Coke formation pressure effect

Effect of Pressure on Coke Formation from Cumene Hydroperoxide... 

Alkane dehydroeyelization with Pt-Sn-alumina catalysts—Continued pressure effect, 120 PtSn alloy formation, 117-118 role of Sn, 117 Sn vs. carbon deposition, 120 Sn vs. coking, 118-119 Sn vs. n-octane conversion, 120-122 Sn vs. selectivity, 118 temperature effect, 119 Alkene hydroformylation, asymmetric catalysis, 24... 

Note that as a first approximation the effect of hydrogen is not taken into account, which implies that the model will hold only for a limited range of hydrogen pressures. As a driving force for the reaction we use the gas-phase concentration, Cq, of the coke precursor Q, is the equilibrium constant of adsorption of Q on the catalyst surface. The rate constant for coke formation, kc, depends on the amount of coke present on the surface ... 

The effects of space velocity, partial pressure, temperature, and catalyst crystallite size on the coke formation and the resulting deactivation in both MTO and the coke forming reactions were easily obtained in the TEOM experiments (39,40,86). Furthermore, the mass desorbed from the catalysts was determined by the transient mass response this information is important for the design of the stripping process in such applications as FCC and MTO. 

Coke on the catalyst is, thus, largely responsible for catalyst deactivation by loss of surface area, and this could be minimized by increasing the hydrogen pressure. However, increasing pressure has been reported to increase vanadium deposition more near the exterior surface of the catalyst pellet (13,14). In essence, an increase in the hydrogen pressure has a beneficial effect in suppressing coke formation, but can lead to shorter catalyst life due to rapid accumulation of vanadium at pore mouths. 

Besides ZSM-5, other zeolites such as ferrierite and mordenite loaded with a noble metal (Pt, Pd) have also been found to be effective lube dewaxing catalysts [171,172]. In this case, high hydrogen pressures are applied to saturate the cracked by-products and to ensure a stable catalyst activity by reducing coke formation, particularly in the case of mordenite which is more susceptible to coking owing to its unidirectional pore system. 

The three feedstocks were processed by hydropyrolysis at selected process conditions. Previous results (1,7) have shown that gas to liquid ratios increase sensitively with increasing temperature. This effect can be offset somewhat by decreasing the residence time. A variation in pressure does not have a major effect on product yields or gross properties, but pressures above about 1200 psig are required to inhibit coke formation. 

The data in Fig. 5 also show that coke formation occurs rapidly at first and becomes increasingly slow as coke piles up. This behavior reflects the deactivating effect of coke on the coking reaction. Since the TEOM microbalance maintains temperature and the pressure time invariant, the mass balance equation for coke-on-catalyst can be described as [17] dC. 

In this case, the process for the production of gasoline from methanol is considered. One of the critical problem in the development of this process is the deactivation of the zeolite catalyst used via coke formation. This deactivation by coke formation in zeolites has been simulated by Guo et al. [12] using a site-bond-site modefwith a two dimensional square lattice. The effect of gaseous pressure on the coke formation was foimd to be similar to that reported in the literature. The authors have not compared their results with kinetic data. 

Coals that soften and then swell prior to coke formation under atmospheric pressure do not always behave similarly when heated in vacuo. In fact, the reduced pressure actually decreases the degree of softening and swelling. On the other hand, if coal is heated under pressure, the softening and swelling increase and a firmer coke is produced, but to obtain an appreciable effect, higher pressures (on the order of 100 psi and more) may be necessary. 

When the temperature reached 713 K, the hydrogen pressure began to decrease at constant rate. Also, there was a tendency for the increased extraction rate and lower coke formation with the increased initial hydrogen pressure. For coals rich in oxygen (approximately 30%), hydrogen pressure was found to have little effect on the extraction rate. 

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