Combined continuous and preparative separation of close-boiling components in a gas-liquid chromatography

Abstract

By use of conventional gas-liquid chromatography, partition coefficient were obtained in terms of column temperature. The feed materials were chosen by close-boiling point as dichlormethane, diethylether, and dimethoxymethane. In a preparative chromatographic column(I.D. 1 cm), the three close-boiling components were separated with dinonylphthalate-coated Chromosorb A as a stationary liquid phase(SLP) and helium as an eluant. Effect of superficial velocity of eluant on axial dispersion coefficient was correlated by Fourier analysis of the response curve as: $$E\,=\,0.71\,D_M\,+\,r_p\,u_0^{1.54}$$ Intraparticle diffusion coefficient of each component was also determined. From sensitivity analysis, the diffusion in SLP was small and not a limiting process. As the superficial velocity of eluant and the column length were increased, the pressure drop was affected considerably on the variation of the velocity. Scaled-up chromatogaphic system was used to separate the two close-boiling components, namely diethylether and dichloromethane. The system was composed of 12 segmented columns and sixty solenoid valves controlled by a programmable controller. Effects of several flow paths on outlet concentration profiles were investigated to find optimum conditions. Compared to a conventional preparative chromatography, moving feed-injection and product-withdrawal enabled to separate the feed mixtures continuously in the partition and desorption sections. From the experimental results, the desirable method was that within a switching time, less-absorbed component was obtained purely in partition section, and in desorption section the remained components were separated by increase in column length. This new process was developed and used for separating the binary feed materials continuously by the gas-liquid chromatography. Advantage of the system was that several columns were added in the desorption section to separate the noneluted components, compared to other continuous chr...