Influence of the Ni-Co/Al-Mg catalyst loading in the continuous aqueous phase reforming of the bio-oil aqueous fraction

p ocesses A icle In luence o he Ni-Co/Al-Mg Ca alys Loading in he Con inuous Aqueous Phase Re o ming o he Bio-Oil Aqueous F ac ion Pablo Lozano, Ana I. Simón, Lucía Ga cía * , Joaquín Ruiz, Mi iam Oli a and Jesús A auzo   Ci a ion: Lozano, P.; Simón, A.I.; Ga cía, L.; Ruiz, J.; Oli a, M.; A auzo, J. In luence o he Ni-Co/Al-Mg Ca alys Loading in he Con inuous Aqueous Phase Re o ming o he Bio-Oil Aqueous F ac ion. P ocesses 2021,9, 81. h ps://doi.o g/10.3390/ p 9010081 Recei ed: 4 Decembe 2020 Accep ed: 29 Decembe 2020 Published: 1 Janua y 2021 Publishe ’s No e: MDPI s ays neu- al wi h ega d o ju isdic ional clai- ms in published maps and ins i u io- nal a ilia ions. Copy igh : © 2021 by he au ho s. Li- censee MDPI, Basel, Swi ze land. This a icle is an open access a icle dis ibu ed unde he e ms and con- di ions o he C ea i e Commons A - ibu ion (CC BY) license (h ps:// c ea i ecommons.o g/licenses/by/ 4.0/). The mochemical P ocesses G oup (GPT), A agon Ins i u e o Enginee ing Resea ch (I3A), Uni e sidad de Za agoza, Ma iano Esquillo S/N, 50018 Za agoza, Spain; [email p o ec ed] (P.L.); [email p o ec ed] (A.I.S.); j uizp@uniza .es (J.R.); mi oli a@uniza .es (M.O.); ja auzo@uniza .es (J.A.) *Co espondence: luciag@uniza .es Abs ac : The e ec o ca alys loading in he Aqueous Phase Re o ming (APR) o bio-oil aqueous ac ion has been s udied wi h a Ni-Co/Al-Mg cop ecipi a ed ca alys . Because o he high con en o wa e in he bio-oil aqueous ac ion, APR could be a use ul p ocess o con e his ac ion in o aluable p oduc s. Expe imen s o APR wi h con inuous eeding o aqueous solu ion o ace ol, bu anol and ace ic acid as he only compound, oge he wi h a simula ed and a eal aqueous ac ion o bio-oil, we e ca ied ou . Liquid p oduc s in he liquid e luen o he APR model compounds we e quan i ied and he eac ion pa hways we e e ised. The inc ease o ca alys loading p oduced an inc ease o gas p oduc ion and a gas wi h highe alkanes con en . Ace ol was he compound wi h he highes eac i i y while he con e sion o ace ic acid was e y low. The p esence o ace ic acid in he eed caused ca alys deac i a ion. Keywo ds: aqueous phase e o ming; Ni ca alys ; bio-oil; ace ol; bu anol; ace ic acid; aqueous ac ion 1. In oduc ion Biomass is a enewable aw ma e ial sou ce o ene gy and chemical compounds. Biomass can be con e ed by biological and he mochemical p ocesses. The mos impo an he mochemical p ocesses a e combus ion, gasi ica ion and py olysis. The py olysis p ocess makes i possible o con e biomass in o gas, liquid and solid p oduc s. The as py olysis o biomass ca ied ou a high hea ing a es, a a inal empe a u e o 450–500 ◦ C and e y sho con ac ime o p oduc s, maximizes he liquid ac ion called bio-oil [ 1 ]. The bio-oil, also called py olysis oil, can be sepa a ed in o an aqueous ac ion and nonaqueous (ligninic) ac ion by adding wa e . The aqueous ac ion con ains mainly compounds de i ed om he depolyme isa ion o cellulose and hemicellulose, such as o ganic acids, including ace ic acid; ke ones, such as ace ol, also named hyd oxyace one; and alcohols, among o he s. These oxygena ed compounds can p oduce hyd ogen and liquid compounds by e o ming p ocesses. Ca aly ic s eam e o ming wo ks a low a mosphe ic p essu es and empe a u es in he ange o 550–800 ◦ C. So, Cho ne e al. s udied he con e sion o he aqueous ac ion o bio-oil by ca aly ic s eam e o ming o hyd ogen p oduc ion and obse ed ha nickel- based ca alys s achie ed a good con e sion o H 2 , al hough coke was p oduced which deac i a ed he ca alys [ 2 – 5 ]. Ga cia e al. [ 6 ] in es iga ed he composi ion o he ca alys in his p ocess using nickel ca alys s modi ied wi h cobal o ch omium o dec ease he amoun o coke ha o med on he ca alys . O he s udies ha e been ca ied ou in ixed and luidized beds o imp o e he p oduc ion o hyd ogen by ca aly ic s eam e o ming o he aqueous ac ion o bio-oil, a ying he ope a ing condi ions, and he nickel ca alys has been suppo ed on alumina, modi ied wi h cobal , coppe , ce ium, magnesium o calcium [ 7 – 10 ]. Howe e , his p ocess equi es a lo o ene gy o apo ize wa e , and he gas ob ained is ich in CO. P ocesses 2021,9, 81. h ps://doi.o g/10.3390/p 9010081 h ps://www.mdpi.com/jou nal/p ocesses P ocesses 2021,9, 81 2 o 17 Aqueous Phase Re o ming (APR) is a p ocess de eloped by Dumesic and co-wo ke s, wi h i s i s e e ence in 2002 [ 11 ]. This p ocess is app op ia e o con e aqueous s eams wi h low o