Article pubs.acs.org/jced
Phase Equilibria in Systems with Levulinic Acid and Ethyl Levulinate Alexander J. Resk, Lars Peereboom, Aspi K. Kolah, Dennis J. Miller, and Carl T. Lira* Michigan State University, East Lansing, Michigan 48824-1226, United States ABSTRACT: P−x data for the vapor−liquid equilibrium (VLE) of four binary systems water + levulinic acid, water + ethyl levulinate, ethanol + levulinic acid, and ethanol + ethyl levulinate were collected at 60 °C. Liquid−liquid equilibrium (LLE) data for ethyl levulinate + water + levulinic acid and ethyl levulinate + water + ethanol were measured at 30 °C. The consistency of the LLE data was confirmed using the Othmer− Tobias method. Data were regressed using ASPEN PLUS software to generate binary interaction parameters for the NRTL-HOC property method. The resulting parameters were able to successfully reproduce experimental VLE data, and were semiquantitative for reproducing experimental LLE data.
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database are used; τij = −0.9852 + 302.237/T(K), τji = 3.7555 − 676.031/T(K). The HOC parameters are ηii = 1.4, ηij = ηji = 1.55, ηjj = 1.7.
INTRODUCTION Biobased chemical manufacturing using environmentally friendly methods is of increasing interest for many chemical producers. Levulinic acid and its derivatives are of significant potential as platform chemicals for biobased materials.1 Levulinic acid is obtained easily by treating six-carbon sugars with acid, or it can be obtained from five-carbon sugars by adding a reduction step before the acid treatment.2 Ethyl levulinate is used primarily as a fuel additive for the oil and gas industry, a fragrance additive in cosmetics, and a flavor additive in some foods. The phase equilibria reported here supports the development of esterification of levulinic acid with ethanol to produce ethyl levulinate with water as a byproduct. Ethyl levulinate can be produced by reactive distillation (RD). RD has significant potential for biobased chemical manufacturing of esters.3 RD has the capability to be more economical than traditional reactor + separator systems because the products can be separated in the column, overcoming equilibrium conversion limitations present in batch or flow reactors. Both LLE and VLE are important because ethyl levulinate has a heteroazeotrope with water. In this study, experimental VLE data for four binary systems were obtained, including the water + levulinic acid system, the water + ethyl levulinate system, the ethanol+ levulinic acid system, and the ethanol + ethyl levulinate system. LLE data for two ternary systems were collected, including the ethyl levulinate + water + levulinic acid system and the ethyl levulinate + water + ethanol system. These data were correlated with the nonrandom two liquid (NRTL) + Hayden-O’Connell method (NRTLHOC). The NRTL model is a local composition theory inspired by the Wilson model.4 The NRTL model is used here because of its ability to model LLE. The Hayden-O’Connell method is used because of the presence of organic acids, alcohols and water. Ethanol (i) + Water (j) System. This work includes modeling incorporating the ethanol + water system for which parameters from the Aspen Plus version 7.3.2 NRTL-HOC © 2014 American Chemical Society
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EXPERIMENTAL DETAILS Chemicals. Reagents and purities are summarized in Table 1. Levulinic acid obtained from Penta Manufacturing was purified by vacuum distillation. The initial overhead fraction (10% of initial volume) and the final reboiler residue (10%) were discarded, while the middle fraction (80%) was collected for use. The vacuum distilled levulinic acid was > 98 % pure, with water as the primary contaminant, as determined by gas chromatography (GC) and Karl Fischer titration (Aqua Counter AQ-2100). The levulinic acid was checked for purity before each use and stored in an airtight container between uses to minimize water absorption from air. P−x Apparatus. A custom P−x apparatus was created for VLE measurements of binary mixtures at temperatures between 303 K and 353 K as shown in Figure 1. The apparatus is a modification of the system described by Vu, et al.5 The main equilibrium chamber has been modified to use a liquid jacket for temperature control, and the liquid pumps and external degassing were eliminated. Valves on the top permit sampling and evacuation. A side valve for the system for liquid sampling is also present, but not used in this study. The main chamber (∼500 mL) usually holds 50 to 100 mL of liquid. A glass stem is attached at the top of the apparatus to allow the connection of the MKS Baratron model PDR 2000 dual capacitance diaphragm absolute pressure gauge. The pressure gauge provides reliable measurements of pressure between 0.013 and 133 kPa with an error of Special Issue: In Honor of Grant Wilson Received: September 10, 2013 Accepted: February 12, 2014 Published: March 3, 2014 1062
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Table 1. Reagents and Purities for Compounds Used compound dimethyl sulfoxide ethyl levulinate ethyl alcohol water, HPLC grade levulinic acid nitrogen (inert gas)
CAS No.
