P r e s e n t e d b y ,R icha Chaudhary
R e s e a r c h G u i d e : D r . P a r e s h L . D h e p e
C a t a l y s i s & I n o r g a n i c C h e m i s t r y D i v i s i o nC S I R - N a t i o n a l C h e m i c a l L a b o r a t o r y , P u n e , I n d i a
T e l . + 9 1 - 2 0 - 2 5 9 0 2 0 2 4 , F a x . + 9 1 - 2 0 - 2 5 9 0 2 6 3 3E m a i l : p l . d h e p e @ n c l . r e s . i n
G r o u p W e b p a g e : h t t p : / / a c a d e m i c . n c l . r e s . i n / p l . d h e p e
Solid base catalyzed depolymerization (liquefaction / valorization) of lignin into low molecular weight aromatic products
Keywords: Biomass, Lignin, Hydrolysis, Depolymerization, Solid base catalyst, Aromatic compounds
Alkaline lignin: (A) XRD, (B) TGA-DTA, (C) 13C NMR, (D) FT-IR
10 20 30 40 50 60 70
Inte
nsity
(a.u
)
2q°
(A)
Cleavage of α- and β-aryl-alkyl-ether linkages
Aliphatic chainsplitting
Aromatic ringdecomposition
(B)
(D)
260 240 220 200 180 160 140 120 100 80 60 40 20 0 -20 -40 -60Chemical Shift (ppm)
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
Norm
alize
d Inte
nsity
21.42
45.48
55.50
69.98
83.23
114.6
312
3.12
129.4
1
147.4
9
182.1
3
208.0
2
228.1
2
Carbonyl groups (Ar-CHO)
Ester groups(Ar/R-CO-R/Ar)
sp2 carbon (C=C) in aromatics and alkenes
Methoxyl groups attached to the aromatic rings
Acetyl and alkanes(CH3-CO/ R3CH)
sp3 carbon next tooxygen
(Ar/R-CH2-O-)
(C)
TPD CO2 profile of various solid base catalysts
100 200 300 400 500 600 700
Temperature (°C)
NaX
NaY
NaP
KLTL
HAP
HT
MgO
CaO
v Order of basicity (mmol/g):
CaO (1.96) > NaX (0.42) ≈ HT (0.40) >NaY (0.34) > MgO (0.24) > KLTL (0.14) ≈ HAP (0.12) > NaP (0.09).
v Order of pH in reaction mixture:
CaO (pH ≥ 13.4) > HT (pH 12.5) > MgO (pH 10.5) > KLTL (pH 9.4) > NaX (pH 9.2) > NaY = NaP (pH 8.7) ≈ HAP (pH 8.5) > Millipore water (pH 6.8).
Characterization of lignin and various solid base catalysts
CatalystN2 sorption TPD-CO2
BET Surface area (m2/g)
Pore volume (cm3/g)
Pore diameter (nm)
Total Basicity(mmol/g)
Peak maxima (°C)
NaX 586 0.32 1.10 0.42 404NaY 575 0.33 1.15 0.34 292NaP 14 0.10 1.8 0.09 171 & 486KLTL 220 0.13 nd 0.14 188HT 207 0.95 9.2 0.40 294 & 603HAP 39 0.18 9.08 0.12 166 & 587CaO 12.4 0.05 8.2 1.96 408 & 673MgO 9.2 0.02 4.8 0.24 604
Substrate M. Wt. (Da) Elemental analysis (%)
TGA-DTA(Residue %)
EDAX(element)
Monomer molecular formula
C H S N2 Air
AlkalineLignin
60,000 52 5 2.05 44 17 C, O, Na, S C8.7H9.1O5.1S0.13
Methodology for separation of products
Extraction with organic solvents
Reaction Mixture
Centrifugation
Solid(Catalyst + Solid)
Solution (EtOH + H2O soluble)
Acidified mixture
HCl (pH 1-2)
Reaction Charge
Depolymerization
Liquid
InsolubleSoluble*
Evaporation
SolidExtraction with organic solvents
InsolubleSoluble*
Evaporation
Aromatic products Aromatic products
v Reaction Condition: Lignin(0.5 g), Catalyst (0.5 g),Solvent (EtOH:H2O = 30 mL,1:2 v/v), 250°C, 1 h
v Solvents used for theextraction of products: diethylether (DEE) & ethyl acetate(EtOAc)
v Organic solvent solubleproducts(*) were analyzed byusing GC, GC-MS and HPLC.
Effect of various solid base catalysts on lignin depolymerization
0
10
20
30
40
50
60Pr
oduc
t yie
ld (w
t%)
Catalysts
DEE EtOAc SR Mix. Sol
24%
34%
51%
18% 17.4%14%
38%34%
30%
10.2%
Reaction condition: Lignin:Catalyst = 1:1 wt/wt, EtOH:H2O (1:2 v/v) 30 mL, 250 oC, 1 h.
