Dielectric characterization of biodegradable wastes during pyrolysis

1  Dielec ic cha ac e iza ion o biodeg adable was es 1 du ing py olysis 2 D. Bene oso1, A. Albe o-O iz2, J. Monzó-Cab e a2, A. Díaz-Mo cillo2, A. 3 A enillas1, J.A. Menéndez1* 4 1Ins i u o Nacional del Ca bón, CSIC, Apa ado 73, 33080 O iedo, Spain 5 2Depa men o Communica ion and In o ma ion Technologies, Technical 6 Uni e si y o Ca agena, Ca agena, Spain 7 Co esponding au ho : Tel.: +34 985 119090 8 E-mail add ess: [email p o ec ed] 9 10 Abs ac 11 The lack o dielec ic p ope ies da a has o en been named as one o he 12 easons ha has hampe ed he simula ion o mic owa e p ocessing o 13 biomass eeds ock and p ocess design. In his wo k, he dielec ic beha io 14 o an o ganic ac ion om municipal solid was es du ing py olysis has been 15 moni o ed as a unc ion o empe a u e. Fu he mo e, he e ec o he 16 addi ion o a mic owa e abso ben ma e ial (ca bonaceous cha ) o he aw 17 biowas e upon he dielec ic p ope ies has been in es iga ed o he i s 18 ime. 19 The e iciency o he con e sion o mic owa e ene gy o hea , measu ed by 20 means o he an δ pa ame e , is shown in his s udy o be nea ly 20 imes 21 highe when he abso ben cha is added o he eac ion bulk a oom 22 empe a u e and his gap is e en g ea e in he 600 – 800 ºC ange. 23 Ne e heless, he esul s sugges ha he addi ion o inc easing amoun s o 24 mic owa e abso ben (up o ca. 40%) impai s mic owa e pene a ion, which 25 gi es ise o a less homogeneous hea ing o he bulk. The e is he e o e an 26 op imum p opo ion ha balances hea con e sion and pene a ion dep h. 27 The esul s o his s udy lend suppo o he use o cha as a means o 28 induce he mochemical ea men s by mic owa es and educe ene gy 29 consump ion in he p ocess. 30 31 Keywo ds: Dielec ic p ope ies, Mic owa e py olysis, Biomass py olysis, 32 Mic owa e hea ing modeling, Mic owa e abso ben 33 34 2  1. In oduc ion 1 On a e age, e e y one o he mo e han 500 million people li ing in he 2 Eu opean Union (EU) h ows away a ound hal a on o household ubbish a 3 yea . This is on op o he huge amoun o was e gene a ed om ac i i ies 4 such as manu ac u ing (360 million ons) and cons uc ion (900 million 5 ons), while he supply o wa e and he p oduc ion o use ul ene gy 6 gene a e ano he 95 million ons. Al oge he , he EU p oduces up o 3 7 billion ons o was e e e y yea [1]. A signi ican p opo ion o was e going 8 o land ill is o ganic ma e ial, (i.e. de i ed om bo h biomass and pe oleum 9 sou ces). The mochemical con e sion p ocesses, in ol ing py olysis and 10 gasi ica ion, can con e his was e a sou ce in o po en ially use ul 11 chemical eeds ocks and uels a e he emo al o he mo e eadily 12 ecyclable ma e ials, such as me als, glass, e c. 13 14 A numbe o p ocesses a e now unde de elopmen o a e a he 15 demons a ion s age, whose aim is o p o ide mo e cos -e ec i e, 16 en i onmen ally and socially accep able al e na i es o incine a ion plan s. 17 One o hese new echnologies is mic owa e py olysis based on dielec ic 18 hea ing. This p ocess bene i s om he main ad an ages o using 19 mic owa es, such as apid, olume ic and selec i e hea ing, and a oids he 20 need o sh ed