Copy igh © 2019 Tech Science P ess
DOI: 10.32604/j m.2019.04291 www. echscience.com
Lique ac ion o K a Lignin a A mosphe ic P essu e
Sil ia Helena Fuen es da Sil a1, Pa icia Soa es Bilhal a dos San os2, Da ci Albe o Ga o3, Ma ia
Angeles And es1 and I zia Egüés1,*
1Chemical and En i onmen al Enginee ing Depa men , Uni e si y o Basque Coun y, Plaza Eu opa 1, 20018, Donos ia-San
Sebas ián, Spain.
2 Facul y o Fo es y Enginee ing, Fede al Uni e si y o Pa á, C. José Po i io, 2515, Al ami a, B azil.
3College o Ma e ial Enginee ing (PPGCEM), Fede al Uni e si y o Pelo as, B azil.
*Co esponding Au ho : I zia Egüés. Email: i zia [email protected].
Abs ac : K a lignin was lique ied using polye hylene glycol #400 (PEG) and
glyce ol (G) in a weigh a io o 80/20 (w/w) and sulphu ic acid (SA) as ca alys
unde a mosphe ic p essu e a 160ºC. The h ee independen a iables: eac ion
ime (60, 80 and 100 min), pe cen age o lignin (15, 20 and 25%, w/w), and
ca alys concen a ion (0, 3 and 6%, w/w), we e a ied esul ing in 27 expe imen al
uns. The e ec o hese eac ion condi ions on he p ope ies o he polyols was
e alua ed. The s a is ical analysis showed ha only “ he pe cen age o lignin” did
no in luence he p ope ies o he lique ied p oduc s, howe e , eac ion ime and
ca alys load we e impo an pa ame e s. The esul ing lique ied p oduc s we e
cha ac e ized by FTIR analysis.
Keywo ds: Biopolyols; K a lignin; lique ac ion; enewable esou ce;
he mochemical con e sion
1 In oduc ion
Fo many yea s, he wo ld economy was mainly based on pe ochemical esou ces. Howe e , he
exponen ial g ow h o popula ion and he p ice o he pe oleum encou age he scien i ic communi y o
sea ch o new enewable esou ces o he p oduc ion o ene gy, uel and chemicals.
Lignin is he main a oma ic compound a ailable in abundance in na u e. I consis s o phenylp opane
uni s which a e linked one each o he mainly by β-O-4’, as well as o he e he and C-C linkages, such as α-
O-4’, 4-O-5’, β-β’, 5-5’ bonds. These s uc u e o ms a building blocks which esul s in a h ee-dimensional
biopolyme [1,2]. Indus ially, K a pulping p ocess is he main sou ce o lignin. This lignin is dissol ed in
he black liquo and i is conside ed as a was e in he p ocess. Al hough, his lignin is bu ned o p o ide powe
o he plan , he e is an excess o lignin ha can be used as enewable esou ce. Lignin has g ea po en ial o
subs i u e pe ochemical phenol due o i s a oma ic s uc u e, as in o mula ions o phenolic esins. Howe e ,
lignin is less eac i e han phenol, due o i s mac omolecule complex s uc u e and ew ac i e si es. One
s a egy is o inc ease he ac i e si es o lignin inc easing he con en o hyd oxyl g oups. The e o e, chemical
modi ica ions a e necessa y. Among he biomass con e sion p ocesses, he lique ac ion is pa icula ly
a ac i e he mochemical con e sion p ocess, since i can be pe o med a ela i e sho ime, low
empe a u e and a a mosphe ic p essu e. The lique ac ion can be ca ied ou wi h polyhyd ic alcohols as
sol en and wi h o wi hou ca alys o con e he lignocellulosic ma e ial o a polyol ich in OH g oups,
making i much mo e eac i e. Red pine wood [3], acid hyd olysis esidue (AHR) o co n [4], enzyma ic
hyd olysis lignin (EHL) [5] and oil palm emp y ui bunch [6] a e some o lique ied lignocellulosic ma e ials
men ioned in he li e a u e using alcohols sol en s and sulphu ic acid as ca alys . In he li e a u e, some wo ks
ha e been also epo ed abou he po en ial use o K a lignin in lique ac ion p ocess using acid-based and
me al oxide ca alys s [7,8].
