CNIE contributes to 2015 AIChE Annual Meeting, Salt Lake City USA, November 8-13, 2015

15 October 2015

The AIChE Annual Meeting is the premier educational forum for chemical engineers interested in innovation and professional growth. Academic and industry experts will cover wide range of topics relevant to cutting-edge research, new technologies, and emerging growth areas in chemical engineering.

As usual, CNIE will be actively participating in the event:

Pattern Formation in Fluidized Beds and Vertically Vibrated Granular Layers: Similarities and Differences

Monday, November 9, 2015: 4:39 PM

254C (Salt Palace Convention Center)

Lilian de Martín, Department of Chemical Engineering, University College London, London, United Kingdom and Marc-Olivier Coppens, Chemical Engineering, University College London, London, United Kingdom


Gas-solid fluidized beds can form dynamical patterns when fluidized with a pulsed flow under certain experimental conditions. In shallow 3D beds, the surface oscillates forming stripes, squares, and hexagons, with a length-scale that depends on the frequency of the pulsed flow. These structures are sub-harmonic and resemble those formed on the surface of vertically vibrated beds in vacuo, suggesting a common mechanism, namely, parametric resonance. In bubbling quasi-2D beds, the pattern formation manifests itself as regular bubble patterns, where bubbles are generated in alternating positions at every pulse and rise, forming vertical hexagonal configurations.

Pattern formation excels as a method to structure fluidized bed dynamics and has great potential to facilitate fluidized bed scale-up; however, it has remained highly unexplored and is far from being understood. Furthermore, opposite to pattern formation in vibrated systems in vacuo, which has been successfully simulated, computational fluid dynamics has not been able to reproduce the experimental patterns in fluidized beds so far [1].

In this contribution, we discuss our last insights on pattern formation in fluidized beds obtained by new experiments and simulations, and comparison with pattern formation in vibrated systems. Similarities and differences between these two systems, i.e., onset to the pattern, boundary effects, hysteresis, driving parameters, and transients, will be discussed.

[1] K. Wu, L. de Martín, L. Mazzei, and M.-O. Coppens. Submitted to Powder Technology


The Nanoscale in Chemical Reaction Engineering: From Analysis to Design

Monday, November 9, 2015: 3:15 PM

355F (Salt Palace Convention Center)

Marc-Olivier Coppens, Chemical Engineering, University College London, London, United Kingdom


Spectroscopy and microscopy, combined with quantum chemical and statistical mechanical calculations, provide increasingly detailed insights into active sites, catalytic mechanisms and kinetics. Many catalysts are nanoporous materials, or employ a nanoporous support, with a network of broader meso- and macropores to reduce diffusion limitations and mitigate effects of catalyst deactivation.

Novel synthesis methods increasingly enable us to realize hierarchically structured porous catalysts or supports with controlled pore sizes, topology and morphology at multiple length scales, as well as supported catalytic species of a controlled structure (varying from nanoparticles to enzymes and metal-organic complexes with tuned chemical structures). A chemist’s dream is to control both the chemical and the geometrical architecture of catalysts with atomic resolution. However, from a chemical engineering point of view, it is especially valuable to learn which structural features matter most and are robust enough to be applied in a scalable manner within the constraints of an industrial chemical reactor.

Besides innovation at the atomistic scale (e.g., the composition of nanoparticle clusters or new microporous catalytic frameworks), there are nanoscale effects that can be engineered to achieve higher catalytic performance. We discuss a few, focusing on nano-confinement effects in supported enzyme and metal-organic catalysis; surface roughness; and the effects of grain boundaries in zeolite catalysis.


Hierarchical Carbon-Based Electrode Materials for Vanadium Redox Flow Batteries

Tuesday, November 10, 2015: 4:35 PM

251F (Salt Palace Convention Center)

Panagiotis Trogadas, Tobias Neville, Dan Brett, Paul Shearing and Marc-Olivier Coppens, Chemical Engineering, University College London, London, United Kingdom


Hierarchical Carbon-based Electrode Materials for Vanadium Redox Flow Batteries

P. Trogadas, T.P. Neville, D.J.L. Brett, P.R. Shearing, and M.-O. Coppens

Centre for Nature Inspired Engineering and Electrochemical Innovation Lab, Department of Chemical Engineering, University College London, Torrington Place London WC1E 7JE United Kingdom.

