A method for dehydrating methyl chloride

Abstract

The invention discloses a method for dehydrating methyl chloroethane, and belongs to the technical field of methyl chloroethane production. The method for dehydrating methyl chloroethane comprises the following steps: S1 cooling the crude methyl chloroethane gas containing water; S2 pressure-increasing treatment; S3 azeotropic distillation treatment, and obtaining methyl chloroethane liquid at the top of the azeotropic distillation tower; the cooling temperature in S1 is determined by the following methods: determining the pressure P of the gas after compression in S2; determining the water content m0 ​​when the methyl chloroethane and water have an azeotropic point when the pressure is P; cooling the crude methyl chloroethane gas containing water to a water content m less than m0; and the reflux ratio is 1.5 to 3. The method for dehydrating methyl chloroethane of the present invention can effectively dehydrate methyl chloroethane through azeotropic distillation to obtain methyl chloroethane with low water content by cooling the methyl chloroethane gas containing water before azeotropic distillation, and determining the water content in the crude methyl chloroethane gas after cooling by a specific method.

Description

Technical Field

[0001] The invention relates to the technical field of methyl chloride production, and more specifically to a method for dehydrating methyl chloride. Background Art

[0002] Methyl chloride is mainly used in downstream production equipment, such as organosilicon synthesis, methane chloride, etc. It is particularly sensitive to water. Therefore, finding a green and environmentally friendly method to separate methyl chloride from water to obtain high-quality methyl chloride is the key research direction of industry workers.

[0003] HCl and methanol generate methyl chloride under the action of zinc chloride or aluminum oxide catalyst, and the gas phase enters the lower part of the alkali washing tower. Under a pressure of 0.1-0.2MPa, the top of the tower is sprayed with a cooled 5%-15% NaOH solution to remove the residual hydrogen chloride gas in the synthesis gas, and the gas is further dehydrated due to cooling. The gas after alkali washing enters the drying tower after being defogged by the alkali demister, and is countercurrently contacted with 93%-98% H2SO4 to remove water and dimethyl ether in the gas. The dried gas comes out from the top of the drying tower and enters the acid demister for defog to obtain a high-purity product with a water content of ≤50ppm and methyl chloride ≥99.99%. The biggest problem with this process route is that due to the water absorption of sulfuric acid and the solubility of methyl chloride, the waste sulfuric acid contains a large amount of organic matter such as methyl chloride, dimethyl ether, and dimethyl sulfate. As industrial waste acid, it is difficult to reuse or treat, and there is a trend of becoming hazardous waste.

[0004] The prior art discloses a method for dehydrating methyl chloroethane, wherein the methyl chloroethane solution enters a reboiler through a dehydration tower, low-pressure steam is passed into the reboiler, and the methyl chloroethane solution is heated by the reboiler and enters the dehydration tower from the top of the reboiler, and methyl chloroethane gas with low water content is obtained at the top of the dehydration tower. The methyl chloroethane with high water content is obtained in the tower kettle of the dehydration tower, and after entering a phase separator through a tower bottom pump, the methyl chloroethane is allowed to stand for stratification, and the upper layer is a saturated methyl chloroethane solution, and the lower layer is water. It can be seen that the materials in the tower kettle are stratified, indicating that the prior art uses ordinary distillation to dehydrate methyl chloroethane. However, methyl chloroethane and water easily form azeotropes. When methyl chloroethane and water enter the dehydration tower in the azeotropic region, the vapor generated by boiling has exactly the same composition as the liquid itself, and further water in the methyl chloroethane cannot be removed by ordinary distillation. Summary of the invention

[0005] The technical problem to be solved by the present invention is to overcome the defects and shortcomings of dehydrating methyl chloride by ordinary distillation in the prior art, in which methyl chloride and water reach an azeotropic point when the methyl chloride enters a distillation tower, and the methyl chloride and water cannot be further separated by azeotropic distillation, resulting in excessive moisture content in the methyl chloride at the top of the distillation tower. A dehydration method for methyl chloride is provided, in which the methyl chloride gas containing water is cooled before azeotropic distillation, and the moisture content in the crude methyl chloride gas after cooling is determined by a specific method, so that the azeotropic tower is effectively avoided from being fed with the methyl chloride content when the methyl chloride content is lower than or equal to the azeotropic point value, and the methyl chloride can be effectively dehydrated by azeotropic distillation to obtain methyl chloride with a lower moisture content.

