3.3. OXYGENATED FUELS
3.3.4. Biodiesel
Biodiesel (Table 3.5) is a fuel produced from biological source[17] and is the generic name for fuels obtained by esterification of vegetable oil. The esterification can be done either by methanol or by ethanol. Biodiesel can be used in a diesel engine without modification and is a clean burning alternative fuel produced from domestic, renewable resources [3]. The fuel is a mixture of fatty acid alkyl esters made from vegetable oils, animal fats, or recycled greases[3].
Biodiesel is produced through a process in which organically derived oils are combined with alcohol (ethanol or methanol) in the pres-ence of a catalyst to form ethyl or methyl ester.
Biodiesel can be made from any vegetable oil, animal fats, waste vegetable oils, or microalgae oils. Soybeans and Canola (rapeseed) oils are the most common vegetable oils used for biodie-sel production[3].
Biodiesel is made through a chemical process (transesterification) e the process leaves behind two products: (1) alkyl esters (the chemical name for biodiesel) and (2) glycerin (used in soaps and other products)[3]:
The oil is extracted by the use of a press and then mixed in specific proportions with other agents that cause a chemical reaction. The results of this reaction are two products, biodie-sel and soap. After a final filtration, the biodiebiodie-sel is ready for use. After curing, the glycerin soap that is produced as a by-product can be used as is or can have scented oils added before use.
The transesterification reaction is affected by alcohol type, molar ratio of glycerides to alcohol, type and amount of catalyst, reaction temperature, reaction time, and free fatty acids and water content of vegetable oils or animal fats [3]. Generally, the reaction temperature is held near the boiling point of the alcohol, and the reactions take place at low temperatures (approximately 65C) and at modest pressures (0.2 MPa). Biodiesel is further purified by washing and evaporation to remove any remaining methanol.
Transesterification reactions can be catalyzed by alkalis or enzymes. Usually, industrial processes use sodium or potassium hydroxide or sodium or potassium methoxide as catalyst [3]. Enzyme-catalyzed procedures, using lipase as catalyst, do not produce side reactions, but the lipases are very expensive for industrial scale production and a three-step process was required to achieve a 95% conversion. The acid-catalyzed process is useful when a high amount of free acids are present in the vegetable oil, but the reaction time is very long (48e96 h), even at the boiling point of the alcohol, and
3. FUELS FOR FUEL CELLS
46
a high molar ratio of alcohol was needed (20:1 wt/wt to the oil).
Biodiesel is a liquid which varies in color between golden and dark brown depending on the feedstock from which it is produced. It is practically immiscible with water and has a high-boiling point and low vapor pressure (ASTM D6751). Typical methyl ester biodiesel has a flash point of approximately 150C (302F), making it rather non-flammable. Biodiesel has a density of approximately 0.88 g/cm3 less than that of water. Biodiesel uncontami-nated with starting material can be regarded as non-toxic.
Biodiesel has a viscosity similar to diesel produced from petroleum (petrodiesel). It can be used as an additive in formulations of diesel to increase the lubricity of pure ultra-low sulfur diesel (ULSD) fuel, which is advantageous because it has virtually no sulfur content [3].
Much of the countries that use biodiesel use the B factor to state the amount of biodiesel in any fuel mix. For example, fuel containing 20% bio-diesel is labeled B20 and pure biobio-diesel is B100.
Blends of 20% biodiesel with 80% petroleum diesel (B20) can generally be used in unmodified diesel engines, but when used in the pure form (B100), biodiesel (B100) may require engine modifications to optimal performance. Biodiesel has about 5e8% less energy density than petro-diesel but better lubricity and more complete combustion than petrodiesel[18].
Pure, non-blended biodiesel can be poured straight into the tank of any diesel vehicle. As with normal diesel, low-temperature biodiesel is sold during winter months to prevent viscosity problems. Some older diesel engines still have natural rubber parts which will be affected by biodiesel.
The extra lubrication provided by biodiesel fuel helps improve the longevity of your engine, as well as boosting engine performance, and also helps eliminate engine knocks and noise.
In addition, biodiesel fuel can be stored in any type of tank and has a much higher flash point
(approximately 300C) compared to petrodiesel approximately (150C).
Biodiesel production is a very modern and technological area for researchers due to the relevance that it is winning everyday because of the increase in the petroleum price and the environmental advantages [19]. The successful introduction and commercialization of biodiesel in many countries around the world has been accompanied by the development of standards to ensure high product quality and user confi-dence [20]. In general, biodiesel compares well to petroleum-based diesel[21,22].
References
[1] Guthrie VB. Petroleum products handbook. 1st ed.
New York, NY: McGraw-Hill; 1960.
[2] Speight JG. The chemistry and technology of petro-leum. 4th ed. Boca Raton, FL: CRC Press/Taylor &
Francis Group; 2007.
[3] Speight JG. Synthetic fuels handbook: properties, processes, and performance. New York, NY: McGraw-Hill; 2008.
[4] Mokhatab S, Poe WA, Speight JG. Handbook of natural gas transmission and processing. Amsterdam, Netherlands: Elsevier; 2006.
[5] Speight JG. Handbook of petroleum product analysis.
Hoboken, NJ: John Wiley & Sons Inc.; 2002.
