Is science sometimes in danger of getting tunnel vision? Recently published ebook author, Ian Miller, looks at other possible theories arising from data that we think we understand. Can looking problems in a different light give scientists a different perspective?

More On Sugars For Biofuel

So far, most of my blogs on biofuels have focused on making sugars with ethanol as the obvious end-point, although most of the arguments would apply equally to any fermentation, such as making butanol or acetone. I have done this not necessarily because I think this is the best option, but rather I have been trying to cover territory in an orderly fashion. There is one further way of making sugars: heat the polysaccharides sufficiently in the presence of a nucleophile. "Sufficient" usually means generating significant pressure, since the appropriate temperatures are usually higher than 250 degrees C. If we use water, we get sugars directly, however we may also get degradation products. If we use something like an alcohol, potentially in the presence of catalysts, glycosides are formed, which are usually more stable but can be hydrolyzed subsequently, and if ethanol is used, the solution can be fermented directly. This process is relatively undefined; once upon a time, mercaptans were used this way to analyze polysaccharides, but there are now “better” methods. To the best of my knowledge, this possible route is invariably absent from proposals. This suggests that either the route is faulty, or there is a general lack of imagination. The question is, which?
 
One of my early efforts in the area of biofuel was to use phenol, and good yields of the phenolic glycosides were obtained. Further, phenol is probably a better leaving group, so hydrolysis of the glycosides is straightforward. Unfortunately, as the perceptive may notice, there is a major drawback. No, it is not that phenol would kill the yeasts that are needed for fermentation; that is a difficulty, but it can be overcome. The real problem is that that if the sugars start to thermally decompose, any formaldehyde so formed couples phenols to form xanthene. This is not a particularly useful material, and it consumes two molecules of phenol for each molecule of formaldehyde. We might note that the lignin is a good source of phenols, and for hardwoods, there would be no xanthene difficulty, however, in this route for making biofuels the phenol glycosides decompose thermally before lignin degradation gets underway at a sufficient rate. As with so many ideas, as presented the use of phenols is a failure.
 
However, in accord with the theme of this blog, there is more than one way to look at a problem. Should more efforts be made to employ ethanol or methanol? Is there an option that is being overlooked? Is the whole concept a bad idea and should be put to a merciful conclusion? What do the readers think? Theory involves a lot more than simply computing; applied theory should in principle be able to make a lot of headway on practical problems such as this so the exercise could be useful.
 
Posted by Ian Miller on Jul 20, 2012 3:32 AM Europe/London

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