Carbon monoxide partial pressure, inhibition

Figure 3.11 illustrates the mass transfer coefficient for batch-grown R. rubrum and was computed with various acetate concentrations at 200 rpm agitation speed, 500 lux light intensity, and 30 °C. As the experiment progressed, there was an increase in the rate of carbon monoxide uptake in the gas phase and a gradual decrease in die partial pressure of carbon monoxide. Also, a decrease in the partial pressure of carbon monoxide was affected by acetate concentration in the culture media. The value of the slope of the straight line increased with the decrease in acetate concentrations, i.e. 2.5 to 1 g-l. The maximum mass transfer coefficient was obtained for 1 g-l 1 acetate concentration (KLa = 4.3-h 1). The decrease in mass transfer coefficient was observed with the increase in acetate concentration. This was due to acetate inhibition on the microbial cell population as acetate concentration increased in the culture media. The minimum KLa was 1.2h 1 at 3g l 1 acetate concentration. 

In this model, the first step is the dissociation of C02 at a carbon free active site (Cfas), releasing CO and forming an oxidized surface complex [C(O)]. In the second step, the carbon-oxygen complex subsequently produces CO and a new free active site. The reverse reaction is relatively slow compared with the forward reaction, so the second reaction can be treated as an irreversible reaction. In this model, desorption of the carbon-oxygen surface complex is the rate-limiting step. The rate for this mechanism can be described by the Lang-muir-Hinshelwood rate equation. Furthermore, the C/C02 reaction rate is dependent on the CO and C02 partial pressures and is inhibited by the presence of carbon monoxide. A widely utilized reaction rate equation based on this mechanism is... 

The kinetics of the above-mentioned biphasic hydroformylation of allyl alcohol (see Eq. 9) was described by the rate Eq. (15) [10], which shows the inhibition of the reaction rate by the partial pressure of carbon monoxide. 

It has been reported that use of a suitable co-solvent increases the concentration of the olefin in water (catalyst) while retaining the biphasic nature of the system. It has been shown that using co-solvents like ethanol, acetonitrile, methanol, ethylene glycol, and acetone, the rate can be enhanced by several times [27, 28], However, in some cases, a lower selectivity is obtained due to interaction of the co-solvent with products (e.g., formation of acetals by the reaction of ethanol and aldehyde). The hydroformylation of 1-octene with dinuclear [Rh2(/t-SR)2(CO)2(TPPTS)2] and HRh(CO)(TPPTS)3 complex catalysts has been investigated by Monteil etal. [27], which showed that ethanol was the best co-solvent. Purwanto and Delmas [28] have reported the kinetics of hydroformylation of 1-octene using [Rh(cod)Cl]2-TPPTS catalyst in the presence of ethanol as a co-solvent in the temperature range 333-353 K. First-order dependence was observed for the effect of the concentration of catalyst and of 1-octene. The effect of partial pressure of hydrogen indicates a fractional order (0.6-0.7) and substrate inhibition was observed with partial pressure of carbon monoxide. A rate eqution was proposed (Eq. 2). 

The effect of reaction parameters, such as the concentrations of catalyst and olefin and the partial pressures of CO and hydrogen, on the rate of reaction has been studied at 373 K [19]. The rate varies linarly with catalyst concentration, olefin concentration, and partial pressure of hydrogen. Typical substrate-inhibited kinetics was observed with the partial pressure of carbon monoxide. Further, a rate equation to predict the observed rate data has been proposed (Eq. 5). 

Rates of formation of methanol and water at 230°C depend strongly on hydrogen pressure. Rate of methanol synthesis is almost independent of partial pressure of carbon monoxide and carbon dioxide at low conversions. At high carbon dioxide content in the feed gas the rate depends strongly on conversion at low carbon dioxide content it is almost independent of conversion. This indicates that the methanol formation is inhibited by water but not by methanol. Initial rates of formation of methanol and water are equal indicating that methanol is formed by hydrogenation of carbon dioxide. Rate of reverse shift reaction is low compared to rate of methanol synthesis. Rate of shift reaction is higher when favoured by equilibrium. 

The strong inhibiting effect of water during the reduction of well-dispersed iron oxide phases on alumina surfaces is also apparent from the infrared spectrum of carbon monoxide adsorbed onto the reduced catalyst prepared from complex iron cyanides according to the above procedure of Boellaard and co-workers Despite the support, the size of the iron particles, and the loading of iron on the support all being essentially the same, the infrared spectrum of the adsorbed carbon monoxide is completely different. The absorption band at 2155 cm is not seen, which indicates that Fe(II) is not present at the alumina surface when reduced in the presence of low partial pressures of water vapor. Rather than bands with frequencies above about 2000 cm bands at 1806, 1884, and 1984 cm are observed (Fig. 5.9). Even at room temperature, disproportionation of carbon monoxide to carbon dioxide and carbon occurs, which is demonstrated by the presence of carbon dioxide adsorbed onto the alumina support. The infrared bands peaking at 1348 and 1598 cm arise from carbon dioxide adsorbed on alumina. 

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