Patent Application
20090165364
The present invention relates to the use of mixtures of aliphatic saturated or unsaturated relatively long-chain monocarboxylic acids or derivatives thereof and polycyclic hydrocarbon compounds in a specific concentration range for improving the storage stability of fuel additive concentrates which comprise at least one detergent and at least one cetane number improver. The invention further relates to a fuel additive concentrate which comprises detergents based on succinic anhydride, cetane number improvers and the abovementioned mixtures in specific ratios.
After they have been produced, and before they are mixed into the fuels in the refineries, fuel additive concentrates typically reside for a long period in transport and storage vessels. This residence time may be from a few weeks up to months. In the course of this, the fuel additive concentrates frequently tend to cloudiness, separation of the components and in some cases even to precipitation.
U.S. Pat. No. 5,591,237 (1) discloses that the storage stability of fuel additive concentrates which comprise detergents based on succinic anhydride, especially polyisobutenylsuccinimides, and cetane number improvers can be improved by adding nitric acid, hydrochloric acid or aliphatic monocarboxylic acids in an amount of from 1500 to 10 000 ppm. In the examples of (1), among other compounds, oleic acid in a concentration of 6000 ppm and hydrochloric acid in a concentration of 10 000 ppm in the concentrate are demonstrated to be effective improvers of storage stability.
EP-A 890 631 (2) describes an additive composition which comprises an ashless detergent based on an acylated nitrogen compound, for example a polyisobutenylsuccinimide, and a relatively long-chain carboxylic acid or an ester thereof, and brings about improved lubricity of fuel oils and better solubility in the fuel oils.
WO 98/04656 (3) describes the use of a fuel additive composed of aliphatic saturated or unsaturated relatively long-chain monocarboxylic acids or derivatives thereof and polycyclic hydrocarbon compounds which are obtained in particular from tall oil for improving the improvement in the lubrication properties of diesel fuels with low sulfur content.
It was an object of the present invention to further improve the storage stability of fuel additive concentrates which comprise detergents and cetane number improvers.
Accordingly, we have found the use of mixtures of
for improving the storage stability of fuel additive concentrates which comprise at least one detergent and at least one cetane number improver, the mixtures of components (A) and (B) being used in a concentration of from 0.7 to 20% by weight based on the total amount of the fuel additive concentrate.
Component (A) in the mixtures mentioned comprises preferably aliphatic saturated or unsaturated monocarboxylic acids having from 14 to 20 carbon atoms, in particular from 16 to 18 carbon atoms. These monocarboxylic acids are generally linear. For component (A), useful monocarboxylic acids are in particular naturally occurring fatty acids, in particular those having from 14 to 20 carbon atoms, in particular from 16 to 18 carbon atoms. Typical representatives of such monocarboxylic acids or fatty acids are lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, linoleic acid, linolenic acid and elaidic acid. Component (A) may consist only of one such monocarboxylic acid or fatty acid or preferably of a mixture of two or more such monocarboxylic acids or fatty acids. Naturally occurring fatty acids, as obtained, for example, from rapeseed oil, soya oil or tall oil, are generally mixtures of a plurality of such monocarboxylic acids.
Component (B), whose natural origin is tree resins, in particular conifer resins from pines or spruces, is formed from one or preferably more so-called resin acids. Resin acids are carboxyl-containing polycyclic hydrocarbon compounds. They include, as the most important representatives, abietic acid, dehydroabietic acid, dihydroabietic acid, tetrahydroabietic acid, neoabietic acid, palustric acid, pimaric acid, isopimaric acid and levopimaric acid. These resin acids may partly also be present in oxidized form as so-called oxy acids.
In a preferred embodiment, components (A) and (B) are used in the mixtures mentioned in a weight ratio of from 65:35 to 99.9:0.1, especially from 90:10 to 99.9:01, in particular from 97:3 to 99.9:0.1.
