Digital Commons Network^™

How Chip Size Impacts Steam Pretreatment Effectiveness For Biological Conversion Of Poplar Wood Into Fermentable Sugars, Jaclyn D. Demartini, Marcus Foston, Xianzhi Meng, Seokwon Jung, Rajeev Kumar, Arthur J. Ragauskas, Charles E. Wyman

Faculty Publications and Other Works -- Chemical and Biomolecular Engineering

Background

Woody biomass is highly recalcitrant to enzymatic sugar release and often requires significant size reduction and severe pretreatments to achieve economically viable sugar yields in biological production of sustainable fuels and chemicals. However, because mechanical size reduction of woody biomass can consume significant amounts of energy, it is desirable to minimize size reduction and instead pretreat larger wood chips prior to biological conversion. To date, however, most laboratory research has been performed on materials that are significantly smaller than applicable in a commercial setting. As a result, there is a limited understanding of the effects that larger biomass particle …

Pstat: Promoting Sustainable Transportation Among Teens, Jordan Bryner, Yi Ying Chin, Candice Patton, Rebekah Patton, Christopher Stanfill, Rick Wheeler, Jeffrey Keith Clark Ii, Paul Frymier, Chris Cherry, David Irick, Leon Tolbert

Faculty Publications and Other Works -- Chemical and Biomolecular Engineering

Can an innovative, team-based, hands-on design and construction project involving high school students change their attitudes and personal preferences for transportation to favor lower impact modes? This was the main question PSTAT (Promoting Sustainable Transportation Among Teens) sought to answer. Since the last decade, global climate change has fuelled increased development of alternative transportation modes that have lesser impact on the environment. However, society is not embracing the change with open arms. Therefore, there is a critical need for a paradigm shift, which could be especially timely for teen-aged students starting to adopt their own personal transportation preferences. By exposing …

The Sustainability Of Coffee Brewing, Richard F Simmerman

Faculty Publications and Other Works -- Chemical and Biomolecular Engineering

In short, over 8.25 million tons of coffee are produced world-wide annually (2009). Remarkably, only two different species of coffee are cultivated to reach almost the entire crop, Coffea canephora (robusta) and C. arabica (arabica). Arabica coffee is a tetraploid, that takes 9 months to ripen, yields 1500-3000 kg beans/ha, has an optimum temperature 15-24°C, an optimal rainfall need of 1500-2000 mm, an optimum altitude 1000-2000 m, is much more susceptible to disease and parasites, with a caffeine content per bean of 0.8-1.4%. Robusta coffee is a diploid, that takes 11 months to ripen, yields 2300-4000 kg beans/ha, …

Supercomputer Design: An Initial Effort To Capture The Environmental, Economic, And Societal Impacts, Marshall T. Mcdonnell

Faculty Publications and Other Works -- Chemical and Biomolecular Engineering

Abstract Currently, the Green500 is possibly the largest effort to direct the evolution of supercomputing towards sustainable design but does not address life-cycle impacts of a supercomputer. Supercomputer assessment with economical, environmental, and societal impacts considered would provide an optimal future supercomputer design that is sustainable. Some of the benefits of such an assessment would help determines the complete impact for bringing a supercomputer online, determine impact “hot spots” in design, and determine optimal locations for construction. By combining process-LCA and EIO-LCA methods, an initial model for in-depth sustainability analysis of supercomputer design has been developed and the results presented. …

Astaxanthin: A Comparative Case Of Synthetic Vs. Natural Production, Khoa Dang Nguyen

Faculty Publications and Other Works -- Chemical and Biomolecular Engineering

Astaxanthin, the “king of carotenoids” has been widely used as an animal feed additive for several decades, mainly in the aquaculture industry. Recent studies have led to its emergence as a potent antioxidant available for human consumption. Traditionally it has been chemically synthesized, but the recent market interest has generated interests in producing it naturally via yeast (Phaffia rhodozyma) fermentation, or algal (Haematococcus pluvialis) induction. This work aims to compare these production processes and their impact on the economical, environmental, and societal scale. We also look at the attempts of increasing production yields by altering various …

