CN115894163B - Method and device for directly producing chloromethane by using byproduct hydrogen chloride of difluoro chloromethane - Google Patents
Method and device for directly producing chloromethane by using byproduct hydrogen chloride of difluoro chloromethane Download PDFInfo
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Abstract
The invention belongs to the technical field of chemical production, and particularly relates to a method and a production device for directly producing chloromethane by using a byproduct hydrogen chloride of difluoro chloromethane. Synthesizing chloromethane by taking a byproduct hydrogen chloride of difluoro chloromethane as a raw material; the reaction output is then treated. The method not only effectively solves the treatment pressure of byproduct hydrogen chloride in the production process of the difluoro-chloromethane, directly saves the treatment cost of the byproduct hydrogen chloride of the difluoro-chloromethane, fully utilizes the byproduct as a resource, efficiently recovers and purifies the trifluoro-methane mixed in the hydrogen chloride, and solves the problem of environmental pollution of the trifluoro-methane. Meanwhile, the method also greatly reduces the production cost of chloromethane, and thus the invention brings double economic benefits to enterprises.
Description
Technical Field
The invention belongs to the technical field of chemical production, and particularly relates to a method and a production device for directly producing chloromethane by using a byproduct hydrogen chloride of difluoro chloromethane.
Background
Difluoro chloromethane (R22) with chemical formula of CHClF 2 Is a hydrogen-containing fluorochlorohydrocarbon, which is colorless and has a slightly sweet smell. Is mainly used as raw materials for preparing tetrafluoroethylene, and raw materials for producing refrigerant, spray, pesticide and the like. A large amount of byproduct hydrogen chloride is generated in the production process of R22. The industrial hydrochloric acid is generally directly absorbed by water to prepare 31 percent industrial hydrochloric acid, and the industrial hydrochloric acid market is saturated, so that the pressure of waste acid treatment or sales exists in enterprises.
In addition, the device also produces a small amount of by-product of the trifluoromethane (R23), and the boiling point of the trifluoromethane is 84.4 ℃ below zero and the boiling point of the trifluoromethane is 85 ℃ below zero, so that the separation is difficult to realize by common rectification, and the trifluoromethane is mixed in the hydrogen chloride to be produced from the device. Trifluoromethane is a greenhouse gas, which must be recovered and disposed of according to environmental ecology requirements.
CN102101651a discloses a method and apparatus for refining by-product hydrogen chloride of difluoro chloromethane and recovering trifluoro methane, the method firstly uses the characteristic that solubility of hydrogen chloride and trifluoro methane in water is very different, a set of hydrochloric acid conventional analysis apparatus is newly built, the separation of trifluoro methane and hydrogen chloride is realized by using absorption analysis principle, HCl gas is resolved through heat and mass transfer process in the analysis tower, HCl gas is collected from the top of the analysis tower, and then high purity HCl gas is obtained through condensation water removal and acid mist trapping water removal. The hydrogen chloride is used for producing vinyl chloride monomer, and the crude trifluoromethane is further used after rectification and purification.
However, this method has the following disadvantages:
1. the equipment investment is large, and the corrosion problems of equipment and pipelines exist. The hydrochloric acid analysis device comprises a falling film absorber, an analysis tower, a reboiler, a condenser, a cooler, a hydrochloric acid tank, a hydrochloric acid pump and other devices, and a large number of fluorine-lined pipelines, wherein the devices and pipelines have high cost, for example, the device investment of a set of 5 ten thousand tons/year hydrogen chloride conventional analysis device is more than 1000 ten thousand yuan, and the total investment is about 3000 ten thousand yuan. And because the reaction pressure of vinyl chloride synthesis in the production of the downstream product polyvinyl chloride is high, partial equipment and pipeline pressure is high, and the pressure of HCl gas needs to reach 0.4-0.5MPa; and the temperature is high and reaches 130-150 ℃, the corrosion is serious, and the production stable operation is adversely affected.
2. The operation cost is high, the dilute hydrochloric acid at the tower bottom of the resolving tower needs to be cooled to 30-40 ℃ in the absorption resolving process, and the reboiler at the tower bottom of the resolving tower needs to be heated to 130-150 ℃, so that a large amount of circulating water and water vapor are consumed. Each ton of hydrogen chloride is treated, 1 ton of steam and 100 degrees of electricity are consumed, and the cost is 300 yuan/ton.
3. Although the solubility of the trifluoromethane in the hydrochloric acid is low, a certain solubility still exists, and finally the trifluoromethane dissolved in the hydrochloric acid in the falling film absorber is resolved together with the hydrogen chloride in the resolving tower. The content of R23 in the resolved hydrogen chloride is 0.05-0.3%, so that the recovery rate of R23 is only between 90-95%.
4. The system pressure is too high, and the requirement on equipment processing is high. Because the boiling point of the trifluoromethane is very low, the recovered crude trifluoromethane needs to be compressed before rectification, the compression pressure is more than 4.0Mpa (G), and the high requirements on compressors, pipelines and equipment are met, so that certain safety risks exist.
