Viscosity increase during oxidation

Oxidation During the combustion process, free radicals are formed which can degrade the oil via oxidation, generally observed as a viscosity increase. If an oil becomes too viscous, it cannot be pumped to where it is required and thus the engine is starved of oil. Engine tests for oxidation are made more severe via extended high-temperature operation, increased blow-by and no oil top-up. 

During long-term storage biodiesel can be easily subject to oxidation under ambient conditions due to the presence of double bonds in the chains of fatty compounds. The reaction of oxidation increases with the increasing of unsaturation level (polyunsaturated compounds are many times more reactive that monounsaturated ones). Some parameters such as acid value, peroxide value or kinematic viscosity increase when autoxidation occurs, thus the fuel s quality is affected. Degradation of the quality of this alternative fuel leads to an increase of deposits on injectors and pump parts and therefore an increase in pressure across filters. 

When the temperature of a carbonate reservoir that is saturated with high-viscosity oil and water increases to 200° C or more, chemical reactions occur in the formation, resulting in the formation of considerable amounts of CO2. The generation of CO2 during thermal stimulation of a carbonate reservoir results from the dealkylation of aromatic hydrocarbons in the presence of water vapor, catalytic conversion of hydrocarbons by water vapor, and oxidation of organic materials. Clay material and metals of variable valence (e.g., nickel, cobalt, iron) in the carbonate rock can serve as the catalyst. An optimal amount of CO2 exists for which maximal oil recovery is achieved [1538]. The performance of a steamflooding process can be improved by the addition of CO2 or methane [1216]. 

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