[Liquid-solid adsorption separation and gas chromatography/mass spectrometry analysis of recycle alkanes in the production of alkyl benzenes].

A method for qualitative and quantitative analysis of recycle alkanes in the production of alkyl benzenes is proposed in this paper. The mixture was separated into saturated hydrocarbons (alkanes and cyclanes) and aromatics by means of adsorption chromatography with silica gel of 100 mesh-200 mesh as stationary phase and n-pentane and dichloromethane as eluents. Results were obtained by analysing these two fractions separately. A total of 21 different kinds of n-, iso-, cyclo and a few light aromatic hydrocarbons were identified in the saturated hydrocarbons which were 97.3% of the mixture, while the rest 2.4% aromatic hydrocarbons included 15 different kinds of indanes, naphthanes and diphenylanes, the majority of which were products of dehydrogenation and alkylation, and the minor part was from original alkanes. By-products can be truely revealed by the qualitative analysis, which can be used to improve the process conditions. Analysis showed that after adsorption separation by silica gel, the low-content aromatic hydrocarbons was concentrated, and thus the analysis accuracy and sensitivity were improved. Preseparation avoided the problems which would appear if the samples were directly analysed by gas chromatography or gas chromatography/mass spectrometry.