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Thermophysical properties of biodiesel and related systems. Part I. Vapour–liquid equilibrium at low pressures of binary and ternary systems involving methanol, ethanol, glycerol, water and NaCl
J. Chem. Thermodynamics 58 (2013) 398–404
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Thermophysical properties of biodiesel and related systems. Part I. Vapour–liquid equilibrium at low pressures of binary and ternary systems involving methanol, ethanol, glycerol, water and NaCl Josamaique G. Veneral a, Tassio Benazzi a, Marcio A. Mazutti b, Fernando A.P. Voll c, Lúcio Cardozo-Filho c, Marcos L. Corazza d, Reginaldo Guirardello e, J. Vladimir Oliveira a,f,⇑ a
Department of Food Engineering, URI – Campus de Erechim, Erechim, RS 99700-000, Brazil Department of Chemical Engineering, UFSM, Santa Maria, RS 97105-900, Brazil c Department of Chemical Engineering, UEM, Maringá, PR 87020 900, Brazil d Department of Chemical Engineering, UFPR, Curitiba, PR 81531-990, Brazil e College of Chemical Engineering, UNICAMP, Campinas, SP 13083-970, Brazil f Department of Chemical and Food Engineering, UFSC, Florianópolis, SC 88040-900, Brazil b
a r t i c l e
i n f o
Article history: Received 22 June 2012 Received in revised form 25 September 2012 Accepted 28 September 2012 Available online 8 November 2012 Keywords: VLE Methanol Ethanol Glycerol NaCl UNIQUAC model
a b s t r a c t Experimental vapour–liquid equilibrium data of several binary mixtures (methanol + glycerol), (ethanol + glycerol) and (glycerol + water) and ternary (methanol + glycerol + water), (ethanol + glycerol + water) and (water + glycerol + NaCl) were obtained over the pressure range of 6.7 kPa to 66.7 kPa through an Othmer-type ebulliometer, allowing the construction of temperature – mass fraction and pressure – temperature diagrams. It is shown that the systems without NaCl were satisfactorily represented by the UNIQUAC model with good agreement between theory and experimental results. It was observed that alcohol concentrations lower than 10 wt% increase the phase transition temperature. The systems investigated show positive deviations in relation to Raoult’s law. Results presented in this work may be relevant in process design towards efficient recovering of components in the biodiesel down-stream processes. Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction Production of biofuels has been widely studied in recent years because of its potential to solve many of the current social problems and concerns, from air pollution and global warming to other environmental improvements and sustainability issues [1,2]. It is well known that biodiesel production affords glycerol as a by-product together with low amounts of alcohol (methanol or ethanol), water and also some salt residues. Ternary and binary mixtures involving these components are commonly found in the downstream of biodiesel manufacturing process [3,4]. Due to surplus glycerol derived from biodiesel production, a substantial decrease in the price of glycerol may be possible in the near future. Glycerol has several different potential uses in medicine, pharmaceutical products (drugs) and personal care preparations (cosmetics and toothpastes), tobacco and food processing ⇑ Corresponding author at: Department of Food Engineering, URI – Campus de Erechim, Erechim, RS 99700-000, Brazil. Tel.: +55 48 37212508; fax: +55 48 37219687. E-mail address: [email protected] (J. Vladimir Oliveira). 0021-9614/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jct.2012.09.032
(as a food additive, solvent, sweetener or a component of food packaging materials) and as a raw material in different chemical industries, for example, in the production of acetals, amines, esters and ethers, mono- and di-glycerides and urethane polymers [5]. Thus, inexpensive and practical methods to recover glycerol and alcohol from aqueous solutions are welcome. Among separation techniques used to recover ternary and binary systems involving these components, distillation is certainly the most reported in literature. The use of this technique requires the determination of experimental vapour–liquid equilibrium data (VLE), which are essential to process design and operation. Although separation processes involving biodiesel systems is of great interest, surprisingly there are just a few reports in the literature regarding VLE data of related systems. For example, only (methanol + glycerol) and (glycerol + water) VLE binary systems have been reported in the literature [6]. Over the past years, extractive distillation using a salt as extractive solvent has attracted much attention. The main idea of using a salt for the extractive distillation is to change the relative volatility of the constituents, a phenomenon known as the salting-in or -out effect on vapour–liquid equilibria [7]. As a result, the azeotropic
J.G. Veneral et al. / J. Chem. Thermodynamics 58 (2013) 398–404
point is shifted or eliminated, when the salt-free mixture has an azeotropic point [8]. For example, Chen and Thompson [9] showed that the activity coefficients of both water and glycerol for the ternary system are decreased over the entire range by the presence of sodium chloride. This fact would be expected as the salt has a marked solubility in both liquids which would tend to reduce the escaping tendency of both water and glycerol. Furthermore, the salt effect was shown to be more pronounced in the case of glycerol, as sodium chloride is more soluble in glycerol. Besides, as demonstrated by Wang et al. [7], a salt can be used as an efficient solvent for the extractive distillation of (ethanol + water) mixtures due to its notable salting-out effect, which lowers the vapour pressure of water, increasing the volatility of ethanol, hence eliminating the azeotropic phenomenon of the (water + ethanol) mixture. In this sense, the main objective of this work is to report lowpressure vapour–liquid equilibrium data for binary and ternary systems involving glycerol, methanol, ethanol, water and sodium chloride. Experimental bubble-point temperature data over a wide composition range for pressures ranging from 6.7 kPa to 66.7 kPa were obtained using an Othmer-type ebulliometer [10]. All results, except those systems with NaCl, were correlated with UNIQUAC activity coefficient model. 2. Experimental 2.1. Materials The provenance and purity of the compounds employed in this work are presented in table 1. Deionised water was used as reagents without previous treatment. TABLE 1 Provenance and purity of the compounds employed in this work. Component
Manufacturer
Minimum mass fraction purity
Methanol Ethanol Glycerol Sodium hydroxide
Merck Merck Nuclear Quimex
0.999 0.999 0.995 0.970
399
2.2. Ebulliometric method Vapour–liquid equilibrium data were obtained in an Othmertype ebulliometer. An absolute pressure transducer (Smar, LD301, A3 model) equipped with a portable programmer (Smar, HT 201), with a precision of 0.3 kPa was used to measure the pressure and two thermo-resistances (PT100) with an accuracy of ±0.1 K (Novus, Brazil). These were connected to a digital acquisition board (FieldLogger, NOVUS) with interval of 30 seconds between each acquisition, which was used for temperature monitoring. A general outline of the experimental apparatus is presented in figure 1. The boiling point temperatures were obtained at several pressures ranging from 6.7 kPa to 66.7 kPa at a fixed global composition. Mixtures of ternary and binary systems were prepared gravimetrically using an analytical balance (Ohaus Analytical Standard with 0.0001 g accuracy). An ultrathermostatic water bath (TE-184 TECNAL) at T = 276.15 K was coupled to the condensers of the ebulliometer in order to prevent vapour losses from the system. After the temperature of the condensers was reached, a sample amount of approximately 300 g was added to the mixing chamber. When the steady-state was reached, characterized by a constant equilibrium temperature and pressure and uniform drop rate for at least 10 min, the temperature was recorded. Subsequently, a new pressure was applied and kept constant and the ebullition temperature was obtained as a new equilibrium value. Experimental apparatus was always operated from the lowest to the highest measured pressure in order to avoid system overheating. The boiling mixture was maintained so that a drop count of 60 drops per minute was achieved, as suggested by Malanowski [11]. 3. Thermodynamic modelling The experimental VLE results without NaCl were correlated using the UNIQUAC model [12]. The boiling temperatures of the pure liquids at the experimental pressures evaluated were obtained from the Antoine equation:
log PSat i =Pa ¼ A B=ðT=K þ CÞ;
ð1Þ
FIGURE 1. Experimental apparatus for vapour–liquid equilibrium measurements. (1) Computer, (2) vacuum pump, (3) data acquisition system, (4) trap, (5) magnetic stirrer, (6) ebulliometer, (7) digital PT100 thermo-resistance, (8) pressure digital transducer, (9) heating tape, (10) voltage regulator, (11) ultrathermostatic bath.
