Supporting Information
Influence of acidic (H3PO4) and alkaline (NaOH) additives
on the catalytic reductive fractionation of lignocellulose
Tom Renders,a Wouter Schutyser, a Sander Van den Bosch,a Steven-Friso Koelewijn,a Thijs Vangeel,a
Christophe M. Courtin,b and Bert F. Sels a*
a
Center for Surface Chemistry and Catalysis, KU Leuven, Celestijnenlaan 200F, 3001 Heverlee, Belgium.
*E-mail: [email protected]
b
Center for Food and Microbial Technology, KU Leuven, Kasteelpark Arenberg 22, 3001 Heverlee, Belgium.
Table of contents
I.
Experimental…………………..………………………….…………………..S2
II.
Figures…….…………………………..………………………….………………S5
III.
Tables……...…………………………………………………….……...……….S19
IV.
References…………………………………………………….……...………..S21
S1
I. Experimental Procedures
Chemicals and materials
All commercial chemicals were analytic reagents and were used without further purification. 5 wt% Pd on carbon, 5
wt% Ru on carbon, guaiacol (2-methoxyphenol, 98%), 4-n-propylguaiacol (>99%), syringol (2,6-dimethoxyphenol,
99%), 4-methylsyringol (>97%), methyl β-D-xylopyranoside (99%), methyl α-D-glucopyranoside (99%), myo-inositol
(99%), 2-isopropylphenol (>98%), methylparaben (>99%) and tetrahydrofuran (>99%) were purchased from Sigma
Aldrich. 4-Ethylguaiacol (98%), 1-butanol (>99%) and ethylene glycol (>99%) were purchased from Acros organics.
Methanol (>99%), ethanol (>99%), dichloromethane (>99%), hydrochloric acid (37 wt%) and sodium hydroxide were
purchased from Fischer Chemical Ltd. 4-n-Propanolguaiacol (3-(4-hydroxy-3-methoxyphenyl)-1-propanol, >98%) was
purchased from TCI chemicals. H3PO4 (85% solution) was purchased from ChemLab.
Sawdust preparation
Dry poplar and pine wood were milled and sieved to obtain a sawdust fraction with a size of 250-500 µm. A Soxtec
extraction was subsequently executed to remove any extractives like fats, waxes, resins and terpenoids/steroids,1 that
can influence the Klason lignin determination. 10 g of oven dried substrate was therefore divided over 4 fritted glass
extraction thimbles and extracted in a Soxtec 2055 Avanti with a 2:1 toluene:ethanol mixture. Prior to a 3 h standard
Soxhlet extraction, a wet step was introduced for 15 min in which the samples were completely submersed in the
toluene:ethanol solution to improve the speed of extraction and thus to reduce the total extraction time needed. After
cooling, the samples were washed with ethanol and dried in an oven at 353 K for one night.
Determination of the Klason lignin content
Product yields in lignin depolymerization literature are typically based on the amount of acid insoluble lignin, also
called Klason lignin, in the lignocellulose sample. The determination of the Klason lignin content of poplar and pine,
was based on a procedure from Lin & Dence.2 Triplicate samples of extracted substrate (1 g each) were transferred to
50 mL beakers after which 15 mL of a 72 wt% H2SO4-solution was added. The mixture was left at room temperature
for 2 h while continuously stirred with a magnetic rod. Afterwards the content of each beaker was transferred to a
round-bottom-flask which already contained 300 to 400 mL of water. The beakers were rinsed and additional water
was added until a H2SO4 concentration of 3 wt% was reached. The diluted solution was boiled for 4 h under reflux
conditions, to maintain a constant volume and acid concentration. After filtration of the hot solution, a brown lignin
precipitate was retained. The precipitate was washed with hot water to remove any leftover acid and the obtained
residue was dried in an oven at 353 K for one night. The reported Klason lignin content was determined relative to
the oven dried substrate by averaging the measured weight of the residues.
