A method for fully continuous production of epoxy diester plasticizer based on series acidification

Abstract

The present invention discloses a method for the fully continuous production of epoxy diester plasticizers based on serial acidification. This method is characterized by using waste edible oil-based fatty acid methyl esters as raw material. After a Claisen esterification reaction and acidification quenching treatment, the method strictly controls the key conditions of the acidification unit to continuously output a material with a stable acid concentration, which serves as a material for direct epoxidation in the second step, ultimately achieving fully continuous production of epoxy diester plasticizers. Compared to existing batch processes, the present invention not only increases the esterification and epoxidation reaction rates but also eliminates the purification step after acidification quenching, saving 52-65% of production time. The resulting bio-based plasticizer product has a high epoxy value and stable quality.

Description

Technical Field

[0001] The invention belongs to the technical field of polyvinyl chloride plasticizers and relates to a method for fully continuously producing epoxy diester plasticizers based on series acidification. Background Art

[0002] Epoxy fatty acid methyl esters (FAMs) are a low-toxic, bio-based plasticizer currently widely used in polyvinyl chloride (PVC) products, partially replacing traditional, toxic petrochemical-based phthalates. In my country, FAMs are typically produced from waste cooking oils through methylation and epoxidation processes after pretreatment, including desalting, degumming, decolorization, and deacidification. However, this type of plasticizer has long suffered from an inherent lack of resistance to migration, limiting its use to auxiliary plasticizers. Consequently, improving the migration resistance of FAM plasticizers has become a pressing technical challenge within the industry.

[0003] The document Apotentially general approach to aliphatic ester-derived PVCplasticizers with suppressed migration as sustainable alternatives to DEHP and patent CN202110223862.0 disclose a method for improving the migration resistance of epoxy fatty acid methyl ester. The core principle is: using dimethyl carbonate as the ester-increasing reagent and reaction solvent, a polar ester group is introduced at the α position of the fatty acid methyl ester through a Claisen ester condensation reaction, thereby strengthening the interaction between the plasticizer and polyvinyl chloride, and then after epoxidation treatment, a migration-resistant epoxy diester bio-based plasticizer is obtained. However, the above method uses traditional batch production technology and includes two independent production processes: (1) using a strong base to catalyze the Claisen condensation esterification reaction between fatty acid methyl ester and dimethyl carbonate to introduce a polar ester group into the α position of the raw material, and then acidifying and quenching, washing the material with water to remove the acid, and distilling to remove the remaining dimethyl carbonate to obtain the primary product fatty acid diester; (2) using a strong acid to catalyze the epoxidation reaction of the unsaturated double bonds contained in the fatty acid diester, and then washing with water to remove the acid and distilling to remove the water to obtain the final product epoxy diester bio-based plasticizer. The above batch process has low production efficiency (total time is about 35 to 42 hours) and unstable product quality: (1) slow reaction and long time consumption, among which the esterification reaction requires 24 hours to achieve a conversion rate of more than 99%, and the epoxidation reaction usually requires 5 to 10 hours; (2) the process is cumbersome, that is, after the acidification and quenching of the esterification reaction, the water washing and deacidification, distillation to remove the remaining dimethyl carbonate purification process, which takes 3 to 4 hours; (3) the product has batch differences and unstable quality. Summary of the Invention

[0004] The purpose of the present invention is to overcome the shortcomings and deficiencies of the prior art and provide a method for the fully continuous production of epoxy diester plasticizers based on series acidification. The method is characterized in that the method comprises an esterification unit, an acidification unit, an epoxidation unit, and a collection unit connected in series. The material passes through each unit in sequence and continuously to efficiently produce high-quality epoxy diester bio-based plasticizers:

[0005] (1) Esterification unit: First, dimethyl carbonate and catalyst are mixed through the first feeder, preheated to 15-25°C, and continuously fed into the tubular reactor; waste cooking oil-based fatty acid methyl ester is preheated to 45-50°C through the second feeder and continuously fed into the tubular reactor; the tubular reactor has a multi-tube parallel structure, and the material is divided into multiple streams. The inner cavity of each tube is a circular hollow tube with an inner diameter of 12-16 mm; after the above materials are mixed in the tubular reactor, they are rapidly heated to 60-70°C, with a flow rate of 0.08-0.09 m / s; the average residence time of the material in the esterification unit is 7.4-8.3 hours;

