Distillate fuel stabilizers

Compounds classified as distillate fuel stabilizers are often mixtures of various compounds having different performance enhancing capabilities. These mixtures are frequently added as a single package to a distillate fuel. Stabilizer packages can possess any combination or all of the following components ... 

Traditional hindered phenol and phenylenediamine free-radical scavenger type antioxidants do not usually provide the stability performance desired in distillate fuel. Stabilizer formulations containing components which provide a wider range of performance are often required. Some of the components commonly used in distillate fuel stabilizers are described as follows ... 

Some distillate fuel stabilizers possess dispersant-like properties. By acting as a dispersant, any sludge or deposit-like component which may form can be suspended in the fuel and maintained as a soluble compound. As a result, deposits do not accumulate onto fuel system components, but remain dispersed in the fuel. However, due to this dispersing action, the fuel may appear dark in color. 

Also, some distillate fuel stabilizers contain metal chelating agents. The purpose of this is to help prevent the metal-catalyzed oxidation of fuel components. However, if a distillate fuel containing a chelating agent is stored in a tank or transferred through lines which are rusted, the stabilizer may act to chelate iron. As a result of this, the fuel containing the stabilizer appears dark. 

USE Separately or together, these different distillate fuel stability methods can be used to help identify the following ... 

Some distillate fuel stabilizers possess the ability to perform as dispersants. By dispersing higher-molecular-weight compounds into fuel, their eventual deposition as fuel-insoluble compounds can be minimized. 

Stavinoha, L. L., and C. P. Henry, Editors. 1981. Distillate Fuel Stability and Cleanliness. Philadelphia American Society for Testing and Materials. 

Oxidation stability (distillate fuel oil) NF M 07-047 ISO/DlS 12205 ASTM D 2274 Measurement of precipitate after 16 h of oxygen sparging at 95°C... 

A variety of non-hydrocarbon species is found in crude oil. These compounds are found in all molecular weight ranges of crude oil components, but seem to concentrate in the heavier distillate and residual oil fractions. The effect of these materials on processing equipment, refining catalysts, and finished product quality can be dramatic. Corrosion, catalyst poisoning, and fuel stability problems can all be due to the effect of these nonhydrocarbon species. 

The antioxidant and acid neutralization properties of most fuel stabilizer formulations help to prevent the initial formation of most acids. Compounds such as tertiary-alkyl primary amines, as shown by the example in FIGURE 6-5, are quite effective distillate fuel additives. These oil-soluble amines can be formulated into stabilizer formulations at relatively low concentrations and can provide a significant boost in overall performance of a fuel stabilizer. 

A fuel oil stabilizer additive listed in QPL-24682 may be blended into naval distillate fuel at rates up to 35 lb/1,000 barrels to protect against degradation and improve storage stability as measured by ASTM D-5304. Method ASTM D-2274 may also be used if the test duration is extended from 16 to 40 hours. 

Distillate fuel fractions can contain naphthenic acids, sulfonic acids, and other hydrophilic compounds. If these hydrophilic compounds are present as sodium salts due to caustic washing of fuel, they become powerful emulsifying agents. Also, heavy resinous compounds in fuel can act to stabilize existing emulsions. 

There are various test methods used throughout the petroleum industry to help determine the stability of distillate fuel. Most methods involve heating the fuel and exposing it to either air or an oxygen-rich mixture for a specific period of time. The basic format for most stability test methods involves the following methodology ... 

The following is a listing and summary of common methods utilized throughout the petroleum industry to rate the stability of distillate fuel ... 

This test method has been demonstrated to be effective for use in predicting the long-term storage stability of distillate fuel. The results obtained closely approximate those obtained after fuel storage at ambient temperature. For example, fuel storage at 110°F (43°C) for 12 to 13 weeks has been shown to correlate well with one year of storage at ambient temperature. 

Oxidation Stability of Distillate Fuel Oil (Accelerated Method)... 

This test method is commonly utilized throughout the world to rapidly determine the oxidative stability of distillate fuel. Although not as effective at predicting the long-term stability of distillate fuel as ASTM D-4625, this method is useful for measuring the resistance of fuel to rapid degradation by oxidation. Metal catalysts such as copper and iron are sometimes added to the fuel to further accelerate... 

This accelerated stability test method is preferred by some fuel refiners and marketers over other test methods used to determine the stability of distillate fuel. The more severe test conditions, relatively short test time period, and similarity of this method to ASTM D-873, Oxidation Stability of Aviation Fuels (Potential Residue Method) contribute to its acceptance. 

Assessing Distillate Fuel Storage Stability by Oxygen Overpressure... 

Effect of various metals on the storage stability of distillate fuel... 

The addition of fuel stabilizers can help inhibit distillate fuel color degradation... 

Nalco Chemical Company. 1987. Procedures for evaluating the stability of distillate fuel oils. TF-9. Sugar Land, Tex. 

As for similar additives for jet and gas-turbine fuels, the literature is sparse on those distillate fuel-oil additives reported to have definite beneficial influence on actual combustion and is confined largely to claims that certain stability improvers also reduce carbon deposits in preheaters and on burner tips. However, a recent report indicates that ferrocene has recently been groomed for a job as combustion catalyst in home heaters (15). As mentioned previously, this substance is reported to have excellent properties for prevention of carbon formation (2). 

The diesel needs to be stabilized with diesel fuel additives that will inhibit diesel polymerization and inhibit oxidation, darkening and agglomeration of certain components of the diesel. One such effective stabilizing additive is Octel FOA-6. Octel FOA-6 and FOA-3 are amine-based antioxidants that are recommended for antioxidant protection of distillate fuels such as diesel. FOA-3 and FOA-6 together with AO-22, generally give then-best performance when added hot and early to the fuel, usually to a cracked component in the run-down from the cracker. 

The stability of the distillate fuels in storage is influenced to a considerable degree by compounds of sulfur and nitrogen that may be present. Thus, sludge formation has been found to be promoted by disulfides, polysulfides, and thiophenol (327), as well as by pyrroles (328). Furthermore, the precipitates that form are much enriched in both sulfur and nitrogen. Pyrrole-type compounds have been identified among the nitrogen compounds in catalytically cracked gas oil (281,329) if present in appreciable amounts, their removal may be necessary (328). 

The volatility of fuel oil must be uniform, from batch to batch, if too-frequent resetting of burner controls is to be avoided and if maximum performance and efficiency are to be maintained. Information regarding the volatility and the proportion of fuel vaporized at any one temperature may be obtained from the standard distillation procedure (ASTM D-86, IP 123). The distillation test is significant for the distillate fuels because it is essential that the fuels contain sufficient volatile components to ensure that ignition and flame stability can be accomplished easily. 

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