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
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