Particularly suitable mixtures of components (A) and (B) are tall oil fatty acid and dimerized tall oil fatty acid. Tall oil fatty acid is prepared from tall oil which is obtained by digestion of resin-rich wood types, in particular from spruce or pinewood. Tall oil fatty acid is a mixture of fatty acids in which the C18-unsaturated monocarboxylic acids, in particular oleic acid, linoleic acid and conjugated C18 fatty acids, and also 5,9,12-octadecatrienoic acid predominate, resin acids and, if appropriate, oxy acids (i.e. oxidized fatty acids and resin acids). Resin acid forms so-called tall resin in which abietic acid, dehydroabietic acid and palustric acid predominant and small fractions of dihydroabietic acid, neoabietic acid, pimaric acid and isopimaric acid are detectable in addition to further resin acids. In the best tall oil fatty acid quality, the fatty acid fraction is at least 97% by weight and the tall resin fraction up to 3% by weight.
The recovery of tall oil fatty acid and of resin acids from tree resins by digestion, extraction and distillation processes is known to those skilled in the art and therefore need not be explained in detail here.
In dimerized tall oil fatty acid, the fatty acid component (A) is present in dimerized form. Dimerizations and trimerizations of monocarboxylic acids or fatty acids can be carried out by the processes customary for this purpose and are known in principle to those skilled in the art.
The monocarboxylic acids or fatty acids and their dimerization or trimerization products of component (A) may be present as free carboxylic acids and/or as ammonium salts, for example as NH4 salts or substituted ammonium salts, such as mono-, di-, tri- or tetramethylammonium salts, and/or in the form of amides, esters and/or nitriles. Typical amide structures have the —CO—NH2, —CO—NH-alkyl or —CO—N(alkyl)2 moieties, where “alkyl” here in particular represents C1- to C4-alkyl radicals such as methyl or ethyl. Ester structures typically include C1- to C4-alkanol ester radicals such as methyl or ethyl ester radicals.
The fuel additive concentrates mentioned may in principle be used to additize any fuels or fuel oils. However, they are suitable in particular for additizing diesel fuels (middle distillate fuels). Diesel fuels (middle distillate fuels) are typically crude oil raffinates which generally have a boiling range from 100 to 400° C. These are usually distillates having a 95% point up to 360° C. or even higher. They may also be so-called “ultra-low sulfur diesel” or “city diesel”, characterized by a 95% point of, for example, not more than 345° C. and a sulfur content of not more than 0.005% by weight, or by a 95% point of, for example, 285° C. and a sulfur content of not more than 0.001% by weight. In addition to the diesel fuels obtainable by refining, whose main constituents are relatively long-chain paraffins, suitable diesel fuels are those which are obtainable by cool gasification or gas liquefaction [“gas-to-liquid” (GTL) fuels]. Also suitable are mixtures of the aforementioned diesel fuels with renewable fuels such as biodiesel or bioethanol. Of particular interest at present are diesel fuels with a low sulfur content, i.e. with a sulfur content of less than 0.05% by weight, preferably of less than 0.02% by weight, in particular of less than 0.005% by weight and especially of less than 0.001% by weight of sulfur. Diesel fuels may also comprise water, for example in an amount of up to 20% by weight, for example in the form of diesel-water microemulsions or as so-called “white diesel”.
Detergents (detergent additives) refer typically to deposition inhibitors for fuels, here in particular diesel fuels. The detergents are preferably amphiphilic substances which have at least one hydrophobic hydrocarbon radical having a number-average molecular weight (Mn) of from 85 to 20 000, especially from 300 to 5000, in particular from 500 to 2500, and at least one polar moiety.
In a preferred embodiment, the mixture of components (A) and (B) is used to improve the storage stability of fuel additive concentrates which, in addition to at least one cetane number improver, comprise at least one detergent having moieties which are derived from succinic anhydride and have hydroxyl and/or amino and/or amido and/or imido groups.
This detergent having moieties which are derived from succinic anhydride and have hydroxyl and/or amino and/or amido and/or imido groups is more preferably a polyisobutenyl-substituted succinimide.
Additives comprising moieties which are derived from succinic anhydride and have hydroxyl and/or amino and/or amido and/or imido groups are preferably corresponding derivatives of polyisobutenylsuccinic anhydride which are obtainable by reacting conventional or highly reactive polyisobutene having Mn=from 300 to 5000, in particular having Mn=from 500 to 2500, with maleic anhydride by a thermal route or via the chlorinated polyisobutene. Of particular interest in this context are derivatives with aliphatic polyamines such as ethylenediamine, diethylenetriamine, triethylenetetramine or tetraethylenepentamine. The moieties with hydroxyl and/or amino and/or amido and/or imido groups are, for example, carboxylic acid groups, acid amides, acid amides of di- or polyamines which, in addition to the amide function, also have free amine groups, succinic acid derivatives having an acid and an amide function, carboximides with monoamines, carboximides with di- or polyamines which, in addition to the imide function, also have free amine groups, and diimides which are formed by the reaction of di- or polyamines with two succinic acid derivatives. Such fuel additives are described in particular in U.S. Pat. No. 4,849,572.
