Process for recycling waste residue from synthesis of hexachlorocyclotriphosphazene

Abstract

Provided is a process for recycling waste residue from the synthesis of hexachlorocyclotriphosphazene. The process comprises: reacting waste residue separated out after a synthesis reaction of hexachlorocyclotriphosphazene is finished with an ammonia source, the ammonia source being liquid ammonia, ammonia gas, ammonia water, ammonium bicarbonate, ammonium carbonate or a combination thereof; adjusting the pH value at an end point to 6-10; subjecting the obtained reaction product to solid-liquid separation so as to obtain a filtrate and a filter cake; subjecting the filter cake to post-treatment so as to obtain a recovered metal chloride catalyst; extracting the filtrate by using chlorobenzene, i.e. an extracting agent, so as to obtain an extract phase and a raffinate phase; rectifying the extract phase to obtain chlorobenzene and recovered pyridine or pyridine derivatives; and dehydrating the raffinate phase to obtain recovered ammonium chloride. By means of the process, high-degree recycling and regeneration of waste residue from the synthesis of hexachlorocyclotriphosphazene are achieved, the recovery rate of pyridine or pyridine derivatives from the waste residue can reach 95-99% or higher, the recovery rate of ammonium chloride and the metal chloride catalyst can reach 98% or higher, and no new waste residue is generated throughout the whole process.

Description

A process for recycling hexachlorocyclotriphosphazene synthesis waste residue Technical Field

[0001] The invention relates to a process for resource recovery of hexachlorocyclotriphosphazene synthesis waste residue, belonging to the technical field of chemical production. Background Art

[0002] Hexachlorocyclotriphosphazene is a very important intermediate. Because it contains two substitutable chlorine atoms on the phosphorus atom, it can produce a variety of derivatives that can be used as flame retardants, adsorbents, antioxidants, etc.

[0003] Hexachlorocyclotriphosphazene is typically prepared by reacting ammonium chloride and phosphorus pentachloride in an inert solvent, using 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 a pyridine derivative (C1-C3 alkoxypyridine) as an acid-binding agent, at a certain temperature. After the reaction is complete, pyridine or a pyridine derivative generates pyridine hydrochloride, which is insoluble in the inert solvent. The pyridine or pyridine derivative is mixed with the metal chloride and excess ammonium chloride to form a solid, which is then separated in a subsequent solid-liquid separation and disposed of as waste residue. Every ton of hexachlorocyclotriphosphazene produced produces approximately 0.6-0.8 tons of this waste residue. This waste residue mainly contains pyridine hydrochloride (or pyridine derivative hydrochloride), ammonium chloride, a metal chloride as a catalyst, and a small amount of solvent. The pyridine hydrochloride (or pyridine derivative hydrochloride) content is 50-70%, the ammonium chloride content is 10-35%, the metal chloride content is 5-20%, and the remainder is chlorobenzene and other impurities. Currently, there are no literature or patent reports on the resource recovery of this waste residue.

[0004] Chinese patent CN201410684338.3 proposes synthesizing hexachlorocyclotriphosphazene by reacting 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 waste residue containing pyridine hydrochloride is removed by filtration, and the crude hexachlorocyclotriphosphazene is obtained by vacuum distillation. The patent does not mention the disposal of the waste residue containing pyridine hydrochloride.

[0005] Chinese patent CN200610116011.1 proposes a method for producing hexachlorocyclotriphosphazene by reacting PCl5 and NH4Cl in chlorobenzene solvent, using a metal chloride such as magnesium chloride, aluminum chloride, or zinc chloride as a catalyst, and pyridine or a C1-C3 alkoxypyridine as an acid-binding agent at reflux temperature. The patent does not mention the disposal of the waste residue containing pyridine hydrochloride.

