Infinite Dilution Binary Diffusion Coefficients for Compounds Derived

Dec 4, 2012 - ABSTRACT: Infinite dilution binary diffusion coefficients (D12) for com- pounds derived from biomass such as furan-2-carbaldehyde (furfu...
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Infinite Dilution Binary Diffusion Coefficients for Compounds Derived from Biomass in Water at 0.1 MPa and Temperatures from (298.2 to 353.2) K Kazuko Yui, Naoto Yamazaki, and Toshitaka Funazukuri* Department of Applied Chemistry, Faculty of Science and Engineering, Chuo University, 1-13-27 Kasuga, Bunkyo-ku, Tokyo, 112-8551, Japan ABSTRACT: Infinite dilution binary diffusion coefficients (D12) for compounds derived from biomass such as furan-2-carbaldehyde (furfural), 5(hydroxymethyl)-2-furaldehyde (5-HMF), 2-methoxyphenol (guaiacol), 4hydroxy-3-methoxybenzaldehyde (vanillin), and phenol in water were measured over the temperature range from (298.2 to 353.2) K at 0.1 MPa using the Taylor dispersion method. The relative expanded uncertainties with level of confidence 0.95 (the coverage factor, k = 2.78 for 4 degrees of freedom) for the measured diffusion coefficients were less than 5.8 % and typically ca. 2.4 %. The diffusion coefficients were correlated with the hydrodynamic equation, D12/T = αηβ, with an average absolute relative deviation, AARD, less than 1.16 %.

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INTRODUCTION

the measurements, which usually take about (1.5 to 2) h. We have estimated the conversions of 0.3 % and 0.03 % for furfural and 5-HMF, respectively, at 353 K after 12 h using the rate data for furfural14 and 5-HMF15 with the assumption of Arrheniustype temperature dependence for the rate constants. Since both compounds can be considered to be stable below 353 K, the present measurements were made from room temperature to 353 K. In this study, first we compared the diffusion coefficients of phenol with those in the literature12,16−18 to validate the apparatus and measured the diffusion coefficients of furfural, 5HMF, guaiacol, and vanillin, which were the major products of the hydrothermal treatment of biomass, in aqueous solutions at temperatures from (298.2 to 353.2) K and ambient pressure by the Taylor dispersion method. The measured data for each compound were correlated by the hydrodynamic equation.

Hydrothermal treatments of biomass have been extensively studied in these decades as versatile processes for extractions of natural organic compounds, hydrolytic conversions of biomass, pretreatments of biomass for enzymatic hydrolysis, and so on, to enhance the yields of extracts or products.1,2 To design reactors and separators for those processes, equilibrium and transport properties of the extracts or the products, that is, natural organic compounds and the compounds derived from biomass or lignocelluloses, are required. Although diffusion coefficients are one of the important transport properties, the data under hydrothermal conditions are extremely limited, and even those at ambient conditions are scarce. Among the compounds derived from biomass, the diffusion coefficients of monosaccharides,3−5 polysaccharides,3,6−9 and aromatic compounds such as catechin and derivatives,10 caffeine,11 orcinol,12 and camphor and cinnamic acid13 in aqueous solutions have been measured with changing temperature. There are still many other compounds for which the diffusion data have not been reported, that is, furan-2-carbaldehyde (furfural) and 5(hydroxymethyl)-2-furaldehyde (5-HMF), which are the common and important products in the hydrothermal treatment of biomass, and 4-hydroxy-3-methoxybenzaldehyde (vanillin), 2-methoxyphenol (guaiacol), and so forth, that are also valuable compounds with relatively simple structures. Temperature dependences of binary diffusion coefficients in aqueous solutions have been measured using the Taylor dispersion method, and we have employed that method. However, concerning the compounds derived from biomass, which are often heat-labile, there is a possibility that the measured values of diffusion coefficients at high temperatures could be influenced by the deterioration of the solutes during © XXXX American Chemical Society

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EXPERIMENTAL SECTION Chemicals. Furfural (Junsei Chemical), 5-HMF (SigmaAldrich Japan), vanillin (Wako Pure Chemicals), guaiacol (Kanto Chemical), and phenol (Wako Pure Chemicals) were used without further purification. Details about the compounds are summarized in Table 1. Procedures. The experimental apparatus and procedures were almost the same as those in the previous studies,5,19,20 but the length of the diffusion column is different (42.03 m in this study). Aqueous solutions of solutes (5 mol·m−3) were Received: September 27, 2012 Accepted: November 22, 2012

