BACKGROUND OF THE INVENTION

1 1. Field of the Invention

2 This invention relates to an improved

3 chemical reactor, especially a polymerization

A reactor. In particular, it relates to a novel, im-

5 proved back-mixed chemical reactor useful in the

6 production of butyl rubber.

7 2. Background

8 Reactors are of various designs, the form

9 and shape thereof depending largely on the nature of 0 the reaction to be conducted therein. In conducting 1 polymerization or condensation reactions where li- 2 quid chemical raw materials are catalytically con- 3 verted into elastomeric solids or semi-solids, as in A the production of synthetic rubber from low boiling 5 hydrocarbons, a reaction mixture is circulated as a 6 slurry in a reactor into which reactants and cata- 7 lystε are injected, and product withdrawn. Where, 8 e.g., isobutylene is polymerized with a diolefin 9 in the presence of a Friedel-Crafts type catalyst, 0 e.g., an aluminum halide catalyst, dissolved in a 1 diluent of low freezing point, i.e., at temperatures 2 of about -100°F to -160°F to produce butyl rubber, a 3 back-mixed reactor is employed; typically a one-tube A pass system as described by reference to U.S. 5 2.A7A.592. Such reactor is charac erized generally 6 as a vertically oriented elongate vessel formed by an 7 enclosing side wall within which is provided an 8 axially mounted draft tube of relatively large 9 diameter surrounded by a relatively large number of 0 small diameter tubes which extend downwardly from an 1 upper common plane to a lower common plane where the 2 upper and lower terminal ends of the small diameter 3 tubes and draft tube, respectively, terminate. An

1 axial flow pump, provided with a rotating impeller,

2 which extends into the draft tube within which it is

3 partially housed, is located in the bottom of the re- A actor to maintain the reaction mixture in a well dis-

5 perεed state, and pump same up the draft tube; the

6 reaction mixture including the diluent, catalyst, and

7 reactantε which are directly introduced into the bot-

8 torn of the reactor, and a portion of the reaction

9 mixture which after upward transport through the 0 draft tube is recycled from the top of the reactor 1 downwardly through the small diameter tubes which 2 surround the draft tube. The outer walls of the re- 3 action vessel form a jacket through which a liquid A hydrocarbon coolant is circulated to remove the 5 exothermic heat of reaction via heat exchange contact 6 with the outer walls of the small diameter tubes, and 7 wall of the central draft tube. 8 Whereas this reactor has been commercially 9 used by the industry for many years for conducting 0 these types of reactions, the reactor is nonetheless 1 far less efficient than desirable. For example, 2 vortex "whirl" at the impeller exit, or cavitation 3 bubbles on the impeller, or both, impairs the A hydraulic efficiency of the pump to a level of about 5 fifty percent of that which is theoretically pos- 6 sible. This results in higher temperature surfaces 7 throughout the reactor and increased heat duty for 8 the reactor. For best operation, it is essential 9 that the temperature of a butyl reactor, due to the high temperature sensitivity of the butyl polymeriza- 1 tion process be maintained between about -130 F and -1A5°F, and as uniform as possible.

1 Polymer fouling is another serious problem

2 encountered in this type of reactor. Polymer depo-

3 sits upon and fouls heat transfer surfaces within the A reaction vessel; the polymer adhering tenaciously

