Silica-Alumina Petroleum Cracking Catalyst WILL H. SHEARON, Jr., Editor, in collaboration with
W. R. FULLEM, W. R. Grace & Co., Davison Chemical Division, Baltimore, Md.
THE
development of catalytic cracking, one of the most significant technical advances of the last three decades, has effectively revolutionized the petroleum industry (8). Nearly 100% of today’s gasoline consists of molecules, made in the refinery, and not present in the original feed stocks. This gasoline represents not only an increase in the amount of fuel available, but also an increase in the fuel value, as so much of this man-made gasoline consists of the high octane fractions. The by-products of the catalytic crackers have led to many new materials, such as plastics and synthetic rubbers, and founded a new industrial complex, the petrochemical industry. Catalytic cracking received its first commercial application in 1936, when Eugene Houdry’s work led to the construction of a 2000-barrel-per-day, fixed bed, three-case cracker. I n the fixed bed catalytic cracker, vaporized gas oil and air are passed alternately over the catalyst bed in each case, or reactor. In the process of cracking, the oil deposits coke on the catalyst, and after purging, this coke is burned off by the passage of the air. Thus, in a three-case unit, one case is cracking while another is burning carbon, and the third is being purged. Another fixed bed plant, with a capacity of 10,000 barrels per day, was completed in 1937, and by the time
World War I1 arrived, there were 16 Houdry units operating or under construction. All in all, 29 fixed bed units with a 375,000 barrel daily charging capacity were built. The next step in developing petroleum cracking substitutes a moving catalyst bed for the original fixed bed. These Thermofor units used mechanical elevators to circulate the catalyst between separate cracking and coke-burning zones. I n newer installations, the mechanical elevators in these moving bed crackers have been replaced by pneumatic lifts, in which the catalyst is raised by gaseous pressure and flows downward by gravity. Moving bed crackers use fairly large granular, pelleted or bead catalysts. This fluid catalytic cracking process satisfied the enormous demand for high octane gasoline during World War 11. Today there is installed capacity in the United States fluid cracking units of about 3,500,000 barrels offeed per day. Catalyst Requirements Are Stringent T h e catalyst used in this process must have a number of striking qualities. I t must be stable to thermal shock, either dry or in the presence of steam. I t is exposed to an endothermic reaction (cracking), and also to a highly exothermic reaction (regeneration). It must show a high degree of activity in the cracker, and it must retain this
Equipment and Alloys Used at Davison’s Lake Charles Plant Major Equipment
Type of Alloy
Spray dryers, 3 Primary filters, 4 Secondary filters, 2 Agitators, 13 Pumps, 26 High pressure pump heads, 4 Pumps, 7 Agitators, 2 Piping
3 10 and 3 0 4 316 316
316
Weight of Alloy, Lb.
150,000 90,000 54,000 11,900
Worthite 10,400 2,200 30 4 Duriron 2,800 3,000 Durimet 20 7,000 316 All control valves and instrument bodies are also Type 3 16 or Durimet.
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activity for a reasonable and economical period of time. I t must be selective, producing the desired distribution of products. During its life in the cracking units, it must stand severe mechanical strain, for excrssive production of easily lost “fines” through abrasion between particles and against the walls of the unit constitutes an economic waste. During the process, the catalyst is exposed to hydrocarbon vapors, sulfur and nitrogen compounds. water vapor, carbon monoxide, carbon dioxide, and air at temperatures up to 1200’ F. The hydrocarbon vapors may contain trace amounts of metallic contaminates which are catalyst poisons ( 3 ) . Two types of fluid catalyst are extensively used commercially-synthetic silica-alumina and activated natural clays. Silica-alumina cracking catalyst is principally manufactured by adding an aluminum salt to a silica hydrogel. It derives its catalytic activity both from chemical composition and the physical characteristics of the available surface (6, 7). It is the most widely used cracking catalyst and is so favored because it yields the highest octane gasoline and the largest amount of petrochemical raw materials, such as butylenes and other Cq hydrocarbons. Davison Is the largest Producer of Fluid-Type Cracking Catalyst
W. R. Grace & Co., Davison Chemical Division, has synthetic fluid cracking catalyst plants at Curtis Bay, Md., and Cincinnati, Ohio, in addition to the Lake Charles, La.,plant described here An affiliate, Davison Chemical Co. Ltd., produces the same catalyst at Valleyfield, Quebec, Can. The domestic plants plus the Davison affiliate have an installed capacity of over 200,000,000 pounds per year. The Davison Division also produces petroleum reforming and specialty catalysts, sulfuric acid, sodium silicate, and a variety of other products for the chemical and fertilizer industries. The Lake Charles site was chosen for this catalyst facility because of the accessibility of raw materials, utilities, and markets. Almost all of the cracking catalyst produced a t Davison is consumed within a radius of 200 miles and a major customer is only a few miles away.
