Batch reactors liquid phase

Fig. 7.1 Nonideal batch reactors liquid-phase batch reactor (a), liquid-phase batch reactor with release of gaseous bubbles (b), semi-batch gas-liquid bubble column (c), and slurry batch reactor (d)...

Amide hydrolysis is a key step in the widespread strategy of protection/deprotection of amino groups for synthetic purposes, usually carried out in homogeneous phase with mineral acids. It is shown here that under mild conditions (batch reactor, liquid phase, 75°C) large pore zeolites (HY, HBeta, HMOR) can catalyse the hydrolysis of various aromatic amides. The best results are obtained over HY zeolite samples with Si/Al ratios of 16 and 30 e.g. complete and selective hydrolysis of 2-nitroacetanilide after 2-4 hours reaction for a zeolite/substrate ratio of 0.5 g/mmol. For similar values of the Si/Al ratio HBeta and rather all HMOR samples are much less active than HY samples, which is probably related to diffusion limitations. 

In batch procedures, liquid phase photobrominations halt in general at conversions between 50 and 70%, the concentration of HBr reaching a level where the back reaction (Eq. -15) becomes more efficient than the productforming step (Eq. 16). Particular reaction conditions and, hence, particular reactor geometries and/or accessories are then required to remove continuously the HBr produced. Photobrominations are preferentially developed at boiling point temperatures, as has been beautifully demonstrated in the industrial synthesis of 1-bromo-diethylcarbonate (Eq. 17) [30]. 

The use of an unnecessarily hot utility or heating medium should be avoided. This may have been a major factor that led to the runaway reaction at Seveso in Italy in 1976, which released toxic material over a wide area. The reactor was liquid phase and operated in a stirred tank (Fig. 9.3). It was left containing an uncompleted batch at around 160 C, well below the temperature at which a runaway reaction could start. The temperature required for a runaway reaction was around 230 C. ... 

Except in the laboratoiy, batch reactors are mostly liquid phase. In semibatch operation, a gas of limited solubility may be fed in gradually as it is used up. Batch reaclors are popular in practice because of their flexibility with respect to reaction time and to the lands and quantities of reactions that they can process. 

In chemical laboratories, small flasks and beakers are used for liquid phase reactions. Here, a charge of reactants is added and brought to reaction temperature. The reaction may be held at this condition for a predetermined time before the product is discharged. This batch reactor is characterized by the varying extent of reaction and properties of the reaction mixture with time. In contrast to the flasks are large cylindrical tubes used in the petrochemical industry for the cracking of hydrocarbons. This process is continuous with reactants in the tubes and the products obtained from the exit. The extent of reaction and properties, such as composition and temperature, depend on the position along the tube and does not depend on the time. 

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. 

Homogeneous reactions are those in which the reactants, products, and any catalysts used form one continuous phase (gaseous or liquid). Homogeneous gas phase reactors are almost always operated continuously, whereas liquid phase reactors may be batch or continuous. Tubular (pipeline) reactors arc normally used for homogeneous gas phase reactions (e.g., in the thermal cracking of petroleum of dichloroethane lo vinyl chloride). Both tubular and stirred tank reactors are used for homogeneous liquid phase reactions. 

Although many industrial reactions are carried out in flow reactors, this procedure is not often used in mechanistic work. Most experiments in the liquid phase that are carried out for that purpose use a constant-volume batch reactor. Thus, we shall not consider the kinetics of reactions in flow reactors, which only complicate the algebraic treatments. Because the reaction volume in solution reactions is very nearly constant, the rate is expressed as the change in the concentration of a reactant or product per unit time. Reaction rates and derived constants are preferably expressed with the second as the unit of time, even when the working unit in the laboratory is an hour or a microsecond. Molarity (mol L-1 or mol dm"3, sometimes abbreviated M) is the preferred unit of concentration. Therefore, the reaction rate, or velocity, symbolized in this book as v, has the units mol L-1 s-1. 

Example 2.2 Derive the batch reactor design equations for the reaction set in Example 2.1. Assume a liquid-phase system with constant density. 