The demand for efficient energy storage has necessitated the search for novel electrode materials for energy storage devices, such as the vanadium redox flow battery (VRFB). 1 To maximize storage capacity and kinetics during charge and discharge cycles, electrode materials must have large surface area, high electronic and ionic conductivity as well as long-term stability. Hierarchical nanostructured electrode materials have attracted much attention nowadays due to their unique properties compared to bulk materials; the interconnectivity between pores of different sizes and the high surface area results in improved diffusivity and utilization of reactants and thus improved battery performance. Key geometric characteristics of meso / nanoporous carbon based materials will be presented along with their synthesis technique and activity / stability measurements. Using a combination of micro-tomography (CT) measurements of voltage-cycled graphite felts (over ca. 30 charge / discharge cycles), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS) measurements of the same felt electrode, the first description of micro-structural evolution processes occurring in VRFB felts during operation is provided.

References

1. A. Weber et al., J. Appl. Electrochem., 41, 1137 (2011).


A Nature-Inspired Approach to the Confinement and Control of Catalytic Active Sites

Wednesday, November 11, 2015: 4:15 PM

355C (Salt Palace Convention Center)

Michael M. Nigra and Marc-Olivier Coppens, Department of Chemical Engineering, University College London, London, United Kingdom


The location of the active site in a catalytic material, specifically the environment that surrounds the active site, often directly influences the activity and selectivity of a catalyst. The best examples of this environmental control of the active sites are found in enzymatic systems where the active site is located in an environment in which there is control of electrostatic interactions, precise placement of chemical functional groups, and control of hydrophobicity/hydrophilicity, as some common examples.

Using inspiration from the GroEL/GroES system in E. coli, a catalyst has been synthesized where rhodium complexes have been immobilized inside of a mesoporous support material, such as SBA-15. In catalytic tests of 1-octene hydroformylation, these nano-confined sites in an inorganic support demonstrate an increased degree of activity and stability, which provide insight into structure-function relationships in catalysis.[1] Additional catalytic examples of using nano-confined Rh complexes will also be presented.

Another bio-inspired method of nano-confinement is demonstrated using a shell of organic ligands as the confining medium around the active site. Examples using calixarene ligands bound to small gold clusters where the accessibility to the surface, cluster stability against agglomeration, and electronic tunablity are controlled by the bound calixarene ligand are demonstrated. [2, 3] Additional examples of the synthesis, characterization, and catalytic activity of noble metal clusters confined in shells of different organic ligands including the use of enzymes as ligands will be discussed. [4] These approaches to nano-confinement of active sites enable a greater understanding of the site requirements for reactions as well as the development of novel approaches to control catalysis on metal cluster surfaces.

References

1. F. Marras, J. Wang, M.-O. Coppens, J. N. H. Reek. Chem. Commun. 2010, 46, 6587.

2. N. de Silva, et al. Nature Chem. 2010, 2, 1062.

3. M. M. Nigra, et al. Dalton Trans. 2013, 42, 12762.

4. M. M. Nigra, et al. Catal. Sci. Technol. 2013, 3, 2976.

To See a World in a Grain of Sand

Thursday, November 12, 2015: 9:20 AM

254C (Salt Palace Convention Center)

Marc-Olivier Coppens, Chemical Engineering, University College London, London, United Kingdom


The dynamics of even modest sand particles still hold many surprises. When air is intermittently blown over sand, meso- and macroscopic structures appear, most magnificently witnessed in the structure of dunes and regularly spaced, striped patterns. Blow air through sand in a column, and a chaotic bubble stream appears above the minimum fluidization velocity of the sand particles. Yet, this same bubble stream becomes remarkably regular when the airflow is pulsed within a range of amplitudes and frequencies. A thin layer of sand on a vertically vibrated plate also forms regular patterns, and similar patterns form when the plate is not vibrated but porous and fluidized under the influence of an oscillating gas flow, again within a continuous range of frequencies.