[6] Mills GA, Ecklund EE. Alcohols as components of transportation fuels. Annu Rev Energy 1987;12:
47e80.
[7] Speight JG. Chemical process and design handbook.
New York, NY: McGraw-Hill; 2002.
[8] Cheng WH, Kung HH. Methanol production and use.
New York, NY: Marcel Dekker Inc.; 1994.
[9] Speight JG. The chemistry and technology of coal. 2nd ed. New York, NY: Marcel Dekker Inc.; 1994.
[10] Brinkman N, Halsall R, Jorgensen SW, Kirwan JE. The development of improved fuel specifications for methanol (M85) and ethanol (Ed85). SAE Technical Paper 940764; 1994.
[11] Speight JG. Lange’s handbook of chemistry. 16th ed.
New York, NY: McGraw-Hill; 2005.
[12] Lied DR. Handbook of chemistry and physics. 84th ed. Boca Raton, FL: CRC Press; 2003.
[13] Ethanol fact book. Clean Fuels Development Coalition 2007, Bethesda, MD, USA.
[14] Dale RT, Tyner WE. Economic and technical analysis of ethanol dry milling: Model description. Purdue
REFERENCES 47
University; 2006.Staff Paper # 06-04, Available from:
http://www.ecn.purdue.edu/wlorre/16/Midwest%
20Consortium/DM%20DescManual%2042006-1.pdf;
2010 [accessed 16.07.10].
[15] Corn Refiners Association Inc. The corn refining process (2002), Available from:http://www.corn.org/
theprocess.htm; 2010 [accessed 16.07.10].
[16] Corn Products International Inc., The corn wet milling process (2007), Available from:http://www.
cornproducts.com/overview/contactus/index.php;
2010 [accessed 16.07.10].
[17] Lee S, Speight JG, Loyola SK. Handbook of alternative fuel technologies. Boca Raton, FL: CRC-Taylor &
Francis Group; 2007.
[18] Kinas JA. Production of biodiesels from multiple feedstock’s and properties of biodiesels and
biodiesel/diesel blends, U.S. DOE Report NREL/
SR-510e31460; 2003.
[19] Machete JM, Miguel VU, Erase AF. Possible methods for biodiesel production. Renewable Sustain Energy Rev 2007;11(6):1300e11.
[20] Knothe G. Dependence of biodiesel fuel properties on the structure of fatty acid alkyl esters. Fuel Proc Tech 2005;86(10):1059e70.
[21] Loreto E, Goodwin Jr JG, Bruce DA, Suwannakarn K, Liu Y, Lopez DE. The catalysis of biodiesel synthesis. In: Spivey JJ, Dooley KM, editors. Catal-ysis. Cambridge, UK: The Royal Society of Chem-istry; 2006. p. 41e83.
[22] Pinto AC, Guarieiro LLN, Rezende MJC, Ribeiro NM, Torres EA, Lopes WA, et al. Biodiesel: an overview.
J Braz Chem Soc 2005;16(6B):1313e30.
3. FUELS FOR FUEL CELLS
48
C H A P T E R
4
Steam Reforming for Fuel Cells
J.R. Rostrup-Nielsen, J. Bøgild Hansen
Haldor Topsøe A/S, Lyngby, Denmark
O U T L I N E
4.1. Routes to Hydrogen 50
4.2. Steam Reforming of Natural Gas 50
4.2.1. Thermodynamics 50
4.2.2. Tubular Reformer 50 4.2.3. Nickel-Based Catalysts 52
4.2.3.1. Support 52
4.2.3.2. Promoters/Alloys 53 4.2.3.3. Catalyst Particles 53 4.2.3.4. Activation 53 4.2.3.5. Nickel Dispersion 54 4.2.3.6. Sintering 54 4.2.4. Non-Nickel Catalysts 54 4.2.5. Non-Metal Catalysts 55
4.2.5.1. Ceria 55
4.2.5.2. Carbides 55
4.2.5.3. Non-Catalytic Reforming 55 4.2.6. Mechanism and Kinetics 55 4.2.7. Sulfur Poisoning 57 4.2.8. Carbon Formation 57 4.3. Steam Reforming of Other Feedstocks 59 4.3.1. Liquid Hydrocarbons 59 4.3.1.1 Carbon Formation 59
4.3.1.2. Effect of Promoters
on Carbon Formation 60 4.3.1.3. Temperature Effects 60
4.3.2. Alcohols 61
4.3.2.1. Methanol 61
4.3.2.2. Ethanol 62
4.3.3. Other Oxygenates 62
4.4. Hydrogen Production 62
4.4.1. Industrial Hydrogen Manufacture by Steam Reforming 62
4.4.2. Heat Recovery 63
4.4.3. Steam Reforming for Fuel Cell
Plants 63
4.4.3.1. Process Configuration for Fuel Cell Applications:
SOFC 64
4.4.3.2. Process Configuration for Fuel Cell Applications:
PEMFC 64
4.4.3.3. Comparison of SOFC and PEMFC processes 66
4.5. Conclusions 68
49
Fuel Cells DOI:10.1016/B978-0-444-53563-4.10004-5 Copyright Ó 2011 Elsevier B.V. All rights reserved.