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- Volume 5, 2014
Annual Review of Chemical and Biomolecular Engineering - Volume 5, 2014
Volume 5, 2014
- Preface
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Plans and Detours
Vol. 5 (2014), pp. 1–9More LessAt various stages of my career, I made and followed plans for progress and growth. However, owing to several unexpected challenges, I had to make detours into unplanned vistas. When I look around at the careers of my former students and younger colleagues, I see fewer long-term, stable positions and frequent changes both in employers and in functions every ten or twenty years. Our curriculum prepares our students for manufacturing careers in the United States, but the current trend of corporate merger and outsourcing can suddenly turn their work into marketing or finance in the Far East. A fox that knows many tricks may be better suited to changing environments than a hedgehog that knows only one single trick. Perhaps future education should not only teach few subjects in depth for immediate career needs but also teach adaptability to unrelated challenges.
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Simulating the Flow of Entangled Polymers
Vol. 5 (2014), pp. 11–33More LessTo optimize automation for polymer processing, attempts have been made to simulate the flow of entangled polymers. In industry, fluid dynamics simulations with phenomenological constitutive equations have been practically established. However, to account for molecular characteristics, a method to obtain the constitutive relationship from the molecular structure is required. Molecular dynamics simulations with atomic description are not practical for this purpose; accordingly, coarse-grained models with reduced degrees of freedom have been developed. Although the modeling of entanglement is still a challenge, mesoscopic models with a priori settings to reproduce entangled polymer dynamics, such as tube models, have achieved remarkable success. To use the mesoscopic models as staging posts between atomistic and fluid dynamics simulations, studies have been undertaken to establish links from the coarse-grained model to the atomistic and macroscopic simulations. Consequently, integrated simulations from materials chemistry to predict the macroscopic flow in polymer processing are forthcoming.
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Modeling Chemoresponsive Polymer Gels
Vol. 5 (2014), pp. 35–54More LessStimuli-responsive gels are vital components in the next generation of smart devices, which can sense and dynamically respond to changes in the local environment and thereby exhibit more autonomous functionality. We describe recently developed computational methods for simulating the properties of such stimuli-responsive gels in the presence of optical, chemical, and thermal gradients. Using these models, we determine how to harness light to drive shape changes and directed motion in spirobenzopyran-containing gels. Focusing on oscillating gels undergoing the Belousov-Zhabotinksy reaction, we demonstrate that these materials can spontaneously form self-rotating assemblies, or pinwheels. Finally, we model temperature-sensitive gels that encompass chemically reactive filaments to optimize the performance of this system as a homeostatic device for regulating temperature. These studies could facilitate the development of soft robots that autonomously interconvert chemical and mechanical energy and thus perform vital functions without the continuous need of external power sources.
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Atmospheric Emissions and Air Quality Impacts from Natural Gas Production and Use
Vol. 5 (2014), pp. 55–75More LessThe US Energy Information Administration projects that hydraulic fracturing of shale formations will become a dominant source of domestic natural gas supply over the next several decades, transforming the energy landscape in the United States. However, the environmental impacts associated with fracking for shale gas have made it controversial. This review examines emissions and impacts of air pollutants associated with shale gas production and use. Emissions and impacts of greenhouse gases, photochemically active air pollutants, and toxic air pollutants are described. In addition to the direct atmospheric impacts of expanded natural gas production, indirect effects are also described. Widespread availability of shale gas can drive down natural gas prices, which, in turn, can impact the use patterns for natural gas. Natural gas production and use in electricity generation are used as a case study for examining these indirect consequences of expanded natural gas availability.
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Manipulating Crystallization with Molecular Additives
Vol. 5 (2014), pp. 77–96More LessGiven the importance of organic crystals in a wide range of industrial applications, the chemistry, biology, materials science, and chemical engineering communities have focused considerable attention on developing methods to control crystal structure, size, shape, and orientation. Tailored additives have been used to control crystallization to great effect, presumably by selectively binding to particular crystallographic surfaces and sites. However, substantial knowledge gaps still exist in the fundamental mechanisms that govern the formation and growth of organic crystals in both the absence and presence of additives. In this review, we highlight research discoveries that reveal the role of additives, either introduced by design or present adventitiously, on various stages of formation and growth of organic crystals, including nucleation, dislocation spiral growth mechanisms, growth inhibition, and nonclassical crystal morphologies. The insights from these investigations and others of their kind are likely to guide the development of innovative methods to manipulate crystallization for a wide range of materials and applications.
