Steam partial pressure

Table 107 Properties and CO conversion rates as a function of temperature over Au catalysts in combination with mesoporous titania using a feed containing 4.494%CO and a steam partial pressure of 31.1 kPa. The catalyst volume was 0.5 cm3 and the space velocity was 4000 1C1 492...

Steam pre-treatment of fluid cracking catalysts has been conventionally employed to represent the deactivation occurring in a commercial FCC unit. Appropriate steam pre-treatment methods have been developed so that the activity and selectivity of the steam pre-treated catalyst is equivalent to a commercially deactivated catalyst (12). However, a unique steaming method may not be suitable for catalysts of varying compositions (12). Two steaming methods designed to simulate deactivation in a commercial unit of the two types of catalysts used in this work were employed. Super-D was treated for 8 hours at 732 C with a steam pressure of 2 atmospheres. The catalysts containing ZSM-5 were treated for 12 hours at 827°C with a steam partial pressure of 0.2 atmosphere. 

Steaming for 12 Hours at 827with Steam partial pressure =. 2... 

Matrix catalyst as well as the catalyst containing ZSM-5 were steamed for 12 hours at 827°C with steam partial pressure =. 2 atmosphere. 

The activity maintenance of ZSM-5 follows the same functional form as that for normal REY/USY cracking catalysts (18). Using this format, ZSM-5 activity (the increase in G plus G. olefins) can be expressed in terms of its age, the regenerator temperature and steam partial pressure according to the following equation ... 

As discussed above, the potential octane boost which can be achieved from ZSM-5 addition is a function of five parameters the regenerator temperature and steam partial pressure (which determine the activity maintenance) the base and ZSM-5 catalyst makeup rates (which determine the catalyst age) and the base gasoline octane. The sensitivity of the model to these parameters is discussed below. 

The severe operating conditions in ATR necessitate catalysts with good mechanical properties and which are stable at the high temperatures of the reaction (650-900 ° C) and at the high steam partial pressure applied. 

The catalyst used in this study corresponds to a fresh commercial catalyst used in one FCC unit of ECOPETROL S.A. This solid is hydrothermal deactivated at the laboratory in cycles of oxidation-reduction (air-mixture N2/Propylene) at different temperatures, different times of deactivation, with and without metals (V and Ni), and different steam partial pressures. Spent catalysts (with coke) are obtained by using microactivity test unit (MAT) with different feedstocks, which are described in Table 10.1. 

Gadsby and co-workers (63) report that for a coal charcoal, the rate of the carbon-steam reaction is greater by a factor of about three than the carbon-carbon dioxide reaction at 800° and a pressure range of 50 to 500 mm. Hg. The results of Pilcher et al. (68) and Walker et al. (85), using the same graphitized carbon rods and apparatus, essentially agree with this finding. At 1100°, the former workers report a reaction rate of 1.6 g./hr. at a steam partial pressure of 142 mm. Hg, which can be extrapolated to 4.8... 

Laboratory steam deactivations represent a significant compromise in the effort to simulate equilibrium catalyst. Since hydrothermal deactivation of FCC catalysts is not rapid in commercial practice, deactivation of the fresh catalyst in the laboratory requires accelerated techniques. The associated temperatures and steam partial pressures are often in substantial excess of those encountered in commercial units. In some instances, the effect of contaminant metals is measured by an independent test not affiliated with steam deactivation. In subsequent yields testing, interactions between different modes of deactivation may be overlooked. Finally, single mode deactivation procedures can not reproduce the complex profile of ages and levels of deactivation present in equilibrium catalyst. 

The reaction is assumed to be first order in steam partial pressure and nth order (to be determined from the kinetic data) with CaBr2 concentration. Similarly, the rate equation for consumption of H20 is given by ... 

The first 10 to 25% of steam has the greatest influence. The zeolite unit cell size reduction, which should give an indication of the zeolite activity loss by dealum[nation [8] is not very sensitive to steam partial pressure, with the exception that some steam is necessary for ceil size shrinkage,... 

A possible explanation for this is that while dealumination in a commercial unit is fastt migration of non-framework alumina from the zeolite structure will be a function of temperature and steam partial pressure [24], This is an area in which the Cyclic Deactivation method approaches the commercial conditions much closer than traditional steaming methods. 

Gasification. The only study on gasification kinetics of Texas lignite has been performed by Bass (23). Using a differential reactor, he obtained rate data at 700°C and for pressures ranging from 61.6 to 225.9 kPa. Rate equations as a function of steam partial pressure and carbon conversion were developed. 

The solid oxide fue( cell (SOFC) have been under development during several decades since it was discovered by Baur and Preis in 1937, In order to commercialise this high temperature (600 - 1000°C) fuel cell it is necessary to reduce the costs of fabrication and operation. Here ceria-based materials are of potential interest because doped ceria may help to decrease the internal electrical resistance of the SOFC by reducing the polarisation resistance in both the fuel and the air electrode. Further, the possibility of using less pre-treatment and lower water (steam) partial pressure in the natural gas feed due to lower susceptibility to coke formation on ceria containing fuel electrodes (anodes) may simplify the balance of plant of the fuel cell system, and fmally it is anticipated that ceria based anodes will be less sensitive to poising from fuel impurities such as sulphur. 

Fig. 4 shows the reactivity of the pure steam experiments as a function of temperature and steam partial pressure. The representative reactivity value has been obtained as the reactivity at 50% conversion. The continuous line shows the n order reaction model for the birch experiments. The figure shows that beech is more reactive than birch at... 

Fig. 4 Reactivity as a function of steam partial pressure and temperature. (Filled symbols beech, hollow symbols birch).

For smaller particle size (dp < 500 m) and lower temperature (1000 °C < T < 1200 °C), char-H20 reaction is chemical reaction controlled. When partial pressure of the steam is low, the reaction order is 1. With increasing steam partial pressure, the reaction order decreases gradually to 0. 

Residual methane is present at the exit of the combustion zone. In the catalytic bed, the methane steam-reforming and the water shift reactions take place. The gas leaving the ATR reactor is in chemical equilibrium. Normally, the exit temperature is above 900-1100°C. The catalyst must withstand very severe conditions when exposed to very high temperatures and steam partial pressures. One example of an ATR catalyst is nickel supported by magnesium aluminum spinel. For compact design, the catalyst size and shape is optimized for a low pressure drop and high activity. 

Figure 2. XC2H4 vs. p°H p ( ) andp°co2 ( ) for T=463 K, Wcat=0.5 g, Ftot=5 mmol s. being most pronounced at low steam partial pressures. Marecot et al. [21] found inhibition due to steam of propane and propene oxidation over Pt/y-Al203. Bart et al. [22] found inhibition of the propane oxidation over a three-way catalyst for reducing conditions and rate enhancement for oxidizing conditions. The inhibition by steam is in contrast to the oxidation of CO by O2 over the same catalyst, where steam was found to strongly enhance the reaction rate [15]. Carbon dioxide also inhibits the reaction rate, although the inhibition is much smaller.

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