During the production process, it mainly controls the temperature, airflow, agitation, pressure and acid value.
1 Temperature control mainly includes the following parts: the temperature of the material in the center of the reactor; the temperature of the material in the wall of the reactor; the temperature of the oil in the jacket; the temperature of the steam at the top of the fractionation column, often referred to as the "head temperature"; Inlet and outlet temperature; material temperature at the center of the dilution tank; medium temperature in the jacket of the dilution tank.
The temperature of the central part of the reaction kettle is the temperature of the reactants, but the material temperature close to the wall of the kettle is directly affected by the temperature of the medium in the jacket, and its temperature is different from that of the central part. Under good agitation, the difference is not large; when the agitation is poor, there is a significant temperature difference, the temperature at which the resin is polymerized is not uniform, and local gel may even occur. The temperature of the oil in the jacket should not be too high, otherwise the reactants will heat up too fast, and coking and scaling may occur on the kettle wall.
The control of the steam temperature at the top of the fractionation column, that is, the "head temperature" is also important. In the polyesterification reaction, the temperature should be controlled at about 100 ℃, because there is a large amount of alcohol in the reactant, the alcohol can form an azeotrope with water, at a lower temperature, the alcohol is distilled off, causing the loss of alcohol, up to Less than synthetic requirements. For ordinary resins, the ratio of phthalic anhydride, maleic anhydride and alcohol is 1:1:2:2, and the loss of alcohol is less. For high content of maleic anhydride or fumaric acid polyester, such as phthalic anhydride, maleic anhydride and ratio of 1:3:4:4, if the top temperature of the fractionation column exceeds 105 ℃, it will cause serious loss of alcohol. Unsaturated polyester is a linear polymer compound with multifunctional groups. It has a polyester chain bond and an unsaturated double bond on its backbone main chain, and has carboxyl groups and hydroxyl groups at both ends of the macromolecular chain.
The double bond on the main chain can undergo copolymerization crosslinking reaction with the vinyl monomer, so that the unsaturated polyester resin changes from soluble and meltable state to insoluble and infusible state. The ester bond on the main chain can undergo a hydrolysis reaction, and an acid or a base can accelerate the reaction. If copolymerized with styrene and cross-linked, the occurrence of hydrolysis reaction can be greatly reduced.
The temperature of each of the above points can be recorded and monitored with a multi-point temperature recorder, and can also be controlled by a computer.