Production method of polyvinyl alcohol powder

Abstract

The invention discloses a polyvinyl alcohol powder production method, which comprises: S1, crushing polyvinyl alcohol particles by using a crushing device; s2, solid and gas separation is conducted on the materials discharged by the smashing device through a solid separation device; s3, screening out 10-mesh polyvinyl alcohol powder with the retention rate of less than or equal to 5% and 60-mesh polyvinyl alcohol powder with the retention rate of less than or equal to 5% from the solids discharged from the solid separation device by using a screening device; in the step S1, the polyvinyl alcohol particles are fed into the crushing device by utilizing air which is generated by the air cooling device and has the temperature lower than the boiling point of methanol. According to the scheme, the problem of how to safely produce the polyvinyl alcohol powder with reliable quality in the prior art is solved.

Description

Technical Field

[0001] The present invention relates to a method for producing polyvinyl alcohol powder. Background Art

[0002] Polyvinyl alcohol (PVA) is a water-soluble and environmentally friendly polymer. It is non-toxic and pollution-free, and has good film-forming properties, emulsifying properties, adhesive properties and spinning properties. Polyvinyl alcohol powder has excellent solubility, film-forming property and adhesion. Polyvinyl alcohol has both hydrophilic and hydrophobic functional groups, so it has certain surface activity and can be used as a protective colloid in polymer emulsification and suspension polymerization reactions. The mesh number of polyvinyl alcohol powder can currently be controlled between 10 and 60 meshes. Because of its good adhesiveness, solubility and film-forming property, it is widely used in products such as thermal insulation mortar, putty, interface agent, building glue, etc.

[0003] At present, polyvinyl alcohol powder is mainly prepared by crushing polyvinyl alcohol particles. Polyvinyl alcohol particles are mainly made from vinyl acetate as raw material and methanol as solvent by solution polymerization and low-alkali alcoholysis method. After the polyvinyl alcohol particles are crushed by a crusher and then screened, the crushed product with ≤5% retention on 10 mesh and ≤5% passing through 60 mesh is the finished polyvinyl alcohol powder.

[0004] Chinese Patent Document CN 113318844 A discloses a method for preparing polyvinyl alcohol powder, which is characterized by including the following steps: loading raw materials into the feeding device, and cooling the raw materials by the pre-cooling machine; the pre-cooling machine conveys the cooled raw materials into the grinding device; the liquid nitrogen device supplies nitrogen to the grinding cavity to grind the raw materials in the grinding device at ultra-low temperature; the grinding device discharges the ground raw materials through the discharge port, and the collecting device simultaneously collects the powder and nitrogen in the grinding cavity and conveys the nitrogen to the liquid nitrogen device. The beneficial effect of this solution is that for the polyvinyl alcohol powder preparation equipment, it first cools the raw materials by the pre-cooling machine to make the raw materials hard, and then sends the raw materials into the grinding cavity for grinding. At the same time, it also supplies nitrogen to the grinding cavity through the liquid nitrogen device to ensure that the grinding cavity is in an ultra-low temperature environment, so that the raw materials ground brittle at ultra-low temperature can become powder without being heated to cause performance changes. In this way, not only the fineness of the produced product can be uniform, reaching more than 200 meshes, but also the solubility is good, the utilization rate is extremely high, and the production cost is greatly reduced. This solution is mainly used for producing powders with very high fineness and requires the use of liquid nitrogen for cooling. Such a device is not suitable for producing polyvinyl alcohol powder products with ≤5% retention on 10 mesh and ≤5% passing through 60 mesh.

[0005] Chinese Patent Document CN101804378A discloses a production process of polyvinyl alcohol micro-powder dry powder capable of obtaining a high product yield, characterized in that: polyvinyl alcohol is separated at multiple levels and rapidly cryogenically cooled multiple times, so that polyvinyl alcohol has cold brittleness multiple times, and the cold-brittle polyvinyl alcohol is pulverized multiple times by a high-speed air flow impact method using an ultrafine pulverization device. The specific steps are as follows: (1) selection of polyvinyl alcohol raw materials; (2) rapid cryogenic cooling; (3) first high-speed air flow impact pulverization; (4) recovery of large-particle solids; (5) continuous rapid cryogenic cooling; (6) second high-speed air flow impact pulverization; (7) selection of powder with a fineness greater than 120 mesh; (8) packaging. The effects of this solution are: the pulverization fineness of polyvinyl alcohol can reach more than 120 mesh, the yield of ultrafine powder can reach more than 95%, the production efficiency is greatly improved, from 20% to 95%, the polyvinyl alcohol becomes micro-powder dry powder, and it is convenient for storage and transportation, can be fully dissolved at room temperature, and is extremely convenient to use. This solution is for the production of ultrafine powder and is not suitable for the production of polyvinyl alcohol powder products with a retention of ≤5% at 10 mesh and a passing rate of ≤5% at 60 mesh.

