Conversion of glucose and sorbitol in the presence of Ru/C and Pt/C catalysts

Article abstract of DOI:10.1039/c4ra14073g

The conversion of glucose and sorbitol in the presence of Ru and Pt catalysts supported on carbon was carried out at different pressure and temperature conditions, using a batch and a semi-batch reactor. Attempts were made to improve the selectivity of glycols and alcohols (ethanol), introducing a promoter and inhibiter of the hydrogenolysis in the reactant mixture. On the basis of these results, which confirm the higher activity of Ru with respect to Pt, and the important role of an inhibitor like sulphur, the mechanism driving these reactions and the promising thermocatalytic conditions are clearer. This journal is

Full text of DOI:10.1039/c4ra14073g

RSC Advances
View Article Online
View Journal | View Issue
PAPER
Conversion of glucose and sorbitol in the presence
of Ru/C and Pt/C catalysts†
Cite this: RSC Adv., 2015, 5, 23086
Stefania Tronci* and Barbara Pittaub
a
The conversion of glucose and sorbitol in the presence of Ru and Pt catalysts supported on carbon was
carried out at different pressure and temperature conditions, using a batch and a semi-batch reactor.
Attempts were made to improve the selectivity of glycols and alcohols (ethanol), introducing a promoter
and inhibiter of the hydrogenolysis in the reactant mixture. On the basis of these results, which confirm
the higher activity of Ru with respect to Pt, and the important role of an inhibitor like sulphur, the
mechanism driving these reactions and the promising thermocatalytic conditions are clearer.
Received 7th November 2014
Accepted 24th February 2015
DOI: 10.1039/c4ra14073g
www.rsc.org/advances
Among them activated carbon exhibits excellent stability (it is
inert and stable at high temperature and pressure) and shows
1
. Introduction
7
The conversion of raw materials of vegetable origin into biofuels large dispersion of active components.
and bio-based chemicals is a promising alternative to exploi-
The products obtained from sugars and polyols hydro-
tation of fossil oil, leading to economic and environmental genolysis depend on process conditions (type of catalyst,
1
2
impacts. As recently highlighted by Ruppert et al., hydro- temperature, pressure, pH) and may include propylene glycols
genolysis of sugars derived by hydrolysis of lignocellulosic and glycerol, as well as ethylene glycol, ethanol, methanol and
materials can offer an encouraging opportunity for future also xylitol and erythritol (selectivities up to 60–90%). The
2
biomass-based renery. In this context, starting from ligno- literature documents that transformation mechanism can
cellulosic biomass as well as from C6-sugars, bioethanol and generate many different compounds with different selectivity.
other biofuels target products are increasing in importance
Also to clarify some aspects as sugar reaction pathway through
3
from a research point of view. For instance, in the recent years the corresponding alcohol or how similar reaction parameters
the interest concerning hydrogenolysis of sorbitol (also apparently give different process improving, we report our
obtained from glucose) to chemicals like propanediol, ethylene contribution to the sugars and sugar alcohols hydrogenolysis
4
glycol and glycerol has increased. Even if currently glycerol can process development via batch and semi-batch operating condi-
be obtained in terms of by-product from biodiesel production, tions. The study examined the role of process parameters such as
the catalytic hydrogenolysis of carbohydrate offers the chance to pressure, temperature, type and amount of catalyst, presence of
use “renewable and less costly resources” to obtain valuable an inhibitor, glucose and sorbitol concentration on product
2
chemicals.
selectivity and reactant conversion. In order to promote reactions
18
Many efforts were made to understand and improve the towards diols and alcohols, the reacting system behaviour was
transformation of sorbitol into di- and polyhydric alcohols, investigated at high temperature ranges, spanning from 453 to
mainly in presence of supported metal catalysts, as summarized 513 K, and at high hydrogen pressure, from 3 to 10 MPa. Two
in the comprehensive review by Ruppert et al. Within this heterogeneous commercial catalytic systems were used: Ru/C and
regard, ruthenium has attracted a great deal of attention,
2
5–16
Pt/C with metal catalyst loading equal to respectively 5% and 3%.
because of its high activity for hydrogenolysis reaction when Ruthenium is indeed considered as the most active catalysts for
compared to other noble metals like rhodium, platinum and hydrogenolysis reactions and for its promising properties has
1
9–21
palladium. The effects of the catalyst on product distribution been recently used by several authors.
have been also investigated for different support materials, ered because it shows less selectivity towards alkane with respect
Platinum was consid-
8,10,17
19,22
such as activated carbon, SiO
2
, TiO
2
, Al
2
O
3
, ZrO
2
, NaY.
to ruthenium,
therefore it seemed a good candidate to drive
the reaction towards the desired oxygenated products. Further-
more, the carbon has been selected as metal support because it is
inert and stable at the conditions used for the experimental
campaign. A thorough analysis of the results in terms of selectivity
was provided and attempts were made to individuate the condi-
a
Dipartimento di Ingegneria Meccanica, Chimica e dei Materiali – Universit a` degli
Studi di Cagliari, Via Marengo 2, I-09123 Cagliari, Italy. E-mail: troncis@unica.it
b
Consiglio Nazionale delle Ricerche, Istituto di Farmacologia Traslazionale uos
Cagliari, Edicio 5, Loc. Piscinamanna, 09010 Pula, CA, Italy
†
The authors would like to thanks Dr Carlo Maria Paciolla for giving them the tions promoting the required combination of C–C and C–O bond
opportunity to gather together and cooperate. This article is dedicated to his
cleavage leading to high selectivity for glycols and alcohols.
memory.
