CN114307920A - Continuous production system and production process of polyol acetate - Google Patents
Continuous production system and production process of polyol acetate Download PDFInfo
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- 238000004519 manufacturing process Methods 0.000 title claims abstract description 37
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- 238000010924 continuous production Methods 0.000 title claims abstract description 32
- -1 polyol acetate Chemical class 0.000 title claims abstract description 27
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- 238000005886 esterification reaction Methods 0.000 claims abstract description 119
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Abstract
The invention discloses a continuous production system of polyol acetate and a production process thereof, wherein the continuous production system comprises an esterification system, a superheater, a membrane separation system and a vacuum condensation system; the esterification system comprises a plurality of esterification reaction kettles which are connected in series, and the esterification reaction kettles are communicated with the superheater; the esterification reaction kettles are internally provided with a stirring device and a heater, and the volume and the height of each esterification reaction kettle are sequentially reduced and arranged in a step manner; the superheater is communicated with the membrane separation system; the membrane separation system comprises a plurality of pervaporation membrane components connected in series; the pervaporation membrane component at the tail end is communicated with the esterification reaction kettle at the head end; the pervaporation membrane component is communicated with the vacuum condensation system; the pervaporation membrane component adopts an inorganic membrane material. The production process of the invention refuses to use catalyst and water-carrying agent, and uses pervaporation membrane component to form a set of membrane separation system to dehydrate esterification reaction, and polyol and acetic acid are subjected to esterification reaction, and then post-treatment such as deacidification, acylation, refining and the like to obtain the finished product of polyol acetate.
Description
Technical Field
The invention relates to the field of chemical production, in particular to a continuous production system of polyol acetate and a production process thereof.
Background
Glyceryl triacetate is colorless, odorless, oily transparent viscous liquid prepared by esterification of glycerol and acetic acid or acetic anhydride, and is nontoxic and slightly soluble in water. In B3 in the appendix list of the list of artificial flavors for food use permitted by GB2760-2007 (the sanitary standard for food additives in the people's republic of china 2007 edition), it is coded as a 3050. The glyceryl triacetate is used as a food additive and widely applied in various fields, such as a solvent and a fixative for flavors and fragrances in the flavor and fragrance industry; in medicine, it can be used as plasticizer and binder for coating of capsule and tablet; in the food field, triacetin is added to chewing gum which is often eaten by people. In addition, the glycerol triacetate is used as a main plasticizer for forming acetate fiber materials for cigarette holders in the tobacco industry as the food additive, and can also improve the mouth feel of smoke smoking in the smoking process.
In the aspect of industrial application, the glyceryl triacetate has the characteristics of safety, no toxicity, easy biodegradation in the natural world and the like, and can be directly used instead of or partially replace a low-molecular-weight plasticizer such as dibutyl phthalate (DBP) and the like in the processing process of adhesives, printing ink and bioplastics in many fields. In the casting industry, the glyceryl triacetate can also be used as a hardening agent for casting molding sand, the molding sand is not required to be dried and hardened during casting, and the molding sand can be naturally hardened after 24 hours. In the prior published technical patents about the synthesis and preparation of triacetin, most methods are to use glycerin and acetic acid to esterify and deacidify under the condition of an acid catalyst to obtain a crude ester product, then to perform an acylation reaction by acetic anhydride, and then to obtain a finished product by a series of post-treatment refining processes.
For the reaction of glyceryl triacetate, the most commonly used catalyst is concentrated sulfuric acid, in the invention patent (publication No. CN106045852B), the concentrated sulfuric acid with the mass of 0.25% of that of glycerol is used as the catalyst, the esterification time is 20-24 hours, and the reaction process is intermittent operation; in the patent of invention granted (No. CN102115444B), p-toluenesulfonic acid is used as a catalyst, the dosage of the p-toluenesulfonic acid is 0.3-1.0 per mill of the total feeding mass, and the esterification reaction process adopts continuous operation. Also, an invention granted patent (granted publication No. CN103706403B) describes the preparation of a polyacid intercalated hydrotalcite catalyst, which is used as a catalyst for the esterification reaction of glyceryl triacetate; there is also relevant literature showing the use of acidic ionic liquids as catalysts for the esterification of glyceryl triacetate.
