example i want to study the degradation of thermal labile compounds at elevated temperature. from literature survey, i found that the kinetic of degradation involves cumulative yield against time. but based on my understanding if we used cumulative then the yield is not consider as degrade but reduce from the initial values at each interval time. lets consider if i run the process in a batch system ( each time i use different sample) and at certain time the yield is degraded after reaching optimum. can i apply kinetic of degradation such as weibull equation?. thank you in advance.
I would like to help, but your question is not clear to me. However, if your temperature is below 150C, isothermal microcalorimetry provides an excellent means for following relatively slow reactions of any kind in real time (reactions that take place over hours or days).
The integral (area under the curve) of heat produced by the reaction vs. time is proportional to the cumulative product of the reaction. The data (cumulative heat vs. time) is stored as a computer file and can be evaluated by curve-fitting software of your choice to see what equation (or sequence of equations) describes it best.
See: https://en.wikipedia.org/wiki/Isothermal_microcalorimetry
hi,
it depends on the shape of the kinetic curve of degradation. typically 3 cases:
- linear with time (e.g hydrolysis or radiolysis) : cumulative
- autoaccelarated (e.g. thermal oxdation of PP): the yield of oxidation after 200 h (for instance) is not necessarily equal to twice the yield after only 100 h
- auto slowing down process (e.g. thermal oxidation of epoxy, polyamides...) : the yield of oxidation after 200 h is higher than twice the yield of oxidation after 100 h.
regards
Hi,
From simple kinetics, the curve for yield vs time is somewhat opposite in shape to that of reactant decomposition vs time. When a compound degrades it changes into one or more compounds, so the build up of one of the products can be monitored with time. The cumulative yield vs time for kinetic studies, as I understand it, can only be applied if the product of degradation is ONE.
Thanks
Hi Ilia,
kinetics of decomposition and the determination of the degree of conversion depends much also on the technique you apply. Foe example, if you study thermooxidation of organic materials, you can use the determination of peroxide value. This value increases practically immediately after beginning of the proces. On the other hand, if you use thermoanalytical techniques (DSC, TG), thermooxidation has at least two stages: (i) induction period where practically no heat evolved (DSC) or mass loss (TG) is registered; (ii) the main oxidation stage. You can also folow the thermooxidative degradation by the determination of the reaction products - again, the kinetics may be different.
Best regards,
Peter Simon.
One thing worth noting about induction periods in rate processes: they have two possible meanings. One is that there is some kind of preparatory process taking place. The other is that the process is at first just below the detection limit of the method used to measure the on-going process.
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