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Arrhenius Parameters from ARC data

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Arrhenius Parameters from ARC data

John Belgrave

Calgary Alberta, Canada John Belgrave Posts: 121

The current graphical method for obtaining activation energy(ies) from Accelerating Rate Calorimeter data is inadequate. There appear to be no established guidelines for determining the appropriate regions on the self-heating rate curve to draw the Arrhenius straight lines. An interpretation framework needs to be (theoretically) developed that accounts for both the low temperature oxidation (LTO) and high temperature oxidation (HTO) regions of the data. Until this has been accomplished, the only acceptable way of inferring Arrhenius parameters would be history matching of the ARC data with nonlinear regression on formulated differential equations describing energy and mass conservation.

RE: Arrhenius Parameters from ARC data

Roy Drayton

Roy Drayton Posts: 2

It is true that the graphical method has limitations, since it it limited to singular reactive systems. However, it can be a very powerful tool even with sequential coupled reactions, provided that each reactive systems is isolated firstly. I developed a method for interpreting singular reactions from overlapping and sequential reaction systems from ARC data. For example in oxidation of oil, the ARC can exibit two oxidative states: LTO and HTO. However, when analyzing the data by ARC or other adiabatic calorimetry for example, it is important to isolate each region and study each region separately. A. So for the LTO phase. There is an onset temperature (To1) and a final temperature (Tf1). The thermal inertia of the system, as we know is defined as phi-factor, f. the psuedo-rate constant can be described as: The zero order k' = (dT/dt)i/{DTad*[(Tf -Ti)/DTad)]^n}. n is the order. By varying n, the k' can eventually have a linear profile. The procedure is repeated for the second oxidation period, i.e. HTO and so on (if there was a third oxidation period). Thus isolate the data only for HTO2 within To2 and Tf2. For Systems where the oxidative profile overlap is a little more complex. However, the problem can be address by plotting Eqn of State, P vs. T. For any gas generating chemical system, the relationship is linear. (NB. of course, the presence of solvent makes the linearity deviate to a slightly curvilinear relationship. However, the general concept is understood. thus, for over the regions where P vs. T is linear with a given slope, defines a chemical region. If multiple slopes are observed each with different gradients, then multiple singular reactions occurred. Select the linear regions, i.e. from Toi to Tfi, where i represents each reaction profile. Then repeat the procedure described in section A.

Post updated at Thursday 24th of January 2013 5:21:05 PM.

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