April 1953
-
.
INDUSTRIAL AND ENGINEERING CHEMISTRY
petitive features of the reactions involved. The present work has shown that ammeline reacts in the presence of ammonium salts t o form guanidine and that guanidine is reconverted to urea when water is added t o the reaction mixture. Hence, both ammeline and guanidine must undergo thermal decomposition at or below 300” to form the same intermediates as urea, Guanidine and ammeline must be formed at a temperature lower than that a t which urea is in equilibrium with its thermal decomposition products; hence there is competition during the cooling period for cyanic acid and cyanamide and in the presence of an acid the rate of formation of guanidine (via cyanamide) is vastly greater than the rate of formation of ammeline. Acknowledgment The work described in this paper was supported by the United States Navy, Bureau of Ordnance, under Contract N123s-67363. Samples of guanidine nitrate, ammeline, and certain other materials that were employed less directly were supplied through the courtesy of J. R. Dudley, American Cyanamid Co. The authors wish also to express their appreciation for the continuing interest of Gilbert B. L. Smith, U. S. Naval Ordnance Test Station, China Lake, Calif., and Sol Skolnik, U. S. Naval Powder Factory,
849
Indian Head, Md., in these studies and related programs currently in progress in these laboratories. literature Cited (1) Bergstrom, F. W., J. Org. Chem., 2, 424 (1937). (2) Blair, J. S., J. Am. Chem. Soc., 48, 87 (1926). (3) Dakin, H. D., “Organic Syntheses,” Vol. 11, p. 555, New York, John Wiley & Sons, 1943. (4) Franklin, E. C., “The Nitrogen System of Compounds,” p. 114, New York, Reinhold Publishing Corp., 1935. (5) Grammont, A., Bull. soc. chim., 33, 123 (1923).
(6) Hill, W. H., Swain, R. C., and Paden, J. H., U. S. Patent
2,252,400 (1941). (7) Horn, D. W., J. Am. Chem. SOC.,37, 620 (1907). (8) Jacobson, R. S., Ibid., 58, 1984 (1936). (9) Johnson, W. C.. and Fernelius. W. C.. J. Chem. Educ., 6, 445 (1929). (10) King, H. J. S., Cruse, A. W., and Angell, F. G., J. Chem. Soc., 1932, 2929. (11) Sander, F., German Patent 527,237 (1928). (12) Smith, G. B. L., Sabetta, V. J., and Steinback., 0. F , Jr., IND.ENG.CHEM.,23, 1124 (1931). (13) Vozarik, A,, 2. angew Chem., 15, 670 (1902). (14) Werner, E A, J. Chem. SOC.,103, 1010 (1913). ACCEPTFD December 5, 1952.
RECEIVED for review May 26, I952
Testing Powdered Cracking Catalysts a PAUL H. JOHNSON
AND
CHRISTOPHER P. STARK
Phillips Petroleum Co., Bartlerville, Okla.
T
-, e .
HE: testing of cracking catalysts has become an important and permanent phase of refinery control. Dating from the earliest use of heat- and steam-sensitive catalysts, activity measurements have been a primary source of information for controlling the operation of a catalytic cracking unit. Of even greater importance than activity measurements is the determination of changes in catalyst characteristics which are caused by contaminants and which result in high carbon deposition and reduced gasoline yields. This phase of catalyst testing is destined to become increasingly significant because of the necessity of processing marginal type crudes. Such stocks, invariably high in nitrogen, sulfur, and active metals, are highly detrimental to the selectivity of cracking catalysts. I n the course of development of the catalytic cracking art, many “standard” methods of testing catalysts have been proposed and utilized and the majority of these methods have served their purpose. Some of the test methods represent a tremendous amount of development work and thought; however, i t has become obvious to workers in this field that many of the test methods have serious drawbacks. This paper describes equipment and procedure for testing powdered catalysts that combine a number of desirable features in one method. This method, i t is believed, is easier than most to operate and yet attains a high degree of reproducibility. Current Test Methods There are a dozen or more catalyst test methods in active use today, many of which have been described in the literature (1).
