Operating temperature catalyst composition affects

The most important factors affecting performance are operating temperature, surface velocity, contaminant concentration and composition, catalyst properties, and the presence or absence of poisons or inhibitors. 

Propene also undergoes conjunct polymerization in the presence of dilute phosphoric acid at high temperatures and pressures (Monroe and Gilliland, 58). When propene was treated with 10-30% phosphoric acid at 260-305° and at 170-410 atmospheres pressure, the only operating variable which appreciably affected the composition of the polymer was the extent to which the feed was polymerized. At constant percentage reaction of the feed under these conditions, the temperature, pressure, and acid catalyst concentration had no effect on the product composition. At low conversions, the polymer consisted of nearly pure dimer at 50% polymerization, two-thirds of the total was dimer and even when the feed was almost completely polymerized, the dimer fraction amounted to 35-40 % of the total polymer. The dimer and trimer fractions obtained at temperatures of 305° or lower using a acid concentrations below 30% contained about 25% paraffins and little or no naphthenes or aromatic hydrocarbons. 

Catalyst composition also depends on the type of reactor used. Fixed-bed iron catalysts are prepared by precipitation and have a high surface area. A silica support is commonly used with added alumina to prevent sintering. Catalysts for fluidized-bed application must be more attrition-resistant. Iron catalysts produced by fusion best satisfy this requirement. The resulting catalyst has a low specific surface area, requiring higher operating temperature. Copper, another additive used in the preparation of precipitated iron catalysts, does not affect product selectivity, but enhances the reducibility of iron. Lower reduction temperature is beneficial in that it causes less sintering. 

Heteropolysalts with composition Kx(NH4)3-xPMoi2O40 were prepared hy precipitation the compounds were tested as catalysts for the oxidative dehydrogenation of isobutyric add to methacrylic add. The heteropolysalts proved to be active and selective in the short-term, leading to methacryUc add with selectivity close to the 70% at total reactant conversion. The calcination temperature of the samples, as well as their cationic composition, affected the performance the best results were obtained with the (NH4)3PMoi2O40 compoimd, caldned at 380C. The effect of the main operative parameters (temperature, residence time and oxygen partial pressme) on the catalytic performance was studied. 

Operational Considerations. The performance of catalytic incinerators (28) is affected by catalyst inlet temperature, space velocity, superficial gas velocity (at the catalyst inlet), bed geometry, species present and concentration, mixture composition, and waste contaminants. Catalyst inlet temperatures strongly affect destmction efficiency. Mixture compositions, air-to-gas (fuel) ratio, space velocity, and inlet concentration all show marginal or statistically insignificant effects (30). 

Three-phase slurry reactors are commonly used in fine-chemical industries for the catalytic hydrogenation of organic substrates to a variety of products and intermediates (1-2). The most common types of catalysts are precious metals such as Pt and Pd supported on powdered carbon supports (3). The behavior of the gas-liquid-sluny reactors is affected by a complex interplay of multiple variables including the temperature, pressure, stirring rates, feed composition, etc. (1-2,4). Often these types of reactors are operated away from the optimal conditions due to the difficulty in identifying and optimizing the critical variables involved in the process. This not only leads to lost productivity but also increases the cost of down stream processing (purification), and pollution control (undesired by-products). 

Hence a goal of the plantwide control strategy7 is to handle variability in production rate and in fresh reactant feed compositions while minimizing changes in the feed stream to the separation section. This may not be physically possible or economically feasible. But if it is, the separation section will perform better to accommodate these changes and to maintain product quality, which is one of the vital objectives for plant operation. Reactor temperature, pressure, catalyst/initiator activity, and holdup are preferred dominant variables to control compared to direct or indirect manipulation of the recycle flows, which of course affect the separation section. 

The DME catalyst must carry out equilibrium conversion of methanol to dimethylether and water with minimum by-product formation. Less than equilibrium conversion will require more heat to be removed in the ZSM-5 circuit, which will result in higher reactor temperature rise. This will increase catalyst deactivation and decrease yield. The higher temperature rise could be reduced by increasing gas recycle, but this will increase operating costs. Excessive decomposition of methanol (e.g., to CO, C02, H2) will result not only in carbon loss, thereby reducing gasoline yields, but will also affect the composition of recycle gas in the ZSM-5 circuit. For example, one percent methanol decomposition to CO and H2 will increase the ZSM-5 reactor temperature rise by 12%. 

On the same topic of DMFC performance with supported vs. unsupported catalysts Smotkin and co-workers concluded that at 363 Kthe supported PtRu (1 1) catalyst with a toad of 0.46 mg cm performed as welt as an unsupported PtRu (1 1) with over four times higher load, i.e., 2 mg cm [266]. It is likely that these differences between various studies are related not only to the intrinsic activity of the respective anode catalys layers but also to the manufacturing procedures such as catalyst layer preparation and application techniques, MEA hot pressing conditions (temperature, pressure and time), presence or absence of other binders (such as PTFE) and fuel cell compression. All these MEA manufacturing variables can affect, in a poorly understood manner at present, the structure, morphology and composition of the catalyst layer in the operating fuel cell. Therefore, in fuel cell experiments it is difficult to isolate the truly physico-chemical effect of the support on the catalytic activity. 

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