CN111499490A - Method for producing methane chloride by using byproduct fluorine-containing hydrogen chloride - Google Patents
Method for producing methane chloride by using byproduct fluorine-containing hydrogen chloride Download PDFInfo
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Abstract
The invention relates to a method for producing methane chloride by using byproduct fluorine-containing hydrogen chloride, which comprises the following steps: (1) cooling and absorbing the byproduct fluorine-containing hydrogen chloride gas, and then preliminarily analyzing and evaporating; (2) recovering hydrogen chloride gas in the fluorine-containing dilute hydrochloric acid; (3) generating crude methane chloride gas by reacting hydrogen chloride gas with methanol; then the methane chloride is prepared after chilling separation, water washing, cooling for acid removal, alkali washing, drying and compression and degassing refining. The method comprises the steps of recovering hydrogen chloride gas from a byproduct fluorine-containing hydrogen chloride generated in the production process of fluorine chemical industry through cooling absorption, primary analysis and deep analysis treatment; and then the recovered hydrogen chloride gas is used for participating in the synthesis reaction of methane chloride, thereby realizing the reutilization of waste resources and saving the production cost. And the purity of the prepared methane chloride can reach 99.9-99.99 percent, and the product requirement is completely met.
Description
Technical Field
The invention relates to a method for producing methane chloride by using byproduct fluorine-containing hydrogen chloride, belonging to the technical field of chemical industry.
Background
In recent years, with the rapid development of the fluorine chemical industry, a large amount of fluorine-containing hydrogen chloride gas is produced as a by-product. The application value of hydrogen chloride is greatly reduced due to the existence of fluorine ions, so that the byproduct fluorine-containing hydrogen chloride gas is excessive, and most enterprises absorb the byproduct fluorine-containing hydrogen chloride gas by using water to form fluorine-containing byproduct hydrochloric acid. The fluorine-containing byproduct hydrochloric acid cannot be sold or directly discharged outside, has high harmless treatment cost, is difficult to bear by production enterprises, is directly used for producing other chemical products, is easy to cause fluorine ion diffusion and secondary pollution, seriously influences economic benefits and brings a series of environmental protection problems.
At present, the production method of methane chloride mainly comprises a gas-solid phase catalysis method and a liquid phase catalysis method, and the gas-solid phase catalysis process mainly comprises the following methods:
chinese patent document CN101440015A discloses a method for producing methane chloride by using dilute hydrochloric acid, wherein dilute hydrochloric acid with the mass ratio of 15-22% and calcium chloride solution with the mass ratio of 40-52% are introduced into a hydrochloric acid analytical tower, under the azeotropic breaking action of calcium chloride, the chlorine chloride in the dilute hydrochloric acid is resolved out, and the dilute calcium chloride solution is dehydrated and recycled at 125-145 ℃ and 0.02-0.1 MPa. The resolved hydrogen chloride is compressed and then reacts with the vaporized methanol to generate methane chloride.
Chinese patent document CN1686983 discloses a production method of high-purity methane chloride, which takes methanol and hydrogen chloride as raw materials, reacts under the conditions of 260-320 ℃ and 0.2-0.6 MPaG in the presence of an active catalyst to generate methane chloride and water, and the methane chloride and the water are chilled, dried, compressed and condensed to obtain a crude methane chloride product, a first rectifying tower is used for removing light components in the methane chloride, a second rectifying tower is used for removing heavy components, and 20% hydrochloric acid is obtained by separation in the production process and is used for producing 31% industrial hydrochloric acid.
