Name: February 24, 2015 EXAM 1 P a g e I 1 / e Below is a blank flow diagram of a generalized distillation column: (10 Points) f -- ' Q. - -- N - - L. PAD"t..t... QatJ11.81L _/cit...b ><"'g Label all of the following components/variables on the chart: Streams Mole Fractions Stages Operations Thermal Terms Feed (F) ZF 1 Total Condenser Qc Distillate (D) Xo n Partial Reboiler UR Bottoms (B) XB N Reflux (Lo) Boilup (V) Vapor {V) liquid (L)
University of Alabama Chemical & Biological Engineering- CHE 305-001Spring2017 Name: February 24, 2015 EXAM 1 P a g e I 2 Based on the diagram and labeling, answer the following (15 Points) In terms of the labels you just used on the flow diagram... What is the overall mole balance? What is the mole balance for the "light component"? Write equations to describe the overall energy balance and balances around the condenser and reboiler. (Although true, LoutHini - LinHini is not a valid answer) Q=AH = ~fl 4 0c_ Oc. = ~(4.~D) - }'v\/ I\ A ~ Gf!-fk = µ,,g '* Hv V - }\~ L What are the definitions of reflux ratio (R) and boilup ratio (V0)? R = Lofi> Vs= -V/s What is the equation for the stripping section operating line? x -
University of Alabama Chemical & Biological Engineering- CHE 305-001 Spring 2017 Name: February 24, 2015 EXAM 1 P a g e I 3 Multiple Choice Questions (SO Points: 25 Questions, 2 pts each) The ideal gas equation of state is most accurate for which conditions? a) High Temperature, High Pressure b) Low Temperature, High Pressure c) Low Temperature, Low Pressure ((if High Temperature, Low Pressur~ van der Waals' equation of state improves on the ideal gas equation of state by: accountin for the volume of the molecule(s) b) ignoring intermolecular interactions c) redefining the universal gas constant, R d) recognizing the dynamic instability of the triple point Which of the following pairs is most likely to deviate from Raoult's Law? a} 1-propanol + 2-propanol @:Water + Acetic Acid) c) Ethyl Acetate + Acetic Acid d) Hexane+ Octane For a two-component system at vapor-liquid equilibrium, what condition defines an azeotrope (if one exists)? In what way are the streams Vs and B the same? a) Phase b) Composition @'Temperatur!I) d) All of the above
Relative Volatility (aii) is defined as: a) Pi*/pi* '@~ C) y/xi d) (Tbou)/(Tboil)i Which of these methods have you used most often on HW for predicting activity coefficients? a) van Laar b) Margules ([Wilsoy d) UNIFAC What is the consequence of operating a small reflux ratio (i.e. R z Rmin)? a} Minimize stages, minimize condenser duty b) Maximize stages, minimize condenser duty c) Maximize stages, maximize condenser duty d) Minimize stages, maximize condenser duty If we define Oto be positive when heat is added, then Oc and OR are: a} Both positive b) Both negative c) Oc == positive, OR == negative @ Oc == negative, OR == positiv0 The feed to a distillation column could be: a) Liquid b) Vapor c) Mixture of liquid and Vapor @Y of the abov~
Name: February 24, 2015 EXAM 1 P a g e I 5 In what way are the streams Lo and D different? a) Phase b) Composition <1f):1owrate:J d} Temperature The distillate and bottoms streams are always: ~ b} Vapors.c) Mixtures of Vapor and Liquid d) Supercritical Fluids Raoult's Law is "corrected" to account for non-ideality by the inclusion of: a) Fugacity Coefficients b) Equations of State @:Activity Coefficjen'tu d) Binary Interaction Parameters At any given stage in a distillation column, which inputs/outputs are in vaporliquid equilibrium? U) fxiting liquid and exitin~ b) Exiting liquid and entering vapor c) Entering liquid and entering vapor d) Entering liquid and exiting vapor The location of the feed stage of a distillation column could be: a) Top stage b) Bottom Stage c) Somewhere between top stage and bottom stage <d}" Any of the abov"e::>
