A process for the preparation of 1,2-difluorotetrachloroethane

Abstract

This invention provides a method for preparing 1,2-difluorotetrachloroethane, relating to the field of 1,2-difluorotetrachloroethane preparation technology. A mixture of halogenated ethylene and halogenated nitrogen is introduced into a gas-liquid phase microchannel reactor, where an addition reaction yields crude 1,2-difluorotetrachloroethane, which is then refined using a purification system to obtain the final product. Compared to traditional methods, the reaction conditions are milder, eliminating the need for high temperature and high pressure, thus significantly reducing energy consumption and improving operational safety. Furthermore, due to the highly efficient mass and heat transfer characteristics of the microchannel reactor, the reaction time is greatly shortened, further reducing energy consumption.

Description

Technical Field

[0001] This invention relates to the field of 1,2-difluorotetrachloroethane preparation technology, and more particularly to a method for preparing 1,2-difluorotetrachloroethane. Background Technology

[0002] 1,2-Difluorotetrachloroethane (R112) is an important chemical intermediate widely used in the preparation of other industrially significant chemical products, such as 1,2-difluorodichloroethylene and perfluoroalkyl vinyl ethers. In recent years, R112 has been used as a raw material in the development of the novel inhaled general anesthetic methoxyflurane, demonstrating its high commercial value.

[0003] CN102766017A discloses a method for preparing tetrachlorodifluoroethane, which involves recovering and utilizing byproducts generated during the production of difluorochloroethane, including high-boiling-point derivatives of difluorodichloroethane, difluorotrichloroethane, and difluorochloroethane. The collected byproducts are then subjected to a photochlorination reaction with chlorine gas under light irradiation to produce tetrachlorodifluoroethane. However, the photochlorination reaction temperature is as high as 150-250℃, and the reaction time is 30-300 seconds, increasing the risk of the reaction and resulting in low synthesis efficiency, thus limiting the widespread application of this 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 carries out a continuous reaction under ultraviolet light irradiation of a specific frequency band to prepare F112a (1,1,1,2-tetrachloro-2,2-difluoroethane). However, this method has high requirements for the reactor, requiring a three-stage series reactor, each equipped with a high-power ultraviolet light generator to initiate the free radical chlorination reaction, resulting in high operating costs.

[0005] CN106397106B discloses a method for the addition of olefins and fluorine using a microchannel reactor. The microchannel structure within 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 teardrop-shaped structure, or a heart-shaped structure, with a channel diameter of 0.5 mm to 10 mm.

[0006] CN109574918B discloses a method for using 2-chloro-5-methylpyridine and chlorine as raw materials. The method involves simultaneously introducing 2-chloro-5-methylpyridine and chlorine into a microchannel reactor for a chlorination reaction. After the reaction is complete, the reaction product is collected, and then crystallized and distilled 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 100-1000 μm and a length of 1-3 m.

[0007] Existing synthesis methods typically require special equipment and conditions, such as catalysts, high temperature, high pressure, and strong light. The reaction process is complex and demanding, the reaction is highly dangerous, the synthesis efficiency is low, and the production cost is high. Summary of the Invention

[0008] The purpose of this invention is to provide a method for preparing 1,2-difluorotetrachloroethane using a microchannel reactor. This method is simple, has mild reaction conditions, low energy consumption, low cost, and high operational safety.

[0009] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted:

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

[0011] A mixture of halogenated ethylene and halogenated nitrogen is introduced into a gas-liquid phase microchannel reactor, and crude 1,2-difluorotetrachloroethane is obtained through an addition reaction. The crude product is then purified by a refining system to obtain the finished product.

[0012] The halogenated ethylene is selected from one or more of tetrachloroethylene, 1,2-difluorodichloroethylene, 1,2-dichloroethylene, and 1,2-difluoroethylene.

[0013] The halogen-nitrogen mixture is selected from one or more of the F2 / N2 mixture and the Cl2 / N2 mixture.

[0014] The following is a detailed explanation:

[0015] The raw materials of this invention can be one of the following:

[0016] 1. The haloethylene is tetrachloroethylene (PCE), the halonitrogen mixture is F2 / N2 mixture, and the reaction equation is: C2Cl4 + F2 → C2Cl4F2;

[0017] 2. The haloethylene is 1,2-difluorodichloroethylene, the halo-nitrogen mixture is a Cl2 / N2 mixture, and the reaction equation is: C2Cl2F2+Cl2→C2Cl4F2;

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

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

[0020] In some embodiments, the volume content of halogen in the halogen-nitrogen mixture is 5% to 30%, and the molar ratio of halogenated ethylene to the halogen-nitrogen mixture is 1:1 to 1:1.5.