[0006] (2) Acidification unit: The material output from the esterification unit directly enters the acidification unit containing hydrochloric acid water. The acidification unit is composed of a first-stage acidifier, a second-stage acidifier, and a third-stage acidifier in series. The material first enters the first-stage acidifier, is mixed and stirred with acid water at a volume ratio of 1:10-12, and is acidified and quenched. The acid concentration in the material output from the first-stage acidifier is 0.8-1.1%. Subsequently, the material continuously enters the second-stage acidifier, is mixed with acid water at a volume ratio of 1:4-6. After passing through the water separator, the separated material continuously enters the third-stage acidifier, is mixed with acid water at a volume ratio of 1:6-8. After passing through the water separator, the acid concentration in the separated material is 0.06- The acid water in the primary acidifier is continuously refluxed, passes through a desalter to remove sodium salt, and after adjusting the acidity to 1.1-1.5 mol / L in an acidity controller, it is then refluxed into the primary acidifier; the acid water in the secondary and tertiary acidifiers flows from the tertiary acidifier into the secondary acidifier, and after flowing out of the secondary acidifier, passes through a water separator, the separated acid water is subjected to a desalter to remove sodium salt, and then the acidity is adjusted to 0.07-0.16 mol / L in an acidity controller, and then refluxed into the tertiary acidifier; the water separator is a conventional kettle-type structure with an inner cavity length-to-diameter ratio of 20:1; the average residence time of the material in the acidification unit is 1-1.5 hours;

[0007] (3) Epoxidation unit: The material output from the acidification unit is mixed with 80-88% formic acid and 40-50% hydrogen peroxide in a mass ratio of 1:0.012-0.015:0.2-0.24 through a feeder, preheated to 55-60°C, and continuously fed into a tubular reactor; the tubular reactor has a multi-tube parallel structure, and the material is divided into multiple streams. The inner cavity of each tube is a circular hollow tube with an inner diameter of 10-14 mm; the above-mentioned material is heated to 60-70°C in the tubular reactor, with a flow rate of 0.13-0.16 m / s; the average residence time of the material in the epoxidation unit is 3.6-4.4 hours;

[0008] (4) Collection unit: The material output from the epoxidation unit is passed through a two-stage water separator according to a conventional continuous method to recover the lower acid water to a collection tank; the material is passed through a stripping tower to recover the remaining dimethyl carbonate to a collection tank; the material is then passed through a vacuum distillation tower to collect the 200-235°C fraction and put it into a storage tank, which is the epoxy diester plasticizer product; the average residence time of the material in the collection unit is 2.5 hours;

[0009] The catalyst in step (1) is one or more of sodium hydride, sodium methoxide, and lithium diisopropylamide;

[0010] The mass ratio of the waste edible oil-based fatty acid methyl ester, dimethyl carbonate, and catalyst in step (1) is 1:2.6-2.7:0.23-1.02;

[0011] The tubular reactors in step (1) and step (3) are one or more of a four-tube parallel structure and a six-tube parallel structure;

[0012] The tubular reactors in step (1) and step (3) are one or more of a horizontal tubular structure and a vertical tubular structure;

[0013] The first, second and third stage acidifiers in step (2) are respectively kettle type, tubular type and kettle type;

[0014] The length-to-diameter ratios of the inner cavities of the first, second, and third stage acidifiers in step (2) are 6-10:1, 200:1, and 3.5-4:1, respectively;

[0015] The temperatures of the first, second and third stage acidifiers in step (2) are 25-32° C., 55-60° C. and 36-40° C., respectively;

[0016] The average residence time of the materials in the first, second and third stage acidifiers in step (2) is 8-18 min, 10-20 min and 15-25 min respectively;

[0017] The stirring speeds of the first and third stage acidifiers in step (2) are 200-230 rpm and 30-40 rpm respectively;

[0018] The desalter in step (2) is one or more of reverse osmosis and electrodialysis.

