Chemical engineering products, processes, and challenges
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Transcript of Chemical engineering products, processes, and challenges
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Chemical processes500.101
Chemical engineering products, processes, and challenges
Commodities Molecules Nanostructures
Key cost speed to market function
Basis unit operations discovery properties
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Chemical processes500.101 A commodity: TiO2 (titanium oxide)
Extremely white, opaque, edible, dirt resistant. Used in paper, food,cosmetics, paint, textiles, plastics. World consumption: 4 million tons/yr.Cost: $2,000/ton. Total world value = $8 billion/yr.
A 1% increase in production efficiency = 0.01*2*103 *4*106 $/yr = $80 million/yr.
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Chemical processes500.101
Molecules
Small and simple: ammonia (NH3) sulfuric acid (H2SO4) ethylene (C2H4) sugar (C12H22O11)
Large and complex: insulin C257H383N65O77S6
Large and simple (polymers): polyethylene[-CH2-CH2]n
See www.psrc.usm.edu/macrog for a verygood introduction to polymers.
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Chemical processes500.101
Polymers, e.g. polyethylene
is made up of many monomers: n22 CHCH
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Chemical processes500.101
Copolymers are made up of two kinds of monomers, say A and B
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Chemical processes500.101
SBS rubber (tires, shoe soles)
The polystyrene is tough; the polybutadiene is rubbery
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Chemical processes500.101 Nano applications of polymers
Organized block copolymer of PMMA (polymethylmethacrylate)and PS (polystyrene).
Spin casting in electric fieldproduces cylinders of PS embeddedin the PMMA which are orientedin the direction of the electric fieldPMMA cylinders are 14nm diameter,24nm apart.
PS can be dissolved withacetic acid to leave holes.
Use as a microscopic filter?
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Chemical processes500.101
Cylindrical holes are electrochemicallyfilled with magnetic cobalt. Each cylindricalhole can then store 1 “bit” of information.
bit/cm = 1 / (2.4*10-7)
bit/cm2 = 1.7*1011
Computer application:
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Chemical processes500.101
Genetic engineering: production of synthetic insulin
1) Extract a plasmid (a circular molecule of DNA) from thebacterium E-coli
2) Break the circle
3) Insert a section of human DNAcontaining the insulin-producinggene
4) Insert this engineered geneback into the E-coli bacterium
5) The E-coli and its offspringnow produce insulin
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Chemical processes500.101
Chemical Engineering
Two strategies for obtaining chemical compounds and materials:
1) Create the desired compound from raw materialsvia one or more chemical reactions in a “reactor”
2) Isolate the compound where it exists in combinationwith other substances through a “separation process”
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Chemical processes500.101
Reactors
raw materials energy
energy
product + contaminants
byproducts
catalyst
catalyst Reactor
fermenters in a brewerypharmaceuticals reactor
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Chemical processes500.101
Separations
Based on differences between individual substances:
Boiling pointFreezing pointDensityVolatilitySurface TensionViscosityMolecular Complexity
SizeGeometryPolarization
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Chemical processes500.101
Separations
Based on differences in the presence of other materials
SolubilityChemical reactivity
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Chemical processes500.101
Separations: Garbage
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Chemical processes500.101
Garbage separation (cont.)
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Chemical processes500.101
Garbage separation (cont.)
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Chemical processes500.101
Separation processes-- “Unit operations”:
A. Evaporation—the removal of a valueless component from a mixture throughvaporization. Mixture is usually a nonvolatile solid or liquid and a volatileliquid. E.g., evaporation of sea-water to obtain salt
B. Distillation—extraction by vaporization and condensation. Depends ondifferent boiling points of components. E.g., distillation of wine to producebrandy.
C. Gas absorption1. gas absorption—the transfer of a soluble component of a gas mixture to
a liquid, e.g. bubbler in a fish tank to oxygenate the water.2. desorption or stripping—the transfer of a volatile component from a
liquid to a gas.
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Chemical processes500.101
D. Solvent extraction1. liquid-liquid extraction—requires two immiscible phases—an “extract”
layer and a “raffinate” layer. Solute partitions between two phases.2. washing—the removal of soluble substance and impurities
mechanically holding on to insoluble solids.3. precipitative extraction—a liquid solution can be split into a liquid-
liquid or liquid-solid by adding a third substance.4. leaching—the extraction of a component in solid phase by a liquid
solvent—e.g., making coffee.
