Modified aluminum hydroxide as well as preparation method and application thereof

Abstract

The invention provides modified aluminum hydroxide as well as a preparation method and application thereof, and the preparation method of the modified aluminum hydroxide comprises the step of mixing aluminum hydroxide and a modifier in water to form the modified aluminum hydroxide, the modifier is selected from one or more of the following components: poly (C2-C12 olefin) monohydric alcohol or polyhydric alcohol, and cellulose containing one or more C1-C16 hydroxyalkyl groups. The modified aluminum hydroxide prepared by the method disclosed by the invention can be used as a dispersing agent to remarkably inhibit foaming in the polymerization reaction process of vinyl chloride, so that the polymerization reaction process is ensured to be smoothly carried out, and the quality of a polyvinyl chloride product is remarkably improved.

Description

Technical Field

[0001] The present application relates to the field of chemical industry, and more specifically to a method for modifying aluminum hydroxide, and using the modified aluminum hydroxide obtained thereby as a dispersant for vinyl chloride polymerization reaction. Background Art

[0002] Polyhaloolefins have been widely used in various fields for a long time. As a typical representative, polyvinyl chloride (PVC) is one of the five general-purpose plastics. It has good physical properties, flame retardancy and processing properties, as well as corrosion resistance, easy transportation, and relatively low price. It is widely used in many fields.

[0003] In the suspension polymerization of vinyl chloride, in order to ensure the smooth progress of the polymerization process, dispersants such as PVA and cellulose ethers must be used in the polymerization reaction system. Due to the effect of these dispersants and the volatile nature of vinyl chloride, foam is easily generated during the polymerization process (especially when the reflux condenser is turned on), as well as during the discharging and stripping processes. Among them, the foam generated in the polymerization kettle due to stirring is called "wet foam". "Wet foam" is generated above the liquid surface of the polymerization system, causing the gas phase polymerization of vinyl chloride, and the inner wall of the kettle above the liquid level produces sticky materials. The sticky materials fall into the kettle, which will increase the yellow and black spots of the product polymer resin, thereby affecting the quality of the polyvinyl chloride resin. In large-scale polymerization kettles equipped with reflux condensers, in order to enhance the cooling effect, the reflux condenser is often enabled in the middle of the polymerization. At this time, a large amount of vinyl chloride vapor passes through the liquid layer and enters the condenser, condenses into liquid in the condenser, and then returns to the polymerization system. In this process, the volatilization of vinyl chloride produces a large amount of foam, which is called "dry foam". After the polymerization reaction is completed, the polyvinyl chloride resin slurry is discharged to the discharge tank, and the unreacted vinyl chloride needs to be recovered. At this time, a large amount of foam will be generated in the discharge tank. These foams are discharged with the unreacted monomers and often cause many problems such as pipeline blockage and waste of materials. At the same time, in the operation of removing and recovering unreacted monomers using a stripping tower, the slurry flows from the top of the tower to the bottom of the tower, and the steam flows upward from the bottom of the tower to fully exchange heat with the slurry in countercurrent. In this process, the slurry on each layer of the tower plate will produce foam, which will hinder the volatilization of vinyl chloride in the slurry and increase the resistance to removing these unreacted monomers; if the foam stays on the tower wall for too long, black and yellow particles will be generated, affecting the product quality. In order to solve these problems, those skilled in the art particularly hope to defoam or suppress the vinyl chloride suspension polymerization system and slurry.

[0004] The technology for eliminating foam in the prior art mainly involves adding reagents that can inhibit or eliminate foam into the system involved in the polymerization reaction, but these prior arts all have serious problems. The above reagents need to be added to various locations in the equipment where foam may be generated, including not only the reactor, but also the stripping tower, condenser and various pipelines, which significantly increases the complexity of the polymerization reaction, thereby causing a significant increase in operating costs and material costs; in addition, the addition of so many reagents often affects the final quality of the product polyvinyl chloride resin. The prior art has invested a lot of money and manpower to study these problems, but has not yet achieved satisfactory results.

[0005] Therefore, the art particularly hopes to develop a novel defoaming technology to effectively solve the above problems in a simple and low-cost manner. In view of the problems existing in the above-mentioned prior art, the inventors of the present application have developed the aluminum hydroxide modification technology of the present invention through a lot of in-depth research, and found that the modified aluminum hydroxide obtained thereby has extremely excellent defoaming and anti-foaming properties, which unexpectedly solves the long-standing problem in the prior art that needs to be solved. Summary of the invention

[0006] The first aspect of the present application provides a method for preparing modified aluminum hydroxide, the method comprising the following steps: mixing aluminum hydroxide and a modifier in water to form the modified aluminum hydroxide;

[0007] The modifier is selected from one or more of the following: poly(C2-C12 olefin) mono- or polyol, cellulose containing one or more C1-C16 hydroxyalkyl groups.

