Continuous production process of dialkyl phosphinate

Abstract

The invention discloses a continuous production process of dialkyl phosphinate, and belongs to the technical field of flame retardants, the continuous production process adopts a microreactor system, and the microreactor system comprises a first-stage microreactor, a second-stage microreactor and a third-stage microreactor which are sequentially connected in series; the continuous production process comprises the following steps: free radical addition and double decomposition; according to the continuous production process, continuous production can be achieved, corrosion to equipment is reduced, the reaction rate is high, the reaction time is short, and the prepared dialkyl phosphinate is high in thermal stability.

Description

Technical Field

[0001] The invention relates to the technical field of flame retardants, and in particular to a continuous production process of dialkyl phosphinate. Background Art

[0002] Dialkyl phosphinate is a halogen-free organic flame retardant with the advantages of low bulk density, small dosage and low smoke density. It is widely used in plastics such as polyamide, polyester, epoxy resin, polyurethane, etc. Due to its high decomposition temperature, it is especially suitable for engineering plastics with high temperature resistance requirements. Moreover, dialkyl phosphinate has good synergistic flame retardant effect with nitrogen flame retardants and various inorganic flame retardants.

[0003] As people pay more and more attention to fire safety, many countries and regions have introduced strict fire safety standards and regulations, resulting in an increasing demand for flame retardant materials. Considering the increasing awareness of environmental protection, as a relatively environmentally friendly flame retardant material, the market demand for dialkyl phosphinates is increasing.

[0004] At present, the commonly used dialkyl phosphinate flame retardants are mainly dialkyl phosphinate aluminum flame retardants and dialkyl phosphinate zinc flame retardants. When preparing dialkyl phosphinate aluminum flame retardants or dialkyl phosphinate zinc flame retardants, the commonly used preparation method is the free radical addition method, specifically, hypophosphorous acid or an alkali metal salt of hypophosphorous acid is used as a raw material, reacted with an olefin under the catalysis of a free radical initiator to generate dialkyl phosphinate or an alkali metal salt of dialkyl hypophosphorous acid, and then reacted with an aluminum salt or a zinc salt to generate a dialkyl phosphinate.

[0005] Chinese patent CN1284787C discloses a method for preparing a salt of dialkylphosphinic acid, which comprises reacting alkylphosphinic acid and / or hypophosphorous acid and / or an alkali metal salt thereof with an olefin in the presence of a free radical initiator to generate dialkylphosphinic acid and / or an alkali metal salt thereof, and then reacting with a metal compound of magnesium, calcium, aluminum, antimony, tin, germanium, titanium, zinc, iron, zirconium, cerium, bismuth, strontium, manganese, lithium, sodium and / or potassium to generate a dialkylphosphinic acid salt of the metal. The method needs to be carried out under acidic conditions, has a long reaction time and a low yield.

[0006] Chinese patent CN103951699B discloses a method for rapidly synthesizing diethyl hypophosphite at low pressure, and its products and applications. First, a soluble hypophosphite is mixed with water to obtain a soluble hypophosphite aqueous solution with a concentration of 10-15wt%; the soluble hypophosphite is selected from at least one of sodium hypophosphite, potassium hypophosphite, and ammonium hypophosphite; then butanol is added to the soluble hypophosphite aqueous solution, and after adjusting the pH value to 2-3, a water-soluble initiator is added, and ethylene is continuously introduced, and the reaction is carried out at 90-110°C and 0.1-0.5MPa for 1-3h to obtain diethyl hypophosphite; the butanol is selected from at least one of n-butanol, isobutanol, sec-butanol, and tert-butanol; the mass ratio of the butanol to the soluble hypophosphite aqueous solution is 1.5-5:100. This method needs to be carried out under acidic conditions, and the reaction time is long and the yield is low.

[0007] In summary, the above-mentioned preparation methods of dialkyl phosphinates all need to be carried out under acidic conditions, the reaction safety is poor, and they are also corrosive to the equipment to a certain extent. In addition, the reaction rate is slow, resulting in a long reaction time. As the reaction time increases, the selectivity and activity of the initiator used decrease, resulting in an increase in side reactions, an increase in the content of by-products in the prepared dialkyl phosphinates, and further resulting in a decrease in the thermal stability of the prepared dialkyl phosphinates. In addition, the above-mentioned methods are all intermittent kettle reactions, and the reaction continuity is poor. Summary of the invention

[0008] In view of the shortcomings of the prior art, the present invention provides a continuous production process of dialkyl phosphinates, which can realize continuous production while reducing the corrosiveness to equipment, has a fast reaction rate, a short reaction time, and the prepared dialkyl phosphinates have high thermal stability.

