Bioconversion of biomass to mixed alcohol fuels



The bioconversion of biomass to mixed alcohol fuels can be accomplished using the MixAlco process. Through bioconversion of yeast fermentation.

The process involves a biological/chemical method for converting any biorefinery[1] [2][3].   The process uses a mixed culture of naturally occurring microorganisms found in natural habitats such as the rumen of cattle, termite guts, and marine and terrestrial swamps to cellulosic ethanol use enzymes that must be isolated first to be added to the biomass and thus convert the starch or cellulose into simple sugars, followed then by yeast fermentation into ethanol. This process does not need the addition of such enzymes as these microorganisms make their own [4].

As the microoganisms anaerobically digest the biomass and convert it into a mixture of carboxylic acids, the vapor-compression evaporation. Further refining of the dewatered fermentation broth may then take place depending on the final product desired.

The condensed distilled water from the vapor-compression evaporation system is recycled back to the fermentation. On the other hand, if sewage or other waste water with high water treatment facility.

Because the system uses a mixed culture of microorganisms, besides not needing any enzyme addition, the fermentation requires no sterility or aseptic conditions, making this front step in the process more economical than in more popular methods for the production of cellulosic ethanol. These savings in the front end of the process, where volumes are large, allows flexibility for further chemical transformations after dewatering, where volumes are small.

Carboxylic acids

For more details on this topic, see Carboxylic acid.

carboxylic acid. In this way, theoretically, no chemicals are consumed or wastes produced during this step. [5]

Ketones

For more details on this topic, see Ketone.

There are two methods for making ketones. The first one consists on thermally converting calcium carboxylate salts into the corresponding ketones. This was a common method for making acetone from calcium acetate during World War I[6]. The other method for making ketones consists on converting the vaporized carboxylic acids on a zirconium oxide [7].

Alcohols

For more details on this topic, see Alcohol.

Primary alcohols

The undigested residue from the fermentation may be used in esterification, and the corresponding primary alcohols (e.g., ethanol, propanol, butanol).

Secondary alcohols

The secondary alcohols (e.g., isopropanol, 2-butanol, 3-pentanol) are obtained by hydrogenating over a catalyst (e.g., Raney nickel) the corresponding ketones (e.g., acetone, methyl ethyl ketone, diethyl ketone)[10].

Acetic acid versus Ethanol

Cellulosic-ethanol -manufacturing plants are bound to be net exporters of electricity because a large portion of the lignocellulosic biomass, namely lignin, remains undigested and it must be burned, thus producing electricity for the plant and excess electricity for the grid. As the market grows and this technology becomes more widespread, coupling the liquid fuel and the electricity markets will become more and more difficult.

Acetic acid, unlike ethanol, is biologically produced from simple sugars without the production of carbon dioxide:

C6H12O6     →     2 CH3CH2OH   +   2 CO2
(Biological production of ethanol)
C6H12O6     →     3 CH3COOH
(Biological production of acetic acid)

Because of this, on a mass basis, the yields will be higher than in ethanol fermentation. If then, the undigested residue (mostly lignin) is used to produce hydrogen by gasification, it is ensured that more energy from the biomass will end up as liquid fuels rather than excess heat/electricity [11].

3 CH3COOH   +   6 H2     →     3 CH3CH2OH   +   3 H2O
(Hydrogenation of acetic acid)
C6H12O6 (from cellulose)   +   6 H2 (from lignin)     →     3 CH3CH2OH   +   3 H2O
(Overall reaction)

A more comprehensive description of the economics of each of the fuels is given on the pages alcohol fuel and ethanol fuel, more information about the economics of various systems can be found on the central page biofuel.

Stage of development

The system has been in development since 1991, moving from the laboratory scale (10 g/day) to the pilot scale (200 lb/day) in 2001. A small demonstration-scale plant (5 ton/day) is under construction as is expected to be operational early in 2008 and a 100 ton/day demonstration plant is expected in 2009.


See also

Energy Portal

References

  1. ^ Advanced Biomass Refinery - Third-Generation 2007 (video)
  2. ^ EPA Presentation on the process
  3. ^ Application
  4. ^ F.K. Agbogbo, M.T. Holtzapple (23 aug 2005). "Fixed-bed fermentation of rice straw and chicken manure using a mixed culture of marine mesophilic microorganisms.". Bioresource Technology 98 (8): 1586-1595. doi:10.1016/j.biortech.2006.06.021. Retrieved on 02 oct 2007.
  5. ^ Williamson, S.A. 2000. Conversion of carboxylate salts to carboxylic acids via reactive distillation. M.S. Thesis
  6. ^ Yeh, H. 2002. Pyrolytic decomposition of carboxylate salts. M.S. thesis
  7. ^ Ingram, D. 2002. Ketonization of acetic acid. B.S. student report.
  8. ^ Bradley, M.W., Harris, N., Turner, K. 1982. Process for Hydrogenolysis of Carboxylic Acid Esters WO 82/03854, Nov. 11
  9. ^ Preparation of esters by reaction of ammonium salts with alcohols.
  10. ^ Aldrett-Lee, S. 2000. Catalytic hydrogenation of liquid ketones with emphasis on gas-liquid mass transfer. Ph.D. dissertation
  11. ^ Eggeman, T., Verser, D., and Weber, E. (2005), An Indirect Route for Ethanol Production US Department of Energy
 
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