23086 | RSC Adv., 2015, 5, 23086–23093
This journal is © The Royal Society of Chemistry 2015

View Article Online
Paper
RSC Advances
Gas carrier: helium.
Oven: 50 C.
Pressure: 20 kPa.
2
. Experimental
ꢁ
2.1 Materials
ꢁ
Activated carbon (C) supported noble metal catalysts 5% Ru/C
Injection: 1 ml split 19 : 1, temperature 50 C.
ꢁ
ꢁ
(Engelhard) and 3% Pt/C (Chimet) were used for the experi-
Detector: TCD, temperature 200 C, lament 180 C.
ments. The reactants were glucose (Sigma-Aldrich, purity 98%)
and sorbitol (Sigma-Aldrich, purity 97%). Reactions in presence
of a base were conducted with sodium hydroxide (Carlo Erba,
purity 98%), whereas the catalysts poisoning were obtained
using sodium hydrosulde hydrate, Na S$9H O, (Sigma-
Liquid products were analysed using both gas chromato-
graphy (TermoQuest GC 8000) and high-performance liquid
chromatography (HPLC Perkin Elmer-200LC). The specic GC
parameters are the following:
2
2
Column: DB-WAX, 30 m ꢂ 0.32 mm i.d., thickness 0.5 mm.
Aldrich, purity 98%).
Gas carrier: helium.
Pressure: 80 kPa.
Temperature program: 35 C ꢂ 5 min; from 35 to 245 C
2
.2 Hydrogenolysis reaction
ꢁ
ꢁ
ꢁ
ꢀ1
ꢁ
Glucose and sorbitol hydrogenolysis was conducted in a 500 ml 10 C min , 245 C ꢂ 2 min.
ꢁ
autoclave stainless steel (AISI 316-Pressure and Products
Industries Inc.) using 300 or 400 ml of an aqueous solution of
Detector: FID, 310 C.
Injection volume: 0.9 ml.
Split: 20 : 1.
ꢀ1
100 g l of reactant. Then the catalyst powder was added. The
sealed autoclave was rst purged at least 3 times with helium
gas to get rid of the air present in the reaction vessel, then it was
purged with hydrogen to eliminate helium. The reactor pressure
was set at the desired value by feeding hydrogen, in such a way
that the set-point pressure was reached when the temperature
was at the desired value. The mixture was stirred at 1000 rpm.
Aer the reaction was nished, the autoclave was cooled with
cold water.
The specic HPLC parameters follow:
Column: carbohydrate Pb; 300 mm ꢂ 7.8 mm i.d.
Mobile phase: water.
ꢀ1
Flow: 0.4 ml min
.
ꢁ
Temperature: 74 C.
Detector: RI.
Injection volume: 20 ml.
The experimental results were analyzed in terms of reactant
conversion and selectivity, according to the following
denition:
The reactor was equipped with a dip tube, connected to a
micrometric valve for liquid sampling. The sample (10 ml) rst

owed in a tube made in a serpentine fashion, which was
ꢁ
immersed in a cold bath to decrease temperature to circa 25 C.
During the experimental runs, samples were collected from the
autoclave every hour, and the rst sample had been taken as
soon as the system reached the operating conditions in terms of
pressure and temperature. Considering the dead volume of the
sampling tube, the rst collected sample volume equal to 5 ml
was not considered for the analysis of the product mixture.
The experiments were carried out in batch and semibatch
reactor mode. In the rst case, the reactor pressure was kept
constant by adding hydrogen. Using the semi-continuous mode,
the gas phase owed continuously through the batch of reactant
solution. In this conguration, it was possible to keep constant
the hydrogen partial pressure and collect gaseous products
during the reaction by 5 litres sample-bag (Chrompack).
g of reactant after reaction
Conversionð%Þ ¼ 100 ꢀ
ꢂ100
g of reactant in the feedstock
g of product
ꢂ100
Selectivityð%Þ ¼
g of converted reactant
It is worth noticing that we did not identify all the obtained
products, but we could only identify C6–C1 sugars or polyols
including also diols and alcohols) classes. According to the
denition, the sum of selectivity could be less then 100.
