A low-cost method for obtaining high-value bio-based propylene glycol from sugar beet pulp

Article abstract of DOI:10.1039/c4ra12839g

A new low-cost pathway for the production of high-value propylene glycol (PG) is proposed. This route of waste biomass utilization employs catalytic reduction of lactic acid obtained from fermented enzymatic digests of sugar beet pulp. This journal is

Full text of DOI:10.1039/c4ra12839g

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A low-cost method for obtaining high-value bio-
based propylene glycol from sugar beet pulp
Cite this: RSC Adv., 2015, 5, 2299
a
b
a
c
b
J. Berlowska,* M. Binczarski, M. Dudkiewicz, H. Kalinowska, I. A. Witonska
d
and A. V. Stanishevsky
Received 21st October 2014
Accepted 26th November 2014
DOI: 10.1039/c4ra12839g
www.rsc.org/advances
A new low-cost pathway for the production of high-value propylene
Another way of obtaining PG is through the reduction of
13–17
glycol (PG) is proposed. This route of waste biomass utilization lactic acid (LA).
employs catalytic reduction of lactic acid obtained from fermented saccharide feed,
LA can be obtained easily by fermentation of
and is an extremely useful building block
1
5,18,19
enzymatic digests of sugar beet pulp.
in the synthesis of chemicals such as acrylic acid, pyruvic acid,
20
2,3-pentanedione, lactic acid esters and propylene glycol.
Hydrogenation of LA into PG has been performed over sup-
Propylene glycol (PG, 1,2-propanediol) is one of the most
16
ported metallic catalysts, mainly based on ruthenium,
1,2
important raw chemical materials in the world. Desirable
properties such as viscosity, no odour, negligible toxicity and a
low freezing point mean that 1,2-propanediol is in great
21
22
22
22
rhenium, platinum, nickel or copper, under mild condi-
ꢀ
13–16,21,22
tions (0.1–14.5 MPa, 70–240 C).
This pathway for the
transformation of LA into PG is of great interest to
3–6
demand from many branches of industry, including the food,
pharmaceutical and cosmetics industries. However, since
4,23–26
industry.
Researchers from Lodz University of Technology, in cooper-
ation with the Polish National Sugar Company Ltd., have
developed a new method of propylene glycol synthesis via
catalytic hydrogenation of lactic acid obtained by the fermen-
tation of sugar beet pulp hydrolyzates (Fig. 1). The cost of raw
materials is one of the key factors that determine the economic
viability of fermentation processes. Pure glucose, sucrose,
starch, etc. are expensive feedstocks for lactic acid production.
Their replacement with inexpensive substrates, such as dairy
byproducts, food and industrial wastes or agricultural residues
industry uses PG on a very large scale (2.81 million tonnes in
6
2
013, increasing by around 8% each year), the sustainability of
traditional production is threatened by the cost and future
availability of crude oil, as well as by environmental concerns.
Most world production of propylene glycol employs non-
catalytic, high-temperature and high-pressure hydrolysis of
propylene oxide, which is obtained from propylene.
In response to the need for new pathways for the production
of PG using renewable raw materials, a more recent method was
developed which uses hydrogenolysis of glycerol derived mainly
(lignocellulose/hemicellulose hydrolyzates, cottonseed hulls,
7
from soybeans and rapeseed. This process can be performed
corn cob, corn stalks, sugarcane pressmud, cassava bagasse,
cellulose, carrot processing waste, corn ber hydrolysates and
ꢀ
successfully under mild conditions (around 1.5 MPa, 200 C)
using nickel, palladium, platinum, copper and copper-chromite
wheat bran) and glycerol, promises to cut the costs of lactic acid
8–12
catalysts.
However, it is not without disadvantages, most
27–30
production.
Moreover,
nding
economical
and
notably the high cost involved, which if this method were
employed on a large scale would lead to increased food prices
on world markets.
environmentally-friendly uses for byproducts of food processing
furthers the aims of sustainable development in the food
industry.
The choice of substrate is usually a question of geographic
availability. An abundant but underexploited residue in Poland
is sugar beet pulp (SBP), which remains aer sucrose extraction.
