Absorbent screening using a hollow fiber membrane contactor for removing volatile methyl siloxanes from biogas

Abstract

This paper studied volatile methyl siloxane (VMS) separation from biogas using a hollow fiber membrane contactor (HFMC). The effects of operating parameters such as temperature, gas velocity, and absorbent velocity of HFMC on typical VMS (hexamethyldisiloxane: L2, octamethylcyclotetrasiloxane: D4, and decamethylcyclopentasiloxane: D5) separation were investigated, and the absorption efficiencies of three absorbents (tetradecane, propylene carbonate: PC, and selexol) were evaluated. The results of the study showed that the VMS absorption efficiency of the three solvents decreased with increasing absorbent temperature from 15 °C to 35 °C. At 15 °C, the VMS removal rates of tetradecane, PC, and selexol ranged from 95.8% to 99.9%, 85.5%–92.6%, and 73.1%–92.8%, respectively. Increasing the gas velocity reduced the removal efficiency of VMS, especially L2. When the gas velocity increased from 300 to 1100 mL/min, the L2 removal rates of selexol, PC, and tetradecane decreased by 19.9%, 28.4%, and 1.9%, respectively. Increasing the absorbent velocity facilitated VMS removal. When the absorbent velocity went up to 250 mL/min, the L2 removal efficiencies of tetradecane, selexol, and PC increased to 99.8%, 74.0%, and 77.2%, respectively. Meanwhile, the D4 and D5 removal rates of the three absorbents exceeded 88%. Additionally, absorbent recycling is important to reduce contamination and use costs. Tetradecane performed excellently with more than 82% VMS removal when the loading of L2, D4, and D5 were 5.4, 21.4, and 21.4 mg/mL, respectively. The VMS content of the three absorbents was almost zero at 100 min of regeneration at 120 °C.