ABSTRACT
Trindade from Brazil, who presented in a keynote the Proalcool program of Brazil which had just started. Ethanol from lignocellulosic matter was identified as an option for research. And one kept also in mind direct liquefaction of biomass by thermochemical means. The preference to methanol given in these assessments was justified by the consideration that the productive yields of lignocellulosic matter is indeed higher than those achieved for sugar
and starch crops, the feedstocks for bioethanol. But seen from today in 2014, experts in those early days got it all wrong. “The devil is in the details.” It was ethanol which made it since then massively into the mainstream of the world’s transport fuel markets. Methanol and ethanol from lignocellulose, too, did not yet really make it out of the R&D field. One had to learn it the hard way: pilot plants were successfully built but the economics and logistical considerations stood in the way of commercial success. One should underline that the development of biomass energy sources and technologies in developing countries was also mentioned for the first time at the conference in Brighton as part of the European R&D strategy on renewable energies. From the nineties the CO2 impact of global warming increased the interest for European R&D on biomass. From this moment, the low CO2 emission rate of biomass exploitation was considered as one of the three-key factor for further European R&D on the subject: energy, environment, and social development. The objectives of the European biomass R&D program became more specifically targeted to: ● security of long-term energy supply in Europe; ● contribution to the development of industrial new markets; ● improvement of the environment by utilizing residues and wastes; ● decreasing the greenhouse gases emission rates; ● diversifying the agricultural production and the management on marginal lands; and ● providing opportunities for less developed regions in Europe. Decentralized electricity production and local cogeneration was also part of this strategy. 4.3 Fundamentals and Assessments
The maximum theoretical efficiency of plants for converting the sun’s radiation into living matter is generally assumed as 6.7%. This figure goes actually back to a study contract of the EU biomass R&D
program with Dr. Jim Coombs, an independent expert from Reading in England, formerly employed by Tate and Lyle Ltd. The results of this extensive study were published in 1983 by Reidel/Kluwer, the Netherlands, for the European Commission in a 200-page book [3]. The book, Plants as Solar Collectors, Optimizing Productivity for Energy, had next to Coombs David Hall and Philippe Chartier, who had supervised the study as coauthors. The study demonstrates that the thermodynamic efficiency of the photochemical conversion for monochromatic light involving 8 quanta has a theoretical maximum at 34%. This efficiency is further reduced, taking into account the photosynthetically available energy due to the particular solar radiation spectrum, light scattering and reflection by the leaf surface, photorespiration, and others. A final conversion efficiency of 6.7% is then calculated on the following assumptions: ● 50% loss, as only half of the solar spectrum, the one between 400 and 700 nm, is photosynthetically usable; ● 20% loss due to reflection and transmission by leafs; ● 72% loss representing quantum efficiency requirements for CO2 fixation in 680 nm light (assuming 8 quanta/CO2); ● 40% loss due to respiration. If 10 quanta were assumed for CO2 fixation the efficiency would come out at 5.5%. In conclusion the study provides a good estimate of the maximum conversion efficiency but it is not scientifically rigorous to the “last decimals after the comma.” The study goes also into details of the photosythetic particularities of C4 and C3 plants. In terms of energy crop cultivation the study recommends that crops be able to grow well on poorer soils and have a high capacity to take up nutrients. The plants should have good water use economy. They should have a high carbohydrate (cellulose) content, resulting in a higher efficiency of use of fixed carbon since less carbon will be lost in respiration than would be the case for plants which accumulate other metabolites such as proteins and oils. A low protein content will also reduce nitrogen requirements. Low rates of dark maintenance respiration and photorespiration would also be an advantage.
