Influence of inorganic salts on the pyrolysis of wood.

摘要

In order to develop an economically viable process for the thermal utilization of biomass, use of a transition metal salt as a dual functional catalyst during a two-stage thermal utilization of biomass has been investigated. The added salt first catalyzes pyrolysis at a moderate temperature, e.g. 350{dollar}spcirc{dollar}C, to produce levoglucosenone and levoglucosan plus a high yield of char; then the transition metal species in the char catalyzes the subsequent gasification at a higher temperature, e.g. 800{dollar}spcirc{dollar}C, to yield CO and hydrocarbons for fuels.; More specifically, in the primary pyrolysis of wood, iron and copper sulfates show advantageous effects for promoting the yields of levoglucosenone and char. The highest yield (4.6%) of levoglucosenone for FeSO{dollar}sb4{dollar} is obtained at a level of 1.69% Fe, while the maximum yield (5.4%) of levoglucosenone for CuSO{dollar}sb4{dollar} is gained at a level of 1% Cu. FeSO{dollar}sb4{dollar} has also been applied to newsprint, and 17.2% of levoglucosan and 3.7% of levoglucosenone as well as other significant products have been obtained from the pyrolysis.; A mechanistic study of levoglucosenone formation indicates: (1) there are some interactions among cellulose, lignin, and the added salt, and the presence of lignin increases the levoglucosenone yield, (2) iron may weakly complex with lignin, and (3) sulfonate groups attached to lignin produce little levoglucosenone.; In the subsequent pyrolytic gasification, transition metal species, such as FeSO{dollar}sb4{dollar}, Fe{dollar}sb2{dollar}(SO{dollar}sb4)sb3,{dollar} and CUSO{dollar}sb4{dollar}, are the most efficient catalysts of those studied. For the iron sulfate-treated samples, 800{dollar}spcirc{dollar}C is the optimum temperature for pyrolytic gasification to produce high yields of CO and hydrocarbons. For the copper sulfate-treated samples, 950{dollar}spcirc{dollar}C is the best temperature for the production of CO and hydrocarbons. After tar has been removed during the 350{dollar}spcirc{dollar}C pyrolysis, the later gasification of the chars produces valuable, tar-free gases. We predict that gasification of the char in CO{dollar}sb2{dollar} and steam will produce significantly higher yields of CO and hydrogen than those in nitrogen.