At present, concentrated sulfuric acid is mainly used as a catalyst for reaction in the traditional industrial production of glyceryl triacetate, and the method has the advantages of high catalytic activity, high reaction speed, low price and the like, but also has a plurality of problems. The most significant problems are: 1) the prepared finished glyceryl triacetate has more or less trace of residual sulfuric acid, and is easy to return acid in the storage process, so that the quality guarantee period of the product is influenced, and therefore, a proper amount of alkali (usually barium hydroxide) is required to be added in the deacidification process to treat the catalyst; simultaneously, raw material acetic acid is also lost by adding alkali, and the generated acetate and sulfate are scaled on equipment to cause difficulty in cleaning; 2) the color of the product is deepened, so that active carbon is added for decoloring in the refining process; 3) due to the strong oxidizing property of concentrated sulfuric acid, side reaction is large, so that by-product impurities are generated, and the quality of a product is influenced; 4) it is difficult to realize a continuous production mode of DCS control.
Similar problems exist for the preparation of glyceryl triacetate using p-toluenesulfonic acid as a catalyst: 1) the prepared product has an acid return phenomenon after being stored in a room temperature environment for about half a year, so an alkali treatment process is needed; 2) the catalyst is carried out, and a certain amount of p-toluenesulfonic acid needs to be supplemented when the distillation residual liquid is used for the next esterification reaction; 3) the distillation raffinate contains catalyst which can be carried into the rectifying tower by the product, so that the tower is blocked by the filler.
At present, the international production method of glyceryl triacetate mainly comprises the traditional batch method. In order to ensure the product quality, no catalyst is added, but the consumption of acetic anhydride is higher, generally at 300-500 kg/ton product. Taking a foreign continuous esterification reaction process technology as an example, acetic acid is fed at the bottom of an esterification tower, glycerol is fed at the top of the esterification tower, and the downward flowing glycerol and the ascending acetic acid steam flow in the reverse direction to perform esterification reaction; the generated water is discharged at the tower top in the form of light acetic acid, and the light acetic acid is recycled to obtain 98 percent acetic acid which is returned to the reaction system for recycling; the esterification material at the bottom of the tower is fed into an acylation tower for deep esterification, and the obtained crude product is subjected to processes such as deacidification, rectification, refining and the like to obtain a finished product. Because no water carrying agent is used, the requirements on the materials of the esterification tower and the dilute acetic acid recovery tower are high, and the equipment height requirement is also more than 20m, the process has the disadvantages of large equipment investment, high reaction energy consumption, higher acetic anhydride consumption and higher production cost.
Membrane separation is a new technology of separation that emerged at the beginning of the 20 th century and grew rapidly after the 60's of the 20 th century. The membrane separation technology has the functions of separation, concentration, purification and refining, and has the characteristics of high efficiency, energy conservation, environmental protection, simple molecular filtration and filtration process, easy control and the like; therefore, the method is widely applied to the fields of food, medicine, biology, environmental protection, chemical industry, metallurgy, energy, petroleum, water treatment, electronics, bionics and the like, generates great economic benefit and social benefit, becomes one of the most important means in the separation science at present, and has the principle as shown in the following figures 1-2. Aiming at the defects of the domestic traditional process and the foreign process technology, the invention provides a continuous production system of polyol acetate and a production process thereof.
Disclosure of Invention
The invention aims to improve the existing industrial production technology and provide a continuous production system of polyol acetate and a production process thereof, which is characterized in that a process without a catalyst and a water-carrying agent is adopted, and a pervaporation membrane separation technology is applied to an esterification reaction system so as to achieve the aim of dehydrating azeotropic mixed gas of acetic acid and water and promote the esterification reaction; compared with the process of the water knockout tower, the process of the invention can reduce the production energy consumption. The application of the technology of the invention in the production of triacetin is reported for the first time.
The invention is realized by the following technical scheme:
a continuous production system of polyol acetate is characterized by comprising an esterification system, a superheater, a membrane separation system and a vacuum condensation system; the esterification system comprises a plurality of esterification reaction kettles which are connected in series, and the esterification reaction kettles are all communicated with the superheater; the esterification reaction kettles are internally provided with a stirring device and a heater, and the volume and the height of each esterification reaction kettle are sequentially reduced and arranged in a step manner; the superheater is communicated with the membrane separation system; the membrane separation system comprises a plurality of pervaporation membrane components connected in series; the pervaporation membrane assembly at the tail end is communicated with the esterification reaction kettle at the head end; the plurality of pervaporation membrane assemblies are communicated with the vacuum condensation system; the pervaporation membrane component adopts an inorganic membrane material. Specifically, the pervaporation membrane module is composed of a plurality of membrane tubes (cores), and the length and the number of the membrane tubes depend on the size of the production scale; the pervaporation membrane module is used for dehydration.
