The Petrochemicals

Industry

Petrochemicals from

C4-based Processes

ChE 313 Industrial Chemistry Lecture

Engr. May V. Tampus

Butadiene

• Chemical formula: C4H6

• Molar mass: 54.092

• Isomers:

– 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 • 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.

• Boiling point : – 4.411 °C

• Melting point: – 108.902 °C

• Vapor pressure: 8690 torr at 25°C

• Density of liquid : 0.6274 g/cm3(15 °C), 0.6211 g/cm3 (20o C), and 0.6194

g/cm3 (25o C)

• Enthalpy of vaporization at 25 °C: 20.88 kJ/mol

• Enthalpy of formation, gaseous, at 298 K, 0.1013 MPa:110.16 kJ/mol

• Entropy of formation, gaseous, at 298 K, 0.1013 MPa: 278.74 J mol–1 K–1

Chemical Properties of Butadiene

• 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

1. Production from Acetylene

2. Production from Ethanol

3. Dehydrogenation of Butane and Butene

4. Isolation of Butadiene from C4 Steam Cracker Fractions

Production Butadiene

Dehydrogenation of Butane and Butenes

• Reactions are endothermic

• Dehydrogenation reactions at 430oC

Butane 1-Butene + H2 ΔH = 131 kJ/mol

Butane cis-2-Butene + H2 ΔH = 118 kJ/mol

cis-2-Butene Butadiene + H2 ΔH = 126 kJ/mol

• Yield is limited by thermodynamics.

• Yield is increased by:

– decreasing the partial pressure of the reaction products

– raising the reaction temperature

• Undesirable reactions: Cracking, Isomerization, Polymerization

Dehydrogenation of Butane: Houdry CatadieneProcess

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

• 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.

• Pressure is about 34-103 kPa (5-15 psi).

• Highly selective

• 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 C4H6 + H2O

• Production methods: Oxo-D process and O-X-D process

Isolation of Butadiene from C4

Steam Cracker Fractions

• Butadiene cannot be separated from this C4 -hydrocarbon mixture by means of simpledistillation, because 1,3-butadiene and butaneform an azeotrope.

• Methods:

–Liquid-liquid Extraction (CAA-cuprous ammoniumacetate- Method)

–Extractive Distillation

BUTENES

• unsaturated olefinic hydrocarbons, C4H8, Mr 56.1080

• Four isomers:

• These isomers are usually coproduced as a mixture and are commonlyreferred to as the C4 fraction.

• The C4 fractions are usually obtained as by-products from petroleumrefinery and petrochemical complexes that crack petroleum fractions andnatural gas liquids.

"Butylenes", the older name for

"butenes", is still used today; 4 is

frequently referred to as

"isobutylene". The designation "n-

butenes" refers to mixtures of 1, 2,

and 3.

BUTENES

• colorless, flammable gases at roomtemperature and atmospheric pressure.

• completely miscible with alcohols, ethers, andhydrocarbons

• only slightly water soluble and water is onlyslightly butene soluble

• main reactions are acid-catalyzed additionreactions, isomerization, and polymerization

Isobutylene

• IUPAC name: 2-methylpropene

• Other names: Isobutene, γ-Butylene, 2-Methylpropylene

• At STP, a colorless flammable gas

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

1

4

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 productionmethods of isobutylene.

2. Write down the chemical reactions (if applicable) ineach of the production methods of isobutylene.

3. Identify the process conditions in each of theproduction methods of isobutylene.

4. Identify the catalyst used (if applicable) in each of theproduction methods of isobutylene.