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Aug-2019

Catalytic lube dewaxing defeats feed
 contamination (TIA)

A base stock manufacturer was experiencing poor lube plant feed quality stemming from refinery equipment problems. The hydrocracker producing the feed to the lube plant had developed a leak in the high pressure feed effluent heat exchanger.

Phillip Parker
ExxonMobil Catalysts and Technology Licensing
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Article Summary
A base stock manufacturer was experiencing poor lube plant feed quality stemming from refinery equipment problems. The hydrocracker producing the feed to the lube plant had developed a leak in the high pressure feed effluent heat exchanger. The unconverted oil (UCO) was therefore contaminated with raw feed containing vacuum gasoil and coker gasoil, causing high nitrogen, sulphur, aromatics, and polynuclear aromatics in the UCO.

This situation could have diminished production capacity and/or undermined the quality of the base stocks. The manufacturer was concerned about maintaining product quality and production rates, which directly impact profitability, while avoiding a costly shutdown.

ExxonMobil engineers worked closely with the operator to assess options and identify the most effective solution for maintaining production rates at the same yields and quality. As an owner-operator, ExxonMobil has a lot of experience and understands how to address similar operational issues.

An analysis of the situation indicated that ExxonMobil’s MSDW technology could easily withstand the increased contamination levels with simple operational adjustments that would not affect production rates nor yields.

MSDW technology indeed handled the refiner’s feed quality issue because of its high tolerance to contamination even when the nitrogen feed content approached 50 wppm. The technology uses proprietary catalysts to hydroisomerise n-paraffins and saturate aromatics for maximum yields of very high quality base stocks.

Over 20 years of operating experience and continuous R&D advances, the performance of the MSDW process has progressed to offer high catalyst activity, yield, and stability. The process is very simple and utilises two temperature stages (see Figure 1). The first stage contains the MSDW selective hydroisomerisation catalyst, and the second contains the Maxsat hydrofinishing catalyst that removes polynuclear aromatics for thermal and oxidative stability, and colour.

Maintained production
The refinery continued to operate the lube plant with nitrogen contamination much higher than 10 wppm for over two years, at full rate and unchanged yields (see Figure 2).

A shutdown to resolve the issues in the hydrocracker was not necessary.

The company estimated the cost savings resulting from the ability to maintain rate, yields, and avoid a shutdown at approximately $75 million. Moreover, the company’s reputation for reliable supply of high quality base stocks was maintained.
 
This short case study originally appeared in PTQ's Technology In Action feature - Q3 2019 issue.

For more information: Phillip.j.parker@exxonmobil.com
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