Susan LeibySRI International Menlo Park, Calif.
Over the past 30 or so years, many improvements in fluid catalytic cracking (FCC) operation have been achieved as the result of innovations in catalyst formulation.
During the 1990s, new environmental regulations on issues such as reformulated gasoline will place new demands on both the refining industry and catalyst suppliers. An overview of cracking catalyst technology therefore seems in order.
Today, high-technology innovations by catalyst manufacturers are rapid, but profit margins are slim. Catalyst formulations are shrouded in secrecy and probably depend almost as much on art as on science.
Special formulations for specific cracking applications get the greatest emphasis today. To illustrate this point, OGJ's Worldwide Catalyst Report lists over 200 FCC catalyst designations (OGJ, Oct. 14, 1991, p. 43). Catalysts containing components to enhance gasoline octane now account for about 70% of total U.S. FCC catalyst usage. 1
Much of the current growth in FCC catalyst usage is attributable to increased cracking of residual feedstocks, with the concomitant need for improved resid catalysts and higher catalyst consumption rates.
ZEOLITE CATALYSTS
The first catalysts were ground up amorphous silica alumina. Whether synthetic or naturally occurring, these catalysts suffered from low activity and poor stability compared to catalysts available today.
In 1946, the use of spray-dried microspheroidal catalysts improved fluidization, providing smoother catalyst circulation and reduced attrition, thus reducing catalyst losses.
This type of catalyst contained 10-14 wt % alumina, and was replaced by higher-alumina (25-30 wt %) catalysts in the late 1950s. 2 The higher-activity catalysts affected higher gasoline selectivity, lower coke selectivity, and improved stability. However, these catalysts also produced somewhat lower gasoline octane.
In 1962, Mobil introduced a new class of crystalline synthetic zeolite FCC catalysts that rapidly dominated the catalyst market. Zeolite catalysts have probably had the single greatest impact on FCC design and operation in the history of the process.
Their vastly superior activity and gasoline selectivity led the way toward all-riser cracking, which substantially reduced reaction time. This helped to minimize overcracking of gasoline to less valuable lighter products and also reduced coke make.
At the same time, the amount of recycle of unconverted feed to the FCC dropped from 40% in 1965 to 5-10% in 1988, because of the higher conversions with zeolite catalysts.
The combination of these factors enabled FCC throughputs to be substantially increased (by 50% or more) with a greatly improved product slate. Moreover, this was accomplished without excessive operating costs or equipment revamp.
By 1976, it was estimated that zeolite FCC catalysts had saved the petroleum industry over $3 billion in reduced crude and refining costs compared to the old silica-alumina catalysts. 3
ZEOLITE STRUCTURE
Zeolites are crystalline aluminosilicate materials. They occur as natural minerals in at least 34 different species, but today synthetic zeolites are more important.
Zeolites are frequently referred to as molecular sieves, because of their microporous structure containing cavities and channels of molecular dimensions from 3 to 12 A. They have a high internal surface area of greater than 600 sq m/g.
The primary building block of the zeolite structure is a tetrahedron of four oxygen atoms surrounding a central silicon atom (SiO4)4-. These tetrahedra are connected through the corners of the shared oxygen atoms to form a wide range of secondary building units, which can be further interconnected to form a wide range of polyhedra.
For FCC purposes, synthetic faujasite zeolites, known as Linde Type X and Y, have been used. These were originally discovered by Union Carbide in the 1950s. In these catalysts, some of the silicon atoms are replaced b aluminum. The replacement of Si4+ by Al3- results in a unit electronic charge that is compensated for by a cation such as Na+, H-, and rare earth cations.
The acidity of the zeolite is derived from the protons that maintain electrical neutrality. The number and strength of the acid sites are complex functions of the nature, the concentration, and location of both the SiO4 and AlO4 tetrahedra and the cations. 3
The framework structure of faujasite zeolite is shown in Fig. 1. The SiO4 and AlO4 tetrahedra form truncated octahedra (sodalite cages), which are joined by hexagonal prisms.
