Preparation Of Distiller’s Grains Biochar And Its Au-supported Catalyst And Selective Catalytic Conversion Of Benzyl Alcohol

Distiller’s grains,a type of biomass resource,is a by-product of Chinese alcohol industry.It does have some drawbacks:high acidity and a tendency to spoil and deteriorate if it is stored improperly or for too long before use,and under those circumstances it can cause serious environmental pollution and resource waste.Therefore,realizing the recycling of DGs is an extremely effective way to reduce the risk of environmental pollution.As an important organic intermediate,benzaldehyde is widely used in medicine,fragrances,dyes,agrochemicals and other industries.However,traditional preparation methods of benzaldehyde have many problems,such as long process,difficult product separation,waste discharge and environment pollution.Then,the development of a green and efficient heterogeneous catalyst for benzyl alcohol oxidation is of great economic and environmental significance.Firstly,the Moutai-flavored dried distiller’s grains（DDGs）was selected as raw material and characterized by proximate and ultimate analysis techniques to analyze its physicochemical properties.The pyrolysis kinetics data of DDGs under four heating rates(10,20,30 and 40 K min^-1)were obtained by non-isothermal thermogravimetric analysis（TGA）.Friedman isoconversion method was used to process the kinetic parameters to analyze the pyrolysis kinetic behavior.Physicochemical properties showed that DDGs samples had higher volatile matter（89.4 wt.%）,carbon content（50.7 wt.%）and HHV value(20.4 MJ kg^-1).Pyrolysis kinetics results showed that the effective activation energy（E_a）of DDGs pyrolysis process changed significantly with the change of conversion rate,and the variation of E_a could be divided into three stages,which corresponded to the thermal decomposition of hemicellulose,cellulose and part of lignin,and remaining lignin.Compared with the decomposition temperature ranges of bio-polymer components in typical lignocellulosic biomass,the corresponding decomposition temperature ranges of DDGs components shifted to the lower temperature.Overall,the findings reveal that DDGs are a potentially viable feedstock for sustainable energy recovery through pyrolysis.Secondly,metal-free carbon catalyst with high oxygen content（Z-X,HZ-X and HZO-X）were prepared using DDGs as raw biomass combined with hydrothermal pretreatment and Zn Cl₂chemical activation for the oxidation of benzyl alcohol to benzaldehyde.Based on the excellent pyrolysis kinetics properties,the effect of pyrolysis temperature（400～800℃）on the material properties were also discussed.The structure,morphology and surface properties of carbon catalyst with different preparation methods and pyrolysis temperatures were analyzed by FT-IR,Raman,N₂ adsorption-desorption,SEM,Zeta potential and XPS characterization.Then the main active sites of the carbon catalyst in benzyl alcohol oxidation were observed.Results showed that with the introduction of hydrothermal process,the types of oxygen functional groups in carbon catalyst did not change,but the content increased significantly,indicating the effectiveness of Zn Cl₂impregnation treatment combined with hydrothermal process.BET results showed that hydrothermal pretreatment could assist in improving the formation of mesoporous structure of activated carbon,because it provides more oxygen functional groups in pyrolysis precursor and enhanced the activity of Zn Cl₂,thereby increasing the porosity of carbon materials.And with the pyrolysis temperature increased,the specific surface area and average pore size of the materials showed an increasing trend.The catalytic activity of the metal-free carbon catalyst after hydrothermal pretreatment was also better than that of the carbon catalyst without the participation of the hydrothermal process,proving that the high oxygen species content introduced by the hydrothermal pretreatment may provide more active sites for the carbon catalyst.The correlation analysis between XPS surface quantitative analysis and benzaldehyde yield indicated that phenolic hydroxyl group may be the main active site for benzyl alcohol oxidation with metal-free carbon catalyst.Finally,based on the carbon materials synthesized in the previous chapter,Au/C catalyst（Au/Z-X,Au/HZ-X,Au/HZO-X）were obtained by using the sol immobilization method to solidify the Au nanoparticles（Au NPs）on carbon supports.The crystal structure,surface properties and particle distribution of the prepared Au catalyst were characterized by FT-IR,XRD,TEM,XPS,BET,ICP techniques,and the possible mechanism of benzyl alcohol oxidation was proposed.The characterization results indicated that C-O group plays a major role in the deposition of Au on carbon support without hydrothermal process（Z-X）,while C=O and-OH are also involved in the deposition of Au NPs on carbon support with hydrothermal process（HZ-X,HZO-X）due to the increasing content of oxygen species in the carbon material.TEM results showed that the sizes of Au NPs varied from 8.3～10.1 nm（Au/Z-X）,7.4～8.9 nm（Au/HZ-X）and 5.7～7.9 nm（Au/HZO-X）,respectively.Combined with ICP,BET characterization,the carbon support with high oxygen content was more conducive to the anchoring of Au NPs,and high specific surface area and well-developed pore structure of carbon support was more favorable for the dispersion of Au NPs,that is,the smaller size of Au NPs.The oxidation results showed that smallest Au NPs size had the highest catalytic activity on Au/HZO-700 catalyst(TOF of 851.7 h^-1).The optimization of reaction condition showed that the yield of benzaldehyde achieved the highest（57.6%）when the catalyst dosage was 100 mg,the reaction temperature and time was 70℃,4 h,respectively.The reusability test demonstrated the excellent cycling performance,and the reactivity substantially declined upon the 4th run.