The feed is charged all at once to a batch reactor, and the products are removed together, with the mass in the system being held constant during the reaction step. Such reactors usually operate at nearly constant volume. The reason for this is that most batch reactors are liquid-phase reactors, and liquid densities tend to be insensitive to composition. The ideal batch reactor considered so far is perfectly mixed, isothermal, and operates at constant density. We now relax the assumption of constant density but retain the other simplifying assumptions of perfect mixing and isothermal operation. 

Example 2.10 Suppose 2A —> B in the liquid phase and that the density changes from po to Poo = Po + Ap upon complete conversion. Find an analytical solution to the batch design equation and compare the results with a hypothetical batch reactor in which the density is constant. 

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. 

This work was initiated for the purpose of evaluating the feasibility of synthesizing hexyl acetate (ROAc) fi-om n-hexyl bromide (RBr) and sodium acetate (NaOAc) by a novel PTC technique. In this new technique, the solid-liquid reaction was catalyzed by a catalyst-rich liquid phase in a batch reactor. Because there a solid phase and two liquid phases coexist, it is called as a SLL-PTC system [3]. Actually, this liquid phase is the third liquid phase in the tri-liquid PTC system. It might be formed when the phase-transfer catalyst is insoluble or slightly soluble in both aqueous and organic phases. Both aqueous and organic reactants can easily transfer to this phase where the intrinsic reaction occurs [4, 5]. 

We have developed a compact photocatalytic reactor [1], which enables efficient decomposition of organic carbons in a gas or a liquid phase, incorporating a flexible and light-dispersive wire-net coated with titanium dioxide. Ethylene was selected as a model compound which would rot plants in sealed space when emitted. Effects of the titanium dioxide loading, the ethylene concentration, and the humidity were examined in batches. Kinetic analysis elucidated that the surface reaction of adsorbed ethylene could be regarded as a controlling step under the experimental conditions studied, assuming the competitive adsorption of ethylene and water molecules on the same active site. 

The prepared photocatal3rsts were tested to know the reactivity and quantum efficiency in the aqueous solution with trichloroethylene(TCE) as a reactant in photocatalytic batch reactor. Also these results were compared the reactivity to the case of P25 catalyst. The liquid phase photocatalytic reaction system was shown in Fig. 1. 

There is an additional point to be made about this type of processing. Many gas-phase processes are carried out in a continuous-flow manner on the macro scale, as industrial or laboratory-scale processes. Hence already the conventional processes resemble the flow sheets of micro-reactor processing, i.e. there is similarity between macro and micro processing. This is a fimdamental difference from most liquid-phase reactions that are performed typically batch-wise, e.g. using stirred glass vessels in the laboratory or stirred steel tanks in industrial pilot or production plants. 

The catalysts most frequently used are based on noble metals (mainly palladium and platinum) on various supports, or on nickel catalysts (mainly Raney type). Hydrogenations are generally performed in the liquid phase, under relatively mild conditions of temperature and pressure (1—40 bar). Most processes are performed batch-wise using powder catalysts in stirred tank or loop-type reactors with sizes up to 10 m . 

An nth-order homogeneous liquid phase reaction is carried out in a batch tank reactor. 

The liquid phase hydrolysis reaction of acetic anhydride to form acetic acid is carried out in a constant volume, adiabatic batch reactor. The reaction is exothermic with the following stoichiometry... 

Chemical Kinetics, Tank and Tubular Reactor Fundamentals, Residence Time Distributions, Multiphase Reaction Systems, Basic Reactor Types, Batch Reactor Dynamics, Semi-batch Reactors, Control and Stability of Nonisotheimal Reactors. Complex Reactions with Feeding Strategies, Liquid Phase Tubular Reactors, Gas Phase Tubular Reactors, Axial Dispersion, Unsteady State Tubular Reactor Models... 

The reactor system, where the kinetic experiments were carried out can be described as a semi-batch reactor. Only the synthesis gas (H2 and CO) was fed into the reactor continuously during the experiments, while 1-butene and the solvent were in the batch mode. All reactions took place in the liquid phase. The mass balance for an arbitrary component in the gas is given by... 

Ethyl acetate is to be manufactured in a batch reactor from the reaction between ethanol and acetic acid in the liquid phase according to the reaction ... 

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