Desktop Biodiesel Plant
Samuel M. Gorton1 and Dr. Roshan J.J. Jachuck2
Process Intensification and Clean Technology (PICT) Group
Department of Chemical & Biomolecular Engineering
Executive Summary
The specific objective of this research was to develop a process for the purification of crude
biodiesel to meet ASTM D6751 for fuel-grade alkyl esters (biodiesel) by applying the novel chemical
engineering design concepts of Process Intensification (PI). A rotating tube reactor (RTR) was harnessed
for the purpose of removing free and bonded glycerol, free fatty acids and sodium hydroxide from crude
biodiesel using pure glycerol as a liquid-liquid extraction solvent. Reactor temperature, rotational speed,
residence time and molar ratio of glycerol to crude biodiesel were the variables tested in this study.
Glycerol is a byproduct of the biodiesel production process and its high density and polarity allow it to be
readily partitioned from the relatively non-polar alkyl esters by gravity separation. Hence, it was
hypothesized that glycerol could serve as an agent in biodiesel purification, especially by employing the
enhanced rates of heat and mass transport attained in intensified modules such as the RTR.
Biodiesel is a renewable, biologically-derived liquid fuel that has physical and combustionrelated characteristics that are similar to those of petroleum distillate fuels. The combustion of biodiesel
in automobiles, fuel oil furnaces and boilers has demonstrated several environmentally-related advantages
over petroleum diesel fuel. Economically speaking however, biodiesel is currently not cost-competitive
with petroleum fuels, and, as such, has not been able to significantly penetrate the liquid fuel market. One
approach to reducing the cost of biodiesel at the fuelling station is to streamline and decentralize its
production through the implementation of a more efficient, scalable production process. To attain this
end, the revolutionary design principles of PI can be employed, which promote the minimization of
process waste generation, energy consumption, and equipment footprints.
A common instrument of PI utilized in chemical processing is the RTR, which primarily consists
of a hollow, thin-walled cylinder, rotated about a horizontal axis at high rotational velocities. For liquidliquid contacting of crude biodiesel with glycerol, the two liquid streams are introduced onto the cylinder
through a conical inlet, which promotes mixing. When the mixture reaches the cylindrical portion of the
RTR, centrifugal forces induced by a high rotational speed cause the fluid mixture to form a thin film on
the walls of the spinning tube. Also, since glycerol and crude biodiesel are immiscible, they separate
1
Bachelor of Science Candidate, Class of 2007, Department of Chemical & Biomolecular Engineering, Clarkson
University Honors Program, Oral Presentation
2
Mentor, Research Associate Professor, Department of Chemical & Biomolecular Engineering
based on a density gradient inside the tube. It is speculated that phase separation creates annular fluid
layers within the tube, a phenomenon which enhances mass and heat transfer. This enhancement is a
product of the high shear rates at the interface between two fluids and between the outer fluid and the tube
wall. High shear rates induce wave and ripple effects in the fluids in the RTR creating more surface area
for heat and mass transfer. Despite these high rates of heat and mass transfer, the RTR also facilitates
instantaneous phase separation at the reactor outlet. This increases the rate of biodiesel purification by
minimizing phase settling time, which is a common drawback in current industrial biodiesel production
processes. Thus, the RTR module may be suitable for enhancing purification of crude biodiesel by liquidliquid contacting with glycerol.
For the purpose of this research, crude biodiesel was produced by reacting refined, commercial
canola oil with the catalyst sodium hydroxide (anhydrous, Fischer Scientific) solvated in methanol
(histological grade, Sigma-Aldrich). This reaction is known as alkali-catalyzed transesterification and
was carried out in a 500 mL flask under conditions that assured a high conversion of canola oil to
biodiesel. Then, the product was poured into a separating funnel and allowed to settle overnight. For
purification, 100 mL of crude biodiesel product was decanted and then brought into intimate contact with
50 mL of pure glycerol (purity >99%, Sigma-Aldrich) at 450C and 500 rpm in a 3-inch diameter RTR.
Biodiesel pH was measured before and after purification by diluting to 10% v/v with isopropanol (HPLC
grade, Mallinckrodt Baker). After three minutes of residence time in the RTR, the pH of crude biodiesel
was reduced from 10.4 to 8.0. This significant drop in pH was a result of residual sodium hydroxide
being transferred from the crude biodiesel phase to the glycerol phase. Additionally, separation of the
glycerol and biodiesel phases was achieved with a short settling time.
Given the reduction of pH observed, it was assumed that sodium hydroxide was removed from
the crude biodiesel via contact with glycerol. Therefore, it was suggested that glycerol could serve as a
suitable purification agent for the removal of other biodiesel contaminants which exhibited an attraction
to the glycerol phase. In order to quantify the removal of other important crude biodiesel contaminants,
the gas chromatography (GC) techniques required for ASTM D6751 certification were adopted for
measurement of free and total glycerin content (ASTM Standard Test Method D6584). A HewlettPackard 5890 Series II GC equipped with a flame ionizing detector (FID) and an HT-5 aluminum clad
capillary column (Scientific Glass Engineering) was used for such analysis. Standard solutions were
obtained from Sigma-Aldrich to develop calibration curves for measuring mass percentages of free and
bonded glycerol as well as methyl esters. Due to the extreme conditions to which the GC equipment is
subjected for biodiesel analysis, namely high temperatures and small sample sizes, results to date have
been inconclusive.
Future laboratory research efforts should include troubleshooting GC analysis to assure
reproducibility of results from standard solutions. This would allow for fast, accurate, in-house testing of
ASTM standard biodiesel. Also, a feed system for the RTR must be developed in order to simulate a
continuous, commercially-viable biodiesel purification process. Finally, processing variables in the RTR
should be optimized for obtaining ASTM-grade biodiesel from a continuous purification process.
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