Considering eight widely used methods, six produce carbon-onthe-catalyst values (at the end of the cycle) of from 4 to as high as 33%, one method approaches average plant operation employing a value of approximately 1.0%, while another method uses a value of near 0.5%. Further examination of these schemes for catalyst testing reveals that three require the catalyst to be pelleted before use, three employ downflow processing through a packed bed with attendant pressure gradient problems, and only two employ the catalyst in a fluidized state. Other drawbacks are inherent with many of the test methods in use today: Excessive time is required to make a complete catalyst evaluation; total amount of oil processed is small, thereby limiting the information that might be gained from the test and limiting the accuracy; and means of determining carbon are inconvenient or difficult. The methods of catalyst testing may be broadly divided into four distinct types, according to the way in which the catalyst is utilized: ( 1 ) as powder in a packed bed, (2) as pellets in a confined bed, (3) as powder in a confined fluidized bed, and (4)as powder in a moving fluidized bed. The latter method has apparently not been widely adopted for routine testing; however, a laboratory-scale fluidized moving bed test unit has been described (@. After consideration of all the methods, i t was concluded that the use of a fluidized bed was the logical approach to testing powdered catalysts. T o minimize control difficulties and t o simplify the equipment, the confined fluidized bed was selected as the most useful laboratory test method. The use of this type of operation permits testing of the powdered catalyst as i t is withdrawn from the commercial unit, thereby eliminating
850
INDUSTRIAL AND ENGINEERING CHEMISTRY
the necessity of pelleting the catalyst or of using it as a packed bed of powder. At least two schemes for utilizing a confined fluidized bed for small scale cracking have been described in the literature ( 4 , 9). Others have discussed the possibility and have reportedly utilized the scheme with some difficulty. The major problem in the use of a confined fluidized bed is solved when consistently good fluidization is achieved. Aside from testing the catalyst with a minimum of handling, the following advantages are also inherent in the confined fluidized bed method:
Vol. 45, No. 4
material increased. For a catalyst containing approximately 12% finer than 20 microns (new montmorillonite clay) a minimum vapor velocity of 55 em. per second was found necessary. Subsequent calculations showed that the oil rate required to produce the minimum velocity for ncw catalyst was approximately the maximum that could be tolerated if other variables were kept within the range of commercial plant operation. Thus, the desire to test new as well as used catalysts in the same equipment and keep the equipment bench scale in size ultimately determined the oil rate to be used for the tePt method.
Temperature distribution is simplified as a result of the continuous circulation of catalyst. Regeneration in situ becomes a simple and accurate means of removing and determining carbon deposition quantitatively. Test conditions can be selected to simulate actual plant conditions more closely.
Table 1.
Standard Operating Conditions
Amount of catalyst, grams Total oil charged, grams Weight ratio of catalyst t o oil Processinn oeriod. minutes Space veloch wt. of oil per hour per wt. of catalyst Pressure, 1b.A;. inch gage Temperature of oil feed F. Average temperature of'catalyst bed using activity standard Carbon on reference catalyst a t end of process period, wt. %'
600
390 1.54 11.5
-3 4
10
F.
980 965 1.12 C O N V E R S I O N , VOLUME
Basic Development Factors
Figure 2.
Routine catalyst testing methods often are pressed into service for studies of new catalyst or of feed stocks. Consequently, a major premise adhered to in the development of this method was that the equipment and procedure should be suitable for rapid refinery control work, yet sufficiently flexible to permit detailed evaluation of new catalysts or feed stocks. This provides a multipurpose unit equally useful in the research or the refinery control laboratory.
