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-
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Copy igh : © 2021 by he au ho s. Li-
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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.
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