Catalyst for preparing polyvinyl alcohol as well as preparation method and application of catalyst

Abstract

The invention discloses a catalyst for preparing polyvinyl alcohol as well as a preparation method and application of the catalyst, the catalyst comprises a palladium salt main catalyst and a phosphine ligand cocatalyst, and the phosphine ligand cocatalyst comprises triphenylphosphine, 2, 3, 4-triphenyl-1, 3, 4-triphenyl-1, 3, 4-triphenyl-1, 3, 4-triphenyl-1, 3, 4- The catalyst is one or more of 2, 2 '-bis (diphenylphosphine)-1, 1'-binaphthalene, bis (2, 6-dimethoxybenzoyl) (2, 4, 4-trimethylpentyl) phosphine oxide, bis [bis (3, 4, 5-trimethoxyphenyl) phosphine], bis (2-diphenylphosphino) ether, 2, 2 '-(di-o-tolyl phosphino) diphenyl ether and bis (dicyclohexylphosphino phenyl) ether, and the catalyst is one or more of 2, 2'-bis (diphenylphosphine)-1, 1 '-binaphthalene, bis (2, 6-dimethoxybenzoyl) (2, 4, 4-trimethylpentyl) phosphine oxide, bis (2, 6-dimethoxybenzoyl) (2, 4, 4-trimethoxyphenyl) phosphine. The catalyst disclosed by the invention has the characteristics of high activity, good stability, safety and easiness in separation from the product polyvinyl acetate, and not only can obviously reduce the potential safety hazard in the PVA preparation process, but also can improve the purity of PVA.

Description

Technical Field

[0001] The invention relates to a catalyst for preparing polyvinyl alcohol, a preparation method and application thereof, and belongs to the technical field of catalysts. Background Art

[0002] Polyvinyl alcohol (PVA) is an important polymer material widely used in textiles, papermaking, coatings, adhesives, and other fields. Traditionally, PVA is prepared by polymerizing vinyl acetate (VAc) followed by alcoholysis. Common catalysts used in traditional polymerization reactions include azobisisobutyronitrile, azobisisoheptanenitrile, dibenzoyl peroxide, tert-butyl peroxyneodecanoate, di(3,5,5-trimethylhexanoyl) peroxide, tert-butyl hydroperoxide, tert-butyl peroxypivalate, and lauroyl peroxide. All of these catalysts are hazardous chemicals, requiring manufacturers to obtain hazardous chemical licenses and be subject to strict regulations. Furthermore, both azobisisobutyronitrile and azobisisoheptanenitrile are highly toxic, flammable, and explosive. They react with water to generate nitrogen gas and toxic organic cyanides. Dibenzoyl peroxide, tert-butyl peroxyneodecanoate, di(3,5,5-trimethylhexanoyl) peroxide, tert-butyl hydroperoxide, tert-butyl peroxypivalate, and lauroyl peroxide are extremely unstable and may explode when exposed to friction, impact, or high temperature.

[0003] Due to the limitations of existing process technology, the catalyst added during the polymerization of vinyl acetate does not have a decontamination process. The added catalyst will enter the PVA finished product as the polyvinyl acetate is hydrolyzed, thereby reducing the purity of the finished product.

[0004] Chinese patent publication number CN111822050B discloses a carbonylation catalyst composition and a method for preparing neopentyl glycol. The catalyst composition comprises: a palladium- or rhodium-containing compound; one or more of diphenylphosphine pyrrole, triphenylphosphine pyrrole, diphenylphosphine-naphthalenesulfonic acid, or triphenylphosphine-naphthalenesulfonic acid; and one or more of copper bromide, p-toluenesulfonic acid, boron trifluoride, or lanthanum trifluoromethanesulfonate. The method for preparing neopentyl glycol comprises the following steps: (1) carbonylating propyne to produce methacrolein; (2) carbonylating methacrolein in the presence of the catalyst composition to produce dimethylmalonaldehyde; and (3) hydrogenating the neopentyl glycol. The catalyst composition is capable of efficiently catalyzing the carbonylation reaction of α,β-unsaturated carbonyl compounds.

[0005] Chinese patent publication number CN104447317B discloses a method for synthesizing ethylene diacetate from methyl acetate, primarily addressing the low conversion rate of methyl acetate and low selectivity of ethylene diacetate in the prior art. The method utilizes MeOAc, CO, and H₂ as raw materials, primarily using SOCl₂ as a solvent, or primarily using a mixture of SOCl₂ and sulfolane as a solvent, to generate ethylene diacetate in the presence of a catalyst. The catalyst comprises a primary catalyst, a co-catalyst, and a promoter. The primary catalyst comprises a VIII metal or a compound thereof; the co-catalyst is a halogen-containing compound; and the promoter is a nitrogen-oxygen organic compound or a phosphorus-containing compound.

[0006] None of the above existing catalysts can be used for the preparation of polyvinyl alcohol, so there is an urgent need to prepare a catalyst for the preparation of polyvinyl alcohol. Summary of the Invention

[0007] In order to overcome the problems existing in the prior art, the catalysts currently used for the preparation of polyvinyl alcohol are all hazardous chemicals and their production is risky. The present invention provides a catalyst for the preparation of polyvinyl alcohol, a preparation method and application thereof, and the specific technical scheme is as follows.

[0008] A catalyst for preparing polyvinyl alcohol, comprising a palladium salt main catalyst and a phosphine ligand co-catalyst, wherein the phosphine ligand co-catalyst comprises one or more of triphenylphosphine, 2,2'-bis(diphenylphosphino)-1,1'-binaphthyl, bis(2,6-dimethoxybenzoyl)(2,4,4-trimethylpentyl)phosphine oxide, bis[bis(3,4,5-trimethoxyphenyl)phosphine], bis(2-diphenylphosphinophenyl) ether, 2,2'-(di-o-tolylphosphino)diphenyl ether, and bis(dicyclohexylphosphinophenyl) ether; The palladium salt main catalyst includes one or more of palladium chloride, palladium chloride hydrate, bistriphenylpalladium chloride, 1,2-bis(diphenylphosphino)ethanepalladium chloride, 1,1'-bis(diphenylphosphino)ferrocenepalladium dichloride, and bistriphenylphosphinepalladium dichloride.