Chinese patent document CN101134708 discloses a process for producing high-purity methane chloride, wherein methanol and hydrogen chloride are vaporized and superheated and then enter a reactor filled with an alumina catalyst to generate a mixture of methane chloride, methane, chloroethane and dichloromethane in the reactor, and the molar ratio of the hydrogen chloride to the methanol is (1.1-1.2): 1; the mixture generated by the reaction enters a chiller, enters an acid washing tower, an alkaline washing tower and a sulfuric acid drying system after being chilled and separated, and is compressed to obtain crude methane chloride, and the crude methane chloride enters a methane chloride refining tower to separate heavy components from the bottom of the tower; and evaporating light components of methane and methane chloride to the top of the tower, then cooling and chilling the light components, liquefying the methane chloride, and emptying the unliquefied methane to an exhaust gas washing tower through a chiller to realize the separation of the methane chloride and the methane so as to obtain the high-purity methane chloride. The liquid phase after the reaction chilling is 20% of dilute hydrochloric acid which is used for absorbing unreacted hydrogen chloride by an acid washing tower, and the hydrochloric acid after the acid washing is used for producing 31% hydrochloric acid.
In the method, the calcium chloride method is adopted to analyze the hydrogen chloride in the byproduct hydrochloric acid, so that the environmental pollution is serious, the operation intensity is high, and the calcium chloride solution with higher concentration is easy to agglomerate under the low-temperature condition, so that the conveying pipeline is blocked, and the operation efficiency of the device is influenced. In addition, the solid phase method for producing the methane chloride mainly adopts hydrogen chloride and methanol as raw materials to carry out catalytic reaction, and then the high-purity methane chloride is prepared through the steps of separation, compression, condensation, refining and the like, the purity of the used hydrogen chloride is relatively high, and the hydrogen chloride with high fluoride content hardly meets the production requirement of the calcium chloride method. Therefore, it is urgently needed to develop a method for producing methane chloride by using fluorine-containing hydrogen chloride gas as a byproduct.
Disclosure of Invention
Aiming at the defects in the prior art, the invention provides a method for producing methane chloride by using fluorine-containing byproduct hydrogen chloride, which solves the problems of low utilization rate, high harmfulness and poor economic benefit after preparing fluorine-containing byproduct hydrochloric acid, and enables the fluorine-containing byproduct hydrogen chloride to be better utilized. The method uses the byproduct hydrogen chloride with higher fluoride content as a raw material for producing the methane chloride, obtains a large amount of hydrogen chloride gas reaching the reaction condition by comprehensively treating the byproduct fluorine-containing hydrogen chloride, and obtains the high-purity methane chloride after the hydrogen chloride gas reacts with methanol, and the high-purity methane chloride is obtained after chilling separation, water washing, alkali washing, compression condensation and degassing refining.
The technical scheme of the invention is as follows:
a method for producing methane chloride by using byproduct fluorine-containing hydrogen chloride comprises the following steps:
(1) cooling and absorbing the byproduct fluorine-containing hydrogen chloride gas to obtain fluorine-containing hydrochloric acid; carrying out primary analysis and evaporation treatment on the fluorine-containing hydrochloric acid to obtain hydrogen chloride gas and fluorine-containing dilute hydrochloric acid;
(2) vacuum exhausting the fluorine-containing dilute hydrochloric acid in the step (1), reducing pressure, removing light hydrocarbons, mixing with byproduct fluorine-containing hydrochloric acid to increase the concentration of the hydrochloric acid to 23-28%, and performing deep analysis evaporation treatment to obtain hydrogen chloride gas with water vapor and dilute hydrochloric acid; cooling the hydrogen chloride gas with water vapor to 0-30 ℃ through twice condensation to obtain the hydrogen chloride gas;
(3) respectively preheating the hydrogen chloride gas and the methanol obtained in the step (1) and the step (2) to 160-220 ℃, mixing in a reactor, adding a catalyst, and reacting under the conditions that the temperature is 200-280 ℃ and the pressure is 0.15-0.4 MPa to generate crude methane chloride gas; then the methane chloride is prepared after chilling separation, water washing, cooling for acid removal, alkali washing, drying and compression and degassing refining.
According to the invention, the fluorine content of the byproduct fluorine-containing hydrogen chloride gas in the step (1) is preferably 2.0-5.0%, the main component is one or more of R22, R32, R125, R134a, R143a and HF, and the temperature is 20-50 ℃.