[0019] To increase reaction rates, both the esterification unit and the epoxidation unit described in this invention utilize multi-tube parallel reactors, which separate the materials into multiple thin streams that flow slowly, similar to plug flow. Compared to batch reactors and continuous single-tube reactors, the multi-tube parallel reactors described in this invention significantly increase reaction rates while minimizing backmixing while maintaining yields.

[0020] To achieve fully continuous production of epoxy diester bio-based plasticizers and improve product quality stability, the present invention, after the first esterification reaction, feeds the material into an acidification unit consisting of a series of first, second, and third-stage acidifiers. The acidity, temperature, average residence time, and stirring speed of the acid water in this unit are strictly controlled within the above-mentioned ranges. This allows the acid concentration in the output material to be regulated to not exceed 0.06-0.1%, thus providing the material for the second-step epoxidation reaction. When the acid concentration in the output material from the acidification unit is higher than 0.1%, the subsequent epoxidation reaction will result in severe ring-opening side reactions. When the acid concentration is lower than 0.06%, the epoxidation rate is extremely slow, the reaction is incomplete, and the product has a low epoxy value. After the epoxidation reaction, conventional continuous purification processes are then utilized to achieve fully continuous production of epoxy diester bio-based plasticizers.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] (1) The multi-tube parallel reactor is used to accelerate the reaction rates of esterification and epoxidation; (2) The hydrochloric acid and dimethyl carbonate remaining in the materials after esterification and acidification quenching are used as catalyst and solvent for epoxidation, respectively, eliminating the purification steps of water washing for deacidification and distillation for removing residual dimethyl carbonate between acidification quenching and epoxidation reaction, thereby simplifying the production process. The average residence time of the reaction materials is only 14.5 to 16.7 hours, which is about 52 to 65% shorter than the time required for batch production in the existing intermittent process. The prepared product has a high epoxy value and stable quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a schematic diagram of the process involved in the present invention.

[0024] In the figure: 1 feeder; 2 feeder; 3 tubular reactor; 4 primary acidifier; 5 secondary acidifier; 6 tertiary acidifier; 7 desalter; 8 acidity controller; 9 water separator; 10 desalter; 11 acidity controller; 12 water separator; 13 feeder; 14 tubular reactor; 15 water separator; 16 water separator; 17 collecting tank; 18 stripping column; 19 collecting tank; 20 vacuum distillation column; 21 accumulator;

[0025] In the figure: the solid arrows in the acidification unit represent materials, and the dotted arrows represent acid water; solid arrows are used in other units. DETAILED DESCRIPTION

[0026] The present invention is specifically described below through examples, which are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Technical engineers in this field can make some non-essential improvements and adjustments to the present invention based on the contents of the above invention.

[0027] Example 1:

[0028] With reference to the present invention Figure 1 The process flow shown in the embodiment involves a fully continuous production technology consisting of an esterification unit, an acidification unit, an epoxidation unit, and a collection unit in series. The material passes through each unit in sequence and continuously to efficiently produce high-quality epoxy diester bio-based plasticizer:

[0029] (1) Esterification unit: First, dimethyl carbonate and sodium hydride are mixed through feeder 1, preheated to 25°C, and continuously fed into tubular reactor 3; waste edible oil-based fatty acid methyl ester with an iodine value of 73 is preheated to 50°C through feeder 2 and continuously fed into tubular reactor 3; the mass ratio of waste edible oil-based fatty acid methyl ester, dimethyl carbonate, and sodium hydride is 1:2.6:0.23; tubular reactor 3 adopts a horizontal tubular type with a four-tube parallel structure inside, and the material is divided into multiple streams. The inner cavity of each tube adopts a circular empty tube with an inner diameter of 12 mm; after the above materials are mixed in the reactor, they are rapidly heated to 70°C with a flow rate of 0.09 m / s; the average residence time of the material in the esterification unit is 7.4 hours;

