Reactors, batch exothermic

Condensation reactions are typically reversible, slow, mildly exothermic and second order. Reversibility implies that the condensation product, AB, must be continuously removed to avoid an equilibrium limitation. Slowness implies that the chain length will change gradually with time in a batch polymerization and gradually with position in a flow reactor. Mild exotherms mean that heat removal is rarely a problem in condensation polymerizations. 

Cooled Batch Reactor with Exothermic Reaction Based on the rate in terms of Xa, Eq. (4.10.44), and the adiabatic temperature rise, Eq. (4.10.48), the heat balance of a cooled batch reactor, Eq. (4.10.45), for cIca =— dX CAfi reads as ... 

Shinskey, F. G., and J. L Weinstein A Dual mode Control System for a Batch Exothermic Reactor, 20th Anmal ZSA Conf., October, 1965. 

Ma.nufa.cture. In general, manufacture is carried out in batch reactors at close to atmospheric pressure. A moderate excess of finely divided potassium hydroxide is suspended in a solvent such as 1,2-dimethoxyethane. The carbonyl compound is added, followed by acetylene. The reaction is rapid and exothermic. At temperatures below 5°C the product is almost exclusively the alcohol. At 25—30°C the glycol predominates. Such synthesis also... 

With a bulk process, resole resins, in neat or concentrated form, must be produced in small batches (ca 2—9.5 m ) in order to maintain control of the reaction and obtain a uniform product. On the other hand, if the product contains a large amount of water, such as Hquid plywood adhesives, large reactors (19 m ) can be used. Melt-stable products such as novolaks can be prepared in large batches (19—38 m ) if the exotherms can be controlled. 

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. 

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. 

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. 

Adequate heat removal facilities are generally important when controlling the progress of exothermic chemical reactions. Common causes of thermal runaway in reactors or storage tanks are shown in Figure 7.4. A runaway reaction is most likely to occur if all the reactants are initially mixed together with any catalyst in a batch reactor where heat is supplied to start the reaction. 

Ethyl aluminum dichloride (EADC) is used in the rnanufacmre of certain catalysts for making LDPE. Occasionally, the batch operation involving the catalyst production results in an off-spec lot. This off-spec lot is washed from the reactor (impregantor) with water and hexane, and must be sent to a waste disposal facility. The facility treats this waste in a hydrolysis reaction (i.e., with water and mild agitation). If the reaction is exothermic, what are the potential air pollution and fire problems associated with the waste treatment ... 

Some batch reactions have the potential for very high energy levels. If all the reactants (and sometimes catalysts) are put into a kettle before the reaction is initiated, some exothermic reactions may result in a runaway. The use of continuous or semi-batch reactors to limit the energy present and to reduce the risk of a runaway should be considered. The term semi-batch refers to a system where one reactant and, if necessary, a catalyst is initially charged to a batch reactor. A second reactant is subsequently fed to the reactor under conditions such that an upset in reacting conditions can be detected and the flow of the reactant stopped, thus limiting the total amount of potential energy in the reactor. 

In a batch reaction plant, an exothermic reaction was cooled by water circulating in a jacket. The circulating pump failed and the reactor went out of control causing a violent explosion. A low flow alarm was present but was inoperable. A critical pump bearing had not been lubricated during maintenance, and the collapse of the bearing had led to the pump failure. 

This must be done with care to avoid lifting the batch and plugging the vent. To safeguard the kettle, a proper vent line on the rupture disc must be provided. This must be sized to allow relieving under the worst conditions of exothermic reaction where a large volume of water vapor must be vented, as well as a viscous liquid layer caused by loss of suspension. Fortunately, the venting problem here is still not as severe as in mass reactors. 

The curves in Figure 5.2 are typical of exothermic reactions in batch or tubular reactors. The temperature overshoots the wall temperature. This phenomenon is called an exotherm. The exotherm is moderate in Example 5.2 but becomes larger and perhaps uncontrollable upon scaleup. Ways of managing an exotherm during scaleup are discussed in Section 5.3. 

Temperature control of a large, highly exothermic semi-batch chemical or polymer reactor can be an involved problem. The reaction may be auto-acceleratlng. Heat transfer rates can vary during the process. Random disturbances can enter the process from many sources. Changes In... 

In case of exothermic reactions, the heat-exchange capacities of the reactor allow to rapidly evacuate the heat generated by the reaction and therefore to perform a transposition of a pure batch operating mode into a continuous one. The main point is the ability to avoid, as far as possible, an initial increase of the temperature as soon as the reactants are mixed. 

Anxionnaz, Z., Cabassud, M., Gourdon, C., and Tochon, P. (2010) Transposition of an exothermic reaction from a batch reactor to an intensified continuous one. Heat Transfer Eng., 31 (9), 788-797. 

With PI, traditional proeess design criteria (particularly those focused around stirred batch reactors) are thrown out and the equipment is designed to mateh the chemistry. It is not unexpected, therefore, to find that PI has been successfully applied to reactions that are very fast and exothermic, where the process is being limited by poor design. Traditionally these proeesses have been handled either by the use of large amounts... 

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