source
539-88-8 64-17-5 7732-18-5 123-76-2
Sigma-Aldrich Sigma-Aldrich Sigma-Aldrich J.T. Baker Penta Mfg. AGA
initial mole fraction purity
purification method
99+ % 99 % 99+ % vacuum distillation 99.998 %
final mole fraction purity 99+ % 99 % 99+ % 99+ % 98+% 99.998 %
analysis method GC Karl Fischer
GC Karl Fischer
liquid for the binary pair. This liquid was loaded using a 70 mL syringe with a needle inserted through the open sampling valve and septum. All valves were then closed, and the vacuum pump was started. After 5 s, the vacuum valve was opened, allowing the pressure to drop below the pure liquid’s vapor pressure. After allowing the liquid to boil for 20 s, the vacuum valve was closed, and the vacuum was turned off. The pressure in the equilibrium chamber was recorded after it remained steady, and the temperature remained constant for 30 s. The vacuum pump was turned on once again, and the vacuum valve opened for 5 s then closed. The pressure was recorded once again after steadying. This process was repeated until the successive pressure readings indicated complete degassing. For binary experiments, the short evacuation of vapor from the apparatus lowered the content of the more volatile component and the pressure readings would trend slightly toward the vapor pressure of the less volatile component. For this reason, when three successive pressure readings exhibited a small constant decline, the degassing was considered complete, and the final pressure would be recorded and liquid sampling would begin. Sampling of the liquid within the equilibrium chamber was done by taking 3 mL of liquid from the bottom of the apparatus. A 10 mL syringe with a long needle was used to gather the samples. The syringe would only allow liquid to travel through the needle when the equilibrium chamber was at a pressure greater than about 20 kPa. So, if the pressure inside the apparatus was below this level, the nitrogen valve was opened to allow nitrogen gas to raise the pressure above 20 kPa. The syringe needle was then inserted through the sampling valve and septum, and the 3 mL sample was gathered. The sample was placed in an airtight vial, and the composition was determined by GC analysis. After the liquid sample with only the less volatile pure component present was taken, a volume of the more volatile liquid was added to allow the liquid composition within the apparatus to reach a composition 5 mol % to 10 mol % richer in the more the volatile component. The steps described previously for determining the vapor pressure and gathering a liquid sample were executed once again. This process was repeated until the liquid in the apparatus contained 90 % to 95 % of the more volatile component. Then, the apparatus was disassembled, cleaned, and prepared once again. The same process was repeated, but this time initiated with the more volatile pure component while the less volatile component was added. Approximately 7 to 12 vapor pressure and liquid composition pairs were recorded for both runs from purities to 90 % to 95 %. This provided 14 to 24 data points on each P−x diagram for a binary pair. Procedure for LLE Experiments. LLE data for ternary mixtures were determined at a constant temperature of 30 °C, selected to provide temperature control with limited concern of volatilization. An isothermal bath was assembled and equipped with a Fischer Scientific Isotemp Immersion Circulator model 730. The temperature of the bath was monitored with an ASTM
Figure 1. Schematic of custom P−x apparatus.