A

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m·s−1 by a syringe pump (DM100, ISCO) to a fused silica diffusion column (Supelco) with 0.5274 mm in diameter, 0.19 m in coil diameter, and 42.03 m in length, which was immersed horizontally in a water bath, the temperature of which was maintained at the prescribed value within the temperature fluctuation of ± 0.1 K. The aqueous solution of a solute was injected to the diffusion column through an HPLC sample injector (7725, Rheodyne) with a 2.0·10−8 m3 sampling loop. The solute concentration at the exit of the diffusion column was detected using a differential refractometer (L-7490, Hitachi) with an integrator (D-2500, Hitachi). The error due to the secondary flow in the diffusion column is estimated within 1 % since the criterion De·Sc1/2 < 8 is fulfilled,21 where De is the Dean number and Sc is the Schmidt number. Analysis. When an aqueous solution is injected at z = 0 to a fully developed laminar flow moving in a circular cross-sectional diffusion tubing, the solute concentration at column exit, z = L, can be expressed as22,23

Table 1. Chemical Name and Properties of Solutes Used in This Study solute phenol

molecular weight/g·mol−1

>99

b

96.08

>98

b

126.11

>99c

124.14

>98b

152.15

>98d

94.11

furan-2-carbaldehyde (furfural) 5-(hydroxymethyl)-2furaldehyde (5-HMF) 2-methoxyphenol (guaiacol) 4-hydroxy-3methoxybenzaldehyde (vanillin) a c

puritya/%

The purities are given by the suppliers. HPLC. dChemical titration.

b

supplier Wako Pure Chemicals Junsei Chemical Sigma-Aldrich Kanto Chemical Wako Pure Chemicals

Gas chromatography.

prepared by dissolving each solute in ultrafiltrated and degassed water (Millipore Direct-Q system). Ultrafiltrated and degassed water was also supplied at a fixed flow velocity of about 7·10−3

Table 2. Measured Binary Diffusion Coefficients (D12) for Phenol and Compounds Derived From Biomass in Water at 0.1 MPa Together with Flow Velocities (u), Fitting Errors (ε), and Criterion for Secondary Flow Effect (De·Sc1/2) solute

T/K

D12a,b/(10−10 m2·s−1)

phenol

298.2 303.2 313.2 323.2 333.2 343.2 353.2 298.2 303.2 313.2 323.2 333.2 343.2 353.2 298.2 303.2 313.2 323.2 333.2 343.2 353.2 298.2 303.2 313.2 323.2 333.2 343.2 353.2 298.2 303.2 313.2 323.2 333.2 343.2 353.2

10.26 (0.33) 11.75 (0.23) 14.82 (0.78) 18.31 (0.15) 22.05 (0.36) 25.92 (0.38) 30.82 (0.40) 11.30 (0.21) 13.36 (0.20) 16.62 (0.32) 20.25 (1.17) 24.21 (0.12) 29.02 (1.20) 33.23 (0.99) 9.169 (0.083) 10.61 (0.19) 13.36 (0.33) 16.50 (0.26) 19.89 (0.38) 23.45 (0.55) 27.56 (1.01) 9.159 (0.188) 10.38 (0.27) 13.11 (0.37) 16.19 (0.60) 19.76 (0.42) 23.48 (0.84) 27.68 (1.04) 8.168 (0.099) 9.298 (0.272) 11.85 (0.27) 14.56 (0.28) 17.82 (0.38) 21.29 (0.42) 24.92 (0.87)

furfural

5-HMF

guaiacol

vanillin

ua,b/(10−3 m·s−1) 7.05 7.06 7.09 7.12 7.16 7.19 7.23 7.06 7.07 7.08 7.09 7.13 7.17 7.23 7.06 7.06 7.09 7.12 7.14 7.19 7.22 7.06 7.06 7.08 7.11 7.15 7.19 7.24 7.06 7.06 7.09 7.11 7.15 7.19 7.23