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TABLE 2 Constants for the Antoine equation and UNIQUAC parameters r and q for pure components.
TABLE 3 VLE experimental data for the system {methanol (1) + glycerol (2)} at various pressures.* w1a
Component
A
B
C
r
q
Methanol Ethanol Glycerol Water
9.2023 11.0835 8.7365 10.1620
1056.52 2085.87 1356.47 1718.37
85.97 7.75 200.00 39.96
1.9011 2.5755 4.7957 0.9200
2.0480 2.5880 4.9080 1.4000
p = 6.7 kPa 0.000 0.050 0.075 0.100 0.200 0.300 0.400 0.500 0.600 0.700 0.800 0.900 1.000
where P Sat is the saturation pressure of component i at temperature i T and A, B and C are adjustable parameters. Due to technical limitations of the ebulliometer used in the present work, data were obtained up to T = 520 K, and hence bubble point data of pure glycerol above this temperature reported by Soujanya et al. [6] were utilized for a best fit of the Antoine equation. The Antoine constants for all pure liquid components are presented in table 2 together with the r and q parameters of the UNIQUAC model, which were calculated using the parameters Rk and Qk reported by Magnussen et al. [13]. The binary interaction parameter fitting were based on the minimization of the following objective function:
OFðTÞ ¼
NP X 2 ðT calc T exp i i Þ ;
ð2Þ
where NP is the number of experimental points, T calc is the calcui lated boiling temperature and T exp is the experimental boiling i temperature. The UNIQUAC model parameters were then used to calculate the activity coefficients of each component in the mixture (ci). These activity coefficients were used to calculate the corresponding vapour phase (ycalc ) in the bubble point, according to the foli lowing equation:
ci xi PSat i Pexp
;
NP X ycalc ¼ 1: i
b *
In the estimation procedure for the parameters, the calculated boiling temperature (T calc p ) and the binary (aij) interaction parameters of the UNIQUAC model were considered as decision variables. The interaction parameters were estimated using the tool ‘‘solver’’ included in the spreadsheet Excel for Windows, together to the ‘‘XSEOS’’ supplements package [14]. The absolute mean deviation (AAD%) between experimental and calculated boiling temperatures was calculated according to the following equation: NP 100 X DT i exp : NP T i i
a
384.45 370.55 361.35 343.45 336.65 332.75 330.55 329.25 328.05 326.75 325.65 324.65
w1
T/K
p = 13.3 kPa 0.000 0.050 0.075 0.100 0.200 0.300 0.400 0.500 0.600 0.700 0.800 0.900 1.000
493.35 340.65 331.65 322.95 308.95 303.05 299.75 298.15 297.05 296.15 295.25 294.45 293.75
p = 40.0 kPa 0.050 0.075 0.100 0.200 0.300 0.400 0.500 0.600 0.700 0.800 0.900 1.000
371.95 358.85 349.75 333.05 326.65 323.05 321.05 319.85 318.75 317.65 316.65 315.75
w1
T/K
p = 20.0 kPa 0.000 0.050 0.075 0.100 0.200 0.300 0.400 0.500 0.600 0.700 0.800 0.900 1.000
505.55 350.45 340.55 331.75 317.05 311.15 307.85 306.25 305.15 304.05 303.05 302.25 301.45
p = 46.7 kPa 0.050 0.075 0.100 0.200 0.300 0.400 0.500 0.600 0.700 0.800 0.900 1.000
376.95 362.95 353.85 336.85 330.35 326.65 324.55 323.35 322.25 321.15 320.05 319.05
w1
T/K
p = 26.7 kPa 0.000 0.050 0.075 0.100 0.200 0.300 0.400 0.500 0.600 0.700 0.800 0.900 1.000
513.95 358.45 347.65 338.75 323.35 317.35 314.05 312.35 311.15 310.05 309.05 308.15 307.35
p = 53.3 kPa 0.050 0.075 0.100 0.200 0.300 0.400 0.500 0.600 0.700 0.800 0.900 1.000
381.25 366.85 357.75 340.25 333.55 329.75 327.55 326.35 325.25 324.15 323.05 322.05
p = 66.7 kPa 0.050 0.075 0.100 0.200 0.300 0.400 0.500 0.600 0.700 0.800 0.900 1.000
388.35 374.05 364.65 346.35 339.35 335.45 333.25 331.95 330.65 329.35 328.25 327.25
w1 Denotes the mass fraction of component 1 in the liquid phase. T, system temperature. Estimated standard error of 0.6%.
ð4Þ
i
AADð%Þ ¼
520.65 365.45 353.95 344.95 328.65 322.35 318.85 316.95 315.75 314.65 313.65 312.65 311.85
p = 60.0 kPa 0.050 0.075 0.100 0.200 0.300 0.400 0.500 0.600 0.700 0.800 0.900 1.000
ð3Þ
where xi is the mole fraction of component i in the mixture and Pexp is the experimental pressure of the system. In equation (5) the vapour phase was assumed to follow ideal behaviour. During the minimization process, the following constraint should be observed:
477.25 324.55 316.35 309.75 296.45 290.65 287.45 285.95 285.25 284.55 283.85 283.15 282.55
p = 33.3 kPa 0.000 0.050 0.075 0.100 0.200 0.300 0.400 0.500 0.600 0.700 0.800 0.900 1.000
i
ycalc ¼ i
T/Kb
ð5Þ
4. Results and discussion Tables 3–5 present, the experimental VLE results for the binary systems {methanol (1) + glycerol (2)}, {ethanol (1) + glycerol (2)} and {water (1) + glycerol (2)}, respectively, which were obtained at different compositions for the pressure range of 6.7 kPa to 66.7 kPa.