he eeds ock and o p e-d y he samples, esul ing in a 21 subs an ial educ ion in he cos s associa ed wi h hese s eps [2-5]. In spi e 22 o hese ad an ages, his echnology has no ye eached indus ial scale 23 3  owing o he lack o economic analyses on a la ge scale and he absence o 1 su icien da a o quan i y he dielec ic p ope ies o he inpu eeds ocks. 2 3 The p ope y ha de e mines he dielec ic esponse o ma e ial unde he 4 in luence o an elec ic ield is he ela i e complex pe mi i i y, ε*, which is 5 exp essed as a unc ion o a eal componen known as he dielec ic cons an 6 (which ep esen s he abili y o dielec ics o s o e elec ical ene gy) and an 7 imagina y componen known as he dielec ic loss ac o (which ep esen s 8 he abili y o a ma e ial o abso b he elec ic ene gy): 9 10 11 12 whe e and ε’ and ε’’ a e he dielec ic cons an and he dielec ic loss 13 ac o ela i e o he co esponding dielec ic p ope ies o ee space. 14 15 An es ima ion o hese p ope ies is essen ial o he e ec i e design and 16 scaling up o mic owa e hea ing p ocesses o ensu e an accu a e p edic ion 17 o he abso bed powe densi y; i.e. he a e a which he elec omagne ic 18 ene gy is con e ed o hea in he ma e ial. Dielec ic p ope ies may a y 19 wi h composi ion, equency, empe a u e and e en ma e ial densi y [6] 20 and, he e o e, i is essen ial o cha ac e ize hei a ia ion in ela ion o 21 hose pa ame e s. 22 23 4  Se e al s udies ha e a emp ed o cha ac e ize he dielec ic p ope ies o 1 coal [7] and some kinds o biomass [8, 9] since i is known ha he dielec ic 2 loss o hese ma e ials a low empe a u es is negligible, making hem 3 anspa en o mic owa es. Howe e , when he subs a es a e subjec ed o 4 highe empe a u es (i.e. empe a u es highe han 600 ºC), he s uc u es 5 become essen ially cha , which is known o be a high mic owa e abso bing 6 ma e ial due o he Maxwell-Wagne e ec which causes a e y high 7 displacemen o π-elec ons on ca bonized s uc u es [10]. I is o his 8 eason ha di e en mic owa e ecep o ma e ials a e added o biomass 9 du ing mic owa e py olysis, so ha a high enough empe a u e is eached 10 o induce py olysis [11, 12]. Howe e , mos published s udies a e ocused 11 solely on he dependence o dielec ic p ope ies upon equency adia ion a 12 oom empe a u e [13-16] and igno e he need o a comp ehensi e s udy o 13 he whole mic owa e py olysis p ocess. In o he wo ds, an in-dep h and 14 ex ensi e s udy o he dependence o dielec ic p ope ies on empe a u e is 15 needed o ob ain a be e unde s anding o he dielec ic esponse o o ganic 16 subs a es du ing mic owa e py olysis and o mixed o ganic subs a es 17 when used wi h mic owa e suscep o s. 18 This pape in es iga es he mic owa e abso p ion capabili y o a 19 biodeg adable was e and i s mix u e wi h mic owa e abso ben cha on he 20 basis o hei dielec ic p ope ies, om oom empe a u e up o 800 ºC a 21 he commonly used equency o 2.45 GHz. 22 23 2. Ma e ials and Me hods 24 5  2.1 Biowas e p epa a ion and cha ac e iza ion 1 The biodeg adable was e used o his s udy was an o ganic ac ion om a 2 municipal solid was e, ob ained om a land ill in Se ille (Spain). The was e 3 was d ied, pa ially cleaned o ine s such as glass o me als and size-4 educed o 1-3 mm. This ac ion has been labelled as MSWd. The p e-5 ea men o his o ganic esidue allows a good homogenei y o his ac ion. 6 Ac ually, his ac ion has been used in o he s udies o p oduce syn hesis 7 gas by means o mic owa e-induced py olysis and he composi ion o he gas 8 was qui e homogeneous when epea ing he es s [17]. 