Process for recovering pyridine or pyridine derivatives from waste residue produced during synthesis of hexachlorocyclotriphosphazene

Abstract

Disclosed in the present invention is a process for recovering pyridine or pyridine derivatives from waste residue produced during the synthesis of hexachlorocyclotriphosphazene. The process comprises: stirring and mixing waste residue separated after the completion of a hexachlorocyclotriphosphazene synthesis reaction with water at a mass ratio of 1:(0.5-2.5) to obtain a mixture, adding an alkali to the mixture to perform a neutralization reaction, controlling the reaction temperature to be 0-50ºC, and adjusting the pH value of an end point to 6-10, so as to obtain a neutralization solution; centrifuging or filtering the neutralization solution to separate out a filtrate, and extracting the filtrate by using chlorobenzene, so as to obtain an extract phase and a raffinate phase; and rectifying the extract phase, so as to obtain chlorobenzene and recovered pyridine or pyridine derivatives. In the present invention, sodium chloride generated by system neutralization can be fully utilized, introduction of an external salt is not needed, salting-out and extraction are successively achieved, and a salting-out water phase is directly returned and reused after extraction, thereby lowering the output of wastewater and energy consumption regarding reuse of wastewater, greatly reducing difficulties in extraction of pyridine or pyridine derivatives, decreasing the use amount of an extraction agent, and reducing the energy consumption of a rectification separation system.

Description

A process for recovering pyridine or pyridine derivatives from hexachlorocyclotriphosphazene synthesis waste residue Technical Field

[0001] The invention relates to a process for recovering pyridine or pyridine derivatives from 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 primarily 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%, and the metal chloride content is 5-20%. 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 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] Regarding pyridine recovery, Chinese patent CN116023325A proposes mixing aqueous pyridine with benzene, separating the pyridine from water through azeotropic distillation, and then distilling the crude pyridine after dehydration at the bottom of the tower to remove heavy components before recycling. This method can produce pyridine with low water content, but it is only suitable for high-concentration aqueous pyridine. For low-concentration aqueous pyridine, the high benzene consumption and energy consumption are issues. This method is also less suitable for recovering pyridine from hexachlorocyclotriphosphazene.

[0008] Chinese patent CN107474010B proposes a process of adding sodium chloride and potassium carbonate to saturated aqueous pyridine and performing two salting-out extractions. This method has a moderate water removal effect and a low pyridine recovery rate.

[0009] Chinese patent CN101074211B proposes a process for extracting aqueous pyridine with biodiesel containing fatty acid methyl esters, which has a very low water solubility, followed by vacuum distillation to recover the pyridine. While this method facilitates separation due to the large boiling point difference between the extractant and pyridine, the single-pass extraction yield is low, the amount of extractant required is high, and a high number of extractions is required to achieve the desired overall extraction rate.

[0010] Chinese patent CN201210581379.0 proposes neutralizing pyridine hydrochloride with alkali at 55-60°C, then distilling it twice with dichloroethane. After the distillate is allowed to stand and separate, the organic phase is distilled to recover pyridine, achieving a pyridine recovery rate of 90-95%. This method can produce high-purity recovered pyridine with a high recovery rate, but it is cumbersome and energy-intensive.

[0011] Summary of the Invention

[0012] In view of the above technical problems existing in the prior art, the object of the present invention is to provide a process for recovering pyridine or pyridine derivatives from hexachlorocyclotriphosphazene synthesis waste residue.

[0013] In order to achieve the above object, the present invention provides the following technical solutions:

[0014] A process for recovering pyridine or pyridine derivatives from hexachlorocyclotriphosphazene synthesis waste residue comprises the following steps:

[0015] 1) Waste residue separated after the synthesis reaction of hexachlorocyclotriphosphazene is stirred and mixed with water to obtain a mixture, wherein the mass ratio of the waste residue to the water is 1:0.5-2.5.

[0016] 2) adding a base to the mixture of step 1) for neutralization reaction, controlling the reaction temperature to 0-50° C., and adjusting the endpoint pH to 6-10 to obtain a neutralized solution. The base is solid sodium hydroxide, sodium hydroxide solution, solid sodium carbonate, sodium carbonate solution, solid sodium bicarbonate, sodium bicarbonate solution, or a mixture thereof.

[0017] 3) The neutralized solution obtained in step 2) is centrifuged or filtered to obtain a filtrate, and the filtrate is extracted with chlorobenzene to obtain an extract phase and a raffinate phase.

