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J. of Supercritical Fluids 65 (2012) 39– 44

Contents lists available at SciVerse ScienceDirect

The Journal of Supercritical Fluids

jou rn al h om epage: www.elsev ier .com/ locate /supf lu

roduction of organic acids from alginate in high temperature water

aku Michael Aidaa,∗, Takuji Yamagataa, Chihiro Abea, Hajime Kawanamib, Masaru Watanabec,ichard L. Smith Jr. a,c

Graduate School of Environmental Studies, Tohoku University, Aramaki Aza Aoba 6-6-11, Aoba-ku, Sendai 980-8579, JapanResearch Center for Compact Chemical System, National Institute of Advanced Science and Technology, Sendai 983-8551, JapanResearch Center of Supercritical Fluid Technology, Tohoku University, Aramaki Aza Aoba 6-6-11, Aoba-ku, Sendai 980-8579, Japan

r t i c l e i n f o

rticle history:eceived 22 December 2011eceived in revised form 10 February 2012ccepted 14 February 2012

eywords:lginate

a b s t r a c t

Hydrothermal treatment was conducted on alginate in the interest of obtaining organic acids. Formicacid, acetic acid, lactic acid, glycolic acid, 2-hydroxybutyric acid, succinic acid, malic acid, mannuronicacid and guluronic acid were obtained by the hydrothermal treatment of alginate. The total yield of theorganic acids were 46% at maximum yield 350 ◦C, 40 MPa and 0.7 s reaction time. The formation of organicacids, suggest that the carboxyl group structure of the alginate was preserved during the hydrothermaldecomposition of the alginate. The formation of dicarboxylic acids is evidence that oxidation reactions

iomassigh temperature wateractic acidalic acidrganic acid

occur during the hydrothermal treatment, introducing carboxyl groups into the decomposition prod-ucts. The product distribution indicates that both acid and base catalyzed reactions occurred during thehydrothermal treatment of alginate. Hydrothermal treatment of an uronic acid, glucuronic acid, gavethe same organic acids as those obtained from hydrothermal treatment of alginate. The reaction fromalginate to organic acids probably proceeds via the formation of hexuronic acid (mannuronic acid andguluronic acid) under hydrothermal conditions.

. Introduction

The production of organic acids from biomass products is ofreat importance in future industries considering the impendinghortage of oil [1–3]. Current methods for producing organic acidsrom biomass require multi-steps such as the conversion of biomasso glucose that is followed by fermentation of glucose to the desiredrganic acids [2,4,5]. Due to the structural differences betweeniomass and the desired organic acid, the chemical conversion ofellulose or glucose to these organic acids does not readily occur6–13] and metal salts [14], or base [15] catalysts and oxidationgents such as hydrogen peroxide [16–18] are often required.

Alginate has a chemical structure that consists of two uroniccids each containing a carboxyl group in its structure and is theajor content of sea algae [19]. Ideally, a high yield of organic

cid could be produced by simple decomposition of the alginatend maintaining its carboxyl group structures. The production ofrganic acids from alginate have been reported by Niemelä andjöström [20]. In that study, those authors treated alginate under

lkali (NaOH) aqueous conditions at temperatures from 95 to35 ◦C and identified the production of monocarboxylic acid andicarboxylic acids in their products. Matsushima et al. [21] treated

∗ Corresponding author. Tel.: +81 22 795 5863; fax: +81 22 795 5863.E-mail address: aida@scf.che.tohoku.ac.jp (T.M. Aida).

896-8446/$ – see front matter © 2012 Elsevier B.V. All rights reserved.oi:10.1016/j.supflu.2012.02.021

© 2012 Elsevier B.V. All rights reserved.

alginate in sub- and supercritical water in the interest of controllingthe decomposition of the polymer, however did not report the pro-duction of organic acids. In our previous research [22], we treatedalginate with high temperature water (180–250 ◦C) without anyadditives and found that the decomposition of alginate occurredreadily at the glycoside bonds of the alginate polymer chain and thisproduced alginate oligomers and monomeric compounds such asmannuronic acid and guluronic acid. Among the reaction products,glycolic acid and lactic acid were detected, which are candidateplatform chemicals for future biomass-based chemical industries[2,23]. These findings gave us the motivation to study the decom-position of alginate in water temperatures higher than 250 ◦C suchthat acid and base catalyzed reaction pathways are enhanced [6].

