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More Update Post: 03_03_2009;
03_09_2009
With the quest for biofuels
that perform comparably with gasoline, attention has also turned to
the use of butanol produced from biomass, yet again, after being
abandoned for a long time. Butanol, by happenstance also performs
comparably to gasoline and as such is just an effective a biofuel as
ethanol, and purportedly also has some other advantages.
However, the fermentation of butanol
has not received as much push as the
fermentation of ethanol
though, most likely because of the poor yielded of butanol relative to
ethanol: The fermentation of biomass into butanol does not readily
provide yields close to ethanol. Remarkably though, is that the yeast culture or inoculums that
produces ethanol also produces butanol; and the alcohol was produced
by this method for a long time many years ago, by the time old
method of butanol production of Acetone Butanol Ethanol (ABE)
resulting from the
fermentative glucose utilization
for butanol by clostridium acetobutylicum.
As with ethanol
Fermentation Processes, the Butanol Fermentation Process, could be deemed to be of two main components:
Fermentation Process Feed System and Fermentation Process, therefore
the process may be partitioned accordingly: The former handles the processing of
the feed prior to being pumped into the Fermentation Reactor, and
the latter beginning with the Fermentation Reactor carries through
the rest of production of the alcohol.
The first component: The Butanol fermentation process
feeds fundamentally has similar process as an ethanol
process: The same substrate for the ethanol
fermentation process is also employed for the Butanol fermentation. The Substrate Feed
Process in the ethanol fermentation process have evolved over time from experimental development with a myriad of feed sources
as
three or four feed sources: Grain, Cellulosic [Grass] Source,
Sugar-cane and Palm Sap. With the empirical utilization of each of
these newer substrate-sources has evolved a
set of
process step and correspondingly engineering equipment set for
the processing of the feed into the feed-sugar [also the substrate]
as synopsized:
Grain Ethanol Feed Process
Cellulosic & Hemicellulosic Feed Process
Palm Juice Feed Process
before being fed, using a
Substrate Mash Feeder, which is specially designed to have the
Mash well mixed and infused with the right concentration of
oxygen before being discharged, into the bioreactor of the Fermentation
Process in which the fermentation microbes effect the oxidative
digestion of the sugar into butanol.
The second component,
however, can be significantly different, being required to possibly
cause the separation of acetone and other products
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as well from butanol, may virtually consists of the following
equipment set:
Fermentation Reactor
Distillation System(s)
Storage Tanks
The operation of the
components follows this progression: Basically, during operation,
the Mash with the proper supplementary substances for the
anabolic reactions is charged into
the Fermentation Reactor to initiate and sustain fermentation. The
Fermentation reaction is allowed to proceed up to a level of
completion as determined by the reaction time allowed, either by the
batch operation or by the residence time in the
reactor. At the set time the fermentation reaction product is
transferred to the distillation system for distillation. The product
of the distillation process should yield butanol.
Indeed, a careful review
of the (ABE)
fermentation process shows that the butanol production occurs by two
reaction networks that constitute two sets of consecutive
reactions: The reaction process apparently initially yields acetic,
lactic, butyric, and propionic acids, then undergoes an instability and spontaneously reacts to form the final mixture
of butanol, acetone, ethanol, and
propanol. The specific yeast flavour
however produces the products in varying ratios. Of particular
interest here, however, is simply the switching dynamic of the
fermentation reactions: The experimental observation
suggests that the reaction continues until the concentration of the lactic
acid reaches a certain concentration at which the
microbe preferentially switches the reaction, and there in is the
cue, the reactor design must be such as to enhance the accumulation
of the lactic acid.
From a chemical reaction analysis perspective it appears
that a set of possibly parallel reactions occur yielding the first
intermediary products: acetic, lactic, butyric, and propionic acids; a chemical thermodynamic potential is then
created
spontaneously which causes an initiation of the second set of reactions
resulting in the final products: butanol, acetone, ethanol, and
propanol. Continuing adoption of this fermentation process for
butanol production therefore must necessarily factor this reaction feature in the
process design. Admittedly, the
specifics of the reactor configuration depends on the process
technology. Yet, of course, it is plausible when considered from the
perspective of consecutive reactions, that a more optimal approach
could be possible from the reaction analysis. Obviously a
thorough understanding of the various reactions and the initiation
of different reactions at different points of progression of the
fermentation should further help clarify the state of reactions path
and help construct reaction paths that so far is unknown. Yet in
developing a bioreactor for this process, the known fact of the
homogeneous reactor yields as being not optimal is admitted as a
basis for excluding reactors of that class. So necessarily, the
attention must shift to heterogeneous bioreactors for a more optimal
design analysis.
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In particular, a
unique bioreactor is suggested. The reactor by configuration is a
Co-axial Cylindrical biofilm Reactor, with the microbes immobilized
on the wall of the inner cylinder. This is simply
a foundational concept reactor for this process, further modified to
allowed for the accumulative recycling of the lactic acid. Further,
the use of the
Fermentation Mash Feeder is essential for ensuring that
the microbes have the required oxygen to begin the fermentation. The
configuration of the Mash Feeder must be based on the general
requirements of nutrients
for a
fermentative glucose utilizing reactor.
However, irrespective of the type of reactor that is deployed,
material balance analysis for these reactors allows for
accounting for the consumption and assimilation of the nutrients
into microbial mass. The consideration of the metabolic reactions as part of the analysis
foundation enables the adoption of
fermentation
reactor design material balance
method that is intrinsic for fermentation reactor designs.
In any case, both reactor
types also require support from the operation of yet another bioreactor,
the
fermentor bioreactor; and the heterogeneous bioreactor
requires the additional
sub-bioprocess for the microbes immobilization, designed around
a
microbes
immobilization reactor.
A note is made, of course,
of other recent technologies distributing the consecutive reactions into a
two reactors fermentation process instead of the otherwise
single reactor original ABE fermentation process, and with the
assertion of obtaining a higher yield than had been possible
otherwise.
However, as noted an effective
chemical reactor engineering may develop a one fermentation reactor
design, even if allowing that such may just be quite complex. The activities here are more
or less conceptual build on the ABE fermentation process reactor for the
fermentation of butanol. Note is also made here that even an
Entrained Bed bioreactor with the same modification as suggested can
be operational for this bioprocess.
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