ABSTRACT
This study demonstrates the application of hollow-fiber membrane contactors (HFMCs) for the recovery of biogas from the ultrafiltration permeate of an anaerobic membrane bioreactor (AnMBR) and synthetic effluents of pure and mixed CH4 and CO2. The developed membrane degassing setup was coupled with a pilot-scale AnMBR fed with synthetic domestic effluent working at 25 °C. The membrane degassing unit was able to recover 93% of the total dissolved CH4 and 83% of the dissolved CO2 in the first two hours of permeate recirculation. The initial recovery rates were very high (0.21 mg CH4 L-1 min-1 and 8.43 mg CO2 L-1 min-1) and the membrane was able to achieve a degassing efficiency of 95.7% for CH4 and 76.2% for CO2, at a gas to liquid ratio of 1. A higher mass transfer coefficient of CH4 was found in all experimental and theoretical evaluations compared to CO2. This could also be confirmed from the higher transmembrane mass transport resistance to CO2 rather than CH4 found in this work. A strong dependency of the selective gas transport on the gas and liquid side hydrodynamics was observed. An increase in the liquid flow rate and gas flow rate favored CH4 transport and CO2 transport, respectively, over each component. The results confirmed the effectiveness of the collective AnMBR and membrane degassing setup for biogas recovery. Still, additional work is required to improve the membrane contactor's performance for biogas recovery during long-term operation.
ABSTRACT
Four ionic liquids (ILs) namely, 1-butylsulfonate-3-methylimidazolium P-toluene sulfonate ([BSmim][tos]), 1-butylsulfonate pyridine P-toluene sulfonate ([BSmpy][tos]), 1-butyl-3-methylimidazolium chloride ([Bmim][Cl]) and 1-butylpyridine chloride ([Bpy][Cl]) were synthesized for the effective separation of gases CO2/N2 and CO2/CH4 through supported ionic liquid membranes (SILMs). ILs were confirmed by NMR and FTIR spectroscopy, and their characteristics and physical properties were studied. The ILs were immobilized on the porous hydrophobic 200 µm thick polyvinylidene difluoride (PVDF) support. Pure and mixed gas separation performances of the prepared SILMs were analyzed in a custom-built gas permeation unit. The SILMs were stable up to 0.6 MPa at room temperature without leaching the ionic liquid. [BSmim][tos] was recorded to have the highest solubility coefficient and permeability for CO2, among other ILs. At 0.5 MPa, for pure CO2/N2 and CO2/CH4, IL [BSmim][tos] was observed with selectivities of 56.2 and 47.5, respectively. Based on the SILMs separation performance, the ILs synthesized for this work can be ranked as [BSmim][tos] > [BSmpy][tos] > [Bmim][Cl] > [Bpy][Cl]. Moreover, the exceptionally high selectivity values of [BSmim][tos] and [BSmpy][tos] confirms the potential use of ILs for CO2 separation through SILMs.