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Urea extraction crystallization
The urea extraction crystallization is a process for separating linear paraffins (n-paraffins, n-alkanes) from hydrocarbon mixtures through the formation of urea-n-paraffin-clathrates. The process is primarily used to lower the pour point of petroleum products, by-products of the process are n-paraffins in high purity. The method may also applied for the separation of fatty acids and fatty alcohols. In addition to urea also thiourea is used in the process.
== Raw materials ==
In addition to the n-alkanes are also unbranched fatty acids with more than four carbon atoms, their esters and unbranched fatty alcohols can migrate into the channels of the crystallized urea and form a clathrate. The initial discovery of the method was based on a study of the fats in milk.〔M. F. Bengen: ''Mein Weg zu den neuen Harnstoff-Einschluß-Verbindungen.'' In: ''Angewandte Chemie.'' 63, 1951, p. 207, .〕 A deviation from the linear molecular geometry, for example, by C=C-double bonds in the molecule, leads to a less stable inclusion compound. Thus stearic acid (C18: 0) forms more stable urea adducts compared to oleic acid (C18: 1 cis -9) or linoleic acid (C18: 2 cis -9, cis -12). A branching in the fatty acid molecule or an autoxidation result in a large deviation from the straight-chain molecular structure, so that these compounds do not form urea adducts. This is used as part of the fatty acid analysis and for the separation or enrichment of specific fatty acids.〔Hans-Dieter Belitz, Walter Grosch: ''Lehrbuch der Lebensmittelchemie'', Springer, 1992, ISBN 3-540-55449-1, p. 151-155〕
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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