gaseous and liquid hydrocarbons remained about the same in constant productivity tests of nitrided catalysts despite increasing temperature. Yields of alcohols were moderately high in some tests ofnitrided catalysts a t temperatures above 300' C. T h e relatively constant amounts of gaseous and liquid hydrocarbons may result from a gradual conversion of t-carbonitride (produced from the e-nitride during synthesis) to Hagg carbide. Catalysts used in constant productivity poisoning tests were less oxidized than catalysts used in constant temperature tests. I n constant productivity tests, the interstitial phase of the original catalyst was still present in substantial amounts after synthesis. T h e smaller extent of oxidation of iron in constant productivity tests was unexpected. As catalysts in constant productivity tests were operated a t low temperatures for about 2 weeks before poisoning, the catalyst a t the start of the poisoning was probably more highly oxidized than a t the end of the test. Conditions favoring reduction of iron oxide would also favor carburization, and Hagg carbide was formed in the nitrided catalyst and probably also in the carbided catalyst during the high-temperature synthesis. I n the constant productivity tests, the gas in contact with the catalyst particles contained larger ratios, H20/H2 and C 0 2 / C 0 . than in constant temperature tests. A previous paper (6) suggested that the inlet of the catalyst bed was inactivated by poisoning, and that this portion of the bed was then, contacted by unreacted synthesis gas which reduced iron oxide formed in the initial part of the test. This mechanism is not important in the constant temperature tests, as both unpoisoned and poisoned catalysts were highly oxidized a t the end of these tests. A better explanation of the smaller extent of oxidation in constant productivity tests involves the degree of ventilation of the pore system of the catalyst. I n tests a t temperatures less than 270' C., the pores of the catalyst are filled with liquid hydrocarbons (73). Mass transport of reactants and products in these liquid-filled pores is sufficiently slow so that large concentration gradients exist from the external surface of the
particle to the interior (8). T h e ratios H20,'Hs and C0,:CO are large a t the interior of the particle, and most of the oxidation occurs within the particle. At temperatures above 300' C.: the catalyst contains only small amounts of high molecular weight hydrocarbons. Most of the pores are relatively accessible, and H90 and COS produced in the synthesis can be readily transported to the main gas stream. Carbon deposition during poisoning a t temperatures above 300' C. was slower than Lvould be expected for tests bvith pure synthesis gas. Sulfur poisoning may inhibit the rate of carbon deposition ; however, the rapid carbon deposition and plugging of fixed beds in tests with pure gas a t high temperatures may be due in part to overheating caused by the rapid rate of synthesis. literature Cited
(1) Anderson, R. B.. J . Catalysis 1, N o . 4, 393 (1962). (2) Anderson, R. B., Seligman. B.: Shultz. J. F.. Kelly, R. E., Elliott, M. A,, Znd. Eng. Chem. 44, 391 (1952). (3) Anderson, R. B.. Shultz, J. F.. Seligman, B.. Hall, LV. K., Storch, H. H., J . A m . Chem. SOC.72, 3502 (1950). (4) Anderson. R. B., Whitehouse, A. M.. Znd. Eng. Chem. 53, 1011 (1961). (5) Hall, LV. K.. Dieter. \V. E., Hofer, L. J. E.. Anderson, R. B., J . A m . Chem. Sot. 75, 1442 (1953). (6) Karn; F. S..Shultz, J. F., Kelly. R. E.. Anderson. R. B., I N D . ESG. CHEM., P R O D . RES. DEVELOP. 2, 43 (1963). (7) Shultz. J. F.. Xbelson. M.. Shakv. L.. Anderson, K. B.; Ind. Eng. Chem. 49, 2055 (1957). (8) Shultz, .J. F., Xhelson, M., Stein. K. C . , Anderson. R. B., J . Phvs. Chem. 63. 496 (1059). (9) Shultz, J. F.. 'Hall,'\V. K.. Seligman. B.. Anderson, R. B., J . A m . Chem. Soc. 77, 213 (1955). (10) Shultz, J. F.. Hofer, L. J. E., Karn. F. S..Anderson, R. B.. J . Phys. Chem. 66, 501 (1962). (11) Shultz, J. F.: Karn. F. S., Anderson, R. B., Znd. Eng . Chrm. 54. 44 11962). (12) Shultz, J: F.. Karn. F. S . Bayer, J., Anderson, R. B.. J . Catalwis 2. 200 11963) (13) Stein, K. C.', Thbrnpson, G. P.. Anderson, R. B., J . Phys. Chem. 61, 928 (1957). RECEIVED for review Septtmbcr 26. 1963 ACCEPTLD .January 8. 1964 Division of Colloid and Surface Chemistry. 145th Meeting. ACS, New York, N. Y., September 1963.
