Chemoselective synthesis of propionic acid from biomass and lactic acid over a cobalt catalyst in aqueous media

Article abstract of DOI:10.1039/c6gc03036j

A new non-fermentative process for the transformation of biomass carbohydrates and lactic acid (LA) into propionic acid (PA) was first reported over a cobalt catalyst in water. The Co catalyst exhibited high catalytic activity for the formation of PA with Zn as a reductant. Various parameters, such as catalyst loading, Zn weight, water volume, temperature and reaction time, were investigated to improve the yield of PA, and the maximum value of 58.8% was achieved in the presence of 4 mmol Co and 10 mmol Zn in 7.5 mL H₂O at 250 °C for 2 h. The recyclability of the Co catalyst showed that Co could be effectively repeated four times without the loss of activity. Moreover, the result showed that in situ-formed ZnO by oxidation of Zn in water could efficiently enhance the catalytic activity of the Co catalyst in the conversion of LA. Besides, direct conversion of carbohydrate biomass, such as glucose, cellulose and starch, or a similar compound such as glycolic acid also afforded the desired products. The present study provides great significance for practical application on the production of PA from LA and biomass carbohydrates.

Full text of DOI:10.1039/c6gc03036j

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Chemoselective synthesis of propionic acid from biomass and
lactic acid over cobalt catalyst in aqueous media
Received 00th January 20xx,
Accepted 00th January 20xx
Zhibao Huo,* Jiefeng Xiao, Dezhang Ren, Fangming Jin,* Tian Wang, Guodong Yao
A new non-fermentative process for the transformation of biomass carbohydrates and lactic acid (LA) into propionic acid
(PA) was first reported over Cobalt catalyst in water. Co catalyst exhibited high catalytic activity for the formation of PA
with Zn as a reductant. Various parameters, such as catalyst loading, Zn weight, water volume, temperature and reaction
time, were investigated to improve the yield of PA, and the maximum value of 58.8% was achieved in the presence of 4
DOI: 10.1039/x0xx00000x
www.rsc.org/
o
mmol Co and 10 mmol Zn in 7.5 mL H2O at 250 C for 2 h. Recyclability of Co catalyst showed that Co could be effectively
repeated four times without the loss of activity. Moreover, the result found that in situ-formed ZnO by oxidation of Zn in
water could efficiently enhance catalytic activity of Co catalyst in the conversion of LA. Besides, direct conversion of
carbohydrate biomass, such as glucose, cellulose and starch, or similar compound such as glycolic acid also afforded the
desired products. The present study provides great significance for practical application on the production of PA from LA
and
biomass
carbohydrates.
Propionibacterium acidipropionici have focused on the
12,
Introduction
conversion of glucose and whey lactose3,
13. Also, some
studies have employed glycerol or lactic acid (LA) as a carbon
source on account that less acetic acid was produced during
consumption of glycerol/LA14, 15. In terms of the properties of
fermentation process: unstable product quality, undesirable
salt waste effluents, small space-time yields and high
purification cost, the fermentation process lacks economically
competitive ability in industrial application in the long run.
Thus, it is extremely essential to develop more efficient
methods to product PA.
Propionic acid (PA) is a good antifungal agents in food industry
and also has been extensively applied as a crucial chemical
intermediate in industrial manufacture. Such as in the
synthesis of cellulose fibers, perfumes, herbicides and
pharmaceuticals, artificial fruit flavors, and preservatives for
food, animal feed, and grain, etc1-3. Due to its excellent
industrial application value, the synthesis of PA has attracted
much attention. Nowadays, PA production is strongly done by
petrochemical routes, such as the direct synthesis of carboxide
and ethylene, oxidation of propionaldehyde and by-product of
acetic synthesis by light paraffin oxidation. However, the
feasibility of PA production based on the petrochemical
industry is facing serious challenges due to the emergence of
environment pollution and energy shortage.
