http://biodieselamerica.org/biosite/index.php?id=25,0,0,1,0,0
What’s NOx?
Engines running on biodiesel sometimes register an increase in Nitrous Oxide (NOx) emissions. NOx
is a low-level emission that contributes to the yellowish haze around cities. NOx emissions are
produced when something is burned in Earth’s atmosphere, (which is about 80% nitrogen and 20%
oxygen). The range of increase in NOx emissions resulting from biodiesel can be anywhere between
1-15% but is generally around 5%. The measurement varies widely according to engine type and
the type of biodiesel fuel used. For example, Cummins engines generally register lower NOx
emissions than Caterpillar engines and biodiesel made from rapeseed has often shown actual
reductions in NOx emissions while biodiesel made from soy generally shows an increase in NOx
emissions. Engine age also affects NOx. Older diesel engine may produce up to 12 grams of NOx
per brake horsepower hour (bhp) whereas newer diesel engines typically produce as little as 1.4
grams of NOx per bhp - less NOx emissions than many gasoline engines.
Solutions to NOx Emissions
Regardless of engine make or biodiesel fuel type, there are two simple methods to reduce NOx
emissions. NOx emissions are a function of temperature. In the case of biodiesel, NOx emissions are
a function of combustion temperature. The higher the heat of combustion, the greater the NOx
emissions. Because biodiesel contains more oxygen than diesel fuel, the heat of combustion is
slightly higher. By retarding engine timing 1-3 degrees, combustion temperature will drop slightly
and the NOx emissions of an engine running on biodiesel will drop to levels at or below those
recorded when the engine was running on diesel fuel. NOx emissions will also decrease with the use
of a catalytic converter, a device that uses rare earth metals to break apart emissions. While
catalytic converters have been standard on gasoline vehicles for some time, they have only recently
become standard on diesel vehicles in the United States. The complete lack of sulfur in biodiesel fuel
allows the use of powerful NOx breaking catalysts that have been unusable until now.
Emission tests on different vegetable oils, chemical properties
Toxicity, raw oils: http://www.uidaho.edu/bae/biodiesel/
http://www.missouri.edu/~pavt0689/biofuel.html
http://www.missouri.edu/~pavt0689/
http://www.iprt.iastate.edu/ccat/nano.html
Many of the "green" feedstocks (vegetable oils, starches, wood fibers, etc.) are molecules with widelyvarying properties. To successfully convert these complex feedstocks with multiple functional groups into
important value-added products such as biodiesel, biodegradable polymers, and other new materials and
chemicals, one has to have the ability to design highly efficient and selective catalysts with control of the
chemistry that takes place at the nano-meter scale is a crucial prerequisite for developing a Green Chemical
Industry in the near future.
Our goal is to: Design heterogeneous solid catalysts using nanoscience methods to realize the superb
selectivity of biocatalysts and homogeneous catalysts with high turnover numbers, minimal wastes, and long
lifetimes of the catalysts.
The Center for Catalysis currently supports several research projects that combine important concepts of the
emerging nanoscience with catalysts design:
(1) Nanoporous Solid Catalysts for Conversion of Soybean Oil to
Biodiesel
John G. Verkade, Iowa State University Department of
Chemistry
Brent H. Shanks, Iowa State University Department of
Chemical Engineering
Victor S.-Y. Lin, Iowa State University Department of
Chemistry
As a result of recent legislation designed to decrease vehicle emissions and the recognition that a
decreased dependence on foreign sources of fuel will enhance national security, interest in the use of
biodiesel (soy diesel) as an alternative fuel has accelerated.
Biodiesel has several advantages over diesel fuel made from petroleum. Biodiesel:
1.
2.
3.
4.
5.
6.
Is biodegradable in water. Up to 98% biodegrades in three weeks.
Contains negligible sulfur and increases lubricity.
Production can enhance rural revitalization.
Is neutral with regard to carbon dioxide emissions.
Use leads to significant reductions in most harmful exhaust emissions.
Has a high flash combustion temperature.