w
s 2
V
8 e
z
Y
: 2.0
I
a w a
e I 0
I .o
w
0.9 3 0.8
$a 6
V
/
Y
0.7 0.6
/
/I
/ I
I
0.5
Figure 1,
Standard Carbon Curve
Consideration was first given to the design of a reactor capable of producing good fluidization of the confined bed. Studies in glass and metal prototype reactors showed that a critically designed tapered reactor was required and that vapor velocity must be maintained above a definite minimum for good fluidization. Further experimentation showed that this minimum vapor velocity, although essentially the same for most plant catalysts which normally contain little or no material finer than 20 microns, had to be increased appreciably as the amount of 20-micron and finer
PER C E N T OF CHARGE
Standard Hydrogen Curve
It is believed that one of the most important factors influencing the activity of a cracking catalyst is the amount of carbon deposited on the catalyst. As i t was desired that the activity measurements reflect the activity of plant catalyst, it appeared that the average (mean value) of carbon on the catalyst used in this method should also approximate plant values. It has been shown that for a given feed stock and cracking intensity (combined effect of temperature, pressure, and specific catalyst activity) carbon deposition is unaffected by space rate but is a parabolic function of catalyst holding time (IO). A change in carbon on the catalyst can also be effected by a change in cracking intensity brought about by varying only temperature. Therefore, practical values for both temperature and catalyst holding time (processing period), for a desired percentage of carbon deposition and an optimum conversion range (45 to SO%), are readily determined. In keeping with the idea of using the test equipment for more detailed cracking studies, i t was desired to have a yield of a t least 100 ml. of gasoline, which would permit determination of octane rating. Based on this and the other considerations already discussed, the operating conditions shown in Table I were selected Description of Test Method Activity and Selectivity. I n this paper, conversion is defined as 100 minus the volume per cent boiling above 400" F. in the cracker effluent, activity is that property of the catalyst which accelerates the conversion of hydrocarbons into products of lower molecular weight, and selectivity is that property which determines the ratio of desirable to undesirable products. For example, a catalyst of good selectivity produces a high ratio of gasoline to coke plus gas. Much has been written on cracking catalyst activity, selectivity, and related subjects (6, 7 ) and i t is beyond the scope of this paper to discuss these theories. A number of ways of obtaining data from cracking tests may be used as an indication of activity and selectivity. Of these, the use of data from standard reference catalysts as a basis for comparison with the catalysts being tested results in a simplification of the problem of reproducing data on units in several different loca-
April 1953
INDUSTRIAL AND ENGINEERING CHEMISTRY
tions, making i t unnecessary to provide exact duplication of conditions and technique. The standard reference catalyst used in this work was a selected batch of new powdered montmorillonite clay. For an activity standard the catalyst was agedby steamand heat (1 100O F., 4 atmospheres of steam, 100 hours) to the approximate activity level of average equilibrium catalyst of a commercial unit. The surface area of this standard was determined as 145 square meters per gram. Under the reaction conditions set forth, this catalyst effects a conversion of 45.05 volume % of the standard gas oil. Activity index is defined by the following expression:
85 1
made having various compositions of aged and new catalyst, resulting in a number of selectivity standards of different activity levels. Standard test runs were made on each blend and curves (Figures 1 and 2) were prepared showing carbon and hydrogen production as a function of conversion.
V V*
Activity index = 100 -'
where Vt = volume per cent conversion produced by the test catalyst using the standard conditions V , = volume per cent conversion produced by the standard catalyst using the standard test conditions . F o r the data presented in this paper, V , = 45.05. This scheme of reporting activity has been employed for several years in connection with both fixed and moving bed cracking units. The standard gas oil was prepared from a mixture of Hutchinson and Gray County, Tex., crudes and has the following properties: Vacuum Distillation",
'
F., 760 Mm.
(Phillips Method)
First drop 509 5% condensed 545 10% condensed 562 507' condensed 656 70% condensed 718 90% condensed 807 95% condensed 853 Gravity OAPI 36.1 21.6 Bureau bf Mines correlation index (8) Distillation run at 5 mm. Hg and temperatures were corrected t o 760" F. using chart by Brown and Badger (SI.
Because the selectivity of a catalyst changes on continued use, the carbon and hydrogen (or gas) production for a given conversion with a used catalyst is higher than that obtained with a new or unpoisoned catalyst. This change in selectivity has been shown to be primarily the result of contamination by metals or the action of sulfur on metallic constituents of the catalyst (6, 6). It appeared that the most convenient way to measure selectivity changes was to compare the carbon and hydrogen production of the test catalyst with the yield of these products from a nonpoisoned catalyst whioh would achieve thg same conversion as the test catalyst. Standards for selectivity were prepared from new montmorillonite clay catalyst representative of that used in the plant. A portion of this catalyst was rapidly aged to a surface area of approximately 10 square meters per gram using a temperature of 1800 O F. and taking all precautions t o maintain the uncontaminated condition of the catalyst. Blends were then
Figure 4.
Control Panel end Reactor-Regenerator Assembly
The selectivity of a catalyst is reported in terms of selectivity factors and is defined by the following expressions: C Carbon factor = -2 C, where Ct = carbon, weight per cent of charge, produced by test catalyst using standard conditions C, = carbon, weight per cent of charge, produced by unpoisoned catalyst a t same conversion obtained with test catalyst. The value of C, is obtained from Figure 1.
