Batch reactor, reaction rates

The activated Ba(OH)2 was used as a basic catalyst for the Claisen-Schmidt (CS) condensation of a variety of ketones and aromatic aldehydes (288). The reactions were performed in ethanol as solvent at reflux temperature. Excellent yields of the condensation products were obtained (80-100%) within 1 h in a batch reactor. Reaction rates and yields were generally higher than those reported for alkali metal hydroxides as catalysts. Neither the Cannizaro reaction nor self-aldol condensation of the ketone was observed, a result that was attributed to the catalyst s being more nucleophilic than basic. Thus, better selectivity to the condensation product was observed than in homogeneous catalysis under similar conditions. It was found that the reaction takes place on the catalyst surface, and when the reactants were small ketones, the rate-determining step was found to be the surface reaction, whereas with sterically hindered ketones the adsorption process was rate determining. 

Baeyer-Vllliger oxidations, effective catalyst of ketones, 139 Batch reactor, reaction rates, 69-70 Benzoquinone-hydroqulnone polymers applications, 145 attachment to polymeric surface, 145-147 Benzylalcohol, cleavage products data, 94f... 

Assuming that the reactions are first order in a constant volume batch reactor, the rate equations for components A, B, C, and D, respectively, are ... 

The rate of polymerization with styrene-type monomers is directly proportional to the number of particles formed. In batch reactors most of the particles are nucleated early in the reaction and the number formed depends on the emulsifier available to stabilize these small particles. In a CSTR operating at steady-state the rate of nucleation of new particles depends on the concentration of free emulsifier, i.e. the emulsifier not adsorbed on other surfaces. Since the average particle size in a CSTR is larger than the average size at the end of the batch nucleation period, fewer particles are formed in a CSTR than if the same recipe were used in a batch reactor. Since rate is proportional to the number of particles for styrene-type monomers, the rate per unit volume in a CSTR will be less than the interval-two rate in a batch reactor. In fact, the maximum CSTR rate will be about 60 to 70 percent the batch rate for such monomers. Monomers for which the rate is not as strongly dependent on the number of particles will display less of a difference between batch and continuous reactors. Also, continuous reactors with a particle seed in the feed may be capable of higher rates. 

The experimental method used for this kinetie study is reaetion ealorimetry. In the ealorimeter, the energy enthalpy balance is continuously monitored the heat signal can then be easily converted in the reaction rate (in the case of an isothermal batch reactor, the rate is proportional to the heat generated or consnmed by the reaction). The reaction orders and catalyst stabihty were determined with the methodology of reaction progress kinetic analysis (see refs. (8,9) for reviews). 

When a material reacts away by any nth order rate (n > 0) in a batch reactor, its rate of disappearance is rapid at the start when the concentration of reactant is high. This rate then slows progressively as reactant is consumed. In an autocata-lytic reaction, however, the rate at the start is low because little product is present it increases to a maximum as product is formed and then drops again to a low value as reactant is consumed. Figure 6.18 shows a typical situation. 

Tamaru (110) also discusses examples from heterogeneous catalysis in which reaction rates of one step seem to be influenced by the adsorption of other components. For example, Nishimura et al 115) studied the dehydrogenation of ethanol to acetaldehyde and hydrogen over a specially prepared Nb/Si02 catalyst at 523 K. The studies were done in a recirculating closed (batch) reactor. The rate is about constant as time increases, and the IR spectrum of an adsorbed intermediate remains constant. A sudden evacuation of the gas-phase ethanol stops the reaction but does not affect... 

We have seen how the kinetics fit into a reactor equation as a constitutive relationship. Elow and reaction come together in these systems to affect the rate of accumulation. Hence when we refer to the "rate" we must be careful to be specific about the reactor—if it is a constant volume batch reactor, then rate means the chemical rate. If the reactor is a transient CSTR or PER, then the rate of change of the concentration at the exit of the reactor is not the chemical rate alone. Mixing effects are important and we have seen how to begin to account for the fluid mechanics in a reactor through the empirical measure of the r.t.d. The r.t.d. does affect the outcome from the reactor, but the sensitivity to the r.t.d. depends upon the kinetics and their fimctional form. 

A liquid-phase chemical reaction with stoichiometry A —> B takes place in a semi-batch reactor. The rate of consumption of A per unit volume of the reactor is given by the first-order rate expression... 

