Loading...
Please wait, while we are loading the content...
Similar Documents
Kinetic Investigation of the Reactions of 2 , 5-Dimethylfuran and 2-Methylfuran with Hydroxyl Radicals
| Content Provider | Semantic Scholar |
|---|---|
| Author | Eble, J. F. Bänsch, Cornelie Olzmann, Matthias |
| Copyright Year | 2015 |
| Abstract | The rate coefficients for the reactions of 2,5-dimethylfuran (DMF) + OH and 2-methylfuran (MF) + OH were experimentally determined in a slow-flow reactor in a pressure range of 7–21 bar (helium as bathgas). The OH radicals were produced by laser flash-photolysis of nitric acid and detected time-resolved by laser induced fluorescence. The rate coefficients determined show a non-Arrhenius temperature dependence; two different regimes can be distinguished. In the first regime the temperature dependence can be described by the following Arrhenius expressions: kOH+DMF = (3.38 ± 1.0) × 10 exp(219 K/T) cm s (T = 295–350 K, P = 7–21 bar) and kOH+MF = (1.23 ± 0.37) × 10 exp(500 K/T) cm s (T = 295–350 K, P = 13–21 bar). Above 350 K a much more pronounced decrease of the rate coefficient with temperature was found. The overall behavior may be explained by non-reversible addition of the OH radical in the first regime and reversible addition in the second regime. Introduction Diminishing fossil fuel reserves and growing concerns about global warming indicate that sustainable energy sources are increasingly needed. A promising biofuel candidate is 2,5-dimethylfuran (DMF), which can be produced from biomass, in particular from crops not destined for human nutrition, via catalytic routes [1]. Compared to ethanol, which is currently the most widely used biofuel, DMF has several advantages as e. g. a larger energy density, a higher boiling point and its low solubility in water [2]. DMF and 2-methylfuran (MF) are directly emitted into the atmosphere from incomplete combustion of fossil fuels, waste and, in particular, from biomass burning [3]. Furthermore, furan derivatives are known to be produced during photooxidation of hydrocarbons [4]. In the atmosphere, their chemical degradation is mainly initiated by reaction with OH radicals. Moreover, fuel + OH reactions are of particular importance in low-temperature combustion. Bierbach et al. [5] and Aschmann et al. [6] have already published experimental studies for the reactions of DMF + OH and MF + OH. Both groups of authors determined the rate coefficients at room temperature and around 1 bar using a relative rate method. The temperature dependence was not measured. Moreover, Zhang et al. [7] carried out quantum chemical calculations on the reaction of OH with MF using several compound methods. They characterized two kinds of reaction pathways including the direct hydrogen abstraction channels and the association channels forming 2-methylfuran-OH adduct. The potential energy surface indicates that an addition mechanism to the double bond is likely for this reaction, and a negative temperature dependence of the rate coefficient is predicted. In this work, we report on experiments at 295–560 K for DMF + OH and 295–410 K for MF + OH in a pressure range of 7–21 bar. We discuss mechanistic aspects and give parameterizations of temperature dependence suitable for modeling purposes. Experimental Section The experimental setup will be only briefly introduced, because it has been described in detail elsewhere [8-13]. The experiments were carried out in a slow-flow reactor by using pulsed laser-photolytic production of OH radicals and pulsed laser-induced fluorescence detection of OH under pseudo-first order conditions in helium as bath gas. Intensity-time profiles of the fluorescence of OH were recorded by changing the delay time between the photolysis and probe laser pulses in steps of 0.2 μs. The reactor was a T-shaped stainless steel cell with three quartz windows and an external resistance heating. The temperature was measured at the inlet and outlet of the cell with NiCr-Ni thermocouples. In each case, the temperature differences between these two thermocouples never exceeded 4 K. As reaction temperature the average of these temperatures was taken. In order to avoid accumulation of reaction products, the flow velocities were controlled with a mass flow controller. The chosen conditions assured that the complete content of the cell was exchanged between successive runs. The precursor of OH radicals was nitric acid, which was photolyzed with a KrF-excimer laser at a wavelength of 248 nm. For OH detection, a XeCl-excimer laser operated at 308 nm was used to pump a dye laser (Coumarin 153) whose output was frequency-doubled with a BBO crystal. The non-resonant fluorescence of OH at 308 ± 7.5 nm was detected perpendicular to the photolysis and probe laser beam with a photomultiplier. In order to minimize scattered light, other wavelengths were filtered out with a monochromator. The time delay between photolysis and probe laser was set by a delay generator. For each given delay, ten measurements were recorded and automatically averaged. The repetition rate was 10 Hz. |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | http://www.ecm2015.hu/papers/P1-06.pdf |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