The objective of this work is to study the conversion of algi-nate to organic acids in hot (150 ◦C, saturation pressure) and hightemperature water (300 and 400 ◦C, 40 MPa). To explore the reac-tion mechanism of alginate, reaction of a hexuronic acid in hightemperature water (300 ◦C, 20 MPa) was also studied.

2. Experimental

2.1. Materials

Sodium alginate (300–400 MPa s) was purchased from WakoPure Chemical Industries. The characteristics of the sodium

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lginate, used in this work are shown in supplementary materialable S1.

Distilled water with a conductivity of 5.5 �s m−1 was preparedy a distillation apparatus (Yamato Co., Model WG-220). Formiccid (>99%, Wako Chemicals), acetic acid (99.7%>, Wako Chemi-als), lactic acid (85%, Wako Chemicals), glycolic acid (>98%, Tokyohemical Industry Co., Ltd., Saitama, Japan), 2-hydroxybutyriccid (Tokyo Chemical Industry Co., Ltd., Saitama, Japan), dihy-roxyacetone dimer (96%, Tokyo Chemical Industry Co., Ltd.,aitama, Japan), glucuronic acid (Sigma–Aldrich), succinic acid>98%, Wako Chemicals) and malic acid (>99%, Wako Chemicals), N-rimethylsilylimidazole in pyridine solution (TMSI-C) (GL-Sciencenc., Fukushima, Japan). Pullulan standards P-82 with known

olecular weight, from 5.9 to 404 kDa, was purchased from Showaenko and was used for the calibration for the GPC analysis.annuronic acid and guluronic acid standards were prepared byethods in the literature [24], and showed no other peaks when

nalyzed by HPLC.

.2. Analytical methods

Product identification in the product effluent was conductedy GC–MS analysis. Prior to the GC–MS analysis, the effluent wasreeze dried and treated with N-trimethylsilylimidazole in pyridineolution (TMSI-C) at room temperature. The TMSI-C treated sam-les were analyzed by GC–MS (GC 5975, Agilent) equipped withgilent HP-5ms capillary GC column (30 m × 0.25 mm × 0.25 m)nd operated at a constant flow rate of He carrier. The tempera-ure program for the GC was as follows: initial oven temperaturef 50 ◦C, then heating to 230 ◦C at a heating rate of 10 ◦C/min andhen held at constant temperature for 9 min. Both retention timend mass spectra fragment patterns of TMSI-C treated standardolution were used for confirmation of the compound. A represen-ative GC–MS chart of product effluent of hydrothermal treatmentf alginate is shown in supplementary material Fig. S1.

The products in the effluent were quantified by HPLC analysis.hree different HPLC systems (HPLC-I, HPLC-II and HPLC-III) weresed for the quantification of the products due to the observedeak overlap in the chromatograms. Typical HPLC chromatogramsf HPLC-I, HPLC-II and HPLC-III for the same experimental sam-le (350 ◦C, 40 MPa and 0.7 s residence time) are shown inupplementary material Fig. S2a–c, respectively. Products (1), (2),3), (7) were quantified by HPLC-I. Product (4) was quantified byPLC-II. Product (5), (8), (9) and (10) were quantified by HPLC-

II. Acetic acid (2) was only obtained in trace amounts and wasot quantified. A representative HPLC chromatogram of prod-ct effluent of hydrothermal treatment of alginate is shown inupplementary material Fig. S2.