(
3
. Results and discussion
3.1 Glucose and sorbitol conversion operating in batch
2.3 Product analysis
mode
Hydrogenolysis products contained the following compounds: The rst experimental campaign has been carried out with a
sugars (C5–C6), polyols (C3–C6), glycols (C6–C2), alcohols batch reactor, using an aqueous solution of glucose and Pt/C or
(
C6–C1), alkanes (C1–C3) and carbon dioxide. Quantitative and Ru/C catalyst, at different operating conditions. Results
qualitative analyses for the products of hydrogenolysis were obtained in presence of Pt/C catalysts are reported in Table 1,
performed by the means of chromatography. where the selectivity of the wide variety of products in the liquid
Gas chromatography analysis of hydrocarbon gases and phase formed during reaction is shown.
carbon dioxide was done using a TermoQuest GC 8000 with a
As shown in Table 1, glucose conversion increases as
Thermal Conductivity Detector (TCD) using a Poraplot-Q temperature varies from 453 to 473 K, reaching almost the total
(
Chrompack) column (10 m ꢂ 0.32 mm ꢂ 10 mm). The conversion. In the same temperature range, sorbitol selectivity
specic instrument parameters follow: decreases, while the two identied C5 polyols have opposite
Column: CP-PoraPLOT Q, 10 m ꢂ 0.32 mm i.d., thickness behaviour (arabitol decreases and xylitol increases), but the
10 mm.
total C5 selectivity decreases of about 33%. As shown by other
This journal is © The Royal Society of Chemistry 2015
RSC Adv., 2015, 5, 23086–23093 | 23087

View Article Online
RSC Advances
Paper
Table 1 Glucose conversion (%) and products selectivity (%) obtained in presence of Pt/C. S ¼ sorbitol, A ¼ arabitol, X ¼ xylitol, G ¼ glycerol,
H ¼ 1,2-hexanediol, B ¼ 2,3- and 1,2-butanediol, P ¼ 1,2-propanediol, Et ¼ 1,2-ethanediol, R.T. ¼ reaction time
Selectivity (%)
ꢀ1
T (K)
P (MPa)
R.T. (h)
Pt/glucose (g g
)
Conversion (%)
S
A
X
G
H
B
P
Et
GPt1
GPt2
GPt3
GPt4
GPt5
GPt6
453.0
453.0
453.0
473.0
493.0
493.0
10.0
5.0
10.0
10.0
10.0
10.0
2.0
3.0
2.0
2.0
2.0
4.0
0.0015
0.0015
0.003
0.003
0.003
0.003
45.5
76.5
73.5
98.7
100.0
100.0
7.0
7.8
16.1
9.4
8.4
8.0
11.6
11.0
9.1
3.5
3.9
0.0
3.0
2.9
4.2
4.6
4.6
0.0
3.1
5.7
12.2
7.1
7.6
7.8
6.9
5.2
8.0
12.4
10.2
1.1
1.6
2.3
1.5
5.6
4.4
0.4
0.7
1.1
5.2
9.0
6.3
1.1
0.7
0.7
2.2
2.8
1.7
4.2
19
authors C–O bond cleavage activity increases with tempera- very low conversion of sorbitol (11.3%) to arabitol and carbon
ture, and this is veried by the greater production of 1,2-hex- dioxide has been observed, but no other compounds were
anediol. The C3–C4 bond cleavage leading to glycerol and detected.
propanediol is favored when passing from 453 to 473 K, because
The bond cleavage of C–C in terminal position of glucose
the selectivity of both compounds increases. C4 and C2 diols are molecule, which is attested by the presence of arabitol and
formed through a C2–C3 bond cleavage and decarbonylation xylitol, does not lead to the production of methanol, but carbon
reactions, but at the intermediate temperature used for this dioxide was found in the gaseous phase, as according to other
9,22
campaign the butanediols selectivity is lower than at 453 K, studies.
while ethanediol increases. It could be hypothesized a C2–C3 The hydrogenolysis of glucose was then carried out in pres-
bond cleavage of arabitol leading to glycerol and ethanediol, ence of ruthenium in batch mode and the operating conditions
because the C5 polyols selectivity decreases in this temperature and results are reported in Table 2. In this experimental
range.
campaign, only the reaction time was varied from 2 to 4 h, while
A further increase of temperature up to 493 K does not temperature and pressure were kept constant at 473 K and 10
signicantly change sorbitol selectivity, which slightly MPa. The conditions were selected considering the experiments
decreases, but it leads to an increase of arabitol and xylitol. At with platinum that led to highest selectivity towards glycols.
