AALTO UNIVERSITY SCHOOL OF CHEMICAL TECHNOLOGY KE-40.4120 Introduction to biorefineries and biofuels Assignment 11: Comparison of biofuels vs. fossil fuels Aino Siirala 309141 Assignment submitted 8.12.2013
Table of contents 1 Ethanol vs. gasoline 1 1.1 Chemical structure 1 1.2 Limitations of ethanol 1 1.3 Production potential of ethanol 2 2 Biodiesel vs. diesel 2 2.1 Chemical structure 2 2.2 Limitations of biodiesel 3 2.3 Production potential of biodiesel 4 3 Biogas vs. natural gas 4 3.1 Chemical structure 4 3.2 Limitations of biogas 4 3.3 Production potential of biogas 4 References 5 Feedback 6
1 Ethanol vs. gasoline 1.1 Chemical structure Gasoline is a refined product of petroleum consisting of hydrocarbons, blending agents and additives. The composition of gasolines vary depending on the crude oil used, the refinery processes available, the overall balance of product demand, and the product specifications. Normally, gasoline hydrocarbons consist of 4-8% alkanes, 2-5% alkenes, 25-40% isoalkanes, 3-7% cycloalkanes, l-4% cycloalkenes and 20-50% total aromatics. Additives and blending agents are added to improve the performance and stability of gasoline. They include anti-knock agents, anti-oxidants, metal deactivators, lead scavengers, anti-rust agents, anti-icing agents, upper-cylinder lubricants, detergents, and dyes. [1] Ethanol has the chemical formula C2H5OH. The energy content of ethanol is only about two-thirds of gasoline. Thus, more ethanol is required to travel the same distance as on gasoline. However, high octane rating and other charasteristics of ethanol increase engine efficiency and performance. [2] Ethanol burns very cleanly and when fully combusted, it produces only CO2 and H2O. 1.2 Limitations of ethanol Fuel ethanol is mostly used as 5% or 10% blend with gasoline. E85 fuel has 85% of ethanol and is suitable for flexifuel vehicles. However, E85 produces 20 times more aldehydes than petrol, even more in cold weather. Aldehydes generate ozone, which is damaging for health. [3] Pure ethanol can not be used without modifying car engines as it effects certain rubber and plastic materials [2]. Also, problems with cold engine starting would occur with pure ethanol [4]. 1
It is discussed whether or not ethanol gasoline blend is damaging car engines and how much ethanol is safe to use. In the US, E15 fuel (15% ethanol) has arised a lot of discussion, while in Brazil, ethanol blends of 25% have been used for years with no harmful effects. [5] Ethanol is mostly produced from first generation biomass such as corn and sugar cane, which compares with food. 1.3 Production potential of ethanol Ethanol is easy and not too expensive to produce but it is normally used only as up to 10% blend with gasoline. If more ethanol were to be used as a vehicle fuel, flexifuel cars should become more common. The price of ethanol is normally close to the price of gasoline. The price of ethanol depends on where it is made and what feedstock is used for producing it. [3] As now ethanol is mostly produced from first generation feedstocks, using agricultural residues or municipal solid waste would be more sustainable. 2 Biodiesel vs. diesel 2.1 Chemical structure Biodiesel molecules are esters consisting of a long chain of carbon atoms, hydrogen atoms and an ester functional group: 2
Diesel molecules are very much the same, the ester functional group is just missing: [6] As biodiesel contains more oxygen than diesel, more biodiesel is required to travel the same distance than on diesel. As the chemical structure of biodiesel and diesel are very similar, biodiesel can be used in diesel engines up to 20% blends without modifications. Only some rubber tubing may need to be replaced as they can soften with biodiesel. [6] 2.2 Limitations of biodiesel Biodiesel is usually used as a 5% or 20% blend with diesel. When using biodiesel, problems with cold-starting can occur. Biodiesel gels in lower temperatures than diesel. By treating the fuel properly, no problems should occur even in cold temperatures. Using high quality biodiesel, blending it with kerosene and blending it with diesel that has been treated with cold weather additives are ways to prevent problems in the cold. [7] Although using biodiesel reduces GHG emissions, NOx emissions are higher. [3] Biodiesel is more expensive than fossil diesel. First generation biodiesel is around 30% more expensive and second generation biodiesel can be douple the price of fossil diesel. [3] 3
2.3 Production potential of biodiesel As the maximum rate of biodiesel in diesel blend is 20% the higher price of biodiesel does not effect on the diesel blend price very much. Blending biodiesel with fossile diesel will be feasible as long as government subsidies are given to decrease the price. The EU s 10% target for the share of renewable fuels in transportation sector gives biodiesel (as well as ethanol) a safe base. 3 Biogas vs. natural gas 3.1 Chemical structure The content of biogas varies depending on the feedstock. While biogas normally contains 50 to 80 % methane, 20% to 50% CO2 and traces of other gases like hydrogen, CO and nitrogen, natural gas is more than 70% methane and the rest is other hydrocarbons,such as propane and butane, and traces of CO2 and other contaminants. [8] The calorific value of crude biogas is around 5,0 5,5 kwh/m3n and of natural gas around 10 kwh/m3n. By processing biogas, the chemical content of natural gas can be nearly obtained. [9] 3.2 Limitations of biogas Raw biogas does not burn efficiently as it contains too much CO2. By refining biogas into biomethane, for example, a higher energy content can be obtained. However, it is not always economically feasible to refine biogas. [10] 3.3 Production potential of biogas Biogas has a good future foresight. Biogas is formed in landfill sites and as it contains methane, it is important to capture. Also, it is feasible for farms to use their 4
manure for biogas production and save in energy bills. When using refined biogas, biomethane, it can be easily injected to the already existing distribution grid. However, refining biogas is still costly. Biogas can also have an future as a transportation fuel, as it is already used as compressed or liquified. References 1 Anonym, ATSDR, http://www.atsdr.cdc.gov/toxprofiles/tp72-c3.pdf. 2 Anonym, Consumer Energy Center, http://www.consumerenergycenter.org/transportation/afvs/ethanol.html, 2.12.2013. 3 Notes from the lectures 4 Anonym, World of Molecyles, http://www.worldofmolecules.com/solvents/ethanol.htm, 2.12.2013. 5 La Jeunesse, W., Automakers warn new ethanol mandate could damage vehicles, Fox News, (2013). 6 Anonym, Goshen College, http://www.goshen.edu/chemistry/biodiesel/chemistryof/, 3.11.2013. 7 Anonym, National Biodiesel Board, http://www.biodiesel.org/docs/default- source/ffs-performace_usage/hot-tips-for-using-biodiesel-in-cold-weather- (general).pdf?sfvrsn=6 8 Anonym, Alternative Fuels Data Center, http://www.afdc.energy.gov/fuels/emerging_biogas.html, 28.9.2013 5
9 Anonym, Gasum, http://www.gasum.fi/tuotteet/biokaasu/sivut/koostumus.aspx, 1.10.2013 10 Charles M Bowen, Bright Hub, http://www.brighthub.com/environment/renewable-energy/articles/124371.aspx, 4.12.2013. Feedback Nice subject. Comparing is a good way to learn. 6