E. Filtration—the process of removing a solid from a liquid/solid or gas/solidmixture.
F. Chromatography—the process of separating fluid components by capillarytransport.
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Chemical processes500.101
Bases for separation:
A. Differential boiling points, e.g., reducing alcohol content in wine-based sauceby cooking.
B. Differential freezing points, e.g., separating fat from broth by refrigerationC. Differential densities, e.g., separating heavier solids from liquids with
centrifugation.D. Differential anything. . .
Unit operations—more details:
A) The transfer of energy and/or material through physical (sometimes physical-chemical) means.
B) Involves multiple phases: gas-liquid, liquid-liquid, solid-gas, etc.C) Phases consist of mixtures of componentsD) Under the right conditions, one phase is enriched with a component as another
is depleted of that component.E) Component transfer
1) single stage2) multiple stage3) continuous
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Chemical processes500.101
Single-stage counter-current process A) Phases are brought into close contact B) Components redistribute between phases to equilibrium concentrations C) Phases are separated carrying new component concentrations D) Analysis based on mass balance
V1 V2
L0 L1
stage 1
L is a stream of one phase; V is a stream of another phase. Use subscripts to identify stage of origination (for multiple stage problems) Total mass balance (mass/time): L0 + V2 = L1 + V1 = M
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Chemical processes500.101
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 xAM
L0 xC0 + V2 yC2 = L1 xC1 + V1 yC1 = M xCM
(equation for B not necessary because xA + xB + xC = 1)
Suppose the following: V is oil (B) contaminated with dye (A). L iswater (C) which is used to extract the dye from the oil. When V comes incontact with L, the dye redistributes itself between the V and L. L and Vare immiscible (i.e., two distinct liquid phases).
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Chemical processes500.101
stage 1 V1 = oil + less dye V2 = oil + dye
L0 = water L1 = water + some dye
Oil flow = V(1-yA) = V′ = constant (conservation of oil)
Water flow = L(1-xA) = L′ = constant (conservation of water)
Then, for mass balance of the A component (dye)
1
1
1
1
2
2
0
0
1111 A
A
A
A
A
A
A
A
y
yV
x
xL
y
yV
x
xL
Mass of dye contained in oiland coming from stage 2.
Mass of dye contained in waterand leaving stage 1.
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Chemical processes500.101
Assume that the dye concentrations in the mixing stage comeinto equilibrium according to Henry’s Law that defines the relativeconcentration of dye in the oil and the water:
yA1 = H xA2 , where H depends on the substances A, B, C
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Chemical processes500.101
S p e c i f i c p r o b l e m : 1 0 0 k g / h r o f d y e - c o n t a m i n a t e d o i l ( 1 % b y w e i g h t ) i sm i x e d w i t h 1 0 0 k g / h r o f w a t e r t o r e d u c e t h e d y e c o n c e n t r a t i o n i n t h e o i l .W h a t i s t h e r e s u l t i n g d y e c o n c e n t r a t i o n i n o i l a f t e r p a s s i n g t h r o u g h t h em i x i n g s t a g e i f d y e e q u i l i b r i u m i s a t t a i n e d a n d H e n r y ’ s c o n s t a n t H = 4 ?
S o l ’ n :
L ’ = 1 0 0 k g / h r V ’ = 1 0 0 ( 1 - . 0 1 ) = 9 9 k g / h r
x A 0 = 0 ( n o d y e i n i n c o m i n g w a t e r )
y A 2 = . 0 1 ( i n i t i a l c o n t a m i n a t i o n i n o i l )
y A 1 = 4 x A 1 ( e q u i l i b r i u m c o n c e n t r a t i o n o f d y e b e t w e e n o i l a n d w a t e r )
1 0 00
1 09 9
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1 0 11 0 0
19 9
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1 1 0 02 5
1 2 59 9
10 0 81
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..
y
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yyA
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AA
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Chemical processes500.101
Single stage countercurrent centrifugal extractor(Rousselet-Robatel)
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Chemical processes500.101
Counter-current heat exchangers in nature
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Chemical processes500.101
Counter-current heat exchangersHow do they work?
limitedheat exchange
goodheat exchange
appendagebody
Tb-out
Tb-in
heat loss
exchanger body appendage
Tb-out
Tb-in
exchanger