[0006] The above-mentioned purpose of the present invention is achieved through the following technical solutions:

[0007] S1. Pretreatment: Cooling the crude methyl chloride gas containing water;

[0008] S2. Pressurization treatment: compressing the gas treated in S1;

[0009] S3 azeotropic distillation treatment: The gas after S2 treatment was subjected to azeotropic distillation to obtain a chloromethane liquid at the top of the azeotropic distillation tower;

[0010] The cooling temperature in S1 is determined by: determining the pressure P of the gas after compression in S2; determining the water content m0 ​​when the azeotropic point of methyl chloride and water appears when the pressure is P; cooling the crude methyl chloride gas containing water to a water content m <m0;

[0011] The reflux ratio is 1.5~3.

[0012] The method for dehydrating methyl chloroethane of the present invention cools the methyl chloroethane gas containing water before azeotropic distillation, and determines the water content in the crude methyl chloroethane gas after cooling by a specific method, thereby effectively avoiding feeding the azeotropic column with the methyl chloroethane content lower than or equal to the azeotropic point value, and can effectively dehydrate the methyl chloroethane through azeotropic distillation to obtain methyl chloroethane with low water content.

[0013] The principle of methyl chloride dehydration of the present invention is as follows:

[0014] In the art, before two materials are separated by azeotropic distillation, a pressure-raising treatment is usually required to provide pressure for the azeotropic distillation.

[0015] In the art, in a two-component system of methyl chloride and water, when boiling under constant pressure, the content of methyl chloride in the gas phase is the same as the content of methyl chloride in the liquid phase, and the boiling temperature at this time is the azeotropic point. When the content of methyl chloride in the material composition entering the azeotropic column is just at the azeotropic point, the components obtained at the top of the tower and the bottom of the tower are the same, that is, they cannot be separated at all.

[0016] In the present invention, the pressure range P of the gas after S2 compression is first determined; and the moisture content m0 ​​when the azeotropic point of methyl chloride and water appears when the pressure is P is calculated. Before the S2 pressure-increasing treatment, the present invention reduces the moisture content m to less than m0 after cooling treatment, so that after the gas enters the S3 azeotropic distillation, the content of methyl chloride in the material composition entering the azeotropic tower is higher than the content of methyl chloride at the azeotropic point value, so that the methyl chloride with a higher content than the feed can be obtained at the top of the tower, the water with a lower content than the feed can be obtained at the top of the tower, and the tower bottom is a homogeneous mixed solution of methyl chloride and water at the azeotropic point without stratification. That is, the present invention can effectively avoid the content of methyl chloride being lower than or equal to the azeotropic point value of the feed, and the methyl chloride is dehydrated by azeotropic distillation to obtain methyl chloride with a low moisture content.

[0017] The S2 pressure boosting process of the present invention can use a compressor to boost the gas pressure. After the pressure boosting process, the temperature increases as the pressure increases.

[0018] In practical applications, a condenser can be used to condense the gas phase at the top of the azeotropic distillation tower, thereby controlling the top temperature of the azeotropic distillation tower. A reboiler can be used to evaporate the methyl chloride gas in the liquid phase of the bottom of the azeotropic distillation tower, thereby controlling the bottom temperature of the azeotropic distillation tower.

[0019] Under the corresponding pressure conditions, controlling the top temperature and bottom temperature of the azeotropic distillation tower is an important basis for separating water from monochloromethane.

[0020] In S3, during the azeotropic distillation treatment, the reflux ratio is 1.5 to 3. The present invention can control the water content of the methyl chloride at the top of the azeotropic distillation tower by controlling the reflux ratio.

[0021] The present invention does not need to use sulfuric acid as a desiccant for dehydration, and prevents sulfuric acid from absorbing water and dissolving methyl chloride, thereby preventing the waste sulfuric acid from containing a large amount of organic hazardous wastes such as methyl chloride, dimethyl ether, and dimethyl sulfate.