The Calcasieu River, which is adjacent to the plant, provides a 30-foot channel leading to the Gulf of Mexico and the Intracoastal Canal. Sulfuric acid, purchased from a nearby installation, can be delivered either by barge or by rail. Silica sands with low iron oxide content sre available in the area, and are used by Davison in producing the sodium silicate needed in the making of the catalyst. The plant, costing $7,000,000, has been designed for continuous and almost automatic operation. At any given time nine men, stationed at five instrument panels, are in complete control of the process. Other employees in maintenance, quality testing and control, materials handling, office and clerical work, and administration bring the total working force, to about 160, for 7-day' 24-hour operation. When fluid cracking catalyst was first produced commercially a t Davison's Curtis Bay plant in 1942, the silicaalumina particles were formed by grinding. The commercial production of spray dried microspheroidal catalyst was started in 1946 and today all synthetic catalyst is made by spray drying. Spray drying produces a form with two major advantages. The relatively uniform particle size contains fewer of the "fines" which are lost through the cyclones of the cat cracker, and the spheroidal shape is more easily fluidized and less sensitive to the production of fines in the cracker by attrition between particles. Silica-alumina microspheroidal material exhibits less attrition than either the old type ground synthetic catalyst or natural catalyst. The spray dried catalyst turned out at Lake Charles is composed of microspheroids principally from 20 to 80 microns in diameter. The particle size may be controlled by the size and shape of the spray dryer nozzles, the pressure in the nozzle head, and the characteristics of the material being dried.
Flow Rates Are Automatically Controlled
The Lake Charles plant is designed for a continuous process for producing silica-alumina gel slurry. The proportions of the various constituents are controlled by instruments which also indicate the flow rates. All of the liquid raw material streams are controlled and measured by flow controlling and recording rotameters. The flow of dilution water a t several points is controlled and indicated by rotameters, and the slurry flows are indicated and controlled by Venturi-type instruments. Continuous operation is assured by an adequate inventory of raw materials. Sodium silicate is made a t the Lake Charles plant and stored as a 40" BC. solution in three 303,000-gallon tanks.
Concentrated acid is diluted and cooled in a two-step operation in this equipment
Composite view of the slurry preparation area: These cypress tanks have a total working volume of 57,960 gallons. Each tank i s equipped with a 7.5-hp. motor-driven stainless steel, paddle-type agitator
The solution is transferred as required from the storage tanks to a single 51,700gallon tank near the catalyst plant. Barge facilities are provided on the river bank for the unloading of 98% sulfuric acid, and a 227,000-gallon storage tank is connected by a pipeline to the three acid storage tanks adjacent to the plant. Each storage tank has a 51,700-gallon capacity. The acid is diluted to 78%, the correct amount of water being adjusted by a ratio controller. After dilution, the acid is cooled from 280' F. to 120' F. in a carbon pipe cooler (6E)consisting of 10 carbon pipes of 1-inch inside diameter, cooled by water. The acid is diluted again to 40'?& in a carbon nozzle and cooled to 130' F. in another carbon tube unit. Diluted 40" B& sodium silicate and 40y0 sulfuric acid are combined at
controlled rates, and the resulting alkaline hydrosol is continuously agitated in one of three cypress tanks. The pH is checked by the operator periodically with phenolphthalein. Gelation time is also determined as a quick check on the progress of the reaction. The acid flow is increased to speed up gelation and decreased to retard it. The hydrosol exists only for a very few minutes, and then changes to a hydrogel dispersed in its own syneresis liquid. Close control is needed to give the desired end characteristics. Concentrations of silicate and acid are carefully checked a t frequent intervals. The operator checks pH and gelation time on the spot, and the temperature, pH, and flow rates are followed on the control panel, a few feet away from the tanks. Agitation must be continuous. VOL. 51, NO. 6
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Each cypress tank is 13 feet deep and has an inside diameter of 10 feet. They are equipped with motor-driven stainless steel, paddle-type agitators, rotated at 25 r.p.m., with five sets of blades pitched at a 45' angle. Agitators are powered with 7.5-hp. motors with a V-belt drive. These tanks have a full volume of 7640 gallons, but working volume is about 6440 gallons, allowing 24 inches for outage. The centrifugal pumps, used to advance slurry from the tanks through the system, have a capacity of 290 gallons per minute a t 114-foot head and are driven by 20-hp. motors. These pumps, and other pumps throughout the gel preparation area, are backed up with spares, because interruption in the time schedule would alter the properties of the slurry. After the initial gel formation, more 40% sulfuric acid is added to complete the gelation and the resulting hydrogel is acidic. The acid is added in a mixing nozzle and the mixture agitated continuously. Tank car delivered anhydrous ammonia is diluted to 30% strength as it is unloaded into one of six horizontal storage tanks, each having a capacity of 41,000 gallons. Ammonia leaves the tank cars under its own pressure, a t 28 to 30 gallons per minute. T h e temperature rises to 175' F. as it is mixed with water from the ammonia storage vent tanks. The mixing nozzle is controlled by manual valves. Water level in the vent tank, used for scrubbing vapors from the tank being loaded, is automatically controlled, and this water is pumped to the dilution nozzle by a cast iron centrifugal pump. The 30% ammonia solution is cooled to 90' F. in a double pipe cooler of 18 G-fin sections, each 23 feet long, with
SILICA- ALUM INA CATALYST
inner tubes of 1.5 inch steel. The outside tube area is 370 square feet and the design is based on an over-all cooling coefficient of 210 B.t.u./hour/square foot/' F. The 185 gallons per minute of cooling water required is recovered and pumped back to the reservoir. Cooling water is automatically regulated to control temperature on the solution leaving the cooler. A back pressure controller on the 30% ammonia line maintains sufficient pressure to prevent flashing in the heat exchanger, and a density indicator enables the flow of water and ammonia to be manually adjusted to maintain proper concentration. Storage tanks, designed for 25-pound-per-square-inch gage, are equipped with rupture disks and pressure safety valves, and level gages are provided for inventory check. The diluted ammonia is combined with the slurry and the ammoniated mix-
Catalyst as Manufactured Is Tailored to the End Use Davison supplies an entire line of catalysts so that the refiner can choose the best suited one. Davison's own Technical Service Department assists the refiner in that choice if he so desires Chemical analysis, wt. %, dry basis Alumina, Ai208 Silica, Si02 Sodium oxide, NazO Iron, Fe Sulfate, SO1 Loss on ignition, 1500° F. Activity (vol. %, D L) Deactivated-1550° F., 3 hr. Deactivated-steam 60 p.s.i.g., 1050O F., 25 hr. Density A.B.D., g./cc. Pore volume, cc./g. Particle size analysis, C.A.E. screen, wt. yo 0-20 p 0-40 p 0-74 p , 200 mesh 0-105 p, 140 mesh 0-149 p , 100 mesh Average particle size, microns