According to the invention, preferably, the cooling absorption in the step (1) is carried out in an absorption tower, the used absorbent is hydrochloric acid with the concentration of 10-20%, the absorption tower is cooled by circulating water, the pressure of the absorption tower is controlled to be 0-0.1 MPa, the temperature is controlled to be 40-60 ℃, and the concentration of the fluorine-containing hydrochloric acid obtained after the cooling absorption is finished is 31-35%.
According to the invention, the temperature of the primary desorption evaporation treatment in the step (1) is preferably 140-160 ℃, and the pressure is preferably 0.30-0.50 MPa.
According to the invention, the concentration of the hydrogen chloride gas obtained after the preliminary analysis and evaporation treatment in the step (1) is preferably more than 99.99%, and the concentration of the fluorine-containing dilute hydrochloric acid is preferably 20-25%.
According to the invention, the pressure reduction and light component removal in the step (2) is preferably to remove light hydrocarbon substances in a vacuum tower, the temperature of the bottom of the vacuum tower is controlled to be 65-75 ℃, and the pressure of the bottom of the vacuum tower is controlled to be-0.2 MPa to-0.01 MPa. Separating light hydrocarbon substances from the top of the vacuum tower.
According to the present invention, the pressure of the deep desorption evaporation treatment in the step (2) is preferably 0.4MPa to 0.55MPa, and the desorption temperature is preferably 155 ℃ to 165 ℃.
According to the invention, the concentration of the dilute hydrochloric acid obtained after the deep analysis evaporation treatment in the step (2) is preferably 10-20%, and the concentration of the hydrogen chloride gas with water vapor is preferably 98.5-99.8%.
Preferably, according to the present invention, the two-time condensation in step (2) is specifically: and (3) cooling the hydrogen chloride gas with the water vapor to 30-60 ℃ through a primary cooler, cooling the hydrogen chloride gas to 0-30 ℃ through a primary condenser, and condensing the water vapor to obtain the hydrogen chloride gas.
The residual hydrogen chloride gas is cooled to-10-0 ℃ through a secondary condenser, the hydrogen chloride temperature is reduced to-20-10 ℃ through a chiller, and the part of hydrogen chloride can be returned to the primary condenser to be used as a refrigerant.
According to the invention, the volume ratio of the hydrogen chloride gas to the methanol in the step (3) is preferably 1 (1-1.5), the preheating temperature is 180-200 ℃, the reaction temperature is 210-260 ℃, and the reaction pressure is 0.16-0.28 MPa.
Preferably according to the invention, the catalyst described in step (3) is a supported alumina.
The supported alumina is an existing conventional catalyst.
According to the invention, the water washing in the step (3) is preferably performed twice in a water washing tower, wherein the first water washing uses dilute hydrochloric acid with the concentration of 15-20% to absorb the incompletely reacted hydrogen chloride, and the second water washing uses pure water or 10-15% dilute hydrochloric acid to absorb the incompletely reacted hydrogen chloride. After the first washing, 10 to 25 percent of dilute hydrochloric acid is obtained and can be recycled for absorbing byproduct fluorine-containing hydrogen chloride gas.
According to the invention, the cooling and acid removing process in the step (3) is preferably as follows: the temperature of the crude methane chloride gas is reduced to 35-50 ℃, and the adopted refrigerants are saline water, dichloromethane or water, so as to further absorb the hydrogen chloride gas which is not completely reacted.
Preferably, the alkaline washing in the step (3) is carried out in an alkaline washing tower, a pH online detection device is arranged in the alkaline washing tower, and the alkaline is intermittently supplemented when the pH value is 9.5-11; the pH on-line detection device is positioned at one of an alkali liquor circulating pipeline, a bottom discharge pipeline of the alkali tower and a waste alkali liquor discharge pipeline. The general pH on-line detection device can be used for discontinuously supplementing alkali, so that the utilization rate of the circulating alkali liquor can be effectively improved.
According to the invention, the degassing refining in the step (3) is preferably carried out by removing the tail gas in a degassing tower, wherein the pressure of the degassing tower is 0.6MPa to 1.0MPa, and the degassing temperature is 10 ℃ to 50 ℃. Degassing and refining can further remove fluorine-containing compounds in the methyl chloride product.