Determination of the carbohydrate content and composition
The carbohydrate content and composition in poplar or pine sawdust as well as in the obtained carbohydrate pulps
after hydrogenolysis were determined, using a standard total sugar determination procedure, adapted with hydrolysis
conditions for cellulose-rich materials.3-5 Samples of 10 mg were pre-hydrolyzed in a 13 M H2SO4-solution (1 mL) at
RT for 2 h and subsequently hydrolyzed in a diluted 2 M H2SO4-solution (6.5 mL) at 373 K for 2 h. The resulting
monosaccharides were reduced to alditols and acetylated to increase their volatility for GC analysis. First, internal
standard (1 mL of a 1 mg mL-1 β-D-allose solution of 1:1 benzoic acid:water) was added to 3 mL of the hydrolyzed
sample. NH3 25% in water (1.5 mL) was added, as well as droplets of 2-octanol to avoid excessive foaming. Reduction
was catalyzed with NaBH4 (0.2 mL of a 200 mg NaBH4/mL 2 M NH3 solution) for 30 min at 313 K and the reaction was
stopped by adding 0.4 mL acetic acid. At this point the procedure was paused by placing the reaction tubes in a cold
environment for 1 night. 1-Methylimidazole (0.5 mL) was added to 0.5 mL of the reduced samples to catalyze the
formation of alditol acetates after addition of acetic acid anhydride (5 mL). After 10 min, 1 mL of ethanol was added
and 5 minutes later, the reaction was quenched by adding 10 mL of water. The reaction vials were placed in an ice
bath and bromophenol blue (0.5 mL of a 0.4 g L-1 water solution) as well as KOH (2 x 5 mL of a 7.5 M solution) were
added to color the aqueous phase blue. The yellow ethyl acetate phase, containing the acetylated monosaccharides,
S2
could then easily be separated with a Pasteur pipette and was dried with anhydrous Na2SO4 before transferring it into
a vial. GC analysis was performed on a Supelco SP-2380 column with helium as carrier gas in a Agilent 6890 series
chromatograph equipped with an autosampler, splitter injection port (split ratio 1:20) and flame ionization detector
(FID). Separation was executed at 498 K with injection and detection temperatures at 543 K. Calibration samples,
containing known amounts of the expected monosaccharides were included in each analysis. To calculate the
carbohydrate content in the analyzed samples, a correction factor was used to compensate for the addition of water
during hydrolysis. Each substrate was analyzed in threefold and the average values were used in the calculation of the
carbohydrate retention.
Lignin hydrogenolysis
In a typical catalytic hydrogenolysis experiment, 2 g of pre-extracted (poplar or pine) sawdust, 0.2 g Pd/C, 40 mL
solvent (MeOH) and H3PO4/NaOH were loaded into a 100 mL stainless steel batch reactor (Parr Instruments Co.).
The reactor was sealed, flushed with N2 and pressurized with 2 MPa H2 at room temperature (RT). The mixture was
stirred at 750 rpm and the temperature was increased to 473 K (~10 K.min -1) at which the pressure reached ~6 MPa
(~11 MPa at 523 K) and the reaction was started. After reaction, the autoclave was cooled in water and depressurized
at RT.
Lignin product analysis
After reductive processing, the liquid and solid reactor contents were quantitatively collected and separated from
each other over a glass fritted filter. For the alkaline reactions, the solution was acidified with a slight excess of dilute
HCl solution (6 wt%). Subsequently, the volatile organic solvent (typically MeOH) was evaporated. This way a brown
oil was obtained, which was subjected to threefold liquid-liquid extractions using dichloromethane (DCM) and water
to separate the soluble lignin products from sugar-derived products, salts and residual mineral acid. Finally the DCMextracted phase was dried to obtain the ‘lignin product oil’. The weight of the lignin oil is then used to determine the
degree of delignification (based on Klason lignin weight).