the highest temperature the highest selectivity of C6 diol is Aer 2 hours of reaction, the most favourite compounds were
obtained, being the C–O bond cleavage favoured, and glycerol is sorbitol and arabitol. Less selectivity was detected for xylitol,
probably transformed to propanediol with the same mecha- threitol and glycerol. The amount of polyols with four carbons
12
nism, because the C3 diol selectivity decreased of about 41%. was very low, indicating two most probably cleavage sites,
In the range 473–493 K, butanediols selectivity increases indi- terminal position (pentols) and central position (glycerol), even
cating higher selectivity for C–O scission and more probably if the latter occurred with less frequency. Increasing the reac-
C2–C3 bond cleavage of C6 sugar or polyols.
tion time, the total amount of compounds in the liquid phase
It is worth noticing that 1,2-hexandiol selectivity is higher decreased, and the selectivity of threitol and glycerol increased,
with respect to other diols, implying that the C–O scission can while sorbitol was almost completely converted into lower
compete with C–C bond cleavage. The precursor of the reaction molecular weight molecules. In presence of ruthenium, the
leading to the elimination of a hydroxyl group (OH) is quite gaseous phase contained high concentration of gaseous
unstable, because it has two double bonds (C]O, C]C). Being hydrocarbon, mostly methane and less quantity of ethane and
the reactor a reducing environment, one of the double bond is propane.
easily hydrogenated but, if the catalyst activity is not enough
The results in Table 2 suggested that ruthenium had a strong
strong, it is possible the persistence of the other double bond activity for hydrogenation and glucose was rst transformed to
which leads to the further break of another C–O bond.
According to this, the glucose maintains the –C–C– chain, but
looses the hydroxyl groups implying hexanediol formation.
A schematic representation of possible products is reported
in Fig. 1. The reaction route is based on the identied products
in the liquid phase, without considering the exact mechanism.
Increasing the reaction time at the highest temperature
value (493 K) does not signicantly change the selectivity of
polyols, indicating that platinum is not able to catalyse dehy-
18
drogenation, the precursors of polyols hydrogenolysis. This
result has been also assessed feeding the reactor with an
ꢀ1
aqueous solution of 100 g l of sorbitol. Experimental runs
have been conducted at 493 K and 10 MPa for two hours and a Fig. 1 Schematic representation of products obtained by hydro-
genolysis of glucose in presence of Pt/C.
23088 | RSC Adv., 2015, 5, 23086–23093
This journal is © The Royal Society of Chemistry 2015

View Article Online
Paper
RSC Advances
Table 2 Glucose conversion (%) and product selectivity (%) in presence of Ru/C. S ¼ sorbitol, A ¼ arabitol, X ¼ xylitol, T ¼ threitol, G ¼ glycerol
Selectivity (%)
ꢀ1
T (K)
P (MPa)
R.T. (h)
Ru/glucose (g g
)
Glucose conversion (%)
S
A
X
T
G
GRu1
GRu2
473.0
473.0
10.0
10.0
2.0
4.0
0.0015
0.0015
100.0
100.0
23.0
7.4
25.0
11.9
11.2
8.6
2.0
6.6
6.2
7.4
sorbitol, which then reacted to form the other polyols, accord-
22
ing to Zhang et al., and C1–C3 straight chain alkanes.
The new experimental campaign was carried on using a
reactant mixture containing sorbitol instead of its sugar, such
as the rst reaction step (hydrogenation) was skipped. The
reactions were conducted at three levels of temperature (453,
4
73, 493 K) and two levels of pressure (5–10 MPa), maintaining
ꢀ
1
constant the reaction time (4 h) and ratio Ru/sorbitol (g g ).
The dependence of sorbitol conversion on pressure and
temperature is summarized in Fig. 2, considering the samples
taken at different reaction time. The obtained results indicate
that pressure favoured conversion of sorbitol at higher
temperature (473 and 493 K), whereas a lower effect was evident
with respect to temperature at 5 MPa. Conversion was almost
constant when temperature was increased from 473 to 493 K.
The increase of hydrogen pressure implied that more hydrogen
molecules could access to Ru active sites, which determined a
higher sorbitol conversion especially at higher temperature. At
4
53 K the effect was less evident, probably because the revers-
ible reactions of the mechanism of sorbitol hydrogenolysis
dehydrogenation and retro-aldol condensation) were not so
(
7
slow.
The main products obtained in the different experimental
runs were pentols, in particular arabitol and xylitol, threitol and
glycerol, as in case of hydrogenolysis of glucose in presence of
ruthenium. The selectivity of the different products is reported
in Fig. 3.
