A synergistic biorefinery based on catalytic conversion of lignin prior to cellulose starting from lignocellulosic biomass

Article abstract of DOI:10.1039/c4gc01911c

Current biomass utilization processes do not make use of lignin beyond its heat value. Here we report on a bimetallic Zn/Pd/C catalyst that converts lignin in intact lignocellulosic biomass directly into two methoxyphenol products, leaving behind the carbohydrates as a solid residue. Genetically modified poplar enhanced in syringyl (S) monomer content yields only a single product, dihydroeugenol. Lignin-derived methoxyphenols can be deoxygenated further to propylcyclohexane. The leftover carbohydrate residue is hydrolyzed by cellulases to give glucose in 95% yield, which is comparable to lignin-free cellulose (solka floc). New conversion pathways to useful fuels and chemicals are proposed based on the efficient conversion of lignin into intact hydrocarbons. This journal is

Full text of DOI:10.1039/c4gc01911c

Green Chemistry
View Article Online
View Journal
PAPER
A synergistic biorefinery based on catalytic
conversion of lignin prior to cellulose starting
Cite this: DOI: 10.1039/c4gc01911c
from lignocellulosic biomass†
Trenton Parsell,‡a,b Sara Yohe,‡b,c John Degenstein,‡b,c Tiffany Jarrell,a,b Ian Klein,a,b
Emre Gencer,b,c Barron Hewetson,b,d Matt Hurt,a,b Jeong Im Kim,b,e
Harshavardhan Choudhari,b,c Basudeb Saha,a,b Richard Meilan,b,f Nathan Mosier,b,d
Fabio Ribeiro,b,c W. Nicholas Delgass,b,c Clint Chapple,b,e Hilkka I. Kenttämaa,a,b
Rakesh Agrawal*b,c and Mahdi M. Abu-Omar*a,b,c
Current biomass utilization processes do not make use of lignin beyond its heat value. Here we report on
a bimetallic Zn/Pd/C catalyst that converts lignin in intact lignocellulosic biomass directly into two meth-
oxyphenol products, leaving behind the carbohydrates as a solid residue. Genetically modified poplar
enhanced in syringyl (S) monomer content yields only a single product, dihydroeugenol. Lignin-derived
methoxyphenols can be deoxygenated further to propylcyclohexane. The leftover carbohydrate residue is
hydrolyzed by cellulases to give glucose in 95% yield, which is comparable to lignin-free cellulose (solka
floc). New conversion pathways to useful fuels and chemicals are proposed based on the efficient con-
version of lignin into intact hydrocarbons.
Received 1st October 2014,
Accepted 1st December 2014
DOI: 10.1039/c4gc01911c
www.rsc.org/greenchem
Significance statement
Introduction
Renewable fuels are of great interest because of depleting
fossil fuel reserves and climate change caused by increased
CO2 emissions. The component of biomass known as lignin
hinders our ability to convert cellulose to ethanol and is cur-
rently wasted. Here we present a chemical method for convert-
ing lignin in two steps to fuels and chemicals while making
the cellulosic carbohydrates more accessible. The described
synergies should improve carbon utilization in the future
biorefinery.
Production of liquid fuels and chemicals from lignocellulosic
biomass is an integral part of the solution to the energy grand
challenge.1 Biorefinery concepts for the production of liquid
fuels and chemicals from biomass have been developed and
some commercially implemented.2–4 However, any renewable
platform must provide both liquid fuels and commodity
chemicals on a large scale. For example, in 2012 the U.S. con-
sumed ∼4.6 billion barrels of liquid fuels and produced
greater than 90 Mton of organic commodity chemicals,
respectively (including ∼8 Mton of benzene).5–7 Cellulosic con-
version methods to ethanol and other liquid fuels make use of
only the carbohydrate components of biomass (∼50–60% by
weight).8–10 In comparison, the lignin component (20–30% by
weight but accounting for ∼37% of the carbon in biomass)
inhibits the conversion of cellulose and constitutes a major
waste stream that is burned for its heat value in most appli-
cations.11 Therefore, lignin represents an opportunity for
meeting the demand for a renewable platform of aromatic
fuels and commodity chemicals (e.g. benzene, toluene, xylene
(BTX), styrene, and cumene). As a result, methods for the
selective conversion of lignin are important.11
aBrown Laboratory and Negishi Brown Institute, Department of Chemistry,
Purdue University, 560 Oval Drive, West Lafayette, IN 47907, USA
bThe Center for Direct Catalytic Conversion of Biomass to Biofuels (C3Bio), Discovery
Park, Purdue University, West Lafayette, IN 47907, USA.