[0022] Preferably, the cooling temperature in S1 is determined by the following method: in S2, the gas pressure is 0.5-0.85 MPa; in S1, after cooling, the moisture content in the crude methyl chloride gas is ≤630 ppm.

[0023] In the art, the pressure of the gas after the compressor pressurization treatment before the azeotropic distillation of methyl chloride and water is generally 0.5-0.8 MPa.

[0024] The inventors have found that in a two-component system of methyl chloride and water,

[0025] When the pressure is 0.1MPa and the temperature is -7.2℃, the content of methyl chloride in the gas phase is higher than that in the liquid phase at the same temperature.

[0026] When the pressure after the boost treatment is 0.5MPa, the moisture content m1=1199ppm when methyl chloride and water have an azeotropic point. When the pressure after the boost treatment is 0.8MPa, the moisture content m2=1807ppm when methyl chloride and water have an azeotropic point. At this time, after S1 is cooled, the moisture content in the crude methyl chloride gas is 630ppm. Since 630ppm is less than m1 and also less than m2, when the pressure after the boost treatment is between 0.5MPa and 0.8MPa, after S2 is boosted, it enters the S3 azeotropic distillation treatment, effectively avoiding the azeotropic tower being fed with methyl chloride content less than or equal to the azeotropic point value. Therefore, methyl chloride can be effectively dehydrated by azeotropic distillation to obtain methyl chloride with ultra-low moisture content.

[0027] More preferably, in S2, the gas treated in S1 is compressed to a gas pressure of 0.8 MPa and a temperature of 90°C.

[0028] Preferably, in S1, the crude chloroform gas containing water is cooled to -7.2 to -7.5°C, and after cooling, the water content in the crude chloroform gas is ≤630 ppm.

[0029] When methyl chloride and water reach the azeotropic point at 0.8 MPa (g), the content of methyl chloride is 0.998193 and the water content is 1807 ppm.

[0030] When methyl chloride and water reach the azeotropic point at 0.6 MPa (g), the methyl chloride content is 0.998801 and the water content is 1199 ppm.

[0031] In the present invention, in S1. pretreatment, the crude chloroform gas containing water is cooled to -7.2 to -7.5°C, at which time the chloroform content in the gas phase is ≥0.999370, that is, the water content in the gas phase is ≤0.000630, that is, the water content is ≤630PPm, avoiding the azeotropic point of 0.8MPa(g) and 0.6MPa(g), and effectively preventing the chloroform content from being lower than or equal to the azeotropic point region. That is, the chloroform gas can be compressed to 0.6MPa or 0.8MPa in the S2 pressure-increasing treatment.

[0032] Preferably, in S3, the top temperature of the azeotropic distillation tower is 27-40°C, and the bottom temperature of the azeotropic distillation tower is 55-70°C.

[0033] When the pressure of the methyl chloride gas is 0.6-0.8 MPa after the pressure-raising treatment in S2, the top temperature of the azeotropic distillation tower is 27-40°C, and the bottom temperature of the azeotropic distillation tower is 55-70°C in S3. The top temperature is relatively low, which can effectively remove moisture from the methyl chloride gas.

[0034] Preferably, in S1, before cooling, the water content of the crude methyl chloride gas containing water is 1600-2000 ppm.

[0035] The invention can process crude methyl chloroethane gas with a moisture content of 1600-2000 ppm before entering the alkali washing tower.

[0036] Preferably, in S3, the top pressure of the azeotropic distillation tower is 0.6-0.78 MPa.

[0037] More preferably, in S3, the top pressure of the azeotropic distillation tower is 0.78 MPa.

[0038] Preferably, in S3, the bottom pressure of the azeotropic distillation tower is 0.62-0.79 MPa.

[0039] More preferably, in S3, the bottom pressure of the azeotropic distillation tower is 0.79 MPa.

[0040] In S3, during the azeotropic distillation treatment, the top pressure of the azeotropic distillation tower is 0.6-0.78 MPa, and the bottom pressure of the azeotropic distillation tower is 0.62-0.79 MPa. Within this pressure range, methyl chloride and water can be effectively separated and the water in the methyl chloride gas can be removed.

