A reaction device and reaction process for efficiently preparing acetoacetylated polyvinyl alcohol

Abstract

The application belongs to the technical field of polyvinyl alcohol reaction equipment, and specifically discloses a reaction device for efficiently preparing acetyl-acetylated polyvinyl alcohol, which comprises a dissolving kettle, a reaction kettle and a condenser; the dissolving kettle is used for dissolving polyvinyl alcohol raw materials; a first nitrogen inlet is arranged at the upper portion of the dissolving kettle, and the first nitrogen inlet is used for introducing nitrogen to remove residual small-molecule alcohol and moisture in the polyvinyl alcohol raw materials. The application provides a reaction device for efficiently preparing acetyl-acetylated polyvinyl alcohol; the nitrogen blowing in the dissolving kettle removes residual small-molecule alcohol and moisture in the PVA raw materials at the source, and eliminates the conditions for the side reaction of acetyl-acetylation reagents; the nitrogen blowing in the reaction kettle continuously removes the generated tertiary butyl alcohol by-product from the reaction system; and thus the modification conversion rate is effectively improved, the reaction period is shortened, the product performance is stable, and the operation is safe and environmentally friendly.

Description

Technical Field

[0001] This invention relates to the field of polyvinyl alcohol reaction equipment technology, and in particular to a reaction apparatus and reaction process for the efficient preparation of acetylated polyvinyl alcohol. Background Technology

[0002] Acetylated polyvinyl alcohol (AA-PVA) is a functionalized modified polymer obtained by introducing acetylacetyl groups into the polyvinyl alcohol (PVA) molecular chain. Due to the high reactivity of the acetylacetyl group, AA-PVA exhibits superior performance compared to ordinary PVA and is widely used in the adhesive field. For example, it is used as a water-based adhesive for bonding PVA optical films and supporting films to polarizers, exhibiting high transparency, excellent film-forming properties, and improved resistance to damp heat in polarizers. When used as a protective colloid in the emulsion polymerization of polyvinyl acetate, it can significantly improve the grafting rate and enhance the stability and rheological properties of the emulsion. AA-PVA also readily undergoes crosslinking reactions with hydrazine, hexamethylenediamine, aminourea, hydroxylamine, or amide compounds at room temperature, effectively improving the initial tack strength, final strength, water resistance, and wet strength of adhesives. It has significant application value in wood processing, paper bonding, building materials, and packaging.

[0003] Currently, the mainstream method for industrial preparation of AA-PVA is the diene method. Although this method can achieve a high degree of acetylation, it has significant drawbacks: diene is highly reactive and prone to side reactions; it has poor thermal stability, posing significant safety risks during transportation and storage; more importantly, diene is highly toxic, which can easily harm the health of operators and the environment during use, failing to meet the requirements of current green chemistry and safe production.

[0004] To overcome the safety and environmental issues of the diene process, some processes have begun to adopt transesterification in recent years, using acetoacetate as a modifier to transesterify PVA. This method has relatively stable raw materials, mild reaction conditions, and no highly toxic substances involved, showing good industrialization potential. However, existing transesterification methods mostly use single-reactor or kneader processes. Since PVA raw materials themselves contain certain small-molecule alcohols (such as methanol) and water, water easily leads to ester hydrolysis, and small-molecule alcohols compete with PVA, resulting in transesterification side reactions. At the same time, the alcohol byproducts generated in the reaction are difficult to remove in a timely and effective manner, which inhibits the forward progress of the reversible transesterification reaction, resulting in problems such as low modification conversion rate, long reaction cycle, and poor batch stability of products. Some existing transesterification processes attempt to remove the alcohol byproducts generated in the reaction by reducing pressure, but this method has problems such as large equipment investment, high energy consumption, strict system sealing requirements, unstable control of modification degree due to vacuum fluctuations, and poor batch repeatability. Meanwhile, high-boiling-point polar aprotic solvents such as N-methylpyrrolidone exhibit strong hydrogen bonding and dipole-dipole interactions with alcohols, resulting in vapor pressures of alcohol byproducts that are far lower than expected under ideal conditions, even when the system pressure is reduced. The byproducts are difficult to "escape" from the liquid phase to the gas phase, leading to low removal efficiency. All of these factors limit the widespread application of transesterification methods.

[0005] In summary, the existing transesterification method for preparing acetylated polyvinyl alcohol using a single reactor or kneader process suffers from side reactions caused by residual small-molecule alcohols and moisture in the polyvinyl alcohol raw material, as well as the difficulty in timely and effectively removing alcohol byproducts generated during transesterification (such as tert-butanol byproducts), resulting in limited reaction equilibrium, low conversion rate, and long reaction cycle. Summary of the Invention

[0006] This invention provides a highly efficient reaction apparatus for preparing acetylated polyvinyl alcohol, which can solve the problems of residual moisture and small molecule alcohols in the polyvinyl alcohol raw material that initiate ester hydrolysis side reactions and competing ester exchange side reactions when using the transesterification method with a single reactor or kneader in the prior art to prepare acetylated polyvinyl alcohol. As well as the difficulty in timely and effectively removing alcohol by-products generated by the transesterification reaction (such as tert-butanol by-product), the reaction equilibrium is limited, the conversion rate is low, and the reaction cycle is long.

[0007] In a first aspect, the present invention provides a reaction apparatus for the efficient preparation of acetylated polyvinyl alcohol, comprising: A dissolving vessel is used to dissolve polyvinyl alcohol raw materials. The upper part of the dissolving vessel is provided with a first nitrogen inlet, which is used to introduce nitrogen gas to purge and remove residual water and small molecule alcohols from the polyvinyl alcohol raw materials. A reaction vessel, which is connected to the dissolving vessel, is used to receive a polyvinyl alcohol solution from the dissolving vessel and carry out a transesterification reaction. The upper part of the reaction vessel is provided with a second nitrogen inlet, which is used to introduce nitrogen gas to carry away and remove alcohol byproducts generated in the transesterification reaction. And a condenser, which is connected to the gas phase outlet of the reactor; Both the dissolving vessel and the reaction vessel are equipped with stirring components, which are used for stirring materials and for dispersing the introduced nitrogen gas into the reaction system.

[0008] Furthermore, the stirring assembly includes a rotating shaft and a stirring impeller fixed on the rotating shaft. The stirring impeller includes an upper impeller and a lower impeller, which are spaced apart along the axial direction of the rotating shaft. The rotating shaft has a hollow structure. The upper end of the rotating shaft is provided with an air inlet, and the lower end of the rotating shaft is connected to the internal cavity of the lower impeller. The lower impeller is provided with an air outlet, which is connected to the internal cavity, so as to realize the bubbling replacement and inert protection of the reactants by nitrogen.

[0009] Furthermore, the ratio of the diameter of the stirring impeller to the inner diameter of the reactor is 0.40 to 0.45.