5 to the metal surfaces as a continuous film, and in

6 severe cases as large masses of rubber. The reason,

7 or reasons, for this phenomenon is not well under-

8 stood though, it is known that mass fouling is

9 caused by local overheating. Nonetheless, polymer 0 fouling presents a serious problem and it has greatly 1 limited the usefulness, as well as the efficiency of 2 this type of reactor. For example, it is reported in 3 U.S. 2.999.08A that "—Commercial experience has de- A monstrated that mass fouling is a limiting factor of 5 prime importance with respect to the rate of produc- 6 tion of tertiary isoolefin polymers in that fouling 7 to an extent sufficient to inhibit adequate refri- 8 geration will occur at erratic and unpredictable 9 intervals within the range of about 10 to 90 hours"; 0 and that "—When this happens, it is necessary to 1 'kill* the reaction medium and clean out the reactor 2 before resuming the polymerization reaction," this 3 normally requiring 10 to 20 hours. At its best, in A any event, polymer fouling results in poor heat 5 transfer, and loss of efficiency in the process 6 operation. At its worse, the usefulness of the re- 7 actor is greatly curtailed. 8 For these reasons there presently exists a 9 need for a new, novel, or improved reactor; parti- 0 cularly a reactor wherein the components of the re- 1 action mixture are better dispersed, there is less 2 polymer fouling of the reactor, and better hydraulic 3 and thermal efficiency in the operation of the reac- A tor.

1 3. Objects

2 It is, accordingly, the primary objective

3 of this invention to supply this need.

A In particular, it is an object of this in-

5 vention to provide a novel, better mixed and more hy-

6 draulically efficient reactor with reduced fouling

7 tendency ; one particularly useful for conducting

8 polymerization reactions wherein liquid chemical raw

9 materials are catalytically converted into polymeric 0 solids or semi—solids, particularly elastomers. 1 A further and more specific object is to 2 provide a reactor, as characterized, for catalyti- 3 cally polymerizing liquified iεobutylene with a A liquified diolefin at low temperatures to form a 5 rubber—like polymer. 6 A. The Invention 7 These objects and others are achieved in 8 accordance with the present invention, embodying 9 apparatus which comprises a vessel formed by an 0 enclosing side, top and bottom wall, or walls, suit— 1 ably an enclosing side wall, or walls, a top cover 2 and bottom cover, with inlet and outlets for the 3 introduction of reactantε and catalysts, and the A removal of product, within which is contained (1) a 5 two—tube pass system, constituted of an inner or 6 center tube bundle through which a mixture or slurry 7 of polymerxzable monomers and catalyst is passed in 8 one direction, and recycled via an outer tube bundle in the opposite direction in essentially even flow distribution, (2) while the tubes of the center and . outer tubular bundles are maintained within a jacke- ted section, or sections of the reactor into which a coolant, or refrigerant, is injected and vaporized

SUBSTITUTESHEET

1 to remove the heat of reaction. The coolant, or

2 refrigerant, in heat exchange relationship with

3 the tubes thus removes the exothermic heat of reac- A tion from the polymerization mixture, and maintains

5 the polymerization mixture at uniformly low tempera-

6 ture. An even flow circulation of the slurry, which

7 . aids in maintaining the uniform low temperature, is

8 provided by the use of (3) a diffuser and (A) mixed

9 flow pumping system, with its impeller, by virtue of 0 which an adequate pressure head of even pressure pro- 1 file is developed across the entry sides of the cen- 2 ter tubes to maintain the even flow distribution 3 within the two—tube pass system at high circulation A rate. There is no vortex whirl at the exit of the 5 impeller-diffuser assembly, and no cavitation bubbles 6 as commonly associated with one-tube pass systems, 7 which employ a central draft tube and axial flow 8 pump. Improved mixing, high hydraulic efficiency, 9 and higher production rates with low polymer fouling, 0 are achieved. 1 The invention, and its principle of opera- 2 tion, will be more fully understood by reference to 3 the following detailed description of a specific and A preferred embodiment, and to the attached drawing to 5 which reference is made in the description. The var- 6 ious features and components in the drawing are re- 7 ferred to by numbers, similar features and components 8 in the different views being represented by similar 9 numbers. Where a subscript is used with a number, 0 the latter is to be taken in a generic sense, the 1 subscripts being used to indicate that the specific 2 unit referred to is constituted of more than one similar component .

SUBSTITUTE SHEET

1 In the drawing:

2 Figure 1 depicts a sectional side elevation

3 view of a polymerization reactor.

A Figure 2 is a section view taken along line

5 2-2 of Figure 1.

6 Figure 3 is a section view taken along line

7 3-3 of Figure 1.