+
c-1
F-1
13 86.8 0.02 0.03 0.3 13
F-2
C-1-26
F-1-25
F-2-25
13 86.8 0.02 0.03 0.3 13
13 86.8 0.02 0.03 0.3 13
25 74.8 0.04 0.03 0.5 13
25 74.8 0.04 0.03 0.5 13
25 74.8 0.04 0.03 0.5 13
52
52
52
52
52
52
31
31
31
35
$5
35
0.45 0.75 1 10 70 91 97
65
0.45 0.75
2
0.45
0.75
0.47 0.7
0.47 0.7
0.47 0.7
80 93 98
4 20 92 99 100
1 10 70 91 97
2 12 80 93 98
4 20 92 99 100
61
54
65
61
54
12
ture is advanced in the system by pumps similar to those used on the initial hydrogel slurry. Alumina hydrate, used to prepare the alum solution, is received in 50-ton closed hopper cars and stored in a 6800 cubic foot silo capable of holding 255 tons. The hydrate is transferred to the silo from the hopper cars by an oscillating conveyor at about 20 tons per hour. The two batch tanks for preparing the alum solution are fed by a bucket elevator, an oscillating conveyor, a weigh hopper, and screw conveyors. The tanks are of rubber-lined, acid-brick-lined construction, 12 feet deep and 11 feet in inside diameter. Total volume is 8300 gallons, with a working volume of 6500 galloh, allowing 30 inches for foaming. A single turbine-type agitator, powered with a 7.5-hp. motor, operates 24 inches above the tank bottom. Water is measured into the tank by a displacement meter and 98% acid is batched in by an automatic totalizing rotameter which can be set for any given batch size. Acid is pumped from storage tanks by centrifugal pumps rated a t 88 gallons per minute at 55 foot head with a 7.5-hp. motor. The finished alum solution is transferred to the rubber-lined alum storage tank by a pump rated a t 150 gallons per minute a t an 85 foot head. The alum solution is then pumped from its storage tank by a corrosion resistant alloy pump rated a t 66 gallons per minute against a head of 85 feet and is recyded through a loop line, with flow rate automatically indicated and maintained. The proper volume of the alum for combining with ammoniated slurry is measured by a timing mechanism which operates a two-position valve. The Active Complex I s Formed by Precipitation with Ammonia
After impregnating the silica hydrosol with aluminum sulfate, ammonia is VOL. 51, NO. 6
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Left. Vacuum pumps used for primary and secondary filtration. Each pump has a rated capacity of 2900 C.F.M. at 20 inches * . of Hg. Right. Spray dryer feeds sjurry pumps. i a c h pump has a rated capacity of 4750 gallons/hour at 1800 p.s.i.g.
added to precipitate alumina and form the catalytically active silica-alumina complex. Correct timing is essential in this process as the age of the silica gel has a direct bearing on the degree to which the alumina and silica plus water interact to form the postulated acidic hydrogen ions ( 7 ) . Fresh silica gel is less completely polymerized than more aged material and therefore is more prone to react with the alumina. I t has more acid groups on the colloid surface, to react with hydrolyzing aluminum salts to form the aluminum complexes. The aluminum in these complexes will be able to share two electrons with the oxygen of a water molecule tending to form the acidic hydrogen ions on the gel surface which are the actual sites of catalytic activity. Alum impregnated slurry is pumped to a mixing nozzle by a 318-gallon-perminute pump (at 128 foot head) driven by a 25-hp. motor. Ammonia flow to the mixing nozzle is automatically controlled, indicated, and recorded. Slurry is collected in one of three cypress tanks. The slurry is then pumped to the filter feed tank by a 15-hp. centrifugal rated a t 300 gallons per minute with a 46 foot head. Filters are drums, 11.5 feet in diameter by 16 feet long, made of Type 316 stainless steel (4E). Each of the four units has a filtering area of 575 square feet. Vacuum is obtained by a rotary water-sealed pump rated at 2900 cubic feet per minute at 20 inches of mercury with a 150-hp. motor (70E). The vacuum line connects to a high vacuum receiver which supplies the suction for the dewatering section of the filter. The low vacuum receivers are taken off the high vacuum receivers. Manual valves control the reduction in vacuum, and both high and low vacuum systems have the same filtrate and vacuum pumps. Slurry is pumped from the filter feed tank to the filters by a centrifugal pump rated a t 460 gallons per minute at an 88-foot head. Excess slurry is recycled back to the feed tank. Filtrate from the
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INDUSTRIAL