ganic con en because i does no need o apo ize wa e , which educes ene gy equi emen s o hyd ogen p oduc ion. The empe a u e is a ound 220–270 ◦ C a mode a e p essu es o 25–50 ba . Ano he ad an age o he APR p ocess is ha empe a u es and p essu es a e a ou able o wa e -gas shi (WGS) eac ion, esul ing in a gas wi h low CO con en . Mo e ad an ages can be ound in he e iew o Da da e al. [ 12 ]. A signi ican numbe o s udies ha e ocused on he APR o alcohols and polialcohols, such as e hylene glycol, glyce ol and so bi ol. Howe e , he s udies o APR which ha e ocused on he con e sion o compounds de i ed om biomass py olysis a e sca ce [13]. The e a e also some s udies o he bio-oil aqueous ac ion e o ming unde supe c i - ical condi ions. Supe c i ical wa e condi ions equi e empe a u es highe han 374 ◦ C and p essu es highe han 221 ba . Supe c i ical wa e e o ming o model compounds o bio-oil aqueous ac ion, such as ace ic acid, ace ol and bu anol wi hou and wi h ca alys , was s udied by O iz and co-wo ke s [ 14 , 15 ]. Chakinala e al. [ 16 ] s udied he e ec o se e al ca alys s o he con e sion o he bio-oil aqueous ac ion in supe c i ical wa e condi ions. Howe e , hese a e condi ions conside ably mo e exigen han hose needed in he APR p ocess. The co osion o ma e ials in supe c i ical wa e is a ele an aspec . A andia e al. [ 17 ] s udied he aqueous phase e o ming o ep esen a i e model compounds o a bio-oil aqueous ac ion, such as ace ic acid, e hanol, ace ol and ca echol, as well as a mix u e o all o hem. They s udied he in luence o di e en nickel-based ca alys s a 230 ◦ C and 32 ba . The expe imen s we e pe o med in a con inuous ixed-bed eac o wi h a ca alys weigh /mass low a e o o ganics o 7.5 g ca alys min/g o ganic. This wo k ocused on gas p oduc ion, and some quali a i e analyses o he liquid phase we e ca ied ou wi h he pu pose o iden i ying he p oduc compounds in liquid phase a e he APR eac ion. Lou’s g oup pe o med some s udies ocused on aqueous phase e o ming o he low boiling ac ion o ice husk py olyzed bio-oil. They employed a eal eed ob ained by e apo a ing o he c ude oil unde acuum. The expe imen s we e pe o med in a s ainless-s eel au ocla e a 260 ◦ C. They analysed he e ec o a pla inum ca alys [ 18 ], he size o P /Al2O3[19] and he ecyclabili y o P ca alys s suppo ed on mixed oxides [20]. Vispu e and Hube s udied hyd ogen and alkane p oduc ion om he aqueous ac ion o bio-oil by aqueous phase p ocessing. A eal aqueous ac ion de i ed om oak wood was i s hyd ogena ed. Then, APR was pe o med o hyd ogen p oduc ion wi h a P /Al 2 O 3 ca alys a 265 ◦C and 55.1 ba [21]. Oasmaa and Meie [22] de e mined he p esence o bu anol in he alcohol ac ion o bio-oil. Bu anol has been conside ed a model compound o bio-oil and i s con e sion o hyd ogen has been s udied by s eam e o ming as he only compound and in mix u es [ 23 – 26 ]. The s udy o he APR o bu anol is ele an bo h as a model compound o bio-oil and because n-bu anol can be p oduced by biological p ocesses and has been p oposed as an al e na i e o con en ional gasoline and diesel uels. This wo k p esen s an expe imen al s udy wi h he pu pose o con e ing he aqueous ac ion o bio-oil and some model compounds in aluable p oduc s by APR. Nickel ca alys s ha e been widely used in his p ocess because hey a e inexpen- si e and ha e high ac i i y and selec i i y o hyd ogen, bu hey can be deac i a ed by ca bon deposi s on hei su ace. Remón e al. de eloped a Ni-based ca alys p epa ed by cop ecipi a ion, which modi ied he suppo wi h Mg and he ac i e phase wi h Co. This ca alys has been employed in s eam e o ming p ocess o glyce ol and he aqueous ac ion o bio-oil [ 27 – 31 ] and has shown good esul s and he lowes coke p oduc ion among all hose es ed. Thus, in he p esen wo k, he e ec o ca alys loading in he APR p ocess employing a Ni-Co/Al-Mg ca alys was s udied. Expe imen s wi h ca alys weigh /o ganic mass low a e (W/m) a io om 5–40 g ca alys min/g o ganic ha e been pe o med eeding ace ol, bu anol and ace ic acid indi idually as model compounds o he aqueous ac ion o bio-oil. Also, a mix u e o ace ol, bu anol and ace ic acid was also P ocesses 2021,9, 81 3 o 17 employed and was inally s udied a eal aqueous ac ion o bio-oil. Ope a ing condi ions in luence he con e sion o he o ganic compounds o gas and liquid p oduc s. In his wo k, quan i a i e analyses o gas and liquid p oduc s o he model compounds we e ca ied ou . Quali a i e analyses o liquid s eam o he APR o he eal aqueous ac ion we e pe o med. To he bes o ou knowledge, his is he i s ime ha ca alys loading has been s udied in he APR o model compounds o he bio-oil aqueous ac ion. This wo k con ibu es o inc easing he knowledge o con e ing he bio-oil aqueous ac ion in o aluable p oduc s, gases and liquids. The speci ic ole o Ni-Co/Al-Mg ca alys on APR has been analysed and p o ides ele an esul s in academic ields, such as yields o p oduc s. Mo eo e , he obse ed ca alys deac i a ion is signi ican o pe o m he p ocess in an indus ial scale. 