H Hydrogen factor = 4
..
RE CONTROL
where Ht = hydrogen, cubic feet per barrel of charge produced by test catalyst using standard conditions H , = hydrogen, cubic feet per barrel of charge, produced by unpoisoned catalyst a t same conversion obtained with test catalyst. The value of H a is obtained from Figure 2.
OIL
I
REACTOR CHARGE PRESSURE METER
CONDENSER INJECTOR P U
Figure 3.
H,
ACCUMULATOR
Flow Diagram
Equipment. The catalyst testing equipment, most of which has been rigidly standardized, can be divided into the following main items: the oil charge system, including a weighing device, pumping unit, and a preheat coil ; a combination reactor-regenerator; a product separation system; gas metering and automatic sampling equipment; and the distillation equipment. A flow diagram is shown in Figure 3 and a picture of the control panel and reactor-regenerator assembly is shown in Figure 4.
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
852
Vol. 45, No. 4
OIL C H ~ R OSYSIKM. E The oil reservoir is a 1000-nil. vessel placed on a torsion balance with an adjustable induction line submerged in the oil. The induction line is fitted n i t h a hook gage for adjustment to a definite depth mith reference to the oil surface when weighing. The charge oil is weighed at the beginning and end of the charge period to determine the TT eight of oil charged. Standard cracking stock is charged by means of a Bosch Diesel injector pump. Such a pump has pioved to be
OIL SHEET METAL
H
WT R A Ns IT E Oil Preheater
Figure 5.
invaluable in this type of work, as it is an excellent nieteiing device and the pumping rate is little affected by minor changes in pressure. A moderate change in pumping rates can be made during operation; a wider range of rates can be covered by either changing the pump speed or installing different plunger and barrel combinations, several sizes of which are available. The charge oil preheater (Figure 5 ) , which consists of an electrically heated refractory core surrounded by a coil of l/s-inch stainless steel tubing, is mounted inside an electrically heated insulating shield. Oil flowing through the coil is heated by radiation from the refractory which is maintained at a high temperature. With this type of heating the oil can be biought to temperature when high velocities are used in the tube, thus minimizing thermal cracking. The radiant-type heater also permits rapid temperature adjustment with a minimum time lag. During standby periods the whole preheater assembly is kept a t an elevated temperature by means of the auxiliary heater in the insulating shield. CAP FLANG
LTER
THERMOCOUPLE WELL
REACTOR INSULATION H EAT1N G W I RE
Removal of Catalyst
serves as a catalyst support is held in place a t this point hy a removable nut, which also serves as an inlet fitting for the oil coil. The top 10.5 inches of the reactor, which serves as the disengaging zone, is a straight-walled section having an inside diameter of 3.5 inches. To complete the chamber, a flange is welded to the top. A companion blind flange, which seals the chamUBiNG ber by means of an aluminum gasket, contains the effluent and pressure fittings and thermocouple n d l . -4cylindrical porous stainless steel filter element mounted on the underside of the hlind flange confines t h e c a t a 1 y 9 t These Dorow stainless steel fil?er elemenis (manufactured by the Micro Metallic Corp., Brooklyn, S . Y.) have a long life and are efficient in. retaining the finest powdered catalysts. The entire reactor-regenerator chamber slides into a metal sleeve, on which are mounted five individually controlled heater elements. This assembly is insulated by 3.5 inches of Sil-0-Cel, rhich is confined by a sheet steel -cvlindrical shell (Figure 6). The assembly ~i~~~~ 8. ~ ~ ~ con~ k rGactor b ~and~ prehegter k denser v ith their respective insulating s. Martin Catseases are mounted in an angle iron frame, 7%hich is in turn mounted on 10s NO.M-7032 trunnions a t the center of gravity of the apparatus.
e
INLET N U T a CATALYST SUPPORT
I Figure 6.
Figure 7.
PREHEATOR SECTION
I
Reactor-Regenerator
REACTOR-REGENER.4TOR. In order to I l l & the requirelllents of size, fluidization, heat capacity, and shape, the reactor was constructed from stainless steel machined in five sections and the sections were welded together as shown in Figure 6.
