Catalytic Hydrogenation of Macroalgae-Derived Alginic Acid into Sugar Alcohols

Article abstract of DOI:10.1002/cssc.201701860

Alginic acid, a major constituent of macroalgae, iss hydrogenated into sugar alcohols over carbon-supported noble metals for the first time. Mannitol and sorbitol are the major products of the catalytic hydrogenation of alginic acid, which consists of two epimeric uronic acids. The main reaction pathway is the consecutive hydrogenations of the aldehyde and carboxyl ends of alginic acid dimers, followed by the cleavage of the C?O?C linkage into monomeric units by hydrolysis. The highest yield of C₆ sugar alcohols is 61 % (sorbitol: 29 %; mannitol: 28 %; galactitol: 4 %). The low sorbitol/mannitol ratio is in contrast to that from cellulose hydrogenation, owing to the composition of alginic acid and isomerization between sugar alcohols under the catalytic system. This new green route to producing sugar alcohols from alginic acid might provide opportunities to diversify biomass resources.

Full text of DOI:10.1002/cssc.201701860

Accepted Article
Title: Catalytic Hydrogenation of Macroalgae-derived Alginic Acid into
Sugar Alcohols
Authors: Chunghyeon Ban, Wonjin Jeon, Hee Chul Woo, and Do Heui
Kim
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ChemSusChem
10.1002/cssc.201701860
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Catalytic Hydrogenation of Macroalgae-derived Alginic Acid into
Sugar Alcohols
[
a]
[b]
[c]
[a]
Chunghyeon Ban, Wonjin Jeon, Hee Chul Woo, and Do Heui Kim*
Abstract: Alginic acid, a major constituent of macroalgae, was
hydrogenated into sugar alcohols over carbon-supported noble
metals for the first time. Mannitol and sorbitol were mainly produced
via the catalytic hydrogenation of alginic acid, which consists of two
epimeric uronic acids. The main reaction pathway is the consecutive
hydrogenation of aldehyde- and carboxyl-end of alginic acid dimers
followed by the cleavage of C-O-C linkage into monomeric units via
hydrolysis. The highest yield of C
6
sugar alcohols is 61% (sorbitol:
29%, mannitol: 28%, and galactitol: 4%). The low value of sorbitol to
mannitol ratio differs to the case of cellulose hydrogenation due to the
composition of alginic acid and isomerization between sugar alcohols
under the catalytic system. Such a new and green route to produce
sugar alcohols from alginic acid would provide opportunities to
diversify biomass resources.
Introduction
The sustainable production of fuels and chemicals from
renewable resources has attracted worldwide attention to resolve
critical energy and environmental issues such as limited fossil fuel
reservoir and fossil fuel-related pollution. Among various
renewables, biomass is the only renewable source of carbon that
can be directly converted to fuels and valuable chemicals.[
Lignocellulosic biomass among the renewables has been
frequently utilized for the production of green fuels and chemicals.
Especially, catalytic conversion of cellulose has been extensively
studied over the last century.[2] Cellulose could be hydrolyzed to
1]
produce glucose selectively over various acid catalysts such as
sulfonated activated carbons[3] and metals supported on
Scheme 1. Schematic reaction paths of sugar alcohol production via
hydrogenation of cellulose and alginic acid.
mesoporous carbon.[ Cellulose could also be converted into
4]
value-added platform chemicals such as 5-hydroxymethyl
catalysts with tunable selectivities between sugar alcohols. For
instance, sugar alcohols can be produced via hydrogenation of
furfural,[ lactic acid, and levulinic acid via catalytic thermal
reaction. In addition, glucose could be further hydrogenated to
produce sugar alcohols or the polyols can directly be produced
via the catalytic hydrogenation of cellulose over various metal
5]
[6]
[7]
[
8]
[9]
cellulose over supported noble metal catalysts such as Pt, Ru,
and Ir, and over non-noble metal catalysts such as Ni[11] and
Cu.[ Among sugar alcohols, sorbitol and mannitol are valuable
sugar alcohols which are used not only as a valuable sweetener
but also as a building block chemical to produce hydrogen for fuel
cell, vitamin C, and resin monomers such as ethylene glycol,
[10]
12]
[
a]
C. Ban, Prof. Dr. D. H. Kim
School of Chemical and Biological Engineering
Institute of Chemical Processes
Seoul National University
[13]
propylene glycol, and isosorb-(or mann-)ide. The commercial
production of sorbitol and mannitol occurs by hydrogenation of
glucose and glucose/fructose mixture, respectively, over Raney
nickel as a catalyst.[14]
1, Gwanak-ro, Gwanak-gu, Seoul (Korea)
E-mail: dohkim@snu.ac.kr
Dr. W. Jeon
Korea Institute of Energy Research
[
[
b]
c]
In recent years, algal biomass, known as a third-generation
152, Gajeong-ro, Yuseong-gu, Daejeon (Korea)
biomass, has been attracting considerable attention as
a
Prof. Dr. H. C. Woo
promising renewable resource since it has more advantageous
features than its terrestrial counterpart, cellulose, with respect to
rapid growth, inedibility, and lignin-free composition. Marine
biomass has been utilized in biorefinery
Department of Chemical Engineering
Pukyong National University
365, Sinseon-ro, Nam-gu, Pusan (Korea)
Supporting information for this article is given via a link at the end of
the document.
