3,527,822 United States Patent 0 cc Patented Sept. 8, 1970 1 2 column with an added-oxygen atmosphere is impractical, 3,527,822 hazardous, and results in sizable production of by DIVINYLBENZENE POLYMERIZATION products. INHIBITORS Herbert L. Benson, Jr., Houston, Tex., assignor to Shell One method for puri?cation of divinylbenzene is .de Oil Company, New York, N.Y., a corporation of scribed in US. 3,217,052 issued Nov. 9, 1965 to Meek Delaware et al., wherein separation is effected by forming a solid No Drawing. Filed Apr. 16, 1969, Ser. No. 816,791 complex of divinylbenzene with .monovalent copper or Int. Cl. C07c 7/08, 7/18; B01d 3/34 silver, separating this solid complex, and then decompos U.S. Cl. 260--666.5 6 Claims ing this complex. This process is illustrative of the cum 10 bersome and costly methods presently used to effect divinylbenzene separation and puri?cation. Clearly, simple ABSTRACT OF THE DISCLOSURE vacuum distillation, which would be made possible by the Certain nitroso derivatives of phenol and naphthol ef discovery of polymerization inhibitors effective in the fectively inhibit divinylbenzene polymerization at elevated absence of air, would be preferable. temperatures in the absence of oxygen (air) and permit STATEMENT OF THE INVENTION the separation and puri?cation of divinylbenzene by vacuum distillation. In accordance with the present invention, polymeriza tion of divinylbenzene is inhibited in the relative absence of oxygen with substantially improved ef?ciency by the BACKGROUND OF THE INVENTION 20 use of selected nitroso derivatives of'phenol and naphthol as inhibitors. Inhibition of divinylbenzene polymerization Divinylbenzene is an important compound, ?nding by the compounds of this invention considerably mini commercial utility as a cross-linking agent in the polym mizes many of the disadvantages generally inherent in erization of styrene and copolymers of styrene. Morever, divinylbenzene polymerization inhibitors used heretofore. it can be copolymerized with various other monomers, 25 Inhibitor compounds of the present invention, because of such as chlorostyrene, butadiene, isoprene, cyclopenta their ability to substantially retain e?iciency in the absence diene, methyl methacrylate, vinyl acetate and other vinyl of oxygen, permit the use of vacuum distillation to effect derivatives to yield polymers with properties differing separation and puri?cation of divinylbenzene. from the homo-polymers of these compounds. ) DETAILED DESCRIPTION OF THE INVENTION It is known that divinylbenzene polymerizes readily. This polymerization is further characterized in liquid Amino and nitroso derivatives of phenol and naphthol mixtures which contain divinylbenzene as a major con generally have some inhibiting effects on divinylbenzene stituent by the formation of a partial or complete gel fol polymerization. Generally, however, they are little, if any, lowing the polymerization of but a minor part of the more effective than conventional inhibitors in the absence divinylbenzene. For example, a 95% solution of divinyl of oxygen. In accordance with ‘the present invention, four benzene gels when about 2 to 3% of the divinylbenzene nitroso derivatives of phenol and naphthol have been has polymerized. This gel is insoluble in common organic found which are markedly more effective than conven solvents. ‘ tional inhibitors and other nitroso and amino compounds Certain divinylbenzene polymerization inhibitor com in the relative absence of oxygen. These preferred inhibi pounds are known. 4-tert-butylcatechol and hydroquinone tors are S-methyl-4-nitroso-2-isopropylphenol (MNIP), are the most generally accepted inhibitors. These inhibitors 1-nitroso-2-naphthol (1N2N), 2 - nitroso - 1 - naphthol are effective only in the presence of oxygen. US. 2,445, (2N1N) and 5' methoxy-Z-nitrosophenol (MNP). Among 941 issued July 27, 1948 to Dreisbach describes the use these inhibitors, 5~methyl-4-nitroso-2-is0propylphenol, 1~ of from about 0.5% to about 1% of 2,4-dichloro-6 nitroso-2-naphthol and Z-nitroso-l-naphthol are preferred. nitrophenol as a divinylbenzene polymerization inhibitor A most preferred inhibitor is 5~methyl-4-nitroso-2-iso in the relative absence of oxygen but requires that large propylphenol. amounts of steam be present. This patent emphasizes the The amount of polymerization inhibitor added can greater polymerization sensitivity of divinylbenzene com vary widely. Generally, the degree of stabilization is pro pared to styrene. portional to the amount of inhibitor added. Inhibitor The need for divinylbenzene polymerization inhibitors concentrations between about 0.03 gram per 1000 grams which are effective in the absence of air becomes critical of divinylbenzene and 5 grams per 1000 grams of divinyl in the separation and puri?cation of divinylbenzene. benzene have generally proven suitable, depending on the Divinylbenzene is generally produced by the dehydro temperature of the divinylbenzene and the degree of in genation of a mixture of the isomers of diethylbenzene. hibition