2. Ma e ials and Me hods The expe imen al sys em was de eloped and manu ac u ed by PID Eng&Tech (Mad id, Spain). This enabled he con inuous eeding o he aqueous solu ion by means o a high- pe o mance liquid ch oma og aphy (HPLC) pump. Tempe a u e and p essu e o he expe imen s we e app op ia ely con olled. The ca alys , wi h a pa icle size be ween 160 m and 250 µ m, was mixed wi h ine sand o he same size and placed inside he ubula eac o be ween qua z wool suppo s. The s ainless s eel ubula eac o had an inne diame e o 9 mm. Mo e de ails abou his ins alla ion can be ound in p e ious wo ks [27,28]. The gas low was analyzed wi h an Agilen 3000 Mic o GC equipped wi h a molecula sie e column, a Plo U column and The mal Conduc i i y De ec o s (TCD), whe e N 2 , H 2 , CH 4 , CO 2 , CO, C 2 H 6 and C 3 H 8 can be quan i ied. The liquid low exi ing om he eac o was dep essu ized, cooled and analysed wi h an Agilen 7820A GC equipped wi h an Agilen 7693A au oma ic injec o , an HP-FFAP Agilen 19091F-105 capilla y column and a Flame Ioniza ion De ec o (FID), whe e liquid p oduc s we e quan i ied. P e iously, he compounds in he liquid p oduc we e iden i ied by Gas Ch oma og aphy-Mass Spec om- e y (GC-MS). Due o he complexi y o he eal aqueous ac ion i s liquid e luen was quali a i ely analysed by GC-MS/FID. All he expe imen s we e ca ied ou a 40 absolu e ba o sys em p essu e, 227 ◦ C o eac ion empe a u e and a eeding low a e o 1 mL/min. The amoun o ca alys in he eac ion bed was adjus ed o ob ain a ca alys weigh /o ganic low a e a io (W/m) om 5 g o 40 g ca alys min/g o ganic. The expe imen s we e pe o med mos ly o 3 h. The ca alys used was p epa ed by cop ecipi a ion in he labo a o y. This ca alys , Ni- Co/Al-Mg, had a Ni mola con en o 28% exp essed as Ni/(Ni+Al+Co+Mg) and Mg/Al and Co/Ni a omic a ios o 0.26 and 0.10, espec i ely. Thus, he mola composi ion o each me al in he ca alys was 54.91% Al, 28% Ni, 14.28% Mg and 2.8% Co. Mo e explana ions abou i s p epa a ion and cha ac e iza ion ha e been desc ibed by Remón e al. [ 8 ]. This ca alys has been employed in he s eam e o ming o glyce ol and he aqueous ac ion o bio-oil [ 29 – 31 ]. The Ni-Co/Al-Mg ca alys was calcined in ai a mosphe e a a inal empe a u e o 750 ◦ C o 3 h. Be o e he APR eac ion, he ca alys was in si u educed wi h a hyd ogen low a e o 100 cm3(STP)/min a 650 ◦C o 1 h. Ace ol (pu i y: ≥ 97.5%, Sigma-Ald ich, S . Louis, MO, USA), 1-bu anol (pu i y: ≥99.5%, Scha lau, Sen mena , Spain) and ace ic acid (pu i y: ≥99.5%, Pan eac, Ba celona, Spain) we e ed as only compound wi h 5 w % in deionized wa e . A simula ed aqueous ac ion o bio-oil wi h 5 w % o ace ol, 5 w % o bu anol and 5 w % o ace ic acid in deionized wa e was also employed as eed. Mo eo e , a eal aqueous ac ion o bio-oil was also used as eed in he APR expe imen s. The bio-oil gene a ed om pine sawdus was supplied by Biomass Technology G oup BV (BTG). The aqueous ac ion was ob ained by adding he bio-oil slowly o dis illed wa e in 1:2 weigh a io wi h cons an s i ing. This was he same p ocedu e employed in he wo k o Remón e al. [ 8 ]. The ul ima e analysis and Ka l Fische analysis o he aqueous P ocesses 2021,9, 81 4 o 17 ac ion o bio-oil can be ound in ha wo k. The chemical analysis o he aqueous ac ion o bio-oil ca ied ou by GC-FID is shown in Table 1. Table 1. Chemical analysis o he aqueous ac ion o bio-oil. Compound A ea FID% Ace one 2.63 Me hanol 9.20 E hanol 16.91 Ace ol 15.29 2-Cyclopen en-one-1 1.23 1-Hyd oxy- 2- bu anone 3.07 Ace ic acid 37.74 Fu u al 1.17 Fo mic acid 0.33 P opanoic acid 2.02 1,2 Cyclopen anedione, 3-me hyl 4.86 Phenol, 2 –me hoxy 1.21 Bu anal, 3-me hyl 2.05 Phenol, 2,6-dime hoxy 1.27 Pen anoic acid, 4–oxo 1.03 The compound wi h highes a ea FID % was ace ic acid (37.74), ollowed by e hanol (16.91) and ace ol (15.29). These main componen s ha e been s udied in o he published wo ks, such as he s udy by Pan e al. [ 18 ], in which ace ic acid and ace ol we e he compounds wi h he highes a ea pe cen age in low-boiling ac ion by GC-MS. The au ho s also de ec ed o he compounds, such as e