Method for preparing chlorophthalic anhydride through piston flow continuous chlorination

Abstract

The invention discloses a method for preparing chlorophthalic anhydride through piston flow continuous chlorination, which comprises the following steps: by taking phthalic acid as a raw material, introducing chlorine under a weakly alkaline condition, and carrying out aromatic electrophilic substitution to prepare chlorophthalic acid with the molar yield of 90-95%. Compared with a traditional reaction kettle, the piston continuous flow chlorination reaction system has the advantages that the efficiency is improved by more than 100 times, the reaction speed is high, the liquid holdup is small, the reaction safety efficiency is high, and the method is suitable for industrial production.

Description

Technical Field

[0001] The invention relates to a method for preparing chlorophthalic anhydride by plug flow continuous chlorination, which belongs to the category of synthetic chemistry. Background Art

[0002] Polyimide is one of the polymer materials with the highest heat resistance, light weight and high strength. Using chlorophthalic anhydride as raw material, dozens of dianhydride monomers can be prepared, and then various polyimide engineering plastics can be synthesized. The preparation methods that have been tried in industry mainly include: 1) a method of passing chlorine gas through a reaction tower kettle of phthalic anhydride. The resulting product contains a large amount of unreacted phthalic anhydride raw material and dichlorophthalic anhydride. The melting and boiling points of the three are close, making separation and purification difficult; 2) a method of gas phase oxidation of chloro-o-xylene. However, this method has a high reaction temperature, severe carbonization corrosion, and a yield of only about 70%. The atom economy is not high, and several industrializations have failed; 3) a method of liquid phase oxidation of chloro-o-xylene. This method must use an expensive titanium kettle, acetic acid as a solvent, and manganese, cobalt, nickel, and bromine as catalysts. Although the reaction yield is relatively high, the reaction requires high-pressure oxidation and a large amount of low-boiling acetic acid as a solvent. The reaction needs to be initiated and maintained at a pressure of 2.0 to 2.4 MPa and above 190°C. The yield is generally below 90%, and it is a dangerous process, and its industrialization is increasingly restricted. In 2018, a patent was filed for microfluidic reaction, but the inner diameter of the microchannel is generally in the micrometer to centimeter range, which limits the throughput and affects the output of a single unit. It should mainly be used for experimental "gram" priced high value-added pharmaceutical products, etc. For halogenated phthalic anhydride with low added value, the investment cost-effectiveness is not high, and it is difficult to make a profit after large-scale production. Summary of the invention

[0003] In order to overcome various deficiencies of the above-mentioned chlorophthalic anhydride preparation system, the present invention provides a method for preparing chlorophthalic anhydride by plug flow continuous chlorination: the method not only utilizes the advantages of the piston continuous flow reaction system with small liquid holding capacity and intrinsic safety, but also directly chlorinates the aqueous solution of phthalic acid under weak alkaline conditions to achieve efficient preparation of monochlorophthalic anhydride. The principle advantage lies in the radial stirring characteristic of 100 times that of the traditional stirred reactor, the piston radial stirring forms a tiny gas-liquid or liquid-liquid interface micro-reaction environment, accelerates the chlorination reaction process, and the continuous unidirectional flow characteristic can reduce the probability of the generated monochlorophthalic anhydride continuing to chlorinate to generate polychlorinated by-products, improve the yield of chlorophthalic anhydride, and reduce the cost. The technical industrialization advantage of the present invention is obvious.

[0004] In order to achieve the above-mentioned invention task, the present invention adopts the following technical scheme: a method for preparing chlorophthalic anhydride by plug flow continuous chlorination, wherein the process specifically comprises the following steps:

[0005] 1) introducing a monosodium phthalate solution with a certain pH value into a piston flow reactor reaction module through a metering pump, and controlling the liquid flow rate to 1-30 kg / min;

[0006] 2) At the same time, the liquid chlorine flow rate is controlled at 0.1 to 3 kg / min, the temperature of the reaction module is controlled at 15 to 70° C., and alkali solution is continuously injected into the reaction module through a metering pump to control the pH in the reaction module to 8 to 10, and the reactants stay in the module for 30 seconds to 3 minutes;

[0007] 3) After the reaction product solution flows out from the reactor outlet, the pH is adjusted to 5-7 with 10% hydrochloric acid, heated and concentrated until solid precipitates, cooled to 15-25° C. to crystallize for 3-8 hours, and the white solid collected by filtration is chlorophthalic acid;

[0008] 4) The obtained mother liquor is further concentrated, and step 3) is repeated, and the crystals are filtered to collect the white solid, which is chlorophthalic acid;

[0009] 5) Combine the two obtained chlorophthalic acids, and dehydrate them under vacuum at 150-200° C. for 2-6 hours to obtain monochlorophthalic anhydride.

