Abstract:
A strongly basic, hydrophobic amine which prevents the deposition of fuel-insoluble carboxylate deposits in fuel tanks and fuel transfer equipment is contained in a fuel additive package which minimizes the degradation of a hydrocarbon fuel during storage.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of the U.S. Provisional Application filed by Leslie R. Wolf, Ser. No. 60/052,461 filed Jul. 14, 1997. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to additives for hydrocarbon fuels. In one aspect it relates to additives for hydrocarbon fuels which minimize the degradation of the hydrocarbon fuels upon storage. In another aspect it relates to additive-containing hydrocarbon fuels which maintain their stability during long term storage of the fuels. 
     BACKGROUND OF THE INVENTION 
     After new automobiles, trucks and motor vehicles, in general, are assembled, their fuel tanks are generally filled to some extent with an appropriate fuel before the vehicles are shipped to their point of sale and delivery to the ultimate customer. Because of the global nature of the motor vehicle industry, with the assembly of the vehicles often times taking place in a different part of the world relative to the point of sale of the vehicle, the fuel that is placed in these fuel tanks often stands unused for extended periods of time during shipment and storage of the vehicles. During these periods of time, the fuel in the fuel tanks, now effectively being in storage, must retain its initial integrity and not degrade with the degradation exhibiting itself through subsequent starting and running problems in the new vehicle and also by the formation of undesirable deposits in the fuel systems of the vehicles leading to longer term operability problems. The fuel so used must resist gum and sediment formation, minimize oxidation and prevent corrosion in the metallic portions of the fuel system as well as passivate fresh metal surfaces. Likewise, the fuel storage facilities, for example, tankage, pumps and plumbing, at the motor vehicle assembly site are also susceptible to the deposition of these unwanted solid materials from the quantities of stored motor fuels awaiting transfer to the newly-assembled vehicles. 
     The desired stability of the fuel is usually attained through the addition of appropriate additives to the fresh fuel. Typically, complex combinations of antioxidants, such as aromatic diamines or hindered phenols, carboxylic acid-based corrosion inhibitors, and metallic ion sequesterants such as salicyclidene diamines are added as a stability-inducing package to the fuel. The term &#34;package&#34; is used typically to indicate the complex combination of the various stability-inducing materials often times diluted with a solvent or solvents compatible with the various individual additive materials and the fuel to be treated. This package is generally prepared as a separate entity prior to its addition to the fuel. 
     If such a stability-inducing additive package is not employed, spontaneous deposition of undesirable deposits of solid, insoluble materials often occurs in the fuel tanks and systems of the new vehicles. These deposits, also referred to as gum, are mainly formed from oxidized and/or polymerized hydrocarbons. If a stability-inducing additive package is employed, gum formation in new vehicles can be reduced or eliminated. However, stability-inducing additive packages that employ carboxylic acid-based corrosion inhibitors and salicylidene diamine sequesterants can lead to the formation of solid, insoluble deposits in the fuel storage and transfer apparatus of the vehicle manufacturing plant. These deposits are mainly hydrophilic carboxylate salts of metal ions arising from corrosion in the fuel storage and transfer systems and also of carboxylate salts of diamine impurities typically found in the salicyclidene diamine sequesterants. These carboxylate salts are virtually insoluble in the hydrocarbon fuel media and, as such, can also be deposited at various points throughout the fuel systems of the newly-manufactured vehicles in question. 
     In attempts to stabilize motor fuel toward oxidative degradation, it is often times found that sufficient oxidative stability is not imparted to the fuel by the use of a single antioxidant material. Hence, more than one specific oxidation-stabilizing material can be added to the fresh fuel to provide for the desired level of oxidative stability. 
     SUMMARY OF THE INVENTION 
     One object of the present invention is to provide a stability-enhancing additive which can be added to a hydrocarbon fuel and which minimizes solid deposit and gum formation upon storage of the fuel. Another object of the invention is to provide a hydrocarbon fuel stability-enhancing additive which does not contain a carboxylic acid or carboxylic acid derivative. A further object of the invention is to provide a hydrocarbon fuel stability-enhancing additive which contains a strongly basic, hydrophobic amine. A still further object of the invention is to provide a hydrocarbon fuel with enhanced stability toward oxidation and solid deposit formation during storage. These objects will be attainable through the use of the invention as described below. 