hanol, o mic acid, u u al and phenol, 2-me hoxy, among o he s. Vispu e and Hube also iden i ied hyd oxyace one (ace ol) and ace ic acid in he aqueous ac ion o bio-oil [21]. Mass balance and ca bon balance we e pe o med o alida e he expe imen s. Mass balance was de e mined as he summa ion o he amoun o gases and liquid e luen s om he eac o di ided by he amoun o he aqueous solu ion ed. The mass balance was conside ed eliable i he esul was 100 ± 5%. Gas p oduc s we e de e mined om he gas analysis ca ied ou by GC. Liquid p oduc s we e de e mined by weigh . Gas analysis was used o p o ide he a e age gas composi ion, yields o gas p oduc s and ca bon con e sion o gases. The H2yield was calcula ed as ollows: H2yield mmolH2 molH2max= nH2 ×1000 nC ed ×R(1) whe e nH 2 a e he moles o H 2 gene a ed, nC ed a e he moles o ca bon a om ed and R is he a io o e o ming. R is he numbe o moles o H 2 pe moles o ca bon a om when he compound p oduces in he e o ming eac ion he maximum amoun o H 2 and CO 2 . R is 7/3 o ace ol, 3 o bu anol and 2 o ace ic acid. nC ed was calcula ed as he moles o compound ed mul iplied by he a oms o ca bon in he compound. Yields o gas p oduc s we e calcula ed as ollows: Yield o gas i mmol C mol C ed= ni Ci ×1000 nC ed (2) whe e ni a e he moles o gas i gene a ed (CH 4 , CO, CO 2 , C 2 H 6 o C 3 H 8 ) and Ci is he numbe o ca bon a oms in one molecule o gas i. The ca bon yield o gases was calcula ed as a pe cen age, di iding he moles o ca bon in gases (CH4, CO, CO2, C2H6and C3H8) by he moles o ca bon in he eed. To al O ganic Ca bon (TOC) analysis o he liquid e luen allowed us o de e mine he ca bon in liquids, which was employed oge he wi h he ca bon con e sion o gases o P ocesses 2021,9, 81 5 o 17 calcula e he ca bon balance. The ca bon in liquids con ained all he o ganic compounds in he liquid e luen , as well as he uncon e ed o ganic compounds ed. GC-FID analysis was employed o quan i a i ely de e mine he liquid p oduc s in he APR expe imen . The ca bon yield o liquids was calcula ed as he pe cen age o ca bon moles in liquid p oduc s excep he o ganic compound ed di ided by he moles o ca bon in he eed. The yields o liquid p oduc s we e calcula ed as ollows: Yield o liquid i mmol C mol C ed= ni Ci ×1000 nC ed (3) whe e ni a e he moles o liquid i gene a ed ( o example, e hanol in he APR o ace ic acid) and Ci is he numbe o ca bon a oms in one molecule o liquid i. Global esul s o he phase gas a e p esen ed o he 3 h o expe imen and he e olu ion o gas yields. Time-on-s eam was s udied in o de o know he ca alys s abili y a he ope a ing condi ions o he APR p ocess. Liquid p oduc s we e collec ed e e y hou o expe imen . The quan i a i e esul s o liquids p oduc s analysed by GC-FID p esen ed in ables co espond o he second hou o he expe imen , which is conside ed mo e ep esen a i e o he whole expe imen . 3. Resul s 3.1. APR o Ace ol Figu e 1shows ca bon yield o gases and ca bon yield o liquids o he expe imen s o ace ol APR wi h W/m o 5, 20 and 40 g ca alys min/g ace ol. P ocesses 2021, 9, x FOR PEER REVIEW 5 o 18 whe e ni a e he moles o gas i gene a ed (CH4, CO, CO2, C2H6 o C3H8) and Ci is he numbe o ca bon a oms in one molecule o gas i. The ca bon yield o gases was calcula ed as a pe cen age, di iding he moles o ca - bon in gases (CH4, CO, CO2, C2H6 and C3H8) by he moles o ca bon in he eed. To al O ganic Ca bon (TOC) analysis o he liquid e luen allowed us o de e mine he ca bon in liquids, which was employed oge he wi h he ca bon con e sion o gases o calcula e he ca bon balance. The ca bon in liquids con ained all he o ganic compounds in he liquid e luen , as well as he uncon e ed o ganic compounds ed. GC-FID analysis was employed o quan i a i ely de e mine he liquid p oduc s in he APR expe imen . The ca bon yield o liquids was calcula ed as he pe cen age o ca - bon moles in liquid p oduc s excep he o ganic compound ed di ided by he moles o ca bon in he eed. The yields o liquid p oduc s we e calcula ed as ollows: Yield o liquid i mmol C mol C ed= ni Ci × 1000 nC ed (3) whe e ni a e he moles o liquid i gene a ed ( o example, e hanol in he APR o ace ic acid) and Ci is he numbe o ca bon a oms in one molecule o liquid i. Global esul s o he phase gas a e p esen ed o he 3 h o expe imen and he e o- lu ion o gas yields. Time-on-s eam was s udied in o de o know he ca alys s abili y a he ope a ing condi ions o he APR p ocess. Liquid p oduc s we e collec ed e e y hou o expe imen . The quan i a i e esul s o liquids p oduc s analysed by GC-FID p esen ed in ables co espond o he second hou o he expe imen , which is conside ed mo e ep esen a i e o he whole expe imen . 