MXPA97005244A - Stabilizers for the prevention of training degoma in gasol - Google Patents

Abstract

The use of aliphatic nitroxide compounds alone or in combination with aromatic amines, such as substituted phenylenediamines or phenolic antioxidants, provides an effective way to avoid oxidative degradation and gum formation in gasolines, especially pyrolysis and coking gasolines.

Description

STABILIZERS FOR THE PREVENTION OF FORMATION OF GUM IN GASOLINE The present invention relates to the use of aliphatic nitroxides either alone or with synergistic co-additives as stabilizers to prevent the formation of gum deposits in gasoline. Gasoline, widely used as fuel for internal fuel engines, is a mixture of different hydrocarbons. Gasoline is prepared by a number of different procedures. The current composition of a gasoline, is determined in part by the methods of prduction used to formulate it and may also vary with the desired end use to be used for fuel. Among the production methods are: fractional distillation of crude oil to prepare gasoline of first distillation, cracking of high molecular weight hydrocarbons, either thermally to prepare coker gasoline or catalytically in a FCC (fluidized catalytic cracker); coupling of low molecular weight propyl and butyl fractions to form dimate gasoline; it can be reformed catalytically to produce high octane gasoline from lower octane feedstocks; and as a byproduct of lower olefin production (ethylene, propylene, etc.) to form pyrolysis gasoline or "pygas".

Quite independent of the method used to produce gasoline, stability especially by oxidative degradation is a serious problem. Gasoline as well as other hydrocarbon fuels are known to form adherent deposits or gums both in storage and under current conditions of use. These gummy residues can cause severe problems: for example, these deposits can cause the valves to stick and these precipitates can cause the filters to clog. These problems can adversely affect both combustion performance and fuel handling. Among the different types of gasolines, pygas and fissured gasoline (both fissure and FCC) are the most tending to oxidation and formation of deposits. Work in the gasoline stabilization area has been developed for many years. A common class of stabilizer for this purpose are phenylenediamines (PDA) used alone or in admixture with other materials. The patents of the U.S.A. Nos. 3,322,520 and 3,556,748 illustrate that phenylenediamine is usually N, N'-disubstituted with substituents that are already aliphatic or aromatic. The patent of the U.S.A. No. 5,509,944 illustrates that mixtures of PDA, hindered phenols and dimethyl sulfoxide (DMSO) perform better than PDA alone. Phenylenediamines do not work well as stabilizers when gasoline has a higher or higher acid number (> 0.1 mg KOH / g gasoline). The patent of the U.S.A. No. 5,169,410 illustrates that the use of a strongly basic organic amine can by preferential reaction with acidic portions increase the stabilizing efficiency of phenylenediamine. The patents of the U.S.A. Nos. 2,305,676 and 2,333,294 demonstrate that the use of N-substituted p-athynylphenol derivatives and certain polyamines are effective in stabilizing a variety of gasolines. The patent of the U.S.A. No. 4,648,885 discloses that a mixture of polyamines and N, N-diethyl-hydroxylamine is an effective stabilizer for distilling fuel oil or fuel oil. GB 1 316 342 suggests diaryl nitroxides as valuable compounds to avoid undesired oxidation of hydrocarbons such as gasoline, lubricating oils, mineral oils or waxes. However, despite these efforts to avoid oxidation of gasoline and resinous or gummy deposits that cause fouling during gasoline use, there remains a need to stabilize gasoline more effectively. This need is greater in the area of less stable pyrolysis and coker gasolines, due to its high level of unsaturation and in gasolines that have a high level of acid impurities. Nitroxides have been known and have been used for a variety of applications for many years. They have been used as polymerization inhibitors for several vinyl monomers. The patent of the U.S.A. No. 5, 254,760 illustrates the use of a stable nitroxyl compound, in conjunction with an aromatic nitro compound to inhibit the polymerization of styrene and other vinyl aromatic compounds. The patent of the U.S.A. No. 5,322,960 disclose mixtures of phenol nitroxide and phenothiazines as an acrylate polymerization inhibitor. The use of nitroxides to stabilize butadiene and other low molecular