Process for recovering pyridine or pyridine derivatives from waste residues of hexachlorocyclotriphosphazene synthesis

Abstract

The application discloses a process for recycling pyridine or pyridine derivatives from waste residues in the synthesis of hexachlorocyclotriphosphazene, comprising: mixing the waste residues separated after the synthesis reaction of hexachlorocyclotriphosphazene with water in a mass ratio of 1:0.5-2.5 to obtain a mixture, adding alkali to the mixture to perform a neutralization reaction, controlling the reaction temperature to be 0-50 DEG C, adjusting the end point pH value to 6-10 to obtain a neutralization liquid; centrifuging or filtering the neutralization liquid to obtain a filtrate, and extracting the filtrate with chlorobenzene to obtain an extraction phase and a raffinate phase; rectifying the extraction phase to obtain chlorobenzene and recycled pyridine or pyridine derivatives. The application can fully utilize sodium chloride generated in the system neutralization, does not need to introduce salt from outside, realizes salting-out and then extraction, and returns the water phase after extraction to directly reuse, thereby reducing the wastewater generation amount and energy consumption for wastewater reuse, greatly reducing the extraction difficulty of pyridine or pyridine derivatives, reducing the amount of extractant, and saving the energy consumption of the rectification and separation system.

Description

Technical Field

[0001] This invention relates to a process for recovering pyridine or pyridine derivatives from the synthesis waste of hexachlorocyclotriphosphazene, belonging to the field of chemical production technology. Background Technology

[0002] Hexachlorocyclotriphosphazene is a very important intermediate. Because the phosphorus atom contains two substituted chlorine atoms, it can generate a variety of derivatives, which can be used as flame retardants, adsorbents, and antioxidants.

[0003] Hexachlorocyclotriphosphazene is typically prepared by reacting ammonium chloride and phosphorus pentachloride in an inert solvent with metal chlorides such as aluminum chloride, ferric chloride, barium chloride, magnesium chloride, cobalt chloride, manganese chloride, copper chloride, nickel chloride, zinc chloride, and calcium chloride as catalysts, and pyridine or pyridine derivatives (C1-C3 alkoxypyridines) as acid-binding agents at a certain temperature. After the reaction is complete, pyridine or pyridine derivatives form pyridine hydrochloride that is insoluble in the inert solvent. This hydrochloride is mixed with the metal chloride and excess ammonium chloride to form a solid, which is then separated in a subsequent solid-liquid separation process and disposed of as waste residue. For every ton of hexachlorocyclotriphosphazene produced, approximately 0.6-0.8 tons of this waste residue are generated. This waste residue mainly contains pyridine hydrochloride (or pyridine derivative hydrochloride), ammonium chloride, metal chloride as a catalyst, and a small amount of solvent. The content of pyridine hydrochloride (or pyridine derivative hydrochloride) is 50-70%, the content of ammonium chloride is 10-35%, the content of metal chloride is 5-20%, and the remainder is chlorobenzene and other impurities. Currently, there are no literature or patent reports on the recovery of pyridine from this waste residue.

[0004] Chinese patent CN201410684338.3 proposes a method for synthesizing hexachlorocyclotriphosphazene using PCl5 and NH4Cl in chlorobenzene solvent, with ferric chloride, zinc chloride, and magnesium chloride as a composite catalyst and pyridine as an acid-binding agent. The residue containing pyridine hydrochloride is removed by filtration, and crude hexachlorocyclotriphosphazene is obtained by vacuum distillation. This patent does not mention the method for disposing of the residue containing pyridine hydrochloride.

[0005] Chinese patent CN200610116011.1 proposes a method to obtain hexachlorocyclotriphosphazene by reacting PCl5 and NH4Cl in chlorobenzene solvent, using metal chlorides such as magnesium chloride, aluminum chloride, or zinc chloride as catalysts, and pyridine or C1-C3 alkoxypyridine as acid-binding agents at reflux temperature. This patent does not mention any method for disposing of waste containing pyridine hydrochloride.

