Glycerol refining

Glycerol. From these different processes for hydrolyzing fats into soap or fatty adds, glycerol is recovered and refined for the various purposes to which it is now appded. Practicady ad glycerol refining is now accomplished by distillation with steam under diminished pressure. 

Refining. The refining of natural glycerol is generally accompHshed by distillation, followed by treatment with active carbon. In some cases, refining is accompHshed by ion exchange (qv). 

Most cmde glycerol is shipped to refiners in standard tank cars or tank wagons. Imported cmde arrives in bulk, in vessels equipped with tanks for such shipment, or in dmms. 

Once harvested, rapeseed is transported to an oil mill where vegetable oil is extracted. The crude vegetable oil is then refined. The refined vegetable oil is converted to FAME by esterification, which generates glycerol as a by-product (see Tables 7.7 to 7.9). 

Refined glycerol of a CP or USP grade is shipped mainly in bulk in tank cars or tank wagons. These are usually stainless steel-, aluminum-, or lacquer-lined. However, pure glycerol has litde corrosive tendency, and may be shipped in standard, unlined steel tank cars, provided they are kept clean and in a rust-free condition. Some producers offer refined glycerol in 4.5-kg (3.8-L or 1-gal) tinned cans and more commonly in 250—259-kg (208-L or 55-gal) drums of a nonretumable type (ICC-17E). These generally have a phenolic resin lining. 

Most of the fatty acids in fats are esterified with glycerol to form glycerides. However, in some fats, particularly where abuse of the raw material has occurred leading to enzymatic activity, considerable (>5%) free fatty acid (FFA) is found. Hydrolysis occurs in the presence of moisture. This reaction is catalyzed by some enzymes, acids, bases, and heat. Most producers of fats attempt to prevent the formation of free fatty acid because certain penalties are assessed if they are present in the trading of crude and refined fats. 

After pH adjustment the crude glycerol is submitted to methanol recovery by vacuum distillation. The bottom product is usually a glycerol-water solution of about 50%. Its concentration can be increased up to 85% by vacuum evaporation. The water is recycled to the washing step. Normally, the glycerol is shipped to a specialized refiner, where the purity can be increased further to 99.5 and 99.7% by ion-exchange techniques and vacuum distillation. 

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