CN112225637B - One-step method for preparing monochloromethane - Google Patents

Abstract

The invention discloses a method for preparing methane chloride by a high-selectivity one-step method, which comprises the following steps: in a reactor, methane gas or methane-containing gas and chlorine salt as chlorine source are reacted at 0-100 deg.c for 10-600 min under light condition in the presence of copper doped titanium dioxide compound as catalyst. The method has high selectivity on the target product, namely the monochloromethane, almost has no polychlorinated methane by-products, and ensures that the chloromethane product after reaction has high purity and is easy to separate. Moreover, the method has the advantages of simple reaction process, short period, mild reaction conditions, cheap and easily-obtained catalyst, reusability, wide source of reactant raw materials, low price and easy obtaining, and especially the capability of directly using natural gas or methane as raw material gas, and the like, provides a new synthesis way for preparing methane chloride products from methane-containing gases such as natural gas, shale gas or methane, and has wide industrial application prospect.

Description

One-step method for preparing monochloromethane

technical field

The present invention relates to a novel method for preparing monochloromethane with high selectivity.

Background technique

As an important chemical raw material, monochloromethane can be used in the production of tetramethylchlorosilane, methylcellulose and quaternary ammonium compounds, etc. It is also widely used as a solvent, extractant, methylation reagent, in construction, textile, Electronics, electrical appliances, machinery, transportation, chemicals, medical food, aviation, aerospace and other industries play an important role. At present, it is commonly used in industry to generate monochloromethane: methane chlorination and methanol hydrochlorination. However, these two methods both require higher temperature and are prone to generate by-products such as dichloromethane, dimethyl ether, etc., and the selectivity of monochloromethane is not ideal, so that further separation and purification is required after the reaction, which leads to an increase in production costs.

Considering the cost of industrial production and the problems of energy crisis and environmental pollution, there is a need in the art for a new method for preparing monochloromethane with more green, simple reaction process, mild reaction conditions and high selectivity.

SUMMARY OF THE INVENTION

In view of the above, the object of the present invention is to provide a green new method for preparing monochloromethane with high selectivity under mild conditions.

To this end, the present invention provides a one-step method for preparing monochloromethane, the method comprising: in a reactor, in the presence of a copper-doped titanium dioxide compound as a catalyst, under illumination conditions, methane gas or The methane-containing gas is reacted with the chloride salt as the chlorine source at the reaction temperature of 0–100 °C for 10–600 min.

In preferred embodiments, the methane-containing gas is natural gas, shale gas, combustible ice or biogas.

In a preferred embodiment, the chloride salt is one or more selected from the group consisting of sodium chloride, potassium chloride, lithium chloride, magnesium chloride and seawater crystalline (table) salt.

In a preferred embodiment, the atomic molar ratio of copper to titanium in the catalyst is 0.005 to 0.1:1.

In a preferred embodiment, the light intensity of the light conditions is 10-2000 mW/cm ² .

In a preferred embodiment, the light source used for the lighting conditions is one or more selected from the group consisting of xenon lamps, LED lamps, tungsten lamps and mercury lamps.

In a preferred embodiment, the reaction temperature is 20-60°C and the reaction time is 100-480 min.

In preferred embodiments, the reactor is a quartz reactor, a glass reactor or a fixed bed reactor.

In a preferred embodiment, the pressure of the methane gas or the methane-containing gas in the reactor is 0.1 MPa to 10 MPa.

In a preferred embodiment, the mass ratio of the catalyst to the chloride salt is 0.01-0.5:1.

The method of the present invention uses a chloride salt as a chlorine source and uses a specific doping catalyst to react under light conditions, and such a photocatalytic reaction can stabilize the methyl radical (·CH ₃ ) formed during the reaction, so that the Almost no by-products of polychloromethane are produced, so the target product monochloromethane has high selectivity (over 70% in general, even as high as over 90%), and the target product after the reaction is easy to separate.

The method of the invention has the advantages of simple reaction process, short period, mild reaction conditions, cheap and easily available catalysts and reusable, wide and cheap and easily available sources of reactant raw materials, in particular, natural gas or biogas can be directly used as raw materials, etc. The high-selectivity preparation of monochloromethane under mild conditions reduces the industrial production process and cost, and can greatly alleviate the energy crisis and environmental pollution problems.

