Process Simulation of Sulfuric Acid Recovery by Azeotropic Distillation: Vapor-Liquid Equilibria and Thermodynamic Modeling

For development of the new process for the recovery of dilute sulfuric acid by azeotropic distillation proposed in our earlier publication [Li et al., hid. Eng. Chem. Res., 2013, 52, 3481-3489], in this paper, the vapor-liquid equilibria (VLE) for the FeSO4 + H2O and H2SO4 + FeSO4 + H2O systems were first determined by the quasi-static ebulliometric method. The azeotropic temperatures of the H2SO4 + H2O + entrainer (cyclohexane and octane) systems were also measured. The corresponding electrolyte nonrandom two-liquid interaction parameters were obtained by regressing the experimental data with a maximum average absolute deviation of boiling points of 0.83 K. The model with newly obtained parameters was verified by comparing its prediction with the experimental azeotropic temperature for the H2SO4 + FeSO4 + H2O + C6H12 quaternary system. The temperature and sulfuric acid concentration ranges of the study were 305.9-396.9 K and 0-86.1 wt %, respectively. Following from the experimental results, semicontinuous distillation experiments for the sulfuric acid recovery were performed with cyclohexane as the entrainer. Equipped with the new parameters, Aspen Plus was adopted to carry out the process simulation for the recovery of dilute sulfuric acid by azeotropic distillation. The simulation results show that when cyclohexane was employed as the entrainer, the dilute sulfuric acid can be concentrated to 68% by a packed column containing 4 theoretical stages and with a reboiler temperature of only 361 K.