The ever-rising demand for clean fuels and environmental concerns arising from fossil fuels combustion has put a lot of pressure on the need to use renewable and clean sources of energy. Lignocellulosic biomass is a promising candidate for biofuels as well as production of chemicals. The most important step in the synthesis of biofuels and chemicals lies in the hydrolysis transformation of cellulose to fermented sugars. However, the sugars in the lignocellulose are resistant to chemical processes. Fortunately, it has been found that wood as well as cellulose can dissolve in 1-butyl-3-methylimidazolium chloride solvent, therefore, making the cellulose chains susceptible to chemical transformations.
Therefore, dissolution of lignocellulosic in different kinds of the chloride solvent implementing mineral acids has attracted numerous research attention. In a recent work is published in Bioresource Technology researchers led by professor Dan Wang from Chongqing University in China implemented sulfonated crosslinked chitosan immobilized with metal ions as excellent catalysts and an ionic solvent in the hydrolysis of cellulose. In their work, they realized that lignocellulosic materials could be effectively hydrolyzed and the chitosan solid acid catalyst would be removed from the hydrolysate easily.
The obtained bamboo samples were milled and their chemical composition determined. The authors prepared the 1-butyl-3-methyl-imidazolium chloride solvent as well as the crosslinked chitosan resin. They placed the reagents; the chloride solvent, bamboo powder, and sulfonated crosslinked chitosan (immobilized with metal ions) in the reactor. The mixture was stirred under normal atmospheric pressure for 24 hours. The authors drew samples from the mixture at different times and subjected them to sugar analysis.
After the hydrolysis process, the authors filtered the mixture and collected the retentate. They added anhydrous ethanol to the hydrolysate in order to recover the ionic liquid. The ethanol could dissolve the ionic liquid but not the reducing sugars. Ethanol was added until a turbid solution was obtained after which it was filtered to separate the ionic liquid from the solids of reducing sugar. The authors concentrated the liquid phase in order to recover the ionic liquid.
The authors observed that the impact of hydrolysis of the chitosan-based solid-acid catalyst on the milled bamboo powder was quite impressive. Chitosan-based solid-acid immobilized with iron (Fe3+) posted the best results. It yielded approximately 73.42% total reducing sugar. Catalysts immobilized with zinc and copper registered 62.43% and 68.75% total reducing sugars respectively, which increasing TRS yield by 68.47%, 43.25% and 57.76% respectively.
The effect of temperature was also investigated on the total reducing sugar yield and the rate of hydrolysis process. They found that 120 °C was the optimum temperature that gave a balance between energy consumption and the rate of hydrolysis and total reducing sugar yield.
The stirring speed and the amount of the chitosan-based catalyst used had an impact on the rate of hydrolysis and reducing sugar yield. The rate of hydrolysis and total reducing sugar yield increased towards a stirring speed of 20 RPM and dropped towards 30 RPM. Total reducing sugar yield increased when the amount of the chitosan-based catalyst was increased. The authors settled for an optimum ratio of 2:1 between the catalyst and the bamboo.
The proposed method of hydrolysis enhancement of the bamboo powder with solid acid catalyst required no pretreatments and enhanced the hydrolysis process. This could be a feasible method towards efficient conversion of biomass products into bio-based products and biofuels.
Jie Cheng1,2, Nan Wang3, Dezhou Zhao1,2, Dandan Qin1,2, Wenqing Si1,2, Yunfei Tan1,2, Shun’an Wei1,2, and Dan Wang1,2. The enhancement of the hydrolysis of bamboo biomass in ionic liquid with chitosan-based solid acid catalysts immobilized with metal ions. Bioresource Technology 220 (2016) 457–463Show Affiliations
- Department of Chemical Engineering, School of Chemistry and Chemical Engineering, Chongqing University, Chongqing 401331, PR China
- Chongqing Key Laboratory of Chemical Process for Clean Energy and Resource Utilization, PR China
- Department of Chemical and Petroleum Engineering, University of Kansas, Lawrence, KS 66045, United States
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