Selectivity feed rate, time

The reaction was studied using the iron phosphate catalyst at 230°C with feed rates of pyruvic acid, air, and water = 10.5, 350, and 480 mmol/h. The main products were citraconic anhydride, acetic acid, and CO2. When the amount of catalyst used was lOg, that is, when the contact time is about 2.6 s, the conversion of pyruvic acid reached 95% and the yields of citraconic anhydride and acetic acid were 50 and 28 mol%, respectively the loss was about 17 mol%. The selectivity to citraconic anhydride is clearly lower and that to acetic acid is higher than in the case of the W-based oxide catalysts. However, the catalytic activity was very stable. No clear change in the yield of citraconic anhydride was observed during the reaction for 10 h. 

Consider the conversion of methanol in a 50-L reactor (volume of catalyst) similar to that shown in Figure 1.2 (which operates like a CSTR). The reactor contains 800 g of catalyst (zeolite H-ZSM5), and the space time through the reactor is 0.1 h The methanol feed rate is 1.3 kg h-1. For each reaction temperature, determine the yield and selectivity to each olefin, and comment on your results. 

Fig. 2 Multiple runs showing the productivity PROD as a function of time for five feed rates of B between 0.05 and 0.01 m3/min. The highest feed rate gives the lowest selectivity.

Ethanol Feed. The ethanol was fed by a dual system. The first was a two flask feed system, used to maintain an ethanol base line feed rate. Each flask contained 4000 ml of ethanol solution. Flask one contained 125 ml of 190 proof ethanol (93.7 g) in 3875 ml of H2O. Flask two contained 3500 ml of 190 proof ethanol (2623 g) plus 500 ml of water. When the system is feeding solution from flask one to the fermenter at a constant rate, r liter/hr, a linear increase in alcohol concentration in the feed will occur. See Figure 2 for details. This will result in a cell mass increase in the fermenter that is second order in time. This base line feed rate will always be less than the desired growth rate as long as the correct feed rate is selected. 

Kinetic studies focus on the selection of an adequate rate expression and determination of the unknown rate parameters it contains (eq 1). Generally, the rate is not measured directly but is derived from a measured quantity, conversion or concentration, at given operating conditions such as catalyst amount and feed rate. Apart from kinetic studies to determine the rate equation, other purposes of measuring rates are comparison of various catalyst formulations in screening of new catalysts, the time-dependent behavior of the catalyst actvity to predict its long term performance and to characterize catalysts such as in temperature programmed reduction (TPR) or sulphidation (TPS) studies. 

The monoalkylation selectivity of the alkylation step refers to the fraction of ethylene that reacts to form ethylbenzene, as opposed to forming polyethylated species. To suppress the formation of PEBs, benzene must be fed to the alkylation reactor in considerable excess (frequently five to seven times the stoichiometric requirement). Equipment in the alkylation reaction and benzene recovery systems must therefore be sized to accommodate the flow of excess benzene, and energy must be expended to recover the excess benzene from the reactor effluent. However, the superior monoalkylation selectivity and stability of MCM-22 permits operation with reduced benzene feed rates - in the range of two to four times the stoichiometric requirement - without excessive PEB formation (see Table 11.1). 

Our selectivity and rate data for catalysts with large x values, as well as independent CO and H2 diffusivity and solubility measurements (22,112), suggest that CO, and not H2, becomes the diffusion-limited reactant for feeds with H2/CO > 1.6. These results disagree with a previous proposal (60) that H2 arrival rates control the rate of hydrocarbon synthesis on Co catalysts with kinetics and volumetric rates very similar to ours. The results obtained on Co and Ru catalysts are remarkably similar (Fig. 14a) because site-time yields (Figs. 2 and 3) and FT synthesis kinetics (Table I) are also similar on the two catalyst systems, and FT synthesis selectivity is controlled by transport limitations due to the catalyst structure and not by the details of the catalytic chemistry. 

The measured intensities of the selected analytical lines are influenced by the various settings such as the plasma operation conditions (the generator output and the gas flow rates), the observation height of the plasma, the sample feed rate, the measurement integration time and the spectral background correction points. The choice of operational settings has to take into account the sample type, the elements analysed and the level of precision required for the analysis. 

Many reactions occur simultaneously in coal gasification systems and it is not possible to control the process precisely as indicated here. But by careful selection of temperature, pressure, reactant and recycle product feed rates, reaction times, and oxygen-steam ratios, it is often possible to maximize certain desired products. When high-energy fuel gas is the desired product, selective utilization of high pressure, low temperature, and recycled hydrogen can result in practically all of the net fuel gas production in the form of methane. 

The effect of varying the total feed rate was studied using 60 mg of catalyst and a methane/oxygen feed ratio of 2/1. The total feed rate varies from 300 to 1200 cc/min corresponding to residence times of about 3 to 0.8 ms respectively. The results (Figure 4) show that, contrary to expectations, upon doubling the flow rate from 300 to 600 cc/min, methane conversion and H2 and CO selectivities remain nearly constant at approximately 65%, 70%, and 80% respectively. In addition, as in the previous results, oxygen conversion remains at 100%. Methane conversion, which is nearly constant at 65% at feed rates of 600 cc/min and below, falls to only 35% at 1080 cc/min. The CO and H2... 

Fig. 4.18. Catalytic behavior and structural changes of glassy Cu7oZr30 alloy during exposure to CO2 hydrogenation conditions [4.23], A) Change of C02 hydrogenation activity and product distribution as a function of time-on-stream. Dashed line indicates the calculated equilibrium conversion. Symbols C02 conversion selectivities to methanol O, carbon monoxide V, and ethanol A. Hydrogenation conditions 1.2 g of sample, feed rates of reactants C02,2.3 mmol/s H2, 7.6 mmol/s total pressure 15 bar. B) X-ray diffraction patterns of active sample after steady-state conversion was reached (Cu K,)...

The tool-electrode feeding rate has to be selected properly. Feed rates faster than the mean material removal rate of the process will result in breaking either the workpiece or the tool-electrode. On the other hand, very slow feed rates will increase drilling times and may result in large heat affected zones around the microhole. So far only a few studies have been carried out on the optimal feeding rate. Typical values reported in the literature are, depending on the tool-electrode... 

Figure 1. Effect of feed rate on the aniline conversion and selectivity over APAl-P catalyst (T 573 K time-on-strean 2h).

---