Kettle reactors

Runaway can be a particular problem in unsteady-state batch reactors, where the rate of reaction, and thereby the rate of heat production, varies with time. The consequences of thermal runaway can be severe, as the incidents at Seveso and Bhopal have shown. The task of specifying the design, operation and control of an apparently simple kettle reactor with stirrer, heating/cooling coils, possibly reflux facilities, and emergency relief venting can be difficult if all the time-dependent parameters are considered. It is a task which requires a systematic approach. 

Corrosion of reactors used for functionalization and ia pipes and valves along transferlines for sulfuric acid is a problem that results ia maintenance shutdowns. Sufficient agitation is needed to keep the resia beads fluidized duting sulfonation. As for copolymer kettles, transfer lines should be sufficiently large to allow reasonably rapid transfer of Hquids and resia slurries. 

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. 

Batch Mass Reactors. The batch-mass reactors used in these processes are of two types low conversion agitated kettles and high conversion static reactors with extended cooling surfaces. 

An example of a low conversion reactor would be a conventionally agitated kettle with large turbine agitators and jacket cooling. The utility of this type of reactor can be extended to intermediate conversions by the use of anchor or helical agitators to partially overcome heat transfer and mixing problems at higher viscosities. 

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. 

In a typical example (33) a fresh feed of 8% polybutadiene rubber in styrene is added with antioxidant, mineral oil, and recycled monomer to the first reactor at 145 lbs./hr. The reactor is a 100-gallon kettle at approximately 50% tillage with the anchor rotating at 65 rpm. The contents are held at 124°C and about 18% conversion. Cooling is effected via the sensible heat of the feed stream and heat transfer to the reactor jacket. In this reactor the rubber phase particles are formed, their average size determined and much of their morphology established. Particle size is controlled to a large measure by the anchor rpm. 

Evaporation can be performed directly from reactors or kettles provided that substances are thermally stable. Such evaporation is time consuming because of the low heat-transfer surface area per unit volume. In the case of temperature sensitive materials, the residence time in the evaporator must be short and the temperature should be as low as possible. Consequently, continuous vacuum evaporators with a short residence time should be used to treat such materials. Falling-film (thin-film) evaporators are suitable to perform such operations. A typical falling-film evaporators is shown in Fig. 7.2-14. Centrifugal evaporators are also commonly used. 

Oil-Based SINs. The SINs produced were based on a castor oil polyester-urethane and styrene crosslinked with 1 mole percent of technical grade (55%) divinyl benzene (DVB) (7). This structure may be written poly[(castor oil, sebacic acid, TDI)-SIN-(Styfene, DVB)], poly[(CO,SA,TDI)-SIN-(S,DVB)]. Benzoyl peroxide (BP) (0.48%) was used as the free radical initiator for the styrene and 1,4-tolylene-diisocyanate (TDI) was used as the crosslinker for the polyester prepolymer. A 500 ml resin kettle equipped with a N inlet, condenser, thermometer, and high torque stirrer was used as the polymerization reactor. 

A reaction kettle equipped with mechanical stirrer was placed in a glove box filled with nitrogen and heated to 120°C for 1 hour to remove moisture. The reactor was then charged with glycolide (200 g), y-caprolactone (200 g), 0.27 ml dodecanol, 700 ml of xylene, and 1.12 ml of stannous octoate and where glycolide component was added over four portions in 2-hour intervals. The mixture was then stirred at 120°C for 90 hours and the product isolated after dissolving in chloroform and precipitated in methanol. 2... 

This is a stainless steel round bottom spouted kettle of 120 1 capacity with a steel jacket and four-bladed stainless steel agitator which rotates at 95 RPM. d)Raise and maintain the temp of soln A at 135-140°F (57.5-60°) by circulating 170°F (ca 76.5°) water through the jacket of the reactor. e)Drop 50 1 of stock soln B/NaNj from the 1000 1 storage tank to a second stainless steel measuring tank of... 

Industrially, polymerizations are carried out to over 99% conversion and thus there is no need to reduce the unreacted monomer unless very low levels are required to meet regulatory. product, or workplace requirements. Most poly(vinyl acetate) emulsions contain less than 0.5 wt % unreacted vinyl acetate. All of the processes are operated in conventional glass-lined or stainless steel kettles or reactors. Control of the process is important to ensure reproducibility of the product. 

In this process, a 500-gallon glass-lined reactor is needed to heat the salicylic acid and acetic anhydride for 2 to 3 hours. The mixture is transferred to a crystallizing kettle and cooled to 3°C. Centrifuging and drying of the crystals yields the bulk aspirin. The excess solution is stored and the acetic acid is recovered to make more acetic anhydride. 

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