The above described bioalcohols are the most commonly discussed for fuel purposes, but they are not the only bioalcohols that can be produced. The procedure described above for producing bio-ethylene glycol from corn residue can be modified to produce erythritol and xylitol.18 These are not common alcohols, but there are more common alcohols that can be produced from biomass. One prime example is propanediol. There are two main forms of propanediol: 1,2-propanediol, which is also called propylene glycol, and 1,3-propanediol. 1,2-propanediol can
be produced from hydrogenating of biologically derived lactate or lactic acid.19

I, 2-Propanediol can also be produced from hydrogenolysis of glycerol with Raney Nickel.20 Although it has not yet been used as a fuel, it is used as a less toxic antifreeze as well as an additive for many commercially available pharmaceutical and cosmetic products. 1,3-Propanediol can enzymatically be produced from bioglycerol.21 Both 1,2- and 1,3-propanediol can be produced by hydrolysis of biomass and then fermentation of the resulting sugars.21 This can also be used to produce butanediol.21 Although it has not been used directly as a fuel, it has been reacted further to produce an octane booster for gasoline. It is important to note that these rare bioalcohols are not currently being researched for fuels, but as we get more serious about renewable energy, we will start focusing on different fuels from different biomass sources for different applications, as needed.

Branched alcohols have also been considered as potential biofuels. Biobutanol researchers have found that they can produce branched alcohols as well. Synthetic biology has allowed for the production of isobutanol in metabolically engineered bacteria with glucose as a carbon source.22 This process diverts 2-ketoacid metabolic intermediates into aldehydes via 2-ketoacid decarboxylase and then to an alcohol via alcohol dehydrogenase. This novel method for producing branched chain alcohols has also been shown to be able to produce 2-methyl-1-butanol, 3-methyl-1-butanol, and 2-phenylethanol and has been licensed to Gevo (Pasadena, CA), which is focusing on commercialization of the technology.23