The cetane number improvers (ignition or combustion improvers) used are typically organic nitrates. Such organic nitrates are in particular nitrate esters of unsubstituted or substituted aliphatic or cycloaliphatic alcohols, usually having up to about 10, in particular having from 2 to 10 carbon atoms. The alkyl group in these nitrate esters may be linear or branched, saturated or unsaturated. Typical examples of such nitrate esters are methyl nitrate, ethyl nitrate, n-propyl nitrate, isopropyl nitrate, allyl nitrate, n-butyl nitrate, isobutyl nitrate, sec-butyl nitrate, tert-butyl nitrate, n-amyl nitrate, isoamyl nitrate, 2-amyl nitrate, 3-amyl nitrate, tert-amyl nitrate, n-hexyl nitrate, n-heptyl nitrate, sec-heptyl nitrate, n-octyl nitrate, 2-ethylhexyl nitrate, sec-octyl nitrate, n-nonyl nitrate, n-decyl nitrate, cyclopentyl nitrate, cyclohexyl nitrate, methylcyclohexyl nitrate and isopropylcyclohexyl nitrate. Also suitable are, for example, nitrate esters of alkoxy-substituted aliphatic alcohols such as 2-ethoxyethyl nitrate, 2-(2-ethoxyethoxy)ethyl nitrate, 1-methoxypropyl nitrate or 4-ethoxybutyl nitrate. Also suitable are diol nitrates such as 1,6-hexamethylene dinitrate. Among the cetane number improver classes mentioned, preference is given to primary amyl nitrates, primary hexyl nitrates, octyl nitrates and mixtures thereof.
In a preferred embodiment, the mixture of components (A) and (B) is used to improve the storage stability of fuel additive concentrates which, in addition to at least one detergent, comprise 2-ethylhexyl nitrate as a cetane number improver. In this case, 2-ethylhexyl nitrate may be present as the sole cetane number improver or in a mixture with other cetane number improvers.
The fuel additive concentrates mentioned, which are suitable in particular for additizing diesel fuels (middle distillate fuels) may, in addition to the detergent component and the cetane number improver component, include further customary additive components, for example corrosion inhibitors, demulsifiers, antifoams, antioxidants and stabilizers, antistats, lubricity improvers, dyes (markers) and/or solvents and diluents.
In the context of the present invention, the mixture of carboxylic acids (A) and the polycyclic hydrocarbon compounds (B) is used in amounts of from 0.7 to 20% by weight, especially from 1.1 to 15% by weight, in particular from 1.5 to 10% by weight, more preferably from 3 to 8% by weight, based in each case on the total amount of the fuel additive concentrate. The use concentration of the mixture of (A) and (B) is a critical parameter, since it has been found that the dosage rate of 6000 ppm (corresponding to 0.6% by weight) recommended in (1) for monocarboxylic acids (by way of example for oleic acid) does not bring about sufficient storage stability for the fuel additive concentrates. The additional amount of the mixture of (A) and (B) in the present invention compared to the teaching of (1) also exhibits additional positive effects in the use of the fuel additive concentrates; in particular, the lubricity of low-sulfur diesel fuel additized therewith is simultaneously improved.
Since some of the fuel additive concentrates mentioned constitute novel substance mixtures, the present invention also provides a fuel additive concentrate which, based in each case on the total amount of the fuel additive concentrate, comprises
The examples which follow are intended to further illustrate the present invention without restricting it.
The two duel additive concentrates 1A and 1B which are suitable for use in diesel fuel have the compositions specified in Table 1 [in % by weight]:
Result of the Storage Experiments:
Concentrate 1A became distinctly cloudy even after 2 weeks of storage at 40° C., whereas concentrate 1B remained clear after 50 weeks of storage at 40° C.
| Number | Date | Country | Kind |
|---|---|---|---|
| 06100505.4 | Jan 2006 | EP | regional |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP07/50234 | 1/11/2007 | WO | 00 | 7/3/2008 |