To date, SBP has been used mainly as animal feed or, in regions
with no livestock farming, sent to landll. Its low dry-matter
(18–23% w/w) content renders beet residue unsuitable for use
a
Institute of Fermentation Technology and Microbiology, Lodz University of
Technology, Wolczanska 171/173, 90-924 Lodz, Poland. E-mail: joanna.berlowska@
p.lodz.pl
b
Institute of General and Ecological Chemistry, Lodz University of Technology,
Zeromskiego 116, 90-924, Lodz, Poland
c
Institute of Technical Biochemistry, Lodz University of Technology, Stefanowskiego 4/ as a fuel in heat and power production. However, its chemical
1
d
0, 90-924 Lodz, Poland
composition makes it a promising candidate for bio-produc-
Department of Physics, University of Alabama at Birmingham, Birmingham, AL
31
tion. Its qualities include a very low lignin level (around 2% of
3
5294, USA
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Fig. 1 Proposed route of propylene glycol fabrication from sugar beet pulp.
dry matter) and high carbohydrate content (75% w/w of dry
Sugar industry by-products have recently received consider-
matter), including pectin (24–32%), cellulose (22–30%) and able attention as possible feedstocks in the production of value-
3
2,33
31
hemicellulose (22–30%).
converted into hexose and pentose feedstocks for use in various tion of monosaccharides for use in bioethanol or biogas
fermentation processes.
Its principal components can be added products. Studies have focused mainly on the produc-
3
1,34
35
15
synthesis from beet waste biomass. Zheng reports lactic acid
Enzymatic saccharication of this complex material requires yield, carbohydrate loss (cellulose and hemicellulose) and
the concerted action of cellulases, hemicellulases (including lignin removal during ensilage of sugar beet pulp. However,
35
19
arabinosidases) and pectinases. In our research, a mixture of until now only molasses had been used to produce lactic acid.
two commercial multienzyme preparations, Viscozyme and Our research suggests that SBP hydrolysate may be a particu-
Ultrao Max from Novozymes, containing these poly- larly suitable feedstock for microbial lactic acid fermentation.
saccharidases (Table 1), was found to efficiently saccharify
polysaccharides contained in the sugar beet pulp, which was requirements, due to their limited biosynthesis capacity.
Lactic acid bacteria (LABs) have complex nutritional
36,37
simply suspended in warm water to achieve a dry matter Agro-industrial residues, which are rich in carbohydrates, are of
27
concentration of around 10% (w/v). The conditions of sacchar- limited use due to their low protein content. The use for LAB
ication were optimized at the laboratory scale and the cultivation of media derived from plant materials has been
composition of the resulting hydrolysates was determined using considered in many combinations, including with nitrogen and
chemical, enzymatic and HPLC methods. Aer 24 hours of
ꢀ
hydrolysis, conducted at 50 C, glucose yields in the hydroly-
sates were over 30% of the initial sugar beet pulp dry matter.
The dominant reducing sugars released during the process were
glucose (around 30% of the total reducing sugars), arabinose
and galacturonic acid (both around 25%), while xylose
accounted for around 2% of all monosaccharides. Concentra-
tions of fermentation inhibitors, such as furfural and phenolic
ꢁ1
acids, were below 1 mg mL
.
Table 1 Activities of selected glycosyl hydrolases in Viscozyme and
ꢀ
Ultraflo Max multi-enzyme preparations (50 C, pH 5.0)
ꢁ
1
Activity (U mL
Cellulases
)
Enzyme
Invertase
Xylanases
Pectinases
Viscozyme
Ultrao Max
22.6
41.8
63.3
0.3
26.3
53.3
174.6
33.3
Fig.
production.
2 Growth dynamics of 4 LAB strains used for lactic acid
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Table 2 The growth, sugars utilization and lactic acid biosynthesis by four strains of lactic acid bacteria
Sugar utilization [%]
Concentration Yield of lactic
of lactic
acid produced [g] to
substrate consumed [g]
ꢁ1
Microorganism CFU/mL
Glucose Fructose Xylose Rhamnose Raffinose Galactose Arabinose acid [g L
]
8
L. lactis
8.27 ꢂ 10 99.13
98.29
98.92
99.06
98.61
0
3.57
19.02
0
0
0
8.18
7.82
8.47
8.40
0.45
0.39
0.39
0.42
PCM 2379
L. acidophilus
PCM 2510
L. delbrueckii
PCM 490
8
7.95 ꢂ 10 98.90
2.16
6.06
13.66
0
0
0
39.31
43.75
38.23
7.26
13.51
26.34
8
5.48 ꢂ 10 99.97
5.08
0
8
L. plantarum II 2.89 ꢂ 10 99.19
vitamin supplements. Enrichment with nutrients, especially few LAB strains are reported to consume lignocelluloses derived
28,29
with MRS growth medium ingredients (mainly yeast extract, sugars simultaneously.
