Research and Development of Biodiesel Production in a
Continuous Process
Biodiesel is gaining widespread attention as an alternative to conventional or ‘fossil’ diesel. Biodiesel
can be produced from virgin oil feedstock (such as rapeseed or soyabeen), animal oil/fats, tallow and
waste cooking oil. This article discusses the benefits of performing this transformation from oil/fat to
biodiesel in a continuous flow process, rather than a regular batch process.
The advantages of biodiesel are that it is renewable, non-toxic and biodegradable. However, one of
the main benefits is that it can be described as ‘carbon neutral’. This means that the fuel produces
no net output of carbon in the form of carbon dioxide (CO2). This effect occurs because when the oil
crop grows it absorbs the same amount of CO2 as that released when the fuel is combusted.
However, this is not entirely true when considering CO2 associated with all steps involved from crop
growth to biodiesel production like: fertilizer production, solvent used in biodiesel formation,
transport etc.
The production of biodiesel needs to be financially motivating when compared to conventional
diesel. Today, biodiesel produced mainly from waste vegetable oil can compete with fossil diesel. For
biodiesel producers, it is extremely important to minimise cost of production and therefore,
solutions for cheaper and more efficient ways to produce biodiesel are very attractive.
Today, biodiesel is mainly produced in batch chemical reactors. This is where the oil/fat is placed in a
temperature controlled, stirred tank and reagents such as an alcohol and catalyst are added
sequentially. The reaction is then stirred for a period of time before draining the contents of the
reactor. A continuous process involves pumping the oil/fat, reagents and catalysts through a
temperature controlled pipe, thus continually producing biodiesel. A continuous process can be less
expensive to set-up and run, easier to control, more consistent and need less storage. Continuous
biodiesel production would therefore become cheaper, more competitive and therefore more
attractive to customers. The same technology can also apply to other biofuels production. As a result
of these potential benefits at the production scale, there is an increasing amount of research and
development effort at the laboratory scale.
Almost all biodiesel is produced using base catalyzed transesterification. This is the most economical
process requiring only moderate temperatures and pressures and producing a 98% conversion yield.
The Transesterification process is the reaction of a triglyceride (fat/oil) with an alcohol catalysed by a
base to form fatty acid esters (Figure 1)
Figure 1. Transesterification of fat/oil into biodiesel
The main limiting factor when scaling up the reaction is not the kinetics of the reaction itself but the
mass transfer due to the immiscibility of the vegetable oil and the alcohol. The shear forces in the
stirred tank reactors are not sufficient to effectively mix the two phases. This slows down the speed
of the whole process. Continuous process reactors offer superior mixing ensuring greater surface
interaction between the two phases and most importantly faster reaction times.
In the world of organic synthesis today, one of the fastest growth areas of research and
development is in the field of continuous or flow chemistry. It has become more widely adopted by
chemists and chemical engineers due to its multiple advantages. Formation of biodiesel is a standard
organic reaction, so this is not a surprise that biodiesel production could benefit from continuous
flow process.
The benefits of continuous flow for biodiesel synthesis are:

Rapid process optimization: Reaction time, reaction temperature, quantities of reagents
and catalysts can be automatically varied and each reaction analysed for purity and
conversion.

Cheaper production: Faster reaction times (due to rapid mixing of biphasic reactions), lower
capital investment and reduced storage requirements enable reduced costs.
o
In the example presented below, a microreactor was used (figure 1), giving a laminar
flow resulting in fast reproducible mixing.

Cleaner products: Higher efficiency mixing (either by diffusion or static mixing) and better
temperature control (due to a much higher surface area: volume ratio), results in
concentration gradients and temperature gradients that cause side reactions to be
minimised.

Greater “batch-to-batch” consistency: As mixing and temperature control are superior in a
flow reactor, the batch-to-batch variations are greatly reduced.