weight olefins during purification is recorded in US Pat. No. 4,670,131. Under specific conditions as illustrated in U.S. Pat. No. 5,412,047, the stable nitroxide radicals can act to control the molecular weight poly-dispersity and produce "active" polymers. Stable nitroxides have also been used as oxidation catalysts as seen in U.S. Pat. Nos. 5,495,045 and 5,136,103. The patent of the U.S.A. No. 5,496,875 illustrates the use of nitroxides as light stabilizers and thermal stabilizers for polymers. Nothing in the prior art illustrates the use of aliphatic nitroxides as stabilizers for gasoline. Since aliphatic nitroxides are not basic (or neutral) they do not react with any acidic components in gasoline as described in US Pat. No. 5,169,401. Thus, aliphatic nitroxides do not require the use of an amine coadivant or the phenylenediamines. The object of this invention is to provide a method by which gasoline, particularly gasoline produced by cracking or as a by-product of olefin synthesis (pygas) can be stabilized against oxidative degradation and deposit formation. The present invention relates to the use of aliphatic nitroxides as an additive for gasoline blends that will inhibit oxidation and prevent the formation of gums or other deposits when processing and storing gasoline. The gasoline mixture may contain, but is not limited to, one or more of the previously discussed gasoline, first distillation, coker, FCC, dimate, reformed or pyrolysis. In particular, highly unstable coker and pyrolysis gasolines are effectively stabilized by the use of the aliphatic nitroxide stabilizers. The present process for the prevention of oxidative degradation and gum or deposit formation comprises: adding to gasoline subject to thermally or oxidatively induced degradation an effective stabilizing amount of an aliphatic nitroxide compound. The effective stabilizing amount of the aliphatic nitroxide compound is from 0.05 to 10,000 ppm, preferably 0.1 to 100 ppm, more preferably 0.5 to 25 ppm.

Preferably, the aliphatic nitroxide is an aliphatic hindered amine nitroxide. The aliphatic nitroxide can be of several different kinds. Aliphatic nitroxides (often hindered amine) are effective in the present process. In particular, the hindered amine nitroxyl radicals are generally preferred, that is to say compounds having at least one NO * group in which the * asterisk denotes an unpaired electron and the nitrogen atom is also flanked by two carbon atoms, to none of which hydrogen atoms are connected. These flanking carbon atoms can also be connected by various bridging groups to form cyclic structures such as for example piperidines with six members, piperazines, pyrrolidines with five members and the like, as exemplified, but not limited by the list below: tert-butyl nitroxyl, l-oxyl-2, 2,6,6-tetramethylpiperidine, l-oxyl-2, 2,6,6-tetramethylpiperidin-4-ol, l-oxyl-2, 2,6,6-tetramethylpiperidine -4-one, l-oxyl-2, 2,6,6-tetramethyliperidin-4-yl acetate, l-oxyl-2, 2,6,6-tetramethylpiperidin-4-yl 2-ethylhexanoate, l-oxyl-2 , 2,6,6-6-tetramethylpiperidin-4-yl stearate, l-oxyl-2, 2,6,6-tetramethylpiperidin-4-yl benzoate, l-oxyl-2,2,6,6-tetramethylpiperidin-4-yl 4-tert-butylbenzoate, bis (l-oxyl-2, 2,6,6-tetramethylpiperidin-4-yl) succinate, bis (l-oxyl-2, 2,6,6-tetramethylpiperidin-4-yl) adipate, bis (l-oxyl-2, 2,6,6-tetramethylpiperidin-4-yl) sebacate, bis (l-oxyl-2, 2,6,6-tetramethylpiperidin-4-yl) n-butylmalonate, bis (l- oxyl-2,2,6,6-tetramet ilpiperidin-4-yl) phthalate, bis (l-oxyl-2, 2,6,6-tetramethylpiperidin-4-yl) isophthalate, bis (l-oxyl-2, 2,6,6-tetramethylpiperidin-4-yl) terephthalate, bis (l-oxyl-2, 2,6,6-tetramethylpiperidin-4-yl) hexahydro-terephthalate, N, N-bis (l-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) adipamide, N- (l-oxyl-2, 2,6,6-tetramethylpiperidin-4-yl) caprolactam, N- (l-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) dodecyl succinic acid, 2, 4,6-tris- (l-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) cyanurate, 2,4,6-tris- [N-butyl-N- (l-oxyl-2, 2 , 6,6-tetramethylpiperidin-4-yl] -s-triazine, l-oxyl-2, 2,6,6-tetramethylpiperidin-4-yl 3,5-di-tert-butyl-4-hydroxyhydrazine or 4, 4'-ethylenebis (l-oxyl-2, 2,6,6-tetramethylpiperazin-3-one). Especially preferred is the aliphatic hindered amine nitroxide bis (l-oxyl-2,2,6,6-tetramethyl-piperidin-4-yl) sebacate, which exhibits excellent activity at a concentration of 5 ppm and shows activity even at concentrations of 1 ppm and lower. Also preferred is 1 -oxy-2, 2, 6, 6-tetramethylpiperidin-4-ol.