Furthermore, the number of the esterification reaction kettles is 3-6; the number of the pervaporation membrane assemblies is 4-8.
Further, the vacuum condensation system comprises a condenser and a penetrating fluid storage tank; and the pervaporation membrane module is sequentially communicated with the condenser and the penetrating fluid storage tank.
Further, the inorganic membrane material is a MOR type structure molecular sieve, the passing pore diameter is 0.4nm, and the membrane flux is 800 g/(m) of 600-2H). Specifically, the passing pore diameter is 0.4nm, which is equivalent to the size of water molecules, so that the passing of the water molecules can be effectively ensured, and the acetic acid molecules are trapped outside the membrane.
Further, the MOR type structure molecular sieve is selected from any one of mordenite molecular sieve, Sn-ZSM-5 type zeolite molecular sieve and ZSM-5 type zeolite molecular sieve doped with atoms. The molecular sieve has high acid resistance and thermal stability, and the pervaporation membrane prepared from the material is applied to dehydration of acetic acid gas, so that the purposes of long-term use and no maintenance can be achieved.
A continuous production process of polyol acetate is characterized in that the continuous production system is adopted for production, and comprises the following steps:
s1, feeding reaction materials into the esterification system, and enabling the reaction materials to sequentially flow into each esterification reaction kettle, wherein the reaction materials are polyhydric alcohol and acetic acid; specifically, the volume and the height of each esterification reaction kettle are sequentially reduced and arranged in a step manner, and reaction materials sequentially overflow from the esterification reaction kettle at the head end to the subsequent esterification reaction kettle naturally and flow; raw materials used for production, namely polyhydric alcohol and acetic acid are mixed according to a certain ratio and enter an esterification reaction kettle of an esterification system, and when the system operates normally, materials can enter a subsequent reaction kettle from a previous reaction kettle in a recursion manner due to liquid level difference;
s2, heating the esterification reaction kettle, heating the azeotropic mixed gas of acetic acid and water in the esterification reaction kettle through the superheater, then feeding the azeotropic mixed gas of acetic acid and water into the membrane separation system, and separating the azeotropic mixed gas of acetic acid and water in a plurality of pervaporation membrane modules; obtaining water vapor and acetic acid vapor; specifically, azeotropic mixed gas of acetic acid and water is separated in a pervaporation membrane module, and water vapor molecules selectively permeate the pervaporation membrane module, are condensed by a condenser and then enter a pervaporation liquid storage tank; acetic acid molecules are trapped at the outer side of the membrane and enter the esterification reaction kettle again through the outlet of the last pervaporation module;
s3, the water vapor enters a permeate storage tank through a condenser, and the acetic acid vapor reenters the esterification system through a pervaporation membrane module at the tail end to react; returning acetic acid vapor to the esterification system for recycling;
and S4, when the materials in the esterification reaction kettle at the tail end reach a preset esterification degree, entering a post-treatment process, wherein the post-treatment process comprises deacidification, acylation and rectification, and obtaining a finished product of the polyol acetate. The recovered acetic acid obtained by the deacidification process can be recycled by the ingredients.
Further, the mass ratio of the polyol to the acetic acid in step S1 is 1: (2.9-3.2); the polyol is selected from glycerol; the number of the esterification reaction kettles is four. Specifically, the four esterification reaction kettles can be respectively marked as esterification reaction kettle one, esterification reaction kettle two, esterification reaction kettle three and esterification reaction kettle four.
Further, the step S2 sequentially heats the four esterification reaction kettles, wherein the temperatures are respectively 120-; the total residence time of the reaction mass in the esterification system is 28-36 hours; the esterification degree of the glycerol in each esterification reaction kettle is 56-60%, 74-78%, 85-88% and 90-93% in sequence; the heating temperature of the superheater is 120-130 ℃.
Further, the number of pervaporation membrane modules described in step S2 is five. The five pervaporation membrane assemblies can be respectively marked as a pervaporation membrane assembly I, a pervaporation membrane assembly II, a pervaporation membrane assembly III, a pervaporation membrane assembly IV and a pervaporation membrane assembly V.
Further, in step S3, the water vapor enters the permeate storage tank through the condenser to obtain esterified water with acetic acid concentration less than 0.5%; the water content of the acetic acid vapor is less than 0.5%. The pervaporation membrane module is used for dehydration.
