Study On Pyrolysis And Product Regulation Of Biomass Components Based On Phosphate Regulation

Lignocellulosic biomass has the advantages of large resource reserves,renewable and carbon neutral,and its application in the energy field can effectively relieve the energy tension and reduce various environmental problems caused by the use of fossil energy.Pyrolysis can transform biomass into solid,liquid and gas products to achieve high efficiency and high value utilization of products.However,the complex chemical composition of biomass makes it difficult to accurately reveal the formation path and reaction mechanism of pyrolysis products.This paper is supported by the National Natural Science Foundation of China（51706210）.In this paper,cellulose,lignin and hemicellulose model compounds were selected to simulate biomass components,and phosphoric acid loading was used to pretreat biomass components.Firstly,thermogravimetric（TG）experiments were conducted to explore the effects of phosphoric acid impregnation on the thermogravimetric properties of biomass components under different heating rates.Secondly,TG-FTIR was used to investigate the effects of phosphorus loading on the bond breaking and small molecule gas precipitation of biomass model components（cellulose,hemicellulose and lignin）during pyrolysis.The effects of phosphoric acid impregnation on the pyrolysis characteristics,product distribution and composition of three components of biomass were investigated in a fixed-bed pyrolysis experiment witha vertical reactor.The main research results of this paper are as follows:（1）The pyrolysis weight loss characteristics and the changes of functional groups of the three components of biomass before and after phosphorus loading were studied by synchronous thermal analyzer and TG-FTIR.It is found that phosphoric acid can promote the pyrolysis and dehydration reaction of biomass and reduce the energy required for biomass decomposition,resulting in the decrease of maximum weight loss peak temperature.With the increase of phosphoric acid impregnation ratio,the maximum weight loss peak temperature of cellulose pyrolysis decreases to 232℃and 215℃.The maximum weight loss peak temperatures of hemicellulose and lignin decreased 180℃,176℃,410℃and 216℃,respectively,compared with the original samples.The results of thermogravimetric infrared spectroscopy showed that the release temperature of H₂O was advanced in the pyrolysis process of the three components of biomass loaded with phosphorus.CH₄ absorption peak intensity weakened;The CO₂ and CO release temperatures of cellulose and hemicellulose were advanced,while the CO release temperatures of lignin pyrolysis gas products were delayed by 110℃.During pyrolysis of cellulose and hemicellulose,the maximum absorption peak temperatures of C=O,C=C and C-O functional groups were advanced.However,during pyrolysis of lignin,the peak temperatures of C=O and C-O decreased,and the stretching vibration peak temperatures were advanced,while the stretching vibration of C=C became stronger.（2）Secondly,the effect of phosphoric acid loading on cellulose pyrolysis was studied in a vertical reactor.It was found that the solid yield of cellulose increased,while the liquid yield and gas yield decreased.The contents of furans in the pyrolysis liquid products increased with the increase of pyrolysis temperature.When the pyrolysis temperature was 700℃,the contents of furans reached 52.8%.Phosphorus loading could effectively improve the contents of furans during cellulose pyrolysis.At the same time,the LGO yield can be effectively improved by loading phosphorus at 400℃.Phosphoric acid impregnation promoted the hydrolysis of cellulose,so the yields of CO,H₂ and CH₄ decreased by 16.23%,3.94%and2.29%,respectively,at 800℃.The volume fraction of H₂ increased by 9.2-19.94%and the calorific value decreased by 1.75-6.22 MJ/Nm~3.（3）Hemicellulose was pyrolyzed by vertical reactor before and after phosphorus loading,and the solid yield of hemicellulose increased by 35.46～36%after phosphorus loading;At400-600℃,the content of acetic acid in pyrolysis liquid products ranges from 83.90℃to93.69%,and with the increase of temperature,the content of acetic acid decreases to disappear.At 500℃,the furan products in H-20 pyrolysis liquid products increased by 61.92%.Phosphorus loading can effectively increase the content of furan compounds and reduce the content of acid compounds.The yield of CO and CH₄ decreased by 0.37-9.4%and0.02-2.13%,respectively.The volume fraction decreased by 21.02-24.38%and 0.79-7.06%,respectively.The calorific value of H-20 decreased by 3.99-6.29 MJ/Nm~3.（4）Finally,a vertical reactor was used to conduct pyrolysis experiments on lignin before and after loading phosphorus.It was found that the solid yield of lignin was significantly higher than that of cellulose and hemicellulose.Phosphoric acid impregnation can promote the further decomposition of lignin,and the precursor of phenol is generated in large quantities,which promotes the demethoxidation reaction,decarboxylation reaction and dehydration reaction,and then generates a large amount of phenol.At 600℃,the content of phenolic substances in the liquid products of lignin reached 18.71%.After loading phosphorus,the yields of CH₄ and H₂ decreased by 0.89～0.96%,0.06～0.18%and 0.94～2.19%,respectively,and the volume fractions decreased by 1.94～2.4%and 10.61～11.03%,respectively.The calorific values of the two groups changed little before and after loading phosphorus.