[0009] The present invention uses a palladium salt main catalyst and a phosphine ligand co-catalyst to interact with each other to promote the alcoholysis of polyvinyl alcohol. The palladium salt main catalyst and the phosphine ligand co-catalyst are loaded on a carrier, which can solve the problem of polyvinyl alcohol obtained by alcoholysis being mixed with a large number of black spots.

[0010] The possible mechanism of the alcoholysis of PVA catalyzed by the catalyst introduced in the present invention is: The first stage: palladium catalyst (usually Pd(0) or Pd(II)) forms active species with phosphine ligands (such as PPh3, dppp, etc.); the second stage: the ester group in polyvinyl acetate coordinates with the active species, polarizes the C=O bond, and further enhances the electrophilicity of carbon; the third stage: water molecules attack the activated carbonyl carbon to form active carboxylic acid; the fourth stage: the active carboxylic acid proton transfers to form PVA and palladium-containing carboxylic acid; the fifth stage: the active carboxylic acid dissociates into carboxylic acid and palladium phosphine active species, and the palladium phosphine active species can continue to catalyze the reaction, completing the catalytic cycle.

[0011] The functions of phosphine ligands include: stabilizing the oxidation state of palladium; regulating electron density; controlling coordination steric hindrance; and adjusting the Lewis acidity of palladium.

[0012] The possible mechanism of PVA alcoholysis catalyzed by palladium and phosphorus ligands is shown in the figure below. Figure 1 shown.

[0013] In a preferred embodiment, the invention further comprises a carrier on which the palladium salt primary catalyst and the phosphine ligand co-catalyst are supported. The carrier comprises one or more of silica gel, alumina, and molecular sieves. The use of such a carrier can resolve the problem of polyvinyl alcohol produced by alcoholysis being interspersed with numerous black spots.

[0014] In one preferred embodiment, the molar ratio of the palladium salt main catalyst to the phosphine ligand co-catalyst is 1:2.05-1:2.30.

[0015] In one preferred embodiment, the mass ratio of the palladium salt main catalyst and the phosphine ligand co-catalyst to the carrier is 1:3.0-1:3.5. The above mass ratio can further improve the catalytic efficiency of the catalyst prepared by the present invention.

[0016] The present invention also discloses a method for preparing the catalyst, comprising the following steps: S1. Under the protection of inert gas, add palladium salt main catalyst, solvent A, and phosphine ligand co-catalyst, stir, react, filter, and vacuum dry to obtain a catalyst precursor; S2. The catalyst precursor and the carrier in S1 are uniformly stirred and calcined to obtain a catalyst.

[0017] In one preferred embodiment, the specific process of the reaction in S1 is to dropwise add the non-polar solvent B within 30 minutes and cool the reaction mixture to an internal temperature of 0-5°C.

[0018] In one preferred embodiment, the vacuum drying pressure in S1 is -0.1 to -0.3 MPa, the temperature is 50 to 60° C., and the vacuum drying time is 13 to 15 hours.

[0019] In one preferred embodiment, the calcination temperature in S2 is 300-400° C., and the calcination time is 12-14 hours.

[0020] Preferably, solvent A in S1 is a polar aprotic solvent, and the stirring time is 1 to 3 hours.

[0021] Preferably, the polar aprotic solvent comprises tetrahydrofuran.

[0022] Preferably, the non-polar solvent B is n-heptane.

[0023] Preferably, S1 is cooled to 0-5°C before filtering.

[0024] Preferably, the stirring time in S2 is 2 to 4 hours, and the stirring speed is 100 to 200 r / min.

[0025] The above process parameters interact with each other and help improve the catalyst yield and catalytic efficiency.

[0026] The present invention also discloses a catalyst for preparing polyvinyl alcohol as described above, or use of the catalyst prepared by the preparation method as described above in preparing polyvinyl alcohol, comprising the following steps: a solvent, vinyl acetate monomer and a catalyst are mixed, the polymerization reaction is carried out, after the reaction is completed, the catalyst is filtered out, and the filtrate is evaporated to obtain a polyvinyl acetate methanol solution; b. alcoholyzing the polyvinyl acetate methanol solution in step a to obtain polyvinyl alcohol.

[0027] Preferably, the polymerization reaction temperature in step a is 50-60° C. and the time is 10-12 h.

[0028] Preferably, the specific steps of step b are adding a solvent and a polyvinyl acetate methanol solution into a container, heating, then dropwise adding a sodium hydroxide methanol solution, filtering, keeping warm, and drying to obtain polyvinyl alcohol.

[0029] Preferably, the heating temperature in step b is 50-60° C. In step b, vacuum drying is adopted, and the drying temperature is 60-70° C. under a pressure of -0.1-0.3 MPa for 5-7 hours.

[0030] Preferably, the mass fraction of the sodium hydroxide methanol solution is 0.01-0.05%.

[0031] Compared with the prior art, the present invention has the following beneficial effects.

[0032] The catalyst of the present invention is highly stable, safe, non-toxic, and highly efficient, effectively reducing safety risks in production. The catalyst is easily separated from polyvinyl acetate, effectively preventing the catalyst from entering the subsequent alcoholysis reaction, thereby improving the purity of the finished PVA and further enhancing the core competitiveness of the enterprise. The catalyst preparation method of the present invention is simple and amenable to industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 The diagram shows the mechanism of PVA alcoholysis catalyzed by palladium and phosphorus ligands. DETAILED DESCRIPTION

[0034] The present invention is described in further detail below.

