Hydrocarbons space time yield

Operating Results Product gas rate, std. cu. ft./hr. Hydrocarbon yield, std. cu. ft./lb. Gaseous hydrocarbon space-time yield, std. cu. ft./cu. ft.-hr. 

Selectivity and Space-Time Yield of Liquid Hydrocarbon.102... 

To synthesize ethanol more effectively from CO2, the Cu-Zn-Al-K mixed oxide catalyst was combined with the Fe-based catalyst. An F-T type Fe-Cu-Al-K mixed oxide catalyst, which has been developed already in our laboratory [1], converted CO2 to both ethanol and hydrocarbons, while the Cu-based catalyst converted CO2 to CO and methanol with high selectivity. Through the combination of these two catalysts, the three functions were harmonized C-C bond growth, partial reduction of CO2 to CO, and OH insertion to the products. Furthermore, combination catalyst of Fe- and Cu-based ones was modified with both Pd and Ga to maintain the desirable reduced state of the metal oxides during the reaction. As the result, the space-time yield of ethanol was enhanced to 476 g/l-h at SV=20,000 h ... 

Molybdenum catalysts have long been recognized as being effective for the Fischer-Tropsch synthesis of light hydrocarbons (refs. 4,5). In our previous study, however, the supported molybdenum catalysts were found to be active in the synthesis of mixed alcohols, which was significantly influenced by support and additive (ref. 6-8). The space time yield over 20 wt% Mo-1.63 wt% K/Si02 amounted to 420 g kg-cat- h- at 573 K, 5.0 MPa. The aim of this paper is to clarify the active species for alcohols and hydrocarbons of the S -supported Mo catalysts for mixed alcohol synthesis and to pursue the pathway to them from CO and H2. It should be noted that Dow and Union Carbide have published a... 

The presence of zinc oxide in thorium catalysts increased the amount of liquid products. The search for a possible substitute for thorium oxide led to the discovery that a two-component catalyst, composed of aluminum and zinc oxides, was capable of catalyzing the formation of higher hydrocarbons as well as that of isobutane. However, the space-time yields obtained with the catalysts of this type are lower than those obtained with the corresponding Th02 catalysts. 

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... 

Based on the development of both catalysts and reactors [4, 5], the Fischer-Tropsch synthesis activity and selectivity of cobalt catalyst have increased as illustrated in Figure 1.1. The volume-based activity has increased by a factor of 10 going from 1940 at space time yield (STY) = 10 to 1990 at STY = 100, and another factor of 3 is expected to lead to STY = 300 by 2010. Most importantly, with increasing activity the catalysts displayed improved selectivities to higher hydrocarbons. 

Figure 1.1 Development of cobalt-based Fischer-Tropsch synthesis in terms of both activity (STY = space time yield) and selectivity to hydrocarbons of five or more...

On the basis of the assumptions of model <22> and <23> the Fischer-Tropsch synthesis in a slurry phase BCR has been modeled [37, 38]. As this hydrocarbon synthesis from synthesis gas (CO + H2) is accompanied by considerable volume contraction, it is clear that gas flow variations have to be accounted for. The developed models are useful to evaluate experimental data from bench scale units and to simulate the behavior of larger scale Fischer-Tropsch slurry reactors. Though only simplified kinetic laws were applied, the predictions of the model are in reasonable agreement with data reported from 1.5 m diameter demonstration plant. Fig. 12 shows computed space-time-yields (STY) as a function of the inlet gas velocity. As the Fischer-Tropsch reaction on suspended catalyst takes place in the slow reaction regime, it is understood that STY passes through a maximum in dependence of uqo- The predicted maximum is in striking agreement with experimental observations [37]. 

Influence of Space Time. Studies on the effect of space time on the methanol conversion and the hydrocarbon distribution clearly showed that Cj-Cg olefins are intermediates in the conversion of methanol to gasoline. This is illustrated in Table 8, which presents the yields of light olefins, aromatics and paraffins as a function of space time and methanol conversion. 

The lower part of Table 8 shows the distribution of light olefins within the hydrocarbon fraction. It is clear that at low space times the main hydrocarbons are olefins, but the yields are very low due to the low conversion. The yield of light olefins increases with space time and reaches a meiximum, indicative of their intermediate character. In the particular example of Table 8 this maximum (16.2 g/100 g MeOH fed) is reached at a conversion of 90%. At this point, however, the Cj-C olefins constitute only 45.7 wt% of the hydrocarbon fraction. An important feature of the methanol conversion on ZSM-5 is that, although the conversion is complete, a further increase of space time results in a continuing change of the hydrocarbon distribution. Therefore, care must be taken in the interpretation and comparison of results at 100% conversion. 

Effect of Residence Time. The effect of average residence time in the reactor on the conversion to the three hydrocarbon gases is indicated by the data shown in Figures 4 and 5. Figure 4 shows conversion data from three different sizes of reactor tubes, each operated at a coal feed rate of 1.2 lbs of coal/hr. These data show only a slight effect of reactor size on the product yields. In Figure 5 the conversions for reactor temperatures in the range 1000-1300°K are plotted vs. the reactor space time,... 

The space-time 3rield of condensed hydrocarbons is plotted against contraction in Fig. 9. Within the limits of heat-transfer capacity of the apparatus, the yield is directly proportional to the contraction when the temperature is varied, because the temperature coefficient of the reaction rate apparently is large enough to overcome the increased retarding effect of the products with increasing conversion. 

It was noted earlier that plots of CO conversion vs. space time (Figure 3) were remarkably linear up to rather high conversions, which allowed analysis of the data from initial slopes. We also can analyze the data in terms of products formed. This was done for CO2 and hydrocarbon yields, separately. Separation of reaction into these two components gives an interesting result, as shown in Figure 4. Here, it can be seen that the hydrocarbon formation shows more curvature on the plot than the overall CO conversion. The curve bends downward as would be expected from the kinetics, i.e., hydrocarbon formation should decrease from linearity with 1/Sy (with conversion). But the CO2 formation curve bends upward. This effect is indicative of a series reaction, in which, as conversion increases, the H2O formed reacts with CO to form CO2 (water-gas shift reaction). This result is in agreement with the contention in the literature that H2O formation is the primary reaction and that CO2 forms by a secondary reaction (6). 

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