E-mail: agrawalr@purdue.edu, mabuomar@purdue.edu
cSchool of Chemical Engineering, Purdue University, West Lafayette, IN 47907, USA
dLaboratory of Renewable Resources Engineering and Department of Agricultural and
Biological Engineering, Purdue University, West Lafayette, IN 47907, USA
eDepartment of Biochemistry, Purdue University, West Lafayette, IN 47907, USA
fDepartment of Forestry and Natural Resources, Purdue University, West Lafayette,
IN 47907, USA
The concept of lignin utilization to produce high-value
products is not new.12,13 However, actual reaction schemes to
effectively convert lignin with high yield to useful end-products
†Electronic supplementary information (ESI) available. See DOI: 10.1039/
c4gc01911c
‡Contributed equally to this work.
This journal is © The Royal Society of Chemistry 2014
Green Chem.

View Article Online
Paper
Green Chemistry
Fig. 1 Selective depolymerization and hydrodeoxygenation (HDO) of lignin first from wood biomass to give a lignin-derived hydrocarbon platform
and glucose from the carbohydrate residue.
remains a significant challenge. There are processes that
produce organosolv lignin separating it from hemicellulose
Selective catalytic conversion of lignin
and cellulose, but the resulting organosolv lignin fraction is an Our biomass conversion process is accomplished via a bi-
extremely complex mixture, which upgrading to a reasonable metallic catalytic system composed of ZnII sites and metallic
number of products in any significant yields is yet to be Pd nanoparticles (3–4 nm) dispersed on a carbon support.
demonstrated.14 Currently one of the few notable commercial This bimetallic system has been shown previously to have a
processes utilizes lingo-sulfonate lignin derived from sulfite synergistic effect that cleaves β-O-4 linkages found in model
pulping to produce vanillin at a maximum yield of only 7.5% compounds more effectively than either component alone.26
by mass.15 Even though new catalysts have been reported for For this catalytic process the biomass was first milled to pass
the cleavage of ether C–O bonds and hydrodeoxygenation through a 40 mesh screen then washed consecutively with
(HDO) of lignin model compounds, only limited successes water and ethanol via soxhlet extraction. Three different types
have been reported with lignin or biomass.16–23 Heterogeneous of pretreated wild-type (WT) poplar (species within the genus
Ni catalysts have been used recently with lignosulfonate to give Populus) wood were reacted with the Zn/Pd/C catalyst in metha-
a mixture of phenolic compounds and dimeric lignin frag- nol (MeOH) at 225 °C and 500 psig of H2 which resulted in
ments with removal of the sulfur as H2S.22 Ford and co- 40–54% of the available lignin being converted to two pro-
workers have reported a catalytic method in supercritical ducts: 2-methoxy-4-propylphenol (dihydroeugenol) and 2,6-
methanol at 300–320 °C and 160–220 bar of H2 that converts dimethoxy-4-propylphenol (Table 1, entries 1, 3, and 4, and
the lignified components of biomass to hydrogenated cyclic Fig. 2A). Based on our experimental results, Zn, Pd, and H2 are
alcohols.23 A recent report has appeared on the conversion of all required for catalysis. Control reactions with poplar
birch sawdust to phenolic compounds utilizing a Ni/C cata- biomass using Zn alone gave minimal conversion to multiple
lyst.24,25 Previously we reported on a catalytic system that could oxygenated products and no products were generated in the
cleave the β-O-4 linkages found in lignin dimeric and poly- absence of H2. Reactions of poplar wood with Pd/C alone gave
meric model compounds with high selectivity and yields.26
low yields of more highly oxygenated methoxypropylphenol
Here we present the use of a bimetallic catalyst based on Zn products. To facilitate separation and recycling (shown in
and nanoparticulate Pd in a selective conversion process com- Table S1†) of the Zn/Pd/C catalyst, we ran the reaction employ-
patible with diverse species of intact woody biomass. The cata- ing a microporous cage (325 mesh) to separate the Pd/C from
lyst produces a single lignin-derived product stream in high the biomass. Such a cage allows the solvent and solute to
yields, leaving essentially all polysaccharide components of the access the catalyst and leaves behind a cellulosic biomass
biomass as a solid residue, which we have demonstrated residue that is Pd/C free. This result is also consistent with the
undergoes enzymatic hydrolysis, resulting in high yields of mechanism proposed in our previous study with model com-
glucose (Fig. 1). In addition to several wild type species of pounds where the Zn can be desorbed from the carbon surface
poplar, conversion of genetically modified poplar that contain and is free to pass in and out of the microporous cage.26
high S type lignin is described.27 This type of bioengineering
The described preparation/pretreatment of biomass is
offers a method to control the potential products from reac- minimal and all the steps are scalable, an important prerequi-
tions involving biomass. Furthermore, methoxypropylphenols site of any process for large-scale application in a biorefinery.
