One of the major problems in designing improved FCC catalysts is that it is very difficult to scale down the commercial FCC process with its short residence time and rapid deactivation processes, according to research conducted by Eelco T. C. Vogt, distinguished advisor in catalysis R&D at Albemarle’s Amsterdam R&D center, as summarized from a more detailed study published September 18, 2015 on the web.
Today’s FCC feedstocks are complex and contain various impurities that can have a major effect on performance, such as Conradson carbon, metals like Ni and V, oxygenates, and nitrogen- and sulfur-containing molecules. Resid feedstocks require a different operation than VGO, and diesel- or propylene-selective applications are completely unique.
Over the years, various more or less standard methods have been developed for testing FCC catalysts. The first was the “MAT”-test, or Micro Activity Test, according to ASTM D-3907. In this test, a small sample of catalyst is tested in a fixed bed. Conversion can be influenced by changing the catalyst-to-oil (CTO) ratio. The test has various drawbacks, but has nevertheless been very popular over the years. The test contacts the catalyst and feed for prolonged periods, during which deactivation of the FCC catalyst proceeds, and coke- and temperature profiles may develop over the catalyst bed. As a result of the prolonged exposure to feedstock, the amount of coke deposited on the catalyst material may be unrealistic. The same holds for the observed gas selectivities.
While FCC catalyst testing is already complicated, the protocol will also have to take into account the deactivation of the catalyst during its lifetime of cracking and regeneration cycles. The deactivation of the catalyst is caused by steaming during the regeneration and assisted by the presence of metals like Ni and V (but also Fe, Na and Ca). Deactivated commercial catalysts may contain thousands of ppms of Ni and V, depending on the operation. Mitchell Impregnation (MI) is used to deposit Ni and V on the catalyst particle, usually prior to steaming. The metals are impregnated throughout the catalyst particle, which is maybe (in part) correct for V, but certainly not for Ni. Simple steaming of the catalyst (with or without metals) at increased temperatures mimics the effect of the regenerator in very crude way.