CN115894163A - Method and production device for directly producing methyl chloride from byproduct hydrogen chloride of monochlorodifluoromethane - Google Patents
Method and production device for directly producing methyl chloride from byproduct hydrogen chloride of monochlorodifluoromethane 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 methyl chloride from a chlorodifluoromethane byproduct hydrogen chloride. Synthesizing methyl chloride by using hydrogen chloride as a byproduct of chlorodifluoromethane as a raw material; the reaction output is then processed. The method not only effectively solves the treatment pressure of the byproduct hydrogen chloride in the production process of the monochlorodifluoromethane, directly saves the treatment cost of the monochlorodifluoromethane byproduct hydrogen chloride, fully utilizes the byproducts as resources, efficiently recovers and purifies the trifluoromethane included in the hydrogen chloride, and solves the environmental pollution problem of the trifluoromethane. Meanwhile, the method also greatly reduces the production cost of the chloromethane, and thus the method 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 methyl chloride from a chlorohydrogen chloride byproduct of difluoro methane.
Background
Chlorodifluoromethane (R22) of the formula CHClF 2 It is a hydrogen-containing chlorofluorohydrocarbon, which is a colorless gas with a slightly sweet smell. It is mainly used as raw material for preparing tetrafluoroethylene, refrigerant, spraying agent, pesticide production raw material, etc. A large amount of hydrogen chloride is produced as a by-product in the production of R22. The industrial hydrochloric acid is generally directly absorbed by water to prepare 31 percent of industrial hydrochloric acid, and enterprises have pressure on waste acid treatment or sale because the market of the industrial hydrochloric acid is saturated.
In addition, the device also produces a small amount of trifluoromethane (R23) as a byproduct, and because the boiling point of the trifluoromethane is-84.4 ℃, the difference between the boiling point of the trifluoromethane and the boiling point of the hydrogen chloride is-85 ℃, the separation is difficult to realize by common rectification, so that the hydrogen chloride is mixed with the trifluoromethane to be produced from the device. Trifluoromethane is a greenhouse gas, and must be recovered and disposed of according to the requirements of the environmental and ecological ministry.
CN102101651A discloses a method and a device for refining hydrogen chloride as a byproduct of chlorodifluoromethane and recovering trifluoromethane, the method comprises the steps of firstly utilizing the characteristic that the solubility of hydrogen chloride and trifluoromethane are greatly different in water, building a set of conventional hydrochloric acid desorption device, utilizing the absorption and desorption principle to realize the separation of trifluoromethane and hydrogen chloride, desorbing HCl gas through the heat and mass transfer process in a desorption tower, collecting HCl gas from the top of the desorption tower, and then carrying out condensation water removal and acid mist water removal to obtain high-purity HCl gas. 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 problems of equipment and pipeline corrosion exist. The hydrochloric acid resolving device comprises falling film absorber, resolving tower, reboiler, condenser, cooler, hydrochloric acid tank and hydrochloric acid pump, and a large amount of fluorine lining pipelines, and the cost of the above equipments and pipelines is high, for example, the equipment investment of a set of 5 ten thousand tons/year hydrogen chloride conventional resolving device is above 1000 ten thousand yuan, and the total investment is about 3000 ten thousand yuan. Moreover, because the reaction pressure of chloroethylene synthesis in the production of downstream products of polyvinyl chloride is high, the pressure of partial equipment and pipelines 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 stable operation of production is adversely affected.
2. The operation cost is high, the tower kettle dilute hydrochloric acid of the desorption tower needs to be cooled to 30-40 ℃ in the process of absorption and desorption of the hydrochloric acid, and a tower kettle reboiler of the desorption tower needs to be heated to 130-150 ℃, so a large amount of circulating water and water vapor need to be consumed. The steam consumption is 1 ton per ton of hydrogen chloride treated, the electricity consumption is 100 ℃, and the cost is reduced to 300 yuan/ton.
3. The trifluoromethane is not completely recovered, and although the solubility of the trifluoromethane in the hydrochloric acid is low, certain solubility still exists, and finally the trifluoromethane dissolved in the hydrochloric acid in the falling film absorber is resolved out in a resolving tower together with the hydrogen chloride. The content of R23 in the resolved hydrogen chloride is 0.05-0.3%, so that the recovery rate of R23 is only 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 over 4.0Mpa (G), and the method has higher requirements on a compressor, a pipeline and equipment and has certain safety risk.
