FCC catalyst accelerates bottoms upgrading
A competitive FCC catalyst trial demonstrated that improved diffusion of feed and products boosts unit performance when residence time is short
HEATHER MORRIS, Shell Canada
MOHAMMAD UMER ANSARI, Shell Global Solutions US
CLINT COOPER, W. R. Grace & Co.
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Maximising diffusion of feed into and products out of an FCC catalyst is critical to unlocking the full value potential of an FCC unit in which the riser residence time is only a few seconds. Rive FCC catalysts incorporate Molecular Highway Y-zeolite (MHY) technology, which engineers a precise series of mesopores into the Y-zeolite framework, the primary active component of all FCC catalysts. This technology enhances diffusion of molecules into and out of the catalyst.
Building on the success of Rive Technology (Rive) and W.R. Grace & Co. (Grace) at a Shell US Gulf Coast refinery in 20161, a customised catalyst solution incorporating MHY zeolite was designed and trialled at a second North American Shell refinery. The primary objective of this trial was to increase FCC bottoms upgrading into valuable gasoline and diesel products.
The trial results again demonstrated the value that this technology can provide to an FCC unit. During the trial, Shell was able to realise uplift in the range $1.45-1.80/bbl (within the boundary of the FCC unit), depending on the market economics.
This article will further investigate the technology and how it was used to improve performance at this refinery.
Molecular Highway Y-zeolite technology
Since 2010, Rive and Grace have jointly developed and commercialised MHY zeolite technology for use in FCC units throughout the world. The MHY zeolite process introduces a network of intermediate-sized (~40 Å) mesopores into the zeolite, which significantly enhances diffusion of the feed and cracked products.
The interconnected network of mesopores permits access for larger feed molecules that vaporise in the FCC unit at temperatures above 950°F (410°C) to the strong acid sites in the zeolite framework. These acid sites are able to crack the larger feed molecules much more selectively than conventional active matrix materials. The improved diffusion within the zeolite drives bottoms upgrading into LPG olefins, gasoline, and LCO, without coke or gas penalties that are often associated with alternate technologies. Additionally, the MHY zeolite helps to channel valuable cracked products out of the catalyst before the products succumb to potentially undesirable reactions such as overcracking into dry gas, olefin saturation via hydrogen transfer, or coke formation via condensation reactions.
In June 2019 (after conclusion of the trial), Grace acquired the assets of Rive, including its patented MHY zeolite technology. This strengthened Grace’s catalyst portfolio by enabling more rapid deployment of the technology across new catalyst frameworks. Through flexible manufacturing technology, Grace can control the amount of mesoporosity in MHY zeolite to help refiners optimise their profitability.
MHY zeolite technology is protected by more than 40 patents and has been applied successfully to more than 10 FCC units globally since 2011. Catalysts containing these zeolites typically provide the highest value in FCC units processing heavier feedstocks, particularly if the refinery is challenged by unit constraints such as maximum regenerator temperature, wet gas compressor rate, or air blower rate. However, refineries processing lighter feeds have still gained substantial uplift (>$0.50/bbl) from the diffusional improvements facilitated by the technology.
The catalyst used at the Shell refinery was customised to meet specific objectives and constraints – namely, using improved diffusion to upgrade slurry into valuable gasoline plus distillate.
In Figure 1, the image on the left shows a scanning electron microscope (SEM) image of a conventional Y-zeolite. Each crystal face contains millions of micropores of 7.5 Å diameter, which cannot be observed even at 100 000x magnification. The image on the right shows a micrograph of MHY zeolite at similar magnification. While the micropores still cannot be seen at this magnification, the extensive network of mesopores is clearly visible.
Mesopores in MHY zeolites are homogeneously distributed and interconnected within the zeolite. Researchers at Stockholm University used novel imaging techniques to investigate the internal architecture. Electron tomography and rotational electron diffraction were utilised to provide an unprecedented, three-dimensional view inside the zeolite crystal, demonstrating that MHY mesopores are homogeneously distributed and interconnected within the zeolite crystal, enabling enhanced diffusion of molecules into and out of the zeolite, and thereby improving catalytic performance.2
Shell North American FCC unit
The FCC unit where the catalyst trial was conducted is a Shell revamped Kellogg design which typically processes low sulphur VGO. The regenerator operates in partial burn, and the unit typically maximises feed rate to the air blower limit. The primary product objectives are to maximise gasoline and diesel. Catalyst circulation rate and LPG production are usually near their maximum rates. Mixed C4s have a minimum olefinicity specification. No purchased Ecat or other catalyst additives are used at this refinery.
Catalyst trial objectives
Grace and Rive together were awarded a trial at the refinery based on pilot testing results from a competitor and proven performance at another Shell refinery using a Rive FCC catalyst. While some of the objectives and constraints differed between these Shell FCCs, both units were able to benefit from improved hydrocarbon diffusion through the catalyst. The primary objective of this trial was to increase product revenue while maintaining the physical properties of the catalyst. Avenues to increasing FCC revenue included:
• Increase conversion and liquid volume
• Decrease slurry yield
• Increase gasoline and diesel yield
• Reduce dry gas yield
• Maintain LPG yield
• Maintain or reduce catalyst addition rate
Through a comprehensive ACE testing program and subsequent modelling and optimisation, Grace and Rive designed a catalyst to meet the refinery’s objectives. Value uplift was predicted to be approximately $0.92/bbl using RFP pricing. Catalyst improvement projections were independently confirmed via laboratory testing at Shell’s Technology Center (Houston) and modelling with Shell’s proprietary Sharc model.
Trial analysis and evaluation was a joint effort by Rive, Grace, Shell’s technology group, and the refinery’s personnel. Several different methods were used to analyse the trial and determine the catalyst’s uplift, including:
• Operating data evaluation (cross-plots; comparing similar time periods)
• Ecat data evaluation (cross-plots; ACE testing at, before and after Ecat turnover to the Rive FCC catalyst)
• FCC kinetic modelling
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