Evolution of Char Structure during the Steam Gasification of Biochars Produced from the Pyrolysis of Various Mallee Biomass Components

Abstract

This study reports the evolution of char structure during the steam gasification of biochars under chemicalreaction-controlled conditions. Partially gasified samples were collected at various conversion levels during the steam gasification of both the raw biochars and the acid-treated biochars that had been prepared via acid-washing of the raw biochars. Results from FT-Raman spectroscopy show that the biochars have highly heterogeneous and disordered structures, which are selectively consumed with progress of steam gasification, leading to enrichment of larger aromatic ring systems, hence the so-called "selective gasification". Selective gasification of biochar can be significantly influenced by the inherent alkali and alkaline earth metallic (AAEM) species in the biochars. The abundant catalysts present in the raw biochars can alter the gasification reaction pathway, but such an alteration appears to have little effect on the evolution of pore surface area, which increases significantly with conversion. While the wood biochar has too low a content of AAEM species to have an apparent effect on selective gasification, for the raw leaf and bark biochars with high contents of AAEM species, selective gasification is considerably less significant in comparison with the respective acidtreated biochars. For acid-treated biochars, gasification seems to take place slowly throughout the biochar on carbon active sites to consume the smaller rings selectively; the reactivity is controlled by the biochar carbon structure. However, for the raw leaf and bark biochars, gasification would be more focused or localized on the catalytic sites so that the activity of carbon active sites becomes less important. The catalytic effect of the inherent AAEM species seems to in turn depend on the carbon structure that probably affects the catalyst dispersion.

Soil Chemical Insights Provided through Vibrational Spectroscopy

“…Through analysis of the Raman shift at 1500 cm −1 (sp 2 carbon), 1150 cm −1 (sp 3 -hyridized carbon), and 1530 cm −1 (sp 2 -hydridized carbon) the amorphous nature of biochar can be evaluated (Schmidt et al, 2002). Similar to the pyrolysis temperature effects evaluated with FTIR, Raman spectroscopy has demonstrated that the amorphous carbon components of biochar decrease with increased duration of steam gasification (Wu et al, 2009). During feedstock conversion to biochar, Raman bands associated with the disordered carbon decrease relative to aromatic and recalcitrant carbon.…”

“…On occasion these two broad peaks have been further deconvoluted into seven peaks and further structural characterization information determined (Kim et al, 2011;Li et al, 2006). A helpful summary of Raman band assignments for charcoal samples is also presented by Wu et al (2009).…”

Effect of ball milling on the hydrolysis of microcrystalline cellulose in hot‐compressed water

“…[4][5][6] It is considered as a second generation renewable feedstock 7 for bioenergy and biofuels production in Australia. [8][9][10][11][12][13][14] Lignocellulosic ethanol production from mallee biomass is one of the key technical routes for producing liquid transport biofuels in Australia, if hemicellulose and cellulose in the biomass can be efficiently converted to fermentable sugars.…”

Biochar can be used to capture essential nutrients from dairy wastewater and improve soil physico-chemical properties

“…A third, alternative means to dispose of excess biomass is controlled pyrolysis for energy production, which produces biochar (charcoal) as a byproduct (Rutberg et al, 2011;Wu et al, 2009;Manyà, 2012). Although the environmental benefits of this latter approach are well appreciated, it still remains a fairly expensive approach for many small-scale growers.…”