Figure 2 presents a comparison between experimental values obtained in this work and those reported by Soujanya et al. [6] for the system {methanol (1) + glycerol (2)}, where good agreement can be observed, thus demonstrating the reliability of the experimental apparatus and procedure adopted for measuring VLE of the systems investigated. Tables 6 and 7 present the experimental VLE data for the ternary systems {methanol (1) + glycerol (2) + water (3)} and {ethanol (1) + glycerol (2) + water (3)} obtained at different overall compositions for pressure ranging from 6.7 kPa to 66.7 kPa. In this work, boiling temperature measurements for the systems with the NaCl electrolyte component was also investigated. Before evaluation of the effect of NaCl on the VLE data, it is necessary to access the region of total miscibility of such compounds to avoid precipitation and formation of a solid phase. For this purpose, the concentrations of NaCl in binary liquid solutions reported by Chen and Thompson [9] were used for VLE measurements. Table 8 presents the experimental VLE data for the ternary system {water (1) + glycerol (2) + NaCl (3)} obtained considering water mass fraction in the range of 0.0 to 0.4 at 7 wt% of NaCl in relation to the {water (1) + glycerol (2)} mixture, while table 9 contains the experimental VLE data for the system {water
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J.G. Veneral et al. / J. Chem. Thermodynamics 58 (2013) 398–404 TABLE 4 VLE experimental data for the system {ethanol (1) + glycerol (2)} at various pressures.* T/Kb
w1a
w1
p = 6.7 kPa 0.000 0.050 0.075 0.100 0.200 0.300 0.400 0.500 0.600 0.700 0.800 0.900 1.000
477.25 335.95 327.35 319.55 307.85 302.55 299.85 298.65 297.75 296.95 296.35 295.75 295.25
0.000 0.050 0.075 0.100 0.200 0.300 0.400 0.500 0.600 0.700 0.800 0.900 1.000
p = 33.3 kPa 0.000 0.050 0.075 0.100 0.200 0.300 0.400 0.500 0.600 0.700 0.800 0.900 1.000
520.65 376.75 365.95 355.85 341.65 334.75 331.55 330.15 329.15 328.05 327.15 326.35 325.65
a b *
394.55 382.95 372.45 355.95 348.55 345.55 343.85 342.65 341.45 340.45 339.55 338.65
493.35 352.65 341.65 334.25 321.55 315.35 312.45 311.25 310.25 309.35 308.55 307.95 307.45
p = 40.0 kPa 0.050 0.075 0.100 0.200 0.300 0.400 0.500 0.600 0.700 0.800 0.900 1.000
p = 60.0 kPa 0.050 0.075 0.100 0.200 0.300 0.400 0.500 0.600 0.700 0.800 0.900 1.000
T/K
p = 13.3 kPa
382.35 371.35 360.85 346.45 338.95 335.65 334.25 333.15 332.05 331.15 330.25 329.55
w1
T/K
w1
p = 20.0 kPa 0.000 0.050 0.075 0.100 0.200 0.300 0.400 0.500 0.600 0.700 0.800 0.900 1.000
505.55 362.85 351.65 343.75 329.85 323.45 320.45 319.25 318.25 317.35 316.45 315.75 315.05
0.000 0.050 0.075 0.100 0.200 0.300 0.400 0.500 0.600 0.700 0.800 0.900 1.000
p = 46.7 kPa 0.050 0.075 0.100 0.200 0.300 0.400 0.500 0.600 0.700 0.800 0.900 1.000
T/K
p = 26.7 kPa 513.95 370.75 359.65 350.55 336.05 329.35 326.65 325.35 324.35 323.45 322.55 321.75 321.05
p = 53.3 kPa
386.45 375.65 364.85 348.75 342.55 339.35 337.85 336.65 335.55 334.55 333.65 332.85
0.050 0.075 0.100 0.200 0.300 0.400 0.500 0.600 0.700 0.800 0.900 1.000
390.45 379.25 368.95 352.85 345.55 342.65 341.05 339.85 338.65 337.65 336.75 335.95
FIGURE 2. Comparison of VLE data for the system (methanol + glycerol).
TABLE 6 VLE experimental data for the system {methanol (1) + glycerol (2) + water (3)} at various pressures.*
397.85 385.95 375.85 359.25 351.35 348.35 346.55 345.35 344.15 343.05 342.05 341.15
a b *
TABLE 5 VLE experimental data for the system {water (1) + glycerol (2)} at various pressures.* T/Kb p = 6.7 kPa 0.000 0.047 0.115 0.227 0.439 1.000 a b *
p = 6.7 kPa
p = 13.3 kPa
p = 26.7 kPa
0.200 0.600 0.200
0.200 0.200 0.600
300.15 287.95 296.85
312.85 300.85 309.55
326.85 314.15 323.75
p = 40.0 kPa
p = 53.3 kPa
p = 66.7 kPa
0.200 0.600 0.200
0.200 0.200 0.600
335.95 322.95 333.15
342.55 329.45 340.05
348.15 334.75 345.95
477.25 360.55 336.75 323.65 316.75 311.15
w1
T/K p = 13.3 kPa
0.000 0.047 0.115 0.227 0.439 1.000
493.35 377.65 352.85 338.05 330.45 324.55
w1
T/K p = 66.7 kPa
0.047 0.115 0.227 0.439 1.000
w1 Denotes the mass fraction of components 1 and 2 in the liquid phase. T, system temperature. Estimated standard error of 0.9%.
TABLE 7 VLE experimental data for the system {ethanol (1) + glycerol (2) + water (3)} at various pressures.*
w1 Denotes the mass fraction of component 1 in the liquid phase. T, system temperature. Estimated standard error of 0.5%.
w1a
w2
p = 66.7 kPa 0.050 0.075 0.100 0.200 0.300 0.400 0.500 0.600 0.700 0.800 0.900 1.000
T/Kb
w1a
428.05 396.65 379.65 368.45 361.85
w1 Denotes the mass fraction of component 1 in the liquid phase. T, system temperature. Estimated standard error of 0.7%.
(1) + glycerol (2) + NaCl (3)} for water mass fraction of 0.5 to 1 at 15 wt% of NaCl. Both systems were evaluated in the pressure range from 6.7 kPa to 66.7 kPa. In order to evaluate the NaCl effect on the {water (1) + glycerol (2) + NaCl (3)} ternary system, presented in figure 3 is a comparison between boiling point temperatures with and without the salt.
a b *
T/Kb
w1a
w2 p = 6.7 kPa
p = 13.3 kPa
p = 26.7 kPa
0.200 0.600 0.200
0.200 0.200 0.600
303.25 298.35 303.85
314.95 310.05 316.65
329.55 323.45 331.35
p = 40.0 kPa
p = 53.3 kPa
p = 66.7 kPa
0.200 0.600 0.200
0.200 0.200 0.600
338.45 332.05 340.95
344.95 338.65 347.85
350.35 343.85 353.45
w1 Denotes the mass fraction of components 1 and 2 in the liquid phase. T, system temperature. Estimated standard error of 0.8%.
From this figure, it can be clearly observed that there is an increase in boiling temperatures of the (water + glycerol) system with increasing NaCl content. Note also the existence of two distinct trends in the (water + glycerol + NaCl) ternary system, viz. in the water ranges of 0.0 to 0.4 and 0.5 to 1. This behaviour may be due to the two different concentrations of NaCl in free-basis utilized in this work. The greatest differences of boiling temperatures between the systems occur in regions of high NaCl saturation in the ternary system. Similar results were obtained by Chen and Thompson [9] in evaluating the same systems, but at atmospheric pressure.
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J.G. Veneral et al. / J. Chem. Thermodynamics 58 (2013) 398–404
TABLE 8 VLE experimental data for the system (water (1) + glycerol (2) + NaCl (3)} at various pressures and 7 wt% NaCl concentration.* w1a
T/Kb
w1
T/K
w1
T/K
w1
T/K
w1
T/K
7 g of NaCl/100 g of mixture p = 6.7 kPa 0.000 0.050 0.075 0.100 0.200 0.300 0.400
479.85 361.65 352.25 345.05 329.95 323.45 320.35
p = 13.3 kPa 0.000 0.050 0.075 0.100 0.200 0.300 0.400
p = 40.0 kPa 0.050 0.075 0.100 0.200 0.300 0.400 a b *
419.45 403.25 392.85 372.35 363.95 359.85
496.05 383.45 370.45 362.35 345.55 338.25 334.55
p = 20.0 kPa 0.000 0.050 0.075 0.100 0.200 0.300 0.400
p = 46.7 kPa 0.050 0.075 0.100 0.200 0.300 0.400
425.15 408.15 397.65 376.45 367.75 363.55
508.25 395.95 382.25 373.05 354.85 347.35 343.45
p = 26.7 kPa 0.000 0.050 0.075 0.100 0.200 0.300 0.400
p = 53.3 kPa 0.050 0.075 0.100 0.200 0.300 0.400
429.95 412.35 401.75 380.25 371.35 367.05
516.75 405.55 390.95 380.95 361.85 354.15 350.25
p = 33.3 kPa 0.000 0.050 0.075 0.100 0.200 0.300 0.400
p = 60.0 kPa 0.050 0.075 0.100 0.200 0.300 0.400
523.55 413.15 397.75 387.55 367.65 359.55 355.55 p = 66.7 kPa
434.45 416.35 405.35 383.55 374.55 370.25
0.050 0.075 0.100 0.200 0.300 0.400
438.45 420.05 408.55 386.55 377.45 373.05
T/K
w1
T/K
w1 Denotes the mass fraction of component 1 in the liquid phase. T, system temperature. Estimated standard error of 0.9%.
