Nov. 5, 1946. A. J. GRACIA METHOD OF REMOVING INHIBITORS 'Filed Aug. 7, 1941 iiilvur,rv,’iI.5 ; x 2,410,779 Patented Nov. 5, I v 2.410.719‘ - > . ivra'rnon or nmuovmo mnmrrons 1 I ' ‘ Albert J. Gracia, Cuyahoga Falls, Ohio, assignor ‘ to Wingfoot Corporation, Akron, Ohio, a cor poration oi’ Delaware 1 ‘ > Application August 7, 1941, Serial No. 405,803 8 Glaims. (Cl. 202—39) This invention relates to an improved method of removing polymerization inhibitors from mon omeric substances prior to the employment of the latter in the preparation of polymers. More par 2 I to distill the butadiene. The inhibitors usually, employed are highly soluble in these “high boll ers” andit is found that as much as 50 tons of ticularly, the invention relates to the removal of polymerization inhibitors from butadiene, a con-, inhibited butadiene may be distilled through 5 gallons of solvent before renewal is indicated. Among inhibitor solvents which may be thus employed are the following: dlbutyl citrate, di stituent of many polymers. It is well known that the substance butadiene enters into the composition of many copolymers, particularly those having rubber-like properties . does not vaporize at the temperatures required 10 butyl phthalate, butyl stearate, dlethyl phthalate, tributyl phosphate, tricresyl phosphate, and other and hence important as substitutes for natural similar esters often employed as plasticizers in rubber. Monomeric butadlene is a gas at nor synthetic resins and the like. In general, it may mal temperatures and is customarily stored in be said‘ that any stable ester having a boiling large tanks under pressure, where it is main point between 500 and 700° F. at atmospheric‘ tained in liquid form. Since it possesses the 15 pressure may be employed, the chief requisite property of self-polymerization, itis necessary to being that the solvent shall not be volatile un incorporate therein a polymerization inhibitor der the conditions of distillation. , in order that the substance shall not polymerize The method may be carried out in any suit during storage. Necessarily, also, this inhibitor able apparatus, one such being illustrated in the must be removed before the butadiene is sub 20 accompanying drawing in which a boiler l is sur :lected to polymerizing conditions, otherwise poly rounded at its lower end with a steam jacket merization is prevented or is very slow and any 2 into which steam is admitted through a pipe rubber formed will have a low extrusion plas 3 and condensate is removed ‘through an outlet ticity indicating a dimcultly workable'materlal. 4. In the lower part of the still is a body of Since the butadiene is a gas under normal con 25 high-boiling solvent 5 into which liquid buta ditions, it would appear that the butadiene could diene is conducted through a line 6, the ?ow be be readily distilled from the inhibitor, which is ing controlled by means of a ?oat control ‘I. The usually a solid. However, difficulties are encoun -butadiene or other monomer is admitted at the tered in performing such distillation ‘and it is an bottom of the still and bubbles up. through the object of the present invention to overcome such 30 solvent body 5 where it loses its inhibitor content. ' The vapors of the puri?ed monomer are then led‘ When the butadlene is distilled from the ‘in off through the duct 8 to a condenser. hibitor, this inhibitor, such as phenyl beta naph When the butadiene or ether monomer con thylamine, concentrates in the undistllled bu tains phenyl beta naphthylamine gas inhibitor, tadiene and gradually builds up until the limit and at present this is the substance most widely 01’ solubility is reached, whereupon some solid in employed as a polymerization inhibitor, tests of hibitor is thrown down. Continued distillation the distilled material by means of ultra violet then results in sublimation of the inhibitor in light show almost no ?uorescence when the pres thecondenser where, of course, it contaminates ent method is employed. Fluorescence under the distilled butadiene. The presence of Water in, 40 ultra violet light is an extremely sensitive test the still does not overcome this dimculty but, for phenyl beta naphthylamine. Butadiene dis instead, complicates the situation due to the fact tilled without the aid of a solvent or in the that water induces the formation of some small presence of water shows pronounced ?uorescence amount of polymerized butadiene. The water in the condenser, thus indicating that the dis- _ does not wet the inhibitor and the solid inhibitor tillatlon was entirely ine?