HPLC-I was configured with a Shodex 8.0 mm × 300 mm KC-811olumn, column oven temperature 80 ◦C, mobile phase; 0.5 mMhosphoric acid aqueous solution at a flow rate of 1 cm3/min. Theonfiguration of HPLC-II and HPLC-I were the same, except the ovenemperature was 60 ◦C for HPLC-II. HPLC-III was configured with ahodex 4.6 mm × 150 mm SH-1011 column, column oven temper-ture 60 ◦C, mobile phase; 0.04 M sulfuric acid aqueous solution at

flow rate of 1.0 cm3/min. All compounds were quantified usingefractive index. UV detectors with a wavelength set to 210 nmere used for qualitative analyses. The product yields were cal-

ulated on a carbon yield basis.The molecular weight distribution of the raw alginate solution

nd the effluent was evaluated by gel permeation chromatographyGPC) analysis. The GPC system was configured with a Asahipak

S-220HQ column and GS-520HQ column (Showa Denko), columnven temperature at 60 ◦C, mobile phase was NaNO3 aqueous solu-ion 0.3 M, at a flow rate of 1.0 cm3/min. The calibration of the GPCas conducted with using pullulan p-82 standards.

cal Fluids 65 (2012) 39– 44

The carbon recovery of the experiment was evaluated by analyz-ing the solution prior to and after the hydrothermal treatment witha total organic carbon detector (Shimadzu, model TOC-5000A).

The TOC analysis of the alginate solution prior to the hydrother-mal treatment did not show good reproducibility probably due tothe high viscosity of the solution. Therefore, pretreatment of thealginate solution by acid decomposition with HCl at mild condi-tions (90 ◦C), followed by a neutralized with NaOH was conductedbefore TOC analysis. On the other hand, the TOC analysis of the efflu-ent showed good reproducibility and therefore pretreatment of theeffluent was not required. Details are shown in the supplementarysection.

2.3. Procedure for hydrothermal treatment of alginate

Hydrothermal treatment of alginate at 150 ◦C was conductedin a batch type apparatus for reaction times from 30 to 90 min.Hydrothermal treatment of alginate at high temperatures (>350 ◦C)were conducted with a continuous flow type reactor for better con-trol of the reaction temperature and residence times.

Hydrothermal treatment of alginate in hot water 150 ◦C wasconducted by the following procedure. First, a 3 g sample of algi-nate solution (1 wt%) was loaded in a 6 ml SUS316 stainless steelbatch reactor. The reactor was purged with nitrogen for removal ofoxygen and sealed under a nitrogen atmosphere. The reactor wasthen introduced into a fluidized sand bath set at 150 ◦C for 30, 60and 90 min. After the reaction, the reactor was quenched in a coldwater bath. The reaction time was defined as the time from intro-ducing the reactor into the fluidized sand bath to quenching thereactor in the water bath. The time required to reach the reactiontemperature water was 2 min and the time required for cooling was2 min. The contents of the reactor was washed with distilled waterand collected for analysis.

Hydrothermal treatment of alginate in high temperature waterwas conducted in a continuous flow type reactor described in pre-vious work [25]. Distilled water was fed into the apparatus by apump at a flow rate of 20 cm3/min and then it was preheated tosupercritical conditions (about 500 ◦C) before entering a mixingtee. From a different line, a 1 wt% alginate solution, kept at roomtemperature, was fed into the mixing point by a pump at a flowrate of 10 cm3/min. The reaction was initiated by the rapid mix-ing of the preheated water and alginate solution at the mixing teeand achieving the reaction temperature. The concentration of thealginate at the mixing point was calculated by the concentrationof the alginate before entering the mixing tee and the flow ratesof the two streams. This reaction stream passed through a reac-tor tube (0.9 mm i.d.) controlled at the reaction temperature. Thelength of the reactor tube was varied from 20 to 80 cm, accordingto desired reaction time (0.1–0.8 s). After the stream passed thoughthe reactor tube, it was cooled by a heat exchanger to terminate thereaction. The stream was depressurized by passing through twoback pressure regulators (Koatsu-System Co. Ltd., Saitama, Japan,model PR-300M) and the effluent was collected for analysis. Experi-ments were conducted at 350 and 400 ◦C and at pressure of 40 MPa.Each high pressure experiment was repeated at least three times,in which the temperature and flow rate were held and pressureswere cycled among the runs to reduce the influence of possiblesystematic errors. The average yields and the reproducibility wereevaluated.