3. Resul s 3.1. APR o Ace ol Figu e 1 shows ca bon yield o gases and ca bon yield o liquids o he expe imen s o ace ol APR wi h W/m o 5, 20 and 40 g ca alys min/g ace ol. 0 20 40 60 40 20 Ca bon yield o p oduc s (%) W/m (g ca alys min/g ace ol) Gases Liquids 5 Figu e 1. Ca bon yield o gases and liquids in he Aqueous Phase Re o ming (APR) o ace ol a di e en ca alys loading (T = 227 °C, 40 ba , 5 w % ace ol, Ni-Co/Al-Mg ca alys , 1 mL/min aque- ous eeding a e). Figu e 1. Ca bon yield o gases and liquids in he Aqueous Phase Re o ming (APR) o ace ol a di e en ca alys loading (T = 227 ◦ C, 40 ba , 5 w % ace ol, Ni-Co/Al-Mg ca alys , 1 mL/min aqueous eeding a e). We obse ed a signi ican inc ease in ca bon yield o gases when he W/m a io inc eased om 5 o 40 g ca alys min/g ace ol. Thus, a 5 and 40 g ca alys min/g ace ol, he ca bon yield o gases was 5.46% and 46.69% espec i ely. The ca bon yield o liquids showed a maximum a W/m a io o 20 g ca alys min/g ace ol wi h a alue o 34.79%. A he highes W/m a io (40 g ca alys min/g ace ol), he ca alys a ou ed gas p oduc ion, p obably by b eaking C-C bonds in he ace ol molecule. The esul s o gases and liquids p oduc s in he APR o ace ol a e shown in Table 2. The gas wi h he highes con en was CO 2 , ollowed by CH 4 and H 2 , since P ocesses 2021,9, 81 6 o 17 hey we e he modynamically a ou ed a he APR condi ions o low empe a u e while he con en o C 2 H 6 and CO was e y small as he modynamically expec ed. We obse ed a clea inc ease in H 2 con en and a dec ease in CO 2 con en when he W/m a io inc eased, as well as an inc ease in he con en o me hane, which indica es ha e o ming, c acking and me hana ion eac ions we e boos ed by he ca alys . CO con en showed a dec ease when he W/m a io inc eased. Alkanes con en , CH 4 and C 2 H 6 , showed a signi ican inc ease when he W/m a io inc eased om 5 g o 20 g ca alys min/g ace ol, while he inc ease om 20 g o 40 g ca alys min/g ace ol was small. The yields o all gases (H 2 , CH 4 , CO, CO 2 and C 2 H 6 ) inc eased when he W/m a io inc eased, which is in acco dance wi h he inc ease o ca bon yield o gases wi h W/m a io (Figu e 1). Table 2. Resul s o he APR expe imen s o ace ol (T = 227 ◦ C, 40 ba , 5 w % ace ol, Ni-Co/Al-Mg ca alys , 1 mL/min aqueous eeding a e). W/m (g Ca alys min/g Ace ol) 5 20 40 Mass balance (%) 100.59 95.18 95.14 Ca bon balance (%) 89.79 90.15 89.78 Mola gas composi ion (%) H210.85 25.36 33.70 CH416.99 23.18 23.72 CO 0.76 0.30 0.18 CO271.25 50.89 42.07 C2H60.14 0.27 0.32 Yields o gas p oduc s H2yield (mmol H2/mol H2max) 2.8 36.7 101.2 CH4yield (mmol C/mol C ed) 10.4 78.4 166.3 CO yield (mmol C/mol C ed) 0.5 1.0 1.3 CO2yield (mmol C/mol C ed) 43.6 172.1 294.9 C2H6yield (mmol C/mol C ed) 0.2 1.8 4.5 Yields o liquid p oduc s Ace aldehyde (mmol C/mol C ed) 16.6 0 10.2 Ace one (mmol C/mol C ed) 11.4 6.6 13.6 E hanol (mmol C/mol C ed) 29.2 112.8 165.0 Ace ic acid (mmol C/mol C ed) 15.7 0 0 1,2-p opanediol (mmol C/mol C ed) 195.2 228.5 133.2 The ca alys in luenced in he WGS eac ion: inc easing H 2 con en and dec easing CO con en . This could ha e also a ou ed me hana ion and Fische –T opsch eac ions o gene a e CH 4 and C 2 H 6 , espec i ely. The gas yield e olu ion wi h ime showed a s able pe o mance, which indica es ha no deac i a ion o he ca alys was obse ed in he APR o ace ol. The liquid p oduc s analysed in he APR o ace ol we e ace aldehyde, ace one, e hanol, ace ic acid and 1,2-p opanediol. Among hem, e hanol and 1,2-p opanediol we e he ones wi h he highes yields in all condi ions. The yield o e hanol inc eased signi ican ly when he W/m a io inc eased om 5 g o 40 g ca alys min/g ace ol, wi h alues o 29.2 and 165.0 mmol C/mol C ed, espec i ely. Howe e , he yield o 1,2-p opanediol showed a maximum a he W/m a io o 20 g ca alys min/g ace ol. These esul s seem o indica e ha 1,2-p opanediol is an in e media e in he ou e o e hanol, and ha he hyd ogena ion o he ace ol i s akes place o p oduce 1, 2- p opanediol. Nex , as he ca alys /o ganic a io inc eases in a subsequen s ep, he c acking and b eaking o C-C bonds a e p oduced o gene a e e hanol. The eac ion pa hways o he con e sion o 1,2-p opanediol o e hanol ha e been p oposed by Remón e al. [27]. These esul s a e in acco dance wi h o he wo ks, which indica e ha ace ol is an in e media e in APR o glyce ol, which is p oduced om he dehyd a ion o glyce ol in he acid cen es o he ca alys suppo , and hen ace ol is hyd ogena ed o 1,2-p opanediol P