[0006] Chinese Patent Document CN111286048A discloses a production process of polyvinyl alcohol powder, which is characterized by including the following steps: 1) Alcoholysis and defoaming: Using polyvinyl alcohol as the raw material, placing it into a polymerization kettle, adding initiator ⅰ and a small amount of water for dilution, with the dilution concentration being 40wt% - 50wt%, stirring for 30 - 40 minutes, then adding a suspension solvent equivalent to 120wt% - 130wt% of the polyvinyl alcohol dilution solution, carrying out alcoholysis reaction for 40 - 50 minutes, with the reaction temperature being 60℃ - 65℃, obtaining solution A, then passing solution A through triple filtration, pumping it into a defoaming kettle, keeping it warm at a temperature of 70℃ - 80℃, and defoaming for 3 - 4 hours; 2) Melting treatment: After swelling treatment of the mixture processed in step 1), adding it into a single-screw extruder for full melting, where the temperatures of each zone of the screw are: feeding section 80 - 100℃, compression section 100 - 120℃, and metering section 60 - 70℃. After the treatment is completed, adding initiator ⅱ and carrying out polymerization within a pressure range of 2.2 - 2.5 atm; 3) Low-temperature pulverization: Putting the substance processed in step 2) into a cooling cylinder in a low-temperature separation device, shooting at the working surface of the pulverizing knife and the surface of the material at an injection angle through the air flow channel, filling the gap to form a jet air curtain layer, then spraying a small amount of liquid nitrogen, and finally sending it into a pulverizer for pulverization. The pulverization temperature is controlled at 50 - 60℃. After pulverization is completed, polyvinyl alcohol powder is obtained. The effects of the present invention are as follows: Using suspension can maintain the stability of the polymerization system, increase the balance of reaction absorption, and make the remaining monomers easier to remove. The low-temperature material pulverization device of the present invention has an air flow channel capable of introducing air flow into the gap between the pulverizing knives, enabling the material pulverization device with this structure to implement the above-mentioned low-temperature material pulverization process method, achieving the purpose of improving the product grade, and having the advantages of large output, low energy consumption, and high efficiency. This scheme has complex processes and is not suitable for producing polyvinyl alcohol powder products with 10-mesh retention ≤ 5% and 60-mesh passing ≤ 5%. Summary of the Invention

[0007] The purpose of the present invention is to provide a production method of polyvinyl alcohol powder to solve the problem of how to safely produce polyvinyl alcohol powder with reliable quality in the prior art.

[0008] To achieve the above purpose, the basic scheme of the present invention provides a production method of polyvinyl alcohol powder, including the following steps: S1. Using a pulverization device to pulverize polyvinyl alcohol particles; S2. Using a solid separation device to separate solids and gases from the materials discharged from the pulverization device; S3. Using a screening device to screen out polyvinyl alcohol powder with 10-mesh retention ≤ 5% and 60-mesh passing ≤ 5% from the solids discharged from the solid separation device. In step S1, using air with a temperature lower than the boiling point of methanol generated by an air cooling device to send polyvinyl alcohol particles into the pulverization device.

[0009] Preferably, in the step S1, compressed air with a temperature lower than the boiling point of methanol generated by an air cooling device is used to send polyvinyl alcohol particles into a pulverizing device.

[0010] Preferably, in the step S1, a cold dryer is used as the air cooling device to generate compressed air with a temperature lower than the boiling point of methanol.

[0011] Preferably, in the step S2, a centrifugal fan and a bag filter are jointly used as a solid separation device to separate solids and gases from the materials discharged from the pulverizing device.

[0012] Preferably, in the step S3, a screening device is used to first screen and remove the foamy materials in the solids discharged from the solid separation device.

[0013] Preferably, in the step S3, the screening device first uses a first layer of sieve mesh with a mesh size of 5 to screen and remove the foamy materials in the solids discharged from the solid separation device, and then uses a second layer of sieve mesh with a mesh size of 10 to screen out the polyvinyl alcohol particles with larger particle sizes in the solids passing through the first layer of sieve mesh, and transports them back to the pulverizing device.