[0018] 4) distilling the extract phase from step 3) to obtain chlorobenzene and recovered pyridine or pyridine derivatives.

[0019] In the above process step 1), further, the mass ratio of waste residue to water is preferably 1:0.5-1.6.

[0020] In the above process step 2), further, the reaction temperature is preferably room temperature to 40° C., and the endpoint pH value is preferably adjusted to 6-8.

[0021] Furthermore, the filtrate in step 3) is allowed to stand for phase separation to obtain an aqueous phase and a salt phase, and then the salt phase is extracted with chlorobenzene first, and then the aqueous phase is extracted to obtain an extract phase, a salt phase raffinate phase and an aqueous phase raffinate phase.

[0022] Furthermore, the aqueous extract raffinate is used in step 1) for stirring and mixing with waste residue to prepare a mixture.

[0023] Furthermore, the salt phase extract residue is subjected to azeotropic distillation to remove the azeotropic component containing residual pyridine, and the azeotropic component is applied to step 3) for extraction with chlorobenzene.

[0024] In the above process step 3), further, the extraction is intermittent extraction or countercurrent continuous extraction, and the number of intermittent extractions is 1-5 times.

[0025] 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 neutralization solution.

[0026] Furthermore, in the countercurrent continuous extraction, the ratio of the mass flow rate of the extractant to the mass flow rate of the neutralizing liquid is 0.3 to 1.8:1.

[0027] In the above process step 4), the extract phase is further 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 from the top of the tower, and the remaining bottom liquid is reused in step 3) as an extractant.

[0028] 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.

[0029] Furthermore, the pyridine or pyridine derivative used is allowed to contain more chlorobenzene, and the chlorobenzene content is ≤90%.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] 1) The present invention has a high pyridine recovery rate, and the recovery rate of high-value pyridine or pyridine derivatives in waste residue can reach more than 95-99%, which greatly reduces the pyridine consumption in synthesizing hexachlorocyclotriphosphazene and saves costs.

[0032] 2) The pyridine recovered by the present invention can be directly reused in the hexachlorocyclotriphosphazene synthesis process even when containing a relatively high amount of chlorobenzene, without affecting the hexachlorocyclotriphosphazene synthesis effect. 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 the residual solvent chlorobenzene before recovery, and the residual chlorobenzene can be recovered, thus saving equipment investment, material consumption, and energy consumption.

[0033] 3) The present invention can fully utilize the sodium chloride generated by the neutralization of the system, without the need to introduce salt externally, thereby achieving salting out first and then extraction, and directly returning the salted-out aqueous phase for reuse after extraction, thereby reducing the amount of wastewater generated and the energy consumption of wastewater reuse. In addition, since the salted-out salt phase has a low pyridine content and the salted-out aqueous phase has a high pyridine content but low water content, the difficulty of extraction can be greatly reduced, the amount of extractant used can be reduced, and the energy consumption of the distillation separation system can be saved. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] FIG1 is a schematic flow chart of a process for recovering pyridine or pyridine derivatives from hexachlorocyclotriphosphazene synthesis waste residue according to the present invention. DETAILED DESCRIPTION

[0035] 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.

[0036] Example 1:

[0037] The process for recovering pyridine or pyridine derivatives from hexachlorocyclotriphosphazene synthesis waste residue using the process framework shown in FIG1 includes the following steps:

[0038] 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.

[0039] The waste residue and water were stirred and mixed in a mass ratio of 1:1.2 to obtain a mixture.

[0040] 2) Slowly adding caustic soda to the mixture of step 1) to carry out a neutralization reaction, controlling the reaction temperature to 25-30° C., and adjusting the end point pH to 6-7 to obtain a neutralized solution;

[0041] 3) The neutralized liquid from step 2) is filtered, and the filtrate is allowed to stand for phase separation to obtain an aqueous phase and a salt phase. The salt phase is first extracted with chlorobenzene and then the aqueous phase is extracted to obtain an extract phase, a salt phase raffinate phase, and an aqueous phase raffinate phase. The aqueous phase raffinate phase is used in step 1) and is stirred and mixed with the waste residue to produce a mixture.

[0042] The extraction is performed in an intermittent extraction manner, the number of extractions is 5 times, and the amount of chlorobenzene used as the extractant each time is 0.3 times the mass of water in the neutralization solution.