ocesses 2021,9, 81 7 o 17 in he me al cen es o he ca alys [ 32 ]. In he APR o ace ol, he hyd ogen needed o hyd ogena e ace ol is supplied by he con e sion o ace ol o gases p oduc s. 3.2. APR o Bu anol Figu e 2shows he ca bon yield o gases and ca bon yield o liquids o he expe imen s o bu anol APR wi h he W/m a ios o 5, 10, 20 and 40 g ca alys min/g bu anol. P ocesses 2021, 9, x FOR PEER REVIEW 7 o 18 and 165.0 mmol C/mol C ed, espec i ely. Howe e , he yield o 1,2-p opanediol showed a maximum a he W/m a io o 20 g ca alys min/g ace ol. These esul s seem o indica e ha 1,2-p opanediol is an in e media e in he ou e o e hanol, and ha he hyd ogena ion o he ace ol i s akes place o p oduce 1, 2-p opane- diol. Nex , as he ca alys /o ganic a io inc eases in a subsequen s ep, he c acking and b eaking o C-C bonds a e p oduced o gene a e e hanol. The eac ion pa hways o he con e sion o 1,2-p opanediol o e hanol ha e been p oposed by Remón e al. [27]. These esul s a e in acco dance wi h o he wo ks, which indica e ha ace ol is an in e media e in APR o glyce ol, which is p oduced om he dehyd a ion o glyce ol in he acid cen es o he ca alys suppo , and hen ace ol is hyd ogena ed o 1,2-p opanediol in he me al cen es o he ca alys [32]. In he APR o ace ol, he hyd ogen needed o hy- d ogena e ace ol is supplied by he con e sion o ace ol o gases p oduc s. 3.2. APR o Bu anol Figu e 2 shows he ca bon yield o gases and ca bon yield o liquids o he expe i- men s o bu anol APR wi h he W/m a ios o 5, 10, 20 and 40 g ca alys min/g bu anol. 0 10 20 30 40 10 40 20 Ca bon yield o p oduc s (%) W/m (g ca alys min/g bu anol) Gases Liquids 5 Figu e 2. Ca bon yield o gases and liquids in he APR o bu anol a di e en ca alys loading (T = 227 °C, 40 ba , 5 w % bu anol, Ni-Co/Al-Mg ca alys , 1 mL/min aqueous eeding a e). We obse ed a signi ican inc ease in he ca bon yield o gases wi h he inc ease o he W/m a io. Thus, he ca bon yield o gases we e 2.28% and 34.67% a W/m a ios o 5 and 40 g ca alys min/g bu anol, espec i ely. The ca bon yield o liquids was smalle han 4% and did no p esen a clea endency. Simila ly o ace ol, he inc ease o he W/m a io a ou ed gas p oduc ion, p obably due o he b eaking o C-C bonds in he bu anol mol- ecule. Howe e , p oduc ion o liquids was signi ican ly lowe han o ace ol ega dless o he amoun o ca alys used. The lowe yield o liquids ob ained om bu anol compa ed o ace ol could be ela ed o he lowe eac i i y o only one –OH g oup in bu anol agains he ca bonyl and –OH g oups in ace ol. Table 3 shows he esul s o gases and liquids p oduc s in he APR o bu anol. The gases ob ained in he APR o bu anol we e H2, CH4, CO, CO2, C2H6 and C3H8. H2 showed he highes con en in he gas a all he W/m a ios s udied. The con en o H2 dec eased wi h he inc ease o W/m a io, wi h alues o 60.96% and 37.94% a 5 and 40 g ca alys min/g bu anol, espec i ely. Howe e , H2 yield inc eased when he W/m a io inc eased, ha is, he ca alys loading inc eased. On he con a y, CH4, CO2, C2H6 and C3H8 con en Figu e 2. Ca bon yield o gases and liquids in he APR o bu anol a di e en ca alys loading (T = 227 ◦C, 40 ba , 5 w % bu anol, Ni-Co/Al-Mg ca alys , 1 mL/min aqueous eeding a e). We obse ed a signi ican inc ease in he ca bon yield o gases wi h he inc ease o he W/m a io. Thus, he ca bon yield o gases we e 2.28% and 34.67% a W/m a ios o 5 and 40 g ca alys min/g bu anol, espec i ely. The ca bon yield o liquids was smalle han 4% and did no p esen a clea endency. Simila ly o ace ol, he inc ease o he W/m a io a ou ed gas p oduc ion, p obably due o he b eaking o C-C bonds in he bu anol molecule. Howe e , p oduc ion o liquids was signi ican ly lowe han o ace ol ega dless o he amoun o ca alys used. The lowe yield o liquids ob ained om bu anol compa ed o ace ol could be ela ed o he lowe eac i i y o only one –OH g oup in bu anol agains he ca bonyl and –OH g oups in ace ol. Table 3shows he esul s o gases and liquids p oduc s in he APR o bu anol. The gases ob ained in he APR o bu anol we e H 2 , CH 4 , CO, CO 2 , C 2 H 6 and C 3 H 8 . H 2 showed he highes con en in he gas a all he W/m a ios s udied. The con en o H 2 dec eased wi h he inc ease o W/m a io, wi h alues o 60.96% and 37.94% a 5 and 40 g ca alys min/g bu anol, espec i ely. Howe e , H 2 yield inc eased when he W/m a io inc eased, ha is, he ca alys loading inc eased. On he con a y, CH 4 , CO 2 , C 2 H 6 and C 3 H 8 con en in he p oduc gas inc eased wi h he inc ease o he W/m a io. As expec ed in APR, he le els o CO we e e y low, and showed a end owa d lowe le els as he W/m a io