[0035] In order to further understand the content and features of the present invention, the present invention is described below with specific embodiments. Example 1

[0036] To a nitrogen-protected reaction flask, 17.73 g of palladium chloride was added, 26.60 g of tetrahydrofuran was added and stirred at room temperature for 10 minutes, and finally 53.77 g of triphenylphosphine was added. After stirring at room temperature for 2 hours, 79.80 g of n-heptane was added dropwise over 30 minutes. After cooling to an internal temperature of 0-5°C, the mixture was filtered and dried in a vacuum drying oven at 55°C under a pressure of -0.1 MPa for 14 hours to obtain 70.57 g of beige catalyst precursor 1 with a yield of 98.0%.

[0037] 70.57 g of the obtained catalyst precursor 1 and 211.71 g of silica gel with a particle size of 300-400 mesh were stirred and mixed in a rotary stirrer for 3 hours at a rotation speed of 110 r / min. The resulting mixture was then calcined in a muffle furnace at 340° C. for 14 hours and naturally cooled to room temperature to obtain the final catalyst 1.

[0038] To a 5000ml reaction flask, add 1200.00g of methanol and 1000.00g of vinyl acetate. Stirring was initiated, nitrogen was introduced to displace the air, and 0.03g of Catalyst 1 was added as an initiator. The reaction flask was heated to an internal temperature of 56°C, and the polymerization reaction timer was started. After 11 hours of reaction, the catalyst was filtered out, and the temperature was then raised to 90°C for 2.5 hours to evaporate the residual monomer and methanol. The solid content of the polyvinyl acetate was measured, and the mass fraction of the polyvinyl acetate was adjusted by adding methanol to prepare a polyvinyl acetate methanol solution with a mass fraction of approximately 30%.

[0039] To a 1500ml reaction flask, add 120.00g of methanol and 200.00g of polyvinyl acetate methanol solution, start stirring and heating, introduce nitrogen to replace the air, and after the internal temperature rises to 56°C, add 100.00g of 0.019% sodium hydroxide methanol solution dropwise over about 2 hours. Maintain the internal temperature at 56°C and react for about 2.5 hours to observe the precipitation of a white flocculent solid. After the solid precipitates, continue to keep the temperature at 56°C and react for one hour. Filter to obtain a white solid, place the obtained solid in an aluminum tray, and place it in a drying oven that can be vacuumed and dried while vacuuming. After drying in a vacuum drying oven at 70°C under a pressure of -0.1MPa for 6 hours, a white powdery PVA is prepared.

[0040] Example 2 To a nitrogen-protected reaction flask, 17.73 g of palladium chloride was added, 26.60 g of tetrahydrofuran was added and stirred at room temperature for 10 minutes, and finally 127.65 g of (2,2'-bis(diphenylphosphine)-1,1'-binaphthyl) was added. After stirring at room temperature for 2 hours, 79.80 g of n-heptane was added dropwise over 30 minutes. After cooling to an internal temperature (the temperature inside the reaction flask) of 0-5°C, the mixture was filtered and dried in a vacuum drying oven at a temperature of 55°C under a pressure of -0.1 MPa for 14 hours to obtain 142.21 g of white catalyst precursor 2 with a yield of 97.8%.

[0041] The obtained 142.21 g of catalyst precursor 2 and 426.63 g of silica gel with a particle size of 300-400 mesh were stirred and mixed in a rotary stirrer for 3 hours at a rotation speed of 110 r / min. The resulting mixture was then calcined in a muffle furnace at 340°C for 14 hours and naturally cooled to room temperature to obtain the final catalyst 2.

[0042] To a 5000ml reaction flask, add 1200.00g of methanol and 1000.00g of vinyl acetate. Stirring was initiated, nitrogen was introduced to displace the air, and 0.03g of Catalyst 2 was added as an initiator. The reaction flask was heated to an internal temperature of 56°C, and the polymerization reaction timer was started. After 11 hours of reaction, the catalyst was filtered out, and the temperature was then raised to 90°C for 2.5 hours to evaporate the residual monomer and methanol. The solid content of the polyvinyl acetate was measured, and the mass fraction of the polyvinyl acetate was adjusted by adding methanol to prepare a polyvinyl acetate methanol solution with a mass fraction of approximately 30%.

[0043] To a 1500ml reaction flask, add 120.00g of methanol and 200.00g of polyvinyl acetate methanol solution, start stirring and heating, introduce nitrogen to replace the air, and after the internal temperature rises to 56°C, add 100.00g of 0.019% sodium hydroxide methanol solution dropwise over about 2 hours. Maintain the internal temperature at 56°C and react for about 2.5 hours to observe the precipitation of a white flocculent solid. After the solid precipitates, continue to keep the temperature at 56°C and react for one hour. Filter to obtain a white solid, place the obtained solid in an aluminum tray, and place it in a drying oven that can be vacuumed and dried while vacuuming. After drying in a vacuum drying oven at 70°C under a pressure of -0.1MPa for 6 hours, a white powdery PVA is prepared.

[0044] Example 3 To a nitrogen-protected reaction flask, 17.73 g of palladium chloride was added, 26.60 g of tetrahydrofuran was added and stirred at room temperature for 10 minutes, and finally 100.56 g of bis(2,6-dimethoxybenzoyl)(2,4,4-trimethylpentyl)phosphine oxide was added. After stirring at room temperature for 2 hours, 79.80 g of n-heptane was added dropwise over 30 minutes. After cooling to an internal temperature of 0-5°C, the mixture was filtered and dried in a vacuum drying oven at 55°C under a pressure of -0.1 MPa for 14 hours to obtain 116.24 g of brown catalyst precursor 3 with a yield of 98.3%.

