midterm3 2005 soln

midterm3 2005 soln - Chemical Engineering 140 Midterm #3...

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Chemical Engineering 140 November 21, 2005 Midterm #3 (170) Researchers at the University of Wisconsin-Madison have recently developed an alternative process for producing H 2 for the hydrogen economy 1 . This approach uses renewable resources such as biomass as opposed to nonrenewable resources such as natural gas and petroleum. In this process, glucose (obtained from starch) is first converted to sorbitol, which is then reformed over a platinum catalyst to form hydrogen. Sorbitol is reformed over a Pt/Al 2 O 3 catalyst in a tubular reactor at 498K and 29 bar according to the following stoichiometry. C 6 O 6 H 14(liq) +6H 2 O (liq) → 13H 2(gas) + 6CO 2(gas) where the subscripts “(liq)” and “(gas)” denote liquid and gas states. Water is fed in 10% excess to sorbitol. Conversion of sorbitol in the tubular reactor is 60%. As a side reaction, carbon dioxide and hydrogen readily react to form methane and water. CO 2(gas) + 4H 2(gas) → CH 4(gas) + 2H 2 O (gas) The effluent of the reactor is sent to a flash tank where a vapor phase and liquid phase exit in equilibrium . Upon analysis of the vapor stream exiting the flash tank, only 40% of the H 2 that would be produced under complete conversion with only the primary reaction is present. Approximate that H 2 , CH 4 , and CO 2 are not present in the liquid phase and that the vapor pressure of sorbitol is negligible. Reactor 498 K 29 bar Sorbitol (liq) H 2 O (liq) Flash 498 K 10 bar vapor liquid 1 Cortright, R. D., Davda, R. R. & Dumesic, J. A. Hydrogen from catalytic reforming of biomass-derived hydrocarbons in liquid water. Nature 418 964-967 (2002).
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50 a) Determine the overall composition of the species leaving the reactor. What is the conversion of the side reaction? Define conversion of the side reaction as: 2, reaction 2 2 H 2 mol H reacted in reaction 2 X = mol H produced in reaction 1 60 b) Determine the compositions of the vapor and liquid streams leaving the flash tank. 20 c) Endothermic reactions in tubular reactors are often heated by condensing steam on the exterior side of the tubes at about 10 ° C above the reaction temperature. If we wish to heat the reactor using this method, what pressure steam (in bar) should be used? 25 d)
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midterm3 2005 soln - Chemical Engineering 140 Midterm #3...

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