inc eased. The yields o mos o gases (H 2 , CH 4 , CO 2 , C 2 H 6 and C 3 H 8 ) inc eased when he ca alys loading inc eased. CO yield did no show a clea endency, wi h e y low alues. These alues we e a consequence o he pa icipa ion o he ca alys in he WGS eac ion. The mos ele an esul in he gas p oduc ion was a signi ican amoun o C 3 H 8 p oduced. Gas p oduc ion also showed he end owa d highe alues as he ca alys /o ganic a io inc eased. Gas composi ion showed some selec i i y endencies wi h he inc ease o ca alys loading: Bu anol e o ming o H 2 was no a ou ed, while C 3 H 8 gene a ion was p omo ed. Me hana ion and Fische –T opsch eac ions we e also p omo ed a high ca alys loading. No deac i a ion o he ca alys was obse ed in he P ocesses 2021,9, 81 8 o 17 APR o bu anol. The highes yields o gases we e gene a ed a he highes W/m a io, wi h alues o 36.6 mmol H 2 /mol H 2 max, 31 mmol CH 4 /mol C ed and 248.1 mmol C in C 3 H 8 /mol C ed. H 2 yield and CH 4 yield p esen ed alues conside ably smalle han hose ob ained in he APR o ace ol a he same W/m a io. Table 3. Resul s o he APR expe imen s o bu anol (T = 227 ◦ C, 40 ba , 5 w % bu anol, Ni-Co/Al-Mg ca alys , 1 mL/min aqueous eeding a e). W/m (g Ca alys min/g Bu anol) 5 10 20 40 Mass balance (%) 97.10 97.61 97.40 97.22 Ca bon balance (%) 92.24 88.64 87.46 86.98 Mola gas composi ion (%) H260.96 42.65 37.69 37.94 CH44.22 7.77 8.75 10.68 CO 0.83 0.19 0.11 0.14 CO218.29 21.58 22.31 22.23 C2H60.18 0.33 0.40 0.49 C3H815.52 27.47 30.73 28.53 Yields o gas p oduc s H2yield (mmol H2/mol H2max) 6.6 19.1 27.1 36.6 CH4yield (mmol C/mol C ed) 1.4 10.4 18.9 31.0 CO yield (mmol C/mol C ed) 0.3 0.3 0.2 0.4 CO2yield (mmol C/mol C ed) 5.9 29.0 48.1 64.4 C2H6yield (mmol C/mol C ed) 0.1 0.9 1.7 2.8 C3H8yield (mmol C/mol C ed) 15.1 110.8 198.6 248.1 Yields o liquid p oduc s Bu aldehyde (mmol C/mol C ed) 37.2 23.7 15.6 13.2 2-pen anone (mmol C/mol C ed) 2.6 9.5 13.6 18.7 The liquids p oduc s iden i ied in he APR o bu anol (bu aldehyde and 2-pen anone) di e ed subs an ially om he APR o ace ol. The yield o bu aldehyde was 37.2 mmol C/mol C ed a he W/m a io o 5 g ca alys min/g bu anol and dec eased o 13.2 a he W/m a io o 40 g ca alys min/g bu anol. The yield o 2-pen anone inc eased om 2.6 o 18.7 mmol C/mol C ed when he W/m a io inc eased om 5 o 40 g ca alys min/g bu anol, espec i ely. 3.3. APR o Ace ic Acid Figu e 3shows ca bon yield o gases and ca bon yield o liquids o he expe imen s o ace ic acid APR wi h W/m a ios o 5, 10, 20 and 40 g ca alys min/g ace ic acid. Like he o he wo model compounds, he p oduc ion o gases was highe when i was used wi h he highes amoun o ca alys pe o ganic. Howe e , a ema kable di e ence is ha he ace ic acid was less eac i e wi h his ca alys han bu anol and ace ol, wi h alues o ca bon yields below 2%, ega dless how much ca alys was used bo h o liquids and o gases. A close look a he esul s o he gases and liquids p oduced is shown in Table 4. The gases de ec ed by GC we e H 2 , CH 4 , CO 2 and C 2 H 6 , wi h he C 2 H 6 in esidual amoun s. The H 2 con en dec eased wi h he inc ease o W/m a io om 50.13% o 34.68% a W/m a ios o 5 and 40 g ca alys min/g ace ic acid, espec i ely. The con en s o CH 4 and CO 2 in he p oduced gas inc eased when he W/m a io inc eased. The yields o all gases (H 2 , CH 4 , CO 2 and C 2 H 6 ) inc eased when he W/m a io inc eased, excep o W/m a ios o 5 and 10 g ca alys min/g ace ic acid, which had e y simila alues. Gas composi ion showed some selec i i y endencies wi h he inc ease o ca alys loading: Ace ic acid e o ming o H 2 was no a ou ed, while me hana ion and Fische –T opsch eac ions we e p omo ed. These esul s can co obo a e he endency obse ed in he APR o ace ol and bu anol, which indica es ha me hana ion was a ou ed using a high ca alys loading. P ocesses 2021,9, 81 9 o 17 P ocesses 2021, 9, x FOR PEER REVIEW 9 o 18 alues o ca bon yields below 2%, ega dless how much ca alys was used bo h o liquids and o gases. A close look a he esul s o he gases and liquids p oduced is shown in Table 4. The gases de ec ed by GC we e H2, CH4, CO2 and C2H6, wi h he C2H6 in esidual amoun s. The H2 con en dec eased wi h he inc ease o W/m a io om 50.13% o 34.68% a W/m a ios o 5 and 40 g ca alys min/g ace ic acid, espec i ely. The con en s o CH4 and CO2 in he p oduced gas inc eased when he W/m a io inc eased. The yields o all gases (H2, CH4, CO2 and C2H6) inc eased when he W/m a io inc eased, excep o W/m a ios o 5 and 10 g ca alys min/g ace ic acid, which had e y simila alues. Gas composi ion showed some selec i i y endencies wi h he inc ease o ca alys loading: Ace ic acid e- o ming o H2 was no a ou ed, while me hana ion and Fische –T opsch eac ions we e p omo ed. These esul s can co obo a e he endency obse ed in he APR o ace ol and bu anol, which indica es ha me hana ion was a ou ed using a high ca alys loading. 