TABLE 9 VLE experimental data for the system {water (1) + glycerol (2) + NaCl (3)} at various pressures and 15 wt% NaCl concentration.* w1a
T/Kb
w1
T/K
w1
T/K
w1
15 g of NaCl for 100 g of mixture p = 6.7 kPa 0.500 0.600 0.700 0.800 0.900 1.000
320.15 318.55 317.15 315.95 314.85 313.85
p = 13.3 kPa 0.500 0.600 0.700 0.800 0.900 1.000
p = 40.0 kPa 0.500 0.600 0.700 0.800 0.900 1.000 a b *
359.85 357.75 356.05 354.35 353.05 352.05
334.65 332.65 331.05 329.65 328.45 327.45
p = 20.0 kPa 0.500 0.600 0.700 0.800 0.900 1.000
p = 46.7 kPa 0.500 0.600 0.700 0.800 0.900 1.000
363.65 361.45 359.75 357.95 356.65 355.65
343.65 341.55 339.95 338.55 337.35 336.35
p = 26.7 kPa 0.500 0.600 0.700 0.800 0.900 1.000
p = 53.3 kPa 0.500 0.600 0.700 0.800 0.900 1.000
367.05 364.85 363.05 361.25 359.95 358.95
350.25 348.15 346.45 344.95 343.65 342.65
p = 33.3 kPa 0.500 0.600 0.700 0.800 0.900 1.000
p = 60.0 kPa 0.500 0.600 0.700 0.800 0.900 1.000
370.25 367.95 366.15 364.25 362.95 361.85
355.55 353.45 351.75 350.15 348.85 347.85 p = 66.7 kPa
0.500 0.600 0.700 0.800 0.900 1.000
373.05 370.75 368.95 367.05 365.75 364.65
w1 Denotes the mass fraction of component 3 in the liquid phase. T, system temperature. Estimated standard error of 0.9%.
FIGURE 3. T–w diagram at different pressures for the ternary system (water + glycerol + NaCl) with different concentrations of NaCl. Values are presented in terms of mass fraction and NaCl free-basis.
The UNIQUAC model parameters for the various systems at the different experimental pressures together with the deviations of the predicted values for the experimental temperatures, represented in terms of the average absolute deviation are presented in table 10. The determination of the parameters was performed in order to obtain global parameters for all pressure ranges examined. Therefore, the binary interaction parameters were obtained first through modelling all boiling point data of each binary system evaluated, which then were fixed during modelling of the ternary systems. It should be noted that the interaction parameters for the (methanol + water) and (ethanol + water) binary systems were obtained through modelling the data reported by Soujanya et al. [6] and Gmehling and Onken [15], respectively. Figures 4–6 contain the comparison between experimental and calculated VLE values for the binary systems formed by (methanol + glycerol), (ethanol + glycerol) and (water + glycerol), respectively, where it can be seen that the thermodynamic modelling is capable of representing the experimental results fairly well, with deviations lower than 0.018% (see table 10). It is also noted from these figures that the phase transition temperature increases shar-
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J.G. Veneral et al. / J. Chem. Thermodynamics 58 (2013) 398–404 TABLE 10 Binary interaction parameters of UNIQUAC model fitted in this work. Systems
Methanol (1) + water (2) Methanol (1) + glycerol (2) Ethanol (1) + water (2) Ethanol (1) + glycerol (2) Water (1) + glycerol (2) a b
Temperature range/K
296.10–362.10 282.55–388.35 295.25–361.85 295.25–397.85 311.15–428.05
UNIQUAC
Duij/Ka
Duji/Ka
AAD/%b
313.7440 319.9054 244.5568 309.6746 197.8038
155.6420 165.3075 36.7978 138.7338 179.1049
0.0017 0.0020 0.0017 0.0021 0.0179
Binary interaction parameters of UNIQUAC model. AAD% denotes the average absolute deviation between all the experimental and calculated boiling temperatures of each system.
FIGURE 4. Temperature (T) versus mass fraction (w) diagram for (methanol + glycerol) binary system at different pressures.
FIGURE 5. Temperature (T) versus mass fraction (w) diagram for (ethanol + glycerol) binary system at different pressures.
ply in mixtures with low alcohol concentration (methanol or ethanol) or water, due to the great difference between the molar mass of the substances contained in the mixtures. Both systems present a highly non-ideal behaviour and positive deviations from Raoult’s law. Note also in figure 6 that our data for the (water + glycerol) system agree within 0.041% with those reported by Gmehling and Onken [15]. Presented in figures 7 and 8 are the experimental and calculated VLE results for the ternary systems constituted by (metha-
FIGURE 6. Temperature (T) versus mass fraction (w) diagram for (water + glycerol) binary system at different pressures.
FIGURE 7. Vapour pressure (p) versus temperature (T) diagram at different overall compositions for the ternary system (methanol + glycerol + water).
nol + glycerol + water) and (ethanol + glycerol + water), respectively. It can be observed that the UNIQUAC model was able to describe satisfactorily the trends of isobar curves in the ternary systems, although higher deviations between experimental and calculated values were verified when compared to the binary systems. It is interesting to observe from figure 7 despite the fact that the boiling temperature of glycerol is greater than that of water, one
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ebulliometer. Systems without NaCl were satisfactorily correlated using the UNIQUAC model. It was observed that low concentrations of alcohol (methanol or ethanol) decrease the phase transition temperature (boiling point temperature) for the systems investigated. All systems evaluated show non-ideal behaviour and positive deviations from Raoult’s Law. Results presented in this report can be useful in the downstream process to recovery of constituents (alcohol and glycerol) of biodiesel industrial plant. Acknowledgements The authors thank CNPq, Fundação Araucaria and Pró-Engenharias/CAPES (Grant no. 076/2008) for the financial support of this work and scholarships. References FIGURE 8. Vapour pressure (p) versus temperature (T) diagram at different overall compositions for the ternary system (ethanol + glycerol + water).
can see that the (methanol + glycerol + water) ternary system at 60 wt% water presents higher phase transition temperatures than those verified at 60 wt% glycerol at the same pressure condition. This may be attributed to the formation of hydrogen bonds between water and methanol molecules, which sharply increase with increasing water concentration. Figure 8 also shows that the presence of strong hydrogen bonds of water and alcohol (in this case ethanol) enhance the mixture boiling temperatures for each system pressure as the water content is enhanced in the ternary mixture of (ethanol + glycerol + water). 5. Conclusions Experimental VLE data at low pressures for several binary systems {methanol (1) + glycerol (2)}, {ethanol (1) + glycerol (2)} and {water (1) + glycerol (1)} and ternary {methanol (1) + glycerol (2) + water (3)}, {ethanol (1) + glycerol (2) + water (3)} and {water (1) + glycerol (2) + NaCl (3)} were obtained using an Othmer-type
[1] H.L. MacLeana, L.B. Laveb, Prog. Energy Combust. Sci. 29 (2003) 1–69. [2] A.S. Ramadhas, S. Jayaraj, C. Muraleedharan, Renew. Energy 29 (2004) 727– 742. [3] A.P. Vyas, N. Subrahmanyam, P.A. Patel, Fuel 88 (2009) 625–628. [4] A.E. Andreatta, L.M. Casás, P. Hegel, S.B. Bottini, E.A. Brignole, Ind. Eng. Chem. Res. 47 (2008) 5157–5164. [5] L.R. Morrison, R.E. Kirk, D.F. Othmer, Encyclopedia of Chemical Technology: Glycerol, fourth ed., John Wiley & Sons, Inc., Boston, 1997. [6] J. Soujanya, B. Satyavathi, T.E.V. Prasad, J. Chem. Thermodyn. 42 (2010) 621– 624. [7] J.F. Wang, X.M. Li, H. Meng, C.X. Li, Z.H. Wang, J. Chem. Thermodyn. 41 (2009) 167–170. [8] H. Yamamoto, T. Terano, Y. Nishi, J. Tokunaga, J. Chem. Eng. Data 40 (1995) 472–477. [9] D.H.T. Chen, A.R. Thompson, J. Chem. Eng. Data 15 (1970) 471–474. [10] R. Coelho, P.G. Santos, M.R. Mafra, L. Cardozo-Filho, M.L. Corazza, J. Chem. Thermodyn. 43 (2011) 1870–1876. [11] S. Malanowski, Fluid Phase Equilib. 8 (1982) 197–219. [12] B.E. Poling, J.M. Prausnitz, P.J. O’Connell, The Properties of Gases and Liquids, fifth ed., McGraw-Hill, New York, USA, 2000. [13] T. Magnussen, P. Rasmussen, A. Fredenslund, Ind. Eng. Chem. Process Des. Dev. 20 (1981) 331–339. [14] M. Castier, XSEOS Thermodynamic Properties using Excess Gibbs Free Energy Models and Equations of State, 2008. [15] J. Gmehling, U. Onken, Vapour–liquid equilibrium data collection: aqueousorganic systems. 2. ed. Part. 1, Frankfurt; DECHEMA, 1991.
