Page 109 - Advances in Eco-Fuels for a Sustainable Environment

82 Advances in Eco-Fuels for a Sustainable Environment

supercritical fluid extraction. Supercritical CO 2 extraction efficiency is affected by
four main factors: pressure, temperature, CO 2 flow rate, and extraction time. These
factors, along with the use of modifiers (most commonly ethanol as a cosolvent),
can be altered and adjusted to optimize extractions [20].
Go ´mez et al. [60] worked on the extraction of grape seed oil using supercritical
carbon dioxide as a solvent. This seed is a byproduct of the wine fermentation indus-
try, and has a high level of unsaturated fatty acids fit for biodiesel production. Chan
and Ismail [68] found SFE technology to be a good alternative extraction method that
is suitable in kenaf seed oil extraction. The effects of pressure, temperature, and par-
ticle size on the SFE extraction of essential oils from the clove bud were investigated
by Guan et al. [69]. Despite the benefits derived from this method, it still faces some
challenges, such as the level of moisture in the sample, high power consumption, and
difficulty in scaling up. The high moisture content can reduce contact time between
the solvent and sample [20].

3.4 Challenges of biodiesel production
and recommended solution

Generally, the challenges of biodiesel production despite the advantages revolve
around the feedstock used, technology adopted, and the government policy in place
[70]. Stages of production from feedstock cultivation and requirements to utilization
of the target product have their intrinsic challenges. Likewise, a collective supply of
fats and oils from various feedstocks is not yet sufficient to replace conventional diesel
[71]. That is, much more work is required for commercial-scale production of biodie-
sel with this feedstock.
Among the several challenges associated with commercial-scale production of bio-
diesel is the cost of production. It is well said that biodiesel is such an environmentally
friendly fuel among other valid qualities, but its cost of production relative to that
required for the production of conventional diesel is on the high side. When the feed-
stock is rich in free fatty acid and water, this tend to form soap through a process called
saponification reaction. The hydrolysis of water with the triglyceride forming diglyc-
eride aids the formation of more fatty acid thereby promoting this reaction [72].In
essence, the free fatty acid and water content tend to represent important limitations
of alkali-catalyzed biodiesel production [73]. Hence, the pretreatment of the feedstock
contributes to the high cost of production and utilization. The technologies associated
with the reduction of the free fatty acid of the feedstock are part of the determining
factors in the overall cost of production. The technologies usually employed include
steam distillation, extraction by alcohol [74], and esterification by acid catalysis [75].
Steam distillation is characterized with low efficiency despite the demand of high tem-
perature condition [73] while the low solubility of fatty acids in alcohol hinders the
removal of the presence of free fatty acid by extraction, unless using a large quantity of
solvent, which complicates the process. Nevertheless, esterification by acid catalysis
uses up the free fatty acids present and transforms them into biodiesel [72]. Promising
techniques are anticipated and forthcoming with the relentless effort of researchers