Both X and Y zeolites have 12-member ring pores and a relatively large pore size of 7.4 A. The atomic silicon/aluminum (Si/Al) ratio varies from 1 to 1.5 for the X zeolite and from 1.5 to 3 for the Y form. The cation is sodium (Na-) and the unit cell varies from 24 to 25 A. 3
Silicon-rich zeolites are more stable than aluminum-rich zeolites because their structure is closer to pure silica. The relatively higher Si/Al ratio found in Type Y, as compared to Type X zeolite, increases catalytic selectivity and thermal stability. thus, Type Y zeolites replaced Type X materials in FCC catalysts many years ago.
Today's so-called conventional FCC zeolite catalysts are sodium Y zeolites (NaY) in which the sodium ions have been exchanged with rare earth cations (RE) and/or ammonium ions, to produce REY, HY, or REHY zeolites.
The rare earths provide stability and increased catalytic activity and gasoline selectivity. The ammonium ions are converted to active acidic sites by subsequent heating to drive off ammonia.
CATALYST MATRIX
FCC catalysts are actually composites containing zeolite dispersed in an amorphous matrix. The zeolite component comprises 10-50 wt % of the catalyst and provides activity, stability, and selectivity. The matrix comprises 50-90% of the catalyst and provides desirable physical properties, as well as some catalytic activity.
Over the years, the amount of active catalytic components-both the zeolite and active matrix-within the FCC catalyst has increased. This increase was prompted by demands on catalysts for higher octane, reduced bottoms yield, resid processing, etc.
The matrix consists of binder and filler materials. Silica, silica-alumina, alumina (sols or gels), or clay are present as binders to dilute catalyst activity.
Clay fillers are used to provide the necessary strength, hardness, and density to preserve the integrity of the catalyst under the severe regeneration conditions required by the process. The matrix also provides desirable heat transfer characteristics that are important in commercial FCC operations.
The matrix itself can contribute to the FCC catalysis, although to a lesser extent than the zeolite component. Silica is inert and was the preferred matrix material for many years. Such an inactive matrix has no effect on product selectivities or properties.
Recent catalyst formulations allow for varying amounts of matrix catalytic activity. An active matrix with some form of silica and alumina can promote cracking reactions on the active sites, with few hydrogen transfer reactions because of the low density of such sites. This type of catalyst produces an olefinic, high-octane gasoline. 4
BOTTOMS CRACKING
The increased cracking activity of the matrix can upgrade the bottoms material in the feed to valuable products because the large-pore matrix permits relatively easy access of very large feed molecules.
Because the pore opening to the zeolite cage structure (the primary cracking site) is only 7.4 A., the zeolite does not accept molecules having a true boiling point greater than about 482 C. (900 F.). This corresponds to molecules of very heavy vacuum gas oil and vacuum resid, having kinetic diameters ranging from 10 A. to more than 100 A.
Heavy molecules crack according to three basic mechanisms:
- Cracking on the external zeolite surface
- Thermal cracking
- Matrix cracking.
Cracking on the external zeolite surface results in minimal bottoms upgrading because the external surface represents only about 3% of the total zeolite surface.
Thermal cracking is nonselective and tends to degrade heavy hydrocarbons to gas and coke.
Matrix cracking permits the most efficient upgrading of bottoms material into higher-valued gasoline and light cycle oil products.
This occurs at the expense of additional coke yield.
The matrix may act synergistically with the zeolite by providing primary cracking sites that generate smaller feed fragments, but larger than gasoline-range molecules which can be selectively cracked within the zeolite.
The proper ratio of zeolite to matrix activity depends on the particular application and feedstock, balancing the multiple objectives of favorable pore space, coke selectivity, bottoms upgrading capability, metals resistance, etc.
For example, a highly active matrix may not be advantageous with heavy resid feedstocks. This is because the poor coke selectivity of a high-activity matrix can adversely affect operation and result in a net increase in bottoms yield.
