A method and apparatus for the continuous production of piperazine pyrophosphate from phosphoric acid by the wet process

Abstract

This invention relates to a method and apparatus for the continuous wet-process preparation of piperazine pyrophosphate from phosphoric acid, belonging to the field of flame retardant technology. The method includes: adding phosphoric acid to at least one reaction vessel, adding deionized water while stirring, and then adding piperazine; after the reaction is complete, the reactants from one reaction vessel are transferred to a filter, and the clarified filtrate is transferred to a cooling vessel, where the filter residue is centrally processed; the reactants from the next reaction vessel are transferred to a filter, and after filtration, the clarified filtrate is transferred to another cooling vessel; after the material in the cooling vessel cools and crystallizes, the material in the cooling vessel is sequentially transferred to a centrifuge; after separation by the centrifuge, the wet material enters a screw conveyor; the filtrate enters a filtrate tank for recycling; the material is dried and then enters a twin-screw reactor; after cooling, pulverizing, and packaging, piperazine pyrophosphate product is obtained. This invention requires no additional catalyst, produces a stable product with excellent performance, and the reaction solution can be recycled.

Description

Technical Field

[0001] This invention relates to the field of flame retardant technology, and in particular to a method and apparatus for the continuous wet phosphoric acid preparation of piperazine pyrophosphate. Background Technology

[0002] Past research has identified many elements as effective flame retardants, such as halogens, phosphorus, nitrogen, silicon, and boron. While halogens offer high flame retardancy, they produce toxic and polluting compounds during combustion, posing significant harm to human health and the environment. With increasing environmental awareness, halogen-based flame retardants are gradually being phased out. Intumescent flame retardants (IFRs) are halogen-free, environmentally friendly flame retardants with excellent flame retardancy, low smoke, and low toxicity, aligning with future research and development directions for flame retardants and already dominating the market.

[0003] Piperazine pyrophosphate (PAPP) is mainly composed of pyrophosphate and piperazine. Phosphoric acid can be used as an acid source, and piperazine can be used as a carbon source and gas source to form a new type of monomolecular IFR. It has the advantages of good carbonization effect, low addition amount, high thermal decomposition temperature and no halogen. It has gradually replaced ammonium polyphosphate as the mainstream product of halogen-free IFR.

[0004] Currently, the commonly used industrial method for preparing PAPP is the high-temperature dehydration method of piperazine diphosphate. Anhydrous piperazine or 68 piperazine is used as raw material to prepare piperazine diphosphate, which is then dehydrated at high temperature to prepare PAPP. The reactions are all batch reactions with long reaction times. The materials are heated unevenly during the reaction, resulting in unstable product quality.

[0005] To address the above problems, there is an urgent need to develop an efficient and continuous method and apparatus for preparing piperazine pyrophosphate. Summary of the Invention

[0006] The purpose of this invention is to provide a continuous production apparatus and method for preparing piperazine pyrophosphate using wet phosphoric acid, thereby solving the problems of unstable product quality and low production efficiency in existing methods.

[0007] The specific solution of the present invention is as follows: A method for continuous wet phosphoric acid preparation of piperazine pyrophosphate includes the following steps: Step S1: Add phosphoric acid to at least one reaction vessel, add deionized water while stirring, and then add piperazine to carry out acid-base neutralization reaction; Step S2: After the reaction is completed, the reactants from one of the reactors are transferred to a filter to remove the filter residue in the filtrate after the neutralization reaction. The clarified filtrate is then transferred to one of the cooling reactors, and the filter residue is centrally processed. The reactants from the next reactor are then transferred to a filter, and after filtration, the clarified filtrate is transferred to another cooling reactor. Step S3: After the material in the cooling kettle cools and crystallizes, the material in the cooling kettle is sequentially transferred to the centrifugal separator. Step S4: After the material is separated by the centrifugal separator, the wet material enters the screw conveyor for conveying and drying; the filtrate enters the filtrate tank for recycling. Step S5: After drying, the material enters a twin-screw reactor for high-temperature dehydration reaction; Step S6: After the reaction is complete, the product is obtained by cooling, pulverizing, and packaging.

[0008] As a preferred embodiment, in step S1, the phosphoric acid concentration is 40-85%; the phosphoric acid to piperazine molar ratio is 2-2.10:0.95-1.10; the amount of deionized water added is 30-50 wt% of the total product mass; the reaction temperature is 75-90℃, the stirring rate is 200-500 rpm, and the reaction time is 0.5-3 h.

[0009] As a preferred embodiment, in step S3, the stirring rate of the cooling vessel is 50-200 rpm, the cooling temperature is 0-10℃, and the cooling time is 20-60 min.

