Background Art "Fuel oil instability"is the phenomenon that causes the precipitation of low- solubility substances in the oil matrix during storage.

"Fuel oil"refers to different kinds of oil mixtures and/or oil mixtures from different sources. In general, it concerns mixtures of heavy distillates, distillation residues (the so-called tar), and hydrocarbon cuts (the so-called flux oil) coming from petrochemical plants and refineries. The different kinds of oil can be used individually or, preferably, in mixtures to generate heat for industrial use (furnaces and boilers) and for heating homes or to produce energy (motors). Normally, fuel oil is obtained either by mixing oils from different sources normally each other compatible (blending from various industrial plants) ; or by mixing oils coming from a single plant (for example, the products of distillation and cracking), forming oil mixtures that are usually non-standard. The incompatibility and/or non-standard nature of the oil mixtures cause problems during storage. In fact, hydrocarbons- the chief components of petroleum products such as paraffin, naphthene, aromatic hydrocarbons, and olefin-are normally unstable since heat, for example, causes them to polymerize and combine with other oil components to form asphaltene-type solid compounds that, along with other possible solids, create stability problems during storage and negatively affect subsequent usage.

Specifically, the following problems arise due to the unstable nature of the fuel oil at the time of usage (combustion): - Plentiful formation of carbon in the preheaters due to coking of heavy carbonic materials - Plentiful formation of soot due to the incomplete combustion of insoluble heavy compounds (precipitates) - Formation of sediments, paraffin, and rubber-like substances in the lines of the combustion system The HFT parameter (method ASTM D 4870) or, alternatively, standard ASTM D

4740 (Stability and Compatibility of Residual Fuels by Spot Test) is used to evaluate oil stability. The preferred method is chosen in view of the utilization of the oil. For example, the HFT method is preferred when the oil is used in heating plants in general. ASTM 4740, instead, is the method of choice when heavy oil (bunker oil or fuel oil) for marine engines, used to sail the ship, must be evaluated.

Table 1 lists the requested characteristics established by CTI (Comitato Termotecnico Italiano-Italian Thermotechnical Committee) concerning fluid fuel oil for civil and industrial thermal applications. The requested characteristics are based on an oil classification that takes into account viscosity (for example, fluid, heavy, heavy IATZ or BTZ-high or low-sulphur content) and the sulphur content, which in Italy, according to antismog law, is 1% for heavy-low oil BTZ.

TABLE 1 Fluid FOa Heavy FOa Heavy Low-Analysis Sulphur FOa Method Appearance Completely Completely Completely Customs opaque opaque opaque standards Flash point 65°C min 65°C min 65°C min ASTM D 93 Viscosity 21. 2-37. 4 cst > 53 cst > 53 cst ASTM D 455 Water and Max 1 % by ASTM D 1796 sediments mass Water Max 1. 5 % by Max 1. 5 % by ASTM D 95 mass mass Sediments Max 0.5 % by Max 0.5 % by ASTM D 473 mass mass Sulphur content Max 3 % by Max 1% by mass EN 41 mass Ash content Max 0.10% by Max 0.20% by Max 0.20% by ASTM D 482 mass mass mass Distillat at Min 65% by vol. Min 65% by vol. Min 65% by vol. ASTM D 86 250°C Distillat at Max 60% by Max 60% by Max 60% by vol. ASTM D 86 300°C vol. vol. Distillate at Min 85% by vol. Min 85% by vol. Min 85% by vol. ASTM D 86 350°C a FO=Fuel Oil Table 2 shows an example of requested characteristics for a Bunker oil, specifically Fuel Oil 380 for Bunkering.

TABLE 2 Requested characteristics Min-Max Value ASTM D/IP Method Density C (kg7m) 991. 0 1298 Flash point P. M. (°C) 61 93 Viscosity at 50°C (mm2/s) 380. 0 455 Viscosity at 100°C (mm2/s) 35. 0 455 Regenerated at 350°C (% v/v) <85 86 Total sulphur (% m/m) 4. 5 1552 Pour point (°C) 30 613 Water (% v/v) 1. 0 97 Sediments per extraction 0.5 95 (% m/m) Ash content (% m/m) 0. 15 473 Compatibility Spot 2 4740 Conradson residue (% m/m) 18 482 Vanadium (ppm) 300 189, 4530 Aluminium + Silicon (ppm) 80 1548, IP 288 Existing HFT (5m/m) 0. 1 IP 375 Potential HFT (% m/m) 0. 1 IP 390B

Refineries aim to use as much low-cost oil as possible when preparing fuel oil, given that fuel oil is the commercial product with lower added value, derived from refining petroleum.