OCTANE CATALYSTS
As mentioned, the advent of synthetic Y-type zeolite catalysts dramatically increased FCC conversion and gasoline yield at the expense of octane number. This was primarily the result of reduced olefin content in the gasoline.4 The zeolites used in today's "octane catalysts" are high-silica (dealuminated) Y zeolites, usually the ultrastable Y (USY) type.
USY zeolites were first developed by Davison Chemical Division, W.R. Grace & Co., in 1964. The Si/Al ratio usually exceeds 3 and the cation is H+.
Another zeolite used today in octane catalysts is ammonium fluorosilicate treated Y (AFSY), introduced by Katalistiks International Inc. in 1986, under the trade name LZ-210. AFSY is a chemically dealuminated and stabilized zeolite. The Si/Al ratio varies from about 6 to 13.
As the zeolite is dealuminated, the unit cell size shrinks as some of the framework alumina is expelled. The more highly dealuminated the zeolite and the lower the unit cell size, the lower the acid site density and the rate of hydrogen transfer reactions. 6
Compared to conventional REY catalysts, USY catalysts reduce gasoline paraffins and increase olefins. Naphthenes and aromatics do not change significantly.
The increase in gasoline olefinicity provided by USY catalysts leads to substantial research octane number (RON) improvements, with the greatest boost in the heavy fraction rather than the lighter fraction. Much less improvement in motor octane number (MON) is seen, because this property is enhanced by increasing gasoline component branching and aromaticity.
The octane increase seen with USY catalyst is accompanied by a significant drop in gasoline selectivity, caused by secondary cracking reactions.
Bottoms cracking may improve, because USY catalysts typically have higher zeolite contents to compensate for lower inherent activity (dealumination reduces catalytic activity). Thus they have a higher external zeolite surface area.
The degree of octane enhancement achievable with USY zeolite also depends on the sodium content and the amount of rare earth exchange.
The presence of rare earth in the USY zeolite (RE/USY), or in combination with conventional Y zeolite (REY/USY), improves gasoline selectivity at the expense of some octane, and is often used to maximize gasoline octane-barrels. Catalysts containing only USY zeolite are used when maximum gasoline octane is the primary objective.
The use of USY catalysts has steadily increased since the early stages of lead phasedown, and now accounts for about 70% of total U.S. FCC catalyst usage. The extra C3 and C4 olefins produced with USY catalyst can be alkylated if additional alkylation capacity is available (unfortunately USY catalyst also decreases the yield of isobutane, which is needed for alkylation).
In addition to increasing the total butylenes yield, USY catalyst can provide a higher ratio of isobutylene to total butylenes than REY catalyst.7 Isobutylene can be used in the manufacture of methyl tertiary butyl ether (MTBE) or ethyl tertiary butyl ether (ETBE) for use in gasoline.
Since the use of USY catalyst does not require any capital investment, it is an easy, cost-effective way to increase gasoline octane. Catalyst cost does increase, however, because USY zeolite is more expensive to manufacture and is less active than conventional Y zeolite.
Also, changing catalyst in an FCC unit (FCCU) is time consuming-the equilibrium catalyst in a commercial unit may consist of mixtures of different Y zeolite catalysts with different activities and degrees of dealumination. Subsequently determining accurate yield and quality shifts with the new catalyst is difficult, even with today's sophisticated instrumentation.
COKE SELECTIVE
In addition to their octane-enhancing characteristics, another important feature of USY catalysts is that they have good coke selectivity, i.e., they produce lower delta coke than a conventional REY catalyst.
Delta coke is an important variable affecting the FCC reactor-regenerator system. It is simply the difference between coke on spent catalyst and coke on regenerated catalyst, and it is related to the catalyst type, feed type, and process conditions. Delta coke is defined as coke yield divided by the catalyst-to-oil ratio (C/O), in lb/lb.
The coke yield (wt % of feed), on the other hand, is determined by the unit heat balance, in which the reactor heat requirements are met by the combustion of coke in the regenerator.
