1
Fabio He nández-Ramos, Ja ie Fe nández-Rod íguez, Ma ía González Al iols, Jalel Labidi, Xabie
E docia, S udy o a enewable capping agen addi ion in lignin base ca alysed depolyme isa ion
p ocess, Fuel, Volume 280, 2020, 118254, ISSN 0016-2361
h ps://doi.o g/10.1016/j. uel.2020.118524
(h ps://www.sciencedi ec .com/science/a icle/abs/pii/S0016236120315209)
Abs ac : The aim o his wo k was o s udy he in luence o a enewable capping agen (CA) in
he p oduc ion o monome ic compounds om he depolyme iza ion o an o ganosol lignin
(Pinus adia a) by a base ca alyzed depolyme iza ion (BCD) p ocess. A e he deligni ica ion
p ocess o he Pinus adia a sawdus , he lignin con ained in he black liquo was subjec ed o a
i s mild depolyme iza ion p ocess, wi hou using any ca alys , in o de o ob ain wo di e en
p oduc s: a lignin which was he eed in he subsequen BCD p ocess and a phenolic oil which
was used as CA in he same BCD p ocess. This p ocess was ca ied ou a 230 °C in h ee
consecu i e cycles o 20 min using di e en amoun s o capping agen dissol ed in a 4% w .
NaOH solu ion wi h a lignin:sol en a io o 1:20. The use o a enewable capping agen de i ed
om lignin was e ec i e no only in e ms o phenolic oil p oduc ion inc easing bu also in
maximizing he monome ic phenolic compounds concen a ion. The use o CA: lignin a io o 1:1
esul ed he mos e ec i e wi h 10.64% o oil yield and almos 44% o monome ic phenolic
compounds concen a ion while minimizing de undesi ed by-p oduc s yield.
Keywo ds: Lignin, Capping agen , Depolyme iza ion, Phenolic monome s, O ganosol .
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S udy o a enewable capping agen addi ion in
lignin base ca alyzed depolyme iza ion p ocess
Fabio He nández-Ramosa, Ja ie Fe nández-Rod ígueza, Ma ía González Al iolsa, Jalel
Labidia, Xabie E dociab*
aBio e ine y P ocesses Resea ch G oup (BioRP), Chemical and En i onmen al
Enginee ing Depa men , Uni e si y o he Basque Coun y (UPV/EHU), Plaza Eu opa
1, 20018, San Sebas ian, Spain
bBio e ine y P ocesses Resea ch G oup (BioRP), Depa men o Applied Ma hema ics,
Uni e si y o he Basque Coun y (UPV/EHU), Ra ael Mo eno “Pichichi” 3, Bilbao,
48013, Spain
*[email p o ec ed]
ABSTRACT
The aim o his wo k was o s udy he in luence o a enewable capping agen (CA) in he
p oduc ion o monome ic compounds om he depolyme iza ion o an o ganosol lignin
(Pinus adia a) by a base ca alyzed depolyme iza ion (BCD) p ocess. A e he
deligni ica ion p ocess o he Pinus adia a sawdus , he lignin con ained in he black
liquo was subjec ed o a i s mild depolyme iza ion p ocess, wi hou using any ca alys ,
in o de o ob ain wo di e en p oduc s: a lignin which was he eed in he subsequen
BCD p ocess and a phenolic oil which was used as CA in he same BCD p ocess. This
p ocess was ca ied ou a 230 ºC in h ee consecu i e cycles o 20 min using di e en
amoun s o capping agen dissol ed in a 4% w . NaOH solu ion wi h a lignin:sol en a io
o 1:20. The use o a enewable capping agen de i ed om lignin was e ec i e no only
in e ms o phenolic oil p oduc ion inc easing bu also in maximizing he monome ic
phenolic compounds concen a ion. The use o CA: lignin a io o 1:1 esul ed he mos
3
e ec i e wi h 10.64% o oil yield and almos 44% o monome ic phenolic compounds
concen a ion while minimizing de undesi ed by-p oduc s yield.
KEYWORDS: Lignin, capping agen , depolyme iza ion, phenolic monome s,
o ganosol .
