Hydrogenation gas-liquid-solid

Kobayashi, Y. and Mori, Y. and Okamoto, K. and Akiyama, R. and Ueno, M. and Kitamori, T. and Kobayashi, S. (2004). A Microfluidic Device for Conducting Gas-Liquid-Solid Hydrogenation Reactions. Science, 304, 1305-1306. 

J. Kobayashi, Y. Mori, K. Okamoto, R. Akiyama, M. Ueno, T. Kitamori, S. Kobayashi, A microfluidic device for conducting gas-liquid-solid hydrogenation reactions, Science 304 (2004) 1305. 

In a triphasic system, (gas, liquid, solid) hydrogenation is a global process which can be divided in three steps - chemisorption of reactants (H2, substrates) - reaction on the surface of the catalyst - desorption of products. Assuming that all reactions presented are under chemical control and not limited by difUisional phenomena (3), solvents can influence the reactions selectivity at each step. 

A hst of 74 GLS reacdions with hterature references has been compiled by Shah Gas-Liquid-Solid Reactions, McGraw-HiU, 1979), classified into groups where the solid is a reactant, or a catalyst, or inert. A hst of 75 reactions made by Ramachandran and Chaudhari (Three-Phase Chemical Reactors, Gordon and Breach, 1983) identifies reactor types, catalysts, temperature, and pressure. They classify the processes according to hydrogenation of fatty oils, hydrodesulfurization, Fischer-Tropsch reactions, and miscellaneous hydrogenations and oxidations. 

Gas-liquid-solid reactions (catalytic hydrogenations and oxidations) 1-5 50-250 250 500... 

Describe the various mass transfer and reaction steps involved in a three-phase gas-liquid-solid reactor. Derive an expression for the overall rate of a catalytic hydrogenation process where the reaction is pseudo first-order with respect to the hydrogen with a rate constant k (based on unit volume of catalyst particles). 

Heterogeneously catalyzed hydrogenation is a three-phase gas-liquid-solid reaction. Hydrogen from the gas phase dissolves in the liquid phase and reacts with the substrate on the external and internal surfaces of the solid catalyst Mass transfer can influence the observed reaction rate, depending on the rate of the surface reaction [15]. Three mass transfer resistances may be present in this system (Fig. 42.1) ... 

Fabrication of catalyst immobilized microchannel reactors usually needs expensive, complex, and multistep methods. On the eontrary, reactors with simple structures (Figure 5) can also perform effieient hydrogenation reaetions. Yoswathananont et al. [21] reported an effieient hydrogenation reaction in a continuous flow system by the use of a gas-liquid-solid tube reactor. 

Abdallah, R. and Fumey, B. and Meille, V. and de Bellefon, C. (2007). Micro-structured reactors as a tool for chiral modifier screening in gas-liquid-solid asymmetric hydrogenation. Catalysis Today, 125, 34-39. 

Light oils are invariably hydroprocessed in gas-liquid-solid catalyst trickle-bed reactors (TBR). In these reactors, both the hydrogen and hydrocarbon streams flow down through one or more catalyst beds. A typical schematic diagram is shown in Figure 5.2—41 as an example of hydrodesulfurization process [60, 61]. 

GAS - LIQUID - SOLID REACTORS FOR HYDROGENATION IN FINE CHEMICALS SYNTHESIS... 

The individual mass transfer and reaction steps occurring in a gas-liquid-solid reactor may be distinguished as shown in Fig. 4.15. As in the case of gas-liquid reactors, the description will be based on the film theory of mass transfer. For simplicity, the gas phase will be considered to consist of just the pure reactant A, with a second reactant B present in the liquid phase only. The case of hydro-desulphurisation by hydrogen (reactant A) reacting with an involatile sulphur compound (reactant B) can be taken as an illustration, applicable up to the stage where the product H2S starts to build up in the gas phase. (If the gas phase were not pure reactant, an additional gas-film resistance would need to be introduced, but for most three-phase reactors gas-film resistance, if not negligible, is likely to be small compared with the other resistances involved.) The reaction proceeds as follows ... 

Hydrogenation is an example of an addition reaction, In order for hydrogenation to occur at nr appreciable rate, a firterogt m ous catalyst is employed. A heterogeneous catalyst is a catalyst that exists in a different phase (i.e. gas, liquid, solid, aqueous, etc,) than the reactants or products. Normally tiny shavings of metal act as the catalyst to promote syn-addition (same side addition). 

This reaction is an example of a heterogeneous reaction with a solid catalyst with one reactant principally in solution and another in the gas phase the gas-liquid-solid mixture has to be mixed thoroughly to promote conversion (see Chapter 5 for more detailed consideration of multiphase reactions). Compared with the examples above, the measurement of the hydrogen uptake delivers an additional signal, which can also be used for the determination of reaction parameters. 

In general, metal-based (Ni, Pt, Ru) catalysts are used for hydrogenation of glucose. For example, a new process has been recently developed in a 1.5 m3 gas-liquid-solid three-phase Airlift Loop Reactor over Raney nickel catalysts.[53] As compared with a Stirred Tank Reactor process, some improvements have been obtained, namely, shorter reaction time, higher yield in sorbitol and less than 1 % yield of mannitol. 

It has also been proposed that porous catalytic membranes may improve the efficiency of gas-liquid solid reactions when the gas-liquid interface is placed within the porous framework of the porous membrane [77], This postulated increase in efficiency has been experimentally supported by Cini and Harold in a comparative study of a CMR and a single-pellet model reactor [78] in the hydrogenation of a-mcthylstyrene into cumene. The authors ascribe this observation to a decrease in the mass transfer resistance. 

Reactions involving gas, liquid, and solid are often encountered in the chemical process industry. The most common occurrence of this type of reaction is in hydroprocessing operations, in which a variety of reactions between hydrogen, an oil phase, and a catalyst have been examined. Other common three-phase catalytic reactions are oxidation and hydration reactions. Some three-phase reactions, such as coal liquefaction, involve a solid reactant. These and numerous other similar gas-liquid solid reactions, as well as a large number of gas-liquid reactions, are carried out in a vessel or a reactor which contains all three phases simultaneously. The subject of this monograph is the design of such gas-liquid -solid reactors. 

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