CHE 448 Chemical Engineering Design

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CHE 448 Chemical Engineering Design
Spring 2006
Class Nr 9 Tuesday February 7
Ice Wall Glacier in lago Argentino
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February 7 milestones

• Olive/Vaughn/Smith GPE for MMA?
• Moore/Slade/Smith Market for AceticAc?
• Tingle/Birdwell/Frisby Biosep. Info?
• Agbenoto/Kean/BruntonDeadline is today! Styrene
  synthesis processes
• Butler/Matheus/Rogers Chemical react.?

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What are raw materials and specifications

• Platts Guide Platts assesses ethylene in
  southeast asia, ..the US Gulf and Mexico. The US
  assessment if for product with a minimum purity
  of 99

OXY Chemical Products Chlorine is available as a
liquid
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Safety, toxicity, environmental impact concerns?

• Chlorine
• NFPA (0-4)Health3, React.1
• HMIS (0-4)Health 3, React. 1
• May cause burns to respiratory tract, skin and
  eyes. May cause chemical pneumonia. May cause
  permanent eye damage. May be lethal in high
  concentrations.
• Unique reactive chemical properties are used in
  the manufacturing of thousand of everyday
  products.
• Ethylene
• Extremely flammable
• In high concentrations may cause asphyxiation.
• In low concentrations may cause narcotic effects.

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Safety, toxicity, environmental impact concerns?

• Dichloroethane
• Probable human carcinogen
• Causes liver damage
• Mutagen, toxic
• Vinyl Chloride
• Extremely flammable
• Known human carcinogen
• Inhalation Humans Lowest Published Toxic
  Concentration 500 ppm

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What is desired production rate and purity of
products?

• What are the uses for vinyl chloride?
• Vinyl chloride is used primarily for production
  of polyvinyl chloride (PVC) resins. In 1996, 22
  million tons of PVC were produced worldwide, of
  which 5.2 million tons were made in Western
  Europe. Western European production increased by
  2 in 1996, compared with rises of 4 in North
  America and 9.5 in Asia. PVC accounts for 99 of
  total worldwide vinyl chloride use, with only
  300,000 tonnes used in non-PVC applications.
• What are the specs for the different
  applications?
• Is there any advantages of further purification
  of products?

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Vinyl Chloride ProcessChlorination followed by
pyrolisis.
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Vinyl Chloride Process Chlorination reactor
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Vinyl Chloride Pirolysis Reactor
How can we cool a stream instantly? What is the
composition of the liquid?
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Chlorination kinetics
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Heuristic 1Select raw materials and chemical
reactions to avoid, or reduce, the handling and
storage of hazardous and toxic chemicals

• Chlorine and Dichloroethane are hazardous.
• To cool down the reactor we need to evaporate a
  large amount of the DChl-HCl mixture. dHvap 30
  kJ/mol.
• What is the size of the reactor if we need to
  recirculate such a large amount of mixture?
• No intermediate storage

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Material Balance
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Heuristic 2 Use an excess of one chemical
reactant in a reaction operation to consume
completely a valuable, toxic, or hazardous
chemical reactant.

• Use an excess of Ethylene to eliminate all
  Chlorine in the reactor effluent (assuming Cl2 is
  more hazardous)

Can we really assure full conversion of Cl2 ?
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Material balance using 10 excess of ethylene
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Gross Economic Potential revised
Costs ethylene 18 c/lb , MW 28, 5.04
/mol Chlorine 11 c/lb , MW 71, 7.81
/mol Hydr. Chlor 18 c/lb, MW 36, 6.48
/mol Vinyl Chlor. 22 c/lb, MW 62.5, 13.75 /mol
Gross economic potential of process assuming 100
conversion 13.756.48-1.02(7.815.04) 7.12
/mol 11.52 c/lb
Gross economic potential of process with 4
excess ethylene 13.756.48-7.81-(1.15.04)
6.88 /mol 11.13 c/lb
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Questions about recycle, purge, and separations

• Should we purify the feed streams before they
  enter the process?
• Should we use a gas recycle and purge streams?
• Should we remove or recycle a reversible
  by-product?
• Should we not bother to recover and recycle some
  reactants?
• What economic trade-offs are associated with
  these variables?

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Heuristic 3When nearly pure products are
required, eliminate inert species before the
reaction operations when the separations are
easily accomplished and when the catalyst is
adversely affected by the inert, but not when a
large exothermic heat of reaction must be removed.
Would it be necessary to remove impurities from
Chlorine and ethylene?
Ethylene has 0.002 molar fraction of acetylene
that will readily convert to Vinyl Chloride in
the presence of HCl.
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Heuristic 4 Should we use a gas recycle and
purge streams?

• Heuristic 4Introduce purge streams to provide
  exists for species that enter the process as
  impurities in the feed or are formed in
  irreversible side reactions, when these species
  are in trace quantities and/or are difficult to
  separate from the other chemicals. Lighter
  species leave in vapor purge streams, and heavier
  species exit in liquid purge streams.

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Heuristic 5 Are we allowed to purge chlorine?

• Heuristic 5 Do not purge valuable species or
  species that are toxic and hazardous, even in
  small concentrations. Add separators to recover
  valuable species. Add reactors to eliminate, if
  possible, toxic and hazardous species.

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Are we venting a valuable reactant/product?
What is the composition of stream 7 in kmol/h?
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Minimize losses of valuable reactants
Use a condenser with cooling water plus a small
chiller with propane as coolant. We may have to
use a Cl scavenger to reduce emissions.
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Heuristic 6 Byproducts

• Byproducts that are produced in reversible
  reactions, in small quantities, are usually not
  recovered in separators or purged. Instead they
  are usually recycled to extinction.
• Should we remove or recycle a reversible
  by-product? Should we not bother to recover and
  recycle some reactants?