267 results found
Carbon capture and storage (CCS) is broadly recognised as having the potential to play a key role in meeting climate change targets, delivering low carbon heat and power, decarbonising industry and, more recently, its ability to facilitate the net removal of CO2 from the atmosphere. However, despite this broad consensus and its technical maturity, CCS has not yet been deployed on a scale commensurate with the ambitions articulated a decade ago. Thus, in this paper we review the current state-of-the-art of CO2 capture, transport, utilisation and storage from a multi-scale perspective, moving from the global to molecular scales. In light of the COP21 commitments to limit warming to less than 2 °C, we extend the remit of this study to include the key negative emissions technologies (NETs) of bioenergy with CCS (BECCS), and direct air capture (DAC). Cognisant of the non-technical barriers to deploying CCS, we reflect on recent experience from the UK's CCS commercialisation programme and consider the commercial and political barriers to the large-scale deployment of CCS. In all areas, we focus on identifying and clearly articulating the key research challenges that could usefully be addressed in the coming decade.
Grant E, Pan Y, Richardson J, et al., 2018, Multi-Objective Computer-Aided Solvent Design for Selectivity and Rate in Reactions, Computer Aided Chemical Engineering, Pages: 2437-2442
© 2018 Elsevier B.V. A hybrid empirical computer-aided methodology to design the solvent for a reaction, incorporating both selectivity and rate, is presented. A small initial set of diverse solvents is used, for which experimental, in situ kinetic data are obtained. A surrogate model is utilized to correlate the reaction kinetics with solvent properties and a computer-aided molecular design (CAMD) multi-objective optimization problem is then formulated to identify solvents with improved performance compared with the initial solvent set. This methodology is applied to an SNAr reaction of 2,4-difluoroacetophenone with pyrrolidine, which demonstrates an interesting effect of solvent on both the selectivity of the ortho-:para-substitution ratio and the overall rate of the reaction. A set of Pareto optimal solutions is identified, highlighting the trade-off between reaction rate and selectivity.
Hutacharoen P, Dufal S, Papaioannou V, et al., 2017, Predicting the solvation of organic compounds in aqueous environments: from alkanes and alcohols to pharmaceuticals, Industrial and Engineering Chemistry Research, Vol: 56, Pages: 10856-0876, ISSN: 0888-5885
The development of accurate models to predict the solvation, solubility, and partitioning of nonpolar and amphiphilic compounds in aqueous environments remains an important challenge. We develop state-of-the-art group-interaction models that deliver an accurate description of the thermodynamic properties of alkanes and alcohols in aqueous solution. The group-contribution formulation of the statistical associating fluid theory based on potentials with a variable Mie form (SAFT-γ Mie) is shown to provide accurate predictions of the phase equilibria, including liquid–liquid equilibria, solubility, free energies of solvation, and other infinite-dilution properties. The transferability of the model is further exemplified with predictions of octanol–water partitioning and solubility for a range of organic and pharmaceutically relevant compounds. Our SAFT-γ Mie platform is reliable for the prediction of challenging properties such as mutual solubilities of water and organic compounds which can span over 10 orders of magnitude, while remaining generic in its applicability to a wide range of compounds and thermodynamic conditions. Our work sheds light on contradictory findings related to alkane–water solubility data and the suitability of models that do not account explicitly for polarity.