[0008] According to one embodiment of the first aspect of the present application, the method is carried out in the following manner:

[0009] Step 1: dispersing aluminum hydroxide in water to form an aqueous dispersion;

[0010] Step 2: adding a modifier to the aqueous dispersion and performing a first mixing;

[0011] Step 3: After the first mixing, the mixture containing aluminum hydroxide, modifier and water is heated to a temperature higher than the temperature of the first mixing, and a second mixing is performed.

[0012] According to another embodiment of the first aspect of the present application, in step 2, the first mixing is performed at a temperature of 0-40°C for 0.5-4 hours. According to another embodiment of the first aspect of the present application, in step 3, after the first mixing, the mixed material containing aluminum hydroxide, modifier and water is raised to a temperature of 60-90°C for second mixing, and the second mixing lasts for 0.5-4 hours.

[0013] According to another embodiment of the first aspect of the present application, the weight ratio of the aluminum hydroxide to the modifier is 100:2 to 100:10. According to another embodiment of the first aspect of the present application, the weight ratio of the water to the aluminum hydroxide is 100:5 to 100:10.

[0014] According to another embodiment of the first aspect of the present application, the modifier is selected from one or more of the following: polyvinyl alcohol, hydroxypropyl methylcellulose, gelatin, methylcellulose, and hydroxyethyl cellulose.

[0015] The second aspect of the present invention provides a modified aluminum hydroxide, which is prepared by the method of any embodiment of the first aspect of the present invention.

[0016] The third aspect of the present invention provides a method for performing vinyl chloride polymerization, the method comprising the following steps: in the presence of an initiator, water, a primary dispersant, an optional auxiliary dispersant and an optional buffer, allowing vinyl chloride to undergo polymerization to form polyvinyl chloride;

[0017] According to one embodiment of the third aspect of the present application, the main dispersant is the modified aluminum hydroxide described in the second aspect of the present invention.

[0018] According to an embodiment of the third aspect of the present application, the amount of the primary dispersant is 0.35-0.50 parts by weight based on 100 parts by weight of vinyl chloride added in the polymerization reaction. According to another embodiment of the third aspect of the present application, the polymerization reaction is carried out at 30-70°C for 5.0-8.0 hours.

[0019] According to another embodiment of the third aspect of the present application, the initiator is selected from one or more of the following: diacyl peroxide, peroxycarboxylic acid ester, peroxydicarbonate, azo initiator, peroxysulfonic acid initiator, cumyl peroxyneodecanoate, tert-butyl peroxyneodecanoate, tert-amyl peroxypivalate. According to another embodiment of the third aspect of the present application, based on 100 parts by weight of the added weight of vinyl chloride in the polymerization reaction, the amount of the initiator used is 0.01-4.5 parts by weight.

[0020] According to another embodiment of the third aspect of the present application, based on 100 parts by weight of vinyl chloride added in the polymerization reaction, the amount of water used is 100-300 parts by weight.

[0021] According to another embodiment of the third aspect of the present application, the dispersant is selected from one or more of the following: magnesium hydroxide, aluminum hydroxide, calcium carbonate, zinc sulfide, aluminum hydroxide, gelatin, methyl cellulose, hydroxyethyl cellulose, hydroxypropyl methyl cellulose. According to another embodiment of the third aspect of the present application, based on 100 parts by weight of the added weight of vinyl chloride in the polymerization reaction, the amount of the dispersant is 0-0.5 parts by weight.

[0022] According to another embodiment of the third aspect of the present application, the buffer is selected from one or more of the following: ammonium bicarbonate, sodium bicarbonate, sodium phosphate, ammonium phosphate, sodium monohydrogen phosphate, sodium dihydrogen phosphate, sodium hydroxide, tricalcium phosphate. According to another embodiment of the third aspect of the present application, based on 100 parts by weight of the added weight of vinyl chloride in the polymerization reaction, the amount of the buffer is 0.01-0.05 parts by weight. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 A picture showing the reaction product synthesized in the examples of the present application;

[0024] Figure 2 A picture showing the reaction equipment used in the examples of the present application;

[0025] Figure 3 The GPC characterization chart of the polyvinyl chloride resin synthesized in the examples of the present application is shown. DETAILED DESCRIPTION

[0026] "Range" disclosed herein is in the form of lower limit and upper limit. It can be one or more lower limits, and one or more upper limits respectively. A given range is defined by selecting a lower limit and an upper limit. The selected lower limit and upper limit define the boundaries of a particular range. All ranges that can be defined in this way are inclusive and combinable, i.e. any lower limit can be combined with any upper limit to form a range. For example, a range of 60-120 and 80-110 is listed for a particular parameter, and it is understood that a range of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are listed, the following ranges can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5.