high vacuum receiver is discharged to the sewer. The filter cake is delivered by a series of belt conveyors to the reslurry tank. The filter cake is repulped with water heated by steam injection. The rate of water addition is controlled by a flow indicator and a hand control valve. The wooden reslurry tank is 9 feet in diameter and 10 feet deep, with a Type 316 stainless steel lining. I t is equipped with a stainless steel double motion agitator, the outer frame rotating at 14 r.p.m. and the paddles at 28 r.p.m. The 30-hp. motor has a spur gear drive. More efficient mixing is attained by recirculation through one of the three centrifugal pumps connected to the tank. These pumps are sized for 400 gallons per minute at an 88 foot head. The other two pumps push the slurry through the two self-cleaning, Type 302 stainless steel lined filters (3E) to the spray dryer feed tank. Two centrifugal pumps connected to this tank feed the suction side of the high pressure pistontype triplex pumps ( S E ) that feed the spray dryers. There are four of these pumps, one for each dryer plus a common spare. Atomizing pressure, automatically controlled. is 1800 pounds per square inch. The pistons are porcelain with rings of hard rubber and leather. Originally these pumps were equipped with stainless steel pistons but maintenance troubles led to their replacement.
Spray Drying Forms Microspheroid Spray drying is accomplished in three 22-foot diameter units (7323) each with a separate furnace (77E) for heating air. Each dryer has a wet collector, to salvage the small portion of the product which goes up the exhaust flue rather than down the dryer cone. The wet collectors are supplied with recirculating liquor by four 20-hp. centrifugal pumps of corrosion resistant alloy. The spray dryer nozzles of Type 316 stainless steel with carboloy inserts are one of the critical pieces of equipment in the plant and determine the final size and size distribution of t h e catalyst
A N D ENGINEERING CHEMISTRY
particles. Plugged nozzles present a problem, and the control panel of the spray dryer is not only equipped with a red light to indicate rising outlet temperature, but also with a horn to warn of excessive temperature. Plugged nozzles are also indicated by the number of strokes per minute of the high pressure pumps. A decrease in the number of strokes is a watched-for warning. At times the nozzle gaskets have burned when the nozzles become plugged and overheated. Changing from a red fiber gasket to an asbestos and stainless steel one largely solved this problem. The control panel for the spray dryer’s air heater is arranged so that the operation sequence for the heaters starts from the center outward. The heaters are protected by several devices which will cut off the gas supply if preliminary warnings are not heeded. The ignition flame for the gas burners is monitored by a n electronic scanner, ivhich actuates a light on the control panel. I n case of excessive dryer inlet temperatures, the air heater will automatically shut down, a horn will sound, and a red light indicating “high temperature dryer inlet” will go on. The high pressure feed pumps will also be shut down, and water is substituted for slurry in the dryer feed. The warning for rising dryer outlet temperature is the lighting of a red light, “rising temperature outlet.” When excessive temperature is reached a horn \ d l blow, and dryer and high pressure feed pumps will automatically shut down, while water again replaces the slurry. If the flamt in the gas burner goes out, a horn sounds and “flame off” lights up. The operator then shuts off the dryer feed, and changes the pumps over to water, before shutting down the unit. Each dryer uses roughly 54,000 cubic feet per hour of gas to dry the dilute slurry fed to it. Particle size is fixed in the spray dryers and 38 to 99% of the dry product is pumped to the two rotary sand table filters (5E) where the catalyst is washed. This dryer product is reslurried and then given a series of
S I L I C A-A LUMlNA CAT A L Y ST washings to remove sodium and ammonium sulfates. The washing is carried out with ion-free water. The washed catalyst, containing about 45y0 water, is removed from each filter by small screw conveyors, or scrolls. These two screw conveyors discharge into a chute which drops the catalyst into two flash drying units (23). Drying takes place in a stream of combustion gases into which the catalyst is dispersed by a 25-hp. cage mill. The catalyst, entrained by the hot gases, is carried into two cyclones which collect the product and deliver it to the conveyor. Two high efficiency collectors (7E) trap the catalyst which passes the cyclones. A fan between each cyclone and collector keeps the air stream moving. The conveyors transfer the material to a bucket elevator which feeds the product silos by a conveyor distributing system, where the material is aerated and permitted to slide down an incline. Five product silos are 60 feet high and 20 feet in diameter, each with a capacity of 350 tons of catalyst. Four of these silos are nested and the inner space is closed off to provide an additional small silo for day storage. Railroad hopper cars can be loaded in two hours by transfer conveyors from the silos. Trucks can be loaded in less than 30 minutes.
