Article pubs.acs.org/jced
Vapor Pressures and Vapor−Liquid Critical Properties of Four Pentene Isomers Christian Ihmels,* Sven Horstmann, and Andreas Grybat Laboratory for Thermophysical Properties LTP GmbH, Associate Institute at the University of Oldenburg, Marie-Curie-Str. 10, 26129 Oldenburg, Germany ABSTRACT: For 1-pentene and the three branched C5H10 isomers (2-methylbut-1-ene, 3-methylbut-1-ene, and 2-methylbut-2-ene), vapor pressures and vapor−liquid critical properties were determined, thus filling several gaps in the thermodynamic database for these compounds. Using a static titanium autoclave with sapphire windows for high temperature and pressure determinations, vapor pressures and critical temperatures, pressures, and density data were measured. The experimental data were used to fit parameters for the Wagner vapor pressure equation and compared to available literature data. The consistency of the critical values was checked with the critical surface equation.
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INTRODUCTION Pentene isomers are byproducts of the catalytic or thermal cracking of petroleum or other hydrocarbon fractions, e.g., for the production of ethylene or propylene. The vapor pressure curve and vapor−liquid critical temperature, pressure, and density or volume are characteristic for the fluid phase behavior of a substance. While literature data of experimental vapor pressures for all pentene isomers at moderate temperatures up to about 370 K are available from different authors,1 values are either missing or are at least of questionable quality at elevated temperatures up to the critical temperatures. According to the corresponding state principle proposed by van der Waals, most equations of state and many simpler correlations are based on the critical properties as parameters and/or reducing constants. Over the past recent decades several scientists including Kenneth Marsh2 reviewed experimental vapor−liquid critical properties for several hundred components. In this series Tsonopoulos and Ambrose3 also reviewed the critical properties for 1-pentene, 3-methylbut-1-ene, and 2methylbut-2-ene. The newest available experimental critical data points for 1-pentene (α-n-amylene) and 3-methlybut-1ene (α-isoamylene) were published in 1991 by Gude et al.4 and Ma et al.5 For 2-methylbut-2-ene (β-isoamylene) and 2methylbut-1-ene (1-isoamylene or γ-isoamylene) no experimental vapor−liquid critical density data are available. For the four butane isomers, Ihmels et al.6 published vapor pressures and critical data determined with a variable volume apparatus with a sapphire tube, which is limited to a maximum temperature of about 430 K. Using a titanium autoclave with sapphire windows for high temperatures and pressures (up to 670 K and 40 MPa), vapor pressures and critical temperatures, pressures, and densities were measured in this work for the pentene isomers. The vapor pressures were determined from about ambient pressure up to the critical points which were © XXXX American Chemical Society
visually determined. For the pentene isomers they are in the range of 451−477 K, between 3.4 and 3.7 MPa and around 243 kg/m3.
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EXPERIMENTAL SECTION Chemicals. 1-Pentene, 2-methylbut-1-ene, 3-methylbut-1ene, and 2-methylbut-2-ene (C5H10, M = 70.13 g/mol, CAS Registry Nos. 109−67−1, 563−46−2, 563−45−1, and 513− 35−9) were obtained from ChemSampCo (USA). All fluids were used without any further purification. The purities (better than 99 mass % for all components) were checked by gas chromatography (see Table 1 for details). The samples were also checked after the measurements, but no additional impurities were found. Apparatus and Procedure. For the measurement of vapor pressures and critical data an equilibrium cell (about 140 cm3 inner volume) was used, which is made of titanium and equipped with two sapphire windows and a magnet coupled stirrer (compare Figure 1). The apparatus can be used up to temperatures of 670 K and pressures of 40 MPa whereby the windows on opposite sides allow a clear view of the cell content and, e.g., the phase boundary. All flanges are sealed with rings of thin gold wire for a broad range of temperature applicability and superior corrosion resistance. Alternatively, for measurements up to about 470 K a sealing of PTFE can be used for the top cover of the cell. The equilibrium cell is thermoregulated in an air thermostat. For evacuation and charging of the cell with defined amounts of substance three valves are embedded in the body of the cell to Special Issue: Memorial Issue in Honor of Ken Marsh Received: February 9, 2017 Accepted: May 24, 2017
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DOI: 10.1021/acs.jced.7b00148 J. Chem. Eng. Data XXXX, XXX, XXX−XXX
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Table 1. Sample Information chem name
CAS registry no.
