Oleic acid-enhanced dissolution of cellulose in high-temperature water

Article abstract of DOI:10.1007/s11164-011-0271-5

This paper reports, for the first time, the enhanced dissolution of cellulose in subcritical water by addition of a fatty acid. Simply adding oleic acid dramatically promoted the dissolution of cellulose. High-pressure in-situ observation showed that cellulose dissolved in high-temperature water at approximately 500 K, which is 70 K lower than without oleic acid. The yield of oligo and monosaccharides with oleic acid at 473 K was seven times higher than without oleic acid.

Full text of DOI:10.1007/s11164-011-0271-5

Res Chem Intermed (2011) 37:415–419
DOI 10.1007/s11164-011-0271-5
Oleic acid-enhanced dissolution of cellulose
in high-temperature water
•
Kimitaka Minami Shiori Goto
•
•
Mehrnoosh Atashfaraz Takanari Togashi
•
•
•
•
Toshihiko Arita Daisuke Hojo Seiichi Takami
Tadafumi Adschiri
Received: 23 July 2010 / Accepted: 25 December 2010 / Published online: 12 February 2011
Ó Springer Science+Business Media B.V. 2011
Abstract This paper reports, for the first time, the enhanced dissolution of cel-
lulose in subcritical water by addition of a fatty acid. Simply adding oleic acid
dramatically promoted the dissolution of cellulose. High-pressure in-situ observa-
tion showed that cellulose dissolved in high-temperature water at approximately
500 K, which is 70 K lower than without oleic acid. The yield of oligo and
monosaccharides with oleic acid at 473 K was seven times higher than without oleic
acid.
Keywords Biomass Á Supercritical water Á Fatty acid Á Co-solvent
Introduction
Bio-ethanol synthesis is a promising biomass conversion method. Biomass is an
important resource that can be converted into ethanol for use as fuel. In this case,
pretreatment to decompose biomass to compounds that can be easily converted to
ethanol with yeast is necessary. In particular, cellulose, which is a major component
of the biomass, is expected to decompose to glucose. Thus far, various methods that
use acid catalysts, for example sulfuric acid, have been proposed for hydrolysis of
cellulose to recover glucose. However, acid-catalyzed reactions require further
environmental considerations and post-reaction separation steps.
K. Minami Á M. Atashfaraz Á T. Togashi Á D. Hojo Á T. Adschiri (&)
WPI Advanced Institute for Materials Research, Tohoku University,
2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan
e-mail: ajiri@tagen.tohoku.ac.jp
S. Goto Á T. Arita Á S. Takami Á T. Adschiri
Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 2-1-1 Katahira,
Aoba-ku, Sendai 980-8577, Japan
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K. Minami et al.
Sasaki et al. [1–3] reported that solid cellulose dissolved in supercritical water
without any catalyst. They also demonstrated that, after supercritical water
treatment, the aqueous cellulose solution could be hydrolyzed to glucose by use
of cellulase at a rate approximately 700 times faster than for untreated cellulose
particles [1]. This is obviously because of homogeneous phase enzymatic hydrolysis
of the cellulose solution. However, this process uses much energy, because this
treatment requires temperatures above 573 K. Thus, dissolving cellulose in lower-
temperature water is an important objective.
Many methods are used for dissolving cellulose in solvent, even at room
temperature [4]. The structure of cellulose has a hydrophilic part that participates in
hydrogen bonding and a hydrophobic part that occurs on the surface [5]. To dissolve
cellulose, solvents should have affinity for the hydrophobic part and break the
hydrogen bonding. A mixture of a polar organic solvent, for example dimethyl-
formamide, and a Lewis acid, for example lithium chloride, has this feature and is a
commonly used cellulose-dissolution solvent for scientific research.
Because fatty acids have both hydrophilic and hydrophobic parts, they may have a
similar effect on dissolution of cellulose. Furthermore, fatty acids are appropriate for
industrial use because they are abundant biomass products and sometimes waste
products of the triglyceride oil recovery process. Interestingly, although the solubility of
fatty acids in water is poor at ambient temperatures, at higher temperatures and higher
pressures fatty acids are soluble in water [6]. Thus, the combined process of cellulose
pre-treatment and waste fatty acid treatment in high-temperature water might be both
environmentally benign and economical. Further, after the treatment, fatty acids can be
separated from water by appropriate reduction of the temperature and pressure.
In this paper, we describe, for the first time, the effect of a fatty acid on
promoting the dissolution of cellulose in subcritical water. In-situ observation of
cellulose dissolution in subcritical water, with and without the fatty acid, and
product analysis were conducted.
Experimental
Experiments were conducted with batch reactors made of Hastelloy-C. The internal
reactor volume was 5.0 cm3. Microcrystalline cellulose was purchased from MERK.
Oleic acid (60%, Wako Pure Chemical Industries) and 10% (w/w) cellulose aqueous
slurry were loaded into the reactor. Loaded reactors were heated and shaken for
10 min in an electric furnace with the temperature controlled at 323–523 K. The
