published on 10 May 2017 in energy
What are they?
The term “biofuels” means liquid or gaseous fuel obtained from biomass, which can be used to power internal combustion engines. They are traditionally used for automotive use, replacing (or mixed with) fossil fuels, but their use is rapidly expanding and the scope of application of biofuels is shifting towards generating electricity and heat, in particular towards cogeneration .
The will and the need to find renewable fuels has increased significantly in recent decades due to the now recognisable environmental and climate impacts generated by fossil fuels and to ensure security of supply. The advantages deriving from the use of biofuels compared to fossil fuels are significant: sustainability, reduction of greenhouse gas emissions, opportunities for economic development at the regional level and an increase in employment and, last but not least, greater security of supply. Finally, let us not forget that the CO2, SO2 and Nox derivative emissions from the combustion of fossil resources are the main cause of air pollution. As for the general reduction in the reserves of fossil fuels expected in the more or less near future, suggested in 1956 by the American geophysicist Marion King Hubbert and recently revived by various scholars, it must be said that the approach of the production peak and subsequent descent are not as imminent as some scholars claim .
In the oil sector dedicated to the automotive segment, the economic and technological efforts of recent years have significantly improved the quality of petrol and diesel and were guided by two key objectives: reduction of consumption and continuous decrease of pollutant emissions . With these aims, technological development in recent decades has been influenced by the gradual introduction of organic components in liquid fuels. In Europe, 1997 can be considered as the start date of this process, following the M/245 mandate of the European Commission, which entrusted CEN with the task of drawing up the standard for fatty acid methyl esters (biodiesel) for automotive use. In other words, the mandate requests the development of a standard that defines the quality specifications and the minimum characteristics necessary for the proper functioning of engines, to reduce pollutant emissions and for distribution safety. The Commission’s objective was twofold: reduce the impact of emissions from combustion on anthropogenic climate change and diversify energy sources.
In the current definition, biofuels are divided into two categories depending on the raw materials and the state of progress of production technologies. Biodiesel, pure vegetable oils, bioethanol produced from grain and from sugary raw materials, bio-ETBE (ethyl-tert-butyl-ether, produced by hydrolysis of bioethanol) and biogas are defined as first generation biofuels . Their production and applications have already started.
Second generation biofuels are represented by bioethanol produced from lignocellulose raw materials, bio-DME, bio-MTBE, biobutanol and synthetic diesel obtained via the Fischer-Torpsch reaction. Other raw materials used for the production of second-generation biofuels are algae, industrial waste or grasses that can be grown on residual land such as miscanthus. In some cases, these are still experimental techniques and not yet in full-scale production, in others the products are already on sale.
Not all biofuels are the same. Their evolution
Why have we switched to the so called second generation biofuels? The choice was dictated by the realisation, reached over time, than using edible raw materials for biofuel production was anything but sustainable. Although first generation biofuel has undeniable environmental benefits, especially in terms of net carbon footprint, on the other it has given way over time to intensive cultivation of sugar cane, rape-seed oil or corn, reserved exclusively for the fuel industry, subtracting land from growing food crops. In fact, food security aside, first generation biofuels are closely related to land grabbing, deforestation and the harmful effects of the change of use of the soil (ILUC – indirect land use change factor). In 2012 alone, the European Union dedicated 3% of its arable land to the production of raw materials for biofuels. In summary, the advantages are: biodegradability, reduction of greenhouse gas emissions, reduction of ozone levels in the lower layers of the atmosphere, reduction of VOC (volatile organic compound) emissions. But if alongside these advantages we consider the environmental disadvantages from deforestation and intensive agriculture, associated with the use of herbicides, fertilizers and pesticides and we add the water for crop irrigation and transport, the final outcome is not so viable.
Other factors to be taken into consideration for assessing the environmental impact of biofuels:
• emissions for the production and transportation of the biomass;
• irrigation and fertilizer use;
• emissions for the production and transportation of the biofuel.
These activities require energy, thus producing CO2. If we consider the entire production cycle, from biomass to the fuel pump, not all biofuels are environmentally SUSTAINABLE!
At our latitudes, vegetable oils for the production of first generation biofuels are derived from oily crops, consisting of rape, sunflower and, to a lesser extent, soy. The Italian surface area used for the production of oily crops shows significant numbers, shown in the table below (data in hectares, source: ISTAT).