8 Figure A is a section view taken along line

9 A-A of Figure 1. 0 Figure 5 is a section view taken along 1 line 5-5 of Figure 1. 2 Figure 6 is an enlarged, exploded view of 3 the lower portion of the reactor depicted by refer- A ence to Figure 1. 5 Figure 7 is an enlarged assembled view of 6 the reactor described in Figure 1. 7 Referring to Figure 1 there is shown a 8 polymerization reactor 10 of a vessel formed by an 9 enclosing side wall 11, formed of upper and lower 0 tubular sections ll _j » ll » respectively, bolted or 1 welded together to form a tubular shell, an enclosing 2 top cover 12 and bottom cover 13 each of which is 3 provided with inlets or outlets, or both, as subse- A quently described for the introduction or withdrawal 5 of catalyst, chemical raw materials or products. 6 A first tube bundle 20 is located at the 7 center of the vessel, the central tube bundle 20 8 containing a large number (n) of tubes 20^, θ —20 _n 9 oriented axially to the shell, and arrayed in a con- 0 venient pattern (e.g., as a triangle, square, or cir- 1 cular pattern as shown) , within the enclosing side 2 wall 11 of the vessel; and the first, or central 3 tube bundle 20 is surrounded by a second tube bundle A 30 containing a large number (n) of 30^, 302—30 _n

SUBSTITUTE SHEET

1 oriented axially to the shell and arranged in cir-

2 cular array (Figure 5). The terminal ends of the

3 tubes of tube bundles 20, 30 extend downwardly

A from an upper common plane, above which there is pro-

5 vided an enclosed upper reactor space, reactor head

6 or chamber 1A, to a lower common plane, below which

7 there is provided a lower reactor space, reactor head

8 or bottom chamber 15 (Figure 6) . A mixed flow pump

9 assembly A0 is mounted in the bottom chamber of the 0 vessel, the "impeller" or "pumping end" of the pump 1 being faced upwardly so that a liquid, or slurry, can 2 be pumped upwardly into a passageway of circuitous 3 shape, or design, containing a diffuser 60 which di- A rects the liquid flow into the tubes 20 _lt 20 ₂ —20 _n of 5 the central tube bundle 20. The liquid, or slurry, 6 after upward passage through tubes 20^, 20 ₂ —20 _n 7 exits into the upper chamber 1A, and a major portion 8 thereof is then recycled, or passed downwardly 9 through the tubes 30 ₂ , 30 ₂ —30 _n of tube bundle 30 and 0 returned to bottom chamber 15. The vessel is jacke- 1 ted and provided with an inlet, or inlets, for the 2 introduction of a coolant, or refrigerant, suitably a 3 liquid coolant, or refrigerant, and an outlet, or A outlets, for the removal of the coolant, or refrige- 5 rant, suitably as a vapor-liquid mixture to more 6 effectively remove the exothermic heat of reaction. 7 The amount of surface area provided by each 8 of the two tubular bundles for heat exchange ranges 9 generally from about 250 ft ² to about A, 000 ft ² , pre- 0 ferably from about 1,500 ft ² to about 2,000 ft ² . 1 Preferably, in a given installation the total heat 2 exchange capacity provided by the central tube bundle 3 ranges from about 3:1 to about 0.33:1, preferably A from about 1.2:1 to about 0.8:1 of that provided by

msτiruϊ

1 the outer tube bundle; and most preferably approxi—

2 mates the heat exchange capacity provided by the

3 outer tube bundle. Suitably the number, size and

A composition of the tubes of the central tube bundle

5 is the same as or approximates that of the outer tube

6 bundle.