1. In oduc ion
Lignin is one o he main componen s o he cell wall o ascula plan s, wi h a mass
con en ha can a y be ween 15-30% depending on he species [1] and i is conside ed
he second mos abundan polyme in na u e a e cellulose. Lignin is a polyphenolic
compound composed by he polyme iza ion o h ee hyd oxy cinnamyl alcohol
monome s, p-couma yl alcohol, coni e yl alcohol and sinapyl alcohol ha p oduce
espec i ely p-hyd oxyphenyl (H), guaiacyl (G) and sy ingyl (S) phenylp opanoid uni s.
The amoun o hese phenylp opanoid uni s in he cell wall depend on he species. In his
sense, ha dwood lignins a e mainly composed o G and S uni s and low H aces, whe eas
so wood lignins only p esen s G uni s and low le els o H uni s. Finally, lignins om
g asses ha e simila amoun o G and S uni s and p esen a highe le el o H uni s han
in o he species. These phenylp opanoid uni s a e linked o each o he mainly ia e he
bonds (α-O-4, β-O-4 and 4-O-5) and ca bon-ca bon bonds [2]. This con e s o he lignin
i s h ee-dimensional s uc u e ha ac s as a esin be ween cellulose and hemicelluloses
[3] which is essen ial o p o ide s uc u al in eg i y o he cell wall and o he s em
esis ance and s i ness. Due o his phenolic na u e, lignin is conside ed as he mos
abundan enewable a oma ic polyme on Ea h [4] and is called o be an al e na i e o
chemical compounds de i ed om pe oleum [5].
Nowadays pulp and pape indus y (P&P) is he main sou ce o lignin and he K a
me hod is he mos employed one o gene a e chemical pulps. Abou 50 M o lignin a e
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gene a ed as a by-p oduc in his p ocess [6], which a e bu ned o gene a e ene gy [7].
Howe e , due o he en i onmen al issues ha can be gene a ed by K a p ocess, he
o ganosol p ocess has been gaining ele ance in he ac iona ion o lignocellulosic
eeds ock [8]. The o ganosol p ocess consis in he deligni ica ion o he lignocellulosic
biomass ia clea age o e he linkages o lignin [9] employing o ganic sol en s such as
e hanol, me hanol, ace one, o ganic acids and polyhyd ic acids. Among hese, he use o
e hanol appea s as he mos a o able due o i s low oxici y [10]. The o ganosol p ocess
has se e al ad an ages compa ed o con en ional me hods such as he possibili y o
eco e ing he sol en by dis illa ion, a lowe en i onmen al impac and ob aining a high
quali y lignin ha can be used in di e en applica ions such as an ioxidan s, bio
dispe san s, polyu e hanes oam and epoxy esins [11].
In o de o ob ain high added alue compounds om lignin, di e en he mochemical
me hods ha e been s udied. Among hese, he BCD p ocess has demons a ed o be a
sui able me hod o ans o m o ganosol lignin in o low molecula weigh compounds
[12]. The use o di e en basic ca alys s in he depolyme iza ion o lignin om oli e ee
p uning was s udied by Toledano e al. [13] concluding ha he use o sodium hyd oxide
(NaOH) as ca alys inc eased he yield o he phenolic oil which is ich in monome ic
compounds. In ano he s udy [14] i was concluded ha he use o NaOH was sui able o
he depolyme iza ion o oli e ee p uning lignin ob ained h ough di e en o ganosol
p ocesses. Usually mos o hese wo ks ha e been ca ied ou in con en ional ba ch
eac o s; howe e , he use o mic owa es has u ned ou o be en i onmen ally iendlie
and a mo e e icien op ion in e ms o ene gy and economic sa ing and selec i i y [15].
Using he mic owa e echnology i is possible o inc ease he depolyme iza ion eac ion
o lignin in sol oly ic p ocesses [16] since he mic owa es acili a es he clea age o he
β-O-4 and C-C bonds [17].
