One of the main aspect of this process that determines the yields are
the type of catalyst. There are three main categories of
catalysts that can be used. These include
alkalis, acids, and enzymatic catalysts, where
alkalis and acids are mostly used as compared to enzymatic catalysts. These
catalysts are characterized as homogeneous and heterogeneous
catalysts are commonly used in the transesterification process of biodiesel
production. Some of these catalysts involve sodium hydroxide (NaOH), potassium
hydroxide (KOH), sodium methoxide (NaOCH3), potassium methoxide
(KOCH3) and sodium ethoxide (NaOCH2CH3). These
catalysts are used due to its ability to catalyze reactions at low reaction
temperatures, atmospheric pressures and gives higher conversions in shorter
Sodium methoxide and
potassium methoxide are better catalysts than sodium hydroxide and potassium
hydroxide because of its ability to dissociate into CH3O-
& Na+ and CH3O- and K+
respectively when compared to biodiesel yields.
However, based on current
research and commercial production of biodiesel on the industrial scale, it has
found that NaOH and KOH are mostly used. “The highest biodiesel yield produced
by Calophyllum inophyllum was
reported by Silitonga et al. (2014) with 98.53% by using 1 wt% KOH and 9:1
methanol to oil ratio. Silva, Camargo, and Ferreira (2011) reported 95% of
biodiesel yield from soybean oil by using NaOH with 1.3 wt% catalyst loading
and ethanol to oil ratio of 9:1.” ~ Talha, N. S. & Sulaiman, S. (2016). OVERVIEW OF CATALYSTS IN BIODIESEL PRODUCTION, 11 (1, January 2016).
the major drawback of using homogeneous base catalyst, is that it cannot be
used directly when the oil contains large amount of free fatty acids; because
it neutralizes the base catalyst to produce soap and water, resulting in a
decrease of catalyst activity. When soap is formed, it inhibits the separation
of glycerol and removal of these saponified catalyst becomes difficult and adds
to extra costs in the production of biodiesel.
Homogeneous Acid Catalyst
catalysts are known to be a better choice when the feedstock contains a higher
quantity of free fatty acids (FFAs). This is because
FFAs can’t be converted to biodiesel with the use of alkaline catalysts.
Commonly used acid catalysts in the transesterification process of biodiesel
production involve sulfuric acid and
hydrochloric acid. Despite its ability to overcome the FFA in the feedstock,
this type of catalyst has a relatively slower reaction rate.
Therefore, when using this
catalyst, the alcohol to oil molar ratio is the
main factor that manipulates the reaction. Adding excess alcohol speeds
up the reaction and favor the biodiesel production.
In a study of
acid-catalyzed transesterification of Jatropha oil; using a two- step process
production by Patil et al., “a
maximum yield of 95% were attained according to the following conditions; at
the first acid esterification, i.e., methanol to oil molar ratio of 6:1,
sulfuric acid of 0.5 wt.%, and reaction temperature of 40 ± 5 °C; followed by
alkaline transesterification with methanol to oil molar ratio of 9:1, KOH of 2
wt.%, and reaction temperature of 60 °C.”~ Thanh, L. T., Okitsu, K., Boi, L. V., & Maeda, Y. (2012).
Catalytic Technologies for Biodiesel Fuel Production and Utilization of
Glycerol: A Review.
Another study showed that
using HCl catalyst for the transesterification process of sunflower oil, “Sagiroglu et al. (2011) reported 95.2% of biodiesel yield with 100?C reaction
temperature and 1.85 wt% catalyst loading. Cao
et al. (2013) used H2SO4 in the acid-catalyzed
transesterification with 0.5 wt% catalyst loading reported 92.5% biodiesel
yield from Chlorella pyrenoidosa.” ~ Talha,
N. S. & Sulaiman, S. (2016). OVERVIEW
OF CATALYSTS IN BIODIESEL PRODUCTION, 11 (1, January 2016).