More preferably, the material of the degassing tower is selected from carbon steel, steel-lined polytetrafluoroethylene, and 316 stainless steel.
The invention has the technical characteristics and beneficial effects that:
1. the invention absorbs the hydrogen chloride by the byproduct fluorine-containing hydrogen chloride gas with the fluorine content of 2.0-5.0% generated in the fluorine chemical production process through the dilute hydrochloric acid, 70-85% of fluoride in the byproduct fluorine-containing hydrogen chloride gas is not absorbed, but is separated from the top of the absorption tower and enters the incineration device, so that the total amount of fluorine-containing compounds in the fluorine-containing hydrochloric acid is greatly reduced. The concentration of the hydrogen chloride gas obtained by depressurization, lightness removal and deep analysis of the fluorine-containing hydrochloric acid reaches 98.5-99.8%, and meanwhile, the acidic wastewater with the acid content of 0.1-0.5% is separated and can be treated and discharged, so that the influence of the fluorine-containing hydrogen chloride on the subsequent reaction is reduced, and the pollution of the wastewater to the environment is avoided.
2. The method uses the hydrogen chloride separated from the fluorine-containing hydrogen chloride gas as a byproduct to participate in the synthesis reaction of methane chloride, realizes the reutilization of waste resources, and saves the production cost. And the reaction temperature is controlled to be 210-260 ℃ and the reaction pressure is controlled to be 0.16-0.28 MPa in the reaction process, the influence of fluorine-containing compounds in the hydrogen chloride on the reaction is reduced by accurately controlling the reaction temperature and the reaction pressure, and the purity of the prepared methane chloride can reach 99.9-99.99 percent through chilling separation, water washing, cooling acid removal, alkali washing, drying compression and degassing refining.
3. In the two-time washing process, 20-25% of dilute hydrochloric acid can be obtained by the first washing, and can be circularly used for absorbing the byproduct fluorine-containing hydrogen chloride gas, so that the generation of a large amount of dilute hydrochloric acid is avoided, and the emission of the byproduct in the production process is effectively reduced; the second water washing can effectively absorb the hydrogen chloride which is not completely reacted in the monochloro methane and reduce the concentration of the hydrogen chloride to 50 ppm-500 ppm. Further, the unreacted hydrogen chloride gas is collected in the freezing and water removing processes, and the concentration of the hydrogen chloride gas is reduced to 20ppm to 200 ppm.
4. The alkaline washing process of the invention uses a pH on-line detection device, and the alkaline is intermittently supplemented according to the monitored pH value, so that the consumption of the alkaline can be reduced by 50-80%. Degassing and refining are carried out in the subsequent treatment process, fluorine-containing compounds such as R22, R32, R125, R134a, R143a, HF and the like are removed and sent to fluorine chemical enterprises for incineration treatment, and the pollution of the fluorine-containing compounds to the environment is avoided.
Drawings
FIG. 1 is a schematic view of the process for producing monochloromethane by using fluorine-containing hydrogen chloride as a by-product of the present invention.
Detailed Description
In order to better highlight the objects, technical solutions and advantages of the present invention, the present invention is further described in detail by combining with a process flow diagram and the following detailed description.