source
purity/(mass %)
anal. method
1-pentene 2-methylbut-1-ene 3-methylbut-1-ene 2-methylbut-2-ene
109−67−1 563−46−2 563−45−1 513−35−9
ChemSampCo ChemSampCo ChemSampCo ChemSampCo
>99 >99 >99 >99
GC GC GC GC
liquid sample from degassing glass bulbs in which the liquids are either distilled under vacuum or degassed by repeated evacuation of the gas phase. Gases can be injected into the cell using a thermoregulated gas bomb of known volume. At a certain pressure the amount of gas inside the bomb can be calculated using the PvT behavior of the gas. The injected amount of gas can then be obtained from the pressure difference in the bomb before and after each injection. Solid substances can be directly weighed into the cell and degassed by evacuation of the cell. The pressure inside the cell is monitored with an oil filled membrane pressure transducer system (from Wika) integrated into the top cover of the cell and a calibrated pressure sensor (Rosemount). The pressure sensor was calibrated using a dead weight pressure balance (Model 26000, Desgranges & Huot). The temperature is measured with a Pt100 platinum resistance thermometer (model 1502A, Hart Scientific, ITS-90) inside the metal body of the cell. The calibrations of the Pt100 thermometer and the pressure sensor were verified by measuring vapor pressures of different reference substances (e.g., water and pentane). The vapor pressure data can be determined with estimated standard uncertainties of u(T) = 0.05 K and u(P) = (0.002(P (kPa)) + 1 kPa). The standard
Figure 1. Schematic diagram of the static apparatus with sapphire windows.
avoid any dead volume. In the case of purified and degassed liquids or liquefied gases, known amounts of substances can be charged by using piston injector pumps (e.g., model 2200-801, Ruska or ISCO 260D) which allow the precise recording of volume differences. Evacuated piston pumps will be filled with Table 2. Experimental Vapor Pressures for Pentene Isomersa 1-pentene
a
3-methylbut-1-ene
2-methylbut-2-ene
2-methylbut-1-ene
T/K
P/kPa
T/K
P/kPa
T/K
P/kPa
T/K
P/kPa
297.86 327.08 336.14 346.92 356.19 356.89 366.77 377.34 387.42 394.67 399.61 403.03 411.19 420.96 426.10 436.17 439.50 445.74 452.59 456.52 457.93 460.95 462.87 463.77 466.59b
84 216 279 372 468 474 600 757 933 1085 1193 1269 1472 1752 1915 2255 2373 2622 2902 3081 3152 3294 3389 3443 3585
302.90 323.75 336.44 350.65 358.20 371.60 382.88 390.84 399.00 405.25 413.20 420.56 431.03 439.90 445.14 447.76 450.48 451.38b
140 264 374 533 635 855 1073 1255 1458 1632 1874 2113 2509 2885 3138 3260 3407 3463
307.63 325.06 340.98 350.14 364.85 372.91 380.97 389.83 397.89 408.17 422.67 430.83 439.09 448.36 453.30 454.71 461.46 464.08 470.72 471.73 473.04 475.16 477.47b
87 157 249 321 463 560 673 811 954 1167 1524 1758 2021 2349 2541 2600 2884 3006 3327 3377 3442 3556 3686
299.27 323.65 341.18 353.77 366.06 368.18 375.63 386.21 398.50 409.28 419.65 429.02 431.24 438.39 448.46 457.43 460.55 463.37 465.49 467.90b
85 190 312 431 579 608 717 898 1149 1402 1695 1985 2065 2316 2723 3118 3271 3409 3523 3652
Standard uncertainties are u(T) = 0.05 K and u(P) = (0.002(P (kPa)) + 1 kPa). bCritical point. B
DOI: 10.1021/acs.jced.7b00148 J. Chem. Eng. Data XXXX, XXX, XXX−XXX
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Table 3. Experimental Critical Data for the Pentene Isomers Including Standard Uncertainties and Literature Values from Tsonopoulos and Ambrose3 Including Available Uncertaintiesa Tc,exp/K 1-pentene 3-methylbut-1-ene 2-methylbut-2-ene 2-methylbut-1-ene a
466.59 451.38 477.47 467.90
± ± ± ±
0.1 0.1 0.1 0.1
Tc,lit./K 464.8 ± 0.5 452.7 ± 0.3 470 ± 1 n.a.
Pc,exp/MPa
Pc,lit./MPa
± ± ± ±
3.56 ± 0.05 3.53 ± 0.03 3.42 ± 0.10 n.a.
3.585 3.463 3.686 3.652
0.01 0.01 0.01 0.01
ρc,exp/(kg m−3) 243.5 239.3 246.6 245.4
± ± ± ±
5 5 5 5
ρc,lit./(kg m−3) 235 ± 5 230 ± 10 n.a. n.a.
n.a. = not available.
