(551g) Saturation Point Calculations in Reactive Systems Based on the RAND Method
AIChE Annual Meeting
2021
2021 Annual Meeting
Engineering Sciences and Fundamentals
Thermophysical Properties and Phase Behavior
Wednesday, November 10, 2021 - 4:40pm to 4:55pm
In this work, we have developed a RAND-based algorithm for calculating the saturation points and phase envelope of a reactive mixture. The RAND algorithm was a non-stoichiometric flash algorithm originally conceived for single-phase ideal mixtures at constant temperature and pressure. It was recently extended to real mixtures, and also to other types of flash specifications. We showed here how to modify the RAND-based flash formulation for real mixtures to solve the β-specification problems. We distinguished between two types of phase fraction, the one based on components and the one based on elements. They led to different constraint equations in the formulation. Furthermore, we introduced element-based partition coefficients, similar to the equilibrium ratios or K-factors used for non-reactive mixtures. Use of these new variables are essential to pass the critical point of a reactive mixture in the phase envelope construction. Since the formulation developed for reactive mixtures is general, it can also be reduced and used for the simpler non-reactive mixtures. We showed how the reduction could be made and how the reduced algorithm served as an alternative approach to the prevailing phase envelope algorithm of Michelsen.
We illustrated the robustness and efficiency of the proposed algorithm using four typical examples (see the attached figure):
- Pxy diagrams for CO2 solubility in an NaCl brine with ion speciation considered, which is a vapor-liquid equilibrium (VLE) problem modeled by a γ-Ï approach;
- a Txy diagram of the solubility of MgCl2 salts in water with ion speciation and solid formation reactions considered, which is a solid-liquid equilibrium (SLE) problem modeled by a γ model;
- a PT phase envelope for a reactive mixture involving an alkene hydration reaction, which is a VLE problem modeled by a Ï-Ï approach; and
- a PT phase envelope for a non-reactive hydrocarbon mixture, which is a VLE problem modeled by a Ï-Ï