Example 1
A method for producing methane chloride by using byproduct fluorine-containing hydrogen chloride comprises the following steps:
(1) introducing the byproduct fluorine-containing hydrogen chloride gas into an absorption tower containing 19.2% dilute hydrochloric acid, cooling the absorption tower by using circulating water, controlling the pressure in the tower to be 0.02MPa and the temperature to be 45.2 ℃, and obtaining 34.5% fluorine-containing hydrochloric acid, 82.5% fluoride and 16% hydrogen chloride; a mixture of 1.5% water, which is separated from the top of the absorption column and enters the incineration plant; conveying the fluorine-containing hydrochloric acid to the top of an analysis tower by a pump for spraying, controlling the analysis temperature to be 156.5 ℃ and the analysis pressure to be 0.41MPa, obtaining hydrogen chloride gas with the concentration of 99.99% at the tower top, and obtaining a byproduct fluorine-containing hydrochloric acid with the concentration of 21.2% at the tower bottom;
(2) conveying the fluorine-containing dilute hydrochloric acid obtained in the step (1) to a vacuum tower by a pump, controlling the temperature to be 73.8 ℃ and the pressure to be-65 KPa, reducing the pressure after vacuum exhaust, removing light hydrocarbon substances, mixing with a byproduct fluorine-containing hydrochloric acid to improve the concentration of the hydrochloric acid to 24.9%; then conveying to an analytical tower, controlling the temperature of the analytical tower to be 162.3 ℃ and the pressure of the analytical tower to be 0.42MPa, and carrying out deep analytical evaporation treatment to obtain hydrogen chloride gas with water vapor and dilute hydrochloric acid with the concentration of 15%; cooling the hydrogen chloride gas with water vapor to 50 ℃ through a primary cooler, cooling the hydrogen chloride gas to 12 ℃ through a primary condenser, condensing the water vapor, and recovering to obtain the hydrogen chloride gas with the concentration of 98.9%;
(3) preheating the hydrogen chloride gas and methanol obtained in the step (1) and the step (2) to 198 ℃ and 192 ℃ respectively, mixing in a reactor according to the volume ratio of 1:1.15, adding supported alumina, and reacting at the temperature of 225 ℃ and the pressure of 0.25MPa to generate crude methane chloride gas; after chilling separation, introducing the hydrogen chloride gas into a water washing tower, washing the hydrogen chloride gas by water to absorb the hydrogen chloride gas which is not completely reacted, introducing the hydrogen chloride gas into a chiller, and cooling and absorbing the hydrogen chloride gas which is not completely reacted by using low-temperature dichloromethane as a refrigerant; and then, the alkali washing liquid enters an alkali washing tower, the pH value in the alkali washing tower is detected in real time by using a pH online analyzer, the pH value of alkali liquor in the alkali washing tower is ensured to be not lower than 9.5, the chloromethane is compressed and liquefied after being dried by three-stage sulfuric acid, and is sent to a degassing tower after being cooled to 32.5 ℃, the temperature of the degassing tower is controlled to be 49.5 ℃, and the pressure of a tower kettle is 1.0MPa, so that the monochloro methane is prepared.
In the step (1), the byproduct fluorine-containing hydrogen chloride gas comprises the following components: 96.4% of hydrogen chloride, 1.3% of R125, 0.9% of R32, 0.4% of R22, 0.25% of R134a, 0.65% of R143a and 0.1% of HF.
The specific process of water washing in the step (3) is as follows: the first water washing adopts dilute hydrochloric acid with the concentration of 15 percent to absorb the hydrogen chloride which is not completely reacted, and the second water washing adopts pure water to absorb the hydrogen chloride which is not completely reacted.
Through detection, the purity of the methane chloride prepared in the embodiment is 99.98%, the content of hydrogen chloride gas in the methane chloride after the first water washing is 180ppm, the content of hydrogen chloride gas in the methane chloride after the second water washing is 55ppm, the usage amount of alkali liquor in the alkali washing process is 9.5kg per ton of methane chloride gas, the main components of tail gas at the top of the degassing tower are R134a, R143a R22, R32 and R125, and the tail gas is separated and then sent to a fluorine chemical enterprise for incineration treatment.
