4.4 - Overbased salicylates
Overbased salicylates that have been tested are both commercial and experimental products. It must be recognized that the BN is brought by CaCO3 and also by organic functions, and that the physical structure can be compared to the structure of the overbased phenates.
Fig. 11 presents the neutralization speed of the additives ranked from BN70 to BN380.
Fig. 10 - Neutralization speed of overbased salicylates
The sample S1a is particular, as this product is a "neutral" salicylate, which means that it has not been carbonated. So logically, as no CaCO3 is available, no CO2 should be produced when introducing the acid and no speed should be measured. But, even if levels are very low. V and BNu are not nil.
The thermal decarboxylation of salicylates should be an explanation of CO2 production [7], but even if the test takes place in thin film, the temperature of test (100℃) seems too low to produce such a phenomenon. It is also known that some processes use salts of acetates and formates as viscosity modifiers and as sources of alkalinity [7]. These products can also react with the acid and produce C02, but there is currently no clue to support the presence of such products in this sample. Another possible explanation is related to Ca(OH)2. Lime is used to neutralize the salicylic acid, precursor of the detergent. This lime contributes to the structure of the "neutral" additive and is naturally trapped, for a part, inside the so-called micelles of detergent. As lime is a basic species, it reacts with the acid introduced during the test and produces water, which can yield to an increase of pressure if it is not well stabilized by the detergent. This assumption is supported by the fact that, as with overbased phenates, the level of BN used for the other overbased salicylates is generally very high and sometimes over 100%.
These entire observations mean that any discussion on the relationship between V and the BN level or the supposed soap content of the products tested, has to be carried out very carefully. Therefore no definitive conclusion will be proposed on this part of the study.
4.5 - Influence of the base oils
Some of the overbased salicylates have been formulated in a blend of 650N/115N basestocks and are compared to the previous blends in 500N/BSS basestocks.
Fig. 12 shows clearly the effect of the basestocks on V, which drops systematically for the four samples tested from 28% to 62%.
This very important observation is the first of the study, which shows that the formulation contributes deeply to the neutralization ability. With this observation it is demonstrated that the neutralization ability depends not only on the capability of the active product, but also on the surrounding components .
Fig. 12 - Effect of base oil on neutralization speed
4.6 - Effect of dispersants
In the overbased sulfonate B4, 2 % w/w of three PIB-succinimide dispersants varying by their molecular weight and by their nitrogen content were added.
Fig. 13 shows the strong effect of this blend on V, which is more than doubled at the best. It can be seen that the chemistry of the dispersant does not seem to have any effect.
Fig. 13 - Effect of dispersants on neutralization speed
It can be seen again from these data that V is probably much more sensitive to the formulation than to the overbased compound itself.
5. CONCLUSIONS
The neutralization ability of various types of single overbased detergents used in marine lubricants has been studied with the NAMO test.
It has been shown that for additives of same BN400 range, the neutralization speed of overbased sulfonates is on average 42% higher than for overbased phenates and 60% higher than for overbased salicylates. A full study of the overbased sulfonate type additives has shown that the soap content influences the neutralization speed more than the BN level itself. Although these two parameters are not independent. The chemical structure of alkylates used to prepare the basic detergents and the process involved has also an influence.
