Mutual Solubilities for the Waterâ2-sec-Butylphenol System and

Article pubs.acs.org/jced

Mutual Solubilities for the Water−2-sec-Butylphenol System and Partition Coefficients for Furfural and Formic Acid in the Water−2sec-Butylphenol System Long Lin,†,‡ Sai Ma,†,‡ Pingli Li,*,†,‡ Tao Zhu,§ and Heying Chang†,‡ †

School of Chemical Engineering and Technology and ‡Collaborative Innovation Center of Chemical Science and Engineering (Tianjin), Tianjin University, Tianjin 300072, People’s Republic of China § Xi’an Thermal Power Research Institute Company Ltd., Xi’an 710032, Shaanxi Province, People’s Republic of China ABSTRACT: Twenty high-boiling hydrophobic solvents were assessed as furfural extraction solvent. 2-sec-Butylphenol with a high furfural partition coefficient, good thermostability, and nonazeotropic property with furfural was chosen as an extraction solvent of furfural for further experimental study. The mutual solubilities for the water−2-sec-butylphenol system were measured in the temperature range of (303.15 to 483.15) K at 2.5·106 Pa by a static method. The results showed that the solubility data were well correlated with a quadratic equation of temperature. The partition coefficients for furfural and formic acid in the water−2sec-butylphenol system were measured with the same conditions and methods, respectively. The results indicated that the partition coefficient data were temperature dependent and could be well correlated with the van’t Hoff equation. This study will have positive influence on further experiments concerning biphasic reaction extraction of furfural and the future industrial production of furfural.

1. INTRODUCTION Concerning the diminishing petroleum reservoir and environmental problems caused by emissions of fossil fuels, the most urgent task is to explore nonfossil resources. Hence, considerable research is being devoted to enhancing the production of suitable biomass-based platform chemicals.1,2 In the study supported by the U.S. Department of Energy, furfural was identified as one of the top 30 high-value biobased chemicals.3 The furfural production process involves the hydrolysis of xylan to xylose and the dehydration of xylose with acidic catalyst in the temperature range of (413 to 473) K.4 Side reactions, as shown in Figure 1,5 between furfural and

extraction process is carried out in a biphasic system which consists of an organic phase and an aqueous phase. The dehydration reactions of xylose with acidic catalyst occur in the aqueous phase, and the organic phase acts as the extraction solvent for continuously transferring furfural from the aqueous reactive phase to the organic solvent phase immediately. Subsequently, furfural is easily recovered by a binary distillation from the organic phase. Suitable acidic catalyst and extraction solvent are absolutely vital for the furfural solvent extraction process. In recent years, formic acid has been suggested as a catalyst for production of furfural.10−13 Yemis and Mazza10 compared the effect of four strong mineral acids (hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid) and two organic acids (acetic acid and formic acid) on furfural yield indicating that formic acid was an effective catalyst. Lamminpää et al.11 studied the kinetics of furfural formation with formic acid as catalyst, and the kinetic modeling was presented. Because formic acid is an organic acid, many shortcomings of mineral acid catalysts (such as serious corrosiveness, difficult separation, and excessive waste disposal, etc.) will be avoided to a certain extent. Additionally, formic acid is formed in the formation process of furfural via degradation reactions of hemicellulose and furfural,5,14 and thermal operation can be easily utilized in formic acid

Figure 1. Simplified scheme of the possible reaction in the furfural production process.

its precursors are primarily responsible for the low yields.6,7 Therefore, furfural should be removed from the reactive liquid phase rapidly and continuously in order to achieve high yield. In comparison with the traditional furfural production process, solvent extraction is a promising, environmentally friendly, and low-energy operation for producing furfural.8,9 Furfural solvent © XXXX American Chemical Society

Received: February 23, 2015 Accepted: May 15, 2015

A

DOI: 10.1021/acs.jced.5b00170 J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

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Table 1. Description of Chemicals Used in This Work

a

chemical name

CAS no.

furfural formic acid ethanol ethyl acetate N,N-dimethylformamide methyl benzoate ethyl benzoate benzyl acetate ethyl salicylate benzyl benzoate methyl 2-methylbenzoate 2,6-dimethylnitrobenzene 2-nitroanisole 4-chloroanisole 4-bromoanisole 4-chloroacetophenone 2-bromotoluene 2-bromochlorobenzene 1,2,3-trimethylbenzene cyclohexylbenzene 1-octanol dioctyl sebacate pentylbenzene 2-sec-butylphenol 1-methylnaphthalene