Example 2
A method for producing methane chloride by using byproduct fluorine-containing hydrogen chloride comprises the following steps:
(1) introducing the byproduct fluorine-containing hydrogen chloride gas into an absorption tower containing dilute hydrochloric acid with the concentration of 18.9%, cooling the absorption tower by using circulating water, controlling the pressure in the absorption tower to be 0.02MPa and the temperature to be 46.3 ℃, and obtaining fluorine-containing hydrochloric acid with the concentration of 35.0%, fluoride with the content of 86.2% and hydrogen chloride with the content of 12.4%; a mixture of 1.4% water, which is separated from the top of the absorption column and enters the incineration plant; conveying the fluorine-containing hydrochloric acid to the top of an analysis tower by a pump for spraying, controlling the analysis temperature to be 156.5 ℃ and the analysis pressure to be 0.42MPa, obtaining hydrogen chloride with the purity of 99.99% at the tower top, and obtaining a byproduct fluorine-containing hydrochloric acid with the concentration of 21.8% at the tower bottom;
(2) conveying the fluorine-containing dilute hydrochloric acid obtained in the step (1) to a vacuum tower by a pump, controlling the temperature at 74.1 ℃ and the pressure at-62 KPa, reducing the pressure after vacuum exhaust to remove light hydrocarbon substances, mixing with a byproduct fluorine-containing hydrochloric acid to improve the concentration of the hydrochloric acid to 24.8%; then conveying to an analytical tower, controlling the temperature of the analytical tower to be 162.3 ℃ and the pressure of the analytical tower to be 0.42MPa, and carrying out deep analytical evaporation treatment to obtain hydrogen chloride gas with water vapor and dilute hydrochloric acid with the concentration of 24.8%; cooling the hydrogen chloride gas with water vapor to 50 ℃ through a primary cooler, cooling the hydrogen chloride gas to 15 ℃ through a primary condenser, condensing the water vapor, and recovering to obtain the hydrogen chloride gas with the concentration of 98.9%;
(3) preheating the hydrogen chloride gas and methanol obtained in the step (1) and the step (2) to 197 ℃ and 195 ℃ respectively, mixing according to the volume ratio of 1:1.15, adding a catalyst, and reacting at the temperature of 227 ℃ and the pressure of 0.26MPa to generate crude methane chloride gas; then chilling and separating, introducing into a water washing tower, washing with water to absorb the hydrogen chloride gas which is not completely reacted, introducing into a chiller, cooling by using low-temperature dichloromethane as a refrigerant, and absorbing the hydrogen chloride gas which is not completely reacted; and then, the alkali washing liquid enters an alkali washing tower, the pH value in the alkali washing tower is detected in real time by using a pH online analyzer, the pH value of alkali liquor in the alkali washing tower is ensured to be not lower than 9.5, the chloromethane is compressed and liquefied after being dried by three-stage sulfuric acid, and is sent to a degassing tower after being cooled to 32.5 ℃, the temperature of the degassing tower is controlled to be 49.67 ℃, and the pressure of a tower kettle is controlled to be 0.98MPa, so that the monochloro methane is prepared.
In the step (1), the byproduct fluorine-containing hydrogen chloride gas comprises the following components: 95.8% of hydrogen chloride, 1.9% of R125, 1.0% of R32, 0.4% of R22, 0.3% of R134a, 0.45% of R143a and 0.15% of HF.
The specific process of water washing in the step (3) is as follows: the first water washing adopts dilute hydrochloric acid with the concentration of 15 percent to absorb the hydrogen chloride which is not completely reacted, and the second water washing adopts pure water to absorb the hydrogen chloride which is not completely reacted.
Through detection, the purity of the methane chloride prepared in the embodiment is 99.99%, the content of hydrogen chloride gas in the methane chloride after the first water washing is 160ppm, the content of hydrogen chloride gas in the methane chloride after the second water washing is 50ppm, the usage amount of alkali liquor in the alkali washing process is 9.5kg per ton of methane chloride gas, tail gas components at the top of the degassing tower mainly comprise R134a, R143a R22, R32 and R125, and the tail gas is separated and then sent to a fluorine chemical enterprise for incineration treatment.
Comparative example 1
A method for producing methane chloride by using byproduct fluorine-containing hydrogen chloride, as shown in example 2, except that,
the step (2) is as follows: conveying the fluorine-containing dilute hydrochloric acid obtained in the step (1) to a vacuum tower by a pump, controlling the temperature to be 72.1 ℃ and the pressure to be-55 KPa, reducing the pressure and removing light hydrocarbon substances after vacuum exhaust, conveying the gas to an analysis tower, controlling the temperature of the analysis tower to be 150.2 ℃ and the pressure of the analysis tower to be 0.35MPa, and performing deep analysis evaporation treatment to obtain hydrogen chloride gas with water vapor and dilute hydrochloric acid with the concentration of 24.6%; cooling the hydrogen chloride gas with water vapor to 50 ℃ through a primary cooler, cooling the hydrogen chloride gas to 15 ℃ through a primary condenser, and condensing the water vapor to obtain 96.68% hydrogen chloride gas;
the purity of the monochloromethane gas prepared in this comparative example was checked to be 98.75%.