528 JRM, 2019, ol.7, no.6
In he p esen wo k, he main objec i e is o s udy he in luence o di e en lique ac ion pa ame e s
(lignin load, ca alys concen a ion and eac ion ime) in he p ope ies o ob ained polyols by s a is ical
analysis. Besides ha , his wo k aims o impulse he alo isa ion o indus y byp oduc s, K a lignin, o
aluable biopolyols p oduc ion. Fo ha , K a lignin was lique ied unde a mosphe ic p essu e using
polye hylene glycol and glyce ol as sol en and sul u ic acid as ca alys . The e ec o he amoun o lignin,
sulphu ic acid as ca alys and he eac ion ime on he lique ied p oduc s we e e alua ed.
2 Ma e ials and Me hods
Ma e ials: K a lignin (KL) was p ecipi a ed om black liquo p o ided by CMPC-Cellulose
Riog andense (B azil) using sul u ic acid. The chemicals polye hylene glycol#400 analy ical g ade,
glyce ol 99% o syn hesis and sul u ic acids 96% echnical g ade we e pu chased o PanReac AppliChem.
All eagen s we e used as ecei ed.
Lique ac ion o K a lignin: K a lignin was lique ied using polyhyd ic alcohols such as polye hylene
glycol #400 (PEG) and glyce ol (G) in a weigh a io o 80/20 (w/w) and sul u ic acid (SA) as ca alys unde
a mosphe ic p essu e. The sol en s and SA we e added oge he in o a neck lask eac o wi h magne ic s i e ,
empe a u e con ol and condense . When he empe a u e eached 160ºC, he K a lignin was added in o he
lask and he ime s a ed o un. Then, he eac o was imme sed in a cooled wa e ba h o quench he eac ion.
Lique ied mix u e was washed wi h ace one unde acuum. Solid esidue was d ied in o en a 105ºC o 24
h and weigh ed o de e mine he p ocess con e sion yield. Ace one was emo ed by o a y e apo a o unde
educed p essu e.
The independen a iables such as eac ion ime (60, 80 and 100 min), pe cen age o lignin (15, 20
and 25%, w/w), and ca alys concen a ion (0, 3 and 6%, w/w) espec o he weigh o sol en s, we e a ied
esul ing in 27 expe imen al uns (Tab. 1) (elabo a ed h ough expe imen al design). The e ec o hese
eac ion condi ions on he p ope ies o he polyols we e e alua ed.
Table 1: Di e en eac ion condi ions (R = eac ion ime, Mass = pe cen age o lignin and Ca = pe cen age
o ca alys ) o lique ac ion o K a lignin a 160ºC and a mosphe ic p essu e
Sample
R (min)
Mass (%)
Ca (%)
Sample
R (min)
Mass (%)
Ca (%)
1C
80
25
3
15C
100
25
3
2C
60
20
0
16C
100
15
3
3C
60
25
6
17C
80
15
6
4C
60
20
3
18C
80
15
3
5C
80
20
0
19C
100
15
6
6C
80
25
0
20C
60
25
0
7C
60
15
6
21C
80
20
3
8C
60
15
0
22C
100
25
0
9C
80
15
0
23C
60
15
3
10C
100
15
0
24C
60
20
6
11C
100
20
6
25C
100
25
6
12C
60
25
3
26C
80
25
6
13C
100
20
0
27C
100
20
3
14C
80
20
6
JRM, 2019, ol.7, no.6 529
The lique ac ion yield was calcula ed as ollows:
Yield = (1-m/m0) * 100 (1)
whe e: Yield = yield o lique ied K a lignin (%); m0 = amoun o lignin used in lique ac ion (g); m = solid
esidue o lique ac ion (g).