At a constant reactor temperature, a coke-selective catalyst reduces the regenerator temperature. Coke-selective catalysts also allow more flexibility in running the FCC, compared to the use of a conventional catalyst-particularly when the regenerator air compressor or temperature are near their maximum.
For example, the reactor temperature can be increased for higher octane, the catalyst circulation or activity can be increased for higher conversion, or heavier feeds can be processed.8
ZSM-5 ADDITIVE
A novel zeolite, ZSM-5, was introduced by Mobil in 1986 as an octane-enhancing additive to other FCC catalysts. ZSM-5 is a high-silica zeolite with an Si/Al ratio from 10 to 500, having a smaller pore size than Y zeolite (5.5 A. vs. 7.4 A.), and an H+ cation.
ZSM-5 selectively cracks low-octane straight chain paraffin and olefin components at the higher end of the gasoline boiling range to mainly C3 and C4 olefins. Some olefins may be isomerized to more branched, higher octane components.
ZSM-5 does not affect aromatics or naphthenes. It is normally used in small quantities, typically 1-5% of the conventional FCC catalyst.
ZSM-5 is an octane booster because of its unique shape-selective properties. The smaller pore openings of ZSM-5, as compared to Y zeolite, restrict the access of branched and cyclic hydrocarbons to the active cracking sites. Gasoline octane is increased because higher-octane branched components and aromatics are maintained and concentrated in the gasoline.
As with USY catalysts, ZSM-5 has the greatest octane-boosting effect on the heavier (C7-C13) gasoline components, and some cycle oil range paraffins may be cracked. Both RON and MON may increase, the latter because low-MON olefins are cracked.
Some gasoline yield loss is associated with ZSM-3 use. If sufficient alkylation capacity is available, this can be offset by converting the extra olefins to alkylate, assuming adequate isobutane availability (from the catalytic reformer, possibly supplemented by off site purchases).
Alternatively, ZSM-5 increases isobutylene yield, thus increasing MTBE production. In either case, the octane advantage of ZSM-5, as with USY catalysts, is further enhanced.
The effect of ZSM-5 is dependent on the composition of the base gasoline. FCC gasoline produced with REY-type catalysts is rich in straight-chain paraffins, the most reactive molecules for ZSM-5 cracking. Increases of 2 RON or higher can be attained with ZSM-5 addition.
If the base catalyst is USY, the base octane is usually higher, and further octane increases via ZSM-3 addition may result in significant gasoline yield loss.9
Since its introduction, the use of ZSM-5 zeolite in fluid catalytic cracking has been growing.10 ZSM-5 does not increase C2- production or coke make. If the regenerator air compressor or the recovery section is limited, ZSM-5 may be more advantageous than other octane-increasing options such as increasing reactor temperature.
ZSM-5 also provides a quicker octane boost than a time-consuming switch to a new FCC octane catalyst. All of the major FCC catalyst suppliers offer ZSM-5 additives that can be used with cracking catalysts (REY, USY, or RE-USY zeolites).
OTHER OCTANE CATALYSTS
Other types of zeolites besides USY, AFSY, and ZSM-5 have also been shown to give higher gasoline octane than can be obtained with conventional Y zeolites, but no commercial applications have yet been reported.
Such zeolites include families of phosphorus-containing zeolites discovered in the early 1980s (SAPO, MeAPO, MeAPSO), mordenite, different members of the ZSM-5 family (ZSM-11, -12, 23, -35, -38), silicate, zeolite 0, and offretite.
RESID CRACKING
Increasing amounts of residual feedstocks are being processed in FCCUS. Research has been devoted to developing FCC catalysts and additives to cope with and mitigate the high levels of coke precursors and metals in resid feeds, while maintaining good conversion and selectivity to valuable liquid products.
Coke-selective and metals-resistant catalysts, metals passivators, and SOx emission-reducing catalysts are now available to refiners. And catalyst manufacturers are seeking further improvements in resid catalysts.
There is no optimum catalyst for all resid processing applications. The important items to consider in choosing a resid FCC catalyst are the objectives and the specific operating constraints of the unit.