[0010] As a preferred embodiment, in step S4, the mesh size of the filter screen in the centrifugal filter is 100-200 mesh; the wet material enters the screw conveyor after centrifugation, and the filtrate is recovered to the reaction vessel; the drying temperature of the screw conveyor is 150-200℃, the rotation speed is 60rpm-200rpm, and the drying time is 10min-30min.

[0011] As a preferred embodiment, in step S5, the twin-screw reactor has a rotational speed of 50-300 r / min, a material dehydration temperature of 230-250℃, a twin-screw length-to-diameter ratio of at least 32, an effective length of 2200-3200 mm, and a material residence time of 5-30 min. After the material enters the twin-screw reactor, it passes through the medium-lead threaded block, the small-lead threaded block, the 45° meshing block, the large-lead threaded block, the small-lead threaded block, the medium-lead threaded block, the small-lead threaded block, the medium-lead threaded block, and the small-lead threaded block in sequence.

[0012] As a preferred embodiment, in step S6, the cooling temperature of the cooler is 10-30℃, and the particle size D50 after pulverization is 5-15μm.

[0013] The present invention also provides an apparatus for the continuous wet phosphoric acid preparation of piperazine pyrophosphate, comprising at least one reaction vessel and at least one cooling vessel; at least one reaction vessel is connected to a filter inlet, the filter clarified liquid outlet is connected to at least one cooling vessel, and at least one cooling vessel is connected to a centrifuge. The centrifuge filtrate outlet is connected to the filtrate tank, and the filtrate tank is connected to at least one reactor inlet. The discharge and inlet ports of the centrifugal separator, screw conveyor, twin-screw reactor, cooler, crusher, and packaging machine are connected in sequence.

[0014] As a preferred embodiment, at least one pipeline from the reactor to the filter and from the filter to at least one cooling vessel is equipped with an insulation layer, and the filter is insulated.

[0015] As a preferred embodiment, the heating temperature of the reactor is 0–100℃, the heating temperature of the cooling vessel is -10–30℃, the heating temperature of the screw conveyor and the twin-screw reactor is 0–300℃, and the cooling temperature of the cooler is 10–30℃.

[0016] As a preferred embodiment, in the twin-screw reactor, a large-lead threaded block is provided at the feed inlet, and along the material movement direction, the sequence is: medium-lead threaded block, small-lead threaded block, 45° meshing block, large-lead threaded block, small-lead threaded block, medium-lead threaded block, small-lead threaded block, medium-lead threaded block, and small-lead threaded block.

[0017] This invention utilizes a neutralization reaction between piperazine and wet-process phosphoric acid to remove impurities from wet-process phosphoric acid. The alternating feeding of the reaction vessel and cooling vessel, the continuous conveying of the screw conveyor, and the enhanced mass and heat transfer of the twin-screw reactor enable continuous feeding of wet-process phosphoric acid and piperazine, and continuous discharge of piperazine pyrophosphate. This process is simple to operate, the process conditions are easy to control, no additional catalyst is required, the product quality is stable, and the reaction solution can be recycled.

[0018] The present invention, through specific raw material ratios, suitable reaction devices and precisely controlled reaction conditions, produces piperazine pyrophosphate products with excellent properties: phosphorus content ≥23%, nitrogen content ≥10%, and 1% thermal decomposition temperature ≥280℃.

[0019] This invention features multiple reaction vessels and multiple cooling vessels to ensure continuous feeding. By controlling the structure of the twin-screw reactor, reaction temperature, and reaction time, continuous preparation of piperazine pyrophosphate is achieved. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a flowchart illustrating one embodiment of the present invention; Figure 2This is a schematic diagram of the screw of a twin-screw reactor according to one embodiment of the present invention. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased.

[0023] Unless otherwise stated, all percentages in this invention represent mass fractions. Ratios are mass percentages, and concentrations are mass concentrations.

[0024] Unless otherwise specified, all materials, instruments, and equipment used below are conventional materials, instruments, and equipment or obtained through commercial channels; all testing methods used are existing methods unless otherwise specified.

[0025] In existing technologies, CN 102482239A uses various equipment to prepare PAPP. First, piperazine diphosphate is prepared using phosphoric acid and piperazine. Then, high-temperature polycondensation is carried out using mixing equipment (including a Banbury mixer and a tubular atmosphere furnace) to obtain white PAPP. The method used in "Application Research of Piperazine Pyrophosphate / Melamine Flame-Retardant Epoxy Resin" involves preparing piperazine diphosphate through acid-base neutralization, followed by dehydration polycondensation at 225℃ in a tubular reactor under nitrogen protection to obtain PAPP. All of these reactions are batch reactions with long reaction times, uneven heating of the materials, and unstable product quality.

