bf these typical reactor-jacket designs, nozzles (4) are simple, cheap, and effective in producing a tangentiol, high velocity water stream
I
I
SIDNEY J. MUM Foster Grant CO, IK., Le
Engineering Aspects of
SCALE-UP
PROM LABORATORY to plant for an emulsion polymerization process requires wnventional chemical engineering principles such as fluid flow, heat transfer, agitation, and distillation. But because of the complex nature of emulsion polymers, both in formation and hished stages, engineering problems are seldom resolved by simple calculation and designs. Particle size, coagulation, skinning, and settling are characteristic difficulties encountered. Also, many polymer emulsions are dilatant, pseudoplastic, or thixompic, and for design purposes require modification of the normal fluid flow and heat transfer laws.
torily handled with conventional, positive action pumps designed for lique6ed pemoleum gas service. For emptying tank cars, compressors are preferred
,
because they permit almost wmplete discharge of the vaporized portion of the tank car contents. Usually, they are piped, first to pump vapor from storage
Fluid Flow Pumps for monomers normally stored a t atmospheric pressure can be standard ---centrifugal or positive action. Deep packing glands are desirable, and wpper or copper-bearing alloys should be avoided in parts of storage or transport systems in contact with monomm br their vapors. Low-boiling monomers such as butadiene and vinyl chloride are satisfac-
VECTOR T EXCHANGER
This typical water-circulating system for a jacketed reactor uses Pfaudler nozzles VOL. 49, NO. I 1
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tank to car, thus causing liquid flow to storage, and then to move vapor from the car to storage by reversing the flow. Thus, tank car pressure can be reduced to 5 to 10 pounds per square inch gage, and several hundred pounds of monomer per car can be recovered by this technique. Another method for emptying pressure tank cars is by pressurizing with inert gas Other ingredients charged to a conventional polymerization process .are either dry solids, liquid organic modifiers, or aqueous solutions of emulsifiers, catalysts, buffers, and protective colloids. Stainless-steel preparation tanks, pipes, and pumps are necessary to prevent corrosion and contamination. Gravity flow to the reactor is frequently used. For pressure operation, positive displacement pumps, either rotary or pistontype, work satisfactorily. Minor quantities of liquid ingredients can be charged t o a reactor through a small pressure vessel using an inert pressurizing gas such as nitrogen. Similarly, compressed air or compressed inert gas can be used to transfer hot or sensitive emulsions from one vessel to another. For processes involving gradual addition of monomer or ingredient to the reactor, adjustablespeed piston pumps (Milton Roy type) work satisfactorily. Rotary pumps perform satisfactorily if compensated for slippage and wear. Pumping and fluid flow problems for handling charge ingredients to a polymerization process are relatively simple but finished emulsions are more difficult to handle. Mechanical stability and frequently dilatancy or thixotropy must be considered. Low speed, positive action rotary or reciprocating pumps are satisfactory for handling mechanically stable finished emulsions. . Pumps with close-fitting sliding vanes should be avoided. Mechanically unstable emulsions cannot be handled in pumps with close tolerances and diaphragm pumps are required. These are satisfactory for most emulsions, but are relatively expensive and require a fair amount of maintenance. Apparent viscosity must be estimated for calculating pump sizes and horsepower and in sizing lines for handling dilatant, pseudoplastic, or thixotropic emulsions. This apparent viscosity should be determined a t a shear value approaching that encountered in the pump or flow line (7, 3), for which Stormer or Brookfield viscometers are useful. Most medium and high viscosity emulsion flow problems occur in the streamline flow region-e.g., a 1000-cp. emulsion flowing in a 2-inch pipe at 50 gallons per minute has a Reynolds number of 80. Solutions of protective colloids such as poly(viny1 alcohol), hydroxyethylcellulose, and methylcellulose are non-Newtonian and for fluid flow calculations, I
