First published in PTQ Q4 2016
Matthew Hutchinson,Technology Manager – Reforming, Axens North America
Organochlorides are typically formed in the catalytic reformer when hydrogen chloride (HCl) reacts with olefins downstream of the reaction system. Olefin formation in the reformer reactor is increased when operating at high reactor temperatures and low hydrogen partial pressure (typically towards the end of the catalyst cycle) as the catalyst becomes coked and the metal functions become compromised.
HCl is present in catalytic reformers to maintain the acid function of the catalyst but can be elevated downstream as a consequence of poor catalyst chloride retention, either from low catalyst surface area or a water upset, which can wash chlorides off the catalyst. Additionally, in the net gas booster section these organochlorides may polymerise to form ‘green oil’.
To avoid organochloride formation operationally, the reactor temperature should be maintained as low as possible to meet the requisite product octane. It is also critical to avoid over-chloriding or moisture upsets.
If these steps do not eliminate the formation of organochlorides then the refiner should consider upgrading to a higher activity, high surface area catalyst with good hydrothermal stability such as Axens Symphony catalyst (either high density or low density). Higher catalyst surface area can accommodate more coke before olefin production becomes a significant issue.
The higher surface area will also retain more chloride for the same water-to-chloride ratio and temperature. A hydrothermally stable catalyst limits attrition, and the resulting surface area retention limits formation of olefins, which tend to form organic chlorides at temperatures well below reactor temperatures.
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