Pyolysis Kinetics And Experiments Of Rice Straw In Molten Salt Media

Biomass is regarded an important renewable resource, and the biomass pyrolysis is one of the most important thermochemical conversion technologies, which is also a hot topic for thermo-chemical conversion in the biomass utilization research field. The kinetics study of biomass pyrolysis can provide the basic theory of the biomass thermo-chemical conversion technologies, and it can present important references for the design of pyrolysis reactor and process optimization, understanding the mechanism and development of thermo-chemical conversion technologies. In this paper, the rice straw was selected as biomass raw material, molten salt was used as a heat carrier, catalyst and dispersant, and the kinetic and experimental research of biomass pyrolysis was carried out in molten salt to produce bio-fuel.The thermo-gravimetric analysis (TGA) method was adopted to investigate the characteristics of rice straw pyrolysis. The effects of operating conditions such as heating rate, material particle size and pretreatment method on the characteristics of biomass pyrolysis were studied, and the kinetic parameters were calculated. The characteristics of rice straw pyrolysis with molten salt which composed of Mg, Ca, Li chloride or K, Na carbonate were also explored. A two-step parallel and a two-step consecutive kinetic model were used to describe the process of rice straw pyrolysis, respectively. Six kinds of commonly solid reaction kinetic mechanism functions were used,and the kinetic parameters were calculated by multivariate linear fitting method. The results showed that, when the particle size is little, the primary pyrolysis reactions are dominant with a low residual weight. For the larger particles, secondary pyrolysis reactions are dominant with a high residual weight. It is beneficial to release of volatile products at high heating rates. The pretreatment methods with water and acid washing affected grately the activation energy of the biomass pyrolysis. The initial released temperature of volatile and termination temperature reduced with the increasing of the ratio of salt weight to biomass weight. The pyrolysis processes under the role of NaCl, MgCl₂ could be described by a two steps parallel reaction, whose types belonged to a simple n stage reaction of Fn model. It was found that others pyrolysis processes were described by a two steps consecutive reaction model and the activation energy of parallel reaction model is higher than that of consecutive reaction model. The MgCl₂-NaCl, CaCl₂-LiCl-NaCl and KCl-LiCl-NaCl have bvious impacts on the pyrolysis process of rice straw.Two molten salt systems such as KCl-LiCl and KCl-LiCl-NaCl were utilised in the pyrolysis experimental of rice straw to produce bio-fuel. The impacts of biomass raw material types, composition of molten salt and pyrolysis temperature on the pyrolysis process were investigated. The compositions of gas and bio-oil were analyzed by gas chromate-graphy and gas chromatography-mass spectrometry, respectively.The results showed that the temperature have more significant influences on biomass pyrolysis, and biomass feedstock and compositions of molten salt have great effects on the distribution of pyrolysis products and the composition of bio-fuel. It was found that H2, CO, CO₂ and CH4 are the main compositions of gas products, and furfural, ketones, phenols are the main composition of the liquid products. These experiments provided the theoretical foundation to study kinetic of biomass pyrolysis in molten salt.