Calcium methoxide as a solid base catalyst for the transesteriﬁcation
of soybean oil to biodiesel with methanol
Xuejun Liu, Xianglan Piao, Yujun Wang
, Shenlin Zhu, Huayang He
State Key Laboratory of Chemical Engineering, Tsinghua University, Beijing 100084, China
Received 11 April 2007; received in revised form 25 May 2007; accepted 30 May 2007
Available online 19 July 2007
In this study, physical and chemical characterizations of calcium methoxide were investigated to assess its performance as an excellent
solid base catalyst using some instrumental methods, such as BET surface area measurement, scanning electron micrographs and particle
size distribution. Then, it was used to catalyze transesteriﬁcation of soybean oil to biodiesel with methanol. The eﬀects of various factors
such as mass ratio of catalyst to oil, reaction temperature and volume ratio of methanol to oil were studied to optimize the reaction
conditions. The results showed that calcium methoxide has strong basicity and high catalytic activity as a heterogeneous solid base cat-
alyst and it was obtained a 98% biodiesel yield within 2 h in this reaction. Besides, the recycling experiment results showed it had a long
catalyst lifetime and could maintain activity even after being reused for 20 cycles.
Ó 2007 Elsevier Ltd. All rights reserved.
Keywords: Calcium methoxide; Biodiesel; Solid base catalyst
There is an increasing worldwide concern for environ-
mental protection and for the conservation of non-renew-
able natural resources. Fatty acid methyl esters (FAME)
show great potential as diesel substitutes, and they are
known as the sources of biodiesel, which is synthesized
by direct transesteriﬁcation of vegetable oils with a
short-chain alcohol in the presence of a catalyst [1–5].
The transesteriﬁcation reaction can be carried out using
both homogeneous (acid or basic) and heterogeneous (acid,
basic or enzymatic) catalysts [6,7]. Homogeneous basic
catalysts provide much faster reaction rates than heteroge-
neous catalysts, but it is considerably costly to separate
homogeneous catalysts from the reaction mixture [8–11].
Heterogeneous catalysis is an economically and ecolog-
ically important ﬁeld in catalysis research because these
catalysts have many advantages: they are noncorrosive,
environmentally benign and present fewer disposal prob-
lems. They are also much easier to separate from liquid
products and they can be designed to give higher activity,
selectivity and longer catalyst lifetimes [12–14]. Because
of these advantages, research on chemical reaction using
solid bases as catalysts has increased over the past decade
. Many types of heterogeneous catalysts, such as alka-
line earth metal oxides, anion exchange resins, various
alkali metal compounds supported on alumina or zeolite
can catalyze many types of chemical reactions, such as
isomerization, aldol condensation, Knoevenagel condensa-
tion, Michael condensation, oxidation and transesteriﬁca-
tion [16–21]. However, for most anion exchange resins
and supported alkali catalysts, the active ingredients are
easily corroded by methanol and they exhibit short catalyst
lifetimes in the transesteriﬁcation reaction [22,23]. In con-
trast, alkaline earth metal compounds are very slightly sol-
uble in organic solvents and they are possibly used to
catalyze transesteriﬁcation reaction as solid base catalysts.
Some researchers found MgO has low activity in transe-
steriﬁcation of vegetable oils to biodiesel and CaO provides
a slow reaction rate to reach an equilibrium state [24,25].
0016-2361/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
Corresponding author. Tel.: +86 10 62773017; fax: +86 10 62770304.
E-mail address: firstname.lastname@example.org (Y. Wang).
Available online at www.sciencedirect.com
Fuel 87 (2008) 1076–1082