CO_(2)气氛耦合粉煤灰催化生物质热解生油特性分析

Characteristics of bio-oil generated from biomass pyrolysis catalyzed by coal fly ash under CO_(2) atmosphere

针对生物质热解生物油中可利用组分富集程度低的问题,该研究以不同颗粒尺寸的玉米秸秆为研究对象,通过固定床热解设备开展了CO_(2)气氛下粉煤灰与秸秆共热解试验,分析粉煤灰对秸秆热解产物分布的影响规律,并重点研究CO_(2)耦合粉煤灰对液相产物中含氧化合物组分的作用机制。结果表明,当颗粒尺寸为0.17~0.21 mm时,生物油产率最大值为44.32%。粉煤灰对大颗粒尺寸生物质热解生油过程的促进作用最为明显,当颗粒尺寸为0.31~0.45 mm时,生物油产率增加量为8.94个百分点。主要原因是粉煤灰所含金属组分间的协同催化作用和生物质颗粒内外传热传质效率的增强。CO_(2)的引入对生物油的形成起抑制作用,且液相产率随着体系内CO_(2)流速的增加而逐渐降低。小颗粒尺寸的生物质与粉煤灰共热解更有助于促进酚类化合物的生成,CO_(2)与体系中氢自由基的强结合能力进一步促进了酚类化合物的富集。经综合分析,当CO_(2)流速为40 mL/min时,液体产物中酚类化合物含量最高。该研究可为煤灰基固废物催化生物质热解制取高品质生物油技术的优化设计和CO_(2)气氛辅助生物质催化热解机理的完善提供理论依据。

Biomass has been one of the most promising renewable energy substitutes for fossil fuels.However,the bio-oil production from biomass pyrolysis has been greatly limited the application value,due to the complex components and low enrichment of available components.An effective way can be to selectively regulate the pyrolysis reaction using the catalyst.Among them,the coal fly ash can be widely expected to serve as the low-cost and high-efficiency catalytic medium,due to the rich pore structure and inorganic mineral composition.Generally,solid waste is produced by the combustion of pulverized coal in the boiler of the thermal power plant.More importantly,CO_(2)rich in carbon source can participate in the pyrolysis process to enrich the platform compounds.Therefore,CO2 and coal fly ash can be applied for the biomass pyrolysis process,in order to improve the quality of bio-oil for the high-value utilization of solid wastes.It is very necessary to explore the co-pyrolysis behavior of coal fly ash and biomass in the CO_(2)atmosphere for the goal of carbon neutralization.This work aims to investigate the effects of coal fly ash on the distribution of the products during the pyrolysis of maize stalks with different particle sizes.The liquid products were also characterized by catalytic pyrolysis under N;/CO_(2)atmosphere.The coupling mechanism of CO_(2)and coal fly ash was proposed,according to the experimental data.Specifically,the particle sizes of corn straw were ranged from 0.1-0.16,0.17-0.21,0.22-0.30,and 0.31-0.45 mm,respectively.The mixing ratio of maize stalk and coal fly ash was 1:1.A catalytic pyrolysis experiment of maize stalk was carried out in a fixed bed reactor,where the temperature was 550±1℃,the flow rate of N;was 100 mL/min,and the flow rates of CO_(2)were 40,70,100,and 130 mL/min.The obtained bio-oil was detected using an elemental analyzer and Gas Chromatography-Mass Spectrometry(GC-MS).The results showed that the particle size dominated the heat and mass transfer behavior of the biomass pyrolysis process.The increase of particle size led to the increase of bio-oil production first and then the decrease in only single biomass pyrolysis.The yield of semi-coke decreased,but the gas increased.The addition of coal fly ash was conducive to the formation of bio-oil,where the maximum bio-oil yield was 44.32%using 0.17-0.21mm of biomass particles.Coal fly ash was also greatly contributed to the biomass pyrolysis with the large particle size,where the bio-oil yield increased by 8.94 percentage point,compared with the blank sample.The main reason was the synergistic effects among metal components in the coal fly ash,thereby enhancing the heat and mass transfer efficiency inside and outside biomass particles.In addition,CO_(2)was introduced to inhibit the formation of bio-oil,and the liquid yield decreased with the increase of CO_(2)flow rate in the system.The co-pyrolysis of coal fly ash and biomass with small particle size was conducive to enhancing the selective phenolic compounds.The strong binding ability of CO_(2)and hydrogen radical was further promoted to enrich the phenolic compounds in the system.The methoxyphenol compounds increased significantly among phenolic compounds in the bio-oil.The relative content of phenolic compounds was the highest-when the flow rate of CO_(2)was 40 mL/min.