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ChemSusChem
10.1002/cssc.201701860
FULL PAPER
processes such as liquefaction, pyrolysis, and
Table 1. Total organic carbon in liquid product after hydrogenation at 150 °C for 12
gasification to produce value-added renewable chemicals,
h under 50 bar of H2
contributing to alleviate the heavy dependence on petroleum-
based chemicals.[15] Recently, attempts have been made to
Total organic carbon
remained in liquid product
Total organic carbon
remained in liquid product
(%)
[
a]
Catalyst
produce value-added chemicals from alginic acid, a major
constituent of macroalgae, via thermochemical methods.
Alginic acid, a renewable biopolymer, consists of two
different uronic acids, mannuronic acid(M) and guluronic
acid(G) linked by β-1,4-glycosidic bond, which is analogous
to the structure of cellulose composed of glucoses also linked
(
mg/L)
17.4
19.0
15.6
17.2
14.5
Ru(5)/C (Alfa)
Pd(5)/C (Alfa)
Pt(5)/C (Alfa)
Rh(5)/C (Alfa)
Ir(1)/C (Alfa)
99.4
108.6
89.1
98.3
82.9
by the ether bond. The ratio of M/G varies with the season,
location, and species.[
16]
Recent studies reported that
versatile platform chemicals such as uronic acids, lactic acid,
and furfural could be produced from alginic acid via catalytic
hydrothermal treatment.[17] However, to the best of our
knowledge, catalytic hydrogenation of alginic acid into sugar
alcohols over metal catalysts has never been reported.
Scheme 1 shows a comparison of the structure between
cellulose and alginic acid, and their conversion to sugar alcohols.
Unlike the case for cellulose, additional hydrogenation steps are
required for the production of sugar alcohols from alginic acid due
to the presence of carboxylic groups. In addition, mannitol is
produced along with sorbitol, since alginic acid consists of two
different monomers (see Scheme S1 for a detailed reaction
network).
In this present work, we introduce for the first time
macroalgae-derived alginic acid as a green alternative to
cellulose for the production of sugar alcohols via hydrogenation of
alginic acid over ruthenium supported on carbon. A screening of
noble metals, kinetic study, isomerization of hexitols, and
durability test of the catalyst were performed. A reaction network
for the hydrogenation of alginic acid is then proposed.
[
a] The values were calculated based on total organic carbon of 1% alginic acid
solution (17.5 mg/L)
The batch-wise hydrolytic hydrogenation was performed
over various carbon-supported metals to produce sugar alcohols
from alginic acid. As shown in Figure 1, the highest yield of C
sugar alcohol (61%) was obtained over Ru whereas carbon-
supported Pd, Pt, Rh, and Ir catalysts hardly produced any C
6
6
sugar alcohols although the complete conversion of alginic acid
over the noble metal supported on carbon was observed by GPC
analysis (Figure S1). This resulted in a significant loss in carbon
balance for the Pd, Pt, Rh, and Ir supported catalysts. However,
as summarized in Table 1, TOC analysis revealed that most of
organic carbons (>80%) were preserved in the liquid products,
indicating that carbon loss to gas phase could be regarded as
marginal. In other words, several byproducts are produced during
the catalytic hydrogenation of alginic acid. It is known that different
metals show different selectivities towards hydrogenation, C-C
cleavage and C-O cleavage. For example, a reaction of glycerol
over ruthenium resulted in the formation of a fully hydrogenated
product, propane,[ or a C-C cleaved product, ethylene glycol.