[0041] Preferably, in S3, the reflux ratio is 2-3.

[0042] The larger the reflux ratio is, the lower the water content in the chloroform is, which is beneficial to improving the quality of the chloroform.

[0043] Preferably, in S3, the liquid phase of the azeotropic distillation tower top gas phase after condensation is returned to the top of the azeotropic distillation tower.

[0044] The process of S3 azeotropic distillation of the present invention is as follows: the gas phase material from S2 enters the middle part of the azeotropic distillation tower, the water and methyl chloride in the material are two key components of the azeotropic distillation, methyl chloride is a light key component, and water is a heavy key component. The light key component methyl chloride rises to the top of the tower through the azeotropic distillation tower, is condensed by the condenser, and changes from gas phase to liquid phase; then enters the reflux tank, and then is sent back to the top of the azeotropic distillation tower as reflux through the reflux pump.

[0045] The condensed methyl chloride and water continuously flow to the bottom of the tower, forming an azeotrope of light and heavy key components and then discharged from the bottom of the tower.

[0046] Since the content of the light key component of methyl chloride in the gas phase is higher than that in the liquid phase at the same temperature and pressure, the gas phase material of the light key component heated by the tower bottom reboiler can transfer mass and heat to the liquid phase returning to the top of the azeotropic distillation tower, thereby achieving the purpose of separating the light key component methyl chloride and the heavy key component water.

[0047] Preferably, the pre-treatment in S1 further includes an alkali washing treatment before the cooling treatment.

[0048] The alkali washing treatment is to treat the crude chloroform gas containing water with dilute sodium hydroxide to remove HCl gas in the crude chloroform gas containing water.

[0049] Preferably, the pressure of the alkali washing treatment is 0.1-0.2 MPa.

[0050] The pressure of the alkali washing tower is 0.1-0.2Mpa. The material is flashed in the alkali washing tower, so that the methyl chloride turns back into gas phase and returns to the original state.

[0051] Preferably, the concentration of the alkaline washing solution is 5% to 15%.

[0052] Preferably, in the S1 pre-treatment, a demisting treatment is also included after the cooling treatment, the gas phase S2 after the demisting treatment is pressurized, and the liquid phase after the demisting treatment is returned to the alkaline washing treatment.

[0053] The function of demisting is to remove trace liquid components entrained in the gas phase.

[0054] Preferably, in S3, the gas treated in S2 is fed from the middle of the azeotropic distillation tower, and the tower bottom material after azeotropic distillation treatment is returned to the alkali washing treatment.

[0055] In S3, the gas treated in S2 can be fed from the middle of the azeotropic distillation tower. After the azeotropic distillation treatment, the azeotropic material in the tower bottom is returned to the alkali washing tower for alkali washing treatment, which can effectively reduce the amount of monochloromethane discharged to the alkaline tower.

[0056] The present invention returns the tower bottom material after azeotropic distillation treatment to the alkali washing tower for alkali washing treatment, thereby preventing the discharge of waste water containing methyl chloride, preventing air pollution and the generation of waste water, and also preventing the occurrence of fire or explosion accidents caused by residual methyl chloride.

[0057] In practical applications, the alkali at the bottom of the alkali washing tower can be returned to the top of the alkali washing tower after circulating reflux cooling, which is beneficial to remove the heat of the alkali washing process and can ensure the required alkali spray density in the tower during the alkali washing process, so that the alkali washing process is thorough.

[0058] Compared with the prior art, the present invention has the following beneficial effects:

[0059] The invention discloses a method for dehydrating methyl chloroethane. The method comprises cooling methyl chloroethane gas containing water before azeotropic distillation, and determining the water content in the crude methyl chloroethane gas after cooling by a specific method, thereby effectively avoiding the methyl chloroethane content being lower than or equal to the azeotropic point region, and being able to effectively dehydrate methyl chloroethane through azeotropic distillation to obtain methyl chloroethane with lower water content.

