Study On Precipitation Characteristics And Intrinsic Kinetics Of Biomass Pyrolysis Gas Products

Pyrolysis is considered to be one of the cutting-edge technologies for converting biomass energy into available intermediate chemicals,but because of the low energy density of biomass,it needs to be pretreated prior to pyrolysis to improve the quality of the biomass.The addition of a suitable catalyst during the pyrolysis process can selectively obtain the desired product and increase the yield.However,the catalytic effect and catalytic mechanism of different metal salts on biomass pyrolysis products are not the same.Therefore,it is of practical value to study the effects of metal salts on corn stover and its three-component pyrolysis gas products.This paper mainly conducts research from the following aspects.Firstly,the experimental research on corn stover and three-component pyrolysis was carried out on a thermogravimetric infrared combined instrument,and the basic data of thermal analysis was obtained to provide reference for subsequent isothermal rapid pyrolysis experiments.The study found that the thermal stability of the three components of corn stover is quite different,and this difference will affect the gas production process.Although the main pyrolysis temperature range is slightly different,after the temperature exceeds 550°C,the pyrolysis of corn stover and three components has been completed,which provides a basis for determining the isothermal pyrolysis test temperature of the micro fluidized bed in the later stage.Secondly,the corn stover and three-component pyrolysis experiments at different temperatures were carried out to analyze the release characteristics of the pyrolysis gas of the single component.Before the pyrolysis experiment,the micro-fluidized bed needs to be debugged to optimize the relevant experimental conditions of corn stover and its three-component pyrolysis,including determination of reaction temperature,selection of fluidized gas volume,and feed amount.It can be seen from the difference in gas release characteristics that the formation mechanism of the four gas components is not the same,which is consistent with the thermogravimetric experimental results.In addition,for each gas component,the residence time to achieve the same conversion rate gradually decreases with increasing temperature,indicating that high temperature is beneficial to the progress of the biomass pyrolysis reaction.Thirdly,the metal salt catalyzed biomass pyrolysis experiment was carried out to further understand the catalytic mechanism of three metal salts?NaCl,K₂CO₃ and Na₂CO₃?on the pyrolysis gas products of corn stover.During the catalytic pyrolysis process,it was found that the addition of K₂CO₃ and Na₂CO₃ promoted the decomposition of carbonyl and carboxyl compounds in the volatiles,which accelerated the conversion of CO and CO₂ at low temperatures.The related reactions of the solution are easy to occur,and the participation of K₂CO₃ and Na₂CO₃ is not obvious,and the metal salt attached to the voids of the three-component structure also hinders the gas from being precipitated from the channel,and the conversion rate of CO and CO2 is slowed down.Unlike cellulose and hemicellulose,the metal salt exacerbates the condensed cyclization of the benzene ring on the lignin,promotes dehydrogenation to form H2,and thus enhances the strength of the lignin pyrolysis product H2.Finally,the intrinsic kinetic analysis was carried out,and the activation energy E value and the pre-exponential factor A value of the gas component were obtained by model integration method,and the fitting results of each model were evaluated to select the most suitable kinetic model.The micro fluidized bed can overcome the influence of the thermal hysteresis of the instrument and obtain the pyrolysis intrinsic kinetics.It is found that the activation energy of CO and CO2 generation is generally smaller than that of CH4 and H2,indicating that CO and CO2 are easier to form than CH4 and H2.At the same time,the addition of three metal salts will change the gas activation energy,which in turn affects the release characteristics and conversion rate of the gas product.