heat-up time was about 3–5 min. The reactors were then removed from the electric
furnace and rapidly quenched in a water bath. Cooling to room temperature required
approximately 1 min. After the reactors were cooled, the products in the reactors
were recovered with 20 cm3 of rinsing water. The products were separated from
oleic acid by centrifugation. Identification and quantification of the water-soluble
products and the precipitates were conducted by high-performance liquid chroma-
tography (HPLC–RI, Shodex KC-811 column, mobile phase; pure water at
1 mL/min) and X-ray diffraction (XRD, Rigaku RINT-2000). Details of the
analytical procedures have been reported elsewhere [1–3].
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Oleic acid-enhanced cellulose dissolution
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For direct observation of the cellulose in subcritical water with and without oleic
acid, a high-temperature and high-pressure optical cell (Taiatsu Techno, TSC-WC-
00014) with a Hastelloy-C body and sapphire windows was used. The cell volume
was 1.4 cm3. Cellulose powder was put on the bottom window and oleic acid was
loaded into the cell. After capping with an upper window, pure water was
introduced to 30 MPa by use of a high-pressure pump (Jasco PU-2086) and a back
pressure regulator (Tescom, model 26-1762-24). The temperature was monitored by
use of a thermocouple (K type) in the cell and was controlled by four cartridge
heaters installed in the cell body. The pressure was kept at 30 MPa by use of a back-
pressure regulator while increasing the temperature.
Results and discussion
The HPLC–RI chromatograms of the liquid products at temperatures from 323 to
473 K, with and without oleic acid, are shown in Fig. 1. When oleic acid was added,
recovery of hydrolysis products (oligosaccharide, cellobiose, glucose, and fructose)
at 473 K increased rapidly, compared with that at 323 and 373 K. Further, the
recovery was higher than that for water only at the same temperature. When oleic
acid was used, the amounts of oligosaccharide, cellobiose, and monosaccharide
obtained were, respectively, 4.5, 15, and 19 times those obtained without oleic acid.
The yield of hydrolysis products with oleic acid was, in total, seven times higher
than that without oleic acid. These results mean that cellulose dissolution and
hydrolysis were accelerated by addition of oleic acid.
From the XRD peaks of precipitates collected after treatment at 503 and 523 K,
shown in Fig. 2, when oleic acid was added cellulose II crystals appeared, as
reported by Sasaki et al. [2] for supercritical water treatment. These results suggest
that cellulose was dissolved by treatment with subcritical water and the fatty acid.
The hydrolysis reaction might be promoted by the acidity of the oleic acid.
Fig. 1 Chromatograms
obtained from recovered liquid
samples
Cellobiose
Glucose
Oligosaccharide
323 K with Oleic acid
373 K with Oleic acid
473 K with Oleic acid
473 K without Oleic acid
Fructose
0
10
20
Retention time [min]
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K. Minami et al.
Crystal I
Crystal I
Fig. 2 XRD peaks of collected
precipitates
Crystal I
without oleic acid
523 K
Crystal II
Crystal I
with oleic acid
523 K
503 K
473 K
373 K
30
10
20
40
2θ
(a) 553 K
(b) 563 K
(c) 573 K
(d) 423 K
(e) 473 K
(f) 503 K
Fig. 3 Direct observation of cellulose in water at 30 MPa: a–c without oleic acid; d–f with oleic acid
Direct observation of cellulose at high temperature and high pressure was
achieved by use of a Hastelloy cell with sapphire windows. The temperature was
increased from room temperature to 573 K in 15 min at a constant rate. Typical
examples of the observation results in water without oleic acid are shown in
Fig. 3a–c. In these images, the white dots are cellulose particles. At approximately
573 K, the cellulose particles disappeared, which indicates that cellulose dissolves
in pure water at approximately 573 K—the same result reported by Sasaki et al. [3]
When oleic acid was added, however, the cellulose particles disappeared at
temperatures as low as 473–503 K, as shown in Fig. 3d–f.
Because oleic acid has both hydrophilic and hydrophobic parts, it acts as a
surfactant. The cellulose structure also has both hydrophilic and hydrophobic parts;
the hydrophilic parts are between cellulose molecules and the hydrophobic parts are
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Oleic acid-enhanced cellulose dissolution
419
on the surface of the structure. The dissolution of cellulose was probably promoted
by the effect of the oleic acid as a surface-active agent.
In summary, the dissolution and hydrolysis of cellulose in subcritical water was
efficiently accelerated in the presence of oleic acid, compared with pure subcritical
water, because oleic acid has surface activity and acid catalyst effects.
References
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2. M. Sasaki, T. Adschiri, K. Arai, AIChE J. 50, 192 (2004)
3. M. Sasaki, Z. Fang, Y. Fukushima, T. Adschiri, K. Arai, Ind. Eng. Chem. Res. 39, 2883 (2000)
4. H. Schneicher, Acta Polym. 34, 63 (1983)
5. L.M.J. Kroom-Batenburg, J. Kroon, M.G. Nordholt, Polym. Commun. 27, 290 (1986)
6. M. Watanabe, T. Iida, H. Inomata, Energy. Conv. Manage. 47, 3344 (2006)
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