EVALUATION OF POTENTIAL 700"F. HYDRAULIC FLUIDS IN A PUMP LOOP V
ER
N H 0P K I NS A N D D0N N E L L R
.
W I LS0N
,
Mtdwest Research Institute, Kansas City 70,.Mo.
Four fluids were pumped in a simulated aircraft hydraulic circuit at 3000 p.s.i.g. and at temperatures as high as 700" F.: bis(phenoxyphenoxy)benzene, phenyl methyl silicone, deep dewaxed mineral oil, and an ester of trimethylolpropane. Bis(phenoxyphenoxy)benzene exhibited good resistance to degradation but phenyl methyl silicone deteriorated during 1 00-hour experiments a t 700' F. The deep dewaxed mineral oil degraded rapidly at 700" F., so the run was terminated after 27 hours. The ester of trimethylolpropane experienced rapid degradation at 650' F. after it had been pumped 25 hours at 550" F. and 25 hours at 600" F. Only the bis(phenoxyphenoxy)benzene warrants further investigation at 700" F. and above. ~ P I Dprogress
in research and the development of hydraulic aircraft and aerospace vehicles has created a need for a method of evaluating potentially useful hydraulic fluids a t high temperatures. Since World War 11: maximum temperatures of hydraulic systems in operating aircraft have advanced from 165' to 275' F. using petroleum-base fluids, and to 400' F. using disiloxanetype fluids. Systems are a t present being designed to operate a t 1000' F. I n the past. hydraulic fluids bvere dynamically
R'fluids and systems for advanced
38
l&EC PRODUCT RESEARCH AND DEVELOPMENT
evaluated in a pump loop assembled Lvith actual aircraft components. Recently, the temperature requirements for advanced vehicles have increased so fast that neither production nor experimental hydraulic circuit components are available for use in evaluating newly developed high-temperature hydraulic fluids. Therefore, a pump loop has been developed for the United States Air Force in kvhich fluids can be suhjected to high shear rates a t pressures to 3000 p.s.i.g. and a t temperatures to 800' F. A detailed description of this loop
and the experimental procedure used has been published (7). This loop is used to evaluate fluids dynamically by subjecting them to high shear stresses for as long as 100 hours. Fluid samples are periodically removed from the circuit and examined for changes in viscosity, flash point and fire point, and neutralization number. Information is also obtained on the tendency of fluids to form lacquer, change molecular structure, form insolubles, and corrode materials normally used in the fabrication of hydraulic systems for advanced aircraft and aerospace vehicles. T h e sludging tendency of the fluid as a function of time is indicated by records of the pressure drop across the filter. This paper discusses results obtained with four experimental fluids pumped a t temperatures to 700" F. Results a t 550" F. for three of these fluids have been published ( 7 ) .