‘ective for the purpose and polymer form a gum which ?oats at the hu indicated, namely, to remove inhibitor prior. to tadiene-water inter phase and tends to clog up polymerization of the butadene. and coat the still boiler. As will be apparent, the method is also appli It has now been found, in accordance with the cable to the distillation of other normally gase» principles of this invention, that all of these ous monomeric materials intended for use in poly dii?cultles may be avoided and a clean separa merlzations, such as vinyl chloride, the solvent tion of monomer and inhibitor e?ected ii" there employed being selected so as to have a boiling is placed in the still a quantity of a high-belle point well above the temperature necessary to ing liquid, such as one of those commonly used effect distillation of the particular monomer un a.“ plass.ilr.~irers. Such a liquid may be any which 55 der treatment. di?lculties. _ _ . 2,410,779 ' 4 . ' . . 3 - While there has been described above a pre ferred embodiment of the invention, it will be apparent to those skilled in the art that various modi?cations and changes may be made therein without departing from the spirit of the inven ‘ the vapors of the puri?ed butadiene from the sur g' face of the body of liquid and condensing the ution or from the scope of the appended claims. I claim: A _ ' 1. A method of removing a. polymerization in vapors. ~ 5. A method of removing substantially vall phenyl beta naphthylamine from butadiene which comprises bubbling the butadiene containing the , phenyl beta naphthylamine up through a body of high-boiling solvent for the phenyl beta naphthyl amine to dissolve substantially all of the latter hibitor from a normally gaseous monomeric sub from the butadlene, leading 03 the vapors of 10 stancewhich comprises bubbling the monomer the puri?ed butadiene from the surface of the containing the inhibitor up through a body of body of liquid and condensing the vapors. high-boiling solventfor, said inhibitor, leading off 6. A method of removing a normally solid pcly- _ the vapors of the puri?ed monomeric substance 7 merization inhibitor from butadiene which com from the surface of the body of liquid and con prises bubbling the butadiene containing the in 15 densing the vapors. hibitor up through a body of liquid dibutyl citrate 2. A method of removing a polymerization in to remove substantially all of the inhibitor from - hibitor from a normally gaseous monomeric sub the butadiene. leading off the vapors of the puri stance which comprises bubbling the monomer ?ecl butadiene from the surface of the body of through a heated . ' containing the inhibitor‘up dibutyl citrate and condensing the vapors. ' body of high-boiling solvent for said inhibitor to 20 7. A method of removing a normally solid’poly dissolve substantially all or the inhibitor there merization inhibitor from butadiene which com from, leading off the vapors of the puri?ed prises bubbling the butadiene containing the in fromthe surface of the monomeric substance hibitor up through a body of liquid dibutyl phthal body of liquid and condensing the vapors. . ate to remove substantially all of the inhibitor 3. A method of removing a normally solid poly 25 from the butadiene, leading oi! the vapors of merization inhibitor from a normally gaseous the puri?ed butadiene from the surface of the monomeric substance which comprises bubbling body of dibutyl phthalate and condensing the the monomer containing the inhibitor'up through ‘ vapors. “ ' a body of high-boiling solvent for said inhibitor 8. A method of removing a normally solid poly to dissolve substantially all the inhibitor there 30 merization inhibitor from butadiene which com from, leading 01! the. vapors of the puri?ed prises bubbling the butadiene containing the in monomeric substance from the surface of they hibitor up through a body of liquid tricresyl phos body of liquid and condensing the vapors. ~ 4. A method-of removing a normally solid poly merization inhibitor from butadienewhich com prises bubbling‘ the butadiene containing the in hibitor up through a body of high-boiling sol- '. vent for said inhibitor to dissolve substantially all of the inhibitor out of the butadien , leading oi! phate to remove subs _ tially all of the inhibitor from the butadiene, leading off the vapors of the puri?ed butadiene from the surface of the body ' oi’ tricresyl phosphate and condensing the vapors. ALBERT J. GRACIA.