5. The competitiveness of the byproduct hydrogen chloride and calcium carbide for producing the polyvinyl chloride by a calcium carbide method is low. Along with the increasing price of the calcium carbide and the long transportation distance, the method has no advantages in the cost of preparing the polyvinyl chloride by the calcium carbide method in the eastern area, and the method has great environmental protection pressure by producing a large amount of calcium carbide mud and mercury-containing catalyst, so that the byproduct hydrogen chloride is not suitable for the production of the polyvinyl chloride by the calcium carbide method due to the regional limitation in the aspects of economy and environmental protection.
Disclosure of Invention
The invention provides a method for directly producing chloromethane by using byproduct hydrogen chloride of difluoromethane, which not only effectively solves the problem of treating pressure of byproduct hydrogen chloride in the production process of difluoromethane, directly saves the treating cost of the byproduct hydrogen chloride of difluoromethane, fully utilizes the byproduct as a resource, efficiently recovers and purifies the trifluoromethane mixed in the hydrogen chloride, and solves the problem of environmental pollution of the trifluoromethane. Meanwhile, the method also greatly reduces the production cost of chloromethane, and thus the invention brings double economic benefits to enterprises.
The specific technical scheme is as follows:
a method for directly producing chloromethane by using a byproduct hydrogen chloride of difluoro chloromethane comprises the following steps:
(1) Synthesizing chloromethane: and (3) the difluoro chloromethane byproduct hydrogen chloride is subjected to reduced pressure metering and overheated and then is mixed with overheated methanol to carry out a methanol hydrochlorination reaction, so as to synthesize chloromethane.
The reaction product in the production of difluoro chloromethane firstly enters a hydrogen chloride tower, and byproduct hydrogen chloride is separated from the tower top. The byproduct hydrogen chloride of difluoro chloromethane mainly comprises the following components in percentage by volume: 97-97.5% of HCl, 0-0.005% of difluoro-chloromethane, 2-2.5% of trifluoro-methane and 0-0.2% of HF. The byproduct hydrogen chloride gas has higher purity, and can be used as a reaction raw material for producing chloromethane. The reaction type of the hydrochlorination of methanol is gas-solid phase catalytic reaction.
(2) Treating reaction discharge:
the reaction discharge of chloromethane, trifluoromethane, methanol, byproduct HCl of chloromethane and dimethyl ether is chilled and cooled, and then enters a washing unit for washing.
The water washing is mainly to remove the byproduct HCl of chloromethane in the reaction discharge material to obtain byproduct hydrochloric acid; and the methanol in the reaction discharge is also removed from the reaction discharge along with water washing, and the methanol is washed with water to become methanol hydrochloric acid solution. If the byproduct hydrogen chloride of difluoromethane contains a small amount of HF, the HF generates hydrofluoric acid after water washing and is removed from the reaction discharge.
The byproduct hydrochloric acid obtained by water washing is directly resolved, and chloromethane and trifluoromethane resolved from the hydrochloric acid are returned to the water washing unit.
The byproduct hydrochloric acid analysis is different from the hydrochloric acid analysis in the prior art, wherein the hydrochloric acid analysis in the prior art is to analyze hydrogen chloride by heating concentrated hydrochloric acid; the invention is to separate out chloromethane and trichloromethane dissolved in dilute hydrochloric acid by heating by-product hydrochloric acid. If the byproduct hydrogen chloride of difluoro-chloromethane contains a small amount of difluoro-chloromethane, the difluoro-chloromethane dissolved in the dilute hydrochloric acid is also resolved.
And (3) sequentially performing alkali washing, sulfuric acid drying and compression on the reaction discharge material after washing, and condensing chloromethane to obtain non-condensable gas containing the trifluoro methane and the chloromethane and condensed chloromethane.
The alkaline washing can be performed by adopting NaOH solution with the mass fraction of 10%, the pH value is controlled to be about 11, and residual hydrogen chloride in the reaction discharge is removed by the alkaline washing. And drying sulfuric acid to remove dimethyl ether and water in the reaction discharge, wherein the dimethyl ether reacts with sulfuric acid to generate dimethyl sulfate.
Rectifying the condensed chloromethane to obtain the gas of the trifluoromethane and the chloromethane with the mass fraction of more than 99.95 percent.
A small amount of the trifluoromethane entrained in the condensation of the chloromethane is removed from the chloromethane as a rectified light component. The temperature of the top of the rectifying tower used for rectifying is 40-45 ℃ and the pressure is 1.1-1.2MPa.
And introducing the trifluoro methane gas and the non-condensable gas containing trifluoro methane and chloromethane into a methane chloride solvent to absorb the chloromethane.
Methyl chloride is absorbed into a methane chloride solvent to form a methyl chloride solution; and (3) the chloromethane solution is subjected to chloromethane analysis, and the resolved chloromethane is returned to the water washing unit.
Methyl chloride, also known as methyl chloride, is an organic compound of the formula CH 3 Cl is colorless gas at normal temperature and pressure and is dissolved in methane chloride solvent.