In addition to the above advantages of being a "green fuel", biodiesel, such as soy diesel (methyl soyate), is
becoming increasingly useful in industrial solvent formulations for removing grease and resins, as carrier
solvents, and as agents for shoreline oil spill clean-up. Apparently, methyl soyate is a viable alternative to
traditional petroleum-derived solvents, which are of environmental concern and are under legislative
pressure to be replaced by biodegradable substitutes. Furthermore, recent progress in developing ethyl
soyate-based solvents (which can be made from ethanol and soy bean oil) offer several additional
advantages over methyl soyate, such as a higher boiling point and lower volatile organic compounds
(VOCs), for even broader commercial applications. Given that ethyl soyate is made from ethanol (which is
produced by the fermentation of corn), the use of ethyl soyate would also expand the corn-based ethanol
market.
Although interest in biodiesel is rapidly increasing, the process by which biodiesel is synthesized has not
changed much. Currently, soy diesel (methyl soyate) is made commercially by an energy and labor-intensive
process wherein soybean oil is reacted with methanol at 140-150oF (sometimes under pressure) in the
presence of sodium methoxide. This process is called "transesterification." Isolation of the desired methyl
soyate from the highly caustic (toxic) catalyst and other products, such as glycerol, involves a precise
neutralization process with strong acids, such as hydrochloric acid (HCl), and extensive washes with water
to remove the resulting sodium chloride (NaCl) salt. Also, the glycerol must be separated from the sodium
chloride salt by vacuum distillation in an energy intensive operation for this high-boiling product. Glycerol is
used primarily in foods, oral care, tobacco and urethane foams. As more alkyl soyates with different alkyl
functional groups, such as ethyl and isopropyl soyates, being rapidly developed to meet the growing needs
of various applications, the level of difficulty in separating the corresponding catalysts, e.g., sodium ethoxide
and sodium isoproxide catalysts, respectively, would unavoidably escalate due to the increasing solubility of
these basic catalysts in the product solution. Clearly, the successful development of a more effective and
economical method to separate the base catalysts from the products is of keen interest to further advance
the techniques of biodiesel production.
In addition to the separation issue, the current base-catalyzed transesterification methods also have several
other limitations. As producers look for feedstocks other than soybean oil, such as waste restaurant oils and
rendered animal fats, they have observed a larger amount of free fatty acids (FFAs) contained in the
feedstocks. FFAs can not be converted into biodiesel using the current base-mediated processes.
As depicted in figure 1, we covalently attached a series of transesterification catalysts onto the pore surface
of an organically functionalized mesoporous silica nanosphere material. As outlined below, this structurally
well-defined mesoporous silica material provides several advantages to the current homogeneous catalysts.
These uniformly shaped silica particles (particle size = 250 nm in diameter) consist of arrays of hexagonal
porous channels with tunable pore diameters ranging from 2 to 10 nm (Figure 1 shows the SEM (a) and
TEM (b) images of a typical mesoporous silica nanosphere). In contrast to the polydispersive amorphous
sol-gel silicas, the uniform particle morphology and large pore sizes of these nanospheres will allow fast
diffusion of soybean oil molecules to the catalytic sites situated inside the porous channel and thereby
enhance the rate of product conversion and release. In addition, the heterogeneous nature of this catalytic
system provides several other advantages, such as easy separation and high reusability.
The large accessible surface area of the mesoporous silica nanospheres (> 600 m 2/g, which is at least 2 or
3 times larger than the surface area per gram of most polymer and sol-gel silica materials) provides an
advantageous platform for high catalyst loading to improve the efficiency of the transesterification. Also, the
hydrophobic organic functional groups render additional incentive (i.e., a hydrophobic solvation effect) for
the hydrophobic reactant (soybean oil) to enter into the porous channels lined with the attached catalyst.
(a)
(b)
(c)
Figure 1. (a) A scanning electron microscopy (SEM) image of the mesoporous silica nanosphere. (b) A
transmission electron microscopy (TEM) image of the cross-section of a mesoporous silica nanosphere showing
the highly regular hexagonal lattice units of the porous framework. (c) Schematic representation of the catalytic
system for methyl soyate and glycerol formation.