Diesel instability

In one case study, anorexia was reported in a man who washed his hands with diesel fuel over several weeks (Crisp et al. 1979). Effects resulting from inhalation versus dermal exposure could not be distinguished in this case. An epidemiological study found a significant increase in neurasthenia (i.e., fatigue, depressed mood, lack of initiative, dizziness, and sleep disturbances) in workers who were chronically exposed to jet fuels by either inhalation, oral, and/or dermal exposure (Knave et al. 1978). Also, attention and sensorimotor speed were impaired in the exposed workers, but no effects were found on memory function or manual dexterity. Results of EEG tests suggest that the exposed workers may have instability in the thalamocortical system. The limitations of the study were discussed in detail in Section 2.2.1.2 under Respiratory Effects. 

The main causes of the deactivation of diesel catalysts are poisoning by lubrication oil additives (phosphorus), and by SOx, and the hydrothermal instability. The SCR by HC is less sensitive to SOx than the NO decomposition. The Cu-based catalysts are slightly inhibited by water vapor and SOx, and suffer deactivation at elevated temperature. Noble metal catalysts such as Pt-MFI undergo low deactivation under practical conditions, are active at temperatures below 573 K but the major and undesired reduction product is N20 (56). 

Similar to petroleum-derived cracking the fractions from plastics pyrolysis can contain a significant concentration of unsaturated hydrocarbons (especially a-olefins) [9]. The mono- and diolefin content makes the diesel fuel prone to instability due to polymerization and the formation of deposits (i.e. gums). Since the plastic-derived diesel fuel has an appreciable olefins content it is important to subject it to a hydrogenation step (e.g. hydrogenation over PCI/AI2O3 at 300-320°C and 3 MPa H2) which lowers the bromine number from typical values of 22-28 g Br2/100 g to less than 0.5 g Br2/100 g [9]. 

This will result in an increase in asphaltene agglomerations, polymerization and a dramatic loss of combustion efficiency. The chemistry of diesel fuel instability involves the chemical conversion of precursors to species of higher molecular weight with limited solubility. The conversion process often involves oxidation of the precursors. Fuel solvency plays a role, since the development of insolubles is always a function of both the presence of higher molecular weight species and the fuel s capacity to dissolve them. 

The next important parameter of diesel fuel is stability or storage stability. As fuel ages, it can become unstable and form insoluble particulates that accumulate and eventually end up on the fuel filter. For the most part, instability involves the chemical conversion of precursors to compounds of higher molecular weight with limited fuel solubility. The precursors are certain nitrogen and/or sulfur containing compounds, organic acids, and reactive olefins. The conversion process often involves oxidation of the precursors. Certain dissolved metals, especially... 

Metal deactivators prevent the catalytic influence of the metals on reactions that can lead to its instability in diesel fuel. They are typically used in concentrations of up to 15 ppm. 

---