Experimental Study On Tar Cracking Catalyst Preparation And Performance

Carbon deposition is harmful which will cause catalyst deactivation during tar catalytic technology, that how to eliminate carbon deposition is the key to solve the problem of tar. Based on the predecessors’researches, the further research about tar catalytic cracking with different catalysts and reaction atmospheres includes the following parts:(1) In small catalyst evaluation device, the influences of partial oxygen atmosphere, residence time on tar cracking over CaO are studied under 800℃. The conversion of tar cracking and carbon deposition in different conditions are discussed. The result show that with the gas phase residence time increasing in partial oxygen, the conversion of tar reduces, carbon deposition increases, and syngas volume percentage inreases. Comprehensive consideration about tar conversion and carbon deposition, the better experimental condition is that the residence time is 0.57s under 800℃. When the the residence time is 0.57s, the tar conversion is 79.2%, the carbon deposit is 33%, the volume percentage of syngas is 36% in partial oxygen catalytic cracking. While the tar conversion is 81%, the carbon deposit is 35%, the volume percentage of syngas is 36% in tar thermal catalytic cracking, this suggest that partial oxygen could be able to reduce carbon deposit.(2) 4%Ni/ZrO2-CeO2-Al2O3 catalyst was prepared by precipitation-loading (Ni-load) method and sol-gel (Ni-gel) method respectively, the activity, stability of catalysts and carbon removal are confirmed by using a model of toluene catalytic cracking reaction. The results concerned the effect of preparation methods and partial oxygen on catalyst activity and sability. Taking into account the activity of various catalysts in toluene cracking, optimized catalyst was prepared by precipitation-loading method. In the toluene cracking reaction over Ni-load catalyst, toluene thermal catalytic cracking conversion is 81.9% while that is 45.3% over Ni-gel catalyst. What is more, partial oxygen could reduce the carbon deposition. In the case of Ni-load catalyst, the 15.6% carbon deposition in N2 decreased to 9.3% in air. In addition, despite the reduction of NiO particles to the metal Ni, the specific surface of Ni-load catalyst increased to 22.44m2/g in air, which was attributed to activity and stability of catalyst for a long time.(3) In order to improve tar conversion,15%Ni/ZrO2-CeO2-Al2O3 catalyst was prepared by precipitation-loading method and sol-gel method respectively. The efficiency of catalysts and carbon removal are confirmed by using a model of toluene and actual tar catalytic cracking reactions in partial oxygen under 800℃ respectively. In order to eliminate carbon deposit, water vapor is added in the experiment, tulene steam partial oxygen reforming reaction for cabon deposition reduction is studied. The results show that the activity of 15% Ni-gel catalyst is better,the conversion of toluene reaches 99%, H2 volume percent reaches 45%. Then the actual tar conversion reaches 100%with syngas volume reaches 70%, the carbon deposit is more than that over Ni-load catalyst. What is more, carbon deposit can be redued in partial oxygen, with the O2 content increasing, H2 volume percent is dreasing and the CO volume percent is increasing. 20%(vol) O2 in Nitrogen,which is equivalent to the proportion in air, is the better propotion for tar catalytic cracking and carbon deposit elimination.