[0010] Furthermore, the upper part of the melting vessel is provided with a first gas outlet, and the lower part is provided with a first jacketed heating / cooling system; The dissolving vessel is also equipped with a PVA feeding port and a solvent inlet at the top, and a material transfer outlet at the bottom; The material transfer outlet is connected to the reaction vessel.

[0011] Furthermore, the upper part of the reactor is also provided with a feed inlet and a PVA solution inlet; The reactor is also equipped with a second jacketed heating / cooling system.

[0012] Furthermore, the loading coefficient in the reactor is 50%~65%; In both the dissolving vessel and the reaction vessel, the height-to-diameter ratio is independently 1.40 to 1.75.

[0013] Furthermore, the outlet of the condenser is connected to a tert-butanol recovery tank.

[0014] Secondly, the present invention also provides a reaction process for efficiently preparing acetylated polyvinyl alcohol, implemented using the reaction apparatus for efficiently preparing acetylated polyvinyl alcohol provided in the embodiments of the first aspect of the present invention, comprising the following steps: S1. Add solvent and polyvinyl alcohol raw material to a dissolving vessel to dissolve the polyvinyl alcohol raw material, and purge with nitrogen gas to remove residual water and small molecule alcohols from the polyvinyl alcohol raw material to prepare a polyvinyl alcohol solution. S2. Transfer the polyvinyl alcohol solution to the reactor, add an acetylation modifier to carry out the transesterification reaction, purge with nitrogen gas, and remove byproducts through a condenser.

[0015] Furthermore, the degree of polymerization of the polyvinyl alcohol is 500-3000, and the degree of alcoholysis is not less than 88%. The solvent added to the dissolving vessel is one or more of N,N-dimethylformamide, N,N-diethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, 2-pyrrolidone, and N-methylpyrrolidone. The acetylation modifying agent is one or more of the following: methyl acetoacetate, ethyl acetoacetate, n-propyl acetoacetate, isopropyl acetoacetate, allyl acetoacetate, isobutyl acetoacetate, sec-butyl acetoacetate, tert-butyl acetoacetate, n-hexyl acetoacetate, n-heptyl acetoacetate, n-octyl acetoacetate, and benzyl acetoacetate.

[0016] Furthermore, in the dissolving vessel 100, during the process of dissolving polyvinyl alcohol raw material, the dissolving temperature is 90℃~140℃ and the dissolving time is 3~6 hours; In the reaction vessel 200, the reaction temperature during the transesterification reaction is 70℃~130℃.

[0017] This invention provides a highly efficient reaction apparatus for preparing acetylated polyvinyl alcohol, which, compared with the prior art, has, but is not limited to, the following beneficial effects: In this efficient apparatus for preparing acetylated polyvinyl alcohol, a dissolving vessel is used to dissolve the polyvinyl alcohol (PVA) raw material. The upper part of the dissolving vessel is equipped with a first nitrogen inlet, which is used to introduce nitrogen gas into the dissolving vessel to purge and remove residual moisture and small-molecule alcohols from the PVA raw material. The PVA raw material itself contains a certain amount of small-molecule alcohols and moisture. If these directly participate in the subsequent transesterification reaction, it can easily lead to hydrolysis of the acetoacetate modifier, and competition between small-molecule alcohols and PVA for transesterification, thereby reducing the modification conversion rate and affecting product quality. By introducing nitrogen purging during the dissolution stage, residual moisture and small-molecule alcohols in the raw material can be carried out with the nitrogen gas flow during PVA dissolution, reducing the adverse effects of moisture and small-molecule alcohols on subsequent reactions from the source.

[0018] The reaction vessel is connected to the dissolving vessel and is used to receive the polyvinyl alcohol solution from the dissolving vessel for transesterification. A second nitrogen inlet is located at the top of the reaction vessel, used to introduce nitrogen gas into the reaction vessel to carry away and remove alcohol byproducts (such as tert-butanol) generated during the transesterification reaction. The transesterification reaction is reversible; if the generated tert-butanol is not removed from the reaction system in time, it will inhibit the forward reaction, leading to a low conversion rate and a prolonged reaction period. By continuously purging with nitrogen gas, the generated alcohol byproducts (such as tert-butanol) can be carried from the liquid phase to the gas phase and discharged with the nitrogen gas flow, thereby breaking the reaction equilibrium and driving the reaction towards the product, effectively improving the conversion rate of acetylation modification.

[0019] The condenser is connected to the gas phase outlet of the reactor. The gaseous material discharged from the reactor with nitrogen (mainly tert-butanol and some solvent vapor) enters the condenser for condensation. The condensed liquid tert-butanol can be further recovered and reused, while the nitrogen is discharged after tail gas treatment.

[0020] Both the dissolving vessel and the reaction vessel are equipped with stirring components. These components serve two purposes: firstly, to mix the materials, ensuring the complete dissolution of PVA in the dissolving vessel and uniform contact and reaction with the acetoacetate modifier in the reaction vessel; and secondly, to disperse the introduced nitrogen gas into the reaction system. Through the shear force and turbulence generated by the rotation of the stirring components, the nitrogen gas introduced through the nitrogen inlet is broken into tiny bubbles and uniformly dispersed in the liquid phase, thereby significantly increasing the gas-liquid contact area and improving the efficiency of nitrogen purging dehydration and removal of byproducts.

[0021] This invention provides a highly efficient reaction apparatus for preparing acetylated polyvinyl alcohol. Nitrogen purging in the dissolving vessel removes residual moisture and small molecule alcohols from the PVA raw material at the source, eliminating the conditions for hydrolysis and transesterification side reactions. Nitrogen purging in the reaction vessel continuously carries away the generated alcohol byproducts (such as tert-butanol byproducts) from the reaction system. This effectively improves the modification conversion rate, shortens the reaction cycle, and ensures stable product performance, safe and environmentally friendly operation. Attached Figure Description

[0022] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this application, illustrate exemplary embodiments of the invention and, together with their description, serve to explain the invention and do not constitute an undue limitation thereof. In the drawings: Figure 1 This is a schematic diagram of a reaction apparatus for the efficient preparation of acetylated polyvinyl alcohol provided by the present invention.

[0023] Explanation of reference numerals in the attached figures: 100. Dissolving vessel; 110. First nitrogen inlet; 200. Reactor; 210. Second nitrogen inlet; 300. Condenser; 10. Rotary shaft; 20. Stirring impeller; 120. First gas outlet; 140. PVA feed port; 150. Solvent inlet; 160. Material transfer outlet; 220. PVA solution inlet; 240. Feed inlet; 400. Tert-butanol recovery tank. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this application clearer, specific embodiments of this application are described clearly and completely below with reference to the accompanying drawings. It should be understood that the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments described in this application without creative effort will fall within the scope of protection of this application.