3. Results

The compounds detected from GC–MS analysis and HPLC analy-sis of the effluent were formic acid (1), acetic acid (2), lactic acid (3),glycolic acid (4), 2-hydroxybutyric acid (5), dihydroxyacetone (6),

T.M. Aida et al. / J. of Supercritical Fluids 65 (2012) 39– 44 41

nt of a

sawhto

3t

sdwncTrp

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Fig. 1. Products obtained from hydrothermal treatme

uccinic acid (7), malic acid (8), mannuronic acid (9) and guluroniccid (10) which are shown in Fig. 1. Fig. 2 shows the moleculareight distribution in the product effluent at hot water (150 ◦C) andigh temperature water (350 and 400 ◦C) conditions. Table 1 showshe carbon balance and the product distribution of the productsbtained in this work.

.1. Decomposition of alginate in hot water (150 ◦C) and highemperature water (350 and 400 ◦C)

Under hot water (150 ◦C) conditions, the production of wateroluble compounds from alginate proceeds mainly through theecomposition of alginate to lower molecular weight compoundshich have molecular weights above its unit hexuronic acid (man-uronic acid and guluronic acid), as shown in Fig. 2a. Insoluble

ompounds such as solids were observed in the product effluent.he formation of solids in the effluent indicates polymerizationeactions also occurred at these conditions. Water soluble com-ounds such as formic acid, malic acid, succinic acid, glycolic acid,

able 1eaction conditions, carbon balances and product distribution from hydrothermalreatment of alginate.

T (◦C) P (MPa) Reaction time Carbon recovery (%)

150 Sat. vap. 30 min 92 ± 160 min 88 ± 190 min 86 ± 1

350 40 0.2 s 89 ± 20.7 s 84 ± 1

400 40 0.1 s 92 ± 20.5 s 90 ± 4

lginate in high temperature water at 350 and 400 ◦C.

mannuronic acid and guluronic acid were detected although, thetotal yield of these compounds was low (22%). These results indi-cate that the decomposition of alginate in hot water proceeded tocompounds with fairly high molecular weight. Therefore, we exam-ined high temperature and short reaction times to possibly converthigh molecular weight products to organic acids.

As shown in Fig. 2b, at high temperature water (>350 ◦C) con-ditions, the decomposition of alginate proceeded to compoundshaving molecular weight below the unit hexuronic acid. HPLC anal-ysis gave the identified organic acids with a total yield of 46% (Fig. 3).No solid formation was observed for the hydrothermal treatmentof alginate at 350 and 400 ◦C, however some gas was observed inthe product effluent. Gasification reactions may have occurred dueto the decarboxylation or decarbonylation reaction of the organicacids as discussed later.

3.2. Effect of reaction conditions on organic acid yields

The effect of reaction conditions on organic acid yields will bediscussed using Fig. 3 and Table 2. Organic acids such as lactic acid,2-hydroxybutyric acid (BA), were only obtained for reactions ofalginate at high temperature water (>350 ◦C) and not at hot water(150 ◦C) conditions. At 350 and 400 ◦C conditions, lactic acid, BAand glycolic acid yields increased with increasing reaction time.Lactic acid, BA and glycolic acid are probably the terminal reactionproducts at the given reaction conditions. Lactic acid is fairly stable

under supercritical water conditions [26–28]. Higher temperaturesand longer reaction times than those studied may increase theyield of lactic acid, BA and glycolic acid from alginate. Lactic acid,BA and glycolic acid may well be the final target products for a

42 T.M. Aida et al. / J. of Supercriti

(a) Mannuroni c and Gulu roni c acid Raw alginate

150oC 90 min.

150oC 60 min.

150oC 30 min.

(b)Mannuroni c and Gulu roni c acid

Raw alginate

350 oC, 0.7 s

350 oC, 0.2 s

(c)

Mannuroni c and Guluroni c acid

Raw alginate

400 oC, 0.5 s

400 oC, 0.1 s

10 15 20

Retention ti me [min.]

