Chemistry of hydrocarbon compounds – Product blend – e.g. – composition – etc. – or blending process... – With nonhydrocarbon additive
Reexamination Certificate
1999-08-10
2002-05-28
Yildirim, Bekir L. (Department: 1764)
Chemistry of hydrocarbon compounds
Product blend, e.g., composition, etc., or blending process...
With nonhydrocarbon additive
C585S832000, C585S004000, C208S002000, C208S0480AA, C208S348000, C208S349000
Reexamination Certificate
active
06395943
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a process for inhibiting the polymerization of vinyl aromatic compounds such as styrene during its distillation. The process involves adding to the vinyl aromatic compound a mixture of at least one nitroso compound such as N,N′-di-2-butyl-N,N′-dinitroso-1,4-diaminobenzene and a dinitrophenol compound such as dinitrocresol, and optionally a stabilizer compound such as an N,N′-dialkyl substituted 1,4-diaminobenzene.
BACKGROUND OF THE INVENTION
Styrene is one of several vinyl aromatic compounds which has considerable commercial utility. Styrene is polymerized into polystyrene which is a clear, readily colored and easily fabricated plastic with many uses. The efficiency of the polymerization process is dependent on the purity of the monomer starting material. Since the processes for producing styrene, and other vinyl aromatic compounds, will contain various reaction products including benzene, toluene, etc., the mixture is distilled to separate these undesirable contaminants. Unfortunately, the temperatures required for distillation, typically 90° C. to about 150° C., leads to the polymerization of the vinyl aromatic compounds. In order to minimize or prevent polymerization of the vinyl aromatic monomer, it is common to add a polymerization inhibitor to the distillation mixture.
The art discloses a variety of compounds which are claimed to inhibit polymerization. These include U.S. Pat. No. 4,050,993, which discloses the use of N,N-dinitroso-methylaniline as a polymerization inhibitor. U.S. Pat. No. 3,988,212, which disclose the use of N-nitrosodiphenyl amine in combination with dinitro-o-cresol. U.S. Pat. No. 4,013,580, which discloses the use of N-nitroso aniline derivatives. U.S. Pat. No. 4,941,800, which discloses the use of a mixture of dinitro-p-cresol and N-nitroso-diphenyl amine. U.S. Pat. No. 4,654,451, which discloses alkyl substituted p-nitroso phenols in combination with p-nitroso phenol. U.S. Pat. No. 5,034,156 which discloses N-nitrosophenyl-hydroxylamine plus hydroquinone monomethyl ether. U.S. Pat. No. 5,396,004, which discloses a phenylenediamine compound plus a hydroxyalkylhydroxyl-amine compound. U.S. Pat. No. 5,254,760, which discloses 1-oxyl-2,2,6,6-tetramethylpiperidine plus an aromatic nitro compound. U.S. Pat. No. 4,929,778, which discloses a phenylenediamine compound plus a hindered phenol compound. U.S. Pat. No. 5,312,952, which discloses the use of the reaction product of a C
9
-C
20
alkyl phenol with sulfuric and nitric acid and, optionally, an aryl or alkyl-substituted phenylenediamine. WO9503263, which discloses 3,5-di-tert-butyl-4-hydroxy-N,N-dimethyl benzyl amine. EP-697386-A2, which discloses 4-acetylamino-2,2,6,6-tetramethyl piperidine N-oxyl in combination with 4-nitroso phenol. JP0701910-A, which discloses phosphite compounds, nitrosoamine compounds or phenol compounds. JP05310815-A, which discloses the ammonium salt of N-nitrosophenyl hydroxylamine. JP03149205-A, which discloses nitrosophenols plus dicyclohexylammonium nitrate. J01226858-A, which discloses the use of substituted nitrosobenzene. U.S. Pat. No. 4,967,027, which discloses p-nitroso phenol plus p-t-butyl catechol. J59029624-A, which discloses the use of N-nitroso compound, e.g., N-nitroso-diphenylamine and a catechol, e.g., p-t-butylcatechol.
Finally, U.S. Pat. No. 5,869,717, discloses the use of N-nitroso derivatives of unsubstituted or dialkyl substituted phenylenediamine.
Applicants have now discovered that N-nitroso derivatives of unsubstituted or dialkyl substituted phenylenediamine (diaminobenzene) can be combined with unsubstituted or alkyl substituted dinitrophenolic compounds.