[0026] Furthermore, embodiments of the present invention provide a method for the continuous wet phosphoric acid preparation of piperazine pyrophosphate, comprising the following steps: Step S1: Add phosphoric acid to at least one reaction vessel, add deionized water while stirring, and then add piperazine to carry out acid-base neutralization reaction; Step S2: After the reaction is completed, the reactants from one of the reactors are transferred to a filter to remove the filter residue in the filtrate after the neutralization reaction. The clarified filtrate is then transferred to one of the cooling reactors, and the filter residue is centrally processed. The reactants from the next reactor are then transferred to a filter, and after filtration, the clarified filtrate is transferred to another cooling reactor. Step S3: After the material in the cooling kettle cools and crystallizes, the material in the cooling kettle is sequentially transferred to the centrifugal separator. Step S4: After the material is separated by the centrifugal separator, the wet material enters the screw conveyor for conveying and drying; the filtrate enters the filtrate tank for recycling. Step S5: After drying, the material enters a twin-screw reactor for high-temperature dehydration reaction; Step S6: After the reaction is complete, the product is obtained by cooling, pulverizing, and packaging.

[0027] The raw materials are first added to more than one reactor, cooled, and then sequentially fed into a filter and then into multiple cooling reactors to ensure continuous feeding.

[0028] The packaged product specifications are: phosphorus content ≥23%, nitrogen content ≥10%, and 1% thermal decomposition temperature ≥280℃.

[0029] Currently, the intermediate products piperazine diphosphate and piperazine pyrophosphate on the market are all prepared by batch processes, making continuous production design difficult. Furthermore, piperazine diphosphate requires high-temperature dehydration, and traditional equipment suffers from uneven mass and heat transfer. This invention provides the intermediate product through a multi-reactor series connection in the first step, using a twin-screw extruder as the main continuous reactor to achieve a continuous design. By selecting a high-temperature twin-screw reactor, material mixing and mass and heat transfer are enhanced, increasing the reaction rate.

[0030] In one embodiment, in step S1, the phosphoric acid concentration is 40-85%; the phosphoric acid and piperazine are fed at a molar ratio of 2-2.10:0.95-1.10; the amount of deionized water added is 30-50 wt% of the total product mass; the reaction temperature is 75-90℃, the stirring rate is 200-500 rpm, and the reaction time is 0.5-3 h.

[0031] The phosphoric acid raw material of this invention is wet-process phosphoric acid, and the piperazine raw material is anhydrous piperazine or 68 piperazine (piperazine concentration is 68%). Using 68 piperazine as the raw material has a cost advantage.

[0032] Phosphoric acid and piperazine can be added manually or by installing a reaction vessel and a raw material transfer pump.

[0033] In one embodiment, in step S3, the stirring rate of the cooling tank is 50-200 rpm, the cooling temperature is 0-10℃, and the cooling time is 20-60 min, so that the material crystallizes and precipitates at low temperature.

[0034] In one embodiment, in step S4, the mesh size of the filter screen in the centrifugal filter is 100-200 mesh; the wet material enters the screw conveyor after centrifugation, and the filtrate is recovered to the reaction vessel; the drying temperature of the screw conveyor is 150-200℃, the rotation speed is 60rpm-200rpm, and the drying time is 10min-30min, so that some of the material undergoes a dehydration reaction.

[0035] In one embodiment, in step S5, the twin-screw reactor speed is 50-300 r / min, the material dehydration temperature is 230-250℃, the twin-screw length-to-diameter ratio is at least 32, the effective length is 2200-3200 mm, and the material residence time is 5-30 min. After entering the twin-screw reactor, the material sequentially passes through the medium-lead threaded block, the small-lead threaded block, the 45° meshing block, the large-lead threaded block, the medium-lead threaded block, the small-lead threaded block, the medium-lead threaded block, and the small-lead threaded block. In step S5, the main indicators of the dried material are phosphorus content ≥21.90% and nitrogen content ≥9.90%. A longer aspect ratio is generally more conducive to material mixing and can enhance mass transfer.

[0036] In one embodiment, in step S6, the cooling temperature of the cooler is 10–30°C, and the particle size D50 after pulverization is 5–15 μm. The product specifications after packaging are: phosphorus content ≥23%, nitrogen content ≥10%, and 1% thermal decomposition temperature ≥280°C.

[0037] This invention also provides an apparatus for the continuous wet phosphoric acid preparation of piperazine pyrophosphate, comprising at least one reaction vessel and at least one cooling vessel; at least one reaction vessel is connected to a filter inlet, the filter clarified liquid outlet is connected to at least one cooling vessel, and at least one cooling vessel is connected to a centrifuge. The centrifuge filtrate outlet is connected to the filtrate tank, and the filtrate tank is connected to at least one reactor inlet. The discharge and inlet ports of the centrifugal separator, screw conveyor, twin-screw reactor, cooler, crusher, and packaging machine are connected in sequence.

