Reactor fixed-bed column

Gisi D, Stncki G, Hanselmann K W (1997) Biodegradation of the pesticide 4,6-dinitro-w//io-cresol by microorganisms in batch cultures and in fixed-bed column reactors, Applied Microbiology Biotechnology 48 441-448. 

Figure L Stability of A4 or B23/alginate beads (20 % wcw, 2.75 % sodium alginate) in a fixed-bed column reactor at 5 °C, feeding 0,4 MADN in 23 mM sodium butyrate/5 mM calcium chloride (pH 7,0) , SCVAM(A4) O, 5CVAM(B23) A, ADN(A4) A, ADN(B23),...

The hydrolysis of lactose in a continuous fixed-bed column reactor containing strongly acidic resins was reported by Chem and Zall. The reaction was first order and the activation energy was 154 kj mol . At 368 K, 99% of the lactose in the whey was hydrolyzed within 3 h of residence time when the substrate was acidified with concentrated nitric acid to a final acid concentration of 0.6 mole 1 . ... 

Column reactors for gas-liquid-solid reactions are essentially the same as those for gas-liquid reactions. The solid catalyst can be fixed or moving within the reaction zone. A reactor with both the gas and the liquid flowing upward and the solid circulating inside the reaction zone is called a slurry column reactor (Fig. 5.4-10). The catalyst is suspended by the momentum of the flowing gas. If the motion of the liquid is the driving force for solid movement, the reactor is called an ebullated- or fluidized-bed column reactor (Fig. 5.4-10). When a catalyst is deactivating relatively fast, part of it can be periodically withdrawn and a fresh portion introduced. 

The activity of calcined HTs was determined in self-condensation reaction of acetone (J.T. Baker) by using a fixed bed catalytic reactor with an on-line GC. Prior to the catalytic test, catalysts were pretreated in-situ under nitrogen atmosphere at 450°C for 5h. Acetone was supplied to the reactor by bubbling nitrogen gas through the acetone container at 0 °C. The reaction temperature was established at 200 C. The products were analyzed by means of GC (Varian CP-3800) using a WCOT Fused silica column, equipped with a FID detector. 

Fixed-bed catalytic reactors and reactive distillation columns are widely used in many industrial processes. Recently, structured packing (e.g., monoliths, katapak, mella-pak etc.) has been suggested for various chemical processes [1-4,14].One of the major challenges in the design and operation of reactors with structured packing is the prevention of liquid flow maldistribution, which could cause portions of the bed to be incompletely wetted. Such maldistribution, when it occurs, causes severe under-performance of reactors or catalytic distillation columns. It also can lead to hot spot formation, reactor runaway in exothermic reactions, decreased selectivity to desired products, in addition to the general underutilization of the catalyst bed. 

An offline measurement apparatus is usually not directly mounted on the reactor, but is fed with samples withdrawn from it manually or automatically. This is the typical case of chromatography, a widely used measurement device for gas and liquid composition. Both gas and liquid chromatographies are based on the separation of the sample by means of selective adsorption on a solid substrate posed in a fixed bed column, and on the detection of the change of a suitable property of the (gas or liquid) carrier, usually thermal conductivity. 

The plug-flow model indicates that the fluid velocity profile is plug shaped, that is, is uniform at all radial positions, fact which normally involves turbulent flow conditions, such that the fluid constituents are well-mixed [99], Additionally, it is considered that the fixed-bed adsorption reactor is packed randomly with adsorbent particles that are fresh or have just been regenerated [103], Moreover, in this adsorption separation process, a rate process and a thermodynamic equilibrium take place, where individual parts of the system react so fast that for practical purposes local equilibrium can be assumed [99], Clearly, the adsorption process is supposed to be very fast relative to the convection and diffusion effects consequently, local equilibrium will exist close to the adsorbent beads [2,103], Further assumptions are that no chemical reactions takes place in the column and that only mass transfer by convection is important. 

Example 4.6 Entropy production in a packed duct flow Fluid flow and the wall-to-fluid heat transfer in a packed duct are of interest in fixed bed chemical reactors, packed separation columns, heat exchangers, and some heat storage systems. In this analysis, we take into account the wall effect on the velocity profile in the calculation of entropy production in a packed duct with the top wall heated and the bottom wall cooled (Figure 4.7). We assume... 