Products adsorption study
v GC chromatographs of mixture of
Phenol, p-cresol, Guaiacol, Eugenol and
Vanillin in EtOH:H2O (1:2 v/v) 30 mL.
(A) Before reaction with CaO
(B) After reaction with CaO at 30 oC
(C) After reaction with CaO at 250 oC
(D) Before reaction with NaX
(E) After reaction with NaX at 250 oC
Reaction Condition: Monomers (0.1 g each), Catalyst (0.5 g), 1 h.
Minutes6 7 8 9 10 11 12 13 14 15
pA
25
50
75
100
125
150
175
pA
25
50
75
100
125
150
175Back SignalPVGEpC (1-2)
Back SignalPVGEpC (1-2) RC30C
Back SignalPVGEpC RC(1-2) 250C
Minutes7 8 9 10 11 12 13 14 15
pA
40
60
80
100
120
140
pA
40
60
80
100
120
140
Back SignalPVGEpC@RT1-2
Back SignalPVGEpC@2501-2
(A)
(B)
(C)
(D)
(E)
Inte
nsity
(a.u
.)
Products adsorption study with single molecules
v GC chromatographs of adsorption
study with single molecules at 30 oC.
(A) Eugenol in EtOH:H2O (1:2 v/v) 6 mL
(B) Eugenol:CaO (1:1 wt/wt) in EtOH:H2O
(1:2 v/v) 6 mL
(C) Eugenol:CaO (2:1 wt/wt) in EtOH:H2O
(1:2 v/v) 6 mL
(D) Vanillin in EtOH:H2O (1:2 v/v) 6 mL
(E) Vanillin:CaO (1:1 wt/wt) in EtOH:H2O
(1:2 v/v) 6 mL
(F) Vanillin:CaO (2:1 wt/wt) in EtOH:H2O
(1:2 v/v) 6 mL
(A)
(B)
(C)
(D)
(E)
(F)
Inte
nsity
(a.u
)
Eugenol
Eugenol + CaO (1:1 wt/wt)
Eugenol + CaO (2:1 wt/wt)
Vanillin
Vanillin + CaO (1:1 wt/wt)
Vanillin + CaO (2:1 wt/wt)
Optimization of pH for lignin depolymerization
Reaction condition: Lignin:Catalyst = 1:1 wt/wt, EtOH:H2O (1:2 v/v) 30 mL, 250 oC, 1 h.
Effect of pH on lignin depolymerization
0
10
20
30
40
50
60
9.2 8.7 8.7 8.7 ≥ 13.4 9.2 10.5 9.2
Prod
uct y
ield
(wt%
)
pH
DEE EtOAc SR Mix. Sol.
NaX NaY NaP CaO MgO
Reaction condition: Lignin, Catalyst, EtOH:H2O (1:2 v/v) 30 mL, 250 oC, 1 h.
Depolymerization of lignin using CaO catalyst
0
10
20
30
40
50
60
0
10
20
30
40
50
0.5 0.1 0.05
Tim
e (m
in.)
Prod
uct Y
ield
(wt%
)
Catalyst weight (g)
DEE EtOAc Time (B)
0
10
20
30
40
50
0.5 0.05 0.005
Prod
uct Y
ield
(wt%
)
Catalyst weight (g)
DEE EtOAc(A)
v Effect of CaO loading on lignin depolymerization
Reaction condition: (A) Lignin (0.5 g), EtOH:H2O (1:2 v/v) 30 mL, 250 oC, 1 h. (B) Lignin (0.5 g), EtOH:H2O (1:2 v/v) 30 mL, 250 oC.
Optimization of reaction condition
0
10
20
30
40
50
60
0.33 0.5 0.66 0.83 1 2P
rodu
ct y
ield
(wt%
)
Time (h)
DEE EtOAc (B)
0
10
20
30
40
50
60
230 240 250 260 240 + 0.3 MPa N2
Pro
duct
yie
ld (w
t%)
Temperature (oC)
DEE EtOAc(A)
Reaction condition: Lignin:NaX = 1:1 wt/wt, EtOH:H2O (1:2 v/v) 30 mL.
(A) Effect of temperature (B) Effect of time
GC-MS spectrum of DEE & EtOAc Soluble products
Reaction condition: Lignin:NaX = 1:1 wt/wt, EtOH:H2O (1:2 v/v) 30 mL, 250 oC, 1 h.
(a) DEE soluble (liquid) (b) EtOAc soluble (liquid)
(c) DEE soluble (solid) (d) EtOAc soluble (solid)
HPLC Spectrum of products
Minutes0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
nRIU
0
5000
10000
15000
20000
25000
30000
nRIU
0
5000
10000
15000
20000
25000
30000
RID: RI SignalULDEE-C
Reaction condition: Lignin:NaX = 1:1 wt/wt, EtOH:H2O (1:2 v/v) 30 mL, 250 oC, 1 h.
