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First-principles flocculation as the key to low energy algal biofuels processing

Hewson, John C.; Mondy, L.A.; Murton, Jaclyn K.; O'Hern, Timothy J.; Parchert, Kylea J.; Pohl, Phillip I.; Williams, Cecelia V.; Wyatt, Nicholas B.; Barringer, David A.; Pierce, Flint P.; Brady, Patrick V.; Dwyer, Brian P.; Grillet, Anne M.; Hankins, M.G.; Hughes, Lindsey G.; Lechman, Jeremy B.

This document summarizes a three year Laboratory Directed Research and Development (LDRD) program effort to improve our understanding of algal flocculation with a key to overcoming harvesting as a techno-economic barrier to algal biofuels. Flocculation is limited by the concentrations of deprotonated functional groups on the algal cell surface. Favorable charged groups on the surfaces of precipitates that form in solution and the interaction of both with ions in the water can favor flocculation. Measurements of algae cell-surface functional groups are reported and related to the quantity of flocculant required. Deprotonation of surface groups and complexation of surface groups with ions from the growth media are predicted in the context of PHREEQC. The understanding of surface chemistry is linked to boundaries of effective flocculation. We show that the phase-space of effective flocculation can be expanded by more frequent alga-alga or floc-floc collisions. The collision frequency is dependent on the floc structure, described in the fractal sense. The fractal floc structure is shown to depend on the rate of shear mixing. We present both experimental measurements of the floc structure variation and simulations using LAMMPS (Large-scale Atomic/Molecular Massively Parallel Simulator). Both show a densification of the flocs with increasing shear. The LAMMPS results show a combined change in the fractal dimension and a change in the coordination number leading to stronger flocs.

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TYPE SAND Report YEAR 2012
OSTIDOI

Finite element analysis of multilayer coextrusion

Rao, Rekha R.; Mondy, L.A.; Schunk, Randy; Hopkins, Matthew M.

Multilayer coextrusion has become a popular commercial process for producing complex polymeric products from soda bottles to reflective coatings. A numerical model of a multilayer coextrusion process is developed based on a finite element discretization and two different free-surface methods, an arbitrary-Lagrangian-Eulerian (ALE) moving mesh implementation and an Eulerian level set method, to understand the moving boundary problem associated with the polymer-polymer interface. The goal of this work is to have a numerical capability suitable for optimizing and troubleshooting the coextrusion process, circumventing flow instabilities such as ribbing and barring, and reducing variability in layer thickness. Though these instabilities can be both viscous and elastic in nature, for this work a generalized Newtonian description of the fluid is used. Models of varying degrees of complexity are investigated including stability analysis and direct three-dimensional finite element free surface approaches. The results of this work show how critical modeling can be to reduce build test cycles, improve material choices, and guide mold design.

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TYPE SAND Report YEAR 2011
OSTIDOI

Creation and characterization of magnesium oxide macroporous ceramics

Materials Engineering and Sciences Division - Core Programming Topic at the 2011 AIChE Annual Meeting

Mondy, L.A.; DiAntonio, Christopher D.; Chavez, Tom C.; Hughes, Lindsey G.; Grillet, Anne M.; Roberts, Christine C.; Ingersoll, David I.

We examine several methods to create a sheet of magnesium oxide (MgO) macroporous ceramic material via tape casting. These methods include the approach pioneered by Akartuna et al.1 in which an oil/water emulsion is stabilized by surface-modified metal oxide particles at the droplet interfaces. Upon drying, a scaffold of the self-assembled particles is strong enough to be removed from the substrate material and sintered. We find that this method can be used with MgO particles surface modified by short amphiphilic molecules. This approach is compared with two more traditional methods to induce structure into a green ceramic: 1) creation of an MgO ceramic slip with added pore formers, and 2) sponge impregnation of a reticulated foam with the MgO slip. Green and sintered samples made using each method are hardness tested and results compared for several densities of the final ceramics. Optical and SEM images of the materials are shown.

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TYPE Conference YEAR 2011
ScopusOSTI
Results 51–75 of 162
Results 51–75 of 162