[0045] 116.24 g of the obtained catalyst precursor 2 and 348.72 g of silica gel with a particle size of 300-400 mesh were stirred and mixed in a rotary stirrer for 3 hours at a rotation speed of 110 r / min. The resulting mixture was then calcined in a muffle furnace at 340°C for 14 hours and naturally cooled to room temperature to obtain the final catalyst 3.

[0046] To a 5000ml reaction flask, add 1200.00g of methanol and 1000.00g of vinyl acetate. Stirring was initiated, nitrogen was introduced to displace the air, and 0.03g of Catalyst 3 was added as an initiator. The reaction flask was heated to an internal temperature of 56°C. The polymerization reaction was started, and after 11 hours, the catalyst was filtered out. The temperature was then raised to 90°C and evaporated for 2.5 hours to recover residual monomers and methanol. The solids content of the polyvinyl acetate was measured, and the mass fraction of the polyvinyl acetate was adjusted by adding methanol to prepare a polyvinyl acetate methanol solution with a mass fraction of approximately 30%.

[0047] To a 1500ml reaction flask, add 120.00g of methanol and 200.00g of polyvinyl acetate methanol solution, start stirring and heating, introduce nitrogen to replace the air, and after the internal temperature rises to 56°C, add 100.00g of 0.019% sodium hydroxide methanol solution dropwise over about 2 hours. Maintain the internal temperature at 56°C and react for about 2.5 hours to observe the precipitation of a white flocculent solid. After the solid precipitates, continue to keep the temperature at 56°C and react for one hour. Filter to obtain a white solid, place the obtained solid in an aluminum tray, and place it in a drying oven that can be vacuumed and dried while vacuuming. After drying in a vacuum drying oven at 70°C under a pressure of -0.1MPa for 6 hours, a white powdery PVA is prepared.

[0048] Example 4 To a nitrogen-protected reaction flask, 17.73 g of palladium chloride was added, 26.60 g of tetrahydrofuran was added and stirred at room temperature for 10 minutes, and finally 94.28 g of di-bis(3,4,5-trimethoxyphenyl)phosphine was added. After stirring at room temperature for 2 hours, 79.80 g of n-heptane was added dropwise over 30 minutes. After cooling to an internal temperature of 0-5°C, the mixture was filtered and dried in a vacuum drying oven at a temperature of 55°C under a pressure of -0.1 MPa for 14 hours to obtain 109.21 g of black catalyst precursor 4 with a yield of 97.5%.

[0049] 109.21 g of the obtained catalyst precursor 4 and 327.63 g of silica gel with a particle size of 300-400 mesh were stirred and mixed in a rotary stirrer for 3 hours at a rotation speed of 110 r / min. The resulting mixture was then calcined in a muffle furnace at 340°C for 14 hours and naturally cooled to room temperature to obtain the final catalyst 4.

[0050] To a 5000ml reaction flask, add 1200.00g of methanol and 1000.00g of vinyl acetate. Stirring was initiated, nitrogen was introduced to displace the air, and 0.03g of Catalyst 4 was added as an initiator. The reaction flask was heated to an internal temperature of 56°C, and the polymerization reaction timer was started. After 11 hours of reaction, the catalyst was filtered out, and the temperature was then raised to 90°C for 2.5 hours to evaporate the residual monomer and methanol. The solid content of the polyvinyl acetate was measured, and the mass fraction of the polyvinyl acetate was adjusted by adding methanol to prepare a polyvinyl acetate methanol solution with a mass fraction of approximately 30%.

[0051] To a 1500ml reaction flask, add 120.00g of methanol and 200.00g of polyvinyl acetate methanol solution, start stirring and heating, introduce nitrogen to replace the air, and after the internal temperature rises to 56°C, add 100.00g of 0.019% sodium hydroxide methanol solution dropwise over about 2 hours. Maintain the internal temperature at 56°C and react for about 2.5 hours to observe the precipitation of a white flocculent solid. After the solid precipitates, continue to keep the temperature at 56°C and react for one hour. Filter to obtain a white solid, place the obtained solid in an aluminum tray, and place it in a drying oven that can be vacuumed and dried while vacuuming. After drying in a vacuum drying oven at 70°C under a pressure of -0.1MPa for 6 hours, a white powdery PVA is prepared.

[0052] Example 5 17.73 g of palladium chloride was added to a nitrogen-protected reaction flask, 26.60 g of tetrahydrofuran was added and stirred at room temperature for 10 minutes, and finally 85.27 g of bis(2-diphenylphosphinophenyl)ether was added. After stirring at room temperature for 2 hours, 79.80 g of n-heptane was added dropwise over 30 minutes. After cooling to an internal temperature of 0-5°C, the mixture was filtered and dried in a vacuum drying oven at a temperature of 55°C under a pressure of -0.1 MPa for 14 hours to obtain 100.00 g of white catalyst precursor 5 with a yield of 97.1%.

[0053] 100.00 g of the obtained catalyst precursor 5 and 300.00 g of silica gel with a particle size of 300-400 mesh were stirred and mixed in a rotary stirrer for 3 hours at a rotation speed of 110 r / min. The resulting mixture was then calcined in a muffle furnace at 340° C. for 14 hours and naturally cooled to room temperature to obtain the final catalyst 5.

[0054] To a 5000ml reaction flask, add 1200.00g of methanol and 1000.00g of vinyl acetate. Stirring was initiated, nitrogen was introduced to displace the air, and 0.03g of Catalyst 5 was added as an initiator. The reaction flask was heated to an internal temperature of 56°C, and the polymerization reaction timer was started. After 11 hours of reaction, the catalyst was filtered out, and the temperature was then raised to 90°C for 2.5 hours to evaporate the residual monomer and methanol. The solid content of the polyvinyl acetate was measured, and the mass fraction of the polyvinyl acetate was adjusted by adding methanol to prepare a polyvinyl acetate methanol solution with a mass fraction of approximately 30%.