[0009] In order to solve the above technical problems, the technical solution adopted by the present invention is as follows: A continuous production process of dialkyl phosphinate, using a microreactor system, the microreactor system comprising a first-stage microreactor, a second-stage microreactor, and a third-stage microreactor connected in series; The first-stage microreactor has an inner diameter of 5 mm and a length of 1 m; The inner diameter of the second-stage microreactor is 8 mm and the length is 12 m; The inner diameter of the third-stage microreactor is 8 mm and the length is 12 m; A continuous production process of dialkyl phosphinate, comprising: free radical addition, double decomposition; The free radical addition is carried out, after the air tightness of the microreactor system is checked, the air in the microreactor system is replaced with nitrogen, the temperature of the first-stage microreactor is controlled to 80-90°C, the temperature of the second-stage microreactor is controlled to 90-95°C, the temperature of the third-stage microreactor is controlled to 95-110°C, the raw material mixed solution and the first oxidation solution are simultaneously introduced into the first-stage microreactor, ethylene gas is introduced into the first-stage microreactor until the gauge pressure is 0.5-0.6MPa, and the feed liquid enters the second-stage microreactor. Ethylene gas is introduced into the reactor until the gauge pressure reaches 0.5-0.6 MPa, and when the feed liquid enters the third-stage microreactor, ethylene gas is introduced into the third-stage microreactor until the gauge pressure reaches 0.5-0.6 MPa, and the reducing liquid and the second oxidizing liquid are simultaneously introduced into the third-stage microreactor, and 9-10 minutes after the material flows out of the third-stage microreactor, the free radical addition product is collected from the outlet of the third-stage microreactor; the free radical addition product is allowed to stand at room temperature to separate layers, the water layer is taken, centrifuged, and the supernatant is taken to obtain a sodium dialkylphosphinate solution; In the free radical addition, the flow rate of the raw material mixture is 200-220 mL / min, the flow rate of the first oxidizing liquid is 105-115 mL / min, the flow rate of the reducing liquid is 50-53 mL / min, and the flow rate of the second oxidizing liquid is 50-53 mL / min; The centrifugal speed during the centrifugation is 5000-6000 rpm, and the time is 10-15 min; The preparation method of the raw material mixed solution is as follows: sodium hypophosphite monohydrate and deionized water are added into a reaction kettle, stirred at a stirring speed of 30-60 rpm for 15-30 minutes at room temperature, cyclohexane, tetrabutylammonium bromide, sodium bisulfite and modified activated carbon are added, and stirred for 30-40 minutes to obtain the raw material mixed solution; In the preparation of the raw material mixture, the dosage ratio of sodium hypophosphite monohydrate, deionized water, cyclohexane, tetrabutylammonium bromide, sodium bisulfite and modified activated carbon is 290-300g:1000-1200mL:2700-3000mL:5-5.3g:7.2-7.5g:10-10.4g.

[0010] The method for preparing the modified activated carbon comprises: preparing water-soluble activated carbon, adsorbing; The water-soluble activated carbon is prepared by mixing activated carbon, citric acid, polyvinyl alcohol and glacial acetic acid and then ball milling. After the ball milling, the mixture is stirred at 120-130° C. and a stirring speed of 20-60 rpm for 3.5-4 hours, the temperature is naturally lowered to room temperature, the stirring speed is increased to 100-150 rpm, deionized water is added, stirred for 30-40 minutes, centrifuged, a precipitate is collected, and vacuum dried to obtain water-soluble activated carbon; In the preparation of water-soluble activated carbon, the particle size of the activated carbon is 300 mesh; The model of the polyvinyl alcohol is polyvinyl alcohol 1788; The dosage ratio of activated carbon, citric acid, polyvinyl alcohol, glacial acetic acid and deionized water is 10-11g:110-130g:25-30g:40-42mL:1200-1300mL; The ball-to-material ratio during the ball milling is 4-5:1, the rotation speed is 300-400rpm, and the time is 30-40min; The centrifugal speed during the centrifugation is 5000-6000 rpm, and the time is 10-15 min; The adsorption comprises mixing tetrabutylammonium bromide and deionized water, stirring at room temperature at a stirring speed of 20-60 rpm for 20-30 min, adding water-soluble activated carbon, stirring for 3-3.5 h, centrifuging, taking a precipitate, and vacuum drying to obtain modified activated carbon; In the adsorption, the usage ratio of tetrabutylammonium bromide, deionized water and water-soluble activated carbon is 34-36g:1000-1100mL:12-13g.

[0011] The centrifugal speed during the centrifugation is 5000-6000 rpm, and the time is 10-15 min; The first oxidation liquid is prepared by mixing sodium persulfate and deionized water, and stirring at room temperature at a stirring speed of 20-60 rpm for 15-30 minutes to obtain the first oxidation liquid; In the preparation of the first oxidizing solution, the dosage ratio of sodium persulfate to deionized water is 7-7.3 g: 2000-2100 mL.

[0012] The preparation method of the reducing solution is as follows: sodium bisulfite and deionized water are added into a reaction kettle, and stirred at a stirring speed of 20-60 rpm for 15-30 minutes at room temperature to obtain the reducing solution; In the preparation of the reducing solution, the dosage ratio of sodium bisulfite to deionized water is 7-7.4 g:1000-1200 mL.

[0013] The second oxidation liquid is prepared by mixing sodium persulfate and deionized water, and stirring at room temperature at a stirring speed of 20-60 rpm for 15-30 minutes to obtain the second oxidation liquid; In the preparation of the second oxidizing solution, the dosage ratio of sodium persulfate to deionized water is 7-7.3 g:1000-1100 mL.

[0014] The double decomposition comprises adding a metal salt to a sodium dialkyl phosphinate solution, stirring at room temperature at a stirring speed of 100-150 rpm for 50-60 min, filtering, taking a precipitate, and vacuum drying to obtain a dialkyl phosphinate; The dialkyl phosphinate is one of dialkyl aluminum phosphinate or dialkyl zinc phosphinate.

[0015] The metal ion in the metal salt is one of aluminum ion or zinc ion, and the anion is one of sulfate ion, chloride ion and nitrate ion; When the dialkyl phosphinate is aluminum dialkyl phosphinate, the molar ratio of the sodium dialkyl phosphinate in the sodium dialkyl phosphinate solution to the metal ion in the metal salt is 3:1.2-1.3; When the dialkyl phosphinate is zinc dialkyl phosphinate, the molar ratio of the sodium dialkyl phosphinate in the sodium dialkyl phosphinate solution to the metal ion in the metal salt is 2:1.2-1.3.