And (3) compressing the trifluoromethane which is not absorbed by the methane chloride solvent, cooling, condensing to remove the chloromethane and the solvent carried by the trifluoromethane, and recovering to obtain the trifluoromethane with the purity of more than 99%. The recovered trifluoromethane has higher purity and can be sent to an incinerator or used for other purposes, such as being used as a solvent for supercritical extraction, a low-temperature refrigerant or used as a fire extinguishing agent and a raw material for manufacturing tetrafluoroethylene. And the condensed chloromethane and solvent are returned to the chloromethane analysis unit.
In the method for directly producing chloromethane by using the byproduct hydrogen chloride of difluoro chloromethane, the mass ratio of the byproduct hydrogen chloride of difluoro chloromethane to methanol in the step (1) is 1.2-1.3:1.
In the invention, the pressure of the hydrogen chloride in the step (1) of the method for directly producing the chloromethane by using the byproduct hydrogen chloride of the difluoro chloromethane is 0.35-0.5MPa after the pressure is reduced; the temperature of the hydrochlorination reaction of the methanol is 220-260 ℃ and the pressure is 0.2-0.4MPa.
In the invention, the reaction discharge in the step (2) of the method for directly producing chloromethane by using the byproduct hydrogen chloride of difluoro chloromethane is chilled and cooled to 30-50 ℃.
In the method, the analysis temperature of the byproduct hydrochloric acid in the step (2) of the method for directly producing chloromethane by using the byproduct hydrogen chloride of difluoro chloromethane is 90-100 ℃, and the analysis pressure is 0.25-0.35MPa; the reaction discharge after sulfuric acid drying is compressed to 0.7-0.9MPa, and chloromethane condensation is carried out at 25-35 ℃.
In the method, the methane chloride solvent in the step (2) of the method for directly producing chloromethane by using the byproduct hydrogen chloride of difluoro chloromethane is one or more of dichloromethane, chloroform and carbon tetrachloride.
In the invention, in the step (2) of the method for directly producing chloromethane by using the byproduct hydrogen chloride of difluoro chloromethane, the methane chloride solvent absorbs the chloromethane under the conditions of the temperature of-10-0 ℃ and the pressure of 0-0.05 MPa.
In the invention, in the step (2) of the method for directly producing chloromethane by using the byproduct hydrogen chloride of difluoro chloromethane, chloromethane solution is subjected to chloromethane analysis under the conditions of the temperature of 110-130 ℃ and the pressure of 0.3-0.5 MPa.
In the invention, after the trifluoromethane is compressed to 0.5-0.7MPa in the step (2) of the method for directly producing chloromethane by using the byproduct hydrogen chloride of difluoromethane, the trifluoromethane is cooled at the temperature of-10-0 ℃. The methyl chloride and solvent can be removed by cooling to a lower temperature at this pressure to achieve the desired purity.
The invention also provides a production device for the method for directly producing chloromethane by using the byproduct hydrogen chloride of difluoromethane, which comprises a chloromethane synthesis reactor, wherein a feed inlet of the chloromethane synthesis reactor is connected with a methanol superheater and a byproduct hydrogen chloride superheater of difluoromethane through pipelines; preferably, the discharge pipe of the methanol superheater and the discharge pipe of the difluoro chloromethane byproduct hydrogen chloride superheater are connected into the feed pipe of the chloromethane synthesis reactor through a gas mixer. In the industrial process, a gas mixer is usually used when two gases are mixed, and the gas mixer is the gas mixer in the prior art.
The discharge port of the chloromethane synthesis reactor is sequentially connected with the first feed port of the quenching tower and the water washing tower;
the water scrubber comprises a water scrubber kettle outlet and a water scrubber tower top outlet; the outlet of the tower kettle of the water washing tower is connected with a first feed inlet of the water washing tower through a hydrochloric acid resolving tower; the top outlet of the water washing tower is sequentially connected with an alkaline washing tower, a sulfuric acid drying tower, a chloromethane compressor and a chloromethane condenser;
the chloromethane condenser comprises a condensate outlet and a noncondensable gas outlet, and the condensate outlet is connected with the chloromethane rectifying tower; the non-condensable gas outlet is connected with a solvent absorption tower after being converged with a top discharge port of the chloromethane rectifying tower;
the solvent absorption tower comprises a solvent absorption tower top outlet and a solvent absorption tower bottom outlet, and the solvent absorption tower top outlet is connected with a trifluoromethane cooler through a trifluoromethane compressor; and the outlet of the tower bottom of the solvent absorption tower is connected with a chloromethane desorption tower. The top outlet of the chloromethane analysis tower is connected with the second feed inlet of the water washing tower through a pipeline.
The beneficial effects of the invention are as follows: along with the expansion of downstream organic silicon, the demand of methyl chloride is increased and the price is kept high, so that the direct production of high-value methyl chloride by utilizing the byproduct hydrogen chloride of difluoro-chloromethane can realize the recycling utilization of low-value byproduct hydrogen chloride, and save the treatment cost of difluoro-chloromethane production on byproduct hydrogen chloride, including the investment of treatment equipment and the subsequent sales pressure; and the production cost of high-value chloromethane is reduced, the purchasing cost of the hydrogen chloride serving as a production raw material is saved, and the economic benefit of chloromethane is further improved. Thus, the method of the invention brings double economic benefits to enterprises.