Adjiman CS, Harrison NM, Weider SZ, 2017, Molecular science and engineering: a powerful transdisciplinary approach to solving grand challenges, Briefing paper, 1
The concept of molecular science and engineering – melding a deep understanding of molecular science with an engineering mind-set – is emerging as a powerful way to create novel, effective and sustainable solutions to global grand challenges, such as the growing threat of antimicrobial resistance. By blurring the boundaries between scientificand engineering disciplines, in this holistic approach, final function and end-use requirements become an integral part of the underlying scientific research. Commercially ready materials can thus become a reality in an accelerated, flexible and economic manner. In other words, molecular science and engineering can fundamentally alter the way molecules are identified and designed for real-world usage. It is not enough to simply make molecules; we must make molecules work for a complex world.The notion of bringing researchers, industry and government communities together to work on grand challenges has a long and illustrious history – think, for instance, of the Manhattan Project, the industrial scale-up of penicillin and the Moon landings. More recently, the idea of ‘convergence’ – tackling grand challenges with a multifaceted array of scientists, engineers, clinicians and beyond – has become more formally recognised as a valuable way to stimulate societally important and ground-breaking research. Molecular science and engineering is a specific, yet far-reaching, part of this convergence landscape.Within the growing worldwide molecular science and engineering community, the Institute for Molecular Science and Engineering (IMSE) was founded in 2015 as Imperial College London’s newest Global Institute. The Institute’s overarching aim is to bring the College’s engineers, scientists, medics and business researchers together with awide array of external stakeholders – and to remove the boundaries between these disciplines – to find innovative molecular-based scie
Adjiman C, Bardow A, 2017, Editorial to iCAMD special issue, Chemical Engineering Science, Vol: 159, Pages: 1-2, ISSN: 0009-2509
Gu B, Adjiman CS, Xu XY, 2016, The effect of feed spacer geometry on membrane performance and concentration polarisation based on 3D CFD simulations, Journal of Membrane Science, Vol: 527, Pages: 78-91, ISSN: 1873-3123
Feed spacers are used in spiral wound reverse osmosis (RO) membrane modules to keep the membrane sheets apart as well as to enhance mixing. They are beneficial to membrane performance but at the expense of additional pressure loss. In this study, four types of feed spacer configurations are investigated, with a total of 20 geometric variations based on commercially available spacers and selected filament angles. The impact of feed spacer design on membrane performance is investigated by means of three-dimensional (3D) computational fluid dynamics (CFD) simulations, where the solution-diffusion model is employed for water and solute transport through RO membranes. Numerical simulation results show that, for the operating and geometric conditions examined, fully woven spacers outperform other spacer configurations in mitigating concentration polarisation (CP). When designed with a mesh angle of 60°, fully woven spacers also deliver the highest water flux, although the associated pressure drops are slightly higher than their nonwoven counterparts. Middle layer geometries with a mesh angle of 30° produce the lowest water flux. On the other hand, spacers with a mesh angle of 90° show the lowest pressure drop among all the filament arrangements examined. Furthermore, the computational model presented here can also be used to predict membrane performance for a given feed spacer type and geometry.
Diamanti A, Adjiman CS, Piccione PM, et al., 2016, Development of Predictive Models of the Kinetics of a Hydrogen Abstraction Reaction Combining Quantum-Mechanical Calculations and Experimental Data, Industrial & Engineering Chemistry Research, Vol: 56, Pages: 815-831, ISSN: 0888-5885
The importance of developing accurate modeling tools for the prediction of reaction kinetics is well recognized. In this work, a thorough investigation of the suitability of quantum mechanical (QM) calculations to predict the effect of temperature on the rate constant of the reaction between ethane and the hydroxyl radical is presented. Further, hybrid models that combine a limited number of QM calculations and experimental data are developed in order to increase their reliability. The activation energy barrier of the reaction is computed using various computational methods, such as B3LYP, M05-2X, M06-2X, MP2 and PMP2, CBS-QB3, and W1BD, with a selection of basis sets. A broad range of values is obtained, including negative barriers for all of the calculations with B3LYP. The rate constants are also obtained for each method, using conventional transition state theory, and are compared with available experimental values at 298 K. The best agreement is achieved with the M05-2X functional with cc-pV5Z basis set. Rate constants calculated at this level of theory are also found to be in good agreement with experimental values at different temperatures, resulting in a mean absolute error of the logarithm (MAEln) of the calculated values of 0.213 over a temperature range of 200–1250 K and 0.108 over a temperature range of 300–499 K. Tunnelling and vibrational anharmonicities are identified as important sources of discrepancies at low and high temperatures, respectively. Hybrid models are proposed and found to provide good correlated rate-constant values and to be competitive with conventional kinetic models, i.e., the Arrhenius and the three-parameter Arrhenius models. The combination of QM-calculated and experimental data sources proves particularly beneficial when fitting to scarce experimental data. The parameters of the model built on the hybrid strategy have a significantly reduced uncertainty (reflected in the much narrower 95% confidence intervals) compa
Sugden IJ, Adjiman CSA, Pantelides C, 2016, Accurate and efficient representation of intramolecular energy in ab initio generation of crystal structures. Part I: Adaptive local approximate models, Acta Crystallographica Section B: Structural Science, Crystal Engineering and Materials, Vol: 72, Pages: 864-874, ISSN: 2052-5206
The global search stage of Crystal Structure Prediction (CSP) methods requires a fine balance between accuracy and computational cost, particularly for the study of large flexible molecules. A major improvement in the accuracy and cost of the intramolecular energy function used in the CrystalPredictor II (Habgood, M., Sugden, I. J., Kazantsev, A. V., Adjiman, C. S. & Pantelides, C. C. (2015). J Chem Theory Comput 11, 1957-1969) program is presented, where the most efficient use of computational effort is ensured via the use of adaptive Local Approximate Model (LAM) placement. The entire search space of relevant molecule’s conformations is initially evaluated using a coarse, low accuracy grid. Additional LAM points are then placed at appropriate points determined via an automated process, aiming to minimise the computational effort expended in high energy regions whilst maximising the accuracy in low energy regions. As the size, complexity, and flexibility of molecules increase, the reduction in computational cost becomes marked. This improvement is illustrated with energy calculations for benzoic acid and the ROY molecule, and a CSP study of molecule XXVI from the sixth blind test (Reilly et al., (2016). Acta Cryst. B, 72, 439-459), which is challenging due to its size and flexibility. Its known experimental form is successfully predicted as the global minimum. The computational cost of the study is tractable without the need to make unphysical simplifying assumptions.