[0016] Compared with the prior art, the present invention has the following beneficial effects: (1) The continuous production process of dialkyl phosphinate of the present invention adopts a microreactor system in free radical addition, wherein the microreactor system comprises a first-stage microreactor, a second-stage microreactor, and a third-stage microreactor connected in series in sequence, thereby realizing continuous production; (2) The continuous production process of dialkyl phosphinate of the present invention uses modified activated carbon in the preparation of the raw material mixture in free radical addition. The preparation method of the modified activated carbon includes preparing water-soluble activated carbon and adsorption. The water-soluble activated carbon is prepared by mixing activated carbon, citric acid, polyvinyl alcohol and glacial acetic acid and then ball milling to promote sufficient mixing of the activated carbon, citric acid, polyvinyl alcohol and glacial acetic acid. The citric acid, polyvinyl alcohol and glacial acetic acid are adsorbed on the surface of the activated carbon, and then heated to 120-130°C. The citric acid and polyvinyl alcohol are subjected to an esterification reaction at 120-130°C. The glacial acetic acid is used as a catalyst to promote the esterification reaction, thereby fixing the citric acid and polyvinyl alcohol on the surface of the activated carbon, thereby improving the water solubility of the activated carbon, and obtaining water-soluble activated carbon. The adsorption is treated with an aqueous solution of tetrabutylammonium bromide to adsorb tetrabutylammonium bromide on the surface of the water-soluble activated carbon to obtain to modified activated carbon; in free radical addition, the role of modified activated carbon is as follows: first, the modified activated carbon can increase the contact area of ​​the reactants and promote the free radical addition; second, the tetrabutylammonium bromide on the surface of the modified activated carbon can catalyze the reaction between the surface reactants and promote the free radical addition; third, since the redox initiation system composed of sodium persulfate and sodium bisulfite is used in the free radical addition of the present invention, while the sodium persulfate and sodium bisulfite react to produce free radicals, sulfur-containing gas may be produced, which affects the color of the product, and the modified activated carbon can adsorb the produced sulfur-containing gas to avoid affecting the color of the product; in addition, in the free radical addition, the reducing liquid and the second oxidizing liquid are introduced into the third-stage microreactor, thereby promoting the free radical addition, thereby increasing the molar percentage of sodium dialkyl phosphinate in the phosphorus-containing compound in the sodium dialkyl phosphinate solution obtained in the free radical addition; (3) The continuous production process of dialkyl phosphinate of the present invention promotes the generation of free radicals by using a redox initiation system consisting of water-soluble activated carbon, sodium persulfate and sodium bisulfite in the free radical reaction, thereby avoiding the problem that free radicals can only be generated in an acidic environment when only sodium persulfate is used for initiation, thereby reducing the corrosiveness to the equipment; (4) The continuous production process of dialkyl phosphinate of the present invention has a fast reaction rate and a short reaction time. In the free radical addition, the molar percentage of sodium dialkyl phosphinate in the phosphorus-containing compound in the obtained sodium dialkyl phosphinate solution is 98.0-98.5%; (5) The continuous production process of dialkyl phosphinate of the present invention has high thermal stability. In the double decomposition, the 1% thermal decomposition temperature of the obtained dialkyl phosphinate is 381-395°C and the appearance is white powder. DETAILED DESCRIPTION

[0017] In order to have a clearer understanding of the technical features, purposes and effects of the present invention, the specific implementation methods of the present invention are now described.

[0018] Example 1 A continuous production process of dialkyl phosphinate, using a microreactor system, the microreactor system comprising a first-stage microreactor, a second-stage microreactor, and a third-stage microreactor connected in series; The first-stage microreactor has an inner diameter of 5 mm and a length of 1 m; The inner diameter of the second-stage microreactor is 8 mm and the length is 12 m; The inner diameter of the third-stage microreactor is 8 mm and the length is 12 m; A continuous production process of dialkyl phosphinate is as follows: 1. Free radical addition: After checking the air tightness of the microreactor system, use nitrogen to replace the air in the microreactor system, control the temperature of the first-stage microreactor to 80°C, the temperature of the second-stage microreactor to 90°C, and the temperature of the third-stage microreactor to 95°C, and introduce the raw material mixed liquid and the first oxidation liquid into the first-stage microreactor at the same time, control the flow rate of the raw material mixed liquid to 200mL / min, and the flow rate of the first oxidation liquid to 105mL / min, and introduce ethylene gas into the first-stage microreactor until the gauge pressure is 0.5MPa. When the feed liquid enters the second-stage microreactor, introduce ethylene into the second-stage microreactor. The gas is added to the third-stage microreactor until the gauge pressure is 0.5 MPa, and when the feed liquid enters the third-stage microreactor, ethylene gas is introduced into the third-stage microreactor until the gauge pressure is 0.5 MPa, and the reducing liquid and the second oxidizing liquid are simultaneously introduced into the third-stage microreactor, and the flow rate of the reducing liquid is controlled to be 50 mL / min, and the flow rate of the second oxidizing liquid is 50 mL / min. After the material flows out of the third-stage microreactor, the free radical addition product is collected from the outlet of the third-stage microreactor 9 minutes later; the free radical addition product is allowed to stand at room temperature for stratification, the water layer is taken, and the centrifugal speed is 5000 rpm for 10 minutes, and the supernatant is taken to obtain a sodium dialkyl phosphinate solution; The preparation method of the raw material mixed solution is as follows: sodium hypophosphite monohydrate and deionized water are added into a reaction kettle, stirred at a stirring speed of 30 rpm for 15 minutes at room temperature, cyclohexane, tetrabutylammonium bromide, sodium bisulfite and modified activated carbon are added, and stirred for 30 minutes to obtain a raw material mixed solution; In the preparation of the raw material mixture, the dosage ratio of sodium hypophosphite monohydrate, deionized water, cyclohexane, tetrabutylammonium bromide, sodium bisulfite and modified activated carbon is 290g:1000mL:2700mL:5g:7.2g:10g.

