Carbon space-time yields

Foreseeable improvements that will increase operability and decrease operating costs of Fischer-Tropsch processes are the development for the fluidized-iron process of a catalyst that will not accelerate the reaction 2CO = C02 + C and will not be appreciably oxidized during the steady-state life of the catalyst and the development of a more active and mechanically stable catalyst for the oil-circulation process so as further to reduce Ci + C2 production. The hot-gas recycle process could be made operable by use of a catalyst that will be less active but more resistant to thermal shock which occurs during regeneration to remove carbon deposits, and during operation at lower end-gas recycle rates. The powdered catalyst-oil slurry process recently has been satisfactorily operated in a pilot plant by K6lbel and Ackerman (21). Although the space-time yield in this operation was low (10 to 20 kg. of C3+ per cubic meter of slurry per hour), the Ci + C2 production was less than one third of that... 

In the hardening of free tallow fatty acids in sc CO2 we measured iodine values (IV) below 1 g I2/IOO g product at a space velocity of 15 h1. In comparison to trickle bed hardening reactions with activated carbon and titania supported 2 wt. % palladium fixed bed catalysts, between 6 to 15 times higher space time yields were determined when the hardening was carried out in sc CO2. The hydrogen partial pressures in both processes were comparable (2.0 MPa H2). 

The anaerobic fermentation of lactic acid is traditionally performed at up to 50°C over 2-8 d at pH 5.5-6.5 (lactic acid bacteria are highly sensitive to acid). The pH is maintained by titration with a base, usually calcium carbonate. The product concentration is kept below approx. 100 g L 1 to prevent precipitation of calcium lactate, as the separation of a precipitate from the biomass would be too elaborate. The stoichiometric yields are high, of the order of 1.7-1.9 mol mob1 (85-95% of the theoretical yield) but the space-time yield, which is ap-... 

In order to synthesize gasoline effectively from carbon dioxide through one-pass reaction system, methanol synthesis catalyst was improved. Pd and Ga were added to Cu-Zn based catalyst to optimize the state of Cu during the reaction. As the result, the space-time yield (STY) of methanol from CO2 was 1,410 gd h at 270, 80 atm and SV=18,800 /h. In second stage reactor in which H-Ga or Al-silicate was packed, methanol was converted to gasoline. Maximum selectivity to gasoline fraction was 54.4 % and STY was 312 gl h at 320 C and 15 atm. 

Obviously only dimethyl carbonate is obtained in acceptable selectivities and space-time yields according to this method, although the analogous preparation of higher dialkyl carbonates and simple cyclic carbonates has also been described. Phenols do not give diaryl carbonates by CuCl-catalyzed oxidative carbonylation. 

If the conditions of the Ruhrchemie/Rhone-Poulenc process are applied to linear a-alkenes (LAOs) with 5-12 carbon atoms, the space-time yield of the hydroformylation reaction decreases with increasing chain length of the substrate. Table 1 summarizes the results of the batchwise hydroformylation of LAOs different at 30-80 bar syngas pressure. 

The catalyst system for the modem methyl acetate carbonylation process involves rhodium chloride trihydrate [13569-65-8]y methyl iodide [74-88-4], chromium metal powder, and an alumina support or a nickel carbonyl complex with triphenylphosphine, methyl iodide, and chromium hexacarbonyl (34). The use of nitrogen-heterocyclic complexes and rhodium chloride is disclosed in one European patent (35). In another, the alumina catalyst support is treated with an organosilicon compound having either a terminal organophosphine or similar ligands and rhodium or a similar noble metal (36). Such a catalyst enabled methyl acetate carbonylation at 200°C under about 20 MPa (2900 psi) carbon monoxide, with a space-time yield of 140 g anhydride per g rhodium per hour. Conversion was 42.8% with 97.5% selectivity. A homogeneous catalyst system for methyl acetate carbonylation has also been disclosed (37). A description of another synthesis is given where anhydride conversion is about 30%, with 95% selectivity. The reaction occurs at 445 K under 11 MPa partial pressure of carbon monoxide (37). A process based on a montmorillonite support with nickel chloride coordinated with imidazole has been developed (38). Other related processes for carbonylation to yield anhydride are also available (39,40). 

The space-time yield (column 5) reaches a maximum at about 4 1./ hour/g. cobalt. In column 6 the space-time yield was calculated as indicated in the footnote. The volume change upon reaction to form chiefly hydrocarbons with 5 to 16 carbon atoms is approximately constant over a wide range of variation of molecular weight distribution therefore the partial pressure of the reaction products is approximately directly proportional to the contraction. The figures in column 6 increase more slowly than those of column 5 with increasing throughput, but there is no maximum. It seems probable that the temperature of the catalyst surface increases... 

CO2 conversion is also dependent upon the space velocity at which the catalyst is operated. Usually, the reactor feed gas und standard conditions related to the catalyst volume present in the reaction chamber is the measure for space velocity, i.e. m gas/m catalyst In practice, values between 7 000 and 12000 are selected. Rising space velocity causes briefer residence time and thus dropping conversion but also permits small catalyst volume, i.e. increasing space time yield, and vice versa. However, there is a maximum in space time yield which cannot be exceeded, even on the space velocity arising furtho-, as the reduction in carbon monoxide conversion is dominant from this point onward. 

Reference [2] also indicates that the most economic route to vinyl acetate, when acetic acid is available, is to convert the raw materials to product in the vapor phase over a palladium catalyst. We therefore asked our research chemists to develop a catalyst suitable for the operation. They found a suitable catalyst by impregnating a silica base with 2% palladium along with some other proprietary chemicals. The chemists performed numerous experiments with the catalyst and found that it is quite selective towards vinyl acetate and quite active as measured in its space time yield (STY, grams of vinyl acetate/hr per liter of catalyst). The only significant side reaction we could notice is the combustion of ethylene to carbon dioxide and water... 

---