Method for preparing 1, 2-difluorotetrachloroethane

Abstract

The invention provides a method for preparing 1, 2-difluorotetrachloroethane, and relates to the technical field of preparation of 1, 2-difluorotetrachloroethane. The method comprises the following steps: introducing halogenated ethylene and halogen-nitrogen mixed gas into a gas-liquid phase microchannel reactor, carrying out an addition reaction to obtain a 1, 2-difluorotetrachloroethane crude product, and refining the crude product through a refining system to obtain a finished product. Compared with a traditional method, the reaction conditions are milder, and high temperature and high pressure are not needed, so that the energy consumption is greatly reduced, and the operation safety is improved. Meanwhile, due to the efficient mass and heat transfer characteristic of the microchannel reactor, the reaction time is greatly shortened, and the energy consumption is further reduced.

Description

Technical Field

[0001] The invention relates to the technical field of 1,2-difluorotetrachloroethane preparation, and in particular to a method for preparing 1,2-difluorotetrachloroethane. Background Art

[0002] 1,2-Difluorotetrachloroethane (R112) is an important chemical intermediate, widely used in the preparation of other chemical products with important industrial significance, such as 1,2-difluorodichloroethylene and perfluoroalkyl (oxy) vinyl ether. In recent years, R112 has been used as a raw material for the new inhaled general anesthetic methoxyflurane, which has extremely high commercial value.

[0003] CN102766017A discloses a method for preparing tetrachlorodifluoroethane, wherein the byproducts produced in the production process of difluoromonochloroethane are recycled, and these byproducts include difluorodichloroethane, difluorotrichloroethane, and high-boiling products of difluoromonochloroethane. Under illumination conditions, the collected byproducts are subjected to photochlorination reaction with chlorine to obtain tetrachlorodifluoroethane. However, the photochlorination reaction temperature is as high as 150-250° C., and the reaction time is 30-300 seconds, which increases the danger of the reaction and the synthesis efficiency is low, which limits the promotion of the method.

[0004] CN110963884A discloses a method for preparing 1,1,1,2-tetrachloro-2,2-difluoroethane. It uses F142 (1,1-difluoro-2-chloroethane) and chlorine as raw materials, and performs continuous reaction under the condition of ultraviolet light of a specific frequency band to prepare F112a (1,1,1,2-tetrachloro-2,2-difluoroethane). However, this method has high requirements on the reactor, requiring a set of three-stage series reactors, each of which needs to be equipped with a high-power ultraviolet generator to induce free radical chlorination reaction, making the use cost of this method high.

[0005] CN106397106B discloses a method for adding olefins and fluorine gas using a microchannel reactor. The microchannel structure in the reaction module of the microchannel reactor includes a direct-flow channel structure and an enhanced mixing channel structure. The direct-flow channel structure is a tubular structure, and the enhanced mixing channel structure is a T-shaped structure, a spherical structure, a spherical structure with baffles, a water drop-shaped structure or a heart-shaped structure, and the channel diameter is 0.5 mm to 10 mm.

[0006] CN109574918B discloses a method of using 2-chloro-5-methylpyridine and chlorine as raw materials, introducing 2-chloro-5-methylpyridine and chlorine into a microchannel reactor at the same time for chlorination reaction, collecting the reaction product after the reaction is completed, and crystallizing and distilling the reaction product to obtain 2-chloro-5-chloromethylpyridine. The microchannel reactor is an enhanced mass transfer type microchannel reactor, including a preheating module, a reaction module and a cooling module; it is a stainless steel microchannel reactor with an inner diameter of 100-1000μm and a length of 1-3m.

[0007] Existing synthesis methods usually require special equipment and conditions, such as relying on catalysts, high temperature, high pressure, strong light, etc. The reaction process is complex and harsh, the reaction risk is high, the synthesis efficiency is low, and the production cost is high. Summary of the invention

[0008] The object of the present invention is to provide a method for preparing 1,2-difluorotetrachloroethane, which adopts a microchannel reactor for preparation, has simple process, mild reaction conditions, low energy consumption, low cost and high operation safety.

