FRom a short review of the chemistry of craeked distillates it is indicated that their stabilities depend on the distribution and type of olefines present. Fractionations of cracked distillate show this to be the case and it is suggested that it might be feasible to segregate the most unstable fractions, sweeten or desulphurise them separately and stabilise them by a suitable addition of inhibitor, finally blending the stabilised material with the refined and more naturally stable residue.
Methods of treatment of cracked distillates are dealt with briefly and details are given of a continuous counter-current method of acid treatment together with the losses involved.
An account is given of the method employed for the evaluation of inhibitors and of the results of testing sixty compounds of possible value. The most effective materials were found to be catechol, hydroquinone, pyrogallol and monobenzyl-paminophenol. Most of the other materials were found to be less efficient than these, and a few of equal activity, caused, the development of colour either on addition to the fuel or -after oxidation in the bomb.
Finally, a description is given of attempts to study. the stabilities of inhibited and uninhibited motor fuels by means of an oxygen bomb method, and by standardised storage at 100 F. and at normal -atmospheric temperature. As far as can be ascertained, the stabilities shown by the bomb are of similar degree and order as those given by standardised storage at 100'F.
From a general historical consideration of this subject, it is interesting to note that two of the main reasons for the early rejection of vapour-phase cracking processes in favour of liquid-phase methods were, firstly, the difficulty of satisfactorily refining the product, and secondly, even when this was possible, to carry out the treatment without. very substantial losses. A review of recent progress in the "art of cracking," however, shows that liquid-phase processes are now either being replaced by cracking in the vapour-phase or by composite methods involving both phases. This change has only been made possible by a much improved knowledge not only of the most suitable methods of refining but also of the chemical nature of the material and its reactions with the refining media. The difficulties encountered during the refining of cracked distillates may be many and varied; apart from the main treatment with the selected reagent, trouble may occur due to emulsion formation in the neutralisation stage or to the development of acidity on re-running. Again, the stability of the finished gasoline with regard to gum formation and colour deterioration may be insufficient, while even odour has hitherto been a fruitful cause of complaint.
In an attempt to place the refining of cracked distillates on a systematic basis, various workers have determined which types of compounds or fractions were chiefly responsible for those