Solubility of Carbohydrates in Subcritical Water

Transcription

1 Solubility of Carbohydrate in Subcritical Water Fernando Montañé 1, Tiziana Fornari 2, Elena Ibáñez 1, Keerthi Sriniva 3 Dongfang Zhang 3 and Jerry W. King *3 1 Intituto de Fermentacione Indutriale (CSIC). C/ Juan de la Cierva 3, Madrid, SPAIN 2 Departamento de Ciencia de la Alimentacion, Univeridad Autonoma de Madrid,28049, SPAIN 3 Univerity of Arkana, 1 Department of Chemical Engineering, Fayetteville, Arkana, USA Correponding author: jwking1@uark.edu; Phone: (+1) ; Fax: (+1) ABSTRACT Carbohydrate olubility in water a a function of temperature i important in a wide range of application in food, pharmaceutical, a well a biofuel technology. Both experimental olubility data along with thermodynamic modeling are required for optimizing the proceing of material containing, e.g., to optimize ugar oligomer-monomer production in bioma converion procee. Thi tudy preent an extenive experimental tudy on the meaurement of high temperature aqueou olubilitie of different carbohydrate (glucoe, maltoe, xyloe, etc.) between 20 and 200 C. Sugar olubility data in the ubcritical water region above the boiling point of water i of particular interet ince carbohydrate polymer in variou bioma (celluloe, hemicelluloe) are frequently hydrolyzed under ubcritical water condition. Sugar olubilitie were meaured by a modification of the Miller-Hawthorne [1] continuou flow technique in which the ugar i aturated at variou temperature in a tream of flowing hot water. HPSEC wa ued to meaure ugar olubility in diluted ample taken during the aturation region of olubility meaurement technique. Due to the large increae in ugar olubility with temperature particularly above the boiling point of water adjutment in the ize and amount of olute in the aturation cell a well a adjutment of the dilution water rate from a econd pump were neceary. The obtained ugar olubility value compare favorably with exiting data below the boiling of water there i no data available for comparion at higher temperature. Above 160 C, ome degradation of the ugar occur reulting in an apparent lowering of ugar olubility, but thi can be alleviated by making the adjutment given decribed in the experimental ection. The meaured olubility data have been correlated uing A-UNIFAC model (which take into conideration aociation effect between carbohydrate and water by introducing a pecific term in the original UNIFAC equation baed on Wertheim aociating theory)[2] - and with data from the literature to predict polyaccharide olubilitie a a function of temperature and molecular tructure. INTRODUCTION The development of more evironmentally-benign method for bioma production and other liquid renewable fuel baed on a green preurized fluid platform technology ha been dicued by King et al.[3]. The topic ha been reviewed recently by Rogalinki et al [4] where it ha been noted that carbohydrate-containing natural biopolymer derived from bioma mut be olubilized and hydrolyzed imultaneouly to lower oligomeric ugar, and prefereably monomeric ugar, for eventual fermentation to bioethanol. Other invetigator [5-7] have conducted tudie to produce monomeric ugar from model carbohydrate polymer or bioma to liquid fuel, or tudied ugar converion to carbochemical [8].

