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This work presents a Computer-Aided Molecular Design (CAMD) method for the synthesis and selection of binary working fluid mixtures used in Organic Rankine Cycles (ORC). The method consists of two stages, initially seeking optimum mixture performance targets by designing molecules acting as the first component of the binaries. The identified targets are subsequently approached by designing the required matching molecules and selecting the optimum mixture concentration. A multiobjective formulation of the CAMD-optimization problem enables the identification of numerous mixture candidates, evaluated using an ORC process model in the course of molecular mixture design. A nonlinear sensitivity analysis method is employed to address model-related uncertainties in the mixture selection procedure. The proposed approach remains generic and independent of the considered mixture design application. Mixtures of high performance are identified simultaneously with their sensitivity characteristics regardless of the employed property prediction method.

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Efficient power generation from low to medium grade heat is an important challenge to be addressed to ensure a sustainable energy future. Organic Rankine Cycles (ORCs) constitute an important enabling technology and their research and development has emerged as a very active research field over the past decade. Particular focus areas include working fluid selection and cycle design to achieve efficient heat to power conversions for diverse hot fluid streams associated with geothermal, solar or waste heat sources. Recently, a number of approaches have been developed that address the systematic selection of efficient working fluids as well as the design, integration and control of ORCs. This paper presents a review of emerging approaches with a particular emphasis on computer-aided design methods.

We propose a Computer Aided Molecular Design (CAMD) method which employs optimization to support the synthesis and selection of high performance molecules for use in process systems and to guide experimental efforts. The method can be used to address challenging applications where a) the desired molecules exhibit phase and chemical equilibrium, b) numerous combinations of molecules need to be evaluated, and c) multiple criteria must be considered to capture the effects of molecular chemistry on the process system performance. The method is applied to the design of solvents in chemical absorption processes for the separation of carbon dioxide (CO 2 ) from gas streams. The molecular design problem is first approached via a fast screening stage where molecules are evaluated based on the simultaneous consideration of multiple performance indices pertaining to thermodynamics, reactivity and sustainability. A few high-performance solvents are further evaluated using an advanced group contribution equation of state to predict reliably the highly non-ideal equilibrium behavior of solvent-water-CO 2 mixtures. Several promising novel solvents for CO 2 capture are proposed and can now be assessed experimentally. The proposed method can readily be applied to other chemical absorption processes to accelerate the identification of novel solvents. AbstractThe identification of improved carbon dioxide (CO 2 ) capture solvents remains a challenge due to the vast number of potentially-suitable molecules. We propose an optimization-based computer-aided molecular design (CAMD) method to identify and select, from hundreds of thousands of possibilities, a few solvents of optimum performance for CO 2 chemisorption processes, as measured by a comprehensive set of criteria. The first stage of the approach consists in a fast screening stage where solvent structures are evaluated based on the simultaneous consideration of important pure component properties reflecting thermodynamic, kinetic, and sustainability behaviour. The impact of model uncertainty is considered through a systematic method that employs multiple models for the prediction of performance indices. In a second stage, high-performance solvents are further selected and evaluated using a more detailed thermodynamic model, namely the group-contribution statistical associating fluid theory for square well potentials (SAFT-γ SW), to predict accurately the highly non-ideal chemical and phase equilibrium of the solvent-water-CO 2 mixtures. The proposed CAMD method is applied to the design of novel molecular structures and to the screening of a dataset of commercially available amines. New molecular structures and commercially-available compounds that have received little attention as CO 2 capture solvents are successfully identified and assessed using the proposed approach. We recommend that these solvents given priority in experimental studies to identify new compounds.

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This work reviews research activities in the development of phase-change CO2 capture solvents and processes. The focus is on liquid–liquid phase-change solvents in which the CO2-lean phase can be recycled to the absorber prior to regeneration hence the energy demands may be substantially decreased compared to nonphase change processes. The review briefly provides the basic chemical and physical principles required to understand the phase-change behavior in postcombustion CO2 capture systems. The reviewed work is further organized per different solvent type into major sections including experimental property measurement studies, experimental pilot plant studies, thermodynamic and kinetic modeling studies, as well as process modeling and technoeconomic assessment studies. In all sections we provide details regarding experimental approaches, operating conditions of pilot plants, implementations in different industries, and performance data. Key findings include operating observations and performance indicators regarding the investigated solvents and processes as well as a substantiated estimation of their technology readiness level.