OPTIMIZATION OF n-HEXANE REFORMING AND KINETICS OF CATALYST REGENERATION

Catalytic naphtha reforming is practiced extensively in the petroleum-refining
industry to convert low research octane number (straight chain paraffin) naphtha feed
into high RON component (aromatics and branch isomers) with minimum average
molecular weight changes needed for the modern auto-industry. A valuable byproduct,
hydrogen, from the process is added bonus needed for hydro processing
operations in the refinery. Depending on the operating conditions, hydrogen may be
consumed in unwanted hydrocracking reactions which directly contribute to
deactivate the catalyst. The present study looks into the optimization of process
variable (pressure, temperature and contact time) to maximize isomerization and
aromatization (increasing RON value) reaction while minimizing the hydrocracking
(catalyst deactivation and reducing RON) reactions in n-hexane reforming using
commercially available Pt/Al2O3 catalyst. From the results it is found that high
temperature (723 K) with low hydrogen partial pressure (300 KPa) and low contact
time (1.78 to 2.4 minutes) favor the production of isomers and aromatics over coke
precursors and cracked product species. Addition of CCl4 to the n-hexane reforming
process which increases the catalyst acidity, promotes the formation of cracked
products. Selective poisoning using dimethyl-disulfide on the other hand is found to
decrease monofunctional metal-catalyzed reactions and increased the activity for the
isomerization reactions..
To understand and enhance n-hexane reforming the kinetics and catalyst
regeneration are also investigated using TGA and TPO analysis. From TPO analysis it
was found that applying slow heating rate was the most efficient and convenient way
to control the regeneration process. The TGA results indicate that there exist three
types of coke categorize as soft, hard and laid coke which can be distinguished by a
temperature profile. It was found that the hard coke followed by soft coke makes up
the major constituent of the coked catalyst which can be removed successfully by
proper regeneration process.