  A totally green chemistry alternative that would lead both to energy
production from renewable feedstocks and to solutions of parts of ecological
problems related to waste disposals would be very attractive. Pyrolysis of used
frying oils seems to be one option for this attractive alternative as we
propose to demonstrate in this study. Since 2002, the whole production of waste
edible oils (around 100 000 tons per year in France) must be collected and
transformed into secondary raw material by specific companies. The general aim
of the present work is to produce one of the following target sources of
energy: (i) H2 for fuel cells, (ii) H2/CO in satisfactory ratios to produce
biodiesel by Fischer-Tropsch (FT) reaction, or (iii) hydrocarbon mixtures with
high added value. Therefore, in this work, the conversion of a crude used
frying oil, named VEGETAMIXOIL^(r); from Ecogras Company (France), was
investigated (weight composition: C 73.6%; O 9.7%; H 12.2%). In support of our
knowledge related to fatty acids and methyl esters, a laboratory pilot plant
was built to study the pyrolysis of used frying oils. Effects of temperature
(700-800 degrees C), residence time, addition of reaction initiator (H2O2) or
inhibitor (thiophene), and diluent (water or nitrogen) were analysed with
regard to the nature and amounts of pyrolysis products. Results led to the
conclusion that the best operating conditions of pyrolysis are 800 degrees C
with water as diluent, leading to the production of dihydrogen (40%) and
hydrocarbons from methane to propylene, essentially. CO and CO2 are also
produced but with low molar fractions. Furthermore, a ratio H2/CO favourable
for low temperature FT is obtained.
