The crude glycerin is distilled, deodorized, and decolored, and good quality industrial glycerin products can be obtained. However, some indicators such as reducing substances, acrolein, and color do not meet the requirements of certain industries. In order to obtain high quality glycerin products (such as medicinal glycerin, explosive glycerin, reagent grade glycerin, etc.), the method adopted in the 1950s was secondary distillation.
In 1850, the phenomenon of ion exchange was discovered, and it was applied in industry and after 60 years. In the late 1960s, with the development of synthetic resin technology, China developed a method for purifying trace impurities in glycerol after deodorization and decolorization using ion exchange resin technology.
Ion exchange resin
The ion exchange resin refers to a resin in which a reactive group in a resin molecule can be ion-exchanged with other substances. Most of them are copolymers of styrene and divinylbenzene. The ion exchange resin is classified into a cation exchange resin and an anion exchange resin depending on the nature of the acidic group or the basic group in the molecule. According to the difference in acidity or alkalinity, the ion exchange resin is divided into strong acidity (sulfonic acid group-SO3H in the molecule), medium acidity (phosphoric acid group-H2PO in the molecule, phosphonic acid group-H2PO3), weak acidity ( The molecule contains a carboxylic acid group – COOH, etc.), strongly basic [containing quaternary ammonium-N(CH3)3OH in the molecule], moderately basic [tetraethylenepentamine-H(HNCH2CH2)4NH2 in the molecule] and weak base Sex (m-phenylenediamine formaldehyde resin, etc.) and numbered separately. Among them, the degree of cross-linking is marked after the number. For example, a sulfonic acid type cation exchange resin containing 12% (i.e., degree of crosslinking) of divinylbenzene is referred to as 1X12.
The ion exchange resin is typically a particulate or spherical solid. It does not dissolve in acids, bases or their salts and other common solvents, only swelling. When it comes into contact with a solution containing an ion, ion exchange occurs, so that the ion in the solution can be removed. Its performance is gradually lost as the amount of exchange increases, and this exchange capability can be regenerated by processing.
The resins which can be used for glycerin purification are styrene strong acid type cation exchange resin, sulfonated coal resin, styrene quaternary ammonium salt strong base type exchange resin, and phenol formaldehyde weak base type resin. A styrene strong acid type cation exchange resin and a sulfonated coal resin can remove cations such as Na+, Mg2+, and Fe3+. The styrene quaternary ammonium salt strong base type exchange resin can remove anions such as CO3, SiO, formic acid, phenol, and fatty acid. The phenol formaldehyde weak base resin can remove strong acid ions such as CI-, sO?-, and PO3-. Large particle adsorption resins (such as X54-1) are mainly used for adsorption decolorization.
