chemical processes2 jrw

Upload: muhammadasim10

Post on 14-Apr-2018

221 views

Category:

Documents


0 download

TRANSCRIPT

  • 7/30/2019 Chemical Processes2 Jrw

    1/35

    Chemical Processes

    What is Engineering?

    July 25, 2007

  • 7/30/2019 Chemical Processes2 Jrw

    2/35

    Chemical Processes Outline

    Motivations

    Reactions Separations

    Calculations using Conservation of

    Mass and Energy Distillation

  • 7/30/2019 Chemical Processes2 Jrw

    3/35

    Chemists vs Chemical Engineers

    Chemists

    Design reaction

    pathways to producea chemical from rawmaterials

    Work in the laboratorysetting to producematerial on the gramto kilogram scale

    Chemical Engineers

    Design a process toscale the chemistsprocess to massproduce the product

    Work in a chemicalplant to producematerial in the ton andbeyond range

  • 7/30/2019 Chemical Processes2 Jrw

    4/35

    Why do we care about Chemical

    Engineering?

    Shampoo

    Soap

    Toothpaste

    Dyes

    Gasoline

    DecaffeinatedCoffee

    Sugar

    Chemicals Are All Around

    Cosmetics

    Paint

    Foodadditives

    Hydrogen

    Fertilizer

    Polymers

    Pharmaceuticals

  • 7/30/2019 Chemical Processes2 Jrw

    5/35

    If that isnt reason enough

    In the United States

    170 Major ChemicalCompanies

    $400 Billion a year

    Employs more than amillion workers

    http://money.cnn.com/2006/02/13/pf/college/starting_salaries/index.htm

  • 7/30/2019 Chemical Processes2 Jrw

    6/35

    Molecules that Chemicals Engineers

    work with

    Small and Simple

    Helium (He)

    Ammonia (NH3)

    Hydrogen Flouride (HF)Trinitrotoluene (C6H2(NO2)3CH3)

    Large and ComplicatedInsulin C257H383N65O77S6

    Large and SimplePolyvinyl Chloride (-CH2-CHCl-)n

  • 7/30/2019 Chemical Processes2 Jrw

    7/35

    How to Produce Chemicals

    Two methods to obtain a desiredchemical

    Design a reactor to produce a chemicalfrom raw materials

    To isolate the compound that exists incombination with other substancesthrough separation processes

  • 7/30/2019 Chemical Processes2 Jrw

    8/35

    Chemical Reactions

    Raw Materials

    Energy

    Catalysts

    ReactorProducts

    Raw Materials

    Byproducts

    EnergyCatalysts

  • 7/30/2019 Chemical Processes2 Jrw

    9/35

    Possible Problem with Exothermic

    Reactions

    Reactor

    Water Bath

    A+B->C

    Energy Produced byreaction is proportional to

    reactor volume L3

    Energy Removed isproportional to surfacearea L2

    L

    Possible Scale up Problem

  • 7/30/2019 Chemical Processes2 Jrw

    10/35

    Separations

    Molecular Property

    Boiling Point

    Freezing Point

    Particle size

    Affinity to astationary phase

    Density

    Selective affinity tosolid particles

    Separation Process

    Distillation

    Crystallization

    Filtration

    Chromatography

    Centrifuge

    Adsorption

    Exploits Differences of Material Properties

  • 7/30/2019 Chemical Processes2 Jrw

    11/35

    Separations: Unit OperationsUse separation processes to:

    Purify raw materials Purify products Purify and separate unreacted feed.

    Most common types: Distillation

    Flash distillation Batch distillation Column distillation

    Absorption

    Stripping

    Extraction

    Chromatography

  • 7/30/2019 Chemical Processes2 Jrw

    12/35

    Mass and Energy Balances

    Balance Equation

    Input + generation Output =

    Accumulation

    ControlVolume

  • 7/30/2019 Chemical Processes2 Jrw

    13/35

    Mass and Energy Balances

    For non-reacting systemsGeneration = 0

    For systems operated at steadystate Accumulation = 0

    Mass and Energy Balances reduce to

    Input = Output

  • 7/30/2019 Chemical Processes2 Jrw

    14/35

    Separations Calculation

    Magic

    Separating

    Machine

    100 moles

    10% C2H5OH

    90% H2O

    V moles

    40% C2H5OH

    80 moles

    x % C2H5OH

  • 7/30/2019 Chemical Processes2 Jrw

    15/35

    Separation Calculation

    Magic

    SeparatingMachine

    100 moles

    10% C2H5OH

    90% H2O

    V moles

    40% C2H5OH

    80 moles

    x % C2H5OH

    Conservation of total Moles 100 (V+80) = 0

    V =20

    Conservation of moles of C2H5OH 100*.1 (.4*V+x*80) = 0

    x = 2.5%

  • 7/30/2019 Chemical Processes2 Jrw

    16/35

    Separations: Distillation

    Magic

    Separating

    Machine

    Equilibrium Stages

    (Distillation Column)

  • 7/30/2019 Chemical Processes2 Jrw

    17/35

    Distillation

    Separates liquids based on differences in volatility!

    Consider a liquid mixture of A and B:

    Boiling point of A: 70 C

    Boiling point of B: 100 C

    What would be the composition of the vapor phase if the entireliquid mixture vaporized?

    As mixture begins to boil, the vapor phase becomesricher in A than the liquid phase!

    As temperature increases, the concentration of B inthe vapor phase increases.

    Condense vapor phase to get a mixture with a higherconcentration of A!

