Hydrogenation in slurry reactors

Substances that have been hydrogenated in slurry reactors include nitrobenzene with Pd-C, butynediol with Pd-CaCO,3, chlorobenzene with Pt-C, toluene with Raney Ni, and acetone with Raney Ni. 

In order to describe the hydrogenation in slurry reactors, and as the reaction is always controlled by mass transfer [1], we must consider both the mass-transfer and the reaction steps. Thus, we must introduce the overall effectiveness factor in the expression of reaction rate [3] ... 

Bern et al. (1976) Chemical-catalytic hydrogenation in slurry reactor Turbine... 

The catalytic hydrogenation of fatty oils, the desulfurization of liquid petroleum fractions by catalytic hydrogenation, Fischer-Tropsch-type synthesis in slurry reactors, and the manufacture of calcium bisulfite acid are familiar examples of this type of process, for which the term gas-liquid-particle process will be used in the following. 

Calderbank et al. (C6) studied the Fischer-Tropsch reaction in slurry reactors of 2- and 10-in. diameters, at pressures of 11 and 22 atm, and at a temperature of 265°C. It was assumed that the liquid-film diffusion of hydrogen from the gas-liquid interface is a rate-determining step, whereas the mass transfer of hydrogen from the bulk liquid to the catalyst was believed to be rapid because of the high ratio between catalyst exterior surface area and bubble surface area. The experimental data were not in complete agreement with a theoretical model based on these assumptions. 

Catalytic hydrogenation is typically carried out in slurry reactors, where finely dispersed catalyst particles (<100 (tm) are immersed in a dispersion of gas and liquid. It has, however, been demonstrated that continuous operation is possible, either by using trickle bed [24] or monoHth technologies [37]. Elevated pressures and temperatures are needed to have a high enough reaction rate. On the other hand, too high a temperature impairs the selectivity of the desired product, as has been demonstrated by Kuusisto et al. [23]. An overview of some feasible processes and catalysts is shown in Table 8.1. 

P7C-3 In J. Catal, 79, 132 (1983), a mechanism was proposed for the catalyzed hydrogenation of pyridine in slurry reactors. Reexamine the data and model using an Eley-Rideai adsorption mechanism and comment on the appropriateness of this new analysis. 

In order to illustrate the application of the developed hybrid algorithm, the optimization of a three-phase hydrogenation catalytic slurry reactor is considered. The study aims to determine the optimal operating conditions that lead to maximization of profit. 

Catalysts are used for the hydrogenation of edible oils such as sunflower oil. Traditionally, silica gel supported nickel catalysts in slurry reactors... 

Catalysts are used for the hydrogenation of edible oils such as sunflower oil. Traditionally, silica gel supported nickel catalysts in slurry reactors have been used. Nickel is now substituted by palladium or platinum in order to reduce the formation of trans isomers in the course of isomerization. Since the catalysts have to be reduced after hydrogenation, reuse is desirable, in particular in the case of noble metal catalysts. 

On Figure 12 are shown the reactions of the production of hydrogen peroxide. The reduction of the anthraquinone is a three phase catalytic process. Raney nickel is used in slurry reactors. 

Also important is the breaking of the catalytic particle due to ultrasoimd action this phenomenon gives more accessibility to the internal catalytic surface for the reagents, but for this effect to occur, the relative size of the particle and the bubble must meet various criteria (p. 172). Other factors are the dispersive action of ultrasound which increases, for gas-liquid-solid systems, the interphasic surface of gas bubbles (this is the situation of some hydrogenation reactions this dispersive action may also include the disaggregation of catalytic particles in slurry reactors) and the removal of the passivated layer of outer oxide for many hydrogenation catalysts (i.e., nickel powder, p. 171). 

In slurry reactors (Figure 4.30), a slurry of liquid containing the reactant B mixed with solid catalyst particles is passed through the reaction vessel while the gas containing reactant A is bubbled through the slurry contained in the vessel. Slurry reactor is used for the hydrogenation of vegetable oil in the presence of Ni catalyst particles. The reaction is... 