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Ne e heless, one o he main p oduc s ha appea s, as a esul o he depolyme iza ion
o lignin is he cha . Cha is composed by coke and esidual lignin ha is gene a ed by
he epolyme iza ion ia condensa ion eac ions o uns able agmen s o lignin. To a oid
hese epolyme iza ion eac ions he e ec o di e en co-sol en s has been s udied [18]
concluding ha he use o a mix u e o wa e and p-c esol inc eased he yield o he
e ahyd o u an (THF) soluble compounds o med du ing he depolyme iza ion. The
e ec o bo ic acid was s udied as capping agen du ing he BCD eac ion o o ganosol
lignin by Robe s e al. [19] and hey concluded ha he use o bo ic acid inc eased he
oil yield while he epolyme iza ion eac ions we e dec eased. Addi ionally, Toledano e
al. [20] compa ed he e ec o bo ic acid and phenol as capping agen s in BCD o he
o ganosol lignin om oli e ee p uning and concluded ha phenol educed he amoun
o cha and inc eased he yield o monome ic compounds. In he same way, o he s udies
had concluded ha phenol ac s a oiding epolyme iza ion eac ions, howe e , due o he
oxic na u e o phenol, he aim o his wo k was o s udy he use o a enewable capping
agen in subs i u ion o his compound. This capping agen was ob ained by he
depolyme iza ion, wi hou using any ca alys , o he lignin con ained in he black liquo
om he deligni ica ion o pine sawdus h ough an o ganosol p ocess. As i was
p e iously, men ioned one o he main obs acles du ing he depolyme iza ion a e he
epolyme iza ion and condensa ion eac ions be ween he ins able agmen s o lignin
which a e in he medium [21]. The hypo hesis was ha he monome s, dime s and
oligome s o he CA could ac linking o he ac i e si es o he ins able molecules a oiding
epolyme iza ion be ween la ge molecules.
2. Ma e ials and me hods
2.1. Ma e ials
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Pinus adia a sawdus was ob ained om Ebaki XXI S.A. in Bizkaia, Spain. E hyl
ace a e, sodium sul a e anhyd ide, Dime hyl Fu u al (DMF) and Te ahyd o u an (THF)
we e pu chased om Fishe Scien i ic, NaOH and sul u ic acid (H2SO4) we e pu chased
om Pan eac and e hanol was ob ained om Scha lab.
2.2. O ganosol ea men
Pinus adia a sawdus was subjec ed o an o ganosol p ocess o deligni ica ion using a
dissolu ion o 50% E OH/wa e (w/w) a 210°C and 75 min wi h cons an s i ing in a
solid:liquid a io o 1:8 [22]. These condi ions we e selec ed since he deligni ica ion
yield was he highes . The ea men was ca ied ou in a 1.5 L s ainless 5500 s eel Pa
eac o wi h a 4848 Pa con olle . Two olumes o acidi ied wa e (pH 2) we e added
o he black liquo ob ained om his p ocess o p ecipi a e he lignin (LBD), which was
sepa a ed by il a ion. Se e al o ganosol ea men s unde he same condi ions we e
ca ied ou o ob ain enough black liquo o he ollowing p ocesses.
2.3. Black liquo cha ac e iza ion
O ganosol liquo om deligni ica ion o Pinus adia a sawdus was cha ac e ized in
e ms o densi y, o al dissol ed solids (TDS), ino ganic ma e (IM) and o ganic ma e
(OM). Densi y was calcula ed by weigh ing a known olume sample o he liquo . TDS
we e de e mined by d ying he sample o 24h a 105 ºC, his me hod is based on TAPPI
T264 cm-97 which is used o de e mine he mois u e con en o he sample. The ino ganic
ma e (IM) was calcula ed bu ning he d ied sample in an o en o 3h a 525 ºC
employing a me hod based on he TAPPI T211 om-93 s anda d used o de e mine he ash
con en . Finally, he o ganic ma e (OM) could be de e mined by he di e ence be ween
TDS and IM.
2.4. Depolyme iza ion p ocesses
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Two depolyme iza ion eac ions we e ca ied ou . Fi s ly, he depolyme iza ion eac ion
o he lignin con ained in he o ganosol black liquo was ca ied ou in a 1.5 L s ainless
5500 s eel Pa eac o wi h a 4848 Pa con olle a 210 ºC o 60 min. This ea men
was conduc ed o he p oduc ion o he phenolic-oil, which will be used as capping agen
in he ollowing BCD eac ions. Secondly, he lignin isola ed om he black liquo a e
his i s depolyme iza ion s ep (LAD) was dissol ed in a 4% w . NaOH solu ion
employing a lignin:sol en mass a io o 1:20. This mix u e was subjec ed o a BCD
eac ion using he p e iously ob ained CA in di e en p opo ions in weigh espec o
he lignin (0, 0.5, 1, 2). These BCD eac ions we e pe o med in a mic owa e eac o
(FlexiWAVE MA186 wi h a 660 Te minal and EasyCONTROL so wa e). The
depolyme iza ion eac ion was ca ied ou wi h cons an s i ing and using he ollowing
p og am: i s ly, he empe a u e was aised o 150 ºC in 135 seconds, his empe a u e
was kep o 30 seconds and hen aised again o he eac ion empe a u e o 230 ºC in
135 seconds. This empe a u e was kep o 20 min and hen go down o 100 ºC in 15
min. This sequence was epea ed 3 imes.