5. The competitiveness of the polyvinyl chloride produced by utilizing the byproduct hydrogen chloride and the calcium carbide through the calcium carbide method is low. With the increasing price of calcium carbide and the long transportation distance, the cost of preparing polyvinyl chloride by the calcium carbide method in the eastern area is not advantageous, and the method produces a large amount of calcium carbide mud and mercury-containing catalyst as byproducts, and the environmental protection pressure is also great, so that the byproduct hydrogen chloride is not suitable for being used for producing 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 chlorodifluoromethane as a byproduct hydrogen chloride, which not only effectively solves the treatment pressure of the chlorodifluoromethane as a byproduct in the production process, but also directly saves the treatment cost of the chlorodifluoromethane as a byproduct, fully utilizes the byproducts as resources, efficiently recovers and purifies the trifluoromethane included in the hydrogen chloride, and solves the problem of environmental pollution of the trifluoromethane. Meanwhile, the method also greatly reduces the production cost of the chloromethane, and thus the method brings double economic benefits for enterprises.
The specific technical scheme is as follows:
a method for directly producing methyl chloride by using hydrogen chloride as a byproduct of monochlorodifluoromethane comprises the following steps:
(1) Synthesis of methyl chloride: the hydrogen chloride byproduct of the monochlorodifluoromethane is subjected to reduced pressure measurement and overheating, and then is mixed with overheated methanol to carry out methanol hydrochlorination reaction, so that the chloromethane is synthesized.
The reaction product in the production of the monochlorodifluoromethane firstly enters a hydrogen chloride tower, and the byproduct hydrogen chloride is separated from the tower top. At the moment, the hydrogen chloride byproduct of the monochlorodifluoromethane mainly contains the following components in volume fraction: 97-97.5% of HCl, 0-0.005% of difluorochloromethane, 2-2.5% of trifluoromethane and 0-0.2% of HF. The byproduct hydrogen chloride gas has high purity and can be used as a reaction raw material for producing methyl chloride. The reaction type of the methanol hydrochlorination reaction is a gas-solid phase catalytic reaction.
(2) Discharging after treatment reaction:
the reaction discharge material containing chloromethane, trifluoromethane, methanol and chloromethane byproduct HCl and dimethyl ether is firstly chilled and cooled, and then enters a water washing unit for water washing.
The water washing mainly removes a chloromethane byproduct HCl in the reaction discharge material to obtain a byproduct hydrochloric acid; methanol in the reaction discharge material is also removed from the reaction discharge material along with water washing, and the methanol becomes methanol hydrochloric acid solution after water washing. If the hydrogen chloride byproduct of the monochlorodifluoromethane contains a small amount of HF, the HF generates hydrofluoric acid after being washed by water and is removed from the reaction discharge material.
And (3) directly resolving by-product hydrochloric acid obtained by washing, and returning chloromethane and trifluoromethane resolved from the hydrochloric acid to the washing unit.
The by-product hydrochloric acid desorption here is different from the hydrochloric acid desorption of the prior art in which hydrochloric acid is desorbed by heating concentrated hydrochloric acid; the invention resolves the chloromethane and the trichloromethane dissolved in the dilute hydrochloric acid by heating the byproduct hydrochloric acid. If the hydrogen chloride byproduct of the chlorodifluoromethane contains a small amount of chlorodifluoromethane, the chlorodifluoromethane dissolved in dilute hydrochloric acid can be resolved.
And after the washed reaction discharge material is sequentially subjected to alkali washing, sulfuric acid drying and compression, methyl chloride is condensed to obtain noncondensable gas containing trifluoromethane and methyl chloride and condensed methyl chloride.
The alkaline washing can adopt NaOH solution with the mass fraction of 10%, the pH value is controlled to be about 11, and the residual hydrogen chloride in the reaction discharge material is removed by the alkaline washing. Drying the sulfuric acid to remove dimethyl ether and moisture in the reaction discharge material, wherein the dimethyl ether reacts with the sulfuric acid to generate dimethyl sulfate.
Rectifying the condensed chloromethane to obtain trifluoromethane gas and chloromethane with the mass fraction of more than 99.95%.
A small amount of trifluoromethane entrained in the condensation of the methyl chloride is removed from the methyl chloride as a light component for rectification. The temperature of the top of the rectifying tower used for rectification is 40-45 ℃, and the pressure is 1.1-1.2MPa.
And introducing the trifluoromethane gas and the noncondensable gas containing the trifluoromethane and the chloromethane into a methane chloride solvent together for absorbing the chloromethane.
Absorbing methyl chloride into a methane chloride solvent to form a methyl chloride solution; and (4) carrying out methyl chloride analysis on the methyl chloride solution, and returning the analyzed methyl chloride to the water washing unit.
Methyl chloride, also known as methyl chloride, is an organic compound of formula CH 3 Cl, a colorless gas at normal temperature and pressure, is dissolved in a 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 high purity and can be used in an incinerator or used for other purposes, such as a solvent for a supercritical extraction method, a low-temperature refrigerant or a fire extinguishing agent and a raw material for manufacturing tetrafluoroethylene. And the condensed methyl chloride and solvent are returned to the methyl chloride resolving unit.
