Characteristics Of The Alkali Lignin Pyrolysis Under Different Systems And Its Pyrolysis Products Regulated By Nano-metal Oxides

As an important biomass resource,lignin has the characteristics in concentrated product distribution,abundant resources and high energy density.The pyrolysis technology can convert lignin efficiently into liquid fuels and high value-added chemicals.However,lignin pyrolysis has the problems like low yield and complicated composition about bio-oil,and high content of oligomers even poor selectivity on monocyclic phenolic compounds.How to improve the quality of bio-oil and the yield of monocyclic phenolic compounds are the key for lignin pyrolysis regulation.Catalytic pyrolysis,as an efficient pyrolysis technology,can influence the pyrolysis products distribution,the contents characteristic and enhance the liquid products quality and the phenolic selectivity.In this research,the raw material was the Eucalyptus sulphate pulping black liquor,from which lignin was extracted with CO₂.We mainly studied the influence of the different pyrolysis systems on lignin pyrolysis behavior,and selected the proper catalysts which contribute to the quality improvement in the pyrolysis oil,and also ananlyzed the mechanism of the nano-metal oxide catalyst for Lignin Catalytic Pyrolysis in Hydrogen-rich atmosphere,the conclusions are as follows,?1?The contents of C,H and O were 11.42%,6.06% and 28.60%,respectively,extracted by carbon dioxide from the black liquor.The weight average molecular weight?Mw?and number average molecular weight?Mn?of alkali lignin were 9119 g · mol-1 and 5304 g · mol-1,respectively.Alkali lignin is mainly linked by the C-C bond,with only 3.8,2.5 and 1.3 units per 100 aromatic ring units linked through the form of ?-O-4',?-? 'and ?-5'.Alkali lignin mainly composed of S-type,accounting for 72%,followed by the G-type,26%,and a small amount of H-type lignin units,2%.?2?In the closed system,when the reacting time was 90 s during the lignin pyrolysis,the tar reached the highest yield?43.97%?.Prolonging the pyrolysis residence time could intensify alkali lignin secondary reaction,and enhance the de-methoxy reaction by decreasing the relative content G-type and S-type phenolic compounds,and increasing the relative content of the H-type phenolic compounds.Under the open system,the yield of bio-oil,gas and char in lignin pyrolysis products was 55.33%,2.25% and 42.42%,respectively.The content of 2,6-Dimethoxyphenol was 2.56 wt.%.For the alkali lignin pyrolysis under the open system,the yield of bio-oil was much higher than that of the closed system,which means it is more suitable for the utilization of lignin pyrolysis with liquid fuel as the target.?3?Under the open pyrolysis system,the addition of the molecular sieve catalyst did not inhibit the char obviously,but it promoted the secondary reaction between liquid products,and reduced the oil yield.In addition,the molecular sieve catalyst has a significant effect on the composition of char.The G-type phenolic compounds were reduced,and the yield of typical monocyclic phenolic compounds decreased greatly.Compared with the molecular sieve catalyst,nano-metal oxide has advantages in improving the yield of bio-oil,promoting deoxidation of the liquid product,and improving the quality of bio-oil.The addition of nano-metal oxides increased the yield of bio-oil and small molecules?predominantly CO and CO₂?,and inhibited formation of char.?4?Hydrogen-rich atmosphere helped to cap the free radicals generated during the alkali lignin pyrolysis,and promoted the degradation of alkali lignin and inhibited the secondary reaction,it also improved the yield of tar and inhibited the formation of gas and coke.Under the hydrogen atmosphere,the addition of nano-Co₃O₄ could obtain the highest yield of bio-oil,about 71%.With the addition of MoO2,the yield of monocyclic phenolic compound 2,6-dimethoxyphenol reached the maximum?2.76 Wt.%?.In the hydrogen-rich atmosphere,the deoxidation path way of alkali lignin pyrolysis was changed,and the yield of CO and CO₂ were decreased.Decreased carbon content of coke,increased conversion rate of alkali lignin,and enhanced proportion of oxygen ahout char helped to reduce the oxygen content of bio-oil.