[0009] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are particularly adopted:

[0010] The present invention provides a method for preparing 1,2-difluorotetrachloroethane, comprising the following steps:

[0011] The mixed gas of ethylene halide and halogen nitrogen is introduced into a gas-liquid phase microchannel reactor to obtain a crude 1,2-difluorotetrachloroethane through an addition reaction, and then refined through a refining system to obtain a finished product;

[0012] The halogenated vinyl is one or more selected from tetrachloroethylene, 1,2-dichlorodifluoroethylene, 1,2-dichloroethylene, and 1,2-difluoroethylene;

[0013] The halogen-nitrogen mixed gas is one or more selected from F2 / N2 mixed gas and Cl2 / N2 mixed gas.

[0014] The following is a detailed description:

[0015] The raw material of the present invention can be one of the following:

[0016] 1. The halogenated vinyl is tetrachloroethylene (PCE), the halogen-nitrogen mixed gas is F2 / N2 mixed gas, and the reaction equation is: C2Cl4+F2→C2Cl4F2;

[0017] 2. The halogenated vinyl is 1,2-difluorodichloroethylene, the halogen-nitrogen mixed gas is a Cl2 / N2 mixed gas, and the reaction equation is: C2Cl2F2+Cl2→C2Cl4F2;

[0018] 3. The halogenated vinyl is 1,2-dichloroethylene, the halogen-nitrogen mixed gas is Cl2 / N2 mixed gas and F2 / N2 mixed gas, and the reaction equation is: C2H2Cl2+Cl2+F2→C2Cl4F2;

[0019] 4. The halogenated vinyl is 1,2-difluoroethylene, the halogen-nitrogen mixed gas is a Cl2 / N2 mixed gas, and the reaction equation is: C2H2F2+2Cl2→C2Cl4F2.

[0020] In some embodiments, the volume content of halogen in the halogen-nitrogen mixed gas is 5% to 30%, and the molar ratio of halogenated vinyl to halogen-nitrogen mixed gas is 1:1 to 1:1.5;

[0021] In some embodiments, the temperature of the addition reaction is -20°C to 30°C, and the gas-liquid contact time is 0.5s to 10s.

[0022] The present invention selects suitable microchannel reactor and refining system:

[0023] The present invention designs a reasonable reaction process, and the gas-liquid phase microchannel reactor can improve the reaction efficiency by connecting in series, thereby reducing equipment investment and operation cost. Preferably, a cascade gas-liquid phase microchannel reactor is used, and each microchannel reactor can be operated independently, which is convenient for maintenance and overhaul.

[0024] Gas-liquid phase microchannel reactors include but are not limited to bubble-type microchannel reactors or sedimentation film microchannel reactors. In a bubble-type microchannel reactor, gas and liquid enter through their respective microchannels and then mix at the confluence. In the gas-liquid two-phase liquid, the flow state of the fluid is similar to that of a bubble tower. As the flow rates of gas and liquid change, typical flow patterns such as bubble flow, throttle flow, annular flow and jet flow will appear. These flow patterns contribute to the full contact and mixing between gas and liquid. In a sedimentation film microreactor, the liquid phase flows in a film-like manner from top to bottom, while the gas contacts the membrane surface. This design allows the gas-liquid two phases to have a larger contact area on the membrane surface, thereby increasing the reaction efficiency.

[0025] The gas-liquid phase microchannel reactor is preferably a bubble-type microchannel reactor, and its channel structure can be T-type, Y-type, cross-type, double T-type, circular wave type, etc. Figure 3 shown.

[0026] The material of the gas-liquid phase microchannel reactor is silicon carbide, which is corrosion-resistant, high-pressure-resistant, high-temperature-resistant and has high thermal conductivity.

[0027] The gas-liquid phase microchannel reactor is preferably a circular wave bubble cap microchannel reactor, such as Figure 2As shown, the radius of the circular wave is 4 to 12 mm, preferably 7 mm, the cross-sectional size (area) of the microchannel is 1.58 mm×2 mm, the liquid holding capacity is 20 ml, and the number of semicircular waves is 245 to 983. The fluid type is turbulent flow.

[0028] The unreacted gas phase after the addition reaction is subjected to tail gas absorption, and the tail gas absorption adopts a water washing and alkali washing absorption method, and the alkali washing concentration is controlled at 3% to 5%.

