US2495147A

US2495147A - Coagulation process and apparatus

Info

Publication number: US2495147A
Application number: US677588A
Authority: US
Inventors: John N Street
Original assignee: Firestone Tire and Rubber Co
Current assignee: Bridgestone Firestone Inc
Priority date: 1946-06-18
Filing date: 1946-06-18
Publication date: 1950-01-17
Anticipated expiration: 1967-01-17

Description

Jan. 17, 1950 J. N. STREET 2,495,147

COAGULATION PROCESS'AND APPARATUS Filed June 18, 1946 2 Sheets-Sheet 1 IN VEN'roQ Jab /V. Jireef ATTORNEYS Jan. 17, 1950 Filed June 18, 1946 J. N. STREET COAGULATION PROCESS AND APPARATUS 2 Sheets-Sheet 2 INVENTOR 56a M Jiree? ATTORNEYS Patented Jan. 17, 1950 2,495,147 COAGULATION PROCESS AND APPARATUS John N. Street, Akron, Ohio, minor to The Firestone Tire & Rubber Company, Akron. Ohio, a corporation of Ohio Application June 18, 1946, Serial No. 677,588 2 Claims. (01. 260-98) This invention relates to the coagulation of dispersions of rubber-like and resinous materials. More particularly, it relates to the coagulation of such materials in the form of a crumb. The invention includes the process and preferred apparatus for carrying out the process.

Prior to this invention it has been customary to coagulate rubber-like and resinous materials from a dispersion of the same by forming a single coagulated mass of all the coagulable material in the dispersion. Because the mass of coagulum isrubber-like or' resinous, it has been difficult or impossible to separate uncoagulated dispersion and coagulant from the coagulum'bec'ause some of it is enclosed in pockets inthe coagulum."

Furthermore, it has been dimcult or impossible to wash the 'coagulum free of such aqueous impurities and to dry the mass.

According to this invention the coagulum is obtained as a crumb; i. e., as discrete particles which are easily filtered and washed and thus separated from aqueous impurities. These particles are quickly dried and are easily handled in further processing. The crumb is obtained by introducing the dispersion of resinous or rubberlike material under the surface of a bath of coagulant. The dispersion is brought into contact with the coagulant as discrete droplets so that the coagulum is produced as crumb. A continuous stream of the dispersion may be used which is broken up into droplets as it comes into contact with the coagulant, or prior thereto. The stream of dispersion may be aspirated with air or other gas if desired. The separated portions of the stream are coagulated out of contact with one another while surrounded by coagulant, and

- the coagulum obtained is in the form of separated particles or crum The-size of the crumb particles may vary from the size of sand to the size of a pea, for example. If the coagulum has a gravity greater than the coagulant solution, the crumb will sink to the bottom of the vessel in which the coagulation is carried out. If it is of lighter gravity, it will rise to the top. The invention relates more particularly to the production of crumb which rises to the top and includes maintaining the particles of crumb in a nonagglomerated or segregated condition and the removal of them from the top of the coagulant bath. Thus, the process may advantageously be carried out on a continuous basis with removal of the crumb from the bath as it is formed. Alternatively, the bath may be agitated suiliciently to produce a uniform slurry of the crumb and coagulant which may be removed from the top or bottom or any other convenient part 0! the bath, and the operation may be continuous if desired. I

A preferred type of apparatus for carrying out the process uses a hollow agitator with hollow agitating arms with an orifice at or near the end of each through which the dispersion is introduced into the coagulating bath. If the crumb is allowed to rise to the surface of the bath and it is tacky (a valuable characteristic in synthetic rubbers), agitation at the surface, preferably just prior to the removal of the crumb from the bath, maintains the particles of the crumb in a segregated condition and facilitates its removal from the bath.

The crumb is advantageously removed from the surface or the bath soon aiter it is formed. It the latex is introduced through the arms 01 a revolving agitator, or other agitator means is used so that a swirling motion is imparted to the entire coagulant bath; and ii the gravity or the crumb is so low that it rises to the surface of the coagulant (which is the case with most rubber-like materials and many resinous materials) the crumb can readily be collected from the surface of the bath by providing an overflow outlet and suitable bellies-e. g., screen baflles which do not impede the flow oi the liquid-or by directing a jet of air or other gas or a liquid against the crumb to direct it to the overflow outlet. Any suitable means for accomplishing this may be employed. A mechanical sweep may be used satisfactorily even though the body of liquid is not swirling.