[0055] To a 1500ml reaction flask, add 120.00g of methanol and 200.00g of polyvinyl acetate methanol solution, start stirring and heating, introduce nitrogen to replace the air, and after the internal temperature rises to 56°C, add 100.00g of 0.019% sodium hydroxide methanol solution dropwise over about 2 hours. Maintain the internal temperature at 56°C and react for about 2.5 hours to observe the precipitation of a white flocculent solid. After the solid precipitates, continue to keep the temperature at 56°C and react for one hour. Filter to obtain a white solid, place the obtained solid in an aluminum tray, and place it in a drying oven that can be vacuumed and dried while vacuuming. After drying in a vacuum drying oven at 70°C under a pressure of -0.1MPa for 6 hours, a white powdery PVA is prepared.

[0056] Example 6 To a nitrogen-protected reaction flask, 17.73 g of palladium chloride was added, 26.60 g of tetrahydrofuran was added and stirred at room temperature for 10 minutes, and finally 74.29 g of 2,2'-(di-o-tolylphosphino)diphenyl ether was added. After stirring at room temperature for 2 hours, 79.80 g of n-heptane was added dropwise over 30 minutes. After cooling to an internal temperature of 0-5°C, the mixture was filtered and dried in a vacuum drying oven at 55°C under a pressure of -0.1 MPa for 14 hours to obtain 90.04 g of white catalyst precursor 6 with a yield of 97.8%.

[0057] The obtained 90.04 g of catalyst precursor 6 and 270.12 g of silica gel with a particle size of 300-400 mesh were stirred and mixed in a rotary stirrer for 3 hours at a rotation speed of 110 r / min. The obtained mixture was then calcined at 340°C in a muffle furnace for 14 hours and naturally cooled to room temperature to obtain the final catalyst 6.

[0058] To a 5000ml reaction flask, add 1200.00g of methanol and 1000.00g of vinyl acetate. Stirring was initiated, nitrogen was introduced to displace the air, and 0.03g of Catalyst 6 was added as an initiator. The reaction flask was heated to an internal temperature of 56°C, and the polymerization reaction timer was started. After 11 hours of reaction, the catalyst was filtered out, and the temperature was then raised to 90°C for 2.5 hours to evaporate the residual monomer and methanol. The solid content of the polyvinyl acetate was measured, and the mass fraction of the polyvinyl acetate was adjusted by adding methanol to prepare a polyvinyl acetate methanol solution with a mass fraction of approximately 30%.

[0059] To a 1500ml reaction flask, add 120.00g of methanol and 200.00g of polyvinyl acetate methanol solution, start stirring and heating, introduce nitrogen to replace the air, and after the internal temperature rises to 56°C, add 100.00g of 0.019% sodium hydroxide methanol solution dropwise over about 2 hours. Maintain the internal temperature at 56°C and react for about 2.5 hours to observe the precipitation of a white flocculent solid. After the solid precipitates, continue to keep the temperature at 56°C and react for one hour. Filter to obtain a white solid, place the obtained solid in an aluminum tray, and place it in a drying oven that can be vacuumed and dried while vacuuming. After drying in a vacuum drying oven at 70°C under a pressure of -0.1MPa for 6 hours, a white powdery PVA is prepared.

[0060] Example 7 To a nitrogen-protected reaction flask, 21.53 g of bistriphenylpalladium chloride was added, 32.30 g of tetrahydrofuran was added and stirred at room temperature for 10 minutes, and finally 53.77 g of triphenylphosphine was added. After stirring at room temperature for 2 hours, 96.90 g of n-heptane was added dropwise over 30 minutes. After cooling to an internal temperature of 0-5°C, the mixture was filtered and dried in a vacuum drying oven at 55°C under a pressure of -0.1 MPa for 14 hours to obtain 78.20 g of white catalyst precursor 7 with a yield of 98.6%.

[0061] The obtained 78.20 g of catalyst precursor 7 and 234.6 g of silica gel with a particle size of 300-400 mesh were stirred and mixed in a rotary stirrer for 3 hours at a rotation speed of 110 r / min. The obtained mixture was then calcined at 340°C in a muffle furnace for 14 hours and naturally cooled to room temperature to obtain the final catalyst 7.

[0062] To a 5000ml reaction flask, add 1200.00g of methanol and 1000.00g of vinyl acetate. Stirring was initiated, nitrogen was introduced to displace the air, and 0.03g of Catalyst 7 was added as an initiator. The reaction flask was heated to an internal temperature of 56°C. The polymerization reaction was started, and after 11 hours, the catalyst was filtered out. The temperature was then raised to 90°C and evaporated for 2.5 hours to recover residual monomers and methanol. The solids content of the polyvinyl acetate was measured, and the mass fraction of the polyvinyl acetate was adjusted by adding methanol to prepare a polyvinyl acetate methanol solution with a mass fraction of approximately 30%.

[0063] To a 1500ml reaction flask, add 120.00g of methanol and 200.00g of polyvinyl acetate methanol solution, start stirring and heating, introduce nitrogen to replace the air, and after the internal temperature rises to 56°C, add 100.00g of 0.019% sodium hydroxide methanol solution dropwise over about 2 hours. Maintain the internal temperature at 56°C and react for about 2.5 hours to observe the precipitation of a white flocculent solid. After the solid precipitates, continue to keep the temperature at 56°C and react for one hour. Filter to obtain a white solid, place the obtained solid in an aluminum tray, and place it in a drying oven that can be vacuumed and dried while vacuuming. After drying in a vacuum drying oven at 70°C under a pressure of -0.1MPa for 6 hours, a white powdery PVA is prepared.