[0029] In some embodiments, the refining system includes a water washing tower, an alkali washing tower, a light removal tower, and a distillation tower, and a condenser is disposed on the top of the distillation tower.

[0030] Preferably, the number of full tower plates of the light-removal tower is 15 to 25, the operating pressure is atmospheric pressure, the tower top temperature is 20 to 40° C., and the tower bottom temperature is 70 to 110° C.;

[0031] Preferably, the number of plates of the distillation tower is 20-55, the operating pressure is atmospheric pressure, the top temperature is 90-100°C, the bottom temperature is 120-200°C, the reflux ratio is 1-5, the cooling medium in the top condenser is circulating water, and the liquid phase is collected.

[0032] 1,2-difluorotetrachloroethane with a purity of more than 99.9% is obtained through distillation and purification, which meets the market demand for high-purity products at the raw material level for inhalation anesthesia.

[0033] In some embodiments, the tail gas generated by the top condenser of the distillation tower can be treated by condensation recovery, activated carbon adsorption, thermal oxidation and other methods, preferably by a cryogenic system and an activated carbon adsorption system, wherein the condensation temperature of the cryogenic system is -65 to -85°C; the activated carbon adsorption system is a cascade treatment system. After treatment, the pollution of the production process to the environment can be effectively reduced.

[0034] The reaction system of the present invention is as follows Figure 1 As shown, it only includes one or more gas-liquid phase microchannel reactors with heat exchange and temperature measurement functions. It is only necessary to introduce halogenated vinyl and halogen nitrogen mixed gas in a certain proportion into the microchannel reactor at a specific temperature to obtain R112 crude product; after passing through a refining system composed of equipment such as a light removal tower and a distillation tower, R112 finished product with a purity of more than 99.9% can be obtained; the exhaust gas can meet the emission standards after being treated by a combined treatment system composed of a deep cooling system and an activated carbon adsorption system, and then discharged into the air.

[0035] Beneficial effects:

[0036] 1. The present invention adopts a microchannel reactor to prepare 1,2-difluorotetrachloroethane. Compared with the traditional method, the reaction conditions are milder and there is no need to carry out the reaction under high temperature and high pressure, thereby greatly reducing energy consumption and improving operation safety.

[0037] 2. The present invention can effectively inhibit the occurrence of side reactions by precisely controlling the reaction conditions, such as reaction temperature, contact time, raw material ratio, etc., thereby improving the purity and yield of the product. Experiments show that the purity of 1,2-difluorotetrachloroethane prepared by the method of the present invention can reach more than 99.9%.

[0038] 3. Since the present invention adopts a microchannel reactor, the scale-up cost can be reduced. At the same time, due to the efficient mass transfer and heat transfer characteristics of the microchannel reactor, the reaction time is greatly shortened, further reducing energy consumption.

[0039] 4. The preparation method of the present invention is simple. It only needs to introduce the unsaturated halogenated hydrocarbon and the halogen nitrogen mixed gas into the gas-liquid phase microchannel reactor at the same time, and the crude 1,2-difluorotetrachloroethane can be obtained through the addition reaction, and the finished product can be obtained through the distillation system, which greatly simplifies the production process and improves the production efficiency. At the same time, the tail gas treatment method of the present invention is simple and easy to operate, can effectively reduce environmental pollution, and meets the national environmental protection requirements.

[0040] The present invention has been described in detail above, but the above embodiments are only illustrative in nature and are not intended to limit the present invention. In addition, this article is not limited by any theory described in the above prior art or invention content or the following examples. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 It is a schematic diagram of the reaction system of the present invention;

[0042] Figure 2 Schematic diagram of the channel structure of the circular wave type gas-liquid phase microchannel reactor of the present invention;

[0043] Figure 3 Schematic diagram of the channel structure of different microchannel reactors. DETAILED DESCRIPTION

[0044] The present invention is further described below in conjunction with examples. It should be noted that the following examples are provided for illustrative purposes only and do not constitute a limitation on the scope of protection claimed for the present invention.

[0045] Unless otherwise specified, the raw materials, reagents, methods, etc. used in the examples are conventional raw materials, reagents, methods in the art.

