Experimental Research On Biomass Hydrothermal Treatment And Physicochemical Properties For Products

Hydrothermal carbonization of biomass(HTC) is one of the effective ways for biomass conversion due to its great significance in carbon sequestration, coping with energy shortage and environmental pollution and promoting sustainable economic development. Supported by the National Nature Science Foundation of China “research on migration and sequestration mechanism of carbon in hydrothermal treatment liquid of biomass”, a comprehensive and systematic research on hydrothermal carbonization was carried out by using typical agricultural waste(straw waste), urban lawn grass and forestry waste(phoenix leaves). The main work has the following aspects:(1) Hydrothermal carbonization experiments were carried out by using the automatic heating high pressure reactor. The effects of reaction conditions and characteristic of raw materials on distribution of products were investigated. Based on carbon content, fixed carbon, and carbon sequestration ratio in hydrochar, the influence of reaction parameters on the property of carbon sequestration were explored. The results show that the increasing of reaction temperature, residence time and ratio of liquid to solid could result the decrease of solid yields. However, the reaction temperature plays a main role in hydrothermal carbonization process. Higher temperature could be lead to the liquefaction occurring and is not favorable to carbon sequestration. Due to the different properties of feedstock, the answer of lawn grass, wheat straw and phoenix leaves to reaction temperature gradually declined.(2) The physicochemical evolution properties and the formation pathway of the HTC solid products were studied by Fourier transform infrared spectrometer(FTIR), X ray diffraction(XRD), thermo gravimetric analyzer(TGA), scanning electron microscopy(SEM) and the elemental analyzer. The effect of reaction conditions on functional groups, microcrystalline structure, micromorphology and element composite of hydrochar and the behaviour of wheat straw were in-depth analyzed. With reaction severity increased, the carbon content of hydrochar from wheat straw HTC increasingly enhanced, the aromatic property became strong, and the thermal stability exhibited well. As the hydrolysis and degradation of amorphous components of biomass, the property of structure was good at 220 ℃and 120 min. Furthermore, the formation of hydrochar during HTC was known about through these results.(3) The major components and concentration distributions of HTC liquid products were quantitatively analyzed by high performance liquid chromatography and mass spectrometer(HPLC-MS), ion chromatography and iodine quantity method. The effect of temperature that is main reaction parameters on the formation of distribution of liquid products was studied. As the temperature increased, the concentration of the reducing sugar, furfural and 5- hydroxyl methyl furfural(5-HMF) gradually elevated until the temperature of 220 ℃began to decrease. The concentration of acetic acid increases with increasing temperature and reaches the maximum concentration at 240 oC. The compounds of reducing sugar, furfural and 5-HMF are sensitive to the change of temperature, the decomposition, cross-linking, and polymerization occured when the temperature increased. Combined the evolution of physico-chemical structure in hydrochar with the change of main components concentration in liquid, the reaction mechanism of HTC was basically analyzed. This is the basis of development of HTC.