Integrated Knowledge-Based Analyses of Socio-Economic Issues

Report Catalogue Data

  Report Class   General Public Report
  Analysis Type   Situation Analysis
  Issue Category   Technology Analysis
  Release Date   06_10_2008
  Last Update   04_07_2009
  Reference Code   GPR-SA.TA.FT-20080610-BFP

Fermentation Technologies
Butanol Fermentation Process Analysis

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

 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.



Available at Okumaye Publishing

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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