[0006] Chinese patent CN202211506957.4 proposes a method of preparing hexachlorocyclotriphosphazene by heating a temperature reaction using a chlorobenzene solution of phosphorus pentachloride and ammonium chloride in a chlorobenzene solvent, with an ionic liquid (prepared by mixing chlorobenzene, a composite metal chloride, and pyridine and then introducing HCl) as a catalyst. The waste residue is removed by filtration, and the chlorobenzene is recovered by vacuum distillation to obtain a mixed solid phosphazene. The patent does not mention the disposal of the waste residue containing pyridine hydrochloride.

[0007] Summary of the Invention

[0008] In view of the technical problem that the existing technology cannot recycle the waste residue generated by the hexachlorocyclotriphosphazene synthesis process, the purpose of the present invention is to provide a process for resource recovery of the hexachlorocyclotriphosphazene synthesis waste residue.

[0009] In order to achieve the above object, the present invention provides the following technical solutions:

[0010] A process for recycling hexachlorocyclotriphosphazene synthesis waste residue comprises the following steps:

[0011] 1) reacting the waste residue separated after the hexachlorocyclotriphosphazene synthesis reaction with an ammonia source, adjusting the end point pH value to 6-10, to obtain a reaction product, wherein the ammonia source is liquid ammonia, ammonia gas, ammonia water, ammonium bicarbonate, ammonium carbonate or a combination thereof.

[0012] 2) performing solid-liquid separation on the reaction product of step 1) to obtain a filtrate and a filter cake.

[0013] 3) extracting the filtrate in step 2) with chlorobenzene as an extractant to obtain an extract phase and a raffinate phase.

[0014] 4) distilling the extract phase in step 3) to obtain chlorobenzene and recovered pyridine or pyridine derivatives.

[0015] In the above process step 1), further, the reaction temperature is 0-50°C.

[0016] In the above process step 1), the waste residue is further mixed with water and then reacted with the ammonia source, and the mass ratio of the waste residue to water is 1:0.5-5.

[0017] In the above process step 1), the pH endpoint is further adjusted to 6-9.

[0018] In the above process step 1), the waste residue is further added to ammonia water, or a solution prepared by water and ammonia water, liquid ammonia, ammonia gas, ammonium carbonate (or a combination thereof) to react.

[0019] Furthermore, the filter cake obtained in step 2) is reacted with hydrochloric acid and then dehydrated to obtain a recovered metal chloride catalyst; the recovered metal chloride catalyst is applied to the reaction for preparing hexachlorocyclotriphosphazene as a catalyst.

[0020] In the above process step 3), the extraction is intermittent extraction or countercurrent continuous extraction, and the number of intermittent extractions is 1-5 times.

[0021] Furthermore, the amount of chlorobenzene used as the extractant in each intermittent extraction is 0.5-5 times the mass of water in the filtrate.

[0022] Furthermore, in the countercurrent continuous extraction, the ratio of the mass flow rate of the extractant to the mass flow rate of the filtrate is 0.5 to 3:1.

[0023] In the above process step 4), the extract phase is first subjected to azeotropic distillation dehydration, molecular sieve dehydration or pervaporation membrane dehydration to obtain a dehydrated extract phase, and then the dehydrated extract phase is distilled to obtain recovered pyridine or pyridine derivatives and chlorobenzene from the top of the tower, and the remaining bottom liquid is reused in step 3) as an extractant.

[0024] In the above process step 4), the recovered pyridine or pyridine derivative is further 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.

[0025] Furthermore, the recovered pyridine or pyridine derivative is allowed to contain more chlorobenzene, and the chlorobenzene content is ≤90%.

[0026] Furthermore, the raffinate phase in step 3) is dehydrated to obtain recovered ammonium chloride.

[0027] Furthermore, the dehydration treatment of the raffinate phase includes the steps of azeotropic distillation, concentration, and drying. Azeotropic distillation is first performed to remove 10-30% of the water in the raffinate phase. The distillate obtained by azeotropic distillation is applied to step 3) for extraction treatment, and then concentrated and dried. After dehydration, the water content of ammonium chloride is ≤1%. The water recovered by concentration and drying is applied to step 2) as filter cake washing water and / or used in step 1) for mixing with waste residue.

