CONTINUOUS PROPYLENE HYDROFORMYLATION IN A GAS-SPARGED REACTOR A R N O L D
H E R S H M A N ,
K .
K .
R O B I N S O N ,
Central Research Department, Monsanto Co., St. Louis, Mo.
J.
H .
C R A D D O C K ,
A N D
J.
F. R O T H
63166
The aryl phosphine-rhodium complex, Rh( P93)2(CO)CI, is a very reactive, stable, and selective hydroformylation catalyst. Because of its unusually high stability, it offers a number of processing variations. The present investigation demonstrates continuous olefin hydroformylation in a gas-sparged reactor which obviates the common problem of product-catalyst separation and recycle of a liquid catalyst stream. Gaseous propylene, hydrogen, and carbon monoxide were sparged through the catalyst solution, and the butyraldehyde product w a s continuously removed in the vapor eftluent. N o noticeable deactivation of the catalyst occurred in over 80 hours' running time. Various operating parameters were also studied to determine their effect on conversion and selectivity.
THEmost
commonly reported catalysts for the liquidphase hydroformylation of olefins to aldehydes are metal carbonyl catalysts such as Con(CO)s (Bird, 1967; Wender et al., 1957). These catalysts employ relatively severe reaction conditions, typical operating temperatures being 100" to 180"C. and carbon monoxide-hydrogen pressures of 250 to 300 atm. (high carbon monoxide pressure, -100 atm., is necessary to prevent catalyst decomposition). Selectivity is also a problem in using these catalysts, since the olefin hydroformylation is accompanied by hydrogenation reactions yielding the corresponding paraffin and alcohols. Recent work has shown that the rhodium-aryl phosphine complex [trans-chlorocarbonyl bis(tripheny1phosphine) rhodium (I)], Rh(P@3)?(CO)Cl,is a very reactive, stable, and selective hydroformylation catalyst (Craddock et al., 1969; Evans et al., 1968; Robinson et al., 1969). I n contrast to other hydroformylation catalysts, this system is very selective for production of aldehydes. Under normal operating caditions no hydrogenation reactions occur that result in paraffin and/or alcohol formation. Generally, catalyst handling is a major problem in commercial homogeneous catalytic processes, since separation and recycle steps are required to remove the soluble catalyst from the liquid product stream and return the catalyst to the reactor. Heterogeneous solid-vapor catalyst systems, on the other hand, eliminate the problem, since the catalyst remains as a solid phase fixed within the reactor while reacting gases and products pass over it. In previous work (Robinson et al., 1969) the continuous hydroformylation of propylene to butyraldehyde in the vapor phase over a fixed-bed catalyst comprised of the complex Rh(P@3)2(CO)Cl dispersed on an inert support was demonstrated. For sufficiently low boiling reactants and products, another reactor system capable of very 372
I & E C PRODUCT RESEARCH A N D DEVELOPMENT
simple catalyst handling analogous to the fixed bed is the gas-sparged reactor which maintains the soluble catalyst dissolved in a high boiling solvent in the reactor. A high partial pressure of aldehyde product necessary for product removal in the gas phase i s maintained by control of the operating conditions. Economic considerations have suggested that a gassparged reactor system employing the Rh(P%)2(CO)Cl catalyst could be potentially cheaper for propylene hydroformylation than a process using a solid catalyst as a fixed or fluid bed. Also, utilization of the catalyst is much more efficient when dissolved in solution rather than dispersed on a support. The objective of the present study, therefore, was t b demonstrate the gas-sparged reactor concept for the hydroformylation of propylene to butyraldehyde. The propylene hydroformylation reaction, in addition to lending itself to the concept of the gas-sparged reactor system because of the volatility of the olefin feed and aldehyde product, has important commercial implications, since the butyraldehyde product can be converted to butanol and 2-ethylhexanol. Experimental
Apparatus. Experiments were performed in a tubular, stainless steel, high pressure, flow reactor 14 inches long and 1 inch in diameter, positioned vertically with a sintered metal gas disperser located in the bottom. The reactor was placed in an electrically heated fluidized sand bath equipped with an automatic temperature controller (West Model JPY control). Isothermal reaction conditions were maintained (less than 2"C. gradient throughout the reactor at 128'C.). Reaction temperature was measured and controlled by an internal thermocouple immersed in the catalyst solution.