7 The central tube bundle 20 generally con—

8 tains from about 20 to about 800 individual tubes

9 of internal diameter ranging from about 1 inch to

10 about 6 inches, preferably from about 30 to about

11 A00 individual tubes of internal diameter ranging 2 from about 2 inches to about A inches. The outer 3 tube bundle 30 generally contains from about 20 to A about 800 individual tubes of internal diameter rang- 5 ing from about 1 inch to about 6 inches, preferably 6 from about 30 to about A00 individual tubes of inter- 7 nal diameter ranging from about 2 inches to about A 8 inches. An arrangement of about 85 stainless steel 9 tubes having an internal diameter of about 3 inches 0 in the central tube bundle, and an outer tube bundle 1 of about 85 stainless tubes having an internal diame- 2 ter of about 3 inches, e.g., proves quite satisfacto- 3 ry. Liquid, or slurry, will flow at high rates far A more uniformly upwardly through the tubes of the cen- 5 tral tube bundle 20, and at high rates far more uni- 6 formly downwardly through the tubes of the outer tube 7 bundle 30 than possible by means of a single draft 8 tube of relatively large diameter as employed in an 9 existing reaction design. Moreover, the large number 0 of tubes located at the center of the reactor enables 1 the removal of the exothermic heats of reaction far 2 more efficiently than a central draft tube as in an 3 existing reactor design. A very uniform, and A constant temperature can be maintained throughout

SUBSTITUTESHEET

1 the reacting mixture. Generally, with this arrange-

2 ment , the temperature variation will be no greater

3 than about 1°F, and typically the temperature varia- A tion will be less than about 1°F.

5 For convenience, because of the length of

6 the reactor 10, the shell 11 of the reactor is fabri-

7 cated in a plurality of sections, generally in two

8 parts H _j _» 11 ₂ bolted or welded one to the other.

9 Likewise, for convenience, the jacket of the reactor 0 10 is generally comprised of a plurality of sections, 1 in this case an upper section and a lower section. 2 Thus, the shell 11 is formed into two parts Hi, H ₂ . 3 bolted or welded one part to the other and separated A by an internal baffle, or partition 16, through which 5 the tubes of tube bundles 20, 30 are extended. The 6 opposite ends of the two internal sections of the re- 7 actor 10 are closed by an upper closure member, or 8 plate A, and a lower closure member, or plate 5. A 9 unique feature of this reactor is that it utilizes a 0 cooling jacket, or a plurality of jacket sections to 1 force full boiling of the coolant in the jackets, and 2 at the same time force nearly equal heat transfer 3 rates in each of the jackets, providing optimum heat A transfer performance. 5 In a conventional commercial butyl reactor, 6 the reactor jackets are chilled by thermosyphoning 7 liquid ethylene from a single head drum above the 8 jackets to the bottom of each of the jackets, and 9 taking vapor and liquid from the top of the jackets 0 back to the head drum. This technique induces a 1 rapid circulation rate of cold liquid from the head 2 drum to the jackets and back again. The impact of 3 this high liquid rate is two-fold. First, a low or A non-boiling zone is set up at the lower portion of

1 each jacket where the heat transfer coefficient is

2 over one order of magnitude lower than for full boil-

3 ing heat transfer. Second, the large quantity of

A subcooled ethylene entering the jacket increases the

5 density of liquid and vapor in the jackets, raising

6 the average boiling temperature of the ethylene in

7 the jackets. Because the bottom jacket is much lower

8 in elevation than the top jacket (therefore having a

9 much larger subcooled non-boiling zone) , a much lar- 0 ger percentage of heat is transferred by the top 1 jacket. 2 Th.e situation can be improved by providing 3 two head drums at different elevations so that the A degree of subcooling of the refrigerant, e.g., 5 ethylene, at the entry point at the bottom of the 6 jackets is essentially equivalent. This however re- 7 quires additional equipment which still leaves the 8 jacket with a non-boiling zone at the bottom. The 9 subcooled ethylene must be heated to the boiling 0 point by the slurry with low heat transfer coeffi- 1 cxent. 2 In the reactor of this invention, this 3 problem is solved by feeding the fresh coolant, i.e., A fresh ethylene liquid, to the reactor system via 5 inlet 8 to the top of the bottom jacket, and feeding 6 liquid from a single head drum (not shown) via inlet 7 17 to the top of the top jacket (via a throttling 8 control valve) . The fresh liquid coolant is heated 9 to its boiling point as it descends through the vapor-liquid froth in the jacket. As a result both jackets operate in full boiling heat transfer, and the liquid rate is controlled to the top jacket to establish the same froth density in both the top and

1 bottom jackets. This in effect provides the best

2 overall heat transfer coefficient and the lowest pos-

3 sible average coolant temperature in the two jackets. A Fresh coolant, e.g., liquid ethylene, is

