Chemical Engineering May 2015 - 11

a highly reactive oxygen plasma that etches away
at the graphene's carbon atoms, until holes are
formed in the layer. The pores themselves are punctuated
with silicon atoms - not oxygen or carbon
- a noteworthy phenomenon that the researchers
attribute to the silicon's potential stabilizing effect
on the pores. The size of the pores depends on the
amount of time that the membrane is exposed to
the oxygen plasma.
Controlling pore size is among the most challenging
tasks in scaling up this technology beyond the currently
demonstrated milliliter scale. As the membrane
surface area gets larger, there will be added difficulty
in maintaining the optimal pore density of one pore per
100 nm2. Ensuring mechanical stability (while remaining
at the desired pore density) as the membranes get
larger will also be key to moving to pilot and commercial
levels. In addition to the oxygen-plasma approach,
the team is also researching alternative, more
controllable methods of pore production to help alleviate
some of these concerns.
Making bioethanol directly
from starch
T
oday, the cost of enzymes continues to make
bioethanol uncompetitive as a fuel. Eliminating
the need for amylases, which are used to hydrolyze
starch into fermentable sugars, would
be a key step toward reducing the operating costs for
producing bioethanol. Such a breakthrough has now
been achieved, by reachers from Japan, led by Jyun
Shima at Ryukoku University (Otsu; www.ryukoku.
ac.jp) and Ayumi Tanimura at Kyoto University (Kyoto,
both Japan; www.kyoto-u.ac.jp). The scientists have
isolated a yeast strain that directly produces ethanol
from starch.
The researchers use a technique called consolidated
bioprocessing (CBP), which integrates enzyme production,
saccharification and fermentation in a single
reactor using a single yeast strain. Their CBP process
is said to be superior to alternative methods that use
genetically modified organisms (GMOs), which require
a complex production process to ensure physical containment
of the GMOs.
In this study, the researchers performed comprehensive
screening to find natural isolates of yeast
that could produce ethanol without having to add
amylases. Of the 530 yeast strains tested, three
strains were found to produce more than 6 g/L of
ethanol. After 10 d of cultivation, ethanol production
by S. shehatae JCM 18690 reached 9.2 g/L. It was
verified that the increase in the ethanol concentration
of S. shehatae JCM 18690 was mainly due to the
increase in its gluco-amylase activity.
The new yeast strain was also shown to be ethanoltolerant,
with the ability to ferment xylose contained
in biomass at temperatures higher than the normal
20-30°C range. The achievement has the potential to
enable ethanol production from inexpensive and abundant
renewable carbon resources, such as cassava
pulp and food wastes.
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Circle 8 on p. 102 or go to adlinks.chemengonline.com/56197-08
http://www.ryukoku http://www.ac.jp http://www.kyoto-u.ac.jp http://www.beumergroup.com http://adlinks.chemengonline.com/56197-08
Chemical Engineering May 2015

Table of Contents for the Digital Edition of Chemical Engineering May 2015
