A compact photomicroreactor design for kinetic studies of gas-liquid photocatalytic transformations

A compact photomicroreactor assembly consisting of a capillary microreactor and small-scale LEDs was developed for the study of reaction kinetics in the gas-liquid photocatalytic oxidation of thiophenol to phenyl disulfide within Taylor flow. The importance of photons was convincingly shown by a suction phenomenon due to the fast consumption of oxygen. Mass transfer limitations were evaluated and an operational zone without mass transfer effects was chosen to study reaction kinetics. Effects of photocatalyst loading and light sources on the reaction performance were investigated. Reaction kinetic analysis was performed to obtain reaction orders with respect to both thiophenol and oxygen based on heterogeneous and homogeneous experimental results, respectively. The Hatta number further indicated elimination of mass transfer limitations. Reaction rate constants at different photocatalyst loadings and different photon flux were calculated. Furthermore, the advantages of this photomicroreactor assembly for studying gas-liquid photocatalytic reaction kinetics were demonstrated as compared with batch reactors. This article is protected by copyright. All rights reserved

A microreactor system for high-pressure, multiphase homogeneous and heterogeneous catalyst measurements under continuous flow

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2011.Cataloged from student-submitted PDF version of thesis.Includes bibliographical references (p. 194-206).The shift towards biomass and lower quality fossil fuel feedstocks will require new conversion approaches. Catalysis will be critical in the processing of these new feedstocks. By studying catalysis at industrially relevant conditions, it may be possible to reduce the time and cost of developing new catalyst systems. Microreactors enable the study of multiphase catalyst systems at pressures that were previously difficult to attain on the laboratory scale. The reduced length scales, characteristic of microchemical systems, provide additional benefits such as enhanced heat and mass transfer and a reduction of hazardous waste. The improved heat and mass transfer allow for kinetics to be probed at isothermal conditions in the absence of complicating mass transfer effects. A high-pressure microreactor system for catalyst study was designed, fabricated, and tested. The system allows for the multiphase study of homogenously and heterogeneously catalyzed systems, with a unique reactor designed for each application. A multicomponent gas phase is delivered simultaneously with a liquid stream, resulting in regular segmented (slug) flow. The isobaric system is operated at pressures of up to 100 bar. Gas and liquid flow rates, and therefore residence time, are specified independently of pressure. The system is capable of being operated at temperatures of up to 350°C and residence times of up to 15 minutes. Inline analysis, using an attenuated total reflection FTIR flow cell, and sample collection for offline analysis can be performed simultaneously. Both homogeneous and heterogeneous catalysis were demonstrated in the high-pressure system. A kinetic expression was derived for the homogeneous hydroformylation of terminal alkenes, catalyzed by Wilkinson's catalyst. The empirical reaction orders for the dependence on catalyst, hydrogen, and carbon monoxide were determined, along with the activation energy and pre-exponential factor. These results were then reconciled with a mechanistic model. The hydrogenation of cyclohexene over platinum catalysts was chosen to demonstrate the performance of the heterogeneous reactor. This reaction proceeded rapidly allowing mass transfer to be characterized in the microreactor. Observed mass transfer rates were two orders of magnitude higher than in traditional systems.by Jaroslav Keybl.Ph.D

Estimation of Two Closely Spaced Frequencies Buried in White Noise Using Linear Programming

Linear programming is used to estimate the spectrum of two sinusoids signals closely-spaced in frequency buried in deep white gaussian noise by employing a-priori knowledge of the spectrum. The method will be illustrated by a number of examples.</jats:p