The specific advantages are as follows:
1. the difluoromethane-chloromethane byproduct hydrogen chloride is used as the raw material to prepare chloromethane, so that the production cost of chloromethane is reduced, the raw material cost is reduced by 300 yuan/ton, and the chloromethane yield is increased by 280 yuan/ton. Meanwhile, compared with a pure hydrogen chloride raw material, the method adopts difluoro chloromethane byproduct hydrogen chloride for the production of chloromethane, has no adverse effect on the yield and selectivity of chloromethane, and can reach more than 99 percent and more than 99 percent of chloromethane selectivity; and the production amount of hydrochloric acid and dimethyl ether which are by-products of chloromethane is not increased.
2. Compared with the prior art, the construction cost and the operation cost of the adsorption and analysis device for the byproduct hydrogen chloride of the difluoro-chloromethane, which are included in a plurality of large-scale falling film absorbers, are saved, the process flow is simplified, and the byproduct hydrogen chloride of the difluoro-chloromethane is not required to be cooled to low temperature after being heated to high temperature, so that a large amount of circulating water and water vapor are avoided being consumed. In the prior art, 1 ton of steam and 100 degrees of electricity are consumed for each ton of hydrogen chloride treatment, which is equivalent to 300 yuan/ton. If the method is calculated according to the scale of a 5 ten thousand ton device, 3000 ten thousand yuan fixed investment and 1500 ten thousand yuan operation cost per year can be saved by adopting the method.
3. The recovery rate of the trifluoromethane is improved, and the method effectively recovers the trifluoromethane dissolved in the hydrochloric acid and condensed in the chloromethane through the analysis of the hydrochloric acid and the rectification of the chloromethane, wherein the recovery rate of the trifluoromethane reaches more than 99 percent.
4. Compared with the patent CN102101651A, the method omits a high-pressure compressor and a trifluoromethane rectifying tower for trifluoromethane with pressure of more than 4.0Mpa (G); according to the characteristic that the solubility difference of the trifluoromethane and the chloromethane in the methane chloride solvent is large, the solvent absorption method is adopted to separate the trifluoromethane from the chloromethane, and then the trifluoromethane gas is only required to be compressed to 0.5-0.7MPa for cooling, so that the operation pressure is low, the operation is safe and easy, and the purity of the trifluoromethane can reach more than 99%.
5. Because the byproduct hydrogen chloride of difluoro chloromethane has no other heavy components, the chloromethane can reach the purity of more than 99.95 percent without arranging a heavy removal rectifying tower in the production flow of the chloromethane, thereby simplifying the flow and saving steam.
In conclusion, the process for producing chloromethane by recycling byproduct hydrogen chloride of the difluoro chloromethane device provided by the invention directly participates in the reaction to produce chloromethane after the byproduct hydrogen chloride is overheated, so that a great amount of fixed investment and operation cost for treating the hydrogen chloride are avoided, the process flow is simplified, and the economic benefit of a company is improved. The method simultaneously realizes efficient recovery and purification of the trifluoromethane, is simple and easy to operate, and has recovery rate of more than 99 percent and purity of more than 99 percent.
Drawings
FIG. 1 is a schematic diagram of a production device used for the method for directly producing chloromethane by using the byproduct hydrogen chloride of difluoro chloromethane.
Wherein: 1 is a difluoromethane byproduct hydrogen chloride superheater, 2 is a methanol superheater, 3 is a chloromethane synthesis reactor, 4 is a quenching tower, 5 is a water washing tower, 6 is an alkaline washing tower, 7 is a sulfuric acid drying tower, 8 is a chloromethane compressor, 9 is a chloromethane condenser, 10 is a chloromethane rectifying tower, 11 is a solvent absorption tower, 12 is a chloromethane analyzing tower, 13 is a trifluoromethane compressor, 14 is a trifluoromethane cooler, and 15 is a hydrochloric acid analyzing tower.
Detailed Description
The invention will be further illustrated with reference to specific examples.
1. Purity of trifluoromethane: the measurement was carried out by infrared spectrometry using a Shimadzu gas chromatograph GC-2014, DB-624 column.
2. Yield of methyl chloride: the conversion of methanol and the ratio of the feed are calculated from the yield of chloromethane.
3. In the examples, the composition of the reaction discharge, the composition of the discharge gas at the top of the tower after hydrochloric acid is resolved, the composition of the discharge gas after sulfuric acid is dried, the composition of the noncondensable gas condensed by chloromethane and the composition of the discharge gas at the top of the chloromethane rectifying tower are all obtained by sampling and detecting by a hydrogen Flame Ionization Detector (FID).
Example 1
The production device for the direct chloromethane production method by using the byproduct hydrogen chloride of the difluoromethane comprises a chloromethane synthesis reactor 3, wherein the chloromethane synthesis reactor 3 is a fixed bed reactor, and the bed layer is filled with a solid catalyst, such as activated alumina or activated carbon impregnated with zinc chloride.
