Method of Improving Oil Compositions

Abstract

A method of improving the low temperature properties of an oil comprising fatty acid alkyl esters derived from plant or animal materials, wherein at least 5% by weight of the fatty acid alkyl esters are derived from C16-C22 saturated fatty acids. The method comprising reacting at least a portion of the oil with a polyalkylene polyamine or an imidazoline compound carrying both a poly-alkylene imine substituent and at least one primary amine group.

Description

This invention relates to a method of improving the low-temperature properties of oils derived from plant or animal materials.

Oils and fats derived from plant or animal materials are increasingly finding application as fuels and in particular, as partial or complete replacements for petroleum derived middle distillate fuels such as diesel. Commonly, such fuels are known as ‘biofuels’ or ‘biodiesel’. Biofuels may be derived from many sources. Amongst the most common are the alkyl, often methyl, esters of fatty acids extracted from plants such as rapeseed, sunflower etc. These types of fuel are often referred to as FAME (fatty acid methyl esters).

There is an environmental drive to encourage the use of such fuels as they are obtained from a renewable source. There are also indications that biofuels produce less pollution on combustion than the equivalent petroleum-derived fuel.

Fuel oils derived from plant or animal materials contain components, e.g., methyl n-alkanoates, that at low temperature tend to precipitate as large, plate-like crystals or spherulites of wax in such a way as to form a gel structure which causes the fuel to lose its ability to flow. The lowest temperature at which the fuel will still flow is known as the pour point.

As the temperature of the fuel falls and approaches the pour point, difficulties arise in transporting the fuel through lines and pumps. Further, the wax crystals tend to plug fuel lines, screens, and filters at temperatures above the pour point. These problems are well-recognised in the art, and various additives have been proposed, many of which are in commercial use, for depressing the pour point of fuel oils; both those derived from petroleum sources and those derived from plant or animal materials. Similarly, other additives have been proposed and are in commercial use for reducing the size and changing the shape of the wax crystals that do form. Smaller size crystals are desirable since they are less likely to clog a filter. Certain additives inhibit the tendency of the waxes formed to crystallize as platelets instead causing them to adopt an acicular habit. The resulting needles are more likely to pass through a filter, or form a porous layer of crystals on the filter, than are platelets. The additives may also have the effect of retaining the wax crystals in suspension in the fuel, reducing settling and thus also assisting in prevention of blockages.

The low temperature properties of the oils derived from plant or animal materials are largely determined by the saturated fatty acid content of the oil, and in particular by the proportion of C₁₆-C₂₂ saturated fatty acids which may be present. The methyl and ethyl esters of these acids may be particularly problematic. Transportation and handling of such oils at or below the temperature at which these species crystallise from a mixture of fatty acid esters is difficult. Oils which contain very little saturated fatty acid esters can sometimes successfully be treated with conventional additives to improve their low-temperature properties. However, oils containing even relatively low amounts of, in particular, esters derived from palmitic and stearic acids, have been found to be unresponsive to conventional additives.

Despite the problems highlighted above, there is a desire to utilise oils derived from plant or animal materials containing C₁₆-C₂₂ saturated fatty acids. This is because they are obtained from comparatively inexpensive and plentiful sources. The present invention provides a solution to the low-temperature transportation and handling problems associated with these oils.

In accordance with the present invention there is provided a method of improving the low temperature properties of an oil comprising fatty acid alkyl esters derived from plant or animal materials, wherein at least 5% by weight of the fatty acid alkyl esters are derived from C₁₆-C₂₂ saturated fatty acids, the method comprising reacting at least a portion of the oil with at least one compound having 3 or more nitrogen atoms, at least one of which nitrogen atoms is present in the form of a primary amine group; wherein the at least one compound having 3 or more nitrogen atoms comprises a polyalkylene polyamine or an imidazoline compound carrying both a poly-alkylene imine substituent and at least one primary amine group.

In the context of the present invention, an improvement in low temperature properties with regard to the oil may constitute an improvement in any one or more of the pour point, the cloud point, the cold filter plugging point (CFPP) or other operability test. Suitable tests will be known to those skilled in the art. Preferably, an improvement in low temperature properties will constitute an improvement in pour point and/or an improvement in CFPP.