The main body of the reactor is 4 inches in outside diameter and 3013/le inches in length. The lower section, which coniprises the reaction zone, is tapered on the inside from a diameter of 3.5 inches t o g9/32 inch; an additional 2.25-inch outside diameter piece, 2.5 inches long, welded to the bottom completes the taper t o 0.5-inch inside diameter. -4porous stainless steel plate which
This feature rnables the catalyst to be removed by tilting tlie entire a_ssenibly, as shown in Figure 7, into an inverted position without having to remove the reactor or disconnect any heating wires, thereby expediting the testing work considerably.
PRODCCT SEPAR TIO ON SYSTCM.Conversion products froin tlie reactor are partially condensed in a metal helical condenser and are collected in an accumulator. Pressure on the reactor is readily controlled within 1 0 . 1 pound per square inch gage h v a manually operated valve between the reactor and condenser. The accumulator, a 1000-ml. round-bottomed flask, is immersed in an ice bath and fitted with a special reflux condenser which is shown in Figure 8. Ice water is circulated through this condenser to minimize variations in composition of the condensed liquid product.
INDUSTRIAL AND ENGINEERING CHEMISTRY
April. 1953
. .
.
Gas COLLECTING SYSTEM It was considered impractical to collect the total gas stream from the process and regeneration Periods because of the difficulty of handling such a large sample. T o collect a convenient aliquot of the total gas, a sampling system, as shown in Figure 9, was devised. This apparatus collects small samples of a definite siae during the test period, the number of Samples being determined by the volume of gas (meter revolutions) produced. The size of the aliquot and the frequency of sampling are selected by the operator prior to a test.
853
DISTILLATION APPARATUS.The distillation apparatus (Figure
;ml. :2 ,receiver. c ~The ~Vigreux~ column ~ has ~ ~total ,length8%k ;:oft ;11.75~ ~ ~ a
inches. The distillation head is fitted with a 18/a8 standardtapered joint for receiving the thermoregulator adaptor. A Special vacuum-jacketed knockback condenser is employed to condense the overhead product. A latch-in type relay circuit cuts off the electric current t o the heating mantle a t the standard cut point and simultaneously opens a solenoid valve, which allows air to be injected into the column jacket for instantaneous quenching. I n this manner all gasoline fractions are cut at a constant, selected temperature. The standard cut point of the I n collecting a sample of the process or regeneration gas, the distillation is defined as the temperature (approximately 412." F,.) confining liquid (20% sodium sulfate) is withdrawn from the required to give 225 grams of overhead product for a total Ilquld sample bottle by vacuum and a corresponding volume of gas charge of 325 grams of a selected depentanized catalytic cracker is drawn into the sample bottle. The flow of confining liquid is liquid effluent. This standard oil has an ASTM distillation range controlled by a solenoid valve which is operated through a conof 171' to 752" F. and a gravity of 38.8 API. A large quantity stant-interval timing device. The timing device in turn is of this oil is kept in storage for periodic standardization of the governed by a switch actuated by the rotation of the meter. distillation unit. Separate sampling systems are used for the regeneration and Test Procedure. A plant, catalyst sampled from the regenerprocess gas streams to prevent contamination of the regeneration ator normally has a deposit of approximately 0.57' carbon, which gas with hydrocarbons. must be burned off before testing. By placing 600 grams of catalyst (carbon-free, dry basis) in the hot reactor and fluidizing it with air at the rate of 2.4 liters per minute for a minimum of 3 hours, the catalyst is conditioned for testing and the reactor temperatures are M simultaneously brought to equilibrium. Prior t o making the test, the reactor must be a t the proper temperature