2 Wyman and colleague [9-10] have emphaized the importance of ugar olubility and it role in controlling the rate and yield in the thermochemical hydrolyi of celluloic-baed polymer a well a it impact on olid loading and ubequent ugar yield due to pot hydrolyi precipitation of the reulting ugar oligomer. There i limited ugar olubility data in hot compreed water above it boiling point, but data from everal tudie [11-12] have been plotted in Figure 1 a a function of temperature. It i apparent from Figure 1 that ugar olubilitie in water increae a a function of temperature, and at leat for lactoe, increae ubtantially with temperature above the boiling point of water. More recently Jondottir et al [13] have meaured olubilitie for everal mono- and di-accharide up to 85 o C. Thi data i often determined in conjunction with the need for ugar olubilitie required for diolution and crytallization tudie of excipient in the pharmaceutical indutry [14], however ugar olubility data at much higher temperature i required for bioma proceing reearch. Here the olubility of glucoe, maltoe monohydrate and xyloe in ubcritical water i preented between 20 and 200 C uing a modification of the Miller and Hawthorne [1] continuou flow technique. Some of the meaured olubility data have been correlated uing the A-UNIFAC model [15], which take into conideration the aociation effect between carbohydrate and water by introducing a pecific term in the original UNIFAC equation [16] baed on Wertheim aociating theory. Figure 1. Solubility (g/l)of common ugar a a function of temperature [9-10]. MATERIALS AND METHODS Sample and reagent Sugar tandard ued for olubility meaurement in ubcritical water, D-(+)-xyloe and D- (+)-maltoe monohydrate, were obtained from Sigma (St. Loui, MO, USA). Glucoe wa purchaed from Fiher Biotech (Wembley, Autralia). Sea and (wahed) wa acquired from EMD (Gibbtown, NJ, USA) MΩcm Ultrapure water quality with 1 5 ppb TOC and < EU/mL pyrogen level (Milli-Q) wa produced in-houe uing a laboratory water

3 purification Milli-Q Synthei A10 ytem (Millipore, Bellerica, MA, USA) wa ued throughout thi tudy. Thi water wa then placed in the water torage tank hown in Figure 2 where it wa blanketed with nitrogen to avoid aborption of air. Solubility meaurement in ubcritical water Solubility meaurement in water of glucoe (DP1), maltoe monohydrate (DP2) and xyloe (DP1) were carried out between 20 and 200 C at approximately 20 o C interval. The experimental procedure i baed in a modification of the Miller-Hawthorne [1] continuou flow technique (Figure 2). The ugar olute wa mechanically-mixed with the ea and in a 1:2 proportion of ugar:and and then packed into one of the aturation cell (12, 20 or 50 ml in volume), which wa then connected to the flow ytem a hown in Figure 2. The experimental procedure involved ampling every 5 minute with water delivered at a flow rate of 0.1 ml/min by an Ico 100D pump through a aturation cell. Due to the large increae in ugar olubility with temperature particularly above the boiling point of water adjutment in the ize and amount of olute in the aturation cell a well a adjutment of the dilution water rate (pump tubing to the mixing tee in Figure 2) were neceary. The aturated olution exiting from the cell contacted exce olvent (water) flowing at a rate of 0.4 ml/min in a mixing tee inide the oven (HP Serie II 5890 Ga Chromatograph, Hewlett-Packard, Palo Alto, CA, USA) to prevent precipitation of ugar when the olution exited the oven through a cooling coil into a ampling vial. The firt ample i taken after 15 minute of equilibration with the next ampling taken every 5 minute over a 25 minute period. Every experimental meaurement at a pecific temperature were run in triplicate. For meaurement at 140ºC, ome degradation of the ugar occurred. To overcome thi problem the flow rate wa increaed five-fold and experimental time reduced five-fold. High performance ize excluion chromatography (HPSEC) uing a Water 2414 refractive index detector (Milford, MA, USA) coupled with two Shodex OH Pac SB-802 and SB-804 HQ column (Shodex, Kawaaki, Japan) wa ued to meaure ugar olubility in diluted ample taken during the aturation plateau region of olubility meaurement technique. The mobile phae employed in HPSEC analyi wa mol/l NaN 3 and 0.1 mol/l NaNO 3 ). All ample were filtered before injection into the HPSEC ytem. Figure 2. Solubility meaurement apparatu

