Production process of hydroxypropyl methylcellulose
Hydroxypropyl methylcellulose (HPMC) is a non-ionic cellulose ether polymer. Depending on the degree of substitution and modification of the substituent group, it has different solubility, surface activity, thermal gelation and compatibility with other substances, thus expanding its application field.
HPMC is a white or off-white powder, mainly used in petrochemicals, coatings, building materials, paint removers, agricultural chemicals, inks, textile printing and dyeing, ceramics, papermaking, and other products as a thickener, stabilizer, emulsifier, excipient, water-retaining agent, film-forming agent, etc.
Ultra-low viscosity hydroxypropyl methylcellulose ether with a viscosity below 100mpa·s is a white powder with good fluidity and good water solubility. Its aqueous solution is transparent and colorless with good stability.
The technical problem that this production process needs to solve is to overcome the defects of the existing technology and provide a method for preparing ultra-low viscosity hydroxypropyl methylcellulose. This technology uses refined cotton as raw material and propylene oxide and methyl chloride as etherifying agents to prepare HPMC. It can greatly reduce the production cost of ultra-low viscosity HPMC, expand its production volume, and expand the scope of use of ultra-low viscosity HPMC.
The weight ratio of raw materials for preparing ultra-low viscosity hydroxypropyl methylcellulose is: 70 parts of toluene isopropanol, 1 part of water, 8 parts of refined cotton, 7 parts of sodium hydroxide, 9 parts of methyl chloride, 3 parts of propylene oxide, and 1.5 parts of glacial acetic acid;
The specific preparation steps are:
1.Mix the raw materials: in the reactor, add the solvent, water, and sodium hydroxide, heat the alkali to 70°C, and keep it warm for 30 minutes;
2.Alkalization: cool the above alkali to 30°C, add refined cotton, stir for 1 hour, and control the temperature at 25-40°C; carry out alkalization reaction;Once alkalization is complete, evacuate the reactor to 0.05–0.07 MPa. Add propylene oxide and methyl chloride, and maintain for 30 minutes to allow their active counterparts to react.
3.Etherification: the temperature is raised to 55±3°C and kept warm for 1.5 hours; then raised to 85±3°C and kept warm for 1.5 hours;
4.neutralization and washing: cool down to below 40°C, add glacial acetic acid for neutralization and washing;
5. is centrifugal drying: centrifuge the material into the dryer through a horizontal spiral centrifuge to dry the material, and then crush the dried material and package it.
