| A process for preparing CO with the CO2 as gasification agent and the rice husk as raw material was reported in this paper. Five kinds of catalysts (Fe2O3, CoO, NiO, CuO, and ZnO) supported on γ-Al2O3 were compared in the gasification, some different preparation methods of catalyst were also compared. The results showed that, ZnO/γ-Al2O3 prepared by coprecipitation with ethylamine exhibited the highest activity. The influences of reaction temperature, pressure system, catalyst loading, space velocity, rice husk particle size and gasification agent on the gasification were studied. At 800 ℃ and at atmospheric pressure, the optimal conditions were as follows:loading of ZnO 7.5%, space velocity 240 h-1 and particle size of rice husk 0.200-0.300 mm. Under such conditions, CO content was 22.1%, with a CO2 conversion of 22.4%, and rice husk conversion of 75.2%. H2 content and CO content could increase as adding water into gasification agent properly.CO2 gasification kinetics for rice husk was investigated. The reaction control conditions, eliminating both inner and outer diffusion effects, were examined. The relationship of carbon conversion versus reaction time for rice husk was measured from 762 ℃ to 837 ℃. The results showed that, increasing temperature or adding a catalyst could accelerate the carbon conversion and reaction rate.The shrinking core model (SCM) was used to correlate the relationship between conversion and time and to obtain the reaction rate constants at different temperatures. Then the reaction activation energy (Ea) and the pre-exponential factor (A) were predicted respectively using the Arrhenius equation. The activation energy values of gasification with ZnO/γ-Al2O3 and no catalyst were 104 kJ/mol and 125 kJ/mol, respectively, and the pre-exponential factor values were 4.51 ×103 min-1 and 2.58 ×104 min-1. This showed that ZnO/γ-Al2O3 could decrease the activation energy of gasification reaction, and the reaction temperature could decrease by 50 ℃. |
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