desired. Often, this reaction is iodinatively effected. Reaction prod During vacuum distillation of divinylbenzene-contain ucts generally contain a mixture of divinylbenzene, ethyl ing mixtures,.the temperature of ‘the reboiler is prefer vinylbenzene, unreacted diethylbenzene, a small quantity ably maintained at from about 185° F. to about 215° F. of naphthalene, and some impurities. by controlling reboiler pressure at from about 15 mm. to Vacuum distillation is a preferred method for separa about 40 mm. of Hg. Under such conditions, inhibitor tion of unstable organic liquid mixtures. This general 60 concentrations from about 0.1 gram to about 1 gram/1000‘ method, however, has heretofore been unsuitable for g. divinylbenzene are suitable with concentrations of from separation of mixtures containing divinylbenzene, such about 0.2 to about 0.5 g./ 1000 g. divinylbenzene being as, for example, the reaction mixture described above, preferred. since the partial pressure of oxygen in a vacuum distilla The inhibitors according to the invention are effective tion column is too low for conventional polymerization in all concentrations of divinylbenzene. inhibitors to be effective. Vacuum distillation, as a means The following examples are provided to further illus of purifying divinylbenzene is therefore rendered impracti trate the use of the inhibitors according to this invention. cal due to divinylbenzene polymerization, gel formation Example 1 and column plugging. Distillation at atmospheric pressure requires distillation kettle temperatures which are too This example illustrates the relative effectiveness of the high to be practical. Operating a vacuum distillation inhibitors according to the invention at low oxygen con 3,527,822 4 centrations. It also illustrates the relative ineffectiveness Example 4 of conventional inhibitors, and nitrogen-containing in This example illustrates the use of the inhibitors ac hibitors not according to the invention at low oxygen cording to the invention to make possible the separation concentrations. and puri?cation of divinylbenzene by distillation. Samples of a feedstock comprising about 95% wt. An 8-inch diameter x 30 feet long distillation column divinylbenzene (DVB), about 4.5% wt. ethylvinylben was packed with Goodloe packing. Column feedstock zene, and about 0.5% wt. naphthalene containing various comprised about 85% wt. divinylbenzene, about 5% wt. concentrations of conventional inhibitors, inhibitors ac ethylvinylbenzene, and about 10% wt. naphthalene and cording to the invention, and other nitrogen-containing other impurities. About 50,000 lbs. of this feed were inhibitors ‘were maintained‘at 160° F. in the presence of charged to the center of this column at a rate of about varying amounts of oxygen (air). The length of time 50 lbs. per hour. Divinylbenzene and naphthalene were required to effect gelling of the mixtures (gel time) was taken off as a bottom product at a rate of about 40 lbs./ measured. Data shown in Table 1 indicate that with access to large amounts of air, inhibitors according to the inven hour. Re?ux rate was about 20 lbs/hour. The columns tion offer no marked advantage over conventional inhibi were operated at a kettle temperature of about 195° F., tors. However, when air availability is cut to one tenth and a kettle pressure of about 210 Hg. The divinyl its original "value, inhibitors according to the invention benzene-naphthalene bottom product was then fed at'a are markedly superior to conventional inhibitors. Other rate of about 30 lbs/hour to a second column of similar nitrogen-containing inhibitors fail to sustain inhibition design operating at a similar pressure, where 95 % purity activity in the absence of oxygen (air). 20 divinylbenzene was taken overhead at a rate of about TABLE I High Oxygen, Air/Divinylbenzene, Low Oxygen, Air/DVB, V/V = 0.06 V/V = 0. 6 35-40% V Air 56% V Air Inhibitor Inhibitor _ cone, Gel time, Relative cone, Gel times, Relative Inhibitor p.p.m. wt; hours gel time 1 p.p.m. wt. hours gel time 1 None _______________________________________ __ 0 3, 5 13 3.0 29 4-tert-butylcatechol (TB 0) _ _ __ ______ _ _ 1, 100 27 (100) 1, 000 10. 5 (100) Hydroquinone ___________________________ __ 1, 000 18 67 950 7. 5 71 5-methoxy-2-nitrosophenol (MN P) __ ____ __ 1, 100 25 93 1, 000 22. 5 215 1-nltroso-2-naphthol (1N 2N) _____ __ 1, 000 27 258 2-nitroso-1-naphthol (2N 1N) _________________ _ _ 1, 000 28 267 5-methyl-4-nitroso-2-isopropylphenol (MNIP) 1,000 43 410 - -- as as 4 . am i no . .met y 1 p eno _ , 950 - 9 86 ?-amino-l-naphthol _____ __ lAssume (TBC) = 100; all runs made at 160° :1; 0. 1 ° F. Example 2 20 lbs/hour. ‘Reflux rate was about 25 lbs/hour. The four inhibitors according to the invention were each This example illustrates the effect (on gel time) of tested, one at a time. 250 ppm. wt. of inhibitor was increasing the amount of inhibitor and also illustrates the added to the feed to the ?rst column and was present effectiveness of the inhibitors according to the invention in the feeds to the second column.