Fig. 3 Selectivity behaviour with respect to sorbitol conversion, with Ru/
ꢀ1
The rst observation is that products obtained through sorbitol equal to 0.0015 g g , for arabitol (plus), xylitol (square), glycerol
C–C bond cleavage of sorbitol in terminal position (pentols) had (circle), and threitol (star), at the following conditions: P ¼ 10 MPa, 453 K
(a), 473 K (b), 493 K (c); P ¼ 5 MPa 453 K (d), 473 K (e), 493 K (f).
a higher selectivity at lower temperature, while as temperature
increased they were converted to lower polyols. Indeed, as
sorbitol conversion increased, arabitol selectivity decreased
being likely converted to threitol and glycerol. Pressure had a
lower effect on pentols selectivity, giving a slight higher value
when it was set at 5 MPa. Arabitol selectivity was always greater
then that of xylitol, but arabitol had also a higher conversion
rate, which increased with temperature. It is worth noticing,
9
that unlike the results shown by Deutsch et al., who carried out
reaction in presence of a base, the hydrogenolysis of sorbitol at
the investigated conditions did not produce ribitol, and xylitol
was not formed in nearly equal quantities to arabitol. This last
observation is therefore in agreement with the work of Sun and
8
Liu, who found that xylitol, in neutral solution, is predomi-
nantly converted to arabitol.
The production of glycerol was favoured by pressure, except
at 453 K, and it increased with temperature. Being the selectivity
of glycerol always higher than that of threitol, it was probably
obtained through a C3–C4 bond cleavage, while the absence of
Fig. 2 Conversion of sorbitol at different sampling time, with Ru/S
equal to 0.0015 (g g ), at 10 MPa (a) and 5 MPa (b) at the following
temperature: 453 K (circle), 473 K (square), and 493 K (star).
ꢀ1
This journal is © The Royal Society of Chemistry 2015
RSC Adv., 2015, 5, 23086–23093 | 23089

View Article Online
RSC Advances
Paper
4
00 ml. The hydrogen ow rate was maintained constant in all
ꢀ
1
the runs and set equal to 1000 Nml min . In this case four
temperature levels (453–473–493–513 K) and three pressure
levels (3–5–10 MPa) were investigated. The results are reported
in Table 3 in terms of selectivity for the products in the liquid
phase.
Fig. 4 Schematic representation of products obtained by hydro-
genolysis of sorbitol in presence of Ru/C.
The rst two experiments led to the total conversion of
sorbitol, but no polyols, diols or alcohols were detected in the
aqueous solution. The analysed outlet gas stream contained
straight chain alkanes, mainly methane and ethane, and pres-
ence of alcohols like butanol and pentanol. Reducing the
reaction time up to 1 h (SSRu3), sorbitol is completely
consumed but the selectivity for polyols increases as they have
not been converted to lower molecular weight products.
Increasing the reaction time of half an hour implies again the
complete conversion of the whole polyols, diols and alcohols
mainly into gaseous straight alkanes.
ethylene glycol could imply that threitol was derived by a bond
cleavage in terminal position of a ve carbon polyol.
The presence of propylene glycol had been detected only at
473 and 493 K, with the greatest selectivity at 10 MPa. The
maximum value of selectivity was around 3%, obtained at the
end of the batch, setting temperature at 493 K and pressure at
10 MPa. It is worth noticing that the presence of ruthenium as
catalyst led to the formation of threitol, whereas this compound
was not detected in presence of platinum.
The gas analysed at the end of the reactions evidenced the
presence of methane, small quantity of ethane and carbon
monoxide.
Fig. 4 shows a scheme of the products obtained by the
hydrogenolysis of sorbitol, without considering the exact
mechanism of reaction.
In order to increase the selectivity for polyols and decrease
the production of methane and ethane, the catalyst concentra-
tion was lowered. The reduction of catalyst has the same effect
of reducing reaction time (cf. SSRu3 and SSRu5). A further
ꢀ1
decrease to 0.0005 (g g ) of the ratio Ru/sorbitol implied a
reduction of the conversion (SSRu6) of sorbitol and increased
selectivity of arabitol and xylitol. The percentage of carbon
converted into gaseous hydrocarbon was strongly reduced.
When increasing the reaction time (SSRu7), the sorbitol
conversion increased while pentols selectivity decreased, being
they converted to lower molecular weight compounds through
C–C bond cleavage in terminal position.
3.2 Sorbitol conversion in semi-continuous reactor
The hydrogenolysis of sorbitol was also conducted operating in
semi-continuous mode, where the gas phase continuously

owed through the vessel. The initial solution consisted of 100 g
Keeping the lower quantity of catalysts in order to favour
production of lower polyols, the effects of temperature and
pressure on the product distribution were analysed, according
of sorbitol in 100 g of water. All the experiments were carried out
with 300 ml of the aqueous sorbitol solution, excepted for the
experiments SSRu1 and SSRu2, where the reactor was lled with
Table 3 Sorbitol (S) conversion and products selectivity. A ¼ arabitol, X ¼ xylitol, T ¼ threitol, G ¼ glycerol, D ¼ diols (butanediols, propanediols
and ethanediol), Al ¼ alcohols (n.d. ¼ not detected)
Selectivity (%)
ꢀ
1
T (K)
P (MPa)
R.T. (h)
Ru/S (g g
)
Sorbitol conversion (%)
A
X
T
G
D
Al
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
3
3
3
3
3
4
4
4
4
4
4
4
4
4
SSRu1
SSRu2
SSRu3
SSRu4
SSRu5
SSRu6
SSRu7
SSRu8
SSRu9
SSRu10
SSRu11
SSRu12
SSRu13
SSRu14b
SSRu15
SSRu16
473
473
473
473
473
473
473
473
473
453
493
493
453
453
493
513
5.0
5.0
5.0
5.0
5.0
4.0
3.0
1.0
1.5
2.0
2.0
4.0
2.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
3 ꢂ 10
3 ꢂ 10
3 ꢂ 10
3 ꢂ 10
1 ꢂ 10
5 ꢂ 10
5 ꢂ 10
5 ꢂ 10
5 ꢂ 10
5 ꢂ 10
5 ꢂ 10
5 ꢂ 10
5 ꢂ 10
5 ꢂ 10
5 ꢂ 10
5 ꢂ 10
100.0
100.0
98.2
100.0
98.0
86.4
91.5
86.4
87.9
71.6
91.0
96.6
73.0
65.5
70.2
98.1
n.d.