In 2009 there were approximately 125,000 hectares of land for the cultivation of sunflower and over 20,000 hectares for rape, used for the production of pure vegetable oil and biodiesel. In addition to vegetable oils from dedicated crops, oils deriving from the preparation and preservation of food, from agro-food industries, from catering, but also from household use can be used. The same goes for animal fat residue from meat processing. These “residual” materials are however of inferior quality, mainly due to their high acidity. They therefore require preliminary “regeneration” before conversion into to biodiesel, mixed with vegetable oils obtained from oily crops , rendering the entire process economically less advantageous. Therefore, the focus of the industry has shifted to the production of second generation biofuels, which do not require the exclusive use of fertile land but rather residual land, and the use of agricultural waste (lignocellulose raw materials). In this way, the biomass is already available!
Bioethanol: is it possible to replace fossil fuels?
The use of ethanol as fuel for internal combustion engines is certainly not new, considering that the first engines designed (we are in the early 20th century) were suitable to be powered by pure alcohol (methanol or ethanol). The Dodge 1800 was the first prototype of a pure ethanol-powered engine.
The use of petrol as a fuel, in fact, became widespread only in the period prior to the first world war. Ethanol has interesting characteristics to be used as fuel in petrol-engine cars: it has, for example, a high octane rating (it is in fact also used to increase the octane rating of petrols) and thus allows the compression ratio to be increased, improving engine efficiency. Already in the early 1970s, in the wake of the energy crisis, the Brazilian Government began to promote the National Alcohol Program, with plans to reduce oil imports and replace fossil fuel with its own and easy-to-be-found source. The main purpose was the partial replacement of diesel of oil origin with ethanol obtained from biomass, in particular from sugar cane. In 1979, the Brazilian Government signed an agreement with the automobile industry and prototypes were developed by several manufacturers (including Fiat) able to use 100% ethanol (Fig. 4). In 1984, 94% of the cars sold in Brazil were alcohol powered. In later years, after the oil crisis, the trend triggered in Brazil gradually declined, but with the increases in petrol prices in recent years, ethanol cars are again in vogue: in 2010, there were as many as 3 million ethanol-powered cars on the roads. The use of ethanol instead of petrol is, however, not without its problems. First of all, ethanol is very soluble in water and very hygroscopic, and when it absorbs a lot, when mixed with petrol, a phase separation can take place which can cause engine damage. It is corrosive and lacking in lubricant properties, so it is necessary to use new materials compared to those used for petroleum-based fuels in storage and distribution systems, as well as in certain mechanical components of the car, such as filters. It can,on the other hand, be used mixed with petrol up to 20-22% without making any changes to the engine of the car. For the reasons mentioned above, only so-called Flexible Fuel Vehicles (FFVs), developed since 2005 by car manufacturers, including FIAT, can be powered solely by ethanol.
How is second generation bioethanol produced?
Second generation bioethanol is obtained from lignocellulosic biomass by enzymatic hydrolysis reaction and is the subject of research since the 1970s. The cellulose and hemicellulose are polysaccharides, which are the raw materials from which, by enzymatic hydrolysis, we obtain simple sugars, to be transformed into ethanol by fermentation. The enzymes selectively “cut” the polysaccharides (cellulose, hemicellulose or starch) allowing simpler glucose molecules to be obtained (Fig. 3).
Subsequently, the glucose is converted into ethanol by a fermentation process and Saccharomycescerevisiae(yeast) is the microrganism generally most used.
The production of ethanol from cellulose, which as mentioned is not new, is considered particularly interesting and is the subject of investment by a number of major industrial players. Its use is particularly advantageous because the lignocellulosic biomass, coming for example from agricultural waste, is an abundant raw material and has no competition with food crop production. The availability of agricultural waste in a number of European countries is shown in Figures 3.
At its meeting of 28 April 2015, the European Parliament adopted the directive on second generation biofuels, pushing to reduce the production of those derived from agricultural crops and starting the trend toward production of advanced biofuels , derived from waste, residues and new sources such as algae. The use of the latter, as demonstrated by recent studies carried out by researchers at the Rice University (Houston, Texas, USA) , would simultaneously solve two environmental problems: the treatment of civil waste water and biofuel production. In fact, the algae used in the experiment were grown using the civil wastewater of a treatment plant in Houston, literally “feeding them” with the phosphorus and nitrates they contain and thus obtaining a purifying effect of this water . In practice, making the algae grow in reactors containing wastewater, producers need no longer resort to fertilizers and more sustainable biofuels can be obtained, together with the treatment of the wastewater used. But this is only one of the possible “solutions” investigated. Technological and biotechnological research in the field of sustainable production of second generation biofuels has in fact become a very vibrant frontier in recent decades and new scenarios emerge in front of the world audience. It is in fact essential that the production of biofuels takes place in a sustainable manner if we really want to totally or partially eliminate the harmful effects associated with the use of fossil fuels.
By Tiziana Perri
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