[0027] In this application, unless otherwise specified, the numerical range "ab" represents an abbreviation of any real number combination between a and b, where a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations.

[0028] In this application, unless otherwise specified, all embodiments and preferred embodiments mentioned herein can be combined with each other to form a new technical solution.

[0029] In this application, unless otherwise specified, all technical features and preferred features mentioned herein can be combined with each other to form a new technical solution.

[0030] In this application, if there is no special explanation, the "including" mentioned herein means open or closed. For example, the "including" may mean that other components not listed may also be included, or only the listed components may be included.

[0031] According to one embodiment of the present application, the preparation method of the modified aluminum hydroxide includes treating aluminum hydroxide with a modifier in an aqueous dispersion system to obtain modified aluminum hydroxide. According to an exemplary embodiment of the present application, the modified aluminum hydroxide can be prepared by a method including the following steps: step 1: dispersing aluminum hydroxide in water to form an aqueous dispersion; step 2: adding a modifier to the aqueous dispersion and performing a first mixing; step 3: after the first mixing, heating the mixture containing aluminum hydroxide, the modifier and water to a temperature higher than the first mixing temperature, and performing a second mixing.

[0032] Specifically, in step 1, aluminum hydroxide is dispersed in water to form a suspension. Based on 100 parts by weight of water in the aluminum hydroxide aqueous suspension, the amount of aluminum hydroxide used is 5-10 parts by weight.

[0033] Then in step 2, a modifier is added to the suspension, the modifier is dissolved in water by stirring, and the mixture containing water, modifier and aluminum hydroxide is first mixed. According to one embodiment of the present application, in the mixture of water, modifier and aluminum hydroxide, the content of the modifier is 2-10 parts by weight, more preferably 5-10 parts by weight, based on 100 parts by weight of aluminum hydroxide. According to another embodiment of the present application, the modifier is selected from one or more of the following: poly (C2-C12 olefin) monohydric alcohol or polyhydric alcohol, cellulose containing one or more C1-C16 hydroxyalkyl groups; or the modifier is selected from one or more of the following: poly (C2-C8 olefin) monohydric alcohol or polyhydric alcohol, cellulose containing one or more C1-C8 hydroxyalkyl groups; the modifier is selected from one or more of the following: poly (C2-C4 olefin) monohydric alcohol or polyhydric alcohol, cellulose containing one or more C2-C4 hydroxyalkyl groups; most preferably, the modifier is polyvinyl alcohol, hydroxypropyl methylcellulose, or a combination thereof. According to an exemplary embodiment of the present application, the molecular weight (Mw) of the polyvinyl alcohol is 10,000 to 300,000, or 15,000 to 200,000, or 20,000 to 150,000.

[0034] According to one embodiment of the present application, the modifiers used in the present invention are all water-soluble.

[0035] According to one embodiment of the present application, in step 2, the first mixing is performed at a temperature of 0-40° C., more preferably at room temperature. According to another embodiment of the present application, the first mixing is performed for 0.5-4 hours, preferably for 1-2 hours.

[0036] Next, in step 3, after the first mixing in step 2, the mixture containing aluminum hydroxide, modifier and water is subjected to a second mixing at an elevated temperature. According to one embodiment of the present application, in step 3, the second mixing is carried out at a temperature of 60-90° C., more preferably at a temperature of 70-80° C. According to another embodiment of the present application, the first mixing is continued for 0.5-4 hours, preferably for 1-2 hours. After the second mixing, the heating is stopped, and the mixture is allowed to cool naturally to room temperature while stirring.

[0037] Then, stirring is stopped, and the treated mixture is subjected to solid-liquid separation, for example, solid-liquid separation can be performed by conventional filtration, vacuum filtration, etc., to obtain modified aluminum hydroxide in solid form.

[0038] For example, the water in the aluminum hydroxide can be initially removed by centrifugal separation or vacuum filtration, and then low-temperature evaporation at 50-60° C. for 24-36 hours can be performed to obtain a modified aluminum hydroxide dispersant that is substantially free of water.

[0039] As described above, the modified aluminum hydroxide of the present invention can be used as a dispersant (referred to herein as the "primary dispersant") in the polymerization reaction system of vinyl chloride, which can effectively achieve the effects of defoaming and suppressing foam in the entire polymerization reaction system while ensuring the smooth progress of the polymerization reaction, thereby significantly improving the quality of the polymerization product (polyvinyl chloride).

[0040] According to one embodiment of the present application, the polymerization reaction of vinyl chloride is carried out by a method comprising the following steps: in the presence of an initiator, a solvent, a primary dispersant (the modified aluminum hydroxide prepared as described above), an optional co-dispersant and an optional buffer, the vinyl chloride monomer is polymerized to form the target product, polyvinyl chloride.

