Stabilization of gasoline mixtures

Abstract: Oxidative stability of gasoline mixtures is improved by adding to the gasoline a phenylenediamine compound (I) in combination with a strongly basic organo-amine compound (II). The compound (II) may comprise hydroxylamines, alkylphenol-polyamine-formaldehyde Mannich reaction products, polyethylene-polyamines, and members of the group of piperazine, aminoalkyl substituted piperazine and amino substituted alicyclic alkanes.

Description: The present invention pertains to compositions for and methods for increasing the oxidative stability of gasoline mixtures and especially those gasoline mixtures contaminated by the presence of acidic impurities therein. The term "gasoline" as used herein includes products known as petrol, benzin and the like. Gasoline is defined as a complex mixture of hydrocarbons that is used as fuel for internal combustion engines. Gasoline manufactured today is derived from petroleum and is used in automobile, aircraft, marine engines and small engines designed for miscellaneous end-uses. The composition and characteristics of gasoline vary with the source, manufacturing method and end-use requirement of the product. Gasoline was initially produced by the simple distillation of crude oil. The types of hydrocarbons found in such "straight-run" gasolines include paraffins, aromatics and naphthenes (e.g., cycloparaffins). The number of carbon atoms in the hydrocarbon fraction, molecules falling within the gasoline boiling range, is usually from about C 4 to C 12 . Today, gasoline is produced in petroleum refineries by a plurality of processes. For example, fractional distillation is still used as one refinery method for gasoline production. However, the gasoline mixtures so produced are usually low in octane content and are therefore normally supplemented with gasolines produced by other methods to increase the octane content. Other production methods include pyrolytic cracking wherein higher molecular weight hydrocarbons, such as those in gas oils, are either catalytically cracked or thermally cracked. Reforming is used to upgrade low-octane gasoline fractions into higher octane components by use of a catalyst. Alkylation of C 3 and C 4 olefins with isobutane is also practised to provide a high octane content gasoline source. Polymer gas or polygas is an olefinic gasoline blending component resulting from a polymerization process. Several polymerization processes exist (Nelson, Petroleum Refining Engineering, 4th Edition, pp. 700-701, 722-735), including thermal polymerization of cracked still gases (C 3 -C 5 ) or acid catalyzed, either phosphoric or sulphuric acid, polymerization of similar feedstocks. Additionally, another commercially important "Polygas" process involves passing the feedstock over a diatomaceous earth impregnated with phosphorus pentoxide. A process referred to as dimerization is used to combine hydrocarbon fractions, such as butenes and propylene, to form higher molecular weight branched hydrocarbons, such as isoheptenes. Gasoline produced by this process is referred to as "dimate" gasoline. The process frequently uses phosphoric acid as a catalyst. Stripper gasoline is obtained by a process that uses steam injected into a fractionator column with the steam providing the heat needed for separation. The gasoline can come from either a hydrodesulfurizer (HDS) unit or a fluidized catalytic cracking (FCC) unit. Normally, stripper gasoline from a FCC unit is highly unstable and only small percentages thereof can be blended with a more stable gasoline product in order to obtain the final motor fuel product. Additionally, isomerization is used to convert low octane paraffins into branched chain isomers with higher octane. Despite the particular method of production, gasolines generally suffer from oxidative degradation. That is, upon storage, gasoline can form gummy, sticky resin deposits that adversely affect combustion performance. Further, such oxidative degradation may result in undesirable colour deterioration. The need for stabilizing treatment is even more acute in those gasolines in which acidic contaminants are present. For example, the presence of naphthenic acids in gasolines contributes to instability. Naphthenic acid is a general term that is used to identify a mixture of organic acids present in petroleum stock or obtained due to the decomposition of the naphthenic or other organic acids. As