Article pubs.acs.org/jced
Isobaric Vapor−Liquid Equilibrium Data for the Binary Systems of Dimethyl Carbonate with Xylene Isomers at 93.13 kPa Satyajeet S. Yadav,‡ Nilesh A. Mali,*,† Sunil S. Joshi,† and Prakash V. Chavan‡ †
Chemical Engineering and Process Development Division, CSIR-National Chemical Laboratory, Dr. Homi Bhabha Road, Pune-08, Maharashtra, India ‡ Chemical Engineering Department, College of Engineering, Bharati Vidyapeeth Deemed University, Pune-08, Maharashtra, India S Supporting Information *
ABSTRACT: Isobaric binary vapor−liquid equilibrium (VLE) data for dimethyl carbonate with xylene isomers (p-xylene, m-xylene, o-xylene, and ethylbenzene) were measured at the local atmospheric pressure of 93.13 kPa by using a dynamic recirculation still. The experimental VLE data were tested and found to be thermodynamically consistent by Herington and Van Ness consistency test. The experimental VLE data were correlated using the Wilson, NRTL, and UNIQUAC activity coefficient models and binary interactions parameters were estimated using a suitable objective function. The absolute mean deviation between the experimental and the model predicted values of vapor phase composition and total pressure was well within acceptable limits. No azeotrope was observed in any of the binary pairs and appeared to be easy for separation using conventional distillation method.
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INTRODUCTION Petroleum product continues to dominate as a major source of energy among various available options worldwide. Ever increasing demands of petroleum products have promoted research on gasoline additives (oxygenated compound) in recent years. Because of high oxygen content and good blending property of dimethyl carbonate (DMC), it can be used directly as fuel additive and also a substitute for dimethyl sulfate, methyl halides, and phosgene for methylation reaction.1 It has been used as a single gasoline additive and coadditive with ethanol or butanol and found to show good results.2 DMC has a high solubility in gasoline that may decrease a gasoline’s flash point and improve engine performance.3 Xylene isomers are normally derived from petroleum fractions and are of great importance to the petrochemical industry and used mainly as a base for synthesis of many organic compounds. Mixed xylene without separation also finds application as gasoline additives.4 Various separation processes are usually optimized using process simulators. Performance of simulators is dependent on the prediction accuracy of fluid thermodynamic properties at different conditions in the process that in turn depends on the thermodynamic model that takes into account nonideal behavior of the system. For liquids, activity coefficient models such as NRTL and UNIQUAC are used. Binary interaction parameters of these models are estimated from the VLE data of the components involved in the process. In the present work, isobaric VLE data in the form of T−x,y have been generated for DMC with four xylene isomers (p-xylene, m-xylene, o-xylene, and ethylbenzene) at local atmospheric pressure of 93.13 kPa using a dynamic type VLE apparatus. No experimental VLE data are reported in the literature for these pairs. The experimental data have been correlated with three activity coefficient © 2017 American Chemical Society
models, Wilson, NRTL, and UNIQUAC, and the binary interaction parameters were estimated that can be used in process modeling.
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EXPERIMENTAL SECTION Materials. Detail specifications of various chemicals used for experimentation are listed in Table 1. The chemicals were used Table 1. Component, Supplier, and Purity chemical name dimethyl carbonate (DMC) p-xylene m-xylene o-xylene ethylbenzene
CAS no.
source
purity (mass %)
616-38-6
Loba chemicals
99
106-42-3 108-38-3 95-47-6 100-41-4
Loba chemicals Loba chemicals Merck chemicals Spectrochem
99 99 99 99
directly without any further purification. Table 2 contains the reported and experimental refractive index (nD) and boiling points (Tb). Apparatus and Procedure. In this study, the VLE experiments were carried out using a glass dynamic type recirculating still. The experimental setup, experimental procedure, and sample analyses were described in detail in previous work by Mali et al.10 Briefly, the apparatus is equipped with a boiling chamber, an insulated Cottrell tube, an insulated equilibrium chamber, a mixing chamber, and a condenser with suitable Received: April 20, 2017 Accepted: July 10, 2017 Published: July 24, 2017 2436
DOI: 10.1021/acs.jced.7b00372 J. Chem. Eng. Data 2017, 62, 2436−2442
Journal of Chemical & Engineering Data
Article
Table 2. Refractive Indices (nD) and Boiling Points (Tb) of Pure Chemicals refractive index (nD) at 25 °C literature
measureda
literature (at 101.325 kPa)
measureda (at 93.13 kPa)
dimethyl carbonate
1.36665,6
1.3664
360.73
p-xylene
1.49328 1.492869 1.49428 1.494439 1.50288 1.501779 1.49308 1.492989
1.4929
363.355 363.607 411.378 411.389 412.218 412.229 417.568 417.559 409.328 409.319
m-xylene o-xylene ethylbenzene a
boiling point (°C)
chemical
1.4943 1.5022 1.4930
408.37 409.13 414.41 406.23
Standard uncertainties u are u(nD) = 0.0001, u(T) = 0.1 K
Table 3. Antoine Constants Antoine constantsa
a
chemical
A
B
C
dimethyl carbonate12 p-xylene4,9 m-xylene4,9 o-xylene4,9 ethylbenzene4,9
6.4338 6.11543 6.13399 6.12644 6.09070
1413.00 1453.43 1462.270 1476.39 1429.55
−44.25 −57.840 −58.039 −59.278 −59.383
units P P P P P
= = = = =
kPa, kPa, kPa, kPa, kPa,
T T T T T
temperature range (K) = = = = =
K K K K K
273.15−548.0 300.15−439.15 302.15−439.15 336.15−418.15 263.15−409.15
Antoine equation no 2.
Figure 1. Calibration curve for p-xylene (1) + DMC (2) system. ⧫, measured nD at 293.15 K versus mole fraction of p-xylene (x1); , third order polynomial.
Figure 2. Calibration curve for m-xylene (1) + DMC (2) system. ⧫, measured nD at 293.15 K versus mole fraction of m-xylene (x1); , third order polynomial.
coolant circulation. A Wika Hand-held thermometer (Model CTH7000) was used for measuring equilibrium temperature with an accuracy of ±0.01 K. In this apparatus, both liquid and vapor phases were continuously recirculated for faster attainment of equilibrium. The outlet of the vapor line in the condenser was kept open to atmosphere that ensures atmospheric pressure in the VLE still that was 93.13 kPa during experimental work. Sufficiently high cooling rate and condenser area were provided to ensure that there is no vapor escape. Once a constant temperature was reached, which indicates attainment of vapor−liquid equilibrium, both liquid and vapor samples were collected from two different sampling points in separate vials and analyzed for composition using a refractometer. A very small amount of samples (