[0014] Preferably, in the step S3, at least two parallel vibrating screens are used as the screening device to screen the solids discharged from the solid separation device.

[0015] Preferably, in the step S1, an iron remover is used to separate iron filings from polyvinyl alcohol particles.

[0016] The present invention has the following beneficial effects:

[0017] 1. Using air with a temperature lower than the boiling point of methanol to send polyvinyl alcohol particles into the pulverizing device can effectively reduce the temperature inside the pulverizing device, which is beneficial to improving the pulverizability of polyvinyl alcohol particles, increasing the pulverization output, and avoiding the accumulation of methanol gas in the pulverizing device, thus eliminating potential safety hazards.

[0018] 2. Using a screening device to timely screen and remove the foamy materials can reduce the load on the pulverizing device, thereby reducing the operating cost and improving the work efficiency.

[0019] 3. Using at least two parallel vibrating screens can effectively reduce the materials that need to be pulverized repeatedly.

[0020] 4. By setting up an iron remover, the iron filings in the polyvinyl alcohol powder can be effectively reduced, thus ensuring the product quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a schematic diagram of an embodiment of a production system for implementing a production method of a polyvinyl alcohol powder according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0022] The following is a further detailed description through specific embodiments:

[0023] The reference numerals in the accompanying drawings of the specification include: a feeding device 1, an air cooling device 2, a pulverizing device 3, a mixing chamber 31, a bag filter 4, a centrifugal fan 5, a vibrating screen 6, a powder bin 7, and a magnetic separator 8.

[0024] Example: As Figure 1 shown, a production system for implementing the production method of polyvinyl alcohol powder of the present invention includes a pulverizing device 3. The feeding end of the pulverizing device 3 is connected to a feeding device 1. In this embodiment, the feeding device 1 is a bin with a rotary valve, and the polyvinyl alcohol granular material for pulverization enters the pulverizing device 3 through the bin. The feeding end of the pulverizing device 3 is also connected to an air cooling device 2. In this embodiment, the air cooling device 2 is preferably a refrigerant dryer, which cools the compressed air entering the pulverizer through the air cooling device 2, so that the temperature inside the system is lower than the boiling point temperature of methanol, especially the temperature inside the pulverizing device 3 is always lower than the boiling point temperature of methanol. In this embodiment, a mixing chamber 31 for mixing materials and air is provided at the feeding end of the pulverizing device 3, so that the polyvinyl alcohol particles are in full contact with the low-temperature air in the mixing chamber 31 before being pulverized and are in a low-temperature state.

[0025] The discharging end of the pulverizing device 3 is connected to a solid separation device. In this embodiment, the solid separation device is preferably a bag filter 4. The bag filter 4 is connected to a centrifugal fan 5. Through the pumping action of the centrifugal fan 5, the materials discharged from the pulverizing device 3 enter the bag filter 4, so that the solid materials are separated from the gas. The discharging end of the solid separation device is connected to a screening device. In this embodiment, the screening device includes two vibrating screens 6 arranged in parallel. Each vibrating screen 6 is provided with a coarse material return port communicating with the mixing chamber 31 at the feeding end of the pulverizing device 3, so that the polyvinyl alcohol particles that are not fully pulverized and screened out are returned to the pulverizing device 3 for re-pulverization. In this embodiment, the vibrating screen 6 includes a first-layer screen mesh with a mesh number of 5 and a second-layer screen mesh with a mesh number of 10. The foamed materials screened out by the first-layer screen mesh are discharged through the discharge port into the foamed material conveying pipe, and the coarse materials remaining after screening by the second-layer screen mesh are returned to the feeding end of the pulverizing device 3 through the coarse material return port and the coarse material conveying pipe. In this embodiment, the material channel formed by the pipeline between the coarse material return port and the mixing chamber 31 is provided with a magnetic separator 8, so as to facilitate the magnetic separation of iron filings in the materials.

[0026] Specifically, the production method of polyvinyl alcohol powder includes the following steps:

[0027] S1. Use the air with a temperature lower than the boiling point of methanol generated by the air cooling device 2 to send the polyvinyl alcohol particles discharged from the feeding device 1 into the pulverizing device 3. In this embodiment, it is preferred to use a cold dryer as the air cooling device 2 to generate compressed air with a temperature lower than the boiling point of methanol, so that the polyvinyl alcohol particles are mixed with the compressed air before entering the pulverizing device 3; then use the pulverizing device 3 to pulverize the polyvinyl alcohol particles. Before the polyvinyl alcohol particles enter the pulverizing device 3, use a magnetic separator 8 to separate the iron filings in the polyvinyl alcohol particles.

