Method of Reducing Fuel Corrosiveness

Abstract

Fuels containing biodiesel, petroleum distillates, or blends of these may be treated by the addition of small amounts of one or more alkanolamines according to formula (I) Rn—N(CH2CHR1OH)3-n ;   (I) wherein n is 1 or 2, R1 is H or CH3, and each R is independently selected from the group consisting of hydrogen and branched, linear, and cyclic C3-C24 alkyl groups, provided that at least one R is not hydrogen. Fuels treated in this manner may be less corrosive toward metals with which they are in contact.

Description

FIELD OF THE INVENTION

The invention relates to fuel oils. More particularly, it relates to fuel oils containing additives that reduce corrosion in systems in contact with the oils.

BACKGROUND OF THE INVENTION

Fuel oils are widely used in a variety of applications, including diesel engines, furnaces, jet engines, and other energy-consuming uses. Traditional fuel oils are well known, and are produced by refining crude petroleum feedstocks via distillation, cracking, and other processes. However, the crude petroleum feedstocks are in limited supply and are non-renewable, and therefore renewable sources of fuel oils are increasingly sought.

One renewable fuel oil source is biodiesel, a clean-burning alternative fuel produced from domestic, renewable resources. Biodiesel contains no petroleum, but it can be blended at any level with petroleum diesel to create a fuel blend. It can be used in compression-ignition (diesel) engines with little or no modification. Biodiesel is biodegradable, essentially nontoxic, and essentially free of sulfur and aromatic compounds, and thus can provide certain environmental advantages.

Biodiesel is essentially a mixture of methyl and/or ethyl esters of fatty acids, made through transesterification of fatty acid triglycerides (oils) with methyl or ethyl alcohol. The most commonly used raw material oils are triglyceride seed oils (e.g., soybean oil, palm oil, rapeseed oil). Biodiesel esters are never produced as 100% pure compounds, and one common impurity in biodiesel is free fatty acids, which can lead to corrosion problems.

Biodiesel may be used alone, petroleum oils may be used alone, or blends may be used. Petroleum oils typically also contain some amount of acidic impurities, especially naphthenic acids. Acids from either source may cause any of a number of problems, including corrosion, poor combustion, elevated pour points, formation of deposits, and poor lubricity. As a result, fuel producers typically try to reduce the acidity of their products, but doing so usually introduces additional costs for these products, which generally sell at low margins. Beyond a certain point, the removal of acids becomes economically unacceptable, and therefore crude petroleum oils with too high a naphthenic acid content or biodiesel feed with too high a free fatty acid content become a liability to the fuel producer. Thus it would be beneficial to provide economical ways of dealing with free acids in fuel oils.

SUMMARY OF THE INVENTION

In one aspect, the invention provides a treated fuel. The treated fuel includes:

• • a) an untreated fuel consisting of a biodiesel, a petroleum distillate, or a blend thereof; and
  • b) one or more alkanolamines according to formula (I)

R_n—N(CH₂CHR¹OH)_3-n   (I);

wherein n is 1 or 2, R¹ is H or CH₃, and each R is independently selected from the group consisting of hydrogen and branched, linear, and cyclic C3-C24 alkyl groups, provided that at least one R is not hydrogen, and wherein the treated fuel is essentially free of added biological control agents.

In another aspect, the invention provides a method of treating a fuel comprising blending together an untreated fuel consisting of a biodiesel, a petroleum distillate, or a blend thereof and one or more alkanolamines according to formula (I) as shown above, wherein the treated fuel is essentially free of added biological control agents.

DETAILED DESCRIPTION OF THE INVENTION

According to the invention, fuels may be treated by the addition of small amounts of one or more alkanolamines according to formula (I)

R_n—N(CH₂CHR¹OH)_3-n   (I);

wherein n is 1 or 2, R¹ is H or CH₃, and each R is independently selected from the group consisting of hydrogen and branched, linear, and cyclic C3-C24 alkyl groups, provided that at least one R is not hydrogen. In some embodiments of the invention, the total number of carbon atoms in the R group(s) taken together is from 4 to 24, and in some preferred embodiments the number is from 6 to 20. Without wishing to be bound by any particular theory or explanation, it is believed that the presence of a significant amount of hydrophobic substitution directly on the amine nitrogen is beneficial to the reduction of corrosion. Exemplary useful alkanolamines of formula (I) include butyidiethanolamine, butylaminoethanol, dibutylaminoethanol, diisopropylaminoethanol, octylaminoethanol, and octyldiethanolamine.

