Characterization of pyrolytic lignins with different activities obtained from bio-oil

Characterization of pyrolytic lignins with different

activities obtained from bio-oil☆

Furong Leng,Yurong Wang,Junhao Chen,Shurong Wang*,Jinsong Zhou,Zhongyang Luo

【摘 要】A B S T R A C T Pyrolytic lignin,the water-insoluble fraction in bio-oil,often shows a high content and has strong intermolecular interactions with other compounds in bio-oil.In order to obtain pure pyrolytic lignin and facilitate the utilization ofaqueous phase obtained from water extraction of bio-oil,methanol–water extraction method was employed to further separate the bio-oil water-insoluble phase in this paper.Different technologies,including Fourier transform infrared spectroscopy,gel permeation chromatography,and nuclear magnetic resonance,were adopted to characterize the structures of pyrolytic lignins with different activities obtained through this method.Both the heating value and the polymerization degree of high-molecular-weight pyrolytic lignin were higher than those of low-molecular-weight pyrolytic lignin.The molecular weight distribution of high-molecular-weight pyrolytic lignin was relatively wider,among which the contents of dimers to pentamers all accounted for 12%–18%,while the low-molecular-weight

pyrolytic

lignin

mainly

consisted

of

trimers(75.38%).The pyrolytic lignins had similar basic structures,both of which contained syringyl and guaiacyl units,whereas the low-molecular-

weight pyrolytic lignin had more abundant syringyl units,reactive carbonyl groups and hydroxyl groups.Meanwhile,thermogravimetric study revealed that the final char residue yield of low-molecular-weight pyrolytic lignin was lower than that of high-molecular-weight pyrolytic lignin.

【期刊名称】中国化学工程学报（英文版） 【年(卷),期】2017(025)003 【总页数】6

【关键词】Keywords:Bio-oil Pyrolytic lignin Separation Characterization

1.Introduction

As a renewable liquid fuel from biomass pyrolysis,bio-oil is expected to replace fossil fuels to deal with energy and environmental crisis[1].However,the crude bio-oil can only be used as a low-grade fuel due to its inferior properties including high oxygen content,low heating value,high acidity,and thermal sensitivity[2,3].Therefore,bio-oil must be upgraded before achieving its high-grade utilization.The common upgrading technologies include catalytic hydrogenation,catalytic cracking,catalytic reforming,catalytic esterification,and supercritical extraction[4,5].As the composition of bio-oilis complicated,single upgrading technology cannot realize the efficient conversion of overall components in bio-oil.In addition,it may reduce economic efficiency when bio-oil is directly upgraded since it has some valuable

compounds.The pre-separation of bio-oil can provide appropriate fractions for subsequent extraction of valuable chemicals and high-efficiency upgrading.Researchers have found that acids and ketones can be converted to polyalcohols,hydrocarbons and alkene under mild conditions with high catalyst stability,whereas sugars and phenols are easy

to

cause

catalyst

deactivation

due

to

carbon

deposition[6,7].Molecular distillation of bio-oil can enrich different chemical families with distinct properties into various bio-oil fractions,which obtains the distilled fraction with high reactivity and the heavy fraction rich in sugars and phenolic compounds[8,9].The distilled fraction can be used to produce hydrogen or bio-gasoline with appropriate upgrading technology,while the heavy fraction is used to produce emulsion fuel or to extract valuable chemicals[10–13].In addition,the separation of large-molecular compounds from bio-oil can be realized based on their distinct properties.Sugars can be dissolved and separated directly using water owing to their strong hydrophilicity[12,14].Pyrolytic lignin(PL),the fragment produced from lignin pyrolysis,is mainly composed of waterinsoluble phenolic polymers,with a content up to 30 wtosed on crude bio-oil[15].It can be converted to monophenols through depolymerization for further upgrading,and can also be used in the synthesis of chemicals like phenolic resin,adhesive,and carbon fiber[16,17].It's worth noting that