Survey of the patent Hterature reveals companies with processes for 1,4-butanediol from maleic anhydride include BASF (94), British Petroleum (95,96), Davy McKee (93,97), Hoechst (98), Huels (99), and Tonen (100,101). Processes for the production of y-butyrolactone have been described for operation in both the gas (102—104) and Hquid (105—108) phases. In the gas phase, direct hydrogenation of maleic anhydride in hydrogen at 245°C and 1.03 MPa gives an 88% yield of y-butyrolactone (104). Du Pont has developed a process for the production of tetrahydrofuran back-integrated to a butane feedstock (109). Slurry reactor catalysts containing palladium and rhenium are used to hydrogenate aqueous maleic acid to tetrahydrofuran (110,111). 

Some slurry processes use continuous stirred tank reactors and relatively heavy solvents (57) these ate employed by such companies as Hoechst, Montedison, Mitsubishi, Dow, and Nissan. In the Hoechst process (Eig. 4), hexane is used as the diluent. Reactors usually operate at 80—90°C and a total pressure of 1—3 MPa (10—30 psi). The solvent, ethylene, catalyst components, and hydrogen are all continuously fed into the reactor. The residence time of catalyst particles in the reactor is two to three hours. The polymer slurry may be transferred into a smaller reactor for post-polymerization. In most cases, molecular weight of polymer is controlled by the addition of hydrogen to both reactors. After the slurry exits the second reactor, the total charge is separated by a centrifuge into a Hquid stream and soHd polymer. The solvent is then steam-stripped from wet polymer, purified, and returned to the main reactor the wet polymer is dried and pelletized. Variations of this process are widely used throughout the world. 

Hydrogenations can be carried out in batch reactors, in continuous slurry reactors, or in fixed-bed reactors. The material of constmetion is usually 316 L stainless steel because of its better corrosion resistance to fatty acids. The hydrogenation reaction is exothermic and provisions must be made for the effective removal or control of the heat a reduction of one IV per g of C g fatty acid releases 7.1 J (1.7 cal), which raises the temperature 1.58°C. This heat of hydrogenation is used to raise the temperature of the fatty acid to the desired reaction temperature and is maintained with cooling water to control the reaction. 

Continuous slurry reactors are generally either of one of two designs. One type uses a reactor loop, generally known as a Buss loop design the other is a co-current hydrogen/fatty acid/catalyst system mainly marketed by Lurgi. Continuous slurry reactors are more popular in Europe, Asia, and South America than in the United States. 

The effect of physical processes on reactor performance is more complex than for two-phase systems because both gas-liquid and liquid-solid interphase transport effects may be coupled with the intrinsic rate. The most common types of three-phase reactors are the slurry and trickle-bed reactors. These have found wide applications in the petroleum industry. A slurry reactor is a multi-phase flow reactor in which the reactant gas is bubbled through a solution containing solid catalyst particles. The reactor may operate continuously as a steady flow system with respect to both gas and liquid phases. Alternatively, a fixed charge of liquid is initially added to the stirred vessel, and the gas is continuously added such that the reactor is batch with respect to the liquid phase. This method is used in some hydrogenation reactions such as hydrogenation of oils in a slurry of nickel catalyst particles. Figure 4-15 shows a slurry-type reactor used for polymerization of ethylene in a sluiTy of solid catalyst particles in a solvent of cyclohexane. 

All these gas-liquid-particle operations are of industrial interest. For example, desulfurization of liquid petroleum fractions by catalytic hydrogenation is carried out, on the industrial scale, in trickle-flow reactors, in bubble-column slurry reactors, and in gas-liquid fluidized reactors. 

In stirred-slurry reactors, momentum is transferred to the liquid phase by mechanical stirring as well as by the movement of gas bubbles. Small particles are used in most cases, and the operation is usually carried out in tank reactors with low height-to-diameter ratios. The operation is in widespread use for processes involving liquid reactants, either batchwise or continuous— for example, for the batchwise hydrogenation of fats as referred to in Section II. 

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