Biochemicals from Pyrolysis
Syngas from biomass gasification may contain hundreds of different biochemical substances. Some of these can be quite valuable and therefore simply using the syngas only for energy (example: burning in a Babington Burner) would be wasteful. Depending on the amount of syngas produced, it may be worthwhile to separate out the complex biochemicals from simpler components (e.g. methane, carbon monoxide, hydrogen). The spectrum of biochemicals varies with feedstock and conditions, such as gasifier temperature, duration, pressure etc.
Other components include:
- organic acids (formic acid, acetic acid, propionic acid, butyric acid, etc);
- phenol group;
- carbonyl group (formaldehyde, acetaldehyde, etc.);
- alcohol (ethanol, methanol, etc);
- neutral materials (levoglucosan, acetol, maltol, etc);
- base (substances like ammonia, methylamine, dimethylamine, etc.)
One major component from the dry distillation of wood is acetic acid, which has many applications and can even be used as an organic herbicide. Methanol is another useful and frequent component. Upgrading to biodiesel is possible but may not be practical or even necessary (methanol IC engines are already widely used).
After gasification, the syngas is first cooled down for distillation. As coolants, water or external air may be used. The liquid phase is then diluted with water, which leads to separation into aqueous and oily layer. So far so good, but then it gets tricky. Simple, low-tech, open-source methods of separation are needed.
Biological methods for catalysis of CO and H to ethanol are being developed at large scale (e.g. Coskata), which turn the various syngas components into ethanol using a bioreactor. This demonstrates a useful principle: distillation products are further processed using (micro-)biological means.
Possible Applications
- organic acids (e.g. formic acid, acetic acid)
- Sugars, flavors
- Pharmaceuticals
- Bioplastics
- the classic: wood preservative [1]
- Fibers, resins, dyes
- Adhesives
Possible Feedstocks
- various kinds of biomass (corn stalks, straw, wood, leaf litter, algae)
- manure incl. humanure
- animal waste, bones
Important considerations
- The big question is: can this be scaled DOWN to village-scale in a practical way ? If so, the products (incl. biochar from pyrolysis) may become important sources of revenue for the community. Being able to create a large number of different potential products with a single separation mechanism would be significant in terms of autonomy and resilience.
- which feedstocks produce which biochemicals in reasonable quantity ? under what pyrolysis conditions ?
- gasifier design / pyrolysis conditons etc.
- distillation and separation of products; one extraction method is using methanol as a solvent [2]
- further processing of products: when used for energy, purity may be less important then when used for pharmaceuticals (for example).
Links
- excellent, very detailed presentation: "Separation of chemicals from pyrolysis oil" by Wytze Meindersma, Eindhoven University of Technology
- Enerkem [3]