Three phase batch reactions

Since most heterogeneously catalyzed, synthetically useful reactions are run in a liquid phase batch reactor, the reaction variables involved in such systems will be discussed first. Table 5.4 lists those reaction variables that can affect the observed 

Effect of reaction variables on the different stages of a three phase catalytic process.24 

Reaction Parameter Primary Influence Secondary Influence Little or No Influence 

Agitation Gas/Liquid Mass Transport Liquid/Solid Mass Transport Chemical Reaction 

Pressure Gas/Liquid Mass Transport Liquid/Solid Mass Transport (Gas Reagent) Chemical Reaction Liquid/Solid Mass Transport (Liquid Reagent) 

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The ways in which reaction parameters affect a two phase batch reaction are similar to those considered above for the three phase systems. Since there is no gas phase, agitation only serves to keep the catalyst suspended making it more accessible to the dissolved reactants so it only has a secondary effect on mass transfer processes. Substrate concentration and catalyst quantity are the two most important reaction variables in such reactions since both have an influence on the rate of migration of the reactants through the liquid/solid interface. Also of significant importance are the factors involved in minimizing pore diffusion factors the size of the catalyst particles and their pore structure. 

We will next look at a three-phase hydrogenation reaction in the production of fine chemicals. The monolith catalyst was prepared by a commercial cordierite skeleton. On the walls of the parallel channels, a solid catalyst phase was synthesized. The basic treatment of the reactor system is very straightforward, since the system can be characterized as a frozen slurry reactor, that is, a traditional batch or a semibatch approach can be utilized. 

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. 

The typical bioreactor is a two-phase stirred tank. It is a three-phase stirred tank if the cells are counted as a separate phase, but they are usually lumped with the aqueous phase that contains the microbes, dissolved nutrients, and soluble products. The gas phase supplies oxygen and removes by-product CO2. The most common operating mode is batch with respect to biomass, batch or fed-batch with respect to nutrients, and fed-batch with respect to oxygen. Reactor aeration is discussed in Chapter 11. This present section concentrates on reaction models for the liquid phase. 

The catalytic ethylene oligomerization was performed in a 0.3 L well-mixed three-phase reactor operating in semi-batch mode, at constant temperature (70 or 150 °C) and pressure (4 MPa of ethylene) in 68 g of n-heptane (solvent). Prior to each experiment, the catalyst was successively pretreated, firstly in a tubular electrical furnace (550 °C, 8 h) and then in the oligomerization autoclave (200 °C, 3 h), under nitrogen flow at atmospheric pressure. After 30 min of reaction, the autoclave was cooled at -20 °C and the products were collected, weighted and analyzed by GC (FID, DB-1 60 m capillary column). 

Govindarao10 also postulated generalized nonisothermal (constant reactor wall temperature) models for batch as well as cocurrent- and countercurrent-flow three-phase gas-liquid-solid systems carrying out a first-order reaction. 

Most synthetically useful heterogeneously catalyzed reactions involve the hydrogenation of functional groups, a reaction that is typically mn as a batch process. As depicted by the schematic in Fig. 6.1, the apparatus in which these, and other three phase reactions are run, must be capable of containing the gas... 

Despite the experience with batch reactors it may be worthwhile to operate continuous reactors also for fine chemicals. Continuously operated reactors only demand for one start-up and one shut-down during the production series for one product. This increases the operating time efficiency and prevents the deactivation of dry catalysts this implies that the reactor volume can be much smaller than for batch reactors. As to the reactor type for three phase systems an agitated slurry tank reactor [5,6] is not advisable, because of the good mixing characteristics. Specially for consecutive reaction systems the yields to desired products and selectivities will be considerably lower than in plug flow type reactor. The cocurrent down flow trickle flow reactor... 

This case study is concerned with a three-phase gas-liquid-solid (catalytic) reaction. A systematic stepwise procedure has been described for determining the rate-controlling step, which depends on the catalyst type, particle size, operating pressure and temperature, mass transfer coefficient, and concentrations of reactants and products. As indicated, the rate-controlling step may change with location in a continuous reactor and with time in a batch reactor. 

Gladkii(16) at the State Scientific Research Institute of Industrial and Sanitary Gas Cleaning at Moscow did work on the three-phase calcium sulfite slurry oxidation system, finding that the liquid phase oxidation (pH 3.6-6) is first order with respect to the sulfite species. He pointed out, on the basis of pH versus time data from his semi-batch reaction, that the slurry oxidation had different periods in which either reaction kinetics or solid-liquid mass transfer controlled the oxidation rate. He also presented an omnibus empirical correlation between pH, temperature, and the liquid phase saturation concentration of calcium sulfite solution for predicting the slurry oxidation rate. The catalytic effect of manganese... 

At the beginning of a batch reaction the continuous aqueous phase contains the water-soluble initiator, emulsifiers, and buffers. Common ionic emulsifiers will be present as molecularly dissolved electrolytes, as surface active agents at the various interfaces, and as molecular clusters called micelles. The monomer will be in three different locations. A small amount will be dissolved in the water phase. Some will be solublized within the emulsifier micelles. The bulk of the monomer, however, will exist in the relatively large (ca. 5 um) monomer droplets. Any oil-soluble components such as chain transfer agents will be distributed with the monomer if the water solubility is sufficient to permit transport from the droplets. 

Figure 3 shows two examples of reactors with a fixed catalyst for gas-liquid reactions, viz. the trickle-bed reactor and the three-phase monolith reaetor. In these reactors the flow of liquid phase usually approaches plug flow. The figure also shows an example of a batch reactor system for a liquid-liquid reaction consisting of a mixing tank and a fixed-bed reactor with upward flow. This set-up is applied in aromatic acylation. 

We studied the hydrogenation of acetophenone, where a great deal of side-reactions and production of intermediaries take place in a three-phase reactor, with liquid batch and gas continuously fed, at constant pressure and temperature. The catalyst is Rhodium (3%) over activated carbon. The solvent is Cyclohexane. Samples are taken at different instants and analysed by gas chromatography. The species for which measures are available are acetophenone, AC, phenyl-ethanol, PE, methyl-cyclohexyl-ketone, ethyl-benzene, EB, ethyl-cyclohexane, cyclohexenyl-ethanol, CNE, methyl-cyclohexenyl-ketone and cyclo-hexyl-ethanol, CE. 

The typical reaction mechanism for tri-liquid PTC in a batch reactor under agitation is illustrated in the schematic diagram of Fig. 9. Three types of reaction scheme considering the partition of the catalyst in the different phases and the place where the inherent reaction occurred have been proposed [226,227]. For the substitution reaction of alkyl halide (RX) and aqueous reactant metal salt (MY) using quaternary ammonium salt (QX) as the catalyst, the different types of reaction are addressed as follows [226]. 

Three-phase reactors are operated in either the semibatch or continuous mode, and batch operation is almost never used because the gas phase is invariably continuous. The general principles of design are the same for all types of reactors for a given mode of operation, semibatch or continuous. They differ with respect to their hydrodynamic features, particularly mass and heat transfer. Thus, for simple first-order reactions. Equation 17.8 is valid for any reactor. The rate constant ky,i would be the same for all of the reactors, but specific to each reactor type is the mass transfer term k/. Hence we consider first the design of... 

Liquid-phase chemiluminescence reactions have been extensively studied and applied to flow analysis, high-performance liquid chromatography, capillary electrophoresis, and batch luminometers. Some of the more important chemistries are listed in Table 2. The discussion that follows will highlight three reactions, which have each been selected to illustrate certain unique attributes. Much more detail on liquid-phase chemiluminescence can be found in a subsequent chapter. 

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