similar to those produced during this catalytic reduction of The two products reflect guaiacyl (G) and syringyl (S) lignin
lignin can be converted quantitatively in a second step using a components present in WT poplar and illustrate the applica-
bifunctional Pt–Mo catalyst to hydrocarbon fuel or propyl- bility of our catalysis to variants within the genus Populus. Fol-
benzene. The latter serves as a platform for production of aro- lowing our single-step catalytic conversion, the starting
matic chemicals.
biomass is fractionated into two forms, the first is a solid
Green Chem.
This journal is © The Royal Society of Chemistry 2014

View Article Online
Green Chemistry
Paper
Table 1 Conversion of lignin starting with intact lignocellulosic biomass over Zn/Pd/C catalyst
Selectivity
Biomass type
%G lignina
%S lignina
% Lignin contentb
Yieldc (wt%)
Poplar WT-717
44
20
40
49
44
34
100
51
73
55
47
49
65
0
19
20
18
19
16
24
31
31
17
28
45
31
30
100
69
83
72
55
69
70
NA
40
36
44
54
52
49
19
Poplar 717-F5H
Poplar WT-NM-6
Poplar WT-LORRE
WT-white birch
WT-eucalyptus
WT-lodgepole pine
a Lignin composition as determined by DFRC (derivatization followed by reductive cleavage) analysis. b Lignin content as determined by ABSL
(acetyl bromide-soluble lignin) lignin analysis. c Yield is calculated using the initial mass of lignin and the mass of the products, factoring in the
loss of two atoms of oxygen for each mole of product produced.
ducts with small amounts of unidentified impurities (Fig. S2
and S3†). The non-ether soluble fraction was also analyzed via
NMR and gave spectra with features consistent with sugars
and aromatic lignin fragments suggesting that a portion of our
unaccounted for lignin is present in the methanol solution
(Fig. S4†). This fraction was then subjected to analysis for
carbohydrates and found to contain a majority of xylans with
smaller amounts of glucans and arabinans (Table S5†).
In comparison to the Pd–Zn catalytic process described
above for intact wood biomass, organosolv lignin contains
hundreds of compounds,15 rendering its conversion to a
reasonable number of products extremely difficult (Fig. S1c†).
Carbohydrate residue retains its value
Fig. 2 Single ion monitoring ESI(−)/HPLC/MS of lignin products (m/z
165 and m/z 195) from (a) WT-717 poplar and (b) 717-F5H, a high-S
transgenic line. CAD MS/MS of (c) deprotonated 2,6-dimethoxy-4-
propyl phenol and (d) deprotonated dihydroeugenol derived from
WT-717 poplar.
To determine the composition of the leftover carbohydrate
residue it was digested by acid hydrolysis, which produced
mainly glucose (Table S6†). This leftover carbohydrate residue
was subjected to cellulase enzyme digestion, giving 95% of the
theoretical glucose yield.28 In comparison, intact poplar wood
released only 11% of theoretical glucose from cellulase
enzyme digestion over the same time period. These results are
consistent with those reported in the literature showing that
cellulose can be hydrolyzed by enzymes once lignin is
removed, as lignin deactivates cellulase enzymes.29 The
sugars from hydrolysis as well as the sugars present in the
MeOH phase were analyzed allowing mass balance closure of
74% of the starting biomass weight in quantified products
(Fig. 3). Our results illustrate the positive impact of lignin con-
version by the Zn/Pd/C catalyst on enhancing sugar yields
from poplar. Furthermore, the released sugar can be upgraded
by known biological and chemical catalytic conversion pro-
cesses that have been developed independently for pure
carbohydrates.30,31
residue that is easily filtered and the second consists of pro-
ducts that are soluble in MeOH. The MeOH liquid-phase con-
tains the methoxypropylphenol products shown in Table 1 and
a small amount of soluble sugars that mostly originate from
hemicellulose (Tables S2 and S5†). An additional phenolic
product of methylparaben was detected and quantified from
the reaction with the poplar species (Table S1†). This product
is extracted in various quantities from all reactions using
poplar, even those without catalyst present, and its exact origin
is unknown as the amounts of H lignin found in the poplar
species is very low (Table S3†). There is no evidence that the
solvent, MeOH, is consumed during this reaction and its vola-
tility makes it easy to separate from both the phenolic pro-
ducts and sugar residue. Upon removal of methanol,
dihydroeugenol and 2,6-dimethoxypropylphenol can be
extracted from the remaining residue using diethylether. NMR
spectra of this extract confirm it consists of mainly two pro-
The availability of the leftover carbohydrate residue for
direct conversion was demonstrated by subjecting the sample
to analytical fast pyrolysis in a pyroprobe/mass spectrometer
developed previously for the determination of primary pyro-
This journal is © The Royal Society of Chemistry 2014
Green Chem.