For example, FOK (Fuel Oil Cracking), a by-product of ethylene production plants, is disposed of by adding it to fuel oil from other sources; however, the more is added, the more the resulting mixture is unstable since asphaltene precipitations occur over time, in addition to the aforementioned soiling of the combustion lines.

The ASTM evaluation methods are useful for checking the requested

characteristics of the oil to be marketed. Moreover, they can be used by refineries to evaluate soiling tendency during storage and the effect of soiling on the quality of combustion when refinery furnaces are supplied with residues produced in the refinery.

In the latter case, no mandatory standards exist; nevertheless, carrying out the analysis to obtain data on oil stability is a useful tool for predicting future problems both in the tank and circuits (clogged injectors, extra air requirements, and poor combustion in general). Thus, the refinery does not need to comply with the optimal commercial requested characteristics, which are evaluated by means of the above ASTM methods, but should anyhow aim to improve the requested characteristics of the oil used to fuel the furnaces.

In short, there is a need for an additive able to make compatible and stabilize fuel oil mixtures in order to minimize the tendency of poorly soluble particles to precipitate in the hydrocarbon matrix of the oil.

Summary of the invention It is an object of this invention to provide an additive able to stabilize and increase the compatibility of fuel oil. The composition of said additive comprises at least a compound belonging to the class of salts of alkylbenzene sulphonic acid with alkaline-earth metals, specifically calcium alkylbenzene sulphonate, more specifically calcium dodecylbenzene sulphonate. This additive increases the stability of fuel oil over time and, at the same time, increases compatibility; thus, it makes it possible to add unstable oil, such as FOK, to products with high added value, belonging to the fuel oil family.

It is another object of the invention to provide a method for stabilizing fuel oil. This method involves adding an effective quantity of the additive in accordance with the invention to fuel oil coming out of a plant, before mixing the fuel oil with other hydrocarbon cuts such as CLO, FOK, and gas oil.

It is another object of the invention to use alkylbenzene sulphonate of alkaline- earth metals as the means to make compatible/stabilize fuel oil.

Other advantages and objects shall be readily apparent from the more detailed description of the invention.

Description of the invention

The additive in accordance with this invention used to make compatible/stabilize fuel oil mixtures has the effect of making the oil stable during storage and hinder the formation of solids. It is added to different kinds of oil that are incompatible by nature but are mixed together for commercial reasons. The composition of the additive comprises, as active substance, at least a compound belonging to the class of salts with alkaline-earth metals of alkylbenzene sulphonic acid (R-C2H4- SO3H, where R= a linear or branched saturated hydrocarbon radical, preferably containing at least 8 carbon atoms); calcium salts are preferred especially calcium alkylbenzene sulphonate, calcium dodecylbenzene sulphonate, and calcium para- dodecylbenzene sulphonate.

The amount of active substance added depends on the amount of oil to be treated and on the desired stability of the oil mixture. Preferably, an amount equal to or greater than 10 ppm of the active substance is added to the oil mixture; preferably it is added in a variable amount that falls within the 100-1000 ppm range, more preferably within the 500-700 ppm range, particularly preferable within the 150- 700 ppm range, and better still within the 150-460 ppm range.

The active substance in accordance with the invention, in the above amounts, can be added as such to the fuel oil to be treated or may be combined with other components to form a composition comprising one or more known asphaltene dispersants, for example: succinimide, highly basic calcium alkylaryl sulphonate, and other classes of compounds that act as dispersing agents, are described in EP 0267673 and in US 3776835, and are used as antifouling agents for lubricating oil. These compounds can be added in amounts that vary between 10- 60% by weight, ideally between 15-40% by weight of the active substance.

The composition can also advantageously include one or more compounds belonging to the class of combustion improvers commonly used to increase the combustion yield of fuel oil, for example: inorganic salts or (preferably) organic salts of metals such as iron, manganese, cerium, and/or alkaline-earth metals (for example, magnesium and calcium) and mixtures of all said salts. Experts in this field will be able to select the appropriate type of salt (s) and decide on the appropriate amount (s) to be added to the composition in accordance with the invention.