As previously discussed, dealuminated catalysts such as USY have an inherently low tendency to produce catalytic coke. This can be an important advantage in processing high-Conradson carbon residue (CCR) resid feeds.
FCC feed CCR content is an indication of its coking potential because much of the CCR produces rapid coke deposition on the catalyst, depending on the e of feed, catalysts and condition. 11 12
A slide valve or plug valve-controlled FCC operates at essentially constant coke make with no additional catalyst-cooling capacity. As the feed CCR increases, the regenerator temperature increases, the C/O ratio decreases, and conversion declines.
Use of a USY catalyst with lower delta coke than conventional REY catalysts can improve the heat balance of the system by lowering the regenerator temperature. Air compressor limitations can also be alleviated.
Some FCCU operators are less concerned with minimum catalyst coke selectivity when processing resid, particularly when catalyst coolers are used for external heat removal from the regenerator.
A moderate amount of matrix activity is valuable for cracking the largest molecules, which cannot gain access to the diffusion-limited zeolite. The zeolite/matrix activity balance should be maintained in the unit, i.e., both should deactivate at similar rates.
A unit constrained by the air blower or regenerator temperature may require a catalyst with very low coke selectivity. 13 An active matrix under these circumstances may have the net effect of lowering conversion and bottoms cracking because of a lower C/O ratio in a heat-balanced unit, because matrix activity has poor coke selectivity.
A USY zeolite catalyst with little or no rare earth or matrix activity and a high zeolite content for high activity may be desirable in this case.
ADDITIVES
FCC catalytic additives are important tools refiners use to meet particular yield, product property, or environmental requirements. Additive choices continue to increase (see related article, OGJ, Sept. 23, 1991, p. 50).
Platinum CO-combustion promoters, introduced by Mobil in 1974, were the first significant application of additive technology to the FCCU. In addition to small-pore ZSM-5 additives for octane enhancement, other additives include:
- Passivation agents routinely used to counteract nickel and vanadium
- SOx-reduction additives used to reduce SOx emissions from the FCC regenerator
- High-density fines used as fluidization aids.
CATALYST MANUFACTURE
There are two categories of FCC catalyst manufacturing:
- Processes where the zeolite is prepared first and then incorporated into a matrix
- Processes where the zeolite is crystallized in situ in the macropores of a calcined, natural clay-derived matrix.
Processes of the first type are used by most catalyst manufacturers. Engelhard, a catalyst manufacturer and a leading producer of natural kaolin clay, has developed processes of the second type.
The first type of process can in turn be divided into two groups:
- The zeolite is ion exchanged with the appropriate cation prior to incorporation into a matrix
- The zeolite is exchanged after its incorporation into a matrix (postexchange).4
The second approach is preferred among catalyst manufacturers.
Manufacturing, practices producing FCC catalyst-primarily 40-60 m particles in their final form-can vary widely. Simplified conceptual schemes are shown in Fig. 2 for both conventional REY zeolite and USY zeolite.
The major operations are synthesis and ion exchange of the zeolite, preparation of the matrix, intimate mixing of the zeolite with the matrix components, and spray drying. USY zeolite catalysts are also postexchanged.
Commercial manufacture of Y-type zeolites involves readily available, inexpensive raw materials, including a silica source, an alumina source, and a strong base such as sodium hydroxide.
The materials, in proper stoichiometric ratios, molarity, and state (solution or colloidal dispersion), are heated at a given temperature for a period that gives the maximum purity of a given structure. NaY "seeds" can be added to the slurry to initiate the crystallization process
Initially crystallized NaY particles are very small- on the order of 1-7 m. Most of the sodium is then removed by cation exchange with rare earth cations, or rare earth cations plus H+ NH4+, which can be converted to H+.
Inexpensive rare earth sources such as monazite or bastnasite sands, generally in chloride salt form, are used. These are rich in cerium, lanthanum, neodymium, praseodymium, etc. 14
USY zeolite can be produced from the NaY zeolite by partially exchanging the sodium with ammonium ions, dealuminizing the zeolite by controlled high-temperature steaming (at about 760 C.), exchanging most of the remaining sodium with ammonium ions, and then calcining to drive off ammonia.