Without wishing to be bound by any theory, it is thought that the amidation of a mixture of the types of fatty acid esters which give rise to poor low temperature properties provides an ‘additive’ which is effective to improve the low temperature properties of an oil where these esters are present in significant amounts. The ‘additive’ is produced in situ by reacting the compound having 3 or more nitrogen atoms directly with the oil containing the problematic saturated fatty acid-derived esters. As is known in the art, the reaction of e.g. a methyl ester with an amine to form an amide is facile.

Preferably the portion of the oil which is reacted with the compound having 3 or more nitrogen atoms is between 0.05-10% by weight of the oil, more preferably 0.05-2% by weight, for example 0.05-1% by weight.

The oil, once reacted with the compound having 3 or more nitrogen atoms, may be used on its own, e.g. as a pure bio-fuel, or be combined in any proportion with a petroleum-derived oil.

In a preferred embodiment, at least one fatty acid is additionally employed. Preferably, a mixture of fatty acids is employed for example, a mixture of fatty acids obtained from plant or animal materials. The at least one fatty acid is co-reacted with the oil and the at least one compound having 3 or more nitrogen atoms, or is added to the oil. The at least one fatty acid and the at least one compound having 3 or more nitrogen atoms may be added to the oil in any order.

By employing at least one fatty acid, the low-temperature properties of an oil derived from plant or animal materials comprising at least 5% by weight of fatty acid alkyl esters derived from C₁₆-C₂₂ saturated fatty acids can be further improved.

It is expected that one (or more if present) of the primary amine groups of the compound having 3 or more nitrogen atoms will react with the fatty acid alkyl esters to form an amide. As mentioned above, this reaction is favourable and can be facilitated by gentle heat. Other nitrogen atoms of the compound may be for example, secondary or tertiary amines. Amide formation from such amine groups is much less favourable and thus it is expected that they will remain unreacted in the presence of the fatty acid alkyl esters. It is presently thought that the addition of a fatty acid may promote the formation of a salt with one or more of the other nitrogen atoms.

The various features of the invention will now be described in more detail.

Mixture of Fatty Acid Alkyl Esters

At least 5% by weight of the mixture of fatty acid alkyl esters is derived from C₁₆-C₂₂ saturated fatty acids. Preferably, at least 10%, more preferably at least 20%, even more preferably at least 30% of the mixture of fatty acid alkyl esters is derived from C₁₆-C₂₂ saturated fatty acids. Preferred are methyl or ethyl esters, especially methyl esters.

In a preferred embodiment the fatty acid alkyl esters derived from C₁₆-C₂₂ saturated fatty acids comprise methyl palmitate, methyl stearate or a mixture thereof.

Preferably, the amount of the mixture of fatty acid alkyl esters derived from C₁₆-C₂₂ saturated fatty acids will not exceed 60% by weight. The majority of the remainder of the mixture of fatty acid esters preferably comprises those derived from unsaturated fatty acids.

Non-limiting examples of suitable materials include palm oil methyl ester (PME), soy oil methyl ester (SME) and rape-seed oil methyl ester (RME). Also suitable are mixtures of materials obtained from different sources for example, a mixture of PME and rape-seed methyl ester (RME) or other similar mixtures.

Compound Having 3 or More Nitrogen Atoms

The compound to be reacted with the oil has at least 3 nitrogen atoms. At least one of these nitrogen atoms is in the form of a primary amine.

In one embodiment, the compound having 3 or more nitrogen atoms is (i) a polyalkylene polyamine.

Suitable are those species comprising amino nitrogens linked by alkylene bridges, which amino nitrogens may be primary, secondary and/or tertiary in nature, provided that at least one amino nitrogen is a primary amine group. The polyamines may be straight chain, wherein all the amino groups will be primary or secondary groups, or may contain cyclic or branched regions or both, in which case tertiary amino groups may also be present, again provided that at least one amino nitrogen is a primary amine group. The alkylene groups may be identical or they may be different within a single molecule. Ethylene or propylene groups are preferred, with ethylene being most preferred.