0 1 2 3 4 5 6 10 40 20 Ca bon yield o p oduc s (%) W/m (g ca alys min/g ace ic acid) Gases Liquids 5 Figu e 3. Ca bon yield o gases and liquids in he APR o ace ic acid a di e en ca alys loading (T = 227 °C, 40 ba , 5 w % ace ic acid, Ni-Co/Al-Mg ca alys , 1 mL/min aqueous eeding a e). Table 4. Resul s o he APR expe imen s o ace ic acid (T = 227 °C, 40 ba , 5 w % ace ic acid, Ni- Co/Al-Mg ca alys , 1 mL/min aqueous eeding a e). W/m (g Ca alys min/g Ace ic Acid) 5 10 20 40 Mass balance (%) 96.66 97.09 98.31 95.78 Ca bon balance (%) 106.02 96.68 95.18 95.02 Mola gas composi ion (%) H2 50.13 48.11 41.24 34.68 CH4 16.46 18.35 21.91 25.92 CO 0 0 0 0 CO2 33.15 33.44 36.63 39.15 C2H6 0.26 0.10 0.22 0.26 Yields o gas p oduc s H2 yield (mmol H2/mol H2 max) 2.3 2.0 2.9 4.5 CH4 yield (mmol C/mol C ed) 1.5 1.6 3.0 6.7 CO yield (mmol C/mol C ed) 0 0 0 0 CO2 yield (mmol C/mol C ed) 3.0 2.8 5.1 10.1 C2H6 yield (mmol C/mol C ed) 0.05 0.02 0.06 0.13 Figu e 3. Ca bon yield o gases and liquids in he APR o ace ic acid a di e en ca alys loading (T = 227 ◦C, 40 ba , 5 w % ace ic acid, Ni-Co/Al-Mg ca alys , 1 mL/min aqueous eeding a e). Table 4. Resul s o he APR expe imen s o ace ic acid (T = 227 ◦ C, 40 ba , 5 w % ace ic acid, Ni-Co/Al-Mg ca alys , 1 mL/min aqueous eeding a e). W/m (g Ca alys min/g Ace ic Acid) 5 10 20 40 Mass balance (%) 96.66 97.09 98.31 95.78 Ca bon balance (%) 106.02 96.68 95.18 95.02 Mola gas composi ion (%) H250.13 48.11 41.24 34.68 CH416.46 18.35 21.91 25.92 CO 0 0 0 0 CO233.15 33.44 36.63 39.15 C2H60.26 0.10 0.22 0.26 Yields o gas p oduc s H2yield (mmol H2/mol H2max) 2.3 2.0 2.9 4.5 CH4yield (mmol C/mol C ed) 1.5 1.6 3.0 6.7 CO yield (mmol C/mol C ed) 0 0 0 0 CO2yield (mmol C/mol C ed) 3.0 2.8 5.1 10.1 C2H6yield (mmol C/mol C ed) 0.05 0.02 0.06 0.13 Yields o liquid p oduc s E hanol (mmol C/mol C ed) 16.7 2.4 2.5 2.6 We also obse ed he dec ease o gas yields wi h ime-on-s eam, which indica es he deac i a ion o ca alys in he APR o ace ic acid. The highes yields o H 2 and CH 4 we e ob ained using he highes W/m a io, which was 4.5 mmol H 2 /mol H 2 max and 6.7 mmol CH 4 /mol C ed. The H 2 and CH 4 yields we e conside able smalle han hose ob ained wi h bu anol. E hanol was he only liquid p oduc analysed. The yields o e hanol we e smalle han 17 mmol C/mol C ed. This low alue o e hanol yield was a consequence o he low amoun o ca bon yield o liquids. 3.4. APR o a Simula ed Aqueous F ac ion o Bio-Oil Besides he s udy o he indi idual model compounds, once he independen be- ha iou o he h ee compounds we e es ablished, we conside ed ha i would be in e - P ocesses 2021,9, 81 16 o 17 Au ho Con ibu ions: Concep ualiza ion, L.G. and M.O.; me hodology, J.R.; alida ion, P.L., J.R., and L.G.; o mal analysis, P.L. and A.I.S.; in es iga ion, P.L.; w i ing—o iginal d a p epa a ion, L.G.; w i ing— e iew and edi ing, L.G., M.O., J.R. and J.A.; isualiza ion, L.G. and J.R.; supe ision, M.O., L.G. and J.A.; p ojec adminis a ion, M.O. and L.G.; unding acquisi ion, M.O., L.G. and J.A. All au ho s ha e ead and ag eed o he published e sion o he manusc ip . Funding: This esea ch was unded by AEI/FEDER, UE (p ojec CTQ2017-86893-R), he A agón Go e nmen ( e . T22_20R), co- unded by FEDER 2014-2020) “Cons uyendo Eu opa desde A agón” and A agón Go e nmen and La Caixa (p ojec 2012/GA LC 088). Da a A ailabili y S a emen : Mos o da a a e a ailable in his manusc ip . Mo e speci ic da a can be eques ed om he co esponding au ho . Acknowledgmen s: The au ho s like o acknowledge Olga Ma ín o he help in he analysis o he liquids p oduc s. Con lic s o In e es : The au ho s decla e no con lic o in e es . The unde s had no ole in he design o he s udy; in he collec ion, analyses, o in e p e a ion o da a; in he w i ing o he manusc ip , o in he decision o publish he esul s. Re e ences 1. Cze nik, S.; B idgwa e , A. O e iew o applica ions o biomass as py olysis oil. Ene gy Fuels 2004,18, 590–598. [C ossRe ] 2. Wang, D.; Cze nik, S.; Mon ane, D.; Mann, M.; Cho ne , E. Biomass o hyd ogen ia as py olysis and ca aly ic s eam e o ming o he py olysis oil o i s ac ions. Ind. Eng. Chem. Res. 1997,36, 1507–1518. [C ossRe ] 3. Wang, D.; Cze nik, S.; Cho ne , E. 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