JCT 12-376
Contents lists available at SciVerse ScienceDirect
J. Chem. Thermodynamics journal homepage: www.elsevier.com/locate/jct
Thermophysical properties of biodiesel and related systems. Part I. Vapour–liquid equilibrium at low pressures of binary and ternary systems involving methanol, ethanol, glycerol, water and NaCl Josamaique G. Veneral a, Tassio Benazzi a, Marcio A. Mazutti b, Fernando A.P. Voll c, Lúcio Cardozo-Filho c, Marcos L. Corazza d, Reginaldo Guirardello e, J. Vladimir Oliveira a,f,⇑ a
Department of Food Engineering, URI – Campus de Erechim, Erechim, RS 99700-000, Brazil Department of Chemical Engineering, UFSM, Santa Maria, RS 97105-900, Brazil c Department of Chemical Engineering, UEM, Maringá, PR 87020 900, Brazil d Department of Chemical Engineering, UFPR, Curitiba, PR 81531-990, Brazil e College of Chemical Engineering, UNICAMP, Campinas, SP 13083-970, Brazil f Department of Chemical and Food Engineering, UFSC, Florianópolis, SC 88040-900, Brazil b
a r t i c l e
i n f o
Article history: Received 22 June 2012 Received in revised form 25 September 2012 Accepted 28 September 2012 Available online 8 November 2012 Keywords: VLE Methanol Ethanol Glycerol NaCl UNIQUAC model
a b s t r a c t Experimental vapour–liquid equilibrium data of several binary mixtures (methanol + glycerol), (ethanol + glycerol) and (glycerol + water) and ternary (methanol + glycerol + water), (ethanol + glycerol + water) and (water + glycerol + NaCl) were obtained over the pressure range of 6.7 kPa to 66.7 kPa through an Othmer-type ebulliometer, allowing the construction of temperature – mass fraction and pressure – temperature diagrams. It is shown that the systems without NaCl were satisfactorily represented by the UNIQUAC model with good agreement between theory and experimental results. It was observed that alcohol concentrations lower than 10 wt% increase the phase transition temperature. The systems investigated show positive deviations in relation to Raoult’s law. Results presented in this work may be relevant in process design towards efficient recovering of components in the biodiesel down-stream processes. Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction Production of biofuels has been widely studied in recent years because of its potential to solve many of the current social problems and concerns, from air pollution and global warming to other environmental improvements and sustainability issues [1,2]. It is well known that biodiesel production affords glycerol as a by-product together with low amounts of alcohol (methanol or ethanol), water and also some salt residues. Ternary and binary mixtures involving these components are commonly found in the downstream of biodiesel manufacturing process [3,4]. Due to surplus glycerol derived from biodiesel production, a substantial decrease in the price of glycerol may be possible in the near future. Glycerol has several different potential uses in medicine, pharmaceutical products (drugs) and personal care preparations (cosmetics and toothpastes), tobacco and food processing ⇑ Corresponding author at: Department of Food Engineering, URI – Campus de Erechim, Erechim, RS 99700-000, Brazil. Tel.: +55 48 37212508; fax: +55 48 37219687. E-mail address: [email protected] (J. Vladimir Oliveira). 0021-9614/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jct.2012.09.032
(as a food additive, solvent, sweetener or a component of food packaging materials) and as a raw material in different chemical industries, for example, in the production of acetals, amines, esters and ethers, mono- and di-glycerides and urethane polymers [5]. Thus, inexpensive and practical methods to recover glycerol and alcohol from aqueous solutions are welcome. Among separation techniques used to recover ternary and binary systems involving these components, distillation is certainly the most reported in literature. The use of this technique requires the determination of experimental vapour–liquid equilibrium data (VLE), which are essential to process design and operation. Although separation processes involving biodiesel systems is of great interest, surprisingly there are just a few reports in the literature regarding VLE data of related systems. For example, only (methanol + glycerol) and (glycerol + water) VLE binary systems have been reported in the literature [6]. Over the past years, extractive distillation using a salt as extractive solvent has attracted much attention. The main idea of using a salt for the extractive distillation is to change the relative volatility of the constituents, a phenomenon known as the salting-in or -out effect on vapour–liquid equilibria [7]. As a result, the azeotropic
J.G. Veneral et al. / J. Chem. Thermodynamics 58 (2013) 398–404
point is shifted or eliminated, when the salt-free mixture has an azeotropic point [8]. For example, Chen and Thompson [9] showed that the activity coefficients of both water and glycerol for the ternary system are decreased over the entire range by the presence of sodium chloride. This fact would be expected as the salt has a marked solubility in both liquids which would tend to reduce the escaping tendency of both water and glycerol. Furthermore, the salt effect was shown to be more pronounced in the case of glycerol, as sodium chloride is more soluble in glycerol. Besides, as demonstrated by Wang et al. [7], a salt can be used as an efficient solvent for the extractive distillation of (ethanol + water) mixtures due to its notable salting-out effect, which lowers the vapour pressure of water, increasing the volatility of ethanol, hence eliminating the azeotropic phenomenon of the (water + ethanol) mixture. In this sense, the main objective of this work is to report lowpressure vapour–liquid equilibrium data for binary and ternary systems involving glycerol, methanol, ethanol, water and sodium chloride. Experimental bubble-point temperature data over a wide composition range for pressures ranging from 6.7 kPa to 66.7 kPa were obtained using an Othmer-type ebulliometer [10]. All results, except those systems with NaCl, were correlated with UNIQUAC activity coefficient model. 2. Experimental 2.1. Materials The provenance and purity of the compounds employed in this work are presented in table 1. Deionised water was used as reagents without previous treatment. TABLE 1 Provenance and purity of the compounds employed in this work. Component
Manufacturer
Minimum mass fraction purity
Methanol Ethanol Glycerol Sodium hydroxide
Merck Merck Nuclear Quimex
0.999 0.999 0.995 0.970
399
2.2. Ebulliometric method Vapour–liquid equilibrium data were obtained in an Othmertype ebulliometer. An absolute pressure transducer (Smar, LD301, A3 model) equipped with a portable programmer (Smar, HT 201), with a precision of 0.3 kPa was used to measure the pressure and two thermo-resistances (PT100) with an accuracy of ±0.1 K (Novus, Brazil). These were connected to a digital acquisition board (FieldLogger, NOVUS) with interval of 30 seconds between each acquisition, which was used for temperature monitoring. A general outline of the experimental apparatus is presented in figure 1. The boiling point temperatures were obtained at several pressures ranging from 6.7 kPa to 66.7 kPa at a fixed global composition. Mixtures of ternary and binary systems were prepared gravimetrically using an analytical balance (Ohaus Analytical Standard with 0.0001 g accuracy). An ultrathermostatic water bath (TE-184 TECNAL) at T = 276.15 K was coupled to the condensers of the ebulliometer in order to prevent vapour losses from the system. After the temperature of the condensers was reached, a sample amount of approximately 300 g was added to the mixing chamber. When the steady-state was reached, characterized by a constant equilibrium temperature and pressure and uniform drop rate for at least 10 min, the temperature was recorded. Subsequently, a new pressure was applied and kept constant and the ebullition temperature was obtained as a new equilibrium value. Experimental apparatus was always operated from the lowest to the highest measured pressure in order to avoid system overheating. The boiling mixture was maintained so that a drop count of 60 drops per minute was achieved, as suggested by Malanowski [11]. 3. Thermodynamic modelling The experimental VLE results without NaCl were correlated using the UNIQUAC model [12]. The boiling temperatures of the pure liquids at the experimental pressures evaluated were obtained from the Antoine equation:
log PSat i =Pa ¼ A B=ðT=K þ CÞ;
ð1Þ
FIGURE 1. Experimental apparatus for vapour–liquid equilibrium measurements. (1) Computer, (2) vacuum pump, (3) data acquisition system, (4) trap, (5) magnetic stirrer, (6) ebulliometer, (7) digital PT100 thermo-resistance, (8) pressure digital transducer, (9) heating tape, (10) voltage regulator, (11) ultrathermostatic bath.