The feed inlet of the chloromethane synthesis reactor 3 is connected with the methanol superheater 2 and the difluoro chloromethane byproduct hydrogen chloride superheater 1 through pipelines; wherein the discharge pipe of the methanol superheater and the discharge pipe of the difluoro chloromethane byproduct hydrogen chloride superheater can be directly connected with the feed pipe of the chloromethane synthesis reactor; or the feed pipe of the chloromethane synthesis reactor can be connected through a gas mixer. The gas mixer is a gas mixer in the prior art, such as JY-QHZ-5 gas mixer.
The discharge port of the chloromethane synthesis reactor 3 is sequentially connected with the first feed ports of the chilling tower 4 and the water washing tower 5.
The cooling tower 4 is a graphite Raschig ring packed tower; the graphite Raschig ring is in the shape of a ring with the outer diameter equal to the height, and has the advantages of simple shape, large specific surface area and good corrosion resistance.
The water washing tower 5 is a plastic pall ring packed tower. The plastic pall ring is an open-pore ring type packing with the outer diameter equal to the height, a plurality of window holes are formed in the annular wall on the basis of the Raschig ring packing, the positions of the upper layer of window holes and the lower layer of window holes are staggered in opposite directions, and the open-pore area generally accounts for about 30% of the total area of the annular wall, so that gas and liquid in the packing tower can freely pass through the window holes, the flow condition of gas and liquid phases in the packing layer is greatly improved, and the hydrodynamic and mass transfer performance of the packing are improved.
The water scrubber 5 comprises a water scrubber kettle outlet and a water scrubber tower top outlet; the outlet of the tower kettle of the water washing tower is connected with a first feed inlet of the water washing tower 5 through a hydrochloric acid resolving tower 15; after the chloromethane and the trifluoromethane carried in the byproduct hydrochloric acid obtained by washing are resolved, the chloromethane and the trifluoromethane enter the first feed inlet of the washing tower 5 from the top outlet of the hydrochloric acid resolving tower 15 and return to the washing tower 5.
The hydrochloric acid analysis tower 15 is a PTFE Raschig ring packed tower. The PTFE Raschig ring is formed by opening six layers of rectangular small windows on the wall of a common Raschig ring, overlapping small window blades at the center of the ring, and overlapping the upper and lower layers of windows. The main difference between the Raschig ring filler and the Raschig ring filler is that a rectangular window hole is arranged on the side wall, the window She Wanru of the window hole is arranged on the ring center, and the distribution performance of gas and liquid is greatly improved compared with that of the Raschig ring due to the opening of the ring wall, and especially the inner surface area of the ring can be fully utilized.
The top outlet of the water washing tower is sequentially connected with an alkaline washing tower 6, a sulfuric acid drying tower 7, a chloromethane compressor 8 and a chloromethane condenser 9.
The alkaline washing tower 6 is a plastic pall ring packing tower, a pH on-line detector is arranged in the alkaline washing tower, and when the pH in the alkaline washing tower is less than 11, waste alkali liquid is discharged, and fresh alkali liquid enters the alkaline washing tower.
The sulfuric acid drying tower 7 is a plastic pall ring packed tower.
The chloromethane condenser 9 comprises a condensate outlet and a noncondensable gas outlet, and the condensate outlet is connected with the chloromethane rectifying tower 10; the non-condensable gas outlet is connected with a solvent absorption tower 11 after being converged with a top discharge port of the chloromethane rectifying tower 10.
The chloromethane condenser 9 is a shell-and-tube condenser. The shell-and-tube condenser is a closed water-cooled condenser which consists of a shell, a tube plate, a heat transfer tube bundle, a cooling water distribution part (a water cover), cooling water, inlet and outlet tube joints of a refrigerant and the like.
The solvent absorption tower 11 comprises a solvent absorption tower top outlet and a solvent absorption tower bottom outlet, and the solvent absorption tower top outlet is connected with a trifluoromethane cooler 14 through a trifluoromethane compressor 13; the outlet of the solvent absorption tower bottom is connected with a chloromethane desorption tower 12. The top outlet of the chloromethane analysis tower 12 is connected with the second feed inlet of the water washing tower 5 through a pipeline.
The solvent absorption tower 11 is a metal pall ring packed tower. The metal pall ring is made of metal sheet by punching, and two rows of window holes with inner extending tongue blades are formed on the ring wall. Five tongue blades are arranged on each row of window holes, each tongue blade is bent into the ring and points to the ring center, the positions of the upper layer of window holes and the lower layer of window holes are almost overlapped at the center, the positions of the upper layer of window holes and the lower layer of window holes are staggered, the total area of the general openings is about 35 percent of the whole annular wall area, and because a plurality of window holes are formed in the annular wall, gas and liquid in the tower can freely pass through the windows, the pressure reduction can be reduced by half, the mass transfer efficiency can be improved by about 20 percent, and the separation efficiency is high when the same treatment amount is achieved.