2.5. P oduc sepa a ion
Fo he sepa a ion o he di e en p oduc s ob ained du ing he p ocess he nex diag am
was ollowed (Figu e 1). Fo he sepa a ion o he monome ic compounds con ained in
he liquo a e he BCD eac ion, he me hod desc ibed by Toledano e al. [20], was used.
The eco e ed liquo and solids ( esidual lignin and coke) we e acidi ied un il pH 1
employing HCl (37% w .) in o de o sepa a e he solids om he liquo in wo well
de ined phases, a solid phase and a liquid phase. The i s one was composed o esidual
lignin and coke while he second, he liquid phase, was ich in phenolic compounds.
8
Figu e 1. Scheme o he CA ob aining p ocess and BCD p ocess (blue box)
These wo phases we e sepa a ed by il a ion and washed wi h acidi ied wa e (pH 1). A
liquid-liquid ex ac ion wi h e hyl ace a e was ca ied ou . In his way, he phenolic
compounds we e sepa a ed om he liquid phase ob aining an o ganic phase whe e he
depolyme iza ion p oduc s a e dissol ed. To emo e he possible aces o mois u e,
anhyd ous sodium sul a e was added o he o ganic ac ion and hen i was il a ed.
A e wa ds, he o ganic phase, ee o mois u e and solids, was e apo a ed in acuum o
sepa a e he e hyl ace a e om he oil ich in phenolic compounds. The solid esidue was
solubilized in 30 mL o e ahyd o u an (THF) wi h cons an s i ing o 3h. Then, in
o de o sepa a e he insoluble cha om he esidual lignin dissol ed in he THF, he
solu ion was il a ed. Finally, he THF solu ion was acuum e apo a ed o eco e he
esidual lignin (RL).
2.6. P oduc cha ac e iza ion
The chemical s uc u e o he di e en lignins (LBD, LAD and esidual lignins) we e
analyzed ia FTIR employing a Pe kinElme Spec um Two FT-IR Spec ome e
Pinus adia a
O ganosol
T ea men
O ganosol
Liquo
LBD
1s Depolyme iza ion
(wi hou lignin p ecipi a ion)
Liquo
LAD
BCD
(Mic oWa e)
Oil
Residual Lignin
Liquid Phase
O ganic Phase (Capping
Agen )
Aqueous Phase
L/L Ex ac ion
P ecipi a ion
P ecipi a ion
Solid
Sie ing
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equipped wi h a Uni e sal A enua ed To al Re lec ance accesso y wi h in e nal e lec ion
diamond c ys al lens. A o al o 18 scans we e accumula ed in ansmission mode wi h a
esolu ion o 4 cm-1 in a ange o 4000-600 cm-1.
To de e mine he a e age molecula weigh (Mw) and polydispe si y index (Mw/Mn) o
he di e en lignins (LBD, LAD and RL) a gel pe mea ion ch oma og aphy (GPC)
analysis was ca ied ou using a JASCO ins umen equipped wi h an in e ace (LC-
Ne ll/ADC) and a e ac i e index de ec o (RI-2031Plus). Two Pola Gel-M columns
(300 mm x 7.5 mm) placed in se ies we e employed. The low a e o he mobile phase
(N,N-Dime hyl o mamide) was 700 mm3min-1 and he analyses we e pe o med a 40 ºC.
Calib a ion was made using polys y ene s anda ds (Sigma-Ald ich) anging om 70000
o 266 g/mol.