In the invention, the mass ratio of the hydrogen chloride byproduct of the difluoromethane chloride to the methanol in the step (1) of the method for directly producing the methyl chloride from the hydrogen chloride byproduct of the difluoromethane chloride is 1.2-1.3.
In the invention, the pressure of the hydrogen chloride after pressure reduction in the step (1) of the method for directly producing methyl chloride by using the byproduct hydrogen chloride of the monochlorodifluoromethane 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.
In the invention, the reaction discharge in the step (2) of the method for directly producing methyl chloride by hydrogen chloride as a byproduct of difluoromethane chloride is chilled and cooled to 30-50 ℃.
In the invention, the desorption temperature of the byproduct hydrochloric acid in the step (2) of the method for directly producing the methyl chloride by using the byproduct hydrogen chloride of the chlorodifluoromethane is 90-100 ℃, and the desorption pressure is 0.25-0.35MPa; the reaction discharge material after the sulfuric acid is dried is compressed to 0.7-0.9MPa, and the chloromethane condensation is carried out at the temperature of 25-35 ℃.
In the invention, the methane chloride solvent in the step (2) of the method for directly producing methyl chloride by hydrogen chloride as a byproduct of chlorodifluoromethane is one or more of dichloromethane, chloroform or carbon tetrachloride.
In the method for directly producing methyl chloride by using hydrogen chloride as a byproduct of monochlorodifluoromethane, the methane chloride solvent in the step (2) absorbs methyl chloride under the conditions that the temperature is-10-0 ℃ and the pressure is 0-0.05 MPa.
In the method, the methyl chloride solution in the step (2) of directly producing the methyl chloride by-product hydrogen chloride of the chlorodifluoromethane is subjected to methyl chloride resolution under the conditions of the temperature of 110-130 ℃ and the pressure of 0.3-0.5 MPa.
In the method for directly producing methyl chloride from hydrogen chloride as a byproduct of monochlorodifluoromethane, the trifluoromethane in the step (2) is compressed to 0.5-0.7MPa and then cooled at the temperature of-10-0 ℃. At this pressure the methyl chloride and solvent can be removed by cooling to a lower temperature to achieve the desired purity.
The invention also provides a production device for the method for directly producing the methyl chloride from the byproduct hydrogen chloride of the chlorodifluoromethane, which comprises a methyl chloride synthesis reactor, wherein a feed inlet of the methyl chloride synthesis reactor is connected with a methanol superheater and a chlorodifluoromethane byproduct hydrogen chloride superheater through pipelines; preferably, the discharging pipe of the methanol superheater and the discharging pipe of the superheater for the hydrogen chloride byproduct of the difluorochloromethane are connected to the feeding pipe of the chloromethane synthesis reactor through a gas mixer. In industrial applications, a gas mixer is usually used to mix two gases, and the gas mixer is a gas mixer in the prior art.
A discharge hole of the chloromethane synthesis reactor is sequentially connected with a first feed inlet of a chilling tower and a first feed inlet of a water washing tower;
the water washing tower comprises a water washing tower kettle outlet and a water washing 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 analysis tower; the outlet of the top of the water washing tower is sequentially connected with an alkaline washing tower, a sulfuric acid drying tower, a methyl chloride compressor and a methyl chloride condenser;
the chloromethane condenser comprises a condensate outlet and a non-condensable gas outlet, and the condensate outlet is connected with a chloromethane rectifying tower; the non-condensable gas outlet is converged with a discharge port at the top of the chloromethane rectifying tower and then connected with a solvent absorption tower;
the solvent absorption tower comprises a tower top outlet of the solvent absorption tower and a tower kettle outlet of the solvent absorption tower, and the tower top outlet of the solvent absorption tower is connected with a trifluoromethane cooler through a trifluoromethane compressor; the outlet of the solvent absorption tower is connected with a chloromethane desorption tower. The outlet of the top of the chloromethane desorption 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: with the expansion of downstream organic silicon, the demand of methyl chloride is more and more large, and the price is kept high, so that the method for directly producing high-value methyl chloride by using the byproduct hydrogen chloride of the chlorodifluoromethane can realize the resource utilization of the low-value byproduct hydrogen chloride, and save the treatment cost of the chlorodifluoromethane for the byproduct hydrogen chloride production, including the investment of treatment equipment and the subsequent sales pressure; but also reduces the production cost of high-value methyl chloride, saves the purchase cost of hydrogen chloride as a raw material for production, and further improves the economic benefit of the methyl chloride. Thus, the method of the invention brings double economic benefits for enterprises.