98-01-1 64-18-6 64−17−5 141-78-6 68-12-2 93-58-3 93-89-0 140-11-4 118-61-6 120-51-4 89-71-4 81-20-9 91-23-6 623-12-1 104-92-7 99-91-2 95-46-5 694-80-4 526-73-8 827-52-1 111-87-5 2432-87-3 538-68-1 89-72-5 90-12-0

source Sinopharm Chemical Sinopharm Chemical Sinopharm Chemical Sinopharm Chemical Sinopharm Chemical Sinopharm Chemical Sinopharm Chemical Sinopharm Chemical Sinopharm Chemical Sinopharm Chemical Sinopharm Chemical Sinopharm Chemical Sinopharm Chemical Sinopharm Chemical Sinopharm Chemical Sinopharm Chemical Sinopharm Chemical Sinopharm Chemical Sinopharm Chemical Sinopharm Chemical Sinopharm Chemical Sinopharm Chemical Sinopharm Chemical Alfa Aesar Co., Inc. Sinopharm Chemical

Reagent Reagent Reagent Reagent Reagent Reagent Reagent Reagent Reagent Reagent Reagent Reagent Reagent Reagent Reagent Reagent Reagent Reagent Reagent Reagent Reagent Reagent Reagent

purity (mass fraction) Co., Co., Co., Co., Co., Co., Co., Co., Co., Co., Co., Co., Co., Co., Co., Co., Co., Co., Co., Co., Co., Co., Co.,

Ltd. Ltd. Ltd. Ltd. Ltd. Ltd. Ltd. Ltd. Ltd. Ltd. Ltd. Ltd. Ltd. Ltd. Ltd. Ltd. Ltd. Ltd. Ltd. Ltd. Ltd. Ltd. Ltd.

Reagent Co., Ltd.

≥ ≥ ≥ ≥ ≥ ≥ ≥ ≥ ≥ ≥ ≥ ≥ ≥ ≥ ≥ ≥ ≥ ≥ ≥ ≥ ≥ ≥ ≥ ≥ ≥

0.990 0.990 0.995 0.995 0.995 0.990 0.990 0.990 0.990 0.990 0.990 0.990 0.990 0.990 0.990 0.990 0.990 0.990 0.910 0.990 0.995 0.990 0.990 0.980 0.990

analysis method HPLCa HPLCa GCb GCb GCb GCb GCb GCb GCb GCb GCb GCb GCb GCb GCb GCb GCb GCb GCb GCb GCb GCb GCb GCb GCb

water (mass fraction) ≤ ≤ ≤ ≤ ≤ ≤ ≤ ≤ ≤ ≤ ≤ ≤ ≤ ≤ ≤ ≤ ≤ ≤ ≤ ≤ ≤ ≤ ≤ ≤ ≤

0.0005 0.0015 0.003 0.00005 0.001 0.001 0.001 0.001 0.003 0.001 0.002 0.0003 0.0002 0.0002 0.0002 0.0015 0.0003 0.0003 0.0002 0.0002 0.002 0.001 0.0002 0.0005 0.0003

b

High-performance liquid chromatography. Gas chromatography.

separation from reaction media.11 So, the selection of formic acid as the catalyst is in accord with the perspective of green chemistry. Some of the key considerations for the suitable solvent for furfural solvent extraction process are good chemical stability, high boiling point (higher than that of furfural), and no azeotrope formation with furfural. Moreover, the mutual solubility of solvent and water should be as low as possible, and the furfural partition coefficient (K) should be as high as possible.15,16 However, few relevant studies in the literature on solvent screening experiment have been introduced. So far only Bo et al.17 have introduced the solvent screening experiment and o-nitrotoluene was screened out to be an effective furfural extraction solvent. The employment of 2-sec-butylphenol as the solvent for the furfural solvent extraction process has received increasing attention recently.9,15,16,18,19 In comparison with onitrotoluene, 2-sec-butylphenol can be more advantageous as it has a higher partition coefficient than that of furfural and can be derived from biomass.16,20 Nonetheless, there is no detailed report about the physical property parameters of 2-secbutylphenol used as a furfural extraction solvent. In this study, 20 high-boiling solvents were appraised as furfural extraction solvents. 2-sec-Butylphenol was screened out to be the appropriate solvent. The mutual solubilities of the water−2-sec-butylphenol system, the partition coefficient of furfural in the water−2-sec-butylphenol system, and the partition coefficient of formic acid in the water−2-secbutylphenol system were experimentally determined from (303.15 to 483.15) K at 2.5·106 Pa, respectively. The measurement method for mutual solubility and the partition coefficient in this study is a static method, and the measuring principle is virtually the same as the one described in previous works.17,21−23

