Neutralization of acetic acid by automobile motor oil

• Neutralization of acetic acid droplets in automobile motor oil was studied.
• Droplets were injected into bulk lubricant by a uniquely pulled micropipette.
• Change in droplet size was monitored by capillary video-microscopy.
• Mathematical model is proposed for droplet shrinkage by neutralization.
• Reaction rate constant and activation energy were determined based on the model.

The neutralization reaction of concentrated and diluted acetic-acid droplets in fully formulated lubricant oil was studied using capillary video-microscopy. Based on video analysis, an interface-reaction-rate-controlled kinetic mechanism is proposed to describe the neutralization process at different conditions. When glacial and diluted acetic acid droplets were neutralized in fully formulated lubricant oil, the experimentally measured shrinking radius agreed very well with the mathematical model. According to Arrhenius equation, the activation energy of neutralization reaction was determined to be constant and its range (Ea>21 kJ/mol) further validated the assumption as interface-controlled reaction kinetics.

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