The concrete advantages are as follows:
1. the method for preparing the methyl chloride by using the byproduct hydrogen chloride of the chlorodifluoromethane as the raw material reduces the production cost of the methyl chloride by 300 yuan/ton, so that the income of the methyl chloride is increased by 280 yuan/ton. Meanwhile, compared with a pure hydrogen chloride raw material, the byproduct hydrogen chloride of the chlorodifluoromethane is used for producing the chloromethane, so that the yield and the selectivity of the chloromethane are not influenced, the yield of the chloromethane can reach more than 99 percent, and the selectivity of the chloromethane can also reach more than 99 percent; and the production amount of chloromethane by-products, namely hydrochloric acid and dimethyl ether is not increased.
2. Compared with the prior art, the construction cost and the operation cost of the adsorption and desorption device for the chlorodifluoromethane byproduct hydrogen chloride including a plurality of large falling film absorbers are saved, the process flow is simplified, the chlorodifluoromethane byproduct hydrogen chloride does not need to be heated to a high temperature and then cooled to a low temperature, and thus, a large amount of circulating water and water vapor are prevented from being consumed. In the prior art, each ton of hydrogen chloride needs to be processed by 1 ton of steam, the electricity consumption is 100 ℃, and the cost is reduced to 300 yuan/ton. If the calculation is carried out according to the scale of a 5-ten-thousand-ton device, 3000-thousand yuan of fixed investment and 1500-thousand yuan of operation cost can be saved by adopting the method.
3. The recovery rate of the trifluoromethane is improved, the method effectively recovers the trifluoromethane dissolved in the hydrochloric acid and condensed in the chloromethane through the resolution of the hydrochloric acid and the rectification of the chloromethane, and the recovery rate of the trifluoromethane reaches more than 99 percent.
4. Compared with the patent CN102101651A, the method of the invention omits a high-pressure compressor and a trifluoromethane rectifying tower which are higher than 4.0Mpa (G) for the trifluoromethane; according to the characteristic that the solubility difference of the trifluoromethane and the chloromethane in the methane chloride solvent is large, the trifluoromethane and the chloromethane are separated by adopting a solvent absorption method, and then the trifluoromethane gas is cooled by only compressing to 0.5-0.7MPa, 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 the monochlorodifluoromethane has no other heavy components, the chloromethane production process can ensure that the purity of the chloromethane reaches more than 99.95 percent without arranging a heavy component removal rectifying tower, simplifies the process and saves steam.
In conclusion, the process for producing the methyl chloride by recycling the hydrogen chloride byproduct of the chlorodifluoromethane device has the advantages that the hydrogen chloride byproduct is overheated and then directly participates in the reaction to produce the methyl chloride, so that a large 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 the high-efficiency recovery and purification of the trifluoromethane, is simple and easy to operate, the recovery rate is up to more than 99 percent, and the purity of the trifluoromethane is up to more than 99 percent.
Drawings
FIG. 1 is a schematic diagram of a production apparatus used in the method for directly producing methyl chloride from hydrogen chloride as a byproduct of methyl difluorochloride.
Wherein: 1 is a difluoro monochloro methane byproduct hydrogen chloride superheater, 2 is a methanol superheater, 3 is a methyl chloride synthesis reactor, 4 is a chilling tower, 5 is a water washing tower, 6 is an alkaline washing tower, 7 is a sulfuric acid drying tower, 8 is a methyl chloride compressor, 9 is a methyl chloride condenser, 10 is a methyl chloride rectifying tower, 11 is a solvent absorption tower, 12 is a methyl chloride analysis tower, 13 is a trifluoromethane compressor, 14 is a trifluoromethane cooler, and 15 is a hydrochloric acid analysis tower.
Detailed Description
The present invention is further illustrated by the following specific examples.
1. Purity of trifluoromethane: the measurement was carried out by infrared spectroscopy using Shimadzu gas chromatograph GC-2014, DB-624 column.
2. Yield of chloromethane: the methanol conversion was calculated from the methyl chloride yield, as a ratio to the feed.
3. In the examples, the composition of the reaction effluent, the composition of the overhead effluent gas after hydrochloric acid desorption, the composition of the effluent gas after sulfuric acid drying, the composition of the non-condensable gas of methyl chloride condensation, and the composition of the overhead effluent gas of a methyl chloride rectification column were obtained by sampling and detecting with a hydrogen Flame Ionization Detector (FID).
Example 1
The production device for the method for directly producing the methyl chloride from the byproduct hydrogen chloride of the chlorodifluoromethane comprises a methyl chloride synthesis reactor 3, wherein the methyl chloride synthesis reactor 3 is a fixed bed reactor, and a bed layer is filled with a solid catalyst, such as activated alumina or activated carbon soaked with zinc chloride.