To analyze the lignin monomers after hydrogenolysis, a weighed amount of external standard (2-isopropylphenol)
was added to the lignin oil after which the content was completely resolubilized in 7 mL methanol. A sample was then
analyzed on a GC (Agilent 6890 series) equipped with a HP5-column and a flame ionization detector (FID). The
following operating conditions were used: injection temperature of 573 K, column temperature program: 323 K (2
min), 15 K min-1 to 423 K, 10 K min-1 to 493 K and 20 K min-1 to 563 K (12 min), detection temperature of 573 K.
Sensitivity factors of most the monomer products were obtained by calibration with commercial standards (section
Chemicals and materials). Sensitivity factors of a few remaining non-commercially available monomers (ethylsyringol,
4-n-propyl syringol and 4-n-propanol syringol) were deduced by interpolation based on (i) the sensitivity factors of
analogues compounds and (ii) taking into account the basic principles of the ‘effective carbon number method’. 6 The
product yield (expressed in C-mol%) is defined as follows:
𝑌𝑖𝑒𝑙𝑑 𝑝𝑟𝑜𝑑𝑢𝑐𝑡 𝐴 (𝐶𝑚𝑜𝑙%) =
𝑤𝑡%𝐶𝑝𝑟𝑜𝑑𝑢𝑐𝑡 𝐴
100
∗ 100 %
𝑤𝑡% 𝐾𝑙𝑎𝑠𝑜𝑛 𝑙𝑖𝑔𝑛𝑖𝑛 𝑤𝑡%𝐶𝐾𝑙𝑎𝑠𝑜𝑛 𝑙𝑖𝑔𝑛𝑖𝑛
𝑚𝑙𝑖𝑔𝑛𝑜𝑐𝑒𝑙𝑙𝑢𝑙𝑜𝑠𝑒 𝑠𝑢𝑏𝑠𝑡𝑟𝑎𝑡𝑒 ∗
∗
100
100
𝑚𝑝𝑟𝑜𝑑𝑢𝑐𝑡 𝐴 ∗
With:
𝑤𝑡%𝐶𝑝𝑟𝑜𝑑𝑢𝑐𝑡 𝐴
12 𝑔 𝑚𝑜𝑙 −1
= #𝐶𝑝𝑟𝑜𝑑𝑢𝑐𝑡 𝐴 ∗
∗ 100 %
100
𝑀𝑊𝑝𝑟𝑜𝑑𝑢𝑐𝑡 𝐴
𝑤𝑡%𝐶𝐾𝑙𝑎𝑠𝑜𝑛 𝑙𝑖𝑔𝑛𝑖𝑛
= #𝐶𝑙𝑖𝑔𝑛𝑖𝑛 𝑚𝑜𝑛𝑜𝑚𝑒𝑟,
100
𝑎𝑣𝑒𝑟𝑎𝑔𝑒
∗
12 𝑔 𝑚𝑜𝑙 −1
𝑀𝑊𝑙𝑖𝑔𝑛𝑖𝑛 𝑚𝑜𝑛𝑜𝑚𝑒𝑟,
∗ 100 %
𝑎𝑣𝑒𝑟𝑎𝑔𝑒
In these definitions, mproduct A is the weight of product A, wt%Cproduct A is the weight percentage of carbon in product
A, mlignocellulose substrate is the weight of the lignocellulose substrate, wt%Klason lignin is the weight percentage of Klason
lignin in the lignocellulose substrate, wt%CKlason lignin is the weight percentage of carbon in the Klason lignin, #Cproduct
A is the number of C-atoms in 1 molecule of product A, MWproduct A is the molecular weight of product A, #Clignin monomer,
average is the average number of C-atoms in 1 lignin monomer and MWlignin monomer, average is the average molecular weight
of a lignin monomer. The MWlignin monomer, average and #Clignin monomer, average were estimated, taking into account the
relative distribution of the main building blocks in the lignin. The chemical structures of p-hydroxyphenyl (H)-,
guaiacyl (G)- and syringyl (S)-units in Klason lignin were herein represented by respectively p-coumaryl, coniferyl
S3
and sinapyl alcohol units with respective molecular weights of 150, 180 and 210 g mol-1 and respective #Clignin monomer
values of 9, 10 and 11. For poplar with a S:G ratio of 55:45, this resulted in a MWlignin monomer, average of 196.5 g mol-1 and a
#Clignin monomer, average of 10.74, corresponding to 64.4 wt% CKlason lignin.7 For pine with a G:S ratio of 98:2, the same
calculations result in a MWlignin monomer, average of 180.6 g mol-1 and a #Clignin monomer, average of 10.02, corresponding to 66.2
wt% CKlason lignin.