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

[0022] This invention selects a suitable microchannel reactor and purification system:

[0023] This invention features a rationally designed reaction process. Gas-liquid phase microchannel reactors can be connected in series to improve reaction efficiency and reduce equipment investment and operating costs. Preferably, a cascaded gas-liquid phase microchannel reactor is used, where each microchannel reactor can operate independently, facilitating maintenance and repair.

[0024] Gas-liquid phase microchannel reactors include, but are not limited to, bubble-cap microchannel reactors or settling film microchannel reactors. In a bubble-cap microchannel reactor, gas and liquid enter through their respective microchannels and then mix at the confluence. In this gas-liquid two-phase reactor, the flow pattern is similar to that of a bubble-cap tower. As the gas and liquid flow rates change, typical flow patterns such as bubble flow, throttling flow, annular flow, and jet flow emerge, which facilitate sufficient contact and mixing between the gas and liquid. In a settling film microreactor, the liquid phase flows downwards in a film-like manner, while the gas contacts the membrane surface. This design allows for a larger contact area between the gas and liquid phases on the membrane surface, thereby increasing reaction efficiency.

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

[0026] The gas-liquid phase microchannel reactor is made of silicon carbide, which has corrosion resistance, high pressure resistance, high temperature resistance and 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 4–12 mm, preferably 7 mm; the cross-sectional area of ​​the microchannel is 1.58 mm × 2 mm; the liquid holding capacity is 20 ml; and the number of semicircular waves is 245–983. The fluid type is turbulent.

[0028] The unreacted gas phase after the addition reaction is absorbed as tail gas. The tail gas absorption adopts a water washing plus 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-light-removal tower, and a distillation tower, with a condenser installed at the top of the distillation tower.

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

[0031] Preferably, the distillation column has 20 to 55 trays, operates at atmospheric pressure, has a top temperature of 90 to 100°C, a bottom temperature of 120 to 200°C, a reflux ratio of 1 to 5, and uses circulating water as the cooling medium in the top condenser, with liquid phase collection.

[0032] 1,2-Difluorotetrachloroethane with a purity of over 99.9% was obtained through distillation and purification, meeting the market demand for high-purity products as raw materials for inhalational anesthesia.

[0033] In some implementations, the tail gas generated by the top condenser of the distillation column can be treated by methods such as condensation recovery, activated carbon adsorption, and thermal oxidation. Preferably, a cryogenic system and an activated carbon adsorption system are used. The cryogenic system has a condensation temperature of -65 to -85°C; the activated carbon adsorption system is a cascade treatment system. This treatment effectively reduces the environmental pollution caused by the production process.

[0034] The reaction system of the present invention is as follows Figure 1 As shown, this involves only one or more gas-liquid phase microchannel reactors with heat exchange and temperature measurement functions. By simultaneously introducing a mixture of halogenated ethylene and halogenated nitrogen at a certain ratio into the microchannel reactor at a specific temperature, crude R112 can be obtained. After passing through a refining system composed of a light-light removal tower and a distillation tower, a finished R112 product with a purity of over 99.9% can be obtained. The waste gas is then treated by a combined treatment system consisting of a cryogenic system and an activated carbon adsorption system to meet emission standards and be discharged at high altitude.

[0035] Beneficial effects:

[0036] 1. This invention uses a microchannel reactor to prepare 1,2-difluorotetrachloroethane. Compared with traditional methods, the reaction conditions are milder and do not require high temperature and high pressure, thus greatly reducing energy consumption and improving operational safety.

[0037] 2. This invention effectively suppresses side reactions by precisely controlling reaction conditions, such as reaction temperature, contact time, and raw material ratio, thereby improving the purity and yield of the product. Experiments show that the purity of 1,2-difluorotetrachloroethane prepared by the method of this invention can reach over 99.9%.

[0038] 3. Because this invention uses a microchannel reactor, scale-up costs can be reduced. Furthermore, due to the highly efficient mass and heat transfer characteristics of the microchannel reactor, the reaction time is significantly shortened, further reducing energy consumption.