The alkanolamine(s) of formula (I) may be incorporated into the treated fuel in any amount. Typically, they will be present in an amount equal to at least 0.8 mol equivalents relative to a total of the fatty and naphthenic acid impurities, and typically in an amount equal to from 0.01 to 2 wt % relative to the untreated fuel, more typically from 0.01 to 1 wt %. It is to be understood that, when reference is made to a treated fuel containing a certain amount of an alkanolamine of formula (I), this includes both alkanolamine that is unreacted and that which has formed a salt (but not an ester or amide) with fatty, naphthenic, or other acid impurities present in the untreated fuel. At least 95 wt % of the alkanolamine(s) of formula (I) added to the untreated fuel is unreacted or in the form of a salt, and preferably at least 98%.

Fuels to be treated with the alkanolamines of formula (I) include biodiesel, petroleum distillates, and blends of these. In some embodiments, the blends contain at least 5 wt % of biodiesel, or they may consist of a blend in which the biodiesel constitutes at least about 20 wt % of the blend, or at least about 80 wt % of the blend, with the balance being a petroleum distillate. Biodiesel derived from any natural or synthetic fat or oil is suitable for treatment according to the invention.

Petroleum distillates suitable for use according to the invention include any of a variety of petroleum-based fuels, including but not limited to those normally referred to as “diesel.” Exemplary distillates may include gasoline, gas-oil, and bunker fuel. Petroleum middle distillates will be used in many applications, and such middle distillates include mineral oils boiling within the range from 120 to 450° C. obtained by distillation of crude oil, for example standard kerosene, low-sulfur kerosene, jet fuel, diesel and heating oil such as No. 2 fuel oil. Exemplary distillates that may be blended with biodiesel for treatment with the alkanolamines of this invention are those which contain not more than 500 ppm, in particular less than 200 ppm, of sulfur and in specific cases less than 50 ppm of sulfur or even less than 5 ppm. Generally, the petroleum distillate may comprise from 0.01 to 1 wt % of the naphthenic acids, but the invention is not limited to this range. Useful distillates, especially middle distillates, are generally those which were subjected to refinement under hydrogenating conditions and which therefore contain only small amounts of polyaromatic and polar compounds that impart natural lubricating activity to them. The alkanolamines according to the invention may also find good use in those distillates that have 95% distillation points of less than 370° C., in particular 350° C. and in special cases less than 330° C.

The untreated fuel typically contains a minor amount of one or more fatty acids and/or naphthenic acids as impurities, although it need not contain either of them. Thus, in some embodiments, the untreated fuel may consist essentially of those impurities and the esters or hydrocarbons of the fuels themselves. In the case of biodiesel, the acids will typically be fatty acids, while naphthenic acids may often be found in petroleum distillates. The amount of fatty and/or naphthenic acids present in the untreated fuels is typically from 0.01 to 5 wt %, more typically from 0.01 to 2 wt %, and most typically between 0.05 and 1 wt %.

An untreated fuel may consist essentially of the biodiesel and/or the petroleum distillates, along with their acid impurities, or it may also contain other optional additives such as those detailed below. Similarly, the treated fuel may consist essentially of the untreated fuel combined with one or more alkanolamines of formula (I), or it may also contain those other additives. It should be noted that certain additives, when used in combination with the alkanolamine(s), may have a substantial effect on certain important properties of the treated fuel. Such properties include the viscosity of the treated fuel at 35° C. (or more generally, at engine operating temperature), the pour point of the treated fuel, the rate or extent of rust formation or other corrosion of metals in contact with the treated fuel, and the growth of bacteria, molds, fungi, slimes, and other microbial forms in the fuel. The effects of such changes may or may not be desirable in a given situation, and therefore some embodiments of the invention preclude the use of such additives in an amount that materially affects one or more of these properties.

Examples of materials that may have a material effect on one or more of the above-mentioned properties, when used in a high enough amount in combination with the alkanolamines of formula (I), include esters or amides of the alkanolamines of formula (I) with fatty or naphthenic acids, and polymers containing vinyl ester and olefin repeat groups. Other such materials include carboxylic acid esters of alkoxylated phenol-aldehyde resins, and certain biological control agents. Examples of the latter include certain triazines, thiazolinones, halogenated compounds, thiocyanates, carbamates, pyrithiones, quaternary ammonium compounds, aldehydes, heterocyclic compounds, soluble metal ions and reactive alkylating agents. Specific examples of biological control agents that may or may not be included in an effective amount include 1,3,5-(2-hydroxyethyl)-s-triazine and benzoisothiazolone.