[0038] The reaction vessel can be a neutralization reaction vessel; the filter can be a general-purpose filter; the cooling vessel is a stirred vessel; the screw conveyor is a single screw conveyor or a twin screw conveyor; the twin screw reactor is a twin screw extruder; the cooler, crusher, and packaging machine are all general-purpose chemical equipment.

[0039] The reactor outlet is connected to the filter inlet; the filter clarified liquid outlet is connected to the cooling tank inlet, and the cooling tank outlet is connected to the centrifuge inlet. The centrifuge, screw conveyor, twin-screw reactor, cooler, crusher, and packaging machine outlets are connected to their respective inlets in sequence. The screw conveyor, twin-screw reactor, and cooler are all equipped with air inlets and outlets. The air inlet is used to introduce inert gas to prevent high-temperature oxidation of piperazine pyrophosphate, and the air outlet is used to discharge water vapor.

[0040] The reactor, filter, cooling vessel, screw conveyor, and twin-screw reactor are all made of 316L stainless steel; each is equipped with a material temperature detector; the reactor and cooling vessel both have a double-blade structure.

[0041] In one embodiment, at least one pipeline from the reactor to the filter, and from the filter to at least one cooling vessel, is equipped with an insulation layer, and the filter is also insulated. Insulating the filter prevents material from cooling and precipitating out and clogging the pipeline, thus preventing material from entering the cooling vessel for cooling and crystallization. The insulation can be achieved using a rock wool insulation jacket.

[0042] The pipelines from the reactor to the filter, from the filter to the cooling vessel, from the cooling vessel to the centrifuge, from the centrifuge to the filtrate tank, and from the filtrate tank to the reactor are all acid-resistant pipelines. The pipelines from the reactor to the filter and from the filter to the cooling vessel can be fitted with existing insulation layers (such as rock wool insulation) to prevent material from precipitating out at low temperatures and clogging the pipelines.

[0043] In one embodiment, the heating temperature of the reactor can be 0–100°C, the heating temperature of the cooling vessel can be -10–30°C, and the heating temperature of the screw conveyor and twin-screw reactor can be 0–300°C; the cooling temperature of the cooler can be 10–30°C. The reactor, cooling vessel, screw conveyor, and twin-screw reactor are all heated by heat transfer oil, while the cooler is heated by circulating water. The screw conveyor and twin-screw reactor can share a single heating system to ensure the heat supply to the above equipment.

[0044] In one embodiment, the twin-screw reactor has a large-lead threaded block at the feed inlet, and along the material movement direction, the components are arranged in sequence: medium-lead threaded block, small-lead threaded block, 45° meshing block, large-lead threaded block, small-lead threaded block, medium-lead threaded block, small-lead threaded block, medium-lead threaded block, and small-lead threaded block.

[0045] The large-lead kneading block at the inlet provides high conveying capacity, increasing the material entry rate into the twin-screw extruder and preventing blockage at the inlet. The medium- and small-lead meshing blocks along the feed path provide high shear force and mixing action, promoting material mixing and dispersion and increasing material reaction time. The 45° meshing blocks balance material mixing and conveying, resulting in more uniform material dispersion. The multi-segment dispersion arrangement enhances the overall mixing effect and reduces the load on single-segment shearing equipment.

[0046] To further illustrate the present invention, the following describes in detail, with reference to embodiments, a method and apparatus for continuous wet phosphoric acid preparation of piperazine pyrophosphate provided by the present invention.

[0047] The analysis of the product's physicochemical properties and thermal decomposition performance shall be conducted in accordance with T / CPCIF 0404-2024 for piperazine pyrophosphate.

[0048] like Figure 1 As shown, the apparatus for the continuous wet phosphoric acid preparation of piperazine pyrophosphate in this embodiment includes two reaction vessels and two cooling vessels, namely reaction vessel A / B and cooling vessel A / B.

[0049] The reactor is a neutralization reactor, the cooling vessel is a stirred vessel; the filter is a general-purpose filter; the screw conveyor is a twin-screw conveyor; and the twin-screw reactor is a twin-screw extruder.

[0050] The outlets of reactors A and B are connected to the inlet of the filter; the outlet of the clarified liquid from the filter is connected to cooling reactors A and B; cooling reactors A and B are connected to the centrifuge; the filtrate outlet of the centrifuge is connected to the filtrate tank; the filtrate tank is connected to the inlet of reactors A and B; the outlets and inlets of the centrifuge, screw conveyor, twin-screw reactor, cooler, crusher, and packaging machine are connected in sequence.

