实验和密度泛函理论分析阿维菌素的热解机理.pdf

DOI:10.1016/S1872-5813(23)60367-6Analyzing the pyrolysis mechanism of avermectin via experiments anddensity functional theoryZHOUHao1，LIUSu-xiang1,*，ZHAOBao-feng1，WANGJing-wei2，GUANHai-bin1，ZHUDi1,*，LIHuan1，SONGAn-gang1（1.Key Laboratory for Biomass Gasification Technology of Shandong Province,Energy Research Institute,Qilu University ofTechnology(Shandong Academy of Sciences),Jinan 250014,China；2.Department of Chemical Engineering,Monash University,Clayton 3800,Australia）Abstract:Inthisstudy,thethermaldegradationmechanismofavermectin(AVM)wasanalyzedviaexperimentsanddensityfunctionaltheorycalculations(DFT).TheexperimentalresultsofAVMDpyrolysisindicatedthattheremovalrateofAVMresiduesreachedpeakvalueof99.88%above250C.ThemainproductofAVMpyrolysiswasalcohols.BasedontheCObondsbreaking,fourpotentialdegradationpathwayswereproposed.Thefindingsofthecalculationswereinagreementwiththoseoftheexperiments.Theseresultsprovidetheoreticalandempiricalguidanceforthedevelopmentofsafeantibioticdisposaltechnology.Key words:avermectin；avermectinmycelialdreg；densityfunctionaltheory；pyrolysis；degradationmechanismCLC number:X786Document code:AAvermectin(AVM),serving as a drug in theavermectinfamily,hasbeenwidelyusedinagricultureandanimalhusbandry.Approximately810tofwetAVMDisgeneratedintheproductionof1tAVM1,whichhasahighyield,highmoisturecontent,andasmall amount of antibiotic residues24.Without safehandling,theresidualantibioticscanbetransferredandaccumulated into the environment510,leading to theevolution and spread of bacterial resistance7,11,andposingarisktotheenvironment1215.Therefore,itiscrucial to safely dispose of AVMD to mitigateenvironmentalpollutionandassociatedhealthhazards.Thetreatmentofantibioticmycelialdregismainlyprocessed via incineration,safe landfilling,andcomposting16.However,due to the high moisturecontentandhighoutputofantimicrobialmycelialdreg,thistreatmentprocessisrathercostlyandalwaysleadsto resource waste and secondary contamination15,17.Similarly,compostingisahighlytime-consumingandinefficientmethodoftreatingantibioticmycelialdreg,associatedwithecologicalrisks.Chenetal.18studiedthemixedcompostingofcephalosporinCfermentationresidue and recorded temperatures above 55 C forthreeconsecutivedays,indicatingthatthecomposthadreached the mature stage.After 110 d of maturitytreatment,thedegradationratewasonly49.1%.Lan19combinedstreptomycesAVMresidue,sludge,andcornstraw powder at a dry weight ratio of 411 andinoculated the mixture with a 5%organic fertilizerfermentation agent.After 40 d of fermentation,theAVMdegradationratecouldbeincreasedto75.36%.Pyrolysishasproventobeaneffectivealternativemethod of treating antibiotic mycelial dreg andantibiotics20.Itcaneffectivelyeliminateinfectionsandorganic contaminants while reducing the amount ofbacterial residue.For example,Wang et al.21 foundthatallpenicillinresiduecanberemovedat600Cfortreating 30 min.Chen et al.22 used a fixed bed toeliminatepenicillinresidue;after60min,allantibioticswere pyrolyzed at a temperature above 400 C.Thepyrolysisofbacterialresiduecanalsoconcentrateandstabilizeheavymetalsandrecoverhigh-valueproducts,suchasgas,liquid,andbiochar23.Incontrasttoothertreatmentmethods,thesimilarphysicochemicalpropertiesofantibioticmycelialdregsallowthemtopyrolysisindependentlyoftheantibioticdregtype24.Pyrolysisisthusapromisingmethodofsafelytreatingand utilizing resources obtained from antibioticmycelialdreg25.Received：2023-02-07；Revised：2023-03-21*Correspondingauthor.E-mail:liusxsdas.org，.TheprojectwassupportedbytheNationalKeyR&DProgramofChina(2018YFE0106400),NaturalScienceFoundationofShandongProvinceofChina(ZR2019MEE069),“20 Colleges and Universities”of Jinan Science and Technology Bureau(202228123,2019GXRC046),Qilu University ofTechnology(ShandongAcademyofSciences)Science,EducationandIndustryIntegrationInnovationPilotProject(2022GH010).