[0025] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used in the specification of this application is for the purpose of describing specific embodiments only and is not intended to limit this application; the terms "comprising," "including," "having," "containing," "comprise," etc., in the specification, claims, and accompanying drawings of this application are open-ended terms, indicating that a method comprises one or more steps, or an apparatus comprises one or more elements, but do not exclude the inclusion of other steps or elements. The terms "first," "second," etc., in the specification, claims, or accompanying drawings of this application are used to distinguish different objects, not to describe a specific order or primary / secondary relationship. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, unless otherwise stated, "a plurality of" means two or more.

[0026] In the description of this application, it should be understood that the terms "upper", "lower", "left", "right", "front", "rear", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0027] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," "linking," and "attachment" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0028] In this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, C and / or B can represent: C existing alone, C and B existing simultaneously, or B existing alone. Additionally, in this application, the character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0029] Firstly, such as Figure 1 As shown, an embodiment of the present invention provides a reaction apparatus for the efficient preparation of acetylated polyvinyl alcohol, comprising a dissolving vessel 100, a reaction vessel 200, and a condenser 300; The dissolving vessel 100 is used to dissolve polyvinyl alcohol raw materials. The upper part of the dissolving vessel 100 is provided with a first nitrogen inlet 110, which is used to introduce nitrogen to purge and remove residual water and small molecule alcohols from the polyvinyl alcohol raw materials. The reaction vessel 200 is connected to the dissolving vessel 100 and is used to receive the polyvinyl alcohol solution from the dissolving vessel 100 and carry out the transesterification reaction. The upper part of the reaction vessel 200 is provided with a second nitrogen inlet 210, which is used to introduce nitrogen to carry away and remove alcohol byproducts (such as tert-butanol byproducts) generated by the transesterification reaction. The condenser 300 is connected to the gas phase outlet of the reactor 200; Both the dissolving vessel 100 and the reaction vessel 200 are equipped with stirring components. The stirring components are used for stirring the materials and also for dispersing the introduced nitrogen gas into the reaction system.

[0030] Specifically, the dissolving vessel 100 is used to dissolve polyvinyl alcohol (PVA) raw materials. The upper part of the dissolving vessel 100 is equipped with a first nitrogen inlet 110, which is used to introduce nitrogen gas into the dissolving vessel 100 to purge and remove residual moisture and small molecule alcohols from the PVA raw materials. PVA raw materials themselves contain a certain amount of moisture and small molecule alcohols. If they directly participate in the subsequent transesterification reaction, it can easily lead to hydrolysis of the acetoacetate modifier and ineffective transesterification side reactions, thereby reducing the modification conversion rate and affecting product quality. By introducing nitrogen purging during the dissolution stage, residual moisture and small molecule alcohols in the raw materials can be carried out with the nitrogen gas flow during the PVA dissolution process, reducing the adverse effects on subsequent reactions from the source.

[0031] The reaction vessel 200 is connected to the dissolving vessel 100 and is used to receive the polyvinyl alcohol solution from the dissolving vessel 100 for transesterification. A second nitrogen inlet 210 is provided at the top of the reaction vessel 200. This inlet 210 is used to introduce nitrogen gas into the reaction vessel 200 to carry away and remove alcohol byproducts (such as tert-butanol byproducts) generated during the transesterification reaction. The transesterification reaction is reversible. If the generated tert-butanol is not removed from the reaction system in time, it will inhibit the forward reaction, resulting in a low conversion rate and a prolonged reaction period. By continuously purging with nitrogen gas, the generated alcohol byproducts (such as tert-butanol byproducts) can be carried from the liquid phase to the gas phase and discharged with the nitrogen gas flow, thereby breaking the reaction equilibrium and driving the reaction towards the product, effectively improving the conversion rate of acetylation modification.

[0032] The condenser 300 is connected to the gas phase outlet of the reactor 200. The gaseous material (mainly tert-butanol and some solvent vapor) discharged from the reactor 200 with nitrogen enters the condenser 300 for condensation. The condensed liquid tert-butanol can be further recovered and reused, while the nitrogen is discharged after tail gas treatment.

[0033] Both the dissolving vessel 100 and the reaction vessel 200 are equipped with stirring components. These components serve two purposes: firstly, to mix the materials, ensuring the PVA is fully dissolved in the dissolving vessel and reacts uniformly with the acetoacetate modifier in the reaction vessel; and secondly, to disperse the introduced nitrogen gas into the reaction system. The impeller rotates at high speed, throwing the liquid outwards by centrifugal force, creating a localized negative pressure in the impeller's central cavity. This negative pressure connects to the air inlet at the top of the hollow shaft. Driven by the pressure difference, external nitrogen gas is automatically drawn into the hollow shaft, flows downwards into the impeller cavity, and is then released from the impeller's outlet. The stirring components, through the shear force and turbulence generated by rotation, break the nitrogen gas introduced through the nitrogen inlet into tiny bubbles and uniformly disperse them in the liquid phase, thereby significantly increasing the gas-liquid contact area and improving the efficiency of nitrogen purging dehydration, removal of small molecule alcohols, and removal of byproducts.

[0034] In this application, nitrogen purging in the dissolving vessel removes residual moisture and small molecule alcohols from the PVA raw material at the source, eliminating the conditions for hydrolysis and ineffective transesterification side reactions; nitrogen purging in the reaction vessel continuously carries away the generated alcohol byproducts (such as tert-butanol byproducts) from the reaction system; thereby effectively improving the modification conversion rate, shortening the reaction cycle, and ensuring stable product performance and safe and environmentally friendly operation.

[0035] The working principle of this application embodiment is as follows: First, solid polyvinyl alcohol (PVA) raw material is added to the dissolving vessel 100 through the PVA feed port 140, along with an organic solvent (such as N-methylpyrrolidone). The stirring assembly is started, and the mixture is heated to a suitable dissolution temperature (typically 90℃~140℃). Simultaneously, nitrogen gas is introduced into the dissolving vessel 100 through the first nitrogen inlet 110. The nitrogen gas is dispersed into the PVA solution by the stirring assembly, forming a large number of microbubbles under stirring. As the bubbles rise in the liquid phase, residual water and small molecule alcohols in the PVA raw material continuously volatilize into the gas phase under heating conditions and are carried away by the nitrogen gas flow, thereby achieving deep dehydration and removal of small molecule alcohols from the raw material. After the PVA is completely dissolved and impurities are removed, the PVA solution is transferred to the reaction vessel 200.

[0036] Subsequently, an acetoacetate modifier (such as methyl acetoacetate or ethyl acetoacetate) is added to reactor 200, the stirring assembly of reactor 200 is started, and the reaction temperature is controlled (usually 70℃~130℃) for transesterification. During the reaction, nitrogen gas is continuously introduced through the second nitrogen inlet 210, and the nitrogen gas is also dispersed into the reaction system by the stirring assembly. The alcohol byproducts generated by the transesterification reaction (such as tert-butanol byproduct) continuously volatilize into the gas phase under the reaction conditions, and enter the condenser 300 through the gas phase outlet of reactor 200 with the nitrogen gas flow. The tert-butanol is cooled into a liquid state in condenser 300 and collected in tert-butanol recovery tank 400, while the nitrogen gas is discharged after tail gas treatment. The continuous removal of tert-butanol disrupts the equilibrium of the transesterification reaction, driving the reaction towards the formation of the product, thereby obtaining a high-conversion acetylated polyvinyl alcohol product in a short time.