(0.04) (0.02) (0.02) (0.02) (0.01) (0.03) (0.02) (0.01) (0.01) (0.02) (0.08) (0.01) (0.01) (0.01) (0.01) (0.00) (0.01) (0.02) (0.04) (0.02) (0.01) (0.01) (0.01) (0.08) (0.01) (0.02) (0.02) (0.02) (0.02) (0.02) (0.03) (0.03) (0.01) (0.02) (0.02)

εa/%

De·Sc1/2 c

0.55 0.60 0.62 0.94 0.81 0.93 1.15 0.86 0.78 0.75 0.95 1.71 1.23 1.38 0.53 0.56 0.80 0.80 0.94 1.04 0.90 0.87 0.48 0.53 0.71 0.63 0.72 0.65 0.53 0.39 0.51 0.80 0.47 0.69 0.72

6.48 6.41 6.31 6.22 6.15 6.11 6.00 6.18 6.01 5.95 5.89 5.85 5.76 5.77 6.86 6.74 6.65 6.55 6.46 6.42 6.33 6.87 6.82 6.70 6.60 6.49 6.42 6.33 7.27 7.20 7.06 6.96 6.84 6.74 6.66

The D12, u, and ε values were obtained as the mean values from five measurements at each condition. bThe expanded uncertainties with level of confidence 0.95 (the coverage factor, k = 2.78 for 4 degrees of freedom, i.e., 5-fold measurements24) for D12 and u are given in parentheses. cDe·Sc1/2 were calculated from the velocities in this table. a

B

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⎡ (L − ut )2 ⎤ m exp⎢ − ⎥ 4Kt ⎦ ⎣ πR 4πKt 2

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coefficients measured in this study are in good agreement with those of Niesner and Heintz12 and Plugatyr and Svishchev,18 though the differences between our values and those in references16,17 are not negligible. The reason of the difference is not clear. The diffusion coefficients at the lowest phenol mole fraction in ref 16, which we cite here in Figure 1, appear to be obtained at not sufficiently dilute conditions, and the extrapolated value to infinite dilution at 323 K from their data (not shown) seems to almost agree with our data. Because our previous measurements for amino-acids using the same experimental setup also agreed with other groups’ values,19 it can be considered that accurate measurements can be made using the present apparatus. Figure 2 shows the temperature dependence of the diffusion coefficients including other compounds. Values of the diffusion

(1)

where K = D12 +

R2u 2 48D12

(2)

c(t) is the solute concentration, m is the amount of solute in the injection solution, u is the average flow velocity, R is the inner radius of the diffusion column, and D12 is the mutual diffusion coefficient. The two unknown parameters of D12 and u were determined simultaneously so that the root-mean-square fitting error ε defined by eq 3 is minimized: 1/2 ⎡ t1 2 ⎤ ⎢ ∫t0 {Cexp(t ) − Ccal(t )} dt ⎥ ε=⎢ ⎥ t ∫t 1 {Cexp(t )}2dt ⎢⎣ ⎥⎦ 0

(3)

where Ccal(t) and Cexp(t) are the calculated and experimentally measured concentrations, respectively, both normalized by peak area, and t0 and t1 are the frontal and latter retention times at 10 % of the peak height, respectively.

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RESULTS AND DISCUSSION Table 2 shows the measured D12 values that are the mean values from five measurements at each condition, together with u, fitting errors (ε), and De·Sc1/2. The numerals in parentheses are the expanded uncertainties with level of confidence 0.95 (the coverage factor, k = 2.78 for 4 degrees of freedom, i.e., 5fold measurements24) for the diffusion coefficients and the velocities, respectively. The relative expanded uncertainties for D12’s on different runs at each condition was generally 0.024 (2.4 %), and the maximum relative expanded uncertainty was 0.058 (5.8 %) of furfural at 323.2 K. Almost all response curves can be fit by the theoretical equation, eq 1, with typical fitting errors less than 1 %. The response curves for furfural showed slight tailing, and the fitting errors for furfural are slightly higher (1.7 %). The reason of the tailing is not clear. It is considered that the D12 values of furfural could be less accurate than those of other solutes. Other solutes showed less tailing at our experimental conditions, and the fitting errors were also small. Figure 1 plots the diffusion coefficients of phenol together with the diffusion coefficients from references. The diffusion

Figure 2. D12 vs T for phenol and compounds derived from biomass in water from (298.2 to 353.2) K. ○, phenol; △, furfural; □, 5-HMF; ▽, guaiacol, and ◇, vanillin.

coefficients were in the order of furfural (Mw = 96.09) > phenol (94.11) > guaiacol (124.13) ≈ 5-HMF (126.11) > vanillin (152.15), appeared to decrease with increasing the molecular weight, except for furfural. Figure 3 shows the logarithmic plots of D12/T versus water viscosity for several solutes. The D12 values were represented with each straight line in eq 4:

Figure 3. D12T−1 vs viscosity of water (η) for phenol and compounds derived from biomass in water from (298.2 to 353.2) K. Straight lines are the fitting results with the hydrodynamic equation (eq 4). The key is the same as in Figure 2.