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should be treated as described previously. Low viscosity or dilute emulsions and protective colloid solutions do not generally exhibit serious non-Newtonian flow characteristics, and the conventional fluid flow equations apply. Another flow problem is encountered in design of circulating systems on reactor jackets. Conventional fluid-flow calculations will determine pipe sizes and pump characteristics. The circulating system should be planned to avoid vapor-locking of the pump. If very hot water is used, the heat exchanger or steam injector is preferably located on the discharge side of the pump. For best temperature response, quantity of circulating water should be kept minimum and rate of circulation should be relatively high. A minimum of 100 gallons per minute should be provided per 1000-gallon reactor capacity. Heat Transfer The heat of polymerization for vinyl acetate is 21 kcal. per mole or 440 B.t.u. per pound. Assuming an adiabatic polymerization of a mixture of 50% monomer and 5070 water, this would indicate a temperature rise of over 300" F. and points out the critical need for adequate heat removal in a polymerization process. Two principal methods for heat removal are used-convection to a surrounding jacket on the reaction vessel, and refluxing in a condenser. The latter method is preferred where applicable because: higher heat transfer coefficients are available from condensing vapors; jacket area on vessels is limited by vessel dimensions, whereas condenser area is unlimited; more uniform reaction temperatures are obtained in a refluxing system; refluxing systems automatically purge air from the reactor. Whether a jacket alone is adequate for complete heat removal depends largely on polymerization rate, amount of agitation and physical properties of the emulsion-i.e., viscosity, specific heat, and thermal conductivity. Many low viscosity systems such as butadienestyrene emulsions are suitably handled by jacket transfer alone. More reactive or viscous systems such as acrylates and vinyl acetate are best handled by reflux or a combination of jacket transfer and reflux. I n reflux-controlled polymerizations, vacuum can be used to lower the reaction temperature, and conversely, pressure can increase temperature. Heat load can be materially reduced by continuously feeding fresh, cold monomer or monomer emulsion to the reaction vessel during polymerization. Heat required to bring this feed u p to reaction temperature will reduce the quantity of heat to be transferred by the jacket or the condenser. In jacket design, the baffled construc-
INDUSTRIAL AND ENGINEERING CHEMISTRY
tion is not too satisfactory because a close fit between shell and baffle is difficult. This causes considerable leakage of circulating water and reduces the desired swirl effect. Leakage can be eliminated by using the angle iron-spiral construction, but this is relatively expensive and, unless carefully welded, may result in considerable warping of the vessel. The dimpled construction has the advantage of reinforcing both the shell and jacket permitting use of thin wall sections. This type of jacket is excellent for steam heating but poor for cooling-water circulation because of the large number of flow paths which reduce water. velocity and consequently the heat transfer coefficient. Pfaudler nozzles ( 4 ) are installed in a jacket to produce a tangential, high velocity, swirling water stream in the jacket. Two and sometimes three Pfaudler nozzles are used per reactor. These are simple, cheap, and effective. Temperature differentials in condensing vapors are not large and range u p to 140' F. Excessive stresses, therefore, do not occur in a straight tube and shell condenser; expansion bellows and floating heads are desirable but not necessary. Vapors should be condensed in the tubes. This is not the most efficient arrangement for heat transfer because 25 to 50% more capacity i s obtained by condensing on the shell side. However, it is recommended because of no pockets where polymer can accumulate. good drainage, easy cleanout in case of fouling, and easy inspection. Tubes are preferably 3 / 4 to 1 inch in size and baffling should be used on the shell side. I n vertical condensers, the tubes should be flush with the upper tube sheet to prevent monomer accumulation. The exit-water connection should be located close as possible to the upper tube sheet to eliminate air pockets. -4 small vent hole drilled through the top tube sheet and located between bolt holes will also aid in venting air. Down-flow vertical condensers are recommended although horizontal condensers have greater heat transfer capacity. Vertical condensers permit appreciable subcooling of condensate and have good drainage characteristics in case of entrainment and foaming. Venting losses can be minimized by providing an auxiliary vent condenser as shown in the arrangements illustrated on page 1800 (No. 4). With this, condensate can be returned to the batch-either to or beneath the surface. Coagulum in many emuIsions systems can be reduced by belowsurface return of condensate. The illustrated condenser setups are easily adapted for use under pressure by suitable valving and by providing inert gas vents a t the uppermost part of the condenser. Knock-back condenser arrangement (No. 3 ) must be carefully