[0037] After the reaction is complete, the product is discharged from the outlet of reactor 200.

[0038] Overall, this technical solution effectively solves the two major problems of side reactions and byproduct suppression by using nitrogen purging for dehydration and removal of small molecule alcohols during the dissolution stage and nitrogen purging for removal of byproducts during the reaction stage, without the need for high vacuum equipment. It significantly improves the modification conversion rate, shortens the reaction cycle, ensures stable product performance, and is safe and environmentally friendly to operate.

[0039] like Figure 1 As shown, in some embodiments of the present invention, the stirring assembly includes a rotating shaft 10 and a stirring impeller 20 fixed on the rotating shaft 10. The stirring impeller 20 includes an upper impeller and a lower impeller, which are spaced apart along the axial direction of the rotating shaft 10. The rotating shaft 10 has a hollow structure. The upper end of the rotating shaft 10 is provided with an air inlet, and the lower end of the rotating shaft 10 is connected to the internal cavity of the lower impeller. The lower impeller is provided with an air outlet, which is connected to the internal cavity to disperse the nitrogen gas introduced through the air inlet into the reaction system.

[0040] Specifically, the hollow rotating shaft can be a drive shaft with an internal axial through hole, which has the dual functions of power transmission and gas conveying. It can be made of stainless steel through machining or welded from seamless steel pipe. The stirring impeller 20 can be a double-layer impeller, that is, the stirring impeller 20 includes an upper impeller and a lower impeller. The double-layer impeller can be two sets of impellers arranged vertically along the axial direction of the rotating shaft 10. It can adopt common impeller structures such as propeller, turbine, paddle, anchor, or W-type. The upper impeller mainly undertakes the function of material mixing and circulation, while the lower impeller integrates gas dispersion function in addition to stirring function. In addition, the lower impeller has an internal cavity that communicates with the hollow rotating shaft, and one or more air outlets are opened on the surface of the lower impeller. The diameter and number of air outlets can be set according to the gas flow rate and dispersion requirements.

[0041] In detail, the rotating shaft 10 is designed as a hollow structure with the air inlet located at the upper end. The impeller rotates at high speed, creating a localized negative pressure in the central cavity. Nitrogen is automatically drawn into the hollow rotating shaft, flows downwards into the impeller cavity, and is then released from the impeller outlet. This simplifies the gas pipeline layout and avoids the need for an additional gas distributor, which would otherwise occupy space within the reactor. Nitrogen is released directly into the impeller region through the outlet of the lower impeller. Under the strong shear force and turbulence generated by the high-speed rotation of the impeller, it is rapidly broken into bubbles and uniformly dispersed in the liquid phase. This significantly increases the gas-liquid contact area and mass transfer coefficient, thereby greatly improving the efficiency of nitrogen purging dehydration, removal of small molecule alcohols, and removal of byproducts.

[0042] like Figure 1 As shown, in some embodiments of the present invention, the ratio of the diameter of the stirring impeller 20 to the inner diameter of the reaction vessel 200 is 0.40 to 0.45.

[0043] Specifically, the ratio of the impeller diameter 20 to the inner diameter of the reactor 200 refers to the proportional relationship between the maximum outer diameter of the lower or upper impeller and the inner diameter of the reactor 200 shell. This ratio determines the relative size of the impeller blades within the reactor and is a key design parameter affecting stirring power, circulation flow rate, and shear strength. Controlling the impeller diameter to the reactor 200 inner diameter within the preferred range of 0.40 to 0.45 ensures sufficient circulation flow rate and shear dispersion capability while avoiding excessive power consumption and the risk of shear degradation, resulting in optimal overall performance.

[0044] like Figure 1 As shown, in some embodiments of the present invention, the upper part of the dissolving vessel 100 is further provided with a first gas outlet 120, and the lower part is provided with a first jacket heating / cooling system. The top of the dissolving vessel 100 is also provided with a PVA feeding port 140 and a solvent inlet 150, and the bottom is provided with a material transfer outlet 160; The material transfer outlet 160 is connected to the reactor 200.

[0045] Specifically, the first gas outlet 120 refers to the exhaust port located on the upper side wall or top of the dissolving vessel 100, used to discharge nitrogen gas and organic solvent vapors carrying small molecule alcohols and water. It can be connected to the tail gas treatment system for purification before being discharged. The first jacket heating / cooling system refers to the jacket structure set on the outer wall of the dissolving vessel 100. Heating media (such as heat transfer oil or steam) or cooling media (such as cooling water) can be introduced into the jacket to achieve precise control of the temperature of the material inside the vessel. The PVA feed port 140 refers to the feed port for adding polyvinyl alcohol solid powder or granules, the solvent inlet 150 refers to the liquid inlet for adding organic solvents, and the material transfer outlet 160 refers to the discharge port located at the bottom of the vessel, used to discharge the dissolved polyvinyl alcohol solution (PVA solution) to the next process.

[0046] like Figure 1 As shown, in some embodiments of the present invention, the upper part of the reactor 200 is further provided with a feed inlet 240 and a PVA solution inlet 220; The reactor 200 is also equipped with a second jacket heating / cooling system.

[0047] Specifically, the PVA solution inlet 220 refers to the inlet located on the upper side wall or top of the reactor 200, which is connected to the material transfer outlet 160 of the dissolving vessel 100 via a pipeline, and is used to receive the polyvinyl alcohol solution from the dissolving vessel 100. The feed inlet 240 is used to add acetoacetate modifiers and other additives to the reactor 200; it can be equipped with a metering pump or a dripping device to achieve precise addition of the modifiers. The second jacket heating / cooling system refers to the jacket structure located on the outer wall of the reactor 200, used to provide the heat required for the transesterification reaction or to cool the product after the reaction.

[0048] like Figure 1 As shown, in some embodiments of the present invention, the loading coefficient in the reactor 200 is 50% to 65%; In both the dissolving vessel 100 and the reaction vessel 200, the height-to-diameter ratio is independently 1.40~1.75.

[0049] Specifically, the loading coefficient refers to the percentage between the volume occupied by the material inside the vessel and the effective volume of the vessel. Its value determines the height of the gas-liquid interface and the size of the top space inside the reactor 200. The vessel height-to-diameter ratio refers to the ratio between the height of the equipment cylinder and the inner diameter of the shell. Its value affects the mixing effect of the material inside the vessel and the gas residence time.

