Esther Forte

Efficient Screening and Selection of Post-combustion CO2 Capture Solvents

We develop an approach for the screening and selection of post combustion CO2 capture solvents using as the performance criteria the molecular and mixture properties associated with thermodynamics, reactivity and sustainability. The proposed approach involves a fast screening stage in which numerous solvents are evaluated based on the simultaneous consideration of pure component properties. Several properties are specifically selected to represent the effects of molecular chemistry on the capture process. A few high-performing solvents are further evaluated using predictive models accounting for the very nonideal mixture behaviour. The prediction of pure component properties is supported by standard group contribution models. The solvent-water-CO2 interactions are represented within the SAFT-VR and SAFT-γ equations of state to predict accurately the mixture vapour-liquid equilibrium behaviour. The proposed developments are tested successfully on a dataset consisting of 126 potential solvent candidates.Alzheimer’s disease (AD) is a progressive neurodegenerative disorder, characterized by irreversible decline of mental faculties, emotional and behavioral changes, loss of motor skills, and dysfunction of autonomic nervous system and disruption of circadian rhythms (CRs). We attempted to describe the morphological findings of the hypothalamus in early cases of AD, focusing our study mostly on the suprachiasmatic nucleus (SCN), the supraoptic nucleus (SON), and the paraventricular nucleus (PVN). Samples were processed for electron microscopy and silver impregnation techniques. The hypothalamic nuclei demonstrated a substantial decrease in the neuronal population, which was particularly prominent in the SCN. Marked abbreviation of dendritic arborization, in association with spinal pathology, was also seen. The SON and PVN demonstrated a substantial number of dystrophic axons and abnormal spines. Alzheimer’s pathology, such as deposits of amyloid-β peptide and neurofibrillary degeneration, was minimal. Electron microscopy revealed mitochondrial alterations in the cell body and the dendritic branches. The morphological alterations of the hypothalamic nuclei in early cases of AD may be related to the gradual alteration of CRs and the instability of autonomic regulation.

Application of a renormalization-group treatment to the statistical associating fluid theory for potentials of variable range (SAFT-VR).

An accurate prediction of phase behavior at conditions far and close to criticality cannot be accomplished by mean-field based theories that do not incorporate long-range density fluctuations. A treatment based on renormalization-group (RG) theory as developed by White and co-workers has proven to be very successful in improving the predictions of the critical region with different equations of state. The basis of the method is an iterative procedure to account for contributions to the free energy of density fluctuations of increasing wavelengths. The RG method has been combined with a number of versions of the statistical associating fluid theory (SAFT), by implementing Whites earliest ideas with the improvements of Prausnitz and co-workers. Typically, this treatment involves two adjustable parameters: a cutoff wavelength L for density fluctuations and an average gradient of the wavelet function Φ. In this work, the SAFT-VR (variable range) equation of state is extended with a similar crossover treatment which, however, follows closely the most recent improvements introduced by White. The interpretation of Whites latter developments allows us to establish a straightforward method which enables Φ to be evaluated; only the cutoff wavelength L then needs to be adjusted. The approach used here begins with an initial free energy incorporating only contributions from short-wavelength fluctuations, which are treated locally. The contribution from long-wavelength fluctuations is incorporated through an iterative procedure based on attractive interactions which incorporate the structure of the fluid following the ideas of perturbation theories and using a mapping that allows integration of the radial distribution function. Good agreement close and far from the critical region is obtained using a unique fitted parameter L that can be easily related to the range of the potential. In this way the thermodynamic properties of a square-well (SW) fluid are given by the same number of independent intermolecular model parameters as in the classical equation. Far from the critical region the approach provides the correct limiting behavior reducing to the classical equation (SAFT-VR). In the critical region the β critical exponent is calculated and is found to take values close to the universal value. In SAFT-VR the free energy of an associating chain fluid is obtained following the thermodynamic perturbation theory of Wertheim from the knowledge of the free energy and radial distribution function of a reference monomer fluid. By determining L for SW fluids of varying well width a unique equation of state is obtained for chain and associating systems without further adjustment of critical parameters. We use computer simulation data of the phase behavior of chain and associating SW fluids to test the accuracy of the new equation.