In addition, the present invention provides a new synthesis route for preparing monochloromethane products from methane-containing gas such as natural gas or biogas, and has broad industrial application prospects.

Description of drawings

Figure 1 is a gas chromatogram (GC) graph of the monochloromethane product obtained according to one embodiment of the present invention.

FIG. 2 is a diagram showing the effect of repeated use of the catalyst copper-doped titanium dioxide compound according to the present invention.

Detailed ways

Through in-depth and extensive research by the inventors of the present invention, a new method for preparing monochloromethane has been unexpectedly discovered by using a chloride salt as a chlorine source and using a specific doping catalyst to react under light conditions , and such a photocatalytic reaction can stabilize the methyl radical (·CH ₃ ) formed during the reaction, so that almost no by-products of polychlorinated methane are produced, so that not only can a highly selective one-step process be achieved under mild conditions Monochloromethane can be prepared by a simple and cost-effective method, and the problems of energy crisis and environmental pollution can be greatly alleviated.

The method for preparing monochloromethane by the one-step method of the present invention comprises: in a reactor, using a copper-doped titanium dioxide compound as a catalyst, and under illumination conditions, methane gas or methane-containing gas and a chlorine salt as a chlorine source are allowed to react at a temperature of 0-100 The reaction is carried out at a reaction temperature of ℃ for 10-600 min, thereby converting methane gas or methane in a methane-containing gas into monochloromethane with high selectivity.

In the method of the present invention, after the reaction is completed, the monochloromethane product can be separated by conventional means, such as, but not limited to, based on the difference in boiling point (the boiling point of the desired product monochloromethane is about −23.7° C., the boiling point of the raw material methane is about −23.7° C. About -161.5 °C, the boiling point of possible by-product ethane is about -88.6 °C), and the target product monochloromethane can be isolated by pressure liquefaction well known in the art.

In the method of the present invention, after the reaction is completed, the product monochloromethane and its selectivity can be determined by conventional means, such as but not limited to the use of gas chromatography GC.

In the method of the present invention, preferably, as the chlorine source, the chloride salt used can be sodium chloride NaCl, potassium chloride KCl, lithium chloride LiCl, magnesium _chloride MgCl and commercially available seawater crystal (table) salt one or more of.

In the method of the present invention, the catalyst used is a copper (Cu)-doped titanium dioxide ( _TiO2 ) compound (ie, a "copper-doped titanium dioxide compound"). In the catalyst of the present invention, titanium dioxide as the base material is not only widely available and inexpensive, but also has very excellent optical properties, chemical stability, thermal stability, super-hydrophilicity and non-migration. Meanwhile, the inventors have found that a copper-doped titania compound obtained by simply doping inexpensive copper during the preparation of titania can be used as a highly efficient catalyst to convert methane gas or methane in methane-containing gas under specific reaction conditions Converted to chloromethane with high selectivity. In addition, the inventors have also found that such a doped catalyst can be recovered by simple separation after use and can be reused for many times with roughly equivalent efficiency, thus making the whole process of the present invention have great industrial application prospects.

In the method of the present invention, preferably, in the catalyst, the atomic molar ratio of copper and titanium is 0.005-0.1:1. It should be noted here that, in the catalyst used in the present invention, the copper (Cu) used for doping may be in the form of metallic copper, or may be in the form of copper oxides such as CuO. Applicants have found that within such atomic molar ratio ranges, the catalyst has higher catalytic efficiency.

In the method of the present invention, the raw material gas used may be in the form of pure methane gas or in the form of methane-containing gas. The term "methane-containing gas" refers to a gas mixture containing methane, preferably a methane-containing gas with a volume content of more than 50% methane, such as but not limited to natural gas, shale gas, combustible ice or biogas.

In the method of the present invention, although the pressure of the methane gas or the methane-containing gas in the reactor is not particularly limited, preferably, the pressure of the methane gas or the methane-containing gas in the reactor is 0.1 MPa to 10 MPa.

In the method of the present invention, preferably, the illumination intensity of the illumination conditions used may be 10-2000 mW/cm ² .

In the method of the present invention, the light source used for the lighting conditions is not particularly limited as long as it can emit optical radiation. Preferably, the light source for lighting conditions may be one or more selected from the group consisting of xenon lamps, LED lamps (ie light emitting diodes), tungsten lamps and mercury lamps.