9 In o de o assess he e ec o adding cha as mic owa e abso be o he 10 biowas e upon he dielec ic esponse, a ca bonaceous solid cha was 11 p epa ed by subjec ing he biowas e sample o a empe a u e o 800 ºC in an 12 elec ic u nace o 1 h in an oxygen- ee a mosphe e. This has been labelled 13 Cha -MSWd. The mix u es o cha :biowas e we e p epa ed in weigh a ios 14 o 0.3:1 and 0.6:1. These wo mix u e a ios we e conside ed on he basis o 15 keeping he amoun o cha as low as possible o induce he mic owa e 16 py olysis. In p e ious s udies [17], we used 0.3:1 a io; hus, we ha e used 17 his same a io in his wo k. Fu he mo e, a la ge amoun (0.6:1 a io) was 18 conside ed o s udy he e ec o adding cha o eeds ock as mic owa e 19 abso ben . 20 The mois u e, ash con en and ola ile ma e da a o he esidues we e 21 ob ained on a LECO TGA-601 de ice. To pe o m he ul ima e analysis, a 22 LECO-CHNS-932 mic o-analyze and a LECO-TF-900 u nace we e used. 23 The mic o-analyze p o ided da a on he ca bon, hyd ogen, ni ogen, and 24 6  sul u pe cen age composi ion. The oxygen con en was de e mined using 1 he LECO-TF-900 u nace. The esul s o p oxima e and ul ima e analyses 2 o he MSWd and cha -de i ed samples a e p esen ed in Table 1. 3 4 Table 1. P oxima e and ul ima e analyses o he MSWd and Cha -MSWd ac ions 5 Residue Municipal solid was e Cha om municipal solid was e Label MSWd Cha -MSWd Mois u e 2.8 3.3 Asha 27.7 66.6 P oxima e analysis (w .%) Vola ile ma e a 61.1 1.7 C 45.1 30.7 H 5.4 0.1 N 2.1 1.0 S 0.4 0.7 Ul ima e analysis (w .%) O 19.3 0.9 6 2.2 Measu emen o dielec ic p ope ies 7 An in e se me hodology o ob ain he pe mi i i y o he di e en biowas es 8 was used (Fig. 1) [18]. This echnique is one o he mos app op ia e; o he 9 echniques such as s anda d coaxial p obes may lead o lowe p ecision 10 since ai bubbles below he coaxial p obe can esul in lowe alues o 11 pe mi i i y; esonan -ca i y echnique is ypically used o low-loss 12 ma e ials (which is no ou case) and iden i ying he esonan equency and 13 quali y ac o (in insic pa ame e s o his echnique) would ha e been 14 di icul due o he high abso p ion o he ma e ials. Fi s , each sample (see 15 Sample R in Fig. 1) was in oduced and uni o mly compac ed in o a qua z 16 ube (i.d. 5 mm, heigh 43 mm; MSWd bulk densi y: 166 kg/m3; cha bulk 17 7  densi y: 353 kg/m3) and hea ed up o a speci ic empe a u e in an oxygen-1 ee a mosphe e by a GALLUR con ec ion o en. The samples we e subjec ed 2 o 25, 50, 100, 200, 300, 400, 500, 600, 700, 800 and 1000 ºC be o e being 3 e y quickly placed (maximum 3 s) in he middle o a WR-340 wa eguide 4 whe e he sca e ing pa ame e s (i.e., S11, S12, S21 and S22) we e measu ed 5 by means o a RHODE & SCHWARZ, model ZVA67 ec o ne wo k analyze 6 se o a equency o 2.45 GHz. S-pa ame e s desc ibe he esponse o an