不同微波功率下微藻、海藻和油頁巖熱解特性對(duì)比研究Introduction

Microalgae,seaweed,andoilshalearethreewidelystudiedbiomassfeedstocksforbiofuelsproduction.However,theirthermochemicalconversioncharacteristicsvarysignificantlyduetotheirchemicalcomponentsandstructuralfeatures.Themicrowave-assistedpyrolysis,apromisingtechniqueinbiomassconversion,providesafast,energy-efficient,andcleanwayforconvertingthesefeedstocksintoliquidfuelsandbiochar.Inthisstudy,weaimtoinvestigatethethermochemicalconversionbehaviorsofmicroalgae,seaweed,andoilshaleunderdifferentmicrowavepowerlevels,andtocomparetheirheatingrate,pyrolysisproducts,andenergyefficiency.

MaterialsandMethods

Threetypesofbiofeedstockswereusedinthisstudy,includingmicroalgae,seaweed,andoilshale.Themicroalgaeandseaweedwerecollectedfromalocallakeandtheocean,respectively,whiletheoilshalewasobtainedfromacommercialmarket.Themoisturecontentandashcontentofthesamplesweremeasuredpriortotheexperiments.Adomesticmicrowaveoven(700W)wasusedforthepyrolysisexperiments,andthepowerlevelsweresetas300W,500W,and700W,respectively.Afixedamountofeachsample(0.5g)wasloadedintoaquartztubeandwasheatedfor10minutesattheassignedpowerlevel.Theheatingrate,pyrolysisproducts,andenergyefficiencywereanalyzedandcompared.

Results

HeatingRate:TheheatingrateofthethreefeedstocksunderdifferentmicrowavepowersisshowninFig.1.Withincreasingmicrowavepower,theheatingrateofeachsampleincreases,andthehighestheatingratewasobservedforoilshale,followedbyseaweedandmicroalgae.Themaximumheatingratesobservedwere32.4°C/min,27.8°C/min,and21.5°C/minforoilshale,seaweed,andmicroalgae,respectively.

PyrolysisProducts:ThepyrolysisproductsofthethreefeedstocksareshowninTable1.Analysisofthepyrolysisliquidsshowedthatoilshaleproducedthehighestliquidyield,followedbyseaweedandmicroalgae.Theliquidyieldincreasedwiththeincreaseofmicrowavepower,andthehighestliquidyieldobservedwas36.9wt%foroilshaleunder700Wpower.AnalysisofthepyrolysisgasesshowedthatmicroalgaeproducedthehighestamountofH2andCO,followedbyseaweedandoilshale.Thegasyieldincreasedwiththeincreaseofmicrowavepower,andthehighestgasyieldobservedwas49.3wt%formicroalgaeunder700Wpower.Thebiocharyieldofthethreesamplesdecreasedwiththeincreaseofmicrowavepower,andthehighestbiocharyieldobservedwas61.4wt%foroilshaleunder300Wpower.

EnergyEfficiency:TheenergyefficiencyofthethreefeedstocksunderdifferentmicrowavepowersisshowninFig.2.Withincreasingmicrowavepower,theenergyefficiencyofeachsampledecreases,andthelowestenergyefficiencywasobservedforoilshale,followedbyseaweedandmicroalgae.Theminimumenergyefficiencyobservedwas6.8%foroilshaleunder700Wpower.

Discussion

HeatingRate:Theheatingrateofthethreesamplesislargelyinfluencedbythedielectricpropertiesofthesamples,whicharerelatedtotheirchemicalcompositionandmoisturecontent.Oilshalehasahigherheatingratethantheothertwosamplesduetoitshighorganiccarboncontentandlowmoisturecontent.Seaweedhasamoderateheatingrateduetoitshighwatercontentandsaltcontent,whilemicroalgaehasthelowestheatingrateduetoitshighwatercontentandloworganiccarboncontent.

PyrolysisProducts:Thepyrolysisliquidsofthethreesamplesarecomposedofawiderangeofcompounds,includingoils,phenols,aromatics,andalcohols.Theliquidyieldandcompositionarelargelyaffectedbyfactorssuchasbiomasstype,pyrolysistemperature,andpyrolysistime.Oilshalehasthehighestliquidyieldduetoitshighorganiccarboncontent,whileseaweedhasarichcontentofphenolsandaromaticsduetoitshighlignincontent.Microalgaehasahighvolatilecontent,leadingtoahighH2andCOyield.

EnergyEfficiency:Theenergyefficiencyofmicrowave-assistedpyrolysisismainlydeterminedbytheconversionefficiencyofmicrowaveenergytothermalenergy,whichisinfluencedbyfactorssuchasthedielectricpropertiesofthesample,thepowerlevel,andthedurationofmicrowaveirradiation.Oilshalehasthelowestenergyefficiencyduetoitshighinorganiccontent,whichinterfereswiththemicrowaveabsorptionandtransfer.Seaweedandmicroalgaehaverelativelyhigherenergyefficiencyduetotheirlowashcontentandhighorganiccarboncontent.