The continuous production system and the production process of the polyol acetate can be used for producing not only triacetin but also glycol diacetate, propylene glycol diacetate, butylene glycol diacetate and the like. The invention relates to a continuous production system of polyol acetate and a production process thereof, wherein the raw materials are polyol and acetic acid, concentrated sulfuric acid or other strong acids are not used as a catalyst, propyl acetate is used as a water-carrying agent, and alkali is used for neutralizing to generate solid waste.
The glyceryl triacetate prepared by the production process has the advantages of high purity, low acid value, light color, no peculiar smell and the like, and is combined with a DCS (distributed control system) automatic control system to achieve the aims of reducing production energy consumption, increasing yield and reducing manual operation, thereby effectively solving various problems in the conventional intermittent production of the glyceryl triacetate by taking concentrated sulfuric acid as a catalyst.
The esterification reaction kettle, the pervaporation membrane component, the deacidification kettle, the acylation kettle, the rectifying tower and other production equipment in the post-treatment process are not particularly limited, and the method can be suitable for industrial production of the glyceryl triacetate, and equipment well known by the technical personnel in the field is generally selected; the size and the number of the devices are not limited.
The invention has the beneficial effects that:
(1) the production process of the invention refuses to use catalysts and water-carrying agents, and adopts a technical scheme that a pervaporation membrane component forms a membrane separation system to dehydrate esterification reaction, glycerin and acetic acid directly generate esterification reaction, and then a series of post-treatments such as deacidification, acylation, refining and the like are carried out to obtain the finished product of the glyceryl triacetate. The glyceryl triacetate produced by the method has the advantages of high purity, low acid value, light color, no peculiar smell and the like, and by combining the DCS automatic control technology, the problems of the traditional intermittent production of the glyceryl triacetate by taking concentrated sulfuric acid as a catalyst are effectively solved, the manual operation is greatly reduced, the steam energy consumption is reduced, the productivity and the production efficiency are improved, the product quality is improved, and the production cost of enterprises is effectively reduced.
(2) The continuous production system and the production process of the polyol acetate apply the pervaporation membrane technology to the continuous production system and the production process of the glyceryl triacetate, and effectively solve the technical problems of more three wastes, poor quality, high energy consumption and low raw material yield caused by the catalysis and neutralization processes of an intermittent method. Compared with the process defects of high requirement on equipment, more investment, high energy consumption, more acetic anhydride consumption, use of water-carrying agents and high production cost of the foreign continuous method, the technical method provided by the invention has remarkable advantages and meets the requirements of green production process.
(3) The continuous production system of the polyol acetate and the production process thereof have the advantages of small project occupation area, low steam energy consumption, less generation of three wastes, and capability of greatly reducing manual operation and reducing the production cost of enterprises by adopting a DCS automatic control technology.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings needed to be used in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without creative efforts.
FIG. 1 is a schematic structural view of a membrane module;
FIG. 2 is a separation schematic of a membrane module;
FIG. 3 is a schematic diagram showing a continuous production system of a polyol acetate of the present invention.
In the figure: 1. esterification reaction kettles I and II, esterification reaction kettles III and III, esterification reaction kettles IV and III, and overheaters 5, pervaporation membrane assemblies I and II 6 and 8, pervaporation membrane assemblies IV and IV 9, pervaporation membrane assemblies V and V10, condensers 11 and penetrating fluid storage tanks 12.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way intended to limit the invention, its application, or uses. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Example 1
A continuous production system of polyol acetate comprises an esterification system, a superheater 5, a membrane separation system and a vacuum condensation system; the esterification system comprises four esterification reaction kettles (namely an esterification reaction kettle I1, an esterification reaction kettle II 2, an esterification reaction kettle III 3 and an esterification reaction kettle IV 4) which are connected in series, and the four esterification reaction kettles are all communicated with the superheater 5; each esterification reaction kettle is provided with a stirring device and a heater, and the volume and the height of each esterification reaction kettle are sequentially reduced and arranged in a step manner (namely, the volume and the height are sequentially reduced from the first esterification reaction kettle 1 to the fourth esterification reaction kettle 4); the superheater 5 is communicated with the membrane separation system; the membrane separation system comprises five pervaporation membrane assemblies (namely a pervaporation membrane assembly I6, a pervaporation membrane assembly II 7, a pervaporation membrane assembly III 8, a pervaporation membrane assembly IV 9 and a pervaporation membrane assembly V10) which are connected in series; the pervaporation membrane assembly five 10 is communicated with the esterification reaction kettle one 1; the vacuum condensation system comprises a condenser 11 and a penetrating fluid storage tank 12; the five pervaporation membrane modules are sequentially communicated with a condenser 11 and a penetrating fluid storage tank 12; the pervaporation membrane component adopts an inorganic membrane material.