Cha ac e iza ion o polyols: The acid numbe (An) and hyd oxyl numbe (OHn) we e de e mined by
i a ion me hod acco ding o he s anda d ASTM D974 [9] and ASTM D4274 [10], espec i ely. Dynamic
heological beha io o he polyols was measu ed wi h a Rheome ic Scien i ic Ad anced Rheome ic
Expansion Sys em (ARES), using pa allel-pla e geome y (25 mm diame e ), and he uppe pla e was se a
he sepa a ion dis ance (gap) o 0.5 mm. F equency sweep measu emen s we e ca ied ou a 25ºC om 0.1
o 500 ad s-1 a a ixed s ain. The changes in he chemical s uc u e was e alua ed by Spec um Two FT-
IR Spec ome e (ATR-IR), wi h a L1050231 Uni e sal A enua ed To al Re lec ance accesso y using a
Pe kin-Elme ins umen wi h he angle o incidence a 45º. Spec a we e eco ded o e 20 scans wi h
eloci y o 2 mm.sec-1, esolu ion o 4 cm-1 in a wa eleng h ange om 4000 o 600 cm-1.
3 Resul s and Discussion
The esul s o yield, OHn, An and iscosi y o he 27 polyols, a e shown in he Tabs. 2-4 and he
s anda dized s a is ical e ec s o he eac ion ime, amoun o lignin and ca alys and i s in e ac ions
( eac ion condi ions) a e shown in Fig. 1. As i can be obse ed in Tab. 2, he lique ac ion yield a ied om
61.97% wi h 15% o lignin, 6% o SA a 60 min, o 98.88% wi h 20% o lignin, 3% o SA a 60 min (Tab.
2). Ba nes e al. [11] ob ained yield a ound 95% o he lique ac ion o o ganosol lignin a highe
empe a u e (300ºC) using wa e and me hylnaph halene as sol en o 60 min. Jin e al. [5] ob ained yield
o e 90% using SA as ca alys in a mass a io ange om 10 o 20 o EHL w/w, his a io is bigge han
hose used in his s udy. On he o he hand, in Fig. 1, i can be seen ha only he ca aly ic in e ac ion di e s
s a is ically in o he yield o he polyols (Fig. 1(a)).
Table 2: Values o he yield o he polyols
Yield (%)
Ca alys (%)
Time (min)
Weigh o lignin (%)
15
20
25
60
68.32
68.41
96.70
0
80
81.58
78.62
94.13
100
81.68
67.78
70.30
60
95.70
98.88
95.40
3
80
97.90
97.26
93.19
100
98.17
96.80
92.10
60
61.97
95.88
79.79
6
80
82.67
81.54
94.98
100
72.24
72.43
84.63
530 JRM, 2019, ol.7, no.6
Figu e 1: Second-o de linea model: s anda dized Pa e o cha showing he e ec s o he independen
a iables ( ime, mass, ca alys ) and i s in e ac ions on he: a) yield, b) hyd oxyl g oups and c) iscosi y o
he polyols. The e ical line ep esen s he signi icance a 95% (p < 0.05)
The di e en eac ion condi ions p omo ed a wide ange on he hyd oxyl numbe alues in he polyols
(Tab. 3). The esul ing OH g oups in he polyols is gene ally associa ed wi h he con e sion eac ion and
he amoun o acid g oups o med du ing he eac ion ime. A 15% o lignin, he OHn alue inc eased om
402 mg KOH/g o 2556.47 mg KOH/g wi hou ca alys and inc easing he eac ion ime om 60 min o 100
min. Unde his condi ion, he lique ac ion yield was simila a 80 and 100 min o eac ion ime (81%, Tab.
