PTQ Q2 2024 Issue

FCC co-processing of biogenic and recyclable feedstocks: Part 2

Part 1 provided a segue into operational concerns ranging from WPO co-processing to maximising oxygen removal and flexible catalytic solutions for FCC operations

Jon Strohm, Darrell Rainer, Oscar Oyola-Rivera and Clifford Avery Ketjen

E merging corrosion concerns surrounding the pro- cessing of fats, oils and greases (FOGs) are highly paraffinic. They will vaporise and crack easily, but some naphthenic acid (TAN) may be present, particularly in tallow or used cooking oil (UCO). TAN has been known to increase corrosion in distillation towers and hydrotreat - ing units. For FCC units, it is generally accepted that the TAN compounds will crack and pose little harm. However, little has been documented on the feed section’s corrosion effects before the riser. As a rule of thumb, the presence of TAN in co-processing feeds follows the order of bio-oils > animal tallow > vege - table oils. Many refiners have a maximum TAN specification to reduce the corrosion in the main column overhead (MC OVHD). A careful inspection of the MC OVHD is important during the turnaround after co-processing. Some co-processing feeds may contain carboxylic acids and other oxygenated species. When these feeds crack, they will form smaller, oxygen-containing compounds. Most of these compounds will crack into the lighter boiling fractions (wet gas compressor [WGC] section). Elevated carbon diox - ide (CO 2), carbon monoxide (CO), and low levels of alcohols are commonly seen. Other compounds observed are esters, ketones, phenolics, and acids (acetic, formic, and propionic). In most cases, the appearance of these compounds will be in low concentrations (wppm or wppb levels). Better analytical methods to measure them should be developed for co-processing. These acids may increase the corrosion concerns in the MC OVHD section. Elevated methyl acrylate gas has been observed in tallow-based feeds in general and UCO feedstocks in particular. Control of deoxygenation pathways, as discussed later, is crucial to minimising light oxygenate formation and the impact on these supporting operations. Light molecular weight (MW) products from co-process - ing will primarily concentrate in the WGC section. The acids will react with ammonia, and the pH of the systems will decrease. Methyl acrylate will most likely form solids. Amine units will have problems with elevated CO and CO2 levels. In general, foaming issues may occur in high-pressure pro- cess units, and corrosion concerns are more common. Many industrial water and process chemical suppliers have developed improved practices when co-processing.

While these issues have been documented, some FCC WGC sections have recorded little to no problems. Process units with no problems have used highly refined or refined/ bleached/deodorised (RBD) FOGs. While FCC units have co-processed up to 100% FOGs, 1 trials seldom exceed 10% of the total feed and are commonly below 5%. Catalyst’s role in FCC co-processing FCC catalysts drive the conversion and selectivity for upgrading heavy feeds to value-added fuel and chemical products. Conventional FCC catalysts are formulated within the constraints of each unit to maximise product value and unit objective. Examples include optimisation for slurry To maximise product value within the unit constraints and drive towards incorporation of renewable and circular carbon, the co-processing catalyst can be formulated and optimised for the specific feed chemistry conversion, metals tolerance, coke selectivity, and maxim - ising gasoline and/or light olefins for a given feed, product targets, and operational constraints. The same holds true for catalyst technologies for FCC co-processing of alternative feedstocks. In addition to the different metals in the alterative feeds, the differences in the hydrocarbon species present alter the conversion chemis - try. To maximise product value within the unit constraints and drive towards the incorporation of renewable and cir - cular carbon, the co-processing catalyst can be formulated and optimised for the specific feed chemistry. Maximising deoxygenation As previously stated, most units may only process small quantities of FOGs. Typically, these units rely on the base cat - alyst already in the unit without consideration of the change in the feed chemistry, resulting in impacts on unit operations

PTQ Q2 2024