throughout the bed with the catalyst in a fluidized state. During the catalyst conditioning period, air (or nitrogen) is circulated through the preheater and into the bottom of the reactor. Good fluidization is denoted by a constant temperature throughout the bed. Approximately 3 minutes before the start of the run nitrogen is substituted for air to purge the reactor and t o maintain fluidization. Ice water is circulated in the knockback condenser and the total liquid product receiver as immersed in an ice-water bath. A master switch simultaneouslystarts the PROCESS GAS REGENERATOR charge pump, energizes the radiant sectionof the preheater, and starts the automatic time clock. GAS SAMPLE As soon as the oil reaches the catalyst section (approximately 30 seconds) the nitrogen purgeis Figure 9. Automatic Gas Sampler shut off and the run is continued to completion
Table II. Typical Data
",zf[$Fn
Y , Oil Z,Product, 'Vi, Process Gas Run Charge, >400° F., Conversion, Activity Volume, Hz content, Cu. Ft./Bbi. Vol. % Grams Index cu.ft. vol. % No. Grams Charged 388.6 232.2 40.4 1 89.7 1.335 10.2 48.1 390.0 233.1 40.4 2 89.7 1.167 10.8 50.1 236.2 40.3 3 393.6 89.5 1.813 7.9 49.7 1 391.5 227.2 42.5 93.6 1.747 26.9 161.4 2 391.7 226.0 42.5 94.2 1.783 27.0 165.3 1 390.5 198.7 49.3 109.4 1.748 14.6 88.0 2 390.9 198.2 49.5 109.8 1.783 14.5 89.2 1 392.2 224.7 42.8 95.0 1.742 24.4 145.6 2 391.8 224.8 42.7 94.8 1.727 24.7 146.2 1 391.2 227.6 41.9 93.0 1.619 20.8 115.6 2 391.7 228.3 41.8 92.8 1.592 21.1 115.2 1 392.0 210.8 46.5 103.2 1,704 18.2 106.1 2 392.4 211.4 46.3 102.8 1.687 17.9 103.1 1 388.8 218.2 43.9 97.4 1.634 20.1 113.5 2 391.0 219.1 44.2 97.9 1.684 20.1 116.4 1 391.9 218.7 44.4 98.6 1.638 19.1 107.2 2 392.1 218.5 44.5 98.7 1.645' 19.3 108.9 1 392.2 217.0 44.9 99.6 1.636 17.0 95.5 2 389.3 216.3 44.7 99.2 1.619 16.8 93.9 1 389.1 214.4 45.1 100.1 1.697 16.1 96.4 2 387.3 214.3 44.9 . 99.7 1.670 16.0 93.7 calculations for catalyst A, run 1
Catalyst Designation A
B C
D E
..'
F
G H I
J Sample
..
-
(5
O.845' 100 = 40.4 0.8479) Vt Hi 48.1 Activity index, = 100 - = 100 - = 89.7 Hydrogen factor = HI = 49.2 = 0.98 VS Ca = wt. % carbon from Figure 1 curve of standard catalyst Ha cu ft./bbl. Ht from Figure 2, curve of standard catalyst Vol. % conversion = 100
-
X
sp.gr. of
Z
100 = 100
-
232'2 ( m 6
- -
Regeneration Gas $~o$,$~~ H drogen Volume, CO Wt. % Carbon COT $actor Charge Factor cu. ft. Vol. %
+
0.98 1.02 1.01 3.06 3.13 1.35 1.37 2.72 2.75 2.23 2.23 1.76 1.72 2.05 2.08 1.91 1.93 1.67 1.65 1.68 1.65
7.148 7.149 7.253 9.298 9.532 9.107 9.134 9.141 9.196 8.997 8.970 9.148 9.109 9.184 9.619 9.223 9.141 9.097 8.990 9.100 9.024
1.47 1.46 1.50 2.06 2.18 2.09 2.18 2.28 2.35 1.71 1.74 1.98 1.97 1.74 1.84 1.71 1.67 1.73 1.77 2.07 2.26
5.56
5.54 4.42 6.04 6.25 6.24 6.49 6.81 6.97 5.28 5.27 5.90 5.90 5.12 5.22 5.05 5.00 5.20 5.32 6.16 6.74 ct
Carbon Factor = --
Cs
=
z 7 1.11 1.32 =
1.11 1.10 1.14 1.38 1.46 0.95 0.98 1.52 1. 54 1.19 1.21 1.06 1.06 1.00 1.04 1.03 1.00 1.01 1.05 1.20 1.31
854
INDUSTRIAL AND ENGINEERING CHEMISTRY
in 11.5 minutes. The preheater outlet temperature is maint,ained at 980" F. by manual control of the current input to the radiant heater during this period. The process gas sampling system is automatic and begins t o function as soon as noncondensable gases are produced. A pressure of 10 pounds per square inch is maintained on the reactor by means of a throttling needle valve in the reactor outlet line. At the completion of the test the automatic time clock shuts off the feed pump and the radiant section of the preheater. Nitrogen purge gas is admitted to the reactor at a rate of 1.3 liters per minute for 3 minutes while the sampling device continues t o collect the effluent gas. At the end of this 3-minute period the purge gas is vented t o the atmosphere and the nitrogen rate is increased to 2.4 liters per minute for 5 minutes. At the end of this final purge the accumulator and contents are transferred to the standard distillation apparatus and the gasoline is removed by distillation.