[0006] Chinese patent CN202211506957.4 proposes a method for preparing hexachlorocyclotriphosphazene by reacting a solution of phosphorus pentachloride and chlorobenzene, ammonium chloride in chlorobenzene solvent, and an ionic liquid (prepared by passing a mixture of chlorobenzene, a complex metal chloride, and pyridine through HCl) as a catalyst at elevated temperature. The waste residue is removed by filtration, and chlorobenzene is recovered by vacuum distillation to obtain a mixed solid phosphazene. This patent does not mention the disposal method for the waste residue containing pyridine hydrochloride.

[0007] For pyridine recovery, Chinese patent CN116023325A proposes mixing aqueous pyridine with benzene, and then separating pyridine from water through azeotropic distillation to remove water from the benzene. The crude pyridine, after dehydration at the bottom of the distillation column, is then distilled to remove heavy components and reused. This method can obtain pyridine with low water content, but it is only suitable for high-concentration aqueous pyridine. For low-concentration aqueous pyridine, it suffers from high benzene consumption and high energy consumption. This method has poor applicability for pyridine recovery from hexachlorocyclotriphosphazene.

[0008] Chinese patent CN107474010B proposes a process involving two salting-out extractions of hydrous pyridine by adding sodium chloride and potassium carbonate until saturation. This method has a generally poor dehydration effect and a low pyridine recovery rate.

[0009] Chinese patent CN101074211B proposes a process for recovering pyridine by extracting it with biodiesel containing fatty acid methyl esters, which has very low water solubility, followed by vacuum distillation. Although this method allows for easy separation of the extractant and pyridine due to their large boiling point difference, the single extraction rate is low, the amount of extractant used is large, and multiple extraction cycles are required to ensure the overall extraction rate.

[0010] Chinese patent CN201210581379.0 proposes a method of neutralizing pyridine hydrochloride with alkali at 55-60℃, followed by two mixed distillations with dichloroethane. After the fractions are allowed to settle and separate into layers, the organic phase is then subjected to fractional distillation to obtain recovered pyridine, with a recovery rate of 90-95%. This method can yield recovered pyridine with high purity and a high recovery rate, but it is cumbersome and energy-intensive. Summary of the Invention

[0011] In view of the above-mentioned technical problems existing in the prior art, the purpose of the present invention is to provide a process for recovering pyridine or pyridine derivatives from the synthesis waste of hexachlorocyclotriphosphazene.

[0012] To achieve the above objectives, the present invention provides the following technical solution:

[0013] A process for recovering pyridine or pyridine derivatives from hexachlorocyclotriphosphazene synthesis waste includes the following steps:

[0014] 1) After the synthesis reaction of hexachlorocyclotriphosphazene is completed, the waste residue separated from it is mixed with water to obtain a mixture. The mass ratio of waste residue to water is 1:0.5 to 2.5.

[0015] 2) Add an alkali to the mixture from step 1) to carry out a neutralization reaction, controlling the reaction temperature at 0-50℃, and adjust the final pH value to 6-10 to obtain a neutralized solution. The alkali is solid sodium hydroxide, sodium hydroxide solution, solid sodium carbonate, sodium carbonate solution, solid sodium bicarbonate, sodium bicarbonate solution, or a mixture thereof.

[0016] 3) The neutralized liquid obtained in step 2) is centrifuged or filtered to obtain a filtrate, and then extracted with chlorobenzene to obtain an extract phase and a raffinate phase.

[0017] 4) The extract phase from step 3) is distilled to obtain chlorobenzene and recovered pyridine or pyridine derivatives.

[0018] In step 1) of the above process, the preferred mass ratio of waste residue to water is 1:0.5 to 1.6.

[0019] In step 2) of the above process, the reaction temperature is preferably room temperature to 40°C, and the final pH value is preferably adjusted to 6-8.

