CN1781888A - Process for preparing methyl chloride and polychloromethane - Google Patents

Abstract

In an alumina catalyst, a hydrogen chloride mixture containing 0.001 to 10 mol% of a fluorocarbon relative to hydrogen chloride is supplied in a gas phase to react with methanol to obtain a methyl chloride-containing reaction gas, and methyl chloride is separated from the methyl chloride-containing reaction gas to obtain purified methyl chloride. Further, the purified methyl chloride is reacted with chlorine gas to obtain a mixture of hydrogen chloride and polychlorinated methane, and the mixture of hydrogen chloride and polychlorinated methane is separated to obtain purified polychlorinated methane and purified hydrogen chloride gas. A method for converting hydrogen chloride containing 0.001 to 10 mol% of a fluorocarbon as an industrial raw material into a high-value compound and a method for converting the obtained methyl chloride into a high-value purified hydrogen chloride and a polychlorinated methane by reacting the methyl chloride with chlorine are provided.

Description

Process for preparing methyl chloride and polychloromethane

technical field

The present invention relates to the preparation method of methyl chloride and polychloromethane. More particularly, it relates to a method for preparing methyl chloride using hydrogen chloride containing fluorocarbon impurities, and a method for preparing polychloromethane.

Background technique

Chloromethane is a useful compound as a starting material for polychloromethanes such as polysilicone and methylene chloride or chloroform. Polychloromethane is a useful compound as a solvent or as a raw material for the production of fluorocarbons, fluorine-containing resins, and the like. For a long time, methyl chloride has been prepared by, for example, reacting hydrogen chloride and methanol in the gas phase in the presence of an alumina catalyst, and polychloromethane is obtained by reacting methyl chloride with chlorine to obtain a mixture of polychloromethanes, which is then refined and separated by distillation. Prepared from polychloromethane.

On the other hand, hydrogen chloride is a widely used industrial basic raw material, and is usually prepared by refining synthetic hydrogen chloride obtained by reacting chlorine and hydrogen. In addition, hydrogen chloride is discharged as a by-product in the production process of fluorocarbons and the like, and usually contains fluorocarbon impurities.

If cheap by-product hydrogen chloride is used instead of expensive synthetic hydrogen chloride, it can be directly used as an industrial raw material without refining, such as the above-mentioned raw material for the preparation of methyl chloride or the reaction of hydrogen chloride, ethylene and oxygen in the presence of copper-alumina catalysts to prepare 1,2 - The application of raw materials for the preparation of dichloroethane has the advantage of being able to prepare the target object at low cost.

However, it is known that hydrogen fluoride reacts with alumina (see "Technology and Regulations for Pollution Control (Atmospheric Chapter)" written by the Ministry of International Trade and Industry's Environmental Protection and Industrial Distribution Bureau Supervision, Pollution Control Technology and Regulations Compilation Committee, 191 pages, Heisei Issued on December 15, 2010), similarly, since heating fluorocarbons will also thermally decompose to generate hydrogen fluoride, it is considered that it has a catalyst toxicity effect on the above-mentioned alumina catalyst. Therefore, until now, hydrogen chloride, a by-product containing fluorocarbon impurities, has not been used as a feedstock for the production of methyl chloride or 1,2-dichloroethane using alumina catalysts.

For this reason, in order to effectively utilize by-product hydrogen chloride containing fluorocarbons, etc., it has been proposed to absorb hydrogen chloride by-produced in the production process of fluorocarbons with water, separate and remove fluorocarbons, and recycle them as an inexpensive hydrochloric acid aqueous solution. , and a method for refining by adsorbing and removing fluorocarbons with an adsorbent (JP-P-8-505833 specification).

However, the former technology is used for recycling as cheap hydrochloric acid, and the latter technology is difficult to say that it is industrially unsuitable because it requires not only the equipment to bring it into contact with the adsorbent, but also the cost of the adsorbent material and the energy for operating the equipment. advantageous.

Contents of the invention

Against this background, the object of the present invention is to provide a process for the conversion of fluorocarbon-containing hydrogen chloride into high-value compounds by directly using it as an industrial feedstock, and for further conversion by reacting the obtained methyl chloride with chlorine gas Process for producing high value refined hydrogen chloride and polychloromethane.

The inventors of the present invention conducted intensive studies in order to solve the above problems. As a result, it was surprisingly found that even when fluorocarbon-containing hydrogen chloride is reacted with methanol in the presence of an alumina catalyst, the conversion rate of methanol hardly decreases, and methyl chloride can be produced over a long period of time, thereby completing the present invention.