[0019] The method for preparing the modified activated carbon comprises: preparing water-soluble activated carbon, adsorbing; The water-soluble activated carbon is prepared by mixing activated carbon, citric acid, polyvinyl alcohol and glacial acetic acid and then ball milling. The ball-to-material ratio during ball milling is controlled to be 4:1, the rotation speed is 300 rpm, and the time is 30 min. After the ball milling is completed, the mixture is stirred at a stirring speed of 20 rpm for 3.5 h at 120° C., the temperature is naturally lowered to room temperature, the stirring speed is increased to 100 rpm, deionized water is added, stirred for 30 min, and centrifuged at a centrifugal speed of 5000 rpm for 10 min. The precipitate is taken and vacuum dried to obtain the water-soluble activated carbon. In the preparation of water-soluble activated carbon, the particle size of the activated carbon is 300 mesh; The model of the polyvinyl alcohol is polyvinyl alcohol 1788; The dosage ratio of activated carbon, citric acid, polyvinyl alcohol, glacial acetic acid, and deionized water is 10 g:110 g:25 g:40 mL:1200 mL; The adsorption is carried out by mixing tetrabutylammonium bromide and deionized water, stirring at a stirring speed of 20 rpm for 20 min at room temperature, adding water-soluble activated carbon, stirring for 3 h, centrifuging at a centrifugal speed of 5000 rpm for 10 min, taking a precipitate, and vacuum drying to obtain modified activated carbon; In the adsorption, the usage ratio of tetrabutylammonium bromide, deionized water and water-soluble activated carbon is 34g:1000mL:12g.

[0020] The first oxidation liquid is prepared by mixing sodium persulfate and deionized water, and stirring at room temperature at a stirring speed of 20 rpm for 15 minutes to obtain a first oxidation liquid; In the preparation of the first oxidizing solution, the dosage ratio of sodium persulfate to deionized water is 7g:2000mL.

[0021] The preparation method of the reducing solution is as follows: sodium bisulfite and deionized water are added into a reaction kettle, and stirred at room temperature at a stirring speed of 20 rpm for 15 minutes to obtain the reducing solution; In the preparation of the reducing solution, the dosage ratio of sodium bisulfite to deionized water is 7g:1000mL.

[0022] The second oxidation liquid is prepared by mixing sodium persulfate and deionized water, and stirring at room temperature at a stirring speed of 20 rpm for 15 minutes to obtain the second oxidation liquid; In the preparation of the second oxidizing solution, the dosage ratio of sodium persulfate to deionized water is 7g:1000mL.

[0023] The content of sodium hypophosphite in the sodium dialkylphosphinate solution is 0, indicating that the conversion rate of sodium hypophosphite is 100%.

[0024] The molar percentage of sodium dialkyl phosphinate in the phosphorus-containing compound in the sodium dialkyl phosphinate solution is 98.3%; 2. Double decomposition: add metal salt to the sodium dialkyl phosphinate solution obtained in step 1, stir at room temperature at a stirring speed of 100 rpm for 50 min, filter, take the precipitate, and vacuum dry to obtain dialkyl phosphinate; The dialkyl phosphinate is aluminum dialkyl phosphinate; The metal salt is aluminum sulfate; The molar ratio of the sodium dialkyl phosphinate in the sodium dialkyl phosphinate solution to the aluminum ions in the aluminum sulfate is 3:1.2.

[0025] The 1% thermal decomposition temperature of the dialkyl aluminum phosphinate obtained in this example is 387° C., and the appearance is white powder.

[0026] Example 2 A continuous production process of dialkyl phosphinate, using a microreactor system, the microreactor system comprising a first-stage microreactor, a second-stage microreactor, and a third-stage microreactor connected in series; The first-stage microreactor has an inner diameter of 5 mm and a length of 1 m; The inner diameter of the second-stage microreactor is 8 mm and the length is 12 m; The inner diameter of the third-stage microreactor is 8 mm and the length is 12 m; A continuous production process of dialkyl phosphinate is as follows: 1. Free radical addition: After checking the air tightness of the microreactor system, use nitrogen to replace the air in the microreactor system, control the temperature of the first-stage microreactor to 85°C, the temperature of the second-stage microreactor to 92°C, and the temperature of the third-stage microreactor to 100°C, and introduce the raw material mixed liquid and the first oxidation liquid into the first-stage microreactor at the same time, control the flow rate of the raw material mixed liquid to 210mL / min, and the flow rate of the first oxidation liquid to 110mL / min, and introduce ethylene gas into the first-stage microreactor until the gauge pressure is 0.55MPa, wait for the feed liquid to enter the second-stage microreactor, and introduce ethylene into the second-stage microreactor. The gas is added to the third-stage microreactor until the gauge pressure is 0.55 MPa, and when the feed liquid enters the third-stage microreactor, ethylene gas is introduced into the third-stage microreactor until the gauge pressure is 0.55 MPa, and the reducing liquid and the second oxidizing liquid are simultaneously introduced into the third-stage microreactor, and the flow rate of the reducing liquid is controlled to be 52 mL / min, and the flow rate of the second oxidizing liquid is 52 mL / min. After the material flows out of the third-stage microreactor, the free radical addition product is collected from the outlet of the third-stage microreactor 9 minutes later; the free radical addition product is allowed to stand at room temperature to separate layers, the water layer is taken, and the centrifugal speed is 5500 rpm for 12 minutes, and the supernatant is taken to obtain a sodium dialkylphosphinate solution; The preparation method of the raw material mixed solution is as follows: sodium hypophosphite monohydrate and deionized water are added into a reaction kettle, stirred at a stirring speed of 40 rpm for 20 minutes at room temperature, cyclohexane, tetrabutylammonium bromide, sodium bisulfite and modified activated carbon are added, and stirred for 35 minutes to obtain a raw material mixed solution; In the preparation of the raw material mixture, the dosage ratio of sodium hypophosphite monohydrate, deionized water, cyclohexane, tetrabutylammonium bromide, sodium bisulfite and modified activated carbon is 295g:1100mL:2800mL:5.2g:7.4g:10.2g.

