The by-product glycerol is obtained by transesterification of oils and fats. It contains alkali catalysts, soap produced by side reactions, a small amount of unreacted oils and unsteamed methanol, and a small amount of protein, hydrocarbons, pigments, precipitates and water,In order to get refined glycerol, we must firstly purify and separate the above impurities.
- Acid treating
With the addition of solvent and inorganic acid solution in the crude glycerol sample, the pH value of the solution is adjusted to acidity, heated and stirred, and the base catalyst is neutralized, and the soap is converted to fatty acid to remove it on the liquid surface, and the inorganic acid can be used as hydrochloric acid and sulfuric acid. The solvent can be used in methanol and water. By measuring the glycerol content in the lower solution after acid treatment, the recovery rate of acid treated glycerin was calculated.
- Degumming
After the acid treatment, the sodium soap is basically converted into fatty acid statically delamination, and the unreacted sodium soap may still exist in the glycerol sample, adding flocculants, a small amount of colloid dispersed soap and other charged impurities to produce electric neutralization and sink under the action of the flocculant metal ions. The commonly used degumming reagents are aluminum sulfate and FeCl3.
- Alkali neutralization
The acid filtrate obtained by the degumming filter contains an excess of FeCl3, and the corrosion of the evaporator is reduced by alkali treatment and acid, and the FeCl3 is converted to Fe (OH) 3 precipitation, and the impurities are adsorbed and removed by filtration. At the same time, there may be fatty acids without separation after acid treatment, and can be fixed in soap form by neutralization to prevent fatty acids from evaporating with glycerin in the distillation process, affecting the quality of glycerol. The amount of lye added to the neutralization process has a great relationship with glycerol quality, recovery rate and evaporation operation. The amount of alkali is too little, and the glycerol is easily dehydrated to produce acryl alcohol or acrolein (ketone) intermediate under acidic condition. The fatty acid can not be fixed in the form of soap. The distillation process is produced with glycerol, causing the loss of glycerol and the decrease of the quality；With excessive alkali, glycerin is easy to polymerized. When evaporating water, it is easy to produce foam, which is easy to run and cause extra glycerol loss and reduce the yield.
- Glycerol concentration and filtration desalination
After neutralization, the crude glycerol was distilled to 110 degrees, evaporated to remove water and filtered to remove the salt.
- Refining of glycerol
Different refining methods can be used according to the different uses of glycerol and the different economic consumption in the production process. In general, distillation, decolorization, distillation, decolorization and ion exchange are used. The glycerol obtained from distillation and decolorization is mainly industrial glycerin. If glycerol is used as a special purpose, such as medicinal and edible, no matter which refining method is used, it is necessary to pass the ion exchange process to ensure that the glycerol is in conformity with the standard of quality.