4 RESULTS AND DISCUSSION Experimental data obtained for three different ugar: glucoe, xyloe, and maltoe, uing the above decribed approach are hown in Figure 3. For all three ugar, there i a monotonic but ignificant increae in ugar olubility with temperature up to the boiling point of the olvent. At approximately the boiling point of water, there i cloe to a ten-fold increae in the olubility of all three ugar in the range of o C relative to their recorded olubilitie at 100 o C. A comparion of the experimental olubility data with literature value (Table 1) taken from the extenive Yakowky and He [14] compendium how an increae in olubility with increaing temperature; although the reported literature value for glucoe are lightly higher than our experimental data, and lightly le for maltoe and for the ingle literature data point for xyloe ued for comparion. Thee olubility trend a function of temperature are imilar to thoe found for other recorded ugar olubilitie in the literature (Figure 1), although there are difference in comparing one et of ugar olubility data with another. Thi in part jutifie the experimental work reported in thi tudy. For the elect olubility data given in Table 1 and Figure 3, the tandard deviation wa approximately 2% of the mean value for triplicate determination. Figure 3 Saccharide olubility in g/l v. temperature. Select olubility data for the three different carbohydrate are ummaried in Table 1. Typical ugar olubilitie between o C range from approximately g/l for glucoe and from g/l for maltoe monohydrate. Thee ugar olubility value compare favorably with exiting data below the boiling of water there i no data available for comparion at higher temperature. For xyloe, the olubility data range between

5 g/l, and comparion with the one data point from the literature with our experimentallydetermined value are very cloe. Table 1. Carbohydrate olubilitie in water Temperature (ºC) Glucoe (g/l) Maltoe H 2 O (g/l) Xyloe (g/l) Literature thi work Literature thi work Literature thi work [14] [14] [14] [14] [14] [14] [14] [14] [14] a a Flow-rate 5 time than in previou experiment Initially when making olubility meaurement above 140 C, it became apparent that ome degradation of the ugar wa occuring which wa reflected in the anaomolouly low olubility value for the ugar. Examination of the content of the aturation cell revealed a char on the and upport and collected extract were dark in color. Carbohydrate tability tudie have hown that ignificant degradation occur when aqueou olution are heated for a prolonged time over 100 o C [17]. There can alo be an increae in the amount of degradation product for concentrated ugar olution due to ph change which will increae the degradation rate of ugar [18]. Moreover, the diaccharide tructure of the carbohydrate tudied (maltoe monohydrate) i more untable than xyloe and glucoe due to the tendency to hydrolyze to the monoaccharide. A noted in the experimental ection, thi problem wa overcome by adjuting the flow rate of pure water through the cell which wa increaed fivefold. The flow rate through aturation cell wa adjuted to 0.5 ml/min and flow rate at mixing tee to 2 ml/min, thereby maintaining a dilution factor of four-fold. Conequently the experimental time wa reduced to 3 minute of equilibration with ampling inacted every minute for 5 minute. Thi technique minimized ugar degradation a judged by the diappearance in HPSEC analyi of additional peak, ince only the peak of the carbohydrate olute wa oberved in the HPSEC profile. The above meaured olubility data were correlated uing A-UNIFAC model. Sugar olubility in water can be etimated conidering the ugar equi-fugacity condition between the olid (pure ugar) and liquid (water + ugar) phae. At temperature below the ugar melting point, the carbohydrate mole fraction x in the aqueou phae can be calculated uing the following expreion: ΔH Δ Δ m T C m p T C m p T ln( x = + + / γ ) 1 1 ln (1) RTm T R T R Tm where T m and ΔH m are, repectively, the carbohydrate normal melting temperature and enthalpy and γ i it activity coefficient in the aqueou phae. In addition, no temperature dependence for ΔC p (the difference between the heat capacity of the pure liquid and olid carbohydrate) wa aumed. In order to convert the ugar mole fraction ( x ) to concentration (g/l), olution denitie were neceary. Solution denitie (ρ) at each experimental temperature wa etimated uing the following equation :