Quantification of identified products
Reaction condition: Lignin:NaX = 1:1 wt/wt, EtOH:H2O (1:2 v/v) 30 mL, 250 oC, 1 h.
Table1Quantificationofidentifiedlignindepolymerisationproducts.Reactioncondition:Lignin:NaX=1:1wt/wt, EtOH:H2O (1:2 v/v) 30 mL,250oC,1h
Monomer Structure Yield(wt%)
Guaiacol
1
Pyrocatechol
0.3
2-methoxy-4-methylphenol
3.7
Resorcinol
0.8
4-hydroxybenzylalcohol
1.4
2,6-dimethoxyphenol
0.03
Eugenol
0.4
1,2,4-trimethoxybenzene
0.03
Vanillin
3.6
3,4-dimethoxyphenol
0.02
4-hydroxy-3-methoxybenzylalcohol
0.3
Acetoguaiacone
4.1
2,4-ditert-butylphenol
0.5
Hexadecane 0.5
Homovanillicacid
0.3
Table1Quantificationofidentifiedlignindepolymerisationproducts.Reactioncondition:Lignin:NaX=1:1wt/wt, EtOH:H2O (1:2 v/v) 30 mL,250oC,1h
Monomer Structure Yield(wt%)
Guaiacol
1
Pyrocatechol
0.3
2-methoxy-4-methylphenol
3.7
Resorcinol
0.8
4-hydroxybenzylalcohol
1.4
2,6-dimethoxyphenol
0.03
Eugenol
0.4
1,2,4-trimethoxybenzene
0.03
Vanillin
3.6
3,4-dimethoxyphenol
0.02
4-hydroxy-3-methoxybenzylalcohol
0.3
Acetoguaiacone
4.1
2,4-ditert-butylphenol
0.5
Hexadecane 0.5
Homovanillicacid
0.3
Lignin and products correlation
Reaction condition: Lignin:Catalyst = 1:1 wt/wt, EtOH:H2O (1:2 v/v) 30 mL, 250 oC, 1 h.
FT-IR of alkaline lignin
FT-IR of (a) DEE and (b) EtOAc soluble products
Characterization Fresh & Spent Catalyst (NaX)
Reaction condition: Lignin:Catalyst = 1:1 wt/wt, EtOH:H2O (1:2 v/v) 30 mL, 250 oC, 1 h.
10 20 30 40 50 60 70
Inte
nsity
(a.u
)
2q°
Fresh
Spent
ARTICLE JournalName
8 |J.Name.,2012,00,1-3 Thisjournalis©TheRoyalSocietyofChemistry20xx
Pleasedonotadjustmargins
Pleasedonotadjustmargins
reaction was carried out in absence of nitrogen pressure at240oC.This suggests thatpressureplaysan important role inachieving higher yields. In our earlier work on solid acidcatalyzeddepolymerization,effectofpressureonthereactionwas studied in detail and it was established that with anincrease in pressure yield of products increases.12,13Subsequently, reaction was performed at highertemperature (260 oC) believing that higher pressures wouldbenefit the reaction but, again slight decrease in yield (46%)was seen, which was against expectation. Thus, 250 oC is anoptimumtemperature tocarryoutdepolymerizationof ligninusingNaXcatalyst.SinceonNaXcatalystunlikeCaOandothercatalysts, only minimal quantity of products were adsorbedunderreactionconditions,itisassumedthatdecreaseinyieldathigher reaction temperatures isdue todegradationand/orrepolymerization reactions. Nevertheless, detailed study isrequiredtocommentfurtheronthismatter. The effect of reaction time on the product yield wasinvestigatedat250oCoverNaXasacatalyst inethanol:water(1:2 v/v) solvent system (Fig. S8(B), ESI). The products yieldwasincreasedupto51%forareactiontimeof1handbeyondthis time products yield started declining.However, a carefullookattheresultsimplythatalthoughoverallyielddecreasedin 2 h, but contribution from DEE soluble products wasincreased in 2 h reaction. This implies that EtOAc solubleproducts like oligomers are over the period of time wereconvertedintolowmolecularweightproducts. Further, tomakesure that there isnota significanteffectfrom series degradation reactions, we have performed thedepolymerizationreactionsbynormalizingthereactiontimetothemassofcatalyst.Detailsarerepresented inFigureSxx.AsseenfromFigureSxx(ESI),whenreactionswereperformedfor1 h, with the decrease in CaO loading, increase in yield wasobserved.ThismaybeduetopHorproductadsorptioneffect.Later, reactionswereperformedwithvaryingcatalyst loadingand accordingly change in reaction time. For e.g. with 0.5 gCaOcatalystloading,reactionwasperformedfor1hhowever,when 0.1 g of CaOwas charged in the reactor, reactionwascarriedout for 20min (i.e. 5 timesdecrease inboth, catalystandtime).Subsequently,reactionwascarriedoutwith0.05gCaOfor10min.Theresults(FigureSxx,ESI)showthatthoughwith decrease in time according to decrease in catalystloading, slight improvement in theyieldswas seen.However,