Eriksen DK, Lazarou G, Galindo A, et al., 2016, Development of intermolecular potential models for electrolyte solutions using an electrolyte SAFT-VR Mie equation of state, Molecular Physics, Vol: 114, Pages: 2724-2749, ISSN: 1362-3028
We present a theoretical framework and parameterisation of intermolecular potentials for aqueous electrolyte solutions using the statistical associating fluid theory based on the Mie interaction potential (SAFT-VR Mie), coupled with the primitive, non-restricted mean-spherical approximation (MSA) for electrolytes. In common with other SAFT approaches, water is modelled as a spherical molecule with four off-centre association sites to represent the hydrogen-bonding interactions; the repulsive and dispersive interactions between the molecular cores are represented with a potential of the Mie (generalised Lennard-Jones) form. The ionic species are modelled as fully dissociated, and each ion is treated as spherical: Coulombic ion–ion interactions are included at the centre of a Mie core; the ion–water interactions are also modelled with a Mie potential without an explicit treatment of ion–dipole interaction. A Born contribution to the Helmholtz free energy of the system is included to account for the process of charging the ions in the aqueous dielectric medium. The parameterisation of the ion potential models is simplified by representing the ion–ion dispersive interaction energies with a modified version of the London theory for the unlike attractions. By combining the Shannon estimates of the size of the ionic species with the Born cavity size reported by Rashin and Honig, the parameterisation of the model is reduced to the determination of a single ion–solvent attractive interaction parameter. The resulting SAFT-VRE Mie parameter sets allow one to accurately reproduce the densities, vapour pressures, and osmotic coefficients for a broad variety of aqueous electrolyte solutions; the activity coefficients of the ions, which are not used in the parameterisation of the models, are also found to be in good agreement with the experimental data. The models are shown to be reliable beyond the molality range considered during parameter estimatio
Smit B, Styring P, Wilson G, et al., 2016, Modelling - from molecules to megascale: general discussion, Faraday Discussions, Vol: 192, Pages: 493-509, ISSN: 1359-6640
Brand CV, Graham E, Rodriguez J, et al., 2016, On the use of molecular-based thermodynamic models to assess theperformance of solvents for CO₂capture processes:monoethanolamine solutions, Faraday Discussions, Vol: 192, Pages: 337-390, ISSN: 1364-5498
Predictive models play an important role in the design of post-combustion processes for the capture of carbon dioxide (CO2) emitted from power plants. A rate-based absorber model is presented to investigate the reactive capture of CO2 using aqueous monoethanolamine (MEA) as a solvent, integrating a predictive molecular-based equation of state: SAFT-VR SW (Statistical Associating Fluid Theory-Variable Range, Square Well). A distinctive physical approach is adopted to model the chemical equilibria inherent in the process. This eliminates the need to consider reaction products explicitly and greatly reduces the amount of experimental data required to model the absorber compared to the more commonly employed chemical approaches. The predictive capabilities of the absorber model are analyzed for profiles from 10 pilot plant runs by considering two scenarios: (i) no pilot-plant data are used in the model development; (ii) only a limited set of pilot-plant data are used. Within the first scenario, the mass fraction of CO2 in the clean gas is underestimated in all but one of the cases, indicating that a best-case performance of the solvent can be obtained with this predictive approach. Within the second scenario a single parameter is estimated based on data from a single pilot plant run to correct for the dramatic changes in the diffusivity of CO2 in the reactive solvent. This parameter is found to be transferable for a broad range of operating conditions. A sensitivity analysis is then conducted, and the liquid viscosity and diffusivity are found to be key properties for the prediction of the composition profiles. The temperature and composition profiles are sensitive to thermodynamic properties that correspond to major sources of heat generation or dissipation. The proposed modelling framework can be used as an early assessment of solvents to aid in narrowing the search space, and can help in determining target solvents for experiments and more detailed modelling.
