Abstract:

Objective: Here,we reported one-pot catalytic conversion of bamboo to liquid fuels,and investigated the effect of reaction factors on the liquefaction products of biomass catalyzed by Cu and Ni-doped porous metal oxides(PMO)in supercritical methanol,revealing the role of active components in liquefaction of bamboo. Method: Cu-Ni-doped PMO catalysts were prepared through coprecipitation using hydrotalcite-like as precursors. The catalysts were characterized by XRD,BET and SEM. The liquefaction of bamboo was accomplished using a one-pot method in supercritical methanol,and the liquefied products were analyzed by GC-MS. Effects of Cu/Ni ratio,catalyst dosage,reaction temperature and time on the composition and distribution of bamboo liquefaction products were investigated by single factor analysis. Result: XRD results suggested that the Cu and Ni doped Mg-Al hydrotalcite crystallized well,showing seven unique diffraction peaks of hydrotalcite and no diffraction peaks of CuO and NiO. The higher doping concentration of Cu and Ni,the smaller specific surface area of PMO. SEM analysis showed that the hydrotalcite-like precursor had a typical layered structure,while the layered structure disappeared and the oxide particles were agglomerated after calcination. The yield of ketones was increased gradually with the increase of Cu/Ni ratio. The yields of alcohols and hydrocarbons were the highest with a Cu/Ni ratio of 1:1,while the phenols and esters were the least. The yields of ketones,alcohols and hydrocarbons were gradually increased along with the catalyst dosage increased. In particular,the rising trend was evident when 20% of catalysts were used. When the reaction temperature was higher than the supercritical temperature of methanol,the products with relatively low oxygen content,such as ketones,alcohols and hydrocarbons,showed a sharp rise. However,esters and other products(mainly including ethers,acids,furans,etc.)were decreased significantly. Conclusion: CuO and NiO are highly dispersed in the complex oxides,and the doped PMO has a smaller specific surface area. The supercritical temperature of methanol is a key factor that affects the composition and distribution of liquefaction products. Hydrogenation of the unsaturated functional groups were occurred by in-situ produced H₂ from methanol cracking along with the liquefaction of bamboo,resulting in alcohols,ketones and hydrocarbon products with relatively lower oxygen content. The addition of Ni can improve the dispersibility of Cu species in the active component of the catalyst,making the structure of the catalyst better as well as the stability of the catalyst; thereby the catalytic activity of the catalysts for depolymerization of biomass was increased. Our observations clearly indicated that the acidity and alkalinity of PMO can be changed with the addition of Ni,and the catalytic activity of PMO was adjusted as well,promoting the directional distribution of the products.

Key words: liquefaction, liquid fuel, metal oxides, supercritical methanol, hydrogenation