A study of differential evolution and tabu search for benchmark, phase equilibrium and phase stability problems

Phase equilibrium calculations (PEC) and phase stability (PS) problems play a crucial role in the simulation, design and optimization of separation processes such as distillation and extraction. The former involve the global minimization of Gibbs free energy function whereas the latter requires the global minimization of tangent plane distance function (TPDF). In this work, two promising global optimization techniques: differential evolution (DE) and tabu search (TS) have been evaluated and compared, for the first time, for benchmark, PEC and PS problems. A local optimization technique is used at the end of both TS and DE to improve the accuracy of the final solution. Benchmark problems involve 2–20 variables with a few to hundreds of local minima whereas PEC and PS problems consist of multiple components with comparable minima. PEC involves both vapor–liquid, liquid–liquid and vapor–liquid–liquid equilibria with popular thermodynamic models. The results show that DE is more reliable but computationally less efficient compared to TS for benchmark, PEC and PS problems tested.