2). Howe e , he numbe o acid (An) o med o e 80 min (16.63 mg KOH/g) is much highe han a 100
min (6.04 mg KOH/g). In his case, he hyd oxyl g oups we e mo e consumed o o m acid subs ances a
80 min (1827.66 mg KOH/g) han a 100 min (2556.47 mg KOH/g). Howe e , a 15% o lignin, 3% o
ca alys and a 100 min, he OH g oups we e diminished conside ably (whe e acid g oups we e also
educed). In his sample he low OH g oups could be due o he dehyd a ion eac ion [12].
Table 3: Hyd oxyl numbe (OHn) and acid numbe (An) o he polyols
(mg KOH/g)
Ca alys
(%)
Time
(min)
Weigh o lignin (%)
15
20
25
OHn
An
OHn
An
OHn
An
60
402.43
8.28
983.09
10.84
1687.97
10.06
0
80
1827.66
16.63
2314.11
14.77
1363.59
50.49
100
2556.47
6.04
904.61
7.57
1773.06
11.96
60
2092.55
17.29
924.97
23.17
1582.62
12.48
3
80
2399.51
24.25
2351.04
13.95
2354.60
12.64
100
544.83
12.42
1731.10
14.22
1672.99
14.23
60
733.45
13.54
2173.90
33.35
1280.53
28.30
6
80
1372.81
26.31
1716.15
37.03
1550.40
34.00
100
1275.65
44.44
902.34
6.39
558.74
15.85
JRM, 2019, ol.7, no.6 531
The iscosi y o he polyols is shown in Tab. 4. The alues we e anged om 0.1361 Pa.s (wi hou
ca alys , 20% o lignin a 60 min) o 1.8456 Pa.s (6% o SA, 25% o lignin a 80 min). S a is ically his
p ope y was in luenced by bo h eac ion ime and ca alys (Fig. 1(c)).
As i can be obse ed, iscosi y was inc eased when he ca alys load inc eased. The highes change was
obse ed in he samples lique ied a 15% and 25% o lignin a 80 min p ocess ime, whe e iscosi ies we e
inc eased om 0.190 o 1.336 Pa.s and om 0.291 o 1.846 Pa.s, espec i ely. This can be a ibu ed o
condensa ion and epolyme iza ion eac ions ha can occu a high ca alys concen a ions [13]. The eac ion
ime also inc eased he iscosi y o he samples up o 80 min, whe e a u he eac ion imes (100 min) he
iscosi y dec eased. Ku imo o e al. [14] ound iscosi ies be ween 0.33 and 31.00 Pa.s wi h eac ion ime
ange om 30 o 90 min.
Table 4: Values o he iscosi y o he polyols
Viscosi y (Pa.s)
Ca alys (%)
Time (min)
Weigh o lignin (%)
15
20
25
60
0.183
0.136
0.267
0
80
0.190
0.261
0.291
100
0.196
0.238
0.282
60
0.556
0.203
0.512
3
80
0.445
0.619
0.386
100
0.426
0.328
0.605
60
0.272
0.791
0.644
6
80
1.336
0.869
1.846
100
0.440
0.688
0.700
E ec o he independen a iables ( eac ion ime, lignin, ca alys ) on he polyols
The a e age esul s o yield, OHn and iscosi y as a unc ion o eac ion condi ions ( ime, mass and
ca alys ) a e shown in Tab. 5.
