Selective Pyrolysis Of Biomass For Chemicals Of Levoglucosan And Levoglucosenone

Biomass can be converted into liquid fuels,and also can be used to produce high value-added chemicals.Levoglucosan(LG)and levoglucosenone(LGO)are two important glycosidic compounds with high value in the field of health care and fine chemical industry.At present,it is necessary of preparing the two chemicals through difficult and complex cyclization and oxidation reaction.While biomass can be prepared to obtain oxygen chemicals because of containing oxygen naturally.This study explored the methods of producing levoglucosan(LG)and levoglucosenone(LGO)from selective fast pyrolysis aimed at obtaining high-yield chemicals.At first,screen raw materials and catalysts and explore pretreatment methods on the Py-GC/MS.Then carry on fast pyrolysis on the fixed bed reactor to investigate influence factors and reveal the reaction mechanism.At last,prepare new catalysts based on the mechanism.There are some valuable conclusions as follows:Fast pyrolysis of cellulose was conducted using pyrolysis chromatography mass spectrometry(Py-GC/MS),impregnating cellulose with appropriate catalysts,then conduct the catalyst selection and optimization.The influence of different impregnation concentrations and pretreatment method were also conducted to conclude best catalytic pyrolysis condition.The results showed that the main product was LG from direct pyrolysis of cellulose.Weak acid can promote the formation of LG,and the optimum LG selectivity was 87.6%under 10%acetic acid catalysis.Strong or medium strong acids such as sulfuric acid and phosphoric acid would promote LGO,and the highest LGO selectivity was61.8%using 10%phosphoric acid.Catalyst pretreatment concentrations can significantly affect the distribution of products,higher acid concentration,stronger dehydration ability,and also higher selectivity of LGO.Heating during pretreatment process can further improve the selectivity of LGO,the highest LGO selectivity 82.6%was obtained by 5%phosphoric acid.Besides acid catalyst,sulfates also promoted the LGO generation from cellulose pyrolysis,and anion SO42-played main role.Catalytic pyrolysis of cellulose for preparation of LG and LGO was did in the fixed bed reactor.More pyrolysis factors were inspected,including pyrolytic carbon and temperature,comparing different catalysts and catalytic models,meanwhile catalytic conversion mechanism was explored.Experimental results proved that pyrolytic carbon which was constantly generated during pyrolysis process have promoted LG and LGO to a certain extent.However,if it was excessive,holes would be plugged and more secondary reactions occurred.Temperature is the key pyrolysis factors and relatively lower temperature was suitable for the production of LGO.Optimum temperature for LGO production catalyzed by phosphoric acid was 270℃,the best selectivity and yield were 77.67%and 1.98 wt%at this point.Acid catalysts and metal salt catalysts were compared,it was found that they all can promote LGO generation.Comparing catalytic models,in-situ catalytic model was better than ex-situ.Best LGO yield was 2.65 wt%through Fe2(SO4)3 in-situ catalysis.Transformation mechanism from cellulose to LG or LGO was cleared,and two ways competed against each other.When there was non-catalytic,thermal effects led to glycosidic bond fracturing directly and LG was generated directly.Under the condition of low temperature with catalysts,dehydration reaction occurred firstly,cellulose transferred into LGO precursor.After enol interconvert and dehydration,LGO was generated Reaction of open loop and broken bond occurred at any time,a small number of furfural and other small molecules were generatied,and pyrolytic carbon made a difference to two competitive ways.Carbon based solid acid catalyst was prepared using cellulose pyrolysis carbon and sulfuric acid,then it was applied in catalytic pyrolysis of biomass to test its performance.The results showed that its catalytic performance was superior and it was suitable for producing LGO.At 300 °C,selectivity of LGO was 46.1%from catalytic pyrolysis of cellulose,and 48.7%from pyrolysis of pine.Comparing liquid acid with carbon based solid acid catalysts,it was found that liquid sulfuric acid can significantly improve LGO selectivity to 59.1%,carbon based solid acid catalyst can significantly promote LGO yield to 1.12 wt%.New carbon based solid acid catalyst has some advantages,including low cost,easy recycling,green and environmental protection,so it has a promotive value.