0.25 % from the reported value. On the upper side of the apparatus, two valves are used to attach rubber hoses, one connected to a vacuum pump, and the other connected to an ultrahigh purity nitrogen tank. The vacuum line uses a dry ice + acetone trap to protect the vacuum pump. A straight connecting glass stopcock is used as a the upper liquid sampling valve. The valve outlet is capped with a septum. When the sample valve is opened, a 25 cm long, 16 gauge syringe needle is passed through the septum and valve orifice to collect liquid samples. A thermowell extending to the bottom of the equilibrium chamber is filled with mineral oil to allow temperature measurement within the apparatus. An Omega DP 460 thermistor readout is used to monitor the temperature within the apparatus using a thermistor calibrated against a certified mercury thermometer with accuracy better than ± 0.01 °C. The equilibrium chamber is surrounded by a water jacket connected to a Thermo Scientific DC10 circulator. Besides a brief, small drop in temperature each time the chamber pressure was lowered with vacuum, the apparatus maintains the target temperature during all experiments with a precision of ± 0.1 °C. A magnetic stir bar placed in the apparatus improves thermal equilibrium and degassing. Electric heating tape and fiberglass insulation are used around the pressure gauge stem attachment to ensure that the stem was always above the equilibrium chamber pressure, preventing condensation. Prior to each use, the P−x apparatus was cleaned, sealed, and checked for leaks. The apparatus was cleaned with acetone, joints were sealed, and valves were heated, coated lightly with vacuum grease, and assembled. After assembly, the pressure was lowered to 0.013 kPa by connecting to a vacuum pump for 10 min. All valves were then closed, and the apparatus was left for 20 min and checked to make sure the pressure had not increased due to leaks. Procedure for VLE Experiments. A temperature of 60.0 °C was selected for VLE experiments that provided for reasonable vapor pressures for water. After testing for leaks, the equilibrium chamber was filled with approximately 50 mL of the less volatile 1063
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collected from experiments starting at each side of the composition range. The P−x line is only moderately nonideal in the liquid with some curvature in the bubble pressure line at high water concentration. For the HOC method, η values of 2.5 for levulinic acid + water and 4.5 for levulinic acid and itself were assumed as summarized in Table 4. These values were based on the assumption that levulinic acid would behave similarly to acetic acid in water and that levulinic acid would have selfinteractions similar to acetic acid. The model compares well with the isobaric T−x−y data reported by Shil’nikova and Ekimova6 as shown in Figure 3. Ethyl Levulinate + Water VLLE System. Isothermal VLLE data for the ethyl levulinate + water system at 60.0 °C are summarized in Table 5. The binary parameters are summarized in Tables 3 and 4, giving γEtLv∞ = 25.2, γwat∞ = 4.35 at 60.0 °C. Figure 4 compares the experimental data and the NRTL-HOC model. The NRTL-HOC bubble line fits the data well at water concentrations less than 45 mol %. At water concentration between 45 mol % and 95 mol %, the three-phase VLLE is at a slightly lower pressure than the data suggests indicated with the asterisk (∗) in Table 5. No effort was taken to identify the experimental L+L phase boundaries with certainty. The value of α = 0.285 is recommended in the ASPEN for systems exhibiting liquid−liquid immiscibility. The η values for the HOC method were 1.3 for ethyl levulinate + water and 0.53 for ethyl levuilnate and itself. These values are based on the assumption that ethyl levulinate would behave similarly to ethyl acetate for the purposes considered. Ethanol + Levulinic Acid VLE System. Isothermal VLE data