Biodiesel production from waste cooking oils catalysed by ionic liquid [BMIM][HSO4]
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abstract
The authors are grateful to the Foundation for Science and Technology (FCT,
Portugal) and FEDER under Programme PT2020 for financial support to CIMO (UIDB/0690/2020).
The environmental and energy problems related to the burning of fuels from fossil resources, i.e. nonrenewable
fuels such as oil, natural gas or coal, leading to an increased concern about global warming,
have directed the scientific community to seek sustainable and renewable energy alternatives. In this
context, biofuels have emerged as a promising way to replace non-renewable fuels, including biodiesel
[1]. Biodiesel is defined as a mix of monoalkyl esters of long fatty acid chains (FAMEs), and can be
obtained by converting vegetable oils or animal fats through transesterification or esterification
reactions. Due to its advantages, such as biodegradability, low viscosity, high flash point and low
environmental impacts, it has potential to be used directly in diesel engines without any modification [2].
The raw materials used in biodiesel production can be divided into edible and inedible. However, the
high cost of edible oils, which correspond to about 70% of the total value of production, as well as
competition with the food market and soil degradation due to large planting scales, are disadvantages
for the production and commercialization of biodiesel [3]. Inedible materials such as Waste Cooking Oils
(WCOs) can also be used. The reuse of WCOs is a sustainable and environmentally friendly solution,
preventing millions of tons of this raw material from being dumped into sanitation systems giving rise to
serious problems in wastewater treatment. Still, one of the disadvantages of using WCOs is its high Free
Fatty Acid (FFA) content that leads to saponification reactions [2]. Homogeneous alkaline catalysts are
the most used in the biodiesel production industry. Compared to homogeneous acid catalysts, they have
many advantages, such as high productivity, low price, allow high reaction speed, shorter reaction time,
low alcohol molar ratio:oil and lower corrosiveness. However, catalysis is mainly affected by the
presence of free fatty acids, leading to decreased reaction yields. In addition, when using these
conventional catalysts, a high amount of clean water is used during the purification process, resulting in
high flows of waste water, which is deposited in rivers, lakes, seas, contaminating the environment. To
solve this problem, the possibility arises of using new catalysts, such as ionic liquids (ILs), which allow
high reaction yields, and can be recovered and reused, making them greener and more economical