The reactor was normally operated about half filled with catalyst solution (150 ml.) and agitated by introducing the reactant gases into the solution through the gas disperser. The complete reactor system shown in Figure 1 could be operated a t a variety of processing conditions. T h e operating parameters wbich could be varied included temperature, gas flow rate of hydrogen and carbon monoxide, pressure, and propylene feed rate. The gas streams (hydrogen and carbon monoxide) were metered separately with an automatic flow control system consisting of an integral orifice differential pressure transmitter used in conjunction with a Foxboro flow controller and a needle control valve. Propylene was metered in as a liquid by means of a Milton Roy chromatographic pump. The hydroformylation reaction was always performed a t temperatures greater than -the critical temperature of propylene (91.9”C.). Consequently, upon entering the heated reactor, the propylene immediately vaporized; however, the solubility of propylene is sufficiently high to accomplish the liquid phase reaction. The mole per cent propylene in the feed and the extent of conversion to butyraldehyde were controlled so that the aldehyde was stripped from the catalyst solution by the effluent gases a t the operating conditions. After contact with the catalyst solution the gaseous reaction effluent exited overhead and was passed through a heated line within the fluidized sand bath heater. The heated gas effluent left a t the bottom of the sand bath and was subsequently cooled by a water condenser. The gas was then chilled to approximately 5 ° C . in a product separator to remove the condensable reaction products (n-butyraldehyde and isobutyraldehyde) from the gas stream. The 1.iquid product and unreacted gas (C3Hs,H1, and CO) were continuously withdrawn from the product separator. The condensed aldehyde product was collected in a glass flask and analyzed by gas chromatography. The remainder of the effluent gas was measured by a wet-test meter; however, it was sampled for GC analysis prior to venting. Reactor Operation. Gaseous propylene plus a large excess (10 moles per mole of propylene) of hydrogen and carbon monoxide was continuously bubbled through the catalyst solution. As aldehyde formed in the liquid phase, it was stripped from the catalyst solution by the unreacted gases. The concentration of aldehyde in the liquid phase is con-
:b Q I
trolled by the vapor-liquid equilibrium (operating temperature and pressure), the gas flow rate and composition, and the extent of conversion of propylene. As the concentration of propylene in the feed (or the propylene conversion) increased, the concentration of aldehyde increased in the liquid (and vapor). Corresponding t o this concentration increase, the volume of the liquid in the reactor also expanded. If proper operating conditions were not maintained, more aldehyde could be formed than was stripped from the catalyst solution, leading to flooding of the reactor. T o eliminate this potential problem and ensure satisfactory reactor operation, a computer program was written which calculated the expansion of the reactor liquid as a function of the operating conditions. If, for any condition, the volume expansion was too large, operating parameters were adjusted-e.g., temperature was increased, pressure was decreased, or the flow rate was increased to decrease conversion correspondingly. The reactor was normally started up by initially flowing the hydrogen-carbon monoxide gas mixture to agitate and mix the catalyst solution. After approximately one-half hour propylene was then introduced into the feed stream, and the reactor was allowed to reach steady state. I t was assumed that the reactor had reached steady state when three consecutive hourly product samples were the same. The reactor was usually on stream (had gas flowing through it) about one third of the time. More specifically, this consisted of 8 hours per day over a one-month period. When not in operation (nights and weekends), the reactor was pressurized with hydrogen-carbon monoxide gas and left heated. Materials. The rhodium hydroformylation catalyst, Rh(P@s)Z(CO)Cl(@ = phenyl), used in this investigation was prepared according to the method of Chatt and Shaw (1966). RhCL-3HZ0 and triphenylphosphine were purchased from the Matthey-Bishop Co., Malvern, Pa., and M & T Chemicals, Inc., Rahway, N. J., respectively. Other reagents were obtained from commercial sources and were the best chemical grade available (reagent grade or equivalent if possible). Propylene “research grade” was obtained from the Phillips Petroleum Co. Carbon monoxide and hydrogen of C.P. grade were obtained from the Matheson Co.
I
Figure 1. Reactor system
t
1.
2. 3.
High pressure regulotor Sporged reactor
Fluidized sand bath Metering pump 5 . Woter-cooled condenser 6. Product separator 7. Product collector 8. Sompling point 9. Wet-test meter 10. tow-pressure regulator
4.