[0028] Furthermore, the recovered ammonium chloride is used as a raw material in the reaction of preparing hexachlorocyclotriphosphazene.

[0029] Beneficial effects of the present invention:

[0030] 1) High-level resource recovery of hexachlorocyclotriphosphazene synthesis waste residue is achieved, with a recovery rate of pyridine or pyridine derivatives in the waste residue reaching over 95-99%, and a recovery rate of ammonium chloride and metal chloride catalysts reaching over 98%. No new waste residue is generated in the entire process. Although wastewater is generated in the catalyst recovery system due to water introduced by hydrochloric acid, this wastewater is easily treated and meets standards for light pollution. While achieving waste residue resource recovery and significantly reducing the production cost of hexachlorocyclotriphosphazene, the present invention also effectively avoids secondary pollution, achieving clean production.

[0031] 2) The recovered pyridine can be directly reused in the hexachlorocyclotriphosphazene synthesis process even when containing a high amount of chlorobenzene, without affecting the synthesis of hexachlorocyclotriphosphazene. This significantly reduces the difficulty of distillation for pyridine recovery and saves energy. Furthermore, the initial waste residue does not need to be pretreated to remove residual chlorobenzene before recycling, and residual chlorobenzene can be recovered, saving equipment investment, material consumption, and energy consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] FIG1 is a framework flow chart of a production device for recycling hexachlorocyclotriphosphazene synthetic waste residue according to the present application. DETAILED DESCRIPTION

[0033] The present invention will be further described below with reference to specific embodiments, but the protection scope of the present invention is not limited thereto.

[0034] Example 1:

[0035] Using the process framework shown in FIG1 , the process for recycling hexachlorocyclotriphosphazene synthesis waste residue includes the following steps:

[0036] 1) The waste residue separated after the completion of the hexachlorocyclotriphosphazene synthesis reaction is composed of the following components by weight: 53.65% pyridine hydrochloride, 26.52% ammonium chloride, 15.66% metal chloride (a mixture of ferric chloride, zinc chloride, and magnesium chloride), and the remainder being chlorobenzene solvent and other impurities.

[0037] The waste residue and water were stirred and mixed in a mass ratio of 1:2 to obtain a mixture, and ammonia gas was introduced to react. The reaction temperature was controlled at 35-40° C., and the end point pH value was adjusted to 6-7 to obtain a reaction product.

[0038] 2) performing solid-liquid separation on the reaction product of step 1) to obtain a filtrate and a filter cake, washing the filter cake with water, and combining the washing water with the filtrate;

[0039] 3) extracting the filtrate of step 2) with chlorobenzene as an extractant to obtain an extract phase and a raffinate phase; the extraction is performed intermittently, the number of intermittent extractions is 4, and the amount of chlorobenzene used in each intermittent extraction is 0.8 times the mass of water in the filtrate;

[0040] 4) The extract phase obtained in step 3) was first subjected to azeotropic distillation dehydration. Referring to FIG1 , the distillate fraction obtained by azeotropic distillation dehydration was reused in step 3). The dehydrated extract phase was then subjected to distillation in a distillation tower. Recovered pyridine containing a high content of chlorobenzene was obtained from the top of the tower. The pyridine content was 53.287%, the chlorobenzene content was 46.690%, and the water content was 0.023%. The remaining bottom liquid, i.e., chlorobenzene, was reused in step 3 as the extractant.

[0041] 5) The raffinate phase obtained in step 3) was dehydrated, and a pyridine-containing aqueous solution accounting for 23% of the total water in the raffinate phase was first azeotropically distilled off. The aqueous solution was then mixed with the filtrate from the next batch in step 3) for extraction. The ammonium chloride was then recovered by concentration and drying. The ammonium chloride had a purity of 98.15%, a water content of 0.46%, and a recovery rate of 98.93%. The water recovered from the concentration and drying was partially used in step 1) to dissolve the filter residue, and partially used in step 2) as filter cake washing water.