[0041] According to one embodiment of the present application, the degree of polymerization of the polyvinyl chloride resin prepared by the method of the present invention is 200-5000, preferably 500-2500.

[0042] According to one embodiment of the present application, based on 100 parts by weight of vinyl chloride added in the polymerization reaction, the amount of the main dispersant (ie, the modified aluminum hydroxide described above) is 0.35-0.50 parts by weight, preferably 0.4-0.45 parts by weight.

[0043] According to another embodiment of the present application, the initiator used in the polymerization reaction may include diacyl peroxide, peroxycarboxylic acid ester, peroxydicarbonate, azo initiator, peroxysulfonic acid initiator, cumyl peroxyneodecanoate, tert-butyl peroxyneodecanoate, tert-amyl peroxypivalate; more specific examples thereof include one or more of the following: azobisisoheptanitrile (ABVN), azobisisobutyronitrile (ABIN), di(2-ethylhexyl) peroxydicarbonate (EHP ), diisopropyl peroxydicarbonate (IPP), dicetyl peroxydicarbonate, di(2-phenoxyethyl) peroxydicarbonate (BPPD), isopropyl peroxyneodecanoate (99-W40), diisobutyl peroxide (187-C30), dilauroyl peroxide (LPO), di(3,5,5-trimethylhexanoyl) peroxide (36-W40), tert-butyl peroxyneodecanoate (23-W40), isopropyl peroxyneodecanoate, butyryl peroxide, etc.

[0044] According to another embodiment of the present application, based on 100 parts by weight of vinyl chloride added in the polymerization reaction, the amount of the main dispersant (ie, the modified aluminum hydroxide described above) is 0.05-4.5 parts by weight, preferably 0.1-1.0 parts by weight.

[0045] In the present invention, the water used in the polymerization reaction is preferably deionized water. According to another embodiment of the present application, based on 100 parts by weight of vinyl chloride added in the polymerization reaction, the amount of water used is 100-300 parts by weight, preferably 180-240 parts by weight.

[0046] According to another embodiment of the present application, in addition to using the modified aluminum hydroxide described in the present invention as the main dispersant, a dispersant can be optionally added. The dispersant can include an inorganic dispersant and an organic dispersant. Examples of the inorganic dispersant include magnesium hydroxide, aluminum hydroxide, calcium carbonate, zinc sulfide, and the like. The aluminum hydroxide used as one of the dispersant options here refers to aluminum hydroxide that has not been modified by a modifier, which is different from the modified aluminum hydroxide used as the main dispersant described above. Examples of the organic dispersant include gelatin, methylcellulose, hydroxyethyl cellulose, hydroxypropyl methylcellulose, and the like.

[0047] The dispersant is an "optional" combination in the polymerization reaction of the present invention, that is, the dispersant may be added or not added in the polymerization reaction.

[0048] In the case of using a dispersant in the polymerization reaction, based on 100 parts by weight of vinyl chloride added in the polymerization reaction, the amount of the dispersant is 0-0.5 parts by weight.

[0049] The buffer used in the polymerization reaction is used to control the pH value of the polymerization system to about 6-8, so as to inhibit the degradation of the polymer product molecules, improve the thermal stability of the polymer resin, improve the dispersant's colloid-retaining effect, adjust the polymerization rate, the product's apparent density, etc. According to one embodiment of the present application, examples of the buffer include ammonium bicarbonate, sodium bicarbonate, sodium phosphate, ammonium phosphate, sodium monohydrogen phosphate, sodium dihydrogen phosphate, sodium hydroxide, tricalcium phosphate, etc. According to another embodiment of the present application, based on 100 parts by weight of the added weight of vinyl chloride in the polymerization reaction, the amount of the buffer used is 0.001-0.05 parts by weight, preferably 0.02-0.04 parts by weight.

[0050] According to one embodiment of the present application, the duration of the polymerization reaction is 5.0-8.0 hours, preferably 5.2-6 hours.

[0051] According to another embodiment of the present application, the reaction temperature of the polymerization reaction is 30-70°C, preferably 45-60°C.

[0052] The advantages of the present invention are:

[0053] 1. The modified dispersant of the present invention can effectively realize the smooth progress of the vinyl chloride polymerization reaction process, can achieve extremely excellent defoaming and anti-foaming effects, and can improve the performance of polyvinyl chloride resin;

[0054] 2. The modified dispersant of the present invention can be prepared by a simple and low-cost process without significantly increasing processing costs and material costs.

[0055] 3. The modified aluminum hydroxide of the present invention will not introduce additional impurities into the polyhaloolefin resin when used as a dispersant, and will not cause contamination of the resin product.