[0060] The method for dehydrating methyl chloride of the present invention can effectively dehydrate methyl chloride with a water content of 1851 ppm to obtain methyl chloride with a water content of less than 2 ppm. Furthermore, under the pressure condition of 0.6-0.8 Mpa in an azeotropic distillation tower, effective dehydration treatment is performed to obtain methyl chloride gas with a water content of less than 1 ppm. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] Figure 1 Schematic diagram of the process of Example 1 of the present invention.

[0062] In the figure: 1-alkali washing tower, 2-first condenser, 3-alkali demister, 4-compressor, 5-azeotropic distillation tower, 6-top condenser, 7-reboiler, 8-reflux tank, 9-second condenser, 10-reflux pump. DETAILED DESCRIPTION

[0063] The present invention is further described below in conjunction with specific embodiments, but the embodiments do not limit the present invention in any form. Unless otherwise specified, the raw materials and reagents used in the embodiments of the present invention are conventionally purchased raw materials and reagents.

[0064] Example 1

[0065] like Figure 1 The method for dehydrating methyl chloride comprises the following steps:

[0066] S1. Pretreatment: The crude methyl chloride gas with a moisture content of 1851 ppm is subjected to alkali washing, cooling and demisting treatment, specifically including:

[0067] Alkali washing treatment: the raw material gas is introduced into the alkali washing tower 1 from the bottom end, and the raw material gas is sprayed with alkali washing liquid at the top of the alkali washing tower 1. The alkali washing liquid is NaOH, and the concentration of the alkali washing liquid is 10%; the pressure of the alkali washing treatment is 0.1Mpa(g).

[0068] The crude chloroform gas containing water is cooled using the first condenser 2, wherein the cooling temperature in S1 is determined by: determining the pressure of the gas after compression in S2 to be 0.8 MPa; determining the water content m0=1807 ppm when the azeotropic point of chloroform and water occurs at 0.8 MPa;

[0069] When the crude chloroform gas containing water is cooled to -7.2°C, the moisture content in the crude chloroform gas after cooling is 630 ppm, which is less than m0 = 1807 ppm;

[0070] Demisting treatment: Use the alkaline demister 3 to demist the cooled gas, and the liquid phase after demisting treatment is returned to the alkaline washing tower 1 for alkaline washing treatment.

[0071] After being treated with S1, the contents of methyl chloride and water were 0.99937 and 0.00063 respectively.

[0072] S2. Pressurization treatment: Compress the gas phase after demisting treatment in S1 using compressor 4 to a gas pressure of 0.8 MPa and a temperature of 90 ° C;

[0073] S3. Azeotropic distillation treatment: The gas treated in S2 was subjected to azeotropic distillation treatment to obtain methyl chloride liquid at the top of the azeotropic distillation tower 5; the contents of methyl chloride and water were 0.9999995 and 0.0000005, respectively.

[0074] Wherein, in S3, during the azeotropic distillation treatment, the top pressure of the azeotropic distillation tower 5 is 0.78 MPa, and the bottom pressure of the azeotropic distillation tower 5 is 0.79 MPa;

[0075] The top temperature of the azeotropic distillation tower 5 is 36.5°C, and the bottom temperature of the azeotropic distillation tower 5 is 65°C;

[0076] The reflux ratio is 2.5.

[0077] Specifically,

[0078] The gas treated with S2 is fed from the middle of the azeotropic distillation tower 5.

[0079] The light key component monochloromethane rises to the top of the azeotropic distillation tower 5, is condensed by the condenser 6, and changes from gas phase to liquid phase; then enters the reflux tank 8, and part of the liquid phase is sent back to the top of the azeotropic distillation tower 5 as reflux through the reflux pump 10.

[0080] The condensed methyl chloride and water in the azeotropic distillation tower 5 continuously flow to the bottom of the tower, and the light key components are evaporated through the bottom reboiler 7, while the formed azeotrope remains in the bottom of the tower.

[0081] Since the content of the light key component of methyl chloride in the gas phase is higher than that in the liquid phase at the same temperature and pressure, the light key component gas phase material heated by the tower bottom reboiler 7 can transfer mass and heat to the liquid phase returning to the top of the azeotropic distillation tower 5.