Struebing H, Obermeier S, Siougkrou E, et al., 2016, A QM-CAMD approach to solvent design for optimal reaction rates, Chemical Engineering Science, Vol: 159, Pages: 69-83, ISSN: 1873-4405
The choice of solvent in which to carry out liquid-phase organic reactions often has a largeimpact on reaction rates and selectivity and is thus a key decision in process design. A systematicmethodology for solvent design that does not require any experimental data on the effect ofsolvents on reaction kinetics is presented. It combines quantum mechanical computations forthe reaction rate constant in various solvents with a computer-aided molecular design (CAMD)formulation. A surrogate model is used to derive an integrated design formulation that combineskinetics and other considerations such as phase equilibria, as predicted by group contributionmethods. The derivation of the mixed-integer nonlinear formulation is presented step-by-step.In the application of the methodology to a classic SN2 reaction, the Menschutkin reaction,the reaction rate is used as the key performance objective. The results highlight the tradeoffsbetween different chemical and physical properties such as reaction rate constant, solventdensity and solid reactant solubility and lead to the identification of several promising solventsto enhance reaction performance.
Gu B, Xu XY, Adjiman CS, 2016, A predictive model for spiral wound reverse osmosis membrane modules: The effect of winding geometry and accurate geometric details, Computers and Chemical Engineering, Vol: 96, Pages: 248-265, ISSN: 1873-4375
A new one-dimensional predictive model for spiral wound modules (SWMs) applied to reverse osmosis membrane systems is developed by incorporating a detailed description of the geometric features of SWMs and considering flow in two directions. The proposed model is found to capture existing experimental data well, with similar accuracy to the widely-used plate model in which the SWM is assumed to consist of multiple thin rectangular channels. However, physical parameters that should in principle be model-independent, such as membrane permeability, are found to differ significantly depending on which model is used, when the same data sets are used for parameter estimation. Conversely, when using the same physical parameter values in both models, the water recovery predicted by the plate-like model is 12–20% higher than that predicted by the spiral model. This discrepancy is due to differences in the description of geometric features, in particular the active membrane area and the variable channel heights through the module, which impact on predicted performance and energy consumption. A number of design variables – the number of membrane leaves, membrane dimensions, centre pipe radius and the height of feed and permeate channels – are varied and their effects on performance, energy consumption and calculated module size are analysed. The proposed spiral model provides valuable insights into the effects of complex geometry on the performance of the SWM as well as of the overall system, at a low computational cost.
Papadopoulos AI, Badr S, Chremos A, et al., 2016, Computer-aided molecular design and selection of CO2 capture solvents based on thermodynamics, reactivity and sustainability, Molecular Systems Design & Engineering, Vol: 1, Pages: 313-334, ISSN: 2058-9689
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.
Jonuzaj S, Adjiman CSJ, 2016, Designing optimal mixtures using generalized disjunctive programming: Hull relaxations, Chemical Engineering Science, Vol: 159, Pages: 106-130, ISSN: 1873-4405
A general modeling framework for mixture design problems, which integrates Generalized Disjunctive Programming (GDP) into the Computer-Aided Mixture/blend Design (CAMbD) framework, was recently proposed (S. Jonuzaj, P.T. Akula, P.-M. Kleniati, C.S. Adjiman, 2016. AIChE Journal 62, 1616–1633). In this paper we derive Hull Relaxations (HR) of GDP mixture design problems as an alternative to the big-M (BM) approach presented in this earlier work. We show that in restricted mixture design problems, where the number of components is fixed and their identities and compositions are optimized, BM and HR formulations are identical. For general mixture design problems, where the optimal number of mixture components is also determined, a generic approach is employed to enable the derivation and solution of the HR formulation for problems involving functions that are not defined at zero (e.g., logarithms). The design methodology is applied successfully to two solvent design case studies: the maximization of the solubility of a drug and the separation of acetic acid from water in a liquid-liquid extraction process. Promising solvent mixtures are identified in both case studies. The HR and BM approaches are found to be effective for the formulation and solution of mixture design problems, especially via the general design problem.