[0027] The method for preparing the modified activated carbon comprises: preparing water-soluble activated carbon, adsorbing; The water-soluble activated carbon is prepared by mixing activated carbon, citric acid, polyvinyl alcohol and glacial acetic acid and then ball milling. The ball-to-material ratio during ball milling is controlled to be 5:1, the rotation speed is 350 rpm, and the time is 35 minutes. After the ball milling is completed, the mixture is stirred at a stirring speed of 40 rpm for 3.5 hours at 125° C., the temperature is naturally lowered to room temperature, the stirring speed is increased to 120 rpm, deionized water is added, stirred for 35 minutes, and centrifuged at a centrifugal speed of 5500 rpm for 12 minutes. The precipitate is taken and vacuum dried to obtain the water-soluble activated carbon; In the preparation of water-soluble activated carbon, the particle size of the activated carbon is 300 mesh; The model of the polyvinyl alcohol is polyvinyl alcohol 1788; The dosage ratio of activated carbon, citric acid, polyvinyl alcohol, glacial acetic acid, and deionized water is 10.5 g:120 g:28 g:41 mL:1250 mL; The adsorption is carried out by mixing tetrabutylammonium bromide and deionized water, stirring at a stirring speed of 40 rpm for 25 minutes at room temperature, adding water-soluble activated carbon, stirring for 3 hours, centrifuging at a centrifugal speed of 5500 rpm for 12 minutes, taking the precipitate, and vacuum drying to obtain modified activated carbon; In the adsorption, the usage ratio of tetrabutylammonium bromide, deionized water and water-soluble activated carbon is 35g:1050mL:12.5g.

[0028] The first oxidation liquid is prepared by mixing sodium persulfate and deionized water, and stirring at room temperature at a stirring speed of 40 rpm for 20 minutes to obtain a first oxidation liquid; In the preparation of the first oxidizing solution, the dosage ratio of sodium persulfate to deionized water is 7.2 g:2050 mL.

[0029] The preparation method of the reducing solution is as follows: sodium bisulfite and deionized water are added into a reaction kettle, and stirred at a stirring speed of 40 rpm for 20 minutes at room temperature to obtain the reducing solution; In the preparation of the reducing solution, the dosage ratio of sodium bisulfite to deionized water is 7.2 g:1100 mL.

[0030] The second oxidation liquid is prepared by mixing sodium persulfate and deionized water, and stirring at room temperature at a stirring speed of 40 rpm for 20 minutes to obtain the second oxidation liquid; In the preparation of the second oxidizing solution, the dosage ratio of sodium persulfate to deionized water is 7.2 g:1050 mL.

[0031] The content of sodium hypophosphite in the sodium dialkylphosphinate solution is 0, indicating that the conversion rate of sodium hypophosphite is 100%.

[0032] The molar percentage of sodium dialkyl phosphinate in the phosphorus-containing compound in the sodium dialkyl phosphinate solution is 98.5%; 2. Double decomposition: add metal salt to the sodium dialkyl phosphinate solution obtained in step 1, stir at room temperature at a stirring speed of 120 rpm for 55 min, filter, take the precipitate, and vacuum dry to obtain dialkyl phosphinate; The dialkyl phosphinate is aluminum dialkyl phosphinate.

[0033] The metal salt is aluminum chloride; The molar ratio of the sodium dialkyl phosphinate in the sodium dialkyl phosphinate solution to the aluminum ions in the aluminum chloride is 3:1.2.

[0034] The 1% thermal decomposition temperature of the dialkyl aluminum phosphinate obtained in this example is 395° C., and the appearance is white powder.

