Glycerol synthesized from epichlorohydrin is a mature process with good product quality. The production equipment was introduced in China in 1980. At present, the annual production capacity of synthetic glycerol in China is above 5kt. However, the production capacity of synthetic glycerol cannot be brought into full play due to the high price of raw material epichlorohydrin. Foreign countries produce a lot of synthetic glycerol, American annual output of glycerol 300kt, including synthetic glycerol 150kt. In the production of epichlorohydrin, a large amount of by-product, trichlorohydrin, can be comprehensively used to produce glycerol by heating hydrolysis.
(1) hydrolysis. Within the reactor with 1 mol, chemical byproduct propane (mixture, the boiling range of 130 ~ 170 ℃), heating reflux, add sodium acetate solution (sodium acetate dosage is 3% of the mass of chemical propane), after the start drops 1.5 mol mass fraction 20% sodium hydroxide solution, add time is about 2 h, reflux temperature from 100 ℃ or so by azeotropic function gradually reduced to about 90 ℃, since then, due to hydrolysis the boiling point is gradually increased, until 110 ℃ (in drop after about 1 h), sampling observation. The oil phase in the reactant disappeared and changed from two phases to one phase. It was kept at 110 ° c for 10 minutes, and then gradually cooled to 70 ° c in the stirring and continued to stir for 1 hour. The vacuum pump was started and degassing was conducted for 10 minutes.
2)purification of glycerine water. The neutralized product is saturated salt solution of glycerin water, adding a small amount of poly aluminum chloride water purifier, let stand overnight, filter to remove unclean impurities, remove the surface oil slick, if there is crystallization salting out, must use a small amount of clean water to remove the adsorbed glycerin on the surface of salt, and then filter the lotion and the first filtrate combined. The product is a light yellow glycerin salt solution.
(3)Desalination. Of the above product in a vacuum (6.666 ~ 10.666 kPa) dehydration, about 50 ~ 60 ℃, boiling point when distillate water quantity is about 1/6 of the total volume, namely the residual liquid filtration desalination, filter out the salt must use not concentrated glycerin solution to washing, reoccupy water washing, wash and concentrate to merge, vacuum distillation desalination, again and again 5 ~ 6 times, until the concentrate of glycerol in the mass fraction of more than 80%, can be used for crude glycerin.
(4)Ion exchange processing. Dilute the crude glycerin with water to the mass fraction of 20% or so, first with the ion exchange column mixed with anion and ion, and then successively with anion resin, cationic resin treatment, so repeated for 3 times, until the glycerin solution does not contain chloride ions or sodium ions, can be deionized glycerin solution.
(5)Concentration and distillation. The above glycerol solution was concentrated at 13.332kPa at about 60 ℃ to a mass fraction of 91.3%, the pH was adjusted to 8.5 with sodium hydroxide, and then distilled at 933.254 Pa at 170 ℃ to obtain pure glycerol with a purity of over 98%.
A rough comparison of raw material consumption between natural oil hydrolysis method and epichlorohydrin method reveals the advantages of natural oil hydrolysis method. The raw material used in natural oil hydrolysis method is waste liquid soap, which has no specification requirements and is cheap .In terms of the total amount of raw materials needed to produce glycerin, the natural oil hydrolysis method is also less than that of epichlorohydrin. Moreover, the equipment for synthesizing glycerin is of large investment and high cost. However, with the change of people’s living habits, the broad market of soap is gradually occupied by washing powder, detergent, etc. Therefore, many chemists turned to the fermentation method to produce glycerin as the direction of their efforts.