Compositions – Preservative agents – Anti-oxidants or chemical change inhibitants
Patent
1998-08-03
2000-11-07
Warden, Jill
Compositions
Preservative agents
Anti-oxidants or chemical change inhibitants
252403, 252404, 25218229, 25218312, 585 5, 585 3, 585 4, C09K 1516, C09K 1522, C09K 1508, C07C 720, C10L 720
Patent
active
061432059
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to mixtures which, in addition to vinyl-containing monomers for preventing their premature polymerization during purification or distillation, also contain at least one nitroxyl and at least one nitro compound, a process for purifying or distilling such monomers without their premature polymerization taking place, and the use of mixtures which contain nitroxyl and nitro compounds for inhibiting the premature polymerization of vinyl-containing monomers.
It is known that many unsaturated compounds tend to polymerize, as a rule by free radical polymerization, when the temperatures increase. For example, vinylaromatic compounds, such as styrene or .alpha.-methylstyrene, must be stabilized with suitable compounds in order to prevent premature polymerization during distillative purification of the crude products obtained on a large industrial scale. Usually, these stabilizers or polymerization inhibitors are added before the purification step to the crude products to be distilled. In spite of this measure, considerable amounts of polymers are still obtained. In individual cases, especially when operational faults occur, complete polymerization of the monomers or monomer mixtures present may occur during purification or distillation. This results in high costs owing to the very complex purification and the loss of production.
USSR patents 1,027,150, 1,558,888 and 1,139,722 describe the stabilization of styrene by the use of nitroxyl or bisnitroxyl compounds.
Japanese publication Hei 1-165 534 discloses I-piperidyloxy derivatives as polymerization inhibitors for styrene. U.S. Pat. No. 35 3,733,326 describes the inhibition of the polymerization of vinyl monomers by using free radical precursor compounds.
Nitro compounds, such as 2-nitro-p-cresol or 2,6-dinitro-p-cresol, are mentioned as polymerization inhibitors in U.S. Pat., No. 4,086,147, 4,105,506 and 4,252,615. U.S. Pat. No. 4,132,602 and 4,132,603 disclose the use of halogenated nitroaromatic compounds for inhibiting the polymerization of vinylaromatics during their distillative working-up.
However, all the stated nitro compounds have only a small stabilizing effect and therefore have to be used in relatively high concentrations. If the relatively high toxicity of these nitrocompounds is also taken into account, their use constitutes a considerable potential danger for the operating personnel and the environment.
The use of inhibitors based on N-nitrosodiphenylamine in combination with dinitrocresol derivatives in the distillation of vinylaromatics under reduced pressure is described in U.S. Pat. Nos. 3,988,212 and 4,341,600. When oxygen is present, polymerization of vinylaromatic compounds on heating can be prevented, according to U.S. Pat. Nos. 4,466,904 and 4,468,343, by using an initiator based on phenothiazine, 4-tert-butylcatechol, 2,6-dinitro-o-cresol or 2,6-dinitro-p-cresol with either phenyldiamine or 4-tert-butylcatechol. According to EP 240 297, polymerization of vinylaromatics on heating can be suppressed by using hydroxylamine derivatives and dinitrophenol. However, a disadvantage of these inhibitor systems is the strong dependence of their efficiency on the oxygen content, i.e. these additives are likely to have different inhibiting effects under the conditions of the purification or distillation, in accordance with the nonuniform distribution of the residual oxygen in the corresponding unit. However, this makes the controlled use more difficult.
U.S. Pat. No. 5,254,760 describes mixtures of nitroxyl and nitro compounds for stabilizing vinylaromatic compounds during purification or distillation. The nitroxyl and nitro compounds are used in amounts of from 5 to 95% by weight and from 95 to 5% by weight, based on the total amount of the mixture. Since nitroxyl compounds are as a rule very expensive, this stabilizing additive, which must be added continuously in a certain amount to the crude product before working-up, constitutes a cost factor which is not negligible.
Furthermore, there is the danger that, when polymeri
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Aumuller Alexander
Sutoris Heinz Friedrich
Uhr Hermann
BASF - Aktiengesellschaft
Cole Monique T.
Warden Jill
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