Continuous Molecular Targeting–Computer-Aided Molecular Design (CoMT–CAMD) for Simultaneous Process and Solvent Design for CO₂ Capture

Abstract

Solvent-based separation systems have a substantial potential for improvement when the solvent and the process conditions are optimized simultaneously. The fully integrated design problem, however, leads to an optimization problem of prohibitive size and complexity owing to the many discrete degrees of freedom in selecting a solvent and the nonlinear nature of the process models. We here implement and extend the method of continuous molecular targeting−computer-aided molecular design (CoMT−CAMD) for the solvent and process optimization of a precombustion CO 2 -capture system with physical absorption. CoMT−CAMD is a deterministic procedure that does not require a preselection of solvent molecules. The process topology considered in our study includes all major process operations of an existing CO 2 -capture system: multistage absorption, desorption (two flash desorption stages with gas recycle) and CO 2 compression. We measure the process performance with a single economic objective function. The objective function captures the process trade-offs and evaluates the potential processsolvent on a common basis. The solvent is represented as the pure component parameters of the perturbed-chain statistical associating fluid theory (PC-SAFT). The optimization problem is formulated with the pure component parameters of the solvent (PC-SAFT parameters) and with the process variables as degrees of freedom. Necessary auxiliary properties of the optimized solvent such as the ideal gas heat capacity and the molar mass are predicted with quantitative structure property relationship models, based on the pure component PC-SAFT parameters. As a result, one gets a unified thermodynamic framework for fluid properties based on the PC-SAFT model. With CoMT−CAMD we obtain a list of the best performing physical solvents for the considered CO 2 -capture application. The resulting list of best performing solvents contains state-of-the-art solvents and new green solvent molecules.

Computer-aided molecular design in the continuous-molecular targeting framework using group-contribution PC-SAFT

“…The same applies for the molar mass of the fluid. Thus, for the molar mass and the ideal gas heat capacity, quantitative structure-property relationships (QSPR) are employed using PC-SAFT parameters as input (Lampe et al, 2014b;Stavrou et al, 2014). For consistency, the coefficients of the QSPR are fitted to data for the same set of components that was used for the fitting of the GC-method.…”

“…In the second case study, we implement the proposed method for designing a solvent for the capture of CO 2 by physical absorption (Enick et al, 2013;Gwinner et al, 2006;Miller et al, 2010;Stavrou et al, 2014). The process topology includes the main absorption, desorption, and CO 2 compression steps of a pre-combustion CO 2 capture application by an IGCC power plant as described in Stavrou et al (2014) (Fig.…”

“…Cubic equations of state have successfully been used for the design of ORC working fluid mixtures (Papadopoulos et al, 2013). Due to their higher predictive power, models based on the statistical associating fluid theory (SAFT) are used for fluid design (Bardow et al, 2010;Lampe et al, 2014b;Mac Dowell et al, 2011;Pereira et al, 2008Pereira et al, , 2011Stavrou et al, 2014).…”

“…In a second step, called mapping, the results of this optimization are used to identify real fluids with a similar performance as the optimal fluid. A database search was used for this mapping step in (Bardow et 2014b; Stavrou et al, 2014). While the CoMT-CAMD approach has successfully been applied to both, solvent design and design of ORC working fluids (Lampe et al, 2014b), the database search allowed only the selection among known fluids.…”

Computer-aided molecular design and selection of CO2 capture solvents based on thermodynamics, reactivity and sustainability

“…, Stavrou et al 61 and Lampe et al 62 using the PC-SAFT EoS, the perturbed-chain version of SAFT 63 and the PCP-SAFT EoS, its extension to polar fluids [64][65][66] . In the context of chemisorption, the SAFT thermodynamic platform has been used to predict the phase and chemical equilibria of CO 2 capture fluids through a parameterization of a group contribution version of the statistical associating fluid theory for potentials of variable range equation of state, SAFT-γ SW 67,68 .…”