(211a) Multiscale Optimization and Intensification of Natural Gas Separation and Storage
Using a multi-scale systems engineering approach, we have designed a CSS process that takes a mixture of CH4/CO2/N2 as feed, and stores CH4 inside an adsorbent-packed column while venting N2 from the system. A non-linear algebraic partial differential equation (NAPDE) model describing the conservation equations and other equations pertaining to adsorption isotherm, mass transfer driving force and pressure drop across the bed is used to study the process. In order to obtain optimal operating conditions, the detailed process model is completely discretized in both space and time into a system of nonlinear equations, whose size increases with the level of discretization. The discrete decisions related to stepwise cyclic operation together with the nonlinear equations result in a large-scale mixed integer nonlinear programming (MINLP) problem. To aid the convergence of the model, simulation-based warm starts are provided to the optimization framework. Optimization is performed to select microporous adsorbents from the database of existing materials and a rank ordered list of candidate materials for different process conditions is generated. Preliminary studies reveal that for achieving simultaneous separation and storage, both purity and storage capacity of CH4 have to be balanced by identifying the best candidate material and the corresponding operating conditions.
Our multiscale framework has the capability to simultaneously optimize the material and the process. Additionally, we will demonstrate that the framework can be used to obtain optimal properties of hypothetical materials, which can serve as a guide for future experimental efforts to design novel materials for combined gas separation and storage.
 First, E. L.; Hasan, M. M. F.; Floudas, C. A. Discovery of Novel Zeolites for Natural Gas Purification through Combined Material Selection and Process Optimization Approach. AIChE Journal, 60(5), 1767â??1785, 2014.
 Siderius, D.W., Shen, V.K., Johnson III, R.D. and van Zee, R.D., Eds. â??NIST/ARPA-E Database of Novel and Emerging Adsorbent Materialsâ?, NIST Standard Reference Database Number 205, National Institute of Standards and Technology, Gaithersburg MD, 20899, http://adsorbents.nist.gov.