Mechanism of action of oxygenates

Abstract

The mechanism of the action of oxygenates is discussed from the standpoint of redox reactions. It is shown that the action of oxygenates on the process of combustion of hydrocarbons is associated with oxidation of the latter in steps. The reason for the increase in octane number upon addition of oxygenates may be different rate of overcoming conformational differences under conditions close to the critical temperature of the hydrocarbon at the pre-ignition combustion stage. The influence of propylene oxide on the performance properties of gasoline is examined.The development of chemmotology presupposes study of the mechanism of the action of various hydrocarbon fuel additives and dopes at the stages of production, storage, and use of the fuel. This relates primarily to oxygenate additives, which are used in millions of tons. It is established experimentally that these additives raise the octane number of gasoline, but the mechanism of their action is not fully clear.For gasoline, mainly single-atom alcohols, ketones, and ethers are used as oxygenates. The content of these oxygenates in terms of oxygen does not exceed 3%. Further rise of their content becomes ineffectual. Of these compounds, the most easily available are ethanol and methanol. Ethanol as a gasoline additive is known since late 19 th century. This alcohol was treated as an "alternative" fuel with a special focus on its strength (water content) and ability to form homogeneous solution with gasoline at low temperatures. Widely used were fuel blends with absolute ethanol with a concentration of up to 99.99 wt. %. With switch over to methanol, stabilization of the blends became complicated.High alcohol content makes ignition of the fuel difficult, so alcohols began to be substituted by ethers, which are highly volatile and ignite at a low temperature. Among the ethers, the most popular in Russia and abroad is methyl-tert-butyl ether. Its production and use in the world in 2001 comprised 26.5 million tons [1].The rise of octane number of alcohols in the sequence C 8 -C 4 -C 1 can be associated with increase in the relative proportion of oxygen in their molecule. This agrees well with reduced knocking under the action of water, in the molecule of which the relative proportion of oxygen is the maximum. As is well known, alcohols and alcohol-gasoline blends are poorly susceptible to tetraethyl lead additive, which may mean different mechanisms of action of these additives [2].

Propylene Oxide Addition Effect on the Chemical Speciation of a Fuel-Rich Premixed n-Heptane/Toluene Flame

“…Since PO is produced in large industrial scales and could be easily transported, it was proposed as an oxygenated additive to transportation fuels , to reduce soot content in the exhaust of diesel engines. Recent study has shown that there is no evidence that typical environmental or occupational exposures to PO constitute a health risk for humans .…”

Determination of mutual solubility in the straight-run naphtha—propylene oxide—water system

“…Propylene oxide (PO) has been examined as another oxygenate [2][3][4]. The mechanism of action of oxygenates, including propylene oxide, was proposed in [5]. The physicochemical and performance characteristics of composite fuels must be investigated for incorporating oxygenate compositions with propylene oxide.…”