SUMMARY OF THE INVENTION
As stated, this invention relates to a process for inhibiting the polymerization of a vinyl aromatic compound during its distillation. One embodiment of the process involves adding to the vinyl aromatic compound an effective amount of a mixture of: 1) a nitroso compound selected from the group consisting of
and mixtures thereof, where R and R, are each independently hydrogen, cyclohexyl, phenyl or an alkyl group having from 1 to 18 carbon atoms and 2) a nitrophenol compound selected from the group consisting of dinitrocresol, dinitrophenol, 2-sec-butyl-4,6-dinitrophenol, and mixtures thereof.
Another embodiment of the invention is a process for inhibiting the polymerization of a vinyl aromatic compound comprising adding to the compound an effective amount of a mixture of: 1) a nitroso compound selected from the group consisting of
and mixtures thereof, where R and R
1
are each independently hydrogen, cyclohexyl, phenyl or an alkyl group having from 1 to 18 carbon atoms; 2) a nitrophenol compound selected from the group consisting of dinitrocresol, dinitrophenol, 2-sec-butyl-4,6-dinitrophenol and C
1
to C
18
alkyl substituted nitrophenols and mixtures of, and 3) a stabilizer selected from the group consisting of phenylenediamine, dihydroxy phenol, diphenylamine, alkyl substituted phenylenediamines, phenol, C
1
to C
18
alkyl substituted phenols and mixtures thereof.
These and other objects and embodiments will become more evident after a detailed description of the invention.
DETAILED DESCRIPTION OF THE INVENTION
The present invention relates to a process for inhibiting the polymerization of a vinyl aromatic compound during its distillation. Vinyl aromatic compounds to which the instant process is applicable include styrene, alpha-methyl styrene, divinylbenzene, vinyl toluene, vinyl naphthalene and polyvinyl-benzene
In most cases this process will be practiced during distillation wherein air is not present. Anaerobic conditions are desired to stabilize vinyl aromatic compounds (inhibit polymerization). These conditions require the special inhibitors of the current invention.
The process generally involves adding a mixture of at least two inhibitor compounds to the vinyl aromatic compound during its distillation. One inhibitor is selected from the group consisting of 1) a nitroso compound selected from the group consisting of
and mixtures thereof, where R and R
1
are each independently hydrogen, cyclohexyl, phenyl or an alkyl group having from 1 to 18 carbon atoms; 2) a nitrophenol compound preferably selected from the group consisting of dinitrocresol, dinitrophenol, 2-sec-butyl-4,6-dinitrophenol and C
1
to C
18
alkyl substituted nitrophenols and mixtures thereof, and 3) a stabilizer selected from the group consisting of phenylenediamine (1,4-diaminobenzene), dihydroxy phenol, diphenylamine, alkyl substituted phenylenediamines, phenols, C
1
to C
18
alkyl substituted phenols and mixtures thereof.
In structures I and II, the R and R
1
groups can each independently be hydrogen, cyclohexyl, phenyl or an alkyl group having from 1 to 18 carbon atoms. Illustrative of the alkyl groups which can be used are methyl, ethyl, propyl, butyl, pentyl, octyl, decyl, sec-butyl, iso-propyl, cyclohexane and isopentyl. Included in structures I and II above are the o, m and p isomers. Preferred compounds encompassed within structure I and II are the following compounds having structure IA and IIA.
The amines used to obtain the nitroso compounds have structures (IV) and (V) below.
The reaction of nitrous acid with an amine is well known in the art. A specific example of the reaction using compound IV (above) is detailed in U.S. Pat. No. 5,869,717. An outline of this method is included here for completeness. Generally, the amine is reacted with nitrous acid at a temperature of about −10° C. to about 120° C. The nitrous acid can be added or it can be generated in situ by reacting sodium nitrite with hydrochloric acid. Further, in the case of a diamine, the amount of nitrous acid added will determine whether the mono or dinitroso compounds are obtained. However, even if a 1:1 stoichiometric amount of nitrous acid:amine is added, a mixture of the mono and dinitroso compounds may still be obtained.
In some cases it is preferred to add a thermal stabilizer to the mixture of inhibitors. A thermal stabilizer can inhibit
Frame Robert R.
Kurek Paul R.
Molinaro Frank B.
Tolomei John G.
UOP LLC
Yildirim Bekir L.
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