Process Water Comes from Wells Plant water requirements, in the range of 1000 gallons per minute, are obtained from two deep wells each with a capacity of 1250 gallons per minute. Wateris passed through a set of four Ferrosand filters (7E) to remove iron present to 1 p.p.m. The filters are dish-end tanks, 10 feet in diameter by 9 feet 10 inches deep. A bed of zeolite selectively removes iron and manganese to the level of 0.1 p.p.m. The zeolite is regenerated with a weak solution of potassium per-
manganate after treatment of each 923,000 gallons of water. Control equipment operates the units on a fully automatic basis, operating on a cycle timer which actuates a series of poppet manifold valves. After treatment, the water is collected in a 250,000-gallon concrete reservoir which acts as a process surge and also as a fire protection supply. Process water is supplied to the catalyst and silicate plants by three 75-hp. pumps, two operating and one reserve. Cation-free water, required for catalyst washing, is produced in a set of cation exchangers (8E). Three tanks, 5 feet 6 inches in diameter by 8 feet high, of rubber-lined steel, are equipped with manifold piping and automatic valves so that two units operate and one regenerates a t all times. Each unit contains 76 cubic feet of ion exchange resin which is regenerated by stage injection of 9870 sulfuric acid into a water stream which is passed through the unit into the sewer. Acid is supplied from a steel tank 3 feet deep and 2 feet in diameter. The readily available natural gas, used a t the rate of 180,000 cubic feet per hour, is one of the attractions of the Lake Charles site. Electric power is supplied a t 69,000 volts, reduced to 440, 220, and 110 volts as required. Steam is supplied by two 15,000-pound-per-hour boilers (72E),one operating and the other a complete spare. These boilers also supply the silicate plant. Feed water is treated in a “hot process’’ water softener (74E),using soda ash and lime.
The Product Is Evaluated The analytical methods employed by Davison in producing cracking catalyst fall into three principal categorieschemical analyses, physical analyses, and performance analyses.
This view looking southeast shows seven sand and soda ash storage tanks or silos and two conveyors which load these silos from hopper cars. Immediately behind the storage silos is a general view of the silicate manufacturing building. On the left foreground can be seen the final product silos
Chemical Analyses. The methods employed here are generally standard analytical techniques. The materials are routinely analyzed for loss on ignition, iron, sulfates, sodium, aluminum, and silicon. Chlorides, nickel, vanadium, copper and calcium are also determined periodically, as they do have effects upon catalyst in use. Generally their percentage is so minute, however, that daily routine checks are not needed. The loss of ignition is determined by igniting a small portion of the catalyst at 1500’ F. for a 1-hour period. The loss, determined under these conditions, includes all free moisture and the sulfates of iron, aluminum, and ammonia. Iron is determined colorimetrically as the thiocyanate using the electrophotometer equipped with 525-mp filter. The iron content is calculated from a standard curve prepared from a Bureau of Standards iron sample. I n determining sulfate content, a catalyst sample is decomposed with hydrofluoric acid, and the fluorine removed by evaporation with perchloric and boric acids. The sulfates are then precipitated as barium sulfate by adding barium chloride. Weighing the precipitated barium sulfate permits easy calculation of the sulfate content. Sodium is determined by flame spectrophotometer. A sample solution from which all silicon has been removed by expelling with hydrofluoric acid is atomized into the flame. The light emitted a t 589-mp wave length is then measured by a standardized spectrophotometer. Sodium can also be determined by the standard analytical technique of precipitating it as the uranyl acetate. Aluminum is precipitated as the hydroxyquinoline salt using %hydroxyquinoline as the reagent. Results are usually calculated as AlzOa content from the weighed aluminum hydroxyquinolate precipitate. Another method used in the industry involves precipitation of aluminum hydroxide. Silicon generally is determined by difference and expressed as silicon dioxide. Silicon content can also be determined by volatilizing it as tetrafluoride, but this method was less accurate than the determination by difference. Standard analytical techniques are used for the small traces of chlorides, nickel, vanadium, copper, and calcium. Physical Analyses. The physical analyses are determined routinely on catalyst production for density, pore volume, particle size distribution, and attrition resistance. Surface area and pore diameter are also determined periodically on the material. The density is determined as a n apparent bulk density by securing the VOL. 51,