Self-Consistent Multiscale Modeling In The Presence Of Inhomogeneous Fields, Ruichang Xiong, Rebecca L. Empting, Ian C. Morris, David J. Keffer

Faculty Publications and Other Works -- Chemical and Biomolecular Engineering

Molecular dynamics (MD) simulations of a Lennard–Jones fluid in an inhomogeneous external field generate steady-state profiles of density and pressure with nanoscopic heterogeneities. The continuum level of mass, momentum, and energy transport balances is capable of reproducing the MD profiles only when the equation of state for pressure as a function of density is extracted directly from the molecular level of description. We show that the density profile resulting from simulation is consistent with both a molecular-level theoretical prediction from statistical mechanics as well as the solution of the continuum-level set of differential equations describing the conservation of mass and …

Effects Of Ultramicroelectrode Dimensions On The Electropolymerization Of Polypyrrole, Benjamin J. Fletcher, Jared T. Fern, Kevin Rhodes, Timothy E. Mcknight, Jason D. Fowlkes, Scott T. Retterer, David J. Keffer, Michael L. Simpson, Mitchel J. Doktycz

Faculty Publications and Other Works -- Chemical and Biomolecular Engineering

Anode geometry can significantly affect the electrochemical synthesis of conductive polymers. Here, the effects of anode dimensions on the electropolymerization of pyrrole are investigated. Band microelectrodes were prepared with widths ranging from 2 to 500 μm. The anode dimension has a significant effect on the resulting thickness of polymer film. The electropolymerization process deviates significantly from that predicted by simple mass transfer considerations when electrode dimensions are less than ∼ 20 μm. Polymer film thickness is thinner than expected when electrode dimensions become less than ∼ 10 μm. A simple mathematical model was derived to explain the observed effects of …

Controlling Accumulation Of Fermentation Inhibitors In Biorefinery Recycle Water Using Microbial Fuel Cells, Abhijeet P. Borole, Jonathan R. Mielenz, Tatiana A. Vishnivetskaya, Choo Y. Hamilton

Faculty Publications and Other Works -- Chemical and Biomolecular Engineering

Background

Microbial fuel cells (MFC) and microbial electrolysis cells are electrical devices that treat water using microorganisms and convert soluble organic matter into electricity and hydrogen, respectively. Emerging cellulosic biorefineries are expected to use large amounts of water during production of ethanol. Pretreatment of cellulosic biomass results in production of fermentation inhibitors which accumulate in process water and make the water recycle process difficult. Use of MFCs to remove the inhibitory sugar and lignin degradation products from recycle water is investigated in this study.

Results

Use of an MFC to reduce the levels of furfural, 5-hydroxymethylfurfural, vanillic acid, 4-hydroxybenzaldehyde and …

Metabolic Engineering Of Escherichia Coli For Efficient Conversion Of Glycerol Into Ethanol, Cong T. Trinh, Friedrich Srienc

Faculty Publications and Other Works -- Chemical and Biomolecular Engineering

Based on elementary mode analysis, an Escherichia coli strain was designed for efficient conversion of glycerol to ethanol. By using nine gene knockout mutations, the functional space of the central metabolism of E. coli was reduced from over 15,000 possible pathways to a total of 28 glycerol-utilizing pathways that support cell function. Among these pathways are eight aerobic and eight anaerobic pathways that do not support cell growth but convert glycerol into ethanol with a theoretical yield of 0.50 g ethanol/g glycerol. The remaining 12 pathways aerobically coproduce biomass and ethanol from glycerol. The optimal ethanol production depends on the …

Atomistic Simulation Of Energetic And Entropic Elasticity In Short-Chain Polyethylenes, T. C. Ionescu, V. G. Mavrantzas, David J. Keffer, B. J. Edwards