E N G I N E E R I N G ASPECTS OF POLYMER PROCESSES designed to avoid flooding at the lower tube sheet. Condenser areas can be calculated from heat load which is determined by polymerization rate, heat transfer coefficients ( Z ) , and economic considerations which balance cost of cooling water and fixed charges against capital outlay for condenser area. For estimating purposes, 100 to 150 square feet of condenser area should be provided for each 1000-gallon reaction capacity. Heat transfer coefficients for agitated vessels, given by Uhl (6), will vary from 50 to 100 for relatively viscous emulsions and from 100 to 150 for less viscous. Agitation and viscosity are important in determining these coefficients. For calculations, viscosities should be estimated by the methods previously described. Finished emulsion batches can be cooled in reactors, but agitated blow down tanks are usually more economical; they can serve as combined cooling, stripping, and blending tanks. Where cooling time is available, jackets are preferred in these cooling vessels for ease in cleaning. When greater heat transfer surface is required, jackets are replaced, or augmented with cooling coils. These should be provided with a liberal pitch and should be located a t least G inches from vessel walls to ensure good circulation and permit easy cleaning. Continuous coolers such as the Votator are effective for viscous, mechanically stable emulsions. Agitation Agitation must serve two purposesprovide sufficient shear to disperse adequately monomer droplets in the aqueous phase and provide sufficient movement of the liquid mass to ensure good heat transfer to the jacket. Turbine agitators are satisfactory for low to medium viscosity emulsion systems (up to 1000 cp.) such as acrylates, vinyl chloride copolymers, butadiene-styrene, and butadiene-acrylonitrile. For these, moderate agitation is required because excessive turbulence may cause too fine a particle size which with corresponding increase of particle surface area, causes emulsifier starvation and subsequent reduction of mechanical stability. This in turn may cause excessive floc formation. Approximately 3- to 5-hp. agitation per 1000-gallon reactor volume should be provided for these low to medium viscosity systems. Baffles, desirable to prevent swirl and to improve top to bottom turnover, should be mounted on clips approximately 2 to 4 inches from the kettle wall to prevent resin deposits in corners and permit easy cleaning. Emulsion systems incorporating protec-
tive colloids such as poly(v cellulose derivatives, and polyelectrolytes, are usually more viscous and more difficult to agitate, Systems of this type include certain vinyl acetate and styrene emulsions. Some normally low viscosity systems made at high solids content (near inversion point) may also show abnormal viscosity increases during polymerization. Although viscosities of finished emulsions may be moderate (1000 to 2000 cp.), during polymerization the batch may go through a relatively thick phase up to 50,000 cp. Turbine agitators are satisfactory for these systems and should be the large diameter, slow speed type. For more viscous systems, low speed paddle, anchor, or gate type agitators are necessary. Facilities for both high and low speed agitation are desirable in kettles used for multipurpose emulsion polymerization. This can be accomplished by a variable speed agitator drive or by combination of a low speed anchor with a high speed propeller or turbine operating between the anchor blades-e.g., the Groen kettle. For viscous emulsions, a minimum of 10 hp. per 1000 gallons should be provided and baffles are generally unnecessary. i
Distillation Many commercial monomers have low inhibitor contents and are sufficiently pure for direct polymerization. Rectification and purification are seldom required. Some, however, contain relatively nonvolatile inhibitors which may interfere with polymerization and must be removed by distillation or extraction. Extractions, usually with mildly alkaline aqueous solutions, are performed in continuous or batch separation vessels fitted with agitators. Inhibitors react with the alkali and are thus removed. Some monomers such as vinyl acetate or the acrylate esters, however, are reactive to cold alkali and must be distilled. Distillation is done in batch or continuous units and to prevent entrainment, packing equivalent to one or two plates is provided. A few monomers containing large quantities of inhibitor require packing equivalent to two to four plates for rectification. High boiling or very reactive monomers are vacuum distilled to prevent polymerization. Design features of distillation equipment for acrylic esters, given by Riddle ( 5 ) , are applicable to other monomers. Distillation problems are also encountered in removing traces of monomer from finished emulsions. In batch emulsion polymerizations, rate of reaction decreases at the end of the cycle. At some point, continuing the reaction becomes uneconomical because the cost of
