Lead susceptibility

Lead Susceptibility—The increase in octane number of gasoline imparted by the addition of a specified amount of tetraethyl lead. 

Especially with propylene as the only olefin, or in a high concentration in the olefin feed, it was difficult to get good enough alkylation conditions so that the alkyl sulfate concentration would not become too high in the reaction mixture. And even today sometimes in commercial alkylation neutral esters end up in the alkylate leaving the reactor. This has been shown by analysis, and in some cases by a temperature rise in the settler, decomposition in the fractionation system, and poor lead susceptibility of the alkylate. Neutral esters are not removed from... 

A similar relationship for the clear base of leaded regular-grade gasolines was developed from more than 200 commercial gasolines obtained from service stations. Knowing the lead content of each fuel and using our updated lead susceptibility charts (2), the clear RON can be estimated. Here again, the data result in a wide band. The best-fit line has been determined, and its equation is ... 

The slope of this best-fit line for the clear base gasolines for the commercial leaded fuels is noticeably less than that for the commercial unleaded fuels. There are several reasons. To make clear fuels below 90 RON, the refiner generally has available several base stocks in addition to reformate that can provide octane numbers. These include alkylate, isomerate, and cata-lytically cracked stocks containing olefins. Furthermore, these stocks plus straightrun have excellent lead susceptibility compared to aromatics. Therefore, one would expect to see less aromatics in leaded fuels and the aromatic increment for each increase in RON would be less. For unleaded fuels above 90 RON, reformate, which consists mostly of aromatics, is the most generally used blending stock to provide the required octane numbers. ... 

To show the relationship between percent aromatics and lead content, we have calculated the curve in Figure 2 using the leaded regular-fuel curve in Figure 1 and a lead susceptibility chart. 

The average relationship between the Research and Motor method octane numbers is indicated in Table 3-3, and the lead susceptibilities of various types of gasolines are shown in Tables 3-11 and 3-12. 

Most of the lead should be used in the blend that contains the low-octane giasoline so that the good lead susceptibility of such materials can be fully utilized. 

By the use of a lead-susceptibility chart (Fig. 3-4) it is possible to assemble the gasoline stocks in various proportions to produce Regular and Premium Grades of gasoline. Some blending proportions result in lead consumptions that are less than half the amounts required by other blending proportions. ... 

Oxidation Processes. These processes convert mercaptans into less odoriferous disulfides by such processes as the doctor, copper chloride, hypochlorite, and lead sulfide, processes. Since disulfides harm the lead susceptibility of gasoline and since the need of reduction of mercaptans to doctor sweet (0.0004 per cent) is being questioned, these processes are being gradually abandoned. However, catalysts or inhibitors of the 7>-phenylenediamine type, which in the presence of air cause mercaptans in some caustic-washed gasolines to be converted during a few days into disulfides (so-called inhibitor sweetening), continue to be used because of the cheapness of such a process. Small amounts of... 

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