Prospects of 2nd generation biodiesel as a sustainable fuel Part: 1 selection of feedstocks, oil extraction techniques and conversion technologies

The transport sector, which heavily depends on oil-derived liquid products such as gasoline and diesel, globally occupies the 3rd place when total energy consumption and greenhouse gas (GHG) emissions are considered (after the industry and the building sectors). This consumption level is predicted to increase by 60% by 2030 mainly because of population growth, industrialization and exposure to better living standards. Biodiesel is one of the sustainable sources of energy for meeting increasing global transport energy demand and reducing GHG emissions significantly. The use of non-edible plant oils is very significant because it can be grown in harsh and marginal lands which require less maintenance, less soil fertility and less water as opposed to arable lands for growing edible vegetable oils. However, it is noted that the 2nd generation feedstocks can also be grown in arable lands, but this is not a general practice and is not recommended. The 2nd generation biodiesel can be considered as a promising alternative because of its feedstocks, such as non-edible vegetable oils, animal fats and waste cooking oils are cheaper in most of the countries in the world than the 1st generation feedstocks which are produced from edible-vegetable oils (food crops). Furthermore, the price of biodiesel depends on the cost of feedstocks which makes up 70-95% of the total production costs. However, extraction of non-edible oils as well as conversion process of oil into biodiesel should be well scrutinized. This paper extensively reviews on the selection of 2nd generation biodiesel feedstocks, oil extraction as well as biodiesel conversion techniques with the aim to identify the most appropriate and cost-effective feedstocks, identify the most suitable oil extraction technique and most efficient technology for producing of the 2nd generation biodiesel which will substitute the current dependence on the fossil fuel worldwide. This paper will contribute to greater understanding of the recent development and prospects of 2nd generation biodiesel as a sustainable transport fuel. (C) 2015 Elsevier Ltd. All rights reserved.