Study On The Effect And Mechanism Of Iron-based Additives On Nitrogen Migration In Pyrolysis Of Corn Straw

In order to relieve energy pressure and protect the ecological environment,the development and utilization of renewable energy is urgent.Biomass has the characteristics of abundant reserves,wide sources,renewability and zero carbon emissions,which has attracted widespread attention.However,due to the relatively high nitrogen content in biomass,nitrogen-containing pollutants will be produced during the utilization process,which will not only pollute the environment but also endanger human health.Pyrolysis is the main processing technology of biomass and the first stage of combustion and gasification.Therefore,the transfer law of nitrogen and the factors affecting the transfer law of the graduate material during the heat treatment process are very important for the green development and utilization of biomass and the reduction of pollutant emissions.In this paper,biomass,which is representative of the vast northern agricultural production waste corn straw,is selected as the research object,and the tube furnace is used to study the nitrogen migration and transformation pathways during the pyrolysis process.At the same time,iron-based additives were introduced to investigate their influence on nitrogen migration and transformation,and the mechanism of iron-based additives on nitrogen transformation was studied.The research has important theoretical significance and application value.The specific research content and main conclusions are as follows:（1）Study on the form of nitrogen in corn stalks and the law of nitrogen migration during pyrolysis.First,in order to clarify the mechanism of nitrogen transfer and transformation during the pyrolysis of corn stalks,this study investigated the pyrolysis of corn stalks in the temperature range of 300 to 700^oC.Studies have shown that the main nitrogen form in corn straw is protein nitrogen,and the pyrolysis is divided into two stages:（1）The devolatilization stage at300～500^oC.At this stage,the protein nitrogen in the corn straw is firstly cyclized into pyrrole nitrogen,pyridine nitrogen and quaternary nitrogen in the coke;the released NH₃ is mainly generated by the deamination reaction of tar and coke,and the released HCN mainly comes from the nitrile nitrogen in the tar.Decomposition,and the main component of tar nitrogen in the devolatilization stage is amine nitrogen,so the yield of HCN in the devolatilization stage is lower than NH₃.（2）The secondary reaction stage at 500～700^oC.At this stage,the nitrogen-containing structure in the coke will be transformed into more stable N-Q and N-X;the released HCN is mainly generated at this stage through the ring-opening reaction of the heterocyclic nitrogen and the dehydrogenation reaction of the nitrile nitrogen.（2）Research on the influence of additives on the changing law of nitrogen migration path during the pyrolysis of corn straw.Based on the previous research results,three iron-based additives（Fe,Fe Cl₃,Fe₂O₃）were selected as the research objects to change the nitrogen migration law of biomass pyrolysis and reduce the generation of pollutant precursors.Studies have shown that the introduction of iron-based additives has a certain catalytic effect on the conversion of coke nitrogen,tar nitrogen,and gas-phase nitrogen to N₂,and the iron-based additives will have solid-solid phase catalysis with heterocyclic nitrogen in the solid phase.Thereby catalyzing the conversion of coke nitrogen to nitrogen;the addition of iron-based additives causes the N atoms in the corn straw to be more easily activated to form N radicals,and further generate N₂through a series of reactions,thereby inhibiting the generation of NH₃ and HCN;The unstable nitrogen-containing heterocycles in tar will be converted into HCN and NH₃ under the action of iron-based additives in the secondary reaction stage;different types of additives have different catalytic effects,among which Fe₂O₃ has the best catalytic effect,which can catalyze the N₂ generation rate Reached 32.27%.（3）Study on the mechanism of additives for the directional conversion of corn straw pyrolysis process into nitrogen.The form of the promoter will change with the increase of the pyrolysis temperature,so it is not clear what form of the promoter plays a catalytic role and the catalytic mechanism.In order to further clarify the mechanism of Fe₂O₃ in the process of straw pyrolysis,this study investigated the changes in the form of Fe₂O₃ during the pyrolysis process to Fe OOH,Fe₃O₄andα-Fe,and found that the catalytic iron form isα-Fe;α-Fe It dissolves with the N-5,N-6and gas phase NH₃ and HCN formed in the coke,and further forms Fe _XN.When the temperature is 500～600^oC,the nano-level Fe _XN will be decomposed in a large amount and converted into N₂ and Fe;α-Fe It will promote the conversion of amine nitrogen in tar to heterocyclic nitrogen and nitrile nitrogen,thereby increasing the yield of NH₃ and HCN in the gas.NH₃ and HCN will be further catalyzed and converted into N₂ under the action of iron-based additives.The catalytic effect of iron-based additives on gas phase nitrogen is relatively stronger than that of coke nitrogen.