The dimer yield was determined in the same way as the monomer yield, yet a derivatization step was added to increase
their volatility before GC analysis. Therefore, 0.2 mL of the resolubilized lignin oil with the internal standard 2isopropylphenol, was dried under a N2 flow and subsequently mixed with 0.5 mL of pyridine and 0.5 mL of N-methylN-(trimethylsilyl)trifluoroacetamide. The vial was sealed and put in an oven at 353 K for 30 min. After this the lignin
products were quantified with GC analysis as described above. Identification of the monomer and dimer signals was
performed with GC-MS using an Agilent 6890 series GC equipped with a HP1-MS capillary column and an Agilent
5973 series Mass Spectroscopy detector. The following operating conditions were used: injection temperature of 523
K, column temperature program: 333 K (2 min), 10 K min-1 to 553 K (13 min), detection temperature of 563 K. Sensitivity
factors were estimated based on the sensitivity factors of the trimethylsililated monomers and taking into account
the basic principles of the ‘effective carbon number method’.6
To get more insight in the degree of lignin depolymerization, the distribution of the molar mass of the lignin products
was investigated using gel permeation chromatography (GPC). Therefore a sample of the lignin oil was solubilized in
THF (~ 2-5 mg mL-1) and subsequently filtered with a 0.2 µm PTFE membrane to remove any particulate matter to
prevent plugging of the columns. GPC analyses were performed at 313 K on a Waters E2695 equipped with a M-Gel
column 3 μm (mixed), using THF as the solvent (1 mL min-1) and a UV detection at 280 nm with a Waters 2988
Photodiode array detector.
Analysis of the solubilized carbohydrates
The solubilized carbohydrates were analyzed similar to the lignin derived dimers. An internal standard, myo-inositol,
was added to the water phase obtained after extraction with DCM. 0.2 mL of the solution was dried under a N2 flow
and subsequently mixed with 0.5 mL of pyridine and 0.5 mL of N-methyl-N-(trimethylsilyl)trifluoroacetamide.
Quantification and identification were performed with GC-FID and GC-MS. Sensitivity factors of the products were
obtained by calibration with methyl β-D-xylopyranoside and methyl α-D-glucopyranoside.
Structural analysis of the carbohydrate pulp after hydrogenolysis
X-ray Diffraction (XRD) measurements were performed 6-fold with a STOE STADI P Combi diffractometer equipped
with a Cu-Kα radiation source (λ = 0.154 nm). Cellulose I crystals have five different crystal planes: (101), (10ī), (021),
(002) and (040).8 The crystallinity indices were determined using the commonly used XRD peak height method
developed by Segal et al.:9
CrI (%) = (I002 -IAM ) / I002 x 100%
where I002 represents the maximal intensity of the (002) reflection and IAM represents the minimal intensity between
the (002) and (101) reflections.
Scanning electron microscopy (SEM) was applied on the pulp to illustrate the structural differences at µm-scale after
fractionation with acidic or alkaline additives. After coating of the samples with gold using a JEOL JSC-1300 sputter,
secondary electron images (SEI) were recorded on a JEOL JSM-6010 JV microscope with an accelerating voltage of 5
kV.
S4
II. Figures
Figure S1. Image of the lignin product oil and solubilized product oil obtained from processing in (a) acidic conditions
(5 g L-1 H3PO4) and (b) alkaline conditions (5 g L-1 NaOH).