In its final form, the zeolite contains less than 1% Na2O and has a unit cell size of about 24.55 0.02 A. The USY zeolite can be made more active by ion exchanging with rare earth cations. The amount of rare earth depends on the desired balance between activity, gasoline selectivity, and octane enhancement. 4
Significant quantities of alumina removed from the zeolite framework during the dealumination process remain as debris in the crystal structure, and function as a nonselective catalytic agent. However, recent studies have shown that the presence of some nonframework aluminum is essential for optimum activity and selectivity in FCC. 15
Some manufacturers remove part of the nonframework aluminum by ion-exchange at low pH (acid leaching). This also reduces the sodium content of the zeolite to about 0.1 wt % Na2O.4
ZSM-5 zeolite can be incorporated into the catalyst matrix by mixing it with other catalyst components prior to spray drying. When ZSM-3 is used as a separate additive it is usually spray dried with an inert binder.4
CHARACTERIZATION
Physical and chemical analyses provide clues in predicting catalyst behavior. Important catalyst properties include attrition resistance, pore volume, pore size distribution, particle size distribution, surface area, zeolite unit cell size, alumina type and content, rare earth content, and sodium content.4
The thermal and hydrothermal stability of zeolites is also important. Short time, high-temperature steam is used to deactivate fresh catalysts, simulating the commercial unit environment, prior to laboratory tests such as the fixed-bed microactivity test (MAT).
The MAT is designed to measure the conversion and selectivity of a catalyst with a standard feed under fixed conditions. Accurate time and temperature control (within 1 C.) is essential for reliable MAT conversion results.
Steam deactivation conditions should be chosen to correlate with commercial equilibrium catalyst performance, both in activity and selectivity. The MAT is usually conducted with both mildly and severely steam-deactivated catalyst samples. Use of a metals-impregnated catalyst and a resid-type feed also demonstrates the catalyst's resid cracking capability.
Laboratory evaluation methods alone are not sufficient to evaluate FCC catalysts. Lab data combined with pilot plant tests on commercial equilibrium samples and reliable commercial test-run data is the best way to evaluate FCC catalysts.
Catalyst comparisons based only on laboratory data can be misleading because of differences in matrix activity. Laboratory steaming conditions may deactivate the zeolite components, but not the active matrix. The MAT results and coke selectivity in particular, may then be overstated with an active matrix catalyst.
FCC CATALYST MARKET
The commercial requirement for FCC catalyst makeup determines the magnitude of the FCC catalyst market. Catalyst makeup is needed to compensate for catalyst loss in the regenerator due to attrition. Also, many FCC operators deliberately withdraw catalyst from the unit to maintain catalyst activity at the desired level or to keep the catalyst metals content within reasonable limits.
Average U.S. FCC catalyst consumption in 1990 was 0.23 lb/bbl (0.10 kg/bbl).lo FCCs running light gas oil feedstocks use about 0.15 lb/bbl (0.07 kg/bbl), while heavy resid feeds may require 0.6-1.0 lb/bbl (0.27-0.45 kg/bbl).
The U.S. dominates the FCC catalyst market with over half of worldwide FCC capacity. As the largest single market for refining catalysts, the U.S. FCC catalyst market is currently about $300 million/yr. The next largest market, Western Europe, is about one third the size of the U.S. market.
Market growth is expected to be steady, but slow. SRI projects U.S. FCC catalyst consumption to increase from 180,000 to 200,000 metric tons/year between 1988 and 1993-an average annual growth rate of 2.2%. Western Europe consumption is expected to increase from 55,000 to 60,000 metric tons/year (1.8%/year) over the same period.
The Far East market is currently small-about 19.8 million lb/year (9,000 metric tons/year)-but shows promise for high growth. Many refineries are now being constructed or planned in that region, and the Japanese refining industry has recently been restructured. Most of the new FCCUs will process at least some heavy resid feedstocks.
