Che363_FinalReview

Che363_FinalReview - 23rd Psaim for Students The Lord is my...

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Unformatted text preview: 23rd Psaim for Students The Lord is my Shepherd? I shall hotfiunk He keepeth me from tying down when i should be studying He leadeth me beside the water cooler fora study break He restores my faith En study guides He leads me to better study habits For my grades‘ sake. Yea, though I walk through the valley of borderline grades I will not have a nervous breakdown For thou art with me My prayers and my friends, they comfort me Thou givest me the answer in moments of blankness Thou anointest my head with understanding My test paper runneth over with questions i recognise. Surely passing grades and flying colours shall foliow me All the days of my examinations And i shall not have to dwell in this exam hail forever. — Author Unknown Appropriate for many faiths CHE 363 Final Review] Study Guide 1. Detaiis: be familiar with each separations process we have studied (key concepts below); you are often concerned with issues like: a. Advantages! disadvantages of each separation — whenit for what type of molecules are you likely to use each separation? b. Picky details like which variables are used and what they refer to (ie, y in absorption vs adsorption vs extraction) What are typical concentration units? 0. Can you identify the relevant i. op line (often a mass balance from lNZOUT), ii. equiiibrium line (relates to driving force) and iii. rate equation (combination of op and eq lines describing the overali separation) d. how tail is the column? (actual height or number of stages to meet flowrate & concentration specs) e. What are the flow rates? How good is the separation? (is, what are then concentrations in the teed and exit streams). What is a typical probtem for each separation? (do you understand it?) We have primariiy considered DELUTE solutions, but in a few cases considered CONCENTRATED solutions (ie, ammonia absorption), what changes? i. What types of molecule is each process appropriate for separating? (ie, two voiatile components with different boiling points? What if they are not thermostabie? Two immiscible tiuids with similar boiling points?) :"h we 2. Big picture: The main theme is EQUiLlBRiUM vs RATE-BASED (or ditferentiai) separations. a. Can you classify each process we have discussed into one of these categories? b. Why might you choose to run your separation as an equilibrium or a rate- based process? c. How do your eq tines, op lines (mass balances) and rate eqns change depending on whether you have an equilibrium or rate-based process? d. How generalizable are the approaches and eqns we used? le, can the Kremser eqn be used for any equilibrium staged process? a. In which case will optimizing your overail mass transfer coefficient improve the separation? 3. Concerns when designing a process (think about this question in terms of each specific separations process; may not apply to ali) a. If you do smali scale piiot experiments in the lab, how will you use this information to design full—scaie equipment? b. If you are not getting the separation you need, what variables might you change to increase the separation? Diffusion Fick’s law, diffusion coefficient versus mass transfer coefficient; thin film vs stab When do use D vs k? How do operating variables (ie, velocity, concentration) affect D and k? Mass transfer How obtain? predict from theory; correlations; experiment Unit conversions, ie, flux N = k*(conc difference) 9 if AP use kp, if A(moielrnole) use kx, if A (mol/vol) use ifoor liquid, kG for gas Little R is from interface to bulk of ONE phase Overall K from bqu to bulk crossing an interface; now reiate K as a function of k? Membranes Rxn in membrane, how affect transfer? How cope with partition coefficients when writing overali mass transfer coefficients? Paraliei vs series resistance Absorption Differences between absorption and stripping columns? Write an op line, size you column! What are NTUs and HTU ~— mathematicaily and what does this teli you about your process? How does a reaction improve the separation? Distillation What are the key components of a distillation column and how do you write a mass balance (=op iine) on each? When to make linear approximations of equilibrium iine (operate over small region of x) Kremser equation a requires linear op line, calc N (ie, ultra-pure products) Fenske eqn — calc Nmm, occurs at total reflux (D=0), thus G=L and op time is y=x Sizing a column: Differential distillation vs Staged distillation (McCabe—Thieie) Extraction Reiies on a partition coefficient such that the moiecuie wilt move up a concentration gradient (ie, from a large voiume of dilute solution to a small volume of concentrated solution) Can be run with counter—current or cross-flow, or like a distillation column... 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Che363_FinalReview - 23rd Psaim for Students The Lord is my...

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