Experimental Study On Microwave-induced Hydrodeoxygenation Upgrading Of Bio-oil

In the face of limited storage of fossil fuels and increasing environmental pollution,there is an urgent need to find an environmentally friendly and renewable alternative energy source.The bio-oil produced by biomass pyrolysis not only helps to alleviate the energy crisis,but also reduces CO2 emissions,which has caused special concern.However,the primary bio-oil produced by pyrolysis has low quality,especially high oxygen content,which makes the bio-oil cannot be directly used as a high-quality fuel.Therefore,the primary bio-oil must be upgraded to reduce the oxygen content.Hydrodeoxygenation is a promising and effective method.However,hydrodeoxygenation is usually carried out by hydrogenation,and requires high.temperature and high pressure reaction conditions,high cost and harsh reaction conditions.Therefore,there is an urgent need to develop an effective method for hydrodeoxygenation under mild conditions.The interaction of microwave with metal/special strong absorbing medium produces strong thermal and plasma effects,which greatly promotes the pyrolysis and chemical reaction processes.Therefore,this paper develops an efficient bio-oil upgrading method using the special action mode of microwave and metal/strong absorbing medium.Firstly,the microwave metal-assisted pyrolysis of peanut shells and the coupling of HZSM-5 catalyst were used to carry out secondary upgrading of the generated pyrolysis gas.The effects of pyrolysis method,catalyst bed temperature and microwave power on product yield and chemical composition in bio-oil were studied.Secondly,the bio-oil model guaiacol was used as the research object,and methanol and tetrahydronaphthalene were used.Hydrogenation agent was studied to study the microwave-induced catalytic guaiacol hydrodeoxygenation mechanism of absorbing medium.The effect of hydrogenation agent type,absorbing medium and hydrogenation agent on the hydrodeoxygenation of guaiacol was investigated by using molecular sieve as catalyst.Pd/ZrO2 was used as catalyst to investigate the catalytic hydrodeoxygenation of guaiacol.In the end,the bio-oil model phenol was used as the research object,and the medium-enhanced coupled Pd-based catalyst was used to carry out the microwave-induced phenol mild(normal pressure,200 ?)hydrogenation upgrading study.The effect of hydrogen flow rate and the different carriers(ZrO2,CeO2 and CeZrO2)on the hydrogenation of phenol were investigated,inferring the hydrogenation pathway and reaction mechanism.The results showed that compared with conventional pyrolysis,microwave metal-assisted pvrolysis promoted the yield of aromatic hydrocarbons,which could be further enhanced by applying ex situ HZSM-5 bed.The catalyst bed temperature has a significant effect on the product yield,bio-oil chemical profile and coke deposits on catalyst.The bio-oil yield reached its maximum value(5.6wt.%)at 600?,with the proportion of oxygen-free hydrocarbons of 67%and coke deposits of 0.6wt.%.With the further increase of temperature to 700?,the proportion of oxygen-free hydrocarbons increased to 77%,that of coke deposits decreased to 0.5wt.%,and that of the bio-oil yield decreased to 4.7wt.%.Besides the catalyst bed temperature,higher microwave power led to higher bio-oil yield;however,the proportion of oxygen-free components decreased slightly owing to the reduction in contact time.Through analysis of bio-oil components,it was found that phenolic substances such as guaiacol and phenol were most difficult to convert before and after upgrading.Therefore,it is necessary to conduct separate studies on the conversion of guaiacol and phenol.The hydrogenation of guaiacol can be achieved by using Pd catalyst,and the products are mainly cyclohexanol and cyclohexanone.Compared with conventional heating,the conversion of phenol and product yield under microwave heating conditions are significantly improved.From the influence of catalyst carrier on the product,the catalytic product of ZrO2 was mainly composed of cyclohexanone.The yield of cyclohexanol was improved by ZrCeO2 as carrier product,and cyclohexanone was still the main product.The catalyst product was supported by CeO2.Mainly cyclohexanol.The product yield reached a maximum of 76.47wt.%(cyclohexanol accounted for 44.16wt.%;cyclohexanone accounted for 32.21wt.%)at a hydrogen flow rate of 200 ml/min(Pd/CeO2).Compared with conventional heating,the conversion of phenol under microwave heating was up to 94.93%(Pd/CeO2),while the conversion of phenol by electric heating was up to 72.17%(Pd/ZrCeO2).The liquid products were mainly cyclohexanol and cyclohexanone;the products using ZrO2 were mainly cyclohexanone,and the products using CeO2 were mainly cyclohexanol;hydrogenation product yield reached 76.47wt.%when hydrogen flow rate was 200ml/min(Pd/CeP2)(cyclohexanol accounted for 44.16wt.%,cyclohexanone accounted for 32.21wt.%).The above studies show that the special effects of microwave and metal/strong absorbing media have a significant effect on the upgrading of bio-oil and its compounds,which provides a new idea for further research on bio-oil upgrading.