Reac ion ime: Fig. 1 shows he in luence o eac ion ime on he ea u es e alua ed o polyols. Take
in o accoun he eac ion ime, he a e age alues o lique ac ion yield ange om 89% (80 min) o 81%
(100 min) (Tab. 5). This dec ease maybe due o he econdensa ion polyme iza ion o he lignin agmen s
o e he ime [4,15]. ANOVA analysis showed ha he eac ion ime is no signi ican ly di e en (p > 0.05),
he e o e, his pa ame e did no in luence he yield o he polyols. Howe e , i a ec ed he hyd oxyl
numbe s, whe e a 60 min was abou 1317.15 mg KOH/g and he highes alue was ob ained a 80 min wi h
1916.65 mg KOH/g (Tab. 5). The eac ion ime o 60 min seems no enough o p omo e g ea e ac i e si es
(OH). In con as , a 100 min, he low a e age alue o OH g oups could be due o condensa ion and
epolyme iza ion o he lignin agmen s [5]. S a is ically, he a e age alues o OH g oups o he polyols
as a unc ion o he eac ion ime we e signi ican ly di e en (ANOVA, p < 0.05). On he o he hand, he
lique ied lignin showed a e age iscosi y o 0.396, 0.694 and 0.433 Pa.s a 60, 80 and 100 min, espec i ely.
Ku imo o e al. [14] ound iscosi ies be ween 0.33 and 31.00 Pa.s. Viscosi ies esul s we e signi ican ly
di e en (ANOVA, p < 0.05) as a unc ion o eac ion ime.
Lignin load: The pe cen age o 15%, 20% and 25% (w/w) o lignin p o ided a e age yields o 82.25%,
84.20% and 89.03%, espec i ely (Tab. 5). Appa en ly, mo e lignin p o ides highe yields, al hough hese
alues a e no s a is ically di e en (ANOVA, p > 0.05). Jo e al. [16] used he same pe cen ages (15, 20
and 25%) o mass and ob ained highe yields (a ound 94%) using 15% o palm ke nel cakes in he
532 JRM, 2019, ol.7, no.6
lique ac ion. As i can be obse ed in Tab. 5, when lignin load is inc eased om 15 o 20%, he OHn alues
we e inc eased (1446.98 o 1555.70 mg KOH/g, espec i ely) and hen, emained cons an a 25% o lignin.
I appea s ha 15% o he lignin was no su icien o eac wi h he sol en s. Howe e , o e 20% o lignin,
eac ions o sel -condensa ion seem o be dominan . The inc ease in lignin om 15 o 25% p omo ed a 38%
inc ease in iscosi y o lique ied lignin, om 0.449 o 0.615 Pa.s. Howe e , Pa e o diag am (Fig. 1) shows
ha he lignin con en did no in luence he iscosi y o he polyols. Ku imo o e al. [14] e i ied he same
end o iscosi y g ow h ( om 0.33 o 31.00 Pa.s) wi h he inc ease o Sugi wood concen a ion
(C ip ome ia japonica D. Don) om 9.6 o 29.8%, espec i ely.
Ca alys load: Tab. 5 shows ha he expe imen s pe o med wi hou ca alys had he lowes a e age
yield (78.64%). Howe e , a 3% o SA he e was an inc ease o 22.28% o he yield, wi h a e age o 96.16%.
The ca alys plays an impo an ole in lique ac ion yield by acili a ing he decomposi ion o lignin and
e a ding he condensa ion eac ions. A highe ca alys load (6 w/w), he concen a ion o lique ied
p oduc s was e y high and he condensa ion eac ions we e dominan [4]. He e, i was obse ed ha he
yield is lowe in he absence o SA han a highe concen a ions (6% w/w). ANOVA analysis shows ha
he yield alues a e s a is ically di e en as a unc ion o ca alys (p < 0.05). The OHn o lique ied lignins
syn hesized in absence o SA inc eased om 1534.78 mg KOH/g o 1739.36 mg KOH/g wi h 3% o SA.
Then, OHn dec ease again o 1284.88 mg KOH/g wi h 6% o SA. The highes OHn alue wi h 3% SA
should be ela ed o he high con e sion o lignin o polyol. Lique ac ion pe o med in absence o ca alys ,
wi h 3% and wi h 6% o SA, esul ed in polyols ha ing an a e age iscosi y o 0.227, 0.453 and 0.843 Pa.s,
espec i ely. As i can be obse ed, he iscosi y was inc eased when he ca alys load inc eased. This can be
a ibu ed o condensa ion and epolyme iza ion eac ions ha can occu a high ca alys concen a ions [13].