is used in the art, the acid neutralization number (mg KOH/gm) (as per ASTM D 664) is a quantitative indication of the acids present in the hydrocarbon. Oftentimes, known gasoline stabilizers, such as the phenylenediamines lose effectiveness in such acidic gasoline mediums. There is a need to provide such stabilization treatment in those gasolines having an acid neutralization number of 0.1 or greater and such treatment is especially desirable when the acid neutralization number is even higher (i.e., 0.15 or greater). Many attempts to stabilize gasolines have been made throughout the years. Phenylenediamines, as taught in US-A- 3 556 748 (Stedman) have been used for years for this purpose. Alkylenediamines such as diethylenetriamine, triethylenetetramine, tetraethylenepentamine, etc., in combination with gum inhibitors, such as N-substituted alkylaminophenols, etc., are used to enhance gasoline stability in US-A-2 305 676 (Chenicek). Similarly, alkylamines, such as diethylamine, tributylamine, ethylamine, or alkylenediamines, such as propylenediamine, and basic cyclic nitrogen compounds, such as piperdine and the like, are taught as being effective in preventing color degradation of gasolines in US-A- 1 992 014 (Rogers). US-A- 1 992 014 indicates that specified amines may be used in combination with gum inhibiting aromatic reducing agents, such as p-phenylenediamine, to stabilize colour deterioration due to exposure of the gasoline to sunlight. In US-A- 2 318 196 (Chenicek), amino-pyridines are used in combination with N-butyl-p-aminophenol to enhance stability of cracked gasolines. US-A- 2 333 294 (Chenicek) teaches the use of substituted alkylenediamines, including N,N-diethylethylenediamine, etc., in combination with known gum inhibitors, such as alkylphenols, N-substituted alkylaminophenols, substituted phenol ethers, and hardwood tar distillates, etc., in the same environment. US-A- 4 647 290 (Reid) teaches the combination of N-(2-aminoethyl)piperazine and N,N-diethylhydroxylamine to enhance colour stability of distillate fuel oils, such as straight-run diesel fuel. US-A- 4 647 289 (Reid) is directed toward combined use of triethylenetetramine and N,N-diethylhydroxylamine for such purpose. The combination of N-(2-aminoethyl)piperazine, triethylenetetraamine and N,N-diethylhydroxylamine is disclosed in US-A- 4 648 885 (Reid) to improve stability of distillate fuel oils. Fouling in oxygen containing hydrocarbons having a bromine number of about 10 or above is inhibited by the combination of unhindered or partially hindered phenols and oil soluble strong amine bases as taught in US-A-4 744 881 (Reid). Here, specifically enumerated amine bases include monoethanolamine, N-(2-aminoethyl)piperazine, cyclohexylamine, 1,3-cyclohexane-bis(methylamine), 2,5-dimethylaniline, 2,6-dimethylaniline, diethylenetriamine and triethylenetetramine. Other patents that may be of interest include US-A-4 720 566 (Martin) and US-A- 4 797 504 (Roling), teaching, respectively, conjoint use of hydroxylamines and para-phenylenediamines to inhibit acrylonitrile polymerization and acrylate ester polymerization. In US-A- 4 051 067 (Wilder) and US-A- 4 016 198, (also Wilder) polyalkylene amines and arylenediamines are used, in combination, to inhibit carboxylic acid ester polymerization. U S-A- 4 749 468 (Roling) teaches deactivation of first row transition metal species in hydrocarbon fluids by use of Mannich reaction products formed via reaction of alkylphenol, polyamines, and aldehyde sources. U S-A -2472349 teaches compositions for inhibiting the deterioration of gasoline in the presence of oxygen. The compositions comprise piperazine or N-substituted piperazines and an arylamine antioxidant. The antioxidant can be N,N'-di-sec-butyl-p-phenylenediamine. FR-A-1,007,389 taches a combination for color stabilization of hydrocarbons and halogenated hydrocarbons. The combination comprises a phenylenediamine and cyclohexylamine compound or derivative. EP-A-0 167 358 teaches a corrosion inhibitor for hydrocarbon fuel which comprises a monoalkenyl succinic acid, an aliphatic amine and a liquid organic solvent. The composition can further comprise a di(sec alkyl)-p-phenylenediamine compound. U S-A-2,147,572 teaches a method for improving the color of cracked hydrocarbon distillates. The methods comprise adding a hydroxylamine compound to improve the color and then adding a stabilizing agent such as a substituted