One problem I am trying to allude to in these blogs is that we have to avoid wastage of effort. We have only so much money to devote to developing new technology, and once something is completed, it should not be left in a form where the knowledge decays. As another example, there is a means of making ethanol through simple pyrolysis, and it is infuriating because while a considerable amount of money was invested in developing it, I have no idea how well it would work in practice. The problem is that it was developed towards the end of the last energy crisis, the scientists will have retired or will be dead, and there is insufficient information available. Results were written up in scientific papers, however the practical experience is lost, as are the answers to questions seemingly omitted from the papers. The omissions were not important at the scale of operations, but they could become critical on scale-up.
The concept is that when cellulose is pyrolysed, the first product formed is mainly levoglucosan, or 1,6-anhydroglucose. This can be readily prepared on the laboratory scale through simple vacuum pyrolysis, and the conditions for doing this were extensively studied by Fred Shafizadeh. The key problem is to get the levoglucosan out of the biomass before it can further react, so Shafizadeh heated small volumes of finely divided cellulose under vacuum. That works well, but it is not that easy to scale up.
Claims for the solution to that problem came from the old Soviet Union. Two separate schools heated biomass chips (presumably reasonably finely divided) in fast-moving steam at about 350 degrees C and about 6 bar. There are now two options. The steam can be cooled and depressurized, in which case the sugars condense out, then the steam can be repressurized and reheated. This is the most energy efficient. The second is the water can also be condensed to give a dilute solution of sugars. There can also be a process that lies in between: some of the steam is condensed to give a stronger solution of sugars. Such processes, provided they are properly engineered to recycle heat, should be reasonably energy efficient,
if they work according to plan. From what I can gather, this system was engineered up to do several kg/hr continuously, but details are hard to come by. Basically, if someone wanted to repeat this, they would have to start from scratch as far as engineering is concerned. There is also no real information available relating to lignin fragmentation products that presumably came over with the sugars. This could be important because phenolics should cause enzymes to cease functioning.
Is this a genuine possible answer to the problem of making biofuels? I have no idea. It passes the test of “looking reasonable”, it should be a net energy producer because the lignin alone should power the system, but there are two problem areas: can the system be engineered to run reliably, and are there too many impurities in the product to produce useful fuel? What is a real shame is that the original scientists and engineers would be able to answer those questions, at least at the level they operated on, but the information is lost. That sort of tragedy should not be repeated.