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TABLE 2 Constants for the Antoine equation and UNIQUAC parameters r and q for pure components.
TABLE 3 VLE experimental data for the system {methanol (1) + glycerol (2)} at various pressures.* w1a
Component
A
B
C
r
q
Methanol Ethanol Glycerol Water
9.2023 11.0835 8.7365 10.1620
1056.52 2085.87 1356.47 1718.37
85.97 7.75 200.00 39.96
1.9011 2.5755 4.7957 0.9200
2.0480 2.5880 4.9080 1.4000
p = 6.7 kPa 0.000 0.050 0.075 0.100 0.200 0.300 0.400 0.500 0.600 0.700 0.800 0.900 1.000
where P Sat is the saturation pressure of component i at temperature i T and A, B and C are adjustable parameters. Due to technical limitations of the ebulliometer used in the present work, data were obtained up to T = 520 K, and hence bubble point data of pure glycerol above this temperature reported by Soujanya et al. [6] were utilized for a best fit of the Antoine equation. The Antoine constants for all pure liquid components are presented in table 2 together with the r and q parameters of the UNIQUAC model, which were calculated using the parameters Rk and Qk reported by Magnussen et al. [13]. The binary interaction parameter fitting were based on the minimization of the following objective function:
OFðTÞ ¼
NP X 2 ðT calc T exp i i Þ ;
ð2Þ
where NP is the number of experimental points, T calc is the calcui lated boiling temperature and T exp is the experimental boiling i temperature. The UNIQUAC model parameters were then used to calculate the activity coefficients of each component in the mixture (ci). These activity coefficients were used to calculate the corresponding vapour phase (ycalc ) in the bubble point, according to the foli lowing equation:
ci xi PSat i Pexp
;
NP X ycalc ¼ 1: i
b *
In the estimation procedure for the parameters, the calculated boiling temperature (T calc p ) and the binary (aij) interaction parameters of the UNIQUAC model were considered as decision variables. The interaction parameters were estimated using the tool ‘‘solver’’ included in the spreadsheet Excel for Windows, together to the ‘‘XSEOS’’ supplements package [14]. The absolute mean deviation (AAD%) between experimental and calculated boiling temperatures was calculated according to the following equation: NP 100 X DT i exp : NP T i i
a
384.45 370.55 361.35 343.45 336.65 332.75 330.55 329.25 328.05 326.75 325.65 324.65
w1
T/K
p = 13.3 kPa 0.000 0.050 0.075 0.100 0.200 0.300 0.400 0.500 0.600 0.700 0.800 0.900 1.000
493.35 340.65 331.65 322.95 308.95 303.05 299.75 298.15 297.05 296.15 295.25 294.45 293.75
p = 40.0 kPa 0.050 0.075 0.100 0.200 0.300 0.400 0.500 0.600 0.700 0.800 0.900 1.000
371.95 358.85 349.75 333.05 326.65 323.05 321.05 319.85 318.75 317.65 316.65 315.75
w1
T/K
p = 20.0 kPa 0.000 0.050 0.075 0.100 0.200 0.300 0.400 0.500 0.600 0.700 0.800 0.900 1.000
505.55 350.45 340.55 331.75 317.05 311.15 307.85 306.25 305.15 304.05 303.05 302.25 301.45
p = 46.7 kPa 0.050 0.075 0.100 0.200 0.300 0.400 0.500 0.600 0.700 0.800 0.900 1.000
376.95 362.95 353.85 336.85 330.35 326.65 324.55 323.35 322.25 321.15 320.05 319.05
w1
T/K
p = 26.7 kPa 0.000 0.050 0.075 0.100 0.200 0.300 0.400 0.500 0.600 0.700 0.800 0.900 1.000
513.95 358.45 347.65 338.75 323.35 317.35 314.05 312.35 311.15 310.05 309.05 308.15 307.35
p = 53.3 kPa 0.050 0.075 0.100 0.200 0.300 0.400 0.500 0.600 0.700 0.800 0.900 1.000
381.25 366.85 357.75 340.25 333.55 329.75 327.55 326.35 325.25 324.15 323.05 322.05
p = 66.7 kPa 0.050 0.075 0.100 0.200 0.300 0.400 0.500 0.600 0.700 0.800 0.900 1.000
388.35 374.05 364.65 346.35 339.35 335.45 333.25 331.95 330.65 329.35 328.25 327.25
w1 Denotes the mass fraction of component 1 in the liquid phase. T, system temperature. Estimated standard error of 0.6%.
ð4Þ
i
AADð%Þ ¼
520.65 365.45 353.95 344.95 328.65 322.35 318.85 316.95 315.75 314.65 313.65 312.65 311.85
p = 60.0 kPa 0.050 0.075 0.100 0.200 0.300 0.400 0.500 0.600 0.700 0.800 0.900 1.000
ð3Þ
where xi is the mole fraction of component i in the mixture and Pexp is the experimental pressure of the system. In equation (5) the vapour phase was assumed to follow ideal behaviour. During the minimization process, the following constraint should be observed:
477.25 324.55 316.35 309.75 296.45 290.65 287.45 285.95 285.25 284.55 283.85 283.15 282.55
p = 33.3 kPa 0.000 0.050 0.075 0.100 0.200 0.300 0.400 0.500 0.600 0.700 0.800 0.900 1.000
i
ycalc ¼ i
T/Kb
ð5Þ
4. Results and discussion Tables 3–5 present, the experimental VLE results for the binary systems {methanol (1) + glycerol (2)}, {ethanol (1) + glycerol (2)} and {water (1) + glycerol (2)}, respectively, which were obtained at different compositions for the pressure range of 6.7 kPa to 66.7 kPa.