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Analysis. The reaction products were analyzed quantitatively using an Aerograph Model 200 gas chromatograph equipped with flame detector and a 40-foot, %inch stainless steel column filled with 10% tetracyanoethylpentaerythritol (TCEPE) on 60- to 70-mesh Anakrom ABS (Analabs, Inc.). Liquid samples were injected into the column maintained isothermally a t 125”c. The hydrogen-carbon monoxide gas mixtures were analyzed isothermally a t 55OC. on a Wilkens Aerograph Model A-90P chromatograph using a thermal conductivity detector and a 6-foot, %-inch stainless steel column with Linde 5A molecular sieve. All chromatograph peak areas were obtained using an electronic integrator with digital printout (Infotronics digital read-out system, Model CRS10HB). Preparation of Catalysts and Reagents. The catalyst solution was prepared by dissolving 1 gram of Rh(P@,),(C0)Cl in 200 ml. of dioctyl phthalate (DOP) solvent. Then, 15.7 grams of “excess” triphenylphosphine ligand was added to the DOP solution. All materials were carefully deaerated and handled to reduce contact with air (02)t o a minimum. The DOP solvent was magnetically stirred under a vacuum of -10 to 15 mm. of Hg. Then, nitrogen was added to “break” the vacuum and all subsequent steps were performed under a nitrogen atmosphere until the reagents were charged to the reactor. The rhodium catalyst was weighed out and transferred to a bottle prepurged with nitrogen. Deaerated solvent was added along with a magnetic stirring bar to the bottle described above, which contained a glass pipet connected to a nitrogen supply and was continuously purged to minimize air. The catalyst solution was stirred magnetically, and the nitrogen purge was continuously bubbled through the stirred solution until all of the solid materials dissolved; subsequently, the “excess” triphenylphosphine ligand was added and dissolved in the stirred, nitrogen-purged solution. The glass pipet was removed, and the bottle was capped and stored until transferred to the reactor. Results and Discussion
The sparged reactor concept for catalytic hydroformylation reactions was evaluated using the propylene hydroformylation reaction, which produces normal and isobutyraldehyde as shown in Equation 1:
HgC=CHCHg
+ HS + CO
CH3CH2CH2CH0
Rh(P%)z(CO)Cl
and CH3CHCH0
Table I. Range of Operating Conditions
(1)
I
CH.3 The “base operating conditions employed were: Catalyst Catalyst charge Temperature Total pressure Feed composition Carbon monoxide Hydrogen Propylene Total flow rate
Rh(P@3)2(CO)C1 plus “excess” 1P%] ligand 150 ml. of solution (DOP solvent) 128“ c. 500 p.s.i.g. 45.5 mole % 45.5 mole % 9 mole % 1750 scclmin.
At these operating conditions the propylene conversion is 4570, with a normal to isobutyraldehyde ratio of 2 374
to 1. Conversion is defined as the number of moles of C, aldehyde produced per unit time divided by the propylene molar feed rade to the reactor (determined from a calibrated metering pump). The rate of C, aldehyde formation was determined from the rate of product collected on cooling the reactor off-gas. Steady-state operation was assumed when the product collection rate was the same for three consecutive hourly samples. Except for small amounts (20,) of propylene, the liquid product contained only C, aldehyde. Neither the liquid samples nor the noncondensed gases contained significant quantities of hydrogenated products-e.g., < 1% alcohols and/ or paraffins-determined by gas chromatographic (GC) analysis. Periodically conversion was re-evaluated a t the base operating conditions. No noticeable change in conversion or product isomer distribution was detected in over 80 hours’ running time (actual time propylene flowed through the reactor). The catalyst solution removed from the reactor a t the conclusion of the experiment was analyzed to determine if high boiling by-products were formed and remained in the catalyst solution. Less than 2% “high boilers” (tentatively identified as aldol condensation products) were detected by GC analysis. The above results demonstrate the feasibility of employing the gas-sparged reactor concept for hydroformylation of propylene to butyraldehyde a t moderate temperature and pressure (128”C., 500 p.s.i.g.), with little by-product formation ( < 1%)in either the butyraldehyde product or catalyst solution, and with stable catalyst activity and product isomer distribution (2 to 1 n/iso ratio) for an extended period of time. In addition to evaluating catalyst activity and product distribution a t the “base” operating conditions, a limited study of the effect of operating variables was performed. The variables investigated were flow rate, hydrogencarbon monoxide ratio, and temperature. The experimental ranges over which each variable was studied are shown in Table I. Except for the variables investigated, the operating conditions were the same for the “base” case. The effect of flow rate-Le., contact time-upon conversion is presented in Table 11. As expected, the conversion increased with increasing contact time (decreasing gas flow rate) but not linearly.
I&EC PRODUCT RESEARCH A N D DEVELOPMENT
Operating Variable
Range Contact time” 0.8 to 3.15 min.
Flow rate
H ydrogen-carbon monoxide ratio Temperature
I
111 to 311 128” to 148” C.
“Defined as volume of catalyst solution (150 cc.) divided by total gas f70u rate at operating temperature and pressure. With gas holdup in liquid probably around I O ? ; , actual gas residence time in reactor is 5 to 20 seconds. Table II. Effect of Flow Rate on Propylene Conversion
Contact Time, M i n . 0.8 1.25 2.05 3.15
Conuersion, Mole 25 35 45 50
cc
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. SOC.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., Linden, N . J . 07036
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 Week, 1967). Other studies have shown that hydrocarbon jet fuels exposed to such high
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
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