Gopinath S, Jackson G, Galindo A, et al., 2016, Outer approximation algorithm with physical domain reduction for computer-aided molecular and separation process design, AICHE Journal, Vol: 62, Pages: 3484-3504, ISSN: 0001-1541
Integrated approaches to the design of separation systems based on computer-aided molecular and process design (CAMPD) can yield an optimal solvent structure and process conditions. The underlying design problem, however, is a challenging mixed integer nonlinear problem, prone to convergence failure as a result of the strong and nonlinear interactions between solvent and process. To facilitate the solution of this problem, a modified outer-approximation (OA) algorithm is proposed. Tests that remove infeasible regions from both the process and molecular domains are embedded within the OA framework. Four tests are developed to remove subdomains where constraints on phase behavior that are implicit in process models or explicit process (design) constraints are violated. The algorithm is applied to three case studies relating to the separation of methane and carbon dioxide at high pressure. The process model is highly nonlinear, and includes mass and energy balances as well as phase equilibrium relations and physical property models based on a group-contribution version of the statistical associating fluid theory (SAFT-γ Mie) and on the GC+ group contribution method for some pure component properties. A fully automated implementation of the proposed approach is found to converge successfully to a local solution in 30 problem instances. The results highlight the extent to which optimal solvent and process conditions are interrelated and dependent on process specifications and constraints. The robustness of the CAMPD algorithm makes it possible to adopt higher-fidelity nonlinear models in molecular and process design.
Reilly AM, Cooper RI, Adjiman CS, et al., 2016, Report on the sixth blind test of organic crystal structure prediction methods., Acta Crystallographica Section B: Structural Science, Crystal Engineering and Materials, Vol: 72, Pages: 439-459, ISSN: 2052-5206
The sixth blind test of organic crystal structure prediction (CSP) methods has been held, with five target systems: a small nearly rigid molecule, a polymorphic former drug candidate, a chloride salt hydrate, a co-crystal and a bulky flexible molecule. This blind test has seen substantial growth in the number of participants, with the broad range of prediction methods giving a unique insight into the state of the art in the field. Significant progress has been seen in treating flexible molecules, usage of hierarchical approaches to ranking structures, the application of density-functional approximations, and the establishment of new workflows and `best practices' for performing CSP calculations. All of the targets, apart from a single potentially disordered Z' = 2 polymorph of the drug candidate, were predicted by at least one submission. Despite many remaining challenges, it is clear that CSP methods are becoming more applicable to a wider range of real systems, including salts, hydrates and larger flexible molecules. The results also highlight the potential for CSP calculations to complement and augment experimental studies of organic solid forms.
Nerantzis D, Adjiman CSJ, 2016, An interval-matrix branch-and-bound algorithm for bounding eigenvalues, Optimization Methods & Software, Vol: 32, Pages: 872-891, ISSN: 1055-6788
We present and explore the behaviour of a branch-and-bound algorithm for calculating validbounds on the k-th largest eigenvalue of a symmetric interval matrix. Branching on theinterval elements of the matrix takes place in conjunction with the application of Rohn’smethod (an interval extension of Weyl’s theorem) in order to obtain valid outer bounds onthe eigenvalues. Inner bounds are obtained with the use of two local search methods. Thealgorithm has the theoretical property that it provides bounds to any arbitrary precision > 0(assuming infinite precision arithmetic) within finite time. In contrast with existing methods,bounds for each individual eigenvalue can be obtained even if its range overlaps with theranges of other eigenvalues. Performance analysis is carried out through nine examples. Inthe first example, a comparison of the efficiency of the two local search methods is reportedusing 4,000 randomly generated matrices. The eigenvalue bounding algorithm is then appliedto five randomly generated matrices with overlapping eigenvalue ranges. Valid and sharpbounds are indeed identified given a sufficient number of iterations. Furthermore, most of therange reduction takes place in the first few steps of the algorithm so that significant benefitscan be derived without full convergence. Finally, in the last three examples, the potential ofthe algorithm for use in algorithms to identify index-1 saddle points of nonlinear functions isdemonstrated.