[0056] The methods of the present application are specifically described in the following examples, the purpose of which is to better understand the content of the present application. It should be understood that these examples are merely illustrative and not restrictive. The reagents used in the examples are all purchased from the market and used directly without further purification.

[0057] Example

[0058] In the following examples, the water used is deionized water, the polyvinyl alcohol used is purchased from Kuraray Co., Ltd. of Japan with the trade name L-9; the hydroxypropyl methylcellulose used is purchased from Dow Chemical Co., Ltd. of the United States with the trade name E50; the other reagents used are of analytical grade and used directly without further treatment.

[0059] Example 1

[0060] In this example, modified aluminum hydroxide was synthesized and used as a primary dispersant in vinyl chloride polymerization.

[0061] First, the aluminum hydroxide is modified. One kilogram of deionized water and 50 grams of aluminum hydroxide are added to a beaker equipped with a stirring device and placed in a water bath. The material in the beaker is stirred to form a suspension. 5 grams of polyvinyl alcohol is added to the suspension and stirred for 2 hours at a room temperature of about 25°C. The temperature is then raised to 70°C and stirring is continued at this temperature for 2 hours. The heating is then stopped and the material in the beaker is allowed to cool naturally to room temperature under continuous stirring. The material in the beaker is removed, the solid matter is collected by centrifugal drying, and dried at 60°C for 24 hours to obtain modified aluminum hydroxide.

[0062] Then the vinyl chloride polymerization reaction is carried out. Figure 2 4800g of deionized water, 8g of modified aluminum hydroxide, and 0.4g of sodium bicarbonate buffer were added to the stainless steel reactor shown, and then the reactor was sealed, and 2000g of vinyl chloride gas was directly filled into it, and then 4g of di(2-ethylhexyl) peroxydicarbonate (EHP) initiator (50wt% aqueous solution) was added to the reactor, and the materials in the reactor were stirred for 10 minutes, and then the temperature of the reactor was raised to 57°C to start the polymerization reaction. The reaction endpoint was determined when the pressure in the reactor dropped by 0.15Mpa. At this time, the reaction continued for 5.30 hours. At this time, acetone thiosemicarbazone terminator was added to the reactor to stop the polymerization reaction, and the temperature of the reactor was lowered to room temperature, and the reactor was opened to unload. The object material was filtered and dried to obtain the product PVC resin, which is Figure 1 The solid powder shown.

[0063] The PVC resin product obtained in this embodiment was subjected to GPC test. Figure 3 As shown, the measured number average molecular weight Mn of the PVC resin is 78645, and the weight average molecular weight Mw is 96788.

[0064] Example 2

[0065] In this example, modified aluminum hydroxide was synthesized and used as a primary dispersant in vinyl chloride polymerization.

[0066] First, the aluminum hydroxide is modified. One kilogram of deionized water and 100 grams of aluminum hydroxide are added to a beaker equipped with a stirring device and placed in a water bath. The material in the beaker is stirred to form a suspension. 10 grams of polyvinyl alcohol is added to the suspension and stirred for 2 hours at a room temperature of about 25°C. The temperature is then raised to 80°C and stirring is continued at this temperature for 2 hours. The heating is then stopped and the material in the beaker is allowed to cool naturally to room temperature under continuous stirring. The material in the beaker is removed, the solid matter is collected by centrifugal drying, and dried at 55°C for 28 hours to obtain dry modified aluminum hydroxide.

[0067] Then, a vinyl chloride polymerization reaction is carried out. 4800 grams of deionized water, 9 grams of modified aluminum hydroxide, and 0.4 grams of sodium bicarbonate buffer are added to a stainless steel reactor, and then the reactor is sealed, and 2000 grams of vinyl chloride gas is filled into it, and then 4 grams of di(2-ethylhexyl) peroxydicarbonate (EHP) initiator (50wt% aqueous solution) is added to the reactor, and the materials in the reactor are stirred for 10 minutes, and then the temperature of the reactor is raised to 57°C to start the polymerization reaction. The reaction endpoint is determined when the pressure in the reactor drops by 0.15Mpa. At this time, the reaction continues for 5.45 hours. At this time, acetone thiosemicarbazone terminator is added to the reactor to stop the polymerization reaction, and the temperature of the reactor is lowered to room temperature, and the reactor is opened to unload. The object material is filtered and dried to obtain the product PVC resin, which is Figure 1 The solid powder shown.

[0068] The PVC resin product obtained in this example was subjected to GPC test, and the number average molecular weight Mn and weight average molecular weight Mw of the PVC resin were measured to be 83729 and 99850, respectively.

[0069] Example 3

[0070] In this example, modified aluminum hydroxide was synthesized and used as a primary dispersant in vinyl chloride polymerization.

