Study On The Synergistic Effect Of Co-pyrolysis Of Coal And Biomass Under The Condition Of Iron-based Catalyst

In the foreseeable future,coal carbon resources will still be one of the most important fossil energy sources in the world,and coal will still be the largest energy material in my country for a long time.As one of the main ways of utilization,the direct combustion of coal produces a large amount of greenhouse gases such as CO2.These greenhouse gases not only cause great harm to the environment,but also do not meet the goal of achieving carbon neutrality.The essence of the coal pyrolysis process is to use heating to separate the hydrocarbon elements in the coal to obtain high-value chemicals and fuels.It is currently recognized as one of the simplest methods for clean and efficient utilization of coal resources.The pyrolysis of coal follows the free radical reaction mechanism.First,the covalent bond in the coal is broken.This process generates a large amount of volatile matter rich in coal free radical fragments.These free radical fragments may undergo self-coupling reactions to form the heavy components in the tar.Fractionated coke,which may also be the precursor of tar,is easily stabilized by hydrogen or small molecular free radicals to form tar.However,because coal contains a large amount of heavy aromatics in its structure and its H/C ratio is relatively low,the pyrolysis process mainly occurs in the coupling reaction of coal free radical fragments,which leads to low coal pyrolysis conversion rate and low pyrolysis tar quality.The entrainment is serious,so a suitable method is needed to improve the yield and quality of coal tar.Biomass has good chemical reaction activity and high H/C.The mixed pyrolysis of biomass with coal can not only make up for the problem of coal's own hydrogen deficiency,but also improve the reaction activity of the reaction system,which is beneficial to increase the conversion rate of coal and the coal tar Yield.However,the oxygen content of biomass is relatively high,and the quality of tar obtained by pyrolysis is poor.It is necessary to find a suitable method to remove oxygen from the biomass.Studies have shown that iron-based catalysts can promote the cleavage of C-O bonds and C-C bonds,not only effectively removing oxygen in the sample,but also improving the pyrolysis conversion rate.This topic uses iron-based catalysts to catalyze bond breaking to reduce the oxygen content in pyrolysis tar and improve the quality of pyrolysis taBased on the above analysis,this project selected 40 coals with different coalification levels as the research object of co-pyrolysis,and deeply explored the influence of coalification degree on the degree of co-pyrolysis synergy,and explained the co-pyrolysis of coal and biomass from the perspective of free radical reaction.For the reaction mechanism of pyrolysis,a variety of characterization methods were used to explore whether the copyrolysis of coal and biomass had a synergistic effect,and the role of iron-based catalysts in the co-pyrolysis process was analyzed.The main conclusions obtained are as follows:(1)The lower the degree of coalification,the lower the carbon content of the coal and the higher the volatile content,the easier it is to have a co-pyrolysis synergistic effect with biomass.This is because the volatile free radical reaction results in the low temperature during the pyrolysis process.The side chain of lignin in the biomass is thermally decomposed to produce volatile components rich in small molecular free radical fragments.These volatile components may adhere to the coal surface to stabilize the coal free radical fragments generated by coal pyrolysis in the high temperature stage,thereby stably forming Tar:The volatile matter rich in coal free radicals generated in the high temperature stage will also adhere to the surface of the biomass semi-coke and induce further pyrolysis of the biomass semi-coke.(2)Co-pyrolysis can increase the yield of light tar,but the quality of solid residual coke slightly increases,which is similar to the results of the thermal weight loss experiment.The content of co-pyrolysis aromatics and phenols increased,indicating that co-pyrolysis promoted the pyrolysis of coal to break bonds.The proportion of light gasoline and diesel in co-pyrolysis coal tar is increased to a certain extent,and the content of vacuum residue and column residue is reduced,indicating that co-pyrolysis can convert part of the heavy tar components into light tar,thereby increasing the tar The purpose of quality.(3)The relative molecular mass of iron-loaded Naomaohu coal pyrolysis tar is smaller than that of unloaded iron;the stable free radical concentration on the surface of pyrolysis semi-coke is high,indicating that iron-based catalysts can catalyze coal pyrolysis to break bonds and generate more Coal free radicals;the pyrolysis of iron-loaded corn stalks can generate more hydrogen-containing small molecule free radicals,which reduces the ratio of heavy tar and coke formed by coupling and condensation of coal free radical fragments,and increases the proportion of light tar.Proportion to improve the quality of tar.