quenching kettle 4, boundary tank 5, methanol recovery tower 6, regulating valve 7, online pH meter 8. DETAILED DESCRIPTION

[0036] The technical solutions in the embodiments of the present application will be clearly and completely described below in combination with specific embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor belong to the scope of protection of the present application.

[0037] Embodiment 1

[0038] A kind of production methyl ethyl carbonate waste catalyst and dimethyl carbonate wastewater treatment system, including rectifying column 1, the bottom of rectifying column 1 is connected with the side of evaporation tower 2 by pipeline;The bottom of evaporation tower 2 is connected with the side of quenching kettle 4 by pipeline;The bottom of nitric acid reduction tower 3 is connected with the side of quenching kettle 4 by pipeline;The bottom of quenching kettle 4 is connected with the side of boundary tank 5 by pipeline;The bottom of boundary tank 5 is connected with the side of methanol recovery tower 6 by pipeline.

[0039] Preferably, the upper part of quenching kettle 4 is connected with the upper part of boundary tank 5 by pipeline, which constitutes a gas phase equilibrium.

[0040] Preferably, the side of boundary tank 5 is connected with the bottom of rectifying column 1 and the side of evaporation tower 2 by pipeline, which constitutes a loop.

[0041] Preferably, the bottom of quenching kettle 4 is provided with an online pH meter 8 on the pipeline connected with the side of boundary tank 5;The bottom of nitric acid reduction tower 3 is provided with a regulating valve 7 on the pipeline connected with the side of quenching kettle 4.

[0042] Preferably, the quenching kettle 4 is provided with a stirring device, a cooling water jacket.

[0043] Preferably, the interface tank 5 is provided with an interface meter, through which the light component of the interface tank 5 returning to the evaporation tower 2 and the heavy component of the interface tank 5 entering the methanol recovery tower are controlled to ensure the stability of the interface of the interface tank 5.

[0044] Example 2

[0045] The treatment method using the system of Example 1 comprises the following steps:

[0046] S1: The reaction rectification tower 1 at the bottom of the ester exchange process for producing methyl ethyl carbonate is used to put the catalyst sodium methoxide into the reaction liquid and into the evaporation tower 2;

[0047] S2: The evaporation tower 2 separates the sodium methoxide from the reaction liquid, and the unreacted dimethyl carbonate and the product methyl ethyl carbonate are taken out from the upper part of the tower, and the waste sodium methoxide, dimethyl carbonate and methyl ethyl carbonate are mainly in the tower kettle; then the waste sodium methoxide, dimethyl carbonate and methyl ethyl carbonate enter the quenching kettle 4;

[0048] S3: The nitric acid waste water from the nitric acid reduction tower 3 of the carbon dioxide carbonylation method for producing dimethyl carbonate enters the quenching kettle 4, and the sodium methoxide and the water in the nitric acid waste water are hydrolyzed to produce sodium hydroxide and methanol and release heat; then the sodium hydroxide reacts with the nitric acid to produce sodium nitrate and water;

[0049] S4: Then the mixture of dimethyl carbonate, methyl ethyl carbonate, methanol and sodium nitrate aqueous solution in the quenching kettle 4 enters the interface kettle 5 for static separation;

[0050] S5: The upper organic phase of the interface tank 5 mainly contains dimethyl carbonate and methyl ethyl carbonate, which is returned to the evaporation tower 2 and taken out from the upper part; the lower salt-containing aqueous phase of the interface tank 5 contains methanol, water and sodium nitrate, which enters the methanol recovery tower 6, and the methanol is taken out from the upper part, and the water and sodium nitrate solution in the tower kettle enter the compound fertilizer production device;

[0051] The waste catalyst and the nitric acid waste water are harmlessly treated.

[0052] Preferably, in the step S2, the main components entering the quenching kettle 4 from the lower part of the evaporation tower 2 include the following components by volume percentage: dimethyl carbonate 35%, methyl ethyl carbonate 55% and sodium methoxide 10%; in the step S3, the components entering the quenching kettle 4 from the lower part of the nitric acid reduction tower 3 include water 50%, methanol 45% and nitric acid 2%, and the balance is other impurities. Water and dimethyl carbonate and methyl ethyl carbonate are immiscible.

[0053] Preferably, in the step S2, in the quenching kettle 4, the mixture of mainly sodium nitrate brine and methanol is in the upper layer, and the mixture of dimethyl carbonate and methyl ethyl carbonate is in the lower layer; the stability of the interface of the quenching kettle 4 is controlled by controlling the liquid amount (the range of the interface meter is 35%) of the lower layer of the quenching kettle 4 entering the methanol recovery tower 6 and controlling the liquid amount of the upper layer of the quenching kettle 4 entering the evaporation tower 2 (the organic phase exists in the upper layer).

[0054] In the step S3, the temperature of the quenching kettle 4 is controlled to be not more than 50°C.