Preferably, the inorganic membrane material is MOR type structure molecular sieve, the passing pore diameter is 0.4nm, the membrane flux is 600-2H); preferably, the MOR-type structural molecular sieve is selected from any one of mordenite molecular sieves, Sn-ZSM-5 type zeolite molecular sieves, and atom-doped ZSM-5 type zeolite molecular sieves.
A continuous production process of glyceryl triacetate adopts the continuous production system to produce, and comprises the following steps:
s1, adding glycerol and acetic acid into the esterification reaction kettle I1, and then sequentially pumping into the esterification reaction kettle I1, the esterification reaction kettle II 2, the esterification reaction kettle III 3 and the esterification reaction kettle IV 4 to reach 65% of the volume of the esterification reaction kettle; the mass ratio of glycerol to acetic acid is 1: 3;
s2, heating each esterification reaction kettle (heating the first esterification reaction kettle 1 to 123 ℃, heating the second esterification reaction kettle 2 to 128 ℃, heating the third esterification reaction kettle 3 to 133 ℃, and heating the fourth esterification reaction kettle 4 to 138 ℃), and recurrently circulating the material in the fourth esterification reaction kettle 4 to the first esterification reaction kettle 1 at a certain flow rate; the gas phase evaporation materials in each esterification reaction kettle are connected by a header pipe, and the azeotropic mixed gas of acetic acid and water in the esterification reaction kettle is heated to the temperature of 120-130 ℃ by the superheater 5 and then sequentially enters a pervaporation membrane assembly I6, a pervaporation membrane assembly II 7, a pervaporation membrane assembly III 8, a pervaporation membrane assembly IV 9 and a pervaporation membrane assembly V10; dehydrating the azeotropic mixed gas of acetic acid and water in a membrane separation system; obtaining water vapor and acetic acid vapor;
s3, allowing water vapor to pass through a condenser 11 and then enter a penetrating fluid storage tank 12, and allowing acetic acid vapor to pass through a pervaporation membrane module five 10 and then enter an esterification reaction kettle I1 again for reaction; namely, acetic acid steam with the water content of less than 0.5 percent is obtained at the outlet end of the fifth 10 pervaporation membrane module; obtaining esterified water with acetic acid concentration less than 0.5% in a penetrating fluid storage tank; returning the acetic acid steam after dehydration to an esterification system for recycling;
s4, when the materials in the esterification reaction kettle IV 4 reach a preset esterification degree, the post-treatment process can be carried out, wherein the post-treatment process comprises deacidification, acylation and rectification, and a finished product of the polyol acetate is obtained; and when the esterification reaction kettle IV 4 discharges materials, the mass ratio of glycerol to acetic acid is 1: 3 feeding the esterification reaction kettle I1.
When the four 4 esterification reaction kettles normally discharge, the system reaches a stable state, the esterification degree of each reaction kettle rises in sequence, the temperature of each reaction kettle also rises in sequence, and the states of each reaction kettle are as shown in the following table 1:
table 1 shows the operating parameters of the esterification reactors during normal operation of the continuous production system of the present invention:
comparative example 1
Compared with the traditional intermittent method, the method has obvious advantages in raw material and energy consumption, effectively solves the problems of more three wastes, poor quality and the like caused by the intermittent process, and meets the requirements of green production process.
The conventional batch process and the process of the present invention produce triacetin with the main raw materials and energy consumption (per ton product) as follows:
table 2 shows the main raw materials and energy consumption required for the batch process and the process for producing each ton of glyceryl triacetate product:
from table 2, it can be seen that the process of the present invention reduces the consumption of the main raw materials of glycerol and acetic acid, and the process of the present invention does not require the use of a catalyst (sulfuric acid), a water-carrying agent and an alkali, thereby effectively solving many problems of the conventional batch production of triacetin by using concentrated sulfuric acid as a catalyst; meanwhile, compared with the traditional gap method, the process disclosed by the invention has the advantages that the energy consumption is lower, and the production cost of enterprises is reduced.