[0030] (2) Acidification unit: The material output from the esterification unit directly enters the acidification unit containing hydrochloric acid water, and the acidification unit is composed of a primary acidifier 4, a secondary acidifier 5, and a tertiary acidifier 6 connected in series; the material first enters the primary acidifier 4, is mixed and stirred with acid water at a volume ratio of 1:10, and is acidified and quenched. The acid concentration in the material output from the primary acidifier 4 is 0.8%; then, the material continuously enters the secondary acidifier 5, is mixed with acid water at a volume ratio of 1:4; after passing through the water separator 9, the separated material continuously enters the tertiary acidifier 6, is mixed with acid water at a volume ratio of 1:6; after passing through the water separator 12, the acid concentration in the separated material is 0.06%, and directly enters the epoxidation unit; the acid water in the primary acidifier 4 is continuously refluxed, and the sodium salt is removed by the desalter 7. After the acidity is adjusted to 1.1 mol / L in the acidity controller 8, it is refluxed into the primary acidifier 4; the secondary acidifier 5 and the tertiary acidifier The acid water of 6 flows from the tertiary acidifier 6 to the secondary acidifier 5. After flowing out of the secondary acidifier 5, it passes through the water separator 9. The separated acid water removes sodium salt in the desalter 10, and then the acidity is adjusted to 0.07 mol / L in the acidity controller 11 before flowing back into the tertiary acidifier 6. The first, second, and third stage acidifiers are kettle type, tubular type, and kettle type, respectively. The length-to-diameter ratios of the inner cavities of the first, second, and third stage acidifiers are 10:1, 200:1, and 4:1, respectively. The temperatures of the first, second, and third stage acidifiers are 25°C, 55°C, and 36°C, respectively. The average residence time of the materials in the first, second, and third stage acidifiers is 8 minutes, 10 minutes, and 15 minutes, respectively. The stirring speeds of the first and third stage acidifiers are 200 rpm and 30 rpm, respectively. The water separator is of a conventional kettle type with an inner cavity length-to-diameter ratio of 20:1. The desalter uses reverse osmosis. The average residence time of the materials in the acidification unit is 1 hour.

[0031] (3) Epoxidation unit: The material output from the acidification unit is mixed with 88% formic acid and 50% hydrogen peroxide in a mass ratio of 1:0.012:0.2 through a feeder 13, preheated to 60°C, and continuously fed into a tubular reactor 14; the tubular reactor 14 is a horizontal tubular reactor with four parallel tubes inside. The material is divided into multiple streams, and the inner cavity of each tube is a circular hollow tube with an inner diameter of 10 mm. The above-mentioned material is heated to 70°C in the tubular reactor with a flow rate of 0.16 m / s. The average residence time of the material in the epoxidation unit is 3.6 hours;

[0032] (4) Collection unit: The material output from the epoxidation unit is passed through two-stage water separators 15 and 16 according to a conventional continuous method, and the lower layer of acid water is recovered to a collection tank 17; the material is passed through a stripping tower 18 to recover the remaining dimethyl carbonate to a collection tank 19; the material is then passed through a vacuum distillation tower 20 to collect the 200-235°C fraction, which is stored in a storage tank 21, namely the epoxy diester plasticizer product; the average residence time of the material in the collection unit is 2.5 hours;

[0033] In Example 1, the conversion rate of the esterification reaction is greater than 99%, and the iodine value is 61gI2 / 100g; the epoxy value of the epoxy diester plasticizer obtained by the epoxidation reaction is 3.3%, and the iodine value is 1.7gI2 / 100g; the total average residence time of the production is 14.5 hours.

[0034] Example 2:

[0035] With reference to the present invention Figure 1 The process flow shown in the embodiment involves a fully continuous production technology consisting of an esterification unit, an acidification unit, an epoxidation unit, and a collection unit in series. The material passes through each unit in sequence and continuously to efficiently produce high-quality epoxy diester bio-based plasticizer:

[0036] (1) Esterification unit: First, dimethyl carbonate and lithium diisopropylamide are mixed through feeder 1, preheated to 15°C, and continuously fed into tubular reactor 3; waste edible oil-based fatty acid methyl ester with an iodine value of 129 is preheated to 45°C through feeder 2 and continuously fed into tubular reactor 3; the mass ratio of waste edible oil-based fatty acid methyl ester, dimethyl carbonate, and lithium diisopropylamide is 1:2.7:1.02; tubular reactor 3 adopts a vertical tube type with a six-tube parallel structure inside, and the material is divided into multiple streams. The inner cavity of each tube adopts a circular empty tube with an inner diameter of 16 mm; after the above materials are mixed in the reactor, they are quickly heated to 60°C with a flow rate of 0.08 m / s; the average residence time of the material in the esterification unit is 8.3 hours;

