Abstract
The effect of chemical speciation (H2O/NH4Ac/HCl-soluble and insoluble) of alkali and alkaline earth metallic species on the steam gasification of sawdust biochar was investigated in a lab-scale, fixed-bed reactor, with the method of chemical fractionation analysis. The changes in biochar structures and the evolution of biochar reactivity are discussed, with a focus on the contributions of the chemical speciation of alkali and alkaline earth metallic species (AAEMs) on the steam gasification of biochar. The results indicate that H2O/NH4Ac/HCl-soluble AAEMs have a significant effect on biochar gasification rates. The release of K occurs mainly in the form of inorganic salts and hydrated ions, while that of Ca occurs mainly as organic ones. The sp3-rich or sp2-sp3 structures and different chemical-speciation AAEMs function together as the preferred active sites during steam gasification. H2O/HCl-soluble AAEMs could promote the transformation of biochar surface functional groups, from ether/alkene C-O-C to carboxylate COO− in biochar, while they may both be improved by NH4Ac-soluble AAEMs. H2O-soluble AAEMs play a crucial catalytic role in biochar reactivity. The effect of NH4Ac-soluble AAEMs is mainly concentrated in the high-conversion stage (biochar conversion >30%), while that of HCl-soluble AAEMs is reflected in the whole activity-testing stage.
Highlights
Compared to fossil fuels, biomass—which is a carbon neutral renewable energy, since the CO2 from its utilization can be captured via photosynthesis—exhibits great prospects for limiting global gas pollution (NOx, SO2 and greenhouse gases) and the energy crisis [1]
The objectives are to understand the steam gasification behavior of pyrolysis biochar with different speciations of alkaline earth metallic species (AAEMs), the key inherent chemical speciation of AAEMs affecting biochar reactivity, and the most probable catalytic route of AAEMs on biochar structure and reactivity during steam gasification, all of which are essential to gasification process design and development
In order to investigate the effects of the solid-phase chemical speciation of AAEMs on the steam gasification of sawdust biochar, the chemical fractionation analysis (CFA) process was carried out
Summary
Biomass—which is a carbon neutral renewable energy, since the CO2 from its utilization can be captured via photosynthesis—exhibits great prospects for limiting global gas pollution (NOx , SO2 and greenhouse gases) and the energy crisis [1]. Many researchers [13,14,15,16,17,18] found that alkali and alkaline earth metallic species (AAEMs) dispersed in biomass and/or biochar as different chemical speciations, play significant catalytic roles in biochar gasification reactivity, and that AAEMs volatilized as a gaseous phase would take part in homogeneous reforming reactions [19]. For coals and had been modified by Zevenhoven-Onderwater et al [38] and Petterson et al [39] for biomass fuels Besides their direct catalytic effects on biochar gasification, the AAEMs could have a dynamic impact on the biochar structures, including the carbon skeleton, side chains and functional groups [21,22,40]. The objectives are to understand the steam gasification behavior of pyrolysis biochar with different speciations of AAEMs, the key inherent chemical speciation of AAEMs affecting biochar reactivity, and the most probable catalytic route of AAEMs on biochar structure and reactivity during steam gasification, all of which are essential to gasification process design and development
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