[0035] Example 3 A continuous production process of dialkyl phosphinate, using a microreactor system, the microreactor system comprising a first-stage microreactor, a second-stage microreactor, and a third-stage microreactor connected in series; The first-stage microreactor has an inner diameter of 5 mm and a length of 1 m; The inner diameter of the second-stage microreactor is 8 mm and the length is 12 m; The inner diameter of the third-stage microreactor is 8 mm and the length is 12 m; A continuous production process of dialkyl phosphinate is as follows: 1. Free radical addition: After checking the air tightness of the microreactor system, use nitrogen to replace the air in the microreactor system, control the temperature of the first-stage microreactor to 90°C, the temperature of the second-stage microreactor to 95°C, and the temperature of the third-stage microreactor to 110°C. The raw material mixed liquid and the first oxidation liquid are simultaneously introduced into the first-stage microreactor, and the flow rate of the raw material mixed liquid is controlled to be 220mL / min, and the flow rate of the first oxidation liquid is controlled to be 115mL / min. Ethylene gas is introduced into the first-stage microreactor until the gauge pressure reaches 0.6MPa. When the feed liquid enters the second-stage microreactor, ethylene is introduced into the second-stage microreactor. The gas is added to the third-stage microreactor until the gauge pressure is 0.6 MPa, and when the feed liquid enters the third-stage microreactor, ethylene gas is introduced into the third-stage microreactor until the gauge pressure is 0.6 MPa, and the reducing liquid and the second oxidizing liquid are simultaneously introduced into the third-stage microreactor, and the flow rate of the reducing liquid is controlled to be 53 mL / min, and the flow rate of the second oxidizing liquid is 53 mL / min. After the material flows out of the third-stage microreactor, the free radical addition product is collected from the outlet of the third-stage microreactor 10 minutes later; the free radical addition product is allowed to stand at room temperature for stratification, the water layer is taken, and the centrifugal speed is 6000 rpm for 15 minutes, and the supernatant is taken to obtain a sodium dialkyl phosphinate solution; The preparation method of the raw material mixed solution is as follows: sodium hypophosphite monohydrate and deionized water are added into a reaction kettle, stirred at a stirring speed of 60 rpm for 30 minutes at room temperature, cyclohexane, tetrabutylammonium bromide, sodium bisulfite and modified activated carbon are added, and stirred for 40 minutes to obtain a raw material mixed solution; In the preparation of the raw material mixture, the dosage ratio of sodium hypophosphite monohydrate, deionized water, cyclohexane, tetrabutylammonium bromide, sodium bisulfite and modified activated carbon is 300g:1200mL:3000mL:5.3g:7.5g:10.4g.

[0036] The method for preparing the modified activated carbon comprises: preparing water-soluble activated carbon, adsorbing; The water-soluble activated carbon is prepared by mixing activated carbon, citric acid, polyvinyl alcohol and glacial acetic acid and then ball milling. The ball-to-material ratio during ball milling is controlled to be 5:1, the rotation speed is 400 rpm, and the time is 40 min. After the ball milling is completed, the mixture is stirred at a stirring speed of 60 rpm for 4 h at 130° C., the temperature is naturally lowered to room temperature, the stirring speed is increased to 150 rpm, deionized water is added, stirred for 40 min, and centrifuged at a centrifugal speed of 6000 rpm for 15 min. The precipitate is taken and vacuum dried to obtain the water-soluble activated carbon. In the preparation of water-soluble activated carbon, the particle size of the activated carbon is 300 mesh; The model of the polyvinyl alcohol is polyvinyl alcohol 1788; The dosage ratio of activated carbon, citric acid, polyvinyl alcohol, glacial acetic acid, and deionized water is 11 g:130 g:30 g:42 mL:1300 mL; The adsorption was carried out by mixing tetrabutylammonium bromide and deionized water, stirring at a stirring speed of 60 rpm for 30 min at room temperature, adding water-soluble activated carbon, stirring for 3.5 h, centrifuging at a centrifugal speed of 6000 rpm for 15 min, taking the precipitate, and vacuum drying to obtain modified activated carbon; In the adsorption, the usage ratio of tetrabutylammonium bromide, deionized water and water-soluble activated carbon is 36g:1100mL:13g.

[0037] The first oxidation liquid is prepared by mixing sodium persulfate and deionized water, and stirring at room temperature at a stirring speed of 60 rpm for 30 minutes to obtain a first oxidation liquid; In the preparation of the first oxidizing solution, the dosage ratio of sodium persulfate to deionized water is 7.3 g:2100 mL.

[0038] The preparation method of the reducing solution is as follows: sodium bisulfite and deionized water are added into a reaction kettle, and stirred at room temperature at a stirring speed of 60 rpm for 30 minutes to obtain the reducing solution; In the preparation of the reducing solution, the dosage ratio of sodium bisulfite to deionized water is 7.4 g:1200 mL.

[0039] The second oxidation liquid is prepared by mixing sodium persulfate and deionized water, and stirring at room temperature at a stirring speed of 60 rpm for 30 minutes to obtain the second oxidation liquid; In the preparation of the second oxidizing solution, the dosage ratio of sodium persulfate and deionized water is 7.3g:1100mL.

[0040] The content of sodium hypophosphite in the sodium dialkylphosphinate solution is 0, indicating that the conversion rate of sodium hypophosphite is 100%.

[0041] The molar percentage of sodium dialkyl phosphinate in the phosphorus-containing compound in the sodium dialkyl phosphinate solution is 98.0%; 2. Double decomposition: add metal salt to the sodium dialkyl phosphinate solution obtained in step 1, stir at room temperature at a stirring speed of 150 rpm for 60 min, filter, take the precipitate, and vacuum dry to obtain dialkyl phosphinate; The dialkyl phosphinate is zinc dialkyl phosphinate; The metal salt is zinc nitrate; The molar ratio of the sodium dialkyl phosphinate in the sodium dialkyl phosphinate solution to the zinc ions in the zinc nitrate is 2:1.3.

[0042] The 1% thermal decomposition temperature of the zinc dialkylphosphinate obtained in this example is 381° C., and the appearance is white powder.

