Lifetime diesel catalysts

A more important deactivation aspect is poisoning. A diesel oxidation catalyst is poisoned by the same elements that poison three-way catalysts, except for lead, which is absent from diesel fuel and the diesel fuel supply chain. Table 25 compares the amount of sulfur, phosphorus and zinc offered to a diesel catalyst and to a three-way catalyst during their lifetime. From this table, it is apparent that a diesel oxidation catalyst has to deal with a considerably higher amount of sulfur during its lifetime than is the case with a three-way catalyst. This is because the diesel fuel specification allows for a higher sulfur content than the gasoline specification. Table 26 gives an overview of the maximum sulfur content in the diesel fuel specification of some selected countries. 

A spent commercial deactivated NiMo/Al203 hydrotreating catalyst, whose chemical analysis data are presented in Table 1, was used in this study. It was considered as a model of a spent industrial catalyst that is commonly discarded after its lifetime. The catalyst was employed in its sulfided form in hydrotreating of diesel fractions for about 3 years in a brazilian refinery. It was not regenerated during its lifetime and was kept in its original form (cylinder extrudates 5mm). 

Table 25. Order of magnitude of lifetime effects comparison between a diesel oxidation catalyst and a three-way catalyst.

Sasol I operates 3 reactors in parallel. The mean catalyst lifetime is 42 days. On the average/ 2.4 reactors are steadily under operation. Each reactor produces 60/000 tns of primary products per year. The product distribution is given in Table 1 and compared with that of the fixed bed process. The Synthol process reveals a maximum in gasoline fuel while the main products of the fixed bed process are higher hydrocarbons like diesel/ heavy oils and wax. 

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