Fa1

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ig. 2. Comparison between GPC chromatograms of the starting alginate solutionnd product effluent obtained after hydrothermal treatment at temperatures: (a)50 ◦C, (b) 350 ◦C and (c) 400 ◦C.

ydrothermal process [1,2]. The formation of lactic acid and gly-olic acid have been reported from reactions of alginate [20] andexuronic acids [29] under base aqueous conditions at lower tem-erature conditions (130 ◦C). The decrease of guluronic acid andannuronic acid yields with increasing residence time implies that

he reactions to form lactic acid and glycolic acid from these hex-ronic acids occurs in high temperature water conditions withoutatalyst.

Dicarboxylic acids such as malic acid and succinic acid werebtained under hot water (150 ◦C) and high temperature water>350 ◦C) conditions. At 150 ◦C, both malic acid and succinic acid

ncreased in yield with increasing reaction time. The maximumield for succinic acid 3.1%, was obtained at hot water conditions150 ◦C). This indicates that succinic acid is not thermally stable

ig. 3. Product yields of organic acids obtained from hydrothermal treatment oflginate.

cal Fluids 65 (2012) 39– 44

under high temperature water conditions. At 350 and 400 ◦C, bothmalic acid and succinic acid yields decreased with increasing reac-tion time. This indicates that secondary reactions from malic acidand succinic acid occurred at high temperature water conditions.Hot water conditions and long reaction times may increase theyield of succinic acid. The maximum yield for malic acid 14% wasobtained at high temperature water conditions (350 ◦C and 0.2 s).Higher temperatures (>400 ◦C) and shorter reaction times thanthose studied may increase the yield of malic acid.

The formation of malic acid and succinic acid from alginate havebeen reported under base aqueous conditions at lower tempera-tures (130 ◦C) [20]. The reaction pathway from alginate to thesedicarboxylic acids begins with the deploymerization of alginateby the �-elimination (so called peeling reaction)[30], followed bythe Lorby de Bruyn–Alberta van Ekenstein Transformation (LBET)and a series of hydrolysis and dehydration reactions. The detailsof the reaction mechanisms are in the literature[20]. Nevertheless,the results show that products that would be formed under basecatalyzed reactions also occur in high temperature water withoutcatalyst.

Formic acid was obtained in both hot water (150 ◦C) and hightemperature water (>350 ◦C) conditions giving a maximum yield of12%. At 400 ◦C, formic acid decreased with increasing reaction time.The consumption of formic acid may be due to the decarboxylationreactions and decarbonylation reactions that are reported to occurreadily under high temperature water conditions [31]. At 150 ◦C,formic acid yield increased with increasing reaction time giving amaximum yield of 12% at 150 ◦C at 90 min. This indicates that thedecarbonylation reaction and decarboxylation reaction of formicacid may not have occurred readily as it did in high temperaturewater (>350 ◦C) conditions. The suppression of decarbonylationand decarboxylation reactions is important to obtain high yields oforganic acids from hydrothermal treatment of alginate. Long reac-tion times under hot water conditions may lead to the formationof formic acid.

Hexuronic acids (mannuronic and guluronic acid) were obtainedunder hot water (150 ◦C) and high temperature water (>350 ◦C)conditions. At 150 ◦C, increasing the reaction time increased thecombined yields of these hexuronic acids up to 2.4%. The maxi-mum total yield of the hexuronic acids was 3.7% that was obtainedat 350 ◦C and 0.2 s. At high temperature water (>350 ◦C) conditions,the combined hexuronic acid yield decreased with increasing res-idence time at constant reaction temperature. This indicates thatreaction pathways from hexuronic acids to other compounds exist.The examination of this pathway will be considered next.

Uronic acids are obtained though the hydrolysis of the 1,4 glyco-side bonds of alginate. The hydrolysis of alginate is an acid catalyzedreaction [32]. On the other hand, the formation of dicarboxylic acidsoccur under base catalyzed conditions [20]. Under base catalyzedconditions the decomposition of alginate in water occurs throughthe �-elimination of the 1,4 glycoside bonds (peeling mechanism)[20,30]. These results suggest the decomposition of alginate occursboth by hydrolysis and �-elimination reaction. Both acid and basecatalyzed reaction pathways of alginate may be promoted by thehigh Kw value of high temperature water [33].