[0042] 6) The filter cake in step 2) is neutralized with hydrochloric acid and then dehydrated to obtain a recovered metal chloride catalyst. The metal chloride (a mixture of ferric chloride, zinc chloride, and magnesium chloride) has a purity of 96.11%, a water content of 0.73%, and a recovery rate of 98.49%.

[0043] When the above production method is operated stably, the recovered pyridine basically contains only two components: pyridine and chlorobenzene. The pyridine content is (50-55)% ± 1%, the chlorobenzene content is about 45-50%, and the remaining impurities are less than 0.05%. The pyridine recovery rate can reach more than 95-99%.

[0044] When the recovered pyridine is used as an acid-binding agent, a metal chloride is used as a catalyst, and ammonium chloride is used as a raw material in a reaction for preparing hexachlorocyclotriphosphazene using chlorobenzene as a solvent and PCl5 as a raw material, the reaction yield of hexachlorocyclotriphosphazene can reach over 90%, which basically achieves the same or similar experimental results as when fresh pyridine is used as an acid-binding agent, fresh metal chloride is used as a catalyst, and fresh ammonium chloride is used as a raw material.

[0045] Example 2:

[0046] Using the process framework shown in FIG1 , the process for recycling hexachlorocyclotriphosphazene synthesis waste residue includes the following steps:

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

[0048] The waste residue is added to 15% ammonia water for reaction, the reaction temperature is controlled at 5-10°C, and the end point pH value is adjusted to 8-9 to obtain a reaction product;

[0049] 2) performing solid-liquid separation on the reaction product of step 1) to obtain a filtrate and a filter cake, washing the filter cake with water, and combining the washing water with the filtrate;

[0050] 3) extracting the filtrate of step 2) with chlorobenzene as an extractant to obtain an extract phase and a raffinate phase; the extraction is intermittent extraction, the number of intermittent extractions is 1, and the amount of chlorobenzene as the extractant of the intermittent extraction is 4 times the mass of water in the filtrate;

[0051] 4) The extract obtained in step 3) was first dehydrated using 4A molecular sieves, and then the dehydrated extract was distilled to obtain recovered pyridine containing a high content of chlorobenzene from the top of the tower. The pyridine content was 13.115%, the chlorobenzene content was 86.850%, and the water content was 0.035%. The remaining bottom liquid, i.e., chlorobenzene, was used in step 3 as the extractant.

[0052] 5) The raffinate phase obtained in step 3) was dehydrated to remove the pyridine-containing aqueous solution by azeotropic distillation, which accounted for 20% of the total water in the raffinate phase. The aqueous solution was then mixed with the filtrate from the next batch in step 3) for extraction. The recovered ammonium chloride was then concentrated and dried to obtain ammonium chloride having a purity of 97.89%, a water content of 0.37%, and a recovery rate of 98.39%. The water recovered by concentration and drying was used in step 2) as filter cake washing water, and the remaining water was treated as wastewater.

[0053] 6) The filter cake in step 2) is neutralized with hydrochloric acid and then dehydrated to obtain a recovered metal chloride catalyst. The metal chloride (a mixture of cobalt chloride, aluminum chloride, and magnesium chloride) has a purity of 96.5%, a water content of 0.42%, and a recovery rate of 98.68%.

[0054] When the above production method is operated stably, the recovered pyridine basically contains only two components: pyridine and chlorobenzene. The pyridine content is (10-15)% ± 0.5%, the chlorobenzene content is about 85-90%, and the remaining impurities are less than 0.05%. The pyridine recovery rate can reach more than 95-99%.

[0055] When the recovered pyridine is used as an acid-binding agent, a metal chloride is used as a catalyst, and ammonium chloride is used as a raw material in a reaction for preparing hexachlorocyclotriphosphazene using chlorobenzene as a solvent and PCl5 as a raw material, the reaction yield of hexachlorocyclotriphosphazene can reach over 90%, which basically achieves the same or similar experimental results as when fresh pyridine is used as an acid-binding agent, fresh metal chloride is used as a catalyst, and fresh ammonium chloride is used as a raw material.

