Steam Cracking and Steam Reforming of Waste Cooking Oil in a Tubular Stainless Steel Reactor with Wall Effects
Résumé
Energy production from renewable feedstocks that would simultaneously solve ecological problems related to waste disposals would be very attractive. The present work is aimed at showing that atmospheric pressure thermal cracking of waste cooking oil in presence of steam would be a potential option, particularly when the operating conditions direct the process either towards steam cracking or towards steam reforming in order to produce specific target bio-energy vectors: hydrogen, synthesis gas, or gaseous fuel. A commercial crude waste cooking oil (VEG) was selected as feed material. Using a bench-scale continuous flow tubular stainless steel reactor, experiments were conducted to study the final product distribution as function of temperature, residence time of the feed material, extent of dilution, addition of a cracking initiator, and addition of a surface catalytic effect inhibitor. Several operating conditions of the VEG thermal cracking in presence of steam were identified to meet the above mentioned objectives. Particularly, when operating steam reforming at 800°C with a very low steam-to-carbon ratio (less than 1), VEG was totally converted into synthesis gas in a hydrogen-to-carbon monoxide molar ratio close to 2 (favorable for low-temperature Fischer-Tropsch catalysis), with additionally hydrogen and light hydrocarbons (methane, ethylene, propylene) production reaching respectively 40 and 27 mol%. Further investigations (conducted with the same equipment) confirmed the occurrence of strong reactor wall effects that led to the formation of coke deposits with catalytic activity during the VEG steam cracking and steam reforming.