VLE measurements

3 EXPERIMENTAL METHODS, EQUIPMENT AND DATA REDUCTION 4.4.3.1 Vapor-liquid equilibrium (VLE) measurements 

Investigations on vapor-liquid equilibrium of polymer solutions are the most important source for obtaining solvent activities in polymer solutions. Therefore, emphasis is laid to the experimental methods which use this equilibrium. These mediods are  

IGC at finite concentrations, and head-space gas-chromatography (HSGC), ebulliometry and 

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READ STANDARD DEVIATIONS OF VLE MEASUREMENTS- ND IS THE NUMBER OF STANDARD DEVIATIONS WHICH ARE DUPLICATED (1.UE.NO.LE-NN). 

The above observation provides useful information to the experimenter when investigating systems that exhibit vapor-liquid-liquid equilibrium. In particular, it is desirable to obtain VLE measurements at a temperature near the one where the third phase appears. Then by performing CLS estimation, it is guaranteed that the EoS predicts complete miscibility everywhere in the actual two phase region. It should be noted, however, that in general the minima of the stability function at each temperature might not change monotonically. This is the case with the C02-n-Hexane system where it is risky to interpolate for intermediate temperatures. Hence, VLE data should also be collected at intermediate temperatures too. 

Bobbo, S., Fedele, L., Scattolini, M., Camporese, R. (2001) Isothermal VLE measurements for the binary mixtures HFC-134a + HFC-245fa and HC-600a + HFC-245fa. Fluid Phase Equilibria 185, 255-264. 

Dr. Denis Doizi of CEA presented about the HIx Vapour Liquid Equilibrium (VLE) measurement. A collection of accurate thermodynamic data for the HIx section is critical for robust modelling of the S-I process. CEA has developed experimental techniques to obtain such data at the high temperatures and pressures expected in a full-scale plant. A tantalum microautoclave was used to collect data, with FTIR spectrometry used to analyse HI and H20 concentrations. UV-visible spectroscopy was used for... 

Based on our experiences regarding the study of VLE measurements for the iodine-sulphur thermochemical cycle, the use of FTIR spectrometry to study the kinetics of the hydrolysis reaction is proposed. The experimental set-up is modified to allow FTIR measurements using a Bruker tensor 27 spectrometer (Figure 7). 

The only remaining undetermined thermodynamic properties are yH 0 and yEtQn Because or the highly nonideal behavior of a liquid solution of ethanol and wat these must be determined from experimental data. The required data, found fro VLE measurements, are given by Otsuki and Williams.t From their results for t ethanol/water system one can estimate values of yH2G and yEt0H at 200°C, (Pressu has little effect on the activity coefficients of liquids.)... 

Process simulation can guide and minimise the experimental research, but not eliminate it. Actually, the calibration of models requires accurate experimental data. It is the experiment that proves the model, and not the opposite Statistical planning of experiments is nowadays in a large extent obsolete. Instead, the experimental research should take profit from the power of rigorous models incorporated in simulation packages, particularly in the field of thermodynamics. For instance, simple vapour-liquid equilibrium (VLE) experiments in laboratory can be used to Increase the reliability of a feasibility study in innovative processes. Conversely, industrial VLE measurements can be used to calibrate the thermodynamic models incorporated in a simulator when experimental information is not available. 

Figure 4.4.13. Schematic of applying head-space gas-chromatography (HSGC) to VLE-measurements in polymer solutions (drawing provided by B. A. Wolf, Univ. Mainz, Germany).

Primary data reduction Equation [4.4.7] is the starting relation for data from VLE-measurements. Two relations are necessary to obtain the solvent activity aj one for the fugacity coefficient of the solvent vapor and one for the standard state fugacity of the liquid solvent. In principle, every kind of equation of state can be... 

Apart from VLE-measurements, membrane osmometry is the next important method that has been used for measuring solvent activities in polymer solutions. This follows from the... 

A static-analytic apparatus, shown in Figure 1, has been employed for accurate VLE measurements on C02-amine-H20 systems. The experiments were carried out in a 100 ml stainless steel vessel at various temperatures from (313 to 393) K and total pressures up to 1 MPa. Both the gas and liquid phases were analysed by a Perkin-Elmer Clams 500 gas chromatograph (GC) to determine the coexisting-phase compositions. The apparatus was validated in... 

Most of the excess properties are available experimentally. While the g -values can be obtained from VLE measurements (see Example 5.3), the excess enthalpies are obtained from calorimetric and the excess volumes from density measurements. When the excess properties mentioned before are known, other excess properties, for example the excess entropy s, can directly be derived, as shown in the next example. 

Bobbo, S. Fedele, L. Camporese, R. Stryjek, R- VLE measurements and modeling for the strongly positive azeotropic R32 +... 

Figurski, G. Emmerling, U. Nipprasch, D. Kehiaian, II. V. Alkyl methanoates + benzene binary mixtures new VLE measurements and DISQUAC analysis of thermodynamic properties Fluid Phase Equilib. 1997,137, 173-183...

Gutsche, B. Knapp, H. VLE measurements of binary mixtures of chlorohydrocarbons and aliphatic ethers. Consistency and correlation problems Pol. J. Chem. 1980,54, 2261-2267... 

Domanska, U. Lachwa, J. Gonzalez, J. A. Thermodynamics of binary mixtures containing N-methyl-2-pyrrolidinone. VLE measurements for systems with ethers - Comparison with the Mod. UNIFAC (Do) and DISQUAC models - Predictions for VLE, GmE, HmE and SLE Fluid Phase Equilib. 2005,235, 182-190... 

At the laboratory of Chemical Engineering at HUT there are facilities for VLE measurements, which have also been used to retrieve parameters that are of interest in the dimerization process. The Laboratory of Industrial Chemistry at HUT has studied reaction kinetics and several kinetic models have been developed. The process models have been developed using the flowsheeting program Flowbat. 

It is through Eq. (5) that low-pressure VLE measurements provide the experimental input required for a quantitative thermodynamic... 

Precise determination of G through low-pressure VLE measurements generally requires the availability of data spanning the entire range of liquid compositions. The experimentalist still has the option, however, of collecting his data either at isobaric or at isothermal conditions. The question then arises whether one type of data is more useful than the other. 

Let us assume the availability of two complete sets of error-free VLE measurements. The first set has been taken at constant pressure, and consists of values of T, x, and y. The second is... 

Hala jet (8) classify VLE measurement techniques in five major groups distillation methods, circulation methods, static methods, dew-point/bubble-point methods, and flow methods. One could add to this list some rather specialized techniques, but in the main most modern low-pressure VLE work is done on two major types of equipment circulation stills and static equilibrium cells. 

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