JPH0254362B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for obtaining a pulverizable dry solid without going through a drying process. Specifically, when polymerizing ammonium acrylate in a highly concentrated aqueous solution, the composition of the monomer aqueous solution is adjusted so that the ratio of water to 1 mole of acrylic monomer is The present invention relates to a method for obtaining polyammonium acrylate with a low water content that can be pulverized without going through a drying step after polymerization by adjusting the amount to 2.5 mol or less, thereby vaporizing water with the heat of polymerization. Polyacrylates have a wide range of uses as flocculants, dispersants, water absorbents, etc., and from the viewpoint of transportation and handling requirements, it is desirable that they be in the form of dry solids. It is well known that vinyl compounds, typified by acrylic monomers, generate a large amount of heat during polymerization, and when carrying out aqueous solution polymerization of water-soluble monomers, high concentration aqueous solution polymerization is performed to vaporize water by the heat of polymerization. It is easy to imagine that a dry polymer solid can be obtained. Regarding the case of acrylamide, see JP-A-52-
137482 is carrying out such high concentration polymerization. However, when polymerizing acrylate in a high concentration aqueous solution, it is not possible to prepare such a high concentration aqueous solution because sodium salt, which is commonly used because it is inexpensive, has low solubility. In other words, the heat of polymerization of acrylic acid is approximately 20 kcal/mol
Since the latent heat of vaporization of water is approximately 9 kcal/mol, the molar ratio of monomer to water in the aqueous solution is approximately 1:
Need to adjust to 2.2. Strictly speaking, the dry solid does not need to be completely anhydrous; it can be pulverized even if the loss on drying is around 10%; in this case, the molar ratio of monomer to water is 1:
2.5 is fine. However, in the case of sodium acrylate, at room temperature
It does not dissolve in 2.5 times molar water. During polymerization, acrylic acid does not necessarily need to be 100% neutralized, and is often polymerized at a neutralization rate of 70 to 80 mol%, but the above situation does not change. Although the solubility of sodium acrylate will increase at high temperatures, there is a risk that thermal polymerization will occur during storage of the prepared monomer aqueous solution. On the other hand, ammonium acrylate has a high solubility and can be easily dissolved in twice the molar amount of water, and almost all of the water can be evaporated by the heat of polymerization to obtain a dry solid. An aqueous ammonium acrylate solution can be easily produced by reacting acrylic acid with ammonia, aqueous ammonia, ammonium carbamate, ammonium hydrogen carbonate, and ammonium carbonate (essentially a mixture of ammonium carbamate and ammonium hydrogen carbonate). However, since free ammonia reacts with double bonds by Michael addition at temperatures above 40°C, neutralization must be carried out while cooling and mixing well to avoid excess ammonia. Needless to say, ammonium acrylate can be used not only in the production of polyacrylates, but also in copolymerization with acrylamide in any proportion. However, the proportion of acrylate is 30% of the total monomers.
If it is below, it is possible to use sodium acrylate, so the advantage of using ammonium acrylate disappears. There are no particular restrictions on the polymerization initiator used in the present invention, and any radical type polymerization initiator can be used as long as it can be uniformly dispersed in the monomer aqueous solution.
Usually, an azo initiator such as azobisisocyanonitrile, azobisamidinopropane, azobisisocyanovaleric acid or a persulfate such as potassium persulfate or ammonium persulfate is selected. The polymerization vessel must be open at the top for convenient dissipation of water vapor, and polymerization on an endless belt gives good results. This dry solid does not necessarily have to be made into a fine powder and can be used in the form of granules or blocks. The present invention will be specifically explained below using Examples. Example Preparation of monomer solution The feasibility of preparing monomer solutions having the compositions shown below at 25°C was investigated.

[Table] Polymerization example 1 0.00005 for monomer aqueous solution with composition No. 1 in the previous table
Mix moles of methylene bisacrylamide,
Polymerization was carried out by mixing 0.003 mol of azobisamidinopropane hydrochloride and 0.5 mol of water for dissolving the catalyst. The drying loss of the obtained polymer was 8%.
It could be easily crushed. When the resulting powder was dispersed in distilled water, it absorbed 700 times its own weight in water. Polymerization Example 2 0.005 mol of ammonium persulfate and 0.5 mol of water were mixed with the monomer aqueous solution having the composition No. 2 in the previous table, and polymerization was carried out on a shallow polyester dish, resulting in a drying loss of 7.
% polymer solids was obtained. After pulverization, the water absorption capacity for distilled water was measured and was 440 times its own weight. Polymerization Example 3 0.00005 for monomer aqueous solution with composition No. 3 in the previous table
mol of sodium bisulfite and 0.005 mol of azobisisobutyronitrile 10% acetone solution were added and polymerized on a Teflon-coated heat-resistant rubber shallow dish to obtain a dry solid with a loss on drying of 7%. After pulverization, it was dissolved in 1N saline and the viscosity of a 1% polymer solution was measured and found to be 8.5CP.

Claims (1)

[Claims] 1 Dissolve a water-soluble acrylic monomer in 2.5 times the molar amount or less of water, perform aqueous polymerization, and evaporate water by the heat of polymerization to obtain a dry polymer solid without going through a drying process.30 mole% of the total monomers. A method for producing a polymer solid, characterized in that the above is ammonium acrylate.