Team:Bielefeld-CeBiTec/Project/Isobutanol/Isobutanol

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Isobutanol

Product Synthesis

The CO2 fixation of module II ends with 3-Phosphogylcerat generated by the Calvin cycle. This 3-Phosphogylcerat is transformed to pyruvate by the glycolysis of the cell. The pyruvate is now used as the initial point for the product synthesis. Pyruvate is the starting point of the producing pathways of a variety of high value products like isobutanol, isoprene, putrescine or even antibiotics. We decided to introduce an isobutanol production pathway which starts with pyruvate and is called 2-keto-acid, or Ehrlich, pathway. (Peralta-Yahya et al., 2012)
For this we use and improve existing BioBricks from iGEM Team NCTU Formosa 2011/2012. We use the coding sequences of the genes of four out of five required proteins for the isobutanol production:

  • AlsS (α-acetolactate synthase)
  • IlvC (Ketol-acid reductoisomerase)
  • IlvD (Dihydroxyacid dehydratase)
  • KivD (α-ketoisovalerate decarboxylase)
Adh (Alcoholdehydrogenase), the fifth required protein, was not available as a BioBrick but because of E.coli's own Adh the pathway works. (Atsumi et al., 2008)


Figure 1: Schematic illustration of module III - the production of isobutanol
The product synthesis can be changed through the modularity of BioBricks so that variable high value products derived from pyruvate can be implemented in the future.

Isobutanol

Isobutanol is an amino-acid-based alcohol which is an organic substance.


Figure 2: Chemical structure of isobutanol.

It can be produced by the 2-keto-acid, or Ehrlich, pathway. In this pathway 2-ketoisovalerate is first decarboxylated into isobutyraldehyde by the ketoacid decarboxylase and then reduced to alcohols. Keto acids are immediate amino-acid precursors. By using this pathway amino-acid-based alcohols can be produced in E. Coli. These include n-butanol from norvaline, n-propanol from isoleucine and isobutanol from valine. Although the energy contents of isobutanol and n-butanol are similar, isobutanol is the closest to industrial use. Isobutanol has a better octane number because it is a branched-chain alcohol in comparison to straight-chain alcohols. This indicates that isobutanol could be a possible alternative to ethanol as a fuel additive. In contrast to ethanol, the traditional biofuel, isobutanol as a higher alcohol has a lower hygroscopicity. We use these facts in one of our application scenarios. (Atsumi et al., 2008; Peralta-Yahya et al., 2012)
In the following table 1 you can find some general information about isobutanol.

Table 1: General information about isobutanol (INCHEM, 2004)
CAS Number78-83-1
IUPAC Name2-methyl-propan-1-ol
Synonymsisobutyl alcohol
IBA, IBOH
fermentation butyl alcohol
1-hydroxymethylpropane
isobutanol
isopropylcarbinol
2-methylpropanol
2-methyl-1-propanol
2-methylpropan-1-ol
2-methylpropyl alcohol
Molecular FormulaC4H10O
Structural Formula(CH3)2-CH-CH2OH
Molecular Weight74.12 g/mol
Physical stateLiquid
Melting point-108°C
Boiling point108°C
Water solubility85.0 g/l at 25°C



Production

In 1998 the U.S. EPA Inventory Update Report (IUR) listed 16 manufacturing facilities in the United States. Altogether these facilities produced between 100 and 500 million pounds of isobutanol, which are 45.4 – 227.3 thousand metric tons. Manufacturing facilities of other regions or countries in 2002 including their manufacturing capacities are listed in the following table 2. (INCHEM, 2004)

Table 2: Information about the producing facilities in various regions and countries including their manufacturing capacities in 2002(INCHEM, 2004)
Region or countryNumber of producersManufacturing capacities
[metric tons]
Western Europe4160,000
Eastern Europe369,000 (including some n-butyl alcohol)
Russia348,000
Iran16,000
Japan343,000
China214,000
Indian.a.8,000 (including some n-butyl alcohol)
Indonesia110,000
Korea225,000
Brazil119,000

Use

Isobutanol has many applications. In the following table 3 you can find a list of uses and how many isobutanol is applied for the various uses in the United States

Table 3:Uses of isobutanol and their required amounts (INCHEM, 2004)
ApplicationAmount [metric tons]
lube oil additives (in which isobutyl alcohol is an intermediate to produce the lube oil additive ZDDP)19,000
conversion to isobutyl acetate10,000
direct solvent9,000
conversion to amino resins7,000
conversion to isobutylamines1,000
conversion to acrylate and methacrylate esters1,000
other uses1,000

As the table shows there are 3 big markets for isobutanol in the United States. The largest one is the production of zinc dialkyldithiophosphates (ZDDP). ZDDP is an additive for lube oils, greases and hydraulic fluids, which work as anti-wear and corrosion inhibitors.
The conversion of isobutanol to isobutyl acetate is the second largest market.
The use of isobutanol as a solvent is the third largest market. It is mainly used for surface coatings and adhesives. Hence it is used as a latent solvent in surface coatings or even as a processing solvent in the production of e.g. pesticides and pharmaceuticals.(INCHEM, 2004) These tables show the importance of isobutanol for industrial use and large amounts are needed all over the world.
Additional applications of isobutanol can be found here

References
  • Pamela P. Peralta-Yahya, Fuzhong Zhang, Stephen B. del Cardayre & Jay D. Keasling, 2012. Microbial engineering for the production of advanced biofuels. In: Nature 488, 320–328
  • INCHEM: SIDS Initial Assessment Report For SIAM 19, version: 10/2014
  • Atsumi S, Hanai T, Liao JC., 2008. Non-fermentative pathways for synthesis of branched-chain higher alcohols as biofuels. In: Nature 451, 86–89.

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