thisincreaseismarginalconsideringwhenreactionwascarriedout for 1 h with 0.05 catalyst (Figure Sxx, ESI). This suggeststhat pH (9.2) along with time is important to achieve betteryields. Mostly,lignindepolymerizationreactionsarecarriedoutinalcohol:water mixture for achieving better yields due tosolubility of lignin in the solvent system which makes thereaction system homogeneous (whenwater soluble catalystsareused).Sincealkalineligninusedinthisstudyiscompletelysolubleinwater(TableS1,ESI),reactionwascarriedoutat250oCwithNaX as a catalyst for 1 h in onlywater. However, noproduct formationwasseen in this reaction.This resultcouldnotbeexplainedonthebasisofpressureeffectaswithwaterasasolventat250oC,totalpressureof4.0MPawasobservedwhilewhenreactioniscarriedoutwithethanol:water(1:2v/v)solventsystem,4.2MPapressurewasmonitoredyet51%yieldwas achieved. So, it can be considered that presence ofethanol in subcritical condition is helpful in forwarding thereaction. Subsequently, reactionswere performed by varyingthe ratio of ethanol-water (2:1, 1:1, 1:5 v/v) and maximumyield was observed in 1:2 (v/v) solvent system. One of thereasonsforreactionstoproceedinpresenceofethanolmightbeduetotheformationofsodiumethoxide(reactionbetweenNa+oncatalystandethanol),whichcanactasstrongbase.Thisscenario is not possible when only water is used in thisreaction. Though, the in-situ formation of sodium ethoxidecould not be confirmed under reaction conditions. Yet, it isexpected that when reaction is completed Na+ willcompensate the negative charge on zeolites. This is becauseduring spent catalyst characterization studies no loss of Na+wasobserved(formoredetailspleaseseesection2.3.9,ESI).3.1.6.Catalystrecyclability
Inthecatalystrecyclabilitystudy,NaXwasrecoveredfromthereactionmixturebycentrifugationand laterwaswashedwithethanol:water (1:2 v/v), and used in the next reaction (fordetails see section 2.3.8, ESI). With fresh catalyst, 51% yieldwasobservedandlaterinthe1strecyclerundecreaseinyieldto 34% was seen. In subsequent recycle run almost similaryieldwas seen (35% in 2nd run, 33% in 3rd run) (Fig. S9, ESI).Nevertheless, it is interesting to note here that though inrecycle runs total yield was decreased but formation of DEE
TPD-CO2,N2sorptionandICP-OESanalysisoffresh&spentNaXcatalyst.
Catalyst TPD-CO2 Nitrogensorption ICP-OES
NaX Totalbasicity(mmol/g)
BETsurfacearea(m2/g)
Poresize(nm)
Porevolume(cm3/g)
Si/AlratioActual
Si/AlratioObserved
NaContent(mg/g)
Fresh 0.42 582 1.1 0.3 1.2 1.2 17.3
Spent 0.41 586 1.1 0.3 - 1.2 20.5
XRD of fresh & spent NaX TPC CO2 of fresh (a) & spent (b) NaX
Conclusions
1. Depolymerization efficiencies of various solid base catalyst were evaluated.
• Shows that NaX is capable to depolymerize high molecular weight lignin (60,000
Da) into low molecular weight aromatic products (51% yield).
2. The optimization of reaction conditions and detailed studies on catalyst properties
was done.
• Reveal that pH 9.2 is optimum to catalyze depolymerization.
• Solid base are effective for lignin depolymerization at milder conditions (T≤ 250 °C,
atmospheric pressure).
3. An unique product adsorption studies was done.
• Indicates that strong bases have more tendency to adsorb the products.
Further readings
1. Solid base catalyzed depolymerization of lignin into low molecular weight
products.
Richa Chaudhary, Paresh L. Dhepe, Green Chemistry, 2016,
DOI:10.1039/C6GC02701F.
http://pubs.rsc.org/en/content/articlelanding/2017/gc/c6gc02701f#!divAbstract
2. Solid base catalyzed depolymerization of lignin.
P. L. Dhepe and Km. Richa, Council of Scientific and Industrial Research, 2016,
INDIAN Patent Application no. 201611007650.
3. Group Webpage: http://academic.ncl.res.in/pl.dhepe
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