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Advances in Mixed-Integer Programming Methods for Chemical Production Scheduling
Vol. 5 (2014), pp. 97–121More LessThe goal of this paper is to critically review advances in the area of chemical production scheduling over the past three decades and then present two recently proposed solution methods that have led to dramatic computational enhancements. First, we present a general framework and problem classification and discuss modeling and solution methods with an emphasis on mixed-integer programming (MIP) techniques. Second, we present two solution methods: (a) a constraint propagation algorithm that allows us to compute parameters that are then used to tighten MIP scheduling models and (b) a reformulation that introduces new variables, thus leading to effective branching. We also present computational results and an example illustrating how these methods are implemented, as well as the resulting enhancements. We close with a discussion of open research challenges and future research directions.
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Population Balance Modeling: Current Status and Future Prospects
Vol. 5 (2014), pp. 123–146More LessPopulation balance modeling is undergoing phenomenal growth in its applications, and this growth is accompanied by multifarious reviews. This review aims to fortify the model's fundamental base, as well as point to a variety of new applications, including modeling of crystal morphology, cell growth and differentiation, gene regulatory processes, and transfer of drug resistance. This is accomplished by presenting the many faces of population balance equations that arise in the foregoing applications.
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Energy Supply Chain Optimization of Hybrid Feedstock Processes: A Review
Vol. 5 (2014), pp. 147–179More LessThe economic, environmental, and social performances of energy systems depend on their geographical locations and the surrounding market infrastructure for feedstocks and energy products. Strategic decisions to locate energy conversion facilities must take all upstream and downstream operations into account, prompting the development of supply chain modeling and optimization methods. This article reviews the contributions of energy supply chain studies that include heat, power, and liquid fuels production. Studies are categorized based on specific features of the mathematical model, highlighting those that address energy supply chain models with and without considerations of multiperiod decisions. Studies that incorporate uncertainties are discussed, and opportunities for future research developments are outlined.
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Dynamics of Colloidal Glasses and Gels
Vol. 5 (2014), pp. 181–202More LessMany household and industrially important soft colloidal materials, such as pastes, concentrated suspensions and emulsions, foams, slurries, inks, and paints, are very viscous and do not flow over practical timescales until sufficient stress is applied. This behavior originates from restricted mobility of the constituents arrested in disordered structures of varying length scales, termed colloidal glasses and gels. Usually these materials are thermodynamically out of equilibrium, which induces a time-dependent evolution of the structure and the properties. This review presents an overview of the rheological behavior of this class of materials. We discuss the experimental observations and theoretical developments regarding the microstructure of these materials, emphasizing the complex coupling between the deformation field and nonequilibrium structures in colloidal glasses and gels, which leads to a rich array of rheological behaviors with profound implications for various industrial processes and products.
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Rheology of Non-Brownian Suspensions
Vol. 5 (2014), pp. 203–228More LessSuspensions of non-Brownian particles are commonly encountered in applications in a large number of industries. These suspensions exhibit nonlinear flow behavior, even in Newtonian suspending fluids under conditions where inertial effects can be ignored and linearity would normally be expected. We review the observed rheological behavior, emphasizing concentrated suspensions of spheres in Newtonian fluids, and we examine both particle-level and continuum approaches to describing the nonlinear behavior. Particle-particle nonhydrodynamic interactions appear to be important in concentrated suspensions. Continuum descriptions are not yet adequate to describe the observed behavior.
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Factors Affecting the Rheology and Processability of Highly Filled Suspensions
Vol. 5 (2014), pp. 229–254More LessSuspensions filled with rigid particles at volume-loading levels that approach their maximum packing fraction are widely encountered, especially in the energetics, ceramics, pharmaceutical, magnetics, composites, food, and personal care industries. Highly filled suspensions, regardless of industrial application, exhibit a number of common rheological and processability traits, including viscoplasticity and wall slip, that necessitate special rheometers and appropriate characterization and numerical simulation methods. Furthermore, various factors, including the dispersion and distribution of the particles and their agglomerates, the entrainment of air, the filtration-based migration of the binder phase, and the shear-induced migration of particles, play important roles and must be considered in the design and optimization of manufacturing operations for processing of highly filled suspensions.
