Search

A new method for predicting the Liquid-Vapor critical point of binary mixture, is presented, which is based in geometrical distances. Actually, the method is based on the minimization of the distance between the experimental and calculated values of the critical temperatures and critical pressures. The SRK and PR equations of state along with classical mixing rules of van der Waals were used as thermodynamic models to calculate the critical point of a given mixture. The proposed method requires that the mixture parameters a, b, and the covolume e = b/v of each equation of state be determined at each iteration by solving the resulting cubic equation. For nine binary mixtures containing: hydrocarbon derivatives, carbon dioxide and alcohols are studied. The AARE of the calculated values is about 0.86% for critical temperature and 2.07% for critical pressure. Good agreements are found between the calculated results and experimental data. The technique is a general purpose one and can be applied in connection with other thermodynamic models. [ABSTRACT FROM AUTHOR]

The critical temperature and critical pressure are two important parameters to characterize a particular fluid. In this paper, we have studied the critical points of 24 binary mixtures containing hydrocarbon derivatives, carbon dioxide and alcohols. Computations were performed using the Heidemann-Khalil method, combined with the following equations of state (Eos): van der Waals (vdW), Soave-Redlich-Kwong (SRK) and Peng-Robinson (PR). The Newton-Raphson method was used to solve a set of nonlinear equations in three independent variables (molar fraction x, temperature T and volume V). Comparisons between predicted and available reference data are given to evaluate the accuracy of the thermodynamic model employed. The average absolute relative error (AARE) of the simulated data was less than 0.2% for critical temperature and 3% for critical pressure. A good agreement has been found between model prediction and reference data. [ABSTRACT FROM AUTHOR]

The theory of Perturbed Chain Statistical Associating Fluid (PC-SAFT) is largely applied in many industrial fields. It requires three parameters: the segment number (m), the hard-core segment diameter (σ), and the segment-segment interaction energy parameter (ε/k) for every pure non-associating fluid. By convention, they are determined by fitting vapor pressure and liquid density data. However, the shortage behind these parameters adopted by their respective authors is that they give excessive values of critical temperatures and critical pressures, which are crucial to forecasting vapor-liquid critical pressure and composition of the mixture at high pressures and temperatures. In this paper, a new approach is proposed to evaluate PC-SAFT parameters of different substances from diverse chemical families. Good fits of saturation pressure and vapor densities values of 94 pure substances are obtained, with an overall AARD of 0.89% and 1.50% respectively. The proposed method requires as input the critical pressure (P c), the critical temperature (T c), and the acentric factor (ω). By using these parameters, PC-SAFT estimates with accuracy the critical properties of pure compounds as well as the successful prediction of vapor-liquid equilibria for many non-associating binary systems at critical regions including mixtures containing ammonia, comparing with other literature values. But the limitation of this method is reflected in underestimated liquid densities. [ABSTRACT FROM AUTHOR]