[0043] Comparative Example 1 A continuous production process of dialkyl phosphinate, based on the technical solution of Example 1, in the first step of free radical addition, in the preparation of the raw material mixture, the addition of modified activated carbon is omitted, and tetrabutylammonium bromide is additionally added, and the amount of the additional tetrabutylammonium bromide is changed to 1 / 10 of the amount of the original modified activated carbon. Specifically, the preparation method of the raw material mixture is changed to: The preparation method of the raw material mixed solution is as follows: sodium hypophosphite monohydrate and deionized water are added into a reaction kettle, stirred at a stirring speed of 30 rpm for 15 minutes at room temperature, cyclohexane, the first portion of tetrabutylammonium bromide, sodium bisulfite, and the second portion of tetrabutylammonium bromide are added, and stirred for 30 minutes to obtain a raw material mixed solution; In the preparation of the raw material mixture, the usage ratio of sodium hypophosphite monohydrate, deionized water, cyclohexane, the first portion of tetrabutylammonium bromide, sodium bisulfite, and the second portion of tetrabutylammonium bromide is 290g:1000mL:2700mL:5g:7.2g:1g.

[0044] In this comparative example, in the first step of free radical addition, the content of sodium hypophosphite in the obtained sodium dialkylphosphinate solution is 0, indicating that the conversion rate of sodium hypophosphite is 100%.

[0045] The molar percentage of sodium dialkyl phosphinate in the phosphorus-containing compound in the obtained sodium dialkyl phosphinate solution is 91.8%; In the second step of double decomposition, the 1% thermal decomposition temperature of the obtained dialkyl aluminum phosphinate is 332°C, and the appearance is a light yellow powder.

[0046] Comparative Example 2 A continuous production process of dialkyl phosphinate, based on the technical solution of Example 1, in the first step of free radical addition, the introduction time and introduction position of the reducing liquid and the second oxidizing liquid are changed. Specifically, the first step of free radical addition is changed to: 1. Free radical addition: After checking the air tightness of the microreactor system, use nitrogen to replace the air in the microreactor system, control the temperature of the first-stage microreactor to 80°C, the temperature of the second-stage microreactor to 90°C, and the temperature of the third-stage microreactor to 95°C, and introduce the raw material mixed solution, the first oxidation solution, the reducing solution, and the second oxidation solution into the first-stage microreactor at the same time, and control the flow rate of the raw material mixed solution to 200mL / min, the flow rate of the first oxidation solution to 105mL / min, the flow rate of the reducing solution to 50mL / min, and the flow rate of the second oxidation solution to 50mL / min. Ethylene gas is introduced into the first-stage microreactor until the gauge pressure reaches 0.5 MPa, and when the feed liquid enters the second-stage microreactor, ethylene gas is introduced into the second-stage microreactor until the gauge pressure reaches 0.5 MPa, and when the feed liquid enters the third-stage microreactor, ethylene gas is introduced into the third-stage microreactor until the gauge pressure reaches 0.5 MPa, and 9 minutes after the material flows out of the third-stage microreactor, free radical addition products are collected from the outlet of the third-stage microreactor; the free radical addition products are allowed to stand at room temperature to separate layers, the water layer is taken, and centrifuged at a centrifugal speed of 5000 rpm for 10 minutes, and the supernatant is taken to obtain a sodium dialkylphosphinate solution.

[0047] In this comparative example, in the first step of free radical addition, the content of sodium hypophosphite in the obtained sodium dialkylphosphinate solution is 0, indicating that the conversion rate of sodium hypophosphite is 100%.

[0048] The molar percentage of sodium dialkyl phosphinate in the phosphorus-containing compound in the obtained sodium dialkyl phosphinate solution is 95.0%; In the second step of double decomposition, the 1% thermal decomposition temperature of the obtained dialkyl aluminum phosphinate is 361°C, and the appearance is white powder.

[0049] After comparing Example 1 with Comparative Examples 1-2, it is found that compared with Example 1, in the first step of free radical addition, the molar percentage of sodium dialkyl phosphinate in the phosphorus-containing compound in the sodium dialkyl phosphinate solution obtained, and the 1% thermal decomposition temperature and appearance of the dialkyl phosphinate obtained in the second step of double decomposition in Comparative Examples 1-2 are worse than those in Example 1. This indicates that in Example 1, the modified activated carbon added in the first step of free radical addition can promote the free radical addition and avoid affecting the appearance of the prepared dialkyl phosphinate; in the first step of free radical addition, the reducing solution and the second oxidizing solution are introduced into the third-stage microreactor, which can also promote the free radical addition.

[0050] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A continuous production process of dialkyl phosphinate, characterized in that: A microreactor system is used, wherein the microreactor system comprises a first-stage microreactor, a second-stage microreactor, and a third-stage microreactor connected in series in sequence; The continuous production process includes: free radical addition and double decomposition; The free radical addition, after checking the air tightness of the microreactor system, using nitrogen to replace the air in the microreactor system, controlling the temperature of the first-stage microreactor to 80-90°C, controlling the temperature of the second-stage microreactor to 90-95°C, and controlling the temperature of the third-stage microreactor to 95-110°C, introducing the raw material mixed solution and the first oxidation solution into the first-stage microreactor at the same time, and introducing ethylene gas to a gauge pressure of 0.5-0.6MPa, waiting for the feed liquid to enter the second-stage microreactor, introducing ethylene gas into the second-stage microreactor to a gauge pressure of 0.5-0.6MPa, waiting for the feed liquid to enter the third-stage microreactor, introducing ethylene gas into the third-stage microreactor to a gauge pressure of 0.5-0.6MPa, and simultaneously introducing the reducing solution and the second oxidation solution into the third-stage microreactor at the same time, collecting the product from the outlet of the third-stage microreactor after the third-stage microreactor runs stably, standing for stratification, taking the water layer, centrifuging, taking the supernatant, and obtaining a sodium dialkylphosphinate solution; The preparation method of the raw material mixed liquid is as follows: sodium hypophosphite monohydrate and deionized water are added into a reaction kettle, stirred at room temperature, cyclohexane, tetrabutylammonium bromide, sodium bisulfite and modified activated carbon are added, stirred to obtain the raw material mixed liquid.