[0064] Example 8 To a nitrogen-protected reaction flask, 57.57 g of 1,2-bis(diphenylphosphino)ethanepalladium chloride was added, 86.36 g of tetrahydrofuran was added and stirred at room temperature for 10 minutes, and finally 53.77 g of triphenylphosphine was added. After stirring at room temperature for 2 hours, 259.08 g of n-heptane was added dropwise over 30 minutes. After cooling to an internal temperature of 0-5°C, the mixture was filtered and dried in a vacuum drying oven at a temperature of 55°C under a pressure of -0.1 MPa for 14 hours to obtain 110.26 g of white catalyst precursor 8 with a yield of 99.0%.

[0065] 110.26 g of the obtained catalyst precursor 8 and 234.6 g of alumina with a particle size of 200-500 mesh were stirred and mixed in a rotary stirrer for 3 hours at a rotation speed of 110 r / min. The resulting mixture was then calcined at 340°C in a muffle furnace for 14 hours and naturally cooled to room temperature to obtain the final catalyst 8.

[0066] To a 5000ml reaction flask, add 1200.00g of methanol and 1000.00g of vinyl acetate. Stirring was initiated, nitrogen was introduced to displace the air, and 0.03g of Catalyst 8 was added as an initiator. The reaction flask was heated to an internal temperature of 56°C. The polymerization reaction was started, and after 11 hours, the catalyst was filtered out. The temperature was then raised to 90°C and evaporated for 2.5 hours to recover residual monomers and methanol. The solids content of the polyvinyl acetate was measured, and the mass fraction of the polyvinyl acetate was adjusted by adding methanol to prepare a polyvinyl acetate methanol solution with a mass fraction of approximately 30%.

[0067] To a 1500ml reaction flask, add 120.00g of methanol and 200.00g of polyvinyl acetate methanol solution, start stirring and heating, introduce nitrogen to replace the air, and after the internal temperature rises to 56°C, add 100.00g of 0.019% sodium hydroxide methanol solution dropwise over about 2 hours. Maintain the internal temperature at 56°C and react for about 2.5 hours to observe the precipitation of a white flocculent solid. After the solid precipitates, continue to keep the temperature at 56°C and react for one hour. Filter to obtain a white solid, place the obtained solid in an aluminum tray, and place it in a drying oven that can be vacuumed and dried while vacuuming. After drying in a vacuum drying oven at 70°C under a pressure of -0.1MPa for 6 hours, a white powdery PVA is prepared.

[0068] Example 9 To a nitrogen-protected reaction flask, 73.17 g of 1,1'-bis(diphenylphosphino)ferrocenepalladium dichloride was added, 109.76 g of tetrahydrofuran was added and stirred at room temperature for 10 minutes, and finally 53.77 g of triphenylphosphine was added. After stirring at room temperature for 2 hours, 329.28 g of n-heptane was added dropwise over 30 minutes. After cooling to an internal temperature of 0-5°C, the mixture was filtered and dried in a vacuum drying oven at a temperature of 55°C under a pressure of -0.1 MPa for 14 hours to obtain 125.12 g of white catalyst precursor 9 with a yield of 98.6%.

[0069] The obtained 125.12 g of catalyst precursor 9 and 375.36 g of molecular sieve with a particle size of 20-60 mesh were stirred and mixed in a rotary stirrer for 3 hours at a rotation speed of 110 r / min. The resulting mixture was then calcined at 340°C in a muffle furnace for 14 hours and naturally cooled to room temperature to obtain the final catalyst 9.

[0070] To a 5000ml reaction flask, add 1200.00g of methanol and 1000.00g of vinyl acetate. Stirring was initiated, nitrogen was introduced to displace the air, and 0.03g of Catalyst 9 was added as an initiator. The reaction flask was heated to an internal temperature of 56°C. The polymerization reaction was started, and after 11 hours, the catalyst was filtered out. The temperature was then raised to 90°C and evaporated for 2.5 hours to recover residual monomers and methanol. The solids content of the polyvinyl acetate was measured, and the mass fraction of the polyvinyl acetate was adjusted by adding methanol to prepare a polyvinyl acetate methanol solution with a mass fraction of approximately 30%.

[0071] To a 1500ml reaction flask, add 120.00g of methanol and 200.00g of polyvinyl acetate methanol solution, start stirring and heating, introduce nitrogen to replace the air, and after the internal temperature rises to 56°C, add 100.00g of 0.019% sodium hydroxide methanol solution dropwise over about 2 hours. Maintain the internal temperature at 56°C and react for about 2.5 hours to observe the precipitation of a white flocculent solid. After the solid precipitates, continue to keep the temperature at 56°C and react for one hour. Filter to obtain a white solid, place the obtained solid in an aluminum tray, and place it in a drying oven that can be vacuumed and dried while vacuuming. After drying in a vacuum drying oven at 70°C under a pressure of -0.1MPa for 6 hours, a white powdery PVA is prepared.

[0072] The PVA prepared in the examples was tested, and the test methods and quality indicators are shown in Table 1.

[0073]

[0074] The test results of the PVA prepared in Examples 1-5 are shown in Table 2, and the test results of the PVA prepared in Examples 6-9 are shown in Table 3.

[0075]

[0076]

[0077]

[0078] Comparative Example 1 53.77 g of triphenylphosphine and 211.71 g of silica gel with a particle size of 300-400 mesh were stirred and mixed in a rotary stirrer at a speed of 110 r / min for 3 hours. The resulting mixture was then calcined in a muffle furnace at 340° C. for 14 hours and naturally cooled to room temperature to obtain the final catalyst 10.

[0079] 1200.00g of methanol and 1000.00g of vinyl acetate were added to a 5000ml reaction flask, stirring was started, nitrogen was introduced to replace the air, and then 0.03g of catalyst 10 was added as an initiator. The reaction flask was heated to an internal temperature of 56°C and the polymerization reaction was started. After 11 hours of reaction time, 200mL of the reaction liquid was taken and the solvent was distilled off under reduced pressure. As a result, all the liquid could be removed and only a very small amount of white solid remained. After gas chromatography, the distilled liquid was the reactant vinyl acetate and the solvent methanol, indicating that the reaction would not occur if the palladium salt main catalyst was removed.