Test Results
Test results are presented for four fluids : bis(phenoxyphenoxy)benzene. phenyl methyl silicone. deep dewaxed mineral oil, and a n ester of trimethylolpropane. T h e bis(phenoxi-phenoxy) benzene and the silicone were tested a t 700" F. for 100 hours. the mineral oil \vas tested a t 700" F. for 2' hours: and the ester was tested from 550' to 650" F. for 77 hours. None of the fluids experienced detectable degradation at 550' F. for 100 hours in a n earlier test series. T h e ester of trimethylolpropane. the base stock for a Mil-L-9236-type fluid, \vas expected to degrade somewhere between 550' and 700" F . ; therefore. it was pumped 25 hours at 550", 25 hours a t 600': and 27 hours a t 650" F. to determine the maxim u m temperature a t which it could he used. A summary of the results for these four fluids is presented in Table I . Corrosion data are presented in Table 11. Curves for pumping rate, filter viscosity. flash point, and fire point data are plotted in Figures 1 through 1 2 . A plot of neutralization number LIS. pumping time is also included for the experiment \vith the ester of trimethylolpropane (Figure 11). Test 1 , MLO 59-692, bis(phenoxyphenoxy)benzene. This fluid experienced little or no degradation in a 100-hour shear stability experiment at 700" F. with a pump discharge pressure of 3000 p.s.i.g. T h e pumping rate dropped from 5 to 3.7 gallons per minute during the first 10 hours of this experiment>and then remained someLvhat constant (see Figure 1 ) . Wear of the Graphitar (United States Graphite Co. name for its carbon and graphite poLvder compacts) primary seal in the pump is thought to account for most of the decrease. There was a substantial increase in the pressure drop across the filter (filter AP) during the first 20 hours (see Figure 1). T h e filter AP increased from 13 p.s.i. a t the start of the test to a maximum of 78 p.s.i. a t 50 hours, declined to 66 p.s.i. a t 60 hours, then to 56 p.s.i. a t 100 hours. Since there was a fairly large filter AP, particles were undoubtedly being forced through the filter. When a filter passes particles in a closed circuit, they are redeposited on the filter in new7 positions which may offer less resistance to fluid flo~v. A reduction in the filter AP could result from this redistribution if the rate at which new particles are collected on the filter is low. Approximately 60 grams of porous: black? carbon-like residue \vas collected on the filter element, T h e viscosity (Figure 2) determined for each fluid sample a t 210" F. changed very little during the test; however, a t 100' F. the viscosity dropped nearly 1270 during warm-up and the first 6 hours of pumping. The test was started after pumping for about 4 hours to raise the fluid to the 700" F. test temperature. T h e neutralization numbers determined for the fluid
80 Y)
70
-
PRESSURE DROP ACROSS FILTER
3
PUMPING RATE
.V II
0
K W
v) Y)
50
J 4 O
I/ 20
IO
30
I
I
I
I
I
40
50
60
70
80
90
".
u
a
a
0
100
HOURS PUMPED
Figure 1 . Effect of pumping time a t 700" F. on pumping rate and pressure drop across filter (MI059-692) I
I
I
I
I
I
1
I
I
-
VISCOSITY AT IOO'F:
300-
Y)
> 50 -
AT 210'F.
/VISCOSITY
,
0
I
,
I
I
1
FLASH POINT
500
i
4001
01 0
IO
I
I
I
1
20
30
40
50
,
I
70
60
80
90
1
100
HOURS PUMPED
Figure 3. Effect of pumping time a t 700" F. on flash point a n d fire point (MLO 59-692)
samples were all less than 0.05 mg. of KOH per gram. The flash and fire points, plotted against pumping time in Figure 3, dropped a little during the 4-hour warm-up period, and then remained essentially constant. Corrosion data (Table 11) indicate that only the beryllium copper corrosion specimens were significantly affected. They turned from a brass to a copper color and small bubbles could be seen on them. New fluid was colorless; the 0- through 50-hour fluid samples were cloudy with a yellow tint, almost the color of cream, The 75-hour sample was amber-colored and less cloudy than the other samples. T h e 100-hour sample was amber-colored and clear (no cloudiness). [$'hen the fluid samples were first withdrawn from the circuit they were clear, but turned cloud>VOL. 3
NO. 1
MARCH
1964
39
;;j
Table 1.
Summary of 700" F. Pump loop Test Results Fluid Designation MLO MLO MLO Data 59-692' QF-258' 60-294C 60-50' Test duration, hr. 100 100 27 77 Average pumping rate, g:P.m. 3 80 4 15 3 67 5 42 Initial charpe at test 51 61 end, 9% 31 44 Total shear cycles 15,200 16,600 3,960 16,700 Filter A P , p.s.i. Initial 13 8 10 9 Final 56 17 13 18 Neutralization number, mg. KOH/g. Sew fluid