A py olysis was ca ied ou o analyze he composi ion o lignins (LBD, LAD and RL)
employing a CDS analy ical Py op obe 5150. The py olysis empe a u e was se a 600
ºC o 15 s employing a hea ing a e o 2 ºC msec-1. A e he py olysis he p oduc s we e
analyzed in a GC (7890A)-MS (5975C ine MSD wi h T iple-Axis De ec o ) Agilen
equipped wi h a HP-5MS ((5%-Phenyl)-me hylpolysiloxane, 30 m x 0.25 mm) capilla y
column. The empe a u e p og am s a ed a 50 ºC and held o 2 min, hen he aised o
120 ºC a 10 ºC/min, kep 5 min, hen inc eased o 280 ºC a 10 ºC/min, kep 8 min, aised
o 300 ºC a 10 ºC/min and held 10 min. Helium was used as he ca ie gas.
The capping agen employed o he BCD eac ions and he oil ob ained a e hese
eac ions we e cha ac e ized by GC-MS. The sample was dissol ed in e hyl ace a e
(HPLC g ade) in a me ic lask. The solu ion was injec ed in GC-MS ins umen desc ibed
p e iously. The empe a u e p og am s a ed a 50 °C; hen, he empe a u e was aised
o 120 °C a 8 ºC/min, held a his empe a u e o 5 min, aised o 280 °C a 8 ºC/min,
held 8 a his empe a u e o min, aised o 300 °C a 10 ºC/min and held a his
16
e ec , ob aining an 8.93% oil yield. This dec ease is an unexpec ed esul conside ing
p e ious s udies in which phenol was used as a capping agen . Fo example, Toledano e
al. obse ed ha an excess o phenol esul ed in an inc ease in he oil yield [20];
none heless he calcula ions we e made wi h espec o he ini ial lignin and yields g ea e
han 100% we e ob ained. In addi ion, in he same s udy, hey p o ed ha an excess o
bo ic acid as capping agen was necessa y o ob ain a highe oil yield. In ano he s udy
ca ied ou by Belkhei i e al. [34] in which lignin K a LignoBoos was depolyme ized
in a eac o wi h eci cula ion using phenol as a capping agen , i was obse ed ha he
yield in oil was e y simila ega dless o he amoun o phenol used.
O he wise, i could also be obse ed ha he expe imen s we e mo e ep oducible in he
cases whe e a CA:lignin a io o 0.5:1 and 1:1 we e used. Rega ding he cha yields, i
was obse ed as i was expec ed, ha he capping agen ac ed dec easing epolyme iza ion
p oduc s.
Figu e 6. Oil (a) and Cha (b) yield (%w .) espec o he o al o ganic ma e
Howe e , i is ema kable he high cha alues ha we e ob ained. This high yield o cha
could be explained by he high esidence ime employed in he BCD eac ions since,
acco ding o Ouyang e al. [17], he econdensa ion eac ions could be a o ed by high
esidence imes unde mic owa e i adia ion condi ions. In his way, he highes cha
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yield was ob ained o he blanc expe imen while in he es o expe imen s his p oduc
dec eased conside ably wi h espec o he blanc by 29.88±0.747% in a e age. Howe e ,
as i can be seen in Figu e 6b, he cha yield in he expe imen s whe e capping agen was
used was p ac ically he same, which deno es ha he concen a ion o capping agen had
li le in luence on he p oduc ion o cha .
I should be no ed ha he ma e ial balances we e no closed a 100% in any o he
expe imen s; his loss o ma e occu s because, du ing he depolyme iza ion eac ion,
gaseous p oduc s a e gene a ed [14] which we e no quan i ied in his case. Mo eo e ,
some p oduc s gene a ed in he eac ion emained in he aqueous phase a e he liquid-
liquid ex ac ion p ocess. This loss o ma e ial o he oil and cha ac ions was mo e
e iden in hose expe imen s in which he capping agen was used, especially o CA_2,
compa ed o he blank expe imen . This could be due o he ac ha , du ing he BCD
depolyme iza ion eac ion, he deg ada ion compounds o he hemicelluloses ha a e
p esen ed in he capping agen could eac c ea ing compounds such as ace ic acid [28]
ha a e e ained in he aqueous phase.