18]
[19]
Results and Discussion
However, the production of a C-O cleaved product, propylene
glycol, was favored over Pt.[
20]
This was evidenced by the
detection of dideoxy-aldonic acid and dideoxy-aldonic acid
lactones by GC-MS only for the cases of carbon-supported Pd, Pt,
Rh, and Ir (data not shown). This was further analyzed by LC-MS
and the result indicates a distinctive difference between carbon-
supported Ru and the other noble metals as shown in Figure S2.
Dideoxy-aldonic acid lactone (m/z=169.05) was observed for all
noble metal supported catalysts whereas C
6
sugar alcohols
(m/z=205.08) were the main product for Ru(5)/C(Alfa). Thus, the
cause of carbon loss could be attributed to the formation of
byproducts via the hydrodeoxygenation of aldonic acid or its
lactone over Pd, Pt, Rh, and Ir supported catalysts. Furthermore,
unidentified compounds having low m/z were also produced over
Pd, Pt, Rh, and Ir supported catalysts. Unfortunately, the
quantification of these byproducts was not possible due to the
absence of standard samples.
The activity of the commercial catalyst, Ru(5)/C(Alfa) was
also compared to that of activated carbon-supported Ru catalysts
synthesized in-house. In the preparation of the Ru catalysts,
activated carbon was oxidized with nitric acid of different
concentrations to vary its acid density. Textural
Figure 1. Product distribution over different carbon-supported noble metals
at 150 °C for 12 h under 50 bar of H .
2
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Table 2. Textural properties of catalysts.
Catalyst
S2urface area
m /g catalyst)
[a]
Total acid density[b]
(mmol/g catalyst)
(
Ru(5)/C (Alfa)
Pd(5)/C (Alfa)
Pt(5)/C (Alfa)
Rh(5)/C (Alfa)
Ir(5)/C (Alfa)
Ru(5)/AC
816.2
0.85
0.51
0.43
0.62
0.43
0.26
1.11
1.11
810.5
886.7
872.5
1017.5
941.8
2
Figure 2. Recycling of Ru(5)/C(Alfa) at 180 °C for 2 h under 50 bar of H .
Ru(5)/AC-N-7
Ru(5)/AC-N-13
894.0
Unfortunately, the quantification of the other byproducts could not
be realized due to the absence of authentic samples.
824.7
Regarding
a practical application of heterogeneous
[
[
a] Surface area was measured by Brunauer-Emmet-Teller method.
b] Total acid density was determined by back titration.
catalysts, durability of catalysts is of great importance. To check
the recyclability of the catalyst, Ru(5)/C(Alfa), in the reaction
system, several identical batch reactions were performed, and
liquid aliquots and spent catalysts were analyzed. As shown in
Figure 2, ruthenium was leached from the catalyst after repeated
properties of the synthesized catalysts (Ru/AC-N-x) are
listed in Table 2. As displayed in Figure 1, among Ru/AC-N-x
catalysts, a catalyst oxidized with higher concentration of HNO
3
6
reactions. The decrease of the yield of C sugar alcohols is in line
exhibited a higher yield of sugar alcohols. The result suggests that
oxygenate functional groups which were induced after nitric acid
treatment such as phenolic OH, =O, and –COOH have a
promotional effect on the hydrolysis of alginic acid. Especially,
amounts of weak acid site, carboxylic groups, was obviously
formed after the modification as evidenced by the evolution of
with the decrease in the amount of residual ruthenium over
repeated reactions. Furthermore, as listed in Table 3, the CO
chemisorption result shows that dispersions of Ru on carbon
decreased from 36% to 11% along with the increase in crystallite
size of the metal from 3.7 nm to 12.2 nm after 4th recycle run.
Thus, the deactivation of the catalyst could be ascribed to the
aggregation of ruthenium as well as to the leaching of the metal.
In addition, Durability of the catalyst in a concentrated alginic acid
solution was also examined since an industrial conversion of
biomass occurs mostly in bulk. As listed in Table S2, the leaching
of ruthenium was accelerated in concentrated solutions of alginic
acid. Ruthenium was leached gradually from 0.5 to 2.40% in
alginic acid solutions of concentration below 10%. However, a
sharp leaching of Ru was observed in the reactant concentration
of 30%. The reason for the intense leaching lies in the acidic
C=O stretching vibration band at 1718 cm- (Figure S3).