[0050] Setting the loading coefficient of reactor 200 to 50%~65% effectively balances the relationship between production efficiency and nitrogen stripping effect. When the loading coefficient is below 50%, the single batch processing capacity is low, the equipment utilization rate is insufficient, and the economic efficiency is poor; when the loading coefficient is above 65%, the liquid level in the reactor is too high, and the gas phase buffer space at the top of the reactor is insufficient. On the one hand, the volatile byproducts removed by nitrogen stripping will quickly accumulate in the limited gas phase at the top of the reactor, the gas phase partial pressure will rise, significantly weakening the mass transfer driving force from the liquid phase to the gas phase and reducing the byproduct removal efficiency; on the other hand, stirring and disturbance at high liquid levels can easily cause material mist entrainment, causing liquid phase material to be carried out of the reactor by the gas flow, resulting in material loss.

[0051] By controlling the loading coefficient within the range of 50% to 65%, sufficient single-batch output is ensured, while also providing ample top space and gas-liquid separation space for nitrogen purging.

[0052] Meanwhile, the height-to-diameter ratio of the dissolving vessel 100 and the reaction vessel 200 is limited to 1.40~1.75. This ensures that the stirring shaft is long enough while avoiding the swaying and stability problems caused by the excessively tall vessel body. This height-to-diameter ratio, combined with the double-layer impeller, allows the stirring components to form an up-and-down circulating flow field in the vessel, eliminating the mixing dead zone and ensuring the uniformity of the material in the entire vessel.

[0053] like Figure 1 As shown, in some embodiments of the present invention, the outlet of the condenser 300 is connected to a tert-butanol recovery tank 400.

[0054] Specifically, a tert-butanol recovery tank refers to a storage tank used to receive and store tert-butanol byproducts after condensation and liquefaction in a condenser 300. The material can be stainless steel or carbon steel depending on the chemical properties of tert-butanol. A level gauge and a drain port can be installed on the tank for easy monitoring and periodic recovery.

[0055] The connection between the outlet of condenser 300 and the tert-butanol recovery tank enables the resource recovery and utilization of byproducts from the transesterification reaction. Tert-butanol vapor and some solvent vapor discharged from reactor 200 with nitrogen gas enter condenser 300 and are condensed into liquid under the heat exchange effect of a cooling medium (such as circulating water). The liquid tert-butanol flows from the outlet of condenser 300 into the tert-butanol recovery tank for collection and storage, while uncondensed nitrogen gas and trace amounts of organic matter are discharged from the top of the recovery tank and enter the tail gas treatment system. The condensation and recovery of tert-butanol avoids environmental pollution caused by direct emission of byproducts, and the recovered tert-butanol can be purified by distillation and reused as a chemical raw material.

[0056] Secondly, the present invention also provides a reaction process for efficiently preparing acetylated polyvinyl alcohol, implemented using the reaction apparatus for efficiently preparing acetylated polyvinyl alcohol provided in the embodiments of the first aspect of the present invention, comprising the following steps: S1. Add solvent and polyvinyl alcohol raw material to dissolving kettle 100, dissolve polyvinyl alcohol raw material, and purge with nitrogen gas to remove residual water and small molecule alcohol in polyvinyl alcohol raw material to prepare polyvinyl alcohol solution. S2. Transfer the polyvinyl alcohol solution to reactor 200, add acetylation modifier to carry out transesterification reaction, purge with nitrogen gas at the same time, and remove by-products (such as tert-butanol by-product) through condenser 300.

[0057] Step S1 involves dissolving solid polyvinyl alcohol in an organic solvent by heating to prepare a homogeneous PVA solution. During this step, nitrogen gas is introduced simultaneously with the dissolution of the material to perform stripping, achieving dehydration and removal of small-molecule alcohols. In step S1, heating promotes complete dissolution of the polyvinyl alcohol and reduces the viscosity of the liquid phase; the stirring component disperses the nitrogen gas into microbubbles, increasing the gas-liquid mass transfer contact area. These two processes work synergistically, using nitrogen stripping to reduce the partial pressure of water and small-molecule alcohols in the gas phase, efficiently removing residual water and small-molecule alcohols carried by the PVA raw material, and reducing the risk of side reactions from the acetylation modifying reagents (such as tert-butyl acetoacetate) in the subsequent transesterification stage.

[0058] Step S2 of the transesterification reaction refers to the chemical conversion process in which polyvinyl alcohol (PVA) undergoes a transesterification reaction with an acetoacetate modifier under heating conditions to produce acetylated PVA and tert-butanol. The core of this process lies in the simultaneous introduction of nitrogen gas for stripping to remove the byproduct tert-butanol. In step S2, nitrogen gas is continuously introduced into the reactor for stripping during the transesterification reaction. The generated tert-butanol vaporizes at the reaction temperature. The nitrogen stripping continuously reduces the partial pressure of tert-butanol in the gas phase, promoting liquid-phase mass transfer. The vaporized tert-butanol is carried out of the reactor by the nitrogen gas flow, causing the reaction equilibrium to shift continuously to the right, significantly improving the reaction conversion rate and reaction rate. The nitrogen purging functions of the two steps are independent yet synergistic—S1 significantly reduces side reaction factors at the source, while S2 overcomes the equilibrium limitation through byproduct removal, jointly ensuring the high efficiency of the transesterification process and the high quality of the product.

[0059] In some embodiments of the present invention, in step S1, the nitrogen flow rate in the dissolving vessel 100 is 2~7 NL / h·kg PVA (NL is a standard liter, referring to the gas volume under standard conditions), and the gas content of the solution is controlled to be 4%-8%.

[0060] Specifically, when the nitrogen purging flow rate is below 2.0 NL / h·kg PVA or the gas content is below 4%, the dehydration and removal of small molecule alcohols are ineffective, which can easily lead to the hydrolysis of the modifier; while when the flow rate is above 7 NL / h·kg PVA and the gas content is above 8%, it will cause material splashing loss and energy waste.

[0061] Since nitrogen is dispersed into the reaction system via the stirring component, the gas content of the solution can be controlled by controlling the stirring speed of the stirring component.

[0062] In some embodiments of the present invention, in step S2, the nitrogen flow rate in the reactor 200 is 4-7 NL / h·kgPVA, and the gas content of the solution is controlled to be 5%-9%.

[0063] When the nitrogen flow rate and gas content are low (nitrogen flow rate below 4 NL / h·kg PVA, gas content below 5%), the removal effect of alcohol byproducts is poor and the degree of modification is low. When the nitrogen flow rate and gas content are too high (nitrogen flow rate above 7 NL / h·kg PVA, gas content above 9%), it will cause material splashing loss and energy waste.

[0064] Since nitrogen is dispersed into the reaction system via the stirring component, the gas content of the solution can be controlled by controlling the stirring speed of the stirring component.

