Using bio-chars as potential catalysts for upgrading wood pyrolysis vapors

Abstract

Pyrolysis is a promising thermochemical conversion method to process lignocellulosic biomass to produce bio-oil that can be further refined into chemicals and fuels compatible with current petrochemical fuels. However, bio-oils are highly reactive and unstable and therefore must be refined immediately, thereby reducing process sustainability. Catalytic modifications of pyrolysis vapors have been researched to improve bio-oil stability. However, using traditional highly active petroleum refining cracking catalysts for catalytic pyrolysis has shown some negative results, for example, increasing biooil moisture content and reducing its calorific value. Therefore, this project aims at understanding decomposition behavior of wood components, its chemical constituent polymers and using moderate catalysts, like bio-chars. Thermo-chemical decomposition behavior for wood components (bark, sapwood and heartwood) and individual wood-polymers (cellulose, hemicellulose and lignin) of typical hardwood is presented. Two hardwood species, namely red oak and yellow-poplar, were separated into their bark, sapwood and heartwood components. The samples were tested for calorific value, specific gravity, proximate analysis, mineral composition, chemical composition, ultimate analysis, and thermo-chemical decomposition behavior. In addition, the thermo-chemical decomposition behaviors of cellulose, xylan, and lignin polymers were tested. The activation energy was calculated for various fractional conversion values using the isoconversion method. The results showed that char yields from lignin, cellulose and xylan polymers were 41.43%, 4.45% and 1.89%, respectively, at the end of pyrolysis. Furthermore, cellulose, xylan and lignin polymers decomposed dramatically in the temperature ranges of 320 °C to 360 °C, 150 °C to 230 °C and 100 °C to 410 °C, respectively, with decomposition peaks at 340 °C, 200 °C and 340°C, respectively. In addition, the maximum activation energy for cellulose was 381 kJ/mol at 360 °C and for xylan it was 348 kJ/mol at 210°C. Catalytic performance of catalysts switchgrass bio-char and red oak bark bio-char during vapor upgrading pyrolysis are documented. The clean woodchip was pyrolyzed with and without vapor upgrading under atmosphere pressure at the target temperature of 500 °C. The catalysts showed significant positive effects on the bio-oil yields, moisture content and pH value of bio-oils. However, the vapor upgrading process significantly decreased the carbon yield of bio-oil when using switchgrass biochar as catalyst. The bio-oil yield decreased from 49.31% (no catalyst) to 44.81% (switchgrass bio-char catalyst) and to 48.68% (red oak bark bio-char catalyst). The lost mass of bio-oil ended-up in the gaseous phase as reflected in hydrogen, carbon dioxide, and carbon monoxide content. As result, at 400°C, hydrogen content increased from 0.82% to 3.74%, carbon dioxide content increased from 21.16% to 32.33%, and carbon monoxide content increased from 16.49% to 23.19% for switchgrass bio-char catalyst compared...

Pyrolysis of dedicated bioenergy crops grown on reclaimed mine land in West Virginia

“…Experimental setup for biomass pyrolysis[26] 2.3 Analytical MeasurementsASTM D3176-15 standard[27] was followed in carrying out the ultimate analyses (carbon, hydrogen, nitrogen and sulfur mass fractions) of the biomass, bio-oil and biochar samples using a CHNS analyzer(Model: Series II CHNS/O Analyzer 2400, PerkinElmer, Waltham, MA). The calorific values of the biomass, bio-oil and biochar samples were estimated using the unified correlation for computation of higher heating value from the elemental analysis of fuels provided by Channiwala and Parikh [28].…”