[0071] First, the aluminum hydroxide is modified. One kilogram of deionized water and 50 grams of aluminum hydroxide are added to a beaker equipped with a stirring device and placed in a water bath. The material in the beaker is stirred to form a suspension. 5 grams of hydroxypropyl methylcellulose is added to the suspension and stirred for 2 hours at a room temperature of about 25°C. The temperature is then raised to 70°C and stirring is continued at this temperature for 2 hours. The heating is then stopped and the material in the beaker is allowed to cool naturally to room temperature under continuous stirring. The material in the beaker is removed, the solid matter is collected by centrifugal drying, and dried at 50°C for 32 hours to obtain dry modified aluminum hydroxide.

[0072] Then, a vinyl chloride polymerization reaction is carried out. 4800 grams of deionized water, 8 grams of modified aluminum hydroxide, and 0.4 grams of sodium bicarbonate buffer are added to a stainless steel reactor, and then the reactor is sealed and filled with 2000g of vinyl chloride gas. Then, 4 grams of di(2-ethylhexyl) peroxydicarbonate (EHP) initiator (50% concentration) are added to the reactor, and the materials in the reactor are stirred for 10 minutes. Then, the temperature of the reactor is raised to 57°C to start the polymerization reaction. The reaction endpoint is determined when the pressure in the reactor drops by 0.15Mpa. At this time, the reaction continues for 5.45 hours. At this time, acetone thiosemicarbazone terminator is added to the reactor to stop the polymerization reaction. The temperature of the reactor is lowered to room temperature, and the reactor is opened to unload. The object material is filtered and dried to obtain the product PVC resin, which is Figure 1 The solid powder shown.

[0073] The PVC resin product obtained in this example was subjected to GPC test, and the number average molecular weight Mn and the weight average molecular weight Mw of the PVC resin were measured to be 78655 and 96764, respectively.

[0074] Example 4

[0075] In this example, modified aluminum hydroxide was synthesized and used as a primary dispersant in vinyl chloride polymerization.

[0076] First, the aluminum hydroxide is modified. One kilogram of deionized water and 100 grams of aluminum hydroxide are added to a beaker equipped with a stirring device and placed in a water bath. The material in the beaker is stirred to form a suspension. 10 grams of hydroxypropyl methylcellulose is added to the suspension and stirred for 2 hours at a room temperature of about 25°C. The temperature is then raised to 80°C and stirring is continued at this temperature for 2 hours. The heating is then stopped and the material in the beaker is allowed to cool naturally to room temperature under continuous stirring. The material in the beaker is removed, the solid matter is collected by centrifugal drying, and dried at 50°C for 36 hours to obtain dry modified aluminum hydroxide.

[0077] Then, a vinyl chloride polymerization reaction is carried out. 4800 grams of deionized water, 9 grams of modified aluminum hydroxide, and 0.4 grams of sodium bicarbonate buffer are added to a stainless steel reactor, and then the reactor is sealed, and 2000 grams of vinyl chloride gas is filled into it, and then 4 grams of di(2-ethylhexyl) peroxydicarbonate (EHP) initiator (50% concentration) is added to the reactor, and the materials in the reactor are stirred for 10 minutes, and then the temperature of the reactor is raised to 57°C to start the polymerization reaction. The reaction endpoint is determined when the pressure in the reactor drops by 0.15Mpa. At this time, the reaction continues for 5.70 hours. At this time, acetone thiosemicarbazone terminator is added to the reactor to stop the polymerization reaction, and the temperature of the reactor is lowered to room temperature, and the reactor is opened to unload. The object material is filtered and dried to obtain the product PVC resin, which is Figure 1 The solid powder shown.

[0078] The PVC resin product obtained in this example was subjected to GPC test, and the number average molecular weight Mn and weight average molecular weight Mw of the PVC resin were measured to be 78338 and 96424, respectively.

[0079] Comparative Example 1

[0080] In this comparative example, polyvinyl alcohol and hydroxypropyl methylcellulose of the prior art were used as dispersants for the polymerization of vinyl chloride.

[0081] 4800g of deionized water, 4g of polyvinyl alcohol, 4g of hydroxypropyl methylcellulose, and 0.4g of sodium bicarbonate buffer were added to a stainless steel reactor, and then the reactor was sealed, and 2000g of vinyl chloride gas was filled into it, and the temperature of the reactor was raised to 57°C, and the materials in the reactor were stirred for 10 minutes, and then 4 grams of di(2-ethylhexyl) peroxydicarbonate (EHP) initiator (50% concentration) were added to the reactor, and polymerization was carried out at a temperature of 57°C under continuous stirring, and the reaction endpoint was determined when the pressure in the reactor dropped by 0.15Mpa. At this time, the reaction continued for 5.60 hours, and at this time, acetone thiosemicarbazone terminator was added to the reactor to stop the polymerization reaction, and the temperature of the reactor was lowered to room temperature, and the reactor was opened to discharge. The object material was filtered and dried to obtain the product PVC resin, which is Figure 1 The solid powder shown.