Description The process includes a fixed-bed alkylation reactor, a fixed-bed transalkylation reactor and a distillation section. Liquid propylene and benzene are premixed and fed to the alkylation reactor (1) where propylene is completely reacted. Separately, recycled polyisopropylbenzene (PIPB) is premixed with benzene and fed to the transalkylation reactor (2) where PIPB reacts to form additional cumene. The transalkylation and alkylation effluents are fed to the distillation section. The distillation section consists of as many as four columns in series. The depropanizer (3) recovers propane overhead as LPG. The benzene column (4) recovers excess benzene for recycle to the reactors. The cumene column (5) recovers cumene product overhead. The PIPB column (6) recovers PIPB overhead for recycle to the transalkylation reactor. 

Description Liquid propylene is mixed with fresh and recycle benzene and then fed to the fixed-bed alkylation reactor (1), where the propylene is completely consumed by alkylation with benzene. Alkylation reactor effluent flows to the depropanizer column (2), where the propane that accompanied the propylene leaves as LPG overhead product. The depropanizer bottoms flows to the benzene column... 

One point concerning the works described above is worth noting. All the reported experimental work has been carried out under atmospheric pressure conditions. For the same gas velocity, the flow characteristics in actual high-pressure reactors may be different. The possible effects of this on the backmixing in various phases are presently not known. It should be noted that this same point is also applicable to other transport processes (such as gas-liquid and liquid-solid mass transfer, etc.) in this type of column, as well as transport and mixing processes occurring in fixed-bed columns described in the previous three chapters. 

The modeling and design of a three-phase reactor requires the knowledge of several hydrodynamic (e.g., flow regime, pressure drop, holdups of various phases, etc.) and transport (e.g., degree of backmixing in each phase, gas-liquid, liquid-solid mass transfer, fluid-reactor wall heat transfer, etc.) parameters. During the past decade, extensive research efforts have been made in order to improve our know-how in these areas. Chapters 6 to 8 present a unified review of the reported studies on these aspects for a variety of fixed bed columns (i.e., co-current downflow, co-current upflow, and counter-current flow). Chapter 9 presents a similar survey for three-phase fluidized columns. 

Consider, for instance, ethylbenzene dehydrogenation to styrene. The traditional plant used in the process industry [32] is based on an fixed-bed catalytic reactor to which a preheated mixture of ethylbenzene and steam, which prevents coke formation, is fed. The reaction products then normally undergo a rather complex separation scheme, mostly based on distillation columns, aimed at recovering styrene (the desired product), benzene, toluene and H2 (by products), and a certain amount of unconverted ethylbenzene, which has to be recycled. The overall conversion per pass is typically around 60%, whereas selectivity is close to 90%. 

Most, but not all, commercial and laboratory applications of ion exchange involve operations where the solution to be treated (feed or influent) is passed downflow through a fixed bed (column) of ion exchange resin contained within a cylindrical vessel. The obvious difference between a stirred reactor (batch) contact of exchanger with the solution and a column process is that the former situation may be defined by a static or true equilibrium. This is not the case with column operations since the position of equilibrium is always changing because ... 

There are several basic operating methods for ion exchangers. They consist of batch reactor, continuously stirred tank reactor, fixed-bed (column), and moving bed reactors. 

A column fermentor is a fixed-bed reactor. Solid medium is put into the column with entries at both ends for aeration [58-60]. Figure 5 shows an experimental apparatus developed by Saucedo-Castaneda et al. [28]. Sterile air can be supplied either by a radial or axial gradient method. The water activity is maintained by humidified air. The temperature for the solid fermentation is monitored and controlled by recycling water in the jacket from an isothermal bath. In a fixed-bed column fermentor, the oxygen transfer and CO2 dissipation are im-... 

Flow of fluids through packed beds of granular particles occurs frequently in chemical processes. Examples are flow through a fixed-bed catalytic reactor, flow through a filter cake, and flow through an absorption or adsorption column. An understanding of flow through packed beds is also important in the study of sedimentation and fluidization. 