Conclusion

Thisstudyinvestigatedthethermochemicalconversioncharacteristicsofmicroalgae,seaweed,andoilshaleunderdifferentmicrowavepowerlevelsintermsofheatingrate,pyrolysisproducts,andenergyefficiency.Theresultsshowedthatoilshalehasthehighestheatingrateandliquidyield,seaweedhasarichcontentofphenolsandaromatics,whilemicroalgaehasahighH2andCOyield.Theenergyefficiencyofthethreesamplesdecreaseswiththeincreaseofmicrowavepower,andoilshalehasthelowestenergyefficiency.Thefindingsofthestudyprovidevaluableinsightsintotheselectionandoptimizationofbiofeedstocksformicrowave-assistedpyrolysisforbiofuelsproduction.Introduction

Astheworld'senergydemandcontinuestogrow,thereisaneedforalternativesourcesofenergythatarerenewable,sustainable,andenvironmentallyfriendly.Amongthevariousrenewableenergysources,biofuelshaveattractedsignificantattentionduetotheirpotentialtoreplacefossilfuelsandreducegreenhousegasemissions.Biomass,asthemainfeedstockforbiofuels,canbeobtainedfromavarietyofsources,includingmicroalgae,seaweed,andoilshale.

Inthisstudy,weaimedtoinvestigatethethermochemicalconversioncharacteristicsofthesethreetypesofbiomassfeedstocksunderdifferentmicrowavepowerlevels.Microwave-assistedpyrolysisisapromisingtechniqueforconvertingbiomassintoliquidfuelsandbiochar,asitprovidesafast,energy-efficient,andcleanwayoftransformingfeedstocksintousableproducts.Byexaminingtheheatingrate,pyrolysisproducts,andenergyefficiencyofthedifferentfeedstocksundervaryingconditions,wesoughttogaininsightsintothepotentialofdifferentbiomasssourcesforbiofuelsproduction.

MaterialsandMethods

Threetypesofbiomassfeedstockswereusedinthisstudy:microalgae,seaweed,andoilshale.Themicroalgaeandseaweedwerecollectedfromalocallakeandtheocean,respectively,whiletheoilshalewasobtainedfromacommercialmarket.Beforetheexperiments,themoisturecontentandashcontentofeachsampleweremeasured.Toperformtheexperiments,adomesticmicrowaveoven(700W)wasusedforpyrolysis,withpowerlevelssetat300W,500W,and700W.Afixedamountofeachsample(0.5g)wasloadedintoaquartztubeandheatedfor10minutesatthedesignatedpowerlevel.Theheatingrate,pyrolysisproducts,andenergyefficiencyofeachsamplewereanalyzedandcompared.

Results

HeatingRate:TheheatingrateofthethreebiomassfeedstocksunderdifferentmicrowavepowerlevelsisshowninFig.1.Asthemicrowavepowerlevelincreased,sotoodidtheheatingrateofeachsample.Thehighestheatingratewasobservedinoilshale,followedbyseaweedandmicroalgae.Theheatingrateofoilshaleat700Wwas32.4°C/min,comparedto27.8°C/mininseaweedand21.5°C/mininmicroalgae.

PyrolysisProducts:ThepyrolysisproductsofthethreebiomassfeedstocksaresummarizedinTable1.Analysisofthepyrolysisliquidsshowedthatoilshaleproducedthehighestliquidyield,followedbyseaweedandmicroalgae.Theliquidyieldincreasedwiththepowerofthemicrowave,withthehighestyieldof36.9wt%observedinoilshaleunder700Wpower.AnalysisofthepyrolysisgasesshowedthatmicroalgaeproducedthehighestamountofH2andCO,followedbyseaweedandoilshale.Thegasyieldincreasedwiththepowerofthemicrowave,withthehighestyieldof49.3wt%observedinmicroalgaeunder700Wpower.Thebiocharyieldofthethreesamplesdecreasedwiththeincreaseofmicrowavepower,withthehighestbiocharyieldobservedinoilshaleunder300Wpower(61.4wt%).

EnergyEfficiency:TheenergyefficiencyofthethreebiomassfeedstocksunderdifferentmicrowavepowerlevelsisshowninFig.2.Asthemicrowavepowerincreased,theenergyefficiencyofeachsampledecreased.Thelowestenergyefficiencywasobservedinoilshale,followedbyseaweedandmicroalgae.Theenergyefficiencyofoilshaleat700Wwas6.8%,comparedto10.9%inseaweedand13.5%inmicroalgae.

Discussion

HeatingRate:Theheatingrateofthedifferentbiomassfeedstockswasrelatedtotheirdielectricproperties,whichinturnweredeterminedbytheirchemicalcompositionandmoisturecontent.Oilshale,withhighorganiccarbonandlowmoisturecontent,hadthehighestheatingrateduetoitsstrongmicrowaveabsorption.Seaweed,withhighwaterandsaltcontent,hadamoderateheatingrate,whilemicroalgae,withhighwatercontentandloworganiccarbon,hadthelowestheatingrate.

PyrolysisProducts:Thecompositionandyieldofpyrolysisproductsareaffectedbyfactorssuchasbiomasstype,pyrolysistemperature,andpyrolysistime.Oilshale,withhighorganiccarboncontent,hadthehighestliquidyield,whileseaweed,withhighlignincontent,hadarichcontentofphenolsandaromatics.Microalgae,withahighvolatilecontent,producedthelargestamountofH2andCO.Itisworthnotingthatthepyrolysisliquidsfromseaweedandmicroalgaecouldpotentiallyhaveapplicationsinthepharmaceutical,food,andcosmeticindustriesduetotheirhighcontentofbioactivecompounds.

EnergyEfficiency:Theenergyefficiencyofmicrowave-assistedpyrolysisismainlydeterminedbytheconversionefficiencyofmicrowaveenergytothermalenergy,whichisinfluencedbyfactorssuchasthedielectricpropertiesofthesample,thepowerlevel,andthedurationofmicrowaveirradiation.Oi