Theinvention is applicable to the coagulation of synthetic rubbers obtained as a dispersion by emulsion polymerization or copolymerization. The rubber may be a polymer of butadiene or isoprene. It may be a copolymer of (1) a coniugated diene-for example, butadiene, isoprene, 2-

'cyanobutadiene, cyclopentadiene, piperylene, di-

methylbutadiene, 2-methyl-1,3-pentadiene, etc.-- and either (2a) a vinyl aromatic compound-for example, styrene, alpha-methylstyrene, nuclearsubstituted styrenes, dichlorostyrene, vinylnaphthalene, vinylbiphenyl, vinylcarbazole, 2-vlnyl-5- ethylpyrldine, 2-ethyl-5-vinylpyridine, etc+-0r (2b) a monomer having the formula when R is hydrogen, methyl, ethyl, propyl or chlorine and X is --CN, CONH2, -COR' 0r -COOR' and R is an alkyl group which contains from one to no more than about flve carbon atoms.

The invention is not limited to the ride, butadiene and assign? coagulation of dispersions of such rubber-like materials but includes also the coagulation of disperslons of other rubber-like materials, regardless of how the dispersions are obtained. Dispersions of resinous materials similarly produced by emulsion polymerization or copolymerization, such as, for example, the polymerization of styrene, vinyl esters such as vinyl chloride, etc., ethylene, tetrafluorethylene, esters of acrylic acid and derivatives thereof such as methyl methacrylate, etc., vinylpyridine, etc., and the copolymerization of vinyl chloride and vinylidine chlostyrene in suitable proportions to produce a resin, etc., or dispersion of resinous material which may be obtained in any other manner, may. likewise, advantageously be coagulated by the process of this invention. The invention, likewise, includes the coagulation of natural rubber latices. Such dispersions are mentioned as illustrative and not in a limiting sense.

The invention applies generally to coagulation with any aqueous coagulant which may, for example, be a water solution of an acid (for example, sulfuric acid, hydrochloric acid or acetic acid. etc.) or a water solution of a salt (for excoagulant acts rapidly.

Ordinary precautions will be used, as, for example. operating in the absence of iron salts in the treatment of rubber-like copolymers of butadiene and styrene.

The invention will befurther described in connection with the accompanying drawings, in

coagulation tank I is 2 driven by a belt 3 the top, bottom or back side of the arm. A multiplicity of orifices may be provided in a single arm. The dispersion introduced through the feed line 9 collects in the feed tank In and is fed from the tank through the shaft 2 into the arms a continuous or a discontinuous stream, but due to the shear forces set up, the efiect is to produce discrete particles. The centrifugal force set up by the rotation of the agitator and the pull of the coagulant on the orifices draws the dispersion through the agitator into the coagulant. Added pressure may be provided by maintaining the feed tank I0 under pressure.

As illustrated, the tank I0 rotates with the agitator. The centrifugal force of the liquid in the tank causes the the shaft 2 so that the dispersion is aspirated as it is introduced into the coagulant. Whether aspirated or not, the dispersion is supplied in the coagulant, the crumb particles rise to the surface of the tank and are indicated at i2.

If the crumb particles are tacky (and rubberlike particles usually are) it may be advantageous coagulant, a jet of air from pipe 20 is blown across the surface of the bath into the mouth of the overflow.

pipe 20 directs the particles of crumb to the overflow outlet Only a small amount of the crumb escapes the action of the air jet or other collection means and completes the circuit of the tank. Most of the crumb is removed from the coagulant bath soon after it is formed.

The mixture of crumb and mother liquor or coagulant which passes out through the overflow a desired coagulant concentration in the tank.

The channel 26 simply serves to support the agitator.

liquid to build up against" with a diameter 01 28 I There is fed through the of the agitator. The plate 52 directs the fresh coagulant from within the cone into the path of the droplets of the dispersion as they are released through the orifices in the ends of the arms 46. The centrifugal force generated by the swirling of-- the liquid outside of the cone 50 makes the level of the liquid outside of the cone higher than that inside, somewhat as indicated. By reducing the area or the surface of the liquid in which the crumb particles collect, the crumb particles are more easily subjected to the action of the blades of the agitator l4 and are more completely removed by the air jet l5.

Modifications in the design of the equipment may be made without departing from the scope of the invention. The dimensions of the coagulation tank and its shape may be altered. The number of agitator arms on the hollow agitator shaft may be varied. Other means for introducing the dispersion into the coagulating bath may be utilized. The proportions of the equipment may be varied. Although rotations of the agitator arms at speeds of 600 and 1200 R. P. M. and even as low as 100 or 200 R. P. M. have proved satisfactory, this may be varied, the

length of the arm having a definite relation to the speed of rotation which might be desirable. Good results have been obtained with the agitator arms submerged a foot under the surface of the bath, but this may be varied. The speed of rotation of the agitator arms, their length, and the depth of their submergence are controlling factors in the pressure at which the dispersion is introduced. The concentration of the Concentrations of 1 sions of different rubber-like copolymers introduced into the coagulant at a depth of about 1 foot. The size and number of the orifices may be varied. Large volumes of dispersion may be through relatively small orifices when the speed of rotation of the agitator arms is high. Eflective operation of the process is not dependent upon any swirling movement being imparted to the body of the coagulant. Thus, the process and design of the apparatus are subject to wide variations. Crumb of various rubber-like copolymers was satisfactorily produced in equipment such as illustrated in Figs. 3 and 4 with a metal tank 5% feet in diameter, using a cone inches at the surface and employing a jet for removing the crumb from the surface of the coagulant through the overfiow outlet.