[0010] Furthermore, the piston-catalyzed continuous flow reactor has a liquid holding capacity of 1 to 10 liters and is composed of 2 to 5 series or 2 to 10 parallel reaction modules;

[0011] Furthermore, the mass concentration of the sodium phthalate solution is 10-35%, and the pH value is 8.5-10; the alkali solution is a NaOH aqueous solution with a mass concentration of 5-10%; and the vacuum degree of the reduced pressure dehydration is 0.1-4 kPa.

[0012] Beneficial technical effects of the present invention:

[0013] The invention discloses a method for preparing chlorophthalic anhydride by plug flow continuous chlorination. The characteristic of unidirectional flow chlorination is that the product is easily removed, and the production problem of polyhalogenated byproducts caused by the long reaction time of traditional tower-bottom type halogenation reaction is avoided to the greatest extent, thereby improving the yield of monohalogenated aromatic hydrocarbons.

[0014] The piston continuous flow reaction system has a smaller liquid holding volume than the traditional tower kettle reactor, has inherent safety characteristics, and occupies a small area (as shown in the left figure below). It is more efficient than the traditional stirring method (as shown in the right figure below). A set of industrial-scale piston continuous flow reaction equipment similar to CofloreATR occupies more than 50% less space than a tower kettle of the same size, and has an annual output more than 3 times higher, which is in line with the development trend of chemical production in the new situation to pursue inherent safety. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 The present invention is a flow chart of a method for preparing chlorophthalic anhydride by plug flow continuous chlorination.

[0016] Figure 2 The utility model relates to a production equipment for preparing halogenated phthalic anhydride by plug flow continuous chlorination.

[0017] Figure 3 This is a diagram of the radial stirring effect of the reaction module of the piston flow reaction system.

[0018] The present invention is specifically described below in conjunction with embodiments, but the present invention is not limited to the scope of the embodiments.

[0019] Example 1

[0020] In a 200-liter batching tank, add 29.6 kg (200 mol) of phthalic anhydride and 60 kg of deionized water, stir and dissolve, then adjust the pH value to ~9 with a 20% sodium hydroxide solution, add a small amount of water to a total mass of 140 kg, at which time the concentration of sodium phthalate is ~30%; use a metering pump to pump the above solution at a flow rate of ~700 g (~1 mol sodium phthalate) / min into two reaction modules with a liquid holding capacity of 3 liters in series, and at the same time, liquid chlorine is passed into the series reaction module at a flow rate of 70 g (~1 mol) / min. The temperature of the reaction module is controlled at ~25°C, and the reactant liquid is at After staying in the module for 2.5 minutes, it flows out from the second reaction module. After collecting all the product solutions, the pH is adjusted to 6.7 with 10% hydrochloric acid, heated to remove water and concentrated until solid precipitates, cooled naturally to 25°C, and then kept at 15°C for 5 hours to precipitate white crystals, the mother liquor is filtered and removed, and the white solid is collected; the obtained mother liquor is further concentrated until solid precipitates, and the above crystallization and filtration operations are repeated; the chlorophthalic acid obtained twice is combined, dehydrated at 150°C and 4kPa for 2 hours, and further dehydrated at 200°C and 0.5kPa for 3 hours until it is dry, and 33 kg of the obtained chlorophthalic anhydride is weighed, with a molar yield of 90%.

[0021] Example 2

[0022] In a 200-liter batching tank, add 29.6 kg (200 mol) of phthalic anhydride and 60 kg of deionized water, stir and dissolve, then adjust the pH value to ~9.5 with 15% sodium hydroxide solution, add a small amount of water to the total mass of the solution to 175 kg, at which time the concentration of sodium phthalate is ~24%; use a metering pump to pump the above solution at a flow rate of ~700 g (~0.8 mol sodium phthalate) / min into 3 reaction modules with a liquid holding capacity of 2 liters in series, and at the same time, liquid chlorine is passed into the series reaction module at a flow rate of 56 g (~0.79 mol) / min, and the temperature of the reaction module is controlled at ~20°C. The reaction liquid stayed in the module for 4 minutes and then flowed out from the third reaction module. After collecting all the product solutions, the pH was adjusted to 7 with 10% hydrochloric acid, heated to remove water and concentrated until solid precipitated. After naturally cooling to 25°C, it was kept at 15°C for 3 hours to precipitate white crystals. The mother liquor was filtered and removed, and the white solid was collected; the obtained mother liquor was further concentrated until solid precipitated, and the above crystallization and filtration operations were repeated; the chlorophthalic acid obtained twice was combined, dehydrated at 150°C and 4kPa for 3 hours, and then dehydrated at 180°C and 0.1kPa for 2 hours until it was dry, and 34 kg of chlorophthalic anhydride was weighed, with a molar yield of 93%.