[0039] 4. The preparation method of this invention is simple. It only requires simultaneously introducing a mixture of unsaturated haloalkanes and halonitrogen into a gas-liquid phase microchannel reactor, where an addition reaction yields crude 1,2-difluorotetrachloroethane. The finished product is then obtained through a distillation system, greatly simplifying the production process and improving efficiency. Furthermore, the tail gas treatment method of this invention is simple and easy to implement, effectively reducing environmental pollution and meeting national environmental protection requirements.

[0040] The present invention has been described in detail above; however, the above embodiments are merely illustrative in nature and are not intended to limit the invention. Furthermore, this document is not limited to the foregoing prior art or the invention itself, or to any theory described in the following embodiments. Attached Figure Description

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

[0042] Figure 2 This is a schematic diagram of the channel structure of the circular wave-shaped gas-liquid phase microchannel reactor of the present invention;

[0043] Figure 3 Schematic diagrams of the channel structures of different microchannel reactors. Detailed Implementation

[0044] The present invention will be further described below with reference to the embodiments. It should be noted that the following embodiments are provided for illustrative purposes only and do not constitute a limitation on the scope of protection of the present invention.

[0045] Unless otherwise specified, the raw materials, reagents, and methods used in the embodiments are all conventional raw materials, reagents, and methods in the art.

[0046] Example 1

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

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

[0049] Step 3: Perform the addition reaction. PCE and an F2 / N2 mixture are simultaneously introduced into a microchannel reactor. The molar flow rate of PCE is 0.3 mol / h, and the molar flow rate of the F2 / N2 mixture is 0.4 mol / h. The feed molar ratio of PCE to the F2 / N2 mixture is 1:1.33. The reaction temperature is -10℃, and the contact time is 5 s. The crude product generated from the reaction is collected.

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

[0051]

[0052] Step 4: Set up the purification system conditions, configuring it as one water washing tower, one alkali washing tower, and one distillation tower, with a condenser installed at the top of the distillation tower. The distillation tower has 53 trays, operates at atmospheric pressure, has a top temperature of 96℃, a bottom temperature of 130℃, a reflux ratio of 4, and uses circulating water as the cooling medium in the top condenser, with liquid phase collection.

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

[0054] Step 6: Tail gas treatment. The tail gas generated from the top condenser of the distillation column in Step 5 is treated using a combined tail gas treatment system of cryogenic system and activated carbon adsorption system. The cryogenic system has a condensation temperature of -80℃ and a maximum processing capacity of 16 kg / h; the activated carbon adsorption system is a cascade treatment system with a maximum processing capacity of 1.7 kg / h.

[0055] Example 2

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

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

[0058] Step 3: Perform the addition reaction. PCE and an F2 / N2 mixture are simultaneously introduced into a microchannel reactor. The molar flow rate of PCE is 0.3 mol / h, and the molar flow rate of the F2 / N2 mixture is 0.4 mol / h. The feed molar ratio of PCE to the F2 / N2 mixture is 1:1.33. The reaction temperature is -10℃, and the contact time is 5 s. The crude product generated from the reaction is collected.

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

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

[0061] Step 4: Set up the purification system conditions, configuring it as one water washing tower, one alkali washing tower, and one distillation tower, with a condenser installed at the top of the distillation tower. The distillation tower has 35 trays, operates at atmospheric pressure, has a top temperature of 96℃, a bottom temperature of 129℃, a reflux ratio of 2.5, and uses circulating water as the cooling medium in the top condenser, with liquid phase collection.

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

[0063] Step 6: Tail gas treatment. The tail gas generated from the top condenser of the distillation column in Step 5 is treated using a combined tail gas treatment system of cryogenic system and activated carbon adsorption system. The cryogenic system has a condensation temperature of -80℃ and a maximum processing capacity of 16 kg / h; the activated carbon adsorption system is a cascade treatment system with a maximum processing capacity of 1.7 kg / h.

[0064] Comparative Experiment 1

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

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

[0067] Step 3: The addition reaction is carried out by simultaneously introducing PCE and a fluorine / nitrogen mixture into a bubble column reactor. The volumetric flow rate of the F2 / N2 mixture is 60 L / h, and the volumetric flow rate of PCE is 50 mL / h. The reaction temperature is -10℃, and the contact time is 5 s. The crude product generated from the reaction is collected.

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

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

[0070] This comparative example shows that, under the same conditions, the synthesis efficiency of a traditional bubble column reactor is much lower than that of a microchannel reactor, demonstrating the improvement effect of this invention on synthesis efficiency and synthesis effect.