3.3.2. Cha ac e iza ion o depolyme ized p oduc s
3.3.2.1. Oil cha ac e iza ion
The monome concen a ion in he oil is ep esen ed in Figu e 7, in which, he e ec o
he capping agen in monome s ob aining can be obse ed. The e was a clea e idence
ha he use o he capping agen a o ed he concen a ion o hese compounds in he oil.
In ac , i can be obse ed ha , as he a io o capping agen was inc eased, he yield o
monome s in he oil inc eased up o 54.26% (CA_2) wi h espec o he blanc expe imen
(CA_0). This imp o emen was also e iden in he expe imen s CA_0.5 and CA_1 whe e
he concen a ion o monome s inc eased wi h espec o he blanc expe imen , by 29.49%
and 54.04%, espec i ely. Howe e , i can be highligh ed he ac ha an excess o
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capping agen did no en ail a signi ican imp o emen , since o CA_2 he e was no
enhancemen wi h espec o he expe imen CA_1. This li le imp o emen in monome s
yield in CA_2 espec o CA_1 (54.26% s. 54.04%, espec i ely) as well as he dec ease
in oil yield (16.07% o dec ease) did no jus i y he use o he highes CA p opo ion.
Figu e 7. Phenolic monome s concen a ion (%w .) in he oil.
Rega ding he compounds p esen ed in he oil, i should o be poin ed ou ha he main
compound in all he expe imen s was guaiacol (Figu e 8). This p oduc was o med by
he hyd olysis o he e he bonds o lignin. Howe e , as i can be obse ed in he blank
expe imen , he eac ion condi ions we e no su icien ly se e e o ob ain some
decomposi ion p oduc s o guaiacol such as ca echol and c esols, ob ained h ough he
deme hoxyla ion o guaiacol uni s [14] and only a small amoun o phenol was ob ained.
The addi ion o he capping agen a o ed he p oduc ion o hese monome s and also
inc emen ed he concen a ion o guaiacol ob aining he maximum o he expe imen
CA_1. Mo eo e , ca echol was o med in he expe imen s whe e CA was used, inc easing
i s yield as he CA: lignin a io was inc eased. All hese indica es ha he p esence o CA
p e en ed he union o he uns able agmen s o lignin du ing he BCD eac ion a o ing
he o ma ion o monome s. In addi ion, he deme hoxyla ion o he monome s which
19
we e al eady p esen in he CA, a o ed he p oduc ion o ca echols and c esols. On he
o he hand, due o he oxida i e cha ac e o he a mosphe e in which he
depolyme iza ion eac ions we e ca ied ou , he second mos abundan compound in all
he eac ions was anillin, coming om he oxida ion o lignin [35]. In addi ion, i could
be obse ed ha , in hose expe imen s in which he capping agen was used, he amoun
o anillin inc eased. This could be due o he oxida ion o hose monome s p esen in he
capping agen such as guaiacol, dihyd oconi e yl alcohol and he coni e yl aldehyde.
Figu e 8. Monome s mass concen a ion (%w .) p esen ed in he oil.
3.3.2.2. Cha cha ac e iza ion
As men ioned abo e, cha is one o he main p oduc s ob ained du ing BCD o lignin.
Cha is mainly composed by esidual lignin and coke o a lesse ex en which is he leas
desi ed p oduc due o i s limi ed e alua ion oppo uni ies. RL and coke pe cen age a e
calcula ed espec he eco e ed cha and a e shown in Figu e 9a and 9b espec i ely. Fo
all eac ions, he esidual lignin yield was highe han 95% while he coke did no exceed
3.5% in he wo s case (CA_0). In addi ion, he yield o RL inc eased in all expe imen s
whe e CA was used dec easing he coke yield a he same ime. In his sense, he lowes
yield o RL and ob iously he highes yield o he undesi able coke was ob ained o he
blanc expe imen , 96.6 % and 3.40% espec i ely. A he same ime as he CA:lignin a io
20
was inc eased he yield o RL inc eased up o 98.46% o he expe imen wi h a a io o
1:1 educing simul aneously he o ma ion o coke up o 45.33% espec o he blanc
expe imen . Howe e , his end was e e sed when an excess o capping agen was used
which seems o indica e ha an excess o CA was no bene icial. I mus o be poin ed ou
ha coke was no analyzed in his case due o he low amoun ha was eco e ed a e
he eac ions. On he o he hand, esidual lignin was cha ac e ized in o de o s udy i s
chemical s uc u e and composi ion.