Figure 1. D12 vs T for phenol in water. ●, this work; +, Niesner and Heintz;12 △, Castillo et al.;16 ▽, Yang and Matthews;17 □, Plugatyr and Svishchev at 0.1 MPa (298 K) and 25 MPa.18 C

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D12T −1 = αη β

sucrose, lactose, glucose, and fructose in the temperature range from (298.15 to 328.15) K. J. Chem. Eng. Data 2006, 51, 1836−1840. (5) Mogi, N.; Sugai, E.; Fuse, Y.; Funazukuri, T. Infinite dilution binary diffusion coefficients for six sugars at 0.1 MPa and temperatures from (273.2 to 353.2) K. J. Chem. Eng. Data 2007, 52, 40−43. (6) Rampp, M.; Buttersack, C.; Lüdemann, H.-D. c,T-Dependence of the viscosity and the self-diffusion coefficients in some aqueous carbohydrate solutions. Carbohydr. Res. 2000, 328, 561−572. (7) Ekdawi-Sever, N.; de Pablo, J. J.; Feick, E.; von Meerwall, E. Diffusion of sucrose and α,α-trehalose in aqueous solutions. J. Phys. Chem. A 2003, 107, 936−943. (8) Blanco, P.; Wiegand, S. Study of the Soret effect in monosaccharide solutions. J. Phys. Chem. B 2010, 114, 2807−2813. (9) Blanco, P.; Kriegs, H.; Arlt, B.; Wiegand, S. Thermal diffusion of oligosaccharide solutions: the role of chain length and structure. J. Phys. Chem. B 2010, 114, 10740−10747. (10) Srinivas, K.; King, J. W.; Howard, L. R.; Monrad, J. K. Binary diffusion coefficients of phenolic compounds in subcritical water using a chromatographic peak broadening technique. Fluid Phase Equilib. 2011, 301, 234−243. (11) Price, W. E.; Trickett, K. A.; Harris, K. R. Association of caffeine in aqueous solution. J. Chem. Soc., Faraday Trans. 1 1989, 85, 3281− 3288. (12) Niesner, R.; Heintz, A. Diffusion coefficients of aromatics in aqueous solution. J. Chem. Eng. Data 2000, 45, 1121−1124. (13) Delgado, J. M. P. Q. Molecular diffusion coefficients of organic compounds in water at different temperatures. J. Phase Equilib. Diff. 2007, 28, 427−432. (14) Jing, Q.; Lü, X.-Y. Kinetics of non-catalyzed decomposition of D-xylose in high temperature liquid water. Chin. J. Chem. Eng. 2007, 15, 666−669. (15) Jing, Q.; Lü, X.-Y. Kinetics of non-catalyzed decomposition of glucose in high-temperature liquid water. Chin. J. Chem. Eng. 2008, 16, 890−894. (16) Castillo, R.; Garza, C.; Orozco, J. Mutual diffusion coefficients in the water-rich region of water/phenol mixtures and their relation to aggregate formation. J. Phys. Chem. 1992, 96, 1475−1478. (17) Yang, X.-N.; Matthews, M. A. Diffusion coefficients of three organic solutes in aqueous sodium dodecyl sulfate solutions. J. Colloid Interface Sci. 2000, 229, 53−61. (18) Plugatyr, A.; Svishchev, I. M. Molecular diffusivity of phenol in sub- and supercritical water: Application of the split-flow Taylor dispersion technique. J. Phys. Chem. B 2011, 115, 2555−2562. (19) Umecky, T.; Kuga, T.; Funazukuri, T. Infinite dilution binary diffusion coefficients of several α-amino acids in water over a temperature range from (293.2 to 333.2) K with the Taylor dispersion technique. J. Chem. Eng. Data 2006, 51, 1705−1710. (20) Umecky, T.; Omori, S.; Kuga, T.; Funazukuri, T. Effects of hydroxyl groups on binary diffusion coefficients of α-amino acids in dilute aqueous solutions. Fluid Phase Equilib. 2008, 264, 18−22. (21) Alizadeh, A.; Nieto de Castro, C. A.; Wakeham, W. A. The theory of the Taylor dispersion technique for liquid diffusivity measurements. Int. J. Thermophys. 1980, 1, 243−284. (22) Taylor, G. Dispersion of soluble matter in solvent flowing slowly through a tube. Proc. R. Soc. London 1953, A219, 186−203. (23) Aris, R. On the dispersion of a solute in fluid flowing through a tube. Proc. R. Soc. London 1956, A235, 67−77. (24) Taylor, B. N.; Kuyatt, C. E. Guidelines for Evaluating and Expressing the Uncertainty of NIST Measurement Results; NIST Technical Note 1297; U.S. Government Printing Office: Washington, DC, September 1994. (25) JSME (Japan Society of Mechanical Engineers) Steam Tables Based on IAPWS-IF97 (International Association for the Properties of Water and Steam Industrial Formulation 1997 for the Thermodynamic Properties of Water and Steam), 5th ed.; JSME: Tokyo, 1999. (26) Reid, R. C.; Prausnitz, J. M.; Poling, B. E. The Properties of Gases and Liquids, 4th ed.; McGraw-Hill: New York, 1988. (27) Wilke, C. R.; Chang, P. Correlation of diffusion coefficients in dilute solutions. AIChE J. 1955, 1, 264−270.