2. The continuous production process of dialkyl phosphinate according to claim 1, characterized in that: The first-stage microreactor has an inner diameter of 5 mm and a length of 1 m; The inner diameter of the second-stage microreactor is 8 mm and the length is 12 m; The inner diameter of the third-stage microreactor is 8 mm and the length is 12 m.

3. The continuous production process of dialkyl phosphinate according to claim 1, characterized in that: In the free radical addition, the flow rate of the raw material mixture is 200-220 mL / min, the flow rate of the first oxidizing liquid is 105-115 mL / min, the flow rate of the reducing liquid is 50-53 mL / min, and the flow rate of the second oxidizing liquid is 50-53 mL / min; The centrifugal speed during the centrifugation is 5000-6000 rpm, and the time is 10-15 min.

4. The continuous production process of dialkyl phosphinate according to claim 1, characterized in that: In the preparation of the raw material mixture, the dosage ratio of sodium hypophosphite monohydrate, deionized water, cyclohexane, tetrabutylammonium bromide, sodium bisulfite and modified activated carbon is 290-300g:1000-1200mL:2700-3000mL:5-5.3g:7.2-7.5g:10-10.4g.

5. The continuous production process of dialkyl phosphinate according to claim 1, characterized in that: The method for preparing the modified activated carbon comprises: preparing water-soluble activated carbon, adsorbing; The water-soluble activated carbon is prepared by mixing activated carbon, citric acid, polyvinyl alcohol and glacial acetic acid and then ball milling. After the ball milling, the mixture is stirred at 120-130° C., the temperature is naturally lowered to room temperature, deionized water is added, stirred, centrifuged, a precipitate is collected, and vacuum dried to obtain the water-soluble activated carbon. For the adsorption, tetrabutylammonium bromide and deionized water are mixed, stirred at room temperature, water-soluble activated carbon is added, stirred, centrifuged, precipitated, and vacuum dried to obtain modified activated carbon.

6. The continuous production process of dialkyl phosphinate according to claim 5, characterized in that: In the preparation of water-soluble activated carbon, the particle size of the activated carbon is 300 mesh; The model of the polyvinyl alcohol is polyvinyl alcohol 1788; The dosage ratio of activated carbon, citric acid, polyvinyl alcohol, glacial acetic acid and deionized water is 10-11g:110-130g:25-30g:40-42mL:1200-1300mL; The ball-to-material ratio during the ball milling is 4-5:1, the rotation speed is 300-400rpm, and the time is 30-40min; The centrifugal speed during the centrifugation is 5000-6000 rpm, and the time is 10-15 min; In the adsorption, the usage ratio of tetrabutylammonium bromide, deionized water, and water-soluble activated carbon is 34-36 g:1000-1100 mL:12-13 g; The centrifugal speed during the centrifugation is 5000-6000 rpm, and the time is 10-15 min.

7. The continuous production process of dialkyl phosphinate according to claim 1, characterized in that: The first oxidation liquid is prepared by mixing sodium persulfate and deionized water, and stirring at room temperature to obtain the first oxidation liquid; In the preparation of the first oxidizing solution, the dosage ratio of sodium persulfate to deionized water is 7-7.3 g: 2000-2100 mL.

8. The continuous production process of dialkyl phosphinate according to claim 1, characterized in that: The preparation method of the reducing solution is as follows: sodium bisulfite and deionized water are added into a reaction kettle, and stirred at room temperature to obtain the reducing solution; In the preparation of the reducing solution, the dosage ratio of sodium bisulfite to deionized water is 7-7.4 g:1000-1200 mL.

9. The continuous production process of dialkyl phosphinate according to claim 1, characterized in that: The second oxidation liquid is prepared by mixing sodium persulfate and deionized water, and stirring at room temperature to obtain the second oxidation liquid; In the preparation of the second oxidizing solution, the dosage ratio of sodium persulfate to deionized water is 7-7.3 g:1000-1100 mL.

10. The continuous production process of dialkyl phosphinate according to claim 1, characterized in that: The double decomposition comprises adding a metal salt to a sodium dialkyl phosphinate solution, stirring at room temperature, filtering, taking a precipitate, and drying in vacuum to obtain a dialkyl phosphinate; The dialkyl phosphinate is one of dialkyl aluminum phosphinate or dialkyl zinc phosphinate; The metal ion in the metal salt is one of aluminum ion or zinc ion, and the anion is one of sulfate ion, chloride ion and nitrate ion; When the dialkyl phosphinate is aluminum dialkyl phosphinate, the molar ratio of the sodium dialkyl phosphinate in the sodium dialkyl phosphinate solution to the metal ion in the metal salt is 3:1.2-1.3; When the dialkyl phosphinate is zinc dialkyl phosphinate, the molar ratio of the sodium dialkyl phosphinate in the sodium dialkyl phosphinate solution to the metal ion in the metal salt is 2:1.2-1.3.