This dissertation examines input output approaches, including analytical and CFD models, aimed at reactor performance assessment for optimal process design. While analytical models can rapidly provide reactor output metrics by forgoing levels of complexity, they are often limited by many underlying assumptions. Conversely, slow-to-solve CFD models are more versatile in their application due to a reduced number of necessary simplifications. To demonstrate the applicability of both approaches in this work, first, an analytical method has been used to accurately calculate outlet concentrations for laminar flow reactors undergoing a steady-state process. Subsequently, detailed CFD modeling approaches are employed to optimize complex adsorption and membrane enhanced reactive processes. Chapter one introduces an analytical model capable of calculating the reactor effluent concentrations for steady-state, non-isothermal Segregated Laminar Flow Reactors (SLFRs) regardless of the reactor geometry. The only requirement is knowledge of the SLFRs residence time density function. The existing analytical model for isothermal SLFRs is extended to also be applicable non-isothermal SLFRs for incompressible fluids. The accuracy of both the existing isothermal and the developed non-isothermal SLFR models are demonstrated in four case studies with two different reactor geometries by comparing the analytical results with results obtained from equivalent CFD simulations. The analytical results are shown to be within 2 % of the CFD generated values, rendering a CFD approach superfluous for SLFRs. Chapter two introduces a novel model of a Partial Pressure Temperature Swing Adsorptive Reactor (PPTSAR) process with application to the water gas shift reaction. In this Sorption Enhanced Water Gas Shift (SEWGS) process, a set of two PPTSARs, filled with both catalyst and adsorbent, are used. Alternating between two PPTSARs, a continuous syngas feed is converted to a stream of hydrogen and steam, free of carbon dioxide, in one reactor, while concurrently, steam is fed to the other PPTSAR to regenerate the adsorbent and capture the released carbon dioxide. This is realized by coupling a temperature and partial pressure swing between the reaction/adsorption and regeneration steps. These intensified PPTSARs can replace conventional water gas shift packed bed reactors in Integrated Gasification Combined Cycle (IGCC) power plants. The PPTASRs achieve carbon monoxide conversions greater than 98 % with simultaneous carbon dioxide capture. Chapter three presents the detailed derivation of the multidomain PPTSAR model including all employed assumptions used in Chapter two. Chapter four presents a significant performance improvement on the PPTSAR process in Chapter two, by demonstrating the effect of performing the regeneration step counter-currently to the reaction/adsorption step, as opposed to co-currently. As a result, an analogous process using Partial Pressure Swing Adsorptive Reactors (PPSARs) without the need for an additional temperature swing is presented. Finally, Chapters five and six present transient and steady-state multiscale membrane reactor models, respectively.