Study On Selective Production Of High Value Products From Co-pyrolysis Of Biomass And Organic Carboxylic Acid

Biomass has attracted much attention nowadays along with the sustainable development of human society.As the only carbon-containing renewable resource,biomass can be converted into different fuels,chemicals,or materials through diverse technical roadmaps,playing a crucial role in carbon neutralization.Fast pyrolysis is one promising thermal technique and has achieved the production of various value-added chemicals,such as anhydrosugars,furans and phenols.Holocellulose is the main component of biomass,which can form a variety of high-value-added anhydrosugars and furans through fast pyrolysis.Selective preparation of specific high-value products can be achieved through targeted regulation of pyrolysis process.In this paper,relevant studies were carried out on the pyrolysis reaction mechanism and directed regulation of the synthesis of anhydrosugars and furans.1.Fast co-pyrolysis of cellulose and oxalic acid to produce 1,4:3,6-dianhydro-α-Dglucopyranose(DGP).We developed a novel strategy,fast co-pyrolysis of cellulose and oxalic acid,which achieved the selective production of a promising anhydrosugar,DGP,for the first time.Effects of temperature and the mass ratio of cellulose-to-oxalic acid(Cell/OA)in their solid mixture were explored.The yield of DGP could be up to 14.0 wt%(based on cellulose)at 400℃ and the Cell/OA mass ratio of 1:9 with a lab-scale setup,about 200 times higher than that from fast pyrolysis of pure cellulose.According to the experiments and density functional theory(DFT)calculations,it was OA rather than its pyrolysis vapors(mainly formic acid)that played the predominant role in the selective generation of DGP,where OA acted as a reactant and a catalyst-like material at the same time.The formation of DGP competed with that of levoglucosan(LG),the most typical product in the fast pyrolysis of pure cellulose,and a small amount of DGP came from the secondary conversion of LG.The esterification of free hydroxyl at C3 or C6 position with OA determined the selective generation of DGP by promoting the formation of the C1=C2 bond and the 3,6-acetal ring,and the generation of the 1,6-acetal ring was inhibited correspondingly which led to the decrease of LG.In addition,the co-pyrolysis process also showed the potential for poly-generation of value-added chemicals,syngas,and char.2.Fast co-pyrolysis of corncob and oxalic acid to produce furfural(FF).FF is an important pyrolysis product from biomass-based materials and a crucial platform compound for energy and fuels.In the present study,we developed a new and green approach to selectively produce FF through the fast co-pyrolysis of corncob(CC)and OA.The FF yield was up to 16.5 wt%(based on raw CC)through the fast pyrolysis of the solid mixture of CC and OA with a ratio of 1:4(CC/OA)at 400℃ during the micropyrolysis coupled with online-detection experiments.The corresponding FF selectivity was 56.5%(based on raw CC).Under similar experimental parameters,a yield of 10.0 wt%(based on raw CC)was achieved with a lab-scale setup.Experiment and DFT calculation results suggested that OA played a catalyst-like role in the selective formation of FF from hemicellulose(mainly xylose units)of CC and meanwhile decomposed during the pyrolysis process.The FA decomposed from OA had a similar but lighter effect than OA.With the assistance of OA,the energy barriers of the FF formation reactions decrease dramatically and the competitiveness of the pathways is also altered,which contributes a lot to the FF selective generation.FF is mainly generated in a chain propagation pattern from the acyclic reducing end and unsaturated(C4=C5 bond)non-reducing end of the xylan chain.