[0037] (2) Acidification unit: The material output from the esterification unit directly enters the acidification unit containing hydrochloric acid water, and the acidification unit is composed of a primary acidifier 4, a secondary acidifier 5, and a tertiary acidifier 6 connected in series; the material first enters the primary acidifier 4, is mixed and stirred with acid water at a volume ratio of 1:12, and is acidified and quenched. The acid concentration in the material output from the primary acidifier 4 is 1.1%; then, the material continuously enters the secondary acidifier 5, is mixed with acid water at a volume ratio of 1:6; after passing through the water separator 9, the separated material continuously enters the tertiary acidifier 6, is mixed with acid water at a volume ratio of 1:8; after passing through the water separator 12, the acid concentration in the separated material is 0.1%, and directly enters the epoxidation unit; the acid water in the primary acidifier 4 is continuously refluxed, and the sodium salt is removed by the desalter 7. After the acidity is adjusted to 1.5 mol / L in the acidity controller 8, it is refluxed into the primary acidifier 4; the acidity of the secondary acidifier 5 and the tertiary acidifier 6 is continuously refluxed. Water flows from the tertiary acidifier 6 into the secondary acidifier 5. After flowing out of the secondary acidifier 5, it passes through a water separator 9. The separated acid water removes sodium salts in a desalter 10, and then the acidity is adjusted to 0.16 mol / L in an acidity controller 11 before flowing back into the tertiary acidifier 6. The primary, secondary, and tertiary acidifiers are of kettle, tubular, and kettle types, respectively. The inner cavity aspect ratios of the primary, secondary, and tertiary acidifiers are 6:1, 200:1, and 3.5:1, respectively. The temperatures of the primary, secondary, and tertiary acidifiers are 32°C, 60°C, and 40°C, respectively. The average residence time of the material in the primary, secondary, and tertiary acidifiers is 18 minutes, 20 minutes, and 25 minutes, respectively. The stirring speeds of the primary and tertiary acidifiers are 230 rpm and 40 rpm, respectively. The water separator is of a conventional kettle type with an inner cavity aspect ratio of 20:1. The desalter uses electrodialysis. The average residence time of the material in the acidification unit is 1.5 hours.

[0038] (3) Epoxidation unit: The material output from the acidification unit is mixed with 80% formic acid and 40% hydrogen peroxide in a mass ratio of 1:0.015:0.24 through a feeder 13, preheated to 55°C, and continuously fed into a tubular reactor 14; the tubular reactor 14 is a vertical tube type with six tubes in parallel. The material is divided into multiple streams, and the inner cavity of each tube is a circular hollow tube with an inner diameter of 14 mm. The above-mentioned material is heated to 60°C in the tubular reactor with a flow rate of 0.13 m / s. The average residence time of the material in the epoxidation unit is 4.4 hours;

[0039] (4) Collection unit: The material output from the epoxidation unit is passed through two-stage water separators 15 and 16 according to a conventional continuous method, and the lower layer of acid water is recovered to a collection tank 17; the material is passed through a stripping tower 18 to recover the remaining dimethyl carbonate to a collection tank 19; the material is then passed through a vacuum distillation tower 20 to collect the 200-235°C fraction, which is stored in a storage tank 21, namely the epoxy diester plasticizer product; the average residence time of the material in the collection unit is 2.5 hours;

[0040] In Example 2, the conversion rate of the esterification reaction is greater than 99%, and the iodine value of the product is 107gI2 / 100g; the epoxy value of the epoxy diester plasticizer obtained by the epoxidation reaction is 5.7%, and the iodine value is 0.8gI2 / 100g; the total average residence time of production is 16.7 hours.