[0082] The PVC resin product obtained in this example was subjected to GPC test, and the number average molecular weight Mn and the weight average molecular weight Mw of the PVC resin were measured to be 78735 and 96860 respectively.

[0083] Comparative Example 2

[0084] In this comparative example, unmodified aluminum hydroxide was used as a dispersant for the vinyl chloride polymerization reaction.

[0085] Add 4800g of deionized water, 8g of unmodified aluminum hydroxide, and 0.4g of sodium bicarbonate buffer to a stainless steel reactor, then seal the reactor, fill it with 2000g of vinyl chloride gas, raise the temperature of the reactor to 57°C, stir the materials in the reactor for 10 minutes, then add 4g of di(2-ethylhexyl) peroxydicarbonate (EHP) initiator (50% concentration) to the reactor, and carry out polymerization reaction at 57°C under continuous stirring. The reaction endpoint is determined when the pressure in the reactor drops by 0.15Mpa. At this time, the reaction continues for 5.55 hours. At this time, add acetone thiosemicarbazone terminator to the reactor to stop the polymerization reaction, lower the temperature of the reactor to room temperature, and open the reactor to unload. The object material is filtered and dried to obtain the product PVC resin, which is Figure 1 The solid powder shown.

[0086] The PVC resin product obtained in this example was subjected to GPC test, and the number average molecular weight Mn and weight average molecular weight Mw of the PVC resin were measured to be 83591 and 99746, respectively.

[0087] Comparative Example 3

[0088] In this comparative example, a physical mixture of unmodified aluminum hydroxide and polyvinyl alcohol was used as a dispersant for the polymerization of vinyl chloride.

[0089] 4800g of deionized water, 8g of unmodified aluminum hydroxide, 1g of polyvinyl alcohol, and 0.4g of sodium bicarbonate buffer were added to a stainless steel reactor, and then the reactor was sealed, and 2000g of vinyl chloride gas was filled into it, and the temperature of the reactor was raised to 57°C, and the materials in the reactor were stirred for 10 minutes, and then 4 grams of di(2-ethylhexyl) peroxydicarbonate (EHP) initiator (50% concentration) were added to the reactor, and polymerization reaction was carried out at a temperature of 57°C under continuous stirring. The reaction endpoint was determined when the pressure in the reactor dropped by 0.15Mpa. At this time, the reaction continued for 5.45 hours, and acetone thiosemicarbazone terminator was added to the reactor to stop the polymerization reaction, and the temperature of the reactor was lowered to room temperature, and the reactor was opened to discharge. The object material was filtered and dried to obtain the product PVC resin, which is Figure 1 The solid powder shown.

[0090] The PVC resin product obtained in this example was subjected to GPC test, and the number average molecular weight Mn and weight average molecular weight Mw of the PVC resin were measured to be 78392 and 96558, respectively.

[0091] The particle sizes of the PVC resins obtained in Examples 1-4 and Comparative Examples 1-3 were measured using a laser particle size analyzer and are shown in Table 1 below.

[0092] Table 1 Particle size of PVC resin obtained in Examples 1-4 and Comparative Examples 1-3

[0093] Particle size (nm) Distance (distribution width) Example 1 162.674 0.837 Example 2 151.348 0.824 Example 3 160.892 0.912 Example 4 150.777 0.950 Comparative Example 1 145.126 0.797 Comparative Example 2 280.825 1.658 Comparative Example 3 240.600 1.575

[0094] From the data shown in Table 1, it can be seen that the use of modified aluminum hydroxide as the main dispersant has a small difference in particle size and diameter distance compared with the normal resin (Comparative Example 1) using a general dispersant. However, Comparative Example 2 uses unmodified aluminum hydroxide as the main dispersant, which makes the particle size and diameter distance of the PVC resin product much larger than the normal value, and the whole presents a coarse material, which indicates that the unmodified aluminum hydroxide cannot achieve the desired dispersion effect in the PVC polymerization reaction system. In addition, Comparative Example 3 uses a physical mixture of modified aluminum hydroxide and polyethanol as a dispersant, which also makes the particle size and diameter distance of the PVC resin product much larger than the normal value, and the whole presents a coarse material, indicating that the use of a mixture of aluminum hydroxide and polyvinyl alcohol cannot achieve the desired dispersion effect.

