Novel technology for concentrating dried waste sulfuric acid of chloromethane synthesis device

Abstract

The invention provides a novel technology for concentrating dried waste sulfuric acid of a chloromethane synthesis device. According to a traditional sulfuric acid recovery process, waste sulfuric acid and water are mixed and hydrolyzed, then rectification and concentration are carried out, during hydrolysis, the waste sulfuric acid usually needs to be diluted to the concentration of about 50%, a large amount of introduced water needs to be removed during rectification and concentration, and steam consumption is huge. The process provided by the invention is as follows: waste sulfuric acid after drying and impurity removal in chloromethane synthesis firstly exchanges heat with concentrated high-temperature concentrated sulfuric acid and then enters a rectifying tower 1, 96% concentrated sulfuric acid is extracted from the tower bottom, most sulfuric acid in the waste sulfuric acid is recovered, and a gas phase at the tower top contains moisture, a small amount of sulfuric acid and organic matters (dimethyl sulfate and the like) and the like. The method comprises the following steps: condensing a gas phase at the top of a rectifying tower 1, mixing with a certain proportion of water, feeding into an upper tower 2 of a hydrolysis tower, hydrolyzing dimethyl sulfate and methyl hydrogen sulfate into sulfuric acid and methanol, removing part of organic matters and water through an upper tower heater, feeding the sulfuric acid in a tower kettle into a lower tower 3 of the hydrolysis tower, and concentrating to 96% through vacuum rectification.

Description

Technical Field

[0001] The invention belongs to the field of chemical industry and relates to a new process for concentrating dried waste sulfuric acid from a chloromethane synthesis device. Background Art

[0002] In the production process of silicone monomers, methyl chloride is the main raw material. During its production process, it needs to be washed with concentrated sulfuric acid to remove water, dimethyl ether and other organic impurities. Dilute sulfuric acid will be produced in this process.

[0003] The dilute sulfuric acid produced as a by-product of the methyl chloride synthesis process usually contains a certain amount of impurities such as methyl chloride, dimethyl ether, and dimethyl sulfate.

[0004] The output of dilute sulfuric acid accounts for about 4.5% of the monomer production. As the scale of organosilicon monomers expands, the output of dilute sulfuric acid increases accordingly.

[0005] The traditional sulfuric acid concentration and recovery process directly hydrolyzes the waste acid by adding water, which introduces a large amount of additional water, increases the processing capacity of the subsequent concentration device, and the dissolved methyl chloride cannot be effectively recovered and utilized. Summary of the invention

[0006] The invention provides a new process for concentrating dry waste sulfuric acid from a chloromethane synthesis device, aiming to effectively recover dissolved chloromethane therein and reduce energy consumption for sulfuric acid concentration.

[0007] The object of the present invention is achieved by the following scheme: A process for concentrating waste sulfuric acid from a chloromethane synthesis unit, comprising the following process route: (a) The waste sulfuric acid synthesized from methyl chloride is heated by heat exchange with the concentrated high-temperature concentrated sulfuric acid after concentration and then enters the distillation tower 1, where it is heated and concentrated after distillation to obtain concentrated sulfuric acid with a concentration of more than 96%. The concentrated sulfuric acid with a concentration of more than 96% is heat exchanged, filtered, and cooled to obtain qualified concentrated sulfuric acid; (b) After the gas phase at the top of the distillation tower 1 is condensed, a portion of it is mixed with water and then enters the upper tower of the hydrolysis tower 2 for hydrolysis, and the other portion is refluxed to the distillation tower 1; (b) A portion of the material from the upper tower of the hydrolysis tower II enters the lower tower of the hydrolysis tower. The material from the lower tower of the hydrolysis tower II is heated and concentrated to obtain concentrated sulfuric acid of more than 96%. The concentrated sulfuric acid of more than 96% is filtered and cooled to obtain qualified concentrated sulfuric acid.