n.d.
4.5
n.d.
4.5
25.6
13.7a
30.2
n.d.
n.d.
3.1
n.d.
0.9
n.d.
n.d.
4.4
n.d.
4.6
11.4
6.9
(see A)
(see A)
n.d.
6.2
n.d.
n.d.
12.1
n.d.
11.5
9.7
14.0
14.2
16.7
8.4
16.5
16.9
10.1
n.d.
17.8
15.9
n.d.
n.d
2.7
n.d.
3.7
1.4
1.1
n.d.
1.8
n.d.
0.7
n.d.
n.d.
1.1
n.d.
2.0
n.d.
<0.1
0.5
5.0
5.0
15.7
9.2
10.0
10.0
10.0
10.0
5.0
5.0
3.0
3.0
10.0
14.2
11.9
12.6
11.0
5.0
13.1
14.0
7.5
a
23.9
1.0
n.d.
2.2
24.0
11.3
10.4
36.0
37.2
23.1
8.3
5.8
3.9
0.7
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
5.3
n.d.
n.d.
3.8
ꢀ4
ꢀ
4
3.0
5.4
2.8
a
b
This selectivity is calculated considering both A and T (the peaks are unresolved). During this test there was also the formation of xylose, with
selectivity equal to 11.4%.
23090 | RSC Adv., 2015, 5, 23086–23093
This journal is © The Royal Society of Chemistry 2015

View Article Online
Paper
RSC Advances
derives from C1–C2 bond cleavage of sorbitol and its selectivity
is higher at lower temperature, because at such condition its
conversion is less likely to occur. The reduction of arabitol
selectivity as temperature increased was due to its conversion to
glycols, alcohols and C1, C2 alkanes (cf. Fig. 5d–f).
The selectivity of xylitol was lower than arabitol at every
investigated condition (Fig. 5c). This result is in agreement with
8
the observation of Sun and Liu, who nd that xylitol prefer-
entially is converted to arabitol, in presence of Ru/C.
Glycerol selectivity increased as temperature varied from 453
to 473 K (Fig. 5d). In the range 473–513 K it seemed less affected
by temperature and at 10 MPa selectivity was almost constant.
Glycerol could be formed from sorbitol by a C3–C4 bond
cleavage, but it seemed not easily converted to lower polyols as
temperature increased.
Alcohols and diols were always present in very small amount
and their selectivity increased as temperature was raised to 493
and 513 K. Fig. 5e shows the selectivity of the sum of diols
(
butanediols, propanediols and ethanediols) and C5–C1
alcohols.
Higher temperature led to higher selectivity for methane and
ethane, whereas at 453 K, no gaseous straight chain alkanes
have been detected at the three pressure values considered
(Fig. 5f). In fact, at lower temperature (453 and 473 K), C–O bond
cleavage rate is disadvantaged with respect to C–C bond
cleavage. Alcohols like propanol, butanol, pentanol, ethanol
and methanol were also detected in the outlet gas stream.
It is worth noticing that at 493 K and 3 MPa (SSRu15), xylose
Fig. 5 Conversion of sorbitol (a), and product selectivity for the
experimental campaign carried out in semi-batch mode, with Ru/
ꢀ4
ꢀ1
sorbitol ¼ 5 ꢂ 10 g g , reaction time ¼ 4 h, hydrogen flow rate was produced by hydrogenolysis of sorbitol, with selectivity
ꢀ1
equal to 1000 Nml min . Arabitol (b), xylitol (c), glycerol (d), diols +
alcohols (e), methane and ethane (f).
equal to 11.4%. The C5 sugar may derive by dehydrogenation of
C5 xylitol, but the subsequent transformation to lower polyols
19
did not occur probably because of the low hydrogen pressure.
to the conditions of the experiments referred as SSRu7, SSRu9–
SSRu16. The obtained results are also summarized in Fig. 5.
