Production Of Value-added Chemicals By Chemical Looping Pyrolysis Of Corn Straw

Pyrolysis is considered to be one of the most effective ways to utilize biomass resources,but traditional biomass catalytic pyrolysis has many problems,such as low quality of bio-oil,easy deactivation of catalysts,and difficult separation of catalysts and biocoke.Biomass chemical looping pyrolysis（BCLPy）utilizes oxygen carriers to decouple the pyrolysis-gasification of biomass into two-stage reactions at different temperatures,which can simultaneously produce high-quality bio-oils/chemicals and clean syngas,which provides a new perspective for efficient and low-pollution conversion and utilization of biomass.In this paper,corn straw was selected as biomass raw material,and the following researches were carried out on biomass chemical looping pyrolysis from the aspects of iron-based composite oxygen carrier screening and biomass directional conversion chemicals:First,alkaline earth metals such as Ca,Sr,Ba,and transition metals such as Cr,Co,Ni,Cu,and Zn were selected to be composited with iron-based oxygen carriers,and nine kinds of iron-based composite oxygen carriers were prepared by sol-gel method.The oxygen-carrying and catalytic properties of the chemical looping pyrolysis of corn straw was investigated by XRD,GC/MS and SEM-EDS characterization.The research shows that nine iron-based composite oxygen carriers have significant ketoneation catalytic performance and deoxidation ability,which promotes the production of ketones and hydrocarbons in bio-oil.The iron-based composite oxygen carrier containing alkaline earth metals not only have good catalysis,but also have excellent redox ability,and are ideal oxygen carriers for chemical looping pyrolysis of corn straw.Among them,the reduced Ca-Fe composite oxygen carrier increased the relative content of 2-pentanone from 0.8% to 16.6%,which showed the best catalytic effect on the ketonylation reaction.The reacted oxygen carrier significantly improves the quality and yield of syngas in the gasification stage of pyrolysis coke,and shows good oxygen supply capacity.Secondly,using the reduced Ca-Fe composite oxide as the oxygen carrier,different target products were selected,and the optimal conditions for the production of chemicals by pyrolysis of corn straw were experimentally explored.Under the optimized conditions obtained with 2-pentanone as the target,the pyrolysis temperature was 550 °C,the ratio of corn straw to oxygen carrier was 3:1,and the peak area ratio of 2-pentanone reached 38.0% under the optimal conditions.According to the standard curve of 2-pentanone content,it was calculated that the content of 2-pentanone accounted for 4.7wt% of the corn straw content;Under the optimized conditions obtained by targeting bio-oil,the pyrolysis temperature is 650 °C,and the ratio of corn straw to oxygen carrier is 3:6.Under the optimal conditions,the oxygenated compounds of bio-oil are reduced by half and the hydrocarbons are increased by 4 times,and the peak area ratio of acid components decreased from 29.4% to 0.3%.And the oxygen carrier still has good oxygen capture,catalysis and oxygen releasing effects after 10 cycles of experiments.Finally,using the oxidized Ca-Fe composite oxide as the oxygen carrier,the experimental study on the pyrolysis of corn straw to produce chemicals was carried out.The research shows that: when the content of oxygen carrier increases,the liquid phase yield shows a decreasing trend,the content of acid components decreases obviously,and the ketones increase under the action of oxygen carrier.Oxidized Ca-Fe oxygen carrier helps to increase the content of 2-pentanone and 2,3-dihydrobenzofuran,when the pyrolysis temperature is 450 ℃,and the ratio of corn straw to oxidized Ca-Fe oxygen carrier is 3:4,it is the best condition to generate 2-pentanone;At the pyrolysis temperature of 600 °C and the ratio of corn straw to oxygen carrier of 3:2,the peak area ratio of 2,3-dihydrobenzofuran reached the maximum value of 11.6%.In conclusion,both oxidized and reduced Ca-Fe composite oxygen carriers have good catalytic and deoxidizing effects on the pyrolysis process of corn straw,and pyrolysis coke gasification can realize the reduction and regeneration of oxygen carriers,and produce high quality syngas.Chemical looping pyrolysis provides a new path for efficient and cascade utilization of biomass resources.