[0008] The waste sulfuric acid synthesized from methyl chloride in step (a) comprises 8-10% dimethyl sulfate, about 10-15% water, 1-3% methyl chloride and a small amount of impurities such as dimethyl ether and methanol. In step (a), the initial temperature of the waste sulfuric acid is 20-40°C. The temperature of the waste sulfuric acid after heat exchange with the high-temperature concentrated sulfuric acid extracted from the distillation tower 1 and the lower tower 3 of the hydrolysis tower is 80-100°C. The waste sulfuric acid is heated to the feed temperature required by the distillation tower 1 through coupled heat exchange, thereby reducing steam consumption and facilitating the smooth operation of the distillation tower 1.

[0009] In step (a), the temperature of the bottom of the distillation tower is controlled at 120-150°C, the temperature of the top of the tower is controlled at 40-80°C, the reflux ratio is controlled at 2-3, and the pressure of the top of the tower is -0.085--0.1MPa. The boiling point of the waste sulfuric acid is reduced by high vacuum, the relative volatility of each component is increased, and the composition of the extracted materials in the bottom and the top of the tower is ensured by controlling the temperature and reflux ratio, ensuring that the concentration of the concentrated sulfuric acid extracted from the bottom of the tower reaches more than 95%, and the gas phase components condensed at the top of the tower are 1-2% sulfuric acid, 5-6% water, and 92-94% dimethyl sulfate.

[0010] In step (b), the mass ratio of the feed to the upper tower of the hydrolysis tower is condensed gas phase: water = 1: 0.3-0.5. The circulation volume and the extraction volume ratio of the material in the upper tower of the second hydrolysis tower are 4-6. The bottom temperature of the upper tower of the second hydrolysis tower is controlled at 60-100°C, and the pressure of the upper tower of the second hydrolysis tower is controlled at 10-50kPa. Dimethyl sulfate is hydrolyzed into sulfuric acid and methanol by adding water, and the temperature of the tower is controlled by heating and circulating reflux of the tower kettle to ensure complete hydrolysis. The composition of the gas phase at the top of the tower is 95-98% methanol and 2-5% water. The composition entering the lower tower of the second hydrolysis tower is 5-15% water, 10-15% methanol, and 75-80% sulfuric acid.

[0011] The bottom temperature of the second lower tower of the hydrolysis tower is controlled at 100-130℃, and the pressure of the lower tower of the hydrolysis tower is -0.08--0.1MPa. The boiling point of sulfuric acid is reduced by high vacuum, and the relative volatility between the components is increased to ensure that the concentration of concentrated sulfuric acid produced from the bottom of the tower reaches more than 95%, and the gas phase components at the top of the tower are 20-30% water and 70-80% methanol.

[0012] The methanol in the gas phase at the top of the upper tower of the second hydrolysis tower and the lower tower of the hydrolysis tower is recovered through a methanol recovery device.

[0013] Advantages of the present invention: 1. The present invention firstly utilizes the heat of concentrated sulfuric acid to preheat the waste sulfuric acid, and raises the temperature of the waste sulfuric acid to the feed temperature required by the distillation tower 1 through coupled heat exchange, thereby reducing steam consumption and facilitating the smooth operation of the distillation tower 1.

