and Bioenergy from Green-crop Refining
Biofuels could be produced without loss of food
production potential from the land, and with a substantial reduction in net
biomass feedstock cost, by harvesting lush green perennial crops like grass or
lucerne (alfalfa) and extracting large quantities of high quality protein as a
costs of the harvesting and processing would be offset by sale of the protein,
which is an established poultry feed, and more recently has been shown to be
suitable for aquaculture.
The straightforward mechanical process can extract
over two tonnes of protein per hectare per year from perennial green crops, and
that protein, as chicken or aquaculture feed, could be worth around US$2500 per
tonne of protein.
A basic form of the extraction process was
developed in the UK, France, New
Zealand and the US in the 1960s through to the
mid-1980s, as a means of creating value from the 30-40% of the typical crop
protein content that is regarded as surplus to livestock requirements 
attempts proved to be technically successful but economically marginal under
the conditions of the time. However, the surviving group of companies in France
has been operating on a large scale (~50,000 hectares) for over 30 years.
My research group piloted new techniques that can
extract up to 80% of the crude protein in the crop. Our high-extraction "biorefinery" process was
developed for the New Zealand Liquid Fuels Trust Board as part of a national
response to the 1980s fuels crisis. The process was extensively tested and
scale-up beyond 1000kg of crop per hour was prevented by the ending of the
there is renewed uncertainty of fuel supply, exacerbated by climate change,
nitrogen pollution, and decline of soils and fisheries. These factors are
changing economic drivers dramatically, and I would like to see the green-crop
refining process reconsidered.
The Green-crop refining process
After intensive protein extraction the fibre
and carbohydrate crop components would be converted by fermentation or
gasification to gaseous or liquid fuels. The process costs would be heavily
offset by the value of the protein by-product.
difference between the well-established moderate-extraction process and our
high-extraction process is in the raw-material grinding stage. In the former
the "pulping" is done with a simple (though unusual) hammer mill, and the
pressing of the protein-rich juice from the pulp is done using screw presses
similar to those used in the wine industry. In the intensive extraction process
there is further fine-milling in a disc mill of the type used for the "mechanical refining" of wood-chips. Recycling loops are used to keep the
properties of the pulp in a workable range. No water or other chemical inputs
need to be added.
lignocellulosic biofuel processes could be adapted to a protein-extracted
feedstock without adding much equipment. Most crops harvested for conversion to
biofuels will require fine grinding anyway to achieve high throughput. In
addition, protein in biofuel feedstocks will have to be dealt with somehow
anyway, or it will form a noxious nitrogenous waste stream that will be
expensive to treat. The operations required to recover the protein are few:
steam-heating of the plant juices, centrifugal separation of the protein
precipitate (a simple decanter centrifuge operation), and optional drying.
energy cost of intense grinding is moderate. In our pilot trials 70-80% protein
extraction was achieved using an energy input of 200kWh per tonne of crop
The residue after extraction of protein from grass or
alfalfa is a finely-divided fibre almost free of cell contents, low in moisture
content, and naturally low in lignin. If non-protein extracted components are
recycled back into the fibre fraction, the material available for biofuels
manufacture is roughly 65% fibre, 30% soluble sugars and minerals, and 5%
non-protein nitrogen compounds, with a yield of around 10 tonnes DM/ha under
common NZ conditions.
Carbon emissions from the soil should be low because
the crops will typically be perennial and need little or no cultivation.
protein concentrate has a ready market as poultry feed, where it provides yolk
and skin pigments as well as a protein rich in the economically-important amino
acids tryptophan, isoleucine and threonine.
The protein concentrate is rich in omega-3 fatty acids.
potential value as a human food of protein concentrates made from lucerne has
been extensively examined, and they have recently been
assessed as safe for human consumption by the European Food Safety Authority.
protein concentrate can be further refined to produce higher-value products,
such as a "white" undenatured protein with food-processing functionality,
omega-3 fatty acids, carotene, xanthophyll (the principal pigment for poultry),
vitamin E, and other nutraceuticals.
Variations on the refining process were developed in the 1980s, and are being
further developed in France
in an EU research programme
crude protein concentrate may have a particular value in aquaculture, which is
projected to treble in size in New Zealand
(to $1B/y) over the next 15 years,
and to increase worldwide .
High-value carnivorous fish prefer diets rich in fishmeal, but the
international commodity price of fishmeal has been rising: the February 2010
FAO fishmeal commodity price was US$1627/tonne (see chart below) .
amino acid profile of leaf protein is quite similar to that of fishmeal. Leaf protein concentrate is already
being offered commercially as an aquaculture feed, with claims of improved
growth and pigmentation benefits.
annual yield of protein concentrate from a hectare of regularly-harvested
high-productivity New Zealand pastoral land, using known processes, should be
about 3.6 tonnes fishmeal-equivalent,
which at current fishmeal prices could be worth more than US$6000 (NZ$8000) per
hectare per year.
with other processes
harvesting is quite seasonal, with peak availability in spring. There may be
opportunities to share much of the process plant and services infrastructure
with other biomass crop-waste sources that tend to have peak availability in
the autumn. There are other potential synergies with livestock abattoirs, where
the excellent ensiling properties and high digestibility of the extracted fibre
have potential to provide high-weight-gain lairage feed for the autumn peak
intake of animals.
Trends in protein-source prices
Chart data source: http://www.fao.org/es/esc/prices
Hamilton. New Zealand
Phone: +64 212268441
 Vaughan SR, McDonald RM,
Donnelly PE, Hendy NA, Mills RA (1984). The Biomass refinery as a route to
fuel alcohol from green crops. Proc. 6th International Symposium on
Fuel Alcohol Technology, Ottawa,
Vaughan SR, McDonald RM, A feasibility
study of the production of ethanol by hydrolysis and fermentation of protein
extracted lucerne fibre, MAFTech Liquid Fuels Trust Board contract 310/13/1,
October 1987 (850 pages). Filed at www.med.govt.nz/upload/30445/energy-bibliography.pdf as LF1134, though
incorrectly titled. (inaccessible 2011)
McDonald RM, Donnelly PE, Mills RA, Vaughan SR (1985). High value products from
Lucerne: a New Zealand perspective. Proc. 15th
International Grasslands Conference, Kyoto,
crop harvest of 16tDM/ha/y at average 25% crude protein content (Nx6.25),
extracting 80% of the crude protein, and recovering 75% of the extracted crude
protein as heat-precipitable true protein. This assumption yields 2.4 tonnes
of protein, or 4.8 tonnes of concentrate at 50% protein content. Equivalence
with fishmeal is adjusted for 65% protein content in fishmeal, with no
allowance for extra value due to potential pigmentation or growth enhancement.
Site updated 1 January 2012