Experimental and Molecular Modeling Study of the Three-Phase Behavior of (n-Decane + Carbon Dioxide + Water) at Reservoir Conditions

Knowledge of the phase behavior of mixtures of oil with carbon dioxide and water is essential for reservoir engineering, especially in the processes of enhanced oil recovery and geological storage of carbon dioxide. However, for a comprehensive understanding, the study of simpler systems needs to be completed. In this work the system (n-decane + carbon dioxide + water) was studied as a model (oil + carbon dioxide + water) mixture. To accomplish our aim, a new analytical apparatus to measure phase equilibria at high pressure was designed with maximum operating temperature and pressure of 423 K and 45 MPa, respectively. The equipment relies on recirculation of two coexisting phases using a two-channel magnetically operated micropump designed during this work, with sampling and online compositional analysis by gas chromatography. The apparatus has been validated by comparison with published isothermal vapor-liquid equilibrium data for the binary system (n-decane + carbon dioxide). New experimental data have been measured for the system (n-decane + carbon dioxide + water) under conditions of three-phase equilibria. Data for the three coexisting phases have been obtained on five isotherms at temperatures from 323 to 413 K and at pressures up to the point at which two of the phases become critical. The experimental work is complemented here with a theoretical effort in which we developed models for these molecules within the framework of the statistical associating fluid theory for potentials of variable range (SAFT-VR). The phase behavior of the three binary subsystems was calculated using this theory, and where applicable, a modification of the Hudson and McCoubrey combining rules was used to treat the systems predictively. The experimental data obtained for the ternary mixture are compared to the predictions of the theory. Furthermore, a detailed analysis of the ternary mixture is carried out based on comparison with available data for the constituent binary subsystems. In this way, we analyzed the observed effects on the solubility when the third component was added.

Experimental and modeling study of the phase behavior of (methane + CO2 + water) mixtures

In this work we report phase equilibrium measurements on the system (methane + carbon dioxide + water) carried out with a high-pressure quasi-static-analytical apparatus. The measurements have been made under conditions of two-phase vapor-liquid equilibrium, three-phase vapor-liquid-liquid equilibrium (VLLE), and four-phase vapor-liquid-liquid-hydrate equilibrium. The compositions of three coexisting fluid phases have been obtained along eight isotherms at temperatures from (285.15 to 303.5) K and at pressures up to either the upper critical end point (UCEP) or up to the hydrate formation locus. Compositions of coexisting vapor and liquid phases have been obtained along three isotherms at temperatures from (323.15 to 423.15) K and pressures up to 20 MPa. The quadruple curve, along which hydrates coexist with the three fluid phases, was also measured along its entire length. The VLLE data obtained for this mixture have been compared with the predictions of the statistical associating fluid theory for potentials of variable range (SAFT-VR), implemented with the square-well potential and using parameters fitted to pure-component and binary-mixture data. Specifically, we used the SAFT-VR parameters reported by Mı́guez and co-workers [Mı́guez, J. M.; dos Ramos, M. C.; Piñeiro, M. M.; Blas, F. J. J. Phys. Chem. B 2011, 115, 9604]. The pressure along the quadruple curve was compared with the predictions of two different thermodynamic models. Furthermore, a detailed study of the ternary mixtures was carried out based on comparison with available ternary data of the type (CO2 + n-alkane + water) and available data for the constituent binary subsystems. In this way, we analyzed the observed effects on the solubility when the n-alkane component was changed or a third component was added.

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

The identification of improved carbon dioxide (CO2) 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 CO2 chemisorption processes, as measured by a comprehensive set of criteria. The first stage of the approach involves 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 the second stage, high-performance solvents are further selected and evaluated using a more detailed thermodynamic model, i.e. 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–CO2 mixtures. The proposed CAMD method is applied to the design of novel molecular structures and to the screening of a data set of commercially available amines. New molecular structures and commercially-available compounds that have received little attention as CO2 capture solvents are successfully identified and assessed using the proposed approach. We recommend that these solvents should be given priority in experimental studies to identify new compounds.