[0082] The bottom material after being treated in the azeotropic distillation tower 5 is returned to the alkali washing tower 1 for alkali washing treatment.

[0083] Among them, the top material of the azeotropic distillation tower can be cooled by cooling water.

[0084] Example 2

[0085] A method for dehydrating methyl chloride, which is different from Example 1 in that:

[0086] S1. Cooling the crude chloroform gas containing water using the first condenser 2, wherein the cooling temperature in S1 is determined by: determining that the pressure of the gas after compression in S2 is 0.6 MPa; determining that at 0.6 MPa, the water content m0 ​​= 1199 ppm when the azeotropic point of chloroform and water occurs;

[0087] When the crude chloroform gas containing water is cooled to -7.2°C, the moisture content in the crude chloroform gas after cooling is 630 ppm, which is less than m0 = 1199 ppm;

[0088] S2. Pressurization treatment: Compress the gas phase after demisting treatment in S1 using compressor 4 to a gas pressure of 0.6 MPa;

[0089] In S3, during the azeotropic distillation treatment, the top pressure of the azeotropic distillation tower 5 is 0.6 MPa, and the bottom pressure of the azeotropic distillation tower 5 is 0.62 MPa;

[0090] The top temperature of the azeotropic distillation tower 5 is 27°C, and the bottom temperature of the azeotropic distillation tower 5 is 55°C;

[0091] The reflux ratio is 1.8.

[0092] The contents of monochloromethane and water obtained were 0.9999991 and 0.0000009 respectively.

[0093] The materials in the bottom of the azeotropic distillation tower 5 after azeotropic distillation treatment are returned to the alkali washing tower 1 for alkali washing treatment.

[0094] Among them, the top material of the azeotropic distillation tower can be cooled by chilled water.

[0095] Example 3

[0096] A method for dehydrating methyl chloride, which is different from Example 1 in that:

[0097] Different from Example 1, the first condenser 2 is used to cool the crude chloroform gas containing water to -7.5°C; after cooling, the water content in the crude chloroform gas is 310 ppm.

[0098] The rest is the same as Example 1 and will not be described again here.

[0099] Example 4

[0100] A method for dehydrating methyl chloride, which is different from Example 1 in that:

[0101] Different from Example 1, the first condenser 2 is used to cool the crude chloromethane gas containing water to -7.1°C; after cooling, the water content in the crude chloromethane gas is 820 ppm.

[0102] The rest is the same as Example 1 and will not be described again here.

[0103] Example 5

[0104] A method for dehydrating methyl chloride, which is different from Example 1 in that:

[0105] Different from Example 1, the first condenser 2 is used to cool the crude chloroform gas containing water to -7.6°C; after cooling, the water content in the crude chloroform gas is 280 ppm.

[0106] The rest is the same as Example 1 and will not be described again here.

[0107] Example 6

[0108] A method for dehydrating methyl chloride, which is different from Example 1 in that:

[0109] S1. Cooling the crude chloroform gas containing water using the first condenser 2, wherein the cooling temperature in S1 is determined by: determining that the pressure of the gas after compression in S2 is 0.92 MPa; determining that at 0.92 MPa, the water content m0 ​​= 2200 ppm when the azeotropic point of chloroform and water occurs;

[0110] When the crude chloroform gas containing water is cooled to -7.2°C, the moisture content in the crude chloroform gas after cooling is 630ppm, which is less than m0=2200ppm;

[0111] In the S2. pressure-increasing process, the gas treated in S1 is compressed and the gas pressure is 0.92 MPa.

[0112] The top pressure of the azeotropic distillation tower was 0.9 MPa, the bottom pressure was 0.91 MPa, the top temperature was 45° C., and the bottom temperature was 76° C. The rest was the same as in Example 1 and will not be described again.

[0113] Example 7

[0114] A method for dehydrating methyl chloride, which is different from Example 1 in that:

[0115] The pressure of the alkaline washing treatment is 0.2Mpa(g).

[0116] The rest is the same as Example 1 and will not be described again here.

[0117] Example 8

[0118] A method for dehydrating methyl chloride, which is different from Example 1 in that the top temperature of S3 is set to 45°C.