Figure S2. (a) Image of poplar sawdust (250-500 µm) used for the hydrogenolysis reactions. (b) Image of the pulp
obtained after reaction. The sawdust structure, i.e. aggregated fiber cells, is retained well; the black colour is due to
the presence of the Pd/C catalyst. Efforts are being taken to separate and reuse the catalyst.
Figure S3. Theoretical (maximum) product yield as a function of the fraction of cleavable ether-type inter-unit bonds
in the lignin structure.10 The calculation assumes that all ether bonds are cleaved upon hydrogenolysis and that these
bonds are randomly distributed within an infinite linear lignin structure. The monomer yield is given by the chance
that two ether bonds [E] are located next to each other and thus equals [E]2. The chance upon formation of a dimer
is calculated by the chance that an ether bond is followed by a non-ether bond [NE] which is in turn followed by an
ether bond [E]. Since a dimer is made up of two subunits, the theoretical yield expressed in wt% equals 2 x [NE][E]2.
In analogy, the theoretical yield (wt%) of any oligomer comprising n subunits can be calculated according to the
following formula: Yn = n x [NE]n-1[E]2.
S5
Figure S4. Gas chromatograms of the trimethylsilylated lignin dimer product obtained from poplar processing in
acidic (5 g L-1 H3PO4), neutral and alkaline (5 g L-1 NaOH) conditions. In support of this figure (also presented in the
article as Figure 3), the corresponding mass spectra for each identified (trimethylsilylated) compound are provided
below, as well as the chemical structure of each dimer. The peak identification was confirmed by literature.11-16
Abbreviations of the phenolic units:
PohS
4-n-Propanolsyringol
EG
4-Ethylguaiacol
PohG
4-n-Propanolguaiacol
S
Syringol
PS
4-n-Propylsyringol
G
Guaiacol
PG
4-n-Propylguaiacol
PHB
para-Hydroxybenzoate
ES
4-Ethylsyringol
S6
Dimer 1: β-1 (EG-G)11, 12, 14-16
Dimer 2: β-1 (EG-S) (moscatilin)11
Dimer 3: β-1 (PohG-G)11, 14-16
S7
Dimer 4: β-β (PS-PS, α-O-γ2) (syringaresinol)13
Dimer 5: β-5 (PohG-PG)11, 12, 14-16
Dimer 6: β-1 (ES-S)11
S8
Dimer 7: β-1 (PohS-G)11
Dimer 8: β-1 (PohG-S)11
Dimer 9: β-5 (PohS-PG)11, 12
S9
Dimer 10: β-1 (PohS-S)11, 12
Dimer 11: β-5 (EG-PohG)12, 14, 15
Dimer 12: 5-5 (PohG-PohG)14
S10
Dimer 13: β-5 (PohG-PohG)14
Dimer 14: ester (PohS-PHB)
Dimer 15: β-5 (ES-PohG)12
S11
Dimer 16: β-5 (PohS-PohG)
Dimer 17: β- β (PohS-PohS)
Dimer 18: 5-5 (EG-EG)11, 12, 15
S12
Dimer 19: β-5 (EG-EG)12, 15, 16
Dimer 20: 5-5 (EG-PohG)
Dimer 21: β-5 (EG-ES)12, 15, 16
S13
Dimer 22: Unknown compound (M•+: 608)
S14
Figure S5. Mass balance of the catalytic reductive fractionation of poplar wood, expressed in wt%. Reaction
conditions: 2 g pre-extracted poplar sawdust, 40 mL MeOH, 0.2 g Pd/C (5 wt%), 2 MPa H2 at room temperature, 3 h.