本文的英文电子版由Elsevier出版社在ScienceDirect上出版(http:/ to research a variety of antibiotics withcomplicated structures through trials26.Quantumchemistry calculation,based on density functionaltheory(DFT),can analyze reaction behaviors andidentify reaction mechanism at the molecular level,which,hence,serving as a compensate for thelimitations of experimental methods of studying thedegradation process27.Dou et al.28 studied thephotocatalyticdegradationofamoxicillinandcefotaximeong-C3N4byDFTcalculationandfoundthatthedegradationpathwayincludedlipidationofthe-lactam ring and direct molecular fragmentation.However,thedegradationofcefotaximefirstoccurredvia de-esterification(3-acetoxy hydrolysis),followedby the decarboxylation.The oxidative degradationmechanismofsulfamethoxazolewasstudiedbySongetal.29usingDFTcalculation.ThisreactionprocessinvolvedthebreakingofSNandSCbonds,nitrationandhydroxylationofthebenzenering,carboxylation,and opening of the oxazole ring.Pelalak et al.30investigated the oxidative breakdown of sulfonamidewiththeaidofDFTcalculations,andtheyidentified31intermediate products and suggested the potentialdegradationpathways.Thus,thepyrolysismechanismsandpathwaysofantibioticmycelialdregcouldbewell-studiedthroughcombinedwithexperimentsandDFTcalculation.AVMDisthesolidwasteafterAVMproduction.Its main components are mycelium,unused culturemediumandmetabolitesproducedduringfermentationanddegradationofculturemediumaswellasasmallamount of AVM.Nowadays,only a few studies onphotolysis,hydrolysis,andstraindecompositionwerecarriedout,whilethatonthethermaldegradationofAVMisnearlyun-reported.Mushtaqetal.investigatedthephotolysisofAVMinthreedifferentsolutionswithpH 7 and obtained a variety of degradationintermediates31.Several other studies focused on theisolation and identification of AVM degradationproducts from treated crops3235.Others analyzed thedecomposition of AVM degradation products bydifferent strains33,36.Therefore,this study mainlyinvestigatedthethermaldegradationofAVMthroughcombinedexperimentsandDFTcalculationtoevaluatetheeffectoftemperatureontheeliminationofAVM.1 Materials and methods 1.1 MaterialsAVMD used in this study was provided by apharmaceuticalcompany.Itwasfirstdriedinanovenat 105 C and then screened for 0.28 mm powder.AvermectinB1a(C48H72O14,Figure1)with98%puritywaspurchasedanddriedat50Cfor24hinavacuumdrying oven for subsequent experiments.PrimarypropertiesofAVMDwaslistedinTable1.HOH3CH3CH3COCH3OCH3CH3CH3CH3CH2CH3CH3OHOOOO131416OO189172223242120OO1237568O8a42519151110OH1214533245 12Figure1StructuralformulaofavermectinB1aTable1PrimarypropertiesofAVMDProximateanalysisw/%Ultimateanalysiswd/%MadVdAdFCdCHNSOa2.4936.6550.4310.4431.134.714.290.1720.56M:moisture;V:volatile;A:ash;FC:fixedcarbon;ad:airdriedbasis;d:drybasis,a:Determinedbydifference 1.2 Experimental methods 1.2.1 Fixed-bed experimentThe AVMD and AVM pyrolysis experimentswere conducted in a fixed-bed reaction system,asshown in Figure 2.First,2 g of raw materials wereplacedinaquartzboat,whichwashungfromthetopofaquartztubewithanironwiretokeepitoutsideoftheheatingarea.Theexperimentaldevicewasconnectedand sealed.Then,the reaction furnace was heatedunder N2 atmosphere(30 mL/min)at a rate of10C/mintoreachthepyrolysistemperatureandholdit,andthetopquartzboatwasquicklyloweredtothetemperaturemeasuringpointinthecenterofthequartztube.A cryostat(with a temperature maintained at0C)wasusedtocondensevolatiles(H2O,CO,CO2,CH4,H2andtar)producedduringtherapidpyrolysisof1138燃料化学学报（中英文）第51卷AVMDandAVMinthepresenceofN2.Thereactionhadadurationof30min.Thecondensablecomponents(tar)werecooledintothecollectionbottle,andthenon-condensable gases were