for the ethanol + levulinic acid system were collected at 60 °C. Owing to the hygroscopic nature of levulinic acid, between 2 mol % and 5 mol % water was detected in each sample, as shown in Table 6. The system was treated as a ternary system for regression of the ethanol + levulinic acid constants. The binary interaction parameters were regressed after the levulinic acid + water regression already established the parameters for that binary pair. Final binary NRTL parameters are shown in Table 3, giving γEtOH∞ = 0.912, γLvA∞ = 1.19 at 60.0 °C. Experimental P−x data are compared to the regressed data using the dash−dot lines in Figure 5. Also included in the plot is the binary prediction of the ethanol + levulinic acid system. The NRTL parameter α = 0.3 was used. The HOC parameters for levulinic acid + ethanol and levulinic acid with itself were 2.5 and 4.5, respectively, as tabulated in Table 4. This assumes that levulinic acid behaves similarly to acetic acid under the conditions considered. Ethanol + Ethyl Levulinate VLE System. Isothermal VLE data for the ethanol + ethyl levulinate system was collected at 60.0 °C, and recorded in Table 7. In each sample, there was less than (0.1 mol %) levulinic acid present, which was ignored in regression, and between 0.5 and 2 mol % water present. The NRTL parameters for this system were regressed using two methods. One regression was conducted as a ternary system by including water, adjusting only the binary NRTL parameters for ethanol + ethyl levulinate. Parameters for ethyl levulinate + water were fixed to values tabulated in Tables 3 and 4. Another regression was performed using water-free mole fractions for ethanol and ethyl levulinate and ignoring the water. Both parameter sets are presented in Table 3. The HOC η parameters for ethyl levulinate + ethanol and ethyl levulinate with itself were set as 1.3 and 0.53, respectively. Bubble calculations were conducted in ASPEN using binary parameters from both regressions as plotted in Figure 6. There is clearly a better fit to the data when the regression is performed ignoring the
certified glass thermometer. A vial holding rack with room for 10 5-cm3 vials was assembled in the center of the bath. Each vial was filled with a ternary mixture of known overall composition within the two phase region. The mixtures were stirred with a magnetic stir bar for two minutes. The vials were then place in the isothermal bath overnight (for at least 16 h) to equilibrate. After, each vial was taken from the bath and a needle syringe was used to collect a 1 cm3 sample from each phase. The samples were placed in 5-cm3 vials for analysis. Analytical Methods. The liquid compositions of samples from VLE and LLE experiments were determined by GC analysis. Samples were prepared with 15 % to 25 % by weight DMSO, used as an internal standard. A 10 μL syringe was used to collect 1 μL of liquid from the sample containing DMSO. This liquid was surrounded by 4 μL of air on each side in the syringe. The sample was then injected by hand. The Varian 3400 gas chromatograph (GC) operated with an initial oven temperature of 200 °C, thermal conductivity detector temperature of 250 °C, and injector temperature of 270 °C. The oven temperature increased at a rate of 20 (°C/min) for 2.5 min and was held for 3 min. The GC was equipped with a 2 m x 2 mm i.d. Chromosorb 101 80/100 column. Standard Uncertainty in Experimental Data and Regression Methods. The GC was calibrated before each set of samples were tested. Two samples of known composition were used to obtain the relationship between the ratio of peak area and the mixture compositions. The standard uncertainty in compositions based on comparisons of repeated injections of standards is u(x) = ± 0.002. Temperature uncertainty is u(T) = ± 0.05 K. Pressure uncertainty is dominated by the degree of outgassing rather than the precision of the Baratron and is estimated as u(p) = ± 0.25 kPa. All data were regressed using the Maximum Likelihood objective function using the Britt-Luecke Algoririthm within ASPEN 7.3.2