As distinct from the foregoing list of additives, certain other additives may typically be included in the treated fuel in an amount sufficient to achieve certain performance advantages. For example, surfactants may be included to help reduce the buildup of deposits. Other ingredients might also include fatty acids as friction modifiers, octane boosters, cetane enhancers, and explosion suppressors (e.g., tetraethyllead or manganocene tricarbonyl). Water may also be present in the treated fuel. If present, it may be in only small amounts, i.e., at less than 2 wt % or even less than 0.5 wt %, most typically less than 500 ppm. It may however be present in larger amounts, for example from 2 to 25 wt % based on the total weight of the resulting mixture, more commonly 10 to 15 wt %, in the form of a solution, stabilized emulsion, or other dispersion.

The alkanolamines of formula (I) may simply be blended with fuel, without any heating or other special processing steps. Thus they may be blended at ambient temperatures, although lower or higher temperatures may be used as long as mixing is reasonably facile and undesired reactions do not occur. Typically, the temperature will be from 10 to 50° C. The pH of the fuel will be increased by the addition of the amine, and the corrosion-reducing effect of the alkanolamine will be realized following the addition. It should be noted that the measured acid number of the fuel will not necessarily change after the alkanolamine is added, since titration in the usual manner (with KOH) may still pick up protons bound by amino nitrogen. However, even though the fuel's acid number does not decrease as much as it would if a stronger base were used instead of the alkanolamine, the fuel still shows marked reduction in corrosiveness. Therefore, in some cases, producers may wish to modify their specification test to account for the fact that amine neutralizing agents are being employed.

Treated fuels according to the invention generally provide relatively low rates of corrosion, making them suitable for use in a number of applications. For example, many applications involve the use of brass parts, either leaded or unleaded, and corrosion caused by some prior art fuels can lead to excessive and deleterious levels of copper and other metals in the fuel. Low corrosion of copper, brass and iron is an important property for many fuels, and such low corrosion is particularly important in biodiesel type fuels, since these fuels need to be compatible with existing engines that contain iron, iron alloy, aluminum alloy, copper, and copper alloy parts. Corrosion of brass in the presence of the treated fuel may produce less than 70 ppm of copper in the treated fuel, as measured by the test methods described in Example 1 below. Without wishing to be bound by any particular theory or explanation, it is believed that the alkanolamines of formula (I) neutralize at least some of the free acids, and that this reduces corrosion.

EXAMPLES

Example 1

Corrosion Inhibition in Aqueous Solutions of Alkanolamine and Fatty Acid

The following data provide an indication of corrosion performance in situations where diesel fuel is exposed to pools of standing water (e.g., fuel tanks, storage containers) and the fatty acids and amines within the fuel are extracted into the pools. Eight aqueous solutions each containing a different alkanolamine at a concentration of 0.3 M along with octanoic acid at a concentration of 0.2 M and with the pH adjusted to 8.5 (at room temperature) by H₃PO₄ and/or KOH addition were prepared as models of heavily neutralized biodiesel type fuel. A 450-gram portion of each of these solutions was weighed carefully and transferred to a wide-mouth screw-cap glass bottle. Brass panels (2″×2″×0.032″) panels were washed with 10% liquid-Nox (Alcanox), buffed dry with a paper towel, and immersed in the solutions described above. Caps were placed tightly on all bottles to insure that no evaporation took place. A 5-gram sample of each solution was collected after 30 days and analyzed by ICP (Inductively Coupled Plasma) atomic emission spectroscopy for metals content. Two types of brass were tested—leaded (CA-360, 3% Pb) and unleaded (CA-260) alloy. The results (passive dissolution of copper, zinc and lead) are shown below.

Day 30, Alkanolamine & Octanoic Acid, Unleaded Brass

Alkanolamine	Cu (ppm)	Pb (ppm)	Zn (ppm)
Alkanolamines of formula (I)
Butylaminoethanol	10	<0.02	7
Butyldiethanolamine	44	<0.02	9
Diisopropylaminoethanol	2	<0.02	0.8
Isopropylaminoethanol	44	<0.02	16
Prior Art Alkanolamines
2-Amino-2-methyl-1-propanol	123	<0.02	66
Diglycolamine	234	<0.02	19
Monoethanolamine	211	<0.02	14
Triethanolamine	171	<0.02	3

Day 30, Alkanolamine & Octanoic Acid, Leaded Brass

Alkanolamine	Cu (ppm)	Pb (ppm)	Zn (ppm)
Alkanolamines of formula (I)
Butylaminoethanol	9	0.2	5
Butyldiethanolamine	66	0.7	12
Diisopropylaminoethanol	1	0.06	0.6
Isopropylaminoethanol	19	0.3	7
Prior Art Alkanolamines
2-Amino-2-methyl-1-propanol	74	1	37
Diglycolamine	168	2	31
Monoethanolamine	134	2	4
Triethanolamine	165	7	2

As can be seen from the results shown in the above tables, solutions containing fatty acids (i.e., octanoic acid) and the alkanolamines of this invention have far less tendency to corrode brass than do solutions in which prior art alkanolamines are used instead.