Another embodiment of the present invention relates to a process wherein the effective stabilizing system comprises a synergistic mixture of an aliphatic nitroxide compound and an aromatic amine, particularly a substituted phenylene diamine or a phenolic antioxidant or mixture of aromatic amine and phenolic antioxidant. Examples and preferences for the aliphatic nitroxide have been described above. Preferably, the aromatic amine is a substituted phenylene diamine. Particularly preferred aromatic amines are: N, N'-di-isopropyl-p-phenylenediamine, N, N'-di-sec-butyl-p-phenylenediamine, N, N'-di-sec-butyl-o-phenylenediamine, N, N'- bis (1,4-dimethylpentyl) -p-phenylenediamine, N, N'-bis (l-ethyl-3-methylpentyl) -p-phenylenediamine, N, N'-bis (1-methylpentyl) -p-phenylenediamine,, N'-dicyclohexyl-p-phenylenediamine, N, N'-dipheny1-p-phenylenediamine, N, N'-di- (2-naphthyl) -p-phenylenediamine, N-isopropyl-N'-phenyl-p-phenylenediamine, N-sec-butyl-N'-phenyl-o-phenylenediamine, N- (1,3-dimethylbutyl) -N'-phenyl-p-phenylenediamine, N- (1-methylheptyl) - '- phenyl-p-phenylenediamine , N-cyclohexyl-N'-phenyl-p-phenylenediamine, N, N'-dimethyl-N, N'-di-sec-butyl-p-phenylenediamine; N, N'-di (1,4-dimethylpentyl) -o-phenylenediamine; diphenylamine, N-allyldiphenylamine, di- (4-isopropoxyphenyl) mine, N-phenyl-1-naphthylamine, N-phenyl-2-naphthylamine, octylated diphenylamine,, p'-di-tert-octyldiphenylamine, di- (4-methoxy) phenyl) amine, Tert-octylated N-phenyl-1-naphthylamine, or a mixture of mono- and dialkylated ter-butyl- / tert-octyl-diphenylamines. Especially preferred amines are N-phenyl-1-naphthylamine, N-phenyl-2-naphthylamine, octylated diphenylamine, p, p'-di-tert-octyldiphenylamine, a mixture of tert-butyl- / tert-octyl-diphenylamines mono- and dialkylated or N, N'-di (2,4-dimethylpentyl) -p-phenylenediamine. Some phenolic antioxidants of interest are listed below. Alkylated Monophenols 2, 6-di-tert-butyl-4-methylphenol, 2,6-di-tert-butylphenol, 2-tert-butyl-, 6-dimethyl-phenol, 2,6-di-1¡ ^ -butyl-4-ethyl-phenol, 2,6-di-tert-butyl-4-n-butylphenol, 2. § di-tert-butyl-4-i-butylphenol, 2,6-di-cyclopentyl-4-methylphenol, 2- (beta-methylcyclohexyl) -4,6-dimethylphenol, 2,6-di-octa-decyl-4-methylphenol, 2,4,6-tri-cyclohexylphenol, 2,6-di-tert-butyl-4-methoxymethylphenol, o-tert-butylphenol . Alkylidene-Bisphenols 2,2-methylene-bis- (6-tert-butyl-4-methylphenol), 2,2'-methylene-bis- (6-tert-butyl-4-ethylphenol), 2,2'-methylene -bis- (4-methyl-6- (alpha-methyl-cyclohexyl) -phenol), 2,2'-methylene-bis- (4-methyl-6-cyclohexylphenol), 2,2'-methylene-bis- ( 6-nonyl-4-methylphenol), 2,2 '-methylene-bis- (4,6-di-tert-butylphenol), 2,2'-ethylidene-bis- (4,6-di-tert-butylphenol) , 2,2'-ethylidene-bis- (6-tert-butyl-4- or -5-isobutylphenol), 2,2'-methylene-bis- (6- (alpha-methylbenzyl-4-nonylphenol), 2, 2'-methylene-bis- (6- (alpha, alpha-di-ethylbenzyl) -4-nonylphenol), 4,4'-methylene-bis- (2,6-di-tert-butyl-phenol), 4, 4'-methylene-bis- (6-tert-butyl-2-methylphenol), 1,1-bis- (5-tert-butyl-4-hydroxy-2-methyl-phenol) -butane, 2.6 -di- (3-tert-butyl-5-methyl-2-hydroxy-benzyl) -4-methyl-phenol, 1,1,3-tris- (5-tert-butyl-4-hydroxy-2-methylphenyl) -3-n-dodecyl) -mercaptobutane, ethylene-glycol-bis- [3, 3-bis- (3'-tert-buty1-4 '-hydroxyphenyl) -butyrate], bis- (3-tert-butyl-4) -hydroxy-5-methylphenyl) -dicyclopentadiene, bis- [2- (3'-tert-butyl-2'-hydroxy) 5'-methyl-benzyl) -6-tert-butyl-4-methyl-phenyl] -terephthalate. The phenolic antioxidant of particular interest is selected from the group consisting of n-octadecyl 3,5-di-tert-butyl-4-hydroxyhydrocinnamate, neopentantetrayl tetrakis (3,5-di-tert-butyl-4-hydroxyhydrocinnamate), n-octadecyl3,5-di-tert-butyl-4-hydroxybenzyl-phosphonate, thiodiethylene bis (3,5-di-tert-butyl-4-hydroxyhydrocinnamate), 1,3,5-trimethyl-2,4,6- tris (3,5-di-tert-butyl-4-hydroxybenzyl) benzene, 3,6-dioxaoctamethylene bis (3-methyl-5-tert-butyl-4-hydroxyhydrocinnamate), 2,6-di-tert-butyl- p-cresol, 2,2'-ethylidene-bis (4,6-di-tert-butylphenol), 1,1,3, -tris (2-methyl-4-hydroxy-5-tert-butylphenyl) utane, 3 , 5-di- (3, 5-di-tert-butyl-4-hydroxybenzyl) mesitol, hexamethylene bis (3,5-di-tert-butyl-4-hydroxy-hydrocinnamate), 1- (3, 5-di -tert-butyl-4-hydroxyanilino) -3,5-di (octylthio) -s-triazine, N, N'-hexamethylene-bis (3,5-di-tert-butyl-4-hydroxyhydrocinnamamide), ethylenebis [3 , 3-di (3-tert-butyl-4-hydroxyphenyl) butyrate], octyl 3,5-di-tert-butyl-4-hydroxy-benzylmercaptoacetate, bis (3,5-di-tert-butyl-4-hydroxyhydro) - cinnamyl) hydrazide, N, N'-bis [2- (3, 5-di * -tert-butyl-4-hydroxy-hydrocinmoyloxy) -ethyl] -oxamide, 2,6-di-tert-butylphenol, octyl 3, 5-di-tert-butyl-4-hydroxyhydrocinnamate and methyl 3,5-di-tert-butyl-4-hydroxyhydrocinnamate. Preferred phenolic antioxidants are neopentan-tetrayl tetrakis (3,5-di-tert-butyl-4-hydroxyhydroxycinnamate), n-octadecyl 3,5-di-tert-butyl-4-hydroxyhydrocinnamate, 1,3,5-tri-methyl -2,4,6-tris (3,5-di-tert-butyl-4-hydroxybenzyl) enzene, 2,6-di-tert-butyl-p-cresol, 2,2'-ethylidene-bis (4, 6-di-tert-butylphenol), methyl 3,5-di-tert-butyl-4-hydroxyhydrocinnamate, octyl 3,5-di-tert-butyl-4-hydroxyhydrocinnamate, 2,6-di-tert-butylphenol or , 6-dioxaocta-methylene bis (3-methyl-5-tert-butyl-4-hydroxyhydro-cinnamate).