View Article Online
Paper
Green Chemistry
Fig. 3 Mass balance after catalytic cleavage and HDO of WT poplar lignin over Zn/Pd/C catalyst. *Mass of phenolic products includes all quantified
phenolics and also accounts for the loss of O into H2O during HDO. Liquid phase sugars were quantified by HPLC analysis. The solid phase residue
was hydrolyzed with acid. Then glucose, arabinose, and xylose were quantified by HPLC analysis.
Fig. 4 Positive mode ammonium attachment atmospheric pressure chemical ionization mass spectra measured for fast pyrolysis32 products of
(a) WT-LORRE poplar, (b) carbohydrate residue from WT poplar after our one-step catalytic conversion of lignin over Zn/Pd/C, and (c) pure crystal-
line cellulose.
lysis products.32 The results obtained for pure cellulose and
the leftover carbohydrate residue derived from woody biomass
Genetic variants control products
are compared in Fig. 4, together with fast-pyrolysis products of Lignin is made by radical polymerization of p-hydroxyphenyl
raw woody biomass. The solid residue behaved similarly to (H), G, and S monomeric units to give various linkage types
pure cellulose, yielding a similar product distribution, the (Fig. 1). The most ubiquitous is the β-O-4 linkage. H, G, and S
main product of which was cellobiosan. This result is in sharp subunit abundance in lignin varies depending on the plant
contrast to the highly complex mixture obtained upon fast species, and the availability of different monomers can be
pyrolysis of the lignified raw biomass (Fig. 4A).
manipulated genetically.33,34 To evaluate whether such engin-
Green Chem.
This journal is © The Royal Society of Chemistry 2014

View Article Online
Green Chemistry
Paper
eered lignins can be successfully converted using our process, propylbenzene were obtained in >97% and ∼0.7% yield,
we employed a genetically engineered line (717-F5H) with respectively (Table S8a†). This is the highest reported yield of
high-S lignin (Table 1, entry 2).27,35 Unmodified WT-717 hydrocarbons from the continuous, vapor-phase reaction of
poplar gives a ∼1 : 2 ratio of dihydroeugenol to 2,6-dimethoxy- lignin-derived methoxypropylphenols to date. The propylcyclo-
4-propylphenol. In comparison the high-S line gives a greater hexane can be aromatized via a dehydrogenation reaction to
yield of 2,6-dimethoxy-4-propylphenol with a final product dis- give additional propylbenzene and return 3 equivalents of the
tribution of 1 : 6 (Fig. 2B). The results from this experiment H2 used in the hydrogenation of methoxypropylphenols over
demonstrate how tailoring biomass through genetic control the Pt–Mo catalyst.36,37 Current work is aimed at the direct pro-
can affect the product distribution.
duction of propylbenzene from methoxypropylphenols.
Wood from other tree species, such as pine, white birch,
The effective lignin processing demonstrated here opens a
and eucalyptus, can also be broken down by our catalyst new direction for biorefinery configurations and synergies.
(Table 1, entries 5–7). Pine contains exclusively G lignin and The catalytic depolymerization of lignin into methoxypropyl-
has very high lignin content (30% by weight). Pine gave exclu- phenols employs the lignin portion of biomass first, while sim-
sively dihydroeugenol as the phenolic product but with lower ultaneously leaving behind an essentially intact solid-
yield compared to poplar and birch, presumably due to the carbohydrate fraction that can be further processed via tra-
high degree of cross-linking in G lignins. Although the lignin ditional biorefinery methods. Utilization of all components of
content of white birch is only 16% by weight, it gave an lignocellulosic biomass feedstock (lignin, cellulose, and hemi-
impressive yield (52%) (Table 1, entry 6); whereas, the combi- cellulose) is critical for maximizing fuel and chemical yield per
nation of high lignin content (24% by weight) and high yield acre. The selective production of two methoxypropylphenols
49% from eucalyptus produced the greatest overall yield of pro- and their further conversion to the hydrocarbon propylcyclo-
ducts from a mass standpoint (∼12% of the total biomass con- hexane/propylbenzene platform reported here enables many
verted to the two phenolic products).
options for the conversion of the natural aromatic structure of
lignin into currently used aromatic chemicals that were pre-
viously not viable. In addition, we envision a biorefinery that
encompasses multiple synergies (as opposed to conventional
biorefineries involving only one processing method) designed
to minimize chemical bond breaking by making products that
exploit the natural structure of biomass.