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Continuous-Flow Differential Mobility Analysis of Nanoparticles and Biomolecules
Vol. 5 (2014), pp. 255–279More LessThe differential mobility analyzer (DMA) is a powerful instrument that continuously separates aerosol particles according to their migration velocities in an electric field with high resolution. Because of the low fields employed, the mobility can be related to particle size or ion cross section. Combined with a sensitive detector, such as a continuous-flow condensation particle counter, the DMA enables differential size distribution measurements to be made within minutes to seconds. Over the past few decades, these capabilities have made the DMA a central tool for aerosol characterization in the 10–1,000-nm size range. DMAs have been adapted recently for measurement of particles as small as 1 nm and are now contributing to our understanding of nucleation, nanotechnology, and gas ions. Moreover, the opposed migration classifier, a new approach to differential mobility analysis, expands the dynamic range and shows promise both for increasing resolution beyond present levels and for changing the way that instruments are built. Thus, the DMA continues to advance methods and capabilities for physical characterization at transition from molecules to clusters to particles.
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From Stealthy Polymersomes and Filomicelles to “Self” Peptide-Nanoparticles for Cancer Therapy
Vol. 5 (2014), pp. 281–299More LessPolymersome vesicles and wormlike filomicelles self-assembled with amphiphilic, degradable block copolymers have recently shown promise in application to cancer therapy. In the case of filomicelles, dense, hydrophilic brushes of poly(ethylene glycol) on these nanoparticles combine with flexibility to nonspecifically delay clearance by phagocytes in vivo, which has motivated the development of “self” peptides that inhibit nanoparticle clearance through specific interactions. Delayed clearance, as well as robustness of polymer assemblies, opens the dosage window for delivery of increased drug loads in the polymer assemblies and increased tumor accumulation of drug(s). Antibody-targeting and combination therapies, such as with radiotherapy, are emerging in preclinical animal models of cancer. Such efforts are expected to combine with further advances in polymer composition, structure, and protein/peptide functionalization to further enhance transport through the circulation and permeation into disease sites.
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Carbon Capture Simulation Initiative: A Case Study in Multiscale Modeling and New Challenges
Vol. 5 (2014), pp. 301–323More LessAdvanced multiscale modeling and simulation have the potential to dramatically reduce the time and cost to develop new carbon capture technologies. The Carbon Capture Simulation Initiative is a partnership among national laboratories, industry, and universities that is developing, demonstrating, and deploying a suite of such tools, including basic data submodels, steady-state and dynamic process models, process optimization and uncertainty quantification tools, an advanced dynamic process control framework, high-resolution filtered computational-fluid-dynamics (CFD) submodels, validated high-fidelity device-scale CFD models with quantified uncertainty, and a risk-analysis framework. These tools and models enable basic data submodels, including thermodynamics and kinetics, to be used within detailed process models to synthesize and optimize a process. The resulting process informs the development of process control systems and more detailed simulations of potential equipment to improve the design and reduce scale-up risk. Quantification and propagation of uncertainty across scales is an essential part of these tools and models.
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Downhole Fluid Analysis and Asphaltene Science for Petroleum Reservoir Evaluation
Vol. 5 (2014), pp. 325–345More LessPetroleum reservoirs are enshrouded in mysteries associated with all manner of geologic and fluid complexities that Mother Nature can inspire. Efficient exploitation of petroleum reservoirs mandates elucidation of these complexities; downhole fluid analysis (DFA) has proven to be indispensable for understanding both fluids and reservoir architecture. Crude oil consists of dissolved gases, liquids, and dissolved solids, known as the asphaltenes. These different fluid components exhibit fluid gradients vertically and laterally, which are best revealed by DFA, with its excellent precision and accuracy. Compositional gradient analysis falls within the purview of thermodynamics. Gas-liquid equilibria can be treated with a cubic equation of state (EoS), such as the Peng-Robinson EoS, a modified van der Waals EoS. In contrast, the first EoS for asphaltene gradients, the Flory-Huggins-Zuo (FHZ) EoS, was developed only recently. The resolution of the asphaltene molecular and nanocolloidal species in crude oil, which is codified in the Yen-Mullins model of asphaltenes, enabled the development of this EoS. The combination of DFA characterization of gradients of reservoir crude oil with the cubic EoS and FHZ EoS analyses brings into view wide-ranging reservoir concerns, such as reservoir connectivity, fault-block migration, heavy oil gradients, tar mat formation, huge disequilibrium fluid gradients, and even stochastic variations of reservoir fluids. New petroleum science and DFA technology are helping to offset the increasing costs and technical difficulties of exploiting ever-more-remote petroleum reservoirs.
