Experimental Research On Liquefaction Of Rape Straw Under Plasma Electrolysis Reaction Condition

With the rapid development of the world economy,the energy crisis and environmental pollution caused by the massive consumption of fossil energy are imminent,and it is of great significance to find green and environmentally friendly alternative energy sources.Biomass,as a resource-rich renewable energy,could be transformed into clean fuels that are convenient for storage and transportation through biomass conversion technology.Its development and utilization are in line with the strategic direction of sustainable development in China.Among the many biomass conversion methods,biomass liquefaction is considered as one of the most promising biomass conversion methods at present,with broad development potential.However,many problems such as high energy consumption and low efficiency need to be solved urgently.Plasma electrolytic liquefaction technology is a liquefaction technology which combines plasma technology and solvent catalytic liquefaction technology.Without an external heating source,the liquefaction system is heated by accelerated collisions of ions under the action of electric field,the plasma electrolysis liquefaction process not only had a fast rate,but also low energy consumption.Moreover,the active free radicals generated in the liquefaction process can also effectively improve the quality of the liquefied product.In this paper,rape straw was used as biomass raw materials,polyethylene glycol 200 and glycerol were used as liquefaction agents,and sulfuric acid and sodium hydroxide were used as catalysts to carry out the experimental research on liquefaction of biomass by plasma electrolysis.Firstly,the experiment of biomass straw liquefaction by plasma electrolysis was carried out under sulfuric acid catalysis.The single factor method was used to explore the influence of liquefaction time,catalyst dosage,liquid-solid ratio and PEG200/glycerol volume ratio on the liquefaction process.On this basis,the central composite orthogonal experiment was designed and completed,and the optimization model of operation parameters was established.With the liquefaction rate as the goal,the optimal condition parameters for plasma electrolytic liquefaction of rape straw were obtained,and the liquefaction products were characterized and analyzed.Secondly,the plasma electrolytic liquefaction of rape straw was carried out under the catalysis of sodium hydroxide.Through the analysis of liquefaction products,the similarities and differences of liquefaction behaviors under different acid-base catalysis were compared.Finally,based on the influence of temperature,discharge non-thermal plasma on the liquefaction process and the influence of catalyst on the operating characteristics of the system,the reasons for the rapid liquefaction of rape straw under plasma electrolysis condition were explored,and the plasma electrolysis liquefaction technology was compared with the traditional liquefaction method.The main work and conclusions are as follows:(1)Experimental study on plasma electrolysis liquefaction of rape straw under sulfuric acid catalysis.The influence of different factors(reaction time,catalyst dosage,liquid-to-solid ratio and PEG200/glycerin volume ratio)on the process of plasma electrolysis liquefaction of rape straw were investigated by single factor experiment.Condition combination:The optimal condition obtained by response surface method as follows:reaction time of 5.82min,catalyst dosage of 2.2wt%,liquid-solid ratio of 7.3,liquefaction agent volume ratio 3.5,and the maximum liquefaction rate was 98.3%under optimal conditions.The results of response surface analysis showed that the interaction between catalyst×liquid-solid ratio was the greatest,and the amount of catalyst in the single factor had the greatest influence on the liquefaction rate.The characterization analysis of liquefaction products showed that dehydration,decarbonylation and decarboxylation occurred in the process of biomass liquefaction.The high calorific value of liquid products was 20.67 MJ/kg,the calorific value of solid residues was 8.57 MJ/kg,and the liquid products were rich in hydrocarbons,ethers,aromatics and esters.(2)Experimental study on plasma electrolysis liquefaction of rape straw under alkali catalysis.When sodium hydroxide was used as the catalyst,the plasma electrolysis liquefaction technology could also achieve the rapid liquefaction of rape straw.The temperature rose rapidly during the liquefaction reaction,and the temperature rose to 230°C in 3 minutes.The liquefaction rate of rape straw reached 85.6%under the reaction conditions of reaction time 12 min,sodium hydroxide dosage 8.0wt%,liquid-solid ratio 7:1,PEG200/glycerol 3:1.The pulse energy of discharge under alkali catalysis was higher than that under acid catalysis,which led to the temperature of solution system higher than that under acid catalysis.But compared with acid catalysis,the catalytic effect of H~+was better than that of OH~-,so the reaction time was longer,the amount of catalyst was higher,and the liquefaction effect was poor under alkali catalysis.(3)The analysis of rape straw liquefaction products under alkali catalysis showed that the elements of liquefaction products under acid-base catalysis were basically the same.The high calorific value of liquid products under alkali catalysis was 22.80 MJ/kg,and the high calorific value of solid residues was only 8.61 MJ/kg.Infrared analysis of liquid products showed that the main peak values of liquid products under acid-base catalysis were basically the same,but the peak intensity was slightly different.Under alkali catalysis,the pH value of the solution increased first and then decreased,and the pH value was 7.52 after 12 min.The liquid products under alkali catalysis were analyzed by GC-MS(gas chromatography mass spectrometry),and the results showed that the composition of the products was basically the same as that under acid catalysis,but the relative content of different compounds changed.The reason was that higher liquefaction temperature accelerated the oxidation of alcohols under alkaline conditions,and acidic compounds reacted further with alcohols to form esters.(4)Research on the cause of rapid liquefaction of rape straw under plasma electrolysis conditions.The results showed that adding a small amount of sulfuric acid to the solution during the plasma discharge reaction could achieve a rapid rise in the temperature of the liquefaction system,and the solution temperature was basically stable at 190.2°C after 4 min.Through traditional oil bath liquefaction tests at different temperatures,it was found that the increase of temperature could greatly reduce the reaction time.The ions in the solution performed regular thermal motion under the action of electric field,and collided with polar molecules to make the temperature of the solution rise rapidly.A large number of free radicals were generated during the discharge reaction,which not only promoted the liquefaction of biomass straw,but also helped to improve the quality of liquefaction products.Compared with traditional liquefaction methods,plasma electrolysis liquefaction technology not only had low energy consumption,fast reaction rate and simple operation,but also could obtain a higher liquefaction rate under normal pressure conditions.