collected in airbags.Allpyrolysisexperimentswereconductedthricetoensuretheaccuracyofexperimentaldata.Temperaturecontrol deviceFine wireGas flow controllerCylinderBiomassAirbagGaschromatographLow-temperaturethermostal condenserQuartz tubeInsulationFigure2Fixed-bedreactionsystemusedforavermectinpyrolysis 1.2.2 Gas chromatographyThegascollectedintheairbagduringpyrolysiswas analyzed using a Micro GC Fusion gaschromatograph(Infocom,Seewen,Switzerland).1.2.3 High-performance liquid chromatographyThe liquid(tar and H2O)and solid products offixed-bedpyrolysiswereweighed,andtheAVMinthisresidue was analyzed using an e2695 SeparationsModule(Waters,Milford,MA,USA)and high-performance liquid chromatography(HPLC)column(4.6mm150mm,5m;Agilent,SantaClara,CA,USA).The column temperature was 35 C,and thedetection wavelength of all target compounds was245 nm.The mobile phase was water-acetonitrile(3070,v/v),with the flow rate of 1.0 mL/min.Theinjectionvolumeoftheanalyticalsolutionwas20L,andtheelutionconditionswereisometric.Ysolid(%)=msolidcsolidm100%（1）Yliquid(%)=mliquidcliquidm100%（2）DAVM=1YsolidYliquid（3）Ysolidmsolidcsolidm Yliquid,mliquidcliquidDAVMwhere,andrepresent the residual amount of AVM in solidproducts,the mass of residual solid,the residualamount of AVM in residual solid,the mass ofreactants,the residual amount of AVM in liquidproducts,themassofresidualliquid,andtheresidualamount of AVM in residual liquid after reaction,respectively 1.2.4 Gas chromatography and mass spectrometryA7890BGasChromatographwascoupledwitha7010SeriesTriple-QuadrupoleMassSpectrometer(Agilent,Santa Clara,CA,USA)to analyze thechanges in solid and liquid products of AVMpyrolysisatdifferenttemperatures.SolidproductsofAVMpyrolysiswereplacedinamortar,groundintopowder,extractedtwiceusingdichloromethane,andthencombinedwiththesolution.Thissolutionwasthen analyzed using GC and mass spectrometry(MS).GaschromatographyanalysiswasconductedinanHP-5MScapillarycolumn(30m0.25mm0.25m;Agilent,SantaClara,CA,USA).Atotalof1.0Lofhelium(99.9999%)wasintroducedasthecarrier gas under a flow rate of 0.8 mL/min usingsplitlessinjection.TheoventemperatureofGCwasmaintainedat100Cfor1min,andthenincreasedto200Catarateof10C/minandfinallyto280Catarateof40C/min.Itwasmaintainedat280Cfor15min.1.3 Calculations methodInthisstudy,theCASTEPmoduleofMaterialsStudio2017wasusedtoconductmolecularmodeling,molecular configuration optimization and transitionstate calculation through TS Search.The generalizedgradient approximation method and PBE exchange-correlationfunctionaltheorywereusedwiththeself-consistentfield(SCF)toleranceof2.0106eV/atom.TheMonkhorst-Packkpoint(111)wasadoptedwithcalculating100stepsinsurfaceoptimization37.TheoptimizedresultsinTSSearchoperationweresubsequentlytreatedbyasearchprotocolofcompletelinearsynchronoustransformation/quadraticsynchronous transformation(complete LST/QST)toobtainthecorrespondingreactantandproduct.Theseparameters included a 2.0 105 eV/atom SCFtolerance,9999maximumconvergenceaccuracycyclesteps,and a maximum QST of 5.In the processbetweencompletingtheLSTcalculationandsettingtheconvergence criterion,the minimum optimization oftheconjugategradientandthecalculationofmaximumQST were conducted cyclically until the calculationwascompleted37.2 Results and discussion 2.1 AVMD pyrolysis 2.1.1 AVMD pyrolysis product yieldsFigure3depictsthesolid,liquid,andgasproduct第8期ZHOUHaoetal.