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JUNE 1959
725
volume of a known weight catalyst. This density has been empirically related to densities encountered in fluid unit operation and thus indicates what to expect from the catalyst operation. A compacted density also is used as a correcting factor in determining particle size distribution. Davison determines particle size distribution both by screen test and by a corrected air elutriation method. T h e screen test is used to determine that part of the distribution coarser than 74 microns (on a 200 U. S. mesh screen). T h e precision of screen tests on screens finer than a 200 U. S. mesh is poor, and determination of particle size on screens finer than that is not recommended. For catalyst distribution less than 74 microns in size, a modified Roller particle size analyzer is used. This unit consists of air humidification and metering facilities, a sample tube equipped with a fritted glass disk of coarse porosity, a glass thimble adapter, fines collection thimble, and four stainless steel cylinders, 9, 41/2, 2l/4, and l1/8 inches in diameter. These diameters are selected to give 0- to lo-, 10- to 20-, 20- to 40-, and 40- to SO-micron separations, respectively. T h e SO+ micron fraction is determined by difference and may be checked by the 744micron determination by screen test. T h e Corrected Air Elutriation (C.A.E.) method attempts to “see” the catalyst as the fluidizing stream in the catalyst cracking unit “sees” it. Because effective particle size distriblition is a function of density and particle diameter, this C.A.E. method incorporates a density correction in determining the final distribution of the catalyst. This density correction is applied to the diameters secured from the modified Roller apparatus, and the corrected diameters are plotted to give the resultant particle size distribution. Various other methods for determining particle size distribution in the fine sizes are used in the industry. Microscopic count (which is then calculated to a weight basis) is often used; sedimentation techniques are also popular. A usual way of determining these is to secure a time-hydrometer reading table as the catalyst settles through a fluid medium (generally isopropyl alcohol). Several package devices on the market use the sedimentation technique, settling the material in air or other media. An attrition test, run routinely on catalyst, attempts to secure a measure of the resistance of the catalyst to interparticle attrition. This test utilizes a high velocity air jet and the 9-inch Roller cylinder. The test is run for 5 hours and the results are calculated for two indices. Either of these indices indicates the attrition resistance. Davison prefers to use the amount of 0- to 20micron material formed during the test, divided by the initial amount of material
726
Catalyst Must Be Stable at High Temperatures I n use, the catalyst is subjected t o severe thermal and steaming treatment. Davison checks its product performance in the laboratory under conditions simulating that found in practice. The following profiles are typical of the values determined
1000
1250 1550 1650 1700 1750 Steamed
60 60 52 43 36 27 31
57 56 52 45 37 28 35
larger than 20 microns, to give a percentage of the amount of 0- to 20-micron fines that could be formed. Surface area is determined by a slight modification of the Brunauer-EmmettTeller method using the nitrogen adsorption isotherm. Pore volume is determined principally by a water displacement method but can also be checked by the Brunauer-Emmett-Teller method. Average pore diameter is calculated from the measured surface and pore volume. Performance Analyses. Davison has adapted a catalyst activity test from the basic structure of the “Jersey D L” (distillate plus loss) test. Activities are expressed as ‘‘yoD L” and can be determined on fresh, thermally deactivated, and steam deactivated samples. Ordinarily the activities are not run on fresh catalyst because of poor precision ( 4 ) . In the same activity test, carbonand gas-forming characteristics are measured. These carbon- and gas-forming characteristics are indices of the selectivity of the catalyst. The entire test is empirical but over a long period of time, the values derived from it have been related to refinery operation. Various other activity methods are used in the industry but almost all use the basic idea of cracking a gas oil under a standard set of conditions.