Multi-step reactions in one sequence: Continuous processes allow post reaction purification
to be performed easily.
o

This is demonstrated in the example below (figure 2) where a transesterification was
performed on a flow microreactor followed by a liquid/liquid extraction performed
with the Syrris FLLEX module (Flow Liquid Liquid Extraction Module). This allows the
continuous removal of the glycerol byproduct from the biodiesel stream.
In-line analysis: This eliminates the need for tedious sample preparation steps and allows
real time analysis of the crude biodiesel. In the example presented below (figure 2), a
sample was taken out of the stream automatically and sent to a mass spectrometer.
Figure 2. Commercial 250 µL continuous flow microreactor channel width 300 µm; the microreactor
had two inputs channels combining at a T-piece and one output channel
Figure 3. Asia Flow Chemistry System – 250μl Syrris Microreactor
Historically, the absence of commercially available lab scale continuous flow chemistry reactors
meant that research and development of continuous biodiesel production was difficult. Now with
the arrival of easy to use flow chemistry systems, investigating the benefits of continuous processing
has been made easy. Syrris microreactor systems such as the Asia system (Figure 3) have been used
to rapidly optimise Biodiesel processes in the laboratory.
The example mentioned below (Figure 4) was performed by the Burnham Institute for Medical
Research in La Jolla, CA with the support of Syrris, Amgen and IonSense Inc. 1 It shows that the use
of microreactors in biodiesel production offers many advantages when compared with traditional
batch processing.
The triolein solution was combined with the methanolic solution in the microreactor. The two
immiscible flow streams formed an alternating slug/plug flow of microdroplets of oil-aqueous-oilaqueous. The admixture exiting the chip was diluted with water in the FLLEX module. Liquid-liquid
extraction of the admixture in flow affords biodiesel in DCM, while the aqueous layer contains the
methanol and glycerol byproducts.
Figure 4. Continuous flow production of biodiesel
Optimization of the transesterification reaction was undertaken by modulation of the residence time
in the microreactor at ambient temperature. A residence time of 2.5 minutes at room temperature
was sufficient for complete conversion of triolein to methyl oleate. This method is significantly faster
than reported microwave flow methods while proceeding at ambient temperature. 2, 3
In summary mixing was achieved in very short time frames, even for immiscible phases. The
continuous flow liquid-liquid separation facilitates rapid and efficient isolation of product while inline analysis allows for real time monitoring.
Another exciting development which is attracting attention in the field of biodiesel research is the
use of biocatalysts. Certain selective enzyme based catalysts such as those belonging to the lipases
family (e.g. triglyceride hydrolases) have proven to be efficient in the biodiesel formation. However,
they are expensive and are proving to be unstable when used in industrial processes. Taking this
into consideration, it is understood why biodiesel production using biocatalysis is not currently more
utilised.
Transferring the biocatalysis batch process to a continuous process is a possibility where the oil/fat
would instead continuously flow over a bed of enzymes. This type of method already exists in flow
chemistry where a substrate flows through a column reactor packed with solid supported catalyst.
This dramatically increases the speed of reaction due to the fact that such small traces of oil/fat are
exposed with a large number of enzymes. Very interesting research has been performed recently at
the CRPP (Centre de Recherches Paul Pascal) in collaboration with other institutes in France on these
types of processes where they managed to irreversibly confine the enzymes in porous matrices. 4,5
This allows good accessibility and improves the product flow over the catalysts. Although this has not
been performed on a production scale, the cellular hybrid biocatalyst has been generated in situ
inside a chromatography column and continuous flow biocatalysis has been performed over a long
period of time. These results are very promising and indeed highlight the great potential for the
application of continuous flow processes for biodiesel production.
It is clear that there are many benefits to produce biodiesel/biofuels in a continuous manner. The
route to success relies on research institutes developing and optimizing processes in the laboratory
which will highlight the clear advantages of a more efficient process on abroad range of alternative
biofuels whilst leading to less expensive manufacturing costs.
This article was written by Yann Lecouturier – Syrris Ltd. info@syrris.com +44 (0)1763 242555
1. Fuel Chemistry Division Preprints 2008, Continuous Biodiesel Production with Continuous LiquidLiquid Extraction and Online MS Analysis
2. Barnard, T. M.; Leadbeater, N. E.; Boucher, M. B.; Stencel, L. M.; White, B. A., Energy Fuels 2007,
21, 1777-1781.
3. Leadbeater, N. E.; Stencel, L. M., Energy Fuels 2006, 20, 2281-2283
4. www2.cnrs.fr/en/1876.htm
5. N.Brun, A.Babeau-Garcia, M.-F.Achard, C.Sanchez, F.Durand, L.Guillaume, M.Birot, H.Deleuze and
R.Backov - Energy & Environmental Science, 2011, DOI:10.1039/C1EE01295A
.