Study On Effect Of Phosphate On Pyrolysis Characteristics Of Corn Stalk

With the rapid growth of biomass application,more and more attention has been paid to the utilization of biomass with high phosphorus content.Biomass pyrolysis can produce carbon,gas and oil products at the same time,which has high energy conversion efficiency and market adaptability.It is a potential utilization way of phosphorus containing biomass.However,the research on the effect of phosphorus on the basic characteristics of biomass pyrolysis is not deep enough,and the mechanism of phosphorus addition on the yield and product composition of pyrolysis carbon gas oil needs to be further studied.In view of this,three kinds of phosphates were selected as additives in this paper,and the pyrolysis experiments of corn straw under different phosphate effects were carried out in a fixed bed reactor,and the effects of phosphate types and contents on the pyrolysis characteristics of corn stalk were studied.The main research contents are as follows:（1）Thermogravimetric analysis was used to study the effect of phosphate on the pyrolysis kinetics of corn stalk in nitrogen atmosphere.Coats Redfern method was used to calculate the pyrolysis kinetics of corn stalk.The results showed that:compared with the original corn stalk,the pyrolysis of corn stalk with phosphate mainly concentrated at 200～400℃,containing a main weight loss peak and an obvious shoulder peak.After adding phosphate,the initial temperature of pyrolysis was advanced by 50～70℃.The addition of phosphoric acid and ammonium dihydrogen phosphate delayed the pyrolysis termination temperature by about 30℃,but the addition of calcium dihydrogen phosphate advanced the pyrolysis termination temperature by about 60℃.The addition of phosphoric acid increased the maximum weight loss rate by about 17%,and the corresponding temperature was almost unchanged;the addition of ammonium dihydrogen phosphate and calcium dihydrogen phosphate reduced the maximum weight loss rate by 14～35%,and the corresponding temperature was 20～50℃earlier.The kinetic analysis showed that the pyrolysis can be divided into two stages,and both of them conformed to the power series reaction model.The addition of phosphate reduced the activation energy of the first stage reaction by 50～60%.（2）Corn stalk pyrolysis experiments were carried out in a fixed bed reactor under the action of three kinds of phosphates.The effects of different kinds of phosphates on the composition and distribution of pyrolysis products were studied.The purpose of this study was to investigate the effects of phosphate types on the pyrolysis characteristics of biomass by analyzing and characterizing the pyrolysis products.The results showed that the solid product yield increased by 8～13%and the gas product yield decreased by15～30%with the addition of three kinds of phosphates;the liquid product yield was decreased with the addition of phosphoric acid,while the liquid product yield was increased by ammonium dihydrogen phosphate and calcium dihydrogen phosphate.In addition to calcium dihydrogen phosphate,the addition of three kinds of phosphates reduced the yields of main gases such as H₂,CO,CO₂ and CH₄.The addition of three kinds of phosphates increased the content of furans by 13～21%,but the phenols decreased to some extent.The addition of phosphate reduced the H/C of coke and improved the stability of coke.The addition of three kinds of phosphates increased the carbon fixation rate by 2.8～4.3%.（3）The pyrolysis experiments of corn stalk samples with different phosphorus contents were carried out.The results showed that with the increase of phosphorus content,the yield of solid products increased,the yield of gas products decreased,and the yield of liquid products increased,but the change was not significant.The yield of organic components decreased and the yield of water increased.CO₂,CO and CH₄ are the main gas products of pyrolysis.The yields of CO₂ and CO decreased with the increase of phosphorus content,and the decrease range of high phosphorus content was reduced.The reduction range of CH₄ yield was small with the increase of phosphorus content.However,the yield of H₂ increased with the increase of ammonium dihydrogen phosphate content,and decreased with the increase of calcium dihydrogen phosphate content.For phosphoric acid and calcium dihydrogen phosphate,the content of furans increased with the increase of phosphorus content,and the increase range was larger.For ammonium dihydrogen phosphate,with the increase of phosphorus content,the content of acids decreased significantly,while alcohols and ketones increased significantly.With the increase of phosphorus content,the H/C molar ratio of phosphoric acid and ammonium dihydrogen phosphate increased,and the activity of coke increased;for calcium dihydrogen phosphate,the H/C molar ratio was low,showing good coke stability.The carbon fixation rate of biochar increased linearly with the increase of phosphate content.Ammonium dihydrogen phosphate had the strongest carbon fixation ability,followed by phosphoric acid,and calcium dihydrogen phosphate had the worst carbon fixation ability.