State of the art on bioethanol production

There are several ways ethanol can become one of the most important commodities in the future. Both pure ethanol and mix of it with gasoline can feed car engines, as it has been successfully proved on commercial scale by the Brazilian experience. One of its numerous derived products, the ETBE, can be used as octane enhancer and internal oxygen source to improve the combustion efficiency. Alternatively to the combustion, ethanol can be catalytically reformed to hydrogen that feeds fuel cells on board of an electrical car. Beside the primary role as energetic product, it is envisaged also an extensive use of ethanol as source of “green” products, e.g. the ethyl-lactate that can substitute some CFC as nonhalogenated and non-toxic solvent. A rapid increase of the ethanol demand would lead to a price boosting of the sugar and grains, the feedstocks from which it is currently produced, making more difficult the competition with the fossil fuels. For example, in Italy the substitution of gasoline with ethanol produced from sugar or grains should be viable only by devoting to this purpose at least 40.000 km2 of fertile land, corresponding to 26% of the agricultural land (13% of the whole national territory). These considerations point out that the bioethanol success is connected to the development of new processes able to produce it from alternative feedstocks largely available and cheap, such as residual biomasses and the organic fraction of RSU. The production of ethanol from cellulose has been investigate since the first decades of the past century, and reached the industrial scale during WWII, when ethanol was produced by acid hydrolysis of wood (the Bergius process). More recently, several pilot facilities were built after the 70’s oil crisis, but they were not scaled up because of the lack of exemption from taxation. Nowadays, significant advances in the process basics have renewed the interest towards the production of ethanol from lignocellulosics. The genetic engineering techniques have provided bacterial and yeast strains able to ferment not only glucose, but also the other sugars available in the feedstock. The improvement of the hydrolytic enzymes is one of the hot topics in this field and relevant progresses are expected in the next few years. At our best knowledge, several plants are under construction or scheduled in North America and Europe. Iogen Corp. has built, and nowadays testing, a $25-million plant near Ottawa. The plant is able to treat up to 40 tonnes per day of feedstock, and is the final step before the construction of fullscale, $200-million commercial plants based on the biological (enzymatic) hydrolysis. The acid hydrolysis will be employed in four plants that are scheduled in USA. The plants will use as feedstocks the lignocellulosic fraction of RSU (New York state, capacity 37 million litres of ethanol per year); bagasse (in Louisiana, 55 million litres per year); rice straw (in California, 55-90 millions litres per year); wood milling waste (Alaska, 22 millions litres per year). In Europe, Sweden is the most active Country with about ten research groups involved in the basic and applied research and a demonstration plant scheduled for the next year. The plant will be based on the acid process and will use wood waste as feedstock. 3 These enterprises appear more than anything as gauge of a process that is viable both from the technical and economic sides. However, it seems that a “standard” process has been not yet assessed. The literature survey shows that both biological (enzymatic) and chemical hydrolysis are under testing, as well different fermentation strategies an byproduct recovery. In such framework, where “everyone try to sell its own product” it is difficult to assess the differences between the processes, the real improvements and the lab to plant scalability. This ‘State of the Art’ has been written within the project ‘Production of clean hydrogen from fuel cells by reformation of bioethanol’ co-funded by the UE, whose goal is to provide a new way of using biomass as energy source for mobile applications, via ethanol. Although lignocellulosic biomasses are the specific subject of the project, it has also been considered the current ethanol production from sugar and starch. In the first section are reported the commercially available processes together with hints to the newest technologies. As regard the ethanol production from lignocellulosic biomass, it has been collected data on the biomass availability in Europe as energy crops, industrial crops, agricultural residues and domestic waste. It is provided a bibliographic study on the technologies and processes under development worldwide for the conversion of lignocellulosics into ethanol. Finally, a brief discussion on the economics highlights the near term viability of producing ethanol by this way.