Comparative example 2
A method for producing methane chloride by using byproduct fluorine-containing hydrogen chloride, as shown in example 2, except that,
the step (3) is as follows: preheating the hydrogen chloride gas and methanol obtained in the step (1) and the step (2) to 197 ℃ and 195 ℃ respectively, mixing according to the volume ratio of 1:1.15, adding a catalyst, and reacting at the temperature of 227 ℃ and the pressure of 0.26MPa to generate a mixture of methane chloride, methane, dichloromethane and chloroethane; chilling separation, water washing, alkali washing, drying by using tertiary sulfuric acid, compressing and liquefying the chloromethane, and cooling to 31.2 ℃ to obtain the monochloromethane.
Through detection, the purity of the methane chloride gas prepared in the comparative example is 98.85%, the content of hydrogen chloride gas in the methane chloride gas after water washing is 3500ppm, and the usage amount of the alkali liquor in the alkali washing process is 47kg per ton of the methane chloride gas.
As can be seen from the examples 1-2 and the comparative example 1, the purity of the hydrogen chloride gas recovered by heat exchange, temperature rise, vacuum desorption and other treatments reaches 98.9 percent, which is obviously higher than 96.68 percent of the comparative example 1, so that the purity of the monochloromethane prepared in the subsequent examples 1-2 reaches 99.98 percent and 99.99 percent, while the purity of the monochloromethane prepared in the comparative example 1 reaches 98.75 percent, which does not meet the product requirement. As can be seen from examples 1-2 and comparative example 2, the removal of the tail gas in the degassing tower can effectively remove the fluoride from the monochloromethane, so that the purity of the monochloromethane prepared in examples 1-2 can reach 99.98% and 99.99%, while the purity of the monochloromethane prepared in comparative example 2 can reach 98.85%, and the product requirement can not be met. As can be seen from examples 1-2 and comparative example 2, the invention further absorbs the hydrogen chloride which is not completely reacted through two times of water washing, and effectively reduces the concentration of the hydrogen chloride to be below 80ppm, while the content of the hydrogen chloride gas in the methyl chloride after the water washing of the comparative example 2 is 3500ppm, and the pH online detection device is used in the alkali washing process, and the alkali is intermittently supplemented according to the monitored pH value, so that the use amount of the alkali is effectively reduced by 79.8%.
Claims (10)
1. A method for producing methane chloride by using byproduct fluorine-containing hydrogen chloride comprises the following steps:
(1) cooling and absorbing the byproduct fluorine-containing hydrogen chloride gas to obtain fluorine-containing hydrochloric acid; carrying out primary analysis and evaporation treatment on the fluorine-containing hydrochloric acid to obtain hydrogen chloride gas and fluorine-containing dilute hydrochloric acid;
(2) vacuum exhausting the fluorine-containing dilute hydrochloric acid in the step (1), reducing pressure, removing light hydrocarbons, mixing with byproduct fluorine-containing hydrochloric acid to increase the concentration of the hydrochloric acid to 23-28%, and performing deep analysis evaporation treatment to obtain hydrogen chloride gas with water vapor and dilute hydrochloric acid; cooling the hydrogen chloride gas with water vapor to 0-30 ℃ through twice condensation to obtain the hydrogen chloride gas;
(3) respectively preheating the hydrogen chloride gas and the methanol obtained in the step (1) and the step (2) to 160-220 ℃, mixing in a reactor, adding a catalyst, and reacting under the conditions that the temperature is 200-280 ℃ and the pressure is 0.15-0.4 MPa to generate crude methane chloride gas; then the methane chloride is prepared after chilling separation, water washing, cooling for acid removal, alkali washing, drying and compression and degassing refining.