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Biocatalysts for Natural Product Biosynthesis
Nidhi Tibrewal, and Yi TangVol. 5 (2014), pp. 347–366More LessNatural products are important sources of pharmaceuticals, in part owing to their diverse biological activities. Enzymes from natural product biosynthetic pathways have become attractive candidates as biocatalysts for modifying the structures and bioactivities of these complex compounds. Numerous enzymes have been harvested to generate innovative scaffolds, large-scale synthesis of chiral building blocks, and semisynthesis of medicinally relevant natural product derivatives. This review discusses recent examples from three areas: (a) polyketide catalytic domain engineering geared toward synthesis of new polyketides, (b) engineering of tailoring enzymes (other than oxidative enzymes) as biocatalysts, and (c) in vitro total synthesis of natural products using purified enzyme components. With the availability of exponentially increasing genomic information and new genome mining tools, many new and powerful biocatalysts tailored for pharmaceutical synthesis will likely emerge from secondary metabolism.
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Entangled Polymer Dynamics in Equilibrium and Flow Modeled Through Slip Links
Vol. 5 (2014), pp. 367–381More LessThe idea that the dynamics of concentrated, high–molecular weight polymers are largely governed by entanglements is now widely accepted and typically understood through the tube model. Here we review alternative approaches, slip-link models, that share some similarities to and offer some advantages over tube models. Although slip links were proposed at the same time as tubes, only recently have detailed, quantitative mathematical models arisen based on this picture. In this review, we focus on these models, with most discussion limited to mathematically well-defined objects that conform to state-of-the-art beyond-equilibrium thermodynamics. These models are connected to each other through successive coarse graining, using nonequilibrium thermodynamics along the way, and with a minimal parameter set. In particular, the most detailed level of description has four parameters, three of which can be determined directly from atomistic simulations. Once the remaining parameter is determined for any system, all parameters for all members of the hierarchy are determined. We show how, using this hierarchy of slip-link models combined with atomistic simulations, we can make predictions about the nonlinear rheology of monodisperse homopolymer melts, polydisperse melts, or blends of different architectures. Mathematical details are given elsewhere, so these are limited here, and physical ideas are emphasized. We conclude with an outlook on remaining challenges that might be tackled successfully using this approach, including complex flow fields and polymer blends.
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Progress and Challenges in Control of Chemical Processes
Jay H. Lee, and Jong Min LeeVol. 5 (2014), pp. 383–404More LessThis review covers key developments and trends in chemical process control during the past two decades. Control methodologies and related supporting technologies are covered, and recent trends in applications are also examined. After the widespread adoption of model-based techniques by industry, control interest has begun to move beyond the traditional realm of readily measured variables to include chemical compositions and particle features. However, the shift is being slowed by the shortage of accurate, reliable, and inexpensive sensing devices. Although the past two decades saw no new major theoretical or methodological advances, several important incremental improvements and extensions have been made to help the ripening of the technologies developed in the preceding two decades. Control is regaining its importance owing to society's renewed focus on energy and the maturation of various emerging technologies, but a community-wide consensus on what general problems should be solved is lacking.
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Force-Field Parameters from the SAFT-γ Equation of State for Use in Coarse-Grained Molecular Simulations
Vol. 5 (2014), pp. 405–427More LessA description of fluid systems with molecular-based algebraic equations of state (EoSs) and by direct molecular simulation is common practice in chemical engineering and the physical sciences, but the two approaches are rarely closely coupled. The key for an integrated representation is through a well-defined force field and Hamiltonian at the molecular level. In developing coarse-grained intermolecular potential functions for the fluid state, one typically starts with a detailed, bottom-up quantum-mechanical or atomic-level description and then integrates out the unwanted degrees of freedom using a variety of techniques; an iterative heuristic simulation procedure is then used to refine the parameters of the model. By contrast, with a top-down technique, one can use an accurate EoS to link the macroscopic properties of the fluid and the force-field parameters. We discuss the latest developments in a top-down representation of fluids, with a particular focus on a group-contribution formulation of the statistical associating fluid theory (SAFT-γ). The accurate SAFT-γ EoS is used to estimate the parameters of the Mie force field, which can then be used with confidence in direct molecular simulations to obtain thermodynamic, structural, interfacial, and dynamical properties that are otherwise inaccessible from the EoS. This is exemplified for several prototypical fluids and mixtures, including carbon dioxide, hydrocarbons, perfluorohydrocarbons, and aqueous surfactants.
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