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RESULTS AND DISCUSSION
Levulinic Acid + Water VLE System. Isothermal VLE data for the levulinic acid + water system at 60.0 °C are summarized in Table 2. The binary NRTL parameters obtained are shown in Table 3, giving γLvA∞ = 3.47, γwat∞ = 1.18 at 60.0 °C. The experimental P−x data are compared with the NRTL Hayden O’Connell (HOC) P−x plot generated by the final binary parameters from the regression in Figure 2. The plot shows data Table 2. Isothermal P−x Data for Levulinic Acid + Water at 60.0 °Ca p/kPa
xwater
p/kPa
xwater
0.49 1.59 3.07 4.77 5.64 7.29 8.37 9.65 11.11 12.15 13.47 14.80
0.038 0.070 0.116 0.192 0.233 0.295 0.334 0.379 0.442 0.494 0.552 0.627
16.15 17.55 18.51 18.83 18.48 17.55 16.00 14.13 12.08 8.92 6.92 4.28
0.709 0.819 0.927 0.952 0.908 0.804 0.683 0.590 0.473 0.334 0.264 0.171
a
Data are listed in the order they were collected. Compositions are in mole fraction. u(x) = ± 0.002, u(p) = ± 0.25 kPa, u(T) = ± 0.05 K. 1064
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Table 3. Summary of Regressed NRTL Parameters, τij = bij/T(K) i
water
levulinic acid
(ternary fit) ethanol
(binary fit) ethanol
ethanol
ethyl levulinate
j
ethyl levulinate
water
ethyl levulinate
ethyl levulinate
levulinic acid
levulinic acid
bij bji α
1014.969 64.60453 0.285
−342.585 880.5534 0.3
−159.872 468.892 0.3
398.2682 −74.662 0.3
585.396 −376.308 0.3
−285.428 336.234 0.3
Table 5. Isothermal P−x Data for Ethyl Levulinate + Water at 60.0 °Ca
Figure 2. P−x diagram for levulinic acid (LvA) + water at 60.0 °C compared with the NRTL-HOC model. Data are shown as collected starting from each side of the composition range.
ethanol
water
levulinic acid
ethyl levulinate
1.4 1.55 2.5 1.3
1.55 1.7 2.5 1.3
2.5 2.5 4.5 2
1.3 1.3 2 0.53
xwater
p/kPa
xwater
1.41 2.89 4.11 5.43 6.75 8.25 9.40 10.68 12.65 14.04 15.60 18.01
0.022 0.034 0.047 0.068 0.080 0.102 0.129 0.142 0.188 0.220 0.256 0.345
19.47 19.77 19.80 19.77 19.80 19.79 19.79 18.83 16.68 12.00 6.09 19.71
0.471 0.993 0.981* 0.961* 0.919* 0.844* 0.712* 0.404 0.309 0.175 0.073 0.689
a
Data are listed in the order they were collected. Compositions are in mole fraction. The approximate three-phase region is denoted by the asterisk (∗) where overall liquid compositions are tabulated, not composition of a single liquid phase. u(x) = ± 0.002, u(p) = ± 0.25 kPa, u(T) = ± 0.05 K.
Table 4. Hayden-O’Connell η Parameters Used in Data Regressiona ethanol water levulinic acid ethyl levulinate
p/kPa
a
All parameters are from the Aspen database except ethyl levulinate and levulinic acid that were assumed to have the same parameters as ethyl acetate and acetic acid, respectively.
Figure 4. P−x diagram for ethyl levulinate + water at 60.0 °C compared with the NRTL-HOC model. Data are shown as collected starting from each side of the composition range.
water in the analysis were not present during the experiment. The fit of the binary system gives γEtOH∞ = 1.84, γEtLv∞ = 2.60 at 60.0 °C. During the course of experiments, we noted that ethyl levulinate purified to less than 200 ppm of water absorbed water from the air quickly enough to contain up to 1.5 % by weight water in less than a few hours. We speculate that samples from this series may have absorbed water from the ambient air while they were being processed outside of the P−x apparatus such as when adding DMSO or taking smaller samples for gas chromatography analysis. This would mean that the recorded vapor pressure values were actually recorded when less water was present than that calculated by GC analysis. Despite the uncertainty in this system, we consider the data will be useful
Figure 3. Comparison of levulinic acid + water T−x−y data of Shil’nikova and Ekimova with the model obtained by fitting the P−x data.