Table 4. Parameters of the Wagner Equation Used for Vapor Pressure Calculations Aw Bw Cw Dw Pc/kPa Tc/K Tmin/K Tmax/K data points AAD/%
1-pentene
3-methylbut-1-ene
2-methylbut-2-ene
2-methylbut-1-ene
−6.95379 1.28766 −2.12782 0.980811 3585 466.59 297.86 463.77 24 0.15
−7.46229 3.22932 −5.77981 13.3318 3463 451.38 302.90 450.48 17 0.10
−7.35459 1.80848 −1.89896 −6.49136 3686 477.47 307.63 475.16 22 0.12
−7.0294 1.19924 −1.40391 −3.53704 3652 467.90 299.27 465.49 19 0.10
uncertainties were estimated according to principles of the guide to the expression of uncertainty in measurement (GUM).7 For the determination of the critical temperature, pressure, and volume the evacuated cell was filled with known amounts of substance and heated approaching the critical point while measuring the vapor pressure data. The phase boundary was continuously kept in the middle of the cell by adjustment of the filling if necessary. At the critical point, the phase boundary disappeared and the critical opalescence was visually observed. The critical point was measured several times by repeated heating starting in the two phase region and cooling from the supercritical region. After the measurement the complete amount of substance was condensed in an evacuated gas cylinder which was cooled with liquid nitrogen. The mass of the substance was determined by weighing the gas cylinder. From the amount of substance and the known volume of the cell the critical density was determined. The critical properties can be determined with estimated standard uncertainties of u(T) = 0.1 K, u(P) = 10 kPa, and about 2% in the critical density.
Figure 2. Experimental vapor pressures and critical point for 1pentene with Wagner correlation, and literature values: blue filled circle, critical point this work; open black circles, vapor pressures this work; black crosses, literature data;8−14 solid black line, Wagner correlation.
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RESULTS The vapor pressures of 1-pentene, 2-methylbut-1-ene, 3methylbut-1-ene, and 2-methylbut-2-ene were measured from about ambient pressure up to near their critical points. The experimental results of the vapor pressure measurements and the critical point data are listed in Tables 2 and 3. The experimental vapor pressures were correlated with the Wagner equation (eq 1) in the “2.5,5” form using the new critical data: ln(P0) = ln(Pc) +
A W (1 − Tr) + B W (1 − Tr)1.5 + C W (1 − Tr)2.5 + D W (1 − Tr)5 Tr
(1)
Figure 3. Experimental vapor pressures and critical point for 3methylbut-1-ene with Wagner correlation, and literature values: filled blue circle, critical point this work; open black circles, vapor pressures this work; black crosses, literature data;15−17 black line, Wagner correlation.
with the vapor pressure P0, critical pressure Pc, and reduced temperature Tr = T/Tc with critical temperature Tc. The parameters are given in Table 4. The experimental values and the Wagner correlation are presented in Figures 2−5 together with literature data from C
DOI: 10.1021/acs.jced.7b00148 J. Chem. Eng. Data XXXX, XXX, XXX−XXX
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Figure 6. Comparison of the vapor pressures and critical points of this work: open black up-triangles, 3-methylbut-1-ene; open blue circles, 1pentene; red plus signs, 2-methylbut-1-ene; green crosses, 2methylbut-2-ene; lines, Wagner correlations.
Figure 4. Experimental vapor pressures and critical point for 2methylbut-2-ene with Wagner correlation, and literature values: blue filled circle, critical point this work; open black dots, vapor pressures this work; black crosses, literature data;8,18−24 black line, Wagner correlation.
methylbut-1-ene are in good agreement with the values from literature. Only the critical densities are somewhat higher than the literature values. For 2-methylbut-2-ene Tsonopoulos and Ambrose3 stated the reviewed critical temperature and pressure as questionable. They also show significant deviations from the new experimental data. For 2-methylbut-1-ene critical temperature (464.75 K) and pressure (3.445 MPa) are only available from Nadejdine,25 but as aforementioned it is not clear if de facto pure 2-methylbut-1-ene was measured. Comparable to the vapor pressures from the same work, significant deviations to the new critical data are obvious. The consistency of the three critical properties temperature, pressure, and density or volume was checked with the critical surface eq 2 published by Ihmels:26
Figure 5. Experimental vapor pressures and critical point for 2methylbut-1-ene with Wagner correlation, and literature values: blue filled circle, critical point this work; open black circles, vapor pressures this work; black crosses, literature data;8,9,14 black line, Wagner correlation.
