Purification of biodiesel using a natural based adsorbent in a packed-bed column
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abstract
In Europe, the Renewable Energy Directiva stimulates the development of renewable energy sources
to reduce greenhouse gas emissions by at least 55% by the year 2030 and to become aclimate-neutral
continent by 2050 [1]. Biodiesel presents advantages over diesel fuel in terms of sulfur content,
biodegradability, flash point, no aromatic content, higher cetane number and miscibility in petroleum
diesel in any ratio [2].
The most used feedstock is high quality vegetable oil, but the use of waste cooking oil adds to the global
reduction of residue, lower costs, and competes less for vegetable oils against the food industry [3]. This
biofuel is obtained through transesterification, and glycerol is formed as a coproduct. lts presence can
cause damage to motors so it must be removed until its final concentration is lower than 0.02wt%. The
most used method is wet washing, but the downside is the great amount of water used and long periods
of time are needed to separate biodiesel from its contaminants through decantation [4]. A promising
altemative is dry washing method through adsorption using biomass activated carbon. For a more
practica! application, packed columns are frequently used in large scale adsorption processes. lt is one
of the most efficient configurations for treating great volumes of effluent and adsorption-desorption
cycles [5].
For this study, crude biodiesel was produced through transesterification from a waste cooking oil
sample, using ethanol and a basic catalyst (NaOH). Afterwards the biodiesel produced was
characterized in terms of glycerol content. In parallel, activated carbon materials were obtained from
olive pits by physical activation at 800°C. The adsorbent materials performance for glycerol removal
from crude biodiesel is assessed using a continuous system based on a packed-bed column according
to the following parameters: fluid rate, removal capacity, pressure drop and adsorbent recovery.
The authors are grateful to the Foundation for Science and Technology (FCT, Portugal) for financia! support through
national funds FCT/MCTES (PIDDAC) to CIMO (UIDB/00690/2020 and UIDP/00690/2020) and SusTEC
(LA/P/0007/2021).