Biodiesel CO2 emissions: A comparison with the main fuels in the Brazilian market
Introduction
In the last three decades, the world has been confronted with energy crises due to the decrease of fossil resources and the increase of environment constraints and prices of oil. This situation brought as consequence the search for alternative and renewable fuels, which need to be not only sustainable, but also environment friendly and techno-economically competitive. The biofuels like ethanol, vegetable oil, biomass, biogas, synthetics fuel, and biodiesel, among others, are becoming of high interest to the developed countries. Some of these fuels can be burned in direct form; however, others need some kind of modification to replace the conventional diesel fuel: gasification or digestion when dealing with biomass, and transesterification when dealing with biodiesel.
The growth of mobility demand in the world was followed by the growth of transportation by road and, consequently, by the increase of greenhouse gas emissions produced from fossil fuel combustion. During the last ten years, it was recognized that greenhouse gases, CO2 in particular, represent a high threat for future generations, causing global warming and climatic changes. The energy consumption of the transportation sector represented, in 1998, 28% of the total CO2. According to the European Commission [1], if nothing is made to change the road transportation tendency, the CO2 emissions in this segment will increase approximately 50% until 2010, in comparison to 1990, reaching 1113 million tons of CO2 per year. Once again, road transportation is the main responsible for this situation, since it represents 84% of the CO2 emissions in comparison with air transportation, which is responsible for 13% [3], [4].
This work consists of the first study about biodiesel engine benefits in Brazil regarding CO2 emissions, in comparison to other Brazilian fuels. Biodiesel is one of the main alternative fuels to replace the conventional diesel fuel. A comparison in respect to CO2 emissions is made with the main current Brazilian fuels in the market. The biodiesel emissions were considered for the fuel in pure form and blended in different proportions with conventional diesel oil. The results show a reduction in the CO2 emissions levels to the atmosphere in the case of replacing the conventional fuel by biodiesel. To conduct the study, data of the National Association Manufacturers of Automotive Vehicles [5] and the National Department of Transit [6], collected for the last five years, were used in the case of the Brazilian road transportation system.
Section snippets
Biodiesel fuel production
Chemical biodiesel is composed of monoalkyl esters of long chain fatty acids derived from renewable feed stock, like animal fats and vegetal oils [8], [9]. According to Larosa [2], a biodiesel industrial plant that utilizes methanol in the transesterification process needs to carry out the following steps: reactants preparation, and transesterification, separation and purification of the obtained phases. Fig. 1 shows a diagram of such production scheme.
The reactants are prepared in the first
Methodology
The emission factors for CO2 were calculated for the fuels commonly used in the Brazilian market, including the biodiesel (pure and mixed with conventional diesel fuel). Following, the average amount of CO2 emitted by an automobile per year was computed for the fuels. Using data reported by [5] and [6], the CO2 emissions by the diesel and the gasoline vehicle fleet in Brazil and the reduction of such emissions in the case of the use of biodiesel (pure or a mixture) were calculated. Projections
CO2 emissions for the last five years in the Brazilian diesel fleets
The national diesel fleets for the last five years are those given in Table 4 [5]. Considering that the Brazilian diesel fleets run 60,000 km/year (Brazilian average for diesel vehicles, including large and small trucks, buses and microbuses; this value was explained in the previous section) using diesel at 5 km/l (5000 km/m3) mean consumption for the last five years (Dec/2002–Jan/2008), the CO2 emissions would reach 87.95 Mton CO2 for the five years. On the other hand, if the diesel fuel were
Conclusions
It was shown that the fuel that less releases CO2 to the atmosphere is ethyl alcohol; on the contrary, the fuel that releases highest CO2 emission to the atmosphere is diesel fuel. Due to the oxygenated nature of biodiesel, where more oxygen is available for burning, this fuel produces decreased rates of unburned hydrocarbon and CO emissions in the exhaust. The main advantage is that CO2 emissions, in the case of use of biodiesel, can be regarded as carbon credit as it is a biofuel, produced by
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