Pc = −0.025 + 2.215
Tc Vc
(2)
with the critical pressure Pc, critical temperature Tc, and critical molar volume Vc. With this equation the critical pressures were calculated from the experimental or literature critical temperature and volume and then compared to the critical pressure of this work or literature. For the new data the experimental and calculated critical pressures for 1-pentene, 3-methylbut-1-ene, 2-methylbut-1-ene, and 2-methylbut-2-ene show good consistency with deviations of 0.1, 1.5, 0.7, and 0.9%, respectively. For vapor− liquid critical data presented by Tsonopoulos and Ambrose3 the deviations are significantly higher for 1-pentene (3.1%) and 3methylbut-1-ene (6.4%).
different available references. The new vapor pressures are in good agreement with most literature values. The average absolute deviation between the literature vapor pressures above ambient pressure of different researchers and the calculation with the Wagner equation is 1.11% for 1-pentene (313−384 K),8−14 0.73% for 3-methylbut-1-ene (294−324 K),15−17 0.47% for 2-methylbut-2-ene (313−373 K),8,18−24 and 0.21% for 2methylbut-1-ene (309−373 K).8,9,14 Nadejdine25 published in 1883 a critical point and vapor pressures for “isoamylene”. It is not clear which isoamylene isomer and purity was used. However, these are the only vapor pressure data measured above 384 K and in comparison with other data the substance was most likely 2-methylbut-1-ene. But the values between 308 and 463 K show a significantly higher average absolute deviation of 4.0% to the Wagner equation. While the isomers 1-pentene and 2-methylbut-1-ene have very similar vapor pressures, 2-methylbut-2-ene has significantly lower and 3-methylbut-1-ene significantly higher vapor pressures, as presented in Figure 6. Similar tendencies can be seen for the critical properties. In Table 3 also the literature critical data from Tsonopoulos and Ambrose3 are listed in comparison to the new experimental data. The new critical properties for 1-pentene and 3-
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CONCLUSIONS New vapor pressure data for 1-pentene and the three branched C5H10 isomers (2-methylbut-1-ene, 3-methylbut-1-ene, and 2methylbut-2ene) are presented over a wide temperature and pressure range from about ambient temperature up to their vapor−liquid critical points. Also the critical temperatures, pressures, and densities were determined with a visual method. For the experiments at high temperature and pressure a titanium autoclave with sapphire windows was used. The vapor pressures and critical points were correlated with the Wagner equation and compared with literature data. The consistency of the critical values was checked with the critical surface equation. The range and quality of available vapor pressures for the D
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(18) Smirnov, V. V.; Saraev, B. A.; Pavlov, S.; Yu; Serafimov, L. A. Dampf-Flüssig-Gleichgewicht in Methylisopropylketonhaltigen Systemen. Prom. Sint. Kaucuka 1976, 3−6. (19) Nagahama, K.; Hirata, M. Binary Vapor-Liquid Equilibria at Elevated Pressures. Bull. Jpn. Pet. Inst. 1976, 18, 79−85. (20) Smirnov, V. V.; Pavlov, S.; Yu; Gorshkov, V. A.; Serafimov, L. A. Dampf-Flüssig-Gleichgewicht in Kohlenwasserstoff (C5)-Systemen. Prom. Sint. Kaucuka 1976, 1−4. (21) Hradetzky, G.; Hauthal, H. G.; Bittrich, H.-J. Phasengleichgewichte binärer Systeme aus C5-Kohlenwasserstoffen und Dimethylsulfoxid sowie aus Isopren bzw. Benzol und 1,4 Thioxan-S-Oxid. Chem. Tech. (Leipzig) 1978, 30, 645−648. (22) Ezekwe, J. N.; Howat, C. S., III; Swift, G. W. Vapor-Liquid Equilibria for the Binary System 2-Methylbutene-2 and 2-Methyl-1,3butadiene at 310.93, 316.48 and 322.04 K. Fluid Phase Equilib. 1981, 7, 75−85. (23) Pavlova, I. P.; Saraev, B. A.; Chaplits, D. H. Dampf-FlüssigGleichgewicht in binären Systemen, die von Methyl-tert-Amylester gebildet werden. Prom. Sint. Kaucuka 1981, 2−4. (24) Wilding, W. V.; Giles, N. F.; Wilson, L. C. Phase Equilibrium Measurements on Nine Binary Mixtures. J. Chem. Eng. Data 1996, 41, 1239−1251. (25) Nadejdine, A. Ueber den kritischen Punkt. Ann. Phys./Beibl. 1883, 7, 678−681. (26) Ihmels, E. C. The Critical Surface. J. Chem. Eng. Data 2010, 55, 3474−3480.
pentene isomers were significantly extended and improved up to the critical points with these new measurements.
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. Tel.: +49 (0)441 36111923. ORCID
Christian Ihmels: 0000-0002-7616-5106 Sven Horstmann: 0000-0001-7285-8880 Notes
The authors declare no competing financial interest.
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REFERENCES
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