JPH0574606B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for producing an acrylamide polymer. [Prior Art] Acrylamide-based polymers are water-soluble polymers that are used, for example, as flocculants or paper strength agents.The method for producing them is usually to prepare an aqueous monomer solution containing acrylamide in a polymerization container. A known method is to obtain a gel-like water-containing polymer by aerating with an inert gas, then allowing the polymer to polymerize by standing without stirring in the presence of a polymerization initiator, and then drying the polymer. This polymerization of acrylamide is an exothermic reaction, but it is usually carried out without cooling or heating the polymerization system, allowing the temperature to rise due to the exotherm of polymerization. However, the maximum temperature at the end of polymerization reaches approximately 70 to 100°C. In this polymerization, it is ideal for the entire polymerization system to proceed under uniform conditions, and usually measures have been taken to protect the peripheral wall of the polymerization container with a heat insulating material to suppress heat dissipation from the peripheral wall. [Problems to be solved by the invention] However, especially when attempting to obtain a polymer with high viscosity by this method, the amount of water-insoluble substances contained in the obtained polymer tends to increase. Ta. [Means for Solving the Problems] In view of the above circumstances, the present inventors have developed various methods for suppressing the content of water-insoluble substances in the obtained polymer even when producing a high-viscosity acrylamide polymer. As a result of our investigation, we found that the formation of this insoluble material was common in the surface layer of the polymerization system, and that it was necessary to introduce steam into the gas phase in the polymerization container during polymerization, from the time the polymer surface became gel-like to the end of polymerization. The present invention was completed based on the discovery that water-insoluble matters in the obtained polymer can be significantly reduced by circulating the polymer and heating the surface of the polymer. The present invention will be explained in detail below. Monomers targeted by the present invention include acrylamide alone or a mixture of acrylamide and a known monomer copolymerizable with acrylamide, such as acrylic acid, sodium acrylate, and 2-acrylamide propane sulfonate. In the case of copolymerization, it is usually preferable that the proportion of acrylamide is 60 mol% or more. The concentration of the monomer aqueous solution is usually 10 to 50% by weight,
Preferably it is 20 to 30% by weight. If the concentration of the aqueous monomer solution is too low, the resulting gel-like water-containing polymer will have high stickiness, and if it is too high, the temperature in the polymerization system will become too high, causing thermal deterioration of the polymer, which is not preferable. On the other hand, examples of the polymerization initiator include azo compounds such as azobis(2-amidinopropane) hydrochloride, or peroxides such as potassium persulfate, ammonium persulfate, and hydrogen peroxide. Examples include those in combination with reducing agents such as sodium, ferrous sulfate, and ferrous chloride. The amount of these polymerization initiators used varies depending on the polymerization conditions and the physical properties of the polymer to be obtained, but
Usually, it is selected from the range of 100 to 10,000 ppm, preferably 200 to 5,000 ppm based on the monomer. The monomer aqueous solution described above is polymerized in the presence of a polymerization initiator, and this operation is usually carried out by charging the monomer aqueous solution into a polymerization container, supplying an inert gas to it, and aerating the system while injecting the polymerization initiator. is added, and after the polymerization has started, the aeration can be stopped and the system can be allowed to stand still without stirring, thereby allowing the polymerization to proceed. Polymerization initiation temperature is usually -10