1
[21]
Similarly, the capability of carboxylic groups to effectively
hydrolyze biomass feedstock was reported both in cellulose and
alginate valorization.[17d, 22] However, the commercial Ru(5)/C
(Alfa) catalyst having lower acid density exhibited higher activity
towards the production of polyhydric alcohols. The result implies
that a metal site could act as an effective acid site to hydrolyze
alginic acid under pressurized H
site. Therefore, it can be deduced that protonic acid sites formed
by spilled-over H on ruthenium could hydrolyze alginic acid
2
atmosphere without any acid
2
nature of the reactant, alginic acid, which can behave as a ligand
to form a metal-alginic acid complex.[26] The above results left us
a future work of the development of a more robust and industrially
effectively as in the case of hydrolytic hydrogenation of cellulose
on Pt.[ In addition, the role of ruthenium as an acid site was
verified in hydrolysis of oligosaccharides into glucose.[ The
higher yields of sugar alcohols over the commercial catalyst
can also be explained by the highest dispersion and the
smallest size of Ru as listed in Table S1. As the effect of the
crystallite size of Ru has already been determined, smaller
Ru favored the formation of hydrogenated intermediate of
23]
4]
[a]
Table 3. Dispersion and crystallite size of ruthenium after the recycle reactions.
[b]
[b]
Dispersion
%)
Crystallite size
(nm)
Recycle Run
(
[
24]
cellobiose and exhibited higher TOF on hydrogenation of
glucose[ . Hence, both the crystallite size of Ru in addition
to the acidity of the catalyst should be taken into account for
the conversion of alginic acid into sugar alcohols. The loss
in carbon yield for ruthenium supported carbon catalysts
were ascribed mainly to byproducts such as n-deoxy
1st (Fresh catalyst)
36
29
19
11
3.7
4.6
25]
2
nd
rd
4th
3
6.9
12.2
hexitols and pentitols, and to few C
analyzed by GC-MS (data not shown). The short chain
sugar alcohols (C -C accounted for less than 2%.
2 4
-C sugar alcohols as
[a] the recycle reactions were performed at 180 °C for 2 h under 50 bar of H2.
[b] Dispersions and crystallite sizes were measured by CO chemisorption.
2
4
)
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Figure 3. LC-MS spectra of products obtained at 90 °C under 50 bar of H
2
for different reaction times over Ru(5)/C(Alfa).
feasible catalyst for a bulk conversion of alginic acid to produce
value-added chemicals.
To investigate plausible reaction pathways for the
hydrogenation of alginic acid, kinetic studies were performed over
Ru(5)/C(Alfa). Alginic acid was hydrolytically hydrogenated at
90 °C, and the resultant liquid products were then analyzed by
LC-MS, as shown in Figure 3. It was observed that alginic acid
was decomposed into chunks of oligomers ranging from dimer
(m/z=393) to undecamer (m/z=1977) with a difference of 176 in
m/z between neighboring peaks. At the early stage of the reaction,
however, no sign of a peak corresponding to monomeric units
(uronic acids, m/z=217) was observed. The above results suggest
that the glycosidic bonds of alginic acid are cleaved in a random
fashion; not in an ordered way releasing the outermost monomer
unit one by one. As the reaction time was prolonged, aldonic acids
(
m/z=219) and sugar alcohols (m/z=205) started to be evolved
along with the production of intermediates (m/z=377, 381, 393,
95) composed of two monomeric units. Unlike the case for the
3
hydrolytic hydrogenation of cellobiose having one reducing
aldehyde group where formation of only one intermediate,
glucopyranosyl-glucitol, was observed,[24] the additional
carboxylic group on monomeric unit causes the evolution of 5
different partially hydrogenated intermediates. From the result
above, it could confidently be suggested that the formation of C
6
sugar alcohols from alginic acid occurs through the consecutive
hydrogenation of both aldehyde- or carboxyl-ends in oligomeric
compounds, which is then followed by the cleavage of the
6
glycosidic bonds between alginic acid monomers to yield C sugar
alcohols. A reaction pathway for the formation of sugar alcohols
through these intermediates was proposed in Scheme S2.
Furthermore, relative amounts of each intermediates are shown
in Figure S4. Only a small amount of aldonic acid (m/z=219) was
produced, whereas the accumulation of intermediates (m/z=381
and 395) was observed. This implies that the hydrolysis of the
glycosidic bond would be a rate-determining step in the catalytic
conversion of alginic acid to sugar alcohols. Similarly, the
cleavage of the ether linkage between glucose in cellulose, viz.