N-7 po ne wo k o ol age signals a each po . The i s numbe in he 8 subsc ip e e s o he esponding po , while he second numbe e e s o 9 he inciden po . Thus S21 means he esponse a po 2 due o a signal a 10 po 1. A e wa ds, he measu emen sys em was modeled (Sample S in Fig. 11 1) by using CST Mic owa e S udio (CST MWS) comme cial so wa e and, by 12 in e se echniques, he alue o he complex pe mi i i y o each sample a 13 he co esponding empe a u e was ob ained. Tha is o say, an op imiza ion 14 me hod (a gene ic algo i hm combined wi h a g adien descen op imiza ion 15 me hod) [18] was applied o he model o ob ain a simula ed ma e ial ha 16 would induce he same sca e ing pa ame e s as hose p e iously measu ed. 17 As ini ial alues o he co esponding op imiza ion me hod, he 18 pe mi i i y o he ma e ials was measu ed in a po able DIMAS 19 dielec ome e , model DIELKITV/DIELKITC a oom empe a u e. The 20 e o s du ing measu emen s a e included in he Supplemen a y Ma e ial. 21 Fu he mo e, o minimize he unce ain y o he sample cooling on he 22 pe mi i i y measu emen s du ing he sample ans e om he o en o he 23 wa eguide, he cooling cu e was p e iously es ima ed and can be ound in 24 8  he Supplemen a y Ma e ial. This cu e allows es ablishing he ope a ing 1 empe a u e o he o en in o de o each he nominal empe a u e in o he 2 wa eguide. 3 4 FIGURE 1 5 6 2.3 Loss angen calcula ion 7 The loss angen is an impo an dielec ic p ope y which is di ec ly ela ed 8 o he abili y o a speci ic ma e ial o con e elec omagne ic ene gy in o 9 hea a a gi en empe a u e and equency. This p ope y is de ined as: 10 11 12 13 Fu he mo e, he ela ionship be ween he dielec ic p ope ies o biowas e 14 and cha was in es iga ed o he wo ma e ial mix u es o e he selec ed 15 empe a u e ange. The dielec ic p ope ies o a mix u e o wo di e en 16 ma e ials can be modeled by using di e en equa ions such as he Landau, 17 Li shi z and Looyenga equa ion (Equa ion 3), as epo ed in [19]: 18 19 20 21 whe e is he olume ic ac ion o he ma e ial MSWd, which was 22 calcula ed om i s densi y, and and a e he pe mi i i y o 23 he biomass and cha ac ions, espec i ely. The accu acy o his model was 24 9  es ed using he expe imen al da a ob ained o e he empe a u e ange 1 selec ed. 2 3 2.4 Skin dep h calcula ion 4 The skin dep h, also known as pene a ion dep h (Ds), is de ined as he 5 dis ance om he su ace in o he ma e ials a which he a elling 6 elec omagne ic wa e powe d ops o e-1 om i s alue a he su ace. The 7 skin dep h can be calcula ed using Equa ion 4 [20]: 8 9 10 11 whe e is he mic owa e wa eleng h in ee space. The skin dep h is an 12 impo an pa ame e since he use o mic owa es as a hea ing medium 13 usually in ol es scaling-up limi a ions due o he di icul y o p ope ly 14 dispe sing he mic owa es as he ma e ial inc eases in olume [21]. 