[0095] Example 5

[0096] In this embodiment, the defoaming / foam suppression performance of the dispersants of Examples 1-4 and Comparative Examples 1-3 is characterized by the following steps: Place the curved gas scrubber into a 500mL measuring cylinder and add the dispersant dispersion. The dispersant uses polyvinyl alcohol at a concentration of 1%, 10g of polyvinyl alcohol with 1000ml of deionized water. Add the dispersant dispersion to the 200ml mark and place it in a constant temperature water bath at a temperature of 30°C. Use an air pump to bubble at a gas flow rate of 500 ml / min, and record the time when the foam height rises to the 500mL mark. The results are summarized in Table 2 below.

[0097] Table 2 Defoaming / foam suppression properties of the dispersants of Examples 1-4 and Comparative Examples 1-3

[0098] Example 1 Unable to reach 500ML Example 2 Unable to reach 500ML Example 3 Unable to reach 500ML Example 4 Unable to reach 500ML Comparative Example 1 30.84 seconds Comparative Example 2 Unable to reach 500ML Comparative Example 3 Unable to reach 500ML

[0099] From the results shown in Table 2, it can be seen that the modified aluminum hydroxides used in Examples 1-4 hardly foam, and as described above, these modified aluminum hydroxides can also achieve excellent dispersion effects in the preparation process of PVC resin. In sharp contrast, Comparative Example 1 foams significantly, and although Comparative Examples 2 and 3 do not foam, their dispersion effects in the polymerization process of PVC resin are very poor.

Claims

1. A method for preparing modified aluminum hydroxide, the method comprising the following steps: mixing aluminum hydroxide and a modifier in water to form the modified aluminum hydroxide; The modifier is selected from one or more of the following: poly(C2-C12 olefin) mono- or polyol, cellulose containing one or more C1-C16 hydroxyalkyl groups.

2. The method according to claim 1, characterized in that The method is carried out in the following manner: Step 1: dispersing aluminum hydroxide in water to form an aqueous dispersion; Step 2: adding a modifier to the aqueous dispersion and performing a first mixing; Step 3: After the first mixing, the mixture containing aluminum hydroxide, modifier and water is heated to a temperature higher than the temperature of the first mixing, and a second mixing is performed.

3. The method according to claim 1, characterized in that In the step 2, the first mixing is performed at a temperature of 0-40° C. for 0.5-4 hours; In step 3, after the first mixing, the mixed material containing aluminum hydroxide, modifier and water is heated to 60-90° C. and subjected to a second mixing, and the second mixing lasts for 0.5-4 hours.

4. The method according to any one of claims 1 to 3, characterized in that The weight ratio of the aluminum hydroxide to the modifier is 100:2 to 100:10; The weight ratio of water to aluminum hydroxide is 100:5 to 100:

10.

5. The method according to any one of claims 1 to 3, characterized in that The modifier is selected from one or more of the following: polyvinyl alcohol, hydroxypropyl methylcellulose, gelatin, methylcellulose, hydroxyethyl cellulose.

6. A modified aluminum hydroxide, prepared by the method according to any one of claims 1 to 5.

7. A method for carrying out vinyl chloride polymerization, the method comprising the following steps: In the presence of an initiator, water, a primary dispersant, an optional auxiliary dispersant, and an optional buffer, allowing vinyl chloride to polymerize to form poly(vinyl chloride); The main dispersant is the modified aluminum hydroxide described in claim 6.

8. The method according to claim 7, characterized in that Based on 100 parts by weight of vinyl chloride added in the polymerization reaction, the amount of the main dispersant used is 0.35-0.50 parts by weight.

9. The method according to claim 7, characterized in that The polymerization reaction is carried out at 30-70° C. for 5.0-8.0 hours.

10. The method according to claim 7, characterized in that The initiator is selected from one or more of the following: diacyl peroxide, peroxycarboxylic acid ester, peroxydicarbonate, azo initiator, peroxysulfonic acid initiator, cumyl peroxyneodecanoate, tert-butyl peroxyneodecanoate, tert-amyl peroxypivalate; based on 100 parts by weight of the added weight of vinyl chloride in the polymerization reaction, the amount of the initiator is 0.01-4.5 parts by weight; Based on 100 parts by weight of vinyl chloride added in the polymerization reaction, the amount of water used is 100-300 parts by weight; The dispersing aid is selected from one or more of the following: magnesium hydroxide, aluminum hydroxide, calcium carbonate, zinc sulfide, gelatin, methyl cellulose, hydroxyethyl cellulose, hydroxypropyl methyl cellulose; based on 100 parts by weight of vinyl chloride added in the polymerization reaction, the amount of the dispersing aid is 0-0.5 parts by weight; The buffer is selected from one or more of the following: ammonium bicarbonate, sodium bicarbonate, sodium phosphate, ammonium phosphate, sodium monohydrogen phosphate, sodium dihydrogen phosphate, sodium hydroxide, tricalcium phosphate; based on 100 parts by weight of vinyl chloride added in the polymerization reaction, the amount of the buffer is 0.01-0.05 parts by weight.

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