Fuel and chemical co-production from tree crops

A concept for the sustainable production of fuels and chemicals from fermentable and oleaginous substrates produced on an annual basis by the reproductive organs (pods, fruits, nuts, berries, etc.) of ‘tree crops’ is presented. The advantages of tree-crop systems include suitability for use on marginal land, potential productivity equivalent to row crops, minimal maintenance and energy input requirements, environmental compatibility, and the possibility of coproduct production. Disadvantages are possible high establishment costs, a long growth period until production commences, and difficulties in harvesting or storage; however, these provide opportunities for potential research impact. Honeylocust, mesquite, persimmon, osage orange, and Chinese tallow are examined as potential US tree-crop species. Other species, including breadfruit and African oil palm, are suggested as tree-crop candidates for the tropical developing world. Fermentation or extraction of treecrop organs and the economics of tree-crop systems are also discussed. Currently the greatest area of uncertainty lies in the actual pod or fruit yields that can be expected from large tree farms under real life conditions. However, ballpark ethanol yield estimates of 650 to 3470 litres ha−1 (69–371 gallons acre−1) and oil yields up to 3900 kg ha−1 (4227 litres ha−1) justify further consideration of treecrop system.