Industrial chemistry
Synthetic Organic
Chemicals
Kazem.R.Abdollah
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1
Introduction
Synthetic organic chemicals are produced by the transformation
of carbonaceous feedstocks into functionalized molecules
through one or more chemical reactions. Such
transformations are accomplished at vast industrial scales and
the resulting products permeate every aspect of modern
society.
The molecules produced find use largely as monomers for
polymer synthesis of ubiquitous plastics, or as task-specific
ingredients for a myriad of applications as divergent as paint
leveling agents to food preservatives.
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• Although many different chemicals can be made from each of the
feedstocks, only a limited number of different types of chemistry have
found particular favor in large-scale commercial production of synthetic
organic chemicals. These include:
• (1) oxidation
• (2) carbonylation
• (3) hydroformylation
• (4) chlorination
• (5) condensation
• (6) hydration/hydrolysis
• (7) esterification
• (8) hydrogenation
• (9) dehydrogenation
• (10) sulfonation
• (11) ammonation/ammoxidation.
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Chemical Raw Materials and
Feedstocks
• Five major types of feedstocks:
1. Light olefins—ethylene and propylene
2. Aromatics—benzene, toluene, xylenes, or BTX
3. C4 hydrocarbons—butanes, butenes, butadiene
4. Kerosene derived C9-C17 paraffins
5. Synthesis gas—a mixture of carbon monoxide
and hydrogen
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Chemical raw material-feedstock-derivatives overview
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Light Olefins C2-C3
• Ethylene and propylene are by far the most
important building blocks of the
petrochemical industry.
Ethane
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Propane
Light olefins can be produced from a variety of raw
materials and methods:
1. Steam cracking (thermal pyrolysis) of hydrocarbon
raw materials ranging from LPG/NGL to naphthas and
gas oils
2. Methanol to olefins
3. Recovery from refinery gases and FCC (fluid catalytic
cracking) gases
4. Interconversion of butenes, ethylene, and propylene
5. Dehydrogenation of propane (propylene only)
6. Dehydration of bio-derived ethanol (ethylene only)
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1.Steam cracking
Steam cracking accounts for almost all of the ethylene
and about 60% of the propylene produced worldwide.
Hydrocarbon raw material
775–9500C
ethylene/ propylene
0.17–0.24 Mpa
In a short residence time tubular reactor/furnace
Steam water
The yield of ethylene vs. propylene is highly dependent on the:
hydrocarbon raw material used as well as the severity of conditions.
 Ethylene production is favored by use of light hydrocarbons and higher
temperature conditions.
 Major by-products are methane, hydrogen, butanes/butenes/butadiene,
pyrolysis gasoline (benzene, toluene, C8 aromatics), and heavy oils.
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2.Methanol to olefins
Methanol could be reacted over acidic zeolites at high
temperatures to produce primarily an aromatic-heavy gasoline as
well as some C2-C4 olefins.
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3.Recovery from refinery gases and FCC
(fluid catalytic cracking) gases
About a third of propylene is recovered from refinery
operations, such as FCC of heavy oils. FCC produces
primarily motor gasoline components, but also 5–9%
propylene, which can be recovered by fractionation.
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C6-C8 Aromatics: BTX (benzene, toluene, o-,m-,pxylenes)
The most important aromatics for chemical production
are benzene and p-xylene.
Globally BTX is produced primarily by catalytic reformer
operations (55–60%), and by recovery from pyrolysis
gasoline (40–45%).
Benