What is Cellulose ether manufacturing process?

The reaction principle of cellulose ether hydroxypropyl methyl cellulose: the production of HPMC hydroxypropyl methyl cellulose uses methyl chloride and propylene oxide as etherification agents. The chemical reaction equation is: Rcell-OH (refined cotton) + NaOH (sodium hydroxide) , Sodium hydroxide) + CspanCl (methyl chloride) + CH2OCHCspan (propylene oxide) → Rcell-O -CH2OHCHCspan (hydroxypropyl methylcellulose) + NaCl (sodium chloride) + H2O (water)

Process flow:

refined cotton crushing—alkaliization—feeding—alkalization—etherification—solvent recovery and washing—centrifugal separation—drying—crushing—mixing —Product packaging

1: Raw materials and auxiliary materials for the production of hydroxypropyl methylcellulose The main raw material is refined cotton, and the auxiliary materials are sodium hydroxide (sodium hydroxide), propylene oxide, methyl chloride, acetic acid, toluene, isopropanol, and nitrogen. The purpose of refined cotton crushing is to destroy the aggregated structure of refined cotton through mechanical energy to reduce crystallinity and polymerization degree and increase its surface area.

2: Measurement and raw material quality control: Under the premise of certain equipment, the quality of any main and auxiliary raw materials and the ratio of the added amount and the concentration of the solvent directly affect the various indicators of the product. The production process system contains a certain amount of water, and water and organic solvents are not completely miscible, and the dispersion of water affects the distribution of alkali in the system. If it is not stirred sufficiently, it will be disadvantageous to uniform alkalization and etherification of cellulose.

3: Stirring and mass transfer and heat transfer: Cellulose alkalization and etherification are all carried out under heterogeneous (stirring by external force) conditions. Whether the dispersion and mutual contact of water, alkali, refined cotton and etherifying agent in the solvent system are sufficiently uniform, will directly affect the alkalization and etherification effects. Uneven stirring during the alkalization process will cause alkali crystals and precipitation at the bottom of the equipment. The upper layer concentration is low and alkalization is not sufficient. As a result, there is still a large amount of free alkali in the system after the etherification is completed. Uniformity, resulting in poor transparency, more free fibers, poor water retention, low gel point, and high PH value.

4: Production process (slurry production process)

(1:) Add the specified amount of solid alkali (790Kg) and water (total system water 460Kg) into the caustic soda kettle, stir and heat to a constant temperature of 80 degrees for more than 40 minutes, and the solid alkali is completely dissolved.

(2:) Add 6500Kg of solvent to the reactor (the ratio of isopropanol to toluene in the solvent is about 15/85); press the alkali into the reactor, and spray 200Kg of solvent to the alkali tank after pressing the alkali. Flush the pipeline; the reaction kettle is cooled to 23°C, and pulverized refined cotton (800Kg) is added. After the refined cotton is added, 600Kg of solvent is sprayed to start the alkalization reaction. The addition of crushed refined cotton must be completed within the specified time (7 minutes) (the length of the addition time is very important). Once the refined cotton comes into contact with the alkali solution, the alkalization reaction begins. If the feeding time is too long, the degree of alkalization will be different due to the time when the refined cotton enters the reaction system, resulting in uneven alkalization and reduced product uniformity. At the same time, it will cause the alkali cellulose to be in contact with the air for a long time to oxidize and degrade, resulting in The viscosity of the product decreases. In order to obtain products with different viscosity levels, vacuum and nitrogen can be applied during the alkalization process, or a certain amount of antioxidant (dichloromethane) can be added. The alkalization time is controlled at 120min, and the temperature is kept at 20-23℃.

(3:) After the alkalization is over, add the specified amount of etherifying agent (methyl chloride and propylene oxide), raise the temperature to the specified temperature and carry out the etherification reaction within the specified time.

Etherification conditions: 950Kg of methyl chloride and 303Kg of propylene oxide. Add the etherification agent and cool and stir for 40 minutes and then raise the temperature. The first etherification temperature is 56°C, the constant temperature time is 2.5h, the second etherification temperature is 87°C, and the constant temperature is 2.5h. The hydroxypropyl reaction can proceed at about 30°C, the reaction rate is greatly accelerated at 50°C, the methoxylation reaction is slow at 60°C, and weaker below 50°C. The amount, proportion and timing of methyl chloride and propylene oxide, as well as the temperature rise control of the etherification process, directly affect the product structure.

The key equipment for producing HPMC is reactor, dryer, granulator, pulverizer, etc. At present, many foreign manufacturers use equipment produced in Germany. Domestically produced equipment, whether it is production capacity or manufacturing quality, cannot meet the needs of high-quality HPMC production.

The All-In-One Reactor produced in Germany can complete multiple process steps with one device, realize automatic control, stable product quality, and safe and reliable production operations.

The main raw materials for the production of HPMC are refined cotton, sodium hydroxide, methyl chloride, and propylene oxide.

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