3.3. Hydrothermal treatment of glucuronic acid at 300 ◦C

The chemistry of hexuronic acids under acid [34], base [29] andneutral [35] aqueous solutions at temperatures below 130 ◦C, havebeen studied extensively. To understand if the reaction pathwayfrom alginates to organic acid proceeds via the formation of hex-

uronic acids in high temperature water, reactions starting frommannuronic acid or guluronic acid would be a logical system tostudy. However, mannuronic acid and guluronic acid are not com-mercially available and they are difficult to obtain in large amounts.

T.M. Aida et al. / J. of Supercritical Fluids 65 (2012) 39– 44 43

Table 2Reaction conditions and product distribution and yields obtained from hydrothermal treatment of alginate.

T (◦C) P (MPa) Reaction time Product yield [%Cbase]

(1) (4) (3) (5) (7) (8) (9) + (10) Total

150 Sat. vap. 30 min 1.3 0.2 0.0 0.0 1.2 0.9 1.1 4.760 min 6.1 1.0 0.0 0.0 1.8 3.5 2.3 14.790 min 10.6 1.4 0.0 0.0 3.1 4.8 2.4 22.3

350 40 0.2 s 11.0 1.9 5.8 4.7 2.1 14.0 3.7 43.29.9 8.3 1.0 10.4 1.7 45.89.6 6.8 1.6 11.1 2.4 45.6

12.3 8.5 1.3 2.6 0.8 36.3

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Table 3Comparison of products obtained from the hydrothermal treatment of cellulose andalginate in high temperature water (>300 ◦C).

Startingmaterial

Treatment Products

Cellulose Hydrothermal [9,38,39] Cellulose oligomers, glucose,fructose

Glucose Hydrothermal [25,40–43] Dihydroxyacetone, glycolaldehyde,erythrose, glyceraldehyde,pyruvaldehyde

Base [18] Lactic acid, acetic acid, formic acid,glycolic acid

Acid [38,44] 5-HMF, furfuralOxidation [16] CO2, acetic acid, formic acid

Alginate Hydrothermal (this work) Mannuronic acid, guluronic acid,formic acid, glycolic acid, lacticacid, malic acid, succinic acid,

0.7 s 11.5 3.0

400 40 0.1 s 10.1 4.0

0.5 s 6.8 4.0

suki et al. [36] treated hexuronic acid (galactsuronic acid and glu-ronic acid) in high temperature water conditions (up to 240 ◦C)n the interest of studying the decomposition kinetics and reportedhe pH of the effluent decreased as the decomposition of the starting

aterial proceeded, suggesting production of acidic organic com-ounds, however the product distribution was not reported. In thisork, we investigated the reactions of commercially available glu-

uronic acid, in high temperature water (300 ◦C, 20 MPa and 13 s)n interest of understanding the reaction pathways from alginateo organic acids.

Fig. 4 shows the GC–MS chromatogram of hydrothermal treat-ent of glucuronic acid at 300 ◦C and 20 MPa for 13 s residence

ime. The products detected from the GC–MS were formic acid (1),cetic acid (2), lactic acid (3), glycolic acid (4), 2-hydroxybutyriccid (5), succinic acid (7) and malic acid (8) and glucuronolactone11). The organic acids obtained from hydrothermal treatment oflucuronic acid and alginate were the same except for glucurono-actone (11). These results suggest that organic acids obtained fromhe hydrothermal treatment of alginate proceeded via hexuroniccids (guluronic acid and mannuronic acid). The formation of dicar-oxylic acids such as succinic acid and malic acid indicate the-elimination reaction of glucronic acid at the carbon 4 positionccurred, which usually only occurs under basic conditions [29,35].olysaccharides consisting of uronic acids probably are good start-ng materials for producing organic acids.