[0028] S2. Use a solid separation device to separate the solid and gas of the material discharged from the pulverizing device 3. In this embodiment, use a centrifugal fan 5 and a bag filter 4 together as the solid separation device to separate the solid and gas of the material discharged from the pulverizing device 3.

[0029] S3. Use a screening device to screen out polyvinyl alcohol powder with ≤5% retained on 10 mesh and ≤5% passed through 60 mesh from the solid discharged from the solid separation device, and the screened polyvinyl alcohol powder products are collected in the powder bin 7. In this embodiment, the screening device first uses a first layer of screen mesh with a mesh number of 5 to screen out the foamed materials in the solid discharged from the solid separation device, and then uses a second layer of screen mesh with a mesh number of 10 to screen out the polyvinyl alcohol particles with larger particle sizes in the solid passing through the first layer of screen mesh and convey them back to the pulverizing device 3. In this embodiment, use two parallel vibrating screens 6 as the screening device to screen the solid discharged from the solid separation device.

[0030] The results of producing different models of polyvinyl alcohol powder by using the production method of the present invention are as follows:

[0031] For the result of producing polyvinyl alcohol powder of model 088-20:

[0032] 088-20 1 2 3 4 5 6 Daily output (tons) 40 45 42 43 46 44 Retention on 10 mesh (%) 3.8 4.2 4.5 4.6 4.0 3.7 Passing through 60 mesh (%) 4.9 4.2 4.3 4.6 4.7 4.5

[0033] For the result of producing polyvinyl alcohol powder of model 088-50:

[0034] 088-50 1 2 3 4 5 6 Daily output (tons) 41 46 50 51 47 43 Retention on 10 mesh (%) 4.8 4.5 4.1 4.5 5.0 4.7 Passing through 60 mesh (%) 4.7 5.8 4.7 4.4 4.9 4.9

[0035] From the results of producing the above two models of polyvinyl alcohol powder, it can be known that by using the production method of the present invention, the output can be satisfied while ensuring the product quality, so that the production method is suitable for industrial application.

Claims

1. A production method of polyvinyl alcohol powder, comprising the following steps: S1, using a crushing device to crush polyvinyl alcohol particles; S2, using a solid separation device to separate solids and gas from the materials discharged from the crushing device; S3, using a screening device to screen out polyvinyl alcohol powder with a retention rate of ≤5% for 10 mesh and a passing rate of ≤5% for 60 mesh from the solids discharged from the solid separation device. It is characterized in that: In step S1, air with a temperature lower than the boiling point of methanol generated by an air cooling device is used to feed the polyvinyl alcohol particles into the crushing device.

2. The production method of polyvinyl alcohol powder according to claim 1, It is characterized in that: In step S1, compressed air with a temperature lower than the boiling point of methanol generated by an air cooling device is used to feed the polyvinyl alcohol particles into the crushing device.

3. The production method of polyvinyl alcohol powder according to claim 2, It is characterized in that: In step S1, a cold dryer is used as the air cooling device to generate compressed air with a temperature lower than the boiling point of methanol.

4. The production method of polyvinyl alcohol powder according to claim 3, It is characterized in that: In step S2, a centrifugal fan and a bag filter are jointly used as the solid separation device to separate solids and gas from the materials discharged from the crushing device.

5. The production method of polyvinyl alcohol powder according to claim 4, It is characterized in that: In step S3, the screening device is used to first screen out the foamed materials in the solids discharged from the solid separation device.

6. The production method of polyvinyl alcohol powder according to claim 5, It is characterized in that: In step S3, the screening device first uses a first layer of sieve mesh with a mesh number of 5 to screen out the foamed materials in the solids discharged from the solid separation device, and then uses a second layer of sieve mesh with a mesh number of 10 to screen out the larger-sized polyvinyl alcohol particles in the solids passing through the first layer of sieve mesh and convey them back to the crushing device.

7. The production method of polyvinyl alcohol powder according to claim 6, It is characterized in that: In step S3, at least two vibration screens arranged in parallel are used as the screening device to screen the solids discharged from the solid separation device.

8. The production method of polyvinyl alcohol powder according to claim 7, It is characterized in that: In step S1, iron filings in the polyvinyl alcohol particles are separated by a magnetic barrier.

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