The thermodynamics of vaporization of ethyl tert-butyl ether, isobutyl tert-butyl ether, and di-isopropyl ether

doi:10.1016/j.jct.2006.05.007

The Journal of Chemical Thermodynamics

Volume 39, Issue 1, January 2007, Pages 142-147

https://doi.org/10.1016/j.jct.2006.05.007 Get rights and content

Abstract

The boiling temperatures of ethyl tert-butyl ether (ETBE), isobutyl tert-butyl ether (IBTBE), and di-isopropyl ether (DIPE) have been measured by comparative ebulliometry over the moderate pressure range 10.8 ⩽ (P/kPa) ⩽ 101.7. The equations of the temperature dependences of the saturated vapour pressures and enthalpies of vaporization have been derived. The normal boiling temperatures of the ethers were computed to be 345.84 K, 386.06 K, and 341.64 K, respectively. The experimental data on the vapour pressure of the ethers under study were extended to the whole range of the liquid phases between critical and triple points by means of corresponding states law and combined treatment of the pT-parameters and low-temperature differences of the heat capacities of ideal gas and liquid, $Δ C_{p} = C_{p}^{\circ} (g) - C_{p}^{\circ} (l)$ , respectively.

Introduction

Branched aliphatic ethers having a number of carbon atoms from 6 to 8 are recently considered as perspective additives to the motor fuel [1]. Addition them to the fuel increases its octane rating and allows more complete combustion of the petrol. Methyl tert-butyl ether (MTBE) {propane, 2-methoxy-2-methyl-} has been widely used all over the world to replace toxic lead as an octane enhancer. But MTBE is found to contaminate ground and drinking water. Some attractive physico-chemical properties of heavier ethers, viz higher heat of combustion, lower solubility in water, and lower volatility make them superior to MTBE. A selection of the alternative ethers for the fuel additives are carried out basing on the key thermodynamic properties, like saturated vapour pressure, normal boiling temperature, the enthalpies of combustion and vaporization, density, and the heat capacity. Data on thermodynamics of vaporization of the substances under study: ethyl tert-butyl ether {propane,2-ethoxy-2-methyl-}, isobutyl tert-butyl ether {propane,1-(1,1-dimethylethoxy)-2-methyl-}, and di-isopropyl ether {isopropyl ether} were reported in references [2], [3], [4], respectively. The vapour pressure of ETBE was determined by ebulliometric method over the small temperature range from (305.5 to 345.8) K using a mercury manometer. An instrumental error of the temperature measurement was S_T = ±0.01 K, but it was impossible to evaluate the uncertainty of the vapour pressure measurement based on the author’s description. The preliminary vapour pressure data of IBTBE was determined by comparative ebulliometry over the small temperature interval (349.0 to 386.2) K for the sample containing 0.26 wt% impurities according to g.l.c.-analysis. A presence of the impurities was confirmed by the difference between the boiling and condensation temperatures, ΔT = 0.07 K measured at the pressure P = 13.4 kPa [3]. The vapour pressure of DIPE was obtained in the temperature range from (284.8 to 365.1) K with accuracy ±0.01 K, the appropriate pressure interval being equal to (from 10.7 to 201.8) kPa. References [5], [6] reported our determination of the low-temperature heat capacities and ideal thermodynamic properties of ETBE, tert-amyl ethyl ether (TAEE) {2-ethyl-2-ethoxypropane}, and IBTBE, respectively.

In this paper we report the temperature dependences of the saturated vapour pressures and related thermodynamic properties for the pure samples of ETBE and IBTBE, that were studied over wider temperature ranges as compared with the references [2], [3]. Both ethers are perspective octane enhancing additives to the motor fuel, besides IBTBE can be also used for extracting pure isobutylene and isoamylene from the gas hydrocarbon fractions C₄, C₅ in the oil processing [7]. The vapour pressure of DIPE was determined for testing our ebulliometric technique.

Section snippets

Experimental

The sample of DIPE was prepared by intermolecular dehydration of isopropyl alcohol in the presence of Al₂O₃ as a catalyst at the temperature range from (493 to 513) K. The residua of alcohol and olefins were removed from a reaction mixture after synthesis by washing with warm water. Residua of the olefins were removed by blowing the sample with nitrogen under vacuum. Then, the ether was dried with calcium chloride and rectified in vacuum. Chromatographic analysis was carried out on a gas-liquid

Results and discussion

Table 2 lists the pressure values for the manometer contacts obtained by calibration with water and n-decane. Main parts of the contacts, from 6 to 20 were calibrated basing on the boiling and condensation temperatures of water. Values of pressure for the 3 to 5 contacts were determined by measuring T_b and T_cond values of the normal decane. Root mean square (r.m.s.) differences between obtained temperatures and pressures, 〈ΔT〉 = 5 · 10⁻³ K and $〈 Δ \bar{P} 〉 = 11 Pa$ , (table 2) are within the error limits of the

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The thermodynamics of vaporization of ethyl tert-butyl ether, isobutyl tert-butyl ether, and di-isopropyl ether

Abstract

Introduction

Section snippets

Experimental

Results and discussion

J. Chem. Thermodyn.

J. Chem. Thermodyn.

Fluid Phase Equilibr.

J. Chem. Eng. Data

Russ. J. Phys. Chem.

Russ. J. Phys. Chem.

Zhurnal Prikladnoi Khimii

Neftekhimiya