We consider a modified Skarstrom PSA cycle which consists of five steps: ). The role and purpose of individual steps are described in detail elsewhere. The main feature of this cycle is that it utilises a dual reflux configuration, which avoids the need to pull deep vacuum below the practical limits of industrial vacuum pumps. This presents an important advantage over the more commonly used 4-step VSA cycle with light product pressurisation, which often requires unphysically low evacuation pressures to achieve high CO2 purities and recoveries. To accurately simulate the separation of CO2 / N2, partial differential equations which describe the mass, energy, and momentum transfer phenomena taking place in the adsorption column are required. A complete description of the governing equations, model parameters, boundary conditions and mathematical criterion used to determine cyclic steady state are provided in supplementary note 2, while other technical details of the PSA simulation are provided elsewhere. We summarise here the key assumptions adopted in our process model as the following: (1) the Ideal Gas law describes the gas phase; (2) the gas phase and solid phase are in thermal equilibrium; (3) mass transfer is controlled by molecular diffusion in the macropores, which is valid for most microporous adsorbents with pore openings greater than 4Å. Furthermore, the mass transfer rate is described by the linear driving force (LDF) approximation; (4) an axially dispersed plug flow model is employed, meaning there are no radial distributions in concentration, pressure, and temperature for both the solid and gas phase; (5) the column is operated adiabatically; (6) the Ergun equation describes the axial pressure drop. These assumptions are largely consistent with the assumptions of several previous studies. therefore be able to achieve this product specification in any given PSA cycle. For the purposes of our investigation, we relax the purity requirement to 90%, and simply refer to the 90% purity and recovery targets as carbon capture and sequestration (CCS) constraints.