[0051] The screw conveyor, twin-screw reactor, and cooler are all equipped with air inlets and outlets. The air inlet is used to introduce inert gas to prevent high-temperature oxidation of piperazine pyrophosphate, and the air outlet is used to discharge water vapor.

[0052] The reactor, cooling vessel, screw conveyor, and twin-screw reactor are all heated by heat transfer oil, while the cooler is heated by circulating water. The screw conveyor and twin-screw reactor can share a single heating system. The heating temperature of the reactor is 0–100℃, the heating temperature of the cooling vessel is -10–30℃, and the heating temperature of the screw conveyor and twin-screw reactor is 0–300℃. The cooling temperature of the cooler is 10–30℃.

[0053] In a twin-screw reactor, a large-lead threaded block is installed at the feed inlet, and along the material movement direction, the sequence is: medium-lead threaded block, small-lead threaded block, 45° meshing block, large-lead threaded block, small-lead threaded block, medium-lead threaded block, small-lead threaded block, medium-lead threaded block, and small-lead threaded block.

[0054] Based on the above apparatus, the specific steps for continuous production of piperazine pyrophosphate in this embodiment are as follows: S1. Add phosphoric acid to reactor A / B, turn on the stirring device, add deionized water while stirring, and then add piperazine for acid-base neutralization reaction; the molar ratio of phosphoric acid to piperazine is 2-2.10:0.95-1.10, the amount of deionized water added is 30-50 wt% of the total product mass, the reaction temperature is 75-90℃, the stirring speed is 200-500 rpm, and the reaction time is 0.5-3 h.

[0055] S2. After the reaction is completed, the reactants in reactor A are pumped to a filter to remove the residue in the filtrate after the neutralization reaction. The clarified filtrate is then pumped to cooling reactor A. Then, the reactants in reactor B are pumped to a filter to remove the residue in the filtrate after the neutralization reaction. The clarified filtrate is then pumped to cooling reactor B.

[0056] After the material cools and precipitates, the material in cooling kettle A and cooling kettle B is alternately transported to the centrifugal separator in sequence; the stirring speed of the cooling kettle is 50-200 rpm, and the cooling temperature is 0-10℃.

[0057] S3. After passing through the centrifuge, the wet material enters the screw conveyor for conveying and drying; the filtrate enters the filtrate tank for circulation, and is then recycled to reactor A or reactor B. The drying temperature of the screw conveyor is 200-250℃. The filtrate can be recycled to the filtrate tank and pumped into the reactor.

[0058] S4. After drying, the material enters a twin-screw reactor for high-temperature dehydration reaction; the twin-screw speed range is 50-300 r / min, the material dehydration temperature is 200-250℃, the twin-screw length-to-diameter ratio is 32, the effective length is 2200-3200 mm, and the material residence time is 5-30 min.

[0059] After the material enters the twin-screw reactor, it passes through the medium-lead threaded block, the small-lead threaded block, the 45° meshing block, the large-lead threaded block, the small-lead threaded block, the medium-lead threaded block, the small-lead threaded block, the medium-lead threaded block, and the small-lead threaded block in sequence to carry out a high-temperature dehydration reaction.

[0060] Inert gas is continuously introduced after the material enters the equipment requiring ventilation.

[0061] S5. After the reaction is complete, the product is cooled by a cooler, crushed by a crusher, and packaged by a packaging machine to obtain piperazine pyrophosphate.

[0062] Example 1 The method for continuous wet phosphoric acid preparation of piperazine pyrophosphate in this embodiment includes: S1. Add phosphoric acid to reactors A / B, turn on the stirrer, and add deionized water while stirring. Then add piperazine for acid-base neutralization. The molar ratio of phosphoric acid to piperazine is 2:1. The amount of deionized water added is 50 wt% of the total product mass. The reaction temperature is 85℃, the stirring speed is 400 rpm, and the reaction time is 2 hours. The concentration of phosphoric acid is 75%, and the concentration of piperazine is 68%.

[0063] S2. After the reaction is complete, the reactants in reactor A are pumped through a pipeline to a filter to remove the filter residue in the filtrate after neutralization. The clarified filtrate is then pumped through a pipeline to cooling reactor A. Similarly, the reactants in reactor B are pumped through a pipeline to a filter to remove the filter residue in the filtrate after neutralization. The clarified filtrate is then pumped through a pipeline to cooling reactor B. The filter residue is then centrally processed.

[0064] After the material cools and precipitates, the material in cooling kettle A and cooling kettle B is alternately transported to the centrifuge in sequence; the stirring speed of the cooling kettle is 100 rpm, the cooling temperature is 5℃ and the cooling time is 30 min, until the product crystallizes and precipitates.

