Recycling of Coal Seam Gas Associated Water by Vacuum Membrane Distillation

Abstract

Coal seam gas associated water (CSGAW) which is a main by-product of CSG production typically contains significant amounts of salts. The chemical composition of CSGAW is complex and may also contaminated with drilling chemicals contain heavy metals, carcinogens such as benzene, toluene, ethylbenzene and xylene, and radioactive elements like uranium. CSGAW has potential environmental issues; therefor it is unsuitable for further uses without proper treatment. The release of CSGAW to the land and rivers without proper treatment may drown vegetation, and endanger the aquatic life and environment. In this study, we aimed to evaluate the applicability of the VMD process for CSGAW treatment and to optimize the operating conditions such as feed flow rate, temperature gradient, and vacuum pressure in a bench-scale VMD process. Also, we studied characteristics of membrane foulants in the VMD process. In the first section of this study, the possible application of the VMD process for CSGAW treatment was examined with a commercial hydrophobic polytetrafluoroethylene (PTFE) membrane. Under the optimum conditions (i.e., Tf = 80 °C, Vf = 240 mL/min, Pv = 3 kPa), water permeability was found to be 5.5 L/m2/h (LMH) after 2 hours VMD operation. The VMD process showed excellent salt rejection efficiency (>99%) in all experiments. However, severe membrane fouling was observed after 8 hours. In the second section, method for fabrication of novel membrane (FTCS / PDMS) suitable for VMD process was introduced to recycle the CSGAW. The super-hydrophobic FTCS/PDMS membrane showed enhance performance in permeate flux (12.3 LMH) and removal of the salts and organic matter from CSGAW in compared to commercial PTFE membrane under the same operation condition. The results of this study demonstrated that the VMD technique can be potentially applied for CSGAW treatment containing organic matter using super-hydrophobic FTCS/PDMS membrane.