1254
I N D U S T R I A L A N D -~ ENGINEERING CHEMISTRY
Vol. 23, No. 11
Peroxides and Gum in Gasoline' J. A. C. Yule and C. P. Wilson, Jr. MEDWAY OIL A N D
HE problem of gum det e r m i n a t i o n is one
T
STORAGB COMPANY,
GASOLINE
0.760 95 0 02 0.14 2
E N G L E R DISTILLATION ( A .
Initial boiling point, 'C. Boiling point at 20%, C. Boiling point at 50%, C. Boiling point at.900/g, 'C. Final boiling point, C. Recovery, % I
.
Received May 18, 1931.
OF
GRAIN, ENGLAND
A method of estimating peroxides in gasoline is described and the chemical properties of peroxides discussed. I t is shown that traces of peroxides interfere with the doctor test, Causing negative results to be obtained even when mercaptans are present. Silica gel is found to remove peroxides and gum from gasoline, but cracked gasoline treated with silica gel is rendered very susceptible to oxidation. A method of estimating dissolved oxygen in oils free from peroxides is described. Investigations of the Properties of peroxides lead to the conclusion that the gum in gasoline 3s usually Present as peroxides which decompose and Polymerize to true gum on evaporation. Tests for preformed gum are discussed.
which is now receiving considerable a t t e n t i o n . I n the p r e s e n t p a p e r the chemical p r o p e r t i e s of peroxides found in gasoline and the relation b e t w e e n gum and peroxides are discussed. The importance of distinguishing between preformed gum (gum which is already dissolved in the gasoline) and potential gum (a measure of the tendency of the gasoline to form gum on storage) was first pointed out by Voorhees and Eisinger (21). Others (18, 16, 63) have shown, but it needs further emphasis, that even so-called preformed gum is not present in gasoline in the form of gum but mainly as intermediate products which are only converted to gum on evaporation. Brooks ( 5 ) first pointed out the important part which peroxides play in gum formation. The authors have found that in the case of cracked gasoline from Baku kerosene the intermediate products are almost entirely peroxides. It follows from this that a study of gum resolves itself into a study of the formation and properties of peroxides. A sensitive and rapid method of estimation of these peroxides was therefore worked out and has proved of great value during the last four years, not only in the investigation of the process of gum formation but also in following the oxidation of gasolines in storage, especially in the initial stages. This test is sensitive enough to detect oxidation in such early stages that the contents of storage tanks may be disposed of through the usual channels immediately after oxidation has commenced, but long before it has proceeded far enough to cause gum deposits in an engine. The method consists in shaking the gasoline with a solution of ferrous sulfate, when a quantity of ferrous sulfate equivalent to the peroxides is oxidized to the ferric salt, which is titrated with titanous chloride solution. Except where otherwise stated, all results given throughout this paper have been determined by this method and are expressed as gram equivalents of active oxygen per 1000 liters gasoline, The oil used by the authors in all the tests described was a Cross cracked gasoline [cracking temperature, oil ex furnace, 500' C.; pressure, 750 pounds per square inch (52.7 kg. per sq. em.)] manufactured from Baku kerosene and washed with sodium carbonate solution to remove hydrogen sulfide. Results of typical tests on the gasoline and cracking stock are as follows:
Sp. gr. at 60° F. (15.6' C ) Iodine value Sulfur "/s Coppekdish gum, g./lOO cc.
LIMITED, ISLE
TOPPED
KEROSENB 0 840
IS8 195
9s
Engler and Weissberg (8) and Stephens (18) estimated the activeoxygen in amylene peroxide and c y c l o h e x e n e peroxide, respectively, with s t a n n o u s chloride. These authors 0 b t a i n e d r e s u l t s lower than the t h e o r e t i c a l values. The total oxygen (by difference, after determining carbon and hydrogen by combustion) was found to agree with the theoretical results. This was explained by the assumption that the peroxide was partly polymerized, a reaction which would involve loss of artive oxygen. Klason (11) estimated thc peroxides in oxidized turpentine by allowing the oi! to stand for 24 hours with an excess of cymene hydrosulfide and titrating the excess with a solution of iodine:
>c-c< I
I
0-0
f 2CioHiaSH
2CioH13SH 4-11
>c-c