[0119] The rest is the same as Example 1 and will not be described again here.

[0120] Comparative Example 1

[0121] A method for dehydrating methyl chloride, which is different from Example 1 in that the reflux ratio at the top of S3 tower is 1.

[0122] The rest is the same as Example 1 and will not be described again here.

[0123] Comparative Example 2

[0124] A method for dehydrating methyl chloride, which is different from Example 1 in that:

[0125] S1. Cooling the crude chloroform gas containing water using the first condenser 2, wherein the cooling temperature in S1 is determined by: determining that the pressure of the gas after compression in S2 is 0.43 MPa; determining that at 0.43 MPa, the water content m0 ​​= 400 ppm when the azeotropic point of chloroform and water occurs;

[0126] When the crude chloroform gas containing water is cooled to -7.2°C, the moisture content in the crude chloroform gas after cooling is 630 ppm, which is greater than m0 = 400 ppm;

[0127] In the S2. pressure-increasing process, the gas treated in S1 is compressed and the gas pressure is 0.43 MPa.

[0128] The set pressure of the azeotropic distillation tower is 0.41MPa, the bottom pressure is 0.42MPa, the top temperature is 13.69℃, and the bottom temperature is 41.24℃.

[0129] The rest is the same as Example 1 and will not be described again here.

[0130] Comparative Example 3

[0131] A method for dehydrating methyl chloride, which is different from Example 1 in that:

[0132] In step S1, cooling of the crude chloromethane gas containing water is not included, the crude chloromethane gas containing water is at room temperature, and the water content in the crude chloromethane gas is 1851 ppm;

[0133] Direct S2. Boost processing.

[0134] The rest is the same as Example 1 and will not be described again here.

[0135] Comparative Example 4

[0136] A method for dehydrating methyl chloride, which is different from Example 2 in that:

[0137] S1. Cooling the crude chloroform gas containing water using the first condenser 2, wherein the cooling temperature in S1 is determined by: determining that the pressure of the gas after compression in S2 is 0.6 MPa; determining that at 0.6 MPa, the water content m0 ​​= 1199 ppm when the azeotropic point of chloroform and water occurs;

[0138] Specifically, in S1, the crude chloroform gas containing water is cooled to 0°C. After cooling, the water content in the crude chloroform gas is 1199 ppm, which is equal to m0=1199 ppm;

[0139] The rest is the same as Example 2 and will not be described again here.

[0140] Results

[0141] The method for dehydrating methyl chloride in the above-mentioned embodiment and comparative example was tested by the following performance test method:

[0142] Determination of water content in chloroform: in accordance with HG / T 3674-2018 Industrial chloroform standard method.

[0143] The specific test results are shown in Table 3 below:

[0144]

[0145] It can be seen from the above data that the method for dehydrating methyl chloride of the present invention can effectively dehydrate methyl chloride with a moisture content of 1851 ppm under the pressure condition of 0.6-0.9 MPa in an azeotropic distillation tower to obtain methyl chloride gas with a moisture content of less than 2 ppm. Furthermore, under the pressure condition of 0.6-0.8 MPa in an azeotropic distillation tower, methyl chloride gas with a moisture content of less than 1 ppm can be effectively dehydrated.

[0146] It can be seen from Comparative Example 1 that the reflux ratio is too low and the water content in the obtained methyl chloride gas is 20 ppm.

[0147] It can be seen from Comparative Example 2 that the water content in the obtained chloroform is 450ppm, which cannot meet the requirements of the water content in chloroform. This is because the pressure P of the gas after S2 compression is determined to be 0.4MPa; it is determined that when the pressure is 0.4MPa, the water content m0=400ppm when chloroform and water have an azeotropic point. In S1, the crude chloroform gas containing water is cooled to -7.2°C. After cooling, the water content in the crude chloroform gas is m=630ppm. In S1, the crude chloroform gas containing water is cooled to a water content m greater than m0. This is because the content of chloroform is lower than the azeotropic point region, that is, the corresponding water content is high, and the gas at the top of the tower under the condition of 0.4MPa pressure of the azeotropic distillation tower is opposite to obtain a material with higher water content than the feed, while the tower bottom obtains a material at the azeotropic point (m0=400ppm), so the requirements of the water content in the chloroform gas cannot be met.