2. The method for producing monochloromethane by using by-product fluorine-containing hydrogen chloride as claimed in claim 1, wherein the fluorine content of the by-product fluorine-containing hydrogen chloride gas in step (1) is 2.0% to 5.0%, and the main component is one or more of R22, R32, R125, R134a, R143a and HF, and the temperature is 20 ℃ to 50 ℃.
3. The method for producing monochloromethane by using by-product fluorine-containing hydrogen chloride as claimed in claim 1, wherein the cooling absorption in step (1) is carried out in an absorption tower using hydrochloric acid having a concentration of 10% to 20%, the absorption tower is cooled by circulating water, the pressure in the absorption tower is controlled to be 0 to 0.1MPa, the temperature is controlled to be 40 ℃ to 60 ℃, and the concentration of the fluorine-containing hydrochloric acid obtained after the cooling absorption is completed is 31% to 35%.
4. The method for producing monochloromethane by using by-product fluorine-containing hydrogen chloride according to claim 1, wherein the temperature of the preliminary desorption evaporation treatment in the step (1) is 140 ℃ to 160 ℃, and the pressure is 0.30MPa to 0.50 MPa; the concentration of the hydrogen chloride gas obtained after the preliminary analysis and evaporation treatment is more than 99.99 percent, and the concentration of the fluorine-containing dilute hydrochloric acid is 20 to 25 percent.
5. The method for producing methane chloride by using byproduct fluorine-containing hydrogen chloride according to claim 1, wherein the step (2) of reducing pressure and removing light hydrocarbons comprises removing light hydrocarbons in a vacuum tower, wherein the temperature of the bottom of the vacuum tower is controlled to be 65-75 ℃, and the pressure of the bottom of the vacuum tower is controlled to be-0.2 MPa-0.01 MPa.
6. The method for producing methane chloride by using byproduct fluorine-containing hydrogen chloride according to claim 1, wherein the pressure of the deep desorption evaporation treatment in the step (2) is 0.4MPa to 0.55MPa, and the desorption temperature is 155 ℃ to 165 ℃; the concentration of the dilute hydrochloric acid obtained after the deep analysis and evaporation treatment is 10-20%, and the concentration of the hydrogen chloride gas with water vapor is 98.5-99.8%.
7. The method for producing methane chloride by using byproduct fluorine-containing hydrogen chloride according to claim 1, wherein the twice condensation in the step (2) comprises: and (3) cooling the hydrogen chloride gas with the water vapor to 30-60 ℃ through a primary cooler, cooling the hydrogen chloride gas to 0-30 ℃ through a primary condenser, and condensing the water vapor to obtain the hydrogen chloride gas.
8. The method for producing methane chloride by using fluorine-containing by-product hydrogen chloride according to claim 1, wherein the volume ratio of hydrogen chloride gas to methanol in the step (3) is 1 (1-1.5), the preheating temperature is 180-200 ℃, the reaction temperature is 210-260 ℃, and the reaction pressure is 0.16-0.28 MPa; the catalyst is supported alumina.
9. The method for producing monochloromethane by using by-product fluorine-containing hydrogen chloride as claimed in claim 1, wherein the water washing in step (3) is performed twice in a water washing column, the first water washing uses dilute hydrochloric acid with a concentration of 15% to 20% to absorb the incompletely reacted hydrogen chloride, and the second water washing uses pure water or 10% to 15% dilute hydrochloric acid to absorb the incompletely reacted hydrogen chloride.
10. The method for producing monochloromethane by using the byproduct fluorine-containing hydrogen chloride as claimed in claim 1, wherein the alkali washing in the step (3) is performed in an alkali washing tower, a pH online detection device is arranged in the alkali washing tower, and the intermittent alkali supplement is performed when the pH value is 9.5-11; the degassing refining is to remove tail gas in a degassing tower, the pressure of the degassing tower is 0.6MPa to 1.0MPa, and the degassing temperature is 10 ℃ to 30 ℃.
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