Dealing with Hydrotreating Catalyst Activity Loss at Higher Severities

Evolving hydrotreating (HDT) operating strategies have resulted in running HDTs at higher H2 partial pressures, higher temperatures, etc. While reactor technology has improved insofar as more efficient internals (better distribution, multiple catalyst beds, improved reactor models, etc.), the catalyst industry has played a primary role in enabling refiners to run their HDTs at higher throughputs and utilization rates. One of the most important developments from catalyst suppliers is the cost-effective supply of more active catalysts.

Hydrotreating discussion at RefComm Bahrain.

By definition, increased catalyst activity equals increased reactor capacity. So a catalyst with 20% higher activity is like adding a new reactor to give 20% more reactor volume – except, of course, a catalyst change can be done immediately, with no physical change to the unit and no capital cost, according to George Hoekstra, independent hydrotreating catalyst consultant. The catalysts suppliers are constantly developing better catalysts, and the products sold today span a broad range of activity.

Most catalyst suppliers have developed good reactor modeling capability to track unit performance and catalyst activity during a cycle. The most common cause of unexpected short cycles is processing difficult feeds. Whenever reactor temperature is increased to meet specifications on difficult feed, there is extra, irreversible activity loss. This may be economically justified; the catalyst suppliers apply their models to help the operator understand the effect of feed changes, thereby facilitating informed decisions on the tradeoff between feed upgrade value and cycle life.

A common request by refinery planners these days is to convert a vacuum gas oil (VGO) hydrotreater to a mild hydrocracker. When considering this, proposals from multiple suppliers are forthcoming, but the refiner is cautious with these proposals from the perspective that the hydrocracking pretreat catalyst performance is not overestimated when considering today’s refractory feeds. For example, mild hydrocrackers that perform well on “normal” feeds will fail to meet quality targets when introducing a difficult feed that demands more pretreat capacity.