Chemical Engineering October 2015 - 14

to the heat and direct current
through electrodes of
nickel and steel. The carbon
nanofibers build up on the
steel electrode, where they
can be removed, according
to Stuart Licht, who leads the
research team GWU.
To power the synthesis, heat
and electricity are produced
through a hybrid concentrating
solar-energy system,
which focuses the sun's rays
on a photovoltaic solar cell to
generate electricity, and on a
second system to generate
heat and thermal energy.
Licht estimates electrical
energy costs of this " solarthermal
electrochemical process "
to be around $1,000
per ton of carbon nanofiber
product, which means the
cost of running the system is
hundreds of times less than
the value of product output.
He says the group is scaling
up the process and " soon
should be in range of making
tens of grams of nanofibers
an hour. "
Putting more 'bio' into biodiesel fuels
B
iodiesel fuels are made by the
transesterification of plant-derived
triglycerides (fats and oils), a process
that generates impure glycerin
as a byproduct while consuming fossil-fuel-derived
methanol. Although there
have been efforts in recent years to utilize
the large volumes of glycerin byproduct
(see Outlets for Glycerin, Chem. Eng. September
2007, pp. 31-37), most of these
efforts focused on cleaning up the glycerin
for applications in pharmaceuticals and
cosmetics, or converting it into other commodity
chemicals, such as propylene glycol,
epichlorohydrin and acrolein.
Now, chemists from the Cardiff Catalyst
Institute, School of Chemistry at Cardiff
University (U.K.; www.cardiff.ac.uk) have
discovered a way to turn crude glycerin into
methanol, which can then be fed back to
the transesterification process. Recycling
the glycerin as methanol can increase the
biodiesel fuel production by an estimated
10%, says professor Graham Hutchings,
director of the institute, and lead author of
the article describing the research that was
published last month in Nature Communications.
In contrast to other processes that
hydrogenate glycerin into methanol using
H2 at high pressure, the Cardiff method
uses water as the source of hydrogen
atoms, he explains.
The researchers demonstrated that glycerin
(10-30 vol.% aqueous solution) reacts
with water over a magnesium-oxide
catalyst to give methanol with high yields
(25% conversion, 40% selectivity). The gasphase
reaction is carried out in a conventional
packed-bed reactor at temperatures
of 523-680K and atmospheric pressure -
much milder conditions than the so-called
Supermethanol concept, which integrates
gylcerin conversion into synthesis gas production
(reforming conditions 24-27 MPa,
950-1,000K) with methanol synthesis (24-
27 MPa, 470-520K).
Although the work is still in the early
stages, Hutchings says the discovery offers
good opportunity to optimize biodiesel production
while making it possible to produce
fatty acid methyl ester (FAME) with 100%
renewable content. The researchers plan to
optimize the catalyst to significantly increase
its activity and selectivity.
n
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Chemical Engineering October 2015

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