The temperature in the system is adjusted to ~20°C, but the temperature within the system eventually reaches 70-100°C due to the heat of polymerization. The polymerization container preferably has an inner wall made of a synthetic resin such as fluororesin, nylon resin, polyester, or polyethylene, and is preferably provided with a heat insulating material around the outer periphery to prevent heat dissipation. The inert gas is usually nitrogen gas, and the amount supplied must be such that oxygen in the system can be sufficiently removed and good polymerization can be initiated. In the present invention, it is essential to flow steam into the gas phase portion of the polymerization container during the polymerization from the time when the polymer surface becomes gel-like until the polymerization is completed. In other words, this steam distribution treatment can suppress the formation of water-insoluble substances, which tend to form in relatively large amounts on the surface layer of the polymerization system. The flow rate of steam is normally adjusted so that the temperature of the gas phase is maintained at about 100°C and the surface of the polymer is heated. The term "completion of polymerization" in the present invention refers to the time when the inside of the polymerization system reaches its maximum temperature, which is usually 60 to 180 minutes after the start of polymerization. Furthermore, gelation of the surface of the polymer in the polymerization system usually occurs 40 to 120 minutes after the start of polymerization. Polymers obtained by polymerization usually have a water content of
It is a gel-like water-containing polymer of 65 to 90% by weight, and this polymer is made into fine particles according to a conventional method and then dried to obtain a particle size polymer. For example, a gel-like hydrous polymer is made into granules with an average particle size of 2 to 5 mm using a meat grinder-type extrusion granulator, and then dried in a hot air dryer at a temperature of about 40 to 130°C until the water content is 10% by weight. It is dried until the Furthermore, in the present invention, the polymer obtained by polymerization may be brought into contact with an alkaline aqueous solution such as sodium hydroxide, potassium hydroxide, or sodium carbonate to hydrolyze a portion of the acrylamide component to form a modified polymer. [Function] According to the present invention, by carrying out polymerization while flowing steam through the gas phase of the polymerization container, the amount of water-insoluble substances produced in the surface layer polymer of the polymerization system can be significantly suppressed. be able to. The reason why such excellent effects can be obtained with the present invention is not clear, but there is a lot of heat dissipation in the surface layer of a normal polymerization system, which makes it difficult for the temperature to reach the theoretical optimum value, and water evaporation due to temperature rise is difficult. This is the reason why good polymerization is not carried out, and it is presumed that these problems can be solved by the flow of steam. [Examples] Next, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to the following Examples unless the gist thereof is exceeded. Example 1 20kg of a 25% acrylamide aqueous solution at a liquid temperature of 10°C was charged into a sealed polymerization vessel whose inner wall was made of fluororesin, and nitrogen gas was passed through the aqueous solution while aerating the system. In this, 2,2-azobis(2-amidinopropane) is added as a polymerization initiator.
Hydrochloride 500ppm and acidic sodium sulfite 50ppm
was added, and when polymerization started and an increase in the viscosity of the aqueous solution was observed, aeration with nitrogen gas was stopped, and the polymerization was allowed to proceed while standing still. Then, when the polymer surface became gel-like (approximately from the start of polymerization) After 100 minutes), steam (1
Kg/cm ² G) was passed at a rate of 5/min to carry out polymerization. Then, when the temperature within the system stops rising and reaches the maximum temperature (87℃), the steam distribution is stopped.
Thereafter, it was left to stand for 3 hours. Of the gel-like water-containing polymer obtained in this polymerization, the polymer in the surface layer (up to 5 cm from the surface) was made into fine particles by a conventional method, and then dried with hot air, and then the polymer viscosity and the amount of water-insoluble matter were measured. The results shown in Table 1 were obtained. Comparative Example 1 Table 1 shows the results when polymerization was carried out in the same manner as in Example 1 except that the steam flow treatment was not performed.

〔Effect of the invention〕

According to the present invention, it is possible to significantly suppress the amount of water-insoluble substances contained in the polymer in the surface layer of the polymerization system. Therefore, since it is possible to obtain a polymer of much higher quality than conventional products, its industrial value is great.

Claims (1)

[Claims] 1 A method for obtaining a gel-like hydrous polymer by aerating an acrylamide-containing monomer aqueous solution in a polymerization container with an inert gas and then polymerizing it in the presence of a polymerization initiator without stirring. 1. A method for producing an acrylamide-based polymer, which comprises heating the surface of the polymer by passing steam through a gas phase in a polymerization container during the polymerization process, from the time the polymer is formed to the end of the polymerization.