The lignin-derived methoxypropylphenols can be used in
the fragrance industry (i.e. dihydroeugenol), as well as be cata-
lytically upgraded to a variety of fuels (e.g. propylbenzene,
toluene, etc.) and chemicals (e.g. propane, methanol, benzene,
cumene, para-xylene, ethylbenzene, styrene, phenol, and
Lignin-derived fuel and chemical
platform
While the methoxypropylphenol products have value as chemi-
cals, we have also developed novel catalysis for their conver-
sion to the high-octane liquid fuel propylbenzene (Fig. 1).
When dihydroeugenol; 2,6-dimethoxy-4-propylphenol; or a
mixture of the two was reacted with H2 over a Pt–Mo bimetallic
catalyst at 300 °C and 342 psig H2, propylcyclohexane and
Fig. 5 Pathways for the production of renewable fuels (in blue) and chemicals (in green) from the lignin portion of biomass. Methoxypropylphenols
can be used as is for the fragrance industry (dihydroeugenol), or can be catalytically tailored to fuels (such as propylbenzene and toluene) or used
for the production of chemicals (such as propane, methanol, benzene, cumene, para-xylene, ethylbenzene, styrene, phenol, and acetone).
This journal is © The Royal Society of Chemistry 2014
Green Chem.

View Article Online
Paper
Green Chemistry
acetone) as shown in Fig. 5. We have demonstrated high-yield Pd/C and Zn system that cleaves and deoxygenates the β-O-4
production of the hydrocarbon propylcyclohexane from lignin. linkages in native lignin. These lignin-derived methoxypropyl-
Propylcyclohexane can be converted via dehydrogenation to phenols can be further converted to a variety of valuable aro-
propylbenzene, which can be hydrocracked subsequently to matic fuels and chemicals. This new approach to utilization of
benzene and propane.38 Benzene can be used as a chemical lignin enables the future biorefinery to obtain higher yields of
building block for production of fuels and chemicals via a fuels and chemicals. The newfound ability to utilize lignin-
variety of known and practiced conversions, such as: alkylation first for fuels and chemicals presents a new paradigm for
of benzene with co-produced propane (propylene after biofuel production in which lignin is potentially more valuable
dehydrogenation) to form cumene, alkylation with co-pro- than cellulose and provides opportunity for plant biologists to
duced MeOH to form toluene or xylenes, or alkylation with tailor biomass that contains more lignin. Mapping of products
ethanol or ethylene to form ethylbenzene and styrene.39,40 The based on the natural structure of lignin identifies new chemi-
propane produced can be dehydrogenated and employed for cal transformations and catalysis that will stimulate target
polymer production or converted further to acetone; which driven fundamental research.
when reacted with phenol forms the polycarbonate monomer,
bisphenol-A.41
The solid carbohydrate fraction can be further processed to
fuels and chemicals by currently employed chemistries such as
liquid-phase (catalytic) processing and biological conversion such
Material and methods
Chemicals
Pd/C (5 wt%) was purchased from Strem Chemicals (Newbury-
as fermentation, or thermochemical processes such as fast hydro-
pyrolysis or gasification followed by further catalytic upgrading.42
port, MA). 4-Allyl-2,6-dimethoxyphenol (98% purity) was pur-
chased from Alfa Aesar (Ward Hill, MA). Isoeugenol, eugenol,
Additionally, the waste from some steps, such as carbonaceous
2-methoxy-4-propylphenol (all >98% purity) and ammonium
residue or char, can be utilized by feeding to a thermo-chemical
unit (fast-pyrolysis or gasification) for conversion into a variety of
(St. Louis, MO). 2-Methoxy-4-methylphenol (98% purity) and
intermediate products that can be upgraded.
New synergies emerge from integration of lignin and carbo-
(Portland, OR). High-performance liquid chromatography-
hydrate chemistries. For example, in Fig. 5, we show alkylation
of benzene with methanol to form para-xylene (an important
chemical) or alkylbenzene molecules as fuels. The methanol
chemicals were used without further purification. A Zorbax
can be sourced from cleavage of the methoxy groups of meth-
formate (>99% purity) were purchased from Sigma-Aldrich
methylparaben (>99% purity) were obtained from TCI America
mass spectrometry (HPLC-MS) grade water and acetonitrile
were purchased from Fisher Scientific (Pittsburgh, PA). All
SB-C18 column (4.6 × 250 mm, 5 μm particle size) was pur-
chased from Agilent Technologies (Santa Clara, CA). 2,6-
Dimethoxy-4-propylphenol was synthesized as outlined below.
oxypropylphenols or produced from the breakdown of the
carbohydrate fraction. Additionally, methanol derived from the
biomass itself can be used as the solvent for the lignin depoly-
merization step with the aforementioned Zn/Pd/C catalyst.
