The current research article’s aim was to provide a comprehensive understanding of biofuels as possible renewable energy sources. Furthermore, the benefits and drawbacks of biofuels were balanced against conventional fossil fuels. Scientific interest in the use of biofuels grew after it was discovered that global fossil fuel stocks were declining, as predicted by the Hubbert peak theory depicted in Figure. Aside from the loss of fossil fuel deposits, it was also discovered that the burning of fossil fuels was to blame for global warming and environmental destruction. The emerging oil crisis has posed a major threat to the long-term viability of modern economies and societies. The US and Brazil were the leading producers of biodiesel and bioethanol globally (Carriquiry, Du, and Timilsina 4222). In 2011, biofuel production in the US and Brazil represented 45 and 27 percent of the global biofuel production, respectively (Coyle and Simmons 153). Most of the biofuels in use today were sourced from plants such as sugarcane, wheat, and corn via the thermochemical transformation through gasification, pyrolysis, and liquefaction. Despite the higher production capacity of biofuels in the US (2 billion gallons per year), the share of biofuels as an energy source for transport purposes was only 5 percent as illustrated in Figure 2 (US Energy Information Administration).
Figure 1 Hubbert peak theory illustrating the decline in crude oil production (Al-Husseini 182)
Figure 2 Share of biofuels in US transport (US Energy Information Administration)
Biofuels have the potential to power automobiles given that global fossil fuel reserves were declining. However, the use of biofuels posed food security and environmental risks.
Benefits of Biofuels
Some of the key benefits of biofuels included the potential to replace fossil fuel based energy sources. Besides, the use of biofuels would reduce the carbon footprint (and the social economic factors associated with CO2 and particulate matter). Given that, biofuels were affordable and locally available (Coyle and Simmons 156); they had the ability to increase the energy independence of countries that were dependent on crude oil imports. The use of biofuels would also contribute to the stabilization of foreign exchange reserves due to low energy imports.
The Demerits of Biofuels
Despite the fact that biofuels represented a renewable and clean source of energy, the production of first-generation biofuels was correlated with higher food insecurity. For instance, the conversion of corn and sugarcane into bioethanol feedstocks exerted more pressure on the global food reserves resulting in the inflation of basic food prices (Coyle and Simmons 154). Notably, biofuel production was not the only cause of higher food prices. Nonetheless, it represented a critical threat to the sustainability of food sources. Another key disadvantage associated with bioethanol was that ethanol-fossil fuel blends were dependent on global crude oil production and prices.
The largescale production of biofuel feedstocks such as corn and sugarcane necessitated the use of machines, which were powered by fossil fuels. Besides, cultivation of the feedstocks for biofuel production resulted in significant changes in land use due to deforestation and destruction of local habitats and by extension the entire ecosystem. Notably, the destruction of the ecosystem led to the absence of vegetation that was integral to the sequestration of CO2 from the environment; thus contributing to higher emissions. In spite of the fact that the natural vegetation was replaced with biomass vegetation, it was noted that natural habitats had a higher CO2 sequestration ability compared to biofuel plants. Besides, planting new crops would upset the natural soil equilibria, resulting in the displacement of terrestrial carbon and compost materials stored in the soil.
Therefore, replacing natural habitats with commercial plants increased the carbon debt years. A case in point, it was estimated that it would take over four centuries for the palm oil vegetation in Asia to recompense the carbon debt. (Fargione et al. 1237). The palm oil plantations were established to serve as sources of biomass feedstocks; the changes in land use largely contributed to the destruction of the environment. The inability of biofuel plants to sequester CO2 as efficiently as natural vegetation resulted in up to 420 times more emission compared to the levels of emissions attributed to the combustion of fossil fuel energy sources.