In he lique ac ion o c ude glyce ol o 90 min a 180ºC, Lou e al. [17] ob ained iscosi y o 0.37 Pa.s wi h
4% o SA.
Table 5: E ec o he independen a iables ( eac ion ime, lignin and ca alys ) on he a e age alues o yield,
OHn and iscosi y o he polyols
Yield (%)
OHn (mg KOH/g)
Viscosi y (Pa.s)
Reac ion ime (min)
60
84.56
1317.15
0.396
80
89.12
1916.65
0.694
100
81.79
1324.42
0.433
Lignin (%)
15
82.25
1467.26
0.449
20
84.20
1555.70
0.459
25
89.03
1536.05
0.615
Ca alys (%)
0
78.64
1534.78
0.227
3
96.16
1739.36
0.453
6
80.68
1284.88
0.843
FTIR analysis: The changes in he chemical s uc u es o he polyols and K a lignin we e analyzed by
FTIR spec oscopy (Fig. 2). All spec a o he polyols showed simila peaks, howe e , hey p esen ed some
di e ences in in ensi y. The spec um o lique ied lignins showed ma ked changes compa ed wi h K a lignin.
The inc ease b oad band in he egion 3665-3144 cm-1 is ela ed o he s e ching OH g oups. This inc ease
was expec ed due o alipha ic OH con ibu ions om polyhyd ic alcohols and a oma ic OH g oups om K a
lignin depolyme isa ion. Besides ha , he peaks a 2937 cm-1 and 2869 cm-1 ela ed o he asymme ic and
JRM, 2019, ol.7, no.6 533
symme ic C-H s e ching in he me hylene and me hyl g oups, inc eased. The s ong peak o me hylene may
be due o he s uc u e o PEG and G. Fo me hyl g oups, may be due o he phenylp opane uni s om K a
lignin. The appea ance o he peak a 1247 cm-1, assigned o C-O in phenol hyd oxyl g oups, con i ms ha
K a lignin had pa icipa ed in he lique ac ion eac ion [5]. The peak a 1350 cm-1 is ela ed o he s e ching
OH in plane de o ma ion. The appea ance o a peak in he egion be ween 1709 and 1732 cm-1 is a ibu ed o
C=O in he unconjuga ed ke ones, ca bonyl and es e g oups s e ching [13,18].
Figu e 2: FTIR spec um o polyols a) 1C o 7C, b) 8C o 14C and c) 22C o 27C and K a lignin
4 Conclusions
In his wo k, he in luence o he eac ion ime, ca alys load and K a lignin pe cen age in he
lique ied p oduc s p ope ies was analyzed. The ob ained esul s indica ed ha he ob ained yield o
lique ied lignins (61.97-98.88%) was s a is ically a ec ed by ca alys loading, whe e hyd oxyl numbe
( alues a ound 402.43-2556.47 mgKOH/g) was in luenced by eac ion ime. Howe e , he iscosi y o
lique ied lignins ( ange be ween 0.183-1.846 Pa.s) was in luenced by eac ion ime and ca alys load.
Finally, he lignin pe cen age had no in luence on polyols p ope ies. The e o e, i can be concluded ha
he mos impo an pa ame e s ha a ec he polyol p ope ies, a e he ca alys load and lique ac ion ime.
On he o he hand, he lique ied lignins p esen ed ma ked changes in FTIR spec a compa ing wi h he
p ecipi a ed K a lignin. This con i ms ha K a lignin pa icipa es in he lique ac ion eac ion.
(a)
(b)
(c)
534 JRM, 2019, ol.7, no.6
Acknowledgmen s: The au ho s would like o hanks o CNPq-B azil o Phd schola ship DGE
(207252/2014-9), he Fede al Uni e si y o Pelo as-UFPel and he Depa men o Educa ion o Basque
Go e nmen (IT1008-16) o inancially suppo ing his esea ch.
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