Non-limiting examples of suitable polyalkylene polyamines include di(ethylene) triamine (DETA), tri(ethylene)tetramine (TETA), tetra(ethylene)pentamine (TEPA), penta(ethylene) hexamine (PEHA) and similar homologs. Polyalkylene polyamines having 5 or more nitrogen atoms are generally preferred over those with 4 or fewer nitrogen atoms.

Mixtures of polyalkylene polyamines are also suitable. As is known in the art, these materials are readily available and comprise polyalkylene polyamines of various sizes. They are commonly referred to as PAM. They may be defined by the average number of nitrogen atoms per molecule of the component, which may preferably be in the range of 5 to 8.5, more preferably 6.8 to 8, for example 6.8 to 7.5 nitrogens per molecule. Heavier materials, so-called HPAM, are also suitable such as amine mixtures comprising polyamines having on average seven and eight, and optionally nine, nitrogen atoms per molecule.

In another embodiment, the compound having 3 or more nitrogen atoms is:

(ii) an imidazoline compound carrying both a poly-alkylene imine substituent and at least one primary amine group. Such compounds may for example be made by reacting a fatty acid or the methyl ester of a fatty acid (e.g. stearic or palmitic) with a polyalkylene polyamine such a TETA, TEPA, PEHA, PAM and the like.

Fatty Acid

Preferred fatty acids are unsaturated fatty acids having between 16 and 20 carbon atoms. Particularly preferred are C₁₈ unsaturated acids such as oleic acid, linoleic acid and linolenic acid. These may be used as pure components, but it preferable to use mixtures of fatty acids obtained from plant or animal materials. Examples are fatty acid mixture obtained from rapeseed oil, tall oil, coriander oil, soyabean oil, cottonseed oil, sunflower oil, castor oil, olive oil, peanut oil, maize oil, almond oil, palm kernel oil, coconut oil, mustard seed oil, jatropha oil, beef tallow and fish oils. Further examples include oils derived from corn, jute, sesame, shea nut, ground nut and linseed oil and may be derived therefrom by methods known in the art. Oils having a high proportion of C₁₈ unsaturated fatty acids, that is in excess of 50% by weight of C₁₈ unsaturated fatty acids, preferably in excess of 70% or 85% by weight are suitable. Fatty acids obtained from tall oil and rapeseed oil are particularly suitable.

One or more co-additives may be used in the present invention. Suitable co-additives are those known in the art as effective to improve the low-temperature properties of fuel oils as well as additives to improve other properties of the oils such as lubricity additives, antioxidants, dispersants, detergents and similar.

In a preferred embodiment, an ethylene polymer may be employed as a co-additive. Examples of these are given below.

Ethylene Polymers

Each polymer may be a homopolymer or a copolymer of ethylene with another unsaturated monomer.

Preferred co-monomers are unsaturated esters or ether monomers, with ester monomers being more preferred. Preferred ethylene unsaturated ester copolymers have, in addition to units derived from ethylene, units of the formula:

—CR³R⁴—CHR⁵—

wherein R³ represents hydrogen or methyl, R⁴ represents COOR⁶, wherein R⁶ represents an alkyl group having from 1-12, preferably 1-9 carbon atoms, which is straight chain, or, if it contains 3 or more carbon atoms, branched, or R⁴ represents OOCR⁷, wherein R⁷ represents R⁶ or H, and R⁵ represents H or COOR⁶.

These may comprise a copolymer of ethylene with an ethylenically unsaturated ester, or derivatives thereof. An example is a copolymer of ethylene with an ester of a saturated alcohol and an unsaturated carboxylic acid, but preferably the ester is one of an unsaturated alcohol with a saturated carboxylic acid. An ethylene-vinyl ester copolymer is advantageous; an ethylene-vinyl acetate, ethylene-vinyl propionate, ethylene-vinyl hexanoate, ethylene-vinyl 2-ethylhexanoate, ethylene-vinyl octanoate or ethylene-vinyl versatate copolymer is preferred. Preferably, the copolymer contains from 5 to 40 wt % of the vinyl ester, more preferably from 10 to 35 wt % vinyl ester. A mixture of two copolymers, for example, as described in U.S. Pat. No. 3,961,916, may be used. The Mn of the copolymer is advantageously 1,000 to 10,000. If desired, the copolymer may contain units derived from additional comonomers, e.g. a terpolymer, tetrapolymer or a higher polymer, e.g. where the additional comonomer is isobutylene or diisobutylene or a further unsaturated ester.