Fig. 6 shows a scheme of the possible reactions, which is based
on the identied products in the liquid phase.
At Ru/sorbitol equal to 5 ꢂ 10 , sorbitol conversion was
generally favoured at high temperature and pressure. The effect
of temperature was less signicant at 3 MPa (Fig. 5a).
The results on arabitol selectivity are reported in Fig. 5b, but
the data at 473 K and 10 MPa are missing because we were not
able to resolve the peaks of the pentol and threitol. Arabitol
3
.3 Sorbitol conversion in presence of an inhibitor of the
reaction
ꢀ
4
6,13
According to previous studies,
the effects of inhibitor of
reaction was considered, and ruthenium was poisoned adding
sulphur at the reactant solutions. The main purpose was to
reduce the selectivity of straight chain alkanes, favouring the
formation of glycols and alcohols. First, a preliminary study was
conducted to analyse the behaviour of the system when starting
4,7,19
from a basic solution.
The experiments were conducted
Table 4 Experimental results of hydrogenolysis of sorbitol aqueous
solution in semi-continuous mode at different pH, with hydrogen flow
ꢀ1
ꢀ1
rate equal to 1000 Nml min , Ru/S ¼ 0.001 (g g ), P ¼ 10 MPa,
T ¼ 513 K, and reaction time equal to 4 h. B ¼ butanediol, P ¼ pro-
panediol, Et ¼ ethanediol, Eth ¼ ethanol
Selectivity
pH
Sorbitol conversion (%)
B
P
Et
6.0
12.4
6.8
Eth
NaSSRu1
14
12
10
100.0
88.7
96.0
—
4.2
4.2
5.3
23.0
9.9
0.7
0.2
1.7
Fig. 6 Schematic representation of products obtained by hydro- NaSSRu2
genolysis of sorbitol in presence of Ru/C carried out in semi-contin- NaSSRu3
uous reaction mode.
This journal is © The Royal Society of Chemistry 2015
RSC Adv., 2015, 5, 23086–23093 | 23091

View Article Online
RSC Advances
Paper
Table 5 Experimental results of hydrogenolysis of sorbitol aqueous solution in semi-continuous mode, with hydrogen flow rate equal to 1000
ꢀ1
Nml min , reaction time equal to 4 h, at 513 K and 10 MPa. S ¼ Sorbitol, A ¼ arabitol, X ¼ xylitol, T ¼ threitol, G ¼ glycerol, B ¼ butanediol,
P ¼ propanediol, Et ¼ ethanediol, Al ¼ alcohols
Selectivity (%)
ꢀ1
ꢀ1
Ru/S (g g
)
Sulfur/Ru (mol mol
)
pH
Sorbitol conversion (%)
A
X
T
G
B
P
Et
3.2
16.9
20.2
9.3
Al
PSSRu1
PSSRu2
PSSRu3
PSSRu4
PSSRu5
0.00625
0.003
0.009
0.009
0.003
4.0
0.3
5.0
0.3
5.0
14
10
10
10
10
100.0
16.0
44.3
40.0
14.0
—
26.9
—
15.0
—
—
9.4
—
9.0
—
—
—
—
15.0
7.0
—
4.7
2.0
—
4.4
—
—
8.3
—
4.3
35.6
24.9
14.4
40.7
5.0
—
8.8
—
25.7
at 523 K, 10 MPa, with catalyst concentration equal to 0.001 g conversion of polyols, platinum showed to be less active, while
Ru/g S. it has favoured the conversion of glucose. Starting from the
The results in terms of selectivity considering the liquid simple sugar in presence of Pt/C, pentols (arabitol and xylitol)
products contained in the reactor at the end of the run have showed the higher selectivity along with carbon dioxide as
been reported in Table 4. It is evident that the solution pH had a gaseous products. It is demonstrated that Pt/C has a highest
great effect on the reaction and, differently from the previous selectivity to C6 (hexanediol) indicating a weaker activity to C–C
19
results here presented, the production of alcohols increases. bond cleavage.
Considering the diols production, the best choice is to select an In presence of ruthenium, results showed higher activity
initial pH equal to 12. Most of the products obtained in pres- with respect to polyols conversion, with the prevalence of
ence of the base, NaOH, has not been recognised with the hydrodeoxygenation reaction and the formation of straight
analytical techniques at our disposal. It is also worth noticing chain alkanes, particularly methane and ethane. The selectivity
that alcohols may be dragged by the gas ow leaving the reactor. of oxygenated compounds, especially glycols and alcohols, had
Starting from this result and considering the patent of been increased by using an inhibitor of the reaction starting
6
Dubeck and Knapp, sulphur has been also added to the reac- with an initial basic environment.
tant solution in order to increase the selectivity of alcohols
(ethanol) and glycols. The experimental runs have been con-
ducted in semi-continuous mode, according to the condition
References
reported in Table 5. The rst experimental run was conducted
6
following the patent of Dubeck and Knapp, considering that
1
H. Heeres, R. Handana, D. Chunai, C. B. Rasrendra,
condition leading to the maximum selectivity of ethanol.
