Investigation of vegetable oil conversion by thermal deoxygenation and cracking for alternative biofuel generation

Abstract

The shortage of worldwide resources, the discussion about the global warming as well as energy independence policies are driving forces for developing new alternative fuel technologies based on renewable sources. One possibility is the conversion of vegetable oil into cracked vegetable oil (CVO) by cracking and deoxygenating in small decentralized plants. This paper describes a study in the context of which the conversion has been investigated on laboratory scale under atmospheric pressure in the absence of catalysts at temperatures from 350 to 400 °C. Under these conditions different feedstocks have been tested such as refined rapeseed oil, crude rapeseed oil, palm oil and used frying oil. Resulting yield of CVO is about 70–80 wt.−%. The measured physical properties of CVO are well complying with the specifications of the diesel standard DIN EN 590. Due to chain length reduction by cracking viscosity is decreased and cold stability is improved in CVO. Even in case of palm oil the resulting CVO stays liquid at room temperature. The kinetics of the deoxygenation of the raw material can be described by the decrease of the oxygen content in the oil during reaction time. The oxygen content can be calculated by the net calorific value which has been confirmed by elemental analysis. In case of rapeseed oil, the oxygen content can be reduced from 11 wt.−% to a level of 3–5 wt.−% while the net calorific value is increased from 37 MJ/kg to a level above 40 MJ/kg. The results indicate a chance to produce alternative fuels from vegetable oils with improved properties compared to biodiesel.