(4)

where T is the absolute temperature, α and β are constants, and η is the viscosity of water quoted from literature.25 Table 3 Table 3. Constants α and β and AARDs in eq 4 for Phenol and Compounds Derived From Biomass in Watera solute

1015 α

β

AARD/%

phenol furfural 5-HMF guaiacol vanillin

3.035 4.119 2.704 2.360 1.945

−1.0022 −0.9751 −1.0034 −1.0204 −1.0321

0.47 1.16 0.65 0.23 0.22

α and β for each compound were determined under the SI units of diffusion coefficients (D12) in m2·s−1, absolute temperature (T) in K−1, and viscosity of water (η) quoted from literature25 in Pa·s. a

presents the values of α and β determined for each solute under the SI units (D12 in m2·s−1, T in K, and η in Pa·s) and the average absolute relative deviations (AARD), defined as AARD =

100 N

N

∑

1−

i=1

D12,prd D12,exp

(5)

where N is the number of data points and D12,prd and D12,exp are the predicted diffusion coefficients and experimentally measured values listed in Table 2, respectively. AARDs are less than 1.16 %. The values of β are all nearly −1. The Wilke−Chang equation,26,27 which has been most commonly used for the prediction of diffusion coefficients in liquid phase, also provided good accuracy with AARD of 2.0 % for all species measured in this study.

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CONCLUSIONS Infinite dilution binary diffusion coefficients for some compounds derived from biomass and phenol in water were measured at 0.1 MPa over the temperature range from (298.2 to 353.2) K by the Taylor dispersion method. The D12 values were well-correlated with water viscosity with correlation errors in AARD less than 1.16 %.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Funding

The authors are grateful to the Ministry of Education, Sports, Culture, Science and Technology of Japan for the financial support through Grant-in-Aid No. 22360325. Notes

The authors declare no competing financial interest.

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REFERENCES

(1) Brunner, G. Near critical and supercritical water. Part I. Hydrolytic and hydrothermal processes. J. Supercrit. Fluids 2009, 47, 373−381. (2) Reverchon, E.; De Marco, I. Supercritical fluid extraction and fractionation of natural matter. J. Supercrit. Fluids 1993, 38, 146−166. (3) Longsworth, L. G. Temperature dependence of diffusion in aqueous solutions. J. Phys. Chem. 1954, 58, 770−773. (4) Ribeiro, A. C. F.; Ortona, O.; Simões, S. M. N.; Santos, C. I. A. V.; Prazeres, P. M. R. A.; Valente, A. J. M.; Lobo, V. M. M.; Burrows, H. D. Binary mutual diffusion coefficients of aqueous solutions of D

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