5 thus introduced into the lower jacket, or lower co -

6 partmented section of the reactor via one or more in—

7 lets, e.g., inlet 8, and removed therefrom via one or

8 more outlets, e.g., outlet 7. Coolant from a head

9 drum is fed into the top jacket via one or more 0 inlets, e. g., inlet 17, and removed therefrom via 1 one or more outlets, e.g., outlet 18. The top cover 2 12, which is bolted to the upper side of the shell 3 11, is provided with a product, or slurry outlet 9, A one or more thermowells, e.g., a thermowell 6, and 5 safety valve nozzle 3. A portion of the liquid, or 6 slurry, from upper chamber 1A is removed via outlet 9 7 as product, and a portion recycled to lower chamber 8 15 via passage through the tubes of the outer tube 9 bundle 30. Coolant introduced into the jacketed 0 portions of the vessel contacts the outer walls of 1 the tubes of tube bundles 20, 30 to absorb the heat 2 of reaction, the coolant exiting the jackets via out- 3 lets 7, 18. A The two-pass reactor design, or design 5 created via the use of two tube bundles, provides 6 considerably more heat transfer area than previous 7 designs utilizing a draft tube (more than double) , 8 the additional surface allowing operation at a 9 much lower heat flux, thereby reducing the tempera- 0 ture gradient across the tubes. This results in a 1 more uniform, cooler slurry temperature, which 2 reduces polymer fouling rate. With the mixed flow 3 pump and diffuser design, the slurry can also be cir- A culated at a high rate (A0% to 50% greater than that

MSΠΠΠE

1 of the conventional reactor utilizing a draft tube

2 and axial flow impeller) , this increasing the amount

3 of shear applied to the slurry; this effect also re- A άucing the polymer fouling rate. Thus, because poly—

5 mer slurries are non-Newtonian, and thin with

6 increasing shear, the higher circulation rate results

7 in a lower slurry viscosity and a higher slurry side

8 heat transfer coefficient. Due to the improved heat

9 transfer capability produced by the higher circula-

10 tion rate, slurry temperature is reduced and the 1 polymer fouling rate significantly lowered. 2 In the reactor 10, the velocity of the 3 liquid, or slurry, will drop only slightly, e.g., A about A5 percent, of the tube velocity when the 5 liquid, or slurry, enters into a reactor head, i.e., 6 chamber 1A, 15. This compares to about a 70 to 75% 7 drop in the conventional draft tube design. This 8 further reduces the propensity for mass fouling as 9 commonly observed within these zones in conventional 0 reactors. 1 The bottom, or central bottom chamber 15 2 houses a passageway of circuitous shape, or design, 3 a mixed flow pump assembly A0 and a diffuser 60, the A impeller end of which is projected upwardly into the 5 passageway. Referring for convenience first to 6 Figure 6, it will be observed that the bottom cover 7 13, which in this view is removed from reactor 10, is 8 secured thereto via bolt connections. A centrally 9 located vertically oriented projection, or nozzle 51 0 of generally tubular design is bolted to the tube- 1 sheet 30, and removable therefroπ Upon, and affixed 2 via an edge to the inside wall of the axial opening 3 through the nozzle 51 there is circumferentially A arrayed a plurality of vanes — in this instance

SUBSTITUTE SH

1 seven (7); 60 _lt 60 ₂ , 60 ₃ , 60^, 60 ₅ , 60g, 60y —

2 constituting a diffuser 60; also depicted by refer-

3 ence to Figure A. Each of the vanes in its vertical A orientation is angled and shaped, and each is separa-