A feed inlet of the methyl chloride synthesis reactor 3 is connected with a methanol superheater 2 and a difluorochloromethane byproduct hydrogen chloride superheater 1 through pipelines; wherein the discharging pipe of the methanol superheater and the discharging pipe of the superheater for the byproduct hydrogen chloride of the difluorochloromethane can be directly connected with the feeding pipe of the chloromethane synthesis reactor; or can be connected into the feeding pipe of the methyl chloride synthesis reactor through a gas mixer. The gas mixer is a gas mixer in the prior art, such as a JY-QHZ-5 gas mixer.
The discharge hole of the chloromethane synthesis reactor 3 is sequentially connected with the first feed inlets of a chilling tower 4 and a water scrubber 5.
The chilling tower 4 is a graphite Raschig ring packed tower; the graphite raschig ring is a circular ring with the same outer diameter and 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 packing tower. The plastic pall ring is an open-pore ring-shaped filler with the same outer diameter and height, and on the basis of the Raschig ring filler, a plurality of window holes are formed in the ring wall, the positions of the upper window hole and the lower window hole are staggered oppositely, and the area of the open pores generally accounts for about 30% of the total area of the ring wall, so that gas and liquid in the filler tower can freely pass through the window holes, the flowing condition of gas-liquid two phases in the filler layer is greatly improved, and the hydrodynamics and mass transfer performance of the filler are improved.
The water washing tower 5 comprises a water washing tower kettle outlet and a water washing tower top outlet; the outlet of the tower kettle of the water washing tower is connected with a first feed inlet of a water washing tower 5 through a hydrochloric acid desorption tower 15; after methyl chloride and trifluoromethane carried in the byproduct hydrochloric acid obtained by washing in the way are resolved, the product enters a first feeding hole of the washing tower 5 from the outlet of the top of the hydrochloric acid resolving tower 15 and returns to the washing tower 5.
The hydrochloric acid resolving 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, wherein the blades of the small windows are overlapped in the center of the ring, and the upper surface layer window and the lower surface layer window are mutually overlapped. The packing material is mainly different from Raschig ring packing in that a rectangular window hole is formed in the side wall, and the window leaf of the window hole is bent into the ring core.
The outlet of the water scrubber is connected with an alkaline scrubber 6, a sulfuric acid drying tower 7, a chloromethane compressor 8 and a chloromethane condenser 9 in sequence.
The alkaline tower 6 is a plastic pall ring packed tower, a pH online detector is arranged in the alkaline tower, waste alkaline liquid is discharged when the pH value in the alkaline tower is less than 11, and fresh alkaline liquid enters the alkaline tower.
The sulfuric acid drying tower 7 is a plastic pall ring packing tower.
The chloromethane condenser 9 comprises a condensate outlet and a non-condensable gas outlet, and the condensate outlet is connected with a chloromethane rectifying tower 10; the non-condensable gas outlet is converged with a discharge port at the top of the chloromethane rectifying tower 10 and then connected with a solvent absorption tower 11.
The chloromethane condenser 9 was a shell-and-tube condenser. The shell-and-tube condenser is a closed water-cooled condenser composed of a shell, a tube plate, a heat transfer tube bundle, a cooling water distribution component (a water cover), a cooling water and refrigerant inlet and outlet pipe joint and the like.
The solvent absorption tower 11 comprises a tower top outlet of the solvent absorption tower and a tower kettle outlet of the solvent absorption tower, and the tower top outlet of the solvent absorption tower is connected with a trifluoromethane cooler 14 through a trifluoromethane compressor 13; the outlet of the solvent absorption tower is connected with a chloromethane desorption tower 12. The outlet of the chloromethane desorption 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 punched by a metal thin plate, and two rows of window holes with inward extending tongue blades are formed on the ring wall. The general area of the opening is about 35% of the whole ring wall area, because of the opening of many window holes on the ring wall, the gas and liquid in the tower can freely pass through the window, when the same treatment capacity is used, the pressure reduction can be reduced by half, the mass transfer efficiency can be improved by about 20%, and the separation efficiency is high.
The trifluoromethane cooler 14 is a shell-and-tube condenser. The chloromethane desorption tower 12 is a metal pall ring packed tower.
Example 2
The method for directly producing methyl chloride from the byproduct hydrogen chloride of monochlorodifluoromethane adopts the production device in the embodiment 1, and comprises the following specific steps:
(1) Synthesis of methyl chloride: the byproduct hydrogen chloride separated from a hydrogen chloride tower in the production device of the difluoromethane chloride is decompressed to 0.35MPa, and is metered to enter a superheater 1 of the byproduct hydrogen chloride of the difluoromethane chloride at the mass flow rate of 5000kg/hr and superheated to 220 ℃.
