The Potential Impact of High-End Capability Computing on Four Illustrative Fields of Science and Engineering (2008) / Chapter Skim
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5 The Potential Impact of HECC in Chemical Separations
5 The Potential Impact of HECC in Chemical Separations
Pages 89-104
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From page 89... ...
Around the world, separation processes are building blocks for a wide range of industrial and environmental processes that impact society broadly and in many ways. For example, chemical separations are essential for the following purposes: • Removal of toxic substances like mercury from the flue gases of coal-fired power plants and removal of a range of organic and inorganic pollutants from wastewater streams.
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From page 90... ...
Historically, energy consumption and its concomitant carbon dioxide release were not deemed to be of great concern, so chemical industries tended to design BOX 5-1 Major Separation Processes and Industries That Depend Heavily on Chemical Separations Separation Processes Distillation Membrane-based Filtration Solvent extraction crystallization Bubble/foam fractionation Supercritical gas extraction Ion exchange Electrodialysis Gas and liquid adsorptions Drying Liquid chromatography Gas absorption Industries Served Organic and inorganic Electronic products Industrial, municipal, and chemical production Food processing agricultural waste Polymer production Biochemical products treatment Petroleum refining Biofuels production Hospitals and other Pharmaceutical production Advanced biotech health-care entities Ore, coal, oil, and gas products Homeland security extraction and cleanup
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From page 91... ...
Given that distillation is by far the most common separation process, used in as much as 80 percent of all the chemical separations listed in Box 5.1, optimization of phase equilibria will remain an important grand challenge for the chemical separations industry. It is also true that distillation is sometimes not an effective option.
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From page 92... ...
MAJOR CHALLENGES FACING CHEMICAL SEPARATIONS There are three major challenges facing those concerned with the development of efficient chemical separations: 1. How can we predict physical properties accurately enough to set the optimal conditions for sepa rating mixtures using distillation and MSA materials?
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From page 93... ...
We now examine the three major challenges in chemical separations in more detail. Major Challenge 1: Accurately Predicting Physical Properties for Phase Equilibria How can we predict physical properties accurately enough to set the optimal conditions for separating mixtures using distillation and MSA materials?
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From page 94... ...
In addition, training and education in computational chemistry and mathematical optimization are not well-integrated into the chemical engineering and chemistry curriculum, thus limiting the extent to which methods and algorithms can inform optimality of phase equilibria and process operation. However, it is likely that these accepted business practices will change in the near future if a green chemical revolution really takes hold.
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From page 95... ...
Major Challenge 3: Designing Optimal Separation Systems with Multiple Separation Units How can we design overall separation systems that incorporate several individual separation units for economically optimal separations of complex mixtures? Once a separation scheme has been proposed, determining the efficiency of the separation, the optimum operating conditions for each unit, and the sizing of the units shown and the connecting piping is rather straightforward if we have a good understanding of the physical properties of the chemicals or mixtures and of the structures and performance of any MSAs used in the process.
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From page 96... ...
• Fast screening of potential solvents or MSAs. Computational approaches have great potential for facilitating more progress on Major Challenges 1 and 2.
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From page 97... ...
To successfully address Major Challenges 1 and 2 requires building on the capabilities of computational chemistry, which now include calculations at the molecular scale with algorithms based on quantum chemical theories and classical analogs that evaluate the energetics of molecular conformations, as well as statistical mechanical methods that sample those conformations consistent with thermodynamic variables such as temperature and pressure. The general strategy typically employed in computational chemistry is to combine these methods based on the following diagram:
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From page 98... ...
In other cases, qualitative insight is not enough and quantitative predictions are necessary. In order for computational chemistry to develop predictive capabilities good enough to overcome Major Challenges 1 and 2, the following are needed: • Scalable algorithms for quantum electronic structure calculations.
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From page 99... ...
CURRENT FRONTIERS OF HECC FOR CHEMICAL SEPARATIONS Algorithms for Quantum Electronic Structure Calculations The 1998 Nobel prize in chemistry went to John Pople for his development of computational methods in quantum chemistry, including the mean field approximation of Hartree-Fock (HF) methods and electron correlation methods that enable increasing levels of accuracy, and to Walter Kohn for his development of an alternative approach to electronic structure, known as density-functional theory (DFT)
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From page 100... ...
For classes of more complex materials, current capabilities of these methods may themselves inherently limit the accurate calculation of phase equilibria data, and coupled cluster methods are to be preferred. Improved Accuracy of Molecular Mechanics Force Fields Empirical force fields derived from electronic structure calculations and experimental data, coupled to classical molecular dynamics or Monte Carlo sampling schemes, are the main component of all computational studies of materials chemistry to date.
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From page 101... ...
The challenge of using empirical force fields in the chemical separations industry is that each new thermal-based separation or MSA material requires empirical force field development based on an affordable electronic structure calculation, and experimental validation is then required in order for those force fields to be usefully deployed. The challenge in constructing a force field from quantum calculations lies in determining the form of the mathematical function.
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From page 102... ...
What distinguishes the usefulness of mathematical optimization in Major Challenges 1 and 2 is that the cost functions and parameter space are relatively well defined in terms of an objective function, while Major Challenge 3 has greater uncertainty in the nature and dimension size of the mathematical model.
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From page 103... ...
Major Challenge 3 currently is more narrowly focused on formulating cost function models that can utilize the large array of mathematical optimization techniques. OTHER ISSUES THAT LIMIT THE VALUE OF HECC TO CHEMICAL SEPARATIONS Productive cooperation and dialogue between experimentalists and modelers is not as extensive as it should be in order for computational approaches to contribute optimally to progress in chemical separations.
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From page 104... ...
1998. Applications of computational chemistry to the study of cyclodextrins.
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