Solid catalyst, ideal reactor with

Ideal Reactors With Solid Catalyst 3.2.4.1 The batch reactor... 

Generally, this implies the use of ideal reactors of the plug flow or well stirred tank type with well defined residence times and residence time distributions under isothermal conditions (with some exceptions, as will be indicated). By-passing part of the catalyst by channeling in a packed bed or uneven flow distributions must be avoided. In three-phase systems (gas/liquid/solid), the even distribution of both fluid phases over the catalyst is crucial. 

In the previous sections the use of catalysts dissolved in ionic liquids has been documented with a variety of examples from the most recent literature. They were classified are catalytic systems based on the adoption of Strategies A, B and C, when solvent-less conditions were not adopted. In an ideal liquid-liquid biphasic system, the IL must dissolve the catalytic intermediates and, in part, the substrate to avoid that mass transfer limits reaction rates. Moreover, products should have a limited solubility in the IL to allow a facile product removal or extraction, and, possibly, the recycle of the ionic liquid-trapped catalyst. The separation of the catalyst from the products is made easier if solid support-immobilised ILs are used. The preference for a solid catalyst is dictated not only by the easier separation but also, as outlined by Mehnert in an excellent review article, " by (i) the possible use of fixed bed reactors, and (ii) the use of a limited amount of IL, a generally expensive chemical which can limit the economic viability of the process. In this section attention will be focused only on the most recent examples of solid-phase assisted catalysis using ionic liquids, following Strategy D. Examples prior to 2006 are covered in recent reviews and will not be discussed here. " ... 

The tubular reactor is so named because the physical configuration of the reactor is normally such that the reaction takes place within a tube or length of pipe. The idealized model of this type of reactor is based on the assumption that an entering fluid element moves through the reactor as a differentially thin plug of material that fills the reactor cross section completely. Thus, the terms piston flow or plug flow reactor (PFR) are often employed to describe the idealized model. The contents of a specific differential plug are presumed to be uniform in temperature and composition. This model may be used to treat both the case where the tube is packed with a solid catalyst (see Section 12.1) and the case where the fluid phase alone is present. 

Derive an equation similar to (1.7.2) for the case of an ideal tubular reactor packed with a solid catalyst. The surface area of the catalyst has the value A per unit length of reactor. 

Equation (3-8a) is the design equation for an ideal, constant-volume, batch reactor for a reaction that is catalyzed by a solid catalyst The symbol Qat represents the mass concentration (massA olume) of the catalyst The catalyst concentration does not change with time if yis constant... 

II. Ease of electrical connection Here the main problem is that of efficient electrical current collection, ideally with only two electrical leads entering the reactor and without an excessive number of interconnects, as in fuel cells. This is because the competitor of an electrochemically promoted chemical reactor is not a fuel cell but a classical chemical reactor. The main breakthrough here is the recent discovery of bipolar or wireless NEMCA,8 11 i.e. electrochemical promotion induced on catalyst films deposited on a solid electrolyte but not directly connected to an electronic conductor (wire). 

Expanded-bed reactors operate in such a way that the catalyst remains loosely packed and is less susceptible to plugging and they are therefore more suitable for the heavier feedstocks as well as for feedstocks that may contain considerable amounts of suspended solid material. Because of the nature of the catalyst bed, such suspended material will pass through the bed without causing frequent plugging problems. Furthermore, the expanded state of motion of the catalyst allows frequent withdrawal from, or addition to, the catalyst bed during operation of the reactor without the necessity of shutdown of the unit for catalyst replacement. This property alone makes the ebullated reactor ideally suited for the high-metal feedstocks (i.e., residua and heavy oils) which rapidly poison a catalyst with the ever-present catalyst replacement issues (Figure 5-8). 

Internal recycle reactors are designed so that the relative velocity between the catalyst and the fluid phase is increased without increasing the overall feed and outlet flow rates. This facilitates the interphase heat and mass transfer rates. A typical internal flow recycle stirred reactor design proposed by Berty (1974, 1979) is shown in Fig. 18. This type of reactor is ideally suited for laboratory kinetic studies. The reactor, however, works better at higher pressure than at lower pressure. The other types of internal recycle reactors that can be effectively used for gas-liquid-solid reactions are those with a fixed bed of catalyst in a basket placed at the wall or at the center. Brown (1969) showed that imperfect mixing and heat and mass transfer effects are absent above a stirrer speed of about 2,000 rpm. Some important features of internal recycle reactors are listed in Table XII. The information on gas-liquid and liquid-solid mass transfer coefficients in these reactors is rather limited, and more work in this area is necessary. 

The latter model type describes the experimentally determined relations between dependent and independent variables with the help of statistical methods and neglects the known physicochemical relations. Such models are primarily used on reactor types difficult to describe deterministically. The cell models are composed of specific networks of mixing cells (e.g. stirred reactor cascades) or of combinations of mixing cells and transport cells (ideal tube reactors). The so-called continuum models, however, handle each phase as a continuum. The continuum models are further distinguished as homogeneous and heterogeneous reactor models. In the heterogeneous reactor model, the fluid phases and the solid phase (catalyst) are considered and mathematically described as individual items. 

Considering that aluminum trichloride is a very important commercial catalyst wifli over 25,000 tonnes produced annually in the USA alone, such hquids containing aluminum trichloride and allowing for differing levels of acidity have been extensively studied as first generation ionic catalytic solvents in a wide variety of synthetic and catalytic processes. Ionic liquids could therefore be used as substitutes for conventional solid or suspended sources of aluminum(III) chloride. As liquid phase catalysts, they allow for tremendous control of reactor inventories and can be cleaned and recycled with ease. Therefore, ionic liquids, in ideal cases, have no waste associated with them, whereas the supported alumi-num(III) chloride catalysts will require large (and annually rising) waste disposal costs. 

A special feature of the direct oxidation process is the large amount of suspended crude terephthalic acid (25-35 wt % depending on the feed concentration of p-xylene, temperature/pressure/catalyst concentration, residence time in the reactor, etc.) that the reactor must handle. This sohd phase must be kept in suspension. At the same time, uniformity in supply of oxygen also must be maintained. Therefore, the impeller speed should be above or N, whichever is higher. Provision of multiple impellers matching with oxygen feed locations should be an ideal option to maintain uniformity in solid suspension/gas dispersion and gas-Uquid mass transfer. 

Continuous-Flow Stirred Tank Reactor (CSTR). In this flow reactor, a tank reactor is continuously fed with reactants that exist in a single fluid phase, which can be either a gas, liquid, or slurry (solids thickly suspended in liquids). The tank reactor may include a catalyst, and the reactants are mixed with a stirring propeller. Ideally, this complete mix creates the desired product, which is continuously removed from the tank. In practice, perfect mixing can be... 

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