Environmental Engineering Reference
In-Depth Information
Recycled
greases
Vegetable oils
Sulfuric acid
+ methanol
Dilute acid
esterification
Methanol + KOH
Transesterification
Crude glycerin
Crude biodiesel
Methanol
recovery
Glycerin
Refining
Refining
Glycerin
Biodiesel
Figure 14.5
Basic technology for biodiesel production via acid/base catalysis.
“ABCs of biofuel,” n.d.
Biobutanol
Biobutanol is an alcohol that can serve as a fuel in internal combustion engines. It is less polar
than ethanol; therefore, it does not have the same corrosion issues and water contamination as
ethanol. This would allow the use of the existing gasoline distribution infrastructure including
pipelines, blending facilities, storage tanks, and retail pumps (“Alternatives and advanced
fuels: Biobutanol,” n.d.).
Biobutanol is a four-carbon alcohol obtained via anaerobic fermentation of sugars.
Microorganisms from the genus
Clostridium
convert a variety of sugars, such as glucose,
galactose, cellobiose, mannose, xylose, and arabinose, into a mixture of butanol, acetone, and
ethanol (Ezeji et al., 2007). Producing biobutanol by fermentation is not a new concept. Up to
the mid-1900s, biobutanol was obtained exclusively by fermentation, but yields and the devel-
opment of the petrochemical industry made the biological route not longer competitive with
petroleum-based butanol (Suszkiw, 2008).
The classical microorganism used to produce butanol is
Clostridium acetobutylicum
. One
of its limitations is that besides butanol produces acetone and ethanol along with other minor
amounts of other compounds. Also butanol becomes toxic for the microorganism after a
certain level, thus limiting the maximum concentration. Therefore, ongoing efforts have been
committed to finding other strains via genetic recombinant DNA and traditional mutagenesis
capable of increasing the amount of butanol produced. In addition, several methods have been
studied to remove butanol as it is produced (see Ezeji et al. [2007] for a more detailed look at
the methods).
From the substrates' viewpoint, biobutanol has the same problems as other chemicals and
fuels obtained by microbial fermentation: sugars are expensive raw materials to produce mas-
sive amounts of these compounds. As a result, researchers are in the process of developing
procedures for the next generation of biobutanol from biomass (Suszkiw, 2008).
