Transesterification of fats and oils to produce by-product glycerol,Containing a base catalyst,a soap generated by a side reaction,lessUnreacted oils and un-distilled methanol, as well as trace amounts of proteins, hydrocarbons, pigments, sediments and waterIn order to obtain refined glycerin, it is necessary to first purify and separate the above impurities.
(1)Acid treatment
Adding a solvent and a mineral acid solution to the crude glycerol sample,Adjustment solution pH Value to acidic,Heat and stir,Neutralizing a base catalyst,At the same time, the soap is converted into fatty acids.Let it float on the liquid surface and remove it,The inorganic acid used canIt is hydrochloric acid and sulfuric acid. The solvent can be methanol or water. By measuring the glycerol content in the lower layer solution after acid treatmentThe amount of acid treated glycerol recovery was calculated.
(2)Degumming
After the acid treatment, the sodium soap is basically converted into a fatty acid to be layered and removed, and the unreacted sodium soap may still beExist in glycerol,Add flocculant,A small amount of colloidally dispersed soap and other charged impurities are flocculatedElectrolyte neutralization and coagulation under the action of the metal ions of the agent. Common degumming reagents are aluminum sulfate and FeCl3.
(3)Alkali neutralization
The acidic filtrate obtained after degumming filtration also contains an excess amount. FeCl3,Neutralizing the acid by alkali treatment,Reduce corrosion on the evaporator,And FeCl3change into Fe(OH)3precipitation,At the same time adsorbing impurities,PassedRemove by filtration.At the same time, there may be no separated fatty acids in the separation process after acid treatment.By subtractionneutralize,Can fix it in the form of soap,Prevent fatty acids from steaming with glycerin during distillationOut, affecting the quality of glycerol, how much lye is added during alkali neutralization, the quality of glycerol, recovery and evaporationOperation has a lot to do withThe amount of alkali is too small,Under acidic conditions, glycerol is easily dehydrated in the molecule to form propenol orA stimulating substance such as acrolein (ketone) intermediate, fatty acid can not be fixed in the form of soap,Distilled with glycerin during distillation,Causing glycerin loss and quality degradation,Adding too much alkali,Glycerin is easy to gatherIt is easy to produce foam when evaporating water, easy to run, causing additional loss of glycerin and reducing yield.
(4)Glycerin concentration and filtration desalting
After neutralization with a base, the crude glycerol is distilled under reduced pressure to 110°C, evaporation of water, filtration and removalSalt.
(5) Refinement of glycerin
Different types of fines can be used depending on the use of glycerin and the economic consumption in the production process.
Method of production. In general, distillation, decolorization, rectification, decolorization, and ion exchange are employed. steamThe glycerin obtained by distillation and decolorization purification is mainly industrial glycerin. If glycerin is used for special purposes, such as medicinal, foodUse, etc.No matter which refining method is used,All must undergo an ion exchange process to ensure glycerol complianceQuality standard requirements.