presence of the small amount of water in the samples. From Figure 6, it is apparent that the bubble pressure from the ternary fit overestimates bubble pressure at high ethyl levulinate mole fractions. The results suggest that the small mole fractions of 1065
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Table 6. P−x Data and Model for Ethanol + Levulinic Acid + Water at 60.0 °C Used to Regress Interaction Parameters for Ethanol + Levulinic Acida
Table 7. P−x Data for the System Ethanol + Ethyl Levulinate at 60.0 °Ca ternary
binary
p/kPa
p/kPa (model)
xwater
xEtOH
xLvA
p/kPa
xEtOH
xEtLv
xwater
xEtOH
xEtLv
4.80 9.20 13.91 18.75 23.12 27.61 32.18 36.50 41.28 44.24 41.72 37.14 30.62 25.72 19.00 12.51 6.57
5.36 9.11 13.51 18.35 22.50 27.43 31.95 36.22 42.01 44.76 42.69 37.45 29.80 24.99 17.69 11.65 6.52
0.041 0.046 0.043 0.040 0.037 0.037 0.035 0.027 0.020 0.013 0.024 0.032 0.039 0.038 0.035 0.029 0.028
0.096 0.171 0.261 0.358 0.441 0.539 0.633 0.732 0.869 0.938 0.880 0.754 0.585 0.489 0.349 0.234 0.129
0.862 0.784 0.696 0.602 0.521 0.424 0.332 0.241 0.111 0.049 0.096 0.214 0.376 0.472 0.616 0.737 0.843
2.68 9.51 12.05 14.95 17.36 19.96 22.49 25.08 28.09 31.44 33.58 36.12 38.81 41.93 44.24 45.58 1.16 5.04 6.95
0.031 0.114 0.155 0.193 0.242 0.286 0.336 0.382 0.457 0.544 0.610 0.671 0.769 0.868 0.941 0.955 0.009 0.055 0.081
0.956 0.871 0.828 0.786 0.743 0.699 0.652 0.603 0.532 0.444 0.380 0.318 0.222 0.126 0.051 0.038 0.979 0.929 0.906
0.012 0.015 0.017 0.021 0.015 0.014 0.012 0.014 0.012 0.013 0.010 0.012 0.009 0.007 0.008 0.006 0.012 0.017 0.013
0.032 0.116 0.158 0.197 0.246 0.290 0.340 0.388 0.462 0.551 0.616 0.679 0.776 0.873 0.949 0.961 0.009 0.056 0.082
0.968 0.884 0.842 0.803 0.754 0.710 0.660 0.612 0.538 0.449 0.384 0.321 0.224 0.127 0.051 0.039 0.991 0.944 0.918
a
The second column provides the bubble pressure from the regressed model at the listed composition. Data are listed in the order collected. Compositions are in mole fraction. u(x) = ± 0.002, u(p) = ± 0.25 kPa, u(T) = ± 0.05 K.
a
Water absorption in the samples is suspected and a second regression is performed on a water-free basis as a binary as discussed in the text. Compositions are in mole fractions. u(x) = ± 0.002, u(p) = ± 0.25 kPa, u(T) = ± 0.05 K.
Figure 5. Comparison of experimental and modeled bubble pressures at 60.0 °C for ethanol + levulinic acid + water as tabulated in Table 6. The fit of the ternary data is shown by the dash−dot line. The solid curves represent the predicted binary behavior of ethanol + levulinic acid after regression.
Figure 6. Comparison of experimental data and models for ethanol + ethyl levulinate at 60.0 °C. For plotting the ternary calculations and experimental data, the abscissa uses the compositions in column five of Table 7 for the corresponding row.