2. EXPERIMENTAL SECTION 2.1. Materials and Instruments. A detailed description of the chemicals used in this study is listed in Table 1. 2-Propanol was of high-purity reagent grade purchased from Merck Co. (Darmstadt, Germany). Its mass fraction was greater than 99.99% and water content was less than 0.005%. The nitrogen used was provided by Tianjin Six-Party Industrial Gases Co., Ltd. (China), and its purity was more than 99.999%. The deionized water was produced in our laboratory, and its electrical conductivity was ca. 0.5 μS·cm−1. All chemicals were used without further purification. All weight measurements in this study were made using an electronic analytical balance (Metler Toledo AL104, Shanghai, China) with an accuracy of ± 0.0001 g. A SF-3 Karl−Fischer moisture titrator (Zibo Coulomb Analyzer Instrument Co., Ltd., China) was used for measuring the water content of the 2-sec-butylphenol phase sample. The organic phase samples were analyzed by using gas chromatography (FULI 9790II, Zhejiang Fuli Analytical Instrument Co., China) with a TCD detector. Gas chromatographic separations were achieved on a fused silica capillary column (HP-FFAP, 30 m × 0.25 mm i.d. × 0.25 μm film thickness). The aqueous phase samples were analyzed with high-performance liquid chromatography (HPLC, Agilent 1200 series), equipped with a column temperature controller (G1316A, Agilent) and a detector (G1315D for UV and G1362A for RID, Agilent). Liquid chromatography separations were achieved on a Bio-Rad Aminex HPX-87H column (300 mm × 7.8 mm). 2.2. Apparatus and Procedures. Figure 2 shows a schematic diagram of the experimental apparatus, which is similar to the one previously described by Bo et al.17 The apparatus consists mainly of a 350 mL stainless steel autoclave (55 mm i.d. × 150 mm height) used as the equilibrium cell, an B



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continuously stirred using an electromagnetic stirrer (17). In the experimental process, the experimental P was maintained at 2.5·106 Pa via an intelligent pressure controller (9), an electromagnetic valve (3), and a buffer vessel (18). The experimental T was regulated by an intelligent temperature controller (14), a thermocouple (13), and an electric jacket (15). The pressure and temperature were kept constant until the end of the experiment. The water−2-sec-butylphenol system was kept stirring vigorously for 10 h after reaching the set temperature to ensure thorough mixing between water and 2sec-butylphenol. After that, the stirring was stopped and the water−2-sec-butylphenol system was allowed to settle down for 10 h to ensure sufficient separation between the aqueous phase and 2-sec-butylphenol phase. Finally, the phase equilibrium was established. The upper phase was 2-sec-butylphenol, and the lower phase was water, because the density of 2-sec-butylphenol is smaller than that of water. The 2-sec-butylphenol phase and aqueous phase were sampled out through the sampling valves (5 and 4), respectively. The samples were cooled to room temperature by coolers 10 and 11. The sampling tube was washed by pushing out approximately 5 mL of each phase before approximately 5 mL of representative sample was collected into an empty 10 mL vial. At each experimental equilibrium condition, three representative samples of each phase were collected for analysis. In the furfural partition coefficient measurement experiments, 150 mL of furfural aqueous solution (with a furfural mass concentration of 5 %) and 150 mL of 2-sec-butylphenol were added into the equilibrium cell. The procedure of the furfural partition coefficient measurement experiments was almost the same as that of the mutual solubility measurement experiments, except for the stirring time which was controlled at 2 h and the phase separation time which was controlled at 30 min. The decomposition rate of furfural was significantly low in such a short time so that the loss of furfural was ignorable.6 The phase separation time was long enough, largely owing to the