The production of value-added chemicals, such as formic
acid, acetic acid, LA, levulinic acid and alcohols, etc., based on
the chemical conversion of the biomass resource has been
reported recently16-28. However, no any methods for PA
production from the biomass conversion was reported
because the degradation products of big molecule biomass are
always low-carbon organics (carbon numbers less than 3).
Even if big molecule biomass can be effectively degraded into
C3 compounds under specific reaction conditions, but the
ultimate products are always LA, propylene glycol or glycerol
but not PA. Hence, the production of PA by the redox of C3
compounds may have a promising future. Previously, we
unexpectedly found the small amount of PA, as another
reduction product of LA, was always detected during the
process for the selective conversion of LA into 1,2-propylene
glycol29, which offered the possibility of PA production from
LA.
Recently, the utilization of biomass and derived materials to
synthesize chemical stocks has been proved a promising
method to replace the petroleum-derived materials since it is
renewable, low-cost, less pollution and abundant4-9
.
Considerable efforts have been made to effectively convert
biomass resource into PA3, 10-15. However, to the best of our
knowledge, only fermentative processes for PA production
have been reported in the last decades. Majority of studies on
PA fermentation production accomplished through
Theoretically, LA can be selectively reduced into 1,2-
propylene glycol or PA under proper reaction conditions
(Scheme 1). However, hydroxyl (-OH) is difficultly reduced in
that the oxidability of carboxyl (-COOH) is much higher than
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Experimental procedure
Experiments were performed by using a series of batch Teflon
reactors (inner volume: 30 mL). The procedure was conducted
as follows. Firstly, the desired concentration of LA solution was
prepared beforehand according to the desired water volume.
Then, the desired catalyst, reductant and LA solution were
added into the reactor chamber. Reactor was brought into the
preheated oven for 20 min to rise to the desired reaction
temperature. After preset reaction time, the reactor was
removed from the oven and cooled down to the room
temperature with the help of electric fan. Finally, liquid sample
was collected and filtered through a 0.45
ꢁm syringe for
Scheme 1.
analysis. Solid sample was collected and washed with
deionized water and ethanol several times and dried in the
oven at 50 oC for 24 h.
hydroxyl group, for which the enthalpy of reaction (ꢀHr)
estimated by bonding energy can partly account for the
reactivity of the hydroxyl and carboxyl group (Eqs 1 and 2).
Therefore, the investigation of redox of hydroxyl in the
presence of carboxyl may have a signification implication for
the organic technology.
Products analysis
The
liquid
samples
were
analyzed
by
gas
chromatography/mass spectroscopy (GC-MS), total organic
carbon (TOC), high-performance liquid chromatography
(HPLC). The Agilent 7890 GC/MS system was equipped with
5985C inert mass selective detector (MSD) with triple-axis
detector while the Agilent 1200 HPLC system was equipped
with Variable wavelength detector (VW) and Refractive index
detector (RI) with a 2 mmol/L H2SO4 solution as the mobile
phase at a flow rate of 1.0 mL/min. The Liquid sample was also
tested by inductively coupled plasma-optical emission
spectrometry (ICP-OES) to measure the metal ion
concentration. Solid sample washed with deionized water and
The aim of this study is to develop a new process for PA
production from the biomass-derived LA and carbohydrates in
high temperature water. Fermentation production of PA from
biomass-derived materials has been thoroughly investigated in
the past several years. However, the research about the
chemical process for PA production by utilizing biomass as the
raw materials is still in its infancy. Here, we first reported that
hydrothermal method is applied to bring off the chemical
process for the production of PA from LA and carbohydrates
(Scheme 2).
o
ethanol several times was dried in an oven at 50 C for 24 h.
Then the precipitate was analyzed by XRD (Bruker D8 Advance
Materials and methods
X-Ray Diffractometer, equipped with Cu K
1.5406 Å , scanning rate : 0.02 o·s-1, 2 ranges: 10-80 o).
