NAMS 2002 Workshop - ICOM 2008

Ultra- and Microfiltration II - Processes – 3
Thursday July 17, 10:00 AM-10:30 AM, Moloka’i
Assuring Biodiesel Quality via Selective Membrane Filtration
M. Gutierrez-Padilla (Speaker), University of Colorado, Boulder, Colorado, USA
J. Downs, University of Colorado, Boulder, Colorado, USA
J. Pellegrino, University of Colorado, Boulder, Colorado, USA - john.pellegrino@colorado.edu
J. Bzdek, Symbios Technologies, LLC, Fort Collins, Colorado, USA
Biodiesel is produced by transesterification/esterification of lipids derived from
vegetable oils and waste fats. As a transportation fuel, biodiesel has some
desirable end-use attributes (including particulate emissions) versus petrodiesel
and thermochemically produced "green" diesel, which support its continued use
as part of the "sustainable" transportation fuel infrastructure. Nonetheless,
commercial experience has shown infrequent incidents of formation of a cloudyhaze,
and vehicle filter clogging problems, presumably due to trace contaminant
species, which need to be resolved. There may be several causes for each of
these quality-related events, and due to the variable feedstock sources, a broad-
based processing approach merits consideration. We have studied crossflow
membrane filtration of biodiesel with a variety of membrane structures and
material chemistries. Besides obtaining some process design-related figures-ofmerit,
for example, the membrane permeances versus applied transmembrane
pressure, we assayed the streams using the modified ASTM 6217 test (aka the
"cold soak" test), which is used as a quality control metric for filterability. We will
report results from several membranes, icluding a polyethylene microfiltration
membrane; several ultrafiltration membranes made from polyethersulfone and
polyvinylidene fluoride, and a solvent resistant nanofiltration membrane. The
filtration process was performed continuously with a retentate recycle until
permeate recoveries of 30 to 75% were obtained. (NB. Commercial processing
can be done to much higher recovery, ~98-99%, using a feed-and-bleed design.)
The main effect we studied was the transmembrane pressure, which was in the
range of 34 to 207 kPa (5 to 30 psi). Membrane cleaning for some membranes
was performed after the filtration tests by running methanol or ethanol across the
top of the membrane. These membranes could be reused after the cleaning.
Permeances in the range of 1.3x10 -7 to 6x10 -8 m/s/kPa could be consistently
obtained with some of the UF membranes. The hazy feedstock and the retentate
from all trials failed the cold soak test, but the ultrafiltration permeates passed it.
The microfiltration membrane was not fully acceptable in assuring that the
permeate passed the cold soak test. In addition, we analyzed our samples using
GCMS to quantify the fatty acid methyl esters (FAME) profile in the original
feedstock (soybean oil-based) and permeate. We found that the filtration process