Solubility Equilibrium of the NaOH–H₂O–Na₂CrO₄–Na₂SiO₃–NaAlO₂ Multicomponent Systems Involved in the Liquid-Phase Oxidation of Chromite

Chromium salts are a group of important chemical raw materials with many applications. While the conventional manufacturing process, i.e. calcium roasting of chromite, has many disadvantages; the novel processes of liquid-phase oxidation, whose main reaction is the oxidation of chromite by oxygen (air) in highly concentrated alkaline solutions, are promising to achieve clean manufacturing. For the oxidation reaction of chromite in NaOH solutions, a significant amount of multicomponent systems consisting NaOH, Na₂CrO₄, Na₂SiO₃, and NaAlO₂ are generated. It is a prerequisite to clarify the solubility equilibrium of the multicomponent systems for exploring highly efficient separation methods of Na₂CrO₄ with Na₂SiO₃ and NaAlO₂. In this paper, Na₂CrO₄ solubility in the ternary system of NaOH–H₂O–Na₂CrO₄ was first measured using the equilibrium analysis method and varying the NaOH concentrations from 100 to 800 g·L^–1 and the temperatures from 353.15 to 403.15 K. Aferwards, the solubility of Na₂CrO₄, NaAlO₂, and Na₂SiO₃ in the other multicomponent systems was analyzed at NaOH concentration = 400, 500, and 600 g·L^–1, respectively

Energy-Saving Optimal Design and Effective Control of Heat Integration-Extractive Dividing Wall Column for Separating Heterogeneous Mixture Methanol/Toluene/Water with Multiazeotropes

To the best of our knowledge, very few efforts have been investigated for separating heterogeneous mixtures methanol/toluene/water with multiazeotropes using extractive dividing-wall column (EDWC). In this work, we propose a systematic approach for the energy-efficient EDWC to achieve less capital cost and operating cost in separating heterogeneous multiazeotropes mixtures, which involves thermodynamic feasible insights via residue curve maps to find separation constraints, global optimization based on a proposed CPOM model, and a dynamic control through Aspen Dynamics simulator to better maintain product purities. An energy-saving EDWC with heat integration (HI-EDWC) flowsheet is then proposed to achieve the minimum total annualized cost (TAC). The computational results show that the TAC of the proposed HI-EDWC is significantly reduced by 15.14% compared with the optimal double-column extractive distillation with an additional decanter. Furthermore, an effective control strategy CS3 with a fixed reboiler duty-to-feed ratio and temperature/(S/F) cascade is proposed to better handle the methanol, toluene, and water product purities than basic control structures CS1 and CS2 while feed flow rate and composition disturbances are introduced in the proposed HI-EDWC process

Life Cycle Sustainability Assessment of Chemical Processes: A Vector-Based Three-Dimensional Algorithm Coupled with AHP

In this study, an integrated vector-based three-dimensional (3D) methodology for the life cycle sustainability assessment (LCSA) of chemical process alternatives is proposed. In the methodology, a 3D criteria assessment system is first established by using the life cycle assessment, the life cycle costing, and the social life cycle assessment to determine the criteria from the environmental, economic, and social pillars, respectively. The methodology incorporates the analytic hierarchy process (AHP) method to convert experts’ judgments on the soft criteria into quantitative data and realize a unitary scale for both quantified soft criteria and normalized hard criteria. After assigning appropriate weights to each pillar and criterion by using the AHP method, the sustainability of the alternative processes can be prioritized by employing a novel vector-based algorithm, which combines the absolute sustainability performance and the relative sustainability deviation of the investigated processes. A case study on the sustainability assessment of three alternative ammonia production processes demonstrates that the proposed methodology is able to serve as a comprehensive and rigorous tool for the stakeholders to rank and identify the most sustainable chemical process alternatives