[0046] Example 1

[0047] Step 1: Prepare a microchannel reactor. The material is silicon carbide, the channel structure is circular wave type, the circular wave radius is 7mm, the channel cross-sectional size is 1.58mm×2mm, and the liquid holding capacity is 20ml.

[0048] Step 2: Prepare raw materials, which are tetrachloroethylene (PCE) with a purity of 99.9% and a water content of 30 ppm, and a F2 / N2 mixed gas with an F2 volume content of 10%.

[0049] Step 3: Perform an addition reaction, and introduce PCE and F2 / N2 mixed gas into the microchannel reactor at the same time, wherein the molar flow rate of PCE is 0.3 mol / h, the molar flow rate of F2 / N2 mixed gas is 0.4 mol / h, the feed molar ratio of PCE to F2 / N2 mixed gas is 1:1.33, the reaction temperature is -10°C, and the contact time is 5s. The crude product generated by the reaction is collected.

[0050] The reaction equation is: C2Cl4+F2→C2Cl4F2. The liquid phase yield is 73%, and the content of each substance is shown in the following table:

[0051]

[0052] Step 4: Set the refining system conditions, configure it as a water washing tower, an alkali washing tower, and a distillation tower, and set a condenser on the top of the distillation tower. The number of plates in the distillation tower is 53, the operating pressure is normal pressure, the top temperature is 96°C, the bottom temperature is 130°C, the reflux ratio is 4, the cooling medium in the top condenser is circulating water, and the liquid phase is collected.

[0053] Step 5: Calculate by mass and feed the distillation system at a rate of 50 parts per hour. After the distillation is completed, the liquid phase output of the top condenser is 19 parts per hour, of which the purity of R112 is 99.9%.

[0054] Step 6: Treat the tail gas. The tail gas generated by the top condenser of the distillation tower in step 5 is treated by a composite tail gas treatment system of a deep cooling system + an activated carbon adsorption system. The condensation temperature of the deep cooling system is -80°C, and the maximum processing capacity is 16kg / h; the activated carbon adsorption system is a cascade treatment system with a maximum processing capacity of 1.7kg / h.

[0055] Example 2

[0056] Step 1: Prepare 4 microchannel reactors made of silicon carbide and install them in series. Each microchannel reactor has a circular wave channel structure with a circular wave radius of 7 mm, a channel cross-sectional size of 1.58 mm × 2 mm, and a liquid holding capacity of 20 ml.

[0057] Step 2: Prepare raw materials, which are tetrachloroethylene (PCE) with a purity of 99.9% and a water content of 30 ppm, and a F2 / N2 mixed gas with an F2 volume content of 10%.

[0058] Step 3: Perform an addition reaction, and introduce PCE and F2 / N2 mixed gas into the microchannel reactor at the same time, wherein the molar flow rate of PCE is 0.3 mol / h, the molar flow rate of F2 / N2 mixed gas is 0.4 mol / h, the feed molar ratio of PCE to F2 / N2 mixed gas is 1:1.33, the reaction temperature is -10°C, and the contact time is 5s. The crude product generated by the reaction is collected.

[0059] The reaction equation is: C2Cl4+F2→C2Cl4F2. The liquid phase yield is 92%, and the content of each substance is shown in the following table:

[0060] R112 <![CDATA[C2Cl4]]> <![CDATA[C3Cl6F2]]> <![CDATA[C4Cl6F3]]> other 63.03％ 3.63％ 11.03％ 17.30％ 5.01％

[0061] Step 4: Set the refining system conditions, configure it as a water washing tower, an alkali washing tower, and a distillation tower, and set a condenser on the top of the distillation tower. The number of plates of the distillation tower is 35, the operating pressure is normal pressure, the top temperature is 96℃, the bottom temperature is 129℃, the reflux ratio is 2.5, the cooling medium in the top condenser is circulating water, and the liquid phase is collected.

[0062] Step 5: Calculate by mass and feed the distillation system at a rate of 50 parts per hour. After the distillation is completed, the liquid phase output of the top condenser is 28 parts per hour, of which the purity of R112 is 99.9%.

[0063] Step 6: Treat the tail gas. The tail gas generated by the top condenser of the distillation tower in step 5 is treated by a composite tail gas treatment system of a deep cooling system + an activated carbon adsorption system. The condensation temperature of the deep cooling system is -80°C, and the maximum processing capacity is 16kg / h; the activated carbon adsorption system is a cascade treatment system with a maximum processing capacity of 1.7kg / h.

