(469a) Landfill Gas Clean-up Using a Flow-Through Catalytic Membrane Reactor

Nair, N. N., University of Southern California
Motamedhhashemi, M., University of Southern California
Egolfopoulos, F., University of Southern California
Tsotsis, T. T., University of Southern California

Landfill gas (LFG) is potentially a valuable renewable fuel because of the methane that it contains. But the presence of impurities in landfill gas presents challenges for its effective utilization. Burning the gas for power generation or even when flaring it, if these impurities are not removed, releases gases such as hydrogen chloride, sulfur dioxide, etc., which are toxic and harmful to both humans and the environment. Therefore, there is a strong incentive to develop effective technologies for removing the toxic compounds from landfill gas prior to its utilization as a fuel. 

In this project a novel catalytic oxidation technology appropriate for landfill gas clean-up based on the concept of a “Flow-through Membrane Reactor” impregnated with an oxidizing nanocatalyst has been studied. For our experiments we have studied a model LFG stream with a VOC composition which was shown previously by our group to simulate well the behavior of real LFG in field-scale investigations. The effects of feed-stream composition, reactor temperature, and catalyst loading were studied.

Multilayer tubular alumina membranes were used in the research and were rendered catalytic by wet impregnation. Their properties were characterized using gas permeation, surface area measurements (BET), and SEM/EDAX analysis. The pore-structure characteristics of these membranes are important in determining the transport mechanism that prevails through the active layer. For membranes with small enough pores, Knudsen flow prevails, leading to an increase in the number of collisions between the reactants and the catalytic sites inside the pores.

When comparing the behavior of the FTCMR with the more conventional reactors the “yardstick” of success is the ability of the FTCMR to operate under lower temperature for a given level of conversion, and/or attain higher conversion under the same conditions and catalyst loading. For the LFG application, light-off temperature experiments showed promising results when compared to the monolith reactor. Also, no catalyst deactivation was observed during the time-on-stream experiments, proving that the FTCMR is robust towards corrosive by-products (e.g., HCl) produced during the oxidation reactions.

A mathematical model was also developed based on the Dusty Gas formulation of gas transport through the porous membrane being utilized in the FTCMR.  The model was used for identifying the advantages of the FTCMR concept compared to the wall-coated catalytic monolith, and also for investigating some of the limitations, which may exist in applying this concept for the aforementioned LFG clean-up application.