the value of conthis reason, emulsion polymerizations are seldom run to completion and traces of monomer up to 1 to 2y0 remain in the finished reactor product. Where particular polymer properties are required-namely, butadiene-styrene GR-S recipes-conversions are sometimes run as low as 60 to 70%. Stripping and recovering of monomer in these systems are described by Whitby (7). When an excess of monomer is present, the rate of its removal in a stripping operation obeys the laws of steam distillation. As monomer content decreases, this rate becomes dependent on diffusion rate of the monomer through the polymer particle in which it is dissolved. Several factors including solubility effects, emulsion particle size, and copolymer composition, determine this diffusion rate. Most emulsion polymerizations are run to the point where rate of monomer removal by stripping is established by a combination of rates for steam distillation and diffusion. The net rate for a particular system is best determined by laboratory or pilot plant experiment. In designing plantscale stripping units, high temperatures or excessive dwell time at moderate temperatures should be avoided-these tend to destabilize most emulsion systems. Commercially, several methods for stripping monomer are used : Vacuum stripping is usually a batch operation where the emulsion is sparged with steam while under vacuum. Heat can simultaneously be applied with hot water in a jacket to prevent excess condensation of steam and resulting dilution of the emulsion. Jacket steam should be avoided, as it causes resin build-up on the kettle walls. Mild agitation improves the stripping rate and reduces skinning. Vapors are condensed to reduce load on the vacuum system. Antifoams are frequently required to prevent emulsion carry-over into the condensing system. Air or gas blowing, used where dilution of the emulsion must be avoided, is similar to vacuum stripping but air or inert gas is substituted for steam. Inert gas is preferred because malodorous oxidation products are sometimes formed with air. Film evaporation, exemplified by the Rodney Hunt evaporator, is easily adaptable to continuous operation. A rotating scraper maintains a thin film of emulsion on the vertical walls of a heated cylindrical vessel under vacuum. The operation is more difficult to control than the batch systems because of foaming tendencies and resin deposition on the walls of the vessel. Spray stripping is a modification of the vacuum stripping system, where the emulsion is continuously pumped and sprayed into the vapor space of a heated VOL. 49, NO. 11
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+WATER
OUT
BAFFLES
.... .--
.ypical
vessel under vacuum. Evaporation of water from the surface of the sprayed particles servul to steam-distill traces of monoma. Other methods for concentrating natural l a w have been adaptcd to emulsion stripping. In one, warm air is blown through a horizontal openend rotating cylinder which d i p into a tmugh of emulsion. A thin film of emulsion adhens to the inner wall and the air evaporates moisture and mon.
omer. An adaptation of this consists of a scries of flat vertically mounted rotating dipks which dip into a trough of emulsion. Warm air is blown across the disk faccs to evaporate volatiles. A redox system is perhaps the k s t method for trace monomer removal. This is usually applied a t the end of the polymerization cycle by adding a small quantity of catalyst followed by a reducing agent. When properly formulated, monomer content of a few tenths per ent is obtained.
SPARE NOZZLE
L 02. PR. WAC. =LIEF
F08
Filtration Filtering emulsions is difficult. Resin emulsions used by the paint, coatings and adhesives, and textile industrim must be essentially free from grors polymer particles. No residue should be left on 100-mesh screen. The particles are usually tacky, slightly flowable, agglomerative, and irxversible film formers. They clog screens rapidly, cannot easily be flushed out, and prevent continued flow of emulsion. Ordinary filters such as plate and frame filter prewx, leaf or vacuum filters, block too quiddy. Mechanical filters such as shake s c ~ c e n s and back flow filters, although far from adequate, do a better job. The best method for filtering emulsions appears to be a relatively primitive onean operator runs the emulsion by gravity through a filter bag or screen, washing, or replacing the filter medium as it becomes clogged. A battery of w e e n baskets mounted in drums or closed pots is useful for speeding up the filtering operation.
LLlNc TO PROCESS CAClLlTlES
Storage and Shipping Conkinerr Skinning is a major problem to consider in designing storage tanks for resin emulsions. Most commercial emulsions have high solids content and irreversible fihn-forminz DroDerties. Surfacc evaw oration of moisNre cauw skin formation, not redispcrsible on agitation, which accounts for grit and floc in finished products. Storage tanks should thcreI .
SCREEN POT
In this simple handling and storing method, skin formation is prevented by supplying the vapor-tight tank wilh moisture-saturated air
1800
INDUSTRIAL AND E f f i l N E E R l f f i CHEMISTRY
.
FNGlNEERlNS ASPECTS OD POLYMER PROCESSES
.