Especially preferred phenolic antioxidants are methyl 3,5-di-tert-butyl-4-hydroxyhydroxycinnamate, octyl 3,5-di-tert-butyl-4-hydroxyhydroxycinnamate or 2,6-di-tert-butylphenol. When this mixture of aliphatic nitroxide compound and aromatic amine, particularly a substituted phenylene diamine or phenolic antioxidant is employed, the amount of effective stabilizer is from 0.05 to 5000 ppm of aliphatic nitroxide and 0.05 to 5000 ppm of aromatic amine, particularly substituted phenylenediamine or phenolic antioxidant, preferably from 0.1 to 100 ppm of aliphatic nitroxide plus 0.1 to 100 ppm of aromatic amine, especially substituted phenylenediamine or phenolic antioxidant or mixture of aromatic amine and phenolic antioxidant. It is also possible to combine the functionalities represented by the synergistic mixture described above in the same molecule. This molecule would be the compound described by L.P. Nethsinghey G.Scott, Rubber Chem. Technology, 57 (5), 918 (1984) as l-oxyl-2, 2,6,6,6-tetramethylpiperidin-4-yl-3,5-di-tert-butyl-4-hydroxyhydrocinnamate. Preferred embodiments of the present invention comprise a process wherein the synergistic mixture is from 1 to 95% by weight of aliphatic nitroxide compound and 99 to 5% by weight of an aromatic amine, phenolic antioxidant or mixture thereof wherein the proportion of amine to phenolic antioxidant is 5: 1 to 1: 5.

A more preferred embodiment comprises the mixture which is from 5 to 75% by weight of aliphatic nitroxide compound and 95 to 25% by weight of an aromatic amine, phenolic antioxidant or its mixture wherein the ratio of amine to phenolic antioxidant is 2: 1 to 1.2. An even more preferred embodiment comprises the mixture which is from 10 to 50% by weight of aliphatic nitroxide compound and 90 to 50% by weight of aromatic amine, phenolic antioxidant or its mixture, wherein the composition of amine to phonic antioxidant is 1 :1. A preferred embodiment is the synergistic mixture wherein the aliphatic nitroxide is bis (l-oxyl-2,2,6,6-tetramethyl-piperidin-4-yl) sebacate, the aromatic amine is N, N'-di (l, 4-dimethyl-pentyl) phenylenediamine, and the phenolic antioxidant is methyl 3,5-di-tert-butyl-4-hydroxy-hydrocinnamate. Yet another embodiment of the present invention relates to a composition stabilized against oxidative degradation and against the formation of undesirable gums or deposits, comprising: (a) gasoline, particularly unstable gasolines such as pyrolysis or coking gasoline, and (b) an effective stabilizing amount of an aliphatic nitroxide compound. Yet another embodiment is a gasoline composition which is stabilized against oxidative degradation and against the formation of undesirable gums or deposits, comprising an effective synergistic mixture of an aliphatic nitroxide compound and an aromatic amine, particularly a substituted phenylenediamine or a phenolic compound or mixture of aromatic amine and phenolic antioxidant. Examples and preferences including preferred proportions and amounts for the individual components have been previously mentioned and also apply to the compositions. Preferably, gasoline is pyrolysis or coking gasoline. The composition can be produced by dissolving the aliphatic nitroxide, the aromatic amine or the phenolic antioxidant directly in the gasoline. However, it is also possible to dissolve the components in a suitable solvent and add the pre-dissolved components to the gasoline. Suitable solvents are for example aliphatic hydrocarbons, aromatic hydrocarbons such as benzene, toluene or xylene, ketones or ethers. Additional embodiments of the present invention relate to the use of an aliphatic nitroxide for the stabilization of gasoline against oxidative degradation and against the formation of undesirable gums or deposits and the use of a synergistic mixture of an aliphatic nitroxide compound and an aromatic amine or an antioxidant phenol or mixture of aromatic amine and phenolic antioxidant for the stabilization of gasoline against oxidative degradation and against the formation of undesirable deposits or gum. The following examples are intended for illustrative purposes only. Several standard accelerated test methods are known for evaluating the stability of fuels in general and gasoline in particular. Two common ASTM methods for gasoline are (1) Test Method D 525 for Gasoline Oxidation Stability (Induction Period Method); and (2) Standard Test Method D 873 for Oxidation Stability of Aviation Fuels (Potential Residue Method). Schrepfer and Stansky reported in the Gasoline Stability Test and Inhibitor Application, National Meeting of Fuels and Lubricants, (1981) that this method was much better for forecasting the formation of long-term deposits in both stable and unstable gasolines. This method is used to evaluate the aliphatic nitroxide stabilizers present. Example 1 The gasoline sample used in the examples is collected from an olefin production unit (pygas). It is a 1: 1 mixture of streams of 5 and 9+ carbon atoms free of inhibitor. The samples are collected in oxygen-free containers, cooled in an ice bath and stored in a refrigerator under nitrogen. According to ASTM D 873-88, a 100 ml sample of pyrolysis gasoline in a pump is heated in a boiling water bath under oxygen for four hours. The stabilized gasoline samples are prepared by adding 2 mL of a solution of toluene stabilizer to 98 mL of pyrolysis gasoline producing a total volume of 100 L. After heating, aged gasoline is removed from the pump and the total gum produced is determined. Table 1 below contains the results obtained when testing the known gasoline stabilizer N, N'-di (1,4-dimethylpentyl) phenylenediamine, either alone or with a hindered phenolic co-stabilizer. These formulations are evaluated in order to act as a sample or standard to compare the effectiveness of aliphatic nitroxide stabilizer systems.

