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Title: The N-oxidation of alkylpyridines using isothermal calorimetry
Author: Gao, Jun
ISNI:       0000 0001 3487 9429
Awarding Body: University of Leeds
Current Institution: University of Leeds
Date of Award: 2006
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In the recent years, the legislation related to the safety of industrial processes has become more rigorous and demanding than in the past. The design of inherently safe processes is currently' viewed as a necessary target of the engineering discipline (Gupta and Ed~ards, 2002).. Alkylpyridines and their N-oxides are being used widely as intermediates and final products in the Phannaceutical Industry. Under typical industrial conditions the N-oxidation reaction is performed catalytically, in the liquid phaSe in a semi-batch mode. Hydrogen peroxide is used as the oxidising agent. It is dosed over the alkylpyridine-catalyst mixture over a period of time. The desired N-oxidation is accompanied by one only additional reaction, the lpldesired decomposition ofhydrogen peroxide. The catalytic N-oxidation of selected picolines, lutidines and collidines were performed in an HEL SIMULAR® lL calorimeter at conditions very close to the industrial'ones, following a certain procedure. The catalytic decomposition of hydrogen peroxide alone, under the same conditions was also studied. A sensitive mass flow-meter MKS 1179A Mass-Flo® was used for the continuous measurement of the oxygen produced by the decomposition of hydrogen peroxide, thus .allowing the split of the power of the two reactions. The heat of reaction has been evaluated for all the selected N-oxidation and hydrogen peroxide decomposition reactions. The concentration of the a1kylpyridines and their N-oxides was measured using HPLC. These measurements confirmed that the hydrogen peroxide decompositio~ was the only parallel reaction. Integration of the thermal power evolution curves also provided a continuous measure of concentration.. These curves were found to be in good agreement with the HPLC measurements. The reactions were studied using heat-flow and power compensation calorimetry at subcooled conditions. Their study shows that their N-oxidation follows Langmuir type kinetics. The paraIlel decomposition ofhydrogen peroxide also follows the same type ofkinetics. Their kinetic study was based on the kinetic model of Sempere et al, 1998, whi~h was improved and refined. The model of Sempere et al., 1998 on a-picoline assumes paths of reaction, in which, the employed· catalyst, phosphotungstic acid, does not participate. However, as reported in our previous work (papadaki et al., 2002a), no reaction takes place in the absence of phosphotungstic acid. The kinetic model proposed by Sempere et al. 1998 has thus been modified to account for those paths. The modified model is, as before, based on the assumption of very fast always in equilibrium reactions or interactions for the formation of intermediates which subsequently react in a number of ways to give the final products. All paths of the modified model are catalytic. The new kinetic model has been tested and found to be,:in good agreement with experimental data. A number of runaway scenarios of the excess of hydrogen peroxide used during the N-oxidation of alkylpyridines, under closed and open conditions, were examined. It was found that, in most cases, if the volume of the liquid hydrogen peroxide solution occupies more than 10% ofthe total volume ofa closed system (e.g. reactor and vent line between reactor and blockage), the production of gases raises the pressure so quickly that evaporation is completely suppressed. Higher that 70% filling levels result in complete expansion of the liquid~The MTSR(t) (the inaximum temperature attained by the synthesis reaction) of the system falls rapidly if th~ normal process temperature is high, but if a runaway.occurs exactly at the end of dosing, MTST (the maximum temperature reached during the synthesis reaction) will be very high and secondary decompositions will rapidly develop. The results of this study are currently being used to critically assess the current approaches and to further the study ofinherently safer designs.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available