Study on the neutralization mechanism of overbased detergents and their formulates.

摘要

The goal of this research is to study the neutralization of sulfuric acid by engine oils, and more specifically study how the presence of different oil additives affects the acid-neutralizing performance of engine oils by using capillary videomicroscopy. Nowadays the formulation of engine oils has been changing due to a trend of different regulations around the world that seek to diminish the emission of atmospheric pollution from all types of vehicles driven by internal combustion engines. In the particular case of large marine ships powered by low-speed two-stroke diesel engines, pollutant emissions are high given that the marine fuel they use can contain up to 4.5 wt. % of sulfur. But this sulfur content cap in marine fuel is bound to diminish dramatically during the ongoing decades due to regulations and therefore, the industry is coming up with new engine oil formulations accordingly as to comply with these changes. Here a technique called capillary videomicroscopy was used to study new changes to engine oil formulations. The reaction and dispersion of a sulfuric acid micro-droplet into formulations of marine cylinder lubricants (MCL) was studied by microscopically observing and measuring the shrinking of a micropipette-produced droplet in real time. It was found that MCL formulations having a base number (BN) of 40 had an acid-neutralizing performance comparable to those of having BN 70. On the other hand, the addition of fatty alcohols as final additives to MCL formulations so as to boost the MCL's acid neutralization performance was found to be slightly effective although phase separation due to alcohol insolubility in MCL at room temperatures and other resilient phases formed upon reaction can be detrimental, hence the use of fatty alcohols for boosting any MCL formulation cannot be generalized and should be studied for each formulation. In the case of passenger car motor oils (PCMO), substitution of traditional oil additives by new sulfur-free additive species is driven by the need to prevent the catalytic converter's poisoning by eliminating any sulfur present in the exhaust gas. The effect of the polymeric dispersant on the acid neutralization performance was also studied. The formation of clear, thin and resilient shells surrounding sulfuric acid droplets upon reaction with some MCLs was noticed to be a detrimental aspect towards their acid neutralization performance and more importantly, due to the formation of potential precursors for cylinder liner engine deposits. Finally it is shown a modification of the capillary videomicroscopy technique that allowed long-term monitoring of the fate of microscopic particles while reacting or dissolving under flow, by suspending them using a balance between buoyancy and drag force from creep flow.