Catalytic Steam Reforming Of Biomass Tar With Char-based Catalysts

Aromatic macromolecular compounds are inevitablely during biomass gasification process. These substances will not only influence the quality of gas product, but also condense into tar in the downstream stage of the gasification device and cause downstream equipments corrosion, affecting the normal work of the device. So removing tar is a crucial problem that must be solved for the biomass gasification technology. Catalytic cracking is considered to be the most efficient way to reduce tar content.Biomass char is the by-product during the process of biomass gasification and pyrolysis. The biomass char has many advantages as tar removing catalyst:biomass char is the remaining solid product during biomass pyrolysis in an inert atmosphere, wide range of sources and inexpensive; During tar catalytic cracking reaction, char gasification can release more gases and control gas product. Therefore, char has a broad prospect as a tar removing catalyst.The process conditions of catalytic steam reforming of biomass tar over coconut shell char (CN-char) was studied in a fixed-bed reactor. Under the optimum condition, the catalytic effect of activated coconut shell char(ACN-char) and activated peach shell char(AWN-char) for steam reforming of tar was investigated, and iron-based catalyst supported on ACN-char was further investigated. The main organic condensates after reaction were also analyzed by GC-MS.The experimental results indicated that the CN-char truly has the catalytic effect for tar steam reforming. The carbon conversion of58.3%and the gas yield of19.7ml/min were reached at the conditions of reaction temperature of800℃, LHSV of0.5h-1and S/C of1.5. The phenomena that the gas carbon conversion was over100%and the CN-char quality decreased show that during the reaction, the CN-char and the coke steam gasification rate is higher than carbon deposition rate, which indicated that CN-char as catalyst has the advantage of resistance to carbon deposition. Compared with CN-char, the catalytic effect of ACN-char and AWN-char is obviously enhanced. After deashing,the catalytic effect of ACN-char was worse than the CN-char, revealing that the mineral in the ACN-char has a better catalytic effect than the pore structure of ACN-char. The catalytic effect of deashing AWN-char is still higher than the ACN-char, indicting that the kinds of char has the largest effect for tar catalytic cracking. The catalytic activity and stability was enhanced after iron impregnated on ACN-char, and the best catalytic performance was abained when iron content reaches10%. The GC-MS analyse results showed that the main organic component in tar was phenol, after reaction, the liquid mainly contained naphthalene, oxygen fluorene, anthracene, pyrene and1-phenyldibenzothiophene under the CN-char effect. While after reforming reaction with the10%Fe/ACN-char, the naphthalene and dibenzofuran further cracking, the relative content of macromolecular aromatic ring compounds increased, such as1-phenyldibenzothiophene, pyrene.