Study On The Microwave Pyrolysis Characteristics And Kinetics Of Microalgae With Composite Additives

With the growth of population and economic development,the global demand for energy is increasing rapidly.The large-scale use of traditional fuels such as coal,oil and natural gas inevitably leads to the problems of environmental pollution.Microalgae as a renewable bioenergy has a broad application prospect.Thermal chemical conversion technology is an effective way for biomass utilization at present,and catalytic pyrolysis is an effective way to improve the distribution and performance of biomass products.Microwave heating is a good heating method for its higher heating efficiency and shorter reaction time than traditional heating.This paper based on Dunaliella salina as raw material,using microwave pyrolysis system for microalgae biomass on basic research.The effects of three kinds of composite additive（blends of activated carbon and Na₂CO₃（AC/Na）,blends of activated carbon and Ca CO₃（AC/Ca）,blends of graphite and Na₂CO₃（GP/NC））under different conditions of different addition amount,different blending ratio on pyrolysis characteristics and kinetics of thermal decomposition were investigated.The main pyrolysis results are as follows:（1）With the increase of composite additive AC/Na=1:1,the total weight loss（M_t）increased.For different blending ratios of AC/Na at addition amount of15%,the maximum M_t（83.06 wt.%）could be obtained at 5AC5Na group.However,the 4AC6Na group showed a strong synergistic effect on the major pyrolysis characteristic parameters,such as the maximum weight loss rate（R_m）,the average weight loss rate（R_v）and the time corresponding to weight stability（t_s）.（2）When composite additive AC/Ca at blending ratio of 1:1,the M_tincreased with the addition of additive.The overall effect of AC/Ca on microalgae pyrolysis was positive.When AC/Ca additives with addition amount of 10%,the minimum t_s,the maximum R_vand the maximum bio-oil and gas production per unit of electricity consumption（W_u）were obtained at 5AC5Ca group.AC/Ca composite additives with different blending ratios had certain inhibitory effects on pyrolysis characteristic parameters R_mand the time（t_m）corresponding to the maximum weight loss rate of Dunaliella salina.（3）AC/Na composite additives group was superior to AC/Ca additives group in weight loss characteristics.Pure activated carbon,pure catalyst（Na,Ca）and composite additives behaved positive effect on the average weight loss rate of pyrolysis of Dunaliella salina.（4）In experimental groups of GP/NC additives（graphite mixed Na₂CO₃）with addition amount of 5%,the initial decomposition temperature（T_i）decreased with the increased of NC proportion in composite additive.The maximum weight loss rate(R_max),average weight loss rate(R_mean)and pyrolysis characteristic index D of the 5GP5NC group were 3.78%/min,1.67%/min and12.35×10^-7,respectively.But the small values of activation energy E（66.28k J/mol）,enthalpy△H（60.46 k J/mol）and Gibbs free energy△G（175.97k J/mol）were achieved at NC group.（5）When changed the addition amount of 5GP5NC（5%,10%and 15%）,15%was considered as a better addition amount due to its maximum D value(13.76×10^-7),minimum E value（52.49 k J/mol）,excellent weightlessness and thermodynamic properties.For NC additives,the maximum value of R_maxappeared at 15%amount,while the maximum value of D and minimum value of E obtained at 5%amount.