The Petr Petrochemic ochemicals als Industry Petrochemicals from C4-based Processes ChE 313 Industria Industriall Chemistry Chemistry Lectur Lecture e Engr. May V. Tampus
Butadiene •
Chemical formula: C 4H6
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Molar mass: 54.092
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Isomers: –
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CH2 =CH –CH=CH2 1,3-Butadiene (economically the most important unsaturated C4-hydrocarbon) CH2 =C=CH –CH3 1,2-Butadiene (thermodynamically less stable thus has no technical importance)
1,3 Butadiene –
a commodity product of the petrochemical industry with a 1989 U.S. production of 3.1 billion pounds
Physical Properties of Butadiene •
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Noncorrosive, colorless, flammable gas at room temperature and atmospheric pressure. Has a mildly aromatic odor Sparingly soluble in water, slightly soluble in methanol and ethanol, and soluble in organic solvents like diethyl ether, benzene, and carbon tetrachloride.
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Boiling point : – 4.411 °C
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Melting point: – 108.902 °C
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Vapor pressure: 8690 torr at 25°C
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Density of liquid : 0.6274 g/cm3(15 °C), 0.6211 g/cm 3 (20o C), and 0.6194 g/cm3 (25o C)
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Enthalpy of vaporization at 25 °C: 20.88 kJ/mol
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Enthalpy of formation, gaseous, at 298 K, 0.1013 MPa:110.16 kJ/mol
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Entropy of formation, gaseous, at 298 K, 0.1013 MPa: 278.74 J mol–1 K–1
Chemical Properties of Butadiene •
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the simplest conjugated diene has two conjugated double bonds and, therefore, can take part in numerous reactions, which include 1,2- and 1,4-additions with itself (polymerization) and with other reagents, linear dimerization and trimerization, and ring formation the conjugation of the double bonds makes it 15 kJ/mole (3.6 kcal/mol) more thermodynamically stable than a molecule with two isolated single bonds The s-trans isomer, often called the trans form, is more stable than the s-cis form at room temperature. Although there is a 20 kJ/mole (4.8 kcal/mol) rotational barrier, rapid equilibrium allows reactions to take place with either the s-cis or s-trans form.
Commercial Uses of Butadiene
Production Butadiene 1. Production from Acetylene 2. Production from Ethanol 3. Dehydrogenation of Butane and Butene 4. Isolation of Butadiene from C4 Steam Cracker Fractions
Dehydrogenation of Butane and Butenes •
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Reactions are endothermic
Dehydrogenation reactions at 430oC Butane 1-Butene + H2 Butane
cis-2-Butene + H 2
cis-2-Butene
Butadiene + H 2
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Yield is limited by thermodynamics.
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Yield is increased by:
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ΔH = 131 kJ/mol ΔH = 118 kJ/mol ΔH = 126 kJ/mol
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decreasing the partial pressure of the reaction products
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raising the reaction temperature
Undesirable reactions: Cracking, Isomerization, Polymerization
Dehydrogenation of Butane: Houdry Catadiene Process Best known one-step dehydrogenation adiabatic process Makes
use of several packed bed reactors, arranged parallel to each other, and operated alternatingly
Catalyst:
Aluminum oxide mixed with approximately 20 % chromium oxide
Cycle
life of the catalyst is about 10 minutes because of coke buildup
Usually
carried out 600 – 700 °C and 10 – 25 kPa
Thermodynamics
limits the conversion to about 30-40% and the ultimate yield is 60-65 wt %
Oxydehydrogenation of n-Butenes •
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Conversion is no longer limited by thermodynamics because of the oxidation of hydrogen to water Reaction temperature is below about 600°C to minimize over oxidation.
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Pressure is about 34-103 kPa (5-15 psi).
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Highly selective
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Exothermic oxidation of hydrogen partially covers the heat requirements of the endothermic dehydrogenation reaction and, in addition, the oxygen, together with steam added during the reaction, reduces the coke deposits on the catalyst. Catalyst: bed of tin, bismuth, and boron C4H8 + 1/2 O2
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C4H6 + H2O
Production methods: Oxo-D process and O-X-D process
Isolation of Butadiene from C4 Steam Cracker Fractions •
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Butadiene cannot be separated from this C4 hydrocarbon mixture by means of simple distillation, because 1,3-butadiene and butane form an azeotrope.
Methods: Liquid-liquid Extraction (CAA-cuprous ammonium acetate- Method) Extractive Distillation –
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BUTENES •
unsaturated olefinic hydrocarbons, C4H8, Mr 56.1080
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"Butylenes", the older name "butenes", is still used today; 4 frequently referred to "isobutylene". The designation
for is as "n-
butenes" refers to mixtures of 1, 2, and 3. •
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These isomers are usually coproduced as a mixture and are commonly referred to as the C4 fraction. The C4 fractions are usually obtained as by-products from petroleum refinery and petrochemical complexes that crack petroleum fractions and natural gas liquids.
BUTENES •
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colorless, flammable gases at room temperature and atmospheric pressure. completely miscible with alcohols, ethers, and hydrocarbons only slightly water soluble and water is only slightly butene soluble main reactions are acid-catalyzed addition reactions, isomerization, and polymerization
Isobutylene •
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IUPAC name: 2-methylpropene Other names: Isobutene, Methylpropylene
γ-Butylene,
At STP, a colorless flammable gas
2-
Properties of Isobutylene Molecular formula
C4H8
Molar mass
56.11 g mol−1
Appearance
Colorless gas
Density
0.5879 g/cm3, liquid
Melting point
−140.3 ºC
Boiling point
-6.9 °C, 266 K, 20 °F
Solubility in water
Insoluble
4 1
0
Industrial Production of Isobutylene: 1. Catalytic or Thermal cracking 2. Steam cracking 3. Catalytic Dehydrogenation of Isobutane
4. Catalytic dehydrogenation of n-butane
Group Assignment INSTRUCTIONS: Write assignment on a short bondpaper. Submit it not later than August 8, MON, 5:00 PM. 1. Identify the raw materials in each of the production methods of isobutylene. 2. Write down the chemical reactions (if applicable) in each of the production methods of isobutylene. 3. Identify the process conditions in each of the production methods of isobutylene. 4. Identify the catalyst used (if applicable) in each of the production methods of isobutylene.