[0020] Furthermore, the filtrate obtained in step 3) is allowed to stand and separate into an aqueous phase and a salt phase. The salt phase is then extracted with chlorobenzene, followed by the aqueous phase, to obtain an extract phase, a salt raffinate phase, and an aqueous raffinate phase.

[0021] Furthermore, the aqueous phase extract residue is applied to step 1) to mix with the waste residue to prepare a mixture.

[0022] Furthermore, the salt phase extractor phase is subjected to azeotropic distillation to remove the azeotropic component containing residual pyridine, and the azeotropic component is then used in step 3) for extraction with chlorobenzene.

[0023] In step 3) of the above process, the extraction is further described as intermittent extraction or countercurrent continuous extraction, with the number of intermittent extractions being 1-5 times.

[0024] Furthermore, in the intermittent extraction, the amount of chlorobenzene used as the extractant each time is 0.3-2 times the mass of water in the neutralized solution.

[0025] Furthermore, in the countercurrent continuous extraction, the ratio of extractant mass flow rate to neutralizing liquid mass flow rate is 0.3–1.8:1.

[0026] In step 4) of the above process, the extract phase is first dehydrated by azeotropic distillation, molecular sieve dehydration or pervaporation membrane dehydration to obtain a dehydrated extract phase. Then, the dehydrated extract phase is distilled to obtain the recovered pyridine or pyridine derivative from the top of the column. The remaining bottom liquid is reused in step 3) as an extractant.

[0027] In step 4) of the above process, the recovered pyridine or pyridine derivative is reused as an acid-binding agent or catalyst in the reaction to prepare hexachlorocyclotriphosphazene using chlorobenzene as solvent and PCl5 and NH4Cl as raw materials.

[0028] Furthermore, the pyridine or pyridine derivative used is allowed to contain a relatively high amount of chlorobenzene, with a chlorobenzene content ≤90%.

[0029] Compared with the prior art, the beneficial effects achieved by the present invention are:

[0030] 1) The present invention has a high pyridine recovery rate, and the recovery rate of high-value pyridine or pyridine derivatives in the waste residue can reach 95-99% or more, which greatly reduces the pyridine consumption in the synthesis of hexachlorocyclotriphosphazene and saves costs.

[0031] 2) The pyridine recovered by this invention can be directly reused in the hexachlorocyclotriphosphazene synthesis process even when there is a high content of chlorobenzene, without affecting the synthesis effect of hexachlorocyclotriphosphazene. This significantly reduces the difficulty of distillation in pyridine recovery and saves energy. At the same time, there is no need to pre-treat the initial waste residue to remove residual solvent chlorobenzene before recovery, and residual chlorobenzene can be recovered, saving equipment investment, material consumption, and energy consumption.

[0032] 3) This invention can make full use of the sodium chloride generated by the neutralization of the system without the need for external salt introduction, realizing salting out before extraction. The aqueous phase after salting out can be directly recycled, reducing the amount of wastewater generated and the energy consumption for wastewater recycling. Furthermore, since the salt phase has a low pyridine content and the aqueous phase has a high pyridine content but low water content, the extraction difficulty can be greatly reduced, the amount of extractant used can be reduced, and the energy consumption of the distillation separation system can be saved. Attached Figure Description

[0033] Figure 1 This is a flowchart outlining the process for recovering pyridine or pyridine derivatives from the synthesis waste of hexachlorocyclotriphosphazene according to the present invention. Detailed Implementation

[0034] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0035] Example 1:

[0036] Adopting such Figure 1 The process framework shown describes a method for recovering pyridine or pyridine derivatives from the synthesis waste of hexachlorocyclotriphosphazene, including the following steps:

[0037] 1) The waste residue separated after the synthesis reaction of hexachlorocyclotriphosphazene consists of the following components by weight fraction: pyridine hydrochloride content is 53.65%, ammonium chloride is 26.52%, metal chloride (a mixture of ferric chloride, zinc chloride and magnesium chloride) is 15.66%, and the remainder is chlorobenzene solvent and other impurities.

