CHM 585 / 490

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CHM 585 / 490

• Chapter 4

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Chapter 4

• Benzene / Toluene / Xylene
• Terephthalic Acid
• Cumene
• Phenol / Acetone / Bisphenol A

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BTX

• Benzene / Toluene / Xylene
• Predominantly ( about 90) from oil
• From reformate gasoline and pyrolysis gasoline
• BTX Content
• Reformate 3/13/18
• Pyrolysis gasoline 40/20/5

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Reformate Gasoline

• Distillation of crude oil gives low octane
  fractions which must be reformed before using
  as gasoline.
• The fractions are mainly branched and unbranched
  alkanes and cycloalkanes
• Reforming involves heating at 500ºC with acidic
  isomerization catalysts (e.g. Al2O3. SiO2) and Pt
  followed by distillation

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Pyrolysis gasoline

• From the cracking of naptha for the production of
  ethylene, propylene, and other olefins.

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Isolation of Aromatics from Reformate and
Pyrolysis Gas

• Problems with fractional distillation
• Cyclohexane, n-heptane, and other alkanes form
  azeotropes with benzene and toluene
• Minor difference between boiling points of the C8
  components. e.g.
• Ethylbenzene 136.2 ºC p-xylene 138.3 ºC
• m-xylene 139.1 ºC o-xylene 144.4 ºC
• Separation requires special processes

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Separation Techniques

• Azeotropic distillation
• Extractive distillation
• Liquid-liquid extraction
• Crystallization
• Adsorption

Lets review azeotropes before continuing
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Fractional Distillation

• Begin at a1 and heat to T2.
• a2 is the liquid composition.
• a2 is the vapor composition.
• Vapor is richer in A than the liquid.
• Cool the vapor until condenses at T3.
• a3 is the liquid composition.
• a3 is the vapor composition.
• Vapor is even richer in A
• Repeat until pure A is obtained.

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Fractionating Column and Efficiency

• The number of theoretical plates is the number of
  effective vaporization and condensation steps
  required to achieve a condensation of given
  composition from a given distillate.

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Azeotropes

• In some real systems, the temperature /
  composition curve is far from ideal. A maximum
  or minimum in the curve is possible this is an
  azeotrope.
• At the azeotrope, the liquid and vapor have the
  same composition

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Low boiling azeotrope
High boiling azeotrope

• Makes physical separation of the two components
  impossible.

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Distillation of Ethanol

• Azeotrope is around 95 ethanol.
• .

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Impossible to distill ethanol to greater than 95.
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Azeotropic Distillation to Isolate Aromatics

• Best when high aromatic content
• The addition of strongly polar agents (amines,
  alcohols, ketones, water) facilitates the removal
  of alkanes and cycloalkanes as lower boiling
  azeotropes
• For example, add acetone to remove nonaromatics
  from the benzene fraction and then extract the
  acetone from the benzene with water.

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Extractive Distillation

• An additive is used to increase the differences
  in boiling points
• For example, add NMP
• (N-methylpyrrolidone)
• This increases the boiling point of the aromatics
  by complexation of the ? electrons in the
  aromatic ring with the NMP and therefore
  facilitates separation

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Liquid-liquid extraction

• Same principle as the separatory funnel, but
  continuous. Based upon countercurrent flow.
• The mixture is added to the middle of a column.
  The extraction liquid is added to the top. The
  non aromatics leave the column at the top and the
  aromatics with solvent exits from the lower part
  of the column
• Most extraction processes provide a mixing zone
  followed by a settling zone.  

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Crystallization

• Mainly to separate xylene isomers
• p xylene can be separated from a mixture by
  cooling to -20 ºC to -75ºC.

Melting point
p-xylene 13.3
o-xylene -25.2
m-xylene -47.9
ethylbenzene -95.0
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Adsorption

• Depends upon selective adsorption on a column,
  followed by desorption
• Molecular sieves zeolites alumino-silicates
  having different pore size
• UOP process involves selective adsorption of
  p-xylene ( from a C8 stream) followed by
  desorption

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p-Xylene

• 7 billion pounds
• BP-Amoco the biggest with 4.6 billion pounds of
  U.S. capacity
• Virtually all goes to production of terephthalic
  acid and dimethyl terephthalate

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Air oxidation. Common catalysts are CoBr2,
MoBr2 or HBr
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By esterification with methanol.
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TA DMT

• Dupont Cape Fear plant makes terephthalic acid (
  sold to Alpek, a Mexican petrochemicals group)
• Kosa ( Wilmington plant) makes terephthalic acid
  and dimethyl terephthalate
• Kosa makes about 1.5 billion pounds per year of
  dimethylterephthalate largest in North America

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Cumene
8 billion pounds used in U.S. Essentially all
used for phenol production
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Cumene Capacity (million pounds) 8.7 Billion total

• Chevron Port Arthur, Tex. 1,000
• Citgo Petroleum, Corpus Christi, Tex. 1,100
• Coastal Eagle Point, Westville, N.J. 140
• Georgia Gulf, Pasadena, Tex. 1,500
• JLM Chemicals, Blue Island, Ill. 145
• Koch Petroleum, Corpus Christi, Tex. 1,500
• Marathon Ashland, Catlettsburg, Ky. 800
• Shell Chemical, Deer Park, Tex. 1,100
• Sun, Philadelphia, Pa. 1,200

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Phenol from Cumene
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Sunoco Phenol PlantHaverhill, Ohio

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Kellogg Phenol Plants
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Phenol Uses

• 41 Bisphenol-A
• 28 phenolic resins
• 13 caprolactam

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Major Phenol Producers

• Sun, Shell, Dow, GE, and Georgia Gulf are major
  producers
• GE plant at 700 million pounds
• JLM has a 95 million pound plant in Illinois
  (same JLM that operates shipping in Wilmington)
• Current demand about 5 billion pounds
• 0.62 pounds acetone per pound phenol

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Bisphenol-A
Cumene gives 1 mole of phenol per mole of
acetone BPA uses 2 moles of phenol per mole of
acetone Typically, phenol is in demand and
acetone is a glut on the market
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On to bigger things!