http://nova.newcastle.edu.au/vital/access/services/Feed ${session.getAttribute("locale")} 5 http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:9804 A detailed reaction mechanism is developed and used to model experimental data on the pyrolysis of CHF₃ and the non-oxidative gas-phase reaction of CHF₃ with CH₄ in an alumina tube reactor at temperatures between 873 and 1173 K and at atmospheric pressure. It was found that CHF₃ can be converted into C₂F₄ during pyrolysis and CH₂=CF₂ via reaction with CH₄. Other products generated include C₃F₆, CH₂F₂, C₂H₃F, C₂HF₃, C₂H₆, C₂H₂ and CHF₂CHF₂. The rate of CHF₃ decomposition can be expressed as 5.2 x 10¹³[s⁻¹]e−295[kJmol⁻¹]/RT. During the pyrolysis of CHF₃ and in the reaction of CHF₃ with CH₄, the initial steps in the reaction involve the decomposition of CHF₃ and subsequent formation of CF₂ difluorocarbene radical and HF. It is proposed that CH₄ is activated by a series of chain reactions, initiated by H radicals. The NIST HFC and GRI-Mech mechanisms, with minor modifications, are able to obtain satisfactory agreement between modelling results and experimental data. With these modelling analyses, the reactions leading to the formation of major and minor products are fully elucidated. 2012-01-13T03:50:04.116Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:9797 The catalytic activity of activated carbon (AC) and activated carbon supported potassium for the decomposition of CHF₃ was investigated at temperatures between 873 and 1173 K and at a space velocity of 4300 h⁻¹. It is found that activated carbon supported potassium shows high and relatively stable activity during the pyrolysis of CHF₃ under the conditions studied. Compared with the gas phase reaction, the conversion of CHF₃ increases by up to 10 times between 873 and 1123 K, with the major products being C₂F₄ and C₃F₆. Selectivities as high as 55% to C₂F₄ and 35% to C₃F₆ are achieved under optimum conditions. The main byproduct HF readily reacts with K₂O in the catalyst, converting the catalyst from K₂O/AC into KF/AC. Selectivity to the major products remains relatively constant following this transformation. 2012-01-12T23:10:05.802Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:9353 Dry reforming of hydrocarbons is accompanied by carbon deposition making it difficult to unambiguously estimate the true reaction metrics (rate constant, yield and selectivity) without the masking effect of coke formation. This study employed a method originally proposed by Levenspiel to determine the intrinsic reaction rate simultaneously with the carbon-induced deactivation coefficient from transient rate data over an extended period of time (up to 72 h), for propane dry reforming over a Co–Ni catalyst at 823–973 K. The rate constant k′ and deactivation coefficient, kd were determined from a fit of the concentration history data to the hyperbolic reaction–deactivation model for 1st-order kinetics in a plug flow reactor. However, the product H₂:CO ratio was generally invariant with time over the 3-day period for different CO₂:C₃H₈ feed ratio values (4–7) but remained within a band of between 0.4 and 0.6. Both k′ and kd exhibited a negative order dependency on the CO₂:C₃H₈ ratio at −0.575 and −2.39, respectively. Arrhenius treatment of these two reaction metrics also yielded activation energy estimates of 92.3 and 164.4 kJ mol⁻¹ for the true reforming reaction and deactivation process, respectively. Catalyst characterization was carried out using XRF, liquid N₂ adsorption, XRD, H₂ chemisorption, temperature programmed desorption of NH₃ and CO₂, temperature-programmed reduction (with H₂) and oxidation (with air) as well as solid TOC content analysis. 2011-11-13T23:10:03.941Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:3300 Conversion of halon 1211 has been studied over γ-Al₂O₃ and supported 0.5% Pd catalysts (Pd/Al₂O₃, Pd/fluorinated Al₂O₃, Pd/AlF₃, Pd/Al₂O₃ pretreated with CH₄ and CHClF₂). The experiments were performed in the temperature range of 443–523 K, in a tubular alumina reactor. The temperature of the reactor was maintained uniformly by a three zone furnace. The reaction products were quantified with a micro gas chromatograph and identified with a gas chromatograph–mass spectrometer. The catalysts were characterised with XRD diffractometry and the content of halogen on the catalysts was determined with an ion chromatograph. The measurements were presented in terms of the conversion of halon 1211 and product selectivity, as functions of catalyst type, catalyst time on stream and composition of inlet gases. Transformation of Pd to Pd carbide is observed in the CH₄ treated Pd/Al₂O₃, but not in the CHClF₂ treated Pd/Al₂O₃ in which case Al₂O₃ was partially fluorinated. In the absence of hydrogen, the conversion of halon 1211 over Al₂O₃ and Pd/Al₂O₃ gives a similar product profile and the reactions follow a heterogeneous halogen exchange reaction pathway, which takes place on the positively charged aluminum ions. Introduction of hydrogen has no apparent effect on either halon 1211 conversion level or the product profile during the conversion of halon 1211 over Al₂O₃. Over supported Pd catalysts, major products are hydrogenated species which include CH₂F₂, CH₄, C₂H₆, C₃H₆, CH₃Br and CHF₃. The most striking feature of the hydrodehalogenation reactions is the increasing CH₂F₂ selectivity with time on stream, especially on Pd/Al₂O₃ and the CH₄ treated Pd/Al₂O₃. The changing selectivity during the catalytic hydrodehalogenation reactions is mainly ascribed to the interaction of support with Pd. 2010-04-27T05:07:31.491Z ]]>