phenylenediamine to fix and maintain the improved color. Despite the efforts of the prior art, there remains a need for stabilizing treatment that is effective with a variety of gasoline types and at relatively low levels of concentration. Additionally, such treatment is even more desirable in those gasolines having acidic impurities therein which, heretofore, have proven especially prone to instability and gum formation. According to the present invention there is provided a method of stabilising gasoline mixtures which comprises adding to the gasoline a combination of (I) a phenylenediamine having at least one N-H group and (II) a strongly basic organo-amine having a pKb of less than 7, said strongly basic organi-amine comprising:- a hydroxylamine having the formula wherein R 10 and R 11 are independently chosen from alkyl, alkaryl and hydrogen. According to the present invention, gasoline mixtures, such as, for example, those formed via "straight-run", pyrolysis, reforming, alkylation, stripper, isomerization and polymerization techniques are stabilized by adding to such gasoline mixtures, a (I) phenylenediamine compound and (II) a said strongly basic organo-amino compound having a pKb less than 7. As to the phenylenediamine compounds (I) that are suitable, these include phenylenediamine and derivatives having at least one N-H group. It is considered that ortho-phenylenediamine or derivatives thereof having at least one N-H group are suitable for use in accordance with the present invention. However, the preferred phenylenediamine is para-phenylenediamine having the formula wherein R 1 , R 2 , R 3 and R 4 are the same or different and are hydrogen, alkyl, aryl, alkaryl, or aralkyl groups with the proviso that at least one of R 1 , R 2 , R 3 or R 4 is hydrogen. More preferably, the alkyl, aryl, alkaryl and aralkyl groups have one to about twenty carbon atoms. The alkyl, alkaryl and aralkyl groups may be straight or branched-chain groups. Exemplary para-phenylenediamines include p-phenylenediamine wherein R 1 , R 2 , R 3 and R 4 are hydrogen; N,N,N'-trialkyl-p-phenylenediamines, such as, for example, N,N,N'-trimethyl-p-phenylenediamine or N,N,N'-triethylphenylene-p-diamine; N,N'-dialkyl-p-phenylenediamines, such as, for example, N,N'-dimethyl-p-phenylenediamine, N,N'-diethyl-p-phenylenediamine, or N,N'-di-sec-butyl-p-phenylenediamine; N-phenyl-N',N'-dialkyl-p-phenylenediamines, such as, for example, N-phenyl-N',N'-dimethyl-p-phenylenediamine, N-phenyl-N',N'-diethyl-p-phenylenediamine, N-phenyl-N',N',-dipropyl-p-phenylenediamine, N-phenyl-N',N'-di-n-butyl-p-phenylenediamine, N-phenyl-N',N'-di-sec-butyl-p-phenylenediamine, N-phenyl-N'-methyl-N'-ethyl-p-phenylenediamine, or N-phenyl-N'-methyl-N'-propyl-p-phenylenediamine; N-phenyl-N'-alkyl-p-phenylenediamines, such as, for example, N-phenyl-N'-methyl-p-phenylenediamine, N-phenyl-N'-ethyl-p-phenylenediamine, N-phenyl-N'-isopropyl-p-phenylenediamine, N-phenyl-N'-butyl-p-phenylenediamine, N-phenyl-N'-isobutyl-p-phenylenediamine, N-phenyl-N'-sec-butyl-p-phenylenediamine, N-phenyl-N'-tert-butyl-phenylenediamine, N-phenyl-N'-n-pentyl-p-phenylenediamine, N-phenyl-N'-n-hexyl-p-phenylenediamine, N-phenyl-N'-(1-methylhexyl)-p-phenylenediamine, N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine or N-phenyl-N'-(1,4-dimethylpentyl)-p-phenylenediamine. Preferably, the paraphenylenediamine is selected from N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine, N,N'-di-sec-butyl-p-phenylenediamine, N-phenyl-N'-(1,4-dimethylpentyl)-p-phenylenediamine and p-phenylenediamine wherein R 1 , R 2 , R 3 and R 4 are all hydrogen. Most preferably, I is N-phenyl-N'-(1,4 dimethylpentyl)-p-phenylenediamine, which is available from Uniroyal under the Trade Mark Naugard I3. In one aspect of the invention, stabilization improvement is shown in those gasolines that are treated with such phenylenediamines (PDA) (I) wherein considerable acidic components exist in the gasoline. That is, in gasolines having acid numbers of about 0.10 (mg KOH/g) and greater, improvement over the traditional use of (I) alone as the gasoline stabilizer is shown by using the amine (II) in combination with the PDA. Although not being bound to any particular theory of operation, it is thought that the PDA performance is adversely affected by such high acid concentrations. Perhaps the addition of the strongly basic organo-amine neutralizes the acids, thus allowing the PDA to better fulfil