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Bimolecular rate coefficients were determined for the reaction CN(v=1) + NO and O2 using continuous wave cavity ringdown spectroscopy in a uniform supersonic flow (UF-CRDS). The well-matched timescales for ringdown and reaction under pseudo first-order conditions allow for the use of the SKaR method (simultaneous kinetics and ringdown) in which the full kinetic trace is obtained on each ringdown. The reactions offer an interesting contrast in that the CN(v=1) + NO system is nonreactive and proceeds by complex-mediated vibrational relaxation, while the CN(v=1) + O2 reaction is primarily reactive. The measured rate coefficients at 70 K are (2.49 ± 0.08) × 10-11 cm3 molecule-1 s-1, respectively, for the reaction of O2 and (10.49 ± 0.22) × 10-11 cm3 molecule-1 s-1 for reaction with NO. The rate for reaction with O2 is a factor two lower than previously reported for v=0 in the same temperature range, a surprising result, while that for NO is consistent with extrapolation of previous high temperature measurements to 70 K. The latter is also discussed in light of theoretical calculations and measurements of the rate constants for the association reaction in the high-pressure limit. The measurements are complicated by the presence of a metastable population of high-J CN formed by photolysis of the precursor BrCN, and a kinetic model is developed to treat the competing relaxation and reaction. It is particularly problematic for reactions at low temperature where the rotational relaxation and reaction have similar rates, precluding a reliable determination of the rate coefficients at 30 K. Also presented are important modifications to the data acquisition and control for the instrument that have yielded considerably enhanced stability and throughput.
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Investigation of Biomass Char Gasification Kinetic Parameters Using a Novel Miniaturized Educational System
A novel miniaturized, transparent reactor system for use as either a research or educational tool was developed for investigating biomass char gasification with oxygen to determine the kinetic parameters. Parametric temperature and pressure data taken can be used to distinguish the validity of assumptions inherent in the Avrami, the random pore (RPM), the unreacted core shrinking (UCSM), and a UCSM hybrid models (HM). The results demonstrate the UCSM for spherical and cylindrical geometries, and an HM variation with a best-fit exponent, that yields residual sums of squares 2 to 4 orders of magnitude lower than other models. An Arrhenius evaluation yielded an activation energy of 84.8 kJ/mol and pre-exponential factor of 1.34 103 s-1. An O2 reaction order of 0.85 indicates O2 adsorption on the char surface is the primary rate-controlling step. Data are consistent with a rapidly decreasing surface area as the reaction nears completion, suggesting available corresponding active sites for rapid chemisorption decrease as the reaction progresses. More importantly, the design of the system is safe to take into the classroom while simultaneously allowing students to view real-time reactions and produce repeatable data; this pushes the bounds on classroom interventions and learning.
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- PAR ID:
- 10119279
- Date Published:
- Journal Name:
- Bioresources
- Volume:
- 14
- Issue:
- 2
- ISSN:
- 1930-2126
- Page Range / eLocation ID:
- 3594-3613
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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