Another raw material methanol enters a methanol superheater 2 to be superheated to 220 ℃ at the mass flow rate of 4000 kg/hr.
And introducing the superheated hydrogen chloride byproduct of the monochlorodifluoromethane and superheated methanol into a chloromethane synthesis reactor 3 according to the mass ratio of 1.25, and reacting at 220 ℃ under the condition of 0.4MPa to synthesize the chloromethane.
(2) Discharging after treatment reaction: the reaction discharge is cooled to 40 ℃ through a chilling tower 4; sampling, infrared spectrometry analysis and calculation show that the reaction discharge material contains 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.
The reaction discharge materials after chilling and temperature reduction enter a water washing tower 5 for water washing, and HCl and methanol in the reaction discharge materials are removed.
The hydrochloric acid byproduct is obtained by washing with water at 2700kg/hr, and the hydrochloric acid byproduct directly enters the hydrochloric acid analysis tower 15 from the tower kettle outlet of the washing tower 5, and is analyzed at 90 ℃ and 0.25MPa, wherein 55kg/hr of methyl chloride and 8kg/hr of trifluoromethane are analyzed in the hydrochloric acid and returned to the washing tower 5 from the tower top of the hydrochloric acid analysis tower 15.
And the reaction discharge material after washing enters an alkaline washing tower 6 through the outlet at the top of the water washing tower 5, and residual HCl in the reaction discharge material is removed by alkaline washing by adopting a NaOH solution with the mass fraction of 10%.
After the reaction discharge material is subjected to alkali washing, the reaction discharge material enters a sulfuric acid drying tower 7, and after moisture and dimethyl ether are removed, methyl chloride with the mass flow rate of 6220kg/hr and trifluoromethane with the mass flow rate of 125kg/hr are obtained respectively.
Introducing the obtained mixed gas of methyl chloride and trifluoromethane into a methyl chloride compressor 8, compressing to 0.8MPa, and sending to a methyl chloride condenser 9 for methyl chloride condensation at 30 ℃; wherein the non-condensable gas comprises 100kg/hr of trifluoromethane and 20kg/hr of methyl chloride.
The condensed chloromethane enters a chloromethane rectifying tower 10 for rectification to remove a small amount of trifluoromethane in the chloromethane, and the tower bottom discharge is 6220kg/hr of product chloromethane with the mass fraction of more than 99.95%; the discharge from the top of the tower is light component trifluoromethane gas, the temperature at the top of the tower is 40 ℃, the pressure is 1.1MPa, and the trifluoromethane gas contains 25kg/hr of trifluoromethane and 25kg/hr of chloromethane.
The above-mentioned non-condensable gas was introduced into the solvent absorption column 11 together with a mixed gas of trifluoromethane gas containing 125kg/hr of trifluoromethane and 45kg/hr of methyl chloride.
Chloroform solvent with mass flow of 5000kg/hr enters from the top of the solvent absorption tower 11, absorbs methyl chloride in gas at-10 deg.C and 0.05MPa, 44.5kg/hr methyl chloride and 0.5kg/hr trifluoromethane are absorbed, and the materials discharged from the tower bottom enter the methyl chloride desorption tower 12, and are desorbed at 110 deg.C and 0.3MPa, and the desorbed 44.5kg/hr methyl chloride and 0.5kg/hr trifluoromethane are returned to the water scrubber 5 from the methyl chloride desorption tower 12.
The gas not absorbed by the chloroform solvent contains 124.5kg/hr trifluoromethane, 0.5kg/hr chloromethane and 0.5kg/hr chloroform, and the gas is discharged from the top of the solvent absorption tower 11, compressed to 0.5MPa by the trifluoromethane compressor 13, and then fed into the trifluoromethane cooler 14 to be cooled at-10 ℃, and 0.5kg/hr chloromethane and 0.5kg/hr chloroform carried in the solvent absorption tower 11 are condensed and returned to the chloromethane desorption tower 12. 124.5kg/hr of the recovered trifluoromethane was incinerated in an incinerator.
By calculation, the recovery of trifluoromethane in this example was 99.6%, the yield of directly produced methyl chloride was 99.9%, and the selectivity of methyl chloride was 99%.
The purity of the recovered trifluoromethane was 99.2% by infrared spectroscopic measurement.
Example 3
The method for directly producing methyl chloride from the byproduct hydrogen chloride of monochlorodifluoromethane adopts the production device in the embodiment 1, and comprises the following specific steps:
(1) Synthesis of methyl chloride: the byproduct hydrogen chloride separated from a hydrogen chloride tower in the production device of the difluoromethane chloride is decompressed to 0.5MPa, and is metered to enter a superheater 1 of the difluorochloromethane byproduct hydrogen chloride with the mass flow of 4900kg/hr and superheated to 260 ℃.
