Fig. 8 - Neutralization speed vs alkylate type

　

Fig. 8 shows that making an overbased sulfonate with one predominant type of alkylate is not an advantage, as in each case V decreases. When NAT alkylates are predominant a drop of V of about 47% is observed. When BAB or DAB alkylates are predominant the drop of V is more or less similar and limited to about 20%. Nevertheless it can be seen in Table 4 that BN_u is higher in the case of predominant DAB than in the case of predominant BAB.

　

Fig. 9-Neutralization speed vs process parametres

　

It can be seen on Fig. 9, when comparing A4a and B4, that contrary to the previous observations, the fact of making the additive with a MAB alkylate predominant is not a disadvantage, as V values are of the same level. Nevertheless it must be taken into account that the alkylation process in the case of A4a uses AlC13 catalyst, while in the case of B4 it uses HF catalyst. Actually it can be seen that this variation of process has a strong effect on V, as V decreases from 7.76 mbar/s for B4 to 5.01 mbar/s for A4l, considering that these two products vary only by this parameter. One could postulate that if A4a had been prepared with HF catalyzed alkylates, its value of V would have been higher than the one of B4.

The addition of carbonation enhancing additive to A4a, does not yield to an increase of V. In both cases A4j and A4j, V decreases from 26% to 31%.

In conclusion it can be considered that using synthetic HF catalyzed alkylates to prepare the overbased sulfonates is an advantage for the neutralization speed. Then using linear alkylates in place of branched alkylates is another advantage. Global data have shown that it is probably better to use an optimized blend of synthetic and natural alkylates in which the synthetic part is predominant. In this case DAB would be preferred as synthetic alkylate.

　

4.3 Overbased phenates

Overbased phenate that have been tested are commercially available products, so they are compared on the basis of their BN Ievel.

Data show that Pla, a BN200 overbased phenate has a very high neutralization speed of 26.15 mbar/s compared to the other phenates of higher BN. It has been previously observed with overbased sulfonates that when "free" soap is available, V is enhanced. So, considering that P1a is equal to P1b (BN250) but only less overbased, it is like that an important amount of "free" soap actually exists and assist to enhance V to an exceptional level. Comparely to an overbased sulfonate, it is well known from the literature that overbased phenates have a different structure. Overbased particles are of higher diameter and are not as well geometrically defined (not so spherical). Consequently "free" phenate detergent might have a higher effect than "free" sulfonate detergent on V, which would explain the very high value measured.

This assumption is supported by the significant difference in V between P1b and the other additives of BN250 issued from other suppliers. Pl1b has a speed of 11 .33 mbar/s while the others have speeds included between 6 and 7 mbar/s.

The basic detergent of an overbased phenate is usually a sulfurized dodecyl benzene phenate. The difference between additives from one supplier to another is generally related to the process (sulfurization stage - overbasing stage - co-surfactants) but also to the amount of detergent used to prepare the product. The results obtained with P1a and P1b may indicate that this supplier is using more detergent to make its products than the others.

On Fig. 10 the speed of the additives P1b to P5 (BN250) and PHI to PH2 (BN380) is represented. It can be seen that, except for P1b, the BN250 overbased phenates have a neutralization speed in the same range. When the BN increases up to 380 the available "free" soap decreases and consequently V decreases.

　

Fig. 10- Neutralization speed of commercial phenates

　

From the data in Table 5 it can be seen that the level of BN used is generally high. In some cases it reaches on average more than 100% which is physically impossible. This can be explained by the fact that overbased phenates are less efficient surfactants than overbased sulfonates. In other terms the water produced during the neutralization of the acid is not as well stabilized and can evaporate for a part. This leads to a fmal increase of the pressure not only due to CO₂. For this reason BN_u cannot be considered as a significant parameter.

A general conclusion of this part of the study is that the neutralization speed of overbased phenates is primarily influenced by the amount of detergent present.

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