The portion of cellulose in the pulp is based on the amount of glucose, whereas the hemicellulose content is estimated
based on the amount of xylose, arbaniso, mannose and galactose, in agreement with the definition of the LFFE. The
residual lignin present in the pulp is calcultated based on the weight of the acquired lignin oil. The moisture content
of the pulp is estimated gravimetrically by drying the sawdust overnight at 80°C. Quantification of the methylated
carbohydrates in the water phase is performed by GC-analysis (Figure S8), a distinction is made between
carbohydrates derived from cellulose (methyl-glucopyranoside) and carbohydrates derived from hemicellulose
(mainly methyl-xylopyranoside). The missing fraction of the mass balance is expected to be mainly made up of soluble
carbohydrate oligomers present in the water phase, or humins which might be formed during the reaction.
S15
Figure S6. Graphical summary of a stability study of the Pd/C catalyst in the acidic environment (5 g L -1 H3PO4 in
MeOH). The catalyst powder was treated in an acidic environment which mimicked the reaction conditions (473 K,
5 g L-1 H3PO4, 2 MPa H2, no sawdust). After 3 h, the reactor was cooled and 2 g poplar sawdust was added. Next, the
reactor was heated again to 473 K for 3 h under hydrogen atmosphere (2 MPa H2). Comparison of the GPC
chromatograms obtained with acid-treated catalyst and with fresh (untreated) catalyst indicates that the degree of
depolymerization is not affected by the acid treatment. In addition, the monomer selectivity is almost the same for
both reactions. To conclude, the acidic environment (H3PO4) does not impair the stability of the Pd/C catalyst, in
agreement with conclusions drawn by Lercher et al.17
Figure S7. Graphical summary of control experiments with respect to the Pd/C catalyst, both for processing with 5 g
L-1 H3PO4 and 5 g L-1 NaOH. Poplar wood was processed in MeOH (473 K, 2 Mpa H2) for 3 h with and without Pd/C.
The Pd/C catalyst is essential in order to efficiently disassemble the extracted lignin and to obtain high monomer
yield. When no catalyst is used, the acquired monomer fraction is significantly lower comprising mainly methyl
paraben. Furthermore, this graph shows that disassembling of the lignin occurs more efficiently in mild acidic
conditions compared to alkaline conditions.
S16
Figure S8. Chromatogram of the water phase obtained after trimethylsilylation (for processing with 5 g L-1 H3PO4).
Methyl-xylopyranoside and methyl-glucopyranoside are the main products, next to some minor quantities of
furanoside isomers, xylitol and glycerol. Identification was confirmed by GC-MS and comparison with commercial
standards.
Figure S9. Chromatogram of the complete product mixture after processing poplar wood with 5 g L -1 H3PO4, and
chromatograms of the purified lignin-oil (via liquid-liquid extraction with DCM:water). Chromatograms were
obtained after trimethylsilylation. Methylated carbohydrates and phosphoric acid are removed upon extraction,
leading to a product oil exclusively composed of lignin products.
S17
Figure S10. X-ray diffactograms for the pulps obtained from processing poplar wood with different amounts of H3PO4
and NaOH (1.25; 2.5 and 5 g L-1), in addition to figure 7.
Figure S11. Scanning electron microscopy images of the pulp obtained with 5 g L-1 H3PO4 (a,c) and 5 g L-1 NaOH (b,d;
43x and 150x magnification). Also presented in the main article as Figure 7.
S18
III. Tables
4-ethylsyrinol
methylparaben
4-n -propylguaiacol
4-n-propylsyringol
4-n-propanolguaiacol
4-n-propanalsyringol
Total monomers
Selectivity monomers b
G/(G+S) ratio
523 K
4-ethylguaiacol
473 K
Neutral c
syringol
Neutral c
guaiacol
Entry
phenol
Table S1. Detailed overview of the phenolic monomer yields (main products, C-mol%) of reactions with poplar wood
illustrated in the article in figure 1.a
0
0
0
0
0
1
<1
2
9
13
27
48
38
0
0
1
<1
1
3
<1
3
14
22
44
52
36
H3PO4
1.25 g
L-1
1
0
0
<1
<1
<1
<1
3
13
18
36
47
39
H3PO4
2.5 g L-1
1
0
<1
<1
<1
<1
1
4
13
20
40
46
38
H3PO4 c
5 g L-1
NaOH
NaOH
NaOH c
<1
0
0
<1
<1
1
1
4
14
21
42
44
38
L-1
1
<1
<1
<1
1
4
<1
2
5
13
26
38
27
L-1
1
<1
<1
1
2
3
<1
2
3
11
25
32
26
1
<1
<1
2
4
2
<1
1
2
8
23
27
27
1.25 g
2.5 g
5g
L-1
a The
reaction conditions are as follows: 2 g extracted poplar sawdust (0.25-0.50 mm), 0.2 g Pd/C, 40 mL MeOH, 473
K (or as specified), 3 h reaction time and 20 bar H2 at RT.