[0064] Comparative test 1

[0065] Step 1: Prepare a bubble column reactor. The specifications of a single unit are: inner diameter 300mm, height 700mm, main body material is high borosilicate glass, and sealing element is PTFE.

[0066] Step 2: Prepare raw materials, which are tetrachloroethylene (PCE) with a purity of 99.9% and a water content of 30 ppm, and a F2 / N2 mixed gas with an F2 volume content of 10%.

[0067] Step 3: Perform an addition reaction, and introduce PCE and a fluorine-nitrogen mixed gas into a bubble column reactor at the same time, wherein the volume flow rate of the F2 / N2 mixed gas is 60 L / h, and the volume flow rate of PCE is 50 mL / h. The reaction temperature is -10°C, and the contact time is 5 s. The crude product generated by the reaction is collected.

[0068] The reaction equation is: C2Cl4+F2→C2Cl4F2. The liquid phase yield is 92%, and the content of each substance is shown in the following table:

[0069] R112 <![CDATA[C2Cl4]]> <![CDATA[C3Cl6F2]]> <![CDATA[C4Cl6F3]]> other 9.32％ 44.21％ 14.85％ 23.07％ 8.55％

[0070] Through this comparative example, we can see that under the same conditions, the synthesis efficiency of the traditional bubble tower reactor is much lower than that of the microchannel reactor, which proves the improvement effect of the present invention on the synthesis efficiency and synthesis effect.

[0071] Comparative test 2: Reactor impact test with different channel structures:

[0072] Step 1: Prepare 4 microchannel reactors and install them independently. The channel structures of each reactor are T-type, Y-type, double T-type, and circular wave type, and the material is silicon carbide. The channel cross-sectional size is 1.58mm×2mm, and the liquid holding capacity is 20ml.

[0073] Step 2: Prepare raw materials, which are tetrachloroethylene (PCE) with a purity of 99.9% and a water content of 30 ppm, and a F2 / N2 mixed gas with an F2 volume content of 10%.

[0074] Step 3: Perform an addition reaction, and introduce PCE and a fluorine-nitrogen mixed gas into four reactors simultaneously, wherein the molar flow rate of the F2 / N2 mixed gas introduced into each reactor is 0.4 mol / h, and the molar flow rate of PCE is 0.3 mol / h. The reaction temperature is -10°C, and the contact time is 5 s. The crude product generated by the reaction is collected.

[0075] The reaction equation is: C2Cl4+F2→C2Cl4F2. The R112 content in the products obtained from each microchannel reactor is shown in the following table:

[0076]

[0077] Through this comparative example, we can see that under the same conditions, the most conventional T-channel microchannel reactor is inferior to other reactors in terms of liquid phase yield and R112 content in the product; the Y-type and double T-type reactors can obtain better mixing performance than the T-type microchannel when the materials meet by optimizing the angle and shape of the T-type microchannel inlet position. However, since the shape of the rear channel is still a straight line, it is impossible to stably trigger the turbulent state of the mixed fluid, resulting in limited overall improvement; the circular wave reactor changes the shape of the reaction channel, making it easier for the mixed fluid to enter the turbulent state, improving the overall mixing performance, and thus obtaining the best reaction effect.

[0078] Comparative test 3: Effect of different circular wave radii:

[0079] Step 1: Prepare 4 microchannel reactors, the channel structure is circular wave type, the material is silicon carbide, the channel cross-sectional size is 1.58mm×2mm, and the liquid holding capacity is 20ml. The circular wave radius of the circular wave in the 4 microchannel reactors is 4mm, 6mm, 7mm, and 12mm respectively.

[0080] Step 2: Prepare raw materials, which are tetrachloroethylene (PCE) with a purity of 99.9% and a water content of 30 ppm, and a F2 / N2 mixed gas with an F2 volume content of 10%.

[0081] Step 3: Perform an addition reaction, and introduce PCE and a fluorine-nitrogen mixed gas into four reactors simultaneously, wherein the molar flow rate of the F2 / N2 mixed gas introduced into each reactor is 0.4 mol / h, and the molar flow rate of PCE is 0.3 mol / h. The reaction temperature is -10°C, and the contact time is 5 s. The crude product generated by the reaction is collected.