The trifluoromethane cooler 14 is a shell-and-tube condenser. The chloromethane analysis tower 12 is a metal pall ring packed tower.
Example 2
The method for directly producing chloromethane by using the byproduct hydrogen chloride of difluoromethane adopts the production device described in the embodiment 1, and comprises the following specific steps:
(1) Synthesizing chloromethane: the byproduct hydrogen chloride separated from a hydrogen chloride tower in a difluoro chloromethane production device is decompressed to 0.35MPa, and enters a difluoro chloromethane byproduct hydrogen chloride superheater 1 at a mass flow rate of 5000kg/hr in a metering way, and is superheated to 220 ℃.
The other raw material methanol is fed into the methanol superheater 2 at a mass flow rate of 4000kg/hr to be superheated to 220 ℃.
And introducing superheated difluoromethane byproduct hydrogen chloride and superheated methanol into a chloromethane synthesis reactor 3 according to a mass ratio of 1.25:1, and reacting at 220 ℃ under 0.4MPa to synthesize chloromethane.
(2) Treating reaction discharge: cooling the reaction discharge material to 40 ℃ through a quenching tower 4; as is known from sampling, infrared spectrometry analysis and calculation, in the reaction discharge at this time, 6220kg/hr of chloromethane, 125kg/hr of trifluoromethane, 25kg/hr of methanol, 392kg/hr of chloromethane byproduct HCl, 18kg/hr of dimethyl ether and 2220kg/hr of water are used.
The reaction discharged material after chilling and cooling enters a water scrubber 5 for water scrubbing to remove HCl and methanol in the reaction discharged material.
The byproduct hydrochloric acid 2700kg/hr is obtained by water washing, the byproduct hydrochloric acid directly enters the hydrochloric acid resolving tower 15 from the tower bottom outlet of the water washing tower 5, and is resolved under the condition of 90 ℃ and 0.25MPa, wherein 55kg/hr of chloromethane and 8kg/hr of trifluoromethane are resolved in the hydrochloric acid, and returned to the water washing tower 5 from the tower top of the hydrochloric acid resolving tower 15.
The reaction discharge after water washing firstly enters an alkaline washing tower 6 through the top outlet of the water washing tower 5, and the residual HCl in the reaction discharge is removed through alkaline washing by adopting NaOH solution with the mass fraction of 10 percent.
The reaction material is alkali washed and then enters a sulfuric acid drying tower 7 to remove water and dimethyl ether, and then methyl chloride with mass flow of 6220kg/hr and trifluoromethane with mass flow of 125kg/hr are obtained.
Introducing the obtained mixed gas of methyl chloride and trifluoro methane into a methyl chloride compressor 8 to be compressed to 0.8MPa, and then delivering the mixed gas to a methyl chloride condenser 9 to be condensed at 30 ℃; wherein the noncondensable gas is 100kg/hr of trifluoromethyl and 20kg/hr of chloromethane.
The condensed chloromethane enters a chloromethane rectifying tower 10 for rectification, a small amount of trifluoromethyl in the chloromethane is removed, and the product chloromethane with the mass fraction of more than 99.95% is discharged from the tower kettle, wherein the mass fraction of the product chloromethane is 6220 kg/hr; the top of the tower is discharged light component trifluoromethane gas, the temperature of the top of the tower is 40 ℃, the pressure is 1.1MPa, and at the moment, the trifluoromethane gas contains 25kg/hr of trifluoromethane and 25kg/hr of chloromethane.
The above-mentioned noncondensable gas was introduced into the solvent absorption column 11 together with a gas of trifluoromethane, wherein 125kg/hr of trifluoromethane and 45kg/hr of chloromethane were contained in the combined gas.
Chloroform solvent with mass flow rate of 5000kg/hr enters from the top of the solvent absorption tower 11, methyl chloride in gas is absorbed under the temperature of-10 ℃ and the pressure of 0.05MPa, 44.5kg/hr of methyl chloride and 0.5kg/hr of trifluoromethyl are absorbed and enter the methyl chloride analysis tower 12 from the tower kettle discharge, the methyl chloride is analyzed under the temperature of 110 ℃ and the pressure of 0.3MPa, and 44.5kg/hr of methyl chloride and 0.5kg/hr of trifluoromethyl are returned from the methyl chloride analysis tower 12 to the water washing tower 5.
The gas which is not absorbed by the chloroform solvent and contains 124.5kg/hr of trifluoromethane, 0.5kg/hr of chloromethane and 0.5kg/hr of chloroform is discharged from the top of the solvent absorption tower 11, compressed to 0.5MPa by the trifluoromethane compressor 13, enters the trifluoromethane cooler 14 to be cooled at-10 ℃, and 0.5kg/hr of chloromethane and 0.5kg/hr of chloroform entrained in the solvent absorption tower 11 are condensed and returned to the chloromethane analysis tower 12. 124.5kg/hr of recovered trifluoromethane is fed into incinerator for incineration.
Calculated, the recovery rate of the trifluoromethane in this example was 99.6%, the yield of the directly produced chloromethane was 99.9%, and the selectivity of the chloromethane was 99%.
