CHEMISTRY OF BIOFUELS AND BIOFUEL ADDITIVES FROM BIOMASS - Biomass as a Sustainable Energy Source for the Future - page 566

processes are all multistep processes with modest yields and thus are not in compliance
with the 12 principles of green chemistry.
A variant on this process is the catalytic depolymerization process, developed by
Alphakat (tinyurl.com/kbqsza3). This process is principally based on direct liquefac-
tion of biomass. In this process, organic biomass is cracked into light oil with the aid of
ion-exchange catalysts at a temperature of 370 C under atmospheric pressure. The
biomass produces a mixture of oil (>40 wt%), water, coal, and gas. In this way,
biodiesel has been produced with an estimated cost price of 0.23

l −1 .
Although this process is cost-effective, its greenness can be questioned, because less
than half of the carbon in the biomass is effectively used.

- 0.40

€

18.6 FUTURE GENERATIONS OF BIOFUEL

Currently, biotechnology is progressing rapidly to implement technologies that allow
the direct fermentation of lignocellulosic streams. In this way, fermentation processes
can overcome their dependence on classical (food-competing) sugar steams. Biotech-
nological production of biofuels as promoted by, e.g., Amyris (tinyurl.com/mzf3sux)
leans on the synthetic biology approach to make microbes synthesize a large variety of
organicmolecules, including diesel-type biofuels. In theory, all synthetic pathways can
be incorporated. For terpenes, which have a favorable C/H ratio of 0.8, promising
results have been obtained. These so-called biohydrocarbons have recently been added
to the top 10 list of platform chemicals to be produced from sugars (see Figure 18.4).
Apart from lignocellulosic streams, algae form another source of biomass. Varia-
tions on classical biodiesel synthesized from soybean oil, palm oil, etc. can be deliv-
ered by, e.g., algae oil. Apart from using the oil from the algae, photosynthetic algae or
cyanobacteria can also be regarded as microbial factories, which take their energy
from sunlight. Biotechnological processes involving cyanobacteria reactors produ-
cing ethanol directly from seawater, sugars, and light have been promoted (tinyurl.
com/pg8mk9g). Synthetic Genomics (tinyurl.com/lajphg8) is at the forefront of
promoting these photogenerated biofuels. They claim that microbes can be engineered
to perform practically any chemical reaction. Ideally, genetically engineered photo-
synthetic cells, when exposed to sunlight and carbon dioxide, could produce and
secrete energy-rich fats, which could then be refined directly into biodiesel fuel.
To circumvent contamination of microbial strains, algae have to be grown in photo-
bioreactors. In addition, in order to make this technology viable, microbes have to be
reused multiple times, and fat produced by the algae should be released instead of
stored. The production and harvesting of algae are surrounded by many agricultural
and societal dilemmas, and the future will learn which technologies will be viable.

CHAPTER SUMMARY AND STUDY GUIDE

The technology to upgrade sugars to biofuels is rapidly progressing. Many fermenta-
tion, thermochemical, and catalytic methodologies are under development to upgrade
lignocellulosic biomass and its constituents, C6 and C5 sugars, to biofuels. Besides