Fixed Bed of Catalyst

In recent years alkylations have been accompHshed with acidic zeoHte catalysts, most nobably ZSM-5. A ZSM-5 ethylbenzene process was commercialized joiatiy by Mobil Co. and Badger America ia 1976 (24). The vapor-phase reaction occurs at temperatures above 370°C over a fixed bed of catalyst at 1.4—2.8 MPa (200—400 psi) with high ethylene space velocities. A typical molar ethylene to benzene ratio is about 1—1.2. The conversion to ethylbenzene is quantitative. The principal advantages of zeoHte-based routes are easy recovery of products, elimination of corrosive or environmentally unacceptable by-products, high product yields and selectivities, and high process heat recovery (25,26). 

The most reliable recycle reactors are those with a centrifugal pump, a fixed bed of catalyst, and a well-defined and forced flow path through the catalyst bed. Some of those shown on the two bottom rows in Jankowski s papers are of this type. From these, large diameter and/or high speed blowers are needed to generate high pressure increase and only small gaps can be tolerated between catalyst basket and blower, to minimize internal back flow. 

Ethylbenzene is dehydrogenated to styrene over a fixed bed of catalyst and in the presence of a large excess of steam at 1150-1200°F and 1 atmosphere. 

The steam reforming of naphthalene was conducted on the fixed bed of catalyst (bed temperature 1173 K, GHSV 3000h ). The detail of the experiment was described in previous papers [7, 8],... 

Reactors with a packed bed of catalyst are identical to those for gas-liquid reactions filled with inert packing. Trickle-bed reactors are probably the most commonly used reactors with a fixed bed of catalyst. A draft-tube reactor (loop reactor) can contain a catalytic packing (see Fig. 5.4-9) inside the central tube. Stmctured catalysts similar to structural packings in distillation and absorption columns or in static mixers, which are characterized by a low pressure drop, can also be inserted into the draft tube. Recently, a monolithic reactor (Fig. 5.4-11) has been developed, which is an alternative to the trickle-bed reactor. The monolith catalyst has the shape of a block with straight narrow channels on the walls of which catalytic species are deposited. The already extremely low pressure drop by friction is compensated by gravity forces. Consequently, the pressure in the gas phase is constant over the whole height of the reactor. If needed, the gas can be recirculated internally without the necessity of using an external pump. 

Fig. 5.5.7 A 2D slice through a H 3D MR image of the fixed-bed of catalyst particles. The catalyst particles appear as black fluid within the inter-particle space is indicated by lighter shades. Chemical conversion within ten selected volumes within each of the three transverse sections indicated is investigated in Figures 5.5.9-5.5.11. The direction of superficial flow (z) is also shown. Reproduced with permission from Ref. [24], copyright Elsevier (2002).

The invention also included catalyst immobilization, which was incorporated to facilitate the separation step. Maintaining the catalytic activity while meeting the requirements of the mechanical properties clearly imposes very restrictive conditions on the immobilization support material. Where and how a fixed bed of catalyst is included in a desalting process, or even a moving phase, is not clearly defined. The patent [251] was issued in 1994, and no further development to this scheme has been published since then. 

Hexall A process for making hexane by dimerizing propylene. The reaction takes place in the liquid phase in a fixed bed of catalyst. Developed by UOP, but not commercialized as of 1992. 

Locap A process for removing mercaptans from gasoline by catalytic oxidation to disulfides, using a fixed bed of catalyst that is continuously treated with aqueous sodium sulfide. Commercialized by Petrolite Corporation in 1963. 

PURASPEC A process for purifying gaseous and liquid hydrocarbons by the use of fixed beds of catalysts and adsorbents which remove impurities by chemical reaction. Developed in 1990 by ICI Katalco to enable natural gas and natural gas liquids to meet pipeline specifications. Installed in approximately 60 plants worldwide in 1996. 

The synthesis of ammonia, N2 + 3H2 = 2NH3, like the oxidation of SO, (Section 1.5.4 and Figure 1.4), is an exothermic, reversible, catalytic reaction carried out in a multistage tubular flow reactor in which each stage consists of a (fixed) bed of catalyst particles. Unlike SO, oxidation, it is a high-pressure reaction (150-350 bar, at an average temperature of about 450°C). The usual catalyst is metallic Fe. 

The reheated vapor is passed through a fixed bed of catalyst where the Claus reaction takes place ... 

A finishing reactor with a fixed bed of catalyst completes the catalytic hydrogenation of any residual, unreacted benzene. The effluent from this reactor is then cooled and flashed to remove most of the hydrogen and then fractionated to produce high purity cyclohexane. 

