SUMMARY

THE Gray process of vapour-phase refining, which has achieved considerable commercial recognition, especially in the United States, in the refining of cracked gasoline, is described in principle and practice. Unstable constituents are removed from the cracked vapours by passing them in contact with an adsorbent of the fuller's earth type. The unstable hydrocarbons are polymerised and the polymers removed from the treated vapours by virtue of their higher boiling range. The refined gasoline has a very low gum content and is of good colour and commer cially stable. The spent adsorbent can be recovered by reburning, but this is not essential to low-cost operation because of the large throughputs (1000- -6000. and more barrels per ton) obtained. Data are presented showing results obtained in refining cracked gasolines from a number of American and other crudes. Installation and operating costs of a plant are given. The process has been so widely adopted because of its economies over acid treating and rerunning, due to the selectivity of the reaction. There is no loss of octane number in treating.

Cracked gasoline not many years ago was regarded in the United States with the same suspicion as still confronts it in many other countries to-day. But the widespread use of the motor-car, adoption of higher compression ratios, and the resultant critical evaluation of motor fuels brought'about, a swift reversal of roles and gave the cracked product a place as the most highly prized component of the fuel blend. There is no reason to doubt that history will repeat itself, and cracking will assume a proportionate status from the world point of view.

Just as the world is letting itself be guided by America's experience in cracking, and this is borne out by the design of the majority of cracking plants in Europe and elsewhere, it is reasonable to expect that American practice in refining the product will be carefully studied. In this way a repetition of early mistakes will be avoided, and modern plants freed from anachronistic tendencies so hard to eradicate once they take root.

There are two justifications for cracking. The first, increasing the available supply of motor fuel, was of paramount importance some years ago, and gave the art its initial impetus. To-day, the state of the industry is such that cracking might appear to be of doubtful economic validity. On the other hand, no measure which tends to conserve a material resource that is of necessity limited in amount can really be held to be uneconomic. The second reason for the vogue of cracking is the fact that, as is now well known, cracked gasoline is a superior motor fuel, especially from the standpoint of anti-detonation value.

The refiner who has a cracking plant producing a raw cracked spirit is confronted with the problem of eliminating certain undesirable constituents while conserving to the utmost the characteri

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