[0055] Preferably, the pH of the medium in the pipeline connecting the bottom of the quenching kettle 4 and the side of the boundary tank 5 is controlled to be 7.

[0056] The process medium entering the quenching kettle 4 is ensured to be in weak alkaline state, sodium methoxide is easy to react with water to produce methanol and sodium hydroxide, the nitric acid at the bottom of the nitric acid reduction tower 3 is completely neutralized and reacted under the condition of weak alkaline state, and the weak alkaline state is harmless to the subsequent process equipment. If the state is acidic, the nitric acid entering the subsequent process may corrode the equipment.

[0057] Example 3

[0058] The treatment method of the system of Example 1 comprises the following steps:

[0059] S1: The bottom of the reaction rectifying tower 1 in the ester exchange production of methyl ethyl carbonate process, the catalyst sodium methoxide and the reaction liquid enter the evaporation tower 2 together;

[0060] S2: The evaporation tower 2 separates the sodium methoxide from the reaction liquid, the unreacted dimethyl carbonate and the product methyl ethyl carbonate are taken out from the upper part of the tower, and the waste sodium methoxide, dimethyl carbonate and methyl ethyl carbonate are mainly in the kettle; then the waste sodium methoxide, dimethyl carbonate and methyl ethyl carbonate enter the quenching kettle 4;

[0061] S3: The nitric acid wastewater from the nitric acid reduction tower 3 of the carbon dioxide carbonylation method for producing dimethyl carbonate enters the quenching kettle 4, the sodium methoxide and the water in the nitric acid wastewater are hydrolyzed to produce sodium hydroxide and methanol and release heat; then the sodium hydroxide reacts with the nitric acid to produce sodium nitrate and water;

[0062] S4: Then the mixture of dimethyl carbonate, methyl ethyl carbonate, methanol and sodium nitrate aqueous solution in the quenching kettle 4 enters the boundary kettle 5 for static separation, and the pH of the quenching kettle 4 is controlled to be 7.5;

[0063] S5: The upper organic phase of the boundary tank 5 mainly contains dimethyl carbonate and methyl ethyl carbonate, which returns to the evaporation tower 2 and is taken out from the upper part; the lower salt water phase of the boundary tank 5 contains methanol, water and sodium nitrate, which enters the methanol recovery tower 6, the methanol is taken out from the upper part, and the water and sodium nitrate solution in the kettle enter the compound fertilizer production device;

[0064] The waste catalyst is harmless treated with nitric acid waste water.

[0065] Preferably, in the step S2, the main components entering the quenching kettle 4 from the lower part of the evaporation tower 2 include the following components by volume percentage: dimethyl carbonate 35%, methyl ethyl carbonate 55%, sodium methoxide 10%; in the step S3, the components entering the quenching kettle 4 from the lower part of the nitric acid reduction tower 3 include the following components: water 50%, methanol 45%, nitric acid 2%, and the rest are other impurities. Water and dimethyl carbonate, methyl ethyl carbonate are immiscible.

[0066] Preferably, in the step S2, in the quenching kettle 4, the main components are the mixture of sodium nitrate salt water and methanol, and the upper layer is the mixture of dimethyl carbonate and methyl ethyl carbonate; the stability of the interface of the quenching kettle 4 is controlled by controlling the amount of liquid entering the methanol recovery tower 6 (the range of the interface is 60%) and the amount of liquid entering the evaporation tower 2 (the upper layer has an organic phase) of the quenching kettle 4.

[0067] Preferably, the pH of the medium in the pipeline connecting the bottom of the quenching kettle 4 and the side of the interface tank 5 is controlled at 8.

[0068] In the step S3, the temperature of the quenching kettle 4 is controlled to be not more than 55℃.

[0069] The process medium entering the quenching kettle 4 is kept in weak alkaline state, sodium methoxide is easy to react with water to produce methanol and sodium hydroxide, and the nitric acid at the bottom of the nitric acid reduction tower 3 is completely neutralized and reacted under weak alkaline condition, keeping the weak alkaline state is harmless to the subsequent process equipment, if the state is acidic, the nitric acid entering the subsequent process may corrode the equipment.

[0070] The above is only a relatively optimal embodiment of the present application, and is not used to limit the present application, any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A wastewater treatment system for the production of methyl ethyl carbonate from spent catalyst and dimethyl carbonate, comprising a distillation column (1) for the transesterification reaction to produce methyl ethyl carbonate, characterized in that, The bottom of the distillation column (1) is connected to the side of the evaporation column (2) by a pipe; the bottom of the evaporation column (2) is connected to the side of the quenching vessel (4) by a pipe; the bottom of the nitric acid reduction column (3) for producing dimethyl carbonate by carbonylation of carbon monoxide is connected to the side of the quenching vessel (4) by a pipe; the bottom of the quenching vessel (4) is connected to the side of the interface tank (5) by a pipe; the bottom of the interface tank (5) is connected to the side of the methanol recovery column (6) by a pipe.