Current U.S. catalyst consumption is only about half of manufacturing capacity. During the time of high crude oil prices and heavier feed processing, catalyst consumption increased and manufacturers expanded facilities. With recent lower crude prices, catalyst market growth has slowed, creating a highly competitive catalyst market.
The number of suppliers has declined through acquisition and joint ventures. Western Europe has more catalyst suppliers than the U.S., though the market is smaller. Because the European catalyst business is already a Europe-wide business, the implementation of a single European market in 1992 is not likely to have a substantial effect on the structure of the industry.
With intense competition, it is not surprising that FCC catalyst profit margins are reportedly no more than 3-4% of sales. Catalyst prices average $1,400-1,500/ton, though USY zeolite octane catalysts are priced higher.
U.S. refiners may be unwilling to pay more than about $2,000/ton because of tight operating budgets, even if they gain extra benefits. FCC catalyst is generally the second greatest refinery operating expense, after crude oil purchases.
ACKNOWLEDGMENT
Donald G. Greenaway, formerly with SRI's petrochemicals, polymers, and energy center, contributed to the information in this article.
REFERENCES
1. Dougan, T.J., et al., "The Role of Fluid Catalytic Cracking (FCC) Process in Reformulating Gasoline," paper presented at the National Conference on Octane and Reformulated Fuels, San Antonio, Mar. 27-29, 1990.
2. Meyers, R.A., Handbook of Petroleum Refining Processes, McGraw-Hill, 1986.
3. Chen, N.Y., et al., "Industrial Catalytic Applications of Zeolites," Chem. Eng. Progress, 84, 1 (February 1988), pp. 32-41.
4. Scherzer, J., "Octane-Enhancing, Zeolitic FCC Catalysts," Catal. Rev.-Sci. Eng., 31, 3 (1989), pp. 215-354.
5. Humphries, A., et al., "Zeolite Components and Matrix Composition Determine FCC Catalyst Performance," Technology, Feb. 6, 1489, pp. 45-51.
6. Pine, L.A., et al., "Prediction of Cracking Catalyst Behavior by a Zeolite Unit Cell Size Model," J. Catalysis, 85 (1984), pp. 466-76.
7. Stokes, G.M., et al., "Impact of Operational and Catalytic Effects on FCC Gasoline Properties," Paper No. AM-90-10, 1990 National Petroleum Refiners Association annual meeting, San Antonio, Mar. 25-27, 1990.
8. Wear, C.C., "Coke Selective Fundamentals," Technical Brochure No. 75, Davison Catalagram, W.R. Grace & Co., Davison Chemical Division (1987), pp. 4-9.
9. Biswas, J., et al., "Octane Enhancement in Fluid Catalytic Cracking. 1. Role of ZSM-5 Addition and Reactor Temperature," Applied Catalysis, 58 (1990), pp.1-18.
10. Hoffman, H.L., "Catalyst Market Estimated," Hydrocarbon Processing, 69, 2 (February 1990), pp. 53-54.
11. Avidan, A.A., "Recent and Future Developments in FCC," Paper No. 191A, AIChE annual meeting, Chicago, Nov. 11-16, 1990.
12. Nieskens, M.J.T.C., et al., "Shell's resid FCC technology reflects evolutionary development," OGJ, June 11, 1990, p. 37.
13. Steoks, G.M,, et al., "FCC Resid Processing: An Overview," Heck, R.H., et al., eds., Fundamentals of Resid Upgrading, AIChE Symposium Series, 273, 85 (1989), pp. 58-77.
14. Wilke, C.R., ed., Fluidization and Fluid-Particle Systems, Reinhold Chemical Engineering Series, Reinhold Publishing Corp., New York.
15. Humphries, A., et al., "Catalyst Helps Reformulation," Hydrocarbon Processing, 70, 4 (April 1991), pp. 69-72.
Copyright 1992 Oil & Gas Journal. All Rights Reserved.