Figu e 9. Residual lignin (a) and Coke (b) yields (%w .) espec cha
3.3.2.2.1. Residual lignin cha ac e iza ion
As i was men ioned abo e, esidual lignin was he main p oduc o lignin
depolyme iza ion in all cases. In o de o de e mine he composi ion and s uc u al
changes ha esidual lignins had su e ed, he samples we e subjec ed o a ious analyses
and compa ed wi h he LAD which was used as e e ence.
The molecula weigh dis ibu ion o esidual lignins we e de e mined by GPC. The
esul ing ch oma og ams a e shown in Figu e 10 and summa ized in Table 3. In Figu e
10 i is shown a i s peak in all ch oma og ams o esidual lignins appea ing a a sho e
e en ion ime. This indica es ha epolyme iza ion and condensa ion eac ions occu ed
simul aneously du ing he depolyme iza ion eac ions, esul ing in a highe Mw ac ion
21
han he LAD. On he o he hand, compa ing he esidual lignins o he expe imen s whe e
he CA was used wi h he blanc expe imen , i was obse ed ha a low CA a io had
con ibu ed o dec ease he Mw and he polydispe si y index o he lignin. This could be
because he monome s, dime s and ime s ha we e p esen in he CA linked o he
eac i e si es o he uns able lignin agmen s a oiding epolyme iza ion be ween la ge
lignin molecules. Howe e , as he CA a io was inc eased, an inc ease in he molecula
weigh s and he polydispe si y index was obse ed, eaching he maximum when an he
highes o CA:lignin a io was used.
Table 3. Mw, Mn and PI o LAD and di e en RL
Sample
Mn
Mw
Mw/Mn
LAD
1010
3638
3.60
RL CA_0
1082
5812
5.37
RL CA_0.5
930
4631
4.98
RL CA_1
995
6099
6.13
RL CA_2
1519
16921
11.14
Figu e 10. Molecula weigh dis ibu ion o Residual Lignin and LAD
In o de o de e mine he chemical s uc u e o esidual lignins hey we e subjec ed o a
FTIR analysis and compa ed wi h he LAD o analyze he possible changes hey su e ed
du ing he depolyme iza ion eac ions.
22
In Figu e 11 he FTIR spec a in he inge p in a ea o all lignins a e shown. I could be
obse ed ha he in ensi y o he peak a 1700 cm-1, which is associa ed wi h he ca bonyl
g oup, is mo e in ense in he esidual lignins as i was men ioned abo e. Ne e heless,
he main di e ence be ween hem lies in he in ensi y o he peaks a 1510 cm-1 and 1028
cm-1, bo h associa ed wi h he a oma ic ing in guaiacyl uni s. The in ensi y o bo h peaks
dec eased as he concen a ion o CA in he BCD eac ions inc eased. This con i ms he
esul s ob ained in he analysis o he oil composi ion whe e i was seen ha inc easing
he concen a ion o he CA, he amoun o bo h guaiacyl and i s de i a i es was
inc eased, which means ha LAD has los guaiacyl uni s du ing BCD eac ion. On he
o he hand, no o he signi ican di e ences we e obse ed in lignins spec a, indica ing
ha esidual lignins main ained i s a oma ic s uc u e. This could be explained by he mild
condi ions employed in he BCD which we e no ha sh enough o change he s uc u e o
he esidual lignins.
Figu e 11. FTIR spec a o RL and LAD
Finally, and wi h he pu pose o unde s anding be e he composi ion o his esidual
lignin, a py olysis-GC-MS analysis was ca ied ou o all esidual lignins. The
23
ch oma og ams o he esidual lignins a e ep esen ed in Figu e 12. A lis o compounds
whose a ea was g ea e han 1% wi h espec o he o al a ea o he ch oma og am is
speci ied in Table 4. As i can be app ecia ed in Figu e 12, he e we e no di e ences
be ween all esidual lignins which p esen ed he same compounds. In all cases, Bu yla ed
Hyd oxy oluene (BHT) appea s as con amina ion because i is used as a s abilize o he
THF ha was employed in he sepa a ion o coke and esidual lignin. The mos abundan
compound o esidual lignin was guaiacol ollowed by 4-me hylguaiacol and 4-
e hylguaiacol. I should be no ed ha hese h ee compounds ep esen mo e han 40% o
he o al a ea o he ch oma og ams in all cases espec o esidual lignin. Among hem,
as men ioned abo e, he compound wi h he highes a ea was guaiacol wi h an a e age
a ea o 25.35±6.36%. On he o he hand, 4-me hylguaiacol ep esen ed 20.43±2.09%
while 4-e hylguaiacol showed an a ea o 6.55±0.31%. Finally, he high abundance o
guaiacyl compounds ha a e p esen ed in he esidual lignins could explain he low oil
yield ob ained in he depolyme iza ion p ocesses.