In the process of the present invention, the reaction temperature of the reactor is usually 0-100°C; preferably, the reaction temperature used may be 20-60°C, most preferably the reaction is carried out at ambient temperature (ie about 25-30°C). When desired, the reactor can be heated to the desired reaction temperature by conventional means such as a water bath or an oil bath.

In the method of the present invention, from the viewpoint of efficiency, the reaction time is usually 10-600 min, and more preferably, the reaction time may be 100-480 min.

In the method of the present invention, the reactor used is not particularly limited, as long as it can withstand a certain pressure and can be sealed. For example, the reactor used can be a quartz reactor, a glass reactor or a fixed bed reactor, etc. .

In the method of the present invention, although the usage amount of the catalyst and the reactant aluminum source is not particularly limited, preferably, the mass ratio of the catalyst used to the chloride salt can be 0.01-0.5:1.

The present invention will be further described below in conjunction with specific embodiments. The following descriptions are only some preferred embodiments of the present invention, but the protection scope of the present invention is not limited to this. Changes or substitutions that can be easily conceived within the technical scope of the present invention are all covered by the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Unless otherwise stated, all the raw materials used in the present invention have no special restrictions on their sources and can be obtained commercially; meanwhile, there are no special restrictions on their purities, and analytical grades are preferably used in the present invention.

The present invention has no particular limitation on the reaction or detection equipment or equipment used, as long as the purpose can be achieved, any conventional equipment or equipment known to those skilled in the art can be used.

catalyst preparation

The preparation of the catalyst (copper-doped titanium dioxide compound) used in the present invention is as follows:

In a glass crystallizing dish, add 50 mg of copper nitrate, 6.8 mL of tetrabutyl titanate, 60 mL of ethanol, 4.6 mL of glacial acetic acid and 4 mL of concentrated hydrochloric acid, and mix them uniformly with a stirring bar. Then, the glass crystallizing dish was put into an oven at 65° C. for evaporative drying for 8 hours to obtain a solid substance. Next, the obtained glass crystallizing dish with a solid substance was calcined in a muffle furnace at 450° C. for 5 hours. Finally, it is naturally cooled to room temperature, thereby obtaining a copper-doped titanium dioxide compound, which is detected by X-ray photoelectron spectroscopy and scanning electron microscopy, wherein the molar content of metal copper Cu atoms relative to titanium atoms is 1% (that is, copper and The atomic molar ratio of titanium is 0.01:1).

Based on the same procedure as above, except that the amount of copper nitrate used was changed accordingly, thereby obtaining a molar content of metallic copper Cu atoms relative to titanium atoms of 2% respectively (ie, the atomic molar ratio of copper and titanium was 0.02:1) and 5% (ie, the atomic molar ratio of copper and titanium is 0.05:1) copper-doped titanium dioxide compound.

Example 1

In a quartz reactor (the reactor is connected through stainless steel valve control and can apply a maximum pressure of 20MPa), 100 mg of copper-doped titania compound (in which the atomic molar ratio of copper and titanium is 0.02:1) is added as a catalyst and 200 mg of chloride Sodium was used as chlorine source, and high-purity (purity greater than 99.9%) methane gas was introduced into a methane cylinder through a pressure reducing valve, and the reactor was sealed (the pressure in the reactor was about 0.2 MPa). At room temperature (about 25°C), the reaction was carried out under irradiation with a light intensity of 200 mW/cm ² using a xenon lamp as a light source for 480 min. The resulting monochloromethane product can be isolated using pressurized liquefaction.

After the reaction, gas samples were taken to determine the product distribution by gas chromatography. Gas chromatography GC detection conditions are: Agilent 7890B GC, Ar carrier gas, FID detector, capillary column, column temperature 60°C. The product was determined to be monochloromethane by gas chromatography and its selectivity was 90%. Figure 1 shows a gas chromatogram (GC) profile of the monochloromethane product obtained according to this example. It should be noted that, from the perspective of the production rate of the target product, the production rate of the obtained monochloromethane is 2.5 mmol/g catalyst/h, which has the potential of industrial application.

Example 2

Concrete reaction process and detection method are identical with embodiment 1, just use potassium chloride to replace sodium chloride as chlorine source. After testing, the selectivity of the target product, monochloromethane, was 94%.