[0038] The above-mentioned waste residue and water were mixed at a mass ratio of 1:1.2 to obtain a mixture.

[0039] 2) Slowly add caustic soda flakes to the mixture in step 1) to carry out a neutralization reaction, control the reaction temperature at 25-30℃, adjust the final pH value to 6-7, and obtain a neutralized solution;

[0040] 3) Filter the neutralized liquid from step 2), and let the filtrate stand to separate the phases to obtain an aqueous phase and a salt phase. Use chlorobenzene as an extractant to first extract the salt phase and then extract the aqueous phase to obtain an extract phase, a salt raffinate phase and an aqueous raffinate phase. The aqueous raffinate phase is reused in step 1) to be stirred and mixed with the waste residue to prepare a mixture.

[0041] The extraction is performed in an intermittent manner, with five extraction cycles. The amount of chlorobenzene used as the extractant in each extraction is 0.3 times the mass of water in the neutralized solution.

[0042] 4) The salt phase raffinate from step 3) is subjected to azeotropic distillation to remove the azeotropic component containing residual pyridine. This azeotropic component is reused in step 3) for chlorobenzene extraction. The distillation residue is disposed of as waste brine. Additionally, the extract phase from step 3) is dehydrated using molecular sieves, and then the dehydrated extract phase is subjected to rectification distillation to obtain recovered pyridine from the top of the column. The pyridine contains a significant amount of chlorobenzene, with a chlorobenzene content of 55.73%. The remaining bottom liquid is reused in step 3) as an extractant.

[0043] When the production process described above is running stably, the recovered pyridine basically contains only two components: pyridine and chlorobenzene. The pyridine content is (55-60)% ± 1%, the chlorobenzene content is about 40-45%, and the moisture content is less than 0.05%. The pyridine recovery rate can reach more than 95-99%.

[0044] When the recovered pyridine is reused as an acid-binding agent in the reaction of preparing hexachlorocyclotriphosphazene with chlorobenzene as solvent, a mixture of ferric chloride, zinc chloride, and magnesium chloride as catalyst, and PCl5 and NH4Cl as raw materials, the reaction yield of hexachlorocyclotriphosphazene can reach more than 90%, basically achieving the same or similar experimental results as using fresh pyridine as an acid-binding agent.

[0045] Example 2:

[0046] Adopting such Figure 1 The process framework shown describes a method for recovering pyridine or pyridine derivatives from the synthesis waste of hexachlorocyclotriphosphazene, including the following steps:

[0047] 1) The waste residue separated after the synthesis reaction of hexachlorocyclotriphosphazene consists of the following components by weight fraction: pyridine hydrochloride content is 67.42%, ammonium chloride is 14.33%, metal chloride (a mixture of cobalt chloride, aluminum chloride and magnesium chloride) is 14.27%, and the remainder is chlorobenzene solvent and other impurities.

[0048] The above-mentioned waste residue and water were mixed at a mass ratio of 1:0.5 to obtain a mixture.

[0049] 2) Add 30% concentration liquid alkali to the mixture in step 1) for neutralization reaction, control the reaction temperature at 45-50℃, adjust the final pH value to 8-9, and obtain the neutralized solution;

[0050] 3) Filter the neutralized liquid from step 2), and let the filtrate stand to separate the phases to obtain an aqueous phase and a salt phase. Use chlorobenzene as an extractant to first extract the salt phase and then extract the aqueous phase to obtain an extract phase, a salt raffinate phase and an aqueous raffinate phase. The aqueous raffinate phase is reused in step 1) to be stirred and mixed with the waste residue to prepare a mixture.

[0051] The extraction is performed in an intermittent manner, with two extraction cycles. The amount of chlorobenzene used as the extractant in each extraction is equal to the mass of water in the neutralized solution.

