SBIR-STTR Award

Municipal landfills produce gas: several million standard cubic feet (SCF) per day from a modest landfill, and upwards to 5-10 million SCF/day from large landfills. Gas generation of this magnitude continues long after landfill closure, perhaps for 15 to 20 years. Landfill gas (LFG) is roughly an equal mix of methane (CH4) and carbon dioxide (CO2), which becomes contaminated with many volatile trace compounds as it migrates through the landfill. LFG collection systems are installed primarily to prevent off-site migration and control odors; reduction of greenhouse gas emissions is an indirect benefit. Most collected LFG is simply flared to convert CH4 to CO2, a non-explosive, non-toxic, less potent greenhouse gas. Economic and technical barriers discourage energy recovery from LFG. The cost of avoided power in many areas does not justify the conversion of LFG to electricity, while the technical difficulty of removing CO2 and trace contaminants coupled with lack of natural gas pipeline access usually causes problems in the conversion of LFG to CH4. Research is being conducted to further develop technology that converts raw LFG to a contaminant-free mixture of CH4 and CO2 to serve as reformer feedstock for methanol synthesis. No hazardous solvents or other separating agents are used; CO2, an environmentally benign "green" solvent condensed directly from LFG, is used as cold liquid absorbent to remove LFG contaminants to below ppm levels. Temperature and pressure are selected to produce a contaminant-free mixture with the desired CH4:CO2 ratio for methanol synthesis, about 2.3:1. Methanol, easily stored and transported from a landfill, enjoys an expanding readily available market, and therefore could make LFG utilization profitable for relatively small landfills. The phase I objective is to demonstrate production of contaminant-free methanol synthesis feedstock gas from landfill gas by contaminant absorption with cold liquid CO2. The amount of simulated LFG gas flowing to the liquid CO2 absorption column will be about 30,000 to 40,000 SCF/day, a scale sufficient to demonstrate both technical and commercial viability to municipal landfill owners and operators.Anticipated Results /Potential Commercial Applications as described by the awardee:Successful demonstration of LFG conversion to CH4 synthesis feedstock will provide landfills with an attractive alternative to electricity or pipeline gas. Cold liquid CO2 absorption of contaminants has wide applicability in gas processing beyond LFG treatment. Applications include acid gas removal from coal gasifier gas or from the partial oxidation of heavy hydrocarbons for the production of hydrogen or synthesis gas, acid gas removal from low quality natural gas, and Claus sulfur plant tail gas cleanup.

Landfill gas (LFG) is roughly an equal mixture of methane (CH4) and carbon dioxide (CO2) which becomes contaminated with many volatile trace compounds as it migrates through the landfill. LFG collection systems are installed primarily to prevent off-site migration and to control odors, an indirect benefit is the reduction of greenhouse gas emissions. Most collected LFG is simply flared to convert CH4 to CO,, a nonexplosive, nontoxic, less potent greenhouse gas. The purpose of this project is to demonstrate the recovery of raw LFG as a contaminant-free mixture of CH4 and CO2 to serve as reformer feedstock for methanol synthesis. No hazardous solvents or other separating agents will be used, and CO2, an environmentally benign "green" solvent condensed directly from LFG, will be used as a cold absorbent to remove LFG contaminants below parts per million levels. In Phase I, the ability of liquid CO2 to absorb LFG contaminants was confirmed. A pilot scale absorption column was used to measure the absorption of six contaminants: dichlorodifluoromethane (Freon-12), methyl chloride, acetone, pentane, ethanol, and ethylene dichloride. Gas phase contaminant concentrations were reduced by factors ranging from 100 to 5000, often to levels below the detection limit of the analytical equipment. These results show that Freon-12 and methyl chloride, the most volatile chlorinated compounds, and therefore the most difficult to remove from LFG, can be reduced to levels which will not poison methanol synthesis catalysts. Phase II will demonstrate the production of contaminant-free, methanol-synthesis feedstock gas from raw LFG by contaminant absorption with cold liquid CO2.Anticipated Results/Potential Commercial Applications as described by the awardee:Applications include acid gas removal from gases containing large amounts of CO2 such as from the partial oxidation of coal or heavy hydrocarbons, low quality natural gas, and Claus sulfur plant tail gas. Methanol from LFG provides a renewable liquid transportation fuel for use as a gasoline additive, as fuel, or converted to methyl tertiary butyl ether. Contaminant absorption with liquid CO2 has wide applicability in gas processing.