b
Monomer selectivity is expressed as the weight ratio of the total monomers to the lignin product oil.
c The
reactions corresponding to these entries were performed in triplicate, the relative error was within a 5% interval
(for the total monomer yield and main monomers).
S19
Catalyst
Solventb
phenol
guaiacol
syringol
4-ethylguaiacol
4-ethylsyrinol
Methylparaben c
4-n -propylguaiacol
4-n-propylsyringol
4-n-propanolguaiacol
4-n-propanalsyringol
Total monomers
Selectivity monomers d
G/(G+S) ratio
Table S2. Detailed overview of the phenolic monomer yields (main products, C-mol%) of additional reactions
performed with poplar wood with other catalysts and solvents in alkaline conditions (5 g L -1 NaOH).a
Ru/C
MeOH
2
<1
1
2
6
<1
<1
5
<1
1
20
23
23
Ni/SiO2
MeOH
1
<1
1
2
4
2
<1
3
<1
2
15
19
24
Pd/C
EtOH
<1
<1
1
1
4
<1
<1
<1
2
5
14
24
18
Pd/C
EtGly
3
<1
<1
3
4
n.d.
<1
4
<1
4
23
n.d.
25
Pd/C
BuOH
1
2
<1
<1
2
<1
<1
<1
2
6
17
30
22
a The
reaction conditions are as follows: 2 g extracted poplar sawdust (0.25-0.50 mm), 0.2 g catalyst, 5 g L-1 NaOH 40
mL solvent, 473 K, 3 h reaction time and 20 bar H2 at RT.
b
Abbreviations: methanol (MeOH), ethanol (EtOH), 1-butanol (BuOH), ethylene glycol (EtGly).
c
Methylparaben or analogue (e.g ethylparaben when processing in ethanol)
d
Monomer selectivity is expressed as the weight ratio of the total monomers to the lignin product oil.
Entry
phenol
guaiacol
syringol
4-ethylguaiacol
4-ethylsyrinol
methylparaben
4-n -propylguaiacol
4-n-propylsyringol
4-n-propanolguaiacol
4-n-propanalsyringol
Total monomers
Selectivity monomers b
Table S3 Detailed overview of the phenolic monomer yields (main products, C-mol%) of reactions with pine wood
illustrated in the article in figure 5. The Klason lignin content of the pre-extracted pine sawdust equals 27.61 wt% a
Neutral 473 K
0
0
0
0
<1
0
<1
<1
9
0
10
42
Neutral 523 K
0
0
0
0
<1
0
<1
1
17
0
19
40
0
<1
0
0
<1
0
1
0
14
0
16
28
0
0
0
<1
<1
0
1
0
15
<1
17
31
0
0
0
<1
<1
0
<1
0
2
0
2
8
0
0
0
<1
<1
0
<1
0
2
0
4
10
H3PO4
H3PO4
2.5 g
5g
L-1
L-1
L-1
NaOH
2.5 g
NaOH
5 g L-1
a
The reaction conditions are as follows: 2 g extracted pine sawdust (0.25-0.50 mm), 0.2 g Pd/C, 40 mL MeOH, 473
K, 3 h reaction time and 20 bar H2 at RT.
b
Monomer selectivity is expressed as the weight ratio of the total monomers to the lignin product oil.
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IV. References
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