fore be vapor tight and provided with moisture-saturated air to prevent d a c e evaporation during filling and emptying. Vertical cylindrical tanks arc preferred over horizontal tar&. This asconstant emulsion surface area in the tank and reduces breakup of d a c e skin. Tanks should be filled using a down spout to avoid foaming and splashing. To minimize settling of sldns and floc in withdrawal connections, discharge connections should be located on the d e s rather than bottom. Manholes provide easy entry to the tank for cleaning purposes. Agitation is desirable for blending and uniformity. Storage temperaNre for large tanks and shipping drums should be kept as uniform as possible to minimizC surface evaporation. As storage temperatwes drop, moisture evaporating from the warm emulsion surface and condensing on the container walls may lead to serious skin formation. Stainla steel, the preferred material of construction for storage tanks. is acceptable for storing practically all emulsions. To facilitate cleaning, a No. 4 polish should be applied to all interior surfaces coming in wntact with emulsions. Glass-lined steel is satisfactory but more difficult to maintain. Steel coated with baked phenolic or epoxy resin is economical but not 9 durable as glass or stainless steel. Jf not properly applied, thm linings may rapidly break down, particularly at the liiuid-vapor-zontainer wall interface. Aluminum w sarisfactory for many
Among the most crucial items in the plant ore devices such as these for relieving reactor pressure
neutral or slightly acidic emulsions. W w d can be used for tank construction, but this is unsatisfactory because of resin build-up by moisture.dXusion through the stavea. Once coated, wood is d s cult to dean becaw dried filma a d h m to its surface. shipping tanks are uwlally constructed of stainless stccl, aluminum, or glaag~ lined or resin-coated steel and should be
completely filled to prevent sloshing in bansit. To maintain uniform temperatures and prevent freezing, they are usually well insulated. The standard small shipping container for resin emulsions is a 55-gdon openor dosed-head steel drum usually lined with a baked phenolic or epoxy resin. A single wating is too porous and usually at least two wats are applied to a sand-blasted or phoaphathd surface. The coating should have some flexibility to pxvent fracture on impact. Bungs should be avoided on these drums because threads cannot be &ectidy w a d and are points for lining failure. Polyethylene liners are frcsuently used in uncoated drums.
Safety Devices The well designed plant should have pmvisions against all potential hazard& Its general design should be that for a typical plant handling highly volatile, Eammable, ‘hazardous liquids. Also,
This is on &&e
temperature control system for a vessel where all heat of polymerization is transferred to the jacket
adequate safety emergency equipment for handling beat of polymeriza!ion must be provided. sOme.major safety featured needed are spoinklus and fire fighting equipment, staticpmof flwm, antistatic drive belts, cxplaionpmof electrical fixnm=s,sparkpmof tools, tar& vented to safe area, safety valved and/or rupture dEsln, with adequate relieving capacity for all -la, good grounding, two sources of cooling water, emergency power generator, good ventilation, explaionproof building wnsmction, emergency dump valves, and cooling water sprays on monomer storage tankq stills, and reactors. / VOL. 49, NO. 11
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I
One of the most critical points in the plant is the reactor itself which should be
by themselves because of low relieving capacity and possibility of fouling with polymer. Rupture disks or a combination of rupture disks and safety valves are preferred. The relief devices should be mounted close to the reactor, and to prevent excessive back pressure, discharge lines should be larger than the safety device. Manufacturers of safety disks and relief valves should be consulted for size recommendations. Unlike conventional pressure vessels, rupture disks for polymerization reactors are preferably rated for the lowest practical pressure, which should be lower than the pressure rating of the vessel. In a runaway reaction, too high a relief pressure will cause a correspondingly high reaction temperature, and because polymerization rates increase rapidly with temperature, a near-explosive condition may develop. For reactions a t atmospheric pressure, rupture disks should be rated at approximately 15 to 20 pounds per square inch. which is the lowest practical limit for low pressure disks. This pressure should be below the vessel design pressure. When alternate pressure and vacuum conditions are used in a reactor, disks should be provided with vacuum supports. Most rupture disk materials will fatigue, particularly when rated for relief near the operating pressure or when subjected to pressure changes. Of the reactor-relief designs illustrated, the double rupture disk assembly (Yo. 3) provides a warning signal should the bottom disk fail from fatigue or develop corrosion pin holes. Losses are prevented because the second disk will support the pressure until the batch is completed and the bottom disk can be replaced. An arrangement to prevent excessive batch losses in cases of overpressure (No. 4) is usually employed for polymerizations which proceed near design pressure of the reactor. When overpressure occurs, the bottom disk ruptures and the relief valve discharges gas. When the pressure drops back, this reseats to prevent complete loss of the batch. If the relief valve has inadequate capacity and the exotherm is too great, the upper disk bursts and the entire batch is vented. The simplest relieving device is a liquid seal (No. 1). To prevent contamination of the seal liquid, a small condensing section is located on the vertical riser. It is important not only to relieve excessive kettle pressure but to direct the discharged contents to a point where they will not create further hazard. Oversized tanks are desirable for this and