Compressed oxygen, and fresh and recycled ethylene, are heated, mixed, and then passed through a reactor with fixed beds of catalyst— silver oxide deposited on alumina pellets. In recent years the catalyst has been improved by the addition of promoters and inhibitors. (Promoters—in this case compounds of alkali or alkaline rare earth metals—enhance the activity of the catalyst inhibitors—in this case chlorine compounds—chloroethane, or vinyl chloride, reduce its rate of activity decline.)... 

So far, no reference has been made to the presence of more than one phase in the reactor. Many important chemicals are manufactured by processes in which gases react on the surface of solid catalysts. Examples include ammonia synthesis, the oxidation of sulphur dioxide to sulphur trioxide, the oxidation of naphthalene to phthalic anhydride and the manufacture of methanol from carbon monoxide and hydrogen. These reactions, and many others, are carried out in tubular reactors containing a fixed bed of catalyst which may be either a single deep bed or a number of parallel tubes packed with catalyst pellets. The latter arrangement is used, for exjimple, in the oxidation of ethene to oxiran (ethylene oxide)... 

Fixed-bed reactors Trickle-flow reactor (TFR) This is a tubular flow reactor with a concurrent down-flow of gas and liquid over a fixed-bed of catalyst (Figure 3.10). Liquid trickles down whereas the gas phase is continuous. This reactor is mainly used in catalytic applications. Typical application examples of this reactor type are the following HDS of heavy oil fractions and catalytic hydrogenation of aqueous nitrate solutions. 

Trickle-bed reactors usually consist of a fixed bed of catalyst particles, contacted by a gas liquid two-phase flow, with co-current downflow as the most common mode of operation. Such reactors are particularly important in the petroleum industry, where they are used primarily for hydrocracking, hydrodesulfurization, and hydrodenitrogenation other commercial applications are found in the petrochemical industry, involving mainly hydrogenation and oxidation of organic compounds. Two important quantities used to characterize a trickle-bed reactor are... 

Reactors batch (B), continuous stirred tank (CST), fixed bed of catalyst (FB), fluidized bed of catalyst (FL), furnace (Furn.), multitubular (MT), semicontinuous stirred tank (SCST), tower (TO), tubular (TU). 

In trickle bed reactors the gas and liquid both flow downward through a fixed bed of catalyst. The gas phase is continuous, and the liquid also is continuous as a film on the particles. Provided that the initial distribution is good, liquid distribution remains substantially uniform at rates of 10-30 m3/... 

Another interesting example of reactive adsorption is the so-called gas-solid-solid trickle flow reactor, in which adsorbent trickles through the fixed bed of catalyst, removing selectively in situ one or more of the products from the reaction zone. In the case of methanol synthesis this led to conversions significantly exceeding the equilibrium conversions under the given conditions (67). 

Abbreviations reactors batch (B), continuous stirred tank (CST), fixed bed of catalyst (FB), fluidized bed of catalyst (FL), furnace (Fum.), monolith (M), multitubular (MT), semicontinuous stirred tank (SCST), tower (TO), tubular (TU). Phases liquid (L), gas (G), both (LG). Space velocities (hourly) gas (GHSV), liquid (LHSV), weight (WHSV). Not available, NA. To convert atm to kPa, multiply by 101.3. 

In many catalytic reactions of hydrocarbon mixtures coke is deposited on the catalyst and must subsequently be removed. This paper describes a mathematical model and associated computer simulation of the oxidation of coke from a fixed bed of catalyst, using nitrogen containing a small proportion of oxygen. 

A trickle-bed reactor is one in which gas and liquid flow cocurrently downward through a fixed bed of catalyst particles. 

The disadvantages of conventional microbalanccs when used as catalytic reactors (vide supra) can apparently be overcome with a recently developed oscillating microbalancc reactor [40]. It provides a fixed-bed of catalyst particles through which the complete gas stream is forced to flow. Changes in the mass of the catalyst, which is located at the tip of an oscillating... 

A wide class of forced unsteady-state processes have already been realized on the commercial scale using specific dynamic phenomenon, that takes place during performance of an exothermic reaction in a fixed bed of catalyst. This phenomenon is referred to in the literature as wrong-way behavior of a fixed bed reactor [20]. Substantial differences in characteristic times of heat and mass transfer in a packed bed reactor result in a surprising rise of temperature inside the reactor after... 

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. 

Catalytic fixed bed reactors with concurrent downflow of gas and liquid reactants are widely spread in the refining as well as in the chemical industry U) They are generally operated in the trickling flow regime i.e. with the gas as the continuous phase and with the liquid trickling on the fixed bed of catalyst. It is well known that, in such tricklp bed reactors, the performances strongly depend on ... 

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