Another raw material methanol enters a methanol superheater 2 to be superheated to 260 ℃ at the mass flow rate of 4000 kg/hr.
And (3) mixing the superheated hydrogen chloride byproduct of the chlorodifluoromethane with superheated methanol in a mass ratio of 1.225.
(2) And (3) treatment of reaction discharge: the reaction discharge is cooled to 50 ℃ through a chilling tower 4; sampling, infrared spectrometry analysis and calculation show that the reaction discharge material contains 6220kg/hr of chloromethane, 122.5kg/hr of trifluoromethane, 25kg/hr of methanol, 294.5kg/hr of chloromethane byproduct HCl294, 18kg/hr of dimethyl ether and 2220kg/hr of water.
The reaction discharge after chilling and temperature reduction enters a water washing tower 5 for water washing to remove HCl and methanol in the reaction discharge.
The hydrochloric acid byproduct is obtained by water washing, 2600kg/hr, and the hydrochloric acid byproduct directly enters the hydrochloric acid desorption tower 15 to be desorbed at 100 ℃ under the condition of 0.35MPa, wherein 55kg/hr of methyl chloride and 8kg/hr of trifluoromethane are desorbed in the hydrochloric acid and are returned to the water washing tower 5 from the top of the hydrochloric acid desorption tower 15.
The reaction discharge after washing with water firstly enters an alkaline tower 6, and residual HCl in the reaction discharge is removed by alkaline washing with 10 mass percent NaOH solution.
The reaction discharge material is alkali-washed and then enters a sulfuric acid drying tower 7, and after moisture and dimethyl ether are removed, the methyl chloride with the mass flow rate of 6220kg/hr and the trifluoromethane with the mass flow rate of 122.5kg/hr are respectively obtained.
Introducing the obtained mixed gas of methyl chloride and trifluoromethane into a methyl chloride compressor 8, compressing to 0.7MPa, and then sending to a methyl chloride condenser 9 for methyl chloride condensation at 25 ℃; wherein the non-condensable gas comprises 100kg/hr of trifluoromethane and 20kg/hr of methyl chloride.
The condensed chloromethane enters a chloromethane rectifying tower 10 for rectification to remove a small amount of trifluoromethane in the chloromethane, and the tower bottom discharge is 6220kg/hr of product chloromethane with the mass fraction of more than 99.95%; the discharge from the top of the tower is light component trifluoromethane gas, the temperature at the top of the tower is 45 ℃, the pressure is 1.2MPa, and the trifluoromethane gas contains trifluoromethane 22.5kg/hr and chloromethane 25kg/hr.
The above-mentioned non-condensable gas was introduced into the solvent absorption column 11 together with a mixed gas of trifluoromethane gas containing 122.5kg/hr of trifluoromethane and 45kg/hr of methyl chloride.
The dichloromethane solvent with mass flow rate of 4000kg/hr enters from the top of the solvent absorption tower 11, absorbs methyl chloride in the gas at 0 ℃ and 0MPa, absorbs 44.5kg/hr of methyl chloride and 0.5kg/hr of trifluoromethane, and then the dichloromethane solvent enters into a methyl chloride analysis tower 12 from the bottom of the tower, and analyzes the methyl chloride at 130 ℃ and 0.5MPa, and the analyzed 44.5kg/hr of methyl chloride and 0.5kg/hr of trifluoromethane return to the water scrubber 5 from the methyl chloride analysis tower 12.
The gas which is not absorbed by the chloroform solvent contains 122kg/hr trifluoromethane, 0.5kg/hr chloromethane and 0.5kg/hr chloroform, the gas is discharged from the top of the solvent absorption tower 11, compressed to 0.7MPa by a trifluoromethane compressor 13, and then enters a trifluoromethane cooler 14 to be cooled at 0 ℃,0.5 kg/hr chloromethane and 0.5kg/hr chloroform carried in the solvent absorption tower 11 are condensed and returned to a chloromethane analysis tower 12, and the recovered 122kg/hr trifluoromethane enters an incinerator to be incinerated.
By calculating: the recovery rate of the trifluoromethane in the embodiment is 99.6%; the yield of the directly produced methyl chloride is 99.9%, and the selectivity of the methyl chloride is 99%.
The purity of the recovered trifluoromethane was 99.1% by infrared spectroscopic measurement.