Other suitable co-monomers include hydrocarbon monomers such as propylene, n- and iso-butylenes, 1-hexene, 1-octene, methyl-1-pentene vinyl-cyclohexane and the various alpha-olefins known in the art, such as 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecane and 1-octadecene and mixtures thereof.

The invention will now be described by way of example only.

EXAMPLE 1

Rape-seed oil methyl ester (RME) having a C₁₆-C₂₂ saturate content of 6.2% by weight was reacted with tetraethylene pentamine (TEPA) in an amount of 0.125% by weight. The reaction was carried out at 140° C. for four hours under a blanket of nitrogen gas. The pour point of the untreated RME was −12° C. After reaction with TEPA, the pour point was reduced to −42° C.

EXAMPLE 2

1-2 moles of diethylene triamine (DETA) was reacted with 1 mole of stearic acid by refluxing in xylene at 160° C. After completion, excess amine was removed together with the solvent by vacuum distillation. 1-aminoethyl-2-heptadecyl-imidazoline was obtained as the product. Soya-oil methyl ester (SME) having a C₁₆-C₂₂ saturate content of 14.6% by weight was reacted with the imidazoline in an amount of 0.5% by weight. The reaction was carried out at 150° C. for four hours under a blanket of nitrogen gas. An ethylene vinyl acetate (EVA) copolymer in an amount of 0.6% by weight was added to the SME and the pour point was measured to be −42° C. By comparison, the pour point of the unreacted SME including the 0.6% of the EVA copolymer was measured at −6° C.

EXAMPLE 3

Triethylene tetramine (TETA) was reacted with stearic acid in the same proportions and under the same reaction conditions as described in Example 2. 1-(N-aminoethyl-aminoethyl)-2-heptadecyl-imidazoline was obtained as the product. Soya-oil methyl ester (SME) having a C₁₆-C₂₂ saturate content of 14.6% by weight was reacted with the imidazoline in an amount of 0.5% by weight. The reaction was carried out at 150° C. for four hours under a blanket of nitrogen gas. An ethylene vinyl acetate (EVA) copolymer in an amount of 0.6% by weight was added to the SME and the pour point was measured to be −51° C. By comparison, the pour point of the unreacted SME including the 0.6% of the EVA copolymer was measured at −6° C.

Claims

1. A method of improving the low temperature properties of an oil comprising fatty acid alkyl esters derived from plant or animal materials, wherein at least 5% by weight of the fatty acid alkyl esters are derived from C16-C22 saturated fatty acids, the method comprising reacting at least a portion of the oil with at least one compound having 3 or more nitrogen atoms comprising a polyalkylene polyamine or an imidazoline compound carrying both a poly-alkylene imine substituent and at least one primary amine group, at least one of which nitrogen atoms is present in the form of a primary amine group.

2. A method according to claim 1 wherein the polyalkylene polyamine has 5 or more nitrogen atoms.

3. A method according to claim 1 wherein the imidazoline compound is made by reacting a fatty acid or the methyl ester of a fatty acid with a polyalkylene polyamine.

4. A method according to claim 1 wherein the portion of the oil which is reacted with the compound having 3 or more nitrogen atoms is between 0.05-10% by weight of the oil.

5. A method according to claim 1 wherein the oil comprising fatty acid alkyl esters derived from plant or animal materials consists substantially of methyl or ethyl esters, preferably methyl esters.

6. A method according to claim 1 wherein the at least 5% by weight of the fatty acid alkyl esters derived from C16-C22 saturated fatty acids comprises methyl palmitate, methyl stearate or a mixture thereof.

7. A method according to claim 1 wherein at least one fatty acid is co-reacted With the oil and the at least one compound having 3 or more nitrogen atoms, or is added to the oil.

8. A method according to claim 6 wherein the at least one fatty acid comprises a mixture of fatty acids obtained from plant or animal material, preferably a mixture having in excess of 50% by weight of C18 unsaturated fatty acids.

9. A method according to claim 1 further comprising adding an ethylene polymer to the oil.