[0014] 2. The traditional sulfuric acid concentration process first performs the hydrolysis process. Because there is a large amount of sulfuric acid in the waste sulfuric acid, the amount of water added is large, the water to be evaporated in the subsequent concentration becomes more, and the steam consumption is high. However, the present invention first uses vacuum distillation to control the vacuum degree (-0.085 to -0.1MPa), temperature (the tower bottom temperature is controlled at 120 to 150°C, and the tower top temperature is controlled at 40 to 80°C) and reflux ratio (2-3) to concentrate most of the sulfuric acid in the waste sulfuric acid (98% of the sulfuric acid in the feed) in the tower bottom, and the dimethyl sulfate to be hydrolyzed is condensed at the top of the tower, and then mixed with process water (70% less water than that introduced by direct hydrolysis) according to the mass ratio for hydrolysis and concentration. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a process flow chart of the present invention, wherein, a distillation tower 1, an upper tower of a hydrolysis tower 2, a lower tower of a hydrolysis tower 3, a sulfuric acid heat exchanger 4, a heat exchanger 1 5-1, a heat exchanger 2 5-2, a heat exchanger 3 5-3, a reflux tank 6, a vacuum pump 1 7-1, a vacuum pump 2 7-2, a heater 8, a condenser 9, a reboiler 10-1, a reboiler 2 10-2, and a filter 11. DETAILED DESCRIPTION

[0016] Example 1 The chloromethane synthesis unit dries the waste sulfuric acid concentration unit, the waste sulfuric acid pipeline is connected to the sulfuric acid heat exchanger 4, the bottom outlet of the sulfuric acid heat exchanger 4 is connected to the distillation tower 1, and the top outlet of the distillation tower 1 is connected to the heat exchanger 2 5-2; The heat exchanger 2 5-2 is connected via a reflux tank 6, the reflux tank 6 and the process water pipeline are connected to the upper tower of the hydrolysis tower 2 2, the lower part of the upper tower of the hydrolysis tower 2 2 is connected to the heater 8 via a pipeline and then connected to the lower tower of the hydrolysis tower 2 2; The bottom of the distillation tower 1 and the bottom of the lower tower of the hydrolysis tower 2 are connected to the sulfuric acid heat exchanger 3 through pipelines to recover concentrated sulfuric acid.

[0017] The reflux tank 6 is connected to the upper part of the distillation tower 1 through a pipeline to achieve partial circulation; the lower part of the upper tower of the hydrolysis tower 2 is connected to the heater 8 through a pipeline and is also connected to the upper tower of the hydrolysis tower 2.

[0018] The reflux tank 6 is provided with a vacuum pump 7-1, which is connected to the incineration tail gas; The top of the lower tower of the hydrolysis tower 2 is connected to the heat exchanger 3 5-3, the heat exchanger 3 5-3 is connected to the condenser 9, the condenser 9 is connected to the vacuum pump 2 7-2, and the vacuum pump 2 7-2 is connected to the methanol recovery tank; the top of the upper tower of the hydrolysis tower 2 is connected to the methanol recovery tank.

[0019] The sulfuric acid heat exchanger 3 is connected to the filter 11, the filter 11 is connected to the heat exchanger 5-1, and the heat exchanger 5-1 is connected to the concentrated sulfuric acid storage tank.

[0020] Example 2 Taking the treatment of 100 tons of methyl chloride to synthesize waste sulfuric acid as an example, the device of Example 1 is used to carry out the following process: The feed rate of waste sulfuric acid is controlled at 0.7t / h. The waste sulfuric acid first enters the sulfuric acid heat exchanger 4, and after heat exchange with the concentrated sulfuric acid, the temperature rises to 80°C, and then enters the distillation tower 1. The temperature of the bottom of the distillation tower 1 is controlled at 140-150°C, and the steam addition rate of the reboiler 10-1 is 0.5t / h; the tower top temperature is controlled at 70-80°C, and the tower top reflux rate is 0.6m 3 / h, the top pressure of the tower is controlled at -0.085~-0.1MPa by the vacuum pump 7-1, the output of the kettle of the distillation tower 1 is 0.55t / h, the material in the reflux tank 6 is mixed with 0.05t / h of process water at 0.13t / h through the pipeline and then enters the upper tower 2 of the hydrolysis tower, the bottom temperature of the upper tower 2 of the hydrolysis tower is controlled at 60~100℃, the steam addition amount of the heater 8 is 0.1t / h, and the pressure of the upper tower 2 of the hydrolysis tower is controlled at 10~50kPa; the bottom temperature of the lower tower 3 of the hydrolysis tower is controlled at 100~130℃, the steam addition amount of the reboiler 10-2 is 0.2t / h, the pressure of the lower tower 3 of the hydrolysis tower is controlled at -0.08~-0.1MPa by the vacuum pump 7-1, and the output of the kettle of the lower tower 3 of the hydrolysis tower is 0.1t / h.

[0021] Example 3 The feed rate of waste sulfuric acid is controlled to be 1.0 t / h. The waste sulfuric acid first enters the sulfuric acid heat exchanger 4, and after heat exchange with the concentrated sulfuric acid, the temperature rises to 81°C, and then enters the distillation tower 1. The temperature of the bottom of the distillation tower 1 is controlled at 120-150°C, and the steam addition rate of the reboiler 10-1 is 0.7 t / h; the tower top temperature is controlled at 40-80°C, and the tower top reflux rate is 0.85m 3 / h, the top pressure of the tower is controlled at -0.085~-0.1MPa by the vacuum pump 7-1, the output of the kettle of the distillation tower 1 is 0.78t / h, the material in the reflux tank 6 is mixed with 0.08t / h of process water through the pipeline at 0.19t / h and then enters the upper tower 2 of the hydrolysis tower, the bottom temperature of the upper tower 2 of the hydrolysis tower is controlled at 60~100℃, the steam addition amount of the heater 8 is 0.15t / h, and the pressure of the upper tower 2 of the hydrolysis tower is controlled at 10~50kPa; the bottom temperature of the lower tower 3 of the hydrolysis tower is controlled at 100~130℃, the steam addition amount of the reboiler 10-2 is 0.28t / h, the pressure of the lower tower 3 of the hydrolysis tower is controlled at -0.08~-0.1MPa by the vacuum pump 7-1, and the output of the kettle of the lower tower 3 of the hydrolysis tower is 0.14t / h.

[0022] Example 4 The feed rate of waste sulfuric acid is controlled to be 1.5t / h. The waste sulfuric acid first enters the sulfuric acid heat exchanger 4, and after heat exchange with the concentrated sulfuric acid, the temperature rises to 83°C, and then enters the distillation tower 1. The temperature of the bottom of the distillation tower 1 is controlled at 120-150°C, and the steam addition rate of the reboiler 10-1 is 1t / h; the tower top temperature is controlled at 40-80°C, and the tower top reflux rate is 1.27m 3 / h, the top pressure of the tower is controlled at -0.085~-0.1MPa by the vacuum pump 7-1, the output of the kettle of the distillation tower 1 is 1.17t / h, the material in the reflux tank 6 is mixed with 0.12t / h of process water through the pipeline at 0.29t / h and then enters the upper tower 2 of the hydrolysis tower, the bottom temperature of the upper tower 2 of the hydrolysis tower is controlled at 60~100℃, the steam addition amount of the heater 8 is 0.23t / h, and the pressure of the upper tower 2 of the hydrolysis tower is controlled at 10~50kPa; the bottom temperature of the lower tower 3 of the hydrolysis tower is controlled at 100~130℃, the steam addition amount of the reboiler 10-2 is 0.42t / h, the pressure of the lower tower 3 of the hydrolysis tower is controlled at -0.08~-0.1MPa by the vacuum pump 7-1, and the output of the kettle of the lower tower 3 of the hydrolysis tower is 0.20t / h.

[0023] Example 5 The device was operated according to the steps and methods in Example 2, and the top pressure of the distillation tower 1 was controlled to be -0.065 to -0.8 MPa. During the operation, the sulfuric acid concentration in the bottom of the distillation tower 1 was only 85%, and contained about 8% dimethyl sulfate.