Figure 2. Schematic diagram of the mutual solubility and partition coefficient measurement apparatus: 1, N2 cylinder; 2, 6, and 8, highpressure valves; 3, electromagnetic valve; 4 and 5, micrometering valve; 7, safety valve; 9, intelligent pressure controller; 10 and 11, cooler; 12, stainless steel autoclave; 13, thermocouple; 14, intelligent temperature controller; 15, electric jacket; 16, magnetic stirring rod; 17, electromagnetic stirrer; 18, buffer vessel.

electromagnetic stirrer, a temperature control section, and a pressure control section. The equilibrium cell is connected by two stainless steel sampling tubes (800 mm long × 1.59 mm o.d. × 0.762 mm i.d.), one for the upper phase and the other for the lower phase. The temperature (T) of the equilibrium cell is regulated via an intelligent temperature controller (accuracy, ± 0.10 K), a thermocouple, and an electric jacket. The pressure (P) is controlled via an intelligent pressure controller (accuracy, ± 5 kPa), an electromagnetic valve, and a buffer vessel with a volume of about 10 L. In the mutual solubility measurement experiments, 150 mL of water and 150 mL of 2-sec-butylphenol were poured into the equilibrium cell (12) with the cap on tight. The air was removed out of the equilibrium cell by aerating high-purity nitrogen for 5 min. The water−2-sec-butylphenol system was

Table 2. Property of Solvents Investigated for the Extraction of Furfural solvent name

bp/Ka

mp/Ka

a d20 4

azeotrope with furfural

thermal stabilityb

partition cofficientc

methyl benzoate ethyl benzoate benzyl acetate benzyl benzoate methyl 2-methylbenzoate 2,6-dimethylnitrobenzene 2-nitroanisole 2-bromochlorobenzene 1,2,3-trimethylbenzene cyclohexylbenzene 1-octanol pentylbenzene 2-sec-butylphenol 1-methylnaphthalene 2-bromotoluene ethyl salicylate 4-chloroanisole 4-bromoanisole 4-chloroacetophenone dioctyl sebacate

472.75 486.35 486.65 597.15 488.15 533.15 550.15 477.15 449.25 513.27 468.15 478.55 500.15 518.15 454.85 504.15 470.65 488.15 510.15 521.15

260.65 238.55 221.65 294.15 223.15 288.15 282.55 260.85 247.75 280.14 257.95 198.15 285.15 242.55 247.15 274.15 255.15 286.15 293.15 218.15

1.0937 1.0509 1.0570 1.1140 1.0680 1.1120 1.2540 1.6387 0.8944 0.9427 0.8239 0.8585 0.9820 1.0202 1.4232 1.1310 1.2010 1.4564 1.1920 0.9130

none none none none none none none none none none none none none none none none none none none none

good good good good good good good good good good good good good good good poor poor poor poor poor

10.03 8.16 7.90 6.52 8.14 8.37 13.58 6.12 2.52 2.50 3.42 2.26 19.78 6.89 5.30 4.70 8.20 7.74 11.16 1.76

a b Boiling point (bp), melting point (mp), and relative density (d20 4 ) were all taken from ref 24. The thermal stability of the solvents was measured at 483.15 K. cThe furfural partition cofficient of the solvents was measured at 303.15 K.

C



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Table 3. Mutual Solubilities for Water and 2-sec-Butylphenol from Temperature T = (303.15 to 483.15) K and Pressure p = 2.5· 106 Paa 2-sec-butylphenol phase T K 303.15 323.15 343.15 363.15 383.15 393.15 403.15 413.15 423.15 433.15 443.15 453.15 463.15 473.15 483.15

aqueous phase 10

2

10 w1

exp

0.3056 0.4090 0.5598 0.7623 1.0777 1.2743 1.5107 1.8746 2.2365 2.7607 3.2790 4.1006 4.8715 5.6825 7.0664

2

10

x1exp

2.4924 3.3112 4.4839 6.0200 8.3286 9.7177 11.3407 13.7423 16.0217 19.1444 22.0418 26.2876 29.9289 33.4457 38.8106

2

102w2cal

w1cal

eq 3

eq 5

10

0.3023 0.4084 0.5589 0.7747 1.0876 1.2950 1.5468 1.8536 2.2283 2.6875 3.2516 3.9469 4.8062 5.8714 7.1958

0.2654 0.3947 0.5756 0.8260 1.1709 1.3893 1.6457 1.9473 2.3028 2.7236 3.2239 3.8226 4.5446 5.4240 6.5087