5 ted or spaced apart one from another over the cross-

6 section of the passageway within which they are con-

7 tained to redirect or change the direction of flow of

8 a liquid, or slurry, impinged thereupon to a verti—

9 cally upward, and substantially linearly direction 0 over the area defined by the bottom cross-section of 1 the tubes of tube bundle 20. The bottom cover 13 is 2 also provided with one or more thermowell nozzles, 3 e.g., a thermowell nozzle '52, one or moe catalyst A inlets, e.g., a catalyst inlet 53, and large bottom 5 opening 5A within which the impeller end of the mixed 6 flow pump A0 can be projected; and a plurality of 7 flange openings by virtue of which both the cover and 8 pump can be bolted in place. 9 Continuing the reference to Figure 6, for 0 convenience, the mixed flow pump A0 is constituted of 1 a bearing housing Al, a connecting drive shaft A2, an 2 impeller A3 mounted to the upper end of the drive 3 shaft, and a nose cone AA of conical shape, the apex A of which is faced upwardly. The lower portion of the 5 impellar A3 and drive shaft A2 are contained within a 6 housing A5 of tubular shape, the upper inside portion 7 of the tube being provided with a circumferential in- 8 wardly bulged ridge A5ι, guide support members A6^, 9 ^2 _* A6 , A6Λ and openings A9. Feed inlet passages 0 A7 provide a means for the introduction of feed to 1 the reactor, and a pump seal A8 is provided at the 2 location wherein the drive shaft A2 connects through 3 bearing housing Al with motor drive shaft and motor, A not shown.

smisTE SHEET

1 The impeller A3, as best shown by reference

2 to Figure 3, is constituted of a plurality of blades

3 — in this instance five (5); ^3^, ^3 ₂ . A3g, A3^, A A3 — circumferentially, evenly spaced apart and

5 located near the upper terminal end of the shaft A2.

6 The blades A3 are peripherally mounted and arrayed

7 about an expanded base section of cone AA located

8 upon the upper end of the shaft A2. A diffuser cone,

9 or nose cone AA rests upon, and is affixed to the ex— 0 panded base section. Activation of the motor (not 1 shown) rotates the drive shaft A2, the impeller A3, 2 and nose cone AA. In place, the mixed flow pump 3 assembly A0, as shown 5 e.g., by reference to Figure A 7, provides a continuous channel in which the slurry, 5 or reaction mixture is received and propelled upward— 6 ly by action of the impeller blades A3. The arrange- 7 ment, and location of the pump assembly A0, notably 8 the impeller A3 and nose cone AA, the diffuser 60, 9 and contour of the channel is such as to eliminate 0 void spaces, this in effect reducing if not 1 altogether eliminating polymer fouling in this zone. 2 In operation, referring specifically to 3 Figure 7, a catalyst is introduced into the reactor A 10 via inlet 53. Hydrocarbon feed and diluent are 5 introduced into the reactor 10 via inlets A7, 6 the feed entering into the reactor through a "feed 7 slot" area bounded on the upper side by the lower 8 face of the rotating impeller A3 and on the lower 9 side by the bottom cover, or suction cover 13 0 creating in effect a "mole hill." The reactant 1 hydrocarbons and diluent, after chilling, are 2 brought via cavities and tubes through the cover 13 3 to the feed slot area, this permitting low pressure A drop and improved cooling as the fluid flows through

su πm SHEE

1 the annular space around the shaft to the feed slot

2 area. Recycle slurry descends through the tubes of

3 tube bundle 30 passing around and then upwardly via A openings 55ι, 55 ₂ to pick up and admix with the feed

5 and diluent in the feed slot area; and catalyst

6 introduced into the reactor via one or a plurality

7 of inlets, e.g., inlet 53. Slurry is picked up at

8 the feed slot area by the rotating blades of impeller

9 A3 and forced upwardly, the liquid exiting, or 0 leaving the mixed flow impeller A3 at an angle in- 1 clined away from the axis of rotation. The angle of 2 flow is, of course, distinctly different from that of 3 an axial flow impeller, as conventionally used, and A this type of flow produces a greater pressure head. 5 The direction of flow, on exiting the impeller, is 6 altered by the vanes of the diffuser 60 which re- 7 directs, or turns the flow of liquid back toward the 8 axis of rotation, and stops the spinning flow, or 9 vortex whirl, which normally occurs at the impeller 0 discharge. Thus, the mixed flow pump initially pumps 1 the liquid at an angle away from a straight line 2 drawn through the impeller inlet and point of dis- 3 charge to the tubes of tube bundle 20, i.e., at an A angle greater than 0°, generally from about 5° to 5 about 75°, and the flow is then redirected by the 6 diffuser 60 such that the net effect is that it is 7 essentially axially ejected on discharge to the tube 8 bundle 20. The slurry is pumped upwardly through 9 tubes 20 at high rates in a far more even flow dis- 0 tribution, and there is no cavitation on the impel- 1 ler blades, or essentially no cavitation at process 2 conditions .

