Vapour–liquid equilibrium for the ethyl ethanoate + 1-butene, +cis-2-butene, +trans-2-butene, +2-methylpropene, +n-butane and +2-methylpropane

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Abstract

Isothermal vapour–liquid equilibrium was measured for ethyl ethanoate + 1-butene, +cis-2-butene, +trans-2-butene, +2-methylpropene, +n-butane and +2-methylpropane at 318.4 K with an automated static total pressure measurement apparatus. The experimental data was correlated with the Wilson activity coefficient model. A good agreement between the experiments and the model was achieved. All six binary systems exhibited positive deviation from Raoult's law.

Introduction

Fuel-grade bioethanol is an ethanol made from cellulose and hemicellulose components of trees, grasses, or some waste materials [1]. It represents a sustainable substitute for gasoline in today's passenger cars [2]. In terms of fuel use, ethanol is mainly of interest as a gasoline additive or substitute. For example MTBE was phased out in various states in the US and ethanol is one oxygenate choice to replace MTBE [3]. Bioethanol can also be processed to ETBE, which can also substitute MTBE as a fuel oxygenate [4]. ETBE is prepared by reacting the isobutene in an olefinic hydrocarbon feedstock with ethanol (e.g. bioethanol) in the presence of an acid catalyst [5].

Small amounts of fermentation side-products remains in purified bioethanol and also some components are formed by oxidation during processing. One of these trace compounds is ethyl ethanoate, which is formed from ethanol and acetic acid. In processes utilizing bioethanol the behaviour of the trace components is of interest, for example to determine if they build up in the recycle streams. In this work our aim was to study the vapour–liquid equilibrium behaviour of binary systems of ethyl ethanoate + 1-butene, +cis-2-butene, +trans-2-butene, +2-methylpropene, +n-butane and +2-methylpropane at 318.4 K. Asatani and Hayduk have reported solubility of trans-2-butene in the ethyl ethanoate at 101.325 kPa and in the temperature range from 278 to 323 K [6]. The solubility of 2-methylpropane and 2-methylpropene in ethyl ethanoate at 101.325 kPa and in the temperature range from 278 to 343 K has been reported by Zhang and Hayduk in [7]. No other phase equilibrium data of binaries studied in this work was found in the literature search.

Section snippets

Materials

Materials and their purity are presented in Table 1. The ethyl ethanoate was dried over molecular sieve (Merck3A) for at least 24 h and degassed. The degassing procedure was performed as suggested by Van Ness and Abbott [8] and modified by Fischer and Gmehling [9]. The C4-components were degassed inside the syringe pump by opening the vacuum line valve 10 times for a period of 10 s. The success of the degassing procedure of components was checked by measuring the pure component vapour pressures

Data reduction

The method proposed by Barker was used to converted the total amount of moles fed in to the cell into mole fractions of both vapour and liquid phase [12]. The method of Barker assumes that there is a model that can predict the bubble point pressure at higher accuracy than the experimental error of the measured total pressure. Barker's method is an iterative method, which needs models for vapour and liquid phase non-idealities. Method for calculating vapour phase fugacity coefficients was chosen

Error analysis

Error estimates for all measured variables were defined. Obtained absolute errors for moles of components and total composition are shown in Table 4, Table 5, Table 6, Table 7, Table 8, Table 9 with the measured values. For cell volume, temperature, injection volume and pressure absolute errors were reported earlier in this article. For total mole fractions zi, a similar error analysis as presented in [14] was done to find out the error margins.

The uncertainty of injection volumes ΔV1 = ±0.02 cm3

Results and discussion

The results of all measured six binary pairs are presented in Table 4, Table 5, Table 6, Table 7, Table 8, Table 9. Injected amount of moles are presented using more significant digits than their errors would indicate. This is required if someone wants to recalculate the measured data. All six binary pairs showed positive deviation from Raoult's law. No azeotropic behaviour was found. In Fig. 2, the symbols present the experimental pressure as a function of liquid and vapour composition

Conclusions

Six isotherms at 318.4 K of ethyl ethanoate and C4-alkanes and alkenes were measured with a total pressure measurement approach leading to PTz data and treated using the method of Barker [12] to provide PTxy data. No azeotropic behaviour was found. All systems measured exhibited positive deviation from Raoult's law. The parameters of Wilson activity coefficient model were optimized.

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