2

w2exp

0.1478 0.2013 0.2734 0.3857 0.5581 0.7228 0.8389 1.0636 1.3372 1.7016 2.1761 2.7751 3.6470 4.4514 5.9452

10

2

x2exp

0.0177 0.0242 0.0329 0.0464 0.0673 0.0872 0.1014 0.1288 0.1623 0.2072 0.2661 0.3411 0.4519 0.5556 0.7523

eq 3

eq 4

0.1480 0.1985 0.2741 0.3899 0.5711 0.6990 0.8618 1.0704 1.3394 1.6883 2.1440 2.7429 3.5351 4.5899 6.0035

0.1593 0.1899 0.2550 0.3699 0.5633 0.7033 0.8824 1.1109 1.4014 1.7692 2.2326 2.8139 3.5386 4.4366 5.5414

a exp

w is the mass fraction solubility obtained from experiments; xexp is the mole fraction solubility obtained from experiments; wcal (eq 3), wcal (eq 4), and wcal (eq 5) are the calculated solubilities according to eqs 3, 4, and 5, respectively. The subscripts 1 and 2 refer to water and 2-sec-butylphenol, respectively. The standard uncertainty u for temperature T and pressure p are u(T) = 0.10 K and u(p) = 5 kPa, respectively. The relative standard uncertainty ur for the mass fraction solubility wexp is ur(wexp) = 0.02.

titrator. The 2-sec-butylphenol mass fraction in the aqueous phase sample was monitored by the FULI 9790II GC equipped with a TCD detector. N, N-Dimethylformamide was chosen as the internal standard, and its mass was weighed by the AL104 electronic balance. In the partition coefficient measurement experiments, the analysis of the organic phase sample was undertaken using the FULI 9790II GC equipped with a TCD detector. High-purity nitrogen was used as the mobile phase. Ethanol was chosen as the internal standard for the determination of furfural, and ethyl acetate was chosen as the internal standard for the determination of formic acid. The masses of the internal standard substances were weighed by the AL104 electronic balance. The analysis of the aqueous phase sample was undertaken using the Agilent 1200 HPLC instrument. A 0.005 mol·L−1 H2SO4 amount was used as the mobile phase. Before injection, 0.22 μm filters were used to filter the samples. Before analyzing, the sample vial was capped to avoid evaporation, contamination, or spillage of the contents. To ensure the reliability and accuracy of the data, all of the measurements were repeated three times, and the average value of the three measurements was taken.

larger density difference between furfural aqueous solution and 2-sec-butylphenol. In the formic acid partition coefficient measurement experiments, 150 mL of formic acid aqueous solution (with a formic acid mass concentration of 5 %) and 150 mL of 2-sec-butylphenol were added into the equilibrium cell. The stirring time and the phase separation time were both controlled at 2 h. The concrete measurement procedure was the same as that mentioned previously. In the solvent screening experiments, 20 high-boiling organic solvents listed in Table 2 were preliminarily chosen as the furfural extraction solvents. The furfural partition coefficient of different organic solvents was measured at 303.15 , K and the measurement procedure was the aforementioned one. The thermostability test of different organic solvents was also performed in the same apparatus. A 30 mL aliquot of solvent and 30 mL of formic acid aqueous solution (with a formic acid mass concentration of 5 %) were added into the stainless steel autoclave. The test condition of 483.15 K and 2.5·106 Pa was maintained for 24 h. After being cooled to room temperature, the solvent−water system was transferred into a 100 mL clean glass test tube. If color variance or the presence of humic-like substances could be observed in the system, the organic solvent was considered poor stability. In the opposite case in which there was no significant change in the system, the aqueous phase and organic solvent phase would be further analyzed by the FULI 9790II gas chromatograph to determine whether degradation of the solvent occurred. 2.3. Analytical Methods and Procedure. Equilibrium phase samples were analyzed according to the following procedure. The vial and sample collected in the vial were weighed using the AL104 electronic analytical balance. Then a known amount by weight of high-purity 2-propanol (approximately 5 mL) was put into the sample vial. The 2-propanol functioned as a homogenizing co-solvent to form a single-phase sample for analysis. In the mutual solubility measurement experiments, the water content of the 2-sec-butylphenol phase sample was detected by the SF-3 Karl−Fischer moisture