[0056] Example 3:

[0057] Using the process framework shown in FIG1 , the process for recycling hexachlorocyclotriphosphazene synthesis waste residue includes the following steps:

[0058] 1) The waste residue separated after the completion of the hexachlorocyclotriphosphazene synthesis reaction is composed of the following components by weight: 67.42% pyridine hydrochloride, 14.33% ammonium chloride, 14.27% metal chloride (a mixture of cobalt chloride, aluminum chloride, and magnesium chloride), and the remainder being chlorobenzene solvent and other impurities.

[0059] The waste residue and water were stirred and mixed in a mass ratio of 1:5 to obtain a mixture, and ammonium carbonate was slowly added to react, the reaction temperature was controlled at 40-45° C., and the end point pH was adjusted to 6-7 to obtain a reaction product;

[0060] 2) performing solid-liquid separation on the reaction product of step 1) to obtain a filtrate and a filter cake, washing the filter cake with water, and using the washing water jacket in step 1) for dissolving waste residue next time;

[0061] 3) extracting the filtrate of step 2) with chlorobenzene as an extractant to obtain an extract phase and a raffinate phase; the extraction is performed intermittently, the number of intermittent extractions is 5, and the amount of chlorobenzene as the extractant used in the intermittent extraction is 0.5 times the mass of water in the filtrate;

[0062] 4) The extract obtained in step 3) was first dehydrated using a pervaporation membrane device, and then the dehydrated extract was distilled to obtain recovered pyridine containing a high content of chlorobenzene from the top of the tower. The pyridine content was 12.334%, the chlorobenzene content was 87.639%, and the water content was 0.027%. The remaining bottom liquid, i.e., chlorobenzene, was used in step 3 as the extractant.

[0063] 5) The raffinate phase obtained in step 3) was dehydrated, and a pyridine-containing aqueous solution accounting for 10% of the total water in the raffinate phase was first azeotropically distilled off. The aqueous solution was then mixed with the filtrate from the next batch in step 3) for extraction. The recovered ammonium chloride was then concentrated and dried to obtain ammonium chloride having a purity of 98.11%, a water content of 0.39%, and a recovery rate of 98.59%. The water recovered from the concentration and drying was partially used in step 1) to dissolve the filter residue, and partially used in step 2) as filter cake washing water.

[0064] 6) The filter cake in step 2) is neutralized with hydrochloric acid and then dehydrated to obtain a recovered metal chloride catalyst. The metal chloride (a mixture of cobalt chloride, aluminum chloride, and magnesium chloride) has a purity of 97.44%, a water content of 0.38%, and a recovery rate of 98.62%.

[0065] When the above production method is operated stably, the recovered pyridine basically contains only two components: pyridine and chlorobenzene. The pyridine content is (10-15)% ± 0.5%, the chlorobenzene content is about 85-90%, and the remaining impurities are less than 0.05%. The pyridine recovery rate can reach more than 95-99%.

[0066] When the recovered pyridine is used as an acid-binding agent, a metal chloride is used as a catalyst, and ammonium chloride is used as a raw material in a reaction for preparing hexachlorocyclotriphosphazene using chlorobenzene as a solvent and PCl5 as a raw material, the reaction yield of hexachlorocyclotriphosphazene can reach over 90%, which basically achieves the same or similar experimental results as when fresh pyridine is used as an acid-binding agent, fresh metal chloride is used as a catalyst, and fresh ammonium chloride is used as a raw material.

[0067] The contents described in this specification are merely an enumeration of implementation forms of the inventive concept, and the protection scope of the present invention should not be considered as being limited to the specific forms described in the embodiments.