Paulavicius R, Kleniati P-M, Adjiman CS, 2016, Global optimization of nonconvex bilevel problems: implementation and computational study of the Branch-and-Sandwich algorithm, 26th European Symposium on Computer Aided Process Engineering (ESCAPE 26), Publisher: Elsevier, Pages: 1977-1982, ISSN: 1570-7946
We describe BASBL, an implementation of the Branch-and-Sandwich deterministic global optimization algorithm,(Kleniati and Adjiman, J. Glob. Opt. 60, 425–458, 2014), for nonlinear bilevel problems, withinthe MINOTAUR toolkit. The algorithm is extended to include heuristics for branching and node selection. Thecomputational performance of the bilevel solver is analyzed for different combinations of the heuristics bysolving nonconvex bilevel test problems from the literature.
Gopinath S, Galindo A, Jackson G, et al., 2016, A feasibility-based algorithm for Computer Aided Molecular and Process Design of solvent-based separation systems, 26th European Symposium on Computer Aided Process Engineering (ESCAPE 26), Publisher: Elsevier, Pages: 73-78, ISSN: 1570-7946
Computer-aided molecular and product design (CAMPD) can in principle be used to find simultaneouslythe optimal conditions in separation processes and the structure of the optimal solvents.In many cases, however, the solution of CAMPD problems is challenging. In this paper, we proposea solution approach for the CAMPD of solvent-based separation systems in which implicitconstraints on phase behaviour in process models are used to test the feasibility of the processand solvent domains. The tests not only eliminate infeasible molecules from the search space butalso infeasible combinations of solvent molecules and process conditions. The tests also providebounds for the optimization of the process model (primal problem) for each solvent, facilitatingnumerical solution. This is demonstrated on a prototypical natural gas purification process.
Jonuzaj S, Adjiman CS, 2016, A Convex Hull Formulation for the Design of Optimal Mixtures, 26th European Symposium on Computer Aided Process Engineering, Publisher: Elsevier, Pages: 2325-2330, ISSN: 1570-7946
The design of mixtures plays an important role in improving process and product performancebut is challenging because it requires finding the optimal number, identities and compositions ofmixture components and using nonlinear property models. To address this, a general modelingframework for mixture design problems is presented. It integrates Generalized Disjunctive Programming(GDP) into Computer-Aided Mixture/blend Design via Hull Reformulation (HR). Thedesign methodology is applied successfully to a case study involving solid-liquid equilibrium calculationsto find an optimal solvent mixture that dissolves ibuprofen. The results show that theproposed GDP-based approach appears very promising for the design of mixture problems. TheHR approach is used to solve mixture problems successfully. Its overall computational efficiencyis found to be better than that of Big-M approach. Numerical difficulties arising from the absenceof components in the final mixture can be avoided, leading to computationally efficient solutions.
Nerantzis D, Adjiman CS, 2016, Enclosure of all index-1 saddle points of general nonlinear functions, Journal of Global Optimization, Vol: 67, Pages: 451-474, ISSN: 1573-2916
Transition states (index-1 saddle points) play a crucial role in determiningthe rates of chemical transformations but their reliable identificationremains challenging in many applications. Deterministic global optimizationmethods have previously been employed for the location of transition states(TSs) by initially finding all stationary points and then identifying the TSsamong the set of solutions. We propose several regional tests, applicable togeneral nonlinear, twice continuously differentiable functions, to accelerate theconvergence of such approaches by identifying areas that do not contain anyTS or that may contain a unique TS. The tests are based on the application ofthe interval extension of theorems from linear algebra to an interval Hessianmatrix. They can be used within the framework of global optimization methodswith the potential of reducing the computational time for TS location. Wepresent the theory behind the tests, discuss their algorithmic complexity andshow via a few examples that significant gains in computational time can beachieved by using these tests.
Jonuzaj S, Akula PT, Kleniati PM, et al., 2016, The formulation of optimal mixtures with Generalized Disjunctive Programming: A solvent design case study, AICHE Journal, Vol: 62, Pages: 1616-1633, ISSN: 0001-1541
Systematic approaches for the design of mixtures, based on a Computer-Aided Mixture/blendDesign (CAMbD) framework, have the potential to deliver better products and processes.In most existing methodologies the number of mixture ingredients is fixed (usually a binarymixture) and the identity of at least one compound is chosen from a given set of candidatemolecules. We present a novel CAMbD methodology for formulating the general mixture designproblem where the number, identity and composition of mixture constituents are optimisedsimultaneously. To this end, Generalized Disjunctive Programming (GDP) is integrated intothe CAMbD framework to formulate the discrete choices. This generic methodology is appliedto a case study to find an optimal solvent mixture that maximises the solubility of ibuprofen.The best performance in this case study is obtained with a solvent mixture, showing the benefitof using mixtures instead of pure solvents to attain enhanced behaviour.