Example 3

The specific reaction process and detection method are the same as in Example 1, except that the copper-doped titanium dioxide compound in which the atomic molar ratio of copper and titanium is 0.01:1 is used as the catalyst. After testing, the selectivity of the target product, monochloromethane, was 82%.

Example 4

The specific reaction process and detection method are the same as in Example 1, except that the copper-doped titanium dioxide compound in which the atomic molar ratio of copper and titanium is 0.05:1 is used as the catalyst. After testing, the selectivity of the target product, monochloromethane, was 90%.

Example 5

The specific reaction process and detection method are the same as those in Example 1, except that an LED lamp is used instead of a xenon lamp as the light source. After testing, the selectivity of the target product, monochloromethane, was 83%.

Example 6

Concrete reaction process and detection method are identical with embodiment 1, just shorten the reaction time to 120min. After testing, the selectivity of the target product, monochloromethane, was 73%.

Example 7

Concrete reaction process and detection method are identical with embodiment 1, just shorten the reaction time to 240min. After testing, the selectivity of the target product, monochloromethane, was 85%.

Example 8

Concrete reaction process and detection method are identical with embodiment 1, just extend the reaction time to 600min. After testing, the selectivity of the target product, monochloromethane, was 93%.

Example 9

The specific reaction process and detection method are the same as in Example 1, except that the temperature of the reaction tank is kept at 50° C. by heating in a water bath to carry out the reaction. After testing, the selectivity of the target product, monochloromethane, was 93%.

Example 10

The specific reaction process and detection method are the same as in Example 1, except that methane-containing natural gas (wherein the volume content of methane is 85%) is used instead of high-purity methane gas. After testing, the selectivity of the target product, monochloromethane, was 72%.

Example 11

The specific reaction process and detection method are the same as in Example 1, except that the high-purity methane gas is replaced by methane-containing biogas (where the volume content of methane is 60%). After testing, the selectivity of the target product, monochloromethane, was 70%.

Examples 12 to 14

The specific reaction process and detection method are the same as those in Example 1, except that the catalyst recovered from Example 1 after being separated by filtration and dried at 65°C was used 1, 2, 3 and 4 times respectively (that is, the catalyst was reused 3 times). ). Figure 2 shows the effect of repeated use of the catalyst of the present invention (selectivity distribution of target product monochloromethane), in this Figure 2, the abscissa is the number of times the catalyst is reused, and the ordinate is the target product methyl chloride of selectivity. It can be seen from FIG. 2 that the catalytic efficiency (ie the selectivity of the target product) of the catalyst of the present invention does not decrease significantly after being used repeatedly for four times.

The above is the preferred mode of the present invention, and the description of the present invention is very detailed, but the present invention is not limited to the specific embodiments described above. Changes and modifications made by those skilled in the art without departing from the technical principles of the present invention should also be regarded as within the scope of protection of the claims of the present invention.

Claims (9)

1. a one-step method prepares a method for monochloromethane, the method comprising: in a reactor, in the presence of a copper-doped titanium dioxide compound as a catalyst, under illumination conditions, methane gas or methane-containing gas is The chlorine salt of the chlorine source is reacted at a reaction temperature of 0-100° C. for 10-600 min, wherein in the catalyst, the atomic molar ratio of copper and titanium is 0.005-0.1:1. 2. The method according to claim 1, wherein the methane-containing gas is natural gas, shale gas, combustible ice or biogas. 3. The method according to claim 1, wherein the chloride salt is one or more selected from sodium chloride, potassium chloride, lithium chloride, magnesium chloride and seawater crystalline salt. 4. The method according to claim 1, wherein the illumination intensity of the illumination condition is 10-2000 mW/cm ² . 5. The method of claim 4, wherein the light source for the illumination condition is one or more selected from the group consisting of xenon lamps, LED lamps, tungsten lamps and mercury lamps. 6 . The method according to claim 1 , wherein the reaction temperature is 20-60° C. and the reaction time is 100-480 min. 7 . 7. The method according to claim 1, wherein the reactor is a quartz reactor, a glass reactor or a fixed bed reactor. 8 . The method according to claim 1 , wherein the pressure of the methane gas or the methane-containing gas in the reactor is 0.1 MPa to 10 MPa. 9 . 9 . The method according to claim 1 , wherein the mass ratio of the catalyst to the chloride salt is 0.01-0.5:1. 10 .

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