Styrene can be produced through an integrated pathway invol-
ving alkylation of benzene using ethylene or renewable
ethanol produced from sugar fermentation.
In addition to the pathways discussed above, the develop-
ment of new and more-direct pathways are immediately recog-
nizable, utilizing the natural aromatic lignin structure
(aromatic ring, alkyl and oxygen substituents) and minimizing
the number of conversion steps to generate renewable com-
modities. For example, cumene could be synthesized directly
from propylbenzene via isomerization of the propyl substitu-
ent, and hydrocracking of propylphenol could afford a direct
route to phenol and propane. Some of these transformations
present the need to develop new chemistries starting from a
variety of different intermediate chemicals that go beyond
“traditional” chemistry used in the petrochemical industry.
Feedstock
Poplar genotype NM-6 (Populus nigra × P. maximowiczii,
WT-LORRE) was provided by Adam Wiese of the USDA North-
ern Research Station in Rhinelander, Wisconsin.43 Hybrid
aspen INRA 717-1B4 (P. tremula × P. alba, WT-717), Poplar
(P. nigra × P. maximowiczii) WT-NM-6, the genetically engin-
eered line 717-F5H and WT-White Birch (Betula papyrifera)
were provided by Purdue University’s Department of Forestry
and Natural Resources Department. The WT lodgepole pine
(Pinus contorta) was provided by Mr Jerry Warner (COL, U.S.
Army Ret.), Managing Director of Defense LifeSciences, LLC
(Alexandria, VA). The WT-Eucalyptus (Eucalyptus grandis ×
E. urophylla) was provided by William H. Rottman, ArborGen,
Inc (Ridgeville, SC).
Preparation of 2,6-dimethoxy-4-propylphenol
2,6-Dimethoxy-4-propylphenol was synthesized through the
hydrogenation of the side chain of 4-allyl-2,6-dimethoxyphe-
nol. 4-Allyl-2,6-dimethoxyphenol was dissolved in a suspension
Conclusion
Catalytic conversion of lignin to discrete phenolic molecules of Pd/C (5 wt%, 105 mg) in 15 mL MeOH (1.945 g, 10.1 mmol).
was achieved with good yields utilizing a process that produces The reaction mixture was placed in a stainless steel Parr
a clean carbohydrate residue. This was accomplished under reactor, pressurized with 500 psig H2 and heated at 60 °C
reasonable conditions (225 °C, 500 psi H2) using a synergistic for 3 hours. Pd/C was removed by filtration and methanol was
Green Chem.
This journal is © The Royal Society of Chemistry 2014

View Article Online
Green Chemistry
Paper
removed in vacuo to yield 2,6-dimethoxy-4-propylphenol as a Commitment and Reportable Outside Activities (http://www.
colorless oil. The reaction product was further purified on a purdue.edu/policies/ethics/iiib1.html).
silica-gel column with a mobile phase of 17% ethyl acetate
and 83% hexanes. [1H]NMR (CDCl3) δ 0.93 (t, 3H, CH3), 1.61
(s, 2H, CH2), 2.50 (t, 2H, CH2), 3.85 (s, 6H, OCH3), 5.42 (s, 1H,
OH), 6.39 (s, 2H, ArH).
Acknowledgements
This work was supported as part of the Center for Direct Cata-
lytic Conversion of Biomass to Biofuels (C3Bio), an Energy
Biomass preparation
Biomass was first milled to pass through a 40 mesh screen
using a Mini Wiley Mill (Thomas Scientific, Swedesboro, NJ).
Biomass was washed consecutively with water and ethanol
soxhlet using the LAP Determination of Extractives in Biomass
procedure.44 Following soxhlet extraction, the biomass was
dried and evaluated using a moisture analyzer (Halogen model
HB43-S, Mettler-Toledo LLC, Columbus, OH).
Frontier Research Center (EFRC) funded by the U.S. Depart-
ment of Energy, Office of Science, Office of Basic Energy
Sciences under Award no. DE-SC0000997. The work by JD and
the purchase of the Pyroprobe were supported by the National
Science Foundation Emerging Frontiers in Research and Inno-
vation (EFRI) under Award no. 0938033. SY was supported by
the National Science Foundation Graduate Research Fellow-
ship Program (#DGE-1333468).