：Analyzingthepyrolysismechanismofavermectinviaexperimentsanddensity1139yields of AVMD pyrolysis at different temperatures.The conversion rate and product yield of AVMDpyrolysis were obviously influenced by temperature.Pyrolysisconversionrateincreasedfrom1%to37.1%withtheincreaseoftemperaturefrom150to350C.However,biocharproductiondecreasedfrom96.8%to60.9%,along with the elevation of gas and liquidproduct yields,where the liquid product yields aremarkedly raised from 1%to 31.2%.Therefore,elevation of temperature increases the AVMDpyrolysis degree that deepens the color of solidproducts.150200250300350020406080100Yield w/%Temperature/SoildLiquidGasFigure3Yieldofresidueproductsinavermectinpyrolysisatdifferenttemperatures 2.1.2 AVM in AVMD degradation analysisFigure4showsthedegradationrateofAVMinAVMD,which increased dramatically from only11.31%at150Cto95.68%at200C.Attemperatureabove 250 C,the degradation rate only slightlyelevated.ThismeansthatmostAVMinsolidproducthad been decomposed,with only a small amount ofresidualremainingintheliquidproduct.At350C,allAVM was effectively removed and the maximumdegradationratereaches99.88%.150200250300350020406080100Degradation rate/%Temperature/25030035099.599.699.799.899.9Figure4Degradationrateofavermectinresidueatdifferenttemperature 2.2 AVM pyrolysis 2.2.1 AVM degradation rate analysisFigure5showstherelationofdegradationrateofAVM with the temperature.The degradation rate ofAVMincreasedsharplyfromonly8.10%at150Cto97.11%at200C,whichisconsistentwiththeresultofdegradationofAVMinAVMD.Thedegradationrateof AVM reached 99.995%at 250 C and only amarginal amount of AVM remained in the liquidproducts.Atthiscondition,AVMdegradationratewasalmostunchangedwiththetemperature,indicatingthatAVMhadalmostcompletelydegraded.150200250300350020406080100Degradation rate/%Temperature/25030035099.99099.99299.99499.99699.998Figure5Degradationrateofavermectinatdifferenttemperature 2.2.2 AVM pyrolysis product yieldsIn order to analyze the thermal degradationmechanismofAVM,thepyrolysisofAVMwith98%puritywasthenperformedintherangeof150350C.The products distribution of AVM pyrolysis in thistemperature range is shown in Figure 6.With theincreaseoftemperaturefrom150to350C,theyieldofsolidproductsdecreasedfrom96.99%to22.40%,whereastheliquidandgasyieldsincreasedfrom0to66.27%and0.02%to6.59%,respectively.Theyieldofgas,inducingH2,CH4,CO,CO2,C2H6andC3H6,wasthesmallestinAVMpyrolysisproducts.At150C,thecondensable volatile products and non-condensableproducts were undetectable due to the almost nocrackingofAVM(withameltingpoint150155C).The liquid yields increased slightly at 200 C,andraised dramatically at 250 C and then graduallyelevatedwiththetemperature,thus,makingtheliquidyields much higher than the gas yields.On thecontrary,solidyieldscontinuouslydecreasedwiththetemperature.Therefore,hightemperaturecouldpromotethedecompositionofAVM.The main liquid products of AVM pyrolysis1140燃料化学学报（中英文）第51卷comprised the following six categories:alcohols,hydrocarbons,acids,aldehydes,esters and ketones.Theseliquidproductsofpyrolysisat200350Cwerethen analyzed,as shown in Figure 7.Alcohols,hydrocarbons,andacidswerethemainliquidproductsof AVM pyrolysis,although the concentrations ofalcohol and acid gradually decreased with thetemperature.As the representative of alcohols andacids,2,3-dimethyl-3-hexanolandsorbicacidaccountedfor25.11%37.59%and11.23%17.95%oftotal liquid products,respectively.In contrast,theyields hydrocarbons and aldehydes gradually raisedwith the temperature,where 2,5-dimethyl-2,3,4-hexatrieneandfurfuralaccountedfor13.03%14.80%and3.78%6.85%oftotalliquidproducts,respectively.Esters yield was unchanged,while that of ketonesdeclined,withtheincreaseoftemperature.150200250300350020406080Yield w/%Temperature/SoildLiquidGas100Figure6Yieldofavermectinpyrolysisproductsatdifferenttemperatures20025030035001020304050Alcohols HydrocarbonsAcidsAldehydesEstersKetoneYield w/%Temperature/Figure7Compositionofliquidpyrolysisproductsatdifferenttemperatures 2.3 DFT calculationsThephotocatalyticdegradationofAVMhasbeenreported in many literatures,giving a variety ofmechanisms and pathwa