[0065] In some embodiments of the present invention, the degree of polymerization of polyvinyl alcohol is 500-3000, and the degree of alcoholysis is not less than 88%. Specifically, the degree of polymerization of polyvinyl alcohol refers to the average number of repeating ethylene alcohol units in the PVA molecular chain, and its value determines the molecular weight and solution viscosity of PVA. The degree of alcoholysis characterizes the molar percentage of vinyl acetate units in the polyvinyl alcohol molecular chain that are converted into hydroxyl groups through alcoholysis, reflecting the hydroxyl content level in the PVA molecule.

[0066] When the degree of polymerization of PVA is below 500, the molecular weight of the modified product is low, resulting in insufficient film-forming properties and mechanical properties. When the degree of polymerization is above 3000, the solution viscosity is too high, which is not conducive to stirring, mixing, and gas dispersion. A degree of alcoholysis of not less than 88% ensures that the PVA molecular chain has a sufficient number of hydroxyl groups for transesterification. If the degree of alcoholysis is too low, the number of hydroxyl sites available for the reaction is small, limiting the potential for further modification.

[0067] In some embodiments of the present invention, the solvent added to the dissolving vessel 100 is one or more of N,N-dimethylformamide, N,N-diethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, 2-pyrrolidone, and N-methylpyrrolidone.

[0068] Specifically, the choice of solvent directly affects the solubility and dissolution temperature of PVA. The common characteristics of the solvents mentioned above are high-boiling-point polar aprotic solvents, meaning that solvents with a boiling point above 150℃ at normal pressure should be selected. These solvents have good solubility for PVA and do not react with acetoacetate under the conditions of this process. Among them, N-methylpyrrolidone has excellent solubility for both polyvinyl alcohol and tert-butyl acetoacetate, and also has good thermal stability and a suitable boiling point; therefore, it is the preferred solvent for this system.

[0069] In some embodiments of the present invention, the acetylation modifier is one or more of methyl acetoacetate, ethyl acetoacetate, n-propyl acetoacetate, isopropyl acetoacetate, allyl acetoacetate, isobutyl acetoacetate, sec-butyl acetoacetate, tert-butyl acetoacetate, n-hexyl acetoacetate, n-heptyl acetoacetate, n-octyl acetoacetate, and benzyl acetoacetate.

[0070] Specifically, the choice of modifying reagent affects the transesterification reaction activity and the degree of acetylation of the product. Among the above-mentioned modifying reagents, acetoacetate esters are used. Different ester group structures result in different reactivity, with methyl acetoacetate and tert-butyl acetoacetate exhibiting higher reactivity and being preferred embodiments.

[0071] In some embodiments of the present invention, during the process of dissolving polyvinyl alcohol raw material in the dissolving vessel 100, the dissolving temperature is 90°C to 140°C and the dissolving time is 3 to 6 hours.

[0072] Specifically, the dissolution temperature refers to the operating temperature range reached and maintained by the material in the dissolution vessel under the heating effect of the jacket, and the dissolution time refers to the time required from the complete addition of PVA solid to complete dissolution.

[0073] When the dissolution temperature is below 90℃, the dissolution rate of PVA in the solvent is too slow, requiring a significantly longer dissolution time. Furthermore, the higher viscosity of the solution hinders the dispersion of nitrogen bubbles and the removal of moisture and small-molecule alcohols. While dissolution temperatures above 140℃ can accelerate the dissolution rate, they approach or exceed the solvent's boiling point, increasing solvent evaporation losses and operational pressure requirements. Additionally, prolonged high-temperature heating may lead to side reactions such as thermal degradation or cross-linking of the PVA molecular chains. Within the preferred temperature range of 90℃ to 140℃, PVA can fully dissolve within 3 to 6 hours to form a homogeneous solution with suitable viscosity, which is beneficial for nitrogen purging dehydration and the removal of small-molecule alcohols.

[0074] In some embodiments of the present invention, the reaction temperature in the reaction vessel 200 during the transesterification reaction is 70°C to 130°C.

[0075] Specifically, the reaction temperature refers to the operating temperature range within the reactor for the transesterification reaction. The transesterification reaction temperature is set at 70℃~130℃, taking into account factors such as reaction rate, equilibrium conversion rate, and side reaction control: too low a temperature results in a slow reaction rate, long reaction time, and low conversion rate; while too high a temperature may increase the reaction rate, it may lead to a darker product color or cross-linking side reactions. This temperature range matches the boiling point of the solvents mentioned above, ensuring the reaction can be carried out under atmospheric or slightly positive pressure, eliminating the need for high-vacuum equipment and reducing equipment investment and operating costs.

[0076] In some embodiments of the present invention, after adding the acetylation modifier in step S2, the reaction continues for 2 to 5 hours.

[0077] Specifically, controlling the reaction time within the range of 2-5 hours fully balances reaction conversion rate and production efficiency. When the reaction time is less than 2 hours, the transesterification reaction has not yet reached equilibrium, resulting in a low modification conversion rate and the degree of acetylation of the product not meeting application requirements. When the reaction time exceeds 5 hours, although the conversion rate may increase slightly, the extended reaction time leads to decreased production efficiency, increased energy consumption, and prolonged high-temperature heating may cause the product to darken in color or cause side reactions. At a reaction temperature of 70℃~130℃, combined with continuous nitrogen purging to remove tert-butanol byproducts, the ideal modification conversion rate can be achieved within 2-5 hours. Compared to the existing single-reactor process, which typically requires more than 8 hours of reaction time, this significantly shortens the reaction cycle and improves production efficiency.

[0078] The following are specific embodiments and comparative examples. Unless otherwise specified, all raw materials used in the following embodiments and comparative examples are commercially available.

[0079] Example 1 This embodiment provides a reaction process for the efficient preparation of acetylated polyvinyl alcohol, including the following steps: S1. 100 kg of PVA (degree of polymerization 1400, degree of alcoholysis 99%, moisture content 1.7%, methanol content 0.5%) and 900 kg of N-methylpyrrolidone were added to a dissolving vessel and dissolved at 110°C for 4 hours. The nitrogen flow rate in the dissolving vessel was 0.45 Nm. 3 The pressure is 2.5 bar (gauge pressure) per hour, the gas content of the solution is 6%, the height-to-diameter ratio of the dissolving vessel is 1.55, the loading coefficient is 57%, and a propeller-type agitator is used, with the ratio of the impeller diameter to the inner diameter of the dissolving vessel being 0.45.

[0080] S2. After dissolution, transfer the PVA solution into a reactor and react at 100°C. Add 2.2 kg of acetylation modifier (methyl acetoacetate) over 2 hours. After the addition is complete, continue the reaction for 4 hours. The nitrogen flow rate in the reactor is 0.55 Nm. 3 The reaction vessel has a flow rate of 1.45 h / h and a gas content of 7%. The height-to-diameter ratio of the reactor is 1.45, and its volume is the same as that of the dissolving vessel. The double-layer impeller in the stirring assembly uses a propeller-type agitator, with an impeller diameter to reactor inner diameter ratio of 0.45. During this process, tert-butanol byproducts are removed via a condenser. After the reaction, the reaction solution undergoes post-treatment processes such as alcohol precipitation, washing, and drying to obtain acetyl-acetyl-modified polyvinyl alcohol.