[0024] Example 6 The device was operated according to the steps and methods in Example 2, and the top temperature of the distillation tower 1 was controlled to 90-100°C (controlled by reducing the reflux ratio). During the operation, the sulfuric acid concentration in the bottom of the distillation tower 1 was qualified, the output of the bottom of the distillation tower 1 was 0.50 t / h, the output of the reflux tank 6 was 0.20 t / h, the sulfuric acid content in the top gas phase increased to about 10%, the process water consumption in the hydrolysis process increased to 0.10 t / h, and the steam consumption of the hydrolysis tower increased simultaneously.

Claims

1. A process for concentrating waste sulfuric acid from a chloromethane synthesis unit, characterized in that: The steps include: (a) The waste sulfuric acid synthesized from methyl chloride is heated by heat exchange with the concentrated high-temperature concentrated sulfuric acid after concentration and then enters the distillation tower 1, where it is heated and concentrated after distillation to obtain concentrated sulfuric acid with a concentration of more than 96%. The concentrated sulfuric acid with a concentration of more than 96% is heat exchanged, filtered, and cooled to obtain qualified concentrated sulfuric acid; (b) After the gas phase at the top of the distillation tower 1 is condensed, a portion of it is mixed with water and then enters the upper tower of the hydrolysis tower 2 for hydrolysis, and the other portion is refluxed to the distillation tower 1; (b) A portion of the material from the upper tower of the hydrolysis tower II enters the lower tower of the hydrolysis tower. The material from the lower tower of the hydrolysis tower II is heated and concentrated to obtain concentrated sulfuric acid of more than 96%. The concentrated sulfuric acid of more than 96% is filtered and cooled to obtain qualified concentrated sulfuric acid.

2. The process for concentrating the dry waste sulfuric acid from the methyl chloride synthesis unit according to claim 1, characterized in that: The waste sulfuric acid synthesized by methyl chloride in step (a) comprises 8-10% of dimethyl sulfate, 10-15% of water and 1-3% of methyl chloride.

3. The process for concentrating the dried waste sulfuric acid from the methyl chloride synthesis unit according to claim 1, characterized in that: In step (a), the waste sulfuric acid is heated to 80-100°C by heat exchange.

4. The process for concentrating the dried waste sulfuric acid from the methyl chloride synthesis unit according to claim 1, characterized in that: In step (a), the temperature of the bottom of the distillation tower is controlled at 120-150°C, the temperature of the top of the tower is controlled at 40-80°C, and the pressure of the top of the tower is controlled at -0.085--0.1 MPa.

5. The process for concentrating the dried waste sulfuric acid from the methyl chloride synthesis unit according to claim 1, characterized in that: In step (b), the mass ratio of the feed to the hydrolysis tower is condensed gas phase: water = 1:0.3-0.

5.

6. The process for concentrating the dried waste sulfuric acid from the methyl chloride synthesis unit according to claim 1, characterized in that: In step (b), the reflux ratio of the distillation tower 1 is 2-3.

7. The process for concentrating the dried waste sulfuric acid from the methyl chloride synthesis unit according to claim 1, characterized in that: The bottom temperature of the upper tower of the second hydrolysis tower is controlled at 60-100°C, and the pressure of the upper tower of the second hydrolysis tower is controlled at 10-50 kPa.

8. The process for concentrating the dried waste sulfuric acid from the methyl chloride synthesis unit according to claim 1, characterized in that: The ratio of the circulation volume to the withdrawal volume of the material in the upper tower of the second hydrolysis tower is 4-6.

9. The process for concentrating the dried waste sulfuric acid from the methyl chloride synthesis unit according to claim 1, characterized in that: The bottom temperature of the second lower tower of the hydrolysis tower is controlled at 100-130°C, and the pressure of the lower tower of the hydrolysis tower is -0.08--0.1MPa.

10. The process for concentrating the dried waste sulfuric acid from the methyl chloride synthesis unit according to claim 1, characterized in that: Methanol is recovered from the top of the second upper tower of the hydrolysis tower and the top of the lower tower of the hydrolysis tower.

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