The purity of the recovered trifluoromethane was 99.2% as determined by infrared spectroscopy.
Example 3
The method for directly producing chloromethane by using the byproduct hydrogen chloride of difluoromethane adopts the production device described in the embodiment 1, and comprises the following specific steps:
(1) Synthesizing chloromethane: the byproduct hydrogen chloride separated from the hydrogen chloride tower in the difluoro chloromethane production device is decompressed to 0.5MPa, and enters a difluoro chloromethane byproduct hydrogen chloride superheater 1 at a mass flow rate of 4900kg/hr to be superheated to 260 ℃.
The other raw material methanol is fed into the methanol superheater 2 at a mass flow rate of 4000kg/hr to be superheated to 260 ℃.
And (3) mixing superheated difluoromethane byproduct hydrogen chloride and superheated methanol according to a mass ratio of 1.225:1, introducing into a chloromethane synthesis reactor 3, and reacting at 260 ℃ under 0.2MPa to synthesize chloromethane.
(2) Treating reaction discharge: cooling the reaction discharge to 50 ℃ through a quenching tower 4; as is known from sampling, infrared spectrometry analysis and calculation, in this reaction, 6220kg/hr of chloromethane, 122.5kg/hr of trifluoromethane, 25kg/hr of methanol, 294.5kg/hr of chloromethane as a byproduct, 18kg/hr of dimethyl ether and 2220kg/hr of water are contained in the reaction mixture.
The reaction discharged material after chilling and cooling enters a water scrubber 5 for water scrubbing to remove HCl and methanol in the reaction discharged material.
Washing with water to obtain 2600kg/hr of byproduct hydrochloric acid, directly feeding the byproduct hydrochloric acid into a hydrochloric acid analysis tower 15, and analyzing at 100deg.C under 0.35MPa, wherein 55kg/hr of chloromethane and 8kg/hr of trifluoromethane are analyzed in hydrochloric acid, and returned to the water washing tower 5 from the top of the hydrochloric acid analysis tower 15.
The reaction discharge after water washing firstly enters an alkaline washing tower 6, and the residual HCl in the reaction discharge is removed by alkaline washing by adopting NaOH solution with the mass percent of 10 percent.
The reaction material was subjected to alkali washing and then fed into a sulfuric acid drying tower 7, and after removing water and dimethyl ether, methyl chloride and trifluoromethane were obtained at a mass flow rate of 6220kg/hr and 122.5kg/hr, respectively.
Introducing the obtained mixed gas of methyl chloride and trifluoro methane into a methyl chloride compressor 8 to be compressed to 0.7MPa, and then delivering the mixed gas to a methyl chloride condenser 9 to be condensed at 25 ℃; wherein the noncondensable gas is 100kg/hr of trifluoromethyl and 20kg/hr of chloromethane.
The condensed chloromethane enters a chloromethane rectifying tower 10 for rectification, a small amount of trifluoromethyl in the chloromethane is removed, and the product chloromethane with the mass fraction of more than 99.95% is discharged from the tower kettle, wherein the mass fraction of the product chloromethane is 6220 kg/hr; the top of the tower is discharged light component trifluoromethane gas, the temperature of the top of the tower is 45 ℃, the pressure is 1.2MPa, and at the moment, the trifluoromethane gas contains 22.5kg/hr of trifluoromethane and 25kg/hr of chloromethane.
The above-mentioned noncondensable gas was introduced into the solvent absorption column 11 together with the gas of trifluoromethane, wherein 122.5kg/hr of trifluoromethane and 45kg/hr of chloromethane were contained in the combined gas.
The methylene dichloride solvent with the mass flow rate of 4000kg/hr enters from the top of the solvent absorption tower 11, the methyl chloride in the gas is absorbed under the condition of 0 ℃ and 0MPa, 44.5kg/hr of methyl chloride and 0.5kg/hr of trifluoromethyl are absorbed and enter the methyl chloride analysis tower 12 from the tower kettle discharge, the methyl chloride is analyzed under the condition of 130 ℃ and 0.5MPa, and the analyzed 44.5kg/hr of methyl chloride and 0.5kg/hr of trifluoromethyl are returned to the water washing tower 5 from the methyl chloride analysis tower 12.
122kg/hr of trifluoromethane, 0.5kg/hr of chloromethane and 0.5kg/hr of chloroform are contained in the gas which is not absorbed by the chloroform solvent, the gas is discharged from the top of the solvent absorption tower 11, compressed to 0.7MPa by the trifluoromethane compressor 13, then enters the trifluoromethane cooler 14 for cooling at 0 ℃,0.5 kg/hr of chloromethane and 0.5kg/hr of chloroform which are entrained in the solvent absorption tower 11 are condensed, and then returned to the chloromethane analysis tower 12, and 122kg/hr of trifluoromethane which is recovered is entered into the incinerator for incineration.
By calculation: the recovery rate of the trifluoromethane in this example was 99.6%; the yield of the directly produced chloromethane is 99.9%, and the selectivity of the chloromethane is 99%.