Nonlinear behavior. Because of the potentially wide range of operation, linearized models may be inaccurate and inadequate for controller design. For example, batch chemical reaction rates may have a nonlinear dependence on temperature and concentration, and a nonlinear relationship may exist between heat transferred from a reactor and the fiow rate of the cooling medium. 

A reaction in which one of the products of reaction acts as a catalyst is called an autocatal 4 ic reaction. In a n-th order in a batch reactor, the rate of product formation or disappearance of reactant is high initially as concentration of the reactant is high, and reaction slows down as the reactant disappears. However, in an autocatalytic reaction, the rate is low initially as little product is present, the rate increases as more and more product gets formed and then drops again because reactant is consumed. 

Fixing the rate of heat transfer in a batch reactor is often not the best way to control the reaction. The heating or cooling characteristics can be varied with time to suit the characteristics of the reaction. Because of the complexity of hatch operation and the fact that operation is usually small scale, it is rare for any attempt to be made... 

The use of alkali or alkaline-earth sulfides cataly2es the reaction so that it is complete in a few hours at 150—160°C use of aluminum chloride as the catalyst gives a comparable reaction rate at 115°C. When an excess of sulfur is used, the product can be distilled out of the reactor, and the residue of sulfur forms part of the charge in the following batch reaction. The reaction is carried out in a stainless steel autoclave, and the yield is better than 98% based on either reactant. Phosphoms sulfochloride is used primarily in the manufacture of insecticides (53—55), such as Parathion. 

The reaction is exothermic reaction rates decrease with increased carbon number of the oxide (ethylene oxide > propylene oxide > butylene oxide). The ammonia—oxide ratio determines the product spht among the mono-, di-, and trialkanolamines. A high ammonia to oxide ratio favors monoproduction a low ammonia to oxide ratio favors trialkanolamine production. Mono- and dialkanolamines can also be recycled to the reactor to increase di-or trialkanolamine production. Mono- and dialkanolamines can also be converted to trialkanolamines by reaction of the mono- and di- with oxide in batch reactors. In all cases, the reaction is mn with excess ammonia to prevent unreacted oxide from leaving the reactor. 

The hquid-phase chlorination of benzene is an ideal example of a set of sequential reactions with varying rates from the single-chlorinated molecule to the completely chlorinated molecule containing six chlorines. Classical papers have modeled the chlorination of benzene through the dichlorobenzenes (14,15). A reactor system may be simulated with the relative rate equations and flow equation. The batch reactor gives the minimum ratio of... 

With batch reactors, it may be possible to add all reactants in their proper quantities initially if the reaction rate can be controlled by injection of initiator or acqustment of temperature. In semibatch operation, one key ingredient is flow-controlled into the batch at a rate that sets the production. This ingredient should not be manipiilated for temperature control of an exothermic reactor, as the loop includes two dominant lags—concentration of the reactant and heat capacity of the reaction mass—and can easily go unstable. 

The well-known difficulty with batch reactors is the uncertainty of the initial reaction conditions. The problem is to bring together reactants, catalyst and operating conditions of temperature and pressure so that at zero time everything is as desired. The initial reaction rate is usually the fastest and most error-laden. To overcome this, the traditional method was to calculate the rate for decreasingly smaller conversions and extrapolate it back to zero conversion. The significance of estimating initial rate was that without any products present, rate could be expressed as the function of reactants and temperature only. This then simplified the mathematical analysis of the rate fianction. 

Chemical engineering inherited the definition for the reaction rate from chemical kinetics. The definition is for closed systems, like batch reactors, in which most of the classical kinetic studies were done. Inside a batch reactor little else besides chemical reaction can change the concentration of reactant A. In a closed system, for the reaction of... 

The batch reactor initially contains 227 kg of acetyiated castor and die initial temperature is 613 K. Complete hydrolysis yields 0.156 kg acetic acid per kg of ester. Eor diis reaction, die specific reaction rate constant k is... 

Thermal runaway reactions are the results of chemical reactions in batch or semi-batch reactors. A thermal runaway commences when the heat generated by a chemical reaction exceeds the heat that can be removed to the surroundings as shown in Figure 12-5. The surplus heat increases the temperature of the reaction mass, which causes the reaction rate to increase, and subsequently accelerates the rate of heat production. Thermal runaway occurs as follows as the temperature rises, the rate of heat loss to the surroundings increases approximately linearly with temperature. However, the rate of reaction, and thus the... 

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