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Chemical regime

For slow reactions, mass and heat balances can be simplified in the limit of small Thiele modulus 1). At steady-state conditions, these profiles are flat inside the particles, due to the comparably fast transport. Solutions at the isothermal conditions are available elsewhere [80]. This means that as a first approximation, [Pg.64]

The particular forms of and T can be obtained by collection of the 0 P ) terms in Equations 3.41 and 3.42. Retaining the most important terms, the effectiveness factor and the averaged internal profiles become [Pg.64]

Equation 3.50 reproduces the solid-phase energy balance in Equation 3.34 in the absence of a chemical reaction (with negligible axial dispersion at steady-state). For large Bih A, T T and this should be valid at least in the bed s core and everywhere if Equation 3.52 is verified. In general, close to the wall (in a layer with thickness in the order of A/Bih), significant temperature [Pg.64]

In these conditions, the profiles in each phase are related by Equation 3.50. Temperature in both phases is identical only [Pg.64]


Fig. 3. Typical isopleth diagram showing the three chemical regimes HC = hydrocarbons (22). Fig. 3. Typical isopleth diagram showing the three chemical regimes HC = hydrocarbons (22).
GL 19] ]R 9] ]P 20] The rate of reaction is proportional to increasing catalyst concentration [63, 66], This result is an indication of operation in a chemical regime. At higher temperature, larger rates are found [66]. [Pg.634]

The general extent of the molecular cloud can be mapped within the sky but the physical conditions and stellar activity lead to different chemical regimes, all of which must be considered if the chemistry of the ISM is to be understood. A... [Pg.114]

The concentration of the substrate S is also uniform throughout the boundary layer. This case is often called chemical regime , because the limiting phenomenon is the chemical reaction and not the physical process of mass transfer. In that case, the gas-liquid contact area (A, o, oL...) is not a crucial parameter conversely, the liquid retention (eL) must be high to promote the reaction. [Pg.1528]

Of the 22 amendments to the EU Marketing and Use Directive (76/769/EEC), only two have come about as a result of formal risk assessment under the new or existing chemicals regimes... [Pg.113]

Because of the importance of reaction kinetics in the context of chemical process safety and optimisation, a further development of tools is needed that enables the easy and quick determination of thermodynamic and kinetic parameters. Particular emphasis has to be put on calorimetric devices that correspond to the conditions in chemical production as far as possible but nevertheless have only a small volume. As already discussed in detail, the combination with additional analytical tools is essential. Furthermore, the devices have to have a wide range of applicability with regard to temperature, pressure, chemical regime, number and types of phases involved and so on. Finally, computer tools are needed that allow a quick and easy determination of kinetic and thermodynamic parameters from the measurements. The systematic application of such improved methods could result in a number of significant improvements in chemical processes in industry. [Pg.225]

Accordingly, operation was in the chemical regime, that is, governed by kinetics and not controlled by mass transfer [271]. For the Pd catalyst, however, the activation energies measured in the mesh reactor and in a well-behaved batch reactor with commercial Pd/Al203 powder catalyst were different, being about 0 and 41 kj/mol,... [Pg.172]

Hydrological and hydro chemical regimes of the delta and especially of the liman are mainly determined by the river fresh water inflow, local climatic conditions, including wind regime, and water exchange between the liman and the sea through the outlet. [Pg.120]

On the basis of laboratory and field results, the soluble acrylic system was chosen for further field trials. The formulation (code //1692) was tested on 210 hectares, 13 separate fields in Arizona and California during the 1982 growing season. Each test field was compared to a standard field, treated either with a chemical regime or a commercial pheromone product, located in the immediate vicinity. The efficacy assessment was based on trap catch reduction and boll infestation control. The treatment rate was 6.9 liters of formulation per hectare. This represented a rate of 3.7 grams pheromone and 36.9 grams pyrethroid per hectare. Treatment intervals were approximately ten days apart and the applications... [Pg.158]

