Patent GB-671456-A (GB)
Title: Extractive crystallisation process
IPC: C07C7/152
Filed: 1948-01-07
Abstract: Urea complexes of straight-chain organic compounds are formed by treating a mixture of organic compounds with an aqueous alcoholic solution of urea, the water-to-alcohol ratio of the solution being from 3 : 1-20 : 1 by volume.  The process effects the separation of straight-chain organic compounds from other compounds which may also be of normal structure, but which do not form complexes under the working conditions of the process, and from branched-chain compounds such as isoparaffins, naphthenes and aromatic compounds.  The alcohol used is a water-miscible monohydric alcohol or a polyhydric alcohol containing 2 or 3 carbon atoms which does not form complexes with urea under the working conditions of the process.  Normal structure organic compounds which form the complexes are hydrocarbons, such as paraffins, olefins and acetylenes, alcohols containing 6 or more carbon atoms, ketones, esters, amines, sulphides, disulphides, mercaptans, acids, halogenated compounds, ethers and nitro compounds. Particular examples of these compounds are given. Non-aqueous, non-alcoholic diluents or solvents may be added to the reaction mixture.  Complexes containing varying proportions of urea may be formed by varying the conditions of reaction.  The complex formation may take place in a series of stages and varying temperatures may be employed to separate complexes crystallizing at different temperatures.  The complexes may be separated, for example by settling, decantation, filtration or centrifuging and may then be decomposed to regenerate the straight-chain organic compounds by methods such as heating, dry distillation, distillation with hot gases, steam distillation or heating with a solvent for urea or a solvent for the organic compound.  The urea or urea solution separated may be recycled to treat further organic compound mixtures while the straight-chain compounds may be fractionally distilled. The process may be particularly applied to the separation of hydrocarbon mixtures and may be used in separating the products of hydrocarbon conversion processes, such as isomerization, alkylation, cyclization, hydrogenation or dehydrogenation processes and also in treating terpenes.  The Specification as open to inspection under Sect. 91 refers also to the treatment of any alcohol, aldehydes, such as butyraldehyde, valeraldehyde, caproaldehyde, palmitic aldehyde, adipic aldehyde and citral, thioaldehydes; acetal, dioxane and paraldehyde; carbohydrates and silicones.  This subject-matter does not appear in the Specification as accepted.ALSO:Oils are refined by treating with an aqueous alcoholic solution of urea, the water-to-alcohol ratio of which is from 3 : 1 to 20 : 1 by volume. The process effects the separation of straight chain hydrocarbons by the formation of crystalline complexes with urea, from other compounds which may also be of normal structure but which do not form complexes under the working conditions of the process, and, from branched chain compounds such as isoparaffins, naphthenes and aromatic compounds.  The alcohol used is a water miscible monohydric alcohol or a polyhydric alcohol containing 2 or 3 carbon atoms which does not form complexes under the working conditions of the process. Non-aqueous, non-alcoholic diluents or solvents may be added to the reaction mixture. Complex formation may take place in a series of stages and varying temperatures may be employed to separate complexes crystallizing at different temperatures.  The complexes may be separated, for example by settling, decantation, filtration or centrifuging and may then be decomposed to regenerate the straight chain hydrocarbons by methods such as heating, dry distillation, distillation with hot gases, steam distillation or heating with a solvent for urea or a solvent for the hydrocarbon.  The urea or urea solution separated may be recycled to treat fresh oil while the straight chain hydrocarbons may be fractionally distilled. The process may be employed for the preparation of blending stocks for the improvement of low quality lubricants, fuels and waxes, for example in concentrating high cetane value fractions for diesel oil blending; for separating the products of hydrocarbon conversion processes, such as isomerization, alkylation, cyclization, hydrogenation or dehydrogenation; for extracting the low octane fractions from gasoline; dewaxing oils; and refining fats and fatty oils.