| Biomass can be used as a good substitute for petrol fuel when it is converted into liquid clean fuel.The bio-oil produced by biomass rapid pyrolysis liquefaction is difficult to be directly used in the engine due to their defects such as high oxygen content,low heating value and strong acidity,so it needs to be upgraded.Catalytic hydrogenation can effectively reduce the oxygen content,improve the heating value and increase the stability of bio-oil,which has been widely concerned,and has become the research focus in the field of bio-oil upgrading in recent years.At present,the main obstacle of the catalytic hydrogenation of bio-oil is the contradiction between the thermal sensitivity of bio-oil and the harsh hydrogenation conditions of high temperature and high pressure.Gas-phase discharge plasma has low-temperature reaction activity,and gas-phase discharge non-thermal plasma reaction technology provides a new feasible way to solve the above contradiction.In view of the problems such as coking and deactivation of catalyst and blockage of reactor in the process of catalytic hydrogenation of bio-oil,a needle-plate dielectric barrier discharge(DBD)hydrogenation reactor was designed based on the working principle of gas-phase discharge plasma reaction,and the effects of peak load voltage,air gap distance,liquid phase height and number of electrodes on the working characteristics of the reactor were discussed.Then,research on bio-oil hydroupgrading was carried out with simulated bio-oil as raw material and hydrogen as hydrogen donor.Through single factor experiments,the variation of deoxidation rate and high hearting value(HHV)of simulated bio-oil with working voltage,gas flow rate and reaction time was studied.With Box-Behnken center combination orthogonal experiment and response surface analysis method were adopted,the optimization model of working parameters was established.The effect of hydrogenation on high heating value,p H value,kinematic viscosity and evaporation characteristics of bio-oil was evaluated.Based on the comparative analysis of simulated bio-oil and its hydrogenation products,the chemical reaction pathways and mechanisms of each component were analyzed.The main work and conclusions are as follows:(1)Research on design and working characteristics of gas-phase discharge plasma hydrogenation reactor.Based on the comparative analysis of common DBD structure features,a needle-plate DBD hydrogenation reactor was designed,and the effects of peak load voltage,air gap distance,liquid phase height and number of electrodes on the working characteristics of the reactor were discussed by emission spectrum diagnosis method and Lissajous figure method.The results showed that the needle-plate DBD hydrogenation reactor had obvious series resonance characteristics,and the resonance frequency decreased gradually with the increase of input voltage.With the increase of peak load voltage,the equivalent capacitance of air gap(Cg)decreased and equivalent capacitance of dielectric(Cd)increased.With the increase of air gap distance,under the same peak load voltage,the equivalent capacity of air gap(Cg)and the equivalent capacity of dielectric(Cd)decreased.Reduced electric field intensity(E/n)increased approximate linearly with the increase of the peak load voltage.The power injection efficiency decreased with the increase of the peak load voltage,indicated that with the increase of peak load voltage,the voltage lost by external circuit increased,and the energy efficiency decreased.As the number of electrodes increased,the number of discharge channels increased,the chance of collision between hydrogen molecules and high-energy electrons increased,so the electron density in discharge reaction space increased.(2)Experimental study on hydrogenation of simulated bio-oil under gas-discharge plasma reaction conditions.According to the components and contents of bio-oil obtained from rice husk pyrolysis,model compounds such as guaiacol,furfural and hydroxyacetone were used to prepare simulated bio-oil,so as to reduce the difficulty of bio-oil hydrogenation mechanism analysis.The results showed that the high heating value and deoxidation rate of simulated bio-oil increased rapidly and then decreased slowly with the increase of working voltage and gas flow rate,and increased first and then stabilized with the increase of reaction time.With the deoxidation rate as the index,the optimization model of working parameters for bio-oil hydrogenation was established,and the optimal working parameters were obtained as follows: working voltage of 14 k V,gas flow rate of 78.69ml/min,reaction time of 117.90 min,and the maximum deoxidation rate was 32.41%.At the same time,three groups of bio-oil hydrogenation experiments were carried out with rice husk pyrolysis bio-oil as raw material,and the average deoxidation rate was 32.15%.Compared with the 31.62% deoxidization rate of simulated bio-oil,the error was smaller,which confirmed the feasibility of using simulated bio-oil to replace bio-oil for hydrogenation research.Under the optimal working parameters,the energy consumption of the device was 2.44 k W·h/kg,and the energy conversion rate was 40.87%.(3)Research on the effect of hydrogenation on the physical and chemical properties of bio-oil.The results showed that after hydrogenation,the high heating value of simulated bio-oil increased from 25.78 MJ/kg to 32.69 MJ/kg,increased by 26.80%,the oxygen content decreased and the energy density increased.The p H value increased from 3.67 to 4.83,the acidity decreased,and the corrosiveness decreased.The kinematic viscosity increased from 4.30 mm2·s-1 to 4.94 mm2·s-1.Thermogravimetric comparative analysis of simulated bio-oil and its hydrogenation products showed that the evaporation characteristics of simulated bio-oil were improved after hydrogenation.Thermogravimetric comparative analysis of B0 and B10 also showed that B10 were easier to be evaporated,and the combustion performance were improved when the diesel was blended with hydrogenated simulated bio-oil.(4)Analysis of chemical reaction mechanism of bio-oil hydrogenation under gas-phase discharge plasma reaction conditions.The results showed that the conversion rates of butyric acid,butanol,furfural,hydroxyacetone,ethyl acetate and guaiacol were 77.56%,81.60%,76.49%,78.77%,58.80% and 36.74% respectively,and the main hydrogenation products were butyl butyrate,butane,furfuryl alcohol,isobutyraldehyde,acetic acid and catechol respectively.It showed that acids,alcohols,aldehydes and ketones are relatively easy to be hydrogenated,while hydrogenation of esters and phenols are relatively difficult.Under gas-phase discharge plasma reaction conditions,hydrogen was ionized to generate highly active species required for reactions such as hydrogen radicals,positive and negative ions,and high-energy electrons.The inelastic collision between high-energy electrons and simulated bio-oil molecules led to the breaking of chemical bonds such as C=C,C=O with low bond energy in simulated bio-oil molecules,and then the broken chemical bonds combined with highly active hydrogen radicals to form hydrogenation products.The main chemical reaction types are unsaturated bond hydrogenation saturation,hydrodehydroxylation and hydrodecarboxylation. |
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