Hydrothermal Carbonization Of Biomass Wastes

Resource limitation and the environmental pollution problem of fossil energy prompt people to look for clean and cheap renewable energy. Biomass waste is the only, renewable substitute of organic oil. However, conventional incineration will not only pollute the environment, but also is a waste of energy. Hydrothermal carbonization (HTC) is a novel biomass conversion technology, yielding carbonaceous products (HTC char) favorable for wide range of applications. HTC can be realized by applying elevated temperatures (150-350℃) to biomass in a suspension with water for several hours. With dehydration and decarboxylation processes, an easy to handle fuel with well-defined properties can be created from biomass wastes. In this study, all experiments were conducted in an autoclave, and the main contents were as follows:The influence of feedstock, reaction temperature and hold time on hydrothermal carbonization was identified by orthogonal analysis. The results showed that the three reaction parameters that affect HTC char yield, energy density and energy yield were feedstock, reaction temperature, and hold time, in a descending order. The C content of four kinds of feedstock increased in such a descending order, hemicellulose, lignin, wood meal and cellulose. And the decrease trend was hemicellulose> cellulose> wood meal> lignin for H and O content, atomic H/C and O/C ratios after HTC. SEM images showed that hemicellulose and cellulose derived HTC chars were accumulated by microspheres, and wood meal HTC chars only generated microspheres under some appropriate conditions. While, there were no cracks and holes produced on the surface of lignin HTC chars.The impact of reaction temperature and hold time on hydrothermal carbonization of microcrystalline cellulose and carbon distribution was studied, and physical, chemical, thermal and structural characteristics of HTC char were also investigated. The results showed that during hydrothermal carbonization of microcrystalline cellulose a significant fraction of initially present carbon, about 71%-75%, was stayed in HTC char, while only a small fraction of the carbon was transferred to the liquid and gas-phases. As the temperature and reaction time increased, the HTC char yield and O/C atom ratio decreased, and its heat value increased. SEM images showed that HTC char consisted of aggregates of microspheres. FTIR spectra indicated that dehydration and aromatization processes took place during hydrothermal carbonization and HTC char possessed hydroxyl groups and carbonyl groups.HTC chars prepared by hydrothermal carbonization of cellulose and cellulose in the presence of acrylic acid, were activated by KOH, and then the four materials were used as adsorbents for Cu2+. The results showed that microspheres on cellulose HTC char were bigger and smoother than that of cellulose and acrylic acid derived HTC char, and the two activated carbon products possessed sponge-like surface. FTIR spectra indicated that adding acrylic acid to HTC could increase the content of oxygen containing functional groups, which would be undermined during chemical activation. Absorption-desorption N2 isotherms figured out that the porosity was developed for activated carbon products, while for HTC chars pore structure was not. The Cu2+ uptake capacity trend of the four materials was cellulose derived activated carbon> cellulose with acrylic acid derived activated carbon> cellulose derived HTC char> cellulose with acrylic acid derived HTC char, which could be explained by absorption-desorption N2 isotherms.According to the work, the influence of feedstock, reaction temperature and hold time on hydrothermal carbonization has preliminarily determined. At the same time, adsorption studies have also affirmed the necessity of the activation process.