  • 7/30/2019 Chemical Processes2 Jrw

    18/35

    Distillation

  • 7/30/2019 Chemical Processes2 Jrw

    19/35

    V1 V2

    L0 L1

    stage 1

    Distillation: Equilibrium Stages

    A) Phases are brought into close contactB) Components redistribute between phases toequilibrium concentrationsC) Phases are separated carrying new componentconcentrations

    D) Analysis based on mass balance

    L is a stream of one phase; V is a stream of another phase. Use subscripts to identify stage of origination (for multiplestage problems) Total mass balance (mass/time): L0 + V2 = L1 + V1 = M

  • 7/30/2019 Chemical Processes2 Jrw

    20/35

    Distillation

    Represent vapor liquid equilibrium data for more volatilecomponent in an x-vs-y graph

    Pressure constant, but temperature is changing!

  • 7/30/2019 Chemical Processes2 Jrw

    21/35

    Distillation: McCabe-Thiele Calculation

    Operating Line

    Calculation of theoretical number of equilibrium stages

    xD

    xF

    xB

  • 7/30/2019 Chemical Processes2 Jrw

    22/35

    Distillation: McCabe-Thiele

  • 7/30/2019 Chemical Processes2 Jrw

    23/35

    Distillation

    Benefits

    Applicable formany liquidsystems

    Technology is welldeveloped

    High Throughput

    Drawbacks

    High heating andcooling costs

    Azeotropes

  • 7/30/2019 Chemical Processes2 Jrw

    24/35

    Azeotrope

    Separations limitation

    Due to molecular interactions. Composition of vaporequal to composition of liquid mixture.

  • 7/30/2019 Chemical Processes2 Jrw

    25/35

    Distillation

    Batch distillationapparatus only oneequilibrium stage!

  • 7/30/2019 Chemical Processes2 Jrw

    26/35

    Conclusions

    Chemicals are produced by

    reactions or separations The driving force for separations are

    property differences

    Mass and Energy are Conserved

    Distillation is the workhorse ofseparations

  • 7/30/2019 Chemical Processes2 Jrw

    27/35

    Todays Laboratory

    Three Parts:

    Energy Transfer

    Chromatography

    Batch Distillation

    (One equilibrium stage)

  • 7/30/2019 Chemical Processes2 Jrw

    28/35

    Todays Laboratory: Energy Transfer

    Want efficient transfer and conversionof energy ($$)

    In lab, will be examining energytransfer in the form of heat:warming a pot of water with a hotplate what is the efficiency ofenergy transport from electricity tothe water?

  • 7/30/2019 Chemical Processes2 Jrw

    29/35

    Todays Laboratory: Chromatography

    Separation technique that takesadvantage of varying affinities of solutesfor a given solvent traveling up a filterpaper. Solutes: colored dyes Solvents: water, methanol, 2-propanol

    Measure the distance traveled by thesolutes and solvents!

    **Methanol and 2-propanol are poisons! Wearsafety goggles, do not ingest or inhale andrinse skin immediately if spilled.

  • 7/30/2019 Chemical Processes2 Jrw

    30/35

    Todays Laboratory: Distillation

    Using distillation to separate a liquidmixture of ethanol and water Ethanol is the more volatile material (it will boil

    first)

    Take samples of distillate with time todetermine the concentration of ethanol inthe mixture!

    **Ethanol is a poison! Wear safety goggles, donot ingest or inhale and rinse skin immediatelyif spilled.

  • 7/30/2019 Chemical Processes2 Jrw

    31/35

    Assume three components: A = dye, B = oil, C =water

    xA = mass fraction of A in stream LyA = mass fraction of A in stream V(e.g., L0 xA0 = mass of component A

    in stream L0 ) Component mass balance (mass/time):L0 xA0 + V2 yA2 = L1 xA1 + V1 yA1

    = M xAML0 xC0 + V2 yC2 = L1 xC1 + V1 yC1

    = M xCM

    (equation for B not necessary becausexA + xB + xC = 1)Suppose the following: V is oil (B) contaminated with dye(A). L is water (C) which is used to extract the dye from theoil. When V comes in contact with L, the dye redistributesitself between the V and L. L and V are immiscible (i.e., two

    distinct liquid phases).

  • 7/30/2019 Chemical Processes2 Jrw

    32/35

    V1 = oil + less dye V2 = oil + dye

    L0 = water L1 = water + some dye

    stage 1

    Oil flow = V(1 - yA) = V = constantWater flow = L(1 - xA) = L = constantThen, for mass balance of the A component:Another assumption: dye concentrations yA1, xA1come into equilibrium according to Henrys Law: yA1 =H xA1 , where H depends on the substances A, B, C.

  • 7/30/2019 Chemical Processes2 Jrw

    33/35

    1000

    1 099

    01

    1 01100

    199

    1

    1

    1

    1

    1

    .

    .

    x

    x

    y

    y

    A

    A

    A

    A

    1 100

    25

    1 25 99 1 008

    1

    1

    1

    11

    .

    . .

    y

    y

    y

    y y

    A

    A

    A

    AA

    Specific problem: 100kg/hr of dye-contaminated oil(1% by weight) is mixed with 100 kg/hr of water toreduce the dye concentration in the oil. What is theresulting dye concentration in oil after passing throughthe mixing stage if dye equilibrium is attained and

    Henrys constant H = 4?Soln:

    L = 100kg/hr V = 100 ( 1 - .01) =99 kg/hr

    xA0 = 0 (no dye in incoming water)yA2 = .01 (initial contamination in oil)

    yA1 = 4 xA1 (equilibrium concentration of dyebetween oil and water)

  • 7/30/2019 Chemical Processes2 Jrw

    34/35

  • 7/30/2019 Chemical Processes2 Jrw

    35/35

    q-line

    zF*

    *

    *

    xD

    xB

    y-int ~ 0.36

    Rectifying operating line

    Stripping operating line

    Nideal = 6 2/3