PTQ Q3 2024 Issue

When resid or coker gasoils are included in the feed, nitrogen will be at least 1,500 ppm. These feed- stocks are generated from the vac- uum tower bottoms, which contain the highest level nitrogen in crude oil. The concentration of nitrogen in the coke also increases, which leads to higher NOx from the regenerator. These feeds will also benefit from high-pressure hydroprocessing. More nitrogen goes into the liq- uid products, reducing its stability and possibly leading to off-spec products. Refiners compensate for the higher nitrogen by increasing catalyst activ- ity (number of acid sites), the cata- lyst-to-oil ratio, and/or the reactor temperature. The latter speeds the desorption of nitrogen from the acid sites. Since the aromatic nature of the feed is higher, the delta coke would increase, causing a lower cat/ oil and a higher regenerator temper- ature. Both result in lower conver- sion. Stripper efficiencies would be poorer with lower reactor tempera- tures. Experience has shown a min- imum reactor temperature of 960ºF, though 980ºF is better with high nitrogen feeds. Catalyst formulations have been altered to provide nitrogen passivation. Matrices are designed to adsorb nitrogen compounds and protect the active cracking sites. Better coke selectivity and hydro- thermal stability will also improve activity maintenance. The nitrogen is removed in the regenerator. The changes made to the catalyst and operating conditions allow a base level of nitrogen to be handled without penalty. This base level is usually between 1,000 and 1,500 ppm. Nitrogen can lead to ammonia salts forming in the reactor, which can precipitate out at the top of the main column and produce off-spec product. A water wash will remove these salts. Keeping the temperature at the top of the tower above the water dew point will prevent this from happening. Halogens Halogens create difficulties when they enter the cracker. Chlorides are

the most common compounds that can reactivate nickel and vanadium, creating high hydrogen yields. They are washed off the catalyst and make the overhead water acidic. Corrosion can increase in the gas plant. Conclusion Catalytic cracking has made monu- mental advances since its inception. The processing of heavier feeds has greatly improved the profit - ability of refining but has created challenges to FCC catalyst integrity. Catalyst suppliers and refiners have consistently overcome obstacles, continually improving products and operations. References 1 O’Connor P, Brevoord E, Wijngaards H N, A Review of catalyst deactivation in fluid catalytic cracking , Dix, Petro. Chem. Natl. Mtg., New Orleans, 24-29 March 1996. 2 Bondi A, Miller R S, Schlaffer W G, Rapid deactivation of fresh cracking catalysts, I&EC Process Design & Development, Vol. 1, No 3, July 1962, pp.196-203. 3 Letzsch W S, The Changing impact of coke on catalyst in FCC operations, AFPM Annual Mtg. AM-14-16. 4 Letzsch W S, Wallace D N, FCC catalysts sensitive to alkali contaminates, Oil & Gas J ., Nov. 29, 1982. 5 Letzsch W S, Upson L L, Ashton A G, Passivate nickel in FCC feeds, Hydrocarbon Processing , June 1991. 6 Senter C, Stockwell D M, Liu B, O’Berry B, Passivating vanadium in FCC operations, Catalysis 2024 , pp.31-34. 7 Wieland W S, Chung D, Simulation of iron contamination, Hydrocarbon Engineering, March 2022. 8 Wei L, Yuxia Z, Huiping T, Jun L, The cat- alytic performance on iron contaminated FCC catalysts , Prep. Paper ACS, Div. of Petro. Chem., 2008, 53 (1), 99. Warren S Letzsch has 56 years of experi- ence in petroleum refining, including petro - leum catalysts, refining and engineering, and design. He has authored more than 100 technical papers and publications and holds eight patents in the field of FCC. He holds BS and MS degrees in chemical engineering from the Illinois Institute of Technology. He is a Fellow of the AIChE. Email: wletzsch@verizon.net

PTQ Q3 2024