Browsing by Author "Kumar, Gaurav"
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Item Enabling the selective conversion of biomass-derived oxygenates to C4-C5 dienes(2021-05) Kumar, GauravThe catalytic conversion of biomass-derived saturated furans over zeotype solid acids affords a potentially renewable route to access conjugated C4-C5 dienes — commodity monomers in tires, plastics, adhesives, and resins. A lack of fundamental understanding of reaction mechanisms and pathways coupled with existing trial-and-error catalyst design approaches have limited diene yields to <60%. Poor catalyst lifetimes, attributed to rapid coking typical for oxygenate conversion reactions, have also remained a challenge. Improving the diene yields and mitigating catalyst deactivation are the first key steps to engender industrial interest in the resulting process technology. In this dissertation,we first highlight the mechanistic details of the tandem-ring opening and dehydration of tetrahydrofuran (THF) to butadiene on the aluminosilicate H-ZSM-5, which enable the formulation of the relative ratio of C-O to C-C scission rates as the diene selectivity descriptor. By considering aluminum-, and boron-substituted zeolites in 2-methyltetrahydrofuran (2-MTHF) dehydration to pentadienes, we demonstrate the weakening of solid acid strength as a strategy to tune this descriptor towards dienes’ production. By exploiting the thermodynamic stability of the desirable C5 conjugated diene (1,3-pentadiene), we further explicate strategies harnessing diffusional hurdles to suppress the production of its non-conjugated isomer (1,4-pentadiene). Combined, these insights lead to ~30% improvement in 1,3-pentadiene yield. Having discovered the utility of mild solid acids, we focus the rest of the dissertation on investigating the broad implications of weak surface binding in dehydration catalysis. Using two distinct classes of solid acid zeotype materials with weak Brønsted acidity (namely, borosilicates, and phosphorous-modified zeosils), we detail how these materials can potentially improve dehydration selectivity and stability, albeit often at a cost of lower overall turnover rates. Tying this discussion back to renewable dienes production on these materials, we conclude this work by underscoring the technological and economic improvements still required to achieve competitive diene prices from this process technology.Item Supporting data for "Catalysis-in-a-Box: Robotic Screening of Catalytic Materials in the Times of COVID-19 and Beyond"(2020-05-29) Kumar, Gaurav; Bossert, Hannah; McDonald, Dan; Chatzidimitriou, Anargyros; Ardagh, Alexander M; Pang, Yutong; Lee, ChoongSze; Tsapatsis, Michael; Abdelrahman, Omar A; Dauenhauer, Paul; hauer@umn.edu; Dauenhauer, Paul, J; Dauenhauer Research GroupThe emergence of a viral pandemic has motivated the transition away from traditional, labor-intensive materials testing techniques to new automated approaches without compromising on data quality and at costs viable for academic laboratories. Reported here is the design and implementation of an autonomous micro-flow reactor for catalyst evaluation condensing conventional laboratory-scale analogues within a single gas chromatograph (GC), enabling the control of relevant parameters including reactor temperature and reactant partial pressures directly from the GC. Inquiries into the hydrodynamic behavior, temperature control, and heat/mass transfer were sought to evaluate the efficacy of the micro-flow reactor for kinetic measurements. As a catalyst material screening example, a combination of four Brønsted acid catalyzed probe reactions, namely the dehydration of ethanol, 2-propanol, 1-butanol, and the dehydra-decyclization of 2-methyltetrahydrofuran on a solid acid HZSM-5 (Si/Al 140), were carried out in the temperature range 403-543 K for the measurement of apparent reaction kinetics. Product selectivities, proton-normalized reaction rates, and apparent activation barriers were in agreement with measurements performed on conventional packed bed flow reactors. Furthermore, the developed micro-flow reactor was demonstrated to be about ten-fold cheaper to fabricate than commercial automated laboratory-scale reactor setups and is intended to be used for kinetic investigations in vapor-phase catalytic chemistries, with the key benefits including automation, low cost, and limited experimental equipment instrumentation.