Maintain High Activity and Attrition Resistance in USY Octane Catalysts
By the end of 1985, U.S. refiners had exhausted about 85% of their lead credits. These credits, which they were accumulating in 1985, had to be utilized in 1986 to meet the drop from 0.5 to 0.1 grams of lead per gallon. In 1985, USY catalyst usage in the U.S. grew steadily from 21% to 47%. In 1986, the percent of USY catalyst used in the U.S. FCC marketplace remained relatively flat. Currently U.S. consumer market trends show increasing demand for premium and mid-grade unleaded gasoline. This means that increased demand for unleaded octane-barrel production from the U.S. refiner can be expected in 1987.
USY Catalysts for Octane Improvement
A number of options are available to the refiner to meet the demand for high octane. Generally the first choice, because it is less costly and more readily implemented, will be to increase operating severity and / or use new catalysts for greater octane production. The brunt of this load in the refinery will fall to the FCC unit and reforming operations. For the FCC unit the use of USY and partial USY catalysts is once again expected to increase. This report discusses FCC catalyst products designed by BASF to help a refiner meet the increasing octane barrel demands for 1987 and beyond, while avoiding the hidden costs of reduced activity and/or poor attrition resistance associated with some FCC octane catalysts.
To meet demands for more octane-barrels, an increasing number of refiners have switched to using ultrastable Y zeolite type FCC catalysts. These catalysts, which feature zeolites with a reduced unit cell size, are a proven means of increasing FCC unit octane. However, there are some tradeoffs associated with using a reduced unit cell size zeolite, and one of the more important properties being affected is catalyst activity.
Research and Motor Octane of the FCC gasoline increase with a reduction in catalyst unit cell size however, as Figure 1 shows, catalyst activity also decreased with a decrease in unit cell size. For a detailed discussion of the impact of reduced unit cell size zeolite, see our previously issued BASF Catalyst Report Tl-762.
Incorporation Method Limitations for USY Catalyst Production
Many catalyst manufacturers produce catalyst by the incorporation method, and in order to compensate for reduced USY zeolite activity add more zeolite to the catalyst composition. This, however, can only be done to a limited extent because of the poor attrition characteristics of these catalysts. While improvements in binders have been sought, incorporation catalysts containing high amounts of zeolite still suffer from poor attrition resistance.
BASF with its DYNAMICS and "in-situ" manufacturing technologies avoids this problem. In order to understand how this is accomplished, the following comparison of the incorporation manufacturing method versus BASF's proprietary "in-situ" production method is given.
Figure 2 shows a block diagram of the traditional incorporation method for manufacturing FCC catalyst. This production scheme is the traditional process used by all fluid cracking catalyst manufacturers, except BASF. In the incorporation method, zeolite and matrix components are manufactured separately and then combined, or incorporated, in various proportions to ultimately produce different catalyst grades and activities. The mixtures are spray dried to form the particles which then undergo an exchange for activation
and stabilization. Physical handling limitations result in large clusters of zeolite crystals and no means to insure location of active cracking sites along the pore channels.
"IN-SITU" Process Produces Superior Matrix Properties
The flow scheme for BASF's FCC "in-situ" catalyst manufacturing process is outlined in Figure 3. Specially selected kaolin, the starting raw material for BASF's "in-situ" catalysts, is slurried and fractionated into desired particle size ranges. It is then dewatered and chemically treated to prepare the resultant feed material for microsphere formulation. The resultant slurry is spray dried to form microspheres.
The microspheres are calcined at extremely high temperatures that give catalysts produced by the "in-situ" method the important advantage of a stable, attrition resistant matrix. It changes very little in the "relatively" lower temperature environment of an FCC regenerator. Such a calcination step is possible because no zeolite is present at this point in the process. The zeolite, which is included in conventional "Incorporation Method" spray dried microspheres, would be destroyed by this severe treatment.
Once the microspheres are calcined they are shipped to a separate BASF manufacturing plant located in Attapulgus, Georgia to begin the second phase of the manufacturing process. At Attapulgus, the microspheres are treated with caustic to leach silica from the particle forming a network of pore channels along which the zeolite crystals are grown "in-situ." This unique synthesis process results in complete zeolite dispersion along the pore walls on the alumina rich matrix.
BASF DYNAMICS technology promotes the growth of an extremely high concentration of zeolites in catalyst. It makes our octane catalysts the highest activity catalysts available in the marketplace today with no sacrifice in traditional attrition resistance. The high geometric surface area of the zeolite reduces destruction caused by vanadium fluxing, making the catalyst vanadium tolerant.
The high surface area alumina matrix, high zeolite dispersion and the easy accessibility of the zeolite are also responsible for the bottoms upgrading benefits of BASF catalysts. Growth of the zeolite within the microsphere pore structure causes a high degree of interaction between the zeolitic and matrix surfaces forming intense chemical bonds. Attrition resistance of the particle actually increases following zeolite crystallization. This matrix zeoiite bond stabilizes the zeolite and makes it extremely resistant to sintering or pore collapse. It is the reason for the outstanding hydrothermal stability of BASF catalysts.
The catalyst is activated by ion-exchanging the sodium out of the zeolite. The sodium can be exchanged either with a hydrogen ion through ammonium nitrate exchange or a rare earth ion through rare earth exchange. Rare earth exchange stabilizes the zeolite. (See Catalyst Report Tl-789 for further details). However, increasing rare earth exchange to a high level typically increases hydrogen transfer reactions during cracking, thus decreasing octane and cetane product quality as illustrated by the commercial data shown in Figure 4.
Because of the intrinsic zeolite stability derived from the "in-situ" process, less rare earth is required to hold a given catalyst activity relative to incorporation process catalysts and this results in improved octane and cetane quality with BASF catalysts. Dewatering and drying complete the "in-situ" process.
Lower Catalyst Make-Up Reduces Costs & Stack Emissions
Because of the inherent high activity and superior attrition resistance of "in-situ" USY catalysts, lower fresh catalyst addition rates are required. This can mean substantial savings in catalyst costs as well as reduced stack opacity and particulate emissions.
BASF measures attrition by grinding a pre-measured, pre-weighed sample of catalyst in contact with an established quantity of silica sand. By screening and weighing the residue at given intervals, the production of fines is established and reported as % loss/sec. A comparison of the attrition resistance of some widely used BASF catalysts, both USY and REY type, with several well known competitive catalysts using the BASF Test Method is shown in Figure 5A. Figure 5B shows commercial examples of the degree of catalyst loss reduction possible when switching from a "incorporation method" catalyst to a USY type catalyst produced by the "in-situ" process.