Distillate fuel degradation

Naphthenic acids and sulfur- and nitrogen-containing heterocycles and naphthenoaromatic compounds can all be found in distillate fuel fractions. Degradation through condensation type reactions rather than through free-radical-initiated polymerization can be more common in distillate fuel. Because of this, degradation products are often quite complex in nature and structurally diverse. 

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 can darken in color and can degrade to form sediment after exposure to air and/or heat for a period of time. Degradation is also accelerated by exposure to dissolved metal ions, especially copper. During this process, oxygen in the air reacts with fuel components to form compounds which are often dark in color and unstable. Also, condensation-type reactions can occur and result in the formation of high-molecular-weight, insoluble organic compounds. 

These short-term tests can be utilized to quickly determine whether distillate fuel has a tendency to degrade in color and form deposits upon storage and use. Although... 

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... 

Add a distillate fuel color degradation control additive. 

Add a distillate fuel color degradation control additive at high rates before fuel enters tankage. 

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

Considerable work has been published on degradation mechanisms for compounds found in petroleum(i 4). Much of the previously reported research involved pure compounds in pure hydrocarbon solvents. The work reported here was performed with additive-free 2 diesel fuel or JP-8, both of which are middle distillate fuels in increasing demand. Much of this work is in progress and only preliminary results can be presented here. 

Hindered phenol and phenylenediamine (PDA) compounds are commonly used and quite effective at preventing free-radical oxidative degradation of fuel. They can be used in gasoline, kerosene, jet fuel, and certain distillates and lubricants. Often, a synergistic effect can be obtained by using a combination of a hindered phenol and a phenylenediamine antioxidant in the same application. 

Ucon HTF-500. Union Carbide Corp. manufactures Ucon HTF-500, a polyalkylene glycol suitable for liquid-phase heat transfer. The fluid exhibits good thermal stability in the recommended temperature range and is inhibited against oxidation. The products of decomposition are soluble and viscosity increases as decomposition proceeds. The vapor pressure of the fluid is negligible and it is not feasible to recover the used fluid by distillation. Also, because the degradation products are soluble in the fluid, it is not possible to remove them by filtration any spent fluid usually must be burned as fuel or discarded. The fluid is soluble in water. 

Eckart and co-workers have published a series of papers on laboratory studies of biodesulfurization of petroleum and petroleum fractions. The ability of various aerobic mixed cultures to desulfurize Romashkino crude oil (1.69 wt.% S) was addressed by Eckart et al. (21). After 5 days of incubation at 30°C in sulfur-free mineral medium with oil as sole source of carbon and sulfur, approximately 55% of the total sulfur was recovered in the aqueous phase from two of the most active cultures. In another study, gas oil (1.2 to 2 wt.% S), vacuum distillates (1.8 to 2 wt.% S) and fuel oil (up to 4 wt.% S) were used as sole carbon and sulfur sources for the oil-degrading microorganisms (36). The addition of an emulsifying agent was required to enhance desulfurization. Sulfur removals of up to 20% from the gas oil, 5% from the vacuum distillates, and 25% from the fuel oil were observed after 5 to 7 days of incubation. In a later study (37). approximately 30% of the sulfur was removed from fuel-D-oil by a mixed population of bacteria. The removal of benzothiophene, dibenzothiophene and naphthobenzothiophene was shown by high resolution MS analysis. Hydrocarbon degradation was observed in each of these studies. For example, in the latter study with fuel-D-oil, the decreases in the n-alkane and aromatic content were 59% and 14%, respectively. 

Energy consumption of the rectification process is reduced via integrated atmospheric and vacuum rectification as well as optimal utilization and operation of heat flows. MIDER claims to save some 50,000 tons of fuel oil per annum compared with a traditional distillation process. The process is characterized by the use of five instead of the usual two distillation columns. The process development was based on the objective of avoiding unnecessary overheating of the light components. Additionally, it avoids degrading the thermal levels associated with the drawing off of heavy fractions. 

In some applications, thermal degradation can be more of a concern than storage stability. Table 6 presents data on several middle distillate synfuels as compared to a petroleum-based fuel. The tube deposits from the Jet Fuel Thermal Oxidation Test (ASTM D3241) are significantly higher for the synfuels, but the pressure buildup is normal except for one case. This indicates either rapid reactions at the hot surface or slow agglomeration. In either case, the deposit level is of concern and may dictate further upgrading. 

---