Our most recent experiments and simulations are revealing new insights in these phenomena. Generally speaking, the patterns are a result of dynamic perturbation of a system out of equilibrium; they represent nonlinear resonance in a dissipative system. However, this generalized description does not tell us when which pattern forms, how stable it is, and how it is influenced by boundary conditions, gas-solid and solid-solid interactions. Conventional two-fluid models do not reproduce the experimentally observed patterns, likely because the long force-chains between particles are not properly accounted for in the two-phase closures of the (Eulerian-Eulerian) two-fluid model. Multiscale models that include discrete particles (a Lagrangian-Eulerian description) are required.

Interestingly, at much smaller length scales (about seven orders of magnitude smaller!), similar patterns are observed in the ordered pore structure of sub-micron sized nanoporous silica particles made by a process involving soft templating in an aerosol reactor. The particles form within seconds when a solution including tri-block copolymer micelles and silica precursors is sprayed through a tubular oven. Ordered polymer-silica composite particles form by evaporation induced self-assembly (EISA). After calcination of the polymeric phase, a regular array of pores emerges instead of the ordered polymeric phase. When a single, spherical particle of mesoporous silica produced in this way is observed by electron tomography, it reveals patterns that compromise between hexagonal order and the spherical surroundings, very similar to the self-assembled structures generated in the fluidized sand, but “frozen” in time. The details of the underlying system are no doubt different, but energy minimisation under constraints leads to very similar structures.

One can really see a world in a grain of sand.


Protein Confinement in Mesoporous Silica – Effects of Surface Curvature Investigated By Neutron Scattering and Catalysis

Thursday, November 12, 2015: 4:15 PM

253A (Salt Palace Convention Center)

Justin Siefker1, Margarita Krutyeva2, Michael M. Nigra1 and Marc-Olivier Coppens1, (1)Department of Chemical Engineering, University College London, London, United Kingdom, (2)JCNS-1/ICS-1, Jülich Centre for Neutron Science, Julich, Germany


Confinement of biomolecules in structured mesoporous materials offers advantages in both biological and synthetic systems1. The application of these systems spans a diverse range of purposes, from industrial production of biofuels to laboratory-on-a-chip diagnosis and controlled drug delivery. Therefore, it is necessary to develop a fundamental understanding of biomolecular confinement. Our previous studies on confinement effects in the ordered mesoporous silica, SBA-15, which contains a hexagonal array of cylindrical pores with tunable diameter, have shown that geometric properties, such as pore surface curvature, and physicochemical properties, such as electric charge and hydrophobicity, play a significant role in the stability of the confined protein 2and that these effects differ from proteins immobilized on the external surface of nanoparticles. High surface curvature, in particular, was shown to have a dramatic stabilization effect for the model proteins. This stabilization was most evident when comparing the secondary structure and extraordinary enzymatic activity of the confined protein samples. Expanding on these results, we have studied the structural and packing effects of curvature using the SBA-15 immobilized myoglobin and lysozyme model proteins with small angle neutron scattering. Additionally, we investigate these model proteins while confined in mesoporous materials with different pore network topologies and pore morphology, with a focus on enzymatic activity, loading capacity, and structural changes.

References:

  1. Siefker J, Karande P, Coppens M-O. Packaging Biological Cargoes in Mesoporous Materials: Opportunities for Drug Delivery. Expert Opin Drug Deliv. 2014 Nov;11(11):1781-93
  2. Sang L-C, Coppens M-O. Effects of surface curvature and surface chemistry on the structure and activity of proteins adsorbed in nanopores. Phys Chem Chem Phys. 2011;13(14):6689
CNIE contributes to 2015 AIChE Annual Meeting, Salt Lake City USA, November 8-13, 2015