The following illustrates more particularly one operation and refers to a single arm although this may be duplicated any desired number of times in a single coagulating bath. The vessel may-be of the general type illustrated in Fig. 1 or Fig. 3.. To start, the vessel is charged about half full with a 1 per cent solution of alum in water. The shaft is rotated at 600 R. P. M.

shaft the latex of a syn- (30 per cent solids, by weight) of butathetic rubber butadiene to 40 parts of acrylonitrile, or other ratio to produce a rubber-like copolymer. The shaft may, for example, have an opening inch in diameter throughout its length, but closed at the bottom end. Each arm may be about 3 inches long and be provided with an orifice inch in diameter-at the end, .the curvature of the arm being approximately that shown in Fig. 4.

. persion are sheared into droplets The arm may, for example, be immersed 20 inches under the surface of the coagulant. The rubber will be coagulated as a fine crumb which will float to the surface and may be removed through a suitable outlet as described. The alum coagulant is replaced as used to maintain the ratio of the volume of the latex to the volume of the alum about 1 to 1 or somewhat less. Other ratios which vary materially from that suggested give satisfactory results, depending upon the concentration of the coagulant, the solids content of the dispersion, etc. In this manner synthetic rubber may be produced at the rate of about 30 to 40 pounds per hour from a single arm.

If the bath is agitated sufficiently to maintain the crumb suspended in the coagulant, a mixture of the crumb and coagulant may be drawn off at any desired level of the tank, with recirculation ofthe liquid after separation of the crumb. The separation may be effected by filtering, centrifuging, etc.

The process is applicable to the coagulation of dispersions of rubber-like and resinous materials generally with any coagulant. Modifications may be made in the apparatus as well as in the process without departing from the scope of the invention which is defined in the appended claims.

What I claim is:

1. The process of coagulating a dispersion which on coagulation produces a rubber-like product, which process comprises maintaining a bath of coagulant, feeding a plurality of streams of the dispersion to rapidly and continuously changing locations under the surface of the bath of the coagulant, whereby the streams of the diswhich on coagulation product a crumb of rubber-like particles, allowing the resulting crumb to rise to the surface of the body of coagulant, breaking up at the surface any agglomerates formed therefrom, and then separating the resultant material from th surface of the body of coagulant.

2. The process of coagulating a dispersion which on coagulation produces a rubber-like product, which process comprises maintaining a bath of coagulant, feeding a plurality of streams of the dispersion to rapidly and continuously changing locations under the surface of the bath of the coagulant, whereby the streams of the dispersion are sheared into droplets which on coagulation produce a crumb of rubber-like particles. I

JOHN N. STREET.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 490,525 Werner June 24, 1893 734,985 Spindler July 28, 1903 1,320,323 Drueker et a1. Oct. 28, 1919 1,505,479 Maitland Aug. 19, 1924 2,074,988 O'Brien et al Mar. 23, 1937 2,239,753 Martin Apr. 29, 1941 2,366,460 Semon Jan. 2 1945 2,392,542 Matuszak Jan. 8, 1946 2,393,208 Waterman et al. Jan. 15, 1946 2,408,128 Squires et al Sept. 24, 1946 2,426,127 Thomas et a1 Aug. 19, 1947 2,431,478 Hill Nov. 27, 1947 2,459,748 Johnson Jan. 18, 1949 Certificate of Correction Patent No. 2,495,147

JOHN N'. STREET It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows:

Column 6, line 39, for the word product read produce;

and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 5th day of September, A. D. 1950.

THOMAS F. MURPHY,

Assistant Oommialz'oner of Patents.

Claims

1. THE PROCESS OF COAGULATING A DISPERSION WHICH ON COAGULATION PRODUCES A RUBBER-LIKE PRODUCT, WHICH PROCESS COMPRISES MAINTAINING A BATH OF COAGULANT, FEEDING A PLURALITY OF STREAMS OF THE DISPERSION TO RAPIDLY AND CONTINUOUSLY CHANGING LOCATIONS UNDER THE SURFACE OF THE BATH OF THE COAGULANT, WHEREBY THE STREAMS OF THE DISPERSION AREA SHEARED INTO DROPLETS WHICH ON COAGULATION PRODUCT A CRUMB OF RUBBER-LIKE PARTICLES, ALLOWING THE RESULTING CRUMB TO RISE TO THE SURFACE OF THE BODY OF COAGULANT, BREAKING UP AT THE SURFACE ANY AGGLOMERATES FORMED THEREFROM, AND THEN SEPARATING THE RESULTANT MATERIAL FROM THE SURFACE OF THE BODY OF COAGULANT.