During world war II, Germany made a certain amount of synthetic fuel by hydrogenating coal (the Bergius process). If one can hydrogenate coal, why not biomass? If we do not have an immediate answer, why not, and what are we prepared to do about it?
In fact there appears to be no good reason why we cannot because it has been done, at least to the workshop level. One process advocated during the previous energy crisis (Kaufman et al., Chemie Ing. Techn. 46, (1974) 14) involved taking finely divided biomass slurried in oil and mixed with nickel hydroxide and heating this to between 400 – 450 degrees C, with at least 5 MPa pressure for about twenty minutes, and in the presence of hydrogen, in which case it makes an oil that has immediate physical properties similar to diesel.
The advantage of this process is that all the biomass is useful, as any carbonaceous material can be hydrogenated and the products, essentially hydrocarbons, fit directly into the oil distribution system. The diesel and jet fuel cuts could probably be used directly, although some form of cracking would be required for petrol. Admittedly, a limited number of nitrogen heterocycles, where the nitrogen is at a position where aromatic rings are fused together are difficult to hydrogenate, but these should not be a problem for most biomass. An important point is the lignin, which contains a high proportion of the energy of the biomass, should hydrogenate smoothly. The yields of useful material obtained from a 50 kg/day unit were impressive, from memory in the low forty per cent range by weight, assuming oven-dried starting material. This included a small amount of pitch-like material made, which might be rehydrogenated, or alternatively used as a bitumen substitute.
So, why is this process almost never advocated? One reason might be that the production of hydrogen could be a problem. Another could be that it is unlikely that this type of process could be protected by patent, although the same is probably true for most oil refining technology. More likely reasons include this work has been essentially forgotten, and that high pressure chemistry is not fashionable. That raises the question, should the future be determined by our reluctance to work on what had been developed previously, our reluctance to visit the literature, or our fashion preferences?