Galindo A, Adjiman, Jackson G, et al., 2015, Application of the SAFT-γ Mie group contribution equation of state to fluids of relevance to the oil and gas industry, Fluid Phase Equilibria, Vol: 416, Pages: 104-119, ISSN: 0378-3812
The application of the SAFT-γ Mie group contribution approach [Papaioannou et al., J. Chem. Phys., 140 (2014) 054107] to the study of a range of systems of relevance to the oil and gas industry is presented. In particular we consider carbon dioxide, water, methanol, aromatics, alkanes and their mixtures. Following a brief overview of the SAFT-γ Mie equation of state, a systematic methodology for the development of like and unlike group parameters relevant to the systems of interest is presented. The determination of group-group interactions entails a sequence of steps including: the selection of representative components and mixtures (in this instance carbon dioxide, water, methanol, aromatics and alkanes); the definition of an appropriate set of groups to describe them; the collection of target experimental data used to estimate the group-group interactions; the determination of the group-group interaction parameters; and the assessment of the adequacy of the parameters and theoretical approach. The predictive capability of the SAFT-γ Mie group contribution approach is illustrated for a selection of mixtures, including representative examples of the simultaneous description of vapour-liquid and liquid-liquid equilibria, the densities of the coexisting phases, second derivative thermodynamic properties, and excess properties of mixing. Good quantitative agreement between the predictions and experimental data is achieved, even in the case of challenging mixtures comprising carbon dioxide and water, n-alkanes and water, and methanol and methane.
Chremos A, Forte E, Papaioannou V, et al., 2015, Modelling the phase and chemical equilibria of aqueous solutions of alkanolamines and carbon dioxide using the SAFT-γ SW group contribution approach, Fluid Phase Equilibria, Vol: 407, Pages: 280-297, ISSN: 0378-3812
The speciation reactions that take place in mixtures of water, carbon dioxide (CO2), and alka-nolamines make the modelling of the chemical and uid-phase equilibria of these systems chal-lenging. We demonstrate for the rst time that the statistical associating uid theory (SAFT),formulated within a group-contribution (GC) framework based on transferable intermolecularsquare-well (SW) potentials (SAFT- SW) can be used to model successfully such complexreacting systems. The chemical reactions in these mixtures are described via a physical associ-ation model. The concept of second-order groups is introduced in the SAFT- SW approach inorder to deal with the multifunctional nature of the alkanolamines. In developing the models,several compounds including ethylamine, propylamine, ethanol, propanol, 2-aminoethanol and3-amino-1-propanol are considered. We present calculations and predictions of the uid-phasebehaviour of these compounds and a number of their aqueous mixtures with and without CO2.The group-contribution nature of the models can be used to predict the absorption of carbondioxide in aqueous solutions of 5-amino-1-pentanol and 6-amino-1-hexanol. The proposed pre-dictive approach offers a robust platform for the identi cation of new solvents and mixturesthat are viable candidates for CO2 absorption, thereby guiding experimental studies.