[0065] S3. After passing through the centrifuge, the wet material enters the screw conveyor for conveying and drying; the filtrate enters the filtrate tank for circulation, and is then recycled to reactors A and B. The screw conveyor temperature is set at 150℃, the speed at 60 r / min, and the drying time at 30 min. The dried material product specifications are: phosphorus content 22.00%, nitrogen content 10.10%. The filtrate can be recycled to the filtrate tank and pumped into the reactors.

[0066] S4. After drying, the material enters a twin-screw reactor for high-temperature dehydration reaction; the twin-screw speed is 100 r / min, the material dehydration temperature is 230℃, the twin-screw length-to-diameter ratio is 32, the effective length is 2392 mm, and the material residence time is approximately 26 min.

[0067] After the material enters the twin-screw reactor, it passes through the medium-lead threaded block, the small-lead threaded block, the 45° meshing block, the large-lead threaded block, the medium-lead threaded block, the small-lead threaded block, the medium-lead threaded block, and the small-lead threaded block in sequence to carry out a high-temperature dehydration reaction.

[0068] S5. After the reaction is complete, the product is cooled by a cooler, crushed by a crusher, and packaged by a packaging machine to obtain piperazine pyrophosphate.

[0069] After the reaction is complete, the material enters the cooler, which is set at a temperature of 20°C. The cooler uses circulating water at the local room temperature. After the product is cooled, it is crushed and packaged to obtain the final product.

[0070] During the reaction, nitrogen gas is introduced into the screw conveyor, twin-screw reactor, and cooler to provide an inert atmosphere and prevent high-temperature oxidation of piperazine pyrophosphate. The inert gas is continuously introduced after the material enters the equipment requiring aeration.

[0071] The heating temperature of the reactor is 85℃, the heating temperature of the cooling vessel is 5℃, and the heating temperatures of the screw conveyor and the twin-screw reactor are 150℃ and 230℃, respectively; the cooling temperature of the cooler is 20℃.

[0072] The final product has the following specifications: phosphorus content of 23.26%, nitrogen content of 10.97%, 1% thermal decomposition temperature of 297.2℃, and particle size of 7.23µm after pulverization.

[0073] Example 2 The method for continuous wet phosphoric acid preparation of piperazine pyrophosphate in this embodiment includes: S1. Add phosphoric acid to reactors A / B, turn on the stirrer, and add deionized water while stirring. Then add piperazine for acid-base neutralization. The feed ratio of phosphoric acid to piperazine is 2.05:1. The amount of deionized water added is 40 wt% of the total product mass. The reaction temperature is 80℃, the stirring speed is 500 rpm, and the reaction time is 1 h. The phosphoric acid concentration is 75 wt%.

[0074] S2. After the reaction is complete, the reactants in reactor A are pumped through a pipeline to a filter to remove the filter residue in the filtrate after neutralization. The clarified filtrate is then pumped through a pipeline to cooling reactor A. Similarly, the reactants in reactor B are pumped through a pipeline to a filter to remove the filter residue in the filtrate after neutralization. The clarified filtrate is then pumped through a pipeline to cooling reactor B. The filter residue is then centrally processed.

[0075] After the material cools and precipitates, the material in cooling vessel A and cooling vessel B is alternately transported to the centrifuge in sequence; the stirring speed of the cooling vessel is 200 rpm, the cooling temperature is 10℃ and the cooling time is 50 min, until the product crystallizes and precipitates.

[0076] S3. After passing through the centrifuge, the wet material enters the screw conveyor for conveying and drying; the filtrate enters the filtrate tank for circulation, and the filtrate is recovered to reactor A and reactor B. The screw conveyor temperature is set at 180°C, the speed is set at 150 r / min, the drying time is set at 25 min, and the product indicators of the dried material are phosphorus content of 21.93% and nitrogen content of 10.16%.

[0077] S4. After drying, the material enters a twin-screw reactor for high-temperature dehydration reaction; the twin-screw speed is 150 r / min, the material dehydration temperature is 240℃, the twin-screw length-to-diameter ratio is 32, the effective length is 2392 mm, and the material residence time is about 18 min.

[0078] After the material enters the twin-screw reactor, it passes through the medium-lead threaded block, the small-lead threaded block, the 45° meshing block, the large-lead threaded block, the small-lead threaded block, the medium-lead threaded block, the small-lead threaded block, the medium-lead threaded block, and the small-lead threaded block in sequence to carry out a high-temperature dehydration reaction.

[0079] S5. After the reaction is complete, the product is cooled by a cooler, crushed by a crusher, and packaged by a packaging machine to obtain piperazine pyrophosphate.

[0080] After the reaction is complete, the material enters the cooler, which is set at 25°C. The cooler uses circulating water at the local room temperature (15-25°C). After the product is cooled, it is crushed and packaged to obtain the final product.