That is, the first aspect of the present invention is a method for preparing methyl chloride, which is characterized in that a hydrogen chloride mixed gas containing 0.001 to 10 mol% of fluorocarbons relative to hydrogen chloride is contacted in a gas phase with methanol in the presence of an alumina catalyst to form Chloromethane.

And, the second aspect of the present invention is a kind of method for preparing polychloromethane, it is characterized in that comprising:

The first step: making a hydrogen chloride mixed gas containing 0.001 to 10 mol % of fluorocarbons relative to hydrogen chloride and methanol in the presence of an alumina catalyst for gas phase contact to generate a reaction product gas containing chloromethane,

The second step: separating methyl chloride from the reaction product gas generated in the first step,

The 3rd process: make the methyl chloride separated in the 2nd process react with chlorine gas to generate the mixture of hydrogen chloride and polychloromethane, and

The fourth step: separating at least polychloromethane from the mixture produced in the third step.

Detailed ways

In the present invention, it is very important to use a mixture containing 0.001 mol % to 10 mol % of fluorocarbons relative to hydrogen chloride (hereinafter sometimes referred to as a hydrogen chloride mixture). For example, methyl chloride can be produced inexpensively by using a fluorocarbon-containing hydrogen chloride mixture that is by-produced in the production process of fluorocarbons instead of expensive synthetic hydrogen chloride. That is, it is possible to produce methyl chloride by industrially advantageous and effective utilization of by-product chlorides of fluorocarbons, which are limited in application and require a large purification cost.

The type of fluorocarbon contained in the hydrogen chloride mixture is not subject to any limitation. For example, it can include at least one general formula C _k H _l Cl _m F _n (wherein, k is an integer of 1 to 4, l is an integer of 0 to 9, m is an integer of 0 to 9, and n is an integer of 1 to 9 An integer of 10, l+m+n equals 2k+2 in the case of saturated compounds and 2k in the case of olefinic compounds) of hydrogen chloride mixtures of saturated or olefinic compounds. Hydrogen chloride mixtures produced by-products in the production process of industrially produced fluorocarbons are preferably preferred, and such hydrogen chloride mixtures include, for example, trichlorofluoromethane, dichlorodifluoromethane, trifluorochloromethane, tetrafluoromethane, difluoromethane, Chlorofluoromethane, difluorochloromethane, trifluoromethane, difluoromethane, monofluoromethane, tetrachlorodifluoroethane, trichlorotrifluoroethane, chloropentafluoroethane, pentafluoroethane, hexafluoroethane Alkanes, difluorochloroethane, difluoroethane, tetrafluoroethylene, octafluorocyclobutane, etc. Particularly suitable is a hydrogen chloride mixture containing a fluorocarbon having a boiling point of -70°C to -100°C, and a hydrogen chloride mixture containing a fluorocarbon forming an azeotropic mixture with hydrogen chloride is also preferred. Hydrogen chloride mixtures containing such fluorocarbons are difficult to separate fluorocarbons from hydrogen chloride, but can easily separate chloromethane from fluorocarbons and/or their reactants from the reaction gas after producing methyl chloride. Specifically, chlorotrifluoromethane, tetrafluoromethane, trifluoromethane, monofluoromethane, chloropentafluoroethane, pentafluoroethane, hexafluoroethane, tetrafluoroethylene and the like are preferable.

The concentration of fluorocarbons in these hydrogen chloride mixtures is 0.001 mol% to 10 mol% relative to hydrogen chloride. If it exceeds 10 mol%, the amount converted into aluminum fluoride increases, and the activity of the alumina catalyst decreases as the reaction time elapses. The concentration of the fluorocarbon is preferably 0.001 mol% to 5 mol%, particularly preferably 0.001 mol% to 2 mol%. It is preferable because the high conversion rate of hydrogen chloride and methanol can be maintained for a long period of time.

In addition, hydrogen fluoride and carbonyl fluoride may coexist in the fluorocarbon-containing hydrogen chloride mixture, and usually, if the total concentration thereof is 0.01 mol%, it does not matter even if they coexist.

In the present invention, methanol, another raw material, is gasified into a gas phase by a gasifier or the like.