Figure 4. Yields of products as a function of reaction temperature (a), yield
of products at 150 °C as a function of reaction time (b), and detailed sugar
alcohol distribution at 150 °C as a function of reaction time (c) over
2
Ru(5)/C(Alfa) under 50 bar of H .
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hydrolysis, is well-reported to be the rate-determining step in the
hydrolytic hydrogenation of cellulose.[
mainly produced from alginic acid. In fact, the production of
mannitol is a distinctive feature of the hydrogenation of alginic
acid since sorbitol is predominantly produced by the hydrolytic
hydrogenation of cellulose over various metal supported
catalysts.[28] The difference in the distribution of sugar alcohols is
most likely attributed to the composition of alginic acid since G
and M can be converted to sorbitol and mannitol, respectively. To
further investigate the origin of mannitol, alginic acid was
analyzed by 13C NMR analysis (Figure S6). The 13C NMR analysis
revealed that the alginic acid used in this work is M-rich,
representing a ratio of M/G of ca. 2.5. In this regard, mannitol
should have been produced more abundantly than sorbitol.
However, as shown in Figure 4(c) and Figure 5(a), sorbitol was
produced in larger quantities than mannitol for all the reaction
conditions. Such discrepancy can be ascribed to two reasons: an
isomerization of produced hexitols and different reaction rates of
intermediates, aldonic acid lactones.
10a]
Since the difficulty lies in separating unreacted alginic acid
from the catalyst and liquid products, conversion of alginic acid in
this work was determined qualitatively by GPC analysis. As
shown in Figure S5, the depolymerization of alginic acid over
Ru(5)/C(Alfa) is promoted as the reaction time and temperature
were increased. At reaction temperatures higher than 90 °C,
alginic acid was completely converted into smaller molecules
within 1 h of reaction. The facile conversion of the biopolymer in
the absence of any acid catalyst is due partly to the increase of
ion product of water at elevated temperatures[ and partly to the
Brønsted acid formed in-situ from Ru on carbon under
27]
pressurized H
2
.[23] The effect of reaction time and temperature on
the hydrolytic hydrogenation of alginic acid is quantitatively shown
in Figure 4(a). As already shown in GPC analysis (Figure S5), the
depolymerization of alginic acid proceeded tardily at low
temperature, 90 °C, resulting in low yields of uronic acids (4.4%)
The isomerization of sugar alcohols has been frequently
[
9a, 10a,
and C
h). The yield of C
elevating the reaction temperature from 90 °C to 150 °C and the
reaction time from 1 h to 12 h. The highest yield of C sugar
6
sugar alcohols (3.2%) even after a prolonged reaction (48
observed during the hydrogenation of cellulose or glucose.
28]
6
sugar alcohols increased sharply upon
Sugar alcohols equilibrate with each other in the presence of
and the isomerization of sugar alcohols is catalyzed by metal
H [
29]
2
6
sites, resulting in different sorbitol to mannitol ratios under various
catalytic systems.[ For example, the ratio was reported to be ca.
30]
alcohols, 61.0%, was obtained when alginic acid was
hydrolytically hydrogenated at 150 °C for 12 h over Ru(5)/C(Alfa)
[
23]
4 over Pt/γ-Al
O
2 3
during the hydrogenation of cellulose and to
[
30]
under 50 bar of H
10 °C reduced the yield of C
decomposition of C
sugar alcohols into lower alcohols.[9a] In the
2
. However, further increase in temperature to
be ca. 2 over Ru/C during the hydrogenolysis of sorbitol. When
alginic acid underwent hydrogenation in our catalytic system, the
ratio was found to be ca. 1.2 over Ru/C as shown in Figure 5(a).
To further investigate the equilibrium between sugar alcohols,
model reactions were conducted under the same reaction
condition using sorbitol, mannitol, glucose, mannose, and
lactones as a reactant. As shown in Figure 5(b), regardless of the
reactants used, the ratios converged to ca. 1.3. Such value is in
accordance with the ratio obtained from raw alginic acid.
2
6
sugar alcohol due to the
6
early stage of the reaction, it was observed that aldonic acid
lactones and sugars were evolved first as intermediates and
disappeared with the production of C sugar alcohols as shown in
6
Figure 4(b). On the other hand, small amounts of uronic acids
were observed, which again suggests that the consecutive
hydrogenation of uronic acids into C
the hydrolysis of alginic acid into uronic acids.