α radiation: λ=
θ
The LA conversion (LAConv.), product i yield (Yi) and selectivity
Materials
LA (DL, ~90%T) was obtained from Sigma-Aldrich Chemical
Reagent Co., Ltd. Zn powder (AR) was obtained from Aladdin
Chemical Reagent Co. Ltd. Co powder (200-mesh, 2N), other
metals and metal oxides were obtained from Sinopharm
Chemical Reagent Co. Ltd., China. The standard reagents PA
(Sigma- Aldrich, >99.7%), 1,2-propylene glycol (PG) (J&K
Chemical, >99.8%), Hydroxyacetone (HA) (Alfa Aesar, >95%),
to product i (Si) were calculated as following equations:
mole of lactic acid atparticulartime
100 (1)
LAConv. (%) =
Yi (%) =
1
-
initial mole of lactic acid
mole of product i
100
(2)
(3)
initial mole of lactic acid
mole of product i
100
Si (%) =
mole of all products f ormed
acetic acid (AA) (Sigma-Aldrich, >99.7%) and 1.0
N
Standardized LA (Alfa Aesar) were employed in qualitative
analysis of liquid example.
Results and discussion
Catalyst screening
Carbohydrate biomass
(Cellulose, Glucose, Starch)
Previous: Bio-fermentation process
Previous research found that small amount of PA as the by-
product was always detected during the production of 1,2-
propylene glycol from LA using CuO as the catalyst29. According
to the reaction mechanism, PA can be obtained by the
selective reduction of hydroxyl of LA. To improve the
selectivity of PA from LA, a series of experiments with different
catalysts were performed. The results in Table 1 demonstrated
that Co showed the best catalytic activity with a 30.9% yield of
PA with other compounds such as PG, HA, AA and NPA
Bio-fermentation
OH
OH
OH
O
OH
Propionic acid
O
OH
This work: Chemical transformation
O
Lactic acid
Scheme 2. PA production from carbohydrates and LA over Co
catalyst.
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Table 1. Catalyst screening for the formation of PA. a
ARTICLE
Yield (%)b
PA
Entry
Catalysts
Reductant
LA conv. (%)
Total (%)
NPA
PG
0
HA
0
AA
1
Co
-
12.1
2.3
5.9
0
5.5
1.3
1.0
<1.0
<1.0
<1.0
<1.0
1.7
<1.0
<1.0
0
0
11.4
1.3
2
-
Zn
Zn
Zn
Zn
Zn
Zn
Zn
Zn
Zn
Zn
Zn
Zn
Zn
Zn
Zn
Zn
0
0
0
3
Co
96.8
46.0
66.6
38.3
14.7
15.3
7.2
30.9
2.0
2.8
1.5
<1.0
2.9
3.1
<1.0
0
47.3
40.0
63.8
36.8
14.6
10.7
3.2
0
<1.0
4.0
<1.0
<1.0
<1.0
<1.0
1.0
0
17.8
0
98.0
47.0
68.6
40.3
17.6
16.3
8.3
4
Cu
5
CuO
Cu2O
Ni
0
6
0
7
0
8
Ni2O3
Fe2O3
Mo
Ti
0
9
0
10
11
12
13
14
15
16
17
1.0
0
2.0
4.3
3.1
0
1.2
0
0
4.3
ZrO2
SiO2
TiO2
MnO2
Cr
1.0
0
1.0
<1.0
<1.0
0
0
1.0
1.0
0
0
1.0
0
0
2.0
6.0
6.0
<1.0
0
<1.0
0
0
8.0
1.0
0
1.0
2.0
1.0
2.0
2.0
0
0
0
2.0
Al2O3
1.0
<1.0
0
0
0
2.0
a Reaction conditions: LA 1.5 mmol, catalyst 4 mmol, reductant 25 mmol, H2O 7.5 mL, 250 C, 2 h. b The yield is calculated as the
o
percentage of products to the initial LA on the carbon base.
3
OH
OH
VWD
1.lactic acid
OH
2.acetic acid
3.propionic acid
O
Propionic acid (PA)
1,2-propylene glycol (PG)
1
OH
OH
O
2
HO
Hydroxyacetone (HA)
O
20
30
40
Lactic acid (LA)
Retention time (min)
OH
3
O
propionaldehyde
OH
4.1,2-propylene glycol
5.propanal
6.n-propanol
RID
O
Acetic acid (AA)
4
1
6
5
2
1-Propanol (NPA)
20
30
40
Retention time (min)
Figure 1. HPLC chromatogram with VW and RI detectors of the liquid sample after reaction (Co 5 mmol, Zn 10 mmol, H2O 7.5 mL,
250 oC, 2 h).