3. RESULTS AND DISCUSSION 3.1. Solvent Screening. The physical property data of the 20 solvents obtained from the Solvents Handbook24 have been collected. On the basis of previous literature,15,25,26 partition coefficient and thermal stability could be used as important criteria of the extraction solvent screening. Experiments were performed to determine the furfural partition coefficient of different solvents at 303.15 K, and the thermal stabilities of the solvents were tested in formic acid aqueous solution at 483.15 K. The results of physical property search and this experimental work are summed up in Table 2. The results showed that 2-secbutylphenol was stable under the harshest condition for the production of furfural and had the physical property of not forming an azeotropic mixture with furfural. Furthermore, the furfural partition coefficient of 2-sec-butylphenol was the D



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highest compared with that of the other solvents listed in Table 2. Therefore, 2-sec-butylphenol was superior to other organic solvents as a furfural extraction solvent. 3.2. Mutual Solubilities for the Water−2-sec-Butylphenol System. The mass fraction solubility of water in 2-secbutylphenol and that of 2-sec-butylphenol in water at different temperatures are given in Table 3, where T is the experimental temperature of the equilibrium cell, wexp is the experimental value of the mass fraction solubility, and xexp is the experimental value of the mole fraction solubility. xexp can be calculated by using eq 1. In the binary components system, the mutual matrixing relation between mass fraction solubility (wa) and mole fraction solubility (xa) is as follows: xa =

wa /Ma wa /Ma + (1 − wa)/Mb

AARD/% =

100 n

n

∑ i=1

wiexp − wical wiexp

(2)

On the basis of the model in the work of ref 17, both the 2sec-butylphenol solubility in water and the water solubility in 2sec-butylphenol were correlated as a quadratic function of T by the following expression: ln w = A + B(T /K) + C(T /K)2

(3)

where T is the experimental temperature (absolute) of the equilibrium cell and A, B, and C are constants. The experimental numeric values of the mutual solubility from Table 3 were fitted with eq 3 by using the least-squares method. The parameter values of eq 3 and the values of the AARD are given in Table 4. The correlated results of the model are listed in Table 3. On the basis of the model in the previous work of ref 22, the following equation, expressing the mole fraction of 2-secbutylphenol as a function of temperature, was selected for 2-secbutylphenol solubility in water:

(1)

where the subscripts a and b denote the solute (2-secbutylphenol or water) and the solvent (water or 2-secbutylphenol), respectively, Ma and Mb are the corresponding molecular weights of them, and wa and xa denote the mass fraction solubility and the mole fraction solubility, respectively. Figure 3 presents the mutual solubility data in Table 3 graphically. It shows that the mutual solubilities for the water−

ln xSBP = A + BTr,SBP−1 + CTr,SBP−2

(4)

where A, B and C are constants, xSBP is the 2-sec-butylphenol mole fraction, and Tr,SBP is the experimental temperature (absolute) divided by the critical temperature of 2-secbutylphenol, Tc,SBP = 730.83 K.27 The water solubility in 2sec-butylphenol was correlated by an equation expressing the mole fraction of water in 2-sec-butylphenol, xw, as a function of temperature as follows: ln x w = A + B ln Tr,w

(5)

where A and B are constants, Tr,w is the experimental temperature (absolute) divided by the critical temperature of water, Tc,w = 647.3 K. The mole fraction solubility of 2-secbutylphenol in water and the mole fraction solubility of water in 2-sec-butylphenol were fitted with eqs 4 and 5 by using the least-squares method, respectively. The parameter values of eqs 4 and 5 and the values of the AARD are given in Table 5. The correlated mole fraction solubility of the model was converted to the mass fraction solubility by using eq 1. The results are also listed in Table 3. The results of Tables 4 and 5 indicate that the average relative error is smaller by eq 3 than by the eqs 4 and 5. Therefore, the correlation by eq 3 is more consistent with the experimental results. The AARD of eq 3 for water solubility in 2-sec-butylphenol and 2-sec-butylphenol solubility in water are 1.54 % and 1.51 %, respectively, which indicate that mutual solubility data of the water−2-sec-butylphenol system would be well correlated by eq 3. 3.3. Partition Coefficients for Furfural and Formic Acid in the Water−2-sec-Butylphenol System. The furfural partition coefficient (K) is defined as the equilibrium ratio of the furfural mass concentration in the organic solvent phase to the furfural mass concentration in the aqueous phase:

Figure 3. Mass fraction mutual solubilities for water and 2-secbutylphenol from temperature T = (303.15 to 483.15) K and pressure p = 2.5·106 Pa: black filled squares, solubility of water in 2-secbutylphenol; red filled circles, solubility of 2-sec-butylphenol in water.