The conventional batch method and the production process of the invention produce the three wastes in the production of triacetin, and the three wastes are shown in the following table 3:
table 3 shows the three wastes generated during the production by the gap method and the process:
as can be seen from Table 3, compared with the conventional gap method, the process of the present invention effectively controls the generation of waste gas, waste water and waste residues, and meets the requirements of green production process.
The product quality of the glyceryl triacetate produced by the traditional batch method and the process is compared:
the above-mentioned preferred embodiments of the present invention are provided for illustration only and not for the purpose of limiting the invention. Obvious variations or modifications of the present invention are within the scope of the present invention.
Claims (10)
1. A continuous production system of polyol acetate is characterized by comprising an esterification system, a superheater (5), a membrane separation system and a vacuum condensation system;
the esterification system comprises a plurality of esterification reaction kettles which are connected in series, and the esterification reaction kettles are all communicated with the superheater (5); the esterification reaction kettles are internally provided with a stirring device and a heater, and the volume and the height of each esterification reaction kettle are sequentially reduced and arranged in a step manner; the superheater (5) is communicated with the membrane separation system; the membrane separation system comprises a plurality of pervaporation membrane components connected in series; the pervaporation membrane assembly at the tail end is communicated with the esterification reaction kettle at the head end; the plurality of pervaporation membrane assemblies are communicated with the vacuum condensation system; the pervaporation membrane component adopts an inorganic membrane material.
2. The continuous production system of polyol acetate as set forth in claim 1, wherein the number of said esterification reaction vessels is 3 to 6; the number of the pervaporation membrane assemblies is 4-8.
3. A continuous production system of polyol acetate as claimed in claim 1 wherein said vacuum condensing system comprises a condenser (11) and a permeate holding tank (12); the pervaporation membrane module is sequentially communicated with the condenser (11) and the penetrating fluid storage tank (12).
4. The continuous production system of polyol acetate as claimed in claim 1, wherein said inorganic membrane material is MOR type structure molecular sieve having a pass pore size of 0.4nm and a membrane flux of 600-2·h)。
5. The continuous production system of polyol acetate as claimed in claim 4, wherein said MOR type structural molecular sieve is selected from any one of mordenite molecular sieve, Sn-ZSM-5 type zeolite molecular sieve, and atom-doped ZSM-5 type zeolite molecular sieve.
6. A continuous production process of polyol acetate, characterized in that the continuous production system of any one of claims 1 to 5 is used for production, comprising the following steps:
s1, feeding reaction materials into the esterification system, and enabling the reaction materials to sequentially flow into each esterification reaction kettle, wherein the reaction materials are polyhydric alcohol and acetic acid;
s2, heating the esterification reaction kettle, heating the azeotropic mixed gas of acetic acid and water in the esterification reaction kettle through the superheater (5), and then enabling the azeotropic mixed gas of acetic acid and water to enter the membrane separation system, wherein the azeotropic mixed gas of acetic acid and water is separated in a plurality of pervaporation membrane modules; obtaining water vapor and acetic acid vapor;
s3, leading the water vapor to enter a penetrating fluid storage tank (12) through a condenser (11), and leading the acetic acid vapor to reenter the esterification system for reaction through a terminal pervaporation membrane module;
and S4, when the materials in the esterification reaction kettle at the tail end reach a preset esterification degree, entering a post-treatment process, wherein the post-treatment process comprises deacidification, acylation and rectification, and obtaining a finished product of the polyol acetate.
7. The continuous production process of polyol acetate according to claim 6, wherein the mass ratio of said polyol to said acetic acid in step S1 is 1: (2.9-3.2); the polyol is selected from glycerol; the number of the esterification reaction kettles is four.
8. The continuous production process of polyol acetate as set forth in claim 7, wherein the step S2 comprises sequentially heating the four esterification reaction vessels at 120-125 ℃, 125-130 ℃, 130-135 ℃ and 135-140 ℃; the total residence time of the reaction mass in the esterification system is 28-36 hours; the esterification degree of the glycerol in each esterification reaction kettle is 56-60%, 74-78%, 85-88% and 90-93% in sequence; the heating temperature of the superheater (5) is 120-130 ℃.
9. The continuous production process of polyol acetate according to claim 7, wherein the number of pervaporation membrane modules in step S2 is five.
10. The continuous process according to claim 6, wherein the water vapor is introduced into the permeate storage tank (12) through the condenser (11) in step S3 to obtain esterified water with acetic acid concentration less than 0.5%; the water content of the acetic acid vapor is less than 0.5%.
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