Hydrogen Production & Storage for Cars: Methane Decomposition & On-Board Methods, Assignments of Green and Environmental Chemistry

Download Hydrogen Production & Storage for Cars: Methane Decomposition & On-Board Methods and more Assignments Green and Environmental Chemistry in PDF only on Docsity! HOMEWORK 6 (DUE 11/13/08) 1. Prob. 15.2 (10%) From Problem 15.1, SO to be removed is: 0.9(533.1) = 479.8 Ibmole/hr Reactions: CaO+H 0 Ca(OH), SO, +H,0 = H,S03 SO; + Ca(OH), > CaSO; -2H,0 overall: CaO + SO, + 2H,0 — CaSO, -2H,O0 Theoretical CaO feed: (479.8 Ib-mole/hr $0} )(1 Ib- mole CaO/Ib- mole SO») (56 Ib/Ib- mole CaO) = 26,870 Ib/hr CaO Actual Lime feed: (26,870 Ibs/hr)(1.03) = 28,240 Ibs/hr (0.98) 2. inerts = (28,240 Ibs/hr)(0.02) = $65 Ibs/hr excess lime =28,240(0.98)— 26,870 = 805 Ibs/hr CaSO; produced (unhydrated CaSO, basis): (479.8 Ibmole/hr SO; )(1 mole CaSO3/mole SO) x (120 Ib/Ibmole) = 57,576 Ib/hr (for unhydrated CaSO; ) or 57,576X oA = 74,849 (for dry CaSO3 x 2H,0) 2 Sludge Solids = 57,576+565 +805 = 58,946 Ibs/hr (dry basis) _ 58,946 Ibs/hr Sludge = 107,175 lb/hr = 1,286 tons/day (wet sludge) The sludge production from a lime scrubber is almost 90% of that of a limestone scrubber. The big difference would be in the reagent feed rates and feed handling systems. *The sludge production is based upon a non-hydrated calcium sulfite, as in 15.1. Prob. 16.5 (6%)  6. Hydrogen has been proposed to be an alternative fuel to gasoline for automobiles. The current technology (such as fuel cell) relies on H2 production through steam reforming of methanol/ethanol on board. Meanwhile, technology has also been developed to generate hydrogen at stationary sites. (a) Find out one method for hydrogen production (either from a patent or a journal article), and briefly discuss its principles. (b) Discuss how hydrogen can be stored for on-board vehicle use. Sources of information are to be reported. (12%) Hydrogen can be obtained from decomposition of methane (natural gas), coal (by a process known as coal gasification), liquid petroleum products, biomass (biomass gasification), high heat sources, or from water using electricity (electrolysis) (DOE, 2005a and c).G. Bonura, O. Di Blasi, L. Spadaro, F. Arena and F. Frusteri (2006) A basic assessment of the reactivity of Ni catalysts in the decomposition of methane for the production of “COx-free” hydrogen for fuel cells application Catalysis Today, 298-303 Thermal decomposition of methane (TDM) The thermal decomposition of methane (TDM) in the presence of a carbon catalyst is one method for producing H2 with reduced CO2 emissions. At temperatures above 700 Celsius and in the absence of oxygen, the CH4 decomposes to H2 and solid carbon, and the carbon deposits onto the carbon catalyst. Depending on whether the required thermal energy is generated by combustion of CH4 or H2 or another approach, TDM yields a 50% or greater reduction in greenhouse gas emissions compared to the steam reforming of CH4. CH4 --> C 2H Transition metals such as Fe, Co and Ni are well known to be effective for methane decomposition into hydrogen and carbon nanofibers. 7. (b) Discuss how hydrogen can be stored for on-board use. Sources of information are to be reported. (15%) Hydrogen can be mechanical or chemically stored for on –board use. On-board hydrogen storage is required to enable a driving range greater than 300 miles for the full platform of light duty automotive vehicles using fuel cell power plants (DOE, 2005a&b; Chalk et al., 2006).This can be improved by storing hydrogen as gas, liquid, and solid phases at greater densities while reducing the weight, energy consumption, and complexity of the storage systems in applications (DOE 2005a; Schlapbach and Züttel, 2001). Types of hydrogen storage considered for an on board fuel cell for vehicles 1. Compressed hydrogen gas tanks Hydrogen can be compressed into high-pressure tanks. This process requires energy to accomplish and the space that the compressed gas occupies is usually quite large resulting in a lower energy density when compared to a traditional gasoline tank. A hydrogen gas tank that contains a source of energy equivalent to a gasoline tank would be more than 3,000 times bigger than the gasoline tank (DOE, 2005c; Schlapbach and Züttel, 2001). However, there is a significant disadvantage: compressing or liquefying the gas is expensive. High-pressure tanks achieve 6,000 psi, and high-pressure vessels present a considerable risk. Therefore, they must be periodically tested and inspected to ensure their safety (DOE 2005a). Compressed hydrogen gas tanks have been commercially available in several prototype fuel cell vehicles. 