for subsequent researchers, and thus provide the full set of data and parameters. LLE for Ethyl Levulinate + Levulinic Acid + Water. Isothermal LLE data were collected at 30.0 °C for the ternary system ethyl levulinate + levulinic acid + water. Data are summarized in Table 8 and plotted in Figure 7. The liquid−liquid immiscibility region is at small levulinic acid concentrations, less than six mole percent. The levulinic acid peak is somewhat broad on the GC, so uncertainty in mole fractions are estimated to be ± 0.002 for this system, which is consistent with the scatter in the figure in the expanded region shown. The consistency of the data is evaluated with the Othmer−Tobias method7 in Figure 8. While the Othmer−Tobias correlation may not always be linear,8 clustering about a common curve is expected for good data. While the experimental data exhibit some scatter, and some
experimental tie lines exhibit minor crossing, the experiments are very challenging and four additional experiments were rejected due to scatter from the plot. The NRTL parameters for ethyl levulinate + levulinic acid were regressed to fit the data in Figure 7 and tabulated in Table 3, giving γEtLv∞ = 0.870, γLvA∞ = 0.864 at 30.0 °C. Parameters for the other constituent binaries are fixed during regression. Despite using these data for the fitting, the LLE region is overpredicted, though the slopes of the tie lines are approximately correct. The LLE region for the ethyl levulinate + water system is slightly too large, which has some effect on the ternary. No further attempts at fitting LLE and VLE simultaneously were pursued since our application of the model operates in the single liquid-phase 1066
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Table 8. Liquid−liquid Data for Ethyl Levulinate + Levulinic Acid + Water at 30.0 °Ca water-rich, β
organic-rich, α
xLvA
xEtLv
xLvA
xEtLv
0.012 0.014 0.026 0.023 0.004 0.002 0.008 0.000 0.010 0.003 0.007 0.016 0.019 0.017 0.025 0.008 0.009
0.034 0.034 0.054 0.040 0.022 0.021 0.027 0.020 0.028 0.022 0.028 0.032 0.037 0.033 0.047 0.025 0.026
0.050 0.051 0.057 0.054 0.029 0.006 0.033 0.000 0.045 0.017 0.038 0.055 0.055 0.052 0.055 0.034 0.037
0.313 0.297 0.197 0.252 0.461 0.517 0.411 0.558 0.395 0.477 0.366 0.322 0.304 0.318 0.208 0.430 0.435
Figure 8. Othmer−Tobias plot for ethyl levulinate + levulinic acid + water at 30.0 °C. α is the organic-rich phase, and β is the water-rich phase. The correlation uses weight fractions, w, and the abscissa uses weight fractions of water.
Table 9. Liquid−Liquid Data for Ethanol + Ethyl Levulinate + Water at 30.0 °Ca
Each row is a tie line. Compositions are in mole fractions. u(x) = ± 0.002, u(p) = ± 0.25 kPa, u(T) = ± 0.05 K. a
water-rich, β
organic-rich, α
xEtOH
xEtLv
xEtOH
xEtLv
0.000 0.030 0.056 0.052 0.018 0.022 0.044 0.036 0.041 0.034
0.021 0.029 0.063 0.052 0.025 0.026 0.040 0.031 0.034 0.029
0.000 0.049 0.078 0.078 0.037 0.041 0.076 0.068 0.069 0.062
0.569 0.414 0.189 0.222 0.485 0.470 0.308 0.351 0.343 0.386
Each row is a tie line. Compositions are in mole fractions. u(x) = ± 0.002, u(p) = ± 0.25 kPa, u(T) = ± 0.05 K. a
Figure 7. Liquid−liquid equilibria behavior of ethyl levulinate + levulinic acid + water at 30.0 °C. Solid lines are from experiments. Dotted lines are calculated with parameters in Table 3 as described in the text.
region and representation of vapor + liquid data is more important. LLE for Ethanol + Ethyl Levulinate + Water. Isothermal LLE data were collected at 30.0 °C for the ternary system ethanol + ethyl levulinate + water. Data are summarized in Table 9 and plotted in Figure 9, and consistency is evaluated with the Othmer−Tobias correlation in Figure 10. The scatter on the Othmer−Tobias plot for this system is minor. The predicted curves in Figure 9 were generated with parameters obtained by fitting the VLE systems discussed above. As with the levulinic acid system in Figure 7, the liquid−liquid region is modeled to be too large.
Figure 9. Liquid−liquid equilibria for the system ethanol + ethyl levulinate + water at 30.0 °C. Solid lines are from experiments. Dotted lines are calculated from parameters in Table 3
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SUMMARY AND CONCLUSIONS Isothermal P−x data were collected at 60 °C for the water + levulinic acid system, the water + ethyl levulinate system, the ethanol + levulinic acid system, and the ethanol + ethyl levulinate system. LLE data were collected isothermally at 30 °C for the
ethyl levulinate + water + levulinic acid system and the ethyl levulinate + water + ethanol system. The VLE data were successfully modeled using the NRTL-HOC method. The parameters represent VLE conditions with good accuracy. The NRTL model fitted to levulinic acid + water P−x measurements 1067
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(5) Vu, D. T.; Lira, C. T.; Asthana, N.; Miller, D. J. Vapor−liquid Equilibria in the Systems Ethyl Lactate + Ethanol and Ethyl Lactate + Water. J. Chem. Eng. Data 2006, 51, 1220−1225. (6) Shil’nikova, L. L.; Ekimova, N. V. Liquid−Vapor Equilibrium in the System Water + Levulinic Acid. Gidroliz. Lesokhim. Prom-st. 1968, 21 (5), 15−16. (7) Othmer, D. F.; Tobias, P. E. Tie-Line Correlation. Ind. Eng. Chem. 1942, 34, 693−696. (8) Carniti, P.; Cori, L.; Ragani, V. A Critical Analysis of the Hand and Othmer-Tobias Correlations. Fluid Phase Equilib. 1978, 2, 39−47.
Figure 10. Othmer−Tobias plot for ethanol + ethyl levulinate + water at 30.0 °C. α is the organic-rich phase and β is the water-rich phase. The correlation uses weight fractions, w.
reproduces previously published T−x−y data. The ethanol + levulinic acid system and the ethyl levulinate + levulinic acid are nearly ideal in the liquid phase. The systems levulinic acid + water and ethanol + ethyl levulinate have moderate positive deviations. The system water + ethyl levulinate has large positive deviations and exhibits a heteroazeotrope. The LLE data were evaluated for consistency using the Othmer−Tobias method. The LLE regions for both ternary systems are small, and the systems thus have limited use for any extraction process. The NRTL-HOC parameters in this work are useful for only semiquantitate modeling of the LLE regions, especially near the Plait point. The size of the LLE region was overpredicted by the NRTL model. Because the VLE and LLE data are evaluated at only one temperature for each case, the accuracies of the temperaturedependences of the NRTL fits are not evaluated except for levulinic acid + water, and thus should be used at temperatures near the experimental conditions.
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS The financial support of Trenton Fuel Works, LLC is gratefully acknowledged. REFERENCES
(1) Werpy, T.; Petersen, G. Top Value Added Chemicals From Biomass; Pacific Northwest National Laboratory (PNNL) and the National Renewable Energy Laboratory (NREL), US Department of Energy: Richland, WA, 2004. (2) Curran, M. A., Biobased Materials. In Kirk-Othmer Encyclopedia of Chemical Technology; John Wiley & Sons: New York, 2010; pp 1−19. (3) Miller, D. J.; Kolah, A. K.; Lira, C. T., Reactive Distillation for the Biorefinery. In Separation and Purification Technologies in Biorefineries; Huang, H. J.; Ramaswamy, S., Eds.; J.W. Wiley and Sons: New York, NY, 2013. (4) Wilson, G. M. Vapor-Liquid Equilibrium. XI. A New Expression for the Excess Free Energy of Mixing. J. Am. Chem. Soc. 1964, 86 (2), 127− 130, DOI: 10.1021/ja01056a002. 1068
dx.doi.org/10.1021/je400814n | J. Chem. Eng. Data 2014, 59, 1062−1068
