Catalytic Pyrolysis Of Cellulose With Ionic Liquid At Low Temperature

With the increasing consumption of non-renewable energy resource in the world,the ecological destruction and greenhouse gas CO2 are accelerated by the fossil fuel exploitation and usage contribution.So it is necessary to satisfying the environmental concerns through developing the alternative energy sources and high-efficiency energy-saving technology.As a kind of renewable,high heating value and few environment pollution carbonic resources,biomass would substitute gradually part of fossil fuel,which is significant for relieving the energy crisis and reducing the environmental pollution.The pyrolysis technology of biomass can meet the development demand and has the prospect in biomass recycle utilization because of its high transformation rate,generation of high heating value fuel gas,fuel oil and high value-added chemical materials.However,researches about the pyrolysis process of biomass and the evolution of pyrolysis product were not adequate.If the evolution law of the biomass pyrolysis products is mastered accurately,there is the possibility of producing the valuable fuel and chemical materials selectively according to the character of the products,which is significant for the development and application of the pyrolysis technology in our country.Biomass is a complex mixture of cellulose,hemicellulose and lignin.Cellulose is the main component of biomass and reached the content from 35%to 50%.Due to the large degree of crystalline and hydrogen bond net structure of inter-and intra-molecular,cellulose is hardly dissolved in major solvents.Therefore,it become the main constraint in biomass conversion and the biomass pyrolysis is greatly influenced by the cellulose pyrolysis characteristics.The new "Green Solvent" room temperature ionic liquids have aroused increasing interest in the dissolution and conversion of cellulose for their unique chemical and physical properties such as strong solvation ability,undetectable vapor pressure,relatively high thermal stability and designability.Because cellulose was dissolved well in ionic liquids and ionic liquids are thermal stable,so ionic liquids can be used as the homogeneous phase catalytic solvent and excellent media for heat transfer,which is beneficial to achieving the cellulose pyrolysis law at different temperatures.In our research,the ionic liquid with best cellulose dissolution at different temperatures was obtained through the experiments of dissolution of cellulose in ionic liquids,the stability of ionic liquids and the structures of ionic liquids before and after pyrolysis.The chosen ionic liquid was applied in the pyrolysis of cellulose and the distribution of the pyrolysis products was analyzed,forming the evolution law of pyrolysis products.The main results were as follows:(1)Based on the structures of ionic liquids and cellulose,three ionic liquids 1-butyl-3-methylimidazole acetate,1-butyl-3-methylimidazole trifluoromethanesulfonate and 1-butyl-3-methylimidazole bromide with strong hydrogen bonds combination were synthesized and characterized by Fourier transformed infrared spectroscopy.The performance of ionic liquid catalytic pyrolysis system was investigated through the thermal stability of ionic liquid and the IR change of composition and structure of 1-butyl-3-methylimidazole trifluoromethanesulfonate before and after pyrolysis.(2)In the 1-butyl-3-methylimidazole trifluoromethanesulfonate,cellulose was pyrolyzed during ten temperatures of 140?,180?,220?,240?,260?,280?,310?,340?,370?and 400?.The pyrolysis products of gas phase,liquid phase and solid phase were characterized by gas chromatography,gas chromatography-mass spectrometry,scanning electron microscope,x-ray diffraction and Fourier transformed infrared spectroscopy.The results showed that,the main pyrolysis products of cellulose were alcohols,phenols,ketones,furans,esters and aromatic compounds,coupling with the production of small-molecule gases such as CO2,CO and H2.From the SEM picture,we can see the the cellulose was more porous,with higher surface area and more holes as the temperature increased.From the temperature of 260? the scales were appeared,then shedded and conglomerated.Untill 400?,the cellulose was completely cracked without visible fibers,indicading the cellulose was strongly destroyed and wholly pyrolyzed.The analysis of X-ray diffraction showed that the crystalline of cellulose after pyrolysis was changed and new diffraction peaks were appeared.Thus,the crystal structure of cellulose was modified due to the rearrangement of crystalline region and amorphous region.The analytical characterization of FT-IR illustrated that the stretching vibration of O-H and C-H of cellulose molecular weakened,indicating the net structure of hydrogen bonds in cellulose were broken and O-H was reacted.In addition,the vibration of C=C,ketone group C=O,carboxyl group C=O were appeared corresponding to the formation of alkene,ketone and carboxylic acid.(3)The possible cellulose pyrolysis products evolution law was as following.With the catalysis of ionic liquid,the cellulose was transformed into levoglucose and chain glucose after dehydration reaction.Then the chemical bonds of levoglucose and chain glucose were broken and rearranged.The chain glucose may have four convertion routes to generate 4-hydroxy-butanoic acid,propionic acid ethenyl ester,3-pentanol,2-ethyl-1-hexanol,hexadienoic acid.The levoglucose may have five convertion routes to generate cycloheptanemethanol,2-butyl-1,3-cyclopentanedione,5-methyl-1,5-hexadien-3-ol,1-acetoxyl-2-butanone,2-furanmethano,5-methyl-2-furancarboxaldehyde,2-furancarboxylic acid-2-tetrahydrofurylmethyl ester,butyrol-actone,3-methyl-cyclohexanone,3-methyl-furan,succinic anhydride,4-methyl-5H-furan-2-one,3,5-dimethyl-2-furanone,3-methyl-2-pentyl-2-cyclopenten-1-one,2-methy 1-2-cyclopenten-1-one,3-methyl-2-cyclopenten-l-one.2-oxo-3_cyclopentene-l-acetaldehyde,3-methyl-1,2-cyclopentanedione.