(1-propanol) among all catalyst we investigated (entry 3, also conversion of LA is very low, only 6% of LA was converted
see Figure 1). XRD patterns of solid residues showed in Figure (entry 14).
SI-1c that Co still existed while Zn was oxidized into ZnO, it was
Co loading had a significant influence in the conversion of LA
obvious that Co acted as a catalyst and Zn acted as a reductant to PA as shown in Figure SI-2 and Table SI-1. The yield of PA
in this process. Further, the concentration of Co ion in liquid reached the maximum value of 58.8% with 88.3% LA
sample was then tested by ICP and very small amount of Co conversion rate when Co loading was 4 mmol, while yields of
ion (112 ppm) was found. Besides, the PA yield was PG and NPA showed a slight change with the increase of Co
significantly lower in the absence of catalyst and/or reductant, loading from 0 to 10 mmol.
which indicated that both catalyst and reductant were
necessary (entries 1 and 2). Other catalysts, such as Cu, CuO, Effect of reductant on the yield of PA
Cu2O, Ni, Ni2O3, Fe2O3, Mo, Ti, ZrO2, SiO2, TiO2, MnO2, Cr, Al2O3,
Next, four active metals, Zn, Al, Fe and Mn, were screened to
were tested and proved to be completely ineffective for the
search for the suitable reductant for the PA production. As
transformation (entries 4-17). It should be noted that the
shown in Figure 2 and Table SI-2, it was obvious that Zn and Al
selectivity of PA is 100% when TiO2 was used as a catalyst,
which was much higher than Co catalyst. However, the
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70
ConvLA
175 o
200 o
225 o
250 o
C
C
C
C
SelPA
80
60
40
20
60
SelPG
SelPAL
50
40
30
20
10
0
0
30
60
90
120
150
180
0
Reaction time (min)
Zn
Al
Fe
Mn
Figure 2. Effect of reductants (LA 1.5 mmol, reductant 10 Figure 4. Effects of temperature and time (LA 1.5 mmol, Zn 10
mmol, Co 4 mmol, H2O 7.5 mL, 250 oC, 2 h).
mmol, Co 4 mmol, H2O 7.5 mL).
100
6 and Table SI-4, with the increase of water volume from 6 to
13.5 mL, a decline of LA conversion was observed while yield
of PA wavered within a narrow range, the yield of PG
decreased a little and yield of NPA kept almost constant. The
results showed that the decrease of concentration of LA due to
the high water volume had a negative effect on the conversion
reaction. In view of the pressure, a lower water volume of 7.5
mL with good PA yield was chosen for the following study.
The effects of temperature and reaction time on the
conversion of LA into PA were shown in Figure 4. During the
temperature range of 175 oC to 250 oC, a big change in the
yield of PA was observed. However, the higher reaction
temperature was not investigated because the tolerated
temperature of the Teflon reactor was 250 oC. But it was
possible that a higher PA yield might be attained at more than
250 oC. As a result, the LA was hard to be converted at low
temperature 175 oC even after prolonged reaction time, but
the effect of reaction time visibly emerged at more than 200
oC, which meant that the reaction only could be motivated at
certain temperature. When time was 2 h, the maximum value
of 58.8% at 250 oC was achieved. Besides, HPLC chromatogram
of liquid samples in Figure 5 showed that yield of PA further
increased which yield of LA was further decreased with the
time increased.