2-sec-butylphenol system are temperature dependent. The 2-secbutylphenol solubility in water and water solubility in 2-secbutylphenol are both increasing with the enhancement of the temperature. In the range of experimental temperature, the values of mutual solubilities are extremely low and the solubility of 2-sec-butylphenol in water is slightly lower than that of water in 2-sec-butylphenol. The mutual solubility data obtained in this study were correlated with two models. The deviations of the experimental solubility value and the solubility value calculated by each model were estimated by calculating the average absolute relative deviation (AARD) between the experimental and the calculated results using the following equation:

Table 4. Parameters of Equation 3 for Mass Fraction Mutual Solubilities of Water and 2-sec-Butylphenol equation parameter water solubility in 2-sec-butylphenol 2-sec-butylphenol solubility in water

A −8.7871 −7.3407

B

C −3

4.9790·10 −8.4756·10−3 E

−5

1.6064·10 3.6939·10−5

AARD/%

R2

1.54 1.51

0.9995 0.9997



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Table 5. Parameters of Equations 4 and 5 for Mole Fraction Mutual Solubilities of Water and 2-sec-Butylphenol equation parameter

A

B

C

AARD/%

R2

water solubility in 2-sec-butylphenol 2-sec-butylphenol solubility in water

0.7734 14.8517

6.0686 −18.8060

3.7722

6.02 4.03

0.9941 0.9980

Table 6. Partition Coefficients for Furfural and Formic Acid in the Water−2-sec-Butylphenol System from Temperature T = (303.15 to 483.15) K and Pressure p = 2.5·106 Paa T

furfural 2

2

formic acid exp

K

10 wORG

10 wAQ

K

303.15 323.15 343.15 363.15 383.15 393.15 403.15 413.15 423.15 433.15 443.15 453.15 463.15 473.15 483.15

4.8304 4.8055 4.7890 4.7721 4.7571 4.7494 4.7443 4.7394 4.7338 4.7282 4.7214 4.7185 4.7144 4.7097 4.7028

0.2442 0.2689 0.2852 0.3020 0.3169 0.3246 0.3297 0.3345 0.3401 0.3456 0.3524 0.3553 0.3593 0.3640 0.3709

19.78 17.87 16.79 15.8 15.01 14.63 14.39 14.17 13.92 13.68 13.4 13.28 13.12 12.94 12.68

cal

K

19.37 18.02 16.91 15.98 15.19 14.84 14.51 14.21 13.92 13.66 13.41 13.17 12.95 12.75 12.55

2

2

10 w′ORG

10 w′AQ

K′exp

K′cal

0.1312 0.1550 0.1743 0.1933 0.2182 0.2308 0.2389 0.2476 0.2583 0.2656 0.2732 0.2796 0.2863 0.2993 0.3059

4.8773 4.8528 4.8350 4.8156 4.7935 4.7795 4.7732 4.7634 4.7525 4.7462 4.7398 4.7334 4.7268 4.7141 4.7076

0.02690 0.03194 0.03605 0.04014 0.04552 0.04829 0.05005 0.05198 0.05435 0.05596 0.05764 0.05907 0.06057 0.06349 0.06498

0.02792 0.03217 0.03646 0.04076 0.04505 0.04717 0.04928 0.05138 0.05347 0.05553 0.05758 0.05961 0.06161 0.06360 0.06556

a exp

K and K′exp are the experimentally determined partition coefficients for furfural and formic acid, respectively; Kcal and K′cal are the calculated partition coefficients (according to eq 7) for furfural and formic acid, respectively. wORG and wAQ are mass concentrations in the organic solvent phase and aqueous phase, respectively. The standard uncertainty u for temperature T and pressure p are u(T) = 0.10 K and u(p) = 5 kPa, respectively. The relative standard uncertainty ur for the mass concentration is ur(w) = 0.02.

