(283e) Energy Efficient Design of Ionic Liquid Based Gas Separation Processes

Gas separation processes have been one of the most important operations in the oil and gas related industries, where gases of interest are present in significant amounts to justify their separation for use as raw gas in chemical production utilization. Currently, the gas separation technologies include energy intensive distillation and solvent based absorption operations or flux limited adsorption and membrane-based operations. For most gas mixtures, however, the most common separation technology applied is distillation, which consumes large amounts of energy to give the high purity products. These distillation columns operate at low temperatures and high pressures and therefore require high energy consumption, leading to negative environmental impacts. In certain regions of their operation, all these technologies work very efficiently. Therefore, an alternative scheme, taking advantage of the regions where each individual technology operate best, a hybrid gas separation scheme of combining distillation with absorption separation processes is considered. In this novel gas separation process design strategy, an absorber is employed followed by flash-evaporation operations with a low energy consumption distillation operation used in a pre-separation step only to reduce flux (if necessary). Since no energy is required in an absorber operation, this hybrid gas separation process strategy can significantly reduce the energy consumption, where distillation is only employed for a partial separation where significantly less energy is required.

Because of non-volatility, good stability, tunable viscosity and designable properties, ionic liquids (ILs) are considered as novel potential solvents and alternative media for gas absorption. Therefore, a strategy for hybrid gas separation process synthesis where distillation and IL-based absorption are employed for energy efficient gas processing has been developed. However, the potentially thousands of ILs that may be applicable, makes it a challenging task to search for the best one for specific gas absorptions in different raw gas systems. Therefore a selection-screening method for ILs is also necessary for the development of novel hybrid gas separation process can be designed.

In this presentation, a three-stage methodology proposed for hybrid gas separation process design and evaluation will be highlighted. The first stage involves IL screening, where a systematic screening method together with a database tool is established to identify suitable ILs based on a collection of gas solubility data, Henry’s constant data as well as data estimated through reliable predictive models (for example, COSMOS-RS). The second stage is process design, where the important design issues (amount of solvent needed, operating temperatures and pressure, evaporation conditions, etc.) are determined. A hybrid gas separation scheme is designed to replace the conventional distillation process. Since the only energy requiring step in the hybrid process is the flash-evaporation step (and the low energy consuming pre-distillation step, if employed), potentially a large reduction of energy consumption is possible by switching from distillation to the hybrid-absorption scheme the selective gas separation tasks. For example, replace distillation by absorption to remove only the gases present in smaller amounts in the gas mixture, thereby letting the larger amounts free to go out as the exit (raffinate) gas. This small amount absorbed gas is then easily separated through evaporation or distillation, which only consumes a small fraction of the total energy of the conventional distillation based process. The third stage involves verification and sustainability analysis based on rigorous process simulation of the generated hybrid gas separation process strategy. The gas separation problem for a model shale gas mixture is selected as a case study to highlight the application of this hybrid separation process design method.

The presentation will highlight the method, the data and applications of the method to generate novel, innovative and sustainable gas separation processes requiring significantly less energy than known processes.