CO2 recycling by reaction with renewably-generated hydrogen

A laboratory-scale reactor system was built and operated to demonstrate the feasibility of catalytically reacting carbon dioxide (CO2) with renewably-generated hydrogen (H-2) to produce methane (CH4) according to the Sabatier reaction: CO2 + 4H(2) -> CH4 + 2H(2)O. A cylindrical reaction vessel packed with a commercial methanation catalyst (Haldor Topsoe PK-7R) was used. Renewable H-2 produced by electrolysis of water (from solar- and wind-generated electricity) was fed into the reactor along with a custom blend of 2% CO2 in N-2, meant to represent a synthetic exhaust mixture. Reaction conditions of temperature, flow rates, and gas mixing ratios were varied to determine optimum performance. The extent of reaction was monitored by real-time measurement of CO2 and CH4. Maximum conversion of CO2 occurred at 300-350 degrees C. Approximately 60% conversion of CO2 was realized at a space velocity of about 10,000 h(-1) with a molar ratio of H-2/CO2 of 4/1. Somewhat higher total CO2 conversion was possible by increasing the H-2/CO2 ratio, but the most efficient use of available H-2 occurs at a lower H-2/CO2 ratio. (C) 2009 Elsevier Ltd. All rights reserved.