Study On Nitrogen Migration And Catalytic Denitrification During Pyrolysis Of Amino Acids

Catalytic fast pyrolysis can effectively solve the pollution and treatment problems of sewage sludge,and realize the green recycling of biomass waste energy.High nitrogen content is an important factor that limits the quality of bio-oil from pyrolysis of sewage sludge.In order to study the mechanism of nitrogen migration,using amino acids with characteristic functional groups as model compounds to simulate the fast pyrolysis and catalytic fast pyrolysis of sludge is an effective research method.In the study of the mechanism of amino acid pyrolysis,the lysine with linear amine side chain and the tryptophan with aromatic nitrogen-containing heterocycle side chain are representative,and there is rare clear mechanism explanation yet.This article also focused on the pyrolysis mechanism and nitrogen migration behavior of two amino acids.Based on a full understanding of the pyrolysis nitrogen migration mechanism of lysine and tryptophan,the catalytic denitrification mechanism of cheap ore catalyst dolomite and limonite was studied.In addition,the catalytic denitrification mechanism of modified HZSM-5（Si O₂/Al₂O₃=25）molecular sieve with different Ni loadings catalyst was also explored.The nitrogen in the non-catalytic pyrolysis product of lysine mainly exists in the bio-oil,a small amount of nitrogen enters the gas in the form of NH₃,and there is almost no residue.Two main reaction pathways occur:one is before 600 ^oC,lysine self-cyclizes to produce a molecule of water and 3-amine caprolactam;the side reaction is the decarboxylation of lysine to form diamine,and a small part of amines dehydrogenate to form nitrile Like substances,most of the amines form a nitrogen-containing heterocyclic ring after removing one molecule of ammonia.Second,after 600 ^oC,3-amine caprolactam is decomposed by heat,releasing CO.The nitrogen in the biomass oil is only in the form of pyridinepyrrole and a small amount of nitriles.The non-catalytic pyrolysis reaction of tryptophan is mainly a process of cleavage of the carboxyl group to release CO₂,forming tryptamine,and gradually deaminating and releasing NH₃.The nitrogen in tryptophan pyrolysis products mainly exists in the form of NH₃ and methyl indole in biomass oil.In the gaseous products,the HCN yields of the two amino acids are very low and are not greatly affected by temperature,while the release of NH₃ will increase with increasing temperature.By comparing the effects of the three types of catalysts on the pyrolysis products and nitrogen distribution of lysine and tryptophan,it is found that their denitrification mechanisms are different.Dolomite has a good ability to convert NH₃ and HCN into N₂.The denitrification effect of dolomite is mainly aimed at the NH₃ and HCN in the product,which combine to form Ca C_xN_y and release nitrogen in the form of N₂.In addition to combining with NH₃ and HCN to form Fe_xN,the denitrification effect of limonite also promotes the deamination reaction of amines and amides,and transfers nitrogen to the gas product.The metal Ni loaded in the pores of the molecular sieve can effectively promote the cracking of small molecules such as alkanes/olefins and promote the formation of H₂.HZSM-5 molecular sieve has a rich specific surface area and microporous structure,which can directional polymerization and reforming of small molecules such as alkanes/olefins into aromatic hydrocarbons.The nitrogen removal efficiency of lysine biomass oil can reach 96%.The ability to reform certain macromolecular nitrogen-containing heterocyclic compounds such as indole and caprolactam into aromatic hydrocarbons.The paper has 30 pictures,9 tables,and 92 references.