We have a catpoly hydrotreater that converts olefins to paraffins to produce petrol diesel and jet fuel. I just want to know the reaction/chemistry that should take place in the poly hydrotreater and the kinetics associated?
Answers
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08/12/2009
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A:
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Alan Goelzer, Jacobs Consultancy, alan.goelzer@jacobs.com
Depending upon the catalyst system and certain operating conditions and spectrum of light olefins in the feed; "catalytic condensation section" will generate either highly branched iso-olefins or moderately branched iso-olefins with some carbon number 'nodes' reflecting multiples of 3X or 4X.
Typically, the content of organic sulphur and organic nitrogen and organic oxygen are down in the 'wppm range' although sometimes organic sulphur might be in the "tenths range".
Consequently, the predominant kinetic reaction in the hydrotreating section will be "olefin hydrosaturation" with one mole of chemical H2 per mole of olefins in each barrel or metric ton of feed.
Olefin hydrosaturation is strongly exothermic, as can be seen by running molar heat of formation calculations using model compounds and converting this to exothermic BTU per SCF H2 and BTU per metric ton feed or BTU per barrel feed.
There is considerable debate about the reaction order of olefin hydrosaturation, but it is possible that this approaches 'second order' [meaning fast and somewhat uncontrollable approach to final state].
Recycle dilution with hydrosaturated product and high first bed deltaT rises are both likely required.
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