Valorisation of waste cooking oils through conversion processes to biodiesel catalysed by ionic liquid [HMIM][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).
To date, fossil fuels prevail as the primary source of energy, with a high consumption in transport and
industries, making them a major problem for our planet, given its weak environmental sustainability due
to its high greenhouse gas emissions to the atmosphere and the limited reserves [1]. In this context,
biodiesel emerges as a biofuel, biodegradable, environmentally sustainable and less toxic when
compared to fossil diesel, which has been acquiring much attention over the years, and it has been used
commercially blended with diesel. Chemically it can be defined as a mix of fatty acid methyl esters
(FAME), produced through transesterification reactions of vegetable oils or animal fats, with an alcohol,
usually methanol, in the presence of basic catalysts, which are highly corrosive and difficult to recover
[2]. Therefore, conventional catalysts present several problems for the environment, and for this reason,
there is a need to develop more environmentally friendly catalysts. Ionic Liquids (IL) have attracted a lot
of attention in recent decades, presenting themselves as the main alternative to traditional catalysts,
being green, non-toxic and non-flammable solvents [3]. On the other the production of 1st generation
biodiesel using raw materials from edible vegetable oils such as palm oil, sunflower oil, rapeseed oil,
among others, has the potential of causing socio-economic conflicts since these oils compete directly with
the food sector. This promoted the search for alternatives, such as the use of waste cooking oils (WCO),
since it is a residue that can be reused and with high energy content. However, these processes still need
better studies, due to the problems associated with the production through transesterification, with
regard to the high content of Free Fatty Acids [1].
Hence, the objective of this work is the study of the application of the IL 1-methylimidiazolium hydrogen
sulfate ([HMIM][HSO4]) in the catalysis of esterification/transesterification reactions of a WCOs with
high free fatty acids contents, through the application of a Response Surface Methodology (RSM) based
in a Box-Behnken Design (BBD) in order to determine the optimal reaction conditions (reaction time,
catalyst dosage, molar ratio methanol:oil and incorporation of oleic acid (OA) in WCO to simulate an oil
with high acidity) for the esterification reaction of waste cooking oil with methanol