ConvLA
YieldPA
YieldPG
YieldPAL
80
60
40
20
0
5
10
15
20
25
Amount of Zn (mmol)
Figure 3. Effect of Zn amount (LA 1.5 mmol, Co 4 mmol, H2O
7.5 mL, 250 oC, 2 h).
were effective and gave much higher yields compared to Fe
and Mn powders. Zn was chosen as the suitable reductant for
the further reaction. From XRD patterns in Figures SI-3 ~ SI-5, it
is worthwhile to note that hydrogen production plays an
important role for the LA conversion, the incomplete oxidation
of Al, Fe and Mn in water decrease hydrogen production which
leads to the low yield of PA.
From Figure 3 and Table SI-3, changing the amount of Zn
found that the LA conversion increased from 0 to 20 mmol,
and then reached a plateau (96.8%) when Zn amount was
increased to 25 mmol. However, PA yield significantly
increased with the increase of Zn amount from 5 to 10 mmol,
and maximum value of 58.8% yield was attained. A dramatic
decrease of PA yield was then observed when Zn amount
increased after 10 mmol while the yields of PG and NPA
further increased, which indicated that more Zn could facilitate
the selectivity of LA into PG and the hydrogenation of PA into
NPA.
Finally, mass balance was conducted at the optimal
conditions by total organic carbon (TOC). The result showed
that approximately 98% organic carbon was converted into
liquid products. The gaseous samples were detected by TCD
and only H2 and trace amount of CH4 and CO2 were found.
Recyclability of Co catalyst
Recyclability of catalyst Co was investigated at the optimal
reaction conditions. Figure SI-7 showed
a simple and
economical method for the separation of Co from the residue
was designed according to their densities. Most of formed ZnO
can be recycled after simple filtering. As shown in Figure 6 and
Table SI-5, the results indicated that Co catalyst still
maintained a high catalytic activity after four cycles for the PA
production. XRD patterns of recycled Co catalyst in Figure SI-8
and SEM images of Co catalyst in Figure 7 did not found the
Influence of parameters on the conversion of LA
Various parameters, such as water volume, temperature and
reaction time were also investigated. As illustrated in Figure SI-
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Table 2. Study on the role of in situ ZnO. a
Entry Co (mmol)
ZnO
Yield of PA (%)
1
2
3
without
with
with
0
OH
without
with
30.2
62.5
OH
with
OH
a Reaction conditions
：LA 1.5 mmol, ZnO 10 mmol, Co 4 mmol,
O
H2 1.10 MPa, 250 oC, 2 h.
Table 3. Co-catalyzed conversion of biomass carbohydrates
into PA. a
O
O
Ni2+, OH-
Cat. Co
Carbohydrate
biomass
OH
LA
OH
OH
PA
Figure 5. HPLC chromatogram of liquid samples at different
time (LA 1.5 mmol, Zn 10 mmol, Co 4 mmol, H2O 7.5 mL, 250
oC).
Yield of products
PA AA PG
16.5 2.9 8.5
5.2 4.2 3.4
Entry Carbohydrate
NPA Othersb
1
2
3
4
5
Glucose
Cellulose
Starch
6.3
2.2
n.d.
n.d.
n.d.
PA yield
15.4 3.8 10.1 5.2
60
Fructose
Saccharose
6.4
5.8
7.3 15.6 n.d. n.d.
7.3 14.4 n.d. n.d.
a Reaction condition: 1) 0.01 M NaOH, 0.01 M Ni2+, 0.035 g
carbohydrates, 2 mL H2O, 300 o C, 1 min, and then directly 2)
40
b
0.76 mmol Co and 1.9 mmol Zn, 300 o C, 60 min. n.d: not
(%)
determined. Here the SUS316 reactor was used for the
reactions.
20
0
O
O
Co (4 mmol), Zn (10 mmol)
H2O (10 mL), 250 oC, 2 h
HO
Unknown
OH
+
+
HO
OH
HO
AA
GA
EG, 9.5%
, 17.2%
1.5mmol
4
3
2
fresh
1
Recycle times
Figure 6. Recyclability of Co catalyst (LA 1.5 mmol, Zn 10
Scheme 3. Conversion of glycolic acid (GA).
mmol, Co 4 mmol, H2O 7.5 mL, 250 oC, 2 h).
performance (entry 1). The absence of ZnO only gave the PA in
30.2% yield, while yield of PA was remarkably increased to
62.5% with the addition of ZnO (entries 2-3). Therefore, it is
suggested that in situ ZnO can enhance the catalytic activity of
Co catalyst and their synergetic effect is effective for the
transformation of LA into PA in water.
