Characteristic studies on the biochars produced by hydro-thermal and steam gasification of canola hull and canola meal fuel pellets

Biochars, based on their production process and biomass precursor, can have a broad range of structural, compositional, chemical, and physical properties. These properties are important for identifying the biochar performance and stability in further applications. Non-food biomass has a great potential to produce biochars. Two inherent agricultural biomasses from Canadian prairies including canola hull and canola meal were used for the production of fuel pellets. This study provides information on the specific features of biochars produced by steam and hydro-thermal gasification of these fuel pellets compared with those of well-known pyrolysis biochars. For steam gasification, the steam to biomass ratio (SBR=0.31, 0.47, and 0.62) and gasification temperature (T=650, 750 and 850 oC) were used as the main process parameters. In contrast, for hydro-thermal (supercritical water) gasification, the effects of gasification temperature (T= 350, 450, 550, and 650 oC) were studied on the biochar properties at a constant pressure, feed concentration and reaction time. Different characterization techniques were used to study the physical, chemical, and structural characteristics of biochar products. Characterization results, for steam-gasified biochars confirmed development of aromatic carbon structure and formation of composite char. XRD spectra for biochars produced through steam gasification showed no retention of biochemical features from the parent precursors in the biochars prepared in different levels of operating conditions. FTIR spectra confirmed the rearrangement of biomass structure at the early stages of steam gasification for all used operating conditions. Elemental analysis and Van Krevelen plot showed that for pellets, the H/C and O/C atomic ratios were in the range of biomass material. However, after gasification, the these atomic ratios for biochars were in the range of them for coal material, especially lignite coal. SEM analysis showed that steam-gasified biochars had much more cracked surface as compared with hydro-thermally prepared biochars. This observation was consistent with the results of porous characteristics for biochars which showed low BET surface area (\u3c11 \u3em2/g) for hydro-thermally produced biochars but it was much larger (\u3e 400 m2/g) for steam-gasified biochars. XRD results for hydro-thermally prepared biochars at 350 oC showed the presence of cellulose I and cellulose II in the material structure, but the related peaks were not observed for the biochar prepared at hydro-thermal gasification temperature of 650 oC. For prepared biochars prepared at the highest temperature of hydro-thermal gasification, Raman analysis showed a large change in ID/IG ratio compared with that for biochar prepared at temperature of 350 oC confirming a drastic structural change in biochar structure. Results from other characterization techniques such as XRD, ICP-MS, and thermogravimetric analysis will be also discussed in the presentation. The degradation of biochars was progressive with the rise in hydro-thermal gasification temperature from 350 to 650°C. Hydro-thermally produced biochars showed characteristics of transition char at low temperature (350 oC as gasification temperature) and properties of amorphous char at high temperature (≥550 oC). For steam-gasified biochars, higher BET surface area indicated the development of composite char. It is noteworthy that characterization results showed that the steam-gasified biochars did not have the compact aromatic structure of turbostratic char and their aromatic structure is not developed as biochars produced via pyrolysis. However, properties of steam-gasified biochars showed their great potential for industrial applications such as adsorptive and/or catalytic applications. In addition, both types of biochars due to their mineral contents can be tested for agricultural applications(soil amendment and productivity)