+
+
As the Petroleum Industry Goes, So
Go the Catalyst Manufacturers An increase of just one octane number in gasoline requirements is a large stimulus to the production of cracking catalyst. The trend toward increased octane ratings is reinforced by the increased compression ratios in modern automobile engines, and the continued use of high octane aviation gasoline. An autumobile with a 12 to 1 compression ratio requires 100 octane fuel ( Z ) , and although the change to low cost, low quality fuels for jet and turbine engines
INDUSTRIAL A N D ENGINEERING CHEMISTRY
is increasing, reciprocating engine aircraft will continue to be used for some time to come. .4n advantage of catalytic cracking, which is indirectly tied in with aviation gas, is the production of gaseous olefins such as propylenes and butylenes, which can be used as the feed stock for alkylation units. T h e oil industry, and consequently the production of fluid catalyst, is tied very closely to world conditions. In a military economy, the production of refined petroleum products, and therefore of the catalyst used to make them, would grow rapidly, while in a peacetime economy, growth would be of a more deliberate nature.
Acknowledgment The authors gratefully acknowledge the assistance of J. B. Jones of Davison Chemical Division, and Kevin J. Bradley, White Weld & Co., formerly assistant editor, I/EC, in the preparation of this article.
References (1) Collier, C. H., “Catalysis in Practice,” p. 64 (1957). (2) Service, W. S., Payne, R. E., .4skey, W. E.. Western Petroleum Refiners
Assoc., 46th .4nnual Meeting, San Antonio. Tex.. March 1958. (3) Shankland, R. V., Advances in Catalysis 6 , 364 (1954). (4) Shankland, R. V., Schmitkons, G. E., Proc. A m . Petrol. Inst. 27, Sect. 111, 55-77 il047)
(5)’-Sitt;g, Marshall, “Petroleum Refiner Process Handbook,” p. 102 (1952). (6) Tamele, M. W., Discussions Faraday Sac. 8, 270 (1950). ( 7 ) Thomas, c. w., Ih-n. ENG.CHEM.41, 2564 (1949). (8) Vage, H. H., “Catalysis,” vol. VI, chap. V, p. 407, 1958.
Processing Equipment (1E) Buell Engineering Co., Inc., New York, N. Y., secondary collectors on flash dryers. (2E) Combustion Engineering, Inc., Raymond Division, Chicago 22, Ill., flash dryers. (3E) Cuno Engineering Corp., Meriden, Conn., filters. (4E) . . Dorr-Oliver Inc., Stamford, Conn., primary filters. (5E) Ibid., secondary filters. (6E) Falls Industries, Solon, Ohio, HzS04 carbon pipe cooler. (7E) Hungerford & Terry Inc., Clayton, N. J., Ferrosand filters. (8E) Ibid.,water deionizers. (9E) Manton-Gaulin Mfg. Co., Inc., Everett, Mass., MS pumps. (10E) Nash Engineering Co., The, Norwalk, Conn., pumps. (11E) Peabody Engineering Corp., New York, N. Y., spray dryer furnaces. (12E) Union Iron Works, Erie, Pa., boilers. (13E) Whiting Corp., Swenson Evaporator Division, Harvey, Ill., spray dryers. (14E) Worthington Corp., Harrison, N. J., boiler water softener. . ’