University of Alabama Chemical & Biological Engineering- CHE 305-001Spring2017 Name: February 24, 2015 EXAM 1 P a g e I 6 Activity coefficients of "'l will be calculated from Regular Solution Theory when the solubility parameters (81, 82) for a given pair of molecules are: ~ b) bi< 82 c) 81 > 82 d) 81+82=0 Compared to the number of stages calculated on a McCabe-Thiele Diagram, the number of actual stages in an operating distillation column is always: a) The same b) Less CMorLJ d) Depends on the design of the tray/packing Which of the following feed conditions will result in equal vapor flowrates in both the rectifying and stripping sections (i.e., V = V)? a) Subcooled liquid ( ) Bubble Point Liqu@) c) Dew Point Vapor d) Superheated Vapor The Carnot Cycle dictates that: a) Energy is conserved C bf Heat can never be fully converted into wo"f'r) c) Cooling a fluid is more difficult than heating it d) Disorder is always increasing When increasing the reflux ratio, the distillation column dimensions will become: Gi Shorter and w~ b) Taller and thinner c) Shorter and thinner d) Taller and wider
University of Alabama Chemical & Biological Engineering - CHE 305-001Spring2017 9 Name: February 24, 2015 EXAM 1 P a g e I 7 Except at "total reflux", the slope of the stripping section operating line is always relative to the slope of the rectifying section operating line: C:~TrGreater than with same sign(+/-) ~ b) less than with same sign c) Greater than with opposite sign d) Less than with opposite sign Which of these is NOT an assumption of the McCabe-Thiele method? a) Components have similar ~Hvap values b) Molar flowrates of V and l are constant in the rectifying section c) Distillation column is well-insulated d} There is a significant pressure drop in the column Which term describes a non-ideal VLE where the equilibrium curve comes close to the 45 line at one or more points but does not cross it at any point? ~)<Pi~h~ b) Flood c) Weep d) Foam Which of the following is NOT a requirement to establish vapor-liquid equilibrium in a sealed container? a) TL=Tv b) PL=Pv ~ d) µl = µv If relative volatility is very large for a given separation, it might be easier to use a unit rather than a distillation column. ---- a) liquid - Liquid Extraction b leaching c) Flash d) Gas Adsorption
Name: ~ February 24, 2015 EXAM 1 P a g e I 8 McCabe Thiele Diagram (25 Points) Use the diagram on the following page and your best estimates (where needed) to sketch a McCabe-Thiele diagram and answer the following questions: Feed is a 50:50 mix of vapor and liquid Mole fraction of the light component in the feed is 0.30 Mole fraction of the light component in the distillate is 0.90 Mole fraction of the light component in the bottoms is 0.10 What is the approximate theoretical minimum number of stages {i.e. when the operating line is the 45 line)? 2+ 02. 3 Estimate the minimum reflux (Rmin) as closely as possible: t "''-'AJ (o.s,o.-a) ~ (0.13 1 0.tlf) ~ ~o.s.to.q, o.q) 4-..",,..,~, o.._.1) ~-= o.f-o.t/7 - O.l(J ; 0..:1 yl("-1 ~ ~'-6 (,) ~ (.'"'*.Q, l>-tf-0 13 - (),")") ~ O:l!'L. = F- """. c;ir,i ;::;, 0. 5',R.... 0.56 = t2.. o.~=o.'lc+fl {t.== /.2.7 \ If operating at 1.5 Rmin, how many stages are required, and which sta e is the feed? \~i l '/ + o L 'S'" 'S7~-S J.6 ~ 1.J ::. /.S{i. 'l-7) ::- ~ ~05 :: R~ -- - ft8> Kr~3 J.'io5 t~os-h..l.lsf'ra ~- ~ ~..-rt lo.2., o.c.t) CAl 't.-&...f~!>p &...f ti.6' Sl.OPt;.::- ~ '1 - t:r4 D. ~ 0.~ ().'f- (). 2- ;; f) '7 Cl.OS~ Tb H1tJ t~())" L.I~ 4\) l./s c..11-e (~~ O SC-) {sc.d>c ~ ( )
Name: )t!ef February 24, 2015 EXAM 1 P a g e I 9 l.00 0.. 90 0.80 0.,70 0.60 >..of 0.50 0.. 40 0.30 0.. 20. ' 0.10 0.. 00 o.. oo 0.10 o.. 20 0~30 o.40 o.. so 0~60 0.10 o.ao o.so 1.00 Extra Credit (up to +3}: In which country was distillation first used to recover ethanol from water? l ~~ i. J1Tf+ c.esnji.} f X.1 (l>~sft<lacet") toss.8c.-"i ~tt.lk IMS>!«~ n"'t;:;" ~ ~IN Who discovered the H-bond and a-helix (although not fully given proper credit)? ~ G&1us; HAv12..,~ Lett""- Under what department of the federal government is NIST7