However, the product isomer distribution was not affected by flow rate-i.e., isomer distribution is not dependent upon conversion-and 8 normal-isobutyraldehyde ratio of 2.0 was observed a t all flow rates studied. Similarly, the effect of hydrogen-carbon monoxide ratio a t constant total pressure was studied as a function of conversion and product isomer distribution. The molar rate of hydrogen to carbon monoxide was varied between 1 and 3. The results presented in Table I11 show that the reaction rate is favored by hydrogen-carbon monoxide ratios greater than 1- Le., the rate is inversely proportional to carbon monoxide partial pressure. Again, there was no effect on product isomer distribution. Temperature influenced reaction rate in an expected manner. On increasing the temperature from 128”C. (base case) to 148°C. a 50c; increase in conversion occurred, corresponding to a 112 of 19 kcal. per gram-mole. The product isomer distribution was only slightly altered from a ratio of 2 to 1 (base case) to a 1.81 to 1 normalisobutyraldehyde at the higher temperature. The effect of temperature is summarized in Table IV. At 148°C. over a fixed-bed catalyst consisting of the complex, Rh(P@3)2(C:O)C1, supported on alumina (Robinson et a1 , 1969) the normal-isobutyraldehyde ratio was 1.9, essentially the same as in Table IV for the sparged liquid system. Although propylene and total gas flow rates were different in the fixed-bed and gas-sparged reactor studies, a rough comparison of productivity can be made. At essentially the same temperature and pressure the propylene conversion in the gas-sparged reactor was 7 1 5 us. 36% in the fixed-bed reactor, in spite of the fact that propylene partial pressure was lower and the total flow rate higher in the sparged reactor system. The weight of Rh(P@3)2(CO)C1 catalyst was the same in each reactor (0.66 gram). The catalyst productivity-Le., efficiency-would be expected to be greater when dispersed (dissolved) in a liquid rather than supported on a solid. Since normal-iso ratio is so little affected by operating conditions (other than a slight temperature effect), it is not unreasonable that the ratio is the same in both reactor systems.
Table Ill. Conversion as a Function of Hydrogen-Carbon Monoxide Ratio
HJidrogen-Carbon Monoxide Ratio
ConLerszon, Mole cG
Normal Is0 Ratio
1.0 2.0 3.0
45.0 53.5 59.2
2.0 2.0 2.0
Table IV. Effect of Temperature upon Conversion and Selectivity
Temp , O C
Concers io n , Mole c c
Normal- Iso Ratio
128 138 148
46.0 57.3 71.0
2.02 1.89 1.83
Acknowledgment
The authors are indebted to F. E. Paulik for valuable discussions about the catalyst systems. Literature Cited
Bird, C. W., “Transition Metal Intermediates in Organic Synthesis,” Chap. 6, Logos Press, London, 1967. Chatt, J., Shaw, B. L., J . Chern. S O C .1966A, 1437. Craddock, J. H., Hershman, A., Paulik, F. E., Roth, J. F., IND. ENG. CHEM.PROD.RES. DEVELOP.8, 291 (1969). Evans, D., Osborn, J. A., Wilkinson, G., J . Chern. Soc. 1968A, 3133. Robinson, K. K., Paulik, F. E., Hershman, A., Roth, J. F., J . Catalysis, in press, 1969. Wender, K., Sternberg, H . W., Orchin, M., “Catalysis,” P. H . Emmett, Ed., Vol. 5, Chap. 2, Reinhold, New York, 1957. RECEIVED for review May 5 , 1969 ACCEPTED September 2, 1969 Presented in part a t the First North American Meeting of the Catalysis Society, Atlantic City, N. J., Feb. 20, 1969.
KINETICS OF DEPOSIT FORMATION FROM HYDROCARBONS Fuel Composition Studies WILLIAM F.
TAYLOR
Government Research Laboratory, Esso Research and Engineering Co., L i n d e n , N . J .
IN
A high speed supeirsonic aircraft, aerodynamic heating causes metal skin temperatures to rise considerably above those encountered in subsonic aircraft. I t has been estimated for a Mach 2.7 plane that the temperature of exterior surfaces can rise to the 450” to 500°F. range, and the temperature of an uninsulated fuel tank could rise to 430°F. (Chemical W e e k , 1967). Other studies have shown that hydrocarbon jet fuels exposed to such high
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temperature stress can degrade and form deposits (Churchill, 1966). One particular problem is the formation of deposits in fuel wing tanks which contain puddles of residual liquid hydrocarbon and hydrocarbon vapors. Such deposits may flake off, contaminate the fuel, and cause malfunctions in the fuel system components. This laboratory is conducting an extensive study of the variables which control the kinetics of deposit formaVOL. 8 NO. 4 DECEMBER 1969
375
To elucidate the effect of hydrocarbon fuel composition on autoxidative deposit formation, the deposit formation tendency of various pure hydrocarbons and binary blends was studied from 200' to 450°F. in the presence of air. The deposit formation tendency of normal paraffins varies with carbon number. For a given carbon number branched paraffins are more deleterious than normal paraffins. The presence of a n aromatic or naphthene in a binary blend with a paraffin inhibits deposit formation, particularly a t lower concentrations and temperatures. Although olefins in general are deleterious toward deposit formation, the effect of individual olefins varies widely. Deposit formation results are compared with oxidation and cooxidation kinetic studies.
tion from hydrocarbons exposed to such high temperature stress. Taylor and Wallace (1967) reported the general features of the complex kinetic reaction system in which such deposits are formed. The deposits form as a result of autoxidative reactions. Taylor and Wallace (1968) reported that trace levels of sulfur compounds can markedly increase the rate of deposit formation; subsequently Taylor (1968b) reported a similar effect for trace levels of nitrogen compounds. Taylor reported (1968a) that both homogeneous metals (soluble) and heterogeneous metals (surfaces) exert a strong influence on the kinetics of deposit formation. Taylor reported (1969) the effect of fuel additives and polymeric surface coatings on the deposit formation process. These previous studies were carried out using actual jet fuels. The present work presents results of studies involving pure compounds and simple blends of pure compounds. The ultimate goal is generation of an understanding of how jet fuel hydrocarbon composition influences the autoxidative deposit formation process. Experimental
Apparatus. Details of the kinetic unit used to measure the rate of deposit formation were reported previously (Taylor and Wallace, 1967). The main section consists of a glass tubular reactor which has five separate reactor heaters, each independently controlled by its own Gardsman temperature controller. The reactor is maintained on a slight incline and liquid fuel flows down the reactor in the presence of a constant stream of air. The reactor heaters are controlled so that the fuel encounters a sequence of rising temperature zones as it flows down the reactor. Carefully weighed pure titanium metal strips approximately 1.0 cm. wide by 10 cm. long are positioned in the center section of each heater zone. A thermowell extends down the length of the tubular reactor, and an individual thermocouple is positioned in each zone. The unit is operated under a controlled, reduced pressure of 3 p.s.i.a. The liquid fuel is presaturated with air prior to admission to the reactor section. At the conclusion of the 4-hour run, hydrocarbon fuel is shut off and a full vacuum is applied to the unit (