The activity of the catalysts was tested in the hydrogenation of crotonaldehyde, cinnamaldehyde and furfural at atmospheric pressure. Before the reaction, the catalysts were reduced in a stream of dihydrogen at 623 K. Hydrogenation reactions were carried out in a standard fixed bed vertical reactor. After the catalyst reduction, the reactor was cooled down to the reaction temperature (423, 470 or 523 K) and unsaturated aldehyde and hydrogen were introduced onto the top of the reactor. The first product sample for analysis was taken after 30 min of reaction (period needed to reach reaction steady state). The identification and analysis of the reaction mixtures were performed by means of GC-MS using HP-50 capillary column. 

Catalytic activity measurements were carried out in a fixed bed quartz reactor of inner diameter 6 mm. The catalyst (usually 200 mg, 125-212 pm fraction) was placed between two glass wool plugs with a bed length of 10-20 mm. For the oxidation of CO and H2, a standard gas containing 1 vol% CO or H2 in air was dried in a silica gel column cooled down to 0°C or -77° C and passed through the catalyst bed at a space velocity of 20,000 h-iml/g-cat.. For the partial... 

The steady-state partial oxidation reaction experiments were carried out in a quartz fixed-bed, flow reactor with 10 mm I.D. and a length of 50 mm. The analytical system consisted of two parts. Gas Chromatography (GC) and High Performance Liquid Chromatography (HPLC). GC was used to analyze on-line the reaction products that were in the gas phase. The GC (HP-5890) was equipped with a Chromosorb PAW 23% SP-1700 column (30 ft. 1/8") for FID, a Hayesep D column (15 ft. 1/8") and a Molecular Sieve 5A column (10 ft. 1/8") connected serially to TCD. Reverse-phase HPLC with a Spherisorb 5 ODS-2 (1 ft. 1/4") column was used off-line to analyze the products that were solid or liquid at room temperature. The details of the experimental procedures have been described elsewhere [12,13]. 

The catalytic oxidation of ethane at 573-648 K was carried out at atmospheric pressure in a fixed bed flow reactor. Mbftures of ethane (4 mol%), oxygen (4-12 mol%), and helium (balance) were fed to the reactor with a residence time of 38 g. h/mol C2H6, using a catalyst load of 0.36 g, (particle size 0.25-0.42 mm) mixed with SiC bits (dilution 1 4 vA) to reduce the heat release per imit volume. Reactants and products were analysed by gas chromatography on a Vaiian 3400, equ ped with a thennal conductivity detector, using Porapak QS (3 m) and molecular sieve 13X (1 m) columns. In all reaction conditions, the mass and carbon balances were within 10012 %. 

If the transport limitation is significant, the catalysis occurs predominantly near the surface of the ionic liquid, and the [Rh(CO)2l2] dissolved in the bulk is not fully utilized. One attempt to address these issues was to use a supported ionic liquid phase (SILP) catalyst, as reported by Riisager et al. [Ill], In this system, the ionic liquid (l-butyl-3-methylimidazolium iodide) was supported as a thin film on solid silica (the thin film offers little mass-transport resistance) and used in a fixed-bed continuous reactor with gas-phase methanol. Rates were achieved that were comparable to those in Eastman s bubble column carbonylation reactor with gas-phase reactants [109], but using a much smaller amount of ionic liquid. 

Catalytic measurements were made using 100 mg catalyst diluted with 400 mg of inactive aAl203 in a fixed-bed flow reactor. The typical gas nuxture consisted of 2000 vpm NO, 2000 vpm CsHg, 10 vol. % O2, balance He, without or with 10 vol. % water (total flow rate 10 1 h ). In the absence of water in the reactant nrixture, the temperature was increased from 300 to 773 K (or 873 K) (heating rate 2 K min ) and then decreased to 423 K. Water was then added at 423 K and the temperature increased and decreased again as above. The analysis was performed by gas chromatography with two columns (porapak and molecular sieve) and a TCD detector for CO2, N2O, O2, N2 and CO, and with a porapak column and a flame ionisation detector for hydrocarbons. Moreover, on-line IR and UV analyzers were used for NO, NO2, CO2, and N2O analysis. The NO conversion was calculated from the N2 production and the nitrogen balance was checked. 

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