The yields of individual C and C sugar alcohols are shown
in Figure 4(c). It was observed that both sorbitol and mannitol are
6
sugar alcohols is faster than
However, at the early stage of hydrogenation of alginic acid,
the ratio reached ca. 1.8. This could be attributed to the different
initial hydrogenation rates of intermediates such as
5
6
Figure 5. Time-course of sorbitol to mannitol ratio over Ru(5)/C(Alfa) during the hydrogenation of (a) alginic acid and (b) model molecules at 150 °C for 12 h
under 50 bar of H
2
.
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mannonolactone and gluconolactone. As seen from the initial
slopes of aldonolactone hydrogenation in Figure S7,
gluconolactone was hydrogenated 5-fold faster than
mannonolactone from which sorbitol and mannitol were produced,
respectively. Thus, the ratio of sorbitol to mannitol could be higher
than the value from the equilibrium at the early stage of the
reaction.
400°C for 2 h under 10% H2 flow (50 ccm) before being used in the
reaction.
Catalyst characterization
The specific surface area of the catalysts was determined by
Brunauer-Emmett-Teller (BET) method on Micromeritics ASAP 2010. The
samples were degassed at 250 °C for at least 4 h before the analysis at -
1
96 °C. FT-IR spectra of the catalysts were measured on Agilent Cary 660
-
1
with resolution of 4 cm using KBr pellets which contains 5wt% of a
catalyst. CO chemisorption was performed on BEL-Cat (BEL JAPAN Inc.)
to determine crystallite sizes and dispersion of ruthenium. Typically, the
sample was pre-reduced at 350 °C for 2 h under 5% H2 flow (50 ccm).
After the sample was cooled to the measurement temperature, 50 °C,
under He flow (50 ccm), a CO pulse (4.98% CO/He, loop volume of 0.8570
cm3) was introduced until the saturated coverage was obtained. The acid
density of the catalysts was analyzed by back titration using 0.01 M of
NaOH solution and 0.02 M of HCl solution with a drop of phenolphthalein
solution.
Conclusions
The hydrolytic hydrogenation of alginic acid into sugar alcohols,
mainly sorbitol and mannitol, was investigated for the first time
over noble metal supported catalysts and a plausible reaction
pathway of such was proposed. Hexitols were mainly produced
over Ru supported on carbon catalysts whereas byproducts of
dideoxy-aldonic acids and their lactones were produced over Pd,
Pt, Rh, and Ir supported on carbon catalysts. The highest yield of
Catalytic reaction
C
6
sugar alcohols was obtained as 61% (sorbitol: 29%, mannitol:
A typical reaction procedure is as follows: hydrolytic hydrogenation
was performed in a stainless-steel autoclave with an inner volume of 100
mL charged with 0.3g of alginic acid, 30 mL of distilled water, and the
proper amount of catalyst. The mass ratio of the reactant to metal was 105.
Air in the reactor was removed by flushing the reactor with 50 bar of helium
28%, and galactitol: 4%) at 150 °C for 12 h under 50 bar of H
2
over ruthenium supported carbon. The consecutive
hydrogenation of dimeric units of alginic acid with two reducible
functional groups, carboxylic- and aldehyde-end, led to the
formation of 5 different partially hydrogenated intermediates
3
times and the reactor was then pressurized with 50 bar of hydrogen. The
reactor was heated to the desired temperature within 30 min in an electric
furnace. The reaction mixture was agitated by a mechanical impeller at
1000 rpm during the reaction. After the desired reaction time, the reactor
was quenched with ice-cold water within 10 min to prevent further reaction.
To evalutate the recyclability of the catalyst, a multi-batch procedure
was designed to compensate a weight loss, which frequently occurs during
the catalyst recovery. Briefly, four indentical batch reactions were
performed as described above. After each reaction, spent catalysts were
retrieved via filtration and washed with distilled water and acetone, and
dried in an oven at 100 °C. The spent catalysts were reused for the second
run in three identical reactors and recovered again after the reaction for
the next run. The same procedure was repeated for the third and fourth
run.
6
before cleaved into C sugar alcohols over carbon-supported Ru.