Claims

1. A process for recycling hexachlorocyclotriphosphazene synthetic waste residue, characterized in that The following steps are involved: 1) reacting the waste residue separated after the synthesis reaction of hexachlorocyclotriphosphazene with an ammonia source, adjusting the end point pH value to 6-10, to obtain a reaction product, wherein the ammonia source is liquid ammonia, ammonia gas, ammonia water, ammonium bicarbonate, ammonium carbonate or a combination thereof; 2) performing solid-liquid separation on the reaction product of step 1) to obtain a filtrate and a filter cake; 3) extracting the filtrate in step 2) with chlorobenzene as an extractant to obtain an extract phase and a raffinate phase; 4) distilling the extract phase in step 3) to obtain chlorobenzene and recovered pyridine or pyridine derivatives.

2. A process for recycling hexachlorocyclotriphosphazene synthetic waste residue as claimed in claim 1, characterized in that In step 1), the reaction temperature is 0-50°C.

3. A process for recycling hexachlorocyclotriphosphazene synthetic waste residue as claimed in claim 1, characterized in that In step 1), the waste residue is mixed with water and then reacted with the ammonia source, and the mass ratio of the waste residue to water is 1:0.5-5.

4. A process for recycling hexachlorocyclotriphosphazene synthetic waste residue as claimed in claim 1, characterized in that In step 1), the pH end point is adjusted to 6-9.

5. A process for recycling hexachlorocyclotriphosphazene synthetic waste residue as claimed in claim 1, characterized in that The filter cake is reacted with hydrochloric acid and then dehydrated to obtain a recovered metal chloride catalyst; the recovered metal chloride catalyst is applied to the reaction of preparing hexachlorocyclotriphosphazene as a catalyst.

6. A process for recycling hexachlorocyclotriphosphazene synthetic waste residue as claimed in claim 1, characterized in that In step 3), the extraction is intermittent extraction or countercurrent continuous extraction, the number of intermittent extractions is 1-5 times, and the amount of chlorobenzene used as the extractant for each intermittent extraction is 0.5-5 times the mass of water in the filtrate; in the countercurrent continuous extraction, the ratio of the mass flow rate of the extractant to the mass flow rate of the filtrate is 0.5-3:

1.

7. A process for recycling hexachlorocyclotriphosphazene synthetic waste residue as claimed in claim 1, characterized in that In step 4), the extract phase is first subjected to azeotropic distillation dehydration, molecular sieve dehydration or pervaporation membrane dehydration to obtain a dehydrated extract phase, and then the dehydrated extract phase is distilled to obtain recovered pyridine or pyridine derivatives and chlorobenzene from the top of the tower, and the remaining bottom liquid is applied to step 3) as an extractant, the chlorobenzene content in the recovered pyridine or pyridine derivative is ≤90%, and it is applied as an acid binding agent or catalyst to the reaction of preparing hexachlorocyclotriphosphazene using chlorobenzene as solvent and PCl5 and NH4Cl as raw materials.

8. A process for recycling hexachlorocyclotriphosphazene synthetic waste residue as claimed in claim 1, characterized in that The raffinate phase in step 3) is dehydrated to obtain recovered ammonium chloride.

9. A process for recycling hexachlorocyclotriphosphazene synthetic waste residue as claimed in claim 1 or 8, characterized in that The raffinate phase is dehydrated, comprising the steps of azeotropic distillation, concentration and drying. Azeotropic distillation is first performed to evaporate 10-30% of the water in the raffinate phase. The fraction evaporated by azeotropic distillation is applied to step 3) for extraction treatment, and then concentration and drying are performed. The water content of ammonium chloride after dehydration is ≤1%. The water recovered by concentration and drying is applied to step 2) as filter cake washing water and / or used in step 1) for mixing with waste residue.

10. A process for recycling hexachlorocyclotriphosphazene synthetic waste residue as claimed in claim 8, characterized in that The recovered ammonium chloride is used as a raw material in the reaction of preparing hexachlorocyclotriphosphazene.

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