[0023] Example 3

[0024] In a 300-liter batching tank, add 29.6 kg (200 mol) of phthalic anhydride and 60 kg of deionized water, stir and dissolve, then adjust the pH value to ~10 with a 20% sodium hydroxide solution, add a small amount of water to a total mass of 200 kg, at which time the concentration of sodium phthalate is ~21%; use a metering pump to pump the above solution at a flow rate of ~1000 g (~1 mol sodium phthalate) / min into 5 reaction modules with a liquid holding capacity of 2 liters in series, and at the same time, liquid chlorine is passed into the series reaction module at a flow rate of 70 g (~1 mol) / min, and the temperature of the reaction module is controlled at ~25°C. The reactants The liquid stays in the module for 5 minutes and then flows out from the second reaction module. After collecting all the product solutions, the pH is adjusted to 6 with 10% hydrochloric acid, heated to remove water and concentrated until solid precipitates, and naturally cooled to 25°C, and then kept at 15°C for 2 hours to precipitate white crystals. The mother liquor is filtered and removed, and the white solid is collected; the obtained mother liquor is further concentrated until solid precipitates, and the above crystallization and filtration operations are repeated; the chlorophthalic acid obtained twice is combined, dehydrated at 150°C and 3kPa for 1 hour, and further dehydrated at 190°C and 0.2kPa for 3 hours until it is dry, and 34.5 kg of the obtained chlorophthalic anhydride is weighed, with a molar yield of 95%.

[0025] The above is a detailed introduction to the method for preparing chlorophthalic anhydride by a piston continuous flow chlorination reaction system provided by the present invention. The principle and implementation mode of the present invention are explained in this article using specific examples. The description of the above embodiments is only used to help understand the method of the present invention and its core idea. It should be pointed out that one of the characteristics of the piston continuous flow reaction is the smaller amplification effect. Therefore, for ordinary technicians in this technical field, without departing from the principle of the present invention, the present invention can also be improved and modified such as flux amplification, and these improvements and modifications also belong to the scope of full protection of the present invention.

Claims

1. A method for preparing chlorophthalic anhydride by plug flow continuous chlorination, characterized in that: The process specifically includes the following steps: 1) introducing a monosodium phthalate solution with a certain pH value into a piston flow reactor reaction module through a metering pump, and controlling the liquid flow rate to 1-30 kg / min; 2) At the same time, the liquid chlorine flow rate is controlled at 0.1 to 3 kg / min, the temperature of the reaction module is controlled at 15 to 70° C., and alkali solution is injected into the reaction module through a metering pump to maintain the pH in the reaction module at 8 to 10. The reactants stay in the module for 30 seconds to 3 minutes; 3) After the reaction product solution flows out from the reactor outlet, the pH is adjusted to 5-7 with 10% hydrochloric acid, heated and concentrated until solid precipitates, cooled to 15-25° C. to crystallize for 3-8 hours, and the white solid collected by filtration is chlorophthalic acid; 4) The obtained mother liquor is further concentrated, and step 3) is repeated, and the crystals are filtered to collect the white solid, which is chlorophthalic acid; 5) Combine the two obtained chlorophthalic acids, and dehydrate them under vacuum at 150-200° C. for 2-6 hours to obtain monochlorophthalic anhydride.

2. A method for preparing chlorophthalic anhydride by plug flow continuous chlorination according to claim 1, characterized in that: The piston-catalyzed continuous flow reactor has a liquid holding capacity of 1 to 10 liters and is composed of 2 to 5 series or 2 to 10 parallel reaction modules.

3. A method for preparing chlorophthalic anhydride by plug flow continuous chlorination according to claim 1, characterized in that: The mass concentration of the sodium phthalate solution is 10-35%, and the pH value is 8.5-10; the mass concentration of the alkali solution used to control the pH value of the reaction module is 5-10% NaOH solution; the vacuum degree during vacuum dehydration is 0.1-4kPa.

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