K=

wORG wAQ

(6)

where wORG and wAQ represent mass concentrations in the organic solvent phase and aqueous phase, respectively. The definition of the formic acid partition coefficient (K′) is the same as that of furfural partition coefficient. The partition coefficients of furfural and formic acid in the water−2-sec-butylphenol system at different temperatures are given in Table 6, where Kexp and K′exp are the experimental values of the partition coefficients for furfural and formic acid, respectively. Figures 4 and 5 visually depict the partition coefficients of furfural and formic acid, respectively. As can be seen, the partition coefficients of furfural and formic acid in the

Figure 5. Partition coefficients of formic acid in the water−2-secbutylphenol system from temperature T = (303.15 to 483.15) K and pressure p = 2.5·106 Pa.

water−2-sec-butylphenol system are both temperature dependent. According to the liquid−liquid phase equilibrium theory, the temperature dependence of K can be correlated with the van’t Hoff equation deduced from the extraction equilibrium theory:28 K = K 0e−ΔH / RT

(7) −1

where ΔH denotes the enthalpy change (J·mol ) for the transfer of furfural or formic acid from aqueous phase to 2-secbutylphenol phase and K0 denotes the extrapolated value for K at infinite temperature. The experimental numeric values of the partition coefficient from Table 6 were fitted with eq 7 by using the least-squares method. The parameter values of eq 7 are presented in Table 7 together with the average absolute relative deviation, which is defined as follows:

Figure 4. Partition coefficients of furfural in the water−2-secbutylphenol system from temperature T = (303.15 to 483.15) K and pressure p = 2.5·106 Pa. F


Journal of Chemical & Engineering Data AARD/% =

100 n

n

∑ i=1

Article

biphasic reaction extraction of furfural and the future industrial production of furfural.

K iexp − K ical K iexp

■

(8)

Table 7. Parameters of Equation 7 for Partition Coefficients of Furfural and Formic Acid ΔH

AARD

solute

K0

(J·mol−1)

%

R2

furfural formic acid

6.0464 0.2761

−2934.20 5775.50

0.89 1.29

0.9920 0.9962

AUTHOR INFORMATION

Corresponding Author

*Tel.: +86-22-27405902. Fax: +86-22-27404347. E-mail: [email protected]. Notes

The authors declare no competing financial interest.

■

REFERENCES

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The results show that the partition coefficient of furfural decreases with increasing temperature. It suggests that the mass transfer of furfural from aqueous phase to 2-sec-butylphenol phase is an exothermic process. This is coincident with the negative enthalpy change as shown in Table 7. The partition coefficient of formic acid increases with increasing temperature. It indicates that the mass transfer of formic acid from aqueous phase to 2-sec-butylphenol phase is an endothermic process. This is also coincident with the positive enthalpy change as shown in Table 7. The partition coefficients for furfural and formic acid fit the van’t Hoff equation well, which identifies that the effect of the low mutual solubilities for the water−2-secbutylphenol system on the partition coefficients can be negligible. The furfural partition coefficient for 2-sec-butylphenol is pretty high and the formic acid partition coefficient is very low within the experimental temperature range. This indicates that 2-sec-butylphenol has a very high selectivity for furfural and a very low selectivity for formic acid under the condition of furfural production in the biphasic solvent extraction process. Therefore, 2-sec-butylphenol used as extraction solvent can effectively facilitate the transfer of furfural from the aqueous phase to the hydrophobic organic solvent phase, which limits the side reactions, giving rise to higher furfural yields. Considering the high selectivity to furfural, the low selectivity to formic acid, and extremely low mutual solubilities with water, 2-sec-butylphenol was considered as a proper extraction solvent for the production of furfural.

4. CONCLUSIONS Twenty organic solvents were evaluated as furfural extraction solvent in the solvent screening experiments. Considering that the furfural partition coefficient for 2-sec-butylphenol was much higher than that for any other organic solvents, 2-secbutylphenol was considered as a better extraction solvent for the production of furfural. The mutual solubilities and partition coefficients in this study were experimentally measured using a static method at (303.15 to 483.15) K and 2.5·106 Pa. Both the 2-sec-butylphenol solubility in water and water solubility in 2sec-butylphenol increased with increasing temperature, and the mutual solubilities were well correlated with a quadratic equation of temperature. The partition coefficients of furfural and formic acid increased with decreasing and increasing temperature, respectively. The partition coefficients were well correlated with the van’t Hoff equation, and the thermodynamic parameter, enthalpy change (ΔH), could be obtained. It was concluded that the mass transfer processes of furfural and formic acid from aqueous phase to 2-sec-butylphenol phase were exothermic and endothermic, respectively. The experimental data and correlation equations in this work will have positive significance on further experimental studies concerning G



Article

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