[0081] During the reaction, nitrogen gas is introduced into the screw conveyor, twin-screw reactor, and cooler to provide an inert atmosphere and prevent piperazine pyrophosphate from being oxidized at high temperatures.

[0082] The heating temperature of the reactor is 80℃, the heating temperature of the cooling vessel is 10℃, and the heating temperatures of the screw conveyor and the twin-screw reactor are 180℃ and 240℃, respectively; the cooling temperature of the cooler is 25℃.

[0083] The final product has the following specifications: phosphorus content of 23.29%, nitrogen content of 10.60%, 1% thermal decomposition temperature of 296.6℃, and particle size of 7.98µm.

[0084] Example 3 The method for continuous wet phosphoric acid preparation of piperazine pyrophosphate in this embodiment includes: S1. Add phosphoric acid to reactors A / B, turn on the stirrer, and add deionized water while stirring. Then add piperazine for acid-base neutralization. The molar ratio of phosphoric acid to piperazine is 2:0.95. The amount of deionized water added is 45 wt% of the total product mass. The reaction temperature is 75℃, the stirring speed is 250 rpm, and the reaction time is 3 hours. The phosphoric acid concentration is 75 wt%.

[0085] S2. After the reaction is complete, the reactants in reactor A are pumped through a pipeline to a filter to remove the filter residue in the filtrate after neutralization. The clarified filtrate is then pumped through a pipeline to cooling reactor A. Similarly, the reactants in reactor B are pumped through a pipeline to a filter to remove the filter residue in the filtrate after neutralization. The clarified filtrate is then pumped through a pipeline to cooling reactor B. The filter residue is then centrally processed.

[0086] After the material cools and precipitates, the materials in cooling kettle A and cooling kettle B are alternately transported to the centrifuge in sequence; the stirring speed of the cooling kettle is 50 rpm, the cooling temperature is 8℃ and the cooling time is 40 min, until the product crystallizes and precipitates.

[0087] S3. After passing through the centrifuge, the wet material enters the screw conveyor for conveying and drying; the filtrate enters the filtrate tank for circulation, and the filtrate is recovered to reactor A and reactor B. The screw conveyor temperature is set at 200℃, the speed is 60r / min, the drying time is about 20min, and the product indicators of the dried material are phosphorus content of 21.95% and nitrogen content of 9.98%.

[0088] S4. After drying, the material enters a twin-screw reactor for high-temperature dehydration reaction; the twin-screw speed is 200 r / min, the material dehydration temperature is 250℃, the twin-screw length-to-diameter ratio is 32, the effective length is 2500 mm, and the material residence time is 10 min.

[0089] After the material enters the twin-screw reactor, it passes through the medium-lead threaded block, the small-lead threaded block, the 45° meshing block, the large-lead threaded block, the small-lead threaded block, the medium-lead threaded block, the small-lead threaded block, the medium-lead threaded block, and the small-lead threaded block in sequence to carry out a high-temperature dehydration reaction.

[0090] S5. After the reaction is complete, the product is cooled by a cooler, crushed by a crusher, and packaged by a packaging machine to obtain piperazine pyrophosphate.

[0091] After the reaction is complete, the material enters the cooler, which is set at 15°C. The cooler uses circulating water at the local room temperature (15-25°C). After the product is cooled, it is crushed and packaged to obtain the final product.

[0092] During the reaction, nitrogen gas is introduced into the screw conveyor, twin-screw reactor, and cooler to provide an inert atmosphere and prevent piperazine pyrophosphate from being oxidized at high temperatures.

[0093] The heating temperature of the reactor is 75℃, the heating temperature of the cooling vessel is 8℃, and the heating temperatures of the screw conveyor and the twin-screw reactor are 200℃ and 250℃, respectively; the cooling temperature of the cooler is 15℃.

[0094] The final product has the following specifications: phosphorus content of 23.38%, nitrogen content of 10.30%, 1% thermal decomposition temperature of 297.1℃, and particle size of 7.52µm.

[0095] Comparative Example 1 The comparative method for the continuous wet phosphoric acid preparation of piperazine pyrophosphate differs from that in Example 1 in that: in S4, the material dehydration temperature is 210°C and the heating temperature of the twin-screw reactor is 210°C.

[0096] The final product has the following specifications: phosphorus content of 22.41%, nitrogen content of 10.16%, thermal decomposition temperature of 260.8℃, and particle size of 7.69µm after pulverization.

[0097] The product specifications of piperazine pyrophosphate in the examples and comparative examples are shown in Table 1 below: Table 1 Comparison of product indicators for piperazine pyrophosphate in the examples and comparative examples It is evident that if the temperature parameters of the twin-screw reactor are insufficient, the dehydration reaction will not proceed completely, and the resulting product will fail to meet the required standards.

