Study on Adsorption and Desorption Performance of Trace C4-C6 Alkanes Mixture on MIL-101(Cr) and WS-480

A deep purification treatment of trace volatile organic compounds (VOCs) in the tail gas emitted from the top of oil storage tanks was performed. Metal organic framework MIL-101(Cr) (hereinafter referred to as MIL-101) was used to remove trace C4-C6 alkane mixture in the tail gas. Compared with the commercial activated carbon, adsorption and desorption processes of trace C4-C6 alkane mixture as well as the adsorption thermodynamic property of n-hexane on MIL-101 were analyzed. Results demonstrate that the adsorption isosteric heat of n-hexane on MIL-101 is 48-52 kJ/mol, 9 kJ/mol lower than that on activated carbon. Trace C4-C6 alkanes on MIL-101 were desorbed by a nitrogen purge at 393 K, and the desorption efficiency of MIL-101 was up to 98.9%, which is 35% higher than that of activated carbon (similar to 64.3%). After 10 adsorption/desorption cycles, the desorption efficiency of MIL-101 exceeds 97%, indicating good cycle stability. The desorption process is affected by the spatial fit between the molecular configurations of alkanes and the three-dimensional tetrahedral cage of MIL-101 or by the one-dimensional slit pore of activated carbon. For alkanes with the same carbon, n-alkanes are preferentially desorbed on MIL-101, whereas isoalkanes are preferentially desorbed on activated carbon. Rich mesopores connected with the tetrahedral cages of MIL-101 are beneficial for desorption of trace C4-C6 alkanes. It provides basic data for the deep treatment of VOCs in the tail gas of oil storage tanks.