1 802
should be adequately vented to a high point where fumes can be safely dissipated to the atmosphere. Water-drowning of discharged batches is sometimes employed. Materials of Construction With good inventory turnover, ordinary carbon steel and cast iron are satisfactory for storing, handling, and pumping conventional monomers such as styrene, vinyl acetate, and acrylates. Moisture should be completely avoided in storage tanks. I t may hydrolyze certain monomers, cause rust, and accelerate stabilizer decomposition. Dry inert gas should be provided to blanket storage tank contents. Preparation, blending, and storage tanks should be constructed from stainless steel as well as pipelines and valves for handling ingredients charged to the reactor. Corrosion conditions are usually not Severe and Type 304 stainless steel is satisfactory, but when iron contamination must be kept at a minimum, Type 316 stainless is preferred. Glass-lined steel and stainless steel are both widely used for reactor construction. Corrosion is usually not an importanr: factor but contamination and ease of cleaning are. Stainless steel, although more expensive than glass, is more durable, and for reactor construction, all interior surfaces should be finished with at least a No. 4 polish, Glass, however, is preferable for sensitive emulsion because floc and skin have a esser tendency to stick to its surface. Highly alkaline emulsion polymers require special glass. Auxiliary equipment for glass reactors, such as condensers, valves, and piping, are made of stainless steel. Instrumentation Conventional instrumentation is used throughout emulsion polymerization plants. Batch temperature is the most important control, and the temperature bulb in the reactor should be properly located-away from dead spots and in an area of good circulation. For safe operation and for cross-checking, both an indicating and recording thermometer should be placed in the reactor. Batches run a t reflux are not susceptible to automatic temperature control because throttling action of control valves, based on temperature setting, is unavailable. However, flow of condenser-cooling water is controllable by operating from condensate temperature, provided subcooling occurs. Reaction progress is usually measured by withdrawing samples from the reactor and determining solids content by evaporation, but direct specific-gravity determinations can sometimes be used. Viscosity and pH determinations can simultaneously be run on portions of the
fNDUSTRlA1 AND ENGINEERING CHEMISTRY
same sample. Continuous recorders for these determinations do not function satisfactorily for batch emulsion systems-particularly under pressure, they tend to become coated with polymer. In polymerization reactions under reflux conditions, batch temperature is a good indication of the reaction progress. Similarly, in most pressure polymerizations, pressure of the system decreases toward the end of the polymerization cycle and indicates completion of reaction. In the illustrated normal instrument layout, output air pressure of the master controller regulates position of the water throttling valve, as indicated by the dotted line. A long lag in temperature response is caused by heat capacities of kettle contents, circulating water, mass of metal in the system, and the temperaturesensitive bulb. If rate of heat evolution from reacting products changes, the temperature recovery chart might resemble that in the lower left corner of the illustration. The lag caused by circulating water can be reduced by using a slave instrument, the pneuma tic-set temperature controller. This receives the output signal from the master controller and quickly brings the circulating water to the new temperature demanded by the master controller. Control is improved as shown in the lower right temperature chart. The slave control also compensates for changes in cooling water supply pressures and temperatures. The output pressure of the slave control can also operate a water-cooling valve over part of the range and over the balance, a steam-heating valve. Thus, the instruments can bring cold batches up to reacting temperature, and the masterslave feature prevents overshooting during this heating operation. Ackn owledg menf Permission by the Borden Co. to publish the information contained here is gratefully acknowledged. literature Cited (1 ) Alves, G. E., Boucher, D. F., Pigford, R. L., Chem. Engr. Progr. 48, No. 8 , 385 (1952).
( 2 ) Kern, D. Q.; “Process Heat Transfer,”
McGraw-Hill, New York, 1950.
(3) Metzner, A. B., Chem. Engr. Progr. 50,
KO.1, 27 (1954).
(4) Pfaudler
Co., Rochester, N. Y., Maintenance Manual, Sect. 3, p. 19. (5’1 Riddle. E. H.. “Monomeric Acrvlic * , Esters,” Reinhold, New York, 1954. ( 6 ) Uhl, V. Mr., Chem. Eng. Progr. Symposium Ser. 51, No. 17, 93 (1955). (7) Whitby, G. S., “Synthetic Rubber,” Chap. 2, Wiley, New York, 1954.
RECEIVED for review April 25, 1957 ACCEPTED August 8, 1957 Division of Industrial and Chemical Engineering, Symposium on Engineering Aspects of Polymer Processes, 131st Meeting, ACS, Miami, Fla., April 1957.
