Refiners Weigh Opportunities Upgrading Highly Contaminated Feedstocks

Refiners Weigh Opportunities Upgrading Highly Contaminated Feedstocks

Rene Gonzalez
Dec 26, 2016

As fluid catalytic cracking (FCC) unit capacity increases, the use of ZSM-5 based FCC additives continues to expand as more feedstocks are entering the refinery contaminated with metals, including iron (Fe), nickel (Ni), vanadium (V), along with other metals. Whether targeting gasoline production or olefins production for the petrochemicals or alkylate market, commercial FCC operations vary in feed metals levels, feed type, unit design and operating conditions.

According to information from Grace Catalyst Technologies, when analyzing commercial equilibrium catalysts (Ecat) for ZSM-5 additive performance, it has been observed that feed metals will preferentially adhere to the base catalyst vs. the ZSM-5 additive. Separation of Ecat into its base catalyst and ZSM-5 additive components shows that the ZSM-5 additive typically only contains about half the metals of the FCC base catalyst. In laboratory deactivation studies by Grace, ZSM-5 additives begin to deactivate at Ni+V loadings of 3,000 ppm and greater. However, based on recent commercial experience, a ZSM-5 additive sample containing 3,000 ppm Ni + V, would likely require approximately 6,000 ppm Ni + V on the circulating base catalyst.

According to refinery researchers, ZSM-5 additives are very stable and maintain activity much longer than other FCC catalysts or additives. The specific half life of a ZSM-5 additive varies from unit to unit, but could easily range from two weeks to significantly longer, depending on the FCC operation. In Grace’s experience, the half life of a ZSM-5 additive strongly depends on unit operating conditions and not as much on the feed type or metals levels. Variables which will impact the half life of a ZSM-5 additive include regenerator temperature, unit pressure and circulation rate, which influences the number of cracking cycles the additive undergoes in the unit each day.

Vanadium will likely have the greatest effect on ZSM-5 deactivation. However, all contaminants in the FCC will have a much stronger effect on base catalyst deactivation before they will adversely impact the ZSM-5 activity. The Grace study shows no noticeable shifts in olefins selectivity (e.g., propylene selectivity) due to contaminant levels or deactivation of ZSM-5.

For evaluating the effectiveness of ZSM-5 additives in a commercial unit a common approach is to monitor propylene and butylene yields as a function of corrected conversion. ZSM-5 additives will increase LPG olefins for each given level of conversion. Another recommended method to measure the effectiveness of ZSM-5 additives is to analyze the increase in gasoline octane by evaluating gasoline octane as a function of reactor outlet temperature.

In any event, many tools are available for monitoring FCC unit performance. Most FCC operators monitor in-process, or “as produced” yields and operating conditions, and additionally they complete unit mass balances at routine intervals (often weekly or more frequently). In many refineries, FCC profitability is driven by overall volume gain, so this is an important key performance indicator.

Unit reliability is also a very important profitability parameter, and (along with a strong routine maintenance program), many refiners monitor in-process operating parameters to ensure that limits are not being exceeded. Some of these parameters are directly measured in the unit, and some are calculated using in-process or mass balanced data.

Measured parameters include unit temperatures (at various points in the unit, including regenerator bed, reactor and regenerator dilute phases, and others), unit pressures (reactor and regenerator), wet gas compressor suction and power, regenerator emissions and slide valve/standpipe differential pressures. Calculated parameters, which are important to monitor, include yield selectivities, coke make, superficial velocities (especially in cyclones) and catalyst circulation (or cat-to-oil ratio).

In summary, ZSM-5 based additives have excellent activity and stability even in high metals applications, giving FCC operators the ability to optimize operations. However, adherence to unit reliability and best practices unit performance all play a role in the final outcome, which is to produce higher quality refined products with lower quality feedstocks.



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