[0071] Comparative Experiment 2: Effects of Reactors with Different Channel Structures on Reactors

[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, respectively. The material is silicon carbide, the channel cross-sectional dimensions are 1.58mm × 2mm, and the liquid holding capacity is 20ml.

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

[0074] Step 3: Conduct the addition reaction. PCE and a fluorine / nitrogen mixture are simultaneously introduced into four reactors. The molar flow rate of the F2 / N2 mixture 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℃, and the contact time is 5 s. The crude product generated from 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 table below:

[0076]

[0077] This comparative example shows that, under the same conditions, the most conventional T-channel microchannel reactor performs worse than other reactors in both liquid phase yield and R112 content in the product. Y-type and double-T-type reactors, by optimizing the angle and shape of the T-channel inlet, can achieve better mixing performance than T-channel reactors when materials meet. However, because the downstream channel shape remains straight, it cannot stably trigger turbulence in the mixed fluid, resulting in limited overall improvement. The circular wave reactor, by changing the shape of the reaction channel, makes it easier for the mixed fluid to enter a turbulent state, improving overall mixing performance and thus achieving the best reaction effect.

[0078] Comparative Experiment 3: Effect of Different Circular Wave Radius on the Test

[0079] Step 1: Prepare 4 microchannel reactors with a circular wave structure, made of silicon carbide, with a channel cross-sectional size of 1.58mm × 2mm and a liquid holding capacity of 20ml. The circular wave radii of the 4 microchannel reactors are 4mm, 6mm, 7mm, and 12mm, respectively.

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

[0081] Step 3: Conduct the addition reaction. PCE and a fluorine / nitrogen mixture are simultaneously introduced into four reactors. The molar flow rate of the F2 / N2 mixture 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℃, and the contact time is 5 s. The crude product generated from 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 table below:

[0083]

[0084] This comparative example shows that, under the current material flow rate, the 12mm radius circular wave reactor has the lowest yield, indicating that it cannot stably trigger the fluid into a turbulent state, resulting in a relatively poor mixing effect. The yields of the 4, 5, and 7mm reactors are similar, with the 7mm reactor having the highest yield. This indicates that the 7mm circular wave channel is sufficient to ensure uniform mixing of the fluid under this flow rate condition. Smaller circular wave radii cannot provide a better mixing effect under this flow rate condition; instead, they can increase the pressure drop and thus reduce the flow rate of the mixed fluid.

[0085] The above embodiments are merely illustrative of the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein, without departing from the spirit and substance defined by the claims of the present invention; and such modifications or substitutions 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, Includes the following steps: A mixture of halogenated ethylene and halogenated nitrogen is introduced into a gas-liquid phase microchannel reactor, and crude 1,2-difluorotetrachloroethane is obtained through an addition reaction. The crude product is then purified by a refining system to obtain the finished product. The haloethylene is tetrachloroethylene, and the halonitrogen mixture is an F2 / N2 mixture. The volume content of halogen in the halogen-nitrogen mixture is 5% to 30%; The gas-liquid phase microchannel reactor is a bubble cap microchannel reactor with a circular wave structure and a radius of 4 mm to 12 mm.

2. The preparation method according to claim 1, characterized in that, The molar ratio of the haloethylene to the halonitrogen mixture is 1:1 to 1:1.

5.

3. The preparation method according to claim 1, characterized in that, The addition reaction temperature is -20℃ to 30℃, and the gas-liquid phase contact time is 0.5s to 10s.

4. The preparation method according to claim 1, characterized in that, The gas-liquid phase microchannel reactor is made of silicon carbide.

5. The preparation method according to claim 1, characterized in that, The radius of the circular wave is 7mm.

6. The preparation method according to claim 1, characterized in that, The microchannel has a cross-sectional size of 1.58mm × 2mm and a liquid holding capacity of 20ml.

7. The preparation method according to claim 1, characterized in that, The refining system includes a water washing tower, an alkali washing tower, a light component removal tower, and a distillation tower, with a condenser installed at the top of the distillation tower.

8. The preparation method according to claim 7, characterized in that, The light-light removal tower has 15 to 25 trays, operates at atmospheric pressure, has a top temperature of 20 to 40°C, and a bottom temperature of 70 to 110°C.

9. The preparation method according to claim 7, characterized in that, The distillation column has 20 to 55 trays, operates at atmospheric pressure, has a top temperature of 90 to 100°C, a bottom temperature of 120 to 200°C, a reflux ratio of 1 to 5, and uses circulating water as the cooling medium in the top condenser, with liquid phase collection.

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