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Alkaline Thermal Treatment of Cellulosic Biomass for H₂ Production Using Ca-Based Bifunctional Materials

Zhao, Ming, Cui, Xiaomin, Ji, Guozhao, Zhou, Hui, Vuppaladadiyam, Arun K., Zhao, Xiao
ACS sustainable chemistry & engineering 2018 v.7 no.1 pp. 1202-1209
biomass, calcium hydroxide, carbon dioxide, catalysts, cellulose, cracking, energy, furans, gas chromatography-mass spectrometry, heat treatment, hydrogen, hydrogen production, nickel, pyrolysis, surface area, temperature
Hydrogen production from cellulosic biomass not only provides a sustainable approach to cope with the growing demand for energy but also facilitates the relief of environmental burden. In this study, we developed a series of Ca-based bifunctional materials (Ca(OH)₂ and Ni composites) for alkaline thermal treatment (ATT) of cellulose to produce high purity hydrogen at moderate temperatures (350–450 °C). Ca(OH)₂ served predominantly as a CO₂ carrier and a H₂O donor, and enlarged the surface area of the materials to improve H₂ production. However, excess Ca(OH)₂ tended to cover Ni particles and block pore structures resulting in a suppressed H₂ production. Ni promoted tar cracking and enhanced H₂ production, but the surface area of catalyst decreased with an increment in Ni, which suppressed H₂ generation. The yield of hydrogen was improved at elevated temperature. The maximum hydrogen yield, 34.5 mmol·g–¹ with 77% volume fraction, was obtained by adopting a molar ratio of cellulose:Ca(OH)₂:Ni as 1:6:2 at 450 °C for 10 min. GC–MS analysis results of tar products revealed that Ca(OH)₂ promoted primary pyrolysis of cellulose, and Ni promoted the decomposition of furan ring derivatives. The reaction temperature affected the distribution rather than the composition of the tar products.