TaE principles governing the application of inhibitors to the refining of motor fuels are discussed and the following, conclusions drawn
Accelerated gumming tests involving the use of oxygen are suitable for studying the action of inhibitors, but the test should be such that a sufficient factor of safety is provided to outweigh any possible variations in the conditions of actual storage. The behaviour of the fuel during the test, however, should be determined with respect to gum formation and not merely with respect to oxygen pressure.
The suitability or otherwise of an inhibitor is governed both by the length of the induction period and by the quantity of gum or non-volatile material formed in the fuel during the induction period.
By selecting an inhibitor that is effective for a predetermined period in an accelerated gumming test, at a temperature appreciably higher than the maximum temperature to which the fuel is likely to be subjected during storage, the effectiveness of the inhibitor under any normal storage conditions can be guaranteed.
In order to determine whether a given substance has a satisfactory inhibiting effect, it is necessary to carry out tests over a fairly wide range of concentrations.
The choice of an inhibitor is governed by the character of the fuel, its effect on colour stability during storage, solubility in the fuel and in water, volatility, corrosiveness, combustion characteristics, quantity necessary and cost. The best inhibitor for any particular fuel is dependent on the relative importance of these factors, according to the conditions under which the fuel is to be used.
In order to obtain the best results, any compounds present in the crude fuel that are capable of acting as inhibitors, as well as those accelerating gum formation, should be removed as far as possible from the fuel before the addition of an inhibitor. When appreciable amounts of such compounds are present, the addition of an inhibitor may produce little effect or may even increase gum formation.
Any additional refining. treatment for removal of sulphur compounds, or of coloured or malodorous compounds, should be applied in such a way as to cause the minimum destruction of unsaturated constituents.
By a combination of the use of gum-inhibitors and suitable refining treatment, it is possible to obtain a satisfactory motor fuel that is stable on storage for periods far longer than is usual in practice.
The use of inhibitors enables both unstable and stable unsaturated hydrocarbons to be conserved for use as motor fuel, and hence the yields obtained are greater than those obtained by any other processes that aim at conserving these hydrocarbons, as such.
An account is given of the application of grim-inhibitors to various motor fuels, with parti