The purity of the recovered trifluoromethane was 99.1% as determined by infrared spectroscopy.
Claims (7)
1. The method for directly producing chloromethane by using the byproduct hydrogen chloride of difluoro chloromethane is characterized by comprising the following steps:
(1) Synthesizing chloromethane: the difluoro chloromethane byproduct hydrogen chloride is mixed with overheated methanol for methanol hydrochlorination after decompression metering and overheating, so as to synthesize chloromethane;
(2) Treating reaction discharge:
firstly, cooling reaction discharge materials containing methyl chloride, trifluoromethyl, methanol, byproduct HCl and dimethyl ether by chilling, and then, washing the reaction discharge materials in a washing unit;
the byproduct hydrochloric acid obtained by water washing is directly resolved, and chloromethane and trifluoromethane resolved from the hydrochloric acid are returned to the water washing unit; wherein the analysis temperature of the byproduct hydrochloric acid is 90-100 ℃, and the analysis pressure is 0.25-0.35MPa;
sequentially performing alkali washing, sulfuric acid drying and compression to 0.7-0.8MPa on the reaction discharge after water washing, and then condensing chloromethane to obtain non-condensable gas containing trifluoro methane and chloromethane and condensed chloromethane; wherein the condensing temperature of chloromethane is 25-30 ℃;
rectifying the condensed chloromethane to obtain the gas of the trifluoromethane and the chloromethane with the mass fraction of more than 99.95 percent;
introducing the trifluoro methane gas and the non-condensable gas containing trifluoro methane and chloromethane into a methane chloride solvent to absorb chloromethane; wherein the absorption temperature is-10-0deg.C, and the pressure is 0-0.05MPa;
methyl chloride is absorbed into a methane chloride solvent to form a methyl chloride solution; the chloromethane solution is subjected to chloromethane analysis, and the resolved chloromethane returns to the water washing unit;
after being compressed to 0.5-0.7MPa, the trifluoromethane which is not absorbed by the methane chloride solvent is cooled at the temperature of minus 10-0 ℃, the chloromethane and the solvent which are carried by the trifluoromethane are removed by condensation, and the trifluoromethane with the purity of more than 99% is recovered; the recovery rate of the trifluoromethane reaches more than 99 percent;
the yield of the chloromethane is more than 99 percent, and the selectivity of the chloromethane is more than 99 percent.
2. The method for directly producing chloromethane by-producing hydrogen chloride from difluoromethane according to claim 1, wherein the mass ratio of the by-produced hydrogen chloride to methanol in the difluoromethane in the step (1) is 1.2-1.3:1.
3. The method for directly producing methyl chloride by using hydrogen chloride as a byproduct of difluoro-chloromethane according to claim 1, wherein the pressure of hydrogen chloride in the step (1) after depressurization is 0.35-0.5MPa;
the temperature of the hydrochlorination reaction of the methanol is 220-260 ℃ and the pressure is 0.2-0.4MPa.
4. The method for directly producing chloromethane by-product hydrogen chloride according to claim 1, wherein the reaction output material in the step (2) is chilled to 30-50 ℃.
5. The method for directly producing chloromethane by-product hydrogen chloride by difluoro-chloromethane according to claim 1, wherein the methane chloride solvent in step (2) is one or more of dichloromethane, chloroform or carbon tetrachloride.
6. The method for directly producing chloromethane by-product hydrogen chloride by difluoro-chloromethane according to claim 1, wherein the chloromethane solution in step (2) is subjected to chloromethane analysis under the conditions of temperature 110-130 ℃ and pressure 0.3-0.5 MPa.
7. A production device for the direct chloromethane production method of the difluoromethane by-product hydrogen chloride according to any one of claims 1-6, which is characterized by comprising a chloromethane synthesis reactor, wherein a feed inlet of the chloromethane synthesis reactor is connected with a methanol superheater and a difluoromethane by-product hydrogen chloride superheater through pipelines;
the discharge port of the chloromethane synthesis reactor is sequentially connected with the first feed port of the quenching tower and the water washing tower;
the water scrubber comprises a water scrubber kettle outlet and a water scrubber tower top outlet; the outlet of the tower kettle of the water washing tower is connected with a first feed inlet of the water washing tower through a hydrochloric acid resolving tower; the top outlet of the water washing tower is sequentially connected with an alkaline washing tower, a sulfuric acid drying tower, a chloromethane compressor and a chloromethane condenser;
the chloromethane condenser comprises a condensate outlet and a noncondensable gas outlet, and the condensate outlet is connected with the chloromethane rectifying tower; the non-condensable gas outlet is connected with a solvent absorption tower after being converged with a top discharge port of the chloromethane rectifying tower;
the solvent absorption tower comprises a solvent absorption tower top outlet and a solvent absorption tower bottom outlet, and the solvent absorption tower top outlet is connected with a trifluoromethane cooler through a trifluoromethane compressor; the outlet of the tower bottom of the solvent absorption tower is connected with a chloromethane desorption tower;
the top outlet of the chloromethane analysis tower is connected with the second feed inlet of the water washing tower through a pipeline.
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