SUBSTITUTE SHET

1 By mounting and integrating the nose cone

2 AA with the rotating impeller A3 stagnant zones are

3 eliminated with the result that polymer fouling is A virtually eliminated. In previous designs, where a

5 nose cone is mounted on the diffuser rather than the

6 impeller this is not the case, and stagnant zones

7 give rise to polymer fouling; this eventually

8 restricting circulation and pump impeller movement

9 which causes the pump to overload and/or seize. A 0 surprising and unexpected additional benefit due to 1 the presence of the rotating nose cone AA is that hy— 2 draulic efficiency is increased, and there is an 3 enhancement in the mixing of feed and catalyst in the A area of the impeller. The arrangement of the impel- 5 ler A3 and diffuser 60 eliminates vortex whirl at the 6 impellar-diffuser outlet, this in itself greatly 7 increasing the hydraulic efficiency of the system, 8 i.e., from about 50% to about 80%. This increase in 9 hydraulic efficiency is particularly important since 0 increased hydraulic efficiency lowers pump heat input 1 to the slurry for a given circulation rate, and 2 decreases the heat duty for the reactor. 3 The use of a mixed flow impeller design is A of particular importance in combination with the two 5 tube pass system, providing a high pump pressure 6 head, with the development of a high circulation 7 rate. The circulation rate developed is at least 50% 8 greater than that of which an axial flow type pump is 9 capable, at the required pressure head. The mixed 0 flow pump performance is matched to the hydraulic 1 characteristics of the vessel to obtain the desired 2 circulation rate and to essentially completely elimi- 3 nate the cavitation bubbles at the impeller, as is A normally associated with the impeller designs

1 employed in conventional reactors. This is accom-

2 pushed in part by rotation of an impeller, e.g., of

3 diameter ranging from about 1 foot to about A feet, A at specific speeds, N _g , ranging from about 2,000 to

5 10,000, where N _g = Ny/ Q; and wherein N = speed

_H 3/A

6 (RPM) , Q = flow (GPM) and H = head (feet); typical

7 speeds ranging from about 200 rpm to about 1000 rpm;

8 matching the blade angles of the impeller to the

9 fluid velocity and velocity of impeller rotation so 0 that the resultant velocity vector and the blade 1 angles are the same. The surprising and unexpected 2 benefit of totally eliminating the cavitation bubbles 3 on the impeller is to provide a significant reduction A in the viscosity of the rubber slurry, and thus a 5 slower warmup rate of the reactor because of a higher 6 slurry side heat transfer coefficient. Cavitation at 7 the impeller causes dissolved inert gases to be 8 pulled from the solution to form a separate bubble 9 phase in the reactor. The bubble phase increases the 0 viscosity of the reactor slurry. 1 The vessel herein described can be effec- 2 tively used to carry out any process for conducting 3 polymerization or condensation reactions where liquid A chemical feeds are catalytically converted into 5 polymeric solids, semi-solids, or liquids, especially 6 elastomers, and particularly elastomers as produced 7 in a butyl polymerization process, i.e., a reaction 8 wherein isobutylene is polymerized with a diolefin in 9 the presence of a Friedel-Crafts catalyst at low 0 temperature to produce butyl rubber. It can provide 1 (1) excellent mixing of feeds and catalyst into a 2 circulating reacting mixture, (2) highly uniform cir- 3 culating fluid temperature, and constant temperature.

SUBSTITUTE SHEET

throughout the reacting mixture, (3) excellent heat removal from the circulating fluid, and (A) ability to handle fouling slurries without a rapid loss in performance. These effects can be provided at high production rates, with low fouling. It is apparent that various modifications and changes can be made without departing the spirit and scope of the invention.

SUBSTITUTE SHEET