In the present invention, the molar ratio of hydrogen chloride and methanol in the hydrogen chloride mixture is not particularly limited, but because there is a tendency for the conversion rate of hydrogen chloride to decrease if methanol is excessive, industrially, the molar ratio of hydrogen chloride and methanol is preferably 1 to 1. 1.5:1, particularly preferably 1-1.1:1.

In the present invention, the alumina catalyst is not particularly limited, and known alumina catalysts can be used. For example, it is most suitable to use alumina alone or to use alumina added with a specific metal oxide.

The specific surface area of alumina is preferably 50 m ² /g or more, particularly preferably 100 m ² /g or more.

Examples of specific metal oxides to be added to alumina include oxides of alkali metals such as sodium and potassium, oxides of alkaline earth metals such as calcium and magnesium, and oxides of zinc, copper, manganese, cobalt, chromium, iron, and nickel. Or oxides such as titanium. One kind or two or more kinds of these metal oxides can also be used. In addition, the addition amount of the above-mentioned metal oxides to alumina can preferably be selected within a range of about 0.01 to 20%. The method of adding these specific metals to alumina is not particularly limited, and known methods such as impregnation method, co-precipitation method, mixing method and the like which are generally used for preparing catalysts can be applied.

The aforementioned alumina catalyst was filled into the reactor to form a packed layer of alumina catalyst. The shape of the packed alumina catalyst may be a known shape. For example, any of granular and crushed shapes can be mentioned, and it can also be shaped into various shapes such as spherical shape, cylindrical shape, and honeycomb shape to be sized and used. In addition, the average particle size of the alumina catalyst is not particularly limited. As the following reaction form, when a fixed bed method is used, it is preferably 0.5 to 20 mm, particularly preferably 1 to 10 mm, and when a fluidized bed method is used, it is preferably 0.001 mm. ~0.5mm, particularly preferably 0.01~0.2mm.

The reaction format is not particularly limited, and examples include a fixed bed method and a fluid bed method, and the fixed bed method is preferred from the viewpoints of relatively low equipment costs and ease of transportation.

In the present invention, a hydrogen chloride mixture containing 0.001 mol % to 10 mol % of fluorocarbons and methanol are supplied to the alumina catalyst layer in a gas phase.

The space velocity (SV) of the reactor is not particularly limited, but is preferably 100 to 10,000 h ^-1 , more preferably 200 to 5,000 h ^-1 . It is preferable to be able to maintain a high conversion of hydrogen chloride and methanol over a long period of time.

The reaction temperature is not particularly limited as long as it is at or above the temperature at which hydrochloric acid does not condense. If the temperature is too high, there will be a tendency for the conversion of the mixture of methanol and hydrogen chloride to decrease as the reaction time elapses. And, if it is too low, then in addition to the slow reaction rate and lower conversion rate, the amount of by-products of methyl ether will increase, and the water by-produced in the reaction of methanol and hydrogen chloride mixture will remain in the reaction system, causing the hydrogen chloride to dissolve and condense. Possibility of corroding reaction equipment. Therefore, it is preferably 120°C to 400°C, more preferably 150°C to 350°C, and particularly preferably 200°C to 300°C. This temperature range is suitable because it can maintain a high conversion rate of hydrogen chloride and methanol for a long time. In addition, in order to maintain the above-mentioned temperature, it is preferable to provide a device for circulating a heat medium outside or inside the reactor at the same time.

The reaction device is not particularly limited as long as it is made of an acid-resistant material. For example, devices made of stainless steel, Inconel, and heat-resistant and corrosion-resistant nickel-based alloys can be used.

In addition, the reaction pressure is not particularly limited, and any of normal pressure, increased pressure, and reduced pressure can be used.

In this way, the inexpensive hydrogen chloride mixture containing 0.001 mol% to 10 mol% of fluorocarbons can be directly and effectively used to produce the highly valuable reaction gas containing chloromethane. The methyl chloride can be separated from the unreacted starting material, the fluorocarbons contained in the hydrogen chloride mixture starting material and the water formed by the reaction by known methods.

In the present invention, the step of obtaining the above-mentioned reaction product gas containing chloromethane is the first step, and after the first step, by combining the steps of preparing polychloromethane, polychloromethane and purified hydrogen chloride can be obtained.

The reaction product gas containing methyl chloride obtained in the first step is supplied to the second step, and the methyl chloride is separated to obtain purified methyl chloride.

