Reactor bubble column, oxidation

Bubble columns in series have been used to establish the same effective mix of plug-flow and back-mixing behavior required for Hquid-phase oxidation of cyclohexane, as obtained with staged reactors in series. WeU-mixed behavior has been established with both Hquid and air recycle. The choice of one bubble column reactor was motivated by the need to minimize sticky by-products that accumulated on the walls (93). Here, high air rate also increased conversion by eliminating reaction water from the reactor, thus illustrating that the choice of a reactor system need not always be based on compromise, and solutions to production and maintenance problems are complementary. Unlike the Hquid in most bubble columns, Hquid in this reactor was intentionally weU mixed. 

It is required to determine the height (h) of a bubble-column reactor and the outlet partial pressure of oxygen (A, pAout) for the hquid-phase oxidation of o-xylene to o-methylbenzoic acid the column diameter (D) is 1 m. The reaction is... 

Repeat Example 24-2 for the xylene (B) oxidation reaction carried out in an agitated tank reactor (instead of a bubble-column reactor). Use the data given in Example 24-2 as required, but assume the diameter D is unknown. Additional data are the power input without any gas flow is 8.5 kW the impeller rotates at 2.5 Hz the height and diameter of the tank are the same (h = D) the impeller diameter is DI3, and the impeller contains 6 blades assume ubr = 1.25usg. In addition to the vessel dimensions for the conversion specified (/B = 0.16), determine the power input to the agitator (P,). 

Example 12-2 An aqueous solution contains 10 ppm by weight of an organic contaminant af molecular weight 120, which must be removed by air oxidation in a lo-cm-diameter bubble column reactor at 25°C. The liquid flows downward in the tube at an average velocity af 1 cm/sec. The air at 1 atm is admitted at 0.1 liter/sec and is injected as bubbles 1 mm diameter, which rise at 2 cm/sec. Assume no coalescence or breakup and that both gas and liquid are in plug flow. The reaction in the Hquid phase has the stoichiometry A + 2O2 products with a rate C. ... 

The alkylated anthraquinone process accounts for over 95% of the world production of H202, mainly because the it operates under mild conditions and direct contact of 02 and H2 is avoided. In this process, 2-alkylanthraquinone (the alkyl group is typically an ethyl, terf-butyl or amyl group) is dissolved in a mixture of a non-polar solvent (C9-Cn alkylbenzene) and a polar solvent [Trioctyl phosphate (TOP), or tetrabutyl urea (TBU) or diisobutyl carbinol (DIBC)] and then hydrogenated over a precious metal (Pd or Ni) catalyst in a three-phase reactor (trickle bed or slurry bubble column) under mild reaction conditions (<5bar, <80 °C) to generate 2-alkylanthrahydroquinone [1-3, 5], The latter is then auto-oxidized with air in a... 

Gas-liquid reactions form an integral part of the production of many bulk and specialty chemicals, such as the dissolution of gases for oxidations, chlorin-ations, sulfonations, nitrations, and hydrogenations. When the gaseous reactant must be transferred to the liquid phase, mass transfer can become the rate-limiting step. In this case, the use of high-intensity mixers (motionless mixers or ejectors) can increase the reaction rate. Conversely, for slow reactions a coarse dispersion of gas, as produced by a bubble column, will suffice. Because a large variety of equipment is available (bubble columns, sieve trays, stirred tanks, motionless mixers, ejectors, loop reactors, etc.), a criterion for equipment selection can be established and is dictated by the required rate of mass transfer between the phases. 

Usually, the typology of batch reactors also includes the semi-batch gas-liquid reactors, in which a gaseous phase is fed continuously in order to provide one of the reactants. A typical example is given by the reactors used both in different oxidative industrial processes and in the active sludge processes for the treatment of wastewater. It is possible to distinguish between the bubble columns (Fig. 7.1(c)), in which the gas rises undisturbed in the liquid phase, and the bubble stirred reactor, in which a mechanical mixer is added. Finally, the slurry reactors can be considered, in which the liquid phase contains a finely dispersed solid phase as well, which can act as a reactant or as a heterogeneous catalyst these reactors assume in general the features of Fig. 7.1(d). 