To obtain the required lactic acid
peptone and meat extract), has in general a positive effect on LA yields from sugar beet pulp hydrolyzate, mixed starter cultures
37
production efficiency. The medium obtained in our experi- could be used as well as sequential inoculation with a strain
ments via hydrolysis was used only as a carbon source, while which has different fermentation abilities. In our study,
non-sugar components of MRS broth provided minerals and complete consumption of glucose and fructose and partial
nutritional ingredients.
utilization of galactose (Lactobacillus strains) and arabinose
The monosaccharide prole of sugar beet hydrolysates was (L. delbrueckii and L. plantarum) was observed with all four
analyzed using high performance liquid chromatography, per- strains. The strains which showed the ability to assimilate the
formed on Waters 600S equipped with a Waters 717 autosam- widest range of carbon sources were isolated from the sugar
pler and a Gilson PrepELS II Light Scattering Detector. Water beet pulp, which had been subjected to enzymatic hydrolysis.
2
+
was used as the mobile phase Ca and sulfonated styrene–
In such complex media as biomass hydrolysates, the pres-
divinylbenzene as the stationary phases in a Rezex™ column. ence of inhibitory substances can cause the elongation of the
The liquid contained around 5.5% (w/v) total reducing saccha- adaptive phase (Fig. 3). Another barrier to using lignocellulosic
rides, including glucose – 1.3%, galactose – 0.7%, xylose – derivatives as fermentation media is that the sugar composition
3
8
0
.55%, rhamnose – 0.5%, arabinose – 0.65%, raffinose – 1.4%, of this biomass is inherently heterogeneous. Moreover, in
and fructose – 0.3%. many lactic acid fermentations, mixed carbohydrate utilization
Three collection strains (Polish Collection of Microorgan- is achieved sequentially, and glucose catabolite repression
28,29
isms) were used in the study: Lactococcus lactis 2379, Lactoba- occurs.
Abdel-Rahman reports lactic acid production (g/g
cillus acidophilus 2510 and Lactobacillus delbrueckii 490, as well substrate consumed) from lignocellulosic biomass materials
as the environmental isolate (from sugar beet pulp) Lactoba- and lignocellulose-derived sugars by lactic acid bacteria in a
cillus plantarum II. Aerobic cultivation of lactic acid bacteria was range from 0.18 for L. delbreuckii NRRL-B445 cultivated on
ꢀ
conducted at 37 C for 48 hours. The growth of bacteria was cellulose to 0.99 for L. delbrueckii UFV H2B20 grown on brewer's
28,29
measured via spectrophotometric (optical density measure- spent grain.
In our study, medium level product yields were
ments) and plate count methods. Lactic acid production was achieved of 0.39–0.45 g LA per g fermentable carbohydrates.
measured by spectrophotometry using a D-/L-lactic acid assay kit However, the fermentation processes were carried out without
(megazyme). All of the strains tested reached the stationary
growth phase aer around 30 hours of cultivation (Fig. 2).
However, the sugar utilization proles and acidication
dynamics were found to be strain-dependent (Table 2 and
Fig. 3). In most cases, lactic acid bacteria such as L. delbrueckii,
L. helveticus and L. acidophilus, are able to convert cellulose-
derived glucose, but not hemicellulose-derived sugars, into
lactic acid. Only certain strains, L. pentosus, L. bifermentans, L.
plantarum, L. brevis, L. delbrueckii, Leuconostoc lactis and Lacc-
toccocus lactis, are also capable of converting xylose into lactic
acid and acetic acid effectively through heterolactic fermenta-
19,20,22
tion.
However, L. lactis PCM 2379 did not utilize pentoses
in our studies. According to Hofvendahl's juxtaposition, sugars
such as xylose, galactose, arabinose, lactose, fructose and
hydrolyzed cellulose are less effective substrates in fermenta-
37
tion processes than glucose. The sequential uptake of various
carbohydrates may, however, result in reduced product yields. A
Fig. 3 Relationship between growth and lactic acid production by the
tested strains of lactic acid bacteria.
