Mechanism of In-Situ Catalytic Cracking of Biomass Tar over Biochar with Multiple Active Sites

Abstract

Biomass tar is the bottleneck in the development of efficient utilization of biomass syngas. The in-situ catalytic cracking biomass tar with multi-active biochar is investigated in a two-stage fluidized bed-fixed bed reactor. It indicates that adding H 2 O or CO 2 is found to improve the homogeneous and heterogeneous cracking of biomass tar. Activation of biochar by H 2 O or CO 2 impacted the morphology of biochar surface and distribution of metal species. H 2 O or CO 2 affects the creation and regeneration of pore structures, influencing the biochar structure and dynamical distribution of alkali and alkaline earth metal species (AAEMs), which ensure enough surface active sites to maintain the catalytic activity of biochar. The tar cracking into low-quality tar or small-molecule gas may be catalyzed by K, while the combination of tar with biochar would be promoted by Ca. The volatilizations of K and Ca, due to their reaction with volatiles, are to a large extent in accordance with their valences and boiling points. The subsequent transformation from the small aromatic ring systems to the larger ones occurs due to the volatile-biochar interaction. During tar cracking over biochar, K and Ca act as the active sites on biochar surface to promote the increase of active intermediates (C▬O bonds and C▬O▬K/Ca).

Catalytic Gasification and Reforming of Residual Biomass in a Bench Scale System with Low Cost Catalysts

“…show a reaction mechanism during biomass gasification using biochar. Over RP the acidity sites of Lewis (metals) and Brönsted (functional groups) combined with molecules (H 2 O, CO, CO 2 ) can form a large number of H/O/OH radicals, which play an important role in the tar cracking and gasification reaction [33,66,80–82] …”

“…Over RP the acidity sites of Lewis (metals) and Brönsted (functional groups) combined with molecules (H 2 O, CO, CO 2 ) can form a large number of H/O/OH radicals, which play an important role in the tar cracking and gasification reaction. [33,66,[80][81][82] The presence of CaO, MgO and CaCO 3 (basic nature) in Dol catalyst allows a progressive rupture of the aromatic and phenolic rings from the biomass, promoting cellulose, hemicellulose and lignin cracking. [62,66,81,[83][84][85] Corella et al [62] propose a mechanism for removing tar with CaO that explains how the rings are progressively, one-by-one, being opened by the catalyst and H 2 O.…”

“…This acid sites on the surface interact with reacted molecules generate carbonium ions by protonation of hydrocarbon, function as the initiation steps in the ionic chain reactions that lead to the products obtained from catalytic cracking. [33,66,80,81,82] In addition, Fe species (Lewis acid) improves the catalytic reforming reactions of the tar generated from the gasification stage. [33,66,[81][82][83][84] Lewis acidity predominates in NiMo/Al, it is related to the electronic availability due to the bimetallic character as a result of its free electron d orbitals.…”

Review of Carbon Fixation Evaluation and Emission Reduction Effectiveness for Biochar in China

“…The surface of the biochar molecule contains a large number of functional groups, such as carboxyl groups, carbonyl groups, lactone groups, hydroxyl groups, ketone groups, etc., so that the biochar has good adsorption, hydrophilic or hydrophobic, buffer acid and alkali, ion exchange, and other characteristics . The chemical interaction between phenol and the functional groups on the biochar surface shows good abilities of absorption and desorption . In Figure b, the biochar has good chemical adsorption ability as a result of the many functional groups on the surface.…”

“…74 The chemical interaction between phenol and the functional groups on the biochar surface shows good abilities of absorption and desorption. 89 In Figure 10b, the biochar has good chemical adsorption ability as a result of the many functional groups on the surface.…”