Table 1 Effect of Stabilizing Systems of Phenylenediamine Substituted in Pygas Rubber Formation in Potential Rubber Test ASTM D 873 Component Concentration in ppm ABC Gum Soluble mg / 100 ml 569 618 583 12.5 12.5 2.2 5 400 5 398 10 19 10 21 5 480 10 219 25 25 1.1 A is N, N'-di (1,4-dimethylpentyl) phenylenediamine B is octyl 3,5-di-tert-butyl-4-hydroxyhydrocinnamate. C is methyl 3,5-di-tert-butyl-4-hydroxyhydrocinnamate. The combination of a substituted phenylenediamine (A) plus a phenolic antioxidant (B), each at a concentration of 12.5 ppm, gives 2.2 mg / 100 mL of gum formation, while the compound (A) in combination with phenolic antioxidant ( C) each at a concentration of 25 ppm reduces "• - Table 2 below - • '' "" '' x Even at a concentration of 1 ppm, an aliphatic nitroxide "equivalent to the phenyl stabilizer" - "" '' '' 1 Effect of Aliphatic Nitroxide Stabilizing Systems on Pygas Rubber Formation in ASTM D 873, Potential Gum Test Concentration of Components in ppm DG Gum Soluble ms / 100 ml 1 30 2.5 6.0 4 3.8 5 2.9 10 2.0 10 2.3 10 2.1 20 1.8 50 1.4 10 2.1 D is bis (l-oxyl-2, 2, 6, 6-tetramethylpiperidin-^ -yl) sebacate.

G is l-oxyl-2,2,6,6-tetramethylpiperidin-4-ol. Aliphatic nitroxides D and G at a concentration of 10 ppm are approximately 10 times more effective than phenylenediamine A at 10 ppm to avoid gum formation. Although the aliphatic nitroxides demonstrate superior stabilization performance against the current state of the art, this performance can be further improved by using synergistic mixtures of these aliphatic nitroxides with various co-stabilizers as can be seen in Table 3. Table 3 Effect of Aliphatic Nitroxide Stabilizing Systems in Pygas Rubber Formation in Potential Rubber Test ASTM D 873 Component Concentration in ppm ACDFG Soluble Rubber mg 100 ml 10 20 (average) 10 2.1 (average) 9. 5 0.5 2.5 9 1 2.1 8 2.5 2.0 6 4 1.7 5 5 1.2 10 10 0.6 12 8 0.6 Table 3 (Cont.) Component Concentration in ppm D F G Soluble Gum mg / lPP mi 5 0.9 9. 5 0. 5 4.2 9 1 1.2 7 .5 2 .5 0.9 6 4 0.7 5 5 5 5 1.6 5 5 0.8 5 5 2.5 10 10 1.3 5 507 1 100 448 3.3 3.3 3.3 1.6 A is N, N-di (l, 4- dimethylpentyl) phenylenediaraine. C is methyl 3,5-di-tert-butyl-4-hydroxyhydrocinnamate. D is bis (l-oxyl-2, 2,6,6-tetramethylpiperidin-4-yl) sebacate. F is di (4-tert-octylphenyl) amine. G is l-oxyl-2,2,6,6-tetramethylpiperidin-4-ol. From Table 3 it is clear that the combination of an aliphatic hindered amine nitroxide D or G with the substituted phenylene dia in A or phenolic antioxidant C gives synergistic stabilization. Even mixtures of aliphatic nitroxide D with diarylamine F which itself is almost inactive alone, give effective stabilization.