[0052] 4) The salt phase raffinate from step 3) is subjected to azeotropic distillation to remove the azeotropic component containing residual pyridine. This azeotropic component is reused in step 3) for chlorobenzene extraction. The distillation residue is disposed of as waste brine. Additionally, the extract phase from step 3) is dehydrated using a pervaporation membrane, and then the dehydrated extract phase is subjected to rectification distillation to obtain recovered pyridine from the top of the column. The pyridine contains a significant amount of chlorobenzene, with a chlorobenzene content of 76.35%. The remaining bottom liquid is reused in step 3) as an extractant.

[0053] When the production process described above is running stably, the recovered pyridine basically contains only two components: pyridine and chlorobenzene. The pyridine content is (75-80)% ± 1%, the chlorobenzene content is about 20-25%, and the moisture content is less than 0.05%. The pyridine recovery rate can reach more than 95-99%.

[0054] When the recovered pyridine is reused as an acid-binding agent in the reaction of preparing hexachlorocyclotriphosphazene with chlorobenzene as solvent, a mixture of ferric chloride, zinc chloride, and magnesium chloride as catalyst, and PCl5 and NH4Cl as raw materials, the reaction yield of hexachlorocyclotriphosphazene can reach more than 90%, basically achieving the same or similar experimental results as using fresh pyridine as an acid-binding agent.

[0055] Example 3:

[0056] Adopting such Figure 1 The process framework shown describes a method for recovering pyridine or pyridine derivatives from the synthesis waste of hexachlorocyclotriphosphazene, including the following steps:

[0057] 1) The waste residue separated after the synthesis reaction of hexachlorocyclotriphosphazene consists of the following components by weight fraction: pyridine hydrochloride content is 53.65%, ammonium chloride is 26.52%, metal chloride (a mixture of ferric chloride, zinc chloride and magnesium chloride) is 15.66%, and the remainder is chlorobenzene solvent and other impurities.

[0058] The above-mentioned waste residue and water were mixed at a mass ratio of 1:1.5 to obtain a mixture.

[0059] 2) Slowly add 30% liquid alkali to the mixture in step 1) to carry out the neutralization reaction, control the reaction temperature at 15-20℃, adjust the final pH value to 9-10, and obtain the neutralized solution;

[0060] 3) Filter the neutralized liquid from step 2), and extract the filtrate with the extractant chlorobenzene to obtain the extract phase and the raffinate phase.

[0061] The extraction is performed in an intermittent manner, with three extraction cycles. The amount of chlorobenzene used as the extractant in each extraction is 1.5 times the mass of water in the neutralized solution.

[0062] 4) The raffinate from step 3) is distilled using azeotropic distillation to remove the azeotropic component containing residual pyridine. This azeotropic component is then reused in step 3) for chlorobenzene extraction. The distillation residue is treated as waste brine. Additionally, the extract phase from step 3) is dehydrated using molecular sieves, and then the dehydrated extract phase is further distilled to obtain recovered pyridine from the top of the column. The pyridine contains a significant amount of chlorobenzene, with a chlorobenzene content of 89.43%. The remaining bottom liquid is reused in step 3) as an extractant.

[0063] When the production process described above is running stably, the recovered pyridine basically contains only two components: pyridine and chlorobenzene. The pyridine content is (85-90)% ± 1%, the chlorobenzene content is about 10-15%, and the moisture content is less than 0.05%. The pyridine recovery rate can reach more than 95-99%.

[0064] When the recovered pyridine is reused as an acid-binding agent in the reaction of preparing hexachlorocyclotriphosphazene with chlorobenzene as solvent, a mixture of ferric chloride, zinc chloride, and magnesium chloride as catalyst, and PCl5 and NH4Cl as raw materials, the reaction yield of hexachlorocyclotriphosphazene can reach more than 90%, basically achieving the same or similar experimental results as using fresh pyridine as an acid-binding agent.