Claims (10)
1. A method for directly producing methyl chloride by using hydrogen chloride as a byproduct of monochlorodifluoromethane is characterized by comprising the following steps:
(1) Synthesis of methyl chloride: hydrogen chloride as a byproduct of the monochlorodifluoromethane is subjected to reduced pressure measurement and overheating, and then is mixed with overheated methanol to carry out methanol hydrochlorination reaction, so that the chloromethane is synthesized;
(2) Discharging after treatment reaction:
the reaction discharge material containing chloromethane, trifluoromethane, methanol, byproduct HCl and dimethyl ether is firstly chilled and cooled, and then enters a water washing unit for water washing;
the byproduct hydrochloric acid obtained by washing is directly analyzed, and the chloromethane and the trifluoromethane analyzed from the hydrochloric acid return to the washing unit;
after the washed reaction discharge material is sequentially subjected to alkali washing, sulfuric acid drying and compression, methyl chloride is condensed to obtain noncondensable gas containing trifluoromethane and methyl chloride and condensed methyl chloride;
rectifying the condensed chloromethane to obtain trifluoromethane gas and chloromethane with the mass fraction of more than 99.95%;
introducing the trifluoromethane gas and the noncondensable gas containing the trifluoromethane and the chloromethane into a methane chloride solvent to absorb the chloromethane;
absorbing methyl chloride into a methane chloride solvent to form a methyl chloride solution; the chloromethane solution is subjected to chloromethane analysis, and the analyzed chloromethane returns to the water washing unit;
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%.
2. The method for directly producing methyl chloride from the byproduct hydrogen chloride of difluoromethane chloride according to claim 1, wherein the mass ratio of the byproduct hydrogen chloride of difluoromethane chloride to methanol in step (1) is 1.2-1.3.
3. The method for directly producing methyl chloride from hydrogen chloride byproduct of difluoromethane chloride according to claim 1, wherein the pressure of the hydrogen chloride after decompression in step (1) 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 methyl chloride from hydrogen chloride byproduct of difluoromethane chloride according to claim 1, wherein the reaction discharge obtained in step (2) is chilled to 30-50 ℃.
5. The method for directly producing methyl chloride from hydrogen chloride byproduct of difluoromethane chloride according to claim 1, wherein the desorption temperature of hydrochloric acid byproduct in step (2) is 90-100 ℃, and the desorption pressure is 0.25-0.35MPa; compressing the reaction discharge material after the sulfuric acid is dried to 0.7-0.9MPa; condensing methyl chloride at 25-35 ℃.
6. The method for directly producing methyl chloride from hydrogen chloride byproduct of difluoromethane chloride as claimed in claim 1, wherein the methane chloride solvent in step (2) is one or more of dichloromethane, chloroform or carbon tetrachloride.
7. The method for directly producing methyl chloride from hydrogen chloride byproduct of difluoromethane chloride as claimed in claim 1, wherein the methane chloride solvent in step (2) absorbs methyl chloride at-10-0 deg.C and 0-0.05 MPa.
8. The method for directly producing methyl chloride from hydrogen chloride byproduct of difluoromethane chloride as claimed in claim 1, wherein the methyl chloride solution in step (2) is subjected to methyl chloride resolution at a temperature of 110-130 ℃ and a pressure of 0.3-0.5 MPa.
9. The method for directly producing methyl chloride from hydrogen chloride byproduct of difluoromethane chloride as claimed in claim 1, wherein the cooling is performed at-10-0 ℃ after the trifluoromethane is compressed to 0.5-0.7MPa in step (2).
10. A production apparatus for the method for directly producing methyl chloride from the hydrogen chloride byproduct of difluoromethane chloride according to any one of claims 1 to 9, which is characterized by comprising a methyl chloride synthesis reactor, wherein a feed inlet of the methyl chloride synthesis reactor is connected with a methanol superheater and a hydrogen chloride byproduct superheater of difluoromethane chloride through pipelines;
a discharge hole of the chloromethane synthesis reactor is sequentially connected with a first feed inlet of a chilling tower and a first feed inlet of a water washing tower;
the water washing tower comprises a tower kettle outlet of the water washing tower and a tower top outlet of the water washing tower; 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 analysis tower; the outlet of the top of the water washing tower is sequentially connected with an alkaline washing tower, a sulfuric acid drying tower, a methyl chloride compressor and a methyl chloride condenser;
the chloromethane condenser comprises a condensate outlet and a non-condensable gas outlet, and the condensate outlet is connected with a chloromethane rectifying tower; the non-condensable gas outlet is converged with a discharge port at the top of the chloromethane rectifying tower and then connected with a solvent absorption tower;
the solvent absorption tower comprises a tower top outlet of the solvent absorption tower and a tower kettle outlet of the solvent absorption tower, and the tower top outlet of the solvent absorption tower is connected with a trifluoromethane cooler through a trifluoromethane compressor; the outlet of the solvent absorption tower is connected with a chloromethane desorption tower;
the outlet of the top of the chloromethane desorption tower is connected with the second feed inlet of the water washing tower through a pipeline.
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