Claims (18)

1. CLAIMS 1. A method for preventing oxidative degradation and gum or deposit formation, characterized in that it comprises adding to a gasoline subject to thermal or oxidative induced degradation, an effective stabilizing amount of an aliphatic nitroxide compound.
2. 2. Method according to claim 1, characterized in that the amount of effective stabilizer of the aliphatic nitroxide compound is 0.05 to 10,000 ppm.
3. 3. Method according to claim 1, characterized in that the stabilizing system comprises an effective stabilizing amount of a synergistic mixture of an aliphatic nitroxide compound and an aromatic amine or a phenolic antioxidant or mixture of aromatic amine and phenolic antioxidant.
4. 4. Method according to claim 1, characterized in that the aliphatic nitroxide is an aliphatic diamine hindered nitroxide.
5. Process according to claim 1, characterized in that the aliphatic nitroxide is di-tert-butyl nitroxyl, l-oxyl-2,2,6,6-tetramethylpiperidine / l-oxyl-2, 2,6,6-tetramethylpiperidine -4-ol, l-oxyl-2, 2,6,6-tetramethylpiperidin-4-one, l-oxyl-2, 2,6,6-tetramethylpiperidin-4-yl acetate, l-oxyl-2, 2, 6,6-tetramethylpiperidin-4-yl 2-ethylhexanoate, l-oxyl-2, 2,6,6-tetramethylpiperidin-4-yl stearate, l-oxyl-2,2,6,6-tetramethyl-piperidin- 4-yl benzoate, l-oxyl-2, 2,6,6-tetramethylpiperidin-4-yl-4-tert-butylbenzoate, bis (l-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) succinate, bis (l-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) adipate, bisfl-oxyl-1 2,2,6,6-tetramethylpiperidin-4-yl) sebacate, bis (l-oxyl-2) , 2,6,6-tetramethylpiperidin-4-yl) n-butylmalonate, bis (l-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) phthalate, bis (l-oxyl-2,2,6 , 6-tetramethylpiperidin-4-yl) isophthalate, bis (l-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) terephthalate, bis (l-oxyl-2,2,6,6-tetramethylpiperidin-4) -il) hexahydroterephthalate, N, N'-bis (l-oxyl-2, 2,6,6-tetramethylpiperidin-4-yl) adipamide, N- (1-oxyl-2, 2,6,6-6-tetramethylpiperidin-4-yl) caprolactam, N- (l-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) dodecyl succinimide, 2,4,6-tris- (l-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) cyanurate, 2,4,6-tris- [N-butyl-N- (l-oxyl-2, 2,6,6-tetramethylpiperidin-4-yl] -s-triazine, l-oxyl-2,2,6,6 -tetramethylpiperidin-4-yl 3,5-di-tert-butyl-4-hydroxy-hydrocinnamate or 4,4'-ethylenebis (l-oxyl-2,2,6,6-tetra-methyl-piperazin-3-one).
6. 6. Process according to claim 3, characterized in that the aromatic amine is a substituted phenylenediamine.
7. Method according to claim 3, characterized in that the aromatic amine is N, N'-di-isopropyl-p-phenylenediamine, N, N'-di-sec.-butyl-o-phenylenediamine, N, N'- di-sec-butyl-p-phenylenediamine, N, N'-bis (1,4-dimethylphenyl) -p-phenylenediamine, N, N'-bis (l-ethyl-3-methylpentyl) -p-phenylene diamine , N, N'-bis (1-methylheptyl) -p-phenylenediamine, N, N'-dicyclohexyl-p-phenylenediamine, N, N'-diphenyl-p-phenylenediamine, N, N-di- (2-naphthyl) -p-phenylenediamine, N-isopropyl-N'-phenyl-p-phenylenediamine, N-sec-butyl-N'-phenol-o-phenylenediamine, N- (1,3-dimethylbutyl) -N'-phenyl-p phenylenediamine, N- (1-methylheptyl) -N'-phenyl-p-phenylenediamine, N-cyclohexyl-N'-phenyl-p-phenylenediamine, N, N '-dimeti1-N, N'-di-sec-butyl -p-phenylenediamine; N, N'-di (1,4-dimethylpentyl) -o-phenylenediamine; diphenylamine, N-allyldiphenyl-a, di- (4-isopropoxyphenyl) amine, N-phenyl-1-naphthylamine, N-phenyl-2-naphthylamine, octylated diphenylamine, p, p'-di-tert-octyl-diphenylamine, di- (4-methoxy-phenyl) amine, N-phenyl-1-naphthylenamine tert-octylated, or a mixture of tert-butyl- / tert-octyldiphenylamines mono- and dialkylated.