Although the invention is illustrated and described herein with reference to specific embodiments, it is not intended that the subjoined claims be limited to the details shown. Rather, it is expected that various modifications may be made in these details by those skilled in the art, which modifications may still be within the spirit and scope of the claimed subject matter and it is intended that these claims be construed accordingly.

Claims

1. A treated fuel comprising:

a) an untreated fuel consisting of a biodiesel, a petroleum distillate, or a blend thereof; and

b) one or more alkanolamines according to formula (I) Rn—N(CH2CHR1OH)3-n   (I);

wherein n is 1 or 2, R1 is H or CH3, and each R is independently selected from the group consisting of hydrogen and branched, linear, and cyclic C3-C24 alkyl groups, provided that at least one R is not hydrogen, and wherein the treated fuel is essentially free of added biological control agents.

2. The treated fuel of claim 1, wherein the treated fuel comprises less than 2 wt % water.

3. The treated fuel of claim 1, wherein the treated fuel further comprises from 2 to 25 wt % water.

4. The treated fuel of claim 1, wherein the untreated fuel consists of said blend and wherein the biodiesel constitutes at least about 5 wt % of the blend.

5. The treated fuel of claim 1, wherein the untreated fuel consists of said blend and wherein the biodiesel constitutes at least about 20 wt % of the blend.

6. The treated fuel of claim 1, wherein the untreated fuel consists of said blend and wherein the biodiesel constitutes at least about 80 wt % of the blend.

7. The treated fuel of claim 1, wherein the untreated fuel consists of the biodiesel.

8. The treated fuel of claim 1, wherein the untreated fuel consists of the petroleum distillate.

9. The treated fuel of claim 1, wherein the biodiesel or the petroleum distillate comprises one or more fatty or naphthenic acid impurities, or both, and wherein the one or more alkanolamines of formula (I) are present in an amount equal to at least 0.8 mol equivalents relative to a total of the fatty and naphthenic acid impurities.

10. The treated fuel of claim 1, wherein the one or more alkanolamines of formula (I) are present in an amount equal to from 0.01 to 2 wt % relative to the untreated fuel.

11. The treated fuel of claim 1, wherein corrosion of brass in the presence of the treated fuel produces less than 70 ppm of copper in the treated fuel.

12. The treated fuel of claim 1, wherein the biodiesel or the petroleum distillate comprises one or more fatty or naphthenic acid impurities, or both, and wherein the biodiesel comprises from 0.01 to 5 wt % of the fatty acid impurities.

13. The treated fuel of claim 1, wherein the untreated fuel consists of said blend.

14. The treated fuel of claim 1, wherein the petroleum distillate comprises No. 2 fuel oil.

15. The treated fuel of claim 1, wherein the petroleum distillate comprises a jet fuel.

16. The treated fuel of claim 1, wherein the biodiesel or the petroleum distillate comprises one or more fatty or naphthenic acid impurities, or both, and wherein the petroleum distillate comprises from 0.01 to 1 wt % of the naphthenic acid impurities.

17. The treated fuel of claim 1, wherein a total number of carbon atoms in the R groups is from 4 to 24.

18. The treated fuel of claim 1, wherein a total number of carbon atoms in the R groups is from 6 to 20.

19. A method of treating a fuel, comprising blending together:

a) an untreated fuel consisting of a biodiesel, a petroleum distillate, or a blend thereof; and

b) one or more alkanolamines according to formula (I) Rn—N(CH2CHR1OH)3-n   (I);

wherein n is 1 or 2, R1 is H or CH3, and each R is independently selected from the group consisting of hydrogen and branched, linear, and cyclic C3-C24 alkyl groups, provided that at least one R is not hydrogen, and wherein the treated fuel is essentially free of added biological control agents.

20. The method of claim 19, wherein the blending is performed at a temperature from 10 to 50° C.

21. The method of claim 19, further comprising blending from 2 to 25 wt % of water, based on the total weight of the resulting mixture, with any of the biodiesel, the petroleum distillates, the untreated fuel, or the treated fuel.