Fixed-bed tests

Table 69 Kinetic parameters from fixed bed testing of metal/ceria catalysts at 300 °C386... 

FIXED-BED AND FLUIDIZED-BED TESTS In the fixed-bed test, a sample of cracking catalyst was contacted with an FCC feed in a manner similar to the standard microactivity test (MAT) prescribed by ASTM (10). One major difference was that the reactor temperature was increased from 900°F to 960°F to better simulate current commercial operations. 

The effect of time averaging on yields in transient tests can be minimized by shortening the duration of the test. Also, a fixed bed test is superior to an FFB activity test in that backmixing is minimized. Furthermore, an isothermal fixed bed test would be easier to interpret than the adiabatic MAT test. This work shows that from the point of view of a catalyst characterization test, a small steady state riser will give the most direct information for catalyst performance in a commercial riser. 

Studies of the Fischer-Tropsch synthesis on nitrided catalysts at the Bureau of Mines have been described (4,5,23). These experiments were made in laboratory-scale, fixed-bed testing units (24). In reference 5, the catalyst activity was expressed as cubic centimeters of synthesis gas converted per gram of iron per hour at 240°C. and at a constant conversion of 65%. Actually, the experiments were not conducted at 240°C., but the activity was corrected to this temperature by the use of an empirical rate equation (25). Conditions of catalyst pretreatment for one precipitated and two fused catalysts are given in Table IV. 

Bureau of Mines studies by M. D. Schlesinger, now in progress, indicate that nitrided fused iron catalysts operate successfully in the slurry process with about the same selectivity as observed in the fixed-bed tests. 

R. W. H. Sargent The maximum concentration of CO2 in the fixed-bed tests was 1000 ppm and there was no measurable rise in gas temperature along the bed. We are currently doing tests with much higher CO2 concentrations and have extended the model to deal with thermal effects. Calculations with this model for the original tests confirm that temperature gradients are negligible, both in the gas phase and in the interior of the pellets. 

Once near steady-state activity had been reached (19 hours), the temperature was decreased 15 °F, and the effect of decreased temperature on conversion and selectivity established, Run 4. An estimated activation energy for the conversion of methylcyclohexane is 28 kcal/mole, only 2 kcal less than the approximate value for the nickel-kieselguhr catalyst. The effect of decreased operating pressure is shown by the data of Run 5. Conversion increased, and efficiency to cyclohexane decreased slightly. The same effect was noted previously in fixed bed tests with Preparation A. 

The catalytic cracking of cumene to propylene and benzene was studied at 800°F using a fiuidized bed 3 inches in diameter [7]. The silica-alumina catalyst had 13% AI2O3 and a BET surface of 490 m /g. The 100-to 200-mesh fraction of the catalyst was used after fiuidizing for several hours to remove fines. The predicted equilibrium conversion was 0.77, and in many of the fixed bed tests this value was almost reached. With a porous-plate distributor and 8-inch initial bed height, the conversion was 62% at 0.1 ft/sec and 50% at 0.2 ft/sec. Treating the reaction as pseudo-first-order, Nf was estimated to be 8.4 for 0.1 ft/sec and 4.2 for 0.2 ft/sec. 

This paper describes the development of BP s Fischer-Tropsch (FT) catalyst from the early days of laboratory scale preparations and micro-reactor tests to commercial scale manufacture and operation at BP s Gas to Liquids (GTL) demonstration facility in Nikiski, Alaska. A detailed description of the catalyst development activities, preparation methods, and experimental facilities is provided by Font Fieide and eoworkers [1]. The initial research was focused on eatalyst development for a fixed bed reactor design. Recent activities inelude the eommereial seale fixed bed tests in progress at Nikiski and development of a novel slurry-based reactor technology. 

Fixed bed tests were undertaken with H2 C0 = 2 1, 30 bar, 1250 h GHSV. In order to best compare the catalytic performance, the temperature in each test was adjusted so as to achieve 62% carbon monoxide conversion. When the performance was steady over at least 36 h the data was recorded for comparative purposes. A brief summary of the performance of all three tests is shown in Table 2. 

Figure 3. Relative selectivity (C5+) for varying pore diameters ofy-aluminas. Fixed-bed tests at...

Figure 8. Selectivity (C5+) for promoted catalysts. Fixed-bed tests at 210 °C and 20 bar with H2/CO inlet ratio of 2.1.

Table 1. Results from Nj-sorption measurements and fixed bed testing for three different materials spray dried with a 1.0 mm nozzle and water as balance. The fixed bed dafa were measured at 210°C, 20 bars and 45% CO conversion.

---