Since the reaction product gas containing chloromethane obtained in the first step contains, in addition to the target chloromethane, unreacted hydrogen chloride and methanol, and fluorocarbons contained in the raw material of the hydrogen chloride mixture and the fluorocarbons contained in the alumina Chlorofluorocarbons generated by reacting with hydrogen chloride under the action, so preferably the second step can be composed of a step of removing hydrogen chloride and methanol and a step of removing fluorocarbons and chlorofluorocarbons, specifically, consisting of the following steps: A step of removing unreacted hydrogen chloride and methanol by continuous washing with water, and a step of removing fluorocarbons and chlorofluorocarbons by known methods such as distillation and partial condensation to obtain purified methyl chloride.

The purified methyl chloride thus obtained can be taken out as a product, but is usually supplied to the third step of reacting the purified methyl chloride with chlorine gas to produce hydrogen chloride and polychloromethane.

In the third step, the method of reacting purified methyl chloride with chlorine gas can be a known method of chlorination reaction for the preparation of polychloromethane (for example, the method described in Patent Publication No. 56-2922). There is no particular limitation thereto. Particularly preferred is a method of reacting methyl chloride and chlorine gas in the presence of radicals generated by a radical initiator and/or ultraviolet rays while the methyl chloride is in a liquid phase. Through this chlorination reaction, a mixture containing hydrogen chloride generated by the reaction of chlorine gas and methyl chloride, and polychloromethane composed of dichloromethane, chloroform, and carbon tetrachloride can be obtained.

Next, the obtained mixture of polychloromethane and hydrogen chloride is separated through the fourth step to obtain refined polychloromethane (dichloromethane, chloroform, carbon tetrachloride) and refined hydrogen chloride. The separation method is generally more suitable to carry out distillation separation from low boiling point substances, specifically, preferably according to the distillation of hydrogen chloride, distillation of unreacted methyl chloride, distillation of dichloromethane, distillation of chloroform, distillation of carbon tetrachloride sequential composition.

Thus, by preparing polychloromethanes from an inexpensive fluorocarbon-containing hydrogen chloride mixture as one of the starting materials, a valuable refined hydrogen chloride by-product can be obtained. Since the obtained purified hydrogen chloride is a high-purity substance free of impurities such as fluorocarbons, it can be used as any industrial raw material, and is most suitable as a raw material for the production of methyl chloride, a raw material for the production of 1,2-dichloroethane, etc. use.

According to the method of the present invention, the hydrogen chloride mixture containing 0.001 mol% to 10 mol% of fluorocarbons can be directly used as an industrial raw material without refining, and methyl chloride can be obtained without reducing the conversion rate of raw materials for a long time. Therefore, the price can be reduced Inexpensive fluorocarbon-containing hydrogen chloride mixtures are converted into high-value compounds. In addition, the obtained methyl chloride can be converted into high-value purified hydrogen chloride and polychloromethane by reacting it with chlorine gas for use. Therefore, the present invention is very valuable industrially.

Example

In order to describe the present invention more specifically, the following examples are given and described, but the present invention is not limited to these examples.

Example 1

A stainless steel reaction tube with an inner diameter of 42 mm is set in the electric furnace, and the specific surface area in the tube is 160 m ² /g, filled with 50 g of cylindrical alumina catalyst particles containing 1% sodium oxide, with a particle size of 5 mm and a height of 5 mm, to make a fixed bed tube type reactor. At a space velocity of 600h ^-1 , hydrogen chloride gas containing 1 mol% trifluoromethane with a molar ratio of 1.05:1 and preheated vaporized methanol were continuously fed in to react at a reaction temperature of 250°C. The output gas was analyzed by gas chromatography to determine the conversion of methanol. The methanol conversions after 1 hour, 100 hours and 1,000 hours were 98%, 97% and 96%, respectively.

Embodiment 2-5

In Example 1, it carried out similarly to Example 1 except having changed the reaction temperature of 250 degreeC into 200 degreeC, 270 degreeC, 390 degreeC, and 410 degreeC. Table 1 shows the conversion of methanol after 1 hour, 100 hours and 1,000 hours at each reaction temperature.

Table 1 Example Reaction temperature (°C) Methanol conversion (%) 1 hour later 100 hours later After 1,000 hours 1 250 98 97 96 2 200 95 94 93 3 270 99 97 95 4 390 99 94 87 5 410 99 85 75

Embodiment 6-9

In Example 1, it carried out similarly to Example 1 except having changed the concentration of trifluoromethane into 0.1 mol%, 2 mol%, 5 mol%, and 9.5 mol%. Table 2 shows the conversion of methanol after 1 hour, 100 hours and 1,000 hours.