2. The wastewater treatment system for the production of methyl ethyl carbonate and dimethyl carbonate according to claim 1, characterized in that: The upper part of the quenching vessel (4) is connected to the upper part of the interface tank (5) by a pipe to form a gas phase balance.

3. The wastewater treatment system for the production of methyl ethyl carbonate and dimethyl carbonate according to claim 1, characterized in that: The side of the interface tank (5) is connected to the bottom of the distillation column (1) and the side of the evaporation column (2) by a connecting pipe, forming a loop.

4. The wastewater treatment system for the production of ethyl methyl carbonate and dimethyl carbonate according to claim 1, characterized in that: An online pH meter (8) is installed on the pipeline connecting the bottom of the quenching vessel (4) to the side of the interface tank (5); a regulating valve (7) is installed on the pipeline connecting the bottom of the nitric acid reduction tower (3) to the side of the quenching vessel (4).

5. The wastewater treatment system for the production of methyl ethyl carbonate and dimethyl carbonate according to claim 1, characterized in that: The quenching vessel (4) is equipped with a stirring device and a cooling water jacket.

6. The wastewater treatment system for the production of ethyl methyl carbonate and dimethyl carbonate according to claim 1, characterized in that: The interface tank (5) is equipped with an interface meter, which controls the flow rate of the light component returning from the interface tank (5) to the evaporator (2) and the heavy component entering the methanol recovery tower from the interface tank (5), thus ensuring the stability of the interface of the interface tank (5).

7. The method for treating wastewater from the production of methyl ethyl carbonate and dimethyl carbonate as described in any one of claims 1-6, characterized in that: The processing method includes the following steps: S1: Sodium methoxide, the catalyst at the bottom of the reactive distillation column (1) of the transesterification process for producing methyl ethyl carbonate, enters the evaporation column (2) together with the reaction liquid. S2: Evaporation tower (2) separates sodium methoxide from the reaction liquid. Unreacted dimethyl carbonate and product ethyl methyl carbonate are collected from the top of the tower. The bottom of the tower mainly contains waste sodium methoxide, dimethyl carbonate and ethyl methyl carbonate. Subsequently, the waste sodium methoxide, dimethyl carbonate and ethyl methyl carbonate enter the quenching tank (4). S3: Nitric acid wastewater enters the quenching vessel (4) from the bottom of the nitric acid reduction tower (3) for the carbonylation method of producing dimethyl carbonate. Sodium methoxide and water in the nitric acid wastewater undergo hydrolysis to produce sodium hydroxide and methanol, which is exothermic. Subsequently, sodium hydroxide reacts with nitric acid to produce sodium nitrate and water. S4: Subsequently, the mixture of dimethyl carbonate, ethyl methyl carbonate, methanol, and sodium nitrate aqueous solution in the quenching vessel (4) enters the interface tank (5) for static separation. S5: The upper organic phase of the interface tank (5) mainly contains dimethyl carbonate and ethyl methyl carbonate, which are returned to the evaporation tower (2) and collected from the top; the lower salt phase of the interface tank (5) contains methanol, water and sodium nitrate, which enter the methanol recovery tower (6), and the methanol is collected from the top. The water and sodium nitrate solution in the tower bottom enter the compound fertilizer production unit. The waste catalyst and nitric acid wastewater were treated to render them harmless.

8. The treatment method of the wastewater treatment system for the production of methyl ethyl carbonate and dimethyl carbonate according to claim 7, characterized in that: In step S2, the components entering the quenching vessel (4) from the bottom of the evaporation tower (2) include, by volume percentage: 30-40% dimethyl carbonate, 52-58% methyl ethyl carbonate, and 8-12% sodium methoxide; in step S3, the components entering the quenching vessel (4) from the bottom of the nitric acid reduction tower (3) include, by volume percentage: 45-55% water, 40-52% methanol, and 1.5-5.5% nitric acid.

9. The treatment method of the wastewater treatment system for the production of methyl ethyl carbonate and dimethyl carbonate according to claim 7, characterized in that: In step S2, the quenching vessel (4) mainly contains a mixture of sodium nitrate brine and methanol, while the upper layer contains a mixture of dimethyl carbonate and ethyl methyl carbonate. The stability of the interface of the quenching vessel (4) is controlled by controlling the amount of liquid entering the methanol recovery tower (6) from the lower layer of the quenching vessel (4) and the amount of liquid entering the evaporation tower (2) from the upper layer of the quenching vessel (4).

10. The treatment method of the wastewater treatment system for the production of methyl ethyl carbonate and dimethyl carbonate according to claim 7, characterized in that: In step S3, the temperature of the quenching kettle (4) is controlled to not exceed 60°C; In step S4, the pH of the medium in the pipe connecting the bottom of the quenching vessel (4) and the side of the interface tank (5) is controlled at 7-8.

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