2. Liquid hydrogen tanks The energy density of hydrogen can be improved by storing hydrogen in a liquid state (0.070 kg/liter). Liquid hydrogen typically has to be stored at -253o C at 1 bar (Schlapbach and Züttel, 2001). It is a common liquid rocket fuel for space shuttle applications. However, the cooling and compressing process requires energy, resulting in a net loss of about 30% of the energy that the liquid hydrogen is storing and large volume for the storage tank. Liquid hydrogen storage becomes very expensive comparative to other methods. 3. Metal hydride Metal hydrides deviate largely from ideal stoichiometry and can exit as multiphase systems and safe and compact hydrogen storage media (DOE, 2005c). Inter-metallic compounds and alloy are capable of storing 5% - 7% of their own weight. Moreover, slow uptake and release kinetics can be improved by adopting catalysts (nickel, platinum, and etc.) Hydrogen can be stored interstitially or held by forming metal hydrides in solid storage metals. Once hydrogen molecules were chemisorbed onto metal surface and were dissociated into hydrogen atoms, hydrogen atoms diffuse into metal lattices and form the nucleation and growth of metal hydride. Light metals, based on lithium, aluminum, or magnesium have a higher storage capacity by weight and are therefore favored for reversible on-board hydrogen storage and release at low temperatures and pressures (Schlapbach and Züttel 2001). Metal hydrides offer the advantages of safely delivering hydrogen at a constant pressure and a thus are valuable solutions to the problem of hydrogen storage. However, low hydrogen capacity, slow uptake and release kinetics, and cyclic stability are challenging issues that need to be addressed (DOE, 2005b). 4. Chemical hydrogen Storage This is a hydrogen storage technology in which hydrogen can be generated through a chemical reaction. The hydrogen is combined in a chemical reaction that creates a stable compound containing the hydrogen (i.e., hydrolysis of metal hydride, organic hydrides, and MgH2 slurries) (DOE, 2005c). However, the weight and volume of reactant, product limit of energy density and endothermic reaction require expensive catalysts and high temperatures. 5. Carbon based materials/high surface area sorbent Carbon materials-based storage (i.e., carbon nanotubes, aerogels, nanofibers, and metal-organic frameworks) technologies absorb hydrogen in microscopic pores on the tubes and within the tube structure by Van der waals forces (Schlapbach and Züttel, 2001). Hydrogen storage could be enhanced by tailored structures. Carbon nanotubes are capable of storing from 4.2% to 6.5% of their own weight in hydrogen (Chalk et al., 2006; Schlapbach and Züttel 2001). This technology is still in the development stage. References Bloch, J. and M. H. Mintz (1997). "Kinetics and mechanisms of metal hydride formationa review." Journal of Alloys and Compounds 253-254: 529-541. Chalk, Steven G., Miller, James F. (2006). “Key challenges and recent progress in batteries, fuel cells, and hydrogen storage for clean energy systems.” Journal of Power Sources, available online DOE (2005a). National Hydrogen Vision and Roadmap. Energy. DOE (2005b). Targets for On-Board Hydrogen Storage Systems. D. O. E. Office of Energy Efficient and Renewable Energy. DOE (2005c). Annual progress report Holtz, R. L. and M. A. Imam (1999). "Hydrogen Storage Characteristics of Ball-Milled Magnesium-Nickel and Magnesium-Iron alloys." Journal of Materials Science 34: 2655- 2663. Iwakura, C., H. Inoue, et al. (2002). "Effects of surface and bulk modifications on electrochemical and physiochemical characteristics of MgNi alloys." Journal of Alloys and Compounds 330-332: 636-639. Liang, G., J. Huot, et al. (1999). "Catalytic effect of transition metals on hydrogen sorption in nanocrystalline ball milled MgH2-Tm (Tm= Ti, V, Mn, Fe, and Ni) systems." Journal of Alloys and Compounds 292: 247-252. Schlapbach, L. and A. Züttel (2001). "Hydrogen-storage materials for mobile applications." Nature 414: 353-358. Graduate Only Review one of the articles listed below, and provide a summary (< 2 pages) (20%). 1. “Nanoparticles and the Environment – A Critical Review Paper”, Biswas, P. and Wu, C. Y., J. Air Waste Management Association, 55, 708-746, 2005. 2. “Separation and Capture of CO2 from Large Stationary Sources and Sequestration in Geological Formations“, White, C. M., Strazisar, B. R., Granite, E. J., Hoffman, J. S. and Pennline, H. W., J. Air Waste Management Association, 53(6), 645-713, 2003.