[0065] The contents described in this specification are merely an enumeration of the implementation forms of the inventive concept, and the scope of protection of this invention should not be regarded as limited to the specific forms described in the embodiments.

Claims

1. A process for recovering pyridine or pyridine derivatives from the synthesis waste of hexachlorocyclotriphosphonates, characterized in that... Includes the following steps: 1) The waste residue separated after the synthesis reaction of hexachlorocyclotriphosphazene is completed is mixed with water to obtain a mixture. The mass ratio of waste residue to water is 1:0.5~2.

5. 2) Add alkali to the mixture in step 1) to carry out a neutralization reaction, control the reaction temperature at 0-50℃, adjust the final pH value to 6-10, and obtain a neutralized solution; the alkali is solid sodium hydroxide, sodium hydroxide solution, solid sodium carbonate, sodium carbonate solution, solid sodium bicarbonate, sodium bicarbonate solution, or a mixture thereof; 3) The neutralized liquid obtained in step 2) is centrifuged or filtered to obtain a filtrate, and then extracted with chlorobenzene to obtain an extract phase and a raffinate phase; 4) The extract phase from step 3) is subjected to distillation to obtain chlorobenzene and recovered pyridine or pyridine derivatives; The filtrate is first subjected to a static phase separation operation to obtain an aqueous phase and a salt phase. Then, the salt phase is extracted with chlorobenzene, followed by the aqueous phase, to obtain an extract phase, a salt raffinate phase, and an aqueous raffinate phase. The aqueous raffinate phase is used in step 1) to mix with the waste residue to prepare a mixture. The salt phase extract residue is subjected to azeotropic distillation to distill off the azeotropic component containing residual pyridine. The distillation residue is waste brine, and the azeotropic component is reused in step 3) for extraction with chlorobenzene. The extract phase described in step 4) is first dehydrated, and then the dehydrated extract phase is distilled to obtain recovered pyridine or pyridine derivatives from the top of the column. The remaining bottom liquid is reused in step 3) as an extractant. The recovered pyridine or pyridine derivative is allowed to contain a relatively high amount of chlorobenzene, wherein the chlorobenzene content is ≤90%. The recovered pyridine or pyridine derivative is used as an acid-binding agent or catalyst in the reaction of preparing hexachlorocyclotriphosphazene using chlorobenzene as solvent and PCl5 and NH4Cl as raw materials.

2. The process for recovering pyridine or pyridine derivatives from hexachlorocyclotriphosphonates synthesis waste as described in claim 1, characterized in that... In step 1), the mass ratio of waste residue to water is 1:0.5~1.

6.

3. The process for recovering pyridine or pyridine derivatives from hexachlorocyclotriphosphonates synthesis waste as described in claim 1, characterized in that... In step 2), the neutralization reaction is carried out at temperatures ranging from room temperature to 40°C.

4. The process for recovering pyridine or pyridine derivatives from hexachlorocyclotriphosphonates synthesis waste as described in claim 1, characterized in that... In step 2), adjust the final pH value to 6-8.

5. The process for recovering pyridine or pyridine derivatives from hexachlorocyclotriphosphonates synthesis waste as described in claim 1, characterized in that... The extraction described in step 3) is either intermittent extraction or countercurrent continuous extraction. The number of intermittent extractions is 1-5 times. The amount of chlorobenzene used as the extractant in each intermittent extraction is 0.3-2 times the mass of water in the neutralized solution. The ratio of the mass flow rate of the extractant to the mass flow rate of the neutralized solution in the countercurrent continuous extraction is 0.3-1.8:

1.

6. The process for recovering pyridine or pyridine derivatives from hexachlorocyclotriphosphonates synthesis waste as described in claim 1, characterized in that... In step 4), the dehydration treatment is carried out by azeotropic distillation, molecular sieve dehydration, or pervaporation membrane dehydration.

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