Mechanism of Acid Neutralization by Overbased Colloidal Additives in Hydrocarbon Media

Abstract

Stopped-flow kinetic studies have been employed to study the mechanism of acid neutralization for the reaction between overbased commercial detergent additives, used as crankcase lubricants, and aqueous strong acids (e.g., HCl and H2SO4) dispersed in the form of water-in-oil microemulsion droplets. Three water-soluble pH indicators, including methyl orange, 4-nitrophenyl-2-sulfonate, and nile blue have been used to monitor the change in pH accompanying the neutralization reaction. This process represents a model reaction involving communication between a nanometer-sized colloidal particle and a similar-sized aqueous droplet with the reactants solubilized inside the respective colloidal speciesdynamic processes in such systems have rarely been studied previously in a systematic way. The state of the system at the end of the neutralization reaction was monitored by the techniques of small angle neutron scattering (SANS) and ultracentrifugation. The rate was studied as a function of the initial concentrations of overbased additive and droplets and the initial acid concentration. The effect of temperature and the nature of the hydrocarbon oil were also systematically investigated, and in addition, the surfactant stabilizing the droplet was also changed. Through these studies, it was found that the model reaction provides fundamental information concerning the mechanism of acid neutralization by detergent additives. It is found, rather surprisingly, that the mechanism involves base transfer from the particle into the water cores of the microemulsion droplets, where neutralization of the solubilized acid occurs.

Spin-probe ESR and molecular modeling studies on calcium carbonate dispersions in overbased detergent additives

“…On the other hand, the surfactant layer should be permeable by the acid molecules produced during the combustion of fuel in order to allow them to reach the carbonate core for neutralization [10].…”

Temperature and acid droplet size effects in acid neutralization of marine cylinder lubricants

“…In 1998, by inventing a rotating vessel technique Roman [2] reported that in the temperature range of 80-120°C, the higher the temperature, the lower the difference of neutralization ability between lubricants of various compositions. In 2000, by using a stop-flow technique, Hone et al [3] investigated the acid neutralization between microemulsion acid droplets and overbased commercial detergent additives in hydrocarbon media. In the temperature range of 10-30°C, the activation energy for the acid neutralization was relatively low and independent of specific pH indicators being used.…”

Preparation, characterization and evaluation of some metallic lube oil additives

“…The surfactants act as a dispersed agent, while the metal carbonate acts as a neutralizing agent, and the diluent oil acts as a compatible agent. The term [8][9][10] "over based" demonstrates that the quantity of colloidal metal carbonate in the particle cores is greater than that is needed to neutralize the surfactant acid, otherwise it is described as "neutral" or "low basicity", indicating that the over based detergents have a greater acid neutralizing capacity than their neutral salts. In the present work, different metallic detergent/dispersant additives will be prepared via reaction of dodecyl phenol with calcium hydroxide in different ratios.…”