its known and intended function in improving stability of the gasoline mixture as evidenced by inhibition of colour and gum formation. The hydroxylamines II that are conjointly used with the p-phenylenediamines (I) to inhibit gum and colour formation in gasoline mixtures may be represented by the formula wherein R 10 and R 11 are the same or different and are hydrogen, alkyl, or alkaryl groups. The alkyl and alkaryl groups may be straight or branched-chain groups. Preferably, the alkyl, or alkaryl groups have one to about twenty carbon atoms. Examples of suitable hydroxylamines include N,N-diethylhydroxylamine; N,N-dipropylhydroxylamine; N,N-dibutylhydroxylamine; N,N-butylethylhydroxylamine; N,N-2-ethylbutryloctylhydroxylamine; N,N-didecylhydroxylamine; N,N-dibenzylhydroxylamine; N-benzylhydroxylamine; N,N-butylbenzylhydroxylamine; N,N-methylbenzylhydroxylamine and N,N-ethylbenzylhydroxylamine. More than one such hydroxylamine, such as mixtures of N-benzylhydroxylamines and N,N-methylbenzylhydroxylamines, may be utilized if desired. Most preferably, the hydroxylamine is N,N-diethylhydroxylamine. The para-phenylenediamine (I) and strongly basic organo-amine compound (II) are added to the gasoline for which stabilization, i.e., inhibition of oxidative degradation, is desired in an amount of 1 to 10,000 parts of the combination (I and II) based upon 1 million parts of the gasoline mixture. Preferably, about 1 to 1500 ppm of the combination is added with a range of from 1 to 100 ppm being even more preferred. The relative ratio (molar) of components (I and II) to be added may be on the order of (I):(II) of from 1:1 to 10:1 with a more preferred ratio being from 5:1 to 10:1. The compounds may be added to the gasoline mixture under ambient conditions as a room or storage temperature stabilizer to stabilize the resulting gasoline mixture in tanks, drums, or other storage or shipment containers. The combined treatment (I and II) is preferably dissolved in an aromatic organic solvent, such as, for example, heavy aromatic naphtha (H.A.N.), or xylene. The acid neutralization number (mg KOH/gm) of the gasoline mixture is preferably about 0.1 or greater, preferably about 0.15 or greater. In order to illustrate the invention more clearly, the data set forth below were developed. The following Examples are included as being illustrative of the invention and should not be construed as limiting the scope thereof. Examples In order to demonstrate the efficacy of the combined treatment of the present invention in stabilizing gasoline, the ASTM D525-80 test procedure was utilized. In accordance with this method, a gasoline sample is placed in a pressure vessel along with the candidate stabilizer or, for purposes of control, no candidate gasoline stabilizer is added. The pressure vessel is closed and oxygen is introduced into the vessel through a Schrader-type valve fitting until an over-pressure of about 689.5 kPa (100 psig) is attained. The vessel is then heated in a water bath to about 100°C until a drop in pressure is noted signifying a loss of antioxidant activity. The period of time elapsing until a pressure drop is indicated is known as the "induction time", with longer induction times signifying increased stabilizer efficacy of the candidate treatment. Using this procedure, the following results were obtained using a variety of different gasoline types. Stripper Gasoline from Midwestern Fcc Unit Candidate Concentration (ppm active) Induction Time (± Standard derivation) Comments Control - 277±18 - PDAI 5 380 - PDAI 8 389 - PDAI (N=3) 10 439±17 - MD 2 263 no effect MD 10 264 no effect Polygas from Eastern Refinery Candidate Concentration (ppm active) Induction Time (± Standard derivation) Comments Control (N=17) - 61±6 - PDAI 25 1146 - PDAI (N=5) 5 377±57 - PDAI 2.5 >240 - PDAI (N=3) 2.0 223±22 - PDAI/DEHA (N=2) 5/2 404±1 - PDAI/DEHA 5/5 445 - PDAI/DEHA 2/5 359 Possible synergism DEHA 5 80 Slight efficacy PDAII 25 1077 - PDAII (N=4) 5 187±54 - PDAII 2.5 178 - PDAII (N=4) 2 118±9 - PDAII/DEHA (N=2) 5/2 314±15 synergism Dimate Gasoline from Texas Refinery Candidate Concentration (ppm active) Induction Time (Min.) Comments Control (N=9) - 36±8 - PDAI 20 316 - PDAI 18 285 - PDAI 10 225±19 - PDAI 5 43 slight efficacy PDAI/DEHA 5/2 43 - PDAII 20 235 - PDAII 5 33 no efficacy butyric acid 100 37 same as blank butyric acid 10,000 27 same as blank PDAI/butyric acid 10/100 228 no change in PDAI efficacy