Table 2 Example Trifluoromethane concentration (mol%) Methanol conversion (%) 1 hour later 100 hours later After 1,000 hours 6 0.1 98 98 97 7 2 98 96 95 8 5 98 93 91 9 9.5 98 90 85

Comparative example 1

In Example 1, it carried out similarly to Example 1 except having changed the concentration of trifluoromethane into 15.0 mol%. The methanol conversions after 1 hour and 100 hours were 92% and 40%, respectively.

Examples 10-17

In Example 1, except that trifluoromethane is replaced by difluorochloromethane, trifluorochloromethane, tetrafluoromethane, monofluoromethane, chloropentafluoroethane, pentafluoroethane, hexafluoroethane or tetrafluoroethylene Other than that, it carried out similarly to Example 1. The conversion of methanol after 1 hour, 100 hours and 1000 hours is shown in Table 3.

table 3 Example Fluorocarbon Methanol conversion (%) 1 hour later 100 hours later After 1,000 hours 10 Difluorochloromethane 98 96 95 11 Chlorotrifluoromethane 98 97 96 12 Tetrafluoromethane 98 96 95 13 Fluoromethane 98 97 96 14 Chloropentafluoroethane 98 96 95 15 Pentafluoroethane 98 95 94 16 Hexafluoroethane 98 97 96 17 Tetrafluoroethylene 98 97 96

Example 18

Except that the consumption of catalyzer is 3.3kg, space velocity is 700h ^-1 , operate similarly with embodiment 1, obtain the reaction gas that contains the methyl chloride of following composition composition with the speed of 2.63m3 ^/ h: 47.5 mol% Chloromethane, 47.3 mol% of water, 1.0 mol% of methanol, 3.4 mol% of hydrogen chloride, 0.5 mol% of trifluoromethane (98% conversion of methanol). Pass all the gas into the spray tower for washing with water, remove unreacted methanol, unreacted hydrogen chloride and water generated by the reaction, cool to -40°C to remove trifluoromethane, and obtain no-containing Chloroform is a liquid refined chloroform.

Then, a cooling coil is installed inside, and in the nickel reactor ^equipped with a reaction gas cooler, 10°C liquid purified methyl chloride, chloromethane, and Chlorine, α,α'-azobisisobutyronitrile dissolved in carbon tetrachloride. Keep the reactor pressure at 2.3MPaG and the temperature at 110°C. The gas phase of the reactor is continuously withdrawn, cooled to 40°C by the reaction gas cooler, a part of it is returned to the reactor, and the other part is supplied to the stainless steel hydrogen chloride separation with 50 layers of perforated trays together with the liquid reactant taken out from the liquid phase of the reactor tower. Adjust the top pressure of the hydrogen chloride separation tower to 1.2 MPaG and the temperature to -25°C. In the hydrogen chloride separation tower, hydrogen chloride gas is drawn from the top of the tower at a rate of 7.4 Nm ³ /h to obtain purified hydrogen chloride completely free of trifluoromethane with a purity of 99.99% or above.

The unreacted methyl chloride and the polychloromethane mixture obtained from the bottom of the hydrogen chloride separation tower are separated in sequence from the low boiling point in the distillation tower, respectively at 4.4L/h, 9.7kg/h, 9.7kg/h, 1.7 The speed of kg/h outputs methyl chloride, dichloromethane, chloroform and carbon tetrachloride.

Claims (3)

1. A method for preparing methyl chloride, which is characterized in that a mixture of hydrogen chloride containing 0.001 to 10 mole percent of fluorocarbons relative to hydrogen chloride is contacted with methanol in a gas phase in the presence of an alumina catalyst to generate methyl chloride. 2. The method according to claim 1, characterized in that said contacting is carried out at 120-400°C. 3. A method for preparing polychloromethane, characterized in that it comprises: The first step: a hydrogen chloride mixture containing 0.001 to 10 mol% of fluorocarbons relative to hydrogen chloride is brought into gas phase contact with methanol in the presence of an alumina catalyst to generate a reaction product gas containing chloromethane, The second step: separating methyl chloride from the reaction product gas generated in the first step, The 3rd process: make the methyl chloride separated in the 2nd process react with chlorine gas to generate the mixture of hydrogen chloride and polychloromethane, and The fourth step: separating at least polychloromethane from the mixture produced in the third step.