15 16 3. Resul s and Discussion 17 The measu ed dielec ic p ope ies o he MSWd and Cha -MSWd ac ions 18 a e shown in Fig. 2 (a) and (b), espec i ely, e sus he inc ease in 19 empe a u e. As can be seen, he dielec ic p ope ies depend g ea ly on he 20 empe a u e du ing py olysis, pa icula ly a high empe a u es. 21 FIGURE 2 22 The dielec ic cons an and loss ac o o MSWd show a nea ly cons an 23 alue om oom empe a u e up o 500 °C, co esponding o he py olysis 24 16  4. Conclusion 1 The dielec ic p ope ies o an o ganic ac ion om a municipal solid was e 2 we e de e mined a 2.45 GHz om oom empe a u e o 800 ºC. The 3 dielec ic p ope ies o he biowas e emained cons an du ing py olysis up 4 o 400 ºC; hen he e was a sha p inc ease in bo h he dielec ic cons an 5 and loss ac o , owing o he elease o ola iles and honeycomb-like ca bon 6 s uc u es wi h a high delocalised elec on densi y. Fu he mo e, he 7 addi ion o cha as mic owa e abso ben o he eeds ock p o ed o be an 8 e ec i e way o educe he ene gy consump ion o he py olysis p ocess, 9 because i p o ided he bulk wi h a high an δ a oom empe a u e, 10 al hough i educed he pene a ion dep h, which esul ed in a mo e 11 he e ogeneous hea ing when a high concen a ion o cha was used. 12 The dielec ic cha ac e iza ion add essed in his pape could se e as a 13 s a ing poin o he design o sui able equipmen o pe o m he 14 mic owa e-induced py olysis a indus ial scale wi h he app op ia e 15 simula ion so wa e. 16 17 Acknowledgmen s 18 The esea ch leading o hese esul s has ecei ed unding om he 19 Eu opean Union’s Se en h F amewo k P og amme o esea ch, 20 echnological de elopmen and demons a ion unde g an ag eemen n° 21 311815 (SYNPOL p ojec ). D. 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In e se me hodology o de e mining he dielec ic p ope ies 4 based on he p ocedu e desc ibed in [18] 5 6 20  1 Figu e 2. Dielec ic p ope ies o he (a) MSWd ac ion (b) Cha -MSWd 2 ac ion du ing py olysis. 3 4 5 21  1 Figu e 3. E olu ion o an δ du ing py olysis o he (a) MSWd and (b) 2 Cha -MSWd ac ions. 3 4 22  1 Figu e 4. Dielec ic cons an o he mix u es 2 3 23  1 Figu e 5. Loss ac o o he mix u es 2 3 24  1 Figu e 6. E olu ion o an δ du ing py olysis o he di e en cha /biowas e 2 mix u es. an δ om MSWd ac ion is also depic ed as a means o 3 compa ison 4 5 25  1 Figu e 7. Mic owa e skin dep h o he mix u es o MSWd wi h Cha -2 MSWd du ing py olysis 3 4 32  1 Mix u e Cha :MSWd (0.6:1) 2 0100 200 300 400 500 600 700 800 0 20 40 60 80 100 120 140 Tempe a u e (ºC) ε ´ ε ´ s Tempe a u e Ma e ial 3 ε ´ ε ´+U ε ´ ε ´-U ε ´ 3 0100 200 300 400 500 600 700 80 0 0 20 40 60 80 100 120 140 Tempe a u e (ºC) ε ´´ ε ´´ s Tempe a u e Ma e ial 3 ε ´´ ε ´´+U ε ´´ ε ´´-U ε ´´ 4 33  0100 200 300 400 500 600 700 800 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 Tempe a u e (ºC) anδ anδ s Tempe a u e Ma e ial 3 anδ anδ+U anδ anδ-U anδ 1 34  1 Cha sample 2 3 0100 200 300 400 500 600 700 80 0 0 20 40 60 80 100 120 140 Tempe a u e (ºC) ε´ ε´ s Tempe a u e Ma e ial 4 ε´ ε´+Uε´ ε´-Uε´ 4 0100 200 300 400 500 600 700 80 0 4 5 6 7 8 9 10 11 12 13 Tempe a u e (ºC) ε´´ ε´´ s Tempe a u e Ma e ial 4 ε´´ ε´´+Uε´´ ε´´-Uε´´ 5 35  0100 200 300 400 500 600 700 80 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 Tempe a u e (ºC) an δ an δ s Tempe a u e Ma e ial 4 1 2 36  1 Cooling down cu e 2 50 100 150 200 250 300 350 400 450 500 0 200 400 600 800 1000 1200 Time (s) Tempe a u e (C) Cooling cu e In e pola ed. Max descen : 22.47 C/s Measu ed 3 4 5