Residence Time Distribution in Micro-Reactors - G. Jovanovic (Chemical Engineering)

Chemical kinetics, transport phenomena, fluid mixing, and contacting are the most important factors which determine yield and product distribution in any reactor vessel. Characteristic microreactor dimensions, in the range of 0.00001 to 0.001[m] open new possibilities for reaction pathways by achieving previously inaccessible residence times and heat transfer rates. Recent experimental studies have provided an increased understanding of fluid mechanics and heat transfer on the micro scale. Using microchannels as a reaction environment is a logical application of already existing capabilities in micro machining.

Our research focuses on the investigation of fluid mixing and contacting patterns in microreactor vessels. Residence time distribution (RTD) of a fluid which passes through the microreactor vessel contains the most comprehensive information about flow regime and the contacting pattern of reacting fluids.

Our objective is to explore different geometric configurations of microreactor vessels and to learn how to take advantage of the characteristic residence time distribution time in fluids in these vessels. In particular, we are interested in RTDs of different network configurations of microreactor vessels which are especially suitable for reaction processes with intermediate products.

Sonic Non-Adiabiatic Nozzle Valve (SNAN) - G. Jovanovic (Chemical Engineering)

One of the most important features in microscale chemical processing is a design of a micro-scale valve that can effectively control the flow of fluids in and out of micro-scale vessels in which unit operations and chemical reactions take place. For example, the operation of any particular reactor configuration network is entirely dependent on a successful control of fluid flow between tow adjacent reactor vessels.

In this research we investigate the use of the Sonic Non-Adiabatic Nozzle valve (SNAN) as a principle techniques for controlling the flow of fluids through a micro-scale vessel. An adiabatic sonic valve provides a simple, accurate flow guage which depends on the upstream pressure (P1) and the cross-sectional area of the nozzle alone as long as P2/P1< 0.5. However, the flow of fluids could be greatly influenced by a heat input q at the nozzle, thus converting the adiabatic nozzle into a SNAN valve operation.

SNAN does not have any moving parts and it can be produced at a much higher density than any other known micro-valve or device system. Theory indicates that with the aid of an adequate heat input, one can successfully control the mass flow rate of reactant gases.

Microscale Separations & Bioanalysis - V. Remcho (Chemistry)

Our research focuses on unraveling the mechanics of separations and applying separation techniques in bioanalytical chemistry and environmental analysis. The thrust of the research effort is in two areas: physical-analytical separation science and analyte/ligand interaction studies. Our efforts in the former focus on optimization of flow dynamics and mass transfer events in separations systems. In the latter, we study affinity-type separations and harness molecular recognition processes to achieve high selectivity separations and obtain information about molecular interactions.

The tools and techniques we are developing include capillary electrokinetic chromatography (CEC), capillary gel electrophoresis (CGE), capillary zone electrophoresis (CZE), and packed capillary high performance liquid chromatography (HPLC). These techniques offer several distinct advantages over more conventional separations techniques - including increased efficiency, high selectivity, and high peak capacity - which are allowing for new inroads to be made in the analysis of trace compounds in complex biological, pharmacological, and environmental matrices.

Capillary electrokinetic chromatography is an emerging separation technique in which mobile phase is electroosmotically pumped in a packed capillary HPLC column. Electroosmotic drive presents an effective means of reducing regional flow velocity inhomogeneities in packed liquid chromatographic columns, thereby minimizing zone spreading, which yields high efficiency and peak capacity. We have achieved even further efficiency enhancements by demonstrating the feasibility of perfusive (through-particle) electroosmotic transport. CEC may be used in combination with many different mechanisms of separation, yielding a variety of selectivities. Examples would include reverse-phase CEC, size exclusion CEC, and affinity CEC.

Molecular recognition processes are also of great interest to us, and are typified by the biospecific interaction of a ligand in the separation medium with an analyte (such as an enzyme, immunoglobulin, nucleic acid, or pharmaceutical agent). The interaction of the ligand and analyte results in a change in the migration or elution behavior of the analyte, which leads to separation. Ligands may be biological receptors, enzyme substrates, etc. An alternative approach to achieving molecular recognition is the employment of molecular-imprinted-polymer technology, in which a chromatographic sorbent is custom produced by polymerization around a template molecule. This ultimately yields a molecular "fingerprint" which is capable of interacting in varying degrees with molecules which are structurally similar to the template. These materials have applications in library screening and chiral separations.

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