[0081] Example 2 This embodiment provides a reaction process for the efficient preparation of acetylated polyvinyl alcohol. Compared with Example 1, in this embodiment, the degree of polymerization of PVA is 1600, the degree of alcoholysis is 92%, the moisture content is 2.0%, the methanol content is 0.4%, and N,N-dimethylacetamide is used as the solvent.

[0082] The acetylation modifier was added within 3 hours. The acetylation modifier was isobutyl acetoacetate, and the amount used was 2.5 kg. After adding isobutyl acetoacetate, the reaction time was 2 hours. Other conditions were the same as in Example 1.

[0083] Example 3 This embodiment provides a highly efficient reaction process for preparing acetylated polyvinyl alcohol. Compared with Example 1, in this embodiment, the nitrogen flow rate in the dissolution vessel is 0.228 Nm. 3 With a solution gas content of 4%, a PVA mass of 114 kg, and an N-methylpyrrolidone mass of 1026 kg, the dissolving vessel loading coefficient is approximately 65%, and the nitrogen flow rate in the reaction vessel is 0.614 Nm³. 3 / h, gas content of solution 5%, other conditions are the same as in Example 1.

[0084] Example 4 This embodiment provides a highly efficient reaction process for preparing acetylated polyvinyl alcohol. Compared with Example 1, the nitrogen flow rate in the dissolution vessel is 0.614 Nm. 3 With a solution gas content of 7%, a PVA mass of 87.7 kg, and an N-methylpyrrolidone mass of 789 kg, the dissolving vessel has a loading coefficient of 50%, and the reaction vessel has a nitrogen flow rate of 0.614 Nm³. 3 / h, gas content of solution 9%, other conditions are the same as in Example 1.

[0085] Example 5 This embodiment provides a highly efficient reaction process for preparing acetylated polyvinyl alcohol. Compared with Example 1, the reaction system and equipment are scaled up. 400 kg of PVA and 3600 kg of N-methylpyrrolidone are added to a dissolving vessel, and the nitrogen flow rate in the dissolving vessel is 1.8 Nm. 3 / h, 8.8 kg of methyl acetoacetate was added to the reactor, and the nitrogen flow rate in the reactor was 2.2 Nm. 3 / h, other conditions remain the same as in Example 1.

[0086] Comparative Example 1 Compared to Example 1, no dissolving vessel was set up. Instead, PVA and N-methylpyrrolidone were added to the reaction vessel and dissolved without transferring the materials. After cooling to the reaction temperature of 100°C, 2.2 kg of acetylation modifier (methyl acetoacetate) was added to carry out the reaction. Other conditions were kept the same as in Example 1.

[0087] Comparative Example 2 Compared to Example 1, no condenser is installed after the reactor. The gaseous materials generated by the reactor (mainly tert-butanol and some solvent vapors) are directly collected as tail gas. Everything else is the same as in Example 1.

[0088] Comparative Example 3 Compared to Example 1, the mass of PVA was 122.8 kg, the mass of N-methylpyrrolidone was 1105.3 kg, the filling coefficient of the dissolving vessel was approximately 70%, and the nitrogen flow rate of the dissolving vessel was 0.508 Nm. 3 / h, nitrogen flow rate in the reactor is 0.675 Nm 3 / h, otherwise the same as in Example 1.

[0089] Comparative Example 4 Compared to Example 1, the nitrogen flow rate in the dissolving vessel was adjusted to 0.15 Nm. 3 The gas content of the solution is 3.5% at a flow rate of 0.35 Nm³ / h, and the nitrogen flow rate in the reactor is 0.35 Nm³ / h. 3 / h, the gas content of the solution is 4.5%, and other aspects are the same as in Example 1.

[0090] Comparative Example 5 Compared to Example 1, the hollow structure of the rotating shaft in the stirring assembly is eliminated, that is, the rotating shaft is a solid rotating shaft, the lower impeller does not have an internal cavity, and the lower impeller does not have an air outlet. Other conditions remain the same as in Example 1, and the gas content of the solution is about 0.5%.

[0091] Comparative Example 6 Compared to Example 1, nitrogen purging and a condenser were not used, and the hollow structure of the rotating shaft in the stirring assembly was eliminated; that is, the rotating shaft was a solid shaft, the lower impeller did not have an internal cavity, and the lower impeller did not have an exhaust port. After the materials were added to the dissolving vessel and methyl acetoacetate was added to the reaction vessel, the operation was changed to depressurization to remove moisture and the byproduct methanol. The system pressure was gradually reduced to 0.03 MPa using a vacuum pump, while other conditions remained the same as in Example 1.

[0092] Test results NMR analysis: Using DMSO-d6 as the deuterated reagent, 1H NMR analysis was performed. In the 1H NMR spectrum, the chemical shift δ=2.17 ppm is the characteristic peak of the methyl group in the acetoacetyl group, and its peak area is denoted as a. The chemical shift δ=1.0~1.8 ppm is the characteristic peak of the methylene group on the PVA main chain, and its peak area is denoted as b. Therefore, the degree of modification of the acetoacetyl group is c1= (a / 3) / (b / 2).

[0093] Calculate the conversion rate of acetoacetate, where the mass of PVA is m1, the molecular weight of the vinyl alcohol repeating unit in PVA is 44, the mass of acetoacetate is m2, the molecular weight of acetoacetate is M, the degree of modification of the acetoacetyl group when acetoacetate is completely reacted is c2 = (m1 / M) / (m2 / 44), and the conversion rate of acetoacetate is c1 / c2.

[0094] The results of the above analysis are shown in Table 1.

[0095] Table 1

[0096] As shown in Table 1, in Examples 1-5, under the reaction parameters within the scope of the present invention, the conversion rate of acetoacetate was between 67.2% and 70.6%.

[0097] Compared to Example 1, Comparative Example 1 involved the dissolution and transesterification modification of PVA in the same reactor without material transfer. After the dissolution stage, water vapor and small molecule alcohol vapor accumulated in the gas phase space of the reactor were not effectively discharged, and a certain amount of water and small molecule alcohol remained in the liquid phase. Direct addition of methyl acetoacetate for the reaction easily led to side reactions of methyl acetoacetate, resulting in a low conversion rate.

[0098] Compared to Example 1, in Comparative Example 2, the byproduct methanol could not be effectively condensed, resulting in the byproducts generated in the reaction not being removed from the reaction system in a timely manner, and the reaction equilibrium was difficult to shift effectively to the forward direction. This led to a decrease in conversion rate.

