The production process of Hydroxypropyl Methylcellulose (HPMC)

The purity of hydroxypropyl methylcellulose in building insulation mortar directly affects the guarantee of construction quality. In the production process of hydroxypropyl methylcellulose, residual oxygen in the reaction kettle leads to degradation and lowering of molecular weight, but the residual oxygen is limited, and it is not very difficult to reattach the broken molecules.

The manufacture of Hydroxypropyl Methyl Cellulose (HPMC) is mainly completed through three reactions: cotton linter alkali treatment, hydroxypropylation, and methylation. Various technological developments in recent years have focused mainly on improving and refining each unit operation. The production of HPMC uses chloromethane and epichlorohydrin as etherifying agents. The chemical reaction equation is: Rcell-OH (refined cotton) + NaOH (caustic soda, sodium hydroxide) + CspanCl (chloromethane) + CH2OCHCspan (epichlorohydrin) → Rcell-O-CH2OHCHCspan (hydroxypropyl methyl cellulose) + NaCl (sodium chloride) + H2O (water). The principle of etherification synthesis of HPMC is not complicated, but involves alkalization, raw material pulverization, etherification, solvent recovery, centrifugal separation, etherification reaction at a certain temperature and pressure, and control of various conditions such as temperature, time, pressure, and material flow control. Auxiliary equipment and control instruments are essential to ensure stable product quality and reliable production system. The manufacturing process of HPMC generally uses one-step slurry method, with the following steps: ① Pretreatment: Refined cotton is crushed into blocks with a diameter of about 1-3 cm by opening machines, and then enters the pulverizer to be rapidly sheared to refine cotton powder of 60-100 mesh. ② Alkalization: The crushed refined cotton powder undergoes alkalization in a dispersal system with 8-10 times the mixed solvent, generating alkaline cellulose with chemical reaction activity. ③ Etherification: Alkaline cellulose, epichlorohydrin, and chloromethane undergo etherification reaction. The methoxy and hydroxypropyl substitution degrees are adjusted by controlling the temperature, reaction time, and formula of the chemical reaction, and the viscosity is adjusted by regulating the purity of oxidant in the system environment and selecting the refined cotton raw material. A computer DCS control system is used for stable product quality and reliable process characteristics. ④ Neutralization: After the chemical reaction is over, an acid is used to neutralize residual alkali, and the pH value of the product is regulated to meet the specifications. ⑤ Solvent recovery: The mixed system after neutralization is heated, and the assimilated solvent is recovered through a condensation and cooling recovery system for repeated recycling. ⑥ Post-treatment: The dissolved compound is separated by a horizontal settling centrifuge, and then processed into a finished product through granulation, drying, assimilation, and packaging. The purity of HPMC directly affects the quality of construction insulation mortar. Residual oxygen in the reaction vessel during HPMC production can cause degradation and molecular weight reduction, but it is relatively limited and can be repaired by reconnecting broken molecules. The water retention rate of HPMC is closely related to hydroxypropyl, but the entire reaction process also determines its water retention rate, with the alkalization effect, the proportion of chloromethane and epichlorohydrin, the concentration of alkali, and the ratio of water to refined cotton all determining the product performance.