At the condition of PSSRu1, most of the products were like-
lihood entrained in the gas stream. The analysis of the aqueous
solution in the trap for volatile compounds downstream
the reactor evidenced a high concentration of ethanol (circa
B. Girisuta and H. J. Heeres, Green Chem., 2009, 11, 1247–
1255.
2
3
4
5
A. M. Ruppert, K. Weinberg and R. Palkovits, Angew. Chem.,
Int. Ed., 2012, 51, 2564–2601.
K. K. Janga, M. B. Hagg and S. T. Moe, BioResources, 2012, 7,
¨
ꢀ1
ꢀ1
30 g l ) and methanol (7 g l ). Other alcohols like propanol,
391–411.
butanol, pentanol were present in lower quantities. The reac-
tion leading to the highest yield in terms of diols and alcohols is
PSSRu3, where the maximum amount of catalyst and poisoning
were used, leading to high catalysts dispersion with low activity.
The presence of sulphur reduced ruthenium activity and mini-
mized the formation of straight chain hydrocarbon, favouring
C2–C3 oxygenates. Decreasing the amount of catalyst, keeping
constant the ratio sulphur on ruthenium, the selectivity of
glycols became quite high, but sorbitol conversion was highly
reduced (PSSRu5).
M. Banu, S. Sivasanker, T. M. Sankaranarayanan and
P. Venuvanalingam, Catal. Commun., 2011, 12, 673–677.
D. K. Sohounloue, C. Montassier and J. Barbier, React. Kinet.
Catal. Lett., 1983, 22, 391–397.
M. Dubeck and G. G. Knapp, US Pat., 4476331, 1984.
L. Zhao, J. H. Zhou, Z. J. Sui and X. G. Zhou, Chem. Eng. Sci.,
6
7
2010, 65, 30–35.
8
9
J. Sun and H. Liu, Green Chem., 2011, 13, 135–142.
K. L. Deutsch, D. G. Lahr and B. H. Shanks, Green Chem.,
2012, 14, 1635–1642.
1
1
0 J. Feng, H. Fu, J. Wang, R. Li, H. Chen and X. Li, Catal.
Commun., 2008, 9, 1458–1464.
1 D. Ariono, C. Moraes de Abreu, A. Roesyadi, G. Declercq and
A. Zoulalian, Bull. Soc. Chim. Fr., 1986, 5, 703–710.
4
. Conclusion
In this work, we investigated the effect of different parameters
on the catalysed conversion of glucose and sorbitol in presence 12 C. Montassier, D. Giraud and J. Barbier, Stud. Surf. Sci.
of hydrogen, in order to clarify the mechanisms driving these Catal., 1988, 41, 165–170.
reactions. A wide variety of compounds had been obtained due 13 C. Montassier, J. C. M ´e n ´e zo, L. C. Hoang, C. Renaud and
to the occurrence of different classes of reactions: C–C bond J. Barbier, J. Mol. Catal., 1991, 70, 99–110.
scissions, C–O bond scission and hydrogenation. Based on the 14 B. Casale and L. Marini, European Patent 0510238, 1991.
23092 | RSC Adv., 2015, 5, 23086–23093
This journal is © The Royal Society of Chemistry 2015

View Article Online
Paper
RSC Advances
1
5 P. M u¨ ller, P. Rimmelin, J. P. Hindermann, R. Kieffer, 18 P. A. Lazaridis, S. Karakoulia, A. Delimitis, S. M. Coman,
A. Kiennemann and J. Carr ´e , Stud. Surf. Sci. Catal., 1991,
9, 237–244.
V. I. Parvulescu and K. S. Triantafyllidis, Catal. Today,
2015, in press.
5
1
6 E. Tronconi, N. Ferlazzo, P. Forzatti, I. Pasquon, B. Casale 19 C. Liu, C. Zhang, K. Liu, Y. Wang, G. Fan, S. Sun, J. Xu, Y. Zhu
and L. Marini, Chem. Eng. Sci., 1992, 47, 2451–2456. and Y. Li, Biomass Bioenergy, 2015, 72, 189–199.
7 M. Banu, P. Venuvanalingam, R. Shanmugan, 20 N. Li and G. W. Huber, J. Catal., 2010, 270, 48–59.
B. Viswanathan and S. Sivasanker, Top. Catal., 2012, 55, 21 K. Wang, M. C. Hawley and T. D. Furney, Ind. Eng. Chem.
1
897–907.
Res., 1995, 34, 3766–3770.
22 J. Zhang, J. Li, S. B. Wu and Y. Liu, Ind. Eng. Chem. Res., 2013,
52, 11799–11815.
This journal is © The Royal Society of Chemistry 2015
RSC Adv., 2015, 5, 23086–23093 | 23093