Pyrolysis of secondary raw material from used frying oils.

Francis Billaud (1) , Julien Gornay (1) , Lucie Coniglio (1)

1 DCPR - Département de Chimie Physique des Réactions

Limitation of oil resources leads to the development of new technologies that can more fully exploit renewable energies such as biomass and derived products, like food-grade vegetable oils (rapeseed or sunflower oils). 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. Until 2002, 80% of waste edible oils were discharge in sewers and only 20% were upgraded into high value chemicals or biofuel. 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® 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. The operating conditions of each pyrolysis experiment are characterized in terms of temperature profile, residence time, nature of diluent(s) and dilution. Liquid and gas products were analyzed by GC-MS and GC with a capillary column, whereas CO and CO2 were quantified by IR analyzer. Effects of temperature (700-800°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°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. This emergent oil and fat chemistry field could lead to new processes coming from vegetable raw material or used frying oils.

Mots clés: Used frying oils; Pyrolysis; Biodiesel; Bioenergy

Domaines: Chimie-Physique [physics.chem-ph]

Francis Billaud, Julien Gornay, Lucie Coniglio. Pyrolysis of secondary raw material from used frying oils.. Récents Progrès en Génie des Procédés, 2007, 94, pp.ISBN 2-910239-68-3. ⟨hal-00139828⟩