6 ρ = ρ water * water volume fraction + ρ ugar * ugar volume fraction (2) A linear variation of ρ ugar with temperature wa aumed uing value at 25 C and 100 C. The activity coefficient of the olute, γ, wa predicted uing the A-UNIFAC model [15] a decribed in the literature [2, 19]. The carbohydrate pure component phyical propertie are given in Table 2 below. Figure 4. Carbohydrate olubilitie. ( ) A-UNIFAC model prediction; ( ) experimental data. Figure 4 how a comparion between the olubilitie meaured in thi tudy and thoe predicted uing Eq. (1) and the A-UNIFAC model. A can be deduced from Figure 4, thi thermodynamic modeling approach provide a reaonable prediction of ugar olubility in ubcritical water at temperature below the carbohydrate melting point the predicted value being higher than the experimentally-recorded ugar olubilitie. Table 2. Carbohydrate phyical propertie Carbohydrate T m (ºC) ΔH m (J/mol) ΔC p (J/mol K) Glucoe Xyloe Maltoe H 2 O CONCLUSIONS Accurate meaurement of carbohydrate olubilitie over a wide range of temperature (20 to 200 C) were carried out uing the above decribed ytem in our laboratory. The obtained olubility data a a function of temperature follow trend previouly reported in the literature [11-14]. Thee meaurement correlate reaonably well with the olubility trend predicted uing the A-UNIFAC model.

7 ACKNOWLEDGMENTS Fernando Montane thank the Spanih Minitry of Science for a FPI grant. Dr. Tiziana Fornari would like to acknowledge the financial upport of the Ramon y Cajal Program from the Minitry of Education and Science. REFERENCES [1] MILLER, D.J., HAWTHRONE, S.B., J.Chem.Eng. Data, 45, 2000, p. 78. [2] FERREIRA, O, BRIGNOLE, E.A., MACEDO, E.A., Ind. Eng. Re. Chem., 42, 2003, p [3] KING, J.W., SRINIVAS, K., DELVALLE, J.M. AND DE LA FUENTE, J., Proceeding ISSF 2006, 2006 Kyoto, Japan. [4] ROGALINSKI, T., INGRAM, T., BRUNNER, G., J. Supercrit. Fluid, 47, 2008, p. 54. [5] SCHACHT, C., ZETZL, C., BRUNNER, G, J. Supercrit. Fluid, 46, 2008, p [6] VAN WALSUM, G.P., SHI, H., Bioreource. Tech., 93, 2004, p [7] KABEL, M.A., BOS, G., ZEEVALKING, J., VORAGEN, A.G.J., SCHOLS, H.A., Bioreouce Technol., 98, 2007, p [8] AIDA, T.M., SATO, Y., WATANABE, M., TAJIMA, K., NONAKA, T., HATTORI, H., ARAI, K., J. Supercrit. Fluid, 40, 2007, p [9] GRAY, M.C., CONVERSE, A.O., WYMAN, C.E., Appl. Biochem. Biotech., , 2003, p [10] GRAY,M.C., CONVERSE, A.O., WYMAN, C.E., Ind. Eng. Chem Re., 46, 2007, p [11] BATES, F.J., Polarimetry, Saccharimetry and the Sugar, National Bureau of Standard C440, Wahington, DC, p. 690 [12] SEIDELL,A., Solubilitie of Organic Compound Vol. II, 3 rd Ed., D. Van Notrand, New York, 1941, 926 pp. [13] JONSDOTTIR, S.O., COOKE, S.A., MACEDO, E.A., Carbohydrate Re., 337, 2002, p [14] YALKOWSKY, S.H., HE, Y., Handbook of Aqueou Solubility Data, CRC Pre, [15] MENGARELLI, A.C., BRIGNOLE, E.A., BOTTINI, S.B., Fluid Phae Equilb., 163, 1999, p [16] FREDESLUND, A., JONES, R.L., PRAUSNITZ, J.M., AIChE J., 21, 1975, p [17] TOMASIK, P., Advance in Carbohydrate Chemitry and Biochemitry, 47, Academic Pre Inc., 1989, p [18] TIIHONEN, J., PEUHA, E.I., LATVA-KOKKO, M., SILANDER, S., PAATERO, E., Sep. Purif. Tech., 44, 2005, p [19] MONTAÑÉS, F., OLANO, A., IBÁÑEZ, E., FORNARI, T., AIChE J., 53, 2007, p