Faculty Publications and Other Works -- Chemical and Biomolecular Engineering

The thermodynamical aspects of polymeric liquids subjected to uniaxial elongational flow are examined using atomistically detailed nonequilibrium Monte Carlo simulations. In particular, attention is paid to the energetic effects, in addition to the entropic ones, which occur under conditions of extreme deformation. Atomistic nonequilibrium Monte Carlo simulations of linear polyethylene systems, ranging in molecular length from C₂₄ to C₇₈ and for temperatures from 300 to 450 K, demonstrate clear contributions of energetic effects to the elasticity of the system. These are manifested in a conformationally dependent heat capacity, which is significant under large deformations. Violations of the hypothesis …

Energetic And Entropic Elasticity Of Nonisothermal Flowing Polymers: Experiment, Theory, And Simulation, T. C. Ionescu, B. J. Edwards, David Keffer, V. G. Mavrantzas

Faculty Publications and Other Works -- Chemical and Biomolecular Engineering

The thermodynamical aspects of polymeric liquids subjected to nonisothermal flow are examined from the complementary perspectives of theory, experiment, and simulation. In particular, attention is paid to the energetic effects, in addition to the entropic ones, that occur under conditions of extreme deformation. Comparisons of experimental measurements of the temperature rise generated under elongational flow at high strain rates with macroscopic finite element simulations offer clear evidence of the persistence and importance of energetic effects under severe deformation. The performance of various forms of the temperature equation are evaluated with regard to experiment, and it is concluded that the standard …

Absorbing Boundary Conditions For Molecular Dynamics And Multiscale Modeling, David J. Keffer, S. Namilae, D. M. Nicholson, P.K. V.V. Nukala, C. Y. Gao, Y. N. Osetsky

Faculty Publications and Other Works -- Chemical and Biomolecular Engineering

We present an application of differential equation based local absorbing boundary conditions to molecular dynamics. The absorbing boundary conditions result in the absorbtion of the majority of waves incident perpendicular to the bounding surface. We demonstrate that boundary conditions developed for the wave equation can be applied to molecular dynamics. Comparisons with damping material boundary conditions are discussed. The concept is extended to the formulation of an atomistic-continuum multiscale scheme with handshaking between the regions based on absorbing boundary conditions. The multiscale model is effective in minimizing spurious reflections at the interface.

Structure Formation Under Steady-State Isothermal Planar Elongational Flow Of N-Eicosane: A Comparison Between Simulation And Experiment, David J. Keffer, T. C. Ionescu, C. Baig, B. J. Edwards, A. Habenschuss

Faculty Publications and Other Works -- Chemical and Biomolecular Engineering

We use nonequilibrium molecular dynamics simulations to investigate the structural properties of an oriented melt of n-eicosane under steady-state planar elongational flow. The flow-induced structure was evaluated using the structure factor s(k) taken as the Fourier transform of the total pair correlation function g(r). We found that the equilibrium liquid structure factor is in excellent agreement with the one determined via x-ray diffraction. Moreover, a new x-ray diffraction experiment has been performed on a crystalline n-eicosane sample. The resulting intramolecular contribution to the structure factor was found to be in very good agreement with the simulated one at …

Rheological And Structural Studies Of Linear Polyethylene Melts Under Planar Elongational Flow Using Nonequilibrium Molecular Dynamics Simulations, David J. Keffer, C. Baig, B. J. Edwards, H. D. Cochran, V. A. Harmandaris

Faculty Publications and Other Works -- Chemical and Biomolecular Engineering

We present various rheological and structural properties of three polyethylene liquids, C₅₀H₁₀₂, C₇₈H₁₅₈, and C₁₂₈H₂₅₈, using nonequilibrium molecular dynamics simulations of planar elongational flow. All three melts display tension-thinning behavior of both elongational viscosities, η₁ and η₂. This tension thinning appears to follow the power law with respect to the elongation rate, i.e., η ∼ E^b, where the exponent b is shown to be approximately −0.4 for η₁ and η₂. More specifically, b of η₁ is shown to be …

A Validation Of The P-Sllod Equations Of Motion For Homogeneous Steady-State Flows, David J. Keffer, B. J. Edwards, C. Baig

Faculty Publications and Other Works -- Chemical and Biomolecular Engineering

A validation of the p-SLLOD equations of motion for nonequilibrium molecular dynamics simulation under homogeneous steady-state flow is presented. We demonstrate that these equations generate the correct center-of-mass trajectory of the system, are completely compatible with (and derivable from) Hamiltonian dynamics, satisfy an appropriate energy balance, and require no fictitious external force to generate the required homogeneous flow. It is also shown that no rigorous derivation of the SLLOD equations exists to date.