General in situ generated catalyst reactions
In a typical experiment, 1.0 g of biomass, 0.10 g Pd/C (5 wt%),
ZnCl2 (5–10 wt%), methanol (30 mL), and glass stir bar were
added to a stainless steel Parr reactor, which was subsequently
sealed. While stirring the mixture was purged with UHP grade
H2 for ∼1 min, then pressurized with H2 (500 psig, 34 bar).
The mixture was heated to 225 °C. This temperature was main-
tained for ca. 12 hours. The reaction was terminated by remov-
ing the heat and cooling the reactor to room temperature
(WARNING! use caution when handling and venting the
reactor; Pd/C is pyrophoric). The reaction mixture was filtered
to remove Pd/C and remaining solid biomass residue. This
Pd/C/biomass mixture was washed with additional MeOH and
the filtrate was collected and diluted in a volumetric flask. This
solution was analyzed by GC-FID and HPLC/MS as described
below to determine amounts of methoxypropylphenols.
Notes and references
1 R. F. Service, Science, 2013, 339, 1374–1379.
2 D. J. Hayes, Catal. Today, 2009, 145, 138–151.
3 M. Wellisch, G. Jungmeier, A. Karbowski, M. K. Patel and
M. Rogulska, Biofuels, Bioprod. Biorefin., 2010, 4, 275–286.
4 M. G. Mandl, Biofuels, Bioprod. Biorefin., 2010, 4, 268–274.
5 M. McCoy, M. Reisch, A. Tullo, J. Tremblay, P. Short,
J. Tremblay and W. Storck, Chem. Eng. News, 2005, 83,
67–76.
6 M. Bomgardner, M. McCoy, M. Reisch, A. Tullo, A. Scott
and J. Tremblay, Chem. Eng. News, 2013, 91, 41.
7 Statistical Review of World Energy, BP, 2013.
8 G. W. Huber, J. W. Shabaker and J. A. Dumesic, Science,
2003, 300, 2075–2077.
9 S. K. Hanson, R. T. Baker, J. C. Gordon, B. L. Scott,
A. D. Sutton and D. L. Thorn, J. Am. Chem. Soc., 2009, 131,
428–429.
Author contributions
TP, SY, and JD performed experiments, analyzed data and
wrote the paper. TJ, MH, and HIK designed and performed MS
analyses. EG performed calculations for the synergistic bio-
refinery concept. IK, BH, and BS performed experiments and
analyzed data. JIK performed ABSL and DFRC analyses. HC
provided technical assistance on experiments with the PtMo
catalysis. RM, CC, and NM supervised and provided technical
knowledge on biomass handling and analyses. FR, WND, RA,
and MMAO designed experiments, analyzed data, and wrote
the paper. All authors provided comments on the paper.
10 A. J. Crisci, M. H. Tucker, M. Y. Lee, S. G. Jang,
J. A. Dumesic and S. L. Scott, ACS Catal., 2011, 1, 719–728.
11 J. Zakzeski, P. C. A. Bruijnincx, A. L. Jongerius and
B. M. Weckhuysen, Chem. Rev., 2010, 110, 3552–3599.
12 J. E. Holladay, J. F. White, J. J. Bozell and D. Johnson, Top
Value-Added Chemicals from Biomass-Volume II—Results of
Screening for Potential Candidates from Biorefinery Lignin,
Pacific Northwest National Laboratory (PNNL), Richland,
WA (US), 2007.
13 F. Cherubini and A. H. Strømman, Biofuels, Bioprod. Bio-
refin., 2011, 5, 548–561.
14 T. M. Jarrell, C. L. Marcum, H. Sheng, B. C. Owen,
C. J. O’Lenick, H. Maraun, J. J. Bozell and H. I. Kenttämaa,
Green Chem., 2014, 16, 2713–2727.
Conflict of interest
MMAO has equity interests with Spero Energy, Inc., a start up 15 H.-R. Bjørsvik and F. Minisci, Org. Process Res. Dev., 1999,
company focused on making specialty chemicals from renew- 3, 330–340.
able sources. NM acts as a consultant for Spero Energy. Activi- 16 A. G. Sergeev and J. F. Hartwig, Science, 2011, 332, 439–443.
ties with Spero Energy have been disclosed to Purdue 17 Z. Strassberger, A. H. Alberts, M. J. Louwerse, S. Tanase
University in accordance with Purdue Policy on Conflicts of
and G. Rothenberg, Green Chem., 2013, 15, 768–774.
This journal is © The Royal Society of Chemistry 2014
Green Chem.

