At first the fresh sodium bisulfite qualified by analysis is added in the preparation still, under room temperature, normal pressure condition, be made into the aqueous solution of 35wt% with distilled water.
Send 2857Kg (concentration: 35wt%) of the prepared sodium bisulfite solution into the ethoxylation reactor. After nitrogen replacement and temperature rise operation, ethylene oxide is added at 90°C to start the reaction, and the temperature is controlled at 90-100°C. Pressure 0～0.1MPag (gauge pressure). After adding 500Kg of ethylene oxide, mature at 90-100°C for 30 minutes, and then unload.
The crude product (concentration 40-45wt%) synthesized in the previous step is sent to the double-effect continuous evaporating recrystallizer, operated in parallel, continuously fed, and intermittently discharged, that is, the dilute solution is advanced to the first-effect evaporator, and after preliminary After concentration, the concentration reaches 55-60wt%. The concentrated solution enters the second-effect evaporator, and after further concentration and evaporation to 72-75wt%, the concentrated solution enters the continuous crystallizer. The centrifuge centrifuges, the solid enters the next process, and the mother liquor returns to the second-effect evaporator to continue to participate in evaporation and concentration. When the content of ethylene glycol in the product reaches below 0.1%wt, it is regarded as qualified, and through analysis and detection, the product purity is greater than 99.5wt%.
A small amount of non-crystallizable raffinate is extracted with 3 times solvent, and the used extractant is dehydrated alcohol, and the sodium isethionate product is separated out in dehydrated alcohol, and a small amount of water and organic impurities, such as ethylene glycol, Polyethylene glycol and isethionate will enter the liquid phase ethanol, then enter the centrifuge for centrifugation, and finally dry the crystals in a disc dryer at 120°C to remove a small amount of residual solvent impurities in the product and moisture. The used extractant ethanol is recovered and reused. Extractant ethanol can be recovered by distillation.