A Comparison Of Simple Rheological Models And Simulation Data Of N-Hexadecane Under Shear And Elongational Flows, David J. Keffer, C. Baig, B. Jiang, B. J. Edwards, H. D. Cochran

Faculty Publications and Other Works -- Chemical and Biomolecular Engineering

The microscopic origins of five rheological models are investigated by comparing their predictions for the conformation tensor and stress tensor with the same tensors obtained via nonequilibrium molecular dynamics simulations for n-hexadecane. Steady-state simulations were performed under both planar Couette and planar elongational flows, and the results of each are compared with rheological model predictions in the same flows, without any fitting parameters where possible. The use of the conformation tensor for comparisons between theory and experiment/simulation, rather than just the stress tensor, allows additional information to be obtained regarding the physical basis of each model examined herein. The character …

An Examination Of The Validity Of Nonequilibrium Molecular-Dynamics Simulation Algorithms For Arbitrary Steady-State Flows, David J. Keffer, Brian J. Edwards, Chunggi Baig

Faculty Publications and Other Works -- Chemical and Biomolecular Engineering

Nonlinear-response theory of nonequilibrium molecular-dynamics simulation algorithms is considered under the imposition of an arbitrary steady-state flow field. It is demonstrated that the SLLOD and DOLLS algorithms cannot be used for general flows, although the SLLOD algorithm is rigorous for planar Couette flow. Following the same procedure used to establish SLLOD as the valid algorithm for planar Couette flow [ D. J. Evans and E. P. Morriss, Phys. Rev. A 30, 1528 (1984) ], it is demonstrated that the p-SLLOD algorithm is valid for arbitrary flows and produces the correct nonlinear response of the viscous pressure tensor.

Rheological And Structural Studies Of Liquid Decane, Hexadecane, And Tetracosane Under Planar Elongational Flow Using Nonequilibrium Molecular-Dynamics Simulations, David J. Keffer, C. Baig, B. J. Edwards, H. D. Cochran

Faculty Publications and Other Works -- Chemical and Biomolecular Engineering

We report for the first time rheological and structural properties of liquid decane, hexadecane, and tetracosane using nonequilibrium molecular-dynamics (NEMD) simulations under planar elongational flow (PEF). The underlying NEMD algorithm employed is the so-called p-SLLOD algorithm [ C. Baig, B. J. Edwards, D. J. Keffer, and H. D. Cochran, J. Chem. Phys. 122, 114103 (2005) ]. Two elongational viscosities are measured, and they are shown not to be equal to each other, indicating two independent viscometric functions in PEF. With an appropriate definition, it is observed that the two elongational viscosities converge to each other at very low elongation …

A Proper Approach For Nonequilibrium Molecular Dynamics Simulations Of Planar Elongational Flow, David J. Keffer, C. Baig, B. J. Edwards, H. D. Cochran

Faculty Publications and Other Works -- Chemical and Biomolecular Engineering

We present nonequilibrium molecular dynamics simulations of planar elongational flow (PEF) by an algorithm proposed by Tuckerman et al. [J. Chem. Phys. 106, 5615 (1997)] and theoretically elaborated by Edwards and Dressler [J. Non-Newtonian, Fluid Mech. 96, 163 (2001)], which we shall call the proper-SLLOD algorithm, or p-SLLOD for short. [For background on names of algorithms see W. G. Hoover, D. J. Evans, R. B. Hickman, A. J. C. Ladd, W. T. Ashurst, and B. Moran, Phys. Rev. A 22, 1690 (1980) and D. J. Evans and G. P. Morriss, Phys. Rev. A 30, 1528 (1984).] We show that there …