Figure 2 presents a comparison between experimental values obtained in this work and those reported by Soujanya et al. [6] for the system {methanol (1) + glycerol (2)}, where good agreement can be observed, thus demonstrating the reliability of the experimental apparatus and procedure adopted for measuring VLE of the systems investigated. Tables 6 and 7 present the experimental VLE data for the ternary systems {methanol (1) + glycerol (2) + water (3)} and {ethanol (1) + glycerol (2) + water (3)} obtained at different overall compositions for pressure ranging from 6.7 kPa to 66.7 kPa. In this work, boiling temperature measurements for the systems with the NaCl electrolyte component was also investigated. Before evaluation of the effect of NaCl on the VLE data, it is necessary to access the region of total miscibility of such compounds to avoid precipitation and formation of a solid phase. For this purpose, the concentrations of NaCl in binary liquid solutions reported by Chen and Thompson [9] were used for VLE measurements. Table 8 presents the experimental VLE data for the ternary system {water (1) + glycerol (2) + NaCl (3)} obtained considering water mass fraction in the range of 0.0 to 0.4 at 7 wt% of NaCl in relation to the {water (1) + glycerol (2)} mixture, while table 9 contains the experimental VLE data for the system {water
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J.G. Veneral et al. / J. Chem. Thermodynamics 58 (2013) 398–404 TABLE 4 VLE experimental data for the system {ethanol (1) + glycerol (2)} at various pressures.* T/Kb
w1a
w1
p = 6.7 kPa 0.000 0.050 0.075 0.100 0.200 0.300 0.400 0.500 0.600 0.700 0.800 0.900 1.000
477.25 335.95 327.35 319.55 307.85 302.55 299.85 298.65 297.75 296.95 296.35 295.75 295.25
0.000 0.050 0.075 0.100 0.200 0.300 0.400 0.500 0.600 0.700 0.800 0.900 1.000
p = 33.3 kPa 0.000 0.050 0.075 0.100 0.200 0.300 0.400 0.500 0.600 0.700 0.800 0.900 1.000
520.65 376.75 365.95 355.85 341.65 334.75 331.55 330.15 329.15 328.05 327.15 326.35 325.65
a b *
394.55 382.95 372.45 355.95 348.55 345.55 343.85 342.65 341.45 340.45 339.55 338.65
493.35 352.65 341.65 334.25 321.55 315.35 312.45 311.25 310.25 309.35 308.55 307.95 307.45
p = 40.0 kPa 0.050 0.075 0.100 0.200 0.300 0.400 0.500 0.600 0.700 0.800 0.900 1.000
p = 60.0 kPa 0.050 0.075 0.100 0.200 0.300 0.400 0.500 0.600 0.700 0.800 0.900 1.000
T/K
p = 13.3 kPa
382.35 371.35 360.85 346.45 338.95 335.65 334.25 333.15 332.05 331.15 330.25 329.55
w1
T/K
w1
p = 20.0 kPa 0.000 0.050 0.075 0.100 0.200 0.300 0.400 0.500 0.600 0.700 0.800 0.900 1.000
505.55 362.85 351.65 343.75 329.85 323.45 320.45 319.25 318.25 317.35 316.45 315.75 315.05
0.000 0.050 0.075 0.100 0.200 0.300 0.400 0.500 0.600 0.700 0.800 0.900 1.000
p = 46.7 kPa 0.050 0.075 0.100 0.200 0.300 0.400 0.500 0.600 0.700 0.800 0.900 1.000
T/K
p = 26.7 kPa 513.95 370.75 359.65 350.55 336.05 329.35 326.65 325.35 324.35 323.45 322.55 321.75 321.05
p = 53.3 kPa
386.45 375.65 364.85 348.75 342.55 339.35 337.85 336.65 335.55 334.55 333.65 332.85
0.050 0.075 0.100 0.200 0.300 0.400 0.500 0.600 0.700 0.800 0.900 1.000
390.45 379.25 368.95 352.85 345.55 342.65 341.05 339.85 338.65 337.65 336.75 335.95
FIGURE 2. Comparison of VLE data for the system (methanol + glycerol).
TABLE 6 VLE experimental data for the system {methanol (1) + glycerol (2) + water (3)} at various pressures.*
397.85 385.95 375.85 359.25 351.35 348.35 346.55 345.35 344.15 343.05 342.05 341.15
a b *
TABLE 5 VLE experimental data for the system {water (1) + glycerol (2)} at various pressures.* T/Kb p = 6.7 kPa 0.000 0.047 0.115 0.227 0.439 1.000 a b *
p = 6.7 kPa
p = 13.3 kPa
p = 26.7 kPa
0.200 0.600 0.200
0.200 0.200 0.600
300.15 287.95 296.85
312.85 300.85 309.55
326.85 314.15 323.75
p = 40.0 kPa
p = 53.3 kPa
p = 66.7 kPa
0.200 0.600 0.200
0.200 0.200 0.600
335.95 322.95 333.15
342.55 329.45 340.05
348.15 334.75 345.95
477.25 360.55 336.75 323.65 316.75 311.15
w1
T/K p = 13.3 kPa
0.000 0.047 0.115 0.227 0.439 1.000
493.35 377.65 352.85 338.05 330.45 324.55
w1
T/K p = 66.7 kPa
0.047 0.115 0.227 0.439 1.000
w1 Denotes the mass fraction of components 1 and 2 in the liquid phase. T, system temperature. Estimated standard error of 0.9%.
TABLE 7 VLE experimental data for the system {ethanol (1) + glycerol (2) + water (3)} at various pressures.*
w1 Denotes the mass fraction of component 1 in the liquid phase. T, system temperature. Estimated standard error of 0.5%.
w1a
w2
p = 66.7 kPa 0.050 0.075 0.100 0.200 0.300 0.400 0.500 0.600 0.700 0.800 0.900 1.000
T/Kb
w1a
428.05 396.65 379.65 368.45 361.85
w1 Denotes the mass fraction of component 1 in the liquid phase. T, system temperature. Estimated standard error of 0.7%.
(1) + glycerol (2) + NaCl (3)} for water mass fraction of 0.5 to 1 at 15 wt% of NaCl. Both systems were evaluated in the pressure range from 6.7 kPa to 66.7 kPa. In order to evaluate the NaCl effect on the {water (1) + glycerol (2) + NaCl (3)} ternary system, presented in figure 3 is a comparison between boiling point temperatures with and without the salt.
a b *
T/Kb
w1a
w2 p = 6.7 kPa
p = 13.3 kPa
p = 26.7 kPa
0.200 0.600 0.200
0.200 0.200 0.600
303.25 298.35 303.85
314.95 310.05 316.65
329.55 323.45 331.35
p = 40.0 kPa
p = 53.3 kPa
p = 66.7 kPa
0.200 0.600 0.200
0.200 0.200 0.600
338.45 332.05 340.95
344.95 338.65 347.85
350.35 343.85 353.45
w1 Denotes the mass fraction of components 1 and 2 in the liquid phase. T, system temperature. Estimated standard error of 0.8%.
From this figure, it can be clearly observed that there is an increase in boiling temperatures of the (water + glycerol) system with increasing NaCl content. Note also the existence of two distinct trends in the (water + glycerol + NaCl) ternary system, viz. in the water ranges of 0.0 to 0.4 and 0.5 to 1. This behaviour may be due to the two different concentrations of NaCl in free-basis utilized in this work. The greatest differences of boiling temperatures between the systems occur in regions of high NaCl saturation in the ternary system. Similar results were obtained by Chen and Thompson [9] in evaluating the same systems, but at atmospheric pressure.
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J.G. Veneral et al. / J. Chem. Thermodynamics 58 (2013) 398–404
TABLE 8 VLE experimental data for the system (water (1) + glycerol (2) + NaCl (3)} at various pressures and 7 wt% NaCl concentration.* w1a
T/Kb
w1
T/K
w1
T/K
w1
T/K
w1
T/K
7 g of NaCl/100 g of mixture p = 6.7 kPa 0.000 0.050 0.075 0.100 0.200 0.300 0.400
479.85 361.65 352.25 345.05 329.95 323.45 320.35
p = 13.3 kPa 0.000 0.050 0.075 0.100 0.200 0.300 0.400
p = 40.0 kPa 0.050 0.075 0.100 0.200 0.300 0.400 a b *
419.45 403.25 392.85 372.35 363.95 359.85
496.05 383.45 370.45 362.35 345.55 338.25 334.55
p = 20.0 kPa 0.000 0.050 0.075 0.100 0.200 0.300 0.400
p = 46.7 kPa 0.050 0.075 0.100 0.200 0.300 0.400
425.15 408.15 397.65 376.45 367.75 363.55
508.25 395.95 382.25 373.05 354.85 347.35 343.45
p = 26.7 kPa 0.000 0.050 0.075 0.100 0.200 0.300 0.400
p = 53.3 kPa 0.050 0.075 0.100 0.200 0.300 0.400
429.95 412.35 401.75 380.25 371.35 367.05
516.75 405.55 390.95 380.95 361.85 354.15 350.25
p = 33.3 kPa 0.000 0.050 0.075 0.100 0.200 0.300 0.400
p = 60.0 kPa 0.050 0.075 0.100 0.200 0.300 0.400
523.55 413.15 397.75 387.55 367.65 359.55 355.55 p = 66.7 kPa
434.45 416.35 405.35 383.55 374.55 370.25
0.050 0.075 0.100 0.200 0.300 0.400
438.45 420.05 408.55 386.55 377.45 373.05
T/K
w1
T/K
w1 Denotes the mass fraction of component 1 in the liquid phase. T, system temperature. Estimated standard error of 0.9%.
