Refining glycerine

Figure 6. Flowsheet of Wurster Sanger glycerine refining plant. Courtesy of Crown Iron Works Co. (9).

The details of glycerine refining via the Crown Iron Works Co. process, which is representative of the continuous distillation process used by a large portion of suppliers for soap lye crude glycerine, are detailed here (Figure 6). 

Hydrolyzer (88%) and soap lye (80%) crude s are crude, unrefined grades of glycerine offered for sale to glycerine refiners. Hydrolyzer crude is concentrated Sweetwater from fat splitting, while soap lye crude comes from soap making and contains some salt. 

The three primary waste streams from a glycerine recovery plant are skimming and filter cake from the treatment plant, contaminants in the vacuum system condensing water, and residue (foots) from the glycerine refining plant. Filter cake discharge is typically sent to a solid landfill. The concentrated residue from a foots still, when allowed to cool, will typically solidify and must be disposed of as required by the local environmental authority. 

In addition to distilled glycerines, refined glycerines which liave only been bleached by bone-charcoal are also irscd in commerce.. For this purpose they are diluted to -TO per cent with water and passed througlr a filter battery. 

In the methyl ester route (Figure 1), refined triglycerides are reacted with methanol in the presence of a sodium methoxide catalyst to form the corresponding fatty acid methyl esters and glycerine (2). 

Recent estimates of the atmospheric loading rate of acrolein from sources in the United States were not located. Anderson (1983) estimated the total loading rate of acrolein in 1978 to be 91,450 pounds from facilities involved in its production and use as a chemical intermediate. Loading rates from various industrial sources were as follows acrylic acid manufacturers, 15,175 pounds refined acrolein and glycerin manufacturers, 55,660 pounds methionine manufacturers, 18,150 pounds and miscellaneous intermediate uses, 2420 pounds. These loading rates were based on a total production volume of 350 million pounds for acrolein in 1978, with 87% of this volume consumed in the production of acrylic acid and its derivatives. 

Ambrette Seed Oil occurs as a clear yellow to amber liquid with the strong, musky odor of ambrettolide. It is a volatile oil obtained by steam distillation from the partially dried and crushed seeds of the plant Abeltnoschus moschatus Moench, syn. Hibiscus abeltnoschus L. (Fam. Malvaceae). It is refined by solvent extraction to remove fatty acids or by precipitation of the fatty acid salts. It is soluble in most fixed oils and in mineral oil, often with cloudiness, but relatively insoluble in glycerin and in propylene glycol. 

Fats and oils can be saponified via the full-boiled process. The saponification process can be briefly described as follows. A refined blend of fats and oils is charged into a kettle and a predetermined amount of soap lye with sufficient concentrations of caustic soda, and salt is added. The mixture is boiled vigorously, using closed steam coils, until saponihcation is almost complete. The amount of caustic soda added is deliberately made less than the stoichiometric requirement, to ensure that the spent soap lye containing the glycerine has minimum alkalinity. The caustic soda in the spent soap lye is neutralized during subsequent treatment of the latter. 

The major use of rendered fats is in the production of tallow soaps and in the area of fat hydrolysis, sphtting triglycerides into fatty acids, and byproduct glycerine. As the soap-making industry grew and became more refined, the quality standards and specifications for animal fat became more precise to meet the soap industry s need. The specihcations and terminology, from the soap industry, form the basis for the quality standards and characteristics used today. 

Fat Settling and Saponification For sweetwaters that have been pretreated by settling alone, the concentrated crude glycerine will require an additional step before the refining step. In this step, any excess fat that has been forced out of the solution during evaporation requires decanting and saponification. 

Formation of nitrogen compounds from proteinaceous matter present in the crude glycerine (not removed in the treatment process) by thermal breakdown these, along with volatile decomposition products, form impurities in the refined glycerin therefore, it is important to limit the time the glycerol is at high temperature as well as the maximum temperamre it is exposed to. 

Stainless steel vessels or stainless-steel-lined vessels are recommended to prevent the formation of color complexes, especially if moisture or residual fatty acids are present in a carbon steel tank. Since glycerine is hygroscopic, care should be taken to exclude moisture from the refined glycerine storage tank. Glycerine subjected to heat should not be stored in vessels containing copper or tin, as copper or iron salts will catalyze oxidation of glycerine under those conditions (23). 

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