     This invention provides for a corrosion inhibitor, as an additive for hydrocarbon fuels, which comprises a strongly basic, hydrophobic high molecular weight organoamine, or a mixture of such amines, drawn from the group consisting of amidine, mono-substituted amidines and multiply-substituted amidines of generalized formula: ##STR1## where R = --H or [--(CH2--CH2)--] 1/2   
     X = --CH 2  -- or --NH--, 
     R&#39; = a hydrocarbon radical containing at least 11 and no more than 24 carbon atoms, and 
     R&#34; = --H, an alkyl hydrocarbon radical containing no more than 5 carbon atoms, or a hydroxyalkyl hydrocarbon radical containing no more than 5 carbon atoms. 
     Because this corrosion inhibitor is not a carboxylic acid or a derivative of a carboxylic acid, the formation of carboxylate salts in the fuel is precluded eliminating the precipitation of hydrocarbon-insoluble carboxylate salts as solid deposits in fuel storage tanks, fuel transfer equipment or vehicle fuel systems. In addition, because the corrosion inhibitor is hydrophobic, and thereby organophilic, any such carboxylate salt which might, in fact, form from the amine and any carboxylic acid or carboxylic acid derivative already present in the hydrocarbon fuel to be treated would remain solubilized and not form undesirable insoluble deposits. 
     In addition, because the corrosion inhibitor is strongly basic, any carboxylate salt which might form by the interaction of a carboxylic acid or carboxylic acid derivative initially present in the fuel with a less basic amine or amines added intentionally or inadvertently with other components of the overall additive package, as described below, are immediately converted to the corresponding organophilic, protonated strongly-basic amidinium or substituted amidinium salt and remain soluble in the hydrocarbon fuel. 
     This invention also uses a combination of a N,N&#39;-dialkyl-p-phenylene diamine and butylated phenols as stabilizers toward hydrocarbon oxidation. This combination provides for good oxidative stability for virtually all types of hydrocarbon fuels. 
     In addition, this invention includes a standard type of metal deactivator, namely, a salicylidene diamine, to passivate fresh metal surfaces of the fuel storage vessels and tanks, and the fuel transfer apparatus and to sequester oxidation-promoting metal ions which may be in the fuel. 
     The present invention employs a mixture of aromatic and alcoholic solvents to solubilize the components of the additive package and to facilitate the handling and addition of the additive package in concentrations convenient and appropriate for addition to the hydrocarbon fuel. 
     Additionally, this invention includes a fuel composition, typically, but not limited to, a motor gasoline, to which the additive package comprising the above described components has been added and which exhibits enhanced stability, especially toward solid deposit formation, during storage. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Fuel stabilization additive packages are typically utilized by adding an amount of the package to fresh fuel such that the resulting fuel shows no deleterious stability problems over a time period at least as long as the anticipated storage period. Thus, the fuel stabilization package of the present invention is added to fresh fuel, typically, motor gasoline, at the rate of from 0.25 gallon to 1.0 gallon of additive package per 1000 gallons of the fresh fuel. In this invention, a preferred blending ratio is 0.5 gallon of the additive package per 1000 gallons of the fresh fuel. 
     The fuel additive package of this invention comprises a combination of stability-enhancing active ingredients added to inert carrier ingredients. Typically, the concentration of the active ingredients ranges from 13 weight percent to 78 weight percent of the final additive package composition with the inert carrier components concentration ranging from 87 weight percent to 22 weight percent, respectively. Preferably, the active ingredients represent 26 weight percent of the additive package with the inert carrier components representing the remaining 74 weight percent. 
     The inert components of the additive package comprise a mixture of aromatic hydrocarbons and alcoholic solvents that effectively solubilize the stability-enhancing active components of the package while at the same time exhibit high solubility in the fuel to be treated. Constraints of cost, compatibility with combustion processes, purity and their own long-term stabilities must be considered when choosing the inert carrier components. It has been found that mixtures of the various isomers of xylene can function as one inert component while a simple aliphatic alcohol, namely 2-propanol, often referred to as isopropanol, can function as another inert ingredient. Preferably, the inert carrier composition is a solution of these two components with the compositional range for the mixed xylene isomers varying from 30 to 70 weight percent and with the compositional range of the isopropanol varying from 70 to 30 weight percent. The most preferred composition for this inert carrier is 60 weight percent mixed xylenes and 40 weight percent isopropanol. 
     In addition to the inert carrier component, the stability-inducing additive package typically contains active components of three different compound classes, namely, antioxidants, metal deactivators (often referred to as metal ion sequesterants) and corrosion inhibitors. 
