Novel Membrane Process to Utilize Dilute Methane Streams

Methane is the second largest contributor to global warming after carbon dioxide. Various technologies and process improvements have been developed to curb methane emissions in the United States. There is still a lack of economically viable technology, however, to utilize dilute methane streams containing 10-40% methane, in which the other component is primarily carbon dioxide. The streams are often vented, contributing to the climate change effects associated with greenhouse gases. Membrane Technology and Research estimates that the methane emissions from these streams could be up to 1.0 Tg (million metric tons) per year with a fuel value of $200-300 million, assuming $4-6/1,000 scf natural gas. A key objective of this project is to develop a simple and low cost membrane process to convert dilute methane waste gas streams into useful fuel, thus reducing methane emissions. In Phase I, high-flux Polaris™ membranes with high carbon dioxide permeance and adequate carbon dioxide/methane and carbon dioxide/nitrogen selectivity were reproducibly produced using MTR’s commercial scale coating machines. A bench-scale countercurrent spiral-wound module containing 0.7 m2 membrane area was prepared successfully. Parametric tests were conducted on membrane stamps and the test module. An analysis of costs to upgrade dilute methane to fuel use using a membrane system was conducted. The payback time for the process is about 8-16 months. The economics improve for dilute methane streams containing more than 20% methane. The process is even more attractive if a credit for reduced greenhouse gas emissions is considered. The key to bringing this technology closer to commercialization is to demonstrate the membrane process under real operating conditions in the field. In Phase II, a pilot-scale membrane unit will be built and operated at a landfill gas plant. The unit will be run for 3 months to prove the technical and economic viability of the process. If successfully developed, the proposed membrane systems provide an economically viable way to use dilute methane waste gas streams, thus curbing methane emissions.