PDAI/butyric acid 10/10,000 128 PDAI efficacy reduced FCC Light Cat Gas from Western Refinery Candidate Concentration (ppm active) Induction Time (Min.) Comments Control (N=7) - 27±4 - PDAI (N=4) 5 63±26 one point of 4 is high - if thrown out, it is 50±6 butyric acid 1,000 23 same as control PDAI/butyric acid (N=2) 5/1,000 39±3 slight reduction of PDAI efficacy PDAI/ascorbic acid 5/5 46 same as PDAI at 5 ppm PDAI/ascorbic acid 5/2 47 same as PDAI at 5 ppm PDAI/DEHA/butyric acid (N=2) 5/2/1000 44±4 PDAI efficacy DMDS (N=2) 1000 28±6 partially restored same as blank PDAI/DMDS 5/1000 74 no effect on PDAI efficacy Legends for Tables N = number of trial runs PDAI = N-phenyl N'- (1,4-dimethylpentyl)-p-phenylenediamine, Naugard I3 - available from Uniroyal Chemical Co. PDAII = N,N'-di-sec-butyl-p-phenylenediamine, available Universal Oil Products as UOP-5 DMDS = dimethyldisulphide DEHA = N,N'-diethyl hydroxylamine. The Examples indicate that the combination of the invention is effective as an efficacious gasoline stabilizer in accordance with the applicable ASTM standard. In fact, several of the combinations exhibit surprising results. In this regard, the PDAII/DEHA and, PDAI/DEHA treatments may be mentioned. In Table I the acid concentration in the gasoline was unknown; therefore, the effects of the herein disclosed mixtures were unforeseen. This Table was included for completeness. The gasoline described in Table II had low acid content and the benefit of the combined treatments was not observed. The combined treatment is especially effective in the Table III and Table IV gasoline mixtures -- which are high in acid number (i.e., ≥ 10 mg KOH/g). Butyric acid was added to the gasoline in Table V resulting in decreased induction times compared to phenylenediamines without acid. Amines restored most of the induction times when added to the gasoline with the phenylenediamine and acid.

Claims: A method of stabilising gasoline mixtures, which comprises adding to the gasoline a combination of (I) a phenylenediamine having at least one N-H group and (II) a strongly basic organo-amine having a pKb of less than 7, said strongly basic organo-amine comprising:- a hydroxylamine having the formula wherein R 10 and R 11 are independently chosen from alkyl, alkaryl and hydrogen. A method according to claim 1, wherein the phenylenediamine (I) has the formula wherein R 1 , R 2 , R 3 and R 4 are the same or different and are hydrogen, alkyl, aryl, alkaryl, or aralkyl groups with the proviso that at least one of R 1 , R 2 , R 3 or R 4 is hydrogen. A method according to claim 2, wherein the alkyl, aryl, alkaryl and aralkyl groups have one to twenty carbon atoms. A method according to claim 2 or 3, wherein the phenylenediamine is N-phenyl-N'-(1,4-dimethylpentyl)-p-phenylenediamine. A method according to claim 2 or 3, wherein the phenylenediamine is N,N'-di-sec-butyl-p-phenylenediamine. A method according to any of claims 1 to 5, wherein the strongly basic organo-amine (II) comprises a hydroxylamine having the formula wherein R 10 and R 11 are independently chosen from C 1 to C 20 alkyl, C 1 to C 20 alkaryl and hydrogen. A method according to claim 6, wherein the hydroxylamine comprises N,N-diethylhydroxylamine. A method according to any of the preceding claims, wherein the molar ratio of (I):(II) is from 1:1 to 10:1. A method according to claim 8, wherein the molar ratio of (I):(II) is from 5:1 to 10:1. A method according to any one of the preceding claims, wherein from 1 to 10,000 parts of the combination is added to the gasoline mixture based upon one million parts of the gasoline mixture. A method according to claim 10, wherein 1 to 1500 parts of the combination is added to the gasoline mixture based upon one million parts of the gasoline mixture. A method according to any one of the preceding claims, wherein the gasoline mixture has an acid neutralization number (mg KOH/gm) of 0.1 or greater. A method according to claim 12, wherein the neutralization number is 0,15 or greater. A method according to any one of the preceding claims, wherein the gasoline mixture comprises (a) dimate gasoline formed by a dimerization procedure; or (b) straight-run distillate gasoline; or (c) pyrolysis gasoline; or (d) stripper gasoline; or (e) polymer gas.

Inventors: WRIGHT BRUCE EDWIN, WRIGHT, BRUCE EDWIN
Applicants: BETZ EUROP INC, BETZDEARBORN EUROPE, INC.
Application year: 1992
Main classification: C10L1
IPC codes: C10L1