Sadeqzadeh M, Papaioannou V, Dufal S, et al., 2015, The development of unlike induced association-site models to study the phase behaviour of aqueous mixtures comprising acetone, alkanes and alkyl carboxylic acids with the SAFT-γ Mie group contribution methodology, Fluid Phase Equilibria, Vol: 407, Pages: 39-57, ISSN: 0378-3812
Providing accurate predictions of the thermodynamic properties of highly polar and hydrogen bonding compounds and their mixtures is challenging from a theoretical perspective. The combination of an equation of state (EoS) based on the statistical associating fluid theory (SAFT) with a group contribution (GC) methodology offers both accuracy and predictive capability for the thermodynamic properties of mixtures. In our current work, the SAFT-γ Mie equation of state is used to capture the underlying complexity of systems in which specific interactions (e.g. hydrogen bonding, dipolar interactions, chemical association) play an important role, by incorporating highly versatile association-site schemes to model mixtures in which unlike induced association interactions occur; this is done by assigning to the functional groups a number of association sites that are inactive in the pure fluid, but become active in certain mixtures. We refer to this type of association mechanism as "unlike induced" association and to the sites involved in this interaction as "unlike induced" association sites. The concept of unlike induced association sites is applied here to develop reliable SAFT-γ Mie group contribution models to describe the properties of acetone, alkyl carboxylic acids, and their mixtures with water and n-alkanes. The parameter table of available SAFT-γ Mie models is expanded to incorporate the corresponding group interaction parameters for acetone, which is treated as a molecular group, the carboxyl group COOH, and their unlike interaction group parameters with water, and the methyl CH<inf>3</inf>, methanediyl CH<inf>2</inf>, and methanetriyl CH alkyl groups. In particular, one unlike induced site is used with the acetone model to mediate hydrogen bonding of the acetone oxygen in mixtures containing hydrogen bond donors, and two pairs of unlike induced sites are included on the COOH group to mediate hydrogen
Papadokonstantakis S, Badr S, Hungerbühler K, et al., 2015, Toward Sustainable Solvent-Based Postcombustion CO<inf>2</inf> Capture: From Molecules to Conceptual Flowsheet Design, Computer Aided Chemical Engineering, Vol: 36, Pages: 279-310, ISSN: 1570-7946
Solvent-based postcombustion carbon dioxide (CO<inf>2</inf>) capture requires minimum retrofitting of current CO<inf>2</inf>-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 CO<inf>2</inf> 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.
Rhazaoui K, Cai Q, Kishimoto M, et al., 2015, Towards the 3D Modelling of the Effective Conductivity of Solid Oxide Fuel Cell Electrodes - Validation against experimental measurements and prediction of electrochemical performance, Electrochimica Acta, Vol: 168, Pages: 139-147, ISSN: 1873-3859
The effective conductivity of thick-film solid oxide fuel cell (SOFC) electrodes plays a key role in their performance. It determines the ability of the electrode to transport charge to/from reaction sites to the current collector and electrolyte. In this paper, the validity of the recently proposed 3D resistor network model for the prediction of effective conductivity, the ResNet model, is investigated by comparison to experimental data. The 3D microstructures of Ni/10ScSZ anodes are reconstructed using tomography through the focused ion beam and scanning electron microscopy (FIB-SEM) technique. This is used as geometric input to the ResNet model to predict the effective conductivities, which are then compared against the experimentally measured values on the same electrodes. Good agreement is observed, supporting the validity of the ResNet model for predicting the effective conductivity of SOFC electrodes. The ResNet model is then combined with the volume-of-fluid (VOF) method to integrate the description of the local conductivity (electronic and ionic) in the prediction of electrochemical performance. The results show that the electrochemical performance is in particular sensitive to the ionic conductivity of the electrode microstructure, highlighting the importance of an accurate description of the local ionic conductivity.
Habgood M, Sugden IJ, Kazantsev AV, et al., 2015, Efficient Handling of Molecular Flexibility in Ab Initio Generation of Crystal Structures, Journal of Chemical Theory and Computation, Vol: 11, Pages: 1957-1969, ISSN: 1549-9626
A key step in many approaches to crystal structure prediction (CSP) is the initial generation of large numbers of candidate crystal structures via the exploration of the lattice energy surface. By using a relatively simple lattice energy approximation, this global search step aims to identify, in a computationally tractable manner, a limited number of likely candidate structures for further refinement using more detailed models. This paper presents an effective and efficient approach to modeling the effects of molecular flexibility during this initial global search. Local approximate models (LAMs), constructed via quantum mechanical (QM) calculations, are used to model the conformational energy, molecular geometry, and atomic charge distributions as functions of a subset of the conformational degrees of freedom (e.g., flexible torsion angles). The effectiveness of the new algorithm is demonstrated via its application to the recently studied 5-methyl-2-[(2-nitrophenyl)amino]-3-thiophenecarbonitrile (ROY) molecule and to two molecules, β-d-glucose and 1-(4-benzoylpiperazin-1-yl)-2-(4,7-dimethoxy-1H-pyrrolo[2,3-c]pyridin-3-yl)ethane-1,2-dione, a Bristol Myers Squibb molecule referenced as BMS-488043. All three molecules present significant challenges due to their high degree of flexibility.
Kleniati P-M, Adjiman CS, 2015, A generalization of the Branch-and-Sandwich algorithm: From continuous to mixed-integer nonlinear bilevel problems, COMPUTERS & CHEMICAL ENGINEERING, Vol: 72, Pages: 373-386, ISSN: 0098-1354
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