Investigation Of Gas-phase Reactions Research Articles

Investigation of gas-phase reactions in the mixing region for hydrocarbon autothermal reforming applications

Mixture preparation technology plays a critical role in ensuring reformate quality during autothermal reforming of liquid fuels. Incomplete mixing can cause temperature overshoots and deposit formation within the catalyst bed. However, the time available for mixing is limited by unwanted gas-phase reactions that produce deposit precursors. We perform an analysis of the gas-phase reactions in the mixing region using a well-tested alkane oxidation mechanism taken from the literature. One particularly interesting prediction is that the time for significant reaction to occur does not monotonically decrease as the temperature increases. This is due to the negative temperature coefficient (NTC) kinetics. By mixing within the NTC temperature window, it should be possible to provide substantially more time for mixing. Similarly, one can expand the mixing time by suitable choices of mixture composition. These results provide important guidance criteria for the optimization of a mixer design to avoid undesirable reactions.

Investigation of Gas-Phase Reactions and Ignition Delay Occurring at Conditions Typical for Partial Oxidation of Methane to Synthesis Gas

Continuous-flow experiments in an empty aluminum oxide tube for the investigation of the homogeneous gas-phase reactions occurring at conditions typical for the partial oxidation of methane to synthesis gas were carried out at pressures from 300 to 800 kPa, temperatures from 1030 to 1300 K, inlet molar ratios of CH4/O2 from 2.1 to 3.1, and residence times from 0.09 to 0.38 s. The oxygen conversion varied from 3% to 43%. A detailed kinetic model based on a free-radical mechanism has been developed, which allows the adequate calculation of the feed conversions and product selectivities. The model includes pressure falloff effects occurring with the unimolecular reactions. The model reveals important features of the complex reaction network with the emphasis on the ignition stage at oxygen conversions between 0% and 5%. The occurrence of both isothermal ignition and thermal ignition can be distinguished in simulations with the model. The model was also used for estimating the ignition delays as a function of the process conditions.

Investigation of gas phase reactions of OH radicals with fluoromethane and difluoromethane using Ar-sensitized pulse radiolysis

Hydroxyl radical reactions were studied in gas phase CH 3F and CH 2F 2 systems using an Ar-sensitized pulse radiolysis-absorption spectroscopy technique. Bimolecular H-atom abstraction rate constants were determined empirically by fitting the observed OH decay data to a first-order law, then plotting the apparent first-order rate constants against substrate concentration. The resulting values of the bimolecular rate constants in cm 3 molec -1 s -1 are (1.71 ± 0.24) × 10 -14 for OH + CH 3F and (0.88 ± 0.14) × 10 -14 for OH + CH 2F 2. Both values are in good agreement with previous results. Kinetic modeling showed a substantial contribution of radical-radical reactions to OH loss in both cases, but the data reduction procedure was successful in distinguishing the contribution due to the bimolecular OH-substrate abstraction process. Observed and computer simulated OH decay curves match satisfactorily for typical experiments, using initial OH concentrations and OH abstraction rate constants which were within ± 10% of the measured values.

Mass spectrometric investigation of gas phase reactions during sublimation

The use of the high temperature mass spectrometric method for the investigation of the vaporization behavior of solids and the determination of thermodynamic properties of gaseous molecules is described. Recent results by this method are reviewed and the application as an auxiliary tool in kinetic studies of sublimation processes is illustrated. The application of high pressure mass spectrometric sampling in problems of crystal growth is projected.