ISSN 1070-4272, Russian Journal of Applied Chemistry, 2014, Vol. 87, No. 8, pp. 1176−1183. © Pleiades Publishing, Ltd., 2014.
A Review of Transesteriﬁ cation from Low-Grade Feedstocks
for Biodiesel Production with Supercritical Methanol
Dan Zeng, Ruosong Li, Bin Wang, Jie Xu, and Tao Fang
School of Chemical Engineering and Technology, Xi’an Jiaotong University, Xi’an, 710049, China
Received August 28, 2014
Abstract—Biodiesel produced from renewable energy sources has been widely researched by different countries
as a potential and ecologically acceptable substitute for the conventional fuel. Considering the increasing material
cost and the human consumption of edible vegetable oils, low-grade raw materials involving non-edible oils, waste
cooking oils, soapstocks and animal fats have drawn much interest for biodiesel production. This paper reviews
the transesteriﬁ cation of low-grade feedstocks to convert into biodiesel with supercritical ﬂ uid technology that is
more efﬁ cient and eco-friendly. This technonogy leads to simpler separation and puriﬁ cation steps compared with
the conventional catalytic methods. The supercritical process is insensitive to free fatty acids or water in feedstocks
and requires relatively short reaction time with high ester conversion yield. Besides, potential intensiﬁ ed technology
has also been provided for reducing the biodiesel production cost to expect an early industrial application.
Biodiesel consisting of fatty acid methyl esters
(FAMEs) is made by triglycerides (TG) though
transesteriﬁ cation with an alcohol (mostly methanol).
It is under great consideration as the potential diesel
oil substitute due to its advantages of environmentally
friendly, non-toxic, biodegradable, almost sulfurless and
non-aromatic [1, 2]. It can both ease the massive demand
of the depleting non-renewable resource, like Petroleum
and coal, and is beneﬁ cial to the sustainable development
and the environment p rotection.
The TG sources are diverse from edible or non-edible
vegetable oil, waste or recycled oil, animal fats, and mi-
croalgae [3–5]. It is not economically feasible for using
edible vegetable oils as the feedstocks due to the high
prices of biodiesel products compared with the conven-
tional diesel fuel. In order to improve its marketability,
low-grade feedstocks with high free fatty acids (FFAs) ,
e.g. restaurant greases, animal fats, waste cooking oils,
and soapstocks, are much more suitable for biodiesel
production . If those waste disposes and accumulates in
the environment, their unpleasant smell and adverse will
seriously impacts on the soil fertility and water quality .
Therefore, reusing all of those low-grade feedstocks by
converting them to biodiesel is one of the proper solutions
and contributing to environment protection.
Four main methods to produce biodiesel are direct
use and blending, micro-emulsion, pyrolysis, and trans-
esteriﬁ cation. Among them, the transesteriﬁ cation is the
most commonly used one to convert the TG from differ-
ent types of lipids with an alcohol . Conventionally,
the transesteriﬁ cation reaction often proceeds with acid,
alkali, or enzyme catalyst [8–16]. However, there are
some drawbacks restricting the catalytic process. The
reaction with an acid catalyst is time-consuming and
requires acid-resistant equipment . While, in the alkali-
catalyzed transesteriﬁ cation method, water and FFAs
always produce negative effects on the yields of methyl
esters since the presence of water and FFAs consumes
catalyst, reduces catalyst effectiveness, and causes soap
formation . For enzymatic production of biodiesel, the
primary obstacles are the expense of lipases, the slower
reaction rate and lipases inactivation caused by methanol
and the by-product glycerol .
For seeking a new method to eliminate the negative
effects of the catalytic processes in biodiesel production,
* The text was submitted by the authors in English.