4
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Table 3 Catalytic conversion of lactic acid in postfermentation media purified to various degrees. LA was obtained through the biological
synthesis described above
C
0LA
Conversion
of LA [%]
Selectivity
to PG [%]
ꢁ
3
Substrate
[mol dm ]
Water solution lactic acid (CHEMPUR)
0.500
0.094
0.081
0.085
0.080
0.078
97.4
2.4
18.3
90.8
91.1
92.3
62.4
0
67.9
61.7
81.1
64.2
Postfermentation broth L. delbrueckii PCM 490a
Postfermentation broth L. delbrueckii PCM 490b
Postfermentation broth L. delbrueckii PCM 490
b
Postfermentation broth L. lactis PCM 2379b
Postfermentation broth L. acidphilus 2510
a
b
5
0 mL of fermentation broth aer purication on 3 g of Cact. 50 mL of fermentation broth aer purication of on the mixture of 3 g of Cact and 5 g
2
SiO .
the chemical removal of lactic acid and product inhibition is containing calcium lactate is ltered, carbon treated, evapo-
thought to have occurred. rated and acidied using sulfuric acid. Hydrolysis, esterication
In further investigations, biologically obtained lactic acid and distillation are then conducted to obtain pure acid. Draw-
was used as a substrate. Aer the biological process and backs of this method include the large amounts of sulfuric acid
biomass separation, the supernatants were puried on a and calcium sulfate that are, respectively, used and generated as
39
mixture of active carbon and silica and then treated. Lactic acid a by-product.
purication is one of the most costly steps in the production Moreover, impurities contained in the nal product must be
process. In the most common procedures, the fermentation removed, involving additional steps such as extraction, ion
28
13,15,19
medium is neutralized using calcium carbonate. The media exchange, membrane separation or electrodialysis.
Due to
Fig. 4 Conversion of LA (X, %), selectivity to PG (S, %) and yield of PG (Y, %) for hydrogenation of commercial lactic acid over 5%Ru/C catalyst.
ꢀ
Standard reaction conditions: t ¼ 4 h, T ¼ 130 C, mcat ¼ 0.5 g, VLA ¼ 25 mL, C0LA ¼ 0.1 M, pH
2
¼ 3.5 MPa.
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the high cost of purifying media post fermentation, we also
studied the effect of impurities on PG formation over 5%Ru/C
catalyst. The postfermentation medium for L. delbrueckii PCM
4 Z. Zhang, D. J. Miller and J. E. Jackson, US Patent 6,403,844
B1, 2002.
5 T. A. Werpy, J. G. Fryye, A. H. Zacher and D. J. Miller, US
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490 was catalytically reduced as an untreated sample, as well as
the samples which had undergone purication on active carbon
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ꢁ
1
(
ERCARBON GE, 3 g 50 mL ) or on a mixture of active carbon
ꢁ
1
and silica (POCH Gliwice SA, 5 g 50 mL ) (Table 3).
Hydrogenation of LA was performed in a 50 mL autoclave
ꢀ
(
Parr Company) at a temperature of 130 C and under 3.5 MPa of
H pressure. The reactions were conducted with equal amounts
2
of catalyst (mcat ¼ 0.5 g). The mixture was stirred at 500 rpm.
The autoclave was ushed with Ar, then ushed again with H ,
2
and pressurized with H
gradually raised to 130 C at a heating rate of 20 C min . The
reaction was sustained for 4 hours. The reaction conditions
2
to 3.5 MPa. The temperature was
ꢀ
ꢀ
ꢁ1
were optimized for 5%Ru/C catalyst (Sigma-Aldrich, CAS 10 M. G. Musolino, L. A. Scarpino, F. Mauriello and
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A new, bio-catalytic method of propylene glycol production
from enzymatic digests of sugar beet pulp enables the replace-
ment of fossil resources with byproducts from food processing.
Appropriate strains of lactic acid bacteria efficiently convert
sugars contained in enzymatic hydrolysates of SBP into lactate,
which is reduced to propylene glycol via heterogenic catalysis.
2
2
2
2
Acknowledgements
2
2
2
2
The authors would like to acknowledge the contribution of the
National Centre for Research and Development, Applied
Research Programme – Project PBS1/B8/3/2012.
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