The total pressure and the compositions of the vapour and liquid phases of the methanol–benzene system have been determined under equilibrium conditions at 100°, 120°, 140°, 160°, 180°, 200° and 220° for ten levels of concentration. The corresponding activity coefficients of methanol and benzene are reported; their values indicate that the equilibrium data are thermodynamically consistent. An azeotrope is found at all temperatures, its methanol content increasing as the temperature is increased. The relationship log Paz = 6·5098—(1,766/T) expresses the interdependence of the azeotrope vapour pressure Paz(lb/in2 abs.) and temperature T(°K). Estimates of integral heat of mixing (HE) and entropy change due to mixing (SE) as functions of liquid composition (xmeth) have been made from the excess free energy of mixing GE,(T) xmeth functions. Both HE and SE at a given x are positive increasing functions of temperature. These phenomena are discussed in terms of the dissociation of methanol ‘polymer’ and the formation of benzene–methanol ‘complexes’.

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An apparatus for determining high-pressure liquid-vapour equilibrium data has been developed and proved to operate satisfactorily. The apparatus operates isothermally. Results have been obtained for the ethanolmethanol system at the following temperatures: loo", 120", 140" and 160". The results are shown to be thermodynamically consistent within the limits of the accuracy of their determination. The 'ideal activity coefficients' (i.e. calculated assuming that the gas phase behaviour is ideal) are correlated with the mole fraction of the component in the liquid phase by Margules-type equations (1) and (2). The accuracy of these equations is greater than predictions based on fugacities.From equations (5), (6) and (1) or (2) in the paper it is possible to estimate any pair of liquid-vapour equilibrium compositions for any specified pressure P and temperature T. Alternatively, for a specified P and liquid composition, the corresponding T and vapour composition may be calculated. IntroductionThe purpose underlying this work is to provide reliable equilibrium data for a number of relatively common binary systems over a wide pressure range above atmospheric pressure. These data are required primarily to evaluate the performance of a sieve tray in a 7-in. dia. high-pressure distillation column.Since it was intended that conditions in the equilibrium apparatus should be adjustable up to the values of temperature and pressure of the critical points of the components, the 'Static Method' as used by Verchoyle' and others2s3 was considered the best practical method. Recirculation stills have been used to obtain equilibrium data up to the critical region of some system^.^*^ However as the pressure of the system is increased, pv+pI and AH, is reduced. These tendencies encourage liquid entrainment in the recirculating vapour and flash evaporation of the condensate as it returns to the reboiler. It also becomes more difficult to prevent partial condensation on the walls of the vessel above the boiling liquid and/or total evaporation of liquid droplets splashing on to these walls.The usefulness of the 'Static Method' increases with increasing pressure. As py increases, the volume of the vapour phase required to produce a given mass of sample decreases, and the withdrawal of this sample causes a smaller thermal disturbance in the system with decreasing AH,. Finally, the mechanical design of such an apparatus is far simpler than that of a recirculation type of still designed to operate at similar pressures.The choice of the methanol-ethanol system for the first investigation which is reported here was influenced by the ease of obtaining materials of high purity of which the behaviour in solution might be anticipated to be nearly ideal and also the ease with which the system could be analysed. These considerations, together with those of thermodynamic consistency would provide a basis for confidence in the reliability of the data obtained from the system. The upper temperature of 160" represented the highest steam temperature then a...

The total vapour pressure and the composition of the liquid and vapour phases of the benzene and n-heptane system have been experimentally determined under equilibrium conditions at 110, 125, 140, 155, 170, 185, 200 and 215 "C. The corresponding composition of the vapour phase was also estimated using an expression for the liquid phase activity coefficient as a function of the composition of the liquid phase. Several expressions were compared and it has been found that the three-constant Redlich and Kister equation gave the best fit of the experimental vapour pressure data than the other equations.Comparison between the calculated and measured vapour compositions has shown a discrepancy of ymeas. -ycalc. of the order of 0.02 mol fraction or 10 times the experimental tolerance. Nevertheless, the experimental values were reasonably thermodynamically consistent.The low values of the liquid phase activity coefficients indicated that the behaviour of this particular system was not far from ideality. Also, it was found that the degree of non-ideality decreased with the increase in temperature. The behaviour of the vapour phase was shown also to be nearly ideal.The excess Gibbs free energy of mixing was calculated, and it was found to be non-symmetrical with mole fraction. On increasing the temperature of the system, the liquid composition corresponding to the maximum GE tended to shift to a higher benzene concentration, whilst at a fixed liquid composition, GE initially decreased and then remained stationary or increased again. This was thought to be due to differences in the molar volumes of the two components. 113?

The heat associated with the formation of 1 mole of sec.-hexyl hydrogen sulphate from 79.57 % w/w aqueous sulphuric acid and 1-hexene at 0" C has been estimated at 32.3 rt 024 kcal, employing an ice calorimetric technique. The results indicated that the subsequent hydrolysis of the sec.-hexyl sulphate to the alcoxonium ion was athermal to within f 0.6 kcal. These determinations have also thrown light upon the nature of the rate-determining process in this heterogeneous sulphation reaction.It is not possible to deduce theoretically the heat associated with the formation of sec.-alkyl hydrogen sulphates from a-olefins and aqueous sulphuric acid because first, there is no reliable information on the nature of the ions involved in the reaction and secondly, few relevant thermodynamic data are known for this class of compounds. Accordingly it was decided to measure this heat calorimetrically.This measurement is difficult for the following reason. The sec.-alkyl hydrogen sulphates, which are formed by the rate-determining addition of a proton to the a-olefin followed by the rapid addition of a hydrogen sulphate anion, can undergo a reversible hydrolysis via the carbonium ion to the corresponding alcoxonium ion.1 The reaction scheme may be represented as slow (fH+)