Experimental Study On Microwave Reforming Of CH₄ With CO₂ Over Activated Carbon

Biomass utilization was an important way of renewable resource utilization, pyrolysis was one of the important approaches to realize resource utilization of biomass, biomass primary pyrolysis gas contained plenty of CH4 and CO2. Therefore the reforming of CH4 with CO2 was not only valuable for technology of conversion of synthesis gas from biomass itself, but also of strategic significance to reduce greenhouse gas emissions. However, the high cost of the metal catalyst used in the reaction frustrated the industrial application of this reaction.The catalyst based on carbon was cheap and widespread when compared to the metal catalysts. Moreover, the carbon produced in the reforming reaction can be used as the catalyst carrier. As a result, the carbon catalyst has received a great deal of attention.Microwave heating has the characteristics of immediacy, integrity, selectivity and efficiency, which has been widely used in industrial and medical field. The microwave-assisted reforming of CH4 with CO2 over activated carbon was brought forward in this paper, the experimental study and thermal equilibrium calculation were carried out.The reforming of CH4 with CO2 experiments were conducted on the integrated microwave-assisted heating system. Primarily, the temperature-rising behavior of different activated carbon was investigated, then the catalytic activity of two types activated carbon on reforming reaction was tested. The results above indicated that the temperature of two types activated carbon was rising within the beginning three minutes,then activated carbon temperature was stable,wood-derived activated carbon was more effective than coal-derived activated carbon.Then, the influences of operating parameters, such as microwave power, the CH4/CO2 ratio and volumetric hourly space velocity, on the reactant gas conversions were investigated. The enhanced conversions of CH4 and CO2, accompanied by a decreasing H2/CO ratio and migration amount on carbon element could be achieved through increasing microwave power, decreasing gas flow rate or reducing the CH4/CO2 ratio.The characteristic of CH4 decomposition,CH4/CO2 reforming and CO2 gasification reaction were compared. The results indicated that carbon deposited from the methane decomposition was the key factor on CH4 conversion,the CO2 could remove portion of carbon deposited from the methane decomposition.The activation of wood-derived activated carbon was tested. The results suggested that an encouraging catalytic activity of the activated carbon was obtained at the beginning, followed by a sharp loss of catalytic activity after 50min. After 90 min activity test,the conversion of CH4 and CO2 was decreased from 82.4% and 62.7% to 25.8% and 27.1% respectively. Several methods of characterization such as elemental analysis, specific surface area test and so on were introduced to investigate the deactivation problem of activated carbon. From these characterization above, conclusions would be achieved as following:deposited carbon produced during the reforming reaction and loss of oxygen functional groups were the main reasons for deactivations of the activated carbon.At last, thermal efficiencies on the reforming reaction were calculated and the heat distributions during reforming reaction were analyzed. The results revealed that the highest efficiency of reforming reaction on this experimental device was 5.81%, which was mainly caused by huge loss of heat transfer. The insulation plate which was transparent to microwave was proposed to prevent the heat loss, the heat loss was reduce by half and the thermal efficiency was increased nearly to 50% through adding insulation plate.