Formation Rules And Pathway Adjustments Of Pyrolysates Derived From Non-wood Lignin Under Different Thermochemical Conditions

Thermochemical conversion techniques and equipments for biomass has been developing quickly, and an ever increasing attention has been paid to the high-value utilization of biomass applied to green bio-energy and high value-added chemicals. The structure of lignin are the most complicated macromolecules in biomass constitute, thus pyrolysis and reaction pathways of lignin are relatively more complex. Therefore, it is truly necessary to separate lignin from the biomass feedstock and then grade pyrolysis for directional conversion. To in-depth deliberate pyrolysis characteristic and reaction pathways of lignin would be required, which provided the theoretical guidance for the control of the desired products on line.Feedstock of bamboo and straw were representative in grass plants, enzymatic hydrolysis/mild acidolysis method was used to isolated lignin from feedstock, the obtained enzymatic hydrolysis/mild acidolysis lignin (named EMAL) had a higher purity and yield. The behavior of EMAL pyrolysis and pyrolytic products distribution were highlighted in this thesis.The physical and chemical characteristics of EMAL were comprehensively investigated in this paper by using elemental analysis, GPC, FT-IR, ¹H-NMR, ¹³C-NMR, quantitative ³¹P-NMR and other sophisticated analytical techniques. The results revealed that EMAL with an unbroken molecular structure was in close proximity to original lignin; EMAL contained main guaiacyl propane unit (G-type), syringyl propane unit (S-type) and a handful of para-hydroxyphenyl propane unit (p-H-type), moreover, G-type unit was superior in structural units of rice straw EMAL and S-type unit was major in bamboo EMAL.?-O-4 ether linkage is an important feature of structural units in bamboo and rice straw EMAL. In addition, rice straw EMAL contained some?-?,?-5 and?-O-4 bonds and banboo EMAL also possesed?-1,?-O-4 and?-5 bonds.The reaction path of lignin pyrolysis and the formation of pyrolyzate were revealed by means of thermogravimetric analysis (TGA), pyrolysis coupled with gas chromatopraphy/ mass spectrometry (Py-GC/MS) and small tube furnace pyrolysis apparatus. TGA studies showed that lignin pyrolysis took place in a long temperature range, and the sharp pyrolysis reactions mainly concentrated at temperature from 400?to 600?. Besides, kinetic parameters of lignin pyrolysis was obtained according to TGA data, and a dynamic order reaction model for lignin pyrolysis was established. TG-FT-IR was applied to detect release rules of gas products from bamboo and rice straw EMAL pyrolysis, which confirmed that most of the gas products were released within a temperature range from 300?to 500?, and CO₂ production was significantly higher than other gas molecules. Bamboo and rice straw EMAL were pyrolyzed on a tube furnace pyrolyzing furnace to collect bio-oil, char and gas products. the yield of obtained bio-oil was significantly higher than that of char and gas, to the highest 60% at 500?. As the pyrolysis temperature increased, the gas yield increased significantly yet char yield decreased, and the aromaticity of char gradually heightened. Besides, lignin pyrolysis at high temperature also produced more CO, H₂ and CH₄. It was also discoverded that pyrolysate yield from rice straw EMAL agreed with that from G-type lignin model, which affirmed that the pyrolysis behaviors and products were closely related to lignin structure.Phenolic compounds were the characteristics products from lignin pyrolysis, accounted for 60% around. In general, the relative content of total phenolics reached maxima at 600?. As the pyrolysis temperature increased, G- and S-type phenol content decreased yet p-H-type phenol content gradually increased; in particular, phenol and 4-methylphenol formed rapidly during 600?800?, which resulted from the secondary cracking of G- and S-type phenol at high temperature. Catalysts of metal salts and permutite added to lignin pyrolysis enhanced the cleavage levels of lignin structure, and caused a thorough split of functional groups (methoxyl, carboxyl, and carbonyl group) from G- and S-type phenolics to produce more small molecules, i.e. the gaseous, benzenes, phenol and alkyl-phenols. It was a great significance for catalytic pyrolysis improved pyrolysate components from biomass pyrolysis.