Claims

1. A method for producing epoxy diester plasticizers based on serial acidification, characterized in that The present invention is composed of an esterification unit, an acidification unit, an epoxidation unit and a collection unit in series. The material passes through each unit in sequence and continuously to efficiently produce high-quality epoxy diester bio-based plasticizer: (1) Esterification unit: First, dimethyl carbonate and catalyst are mixed through the first feeder, preheated to 15~25℃, and continuously fed into the tubular reactor; waste cooking oil-based fatty acid methyl ester is preheated to 45~50℃ through the second feeder and continuously fed into the tubular reactor; the tubular reactor has a multi-tube parallel structure, and the material is divided into multiple streams. The inner cavity of each tube is a circular hollow tube with an inner diameter of 12~16mm; after the above materials are mixed in the tubular reactor, they are quickly heated to 60~70℃, with a flow rate of 0.08~0.09m / s; the average residence time of the material in the esterification unit is 7.4~8.3 hours; (2) Acidification unit: The material output from the esterification unit directly enters the acidification unit containing hydrochloric acid water. The acidification unit is composed of a first-stage acidifier, a second-stage acidifier, and a third-stage acidifier in series. The material first enters the first-stage acidifier and is mixed and stirred with acid water at a volume ratio of 1:10~12, acidified and quenched. The acid concentration in the material output from the first-stage acidifier is 0.8~1.1%; then, the material continuously enters the second-stage acidifier and is mixed with acid water at a volume ratio of 1:4~6; after passing through the water separator, the separated material continuously enters the third-stage acidifier and is mixed with acid water at a volume ratio of 1:6~8; after passing through the water separator, the acid concentration in the separated material is 0.06~ The acid water in the primary acidifier is continuously refluxed, passes through a desalter to remove sodium salts, and after adjusting the acidity to 1.1-1.5 mol / L in an acidity controller, it is returned to the primary acidifier. The acid water in the secondary and tertiary acidifiers flows from the tertiary acidifier into the secondary acidifier. After flowing out of the secondary acidifier, it passes through a water separator, and the separated acid water is removed from the desalter to remove sodium salts. The acidity is then adjusted to 0.07-0.16 mol / L in an acidity controller and returned to the tertiary acidifier. The water separator is a conventional kettle-type structure with an inner cavity length-to-diameter ratio of 20:

1. The average residence time of the material in the acidification unit is 1-1.5 hours. (3) Epoxidation unit: The material output from the acidification unit is mixed with 80~88% formic acid and 40~50% hydrogen peroxide in a mass ratio of 1:0.012~0.015:0.2~0.24 through a feeder, preheated to 55~60℃, and continuously fed into a tubular reactor; the tubular reactor has a multi-tube parallel structure, and the material is divided into multiple streams. The inner cavity of each tube is a circular hollow tube with an inner diameter of 10~14mm; the above-mentioned material is heated to 60~70℃ in the tubular reactor, with a flow rate of 0.13~0.16m / s; the average residence time of the material in the epoxidation unit is 3.6~4.4 hours; (4) Collection unit: The material output from the epoxidation unit is passed through a two-stage water separator according to a conventional continuous method to recover the lower acid water to a collection tank; the material is passed through a stripping tower to recover the remaining dimethyl carbonate to a collection tank; the material is then passed through a vacuum distillation tower to collect the 200-235°C fraction and put it into a storage tank, which is the epoxy diester plasticizer product; the average residence time of the material in the collection unit is 2.5 hours; The catalyst in step (1) is one or more of sodium hydride, sodium methoxide, and lithium diisopropylamide; The mass ratio of the waste edible oil-based fatty acid methyl ester, dimethyl carbonate, and catalyst in step (1) is 1:2.6-2.7:0.23-1.02; The tubular reactors in step (1) and step (3) are one or more of a four-tube parallel structure and a six-tube parallel structure; The tubular reactors in step (1) and step (3) are one or more of a horizontal tubular structure and a vertical tubular structure; The first, second and third stage acidifiers in step (2) are respectively kettle type, tubular type and kettle type; The length-to-diameter ratios of the inner cavities of the first, second, and third stage acidifiers in step (2) are 6-10:1, 200:1, and 3.5-4:1, respectively; The temperatures of the first, second and third stage acidifiers in step (2) are 25-32°C, 55-60°C and 36-40°C respectively; The average residence time of the materials in the first, second and third stage acidifiers in step (2) is 8-18 min, 10-20 min and 15-25 min respectively; The stirring speeds of the first and third stage acidifiers in step (2) are 200-230 rpm and 30-40 rpm respectively; The desalter in step (2) is one or more of reverse osmosis and electrodialysis.

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