| Bio-oil can be separated naturally by aging,with the upper layer being the water phase and the bottom layer being the oil phase.However,the aqueous phase of bio-oil(APBO)contains a lot of water(80-90 wt.%)and a small number of organics,which limits its upgrading and application.If APBO is used as the reaction medium for biomass hydrothermal carbonization(HTC),it may alter the HTC reaction of biomass and affect the properties of hydrochar.In this paper,the APBO was used as a reaction solvent for cellulose and lignin to investigate changes in the yield and properties of hydrothermal products,and to infer possible reaction pathways.The main results are as follows:1.The HTC of cellulose was studied using APBO/water as the reaction solvent at temperatures from 180 to 260 ℃.The results showed that the organics such as sugars,sugarderivatives and phenolics in APBO could adsorb on the surface of cellulose and suppress the hydrolysis at lower temperature(i.e.180 °C),while they could cross-polymerize with cellulose derivatives at higher temperatures(i.e.220 or 260 °C).Compared with the hydrochar obtained in water,the APBO remarkably enhanced hydrochar yield by 11.3% and resulted in the abundant formation of aliphatic structures,making the hydrochar carbon and hydrogen-rich but with a lower thermal stability.In addition,the involvement of the APBO organics interfered with the nucleation of the sugars/furans and inhibited the formation of the spheres with a hydrophilic shell and a hydrophobic core,resulting in the formation of an irregularly shaped hydrochar.Such a process also made the hydrochar rather hydrophobic,while the combustion performance was highly improved,exhibiting a lower ignition temperature.2.Subsequently,the HTC of lignin in the APBO was studied.The results indicated that furans,aldehydes,ketones,sugars and the organics with π-conjugated structure in APBO crosspolymerized with both the lignin and the organics from hydrolysis of lignin.The interaction caused by this cross-polymerization reaction is greater than that of cellulose,greatly improving the energy retention rate,resulting in a yield of lignin derived hydrochar to exceed 100%.In addition,the surface properties,elemental composition and thermal stability of the lignin derived hydrochar obtained from lignin in the APBO are similar to those of cellulose derived hydrochar.3.The co-HTC of bio-oil of the same origin with poplar sawdust was conducted at 180 to260 ℃.The results showed that the HTC in a water medium containing 10% bio-oil could enhanced the yield of hydrochar by ca.36% at 220 or 260 ℃ through the cross-polymerization of the sugar-derived furans and ketones/aldehydes as well as the phenolics in bio-oil with the sawdust-derived organics.Furans/sugars in bio-oil showed much more contribution to the increase of hydrochar yield than the phenolics like guaiacol.The highly reactive organics in bio-oil even could react with the crystal region of cellulose at 180 ℃,and affected property of hydrochar at especially the higher temperatures by promoting deoxygenation,enhancing carbonization,eliminating polar functionalities like-OH,retaining C=O for continued polymerization,etc.The co-existence of aliphatic organics and phenolics in bio-oil renders the simultaneous formation of highly volatile fraction and aromatic structures in the hydrochar.These created the carbon-rich hydrochar with higher crystallinity,lower hydrophilicity and improved comprehensive combustion index. |
PDF Full Text Request