news of the week OCTOBER 28, 2013 EDITED BY WILLIAM G. SCHULZ & SOPHIA L. CAI
TAKING REACTOR TEMPERATURES NMR THERMOMETRY: New method could fine-tune product output and energy efficiency F RESEARCHERS COULD ONE DAY look inside
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equipment and subject the sample to a nonuniform magnetic field as is commonly done in NMR experiments. As cool gas molecules move sluggishly through the nonhomogeneous field, they experience a broad distribution of field strengths that “read” as broad NMR line widths, Bouchard explains. In contrast, hot gases zip around quickly, causing those molecules to experience a narrowly defined average field strength, which reads as sharper line widths. These temperature-based changes in line width, then, can be used to measure temperatures inside the reactor.
LOUIS-S BOUCHARD/UCLA (BOTH)
working reaction vessels to see and precisely meaFEEL THE HEAT As propylene and hydrogen flow (left to right) through a sure a variety of aspects of chemical reactions as millimeter-diameter reactor packed with platinum particles and form propane, they occur, that knowledge could transform many iman NMR thermometry method maps the gas portant industrial processes. It would allow engineers to customize reactor geometry and dimensions and tai- temperature. Yellow and red regions are hottest; blue regions lor catalyst distribution to maximize energy efficiency, are coolest. product output, and chemical selectivity. That day may be at hand. A team of researchers led by University of California, Los Angeles, chemists Nanette N. Jarenwattananon and Louis-S. Bouchard has developed a rudimentary method for peering inside reactor vessels while they are running and measuring the temperature of gases involved in the process under way. The technique, based on nuclear magnetic resonance imaging, is noninvasive and provides thermal In a proofmaps with millimeter spatial and high thermal resoluof-concept test, tion (Nature 2013, DOI: 10.1038/nature12568). the team fashioned a millimeter-diameter This NMR technique could be the breakthrough that reactor filled with precious-metal catalyst and gives researchers a tool, based on familiar technology, monitored NMR signals as propylene and hydrogen to monitor reactants as they flow flowed through the tube and reacted past catalysts and turn into products, to form propane. As a result of the reBouchard says. They would be able action energetics, the positions of the to pinpoint where within a reactor inlet and outlet, and the nonuniform the chemistry takes place and which distribution of catalyst particles, the regions are chemically hot and which gas temperature varied widely across are not, he says. the reactor. Those variations were In many industrial reactors, such readily identified by the new method. as those used in petrochemical refin“This robust NMR method for 3-D ing, chemistry occurs at the interface imaging of gas temperatures with milbetween gas-phase reactants and limeter precision opens many new solid catalysts. Researchers have possibilities for in situ investigations tried to develop optical probes and of catalytic reactors,” says University various kinds of sensors to monitor of Washington, Seattle, catalysis speheat and gas flow inside reactors, cialist Charles T. Campbell. He adds but these devices work poorly inside that the technique provides a powerful An NMR thermometry method equipment that is packed with solid new way to validate complex but apcan probe variations in gas catalysts, and in some cases the temperature with high thermal proximate mathematical models of and spatial resolution as monitoring apparatus can perturb reactors that combine kinetics, therpropylene (purple) and hydrogen modynamics, heat transfer, and fluid the flow of reactants and products. (yellow) react to form propane The UCLA group developed the mechanics. “Such models are essential (blue) as they flow through a new NMR thermometry method to porous metal-organic framework for designing and optimizing indussidestep all of those problems. They trial catalytic reactors,” Campbell loaded with palladium place the reactor inside the NMR nanoparticles. says.—MITCH JACOBY CEN.ACS.ORG
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OCTOBER 28, 2013