View Article Online
Paper
Green Chemistry
18 A. L. Jongerius, R. Jastrzebski, P. C. A. Bruijnincx and 32 M. R. Hurt, J. C. Degenstein, P. Gawecki, D. J. Borton II,
B. M. Weckhuysen, J. Catal., 2012, 285, 315–323.
19 W. Xu, S. J. Miller, P. K. Agrawal and C. W. Jones, Chem-
SusChem, 2012, 5, 667–675.
N. R. Vinueza, L. Yang, R. Agrawal, W. N. Delgass,
F. H. Ribeiro and H. I. Kenttämaa, Anal. Chem., 2013, 85,
10927–10934.
20 R. N. Olcese, G. Lardier, M. Bettahar, J. Ghanbaja, 33 N. D. Bonawitz and C. Chapple, Annu. Rev. Genet., 2010, 44,
S. Fontana, V. Carré, F. Aubriet, D. Petitjean and A. Dufour,
ChemSusChem, 2013, 6, 1490–1499.
21 A. C. Atesin, N. A. Ray, P. C. Stair and T. J. Marks, J. Am.
Chem. Soc., 2012, 134, 14682–14685.
337–363.
34 R. Vanholme, K. Morreel, C. Darrah, P. Oyarce,
J. H. Grabber, J. Ralph and W. Boerjan, New Phytol., 2012,
196, 978–1000.
22 Q. Song, F. Wang and J. Xu, Chem. Commun., 2012, 48, 35 R. Franke, C. M. McMichael, K. Meyer, A. M. Shirley,
7019–7021. J. C. Cusumano and C. Chapple, Plant J., 2000, 22, 223–234.
23 T. D. Matson, K. Barta, A. V. Iretskii and P. C. Ford, J. Am. 36 S. Hama, X. Li, K. Yukawa and Y. Saito, Chem. Lett., 1992,
Chem. Soc., 2011, 133, 14090–14097. 21, 2463–2466.
24 Q. Song, F. Wang, J. Cai, Y. Wang, J. Zhang, W. Yu and 37 R. T. Baker, A. P. Sattelberger and H. Li, US 8524963 B2,
J. Xu, Energy Environ. Sci., 2013, 6, 994–1007. 2013.
25 C. Li, M. Zheng, A. Wang and T. Zhang, Energy Environ. 38 C. L. Russell, M. T. Klein, R. J. Quann and J. Trewella,
Sci., 2012, 5, 6383–6390. Energy Fuels, 1994, 8, 1394–1400.
26 T. H. Parsell, B. C. Owen, I. Klein, T. M. Jarrell, 39 S.-S. Chen and Updated by Staff, Styrene in Kirk-Othmer
C. L. Marcum, L. J. Haupert, L. M. Amundson,
H. I. Kenttämaa, F. Ribeiro, J. T. Miller and M. M. Abu-
Omar, Chem. Sci., 2013, 4, 806–813.
Encyclopedia of Chemical Technology, John Wiley & Sons,
Inc., 2000.
40 K. H. Chandawar, S. B. Kulkarni and P. Ratnasamy, Appl.
Catal., 1982, 4, 287–295.
41 J. Wallace and Updated by Staff, Phenol in Kirk-Othmer En-
cyclopedia of Chemical Technology, John Wiley & Sons, Inc.,
2000.
27 S. D. Mansfield, K.-Y. Kang and C. Chapple, New Phytol.,
2012, 194, 91–101.
28 M. Selig, N. Weiss and Y. Ji, Enzymatic Saccharification of
Lignocellulosic Biomass: Laboratory Analytical Procedure,
National Renewable Energy Laboratory, 2008, issue date, 42 D. Mohan, C. U. Pittman and P. H. Steele, Energy Fuels,
3/21/2008. 2006, 20, 848–889.
29 Y. Kim, E. Ximenes, N. S. Mosier and M. R. Ladisch, 43 C. E. Wyman, B. E. Dale, R. T. Elander, M. Holtzapple,
Enzyme Microb. Technol., 2011, 48, 408–415.
M. R. Ladisch, Y. Y. Lee, C. Mitchinson and J. N. Saddler,
30 E. I. Gürbüz and J. A. Dumesic, in Catalysis for the Conver-
Biotechnol. Prog., 2009, 25, 333–339.
sion of Biomass and Its Derivatives, ed. M. Behrens and 44 A. Sluiter, R. Ruiz, C. Scarlata, J. Sluiter and D. Templeton,
A. K. Datye, Open Access, 2013, pp. 293–359.
31 G. W. Huber, J. N. Chheda, C. J. Barrett and J. A. Dumesic,
Science, 2005, 308, 1446–1450.
Determination of extractives in biomass, National
Renewable Energy Laboratory, 2005, vol. 1617, issue date,
7/17/2005.
Green Chem.
This journal is © The Royal Society of Chemistry 2014