Preferably, the active substance, as such or mixed with other components, can be used in a mixture with heavy aromatic naphtha having a distillation range between 187-208°C or 190-300°C."Naphtha", in general, refers to products that distil in the temperature range included between 30°C and 310°C ; these products can be obtained directly from crude oil or from semifinished products of the petrochemical industry or from distillates obtained from the distillation of carboncoke.

If the active substance is used as such in a mixture with naphtha, the corresponding proportions can vary ideally within the following range: active substance between 5-95% by weight and naphtha between 95-5% by weight.

Furthermore, depending on usage, the amounts may preferably vary within the following ranges: active substance between 30-50% by weight and naphtha between 70-50% by weight to obtain a composition that maximizes stability; or active substance between 40-60% by weight and naphtha between 60-40% by weight to obtain a composition that maximizes compatibility.

The composition in accordance with the invention can be added to nonstandard fuel oil or to standard fuel oil that is then mixed with hydrocarbon cuts (such as CLO, FOK, and gas oil) that make it nonstandard. The addition can be carried out on the line that goes from the bottom of the stripping column to the storage tank.

Advantageously, the additive in accordance with the invention is used as follows : - To standardise fuel oil for civil or industrial heat applications or for bunkering use, i. e. make the fuel oil comply with the requested characteristics set forth in HFT and/or ASTM 4740 - To maximize the absorption, into standard fuel oil, of residual fractions from cracking with low added value and poor compatibility, maintaining the quality characteristics requested by the market requested characteristics or by the end user.

The advantages of the additive in accordance with the invention can be summarized as follows : increase in the stability of the oil during storage, which minimizes the problems in the lines, in the preheating devices, in the heat exchangers, in the boilers, and in other civil and/or industrial plants due to poor combustion; and financial gain due to maximizing the amount of a low added value product (FOK) mixed with another oil with high added value, controlling the

soiling capacity of the resulting mixture.

Other advantages of the invention shall be readily apparent from the examples below, given as nonlimiting examples that do not limit the scope of the invention.

Discussion on the Results of the Examples The HFT method: measures the total sediments in the oil sample up to 0.5% p/p (ASTM D 4870). On an increasing scale, the usually accepted standard value is <0. 1.

The spot method or"Stability and Compatibility of Residual Fuels by Spot Test" : ASTM D 4740, applies to oil samples with a viscosity of up to 50 cst at 100°C and gives precise data on stability (absence of suspended solids) through a classification according to the intensity of the spots left from residues found in the oil after appropriate filtering. On an increasing scale, the usually accepted standard value is up to spot 2.

Example 1-Bunker Oil Characteristics of the treated sample : density = 0.9909 g/cc, viscosity at 50°C = 330 cst, ASTM D 4740 specification = spot 4 (nonstandard).

Sample preparation: the oil was heated for approximately 20 min in a stove at 110°C ; a sample of 100g was taken and placed in a beaker. The obtained sample was placed on a plate at 105°C and the additive was added; this additive consisted of a mixture made up 70% by weight of heavy aromatic naphtha (distillation range between 190 and 300°C) and 30% by weight of calcium dodecylbenzene sulphonate. The mixture was prepared in advance by adding the sulphonate to the naphtha at room temperature and making the sample homogenous by using a magnetic stirrer or a glass rod.

The mixture was stirred on the plate for 15 min.

The control was prepared in the same way but without adding the additive.

Once the samples were ready, the procedure described in ASTM D4740 was carried out. The results obtained with and without adding the additive are summarized in Table A.

Table A Proportion of ASTM D 4740 Ingredients * - (control) Spot 4 500 Spot 1-2 700 Spot 1 * ppm of added calcium dodecylbenzene sulphonate

As can be seen in Table A, adding 500ppm of sulphonate is enough to make the sample comply with the market requested characteristics.

Example 2-Fuel Oil with Added FOK Characteristics of the treated samples : Fuel oil (FO): density = 0.9905 g/cc, viscosity at 50°C = 330 cst, ASTM D 4870 specification HFT = <0.1 (standard) FOK, as described in Table 3, HFT = 0.4 (nonstandard).