TABLE 9 VLE experimental data for the system {water (1) + glycerol (2) + NaCl (3)} at various pressures and 15 wt% NaCl concentration.* w1a
T/Kb
w1
T/K
w1
T/K
w1
15 g of NaCl for 100 g of mixture p = 6.7 kPa 0.500 0.600 0.700 0.800 0.900 1.000
320.15 318.55 317.15 315.95 314.85 313.85
p = 13.3 kPa 0.500 0.600 0.700 0.800 0.900 1.000
p = 40.0 kPa 0.500 0.600 0.700 0.800 0.900 1.000 a b *
359.85 357.75 356.05 354.35 353.05 352.05
334.65 332.65 331.05 329.65 328.45 327.45
p = 20.0 kPa 0.500 0.600 0.700 0.800 0.900 1.000
p = 46.7 kPa 0.500 0.600 0.700 0.800 0.900 1.000
363.65 361.45 359.75 357.95 356.65 355.65
343.65 341.55 339.95 338.55 337.35 336.35
p = 26.7 kPa 0.500 0.600 0.700 0.800 0.900 1.000
p = 53.3 kPa 0.500 0.600 0.700 0.800 0.900 1.000
367.05 364.85 363.05 361.25 359.95 358.95
350.25 348.15 346.45 344.95 343.65 342.65
p = 33.3 kPa 0.500 0.600 0.700 0.800 0.900 1.000
p = 60.0 kPa 0.500 0.600 0.700 0.800 0.900 1.000
370.25 367.95 366.15 364.25 362.95 361.85
355.55 353.45 351.75 350.15 348.85 347.85 p = 66.7 kPa
0.500 0.600 0.700 0.800 0.900 1.000
373.05 370.75 368.95 367.05 365.75 364.65
w1 Denotes the mass fraction of component 3 in the liquid phase. T, system temperature. Estimated standard error of 0.9%.
FIGURE 3. T–w diagram at different pressures for the ternary system (water + glycerol + NaCl) with different concentrations of NaCl. Values are presented in terms of mass fraction and NaCl free-basis.
The UNIQUAC model parameters for the various systems at the different experimental pressures together with the deviations of the predicted values for the experimental temperatures, represented in terms of the average absolute deviation are presented in table 10. The determination of the parameters was performed in order to obtain global parameters for all pressure ranges examined. Therefore, the binary interaction parameters were obtained first through modelling all boiling point data of each binary system evaluated, which then were fixed during modelling of the ternary systems. It should be noted that the interaction parameters for the (methanol + water) and (ethanol + water) binary systems were obtained through modelling the data reported by Soujanya et al. [6] and Gmehling and Onken [15], respectively. Figures 4–6 contain the comparison between experimental and calculated VLE values for the binary systems formed by (methanol + glycerol), (ethanol + glycerol) and (water + glycerol), respectively, where it can be seen that the thermodynamic modelling is capable of representing the experimental results fairly well, with deviations lower than 0.018% (see table 10). It is also noted from these figures that the phase transition temperature increases shar-
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J.G. Veneral et al. / J. Chem. Thermodynamics 58 (2013) 398–404 TABLE 10 Binary interaction parameters of UNIQUAC model fitted in this work. Systems
Methanol (1) + water (2) Methanol (1) + glycerol (2) Ethanol (1) + water (2) Ethanol (1) + glycerol (2) Water (1) + glycerol (2) a b
Temperature range/K
296.10–362.10 282.55–388.35 295.25–361.85 295.25–397.85 311.15–428.05
UNIQUAC
Duij/Ka
Duji/Ka
AAD/%b
313.7440 319.9054 244.5568 309.6746 197.8038
155.6420 165.3075 36.7978 138.7338 179.1049
0.0017 0.0020 0.0017 0.0021 0.0179
Binary interaction parameters of UNIQUAC model. AAD% denotes the average absolute deviation between all the experimental and calculated boiling temperatures of each system.
FIGURE 4. Temperature (T) versus mass fraction (w) diagram for (methanol + glycerol) binary system at different pressures.
FIGURE 5. Temperature (T) versus mass fraction (w) diagram for (ethanol + glycerol) binary system at different pressures.
ply in mixtures with low alcohol concentration (methanol or ethanol) or water, due to the great difference between the molar mass of the substances contained in the mixtures. Both systems present a highly non-ideal behaviour and positive deviations from Raoult’s law. Note also in figure 6 that our data for the (water + glycerol) system agree within 0.041% with those reported by Gmehling and Onken [15]. Presented in figures 7 and 8 are the experimental and calculated VLE results for the ternary systems constituted by (metha-
FIGURE 6. Temperature (T) versus mass fraction (w) diagram for (water + glycerol) binary system at different pressures.
FIGURE 7. Vapour pressure (p) versus temperature (T) diagram at different overall compositions for the ternary system (methanol + glycerol + water).
nol + glycerol + water) and (ethanol + glycerol + water), respectively. It can be observed that the UNIQUAC model was able to describe satisfactorily the trends of isobar curves in the ternary systems, although higher deviations between experimental and calculated values were verified when compared to the binary systems. It is interesting to observe from figure 7 despite the fact that the boiling temperature of glycerol is greater than that of water, one
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ebulliometer. Systems without NaCl were satisfactorily correlated using the UNIQUAC model. It was observed that low concentrations of alcohol (methanol or ethanol) decrease the phase transition temperature (boiling point temperature) for the systems investigated. All systems evaluated show non-ideal behaviour and positive deviations from Raoult’s Law. Results presented in this report can be useful in the downstream process to recovery of constituents (alcohol and glycerol) of biodiesel industrial plant. Acknowledgements The authors thank CNPq, Fundação Araucaria and Pró-Engenharias/CAPES (Grant no. 076/2008) for the financial support of this work and scholarships. References FIGURE 8. Vapour pressure (p) versus temperature (T) diagram at different overall compositions for the ternary system (ethanol + glycerol + water).
can see that the (methanol + glycerol + water) ternary system at 60 wt% water presents higher phase transition temperatures than those verified at 60 wt% glycerol at the same pressure condition. This may be attributed to the formation of hydrogen bonds between water and methanol molecules, which sharply increase with increasing water concentration. Figure 8 also shows that the presence of strong hydrogen bonds of water and alcohol (in this case ethanol) enhance the mixture boiling temperatures for each system pressure as the water content is enhanced in the ternary mixture of (ethanol + glycerol + water). 5. Conclusions Experimental VLE data at low pressures for several binary systems {methanol (1) + glycerol (2)}, {ethanol (1) + glycerol (2)} and {water (1) + glycerol (1)} and ternary {methanol (1) + glycerol (2) + water (3)}, {ethanol (1) + glycerol (2) + water (3)} and {water (1) + glycerol (2) + NaCl (3)} were obtained using an Othmer-type
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JCT 12-376