[0080] Comparative Example 2 17.73 g of palladium chloride and 211.71 g of silica gel with a particle size of 300-400 mesh were stirred and mixed in a rotary stirrer for 3 hours at a rotation speed of 110 r / min. The resulting mixture was then calcined in a muffle furnace at 340°C for 14 hours and naturally cooled to room temperature to obtain the final catalyst 11.

[0081] 1200.00 g of methanol and 1000.00 g of vinyl acetate were added to a 5000 ml reaction flask, stirring was started, nitrogen was introduced to replace the air, and then 0.03 g of catalyst 11 was added as an initiator. The reaction flask was heated to an internal temperature of 56°C and the polymerization reaction was started. After 11 hours of reaction time, 200 mL of the reaction liquid was taken and the solvent was distilled off under reduced pressure. As a result, all the liquid could be removed and only a very small amount of white solid remained. After gas chromatography, the distilled liquid was the reactant vinyl acetate and the solvent methanol, indicating that the reaction would not occur even if the co-catalyst was removed.

[0082] Comparative Example 3 The precursor 1 obtained in Example 1 was not loaded on a carrier and was directly used to catalyze the alcoholysis of polyvinyl alcohol. The specific effects are as follows:

[0083] To a 5000ml reaction flask, add 1200.00g of methanol and 1000.00g of vinyl acetate. Stirring was initiated, nitrogen was introduced to displace the air, and 0.03g of catalyst precursor 1 was added as an initiator. The reaction flask was heated to an internal temperature of 56°C, and the polymerization reaction timer was started. After 11 hours of reaction, insoluble matter was filtered out. The temperature was then raised to 90°C and evaporated for 2.5 hours to recover residual monomers and methanol. The solids content of the polyvinyl acetate was measured, and the mass fraction of the polyvinyl acetate was adjusted by adding methanol, ultimately resulting in a polyvinyl acetate methanol solution with a mass fraction of approximately 30%.

[0084] 120.00g of methanol and 200.00g of polyvinyl acetate methanol solution were added to a 1500ml reaction bottle, stirring and heating were started, nitrogen was introduced to replace the air, and after the internal temperature rose to 56°C, 100.00g of 0.019% sodium hydroxide methanol solution was added dropwise over a period of about 2 hours. The internal temperature was maintained at 56°C and the reaction was carried out for about 2.5 hours. A white flocculent solid was observed to precipitate, and some small black particles were mixed in the solid. After the solid precipitated, the temperature was continued to be kept at 56°C for one hour. A white solid mixed with a large number of black spots was obtained by filtration. The obtained solid was placed in an aluminum tray and placed in a drying oven that can be vacuumed and dried while vacuuming. PVA was prepared after drying in a vacuum drying oven at 70°C under a pressure of -0.1MPa for 6 hours. However, the prepared PVA was mixed with a large number of black spots, which could not be effectively removed by the process. This PVA mixed with a large number of black spots was not accepted by the market. Although this method can also produce PVA, it creates new problems and has no practical application value under the current technological background.

[0085] The large number of black spots in the PVA prepared in Comparative Example 3 may be caused by palladium generating palladium hydroxide in an alkaline environment. Palladium hydroxide is unstable and will continue to decompose into black palladium oxide during heating and drying. The specific chemical reaction is as follows:

[0086] Comparative Example 4 70.57 g of the catalyst precursor 1 obtained in Example 1 and 211.71 g of zeolite with a particle size of 1-5 mm were stirred and mixed in a rotary stirrer at a rotation speed of 110 r / min for 3 hours. The resulting mixture was then calcined in a muffle furnace at 340°C for 14 hours and naturally cooled to room temperature to obtain the final catalyst 12.

[0087] To a 5000ml reaction flask, add 1200.00g of methanol and 1000.00g of vinyl acetate. Stirring was initiated, nitrogen was introduced to displace the air, and 0.03g of catalyst 12 was added as an initiator. The reaction flask was heated to an internal temperature of 56°C, and the polymerization reaction timer was started. After 11 hours of reaction, the catalyst was filtered out, and the temperature was then raised to 90°C for 2.5 hours to evaporate the residual monomer and methanol. The solid content of the polyvinyl acetate was measured, and the mass fraction of the polyvinyl acetate was adjusted by adding methanol to prepare a polyvinyl acetate methanol solution with a mass fraction of approximately 30%.

[0088] To a 1500ml reaction flask, 120.00g of methanol and 200.00g of polyvinyl acetate methanol solution were added, stirring and heating were started, nitrogen was introduced to replace the air, and after the internal temperature rose to 56°C, 100.00g of a 0.019% sodium hydroxide methanol solution was added dropwise over a period of about 2 hours. The internal temperature was maintained at 56°C and the reaction was continued for about 2.5 hours. A white flocculent solid was observed to precipitate. After the solid precipitated, the temperature was continued to be maintained at 56°C for one hour. The white solid was filtered to obtain the white solid. The obtained solid was placed in an aluminum tray and placed in a drying oven that can be vacuumed and dried while vacuuming. PVA was prepared after drying in a vacuum drying oven at a temperature of 70°C under a pressure of -0.1MPa for 6 hours. However, the prepared PVA was mixed with a large number of black spots, which could not be effectively removed by the process. This PVA mixed with a large number of black spots was not accepted by the market. The possible reason for the black spots is that zeolite has difficulty in adsorbing or insufficient adsorption of palladium phosphine catalyst, resulting in a large amount of catalyst precursor 1 being dissolved in methanol. Therefore, filtering the catalyst cannot effectively remove the catalyst precursor 1. The catalyst precursor 1 dissolved in methanol produces palladium hydroxide when it encounters sodium hydroxide solution. The palladium hydroxide decomposes into black palladium oxide during the heating and drying process, thereby introducing black spots.

