Separation of NH3/CO2 from melamine tail gas with ionic liquid: Process evaluation and thermodynamic properties modelling

Abstract

• The thermodynamic properties models are developed to the NH 3 -IL systems. • A systematic computer-aided IL design for separation of NH 3 /CO 2 is performed. • A hydroxyl-functionalized IL is selected and applied for process simulation. • The IL-based process is evaluated by tech-economical assessment. Melamine, as a typical chemical intermediate, is widely applied in the plastics and coatings industry. However, its synthesis process releases large amounts of NH 3 and CO 2 gas mixtures. A tail gas treatment is therefore a necessary process followed by its production steps. The traditional separation technology for tail gas treatment is water scrubbing for NH 3 absorption, but this option suffers from high energy consumption and lots of NH 3 -containing waste water. In this work, a novel ionic liquid (IL)-based solvent, is proposed for the separation of NH 3 /CO 2 mixtures from melamine tail gas. As models for prediction of solubility of NH 3 in ionic liquids are not available, first the UNIFAC-IL model is adopted and extended to the NH 3 -IL systems based on available measured data together with other Group Contribution-based pure component property models. Then, a systematic computer-aided IL design for NH 3 /CO 2 separation is performed by formulating and solving a mixed-integer nonlinear programming problem. Considering NH 3 solubility, NH 3 /CO 2 selectivity and feasibility for industrial application as selection criteria, a hydroxyl-functionalized imidazolium-based IL is found to be optimal. Based on the established thermodynamic models, both the IL-based process and a traditional water scrubbing process for NH 3 /CO 2 separation are simulated and evaluated in terms of energy consumption, economic analysis and net CO 2 emission under the same NH 3 recovery. The simulation results show that compared with the traditional processes, the IL-based process represents a 45%, 35% and 19% reduction in overall equivalent energy, separation cost and net CO 2 emission, respectively.