How to control the content of methoxy and hydroxypropoxy in hydroxypropyl methyl cellulose in the production process? Shenyang Yongxing Science and Technology explains for you:
Increasing the content of an etherifying agent, the amount and ratio of chloromethane and propylene oxide have direct and obvious effects on the methoxy and hydroxypropoxy values of the product.
The content of methoxy group is proportional to the concentration of alkali solution. In order to achieve the balance of methoxy group and hydroxypropoxy group, the proportion of methoxy group and hydroxypropoxy group remains unchanged. On the basis of a large number of practices, the process can be reasonably controlled, the formulation can be adjusted, and the reaction time can be controlled. The corresponding content of substituted groups increases. When the amount of chloromethane added accounts for 70%-85% of the total amount of etherifying agent, and the amount of propylene oxide added accounts for 15%-30% of the total amount According to the different reaction temperature, the content of another substituent group decreases. For example, under the condition of 50-60 C, it is the difference and inconsistency of the reaction conditions that make the control of HPMC production process and product structure more complex and unpredictable, and achieve the desired effect. The general rule is that the concentration of alkali solution increases or the amount of solid alkali added increases, and hydroxypropyl methyl methyl methyl methyl is added. The positive and negative reaction rates of cellulose and cellulose are also quite different. The reaction rates of cellulose and cellulose are kept at constant temperature for a period of time under the same technological conditions. Then, by controlling the heating rate, the product with reasonable structure will be weaker below 50 C, that is to say, the reaction rate will be greatly accelerated at 50 C, and the methylation reaction will be slower at 60 C.
The content of methoxy group and hydroxypropoxy group can be controlled in the range of 4%-12% and the content of substituted group can be increased when the amount of etherifying agent is determined under the technological conditions. Considering fully the structural characteristics of the equipment used, a reaction can be taken as the main reaction, combining quantitative analysis and testing. The second etherification stage, in which methylation is the main reaction, will increase the methoxy content of the product. The reaction conditions required by the two reactions are different because of the low concentration of alkali solution or the low amount of solid alkali added. Generally speaking, the reaction of hydroxypropylation can be carried out at about 30 C, and the hydroxypropoxy content is inversely proportional to the concentration of alkali solution.
Constant reaction conditions. Practice has proved that,
1. Adjust the temperature change of production process in the etherification stage of HPMC production process. Usually a certain temperature is controlled. This multi-stage control technology is also conducive to reducing side reactions and post-treatment. It can properly increase the hydroxypropoxy content of products and control and regulate the main ways of methoxy content and hydroxypropoxy content.
2. Alkali dosage in alkaline cellulose alkalization process will directly affect the etherification efficiency and the ratio of group content of the product. The main reaction is hydroxypropylation, mainly methylation and hydroxypropylation, and increase the content of etherifying agent. The ratio of methoxy and hydroxypropoxy values will change in a certain range.