[0089] Comparative Example 5 70.57 g of catalyst precursor 1 obtained in Example 1 and 211.71 g of activated carbon were stirred and mixed in a rotary stirrer at a rotation speed of 110 r / min for 3 hours, and then the resulting mixture was calcined at 340°C in a muffle furnace. After calcination for 8 minutes, it was found that the activated carbon spontaneously combusted, indicating that the activated carbon could not withstand calcination at 340°C.

[0090] Comparative Example 6 70.57 g of catalyst precursor 1 obtained in Example 1 and 211.71 g of activated carbon were stirred and mixed in a rotary stirrer at a speed of 110 r / min for 3 hours. The resulting mixture was then calcined in a muffle furnace at 180° C. for 24 hours and naturally cooled to room temperature to obtain the final catalyst 13.

[0091] To a 5000ml reaction flask, 1200.00g of methanol and 1000.00g of vinyl acetate were added, stirring was started, nitrogen was introduced to replace the air, and then 0.03g of catalyst 13 was added as an initiator. The reaction flask was heated to an internal temperature of 56°C and the polymerization reaction started. After 11 hours of reaction time, the catalyst was filtered out. During the filtration process, it was found that the activated carbon would block the filter paper, resulting in the inability to continue subsequent filtration. The titanium rod filter was replaced by pressure filtration. At the beginning, it was able to filter smoothly, but the filter would also be blocked later. Therefore, the use of activated carbon to support the catalyst precursor has no practical feasibility in the production process.

[0092] The amounts of the palladium salt primary catalyst, phosphine ligand co-catalyst and carrier used in each embodiment and comparative example are shown in Table 4:

[0093] Other porous materials, such as MOFs and COFs, have no large-scale industrial applications under the existing technological background and are extremely expensive. Using these two materials as loading materials will greatly increase the selling price of PVA, and there is no possibility of market acceptance. Therefore, these two materials have no practical application value.

[0094] The embodiments of the present invention are described above. Unless there is a conflict, the embodiments and features of the embodiments may be combined with each other. The present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. A person skilled in the art, guided by the present invention, may devise various embodiments without departing from the spirit of the present invention and the scope of protection of the claims. All of these embodiments fall within the scope of protection of the present invention.

Claims

1. A catalyst for the preparation of polyvinyl alcohol, comprising a palladium salt main catalyst and a phosphine ligand co-catalyst, characterized in that: The phosphine ligand co-catalyst includes one or more of triphenylphosphine, 2,2'-bis(diphenylphosphino)-1,1'-binaphthyl, bis(2,6-dimethoxybenzoyl)(2,4,4-trimethylpentyl)phosphine oxide, bis[bis(3,4,5-trimethoxyphenyl)phosphine], bis(2-diphenylphosphinophenyl) ether, 2,2'-(di-o-tolylphosphino)diphenyl ether, and bis(dicyclohexylphosphinophenyl) ether; The palladium salt main catalyst includes one or more of palladium chloride, palladium chloride hydrate, bistriphenylpalladium chloride, 1,2-bis(diphenylphosphino)ethanepalladium chloride, 1,1'-bis(diphenylphosphino)ferrocenepalladium dichloride, and bistriphenylphosphinepalladium dichloride.

2. The catalyst for preparing polyvinyl alcohol according to claim 1, wherein The invention also comprises a carrier, in which the palladium salt main catalyst and the phosphine ligand co-catalyst are loaded, and the carrier comprises one or more of silica gel, alumina and molecular sieve.

3. The catalyst for preparing polyvinyl alcohol according to any one of claims 1 to 2, characterized in that The molar ratio of the palladium salt main catalyst to the phosphine ligand co-catalyst is 1:2.05-1:2.

30.

4. The catalyst for preparing polyvinyl alcohol according to claim 2, wherein The mass ratio of the palladium salt main catalyst and the phosphine ligand co-catalyst to the carrier is 1:3.0-1:3.

5.

5. A method for preparing a catalyst for preparing polyvinyl alcohol according to any one of claims 1 to 4, characterized in that: The following steps are involved: S1. Under the protection of inert gas, add palladium salt main catalyst, solvent A, and phosphine ligand co-catalyst, stir, react, filter, and vacuum dry to obtain a catalyst precursor; S2. The catalyst precursor and the carrier in S1 are uniformly stirred and calcined to obtain a catalyst.

6. The method for preparing a catalyst for preparing polyvinyl alcohol according to claim 5, wherein: The specific process of the S1 reaction is to add the non-polar solvent B dropwise within 30 minutes and cool the mixture to 0-5°C.

7. The method for preparing a catalyst for preparing polyvinyl alcohol according to claim 5, wherein: The vacuum drying pressure in S1 is -0.1~-0.3 MPa, the temperature is 50~60°C, and the vacuum drying time is 13~15 hours.

8. The method for preparing a catalyst for preparing polyvinyl alcohol according to claim 5, wherein: The calcination temperature in S2 is 300-400° C., and the calcination time is 12-14 hours.

9. A catalyst for preparing polyvinyl alcohol according to any one of claims 1 to 4, or a catalyst prepared by the preparation method according to any one of claims 5 to 8, in the preparation of polyvinyl alcohol, characterized in that: The following steps are involved: a solvent, vinyl acetate monomer and a catalyst are mixed, the polymerization reaction is carried out, after the reaction is completed, the catalyst is filtered out, and the filtrate is evaporated to obtain a polyvinyl acetate methanol solution; b. alcoholyzing the polyvinyl acetate methanol solution in step a to obtain polyvinyl alcohol.

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