Scope of biomass carbohydrates for PA production
Further expanding the scope of the feedstock was conducted
with various biomass carbohydrates. With the conditions
reported previously in the first step process30 and the
optimum reaction conditions in the second step process from
above, we conducted the two-step reactions with glucose,
cellulose and starch to produce PA, and the results were
summarized in Table 3. Maximum PA yields of 16.5% from
glucose, 5.2% from cellulose and 15.4% from starch were
obtained using the two-step process.
Figure 7. SEM images of Co catalyst. Left: fresh, right: after
four cycles.
obvious change before and after the reaction. Though yield of
PA decreased a little to 56.0%, it might be due to in situ ZnO
adsorbed on the surface of Co catalyst to decrease the surface
area during the reaction.
We next carried out the conversion from glycolic acid (GA)
to acetic acid (AA) could happen by this method. The reaction
of GA was conducted in the presence of 10 mmol Zn and 4
Role of in situ ZnO
To investigate the role of in situ ZnO generated by the
oxidation of Zn in water, the conversion reaction of LA was
performed with gaseous hydrogen as the reductant instead of
in situ hydrogen in the presence/absence of ZnO, the results
was summarized in Table 2. No desired PA was observed when
only ZnO was used, indicating that ZnO did not exhibit catalytic
o
mmol Co in water at 250 C for 2 h and gave the expected AA
and ethylene glycol (EG) in 17.2% and 9.5% yields, respectively
(Scheme 3).
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14. T. Dishisha, M. H. Ibrahim, V. H. Cavero, M. T. Alvarez
and R. Hatti-Kaul, Bioresource Technol., 2015, 176, 80-
87.
Conclusions
We developed a non-fermentative process for PA production
from LA and biomass over Co catalyst in hydrothermal
conditions. Co showed significantly catalytic activity and gave
the yield of 58.8% in the presence of 4 mmol Co and 10 mmol
15. Y. Liu, Y. G. Zhang, R. B. Zhang, F. Zhang and J. Zhu,
Curr. Microbiol., 2011, 62, 152-158.
16. F. M. Jin and H. Enomoto, Bioresources, 2009, 4, 704-
o
Zn in H2O at 250 C for 2 h. The result indicated that Co and
713.
ZnO had a synergetic effects on the production of PA from LA.
The Recyclability of Co catalyst proved that Co could be
repeatedly used four times without the loss of its activity.
Biomass carbohydrates such as glucose, cellulose and starch,
could also produce the product PA with two-step process. This
method can be also used for the conversion from glycolic acid
(GA) to acetic acid (AA) and ethylene glycol. The present study
afforded a potential and economical utilization of biomass
carbohydrates into PA by the novel chemical method.
17. F. Jin and H. Enomoto, Energy Environ. Sci., 2011, 4,
382-397.
18. L. Testova, K. Nieminen, P. A. Penttila, R. Serimaa, A.
Potthast and H. Sixta, Carbohydr. Polym., 2014, 100
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Acknowledgements
22. G. Miao, C. C. Zhu, J. J. Wang, Z. C. Tan, L. Wang, J. L.
Supported by the State Key Program of National Natural
Science Foundation of China (Grant No. 21436007). Key Basic
Research Projects of Science and Technology Commission of
Shanghai (14JC1403100). The Program for Professor of Special
Appointment (Eastern Scholar) at Shanghai Institutions of
Higher Learning (ZXDF160002). We thank the all reviewers and
editors for reviewing the manuscript and providing valuable
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Green Chemistry
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DOI: 10.1039/C6GC03036J
Chemoselective synthesis of propionic acid from biomass and lactic
acid over cobalt catalyst in aqueous media
Zhibao Huo,* Jiefeng Xiao, Dezhang Ren, Fangming Jin,* Tian Wang, Guodong Yao