-rn ELECTIRONIC RELAY
\
Y
THERMOREGULATOR KNOCK-BACK CONDENSER
0
RECEIVER
$;"i u
Vol. 45, No. 4
The aliquot sample of regeneration gas is analyzed for carbon digxide and carbon monoxide in an Orsat apparatus employing a special 5-ml. microburet having a 97-ml. bulb a t the top and two smaller bulbs of 4-ml. capacity in series a t the bottom. This arrangement allows flexibility of operation in that volume reduction, after combustion and absorption, can vary from 0 to 13 ml. and the final reading can be adjusted to fall on the graduated section of the microburet. Typical Data Data obtained in the course of routine testing of commercial plant catalyst, together with representative calculations, are presented in Table 11. The normal procedure is to make at least two tests on each catalyst sample, with the requirement that the difference between tests be not more than one unit of activity index. The data in Table I1 also show how well the flow rate is maintained by the Bosch pump. This repeatability is an important consideration in obtaining accurate results. No data on weight recoveries are shown in Table 11, as a weight balance is not normally made in routine catalyst testing. I n using this equipment for feed stock evaluation, weight recoveries of 98.5% or better are expected and runs with recoveries below this are discarded. Typical results on catalyst samples, periodically withdrawn from a commercial unit over a period of time from the initial start-up, are shown in Figure 11. This plot of activity index and selectivity factors versus time demonstrates the sensitivity of the method in detecting changes in catalyst characteristics. The leveling off of these factors in the latter part of the period is the result of the stabilizing effect of periodic additions and withdrawals of catalyst plus a general reduction in the metal content of the feed stock.
ACCUMULATOR
Figure 10.
Standard Distillation Apparatus
Special Procedure for Determination of Hydrogen The process gas sample obtained, when the type of effluent condensing system described for this method is used, contains hydrocarbons heavier than Cz. Therefore, the usual combustion methods for determining hydrogen cannot be employed and other conventional methods are not satisfactory for routine work. The following method of handling this type of sample has proved to be rapid and accurate.
Hydrogen in the process gas is determined by a special method yield is used in obtaining the described below. The hydrogen . hydrogen factor as alreadv described. n order to make a complete weight balance, the density of the process gas may be determined by means of a density bulb. After the process period, regeneration of the catalyst is accomplished by fluidizing the bed with air a t a rate of 4.8 liters per minute. No attempt is made to control the regeneration temperature, since the high heat capacity of the heavy-walled reactor, together with the rapid distribution effect of good fluidization, permits the temperature to rise gradually to a maximumof 1050' F. Regeneration of thecataIyst is usually complete after approximately 280 liters of air have passed through the bed. The sampling system is adjusted to collect an aliquot of theeffluFigure 11. ent gas during regeneration. 1
-
tBON :TOR
2.o
1.5
1.0
I
Typical Test Data from Commercial Unit
April 1953
. -
INDUSTRIAL AND ENGINEERING CHEMISTRY
The equipment consists of a standard Orsat provided with the usual combustion tube. A 1000-ml. buret and a Krassel tube filled with 20/48 mesh activated charcoal are added as extra equipment and connected in series with the 100-ml. buret of the Orsat. A three-way stopcock is provided a t the outlet of the charcoal tube to permit evacuation, purging, and introduction of the gas sample. Prior t o making a determination, the charcoal tube is submerged in a bath a t room temperature. Residual gases are removed by evacuating the tube t o a pressure of less than 1 mm. of mercury and the tube is then filled with nitrogen. Approximately 1000 ml. of sample are taken into the larger buret, the connection t o the charcoal tube is opened, and approximately one half of the sample is vented t o the air through the .charcoal. This allows the charcoal to become essentially saturated with respect t o hydrogen but not t o the heavier hydrocarbons. After an accurate reading has been taken on the large buret, a sufficient volume of the process gas sample is passed through the charcoal tube to give approximately 100 ml. of hydrogen-rich gas in the small buret. A volume reading is again taken on the large buret in order t o obtain the volume of the sample being analyzed. The sample in the small buret is essentially free of the heavier interfering hydrocarbons and after removal of the acidic gases, olefins, and oxygen, the remaining gas concentrate is handled in the usual manner for hydrogen. This method has been repeatedly checked against results from low temperature fractional analyses and has proved to be accurate within 2%. Use of Method for Testing Pelleted Catalyst
855
equipment and procedure for testing both powdered and pelleted catalysts would simplify the testing problem for owners of several types of catalytic crackers. Acknowledgment The authors wish to express their appreciation to the Phillips Petroleum Co. for permission t o publish this work. They also wish to acknowledge the valuable assistance of Karl Meixner for his work on constructional details, L. G. Larson for his development work on the hydrogen determination method and on the electronic control systems used, and J. H. Rainwater for his work in the early development of the catalyst test method. Literature Cited (1) Am. Petroleum Inst., Proc. Am. Petroleum Znst., (111) 27, 9 (1947).
