Preparative Scale Separation of Organic Mixtures by Semi-Continuous Gas-Liquid Chromatography

Abstract

A review is given of general chromatographic theory, the use of G.L.C. (gas-liquid chromatography) for the prediction of thermodynamic data, and the scale-up of the chromatographic process for preparative and production level separations. The application of G.L.C. for the separation of fatty acids is also reviewed and its industrial importance is discussed. The design and construction of a sequential continuous chromatographic refiner (SCCR-2) for high temperature (up to 200°C) preparative-scale G.L.C. separations is described. In this equipment, the counter-current movement between the gas and liquid phase is simulated by sequencing a system of inlet and outlet port functions around twelve fixed, 2.21 cm diameter and 61 cm long, columns. The separating capabilities and other operating characteristics of the SCCR-2 unit have been investigated using mixtures of different separation difficulty and volatility. The feed mixtures selected had separation factors in the range of 1.1-5.8 and required equipment operation in the range of 55-200°C, while using F.F.A.P. (free fatty acid phase) on Chromosorb W or OV-275 (a cyanosilicone) on Chromosorb P, as chromatographic packing material. Initially, the separation of the equivolume halocarbon mixture of “Arklone" P/"Genklene" P was attempted and purities greater than 99.8% have been achieved for both products, at feed rates of 21 cm3h-1 and operating at about 60°C. In addition, the more difficult separation of a 50/50 V/V mixture of methyl chloroacetate/ethyl lactate (SF 1.5) was studied and the ability of the SCCR-2 unit to separate the mixture into two products with purities in excess of 99.8% has been demonstrated at feed rates up to 80 cm3h-1 and operating temperature within the range of 110-130°C. With lower separation factor systems (SF 1.2) such as "fungal oil," the equipment was found to have inadequate column length for successful separations. A knowledge of the vapour-liquid equilibrium data for the systems used was necessary for the determination of the operating characteristics of the SCCR-2 equipment. Therefore, part of the present work was initiated with the aim of providing vapour-liquid equilibrium data