The liquid-phase oxidation of toluene with molecular oxygen is another example of a well established process (Table 4, entry 40). A cobalt catalyst is used in the process and the reaction proceeds via a free-radical chain mechanism. Heat of reaction is removed by external circulation of the reactor content and both bubble columns or stirred tanks are employed. It is important to note that air distribution is critical to prevent the danger of a runaway. Another example of direct oxidation is the commercial production of nitrobenzoic acid by oxidation of 4-nitrotoluene with oxygen (Table 4, entry 41). 

In the design of upflow, three phase bubble column reactors, it is important that the catalyst remains well distributed throughout the bed, or reactor space time yields will suffer. The solid concentration profiles of 2.5, 50 and 100 ym silica and iron oxide particles in water and organic solutions were measured in a 12.7 cm ID bubble column to determine what conditions gave satisfactory solids suspension. These results were compared against the theoretical mean solid settling velocity and the sedimentation diffusion models. Discrepancies between the data and models are discussed. The implications for the design of the reactors for the slurry phase Fischer-Tropsch synthesis are reviewed. 

Bubble column reactors are quite commonly employed in the petrochemical industries for many oxidation and hydrogenation reactions (1 ). This type of reactor is ideal for reactions occurring in the slow reaction regime in which relatively low energy input is required to minimize the effect of mass transfer resistance. Nevertheless, attention has been drawn to the... 

In cases when the feed stream is a liquid, which requires rather long residence times, the suspension bubble column or an agitated tank reactor is used (Figures 1.2(b) and 1.2(c)). Here, in the reactor exit, quite elaborate filtering systems are required to remove the catalyst from the liquid stream. In these reactors a gas generally is supplied, because these suspension reactors are mostly used for hydrogenations and oxidations. 

Kawakami, W., et al. (1978). Electron-beam oxidation treatment of a commercial dye by use of a dual-tube bubbling column reactor. Environ. Science Technol. 12, 189-194. 

Oxidation of organic and inorganic species in aqueous solutions can find applications in fine chemical processes and wastewater treatment. Here, the oxidant, often either air or pure oxygen, must undergo all the mass transfer steps mentioned above in order for the reaction to proceed. During the last decade, increased environmental constraints have resulted in the application of novel processes to the treatment of waste streams. An example of such a process is wet air oxidation. Here, the simplest reactor design is the cocurrent bubble column. However, the presence of suspended organic and inert solids makes the use of monolith reactors favorable. 

The FT process is well known and already applied on a large scale [9,10,11,12]. Currently, the two players that operate commercial Fischer-Tropsch plants are Shell and Sasol. In the Sasol and Shell plants gasification of coal and partial oxidation of natural gas, respectively, produce the syngas for the FT synthesis with well-defined compositions. Shell operates the SMDS (Shell Middle Distillate Synthesis) process in Bintulu, Malaysia, which produces heavy waxes with a cobalt catalyst in multi-tubular fixed bed reactors. Sasol in South Afirica uses iron catalysts and operates several types of reactors, of which the slurry bubble column reactor is the most versatile (i.e. applied in the Sasol Slurry Phase Distillate SSPD),... 

Stirred tank gas-liquid contactors. To illustrate the design methodology, the design of a typical industrial-scale stirred tank oxidation reactor is presented in a worksheet. Gas-liquid contact in bubble columns, packed beds, thin films, and venturi scrubbers is also discussed in related chapters. 

The oxidation and reduction steps in the RAQ/RAHQ cycle are performed in two separate reactors. A bubble column is applied for the oxidation of the RAHQ, during which HP is produced. For the Pd-catalyzed hydrogenation of the quinones, a slurry, fixed-bed or monolith reactor can be used. After the reactor and L/L settler, a diluted H P-containing water-methanol stream is finally obtained. After the epoxidation step, crude PO is separated and the water-methanol mixture is returned to the HP synthesis process, thus realizing an efficient process integration. 

The oxidation is mostly carried out in traditional bubble column reactors series of two to six reactors, up to 20 m high, are common in industry. The reaction is exothermic 120kJ are released per mole of produced hydroperoxide, and must be removed by cooling. The final reaction mixture, containing 20-30% of cumyl hydroperoxide, is then concentrated by distilling off some unreacted cumene to obtain a 65-85% hydroperoxide to be fed to the cleavage step (Figure 13.2). 

