Research On Upgrading The Biomass Pyrolysis Oil Via Esterification Combined With Alkylation And Its Combustion Application

Biomass pyrolysis oil as a new liquid fuel with great potential attracts the attention of many scholars.However,due to its disadvantages of superfluous moisture,strong corrosiveness and easy polymerization,it may cause problems such as difficult ignition,corrosion of fuel pipeline and blockage of injector nozzle when it is fed to a vehicle.Therefore,in order to raise the fuel property of biomass pyrolysis oil for efficient application in engines,it is necessary to adopt appropriate processing steps.In this paper,dichloromethane was used to remove water from the biomass pyrolysis oil to obtain crude bio-oil.Then,based on the catalytic esterification of crude bio-oil with n-butanol,2-methylfuran was introduced for alkylation to obtain the upgraded bio-oil.The relative contents of main components of the crude bio-oil and upgraded bio-oil were compared in order to optimize the process parameters and deduce the main reaction mechanisms.Fuel blends B5,B10 and B15 were prepared by mixing 5%,10%and15%volume fractions of upgraded bio-oil with diesel.The main physicochemical properties of biomass pyrolysis oil,upgraded bio-oil and fuel blends were analyzed,and their volatilization and oxidation performances were evaluated.The applicability of the upgraded bio-oil was explored based on the engine performances tests.The main research contents and achievements are as follows:(1)Effects of technology parameters of catalytic esterification combined with alkylation which was designated to upgrade the fuel quality of biomass pyrolysis oil was studied.The experimental devices of dehydration pretreatment and catalytic esterification combined with alkylation were constructed.The compositions of crude bio-oil and upgraded bio-oil were determined via GC-MS.The single factor method and response surface method were respectively adopted to investigate the effects of temperature,alcohol/oil mass ratio,2-methylfuran addition and catalyst content on upgrading efficiency.For 50 g crude bio-oil sample,the catalytic esterification combined with alkylation achieved the best effect after 4 h under the temperature of 100?,the alcohol/oil mass ratio of 0.95,the 2-methylfuran addition of 21.74 g and the catalyst content of 9.27%.The contents of unstable acids and aldehydes with ketones of crude bio-oil decreased by 85.0%and 80.5%respectively after upgrading,and converted into esters and ethers which significantly increased to 9.6%and 37.8%respectively.The carbon number of the upgraded bio-oil was basically located in the range of C5~C16,while that of the alkylation product was in the range of C11~C16.(2)The physicochemical properties of biomass pyrolysis oil were measured,and its evaporation and oxidation performances were evaluated based on thermogravimetryic experiments.The physicochemical parameters such as acid value,viscosity and low calorific value of biomass pyrolysis oil,upgraded bio-oil and fuel blends(B5,B10 and B15)were measured and calculated via appropriate experiments or from empirical formulas.Compared with biomass pyrolysis oil,the acid value and viscosity of the upgraded bio-oil decreased by82.7%and 16.7%respectively,while its low calorific value increased by 53.1%.The acid values and viscosities of B5,B10 and B15 increased in sequence,while their low calorific values presented the opposite trend.The evaporation and oxidation performance of several fuels were determined,evaluated and analyzed based on thermogravimetryic experiments.Compared with biomass pyrolysis oil,the initial temperature of weight loss of the upgraded bio-oil increased by 6.2?,while its final temperature of weight loss decreased by 5.8?.At high temperature,the upgraded bio-oil formed the less carbon deposition than the biomass pyrolysis oil.Compared with diesel,the initial temperatures of weight loss of B5,B10 and B15 decreased by 1.9?,4.0?and 6.6?respectively,while their final temperatures of weight loss increased by 1.6?,3.5?and 5.3?respectively.On average,the evaporation and oxidation processes of fuel blends in low temperature region were accelerated,however,their combustion in high temperature region was slightly slowed down.(3)Economy characteristics of fuel blends containing different fractions of upgraded bio-oil were evaluated.The equivalent specific fuel consumptions and effective thermal efficiencies of Diesel,B5,B10 and B15 at 1800 r/min were analyzed.Under the identical load conditions,increasing the ratio of the upgraded bio-oil in fuel blends lead to a gradual deterioration in the equivalent brake specific fuel consumption as well as the effective thermal efficiency.This was mainly because some volatile components of low boiling point with the large latent heat of vaporization could reduce the temperature in cylinder prior to combustion.Moreover,some heavy components hindered the coumbstion process,which delayed the heat release,extended the combustion duration and decreased the heat utilization rate released by combustion.In addition,at the low load,the lower temperature in cylinder was enlarged the effect of the non-flammable components in fuel blends to extend combustion duration,and correspondingly the heat release phase was far from the top dead center.Therefore,the low load had a large difference in the equivalent specific fuel consumptions and effective thermal efficiencies of four fuels compared with the high load.(4)Combustion and heat release characteristics of fuel blends containing different fractions of upgraded bio-oil were analyzed.The in-cylinder pressure and instantaneous heat release rate of Diesel,B5,B10 and B15 under different loads at 1800 r/min were measured and calculated respectively.Under the identical load conditions,with the increase of upgraded bio-oil's fraction in fuel blends,the ignition timing was advanced,and hence,the ignition delay was reduced.The initial peak of heat release and the first peak of pressure decreased in sequence due to the burning of the first-injection fuels,while the main peak of heat release and the second peak of pressure,which corresponded well to the burning of the main-injection fuels,rose in sequence.This was mainly because some flammable components with long carbon chain in the blended fuels led to an advance in the combustion.Though the first-injection fuels brought about a low initial heat release peak,it effectively boosted the basic temperature in cylinder and promoted the mixing of the main-injection fuels with air and intensified the following combustion.In addition,some volatile components of low boiling point in fuel blends were beneficial to forming more combustible mixtures,and the residual unburned first-injection fuels proceeded to oxidize and combust coupled with the burning of the main-injection fuels.On account of strategies for optimal combustion under different loads,the combustion phase at the 50%load was about 10°CA later than that at the 100%load,and a higher first-injection fuel amount was adopted,which corresponded to a higher initial peak in the instantaneous heat release rate.(5)Effects of the addition ratio of upgraded bio-oil in fuel blends on emissions were interpreted.The exhaust emission performances of Diesel,B5,B10 and B15 under different loads at 1800 r/min were measured.Under the same load conditions,with the increase of the fraction of upgraded bio-oil,the HC,CO and soot emissions of B5,B10 and B15 increased in sequence,while the NO_x emissions ascended first and then descended.Among them,B5 and B10 produced lower HC,CO and soot emissions than diesel,while B15 presented the opposite trend;Nevertheless,B5,B10 and B15 emitted more NO_x than diesel.On the one hand,the oxygen-containing components in the fuel blends improved the complete degree of oxidation reaction during combustion process,on the other hand,non-flammable components slowed down the combustion and oxidation speed to reduce the temperature in cylinder and extend the combustion duration.These factors together contributed to the emission characteristics of the upgraded bio-oil/diesel fuel blends.In addition,at the low load,since the low bulk gas temperature was relatively low due to the small amount of injection fuel per cycle,HC and CO were impeded to be oxidized further,and less NO_x and smoke were generated as well.Therefore,compared with that at high loads,HC and CO emissions of four fuel cases differed greatly,while NO_x and smoke emissions deviated a little.