Peroxide determination 1

[thiru4vino]

Dear all!

We have a merox reactor, which is used to make ATF.

I want to know what is peroxide number and how it is determined?

What is the significance other than potential gum formation?

Thanks for everything you do,

cheers

atm

 

[25362]

I recommend you get hold of the ASTM Manual of significance of Tests for Petroleum Products to read of the importance of peroxide content in virgin as well as hydrotreated ATF's.
Perusal of tests D 3703-99(2004) and D 6477-03 may also be of help.

 

[25362]

The Merox sulfur reduction is not just meant to reduce air pollution but mainly refers to the effect it has on a self-accelerating reaction called autoxidation taking place in the fuel with oxygen from dissolved air.

Air solubility increases with lower densities, lower surface tension, and lower viscosity of the fuels. Hence wide-cut turbo fuels will dissolve more air than will the kerosine type or the so-called high-flash-point fuel.

If the initial concentration of air at sea level in a kero-type fuel is 11.5% vol/vol, then on climbing to 10 km (200 mm Hg pressure) 8.5% of air will be expelled taking fuel vapor with it, with possible frothing and a considerable fuel loss. A wide-cut would show a drop from 18.5% to 5% = 13.5% in the equilibrium concentration of air.

Autoxidation is a free radical reaction. It may start at temperatures as low as 30[sup]o[/sup]C. In the presence of sulfur compounds even stable fuels are capable of absorbing oxygen when subjected to heat. The reaction rate increases with time and temperature. The end result of these reactions is the precipitation of a solid phase insoluble in the fuel.

Gums, hard varnish-like deposits are known to contain sulfur, HC's, oxygen, and sometimes nitrogen. Thus, to ensure that turbo-fuels do not react in this way, strict control is maintained on total sulfur and mercaptan sulfur (considered pro-oxidants), as well as on the thermal stability and the gum content.

Oxygen, although not limited by specs., is controlled by an acidity test, when present as naphthenic acids or phenols.

All oxidative processes with oxygen have a common reaction pattern attributable to the diradical status of oxygen.
An oxygen molecule as found in air has two unpaired electrons qualifying it as a diradical. Diradical oxygen removes the most susceptible hydrogen from the HC for example, secondary or tertiary hydrogens, leading to the formation of hydroperoxides. These hydroperoxides are unstable and quickly degrade forming mixtures that tend to polymerize and serve as sludge precursors.

As for many other free radical reactions (no politics meant), autoxidation consists of distinct stages: a. initiation, slow, with partial pressures of oxygen greater than 50 torr and in the presence of traces of transition metals as catalysts; b. propagation and chain branching, quicker, with the formation of more HC radicals; c. termination, by the formation of a polymer by two reacting HC radicals; sometimes followed by d. decomposition, by which peroxides are susceptible to decomposition beginning a new polymerization cycle.

The most oxidation-susceptible HC's are the diolefins. The series drops in susceptibility as follows: diolefins[→]olefins[→]side chains of aromatic compounds[→]ethers[→]aldehydes[→]ketones[→]paraffins.

Antioxidants and a variety of other additives are presently being used in ATF "formulations".

 

[25362]

BTW, one must be careful when using the ATF acronym. It is also frequently used to designate automatic transmission fluids.