8. 8. Process according to claim 7, characterized in that the aromatic amine is N-phenyl-1-naphthylamine, N-phenyl-2-naphthylamine, octylated diphenylamine, p, p'-di-tert-octyldiphenylamine, a mixture of -butyl- / tert-octyl-diphenylamines mono- and dialkylated or N, N'-di (1,4-dimethylpentyl) -p-phenylenediamine.
9. 9. Method according to claim 3, characterized in that the phenolic antioxidant is neopentantetrail tetrakis (3, 5-di-tert-butyl-4-hydroxyhydro-cinnamate), n-octadecyl-3,5-di-tert-butyl-4-hydroxy-hydrocyhamate, 1,3,5-trimethyl-2,4,6-tris (3,5-di-tert-butyl-4-hydroxybenzyl) -benzene, 2,6-di-tert-butyl-p-cresol, 2,2'-ethylidene-bis (4,6-di-tert-butylphenol) ), methyl 3,5-di-tert-butyl-4-hydroxyhydrocinnamate, octyl 3,5-di-tert-butyl and 1-4-hydroxyhydrocinnamate, 2,6-di-tert-butyl-phenol or 3,6- dioxaocta ethylene bis (3-methi 1-5-ter-buti 1-4-hydroxyhydrocinnamate).
10. 10. Process according to claim 9, characterized in that the phenolic antioxidant is methyl 3,5-di-tert-butyl-4-hydroxyhydrocinnamate, octyl 3,5-di-tert-butyl-4-hydroxyhydrocinnamate or 2,6- di-tert-butylphenol.
11. Method according to claim 3, characterized in that the effective stabilizing synergistic mixture comprises 0.05 to 5000 ppm of aliphatic nitroxide compound and 0.05 to 5000 ppm of an aromatic amine, phenolic antioxidant or mixture of aromatic amine and phenolic antioxidant.
12. Method according to claim 3, characterized in that the synergistic mixture is from 1 to 95% by weight of aliphatic nitroxide compound and 99 to 5% by weight of an aromatic amine, phenolic antioxidant or its mixture, wherein the proportion from amine to phenolic antioxidant is 5: 1 to 1: 5.
13. 13. Process according to claim 3, characterized in that the aliphatic nitroxide is bis (l-oxyl-2, 2,6,6-tetramethylpiperidin-4-yl) sebacate, the aromatic amine is N, N'-di (l). , 4-dimethylpentyl) -phenylenediamine and the phenolic antioxidant is methyl 3,5-di-tert-butyl-4-hydroxyhydrocinnamate.
14. 14. A stabilized composition against oxidative degradation and against the formation of undesirable gums or deposits, characterized in that it comprises: (a) gasoline subject to oxidative degradation, and (b) an effective stabilizing amount of an aliphatic nitroxide compound, with the proviso that that the aliphatic nitroxide compound is not di-tert-butyl nitroxyl or l-oxyl-2,2,6,6-tetramethylpiperidine.
15. 15. A composition according to claim 14, characterized in that the gasoline is pyrolysis or coking gasoline.
16. 16. A composition according to claim 14, characterized in that the stabilizing system comprises an effective stabilizing amount of a synergistic mixture of an aliphatic nitroxide compound and an aromatic amine or a phenolic antioxidant or mixture of aromatic amine and phenolic antioxidant.
17. 17. Use of aliphatic nitroxide for the stabilization of gasoline against oxidative degradation and against the formation of rubber or undesirable products.
18. 18. Use of a synergistic mixture of an aliphatic nitroxide compound and an aromatic amine or a phenolic antioxidant or mixture of aromatic amine and phenolic antioxidant, for the stabilization of gasoline against oxidative degradation and against the formation of undesirable deposits or gum.