(177c) Challenges in Processing of Shale Oil in FCC Unit

The introduction of Shale gas and oil in the recent years has had a strong impact on the Petroleum market in North America and around the globe. Due to attractive prices of Shale oil, refiners have taken advantage of this stream to improve their profit margin. The use of shale oil in FCC units comes with its own challenges as Shale oils are more paraffinic than conventional crudes and contain a different combination of contaminant metals. Shale oils also generally make lower coke, reducing the FCC regenerator temperature.  While this is beneficial with respect to catalyst deactivation, it can become an operational limit, especially where the FCC is being operated at reduced severity in diesel mode operations. The high paraffinic nature of Shale oils leads to higher gasoline volume but lower octane and lower LPG olefinicity, resulting in poorer quality alkylation unit feed. Lowering the Rare Earth of the catalyst can help improve olefinicity, but a more flexible and effective approach is to add a high activity ZSM-5 additive, such as Super Z Excel. ZSM-5 additives boost gasoline octane and increase the olefinicity of C3 and C4 hydrocarbons. The usage of ZSM-5 in North American FCCUs has been increasing as a result of Shale oil processing.

As the metal contaminants of Shale oils, such as Fe, Ca, Na, K, are usually higher than in conventional crudes, their accumulation can lead to more accelerated deactivation of FCC catalysts. Fe present in the FCC feed usually builds up an impervious or glassy layer on the catalyst surface, usually manifested as Fe nodules on particles. This inhibits access to inner particle, and hence results in loss of conversion, deterioration of bottoms  selectivity, and potentially catalyst circulation problem. In severe Fe poisoning cases, the emission of SOx in the flue gas also increases as the Fe carries over some sulfur from the reactor to the regenerator. These negative impacts are usually referred to as Fe poisoning. Ca, K and Na make Fe poisoning worse as they acts as fluxing agents along with the other contaminants, restricting access to the active components in the particle interior. To alleviate the impact of Fe, flushing equilibrium catalyst (Ecat) is typically used to dilute metal contaminants. Until recently, this flushing strategy was the only practical solution, however, effective metal trap additives, such as Cat-Aid, have been shown to mitigate the effects of Fe poisoning significantly. Electron microscopy has shown that Cat-Aid reduces Fe nodules and smoothens the catalyst surface, allowing hydrocarbons into and out of the catalyst interior. Thereby conversion recovers, improving gasoline and bottoms selectivity and lowering dry gas and H2 yields. In some operations, the need for addition of flushing Ecat has been completely eliminated and the fresh catalyst addition rate has also been lowered.