Figu e 12. Py-GC-MS o Residual Lignins
24
Table 4. Py olysis p oduc s iden i ied by Py olysis-GC-MS o esidual lignins
RT
(min)
lib a y/ID
A ea (%)
CA_0
CA_0.5
CA_1
CA_2
3.34
Fu an, 2,5-dime hyl-
N.D.
N.D.
N.D.
1.26
7.47
Phenol
1.03
1.17
1.04
1.01
8.70
O-C esol
1.11
1.09
N.D.
1.13
9.03
m-C esol
1.35
1.63
1.52
1.49
9.35
Guiacol
22.71
19.13
22.47
12.50
10.34
Phenol, 2,4-dime hyl-
1.30
1.14
1.30
1.93
11.07
3-Me hylguaiacol
1.56
1.86
1.74
1.97
11.42
4-Me hylguaiacol
14.84
16.93
16.64
13.53
12.53
3,4-Dime hoxy oluene
N.D.
1.13
N.D.
1.28
13.89
4-E hylguaiacol
4.68
5.06
5.40
4.74
14.18
4-Me hylguaiacol
1.61
1.62
1.65
1.69
15.03
4-Vinylguaiacol
1.80
2.27
2.32
2.00
16.46
Guaiacylp opane
N.D.
1.02
1.27
1.30
17.24
Vanillin
2.22
2.86
3.35
3.23
18.99
Ace o anillone
1.47
1.46
1.32
N.D.
19.43
Bu yla ed Hyd oxy oluene
26.46
25.57
20.82
23.60
21.45
Me hyl Homo anilla e
N.D.
N.D.
N.D.
1.34
24.98
n-Hexadecanoic acid
1.20
1.01
1.85
2.47
26.89
Oc adecanoic acid
0.39
0.52
N.D.
1.24
4. Conclusions
The depolyme iza ion o o ganosol lignins om Pinus adia a using a enewable
capping agen had a posi i e e ec on he oil yield compa ed o he blank expe imen . In
addi ion, he yield o monome ic compounds also inc eased, especially he yield o
guaiacol and anillin. I could also be obse ed, ha he use o he capping agen a o ed
he deme hoxyla ion o he guaiacyl uni s o o m monome s such as ca echol, dec easing
he epolyme iza ion eac ions and educing, as i was expec ed, he solid yield espec o
he blank expe imen . On he o he hand, i was obse ed ha as he capping agen a io
inc eased, he yields in oil and monome ic compounds also inc eased, ob aining he
maximum oil yield o he expe imen CA_1. Howe e , his endency was e e sed when
an excess o capping agen was used as i can be seen in expe imen CA_2 whe e he oil
yield dec eased. Ne e heless, he monome s yield was he highes o he expe imen
25
whe e an excess o capping agen was used bu his inc emen was negligible. In addi ion,
he GPC analysis demons a ed ha an excess o he CA esul ed in a esidual lignin wi h
highe molecula weigh s. Finally, he chemical s uc u e and composi ion o all esidual
lignins we e simila o each o he ; in all cases guaiacol and i s de i a i es we e he main
compounds a e esidual lignins py olysis so hei s uc u es main ained an a oma ic
na u e which will be posi i e o u he alo iza ion. Taking all his in o accoun , he use
o CA:lignin a io o 1:1 was selec ed as he mos sui able op ion o lignin
depolyme iza ion p ocess as i can ac like any o he comme cial capping agen , such as
phenol.
Acknowledgemen s
This wo k was inancially suppo ed by he Spanish Minis y o Science, Inno a ion and
Uni e si ies (CTQ2016-78689-R).
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