[0043] 4) Azeotropic distillation is performed on the salt phase extract raffinate of step 3) to remove an azeotropic component containing residual pyridine. The azeotropic component is then used in step 3) for extraction with chlorobenzene, and the distillation residue is disposed of as waste brine. Additionally, the extract phase of step 3) is dehydrated with molecular sieves and then subjected to rectification to recover pyridine from the top of the tower. The pyridine contains a relatively high amount of chlorobenzene, with a chlorobenzene content of 55.73%. The remaining bottoms liquid is used in step 3) as the extraction agent.

[0044] When the above production method is operated stably, the recovered pyridine basically contains only two components, pyridine and chlorobenzene, with a pyridine content of (55-60)% ± 1%, a chlorobenzene content of about 40-45%, and a moisture content of less than 0.05%. The pyridine recovery rate can reach above 95-99%.

[0045] When the recovered pyridine is used as an acid-binding agent in a reaction for preparing hexachlorocyclotriphosphazene using chlorobenzene as a solvent, a mixture of ferric chloride, zinc chloride, and magnesium chloride as a catalyst, and PCl5 and NH4Cl as raw materials, the reaction yield of hexachlorocyclotriphosphazene can reach over 90%, essentially achieving the same or similar experimental results as using fresh pyridine as an acid-binding agent.

[0046] Example 2:

[0047] The process for recovering pyridine or pyridine derivatives from hexachlorocyclotriphosphazene synthesis waste residue using the process framework shown in FIG1 includes the following steps:

[0048] 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.

[0049] The waste residue and water were stirred and mixed in a mass ratio of 1:0.5 to obtain a mixture.

[0050] 2) adding 30% concentrated liquid caustic soda dropwise to the mixture of step 1) for neutralization reaction, controlling the reaction temperature to 45-50° C., and adjusting the end point pH to 8-9 to obtain a neutralized solution;

[0051] 3) The neutralized liquid from step 2) is filtered, and the filtrate is allowed to stand for phase separation to obtain an aqueous phase and a salt phase. The salt phase is first extracted with chlorobenzene and then the aqueous phase is extracted to obtain an extract phase, a salt phase raffinate phase, and an aqueous phase raffinate phase. The aqueous phase raffinate phase is used in step 1) and is stirred and mixed with the waste residue to produce a mixture.

[0052] The extraction is performed in an intermittent extraction manner, the number of extractions is 2, and the amount of chlorobenzene used as the extractant each time is 1 times the mass of water in the neutralization solution.

[0053] 4) Azeotropic distillation is performed on the salt phase extract raffinate of step 3) to remove an azeotropic component containing residual pyridine. The azeotropic component is then used in step 3) for extraction with chlorobenzene, and the distillation residue is disposed of as waste brine. Additionally, the extract phase of step 3) is dehydrated using a pervaporation membrane and then subjected to rectification to recover pyridine from the top of the tower. The pyridine contains a relatively high amount of chlorobenzene, with a chlorobenzene content of 76.35%. The remaining bottoms liquid is then used in step 3) as an extractant.

[0054] When the above production method is operated stably, the recovered pyridine basically contains only two components, pyridine and chlorobenzene, with a pyridine content of (75-80)% ± 1%, a chlorobenzene content of about 20-25%, and a moisture content of 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 in a reaction for preparing hexachlorocyclotriphosphazene using chlorobenzene as a solvent, a mixture of ferric chloride, zinc chloride, and magnesium chloride as a catalyst, and PCl5 and NH4Cl as raw materials, the reaction yield of hexachlorocyclotriphosphazene can reach over 90%, essentially achieving the same or similar experimental results as using fresh pyridine as an acid-binding agent.

[0056] Example 3:

[0057] The process for recovering pyridine or pyridine derivatives from hexachlorocyclotriphosphazene synthesis waste residue using the process framework shown in FIG1 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: 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.

[0059] The waste residue and water were stirred and mixed in a mass ratio of 1:1.5 to obtain a mixture.

[0060] 2) slowly adding 30% liquid caustic soda to the mixture of step 1) for neutralization reaction, controlling the reaction temperature to 15-20° C., and adjusting the end point pH value to 9-10 to obtain a neutralized solution;

[0061] 3) filtering the neutralized solution obtained in step 2), and extracting the filtrate with chlorobenzene as an extractant to obtain an extract phase and a raffinate phase.

