Fuel Science 431 Test Questions – Flashcards
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| GLOBAL CARBON CYCLE |
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| see diagram |
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| PHOTOSYNTHESIS MECHANISM |
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| see diagram |
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| the link joining two cyclic sugars is called ___, ___, and ___ |
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| acetal linkage saccharide linkage glycoside linkage |
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| catalyst |
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| enhances the rate of the rxn without being consumed or permanently altered |
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| catalysts usually work by... |
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| ...reducing activation energy, usually by providing a different rxn mechanism |
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| catalysts operate on ___ |
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| kinetics, not thermodynamics, so they can't change the position of equilibrium, only help to get there faster |
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| homogeneous catalysts |
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| 1. in the same phase as reactants and products 2. no problem getting the reactants to the catalyst, but at the end, you have to separate them 3. biochemical rxns (enzymes) |
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| heterogeneous catalysts |
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| 1. in a different phase than the reactants and products 2. trouble getting the reactants to the catalyst, but at the end, separation needed 3. industrial rxns |
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| protein structure |
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| 1*: sequence of amino acids 2*: alpha coils and beta pleats 3*: 3-D conformation 4*: multiple proteins joined together |
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| rating a catalyst |
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| 1. activity- how fast it works 2. turnover frequency- (# of rxns per catalyst site)/time 3. selectivity- (desired product)/(all products) |
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| homogeneous vs. heterogeneous catalysts |
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| homogeneous catalysts (enzymes) have very high turnover frequency (~1000/sec) and good selectivity (~100%) |
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| CONVERSION OF POLYSACCHARIDES TO ETHANOL |
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| see diagram |
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| ETHANOL PRODUCTION |
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| see diagram |
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| fermentation rxn |
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| C6H12O6 -> 2C2H6O + 2CO2 |
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| ethanol fermentation details |
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| catalyst is yeast max ethanol conc. is 8-12%, because above that, the alcohol kills the yeast after that, distillation is used to increase the concentration |
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| 95% azeotrope: options |
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| 1. use directly as fuel (slight energy penalty because of the 5% water) 2. make 100% ethanol by A. add a third component like benzene to shift the equilibrium B. react the water away C. cleverly separate the ethanol and water (membranes, etc.) |
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| ethanol: pro #1 |
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| theoretically CO2 neutral |
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| ethanol: pro #2 |
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| principally renewable (concerns: soil depletion and monoculture dependence) |
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| ethanol: pro #3 |
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| secure, domestic energy resource |
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| ethanol: pro #4 |
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| very high octane number--suitable for high compression engines |
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| ethanol: pro #5 |
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| partially oxygenated -> shifts combustion chemistry in the engine to reduce emissions of CO and unburned fuel |
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| ethanol: con #1 |
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| infinitely miscible with water |
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| ethanol: con #2 |
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| lower volumetric energy density than gasoline (lower MPG) |
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| ethanol: con #3 |
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| materials compatibility--ethanol is an alcohol (gasoline is a hydrocarbon) -> different interactions with parts of the fuel system (not a big deal--largely solveable) |
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| ethanol: con #4 |
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| food vs. fuel argument--is it ethical? |
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| ethanol: con #5 |
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| low energy balance--1.5 (compared to gasoline's 20) waste of energy is due to distillation (water has a high specific heat) |
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| ethanol: con #6 |
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| can we grow enough? |
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| energy balance of fuel |
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| (energy liberated by burning)/(energy used to make) |
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| ethanol challenges |
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| 1. find hardy plants (low-maintenance, grow on crappy soil) 2. find easy hydrolysis of cellulose at mild conditions 3. find yeast that can tolerate >12% ethanol 4. find low energy separation processes (so that we don't have to use distillation) |
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| plant oils |
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| long-term energy storage for plants |
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| plant oil/biodiesel con #1 |
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| high molecular wt -> low vapor pressure -> hard to vaporize for combustion -> hard to use in cold weather |
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| plant oil/biodiesel con #2 |
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| high viscosity (and viscosity increases as temp. decreases) |
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| plant oil/biodiesel con #3 |
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| oil molecules tangle with each other and form gums in the engine |
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| petrodiesel |
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derived from petroleum; made of alkanes 12-20 carbons long |
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| biodiesel |
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| take apart the plant oil molecule to get the carbon chains |
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| BIODIESEL PRODUCTION |
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| see diagram |
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| ester hydrolysis of plant oil to get the carbon chains can be ___ or ___ |
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| base induced (not a catalyst) acid catalyzed |
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| base-induced hydrolsis is used over acid-catalyzed hydrolysis for plant oils because... |
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| ...the last step of the base-induced rxn is a forward-only rxn |
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| the RCOO- formed in base-induced hydrolysis is acidic and bad for the engine, so... |
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| ...it is re-sterified, but with the smallest alcohol, methanol |
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| biodiesel vs. petrodiesel |
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| biodiesel has no sulfur and no aromatic compounds -> very clean burning the couple of oxygens in biodiesel give a small energy penalty |
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| biodiesel vs. ethanol |
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| biodiesel is much easier to make but we need to figure out what to do with the glycerol that forms we also need a plant oil source |
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| plant oil/biodiesel pro #1 |
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| easy to make compared to ethanol |
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| plant oil/biodiesel pro #2 |
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| more clean-burning than petrodiesel |
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| plant oil/biodiesel pro #3 |
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| it can be used in a petrodiesel engine |
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| transesterification |
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| plant oil + methanol -> 3 FAs + glycerol |
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| pyrolysis |
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| use of thermal energy to split molecules |
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| pyrolysis is also called ___ and ___ |
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| thermal decomposition carbonization |
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| why does charcoal have a higher calorific value than wood? |
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| wood is 35-45% oxygen (it's already partially oxidized, so there's less to oxidize/burn), while charcoal has most of the oxygen already gone |
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| products of wood pyrolysis |
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| gas: CO2, CO, CH4, small hydrocarbons liquid: pyroligneous acid |
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| hardwood pyroligneous acid |
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| aqueous phase: methanol, acetic acid, acetone heavy organic phase |
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| softwood pyroligneous acid |
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| light organic phase: turpentine, pine oil aqueous phase: methanol, acetic acid, acetone heavy organic phase: wood creosote |
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| methanol can be made from wood by ___ and ___ |
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| pyrolysis gasification |
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| wood -gasification-> methanol |
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| 1. endothermic, so the heat from combustion rxn is used to power it 2. product is synthesis gas (CO and H2), which can be made into methanol 3. 90% yield of methanol |
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| GASIFICATION MECHANISM |
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| see diagram |
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| wood -pyrolysis-> methanol |
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| 1. endothermic, so the heat from combustion rxn is used to power it 2. methanol is separated out from the organic and aqueous phases 3. 2% yield of methanol |
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| PYROLYSIS MECHANISM |
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| see diagram |