[0099] Compared to Example 1, Comparative Example 3 has a reduced gas phase space inside the reactor, a shorter nitrogen purging path, and insufficient gas-liquid contact time and area. This makes it difficult for moisture, small molecule alcohols, and alcohol byproducts generated in the reaction to escape effectively from the PVA, resulting in a lower conversion rate.

[0100] Compared to Example 1, Comparative Example 4 showed that the low nitrogen flow rate resulted in a low gas content in the solution, which prevented the stirring component from fully dispersing and significantly reduced the gas-liquid mass transfer efficiency. Incomplete dehydration and removal of small-molecule alcohols during the dissolution stage meant that byproduct alcohols could not be carried away by nitrogen in time during the reaction, severely hindering the forward progress of the transesterification reaction and leading to a decrease in conversion rate.

[0101] Compared to Example 1, Comparative Example 5, by removing the stirring assembly provided in this application, shows that nitrogen cannot be effectively drawn in and dispersed into microbubbles through the hollow shaft, resulting in extremely low gas content in the solution and a significant reduction in gas-liquid contact area and mass transfer efficiency. Whether it's the removal of water and small molecule alcohols during the dissolution stage, or the removal of byproduct alcohols during the reaction stage, the effects are significantly worse, failing to achieve the efficient stripping process emphasized in this invention.

[0102] Comparative Example 6 used a reduced-pressure alcohol removal method. Compared with Example 1, although it could remove the alcohol byproducts generated in the reaction to a certain extent, the byproducts and solvents had strong interactions in the high-boiling-point solvent system. Furthermore, problems such as foaming, uneven gas-liquid mass transfer, and vacuum fluctuations easily occurred under vacuum conditions, resulting in low byproduct removal efficiency and insufficient forward shift of the reaction equilibrium. Ultimately, the conversion rate of acetoacetate was only 57.2%, significantly lower than the 68.9% of Example 1.

[0103] While the present invention has been disclosed above, its scope of protection is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention, and all such changes and modifications will fall within the scope of protection of the present invention.

Claims

1. A highly efficient reaction apparatus for preparing acetylated polyvinyl alcohol, characterized in that, include: A dissolving vessel (100) is used to dissolve polyvinyl alcohol raw materials. The upper part of the dissolving vessel (100) is provided with a first nitrogen inlet (110). The first nitrogen inlet (110) is used to introduce nitrogen to purge and remove residual water and small molecule alcohols from the polyvinyl alcohol raw materials. A reaction vessel (200), which is connected to the dissolving vessel (100), is used to receive a polyvinyl alcohol solution from the dissolving vessel (100) and carry out an ester exchange reaction. The upper part of the reaction vessel (200) is provided with a second nitrogen inlet (210), which is used to introduce nitrogen gas to carry away the alcohol byproducts generated by the ester exchange reaction. And a condenser (300) connected to the gas phase outlet of the reactor (200); Both the dissolving vessel (100) and the reaction vessel (200) are equipped with stirring components. The stirring components are used for stirring materials and for dispersing the introduced nitrogen gas into the reaction system.

2. The apparatus for the efficient preparation of acetylated polyvinyl alcohol according to claim 1, characterized in that, The stirring assembly includes a rotating shaft (10) and a stirring impeller (20) fixed on the rotating shaft (10). The stirring impeller (20) includes an upper impeller and a lower impeller, which are spaced apart along the axial direction of the rotating shaft (10). The rotating shaft (10) has a hollow structure. The upper end of the rotating shaft (10) is provided with an air inlet. The lower end of the rotating shaft (10) is connected to the internal cavity of the lower impeller. The lower impeller is provided with an air outlet, which is connected to the internal cavity, so as to disperse the nitrogen gas introduced through the air inlet into the reaction system.

3. The apparatus for the efficient preparation of acetylated polyvinyl alcohol according to claim 2, characterized in that, The ratio of the diameter of the stirring impeller (20) to the inner diameter of the reactor (200) is 0.40~0.

45.

4. The reaction apparatus for the efficient preparation of acetylated polyvinyl alcohol according to claim 1, characterized in that, The upper part of the dissolving vessel (100) is also provided with a first gas outlet (120), and the lower part is provided with a first jacketed heating / cooling system; The dissolving vessel (100) is also provided with a PVA feeding port (140) and a solvent inlet (150) at the top, and a material transfer outlet (160) at the bottom. The material transfer outlet (160) is connected to the reactor (200).

5. The apparatus for the efficient preparation of acetylated polyvinyl alcohol according to claim 1, characterized in that, The upper part of the reactor (200) is also provided with a feed inlet (240) and a PVA solution inlet (220). The reactor (200) is also equipped with a second jacketed heating / cooling system.

6. The apparatus for the efficient preparation of acetylated polyvinyl alcohol according to claim 1, characterized in that, The loading coefficient in the reactor (200) is 50%~65%; In the dissolving vessel (100) and the reaction vessel (200), the ratio of height to diameter is independently 1.40~1.

75.

7. The apparatus for the efficient preparation of acetylated polyvinyl alcohol according to claim 1, characterized in that, The outlet of the condenser (300) is connected to a tert-butanol recovery tank (400).

8. A highly efficient reaction process for preparing acetylated polyvinyl alcohol, implemented using the reaction apparatus for preparing acetylated polyvinyl alcohol as described in any one of claims 1 to 7, characterized in that, Includes the following steps: S1. Add solvent and polyvinyl alcohol raw material to dissolving kettle (100), dissolve polyvinyl alcohol raw material, and purge with nitrogen gas to remove residual water and small molecule alcohol in polyvinyl alcohol raw material to prepare polyvinyl alcohol solution. S2. The polyvinyl alcohol solution is transferred to the reactor (200), an acetylation modifier is added to carry out the transesterification reaction, nitrogen gas is introduced for purging, and byproducts are removed through the condenser (300).

9. The reaction process for efficiently preparing acetylated polyvinyl alcohol according to claim 8, characterized in that, The degree of polymerization of the polyvinyl alcohol is 500-3000, and the degree of alcoholysis is not less than 88%. The solvent added to the dissolving vessel (100) is one or more of N,N-dimethylformamide, N,N-diethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, 2-pyrrolidone, and N-methylpyrrolidone; The acetylation modifying agent is one or more of the following: methyl acetoacetate, ethyl acetoacetate, n-propyl acetoacetate, isopropyl acetoacetate, allyl acetoacetate, isobutyl acetoacetate, sec-butyl acetoacetate, tert-butyl acetoacetate, n-hexyl acetoacetate, n-heptyl acetoacetate, n-octyl acetoacetate, and benzyl acetoacetate.

10. The reaction process for efficiently preparing acetylated polyvinyl alcohol according to claim 8, characterized in that, In the dissolving vessel (100), during the process of dissolving polyvinyl alcohol raw material, the dissolving temperature is 90℃~140℃ and the dissolving time is 3~6 hours; In the reactor (200), the transesterification reaction is carried out at a temperature of 70℃~130℃.

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