Table 3 Method Test U. M. FOK IP 143/96 Asphaltene % by 5. 5 weight ASTM D 93/94 Flash point °C 81 IP 375/94 HFT existing sediments % by 0.12 weight CAM CR 6 Density at 20°C g/cc 1.07 ASTM D5853 Pour point °C -32 CAM CR 24 Viscosity at 50°C Cps 42. 49 CAM CR 24 Viscosity at 75°C Cps 15. 18 CAM CR 24 Viscosity at 99°C Cps 7.52 ASTM D 1160/95 First distillation 225 5% distillate °C 252 10% distillate °C 256 20% distillate °C 262 30% distillate °C 272 40% distillate °C 297 50% distillate °C 344 60% distillate °C 408 70% distillate °C 468 80% distillate °C 519 90% distillate °C 95% distillate °C Final distillation °C 544 (86.5% V)

Sample preparation: the fuel oil was heated for approximately 20 min in a stove at 110°C, three samples of 100g each were taken and placed in a beaker, and three parts equal to 5%, 10%, and 15% by weight of FOK were added to each. The obtained samples were placed on a plate at 105°C and the additive was added; this procedure differed from the one described in Example 1 in the used amounts of naphtha (60% by weight) and sulphonate (40% by weight).

The mixtures were stirred on the plate for 15 min.

The controls were prepared in the same way but without adding the additive.

Once the samples were ready, the procedure described in ASTM D4870 was carried out to determine HFT. The obtained results are shown in Table B.

Table B Sample Mixture Control HFT (p/p) HFT-Proportion of (% by weight) Ingredients * FOK (0%) + FO (100%) <0. 1 0. 1-0ppm FOK (5%) + FO (95%) 0. 4 <0. 1-150 ppm FOK (10%) + FO (90%) 0. 5 <0. 1-200 ppm FOK (15%) + FO (85%) 0. 5 <0. 1-350 ppm FO = fuel oil * ppm of added calcium dodecylbenzene sulphonate The data of Table B confirm that, as the amount of FOK increases in the fuel oil sample, which was initially standard, the value of nonstandard HFT increases.

Increasing amounts of the additive in accordance with the invention, make the FO+FOK mixture fall within the market requested characteristics.

Example 3-Fuel Oil for Internal Use in Refineries (heavy oil produced in a refinery of Northern Europe) Characteristics of the sample (see Table 4).

Table 4 Characteristics Measured Value Specific gravity at 15°C 1001-1033* Viscosity at 50°C (cst) 95-130* Viscosity at 100°C (cps) 9. 7** Pour point (°C) 25-36 Water for distillation (% v/v) 0. 08-0. 05* Ashes, inhibited, (% v/v) 0.07-0. 15* Flash point (PMCC), °C 110130* Calorific value (Cal/kg) 9300-9700* Sulphur (% p/p) 2-2.3*** Carbon residue-CCR 7-15* Vanadium content (% p/p) 0.013 Nickel content (% p/p) 0.005 Asphaltene content (% p/p) 13.0 Sodium content (% p/p) 0.014 Contaminating solids (% by mass) 0. 2-1.5 * Internal method of the refinery

**ASTM D 445 ***ASTM D 4294 Preparation of the sample and of the control : in compliance with Example 1.

Once the samples were ready, the procedure described in ASTM D4740 was carried out. The obtained results with and without the addition of the additive are summarized in Table C.

Table C Additive Proportion of ASTM D 4740 Ingredients * - (control) Spot 4 40% calcium alkylbenzene 300 Spot 3 sulphonate-60% heavy aromatic naphtha 40% calcium alkylbenzene 500 Spot 2 sulphonate-60% heavy aromatic naphtha 50% succinimide-50% heavy 300 Spot 4 aromatic naphtha 50% succinimide-50% heavy 500 Spot 4 aromatic naphtha 40% highly basic calcium alkylaryl 300 Spot 4 sulphonate-60% heavy aromatic naphtha 40% highly basic calcium alkylaryl 500 Spot 3 sulphonate-60% heavy aromatic naphtha * ppm

Table C shows that adding the additive as in example 1, equal to 500 ppm, makes the sample fall within the market requested characteristics. In any case, considering that the additive in accordance with the invention can improve the mixture already in amounts less than 500 ppm, the refinery could also accept spot 3 samples.

The additive formulations without alkylbenzene sulphonate (meaning with only succinimide or highly basic alkylaryl sulphonate) are not as effective as the ones with alkylbenzene sulphonate in accordance with the invention, although large amounts of succinimide or highly basic alkylaryl sulphonate could have positive results.