[0082] The reaction equation is: C2Cl4+F2→C2Cl4F2. The R112 content in the products obtained from each microchannel reactor is shown in the following table:

[0083]

[0084] Through this comparative example, we can see that under the current material flow rate state, the circular wave reactor with a radius of 12mm has the lowest yield, indicating that it cannot stably trigger the fluid to enter a turbulent state, and the mixing effect is relatively poor; the yields of the 4, 5, and 7mm reactors are similar and the 7mm reactor has the highest yield, indicating that the 7mm circular wave channel can make the fluid evenly mixed under the flow rate conditions. A smaller circular wave radius cannot provide a better mixing effect under the flow rate state, but will increase the pressure drop, thereby reducing the flow rate of the fluid after mixing.

[0085] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that the technical solutions described in the above embodiments may be modified, or some or all of the technical features thereof may be replaced by equivalents, without departing from the spirit and essence of the claims of the present invention; and these modifications or replacements are still within the scope defined by the claims of the present invention.

Claims

1. A method for preparing 1,2-difluorotetrachloroethane, characterized in that: The following steps are involved: The mixed gas of ethylene halide and halogen nitrogen is introduced into a gas-liquid phase microchannel reactor to obtain a crude 1,2-difluorotetrachloroethane through an addition reaction, and then refined through a refining system to obtain a finished product; The halogenated vinyl is one or more selected from tetrachloroethylene, 1,2-dichlorodifluoroethylene, 1,2-dichloroethylene, and 1,2-difluoroethylene; The halogen-nitrogen mixed gas is one or more selected from F2 / N2 mixed gas and Cl2 / N2 mixed gas.

2. The preparation method according to claim 1, characterized in that: The halogenated vinyl is tetrachloroethylene, and the halogen-nitrogen mixed gas is a F2 / N2 mixed gas; or, The halogenated vinyl is 1,2-difluorodichloroethylene, and the halogen-nitrogen mixed gas is a Cl2 / N2 mixed gas; or, The halogenated vinyl is 1,2-dichloroethylene, and the halogen-nitrogen mixed gas is a Cl2 / N2 mixed gas and a F2 / N2 mixed gas; or, The halogenated vinyl is 1,2-difluoroethylene, and the halogen-nitrogen mixed gas is a Cl2 / N2 mixed gas.

3. The preparation method according to claim 1, characterized in that: The volume content of halogen in the halogen-nitrogen mixed gas is 5% to 30%, and the molar ratio of halogenated vinyl to the halogen-nitrogen mixed gas is 1:1 to 1:1.

5.

4. The preparation method according to claim 1, characterized in that: The temperature of the addition reaction is -20°C to 30°C, and the gas-liquid contact time is 0.5s to 10s.

5. The preparation method according to claim 1, characterized in that: The material of the gas-liquid phase microchannel reactor is silicon carbide.

6. The preparation method according to claim 1, characterized in that: The gas-liquid phase microchannel reactor is a circular wave bubble-cap microchannel reactor.

7. The preparation method according to claim 6, characterized in that: The circular wave radius of the circular wave bubble cap microchannel reactor is 4 mm to 12 mm, preferably 7 mm, the cross-sectional size of the microchannel is 1.58 mm×2 mm, and the liquid holding capacity is 20 ml.

8. The preparation method according to claim 1, characterized in that: The refining system includes a water washing tower, an alkali washing tower, a light removal tower, and a distillation tower, and a condenser is arranged on the top of the distillation tower.

9. The preparation method according to claim 8, characterized in that: The total number of tower plates of the light removal tower is 15 to 25, the operating pressure is normal pressure, the tower top temperature is 20 to 40°C, and the tower bottom temperature is 70 to 110°C.

10. The preparation method according to claim 8, characterized in that: The number of plates of the distillation tower is 20-55, the operating pressure is normal pressure, the top temperature is 90-100°C, the bottom temperature is 120-200°C, the reflux ratio is 1-5, the cooling medium in the top condenser is circulating water, and the material is collected in liquid phase.

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