Mannitol was produced as much as sorbitol owing to the
composition of alginic acid which is composed of two epimeric
monomers and to the isomerization of hexitols. The leaching and
aggregation of the active metal, Ru, after the reaction caused the
deactivation of the catalyst. A green route proposed herein to
produce sugar alcohols from alginic acid instead of cellulose could
provide new opportunities to alleviate large dependence on
lignocellulosic biomass and to better utilize macroalgae as an
alternative renewable feedstock.
Liquid products were analyzed by LC-MS, GC-MS, GPC, TOC, and
ICP as described below.
Experimental Section
Analytical methods
Materials
Gel permeation chromatography (GPC) was conducted on Ultimate
Alginic acid and gluconic acid were purchased from Sigma-Aldrich.
Mannuronic acid and guluronic acid were obtained from Qingda BZ
Biotech. Sorbitol, mannitol, galactitol, arabitol, ribitol, xylitol, glycerol,
propylene glycol, gluconolactone, mannose, and glucose were purchased
from Alfa Aesar. Mannolactone was obtained from TCI Chemicals. The
above authentic samples were used as received. Activated carbon was
purchased from Sigma-Aldrich. The commercial catalysts, Pd(5)/C,
Pt(5)/C, Rh(5)/C, and Ir(1)/C, were purchased from Alfa Aesar and used
without further pretreatment.
3
000 (Dionex) equipped with a refractive index detector and a series of
three columns (Waters Ultrahydrogel 120, 150, and 1000) maintained at
0 °C. 0.1M of sodium azide solution as a mobile phase was eluted at a
4
flow rate of 1.0 mL/min. The instrument was calibrated with Pullulan having
a molecular weight distribution of 342-80,500. The amount of Ru leached
from the catalyst was measured by inductively coupled plasma-atomic
emission spectroscopy (ICP-AES, PerkinElmer/Optima-4300 DV). The
total organic carbon was measured using Sievers 5310 (GE) with an
autosampler. Liquid chromatography-mass spectrometry (LC-MS) was
performed on LCQ Deca XP Plus, Thermo Finnigan equipped with an
electrospray ionization module working in a positive mode. The liquid
sample was infused into the equipment with 0.1% formate buffer. The
values of m/z are 23 higher than the actual molecular weight of molecules
due to the formation of sodium adduct during the analysis. The qualification
of reaction products was conducted using gas chromatography-mass
spectrometry (GC-MS) equipped with a DB-5MS column (60 m × 0.25 mm
Catalyst preparation
Activated carbon was partially oxidized with nitric acid of different
concentrations to impart different amount of acid functionality. Typically,
activated carbon was mixed with nitric acid with a volume to mass ratio of
1
0. After 3 h at 110 °C, the resultant carbon was retrieved by filtration,
washed with distilled water until the filtrate became neutral, and then oven-
dried at 100 °C overnight. The resulting activated carbons were denoted
as AC-N-x, where x represents the molar concentration of nitric acid. 5
wt% of Ruthenium (Ru) was impregnated on the above activated carbons
by conventional wet impregnation method. Ru(5)/AC-N-x was reduced at
×
0.25 μm). Since the resolution of GC for the separation of various sugar
alcohols is superior to that of liquid chromatography, the quantification of
products was performed on GC equipped with a DB-5 column (60 m × 0.25
mm × 0.25 μm). The liquid aliquot was silylated before being injected to
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ChemSusChem
10.1002/cssc.201701860
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GC according to the method previously reported.[31] The carbon-based
yield was calculated as follows:
Carbon yield (%) = 100 × (number of carbon atoms in an organic
compounds/6) × (moles of an organic compounds in the product obtained
by GC/moles of a repeating unit in alginic acid)
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Acknowledgements
This work was supported by the Ministry of Oceans and
Fisheries, Republic of Korea (Contract No. 20140559) as well as
by the New & Renewable Energy Core Technology Program of
the Korea Institute of Energy Technology Evalutation and
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ChemSusChem
10.1002/cssc.201701860
FULL PAPER
Entry for the Table of Contents
Layout 2:
FULL PAPER
Chunghyeon Ban, Wonjin Jeon, Hee
Chul Woo, and Do Heui Kim*
Page No. – Page No.
Catalytic Hydrogenation of
Macroalgae-derived Alginic Acid into
Sugar Alcohols
Sugar alcohols, mainly sorbitol and mannitol, were produced via the hydrogenation
of macroalgae-derived alginic acid over noble metal supported on carbon.
Ruthenium exhibited the highest yield of sugar alcohols among other noble metals.
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