Patent GB-527030-A (GB)
Title: A process for the extraction of mixtures of isomeric organic compounds
IPC: C07C51/48
Filed: 1939-03-28
Abstract: 527,030. Separating mixtures of isomers. FIFE, J. G. (Naamlooze Vennootschap de Bataafsche Petroleum Maatschappij). March 28, 1939, No. 9711. Drawings to Provisional Specification. [Class 2 (iii)] Mixtures of isomeric organic compounds whose isomerism is due to a difference in the position of the polar groups present are separated by extraction with two solvents, preferably moving in countercurrent, which have such a difference in polarity that two liquid phases are formed. The extraction apparatus may comprise alternate mixing and settling zones or centrifugal separators, the solvents being introduced at spaced points and the mixture of isomers preferably introduced at an intermediate point. The temperature in the extraction zone may be regulated, by means of heat-exchange coils, to give either a uniform temperature or a temperature gradient. When the dissolving capacity of one solvent is much greater than that of the other, it may be necessary to reduce the solvent power of one solvent or increase that of the other by using a mixture of solvents in place of one or both of the solvents, the mixture being chosen according to various considerations discussed in the Specification. If the mixture contains more than two isomers, it is possible to separate a single isomer from a combination of isomers, according to the conditions employed. When the initial mixture contains the isomers to be separated and a third component which is a solvent for at least one of the isomers, the third component may serve as one of the solvents and it is necessary to add only one solvent for the extraction. As mixtures of isomers are specified o- and p-chlornitrobenzene, o- and p-nitrophenol, o- and p-vanillin, o- and p-hydroxybenzaldehyde, o- and p-xylene, o- and p-cetylbenzenesulphonic acid, and primary and secondary butyl alcohol; also mixtures of methylpropylketone and diethylketone, methylsuccinic acid and glutaric acid, and of resorcinol, pyrocatechol and hydroquinone. Examples of polar solvents that may be used are water, methanol, ethanol, benzyl alcohol, furfural, nitrobenzene, propionitrile, phenol, cresol, aniline, the lower fatty acids, e.g. acetic acid and the lower ketones, e.g. methylethylketone. Non-polar or less polar solvents mentioned are pentane, gasoline, benzene, kerosene, gas oil, lubricating oil, ether, trichlorethylene and carbon tetrachloride. The examples describe the isolation of p-vanillin from a crude vanillin mixture, and the separation of o- and p-nitrophenol, o- and p-dihydroxybenzene, o- and p-hydroxybenzaldehyde, o- and p-methoxyphenol, o- and p-ethoxyaniline, and of propane -1:1- and -1 : 3-dicarboxylic acid. In a typical example, a mixture of equal parts of o- and p-nitrophenol are introduced into the middle of an extraction system of 7 stages, each consisting of a mixing and settling space. At stage 1 is introduced 50 per cent. aqueous ethanol and at stage 7 a mixture of equal parts by volume of gasoline and benzene. From the alcohol phase leaving at stage 7 p-nitrophenol is obtained by distillation, whilst the gasoline phase withdrawn at stage 1 yields o-nitrophenol. Specifications 355,294, 417,617, [Group III], and 452,427 are referred to.