Despite the adverse effects associated with land use changes, leading producers of biofuel around the world were accelerating the conversion of virgin farmlands into biofuel plantations. For instance, due to the growing demand for biofuels, Brazil had converted its Amazon forests into soybean and sugarcane farmlands. Similar trends were observed in Indonesia where close to 2.8 million ha of tropical rainforests had been converted into palm oil plantations. Besides, growing demand for biofuel production in the US was posing a threat to the US Conservation Reserve (Fargione et al. 1236). Therefore, from a broader perspective the use of biofuels, indirectly contributed to environmental emission. The prevailing perception that first generation biofuels would contribute to the decrease in CO2 emission was based on misinformation.
Production of Biofuels
The advances in technology had resulted in the development of novel technologies for the production of biofuels from biomass feedstocks. The technology adopted in the production of biofuels was largely dependent on the type of biofuel – first generation or second-generation. The former biofuels were primarily produced from basic feedstocks such as sugarcane, oilseeds, and corn while second-generation feedstocks were produced from advanced materials such as algae and cellulose. Currently, wheat straw, corn stover, and forest residues were considered as some of the potential sources of cellulose for bioethanol production (Coyle and Simmons 155).
It is of note that hybrid and thermochemical processes had the capacity to yield bio-gasoline, jet fuel, and green diesel. Sugarcane to ethanol and corn to ethanol had favorable energy ratios of 9:1 and 1:6. However, sugarcane had a higher energy ratio compared to corn; thus explaining why sugarcane was highly preferred in the production of biofuels (Coyle and Simmons 156).
The production of ethanol from corn involved multiple phases namely milling (wet or dry milling), liquefaction of the corn powder, saccharification, fermentation, distillation, and concentration of the ethanol. On one hand, wet milling facilitated the breakdown of corn biomass into proteins, corn germ, fiber, and starch through pretreatment with H2SO4. Corn syrup was one of the main products derived from the milling process; other products included gluten and corn oil. On the other hand, distiller’s grains, CO2, and ethanol were the main products derived from the dry milling process (The Pennsylvania State University).
Sustainable Biofuel Feedstocks
Algae were considered as one of the sustainable feedstocks because it did not pose any threat to food security and agricultural farmlands. Besides, algae could be cultivated in wastelands and saline water. The development of recent technologies had helped to reduce the cost of production of bioethanol from microalgae. Notably, microalgae had a higher theoretical yield (100g/m2/d) compared to sugarcane and corn. Jatropha was also explored as an alternative to algae; however, inconsistent ethanol yields had impeded its commercial application (Carriquiry, Du, and Timilsina 4224).
Material Properties of Biofuels
A comparative analysis of biofuels and fossil fuels by (Borhanipour et al. 2) established that increasing the ethanol fraction in biodiesel resulted in a lower calorific value, which was detrimental to the fuel’s performance given that the calorific value determined the energy density of the blend. In particular, the calorific value declined from 45.8 MJ/kg to 39.9 MJ/kg, the decline in the calorific value was attributed to higher carbon ratios and oxygen content in the biofuels. Additionally, it was noted that the acidity of biofuel blends was elevated at higher ethanol volume fractions. Higher acidity was detrimental to the structural integrity of the engine components such as the fuel pump. The viscosity of diesel and petrol decreased with an increasing ratio of ethanol. A higher viscosity suppressed fuel atomization and volatilization, it also contributed to the clogging of the injectors due to soot deposition (Borhanipour et al. 6).
The adoption of ethanol-petrol/diesel blends in the US and other countries was still low compared to the growing use fossil fuels in automobiles. The low adoption of biofuels and biofuel blends was partly attributed to the unsuitable material properties of fossil fuel-ethanol blends. Besides, it was noted that higher production of first-generation biofuels contributed to global warming through changes in land use and destruction of natural habitats. Nonetheless, second-generation biofuels had a lower carbon debt. Therefore, based on the current state of the biofuel technology and economy, it was deduced that biofuels were less favorable compared to traditional fossil fuels. The view was informed by environmental and food security consideration and the need to maintain the structural integrity of automobile engines.
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