An important aspect for emission reduction policies is the study of the regional sensitivity to precursor emission reduction. For this purpose indicator species are computed to asses reduction in NOx and VOC over the whole Italy and on subdomains centered on specific spots the Milan and Rome areas and some of the major industrial areas. Different periods were selected, and runs with both chemical schemes were performed over Italy comparing indicator species computed for different reduction scenarios. For all the periods investigated, it was found that Italy, including the large islands Sicily and Sardinia, is mostly dominated by NOx chemical regimes, independently of the photochemical mechanism used. However, the effect of the NOx reduction predicted with the CB-IV mechanism is lower than that predicted with S APRC90 mechanism. In addition, the urban areas... [Pg.91]

The Amazon drainage basin contains 40% of the world s tropical rain forest (dos Santos, 1987) and is home to countless species of plants and animals. The river itself contains some 2000 described species of fish. Nevertheless, the Amazon is a classic river basin, with a vast central plain bordered by highlands and an extensive floodplain (varzea). Even now, the Amazon is largely undisturbed by anthropogenic activity and includes a series of hydrological and chemical regimes that are representative of world rivers. [Pg.275]

Tronconi et al. [44] have included Eq. (9) in a complete model for DeNO reaction and SO2 oxidation, showing that, opposite to the former reaction, the latter one occurs in a chemical regime due to its very low rate Dedicated experiments have indicated in fact that SO2 oxidation involves the whole catalyst volume also, application of literature cntena [45] have confirmed the absence of external and intraporous gradients of SO2 concentration [18. ... [Pg.132]

After drying and reduction, the Pd-Ag/C catalysts are composed of bimetallic Eilloy nanoparticles ( 3 nm). CO chemisorption coupled to TEM and XRD analysis showed that that, for catalysts 1.5% wt. in each metal, the bulk composition of the alloy is close to 50% in each metal, whereas the surface is 90% in Ag and 10% in Pd [9]. Mass transfer limitations can be detected by testing the same catalyst with various pellet sizes [18]. Indeed, if the reactants diffusion is slow due to small pore sizes, the longer the distance between the pellet surface and the metal particle, the larger the influence of the difiusion rate on the apparent reaction rate. Pd-Ag catalysts with various pellet sizes were thus tested in hydrodechlorination of 1,2-dichloroethane. Results were compared to those obtained with a Pd-Ag/activated charcoal catalyst. Fig. 4 shows the evolution of the effectiveness factor of the catalysts, i.e. the ratio between the apparent reaction rate and the intrinsic reaction rate, as a function of the pellet size. The intrinsic reaction rate was considered equal to the reaction rate obtained with the smallest pellet size. When rf = 1, no diffusional limitations occur, and the catalyst works in chemical regime. When j < 1, the observed reaction rate is lower than the intrinsic reaction rate due to a slow diffusion of the reactants and products and the catalyst works in diffusional regime [18]. [Pg.116]

The evolution of the chemical regime in the unsaturated zone surrounding a heat source is closely related to the spatial distribution of temperature and the transport of water and vapor. An important aspect of the unsaturated fractured tuff at Yucca Mountain is that the highly permeable fractures are nearly dry, whereas the low permeability and porosity rock matrix has a water saturation of about 90 percent. Thus, heating of the rock induces boiling of the matrix pore water, transport of water vapor into fractures, and condensation along fracture walls. [Pg.348]

The net result was that the average activity of the monolith, which is measured by the product q kc, kept practically constant in the three samples. This is further expressed in dimensionless form by the corresponding values of the Damkholer number. Da, which represents the ratio between the rate of the chemical reaction at the wall and the rate of gas-solid diffusion. It is observed that values of the Da parameter in the order of unity are representative of mixed diffiision-chemical regime and are typical of the SCR process. [Pg.154]

Such an example of a 2 1 complex is interesting because, for our part, we observed nonlinear effects during the hydroformylation of various heavy alkenes, which led us to propose the association of two cyclodextrin units in the interphase [58]. Experiments, carried out at 5 bar, 80°C, and in the conditions of a chemical regime for the stirring of the biphasic system, with the dinuclear [Rh2(/r-StBu)2(CO)2(TPPTS)2] complex, show interesting trends. [Pg.128]

Within the molecular quantum-chemical regime, various strategies on how to generate sets of pseudopotentials have been followed, such as the shape-consistent pseudopotentials for which the pseudo-valence orbital is identical... [Pg.141]


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