Experimental Study On Catalytic Cracking Of Biomass Tar Using A Model Compound

Biomass gasification technology is one of the most effective methods in the process of bioenergy utilization. However, tar which comes from the process of biomass gasification is greatly harmful to the whole biomass gasification system. It can easy condense into liquid in low temperature (<200℃) and combined with water, carbon and fly ash in pipes or equipments, leading to choking and corrosion. Tar also result in a decrease of total efficiency and an increase in the cost of the process. Tar elimination from the gasification product is necessary before additional usage in any application. How to efficiently, environmental friendly remove the tar have attached great importance to the world. On the basis of our predecessors' researches, this article did an experimental study on the bench scale catalyst evaluated device (WFS-3015), taking toluene as a model compound, researching its thermal and catalytic cracking.This research mainly includes the following aspects:(1) On the bench scale catalyst evaluated device, study how the reaction temperature affect to the cracking efficiency, deposit carbon efficiency and generated gas efficiency of toluene, and analysis the main compositions of products of toluene after being thermal cracked.(2) On the basis of thermal cracking of toluene, the author observed the effect of calcination time and temperature, reaction temperature, S/C mass ratio to the cracking efficiency, deposit carbon efficiency and generated gas efficiency of toluene after being catalytic cracking.(3) In the same reaction conditions, different catalysts were evaluated to the catalytic pyrolysis of toluene.Experimental results show that:A mixture of gases containing mainly pahs, carbon and combustible gas was obtained as the product of toluene being thermal cracked and polycondensation in high temperatures. In thermal cracking condition, the conversion of toluene was 64.53% at 800℃and 79.19% at 900℃. Meanwhile, the cracking efficiency of toluene was rising with the reaction temperature increasing. This was mainly due to that thermal cracking of toluene was heat-sink reaction, and temperature increasing was helpful of reaction.However, the calcination time and temperature of catalyst has greatly influence on the catalytic activity in the catalytic cracking of toluene experiment. The higher the calcination temperature, the longer the calcination time, the catalyst specific surface area decreased, and catalytic activity reduced. The different calcination temperature and time of NiO/Al2O3 catalyst were evaluated to toluene removal in a fixed-bed reactor of bench-scale catalyst evaluated device. The NiO/Al2O3-650℃catalyst which was calcinated for 6 h was found to be the most effective catalysts. It not only improved the cracking efficiency of toluene, reduced the carbon and generated more combustible gases.In the same reaction conditions, comparison of pyrolysis performance of different catalysts which were used in the catalytic pyrolysis reaction of toluene, the catalytic effect of them arranged for:Co>Co/La2O3>NiO/CeO2/Al2O3-a>NiO/Al2O3> NiO/CeO2/Al2O3-c>Ni>NiO/CeO2/Al2O3-b>Ni/La2O3>Al2O3. However, the conversion of toluene was 95% at 800℃with Co, Co/La2O3 and NiO/CeO2/Al2O3 catalysts.