[0062] The extraction is performed in an intermittent extraction manner, the number of extractions is 3, and the amount of chlorobenzene used as the extractant each time is 1.5 times the mass of water in the neutralization solution.

[0063] 4) The raffinate phase of step 3) is subjected to azeotropic distillation to remove an azeotropic component containing residual pyridine. The azeotropic component is then used in step 3) for extraction with chlorobenzene, and the distillation residue is disposed of as waste brine. Additionally, the extract phase of step 3) is dehydrated with molecular sieves and then subjected to rectification to recover pyridine from the top of the tower. The pyridine contains a relatively high amount of chlorobenzene, with a chlorobenzene content of 89.43%. The remaining bottoms liquid is used in step 3) as an extraction agent.

[0064] When the above production method is operated 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%.

[0065] When the recovered pyridine is used as an acid-binding agent in a reaction for preparing hexachlorocyclotriphosphazene using chlorobenzene as a solvent, a mixture of ferric chloride, zinc chloride, and magnesium chloride as a catalyst, and PCl5 and NH4Cl as raw materials, the reaction yield of hexachlorocyclotriphosphazene can reach over 90%, essentially achieving the same or similar experimental results as using fresh pyridine as an acid-binding agent.

[0066] 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 recovering pyridine or pyridine derivatives from hexachlorocyclotriphosphazene synthesis waste residue, characterized in that The following steps are involved: 1) mixing the waste residue separated after the synthesis reaction of hexachlorocyclotriphosphazene with water to obtain a mixture, wherein the mass ratio of the waste residue to the water is 1:0.5-2.5; 2) adding a base to the mixture of step 1) for neutralization reaction, controlling the reaction temperature to 0-50° C., adjusting the endpoint pH value to 6-10, and obtaining a neutralized solution; the base 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 solution obtained in step 2) is centrifuged or filtered to obtain a filtrate, and the filtrate is extracted with chlorobenzene 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 recovering pyridine or pyridine derivatives from hexachlorocyclotriphosphazene synthesis waste residue as claimed in claim 1, characterized in that In step 1), the mass ratio of waste residue to water is 1:0.5-1.

6.

3. A process for recovering pyridine or pyridine derivatives from hexachlorocyclotriphosphazene synthesis waste residue as claimed in claim 1, characterized in that In step 2), the neutralization reaction temperature is from room temperature to 40°C.

4. A process for recovering pyridine or pyridine derivatives from hexachlorocyclotriphosphazene synthesis waste residue as claimed in claim 1, characterized in that In step 2), the end point pH value is adjusted to 6-8.

5. A process for recovering pyridine or pyridine derivatives from hexachlorocyclotriphosphazene synthesis waste residue as claimed in claim 1, characterized in that The filtrate is first subjected to a phase separation operation of standing to obtain a water phase and a salt phase, and then chlorobenzene is used to extract the salt phase and then the water phase to obtain an extraction phase, a salt phase raffinate phase and a water phase raffinate phase. The water phase raffinate phase is applied to step 1) for stirring and mixing with the waste residue to prepare a mixture.

6. A process for recovering pyridine or pyridine derivatives from hexachlorocyclotriphosphazene synthesis waste residue as claimed in claim 5, characterized in that The salt phase extract residue is subjected to azeotropic distillation to evaporate the azeotropic component containing residual pyridine, and the distillation residue is waste brine. The azeotropic component is applied to step 3) to extract with chlorobenzene.

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

1.

8. A process for recovering pyridine or pyridine derivatives from hexachlorocyclotriphosphazene synthesis waste residue as claimed in claim 1, characterized in that The extract phase in step 4) is first dehydrated by azeotropic distillation, molecular sieve dehydration or pervaporation membrane dehydration, and then the dehydrated extract phase is distilled to obtain recovered pyridine or pyridine derivatives from the top of the tower, and the remaining bottom liquid is used in step 3) as an extractant.

9. A process for recovering pyridine or pyridine derivatives from hexachlorocyclotriphosphazene synthesis waste residue as claimed in claim 8, characterized in that The recovered pyridine or pyridine derivative is allowed to contain more chlorobenzene, wherein the chlorobenzene content is ≤90%. The recovered pyridine or pyridine derivative is used as an acid binding agent or catalyst set in the reaction of preparing hexachlorocyclotriphosphazene with chlorobenzene as solvent and PCl5 and NH4Cl as raw materials.

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