     This invention uses a combination of N,N&#39;-dialkyl-p-phenylene diamine and poly-butylated phenols to provide the antioxidant functionality in the stability-inducing additive package. This combination has been found to provide good oxidation stability for virtually all hydrocarbon fuels, including motor gasoline. The preferred oxidation stabilizers have been determined to be N,N&#39;-di-sec-butyl-p-phenylene diamine and 2,6-di-t-butyl phenol. Lesser amounts of other isomers of the 2,6-di-t-butyl phenol can also be present without impeding the efficacy of the components. The stability-inducing additive package typically contains 4 to 22 weight percent of the N,N&#39;-di-sec-butyl-p-phenylene diamine and 1.5 to 12 weight percent of the butylated phenols. The preferred composition of the stability-inducing additive package contains 7.3 weight percent N,N&#39;-di-sec-butyl-p-phenylene diamine and 2.8 weight percent 2,6-di-t-butyl phenol with 0.9 weight percent other isomers of this phenol. 
     The metal inactivation (metal ion sequestering) functionality of the stability-inducing additive package of the present invention is provided by N,N&#39;-bis-salicyclidene-1,2-propane diamine. Typically this component can be utilized in the practice of this invention in the 5 to 30 weight percent range. Preferably, this component is utilized at the 9.8 weight percentage level in the additive package to be added to a fuel. 
     As opposed to the current practice of using carboxylic acid corrosion inhibitors in stability-inducing additive packages, this invention employs a strongly basic (i.e., caustic) component as the corrosion inhibitor. Likewise, the corrosion inhibitor of this invention is hydrophobic and, hence, organophilic. This allows any subsequent material formed by the corrosion inhibitor to remain soluble in the hydrocarbon fuel precluding the deposition of undesirable solid materials in the various storage vessels and other pieces of apparatus exposed to the treated fuel. 
     The strongly basic, organophilic characteristics of the corrosion inhibitor are exhibited by selected organo-amines, specifically those characterized by pK b  values of 4.0 and less, with pK b  being the negative logarithm of their basic dissociation constants in aqueous solution. As is well know in the art, the chemical interaction of a strong base, B, with water in an aqueous solution can be depicted by the following reaction: ##STR2## The basic dissociation constant, Kb, can then be defined by the expression: ##EQU1## 
     Compounds applicable in this invention with these properties include substituted amidines of generalized formulation ##STR3## where R = --H or [--(CH 2  --CH 2 )--] 1/2   
     X = --CH 2  -- or --NH-- 
     R&#39; = a hydrocarbon radical containing at least 11 and no more than 24 carbon atoms, and 
     R&#34; = --H, an alkyl hydrocarbon radical containing no more than 5 carbon atoms, or a hydroxyalkyl hydrocarbon radical containing no more than 5 carbon atoms. 
     Members of this family which are preferred compounds for providing corrosion inhibition in this invention are: ##STR4## where R&#39; = a hydrocarbon radical containing at least 11 and no more than 24 carbon atoms, and 
     R&#34; = --H, an alkyl hydrocarbon radical containing no more than 5 carbon atoms, or a hydroxyalkyl hydrocarbon radical containing no more than 5 carbon atoms; ##STR5## where R&#39; = a hydrocarbon radical containing at least 11 and no more than 24 carbon atoms, and 
     R&#34; = --H, an alkyl hydrocarbon radical containing no more than 5 carbon atoms, or a hydroxyalkyl hydrocarbon radical containing no more than 5 carbon atoms; 
     and ##STR6## where R&#39; = a hydrocarbon radical containing at least 11 and no more than 24 carbon atoms, and 
     R&#34; = --H, an alkyl hydrocarbon radical containing no more than 5 carbon atoms, or a hydroxyalkyl hydrocarbon radical containing no more than 5 carbon atoms. 
     Most preferably, this invention is practiced using a high molecular weight imidazoline, specifically, 2-(8-heptadecyl)-4,5-dihydro-1H-imidazole-1-ethanol, as the corrosion inhibitor. This imidazoline is sold commercially as Amine O® by CIBA-GEIGY and is preferably included in the stability-enhancing additive package in the concentration range of 2 weight percent to 15 weight percent. Most preferably this amine is utilized in the additive package at the 5.2 weight percent level. 
     The most-preferred embodiment of the stability-enhancing package of this invention is summarized as follows: 
     
         ______________________________________COMPONENT        WEIGHT PERCENTAGE______________________________________N,N&#39;-di-sec-butyl-p-            7.3phenylene diamine2,6-di-t-butyl phenol            2.8other phenols    0.9N,N&#39;-bis-salicylidene-1,2-            9.8propane diamineAmine O ®    5.2Xylene           44.02-propanol       30.0TOTAL            100.0______________________________________ 
    
     This mixture is added to commercial gasoline at the rate of 0.5 gallons per 1000 gallons of gasoline to give a highly stabilized gasoline.