It is well known that alumina, titania [10,11,12] and magnesium oxide [13,14] dissolve in acidic aqueous solutions and even at pH values close to the isoelectric point [15,16], In this study, it will be shown that these support surfaces were modified with promoters to increase the inertness thereof to acidic/aqueous environments, and not to stabilise the support against sintering and loss in surface area at high temperatures [17,18], This paper will deal with the modification of alumina and titania supports for cobalt based slurry phase Fischer-Tropsch catalysts to ensure the successful operation of slurry phase bubble column reactors on commercial scale,... 

After these experiments, concerning the oxidative cleavage of aliphatic ketone, the methyl-keto fatty adds, prepared by direct oxidation of co-unsaturated fatty acids, were put to use. The oxidations were carried out in a bubble column reactor at 115 °C over a retention time of 60 min with 2 mol-% Mn(stearate)2 as catalyst. Afterwards the reaction mixture was cooled to room temperature and the solvent acetic acid was removed at 30 °C in vacuum. 

DuPont s new tetrahydrofuran plant, which is slated to start up in the second quarter of 1996 in Asturias, Spain, is based on a new process that is claimed to be environmentally friendly [133], The process is harnessed with a circulating fluidized-bed (CFB) reactor for the partial oxidation of n-butane. The catalyst used for this stage is vanadium phosphorus oxide (VPO). To enhance the catalytic life in the CFB reactor, attrition-resistant catalyst particles have been developed. A highly selective catalyst for hydrogenation of maleic acid to THF also has been developed. This THF conversion reaction is carried out in a bubble column reactor under relatively mild conditions. This process has several significances ... 

This case study on oxidation of sodium sulfide illustrates the design of a variety of gas-liquid reactors and compares their performances. Bubble column reactors are particularly attractive, as they offer advantages such as simplicity of construction and operation, but they suffer from such drawbacks as high pressure drop and backmixing in the liquid phase. To reduce the pressure drop, two modifications have been considered an external-loop air-lift reactor and a horizontal sparger reactor. Both result in substantial energy savings (because of low AP) under similar conditions of capacity and conversions in the gas and liquid phases. 

Low feed rates are suitable for trickle bed reactors where for gas-liquid-solid mixing, the gas and the liquid are fed into the top of the reactor. This gives long gas residence times but short liquid residence times. Such a configuration is often used in hydrogenation reactions. When the gas-liquid is fed into the bottom of the reactor, it is known as a bubble reactor. Here the gas residence times are short but the liquid residence times are relatively long. This is commonly used in oxidation reactions. Heat transfer can be a major problem with both trickle and bubble reactors and in such cases a slurry bubble column reactor can be employed. 

A new process to manufacture THF and 1,4 butanediol from maleic anhydride is currently slated for start-up by DuPont in Asturias, Spain in 1996. The process involves the oxidation of n-butane in a transport bed reactor to form maleic anhydride. Recovery of maleic anhydride is accomplished by scrubbing with water which converts the anhydride immediately to maleic acid. The maleic acid is then hydrogenated to tetrahydrofuran in a bubble column reactor. By varying operating conditions in the hydrogenation reactor the alternate or coproduction of 1,4 butanediol can be accomplished. 

Although absorption plus chemical reaction sounds more complex than physical absorption or desorption, the absorption of oxygen in sulfite solutions is often used to characterize the performance of bubble columns or stirred reactors. With a 0.2-1.0 N solution of sodium sulfite and a small amount of copper sulfate as catalyst (10 M), the rate of oxidation is independent of sulfite concentration, and the oxygen absorption rate is constant until nearly all the sulfite has reacted ... 

The oxidation of cumene to CHP is a slow reaction. As a rule of thumb, the mean residence time in a continuously operated process is around 10 h at temperatures in the range of 80-120°C. Thus, large bubble columns are preferred for this purpose with, for example, three reactors arranged in series [9]. A cascade of only two reactors [22] or even four reactors [23] is also used in commercial plants. The bubble columns are operated at high pressures ranging from atmospheric to approximately 700 kPa. 

Over the last decades, the reactor design for cumene oxidation made tremendous progress. In the beginning, aerated stirred-tank reactors were used for cumene oxidation [49], at present state-of-the-art bubble column reactors are used. 

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