Separation of 1,3,5-trimethylbenzene and 1,2,4-trimethylbenzene by metal-organic framework Co(aip)(bpy)0.5

Abstract

BackgroundThe separation of trimethylbenzene isomers is one of the most challenging problems in chemical industry because of their similar boiling points and kinetic diameters. The adsorption performance of 1,3,5-trimethylbenzene (1,3,5-TMS) and 1,2,4-trimethylbenzene (1,2,4-TMS) (1,3,5-TMS/1,2,4-TMS = 1:1) on Co(aip)(bpy)0.5 with cobalt-based columnar lamellae were investigated in this paper. MethodsIn this study, we used competitive adsorption experiments, kinetic and thermodynamic experiments, and regeneration experiments to investigate the adsorption amount and relative selectivity of 1,3,5-TMS and 1,2,4-TMS on Co(aip)(bpy)0.5, adsorption mechanism, and regeneration properties of Co(aip)(bpy)0.5. Significant findingsCompetitive adsorption experiments showed that Co(aip)(bpy)0.5 presented the highest relative selectivity α1,2,4-TMS/1,3,5-TMS among the eight MOFs studied. Both pseudo-first-order (PFO) and pseudo-second-order (PSO) kinetic models were used to fit the data, which indicated that the PSO model was more compatible. Thermodynamic data was fitted by Langmuir, Freundlich, and Temkin models, from which the Langmuir model was most suitable. Thermodynamic parameters demonstrated that the adsorption was spontaneous and exothermic. The α1,2,4-TMS/1,3,5-TMS could reach 3.5 at 298.15 K. The crystal structure and adsorption experiments suggested that the separation of 1,3,5-TMS from 1,2,4-TMS on Co(aip)(bpy)0.5 was mainly due to π-π interaction, unsaturated metal ions, and Lewis acid-base interaction. After five adsorption-regeneration cycles, the adsorption amount of 1,3,5-TMS and 1,2,4-TMS decreased by 0.12 % and 0.05 %, respectively, and α1,2,4-TMS/1,3,5-TMS remained above 3.0.