.4. Comparison of products obtained from hydrothermalreatment of cellulose and alginate

The comparison of the products obtained from hydrothermalreatment of cellulose, glucose and alginate is shown in Table 3.he hydrothermal treatment with and without additives have beeneported in a number of reviews [6,12,37], where the hydrother-al treatment of cellulose[9,38,39] or glucose [25,40–43] mainly

esults in cellulose oligomers, sugars and aldehydes. Hydrother-al treatment of cellulose and glucose with base catalyst result in

rganic acids [18], and acid catalyst give furans such as 5-HMF andurfural [38,44].

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4

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ig. 4. GC–MS chromatograms of the TMS pretreated effluent obtained by theydrothermal treatment of Glucuronic acid in high temperature water at 300 ◦C,0 MPa and 13 s.

2-hydroxybutyric acid,dihydroxyacetone

The hydrothermal treatment of alginate gives many types oforganic acids (Table 3). This indicates that the carboxyl group in thealginate polymer chain is preserved as the decomposition proceedsto the products. Considering the chemical structure of alginate, theproduction of dicarboxylic acids such as succinic acid and malicacid are evidence that oxidation reactions introducing additionalcarboxyl groups also occurred during the hydrothermal decompo-sition of alginate. In the work of Ross et al. [45], cyclic compoundssuch as phenol, furan cyclopentenone derivatives were obtainedfrom pyrolysis of alginates. In Klingler and Vogel [16], organic acidssuch as acetic acid, succinic acid, glycolic acid and formic acid wereobtained from the oxidation of glucose under high temperaturewater (250–480 ◦C, 25–34 MPa) using hydrogen peroxide. In theirwork they concluded that the organic acids formed by decompo-sition of glucose was followed by oxidation. Further investigationof the reaction pathways of alginate to these organic acids is aninteresting future topic.

4. Conclusion

In this work we studied the hydrothermal treatment of alginatefrom 150 to 400 ◦C. Organic acids such as formic acid, lacticacid, 2-hydroxybutyric acid, glycolic acid, succinic acid, malicacid, guluronic acid and mannuronic acid were obtained fromthe hydrothermal treatment of alginate at high temperatures(150–400 ◦C). The major reaction at 150 ◦C conditions were thedecomposition of alginate into low molecular weight polymers,where at 350 and 400 ◦C conditions, alginate was convertedinto compounds below its unit hexuronic acid. Increasing thereaction temperature from 150 ◦C to 350 and 400 ◦C enhancedthe conversion of alginate to low molecular organic acids and

increased the total yield of the organic acids to a maximum yieldto 46% at 350 ◦C, 40 MPa and 0.7 s reaction time. Lactic acid and2-hydroxybutyric acid were obtained at 350 and 400 ◦C conditionsbut not at 150 ◦C. Hydrothermal treatment of a hexuronic acid

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glucuronic acid) at 300 ◦C gave products such as formic acid, lacticcid, 2-hydroxybutyric acid, glycolic acid, succinic acid and maliccid. The reactions of alginate to these organic acids probablyroceeded via the production of the unit hexuronic acid of alginatemannuronic acid and guluronic acid). The formation of organiccids and hexuronic acids (guluronic acid and mannuronic acid)uggest reactions of alginate occur both through base and acidatalyzed reaction pathways in high temperature water. Alginiccid and alginate containing marine algae can be a promisingeedstock for future biomass refinery processes.

cknowledgments

Drs. A. Kobayashi, M. Noguchi, and M. Ishihara of Tohoku Univer-ity, are gratefully acknowledged for their constructive commentsuring the preparation of this manuscript. Dr. S. Mochizuki andr. S Kayamori of the Instrumental Analysis Group (Tohoku Uni-

ersity) provided much support for the GC–MS and NMR analysis.e would like to thank Dr. Masao Konno, Riken Shokuhin Co.

td. (Japan, Miyagi), for providing the monosaccharides standards.inancial support from Japan Society for the Promotion of Scienceith Grant-in-Aid for Scientific Research is gratefully acknowl-

dged.

ppendix A. Supplementary data

Supplementary data associated with this article can be found, inhe online version, at doi:10.1016/j.supflu.2012.02.021.

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