[0148] It can be seen from Comparative Example 3 that the water content in the obtained chloroform is 1903ppm, which cannot meet the requirements of the water content in chloroform. This is because the pressure P of the gas after S2 compression is determined to be 0.8MPa; it is determined that when the pressure is 0.8MPa, the water content m0=1807ppm when chloroform and water have an azeotropic point. Without the S1 pre-treatment: cooling the crude chloroform gas containing water, the water content m=1851ppm in the crude chloroform gas containing water is greater than m0. This is also because the content of chloroform is lower than the azeotropic point area, that is, the corresponding water content is high, and the gas at the top of the azeotropic distillation tower under the condition of 0.8MPa pressure is opposite to obtain a material with higher water content than the feed, while the tower bottom obtains a material at the azeotropic point (m0=1807ppm), so the requirements of the water content in the chloroform gas cannot be met.

[0149] As can be seen from Comparative Example 4, it is determined that the pressure P of the gas after S2 compression is 0.6MPa; it is determined that when the pressure is 0.6MPa, the moisture content m0=1199ppm when methyl chloride and water have an azeotropic point. In S1, the crude methyl chloride gas containing water is cooled to 0°C. After cooling, the moisture content in the crude methyl chloride gas is 1199ppm. In S1, the crude methyl chloride gas containing water is cooled to a moisture content m equal to m0. After S3 azeotropic distillation treatment, the moisture content in the obtained methyl chloride is 1199ppm, which does not meet the requirements. This is because the composition ratio of methyl chloride and water in the gas phase develops in the same direction as the composition ratio of methyl chloride and water in the liquid phase under the condition of 0.6MPa pressure in the azeotropic distillation tower, that is, an azeotropic point of 1199ppm appears, and the top of the tower and the bottom of the tower obtain products with the same moisture content, that is, no further azeotropic distillation treatment can be performed, so the requirement for the moisture content in the methyl chloride gas cannot be met.

[0150] It can be seen from Example 8 that, compared with Example 1, the top temperature of S3 is controlled at 45°C. The higher the temperature of the azeotropic distillation tower, the easier it is for the material in the bottom of the tower to be evaporated to the top of the tower. At this time, the water content in the chloroform is 2ppm, which is slightly higher than the water content in the chloroform in Example 1.

[0151] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the embodiments here. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A method for dehydrating methyl chloride, characterized in that: The steps include: S1. Pretreatment: Cooling the crude methyl chloride gas containing water; S2. Boosting treatment: compressing the gas treated in S1; S3 azeotropic distillation treatment: The gas after S2 treatment was subjected to azeotropic distillation to obtain a chloromethane liquid at the top of the azeotropic distillation tower; The reflux ratio of azeotropic distillation is 1.5~3; In S1, the crude chloroform gas containing water is cooled to -7.2~-7.5°C; after cooling, the water content in the crude chloroform gas is ≤630ppm; In S2, the gas pressure is 0.5~0.85MPa; In S3, the top temperature of the azeotropic distillation tower is 27-40°C, and the bottom temperature of the azeotropic distillation tower is 55-70°C; In S3, the top pressure of the azeotropic distillation tower is 0.6~0.78MPa; the bottom pressure of the azeotropic distillation tower is 0.62~0.79MPa.

2. The method for dehydrating methyl chloride as claimed in claim 1, characterized in that: In S1, before cooling, the water content of the crude methyl chloride gas containing water is 1600-2000 ppm.

3. The method for dehydrating methyl chloride according to claim 1, characterized in that: In S3, the reflux ratio is 2~3.

4. The method for dehydrating methyl chloride according to claim 1, characterized in that: In S3, the liquid phase of the gas phase at the top of the azeotropic distillation tower is condensed and returned to the top of the azeotropic distillation tower.

5. The method for dehydrating methyl chloride according to claim 1, characterized in that: In the S1 pre-treatment, an alkali washing treatment is also included before the cooling treatment, and the pressure of the alkali washing treatment is 0.1-0.2Mpa.

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