(2) Grote, H. W., Hoekstra, J., and Tobiasson, G. T., IND.ENG. CHEM.,43,545 (1951). (3) Katz, D. L., and Brown, G. G., I b X , 25, 1373 (1933). (4) McReynolds, H., Proc. Am. Petroleum Znst., (111)27, 78 (1947). (5) Mills, G. A., IND. ENQ.CHEM.,42, 182 (1950). (6) Mills, G. A., and Shabaker, H. A.,Petroleum Refiner, 30, 97 (1951).
(7) Shankland, R. V., and Schmitkons, G . E., Proc. Am. Petroleum Inst., (111) 27, 57 (1947). ( 8 ) Smith, H. M., Bur. Mines, Tech. Paper 610 (1940). (9) Thomas, C . L., and Hoekstra, J., IND.ENG.CHEM.,37, 332 (1945).
The method has been adapted to the testing of pelleted catalyst. Preliminary experimental work has shown that the equipment described in this paper can be used with only minor.alterations for testing TCC pelleted catalyst. The use of the same
(10) Voorhies, A.,Zbid., 37, 318 (1945). RECEIVED for review December 31,1951. ACCEPTED December 4, 1952. Presented at the Seventh Southwest Regional Meeting of the AMERICAN CHIMICAL SOCIETY, Austin, Tex., December 6 to 8, 1951.
0
Dehydration of Ethyl Alcohol over Alumina 0
HANS FEILCHENFELD' Deparfmenf o f Chemisfry, Northwesfern Universify, Evansfon,
T
HE dehydration of ethyl alcohol to diethyl ether in the
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vapor phase over a n alumina catalyst has been extensively studied (1, 3, 4, 6 , 7, 9). I n general, the conversion of ethyl alcohol t o ether increased with increasing contact time (or, in flow systems, with decreasing space velocity), passed through a maximum, and decreased. This decrease was explained by the formation of ethylene, e i d e r in competition with ether or by further dehydration or disproportionation of ether. I n this investigation the conversion of ethyl alcohol to ether has been studied under superatmospheric pressure which suppressed ethylene production. If even then the rate of production of ether a t low space velocities leveled off to zero, this could not be due to ethylene formation but either to the thermodynamic equilibrium between the reactant and the products or to inactivation of the catalyst.
111.
The liquid feed was pumped from a pressure charger; the gaseous feed was introduced by water displacement a t a predetermined rate; and the reactants were passed through the catalyst tube from the bottom instead of from the top, the preheater and spacer having been interchanged. The products were passed consecutively through a water-cooled trap and a dry ice-acetone trap. Absolute alcohol waa used as the standard feed. Water, ether, and ethylene were added t o it in order to determine their influence upon the reaction. I n order t o reduce the effect of the small but varying amounts of ethylene formed a t different feed rates, the absolute alcohol was always saturated with ethylene a t 1 atmosphere gage pressure; the amount of ethylene produced was measured. The composition of the li uid product was determined by fractional distillation, the me%od of Hodgson and Glover (6) having proved unsatisfactory, probably because of the presence of dissolved ethylene in the liquid product. The catalyst was in all cases alcoa F-10 alumina and was not further pretreated.
Experimental Work
Results and Discussion
The apparatus was arranged according to the continuous flowtype system (IO), but with the following changes:
To determine the conditions under which a reasonable amount of ether could be produced without the formation of appreciable amounts of ethylene, a preliminary reaction was run a t 20 atmospheres and varied temperature. No temperature was found
1 Present
address, Research Council of Israel, Jerusalem, Israel.
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