Chapter 11 – Toward Sustainable Solvent-Based Postcombustion CO2 Capture: From Molecules to Conceptual Flowsheet Design

Solvent-based postcombustion carbon dioxide (CO2) capture requires minimum retrofitting of current CO2-emitting power plants but is challenging because of the high energy penalty in solvent regeneration and the environmental impacts of solvent degradation. Research efforts are predominantly based on lab and pilot-scale experiments to select solvents and process systems which improve the overall performance of this technology. Notwithstanding the value of the experimental efforts, this study proposes an efficient computational approach for screening a vast number of commercial and novel solvents and process configurations. Computer-aided molecular design, advanced group contribution methods, process synthesis, and multicriteria sustainability assessment are combined to provide new insights in solvent-based CO2 capture. This study provides details of the data requirements, highlights several high-performance solvents and process configurations, and quantifies the benefits from economic, life cycle, and hazard assessment perspective. Thus, it also provides information for the experimental approaches, focusing on a narrower, near-optimum design space.

Predicting the adsorption of n-perfluorohexane in BAM P109 standard activated carbon by molecular simulation using SAFT-gamma Mie coarse-grained force fields

This work is framed within the Eighth Industrial Fluid Properties Simulation Challenge, with the aim of assessing the capability of molecular simulation methods and force fields to accurately predict adsorption in porous media for systems of relevant practical interest. The current challenge focuses on predicting adsorption isotherms of n-perfluorohexane in the certified reference material BAM-P109 standard activated carbon. A temperature of T = 273  K and pressures of p / p 0 = 0 . 1 , 0.3, and 0.6 relative to the bulk saturation pressure p0 (as predicted by the model) are the conditions selected in this challenge. In our methodology we use coarse-grained intermolecular models and a top-down technique where an accurate equation of state is used to link the experimental macroscopic properties of a fluid to the force-field parameters. The state-of-the-art version of the statistical associating fluid theory (SAFT) for potentials of variable range as reformulated in the Mie group contribution incarnation (SAFT-γ Mie) is employed here. The parameters of the SAFT-γ Mie force field are estimated directly from the vapour pressure and saturated liquid density data of the pure fluids using the equation of state, and further validated by molecular dynamic simulations. The coarse-grained intermolecular potential models are then used to obtain the adsorption isotherm kernels for argon, carbon dioxide, and n-perfluorohexane in graphite slit pores of various widths using Grand Canonical Monte Carlo simulations. A unique and fluid-independent pore size distribution curve with total micropore volume of 0.5802 cm3/g is proposed for the BAM-P109. The pore size distribution is obtained by applying a non-linear regression procedure over the adsorption integral equation to minimise the quadratic error between the available experimental adsorption isotherms for argon and carbon dioxide and purpose-built Grand Canonical Monte Carlo kernels. The predicted adsorption levels of n-perfluorohexane at 273 K in BAM-P109 are 72.75 ± 0.01, 73.82 ± 0.01, and 75.44 ± 0.05 cm3/g at Standard Temperature and Pressure (STP) conditions for p / p 0 = 0 . 1 , 0.3, and 0.6, respectively.

Towards Unified Thermodynamic Modeling of Fluids in Carbonate Reservoir Environments

We provide a brief overview of the SAFT-VR Mie theory and its application to reservoir-relevant fluids, including aqueous mixtures incorporating CO2 and hydrocarbons; we feature its use in conjunction with experimental thermophysical-property measurements. The modeling of electrolyte solutions, such as brines, illustrates its straightforward extension to include more-complex interactions. We introduce our molecular-based approach to modeling interfacial tension, highlighting its close connection with SAFTVR Mie. We discuss our method for characterising the interaction between a fluid and a solid substrate, demonstrating how this will be incorporated in an integrated approach with SAFT-VR Mie to calculate, for example, adsorption on the rock surface. Together, these will provide an integrated framework for the calculation of fluid thermodynamics in injection and production processes.