[0098] Generally, the water solubility of piperazine pyrophosphate is less than or equal to 1.5 g / 100 ml H2O, while the water solubility of the intermediate product piperazine diphosphate is greater than 10 g / 100 ml H2O. This can be used to determine whether the product is completely dehydrated. It can be concluded that the product in Comparative Example 1 was not completely dehydrated into piperazine pyrophosphate, but was a mixture of the intermediate product piperazine diphosphate and piperazine pyrophosphate.

[0099] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for continuous wet phosphoric acid preparation of piperazine pyrophosphate, characterized in that: Includes the following steps: Step S1: Add phosphoric acid to at least one reaction vessel, add deionized water while stirring, and then add piperazine to carry out acid-base neutralization reaction; Step S2: After the reaction is completed, the reactants from one of the reactors are transferred to a filter to remove the filter residue in the filtrate after the neutralization reaction. The clarified filtrate is then transferred to one of the cooling reactors, and the filter residue is centrally processed. The reactants from the next reactor are then transferred to a filter, and after filtration, the clarified filtrate is transferred to another cooling reactor. Step S3: After the material in the cooling kettle cools and crystallizes, the material in the cooling kettle is sequentially transferred to the centrifugal separator. Step S4: After the material is separated by the centrifugal separator, the wet material enters the screw conveyor for conveying and drying; the filtrate enters the filtrate tank for recycling. Step S5: After drying, the material enters a twin-screw reactor for high-temperature dehydration reaction; Step S6: After the reaction is complete, the product is obtained by cooling, pulverizing, and packaging.

2. The method according to claim 1, characterized in that: In step S1, the phosphoric acid concentration is 40-85%; the phosphoric acid to piperazine molar ratio is 2-2.10:0.95-1.10; the amount of deionized water added is 30-50 wt% of the total product mass; the reaction temperature is 75-90℃, the stirring rate is 200-500 rpm, and the reaction time is 0.5-3 h.

3. The method according to claim 1, characterized in that: In step S3, the stirring rate of the cooling vessel is 50-200 rpm, the cooling temperature is 0-10℃, and the cooling time is 20-60 min.

4. The method according to claim 1, characterized in that: In step S4, the mesh size of the filter screen in the centrifugal filter is 100-200 mesh; after centrifugation, the wet material enters the screw conveyor, and the filtrate is recovered to the reaction vessel; the drying temperature of the screw conveyor is 150-200℃, the rotation speed is 60rpm-200rpm, and the drying time is 10min-30min.

5. The method according to claim 1, characterized in that: In step S5, the twin-screw reactor speed is 50-300 r / min, the material dehydration temperature is 230-250℃, the twin-screw length-to-diameter ratio is at least 32, the effective length is 2200-3200 mm, and the material residence time is 5-30 min. After the material enters the twin-screw reactor, it passes through the medium-lead threaded block, the small-lead threaded block, the 45° meshing block, the large-lead threaded block, the small-lead threaded block, the medium-lead threaded block, the small-lead threaded block, the medium-lead threaded block, and the small-lead threaded block in sequence.

6. The method according to claim 1, characterized in that: In step S6, the cooling temperature of the cooler is 10-30℃, and the particle size D50 after pulverization is 5-15μm.

7. An apparatus for the continuous wet phosphoric acid preparation of piperazine pyrophosphate, characterized in that: It includes at least one reaction vessel and at least one cooling vessel; at least one reaction vessel is connected to the filter inlet, the filter clarified liquid outlet is connected to at least one cooling vessel, and at least one cooling vessel is connected to a centrifuge. The centrifuge filtrate outlet is connected to the filtrate tank, and the filtrate tank is connected to at least one reactor inlet. The discharge and inlet ports of the centrifugal separator, screw conveyor, twin-screw reactor, cooler, crusher, and packaging machine are connected in sequence.

8. The apparatus according to claim 7, characterized in that: At least one pipeline from the reactor to the filter and from the filter to at least one cooling vessel is equipped with an insulation layer, and the filter is insulated.

9. The apparatus according to claim 7, characterized in that: The heating temperature of the reactor is 0-100℃, the heating temperature of the cooling vessel is -10-30℃, the heating temperature of the screw conveyor and twin-screw reactor is 0-300℃, and the cooling temperature of the cooler is 10-30℃.

10. The apparatus according to claim 7, characterized in that: In a twin-screw reactor, a large-lead threaded block is installed at the feed inlet, and along the material movement direction, the sequence is: medium-lead threaded block, small-lead threaded block, 45° meshing block, large-lead threaded block, small-lead threaded block, medium-lead threaded block, small-lead threaded block, medium-lead threaded block, and small-lead threaded block.

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