Bioconversion of biomass to mixed alcohol fuels

The bioconversion of biomass to mixed alcohol can be accomplished using the MixAlco process. Through bioconversion of biomass to a mixed fuel oil , more energy from the biomass will be used in converting biomass to ethanol by yeast fermentation.

The process involves a biological / chemical method for converting any biodegradable material (eg, urban waste, such as municipal solid waste , biodegradable waste , and sewage sludge , agricultural residues such as corn stover , bagasse sugarcane , cotton gin trash, manure ) into useful chemicals, Such as carboxylic acids (eg, acetic , propionic , butyric acid ), ketones (eg, acetone, methyl ethyl ketone , diethyl ketone ) and biofuelsSuch a mixture of primary alcohols (eg, ethanol, propanol , n- butanol ) and / or a mixture of secondary alcohols (eg, isopropanol , 2-butanol , 3-pentanol). Because of the many products that can be economically produced, this process is a true biorefinery . [1] [2] [3]

The process uses a mixed culture of naturally occurring microorganisms in such habitats as the rumen of cattle, termite guts, and marine and terrestrial swamps to anaerobically digest biomass into a mixture of carboxylic acids produced during the acidogenic and acetogenic stages of anaerobic digestion , with the inhibition of the methanogenic final stage. The most popular methods for producing ethanol and cellulosic ethanoluse enzymes in the form of simple sugars, followed by fermentation in ethanol. This process does not require the addition of these 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 pH must be controlled. This is done by the addition of a buffering agent (eg, ammonium bicarbonate , calcium carbonate ), thus yielding a mixture of carboxylate salts. Methanogenesis , being the natural end stage of anaerobic digestion, is inhibited by the presence of ammonium ions by the addition of an inhibitor (eg, iodoform ). The resulting fermentation broth contains the carboxylate salts that must be dewatered. This is achieved efficiently by vapor-compression evaporation. Further chemical refining of the dewatered fermentation may then take place depending on the final chemical or biofuel product desired.

The condensed distilled water of the vapor-compression evaporation system is recycled back to the fermentation. On the other hand, if raw sewage or other waste water with high BOD in need of treatment is used as the water for the fermentation, the condensed distilled water from the evaporation can be recycled back to the city or to the original source of the high -BOD waste water. Thus, this process can also serve as a water treatment facility, while producing valuable chemicals or biofuels.

Because the system uses a mixture of microorganisms, besides not needing any additional enzyme, the fermentation requires more or less sterile conditions, making this process more economical for the production of cellulosic ethanol. These savings in the front end of the process, where volumes are large, allow flexibility for further chemical transformations after dewatering, where volumes are small.

Carboxylic acids

For more details on this topic, see Carboxylic acid .

Carboxylic acid can be regenerated from the carboxylate salts using a process known as “acid springing”. This process makes use of a high-molecular-weight tertiary amine (eg, trioctylamine), which is switched with the cation (eg, ammonium or calcium). The resulting amine carboxylate can then be thermally decomposed into the amine itself, which is recycled, and the corresponding carboxylic acid . In this way, theoretically, no chemicals are consumed or wastes produced during this step. [5]


For more details on this topic, see Ketone .

There are two methods for making ketones. The first one is 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 of converting the vaporized carboxylic acids to a catalytic bed of zirconium oxide . [7]


For more details on this topic, see Alcohol .

Primary alcohols

The undigested residue of the fermentation may be used in gasification to make hydrogen (H 2 ). This H 2 can Then be used to hydrogenolyze the esters over a catalyst (eg, copper chromite), [8] qui are produced by esterifying Either the carboxylate ammonium salts (eg, acetate ammonium , propionate, butyrate) or the carboxylic acids (eg , acetic, propionic, butyric acid) with a high-molecular-weight alcohol (eg, hexanol , heptanol ). [9] From the hydrogenolysis, the final products are high-molecular-weight alcohol, which is recycled back toesterification , and the corresponding primary alcohols (eg, ethanol, propanol, butanol).

Secondary alcohols

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

Drop-in biofuels

The primary or secondary biofuels , which are compatible with current fossil fuel infrastructure such as biogasoline , green diesel and bio-jet fuel. Such is done by the subject of dehydration followed by oligomerization using zeolite catalysts in a similar manner to the methanex process, which used to produce gasoline from methanol in New Zealand. [11]

Acetic acid versus ethanol

Cellulosic ethanol manufacturing is an important component 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, the liquid fuel and the electricity markets will become more and more difficult. quote needed ]

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

6 H 12 O 6 → 2 CH 3 CH 2 OH + 2 CO 2
(Biological production of ethanol)
6 H 12 O 6 → 3 CH 3 COOH
(Biological production of acetic acid )

Because of this, we have mass basis, the yields will be higher than ethanol fermentation. If then, the undigested residue (mostly lignin) is used to produce hydrogen by gasification, it is ensured that the energy of the biomass will be higher than that of excess heat / electricity. [12]

3 CH 3 COOH + 6H 2 → 3 CH 3 CH 2 OH + 3H 2 O
(Hydrogenation of acetic acid)
6 H 12 O 6 (from cellulose ) + 6 H 2 (from lignin) → 3 CH 3 CH 2 OH + 3 H 2 O
(Overall reaction)

A more comprehensive description of the economics of the fuel oil and ethanol fuel , more information about the economics of various systems can be found on the biofuel central page .

Stage of development

The system has been developed since 1991. The size of the scale has been increased (200 lb / day) in 2001. A small demonstration-scale plant (5 ton / day) under operation and a 220 ton / day demonstration plant is expected in 2012.

See also

  • Anaerobic digestion
  • Bioreactor
  • Mechanical biological treatment


  1. Jump up^ Advanced Biomass Refinery – Third-Generation 2007 (video)Archived1 July 2010 at theWayback Machine.
  2. Jump up^ EPA Presentation on the process [ permanent dead link ]
  3. Jump up^ Application
  4. Jump up^ FK Agbogbo, MT Holtzapple (23 August 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 . PMID  16962320 .
  5. Jump up^ Williamson, SA 2000. Conversion of carboxylate salts to carboxylic acids via reactive distillation. MS Thesis
  6. Jump up^ Yeh, H. 2002. Pyrolytic decomposition of carboxylate salts. MS thesis
  7. Jump up^ Ingram, D. 2002. Ketonization of acetic acid. BS student report.
  8. Jump up^ Bradley, MW, Harris, N., Turner, K. 1982. Process for Hydrogenolysis of Carboxylic Acid Esters WO 82/03854, Nov. 2011
  9. Jump up^ Preparation of esters by reaction of ammonium salts with alcohols.
  10. Jump up^ Aldrett-Lee, S. 2000. Catalytic hydrogenation of liquid ketones with emphasis on gas-liquid mass transfer. PhD dissertation
  11. Jump up^ Production of gasoline from methanol.
  12. Jump up^ Eggeman, T., Verser, D., and Weber, E. (2005), An Indirect Road for Ethanol Production US Department of Energy