Fuel crack formation

Mechanical integrity is one of the most important prerequisites for fuel cell membranes in terms of handhng and fabrication of membrane electrode assemblies, and to offer a durable material. Robust fuel cell membranes are required because of the presence of mechanical and swelling stresses in the application [172]. Moreover, membranes should possess some degree of elasticity or elongation to prevent crack formation. 

The main problem in elevated-temperature-polymer electrolyte fuel cell operation is degradation of the membrane at the higher temperature. Marked water loss raises the ohmic resistance of the membrane, causes brittleness, and may give rise to crack formation. For this reason, most polymer electrolyte fuel cells research at present addresses the question of how to maintain the membrane in good working condition in an elevated-temperature-polymer electrolyte fuel cell. 

Figure 3.10. Crack formation in irradiated fuel pellets longitudinal and cross-sectional view (By courtesy of Siemens/KWU)...

The visbreaking process thermally cracks atmospheric or vacuum residues. Conversion is limited by specifications for marine or Industrial fuel-oil stability and by the formation of coke deposits in equipment such as heaters and exchangers. 

Through the 19.30s, Ipatieff led UOP in its effort to develop two catalytic processes for the production of high-octane fuel alkylation and polymerization— the first, a reaction of a hydrocarbon with an olefin (double-bonded compound) the second, the formation of long molecules from smaller ones. Both processes produce high-octane blending compounds that increase the quality of cracked gasoline. 

By the mid-1930s, catalytic technology entered into petroleum refining. To a greater extent than thermal cracking, catalysis permitted the close control of the rate and direction of reaction. It minimized the formation of unwanted side reactions, such as carbon formation, and overall improved the yield and quality of fuel output. 

The high-surface-area TUD-1 can serve as an anchor for many catalysts. Si- or Al-Si-TUD-1 (24,25) can be used as a support for various noble metals (Pt, PtPd, Ir, etc.). This will provide catalysts suitable for the hydrogenation of olefins and aromatics. In the refining industry, one use is the hydrogenation of polynuclear aromatics ( PNAs ) in diesel fuel, which can lower the fuel s toxic properties. Also, jet fuel has an aromatics constraint, designed to lessen smoke formation. Cracked stocks (e.g., coker or visbreaker liquids) generally have undesirable olefins (especially a-olefins) that also need to be saturated prior to final processing. 

Gray, M. R., and McCaffrey, W. C., Role of Chain Reactions and Olefin Formation in Cracking, Hydroconversion, and Coking of Petroleum and Bitumen Fractions. Energy Fuels, 2002. 16(3) pp. 756-66. 

Acidic chloroaluminate ionic liquids are excellent media for polymer cracking reactions. With the huge quantities of polymers that need to be disposed of each year the ability to break them down into useful compounds for new synthesis or to use as liquid fuels is extremely important. While certain polymers such as poly(methyl methacrylate) are easily cracked into their constituent monomers that can be reused, the majority of polymers are extremely difficult to crack into useful organic compounds. However, merely dissolving polyethylene in acidic chloroaluminate ionic liquids containing a proton source results in the formation of a mixture of alkenes and cyclic alkenes [48], The key compounds produced are shown in Figure 10.10. 

Gums Conjugated diolefins and other olefinic compounds formed during catalytic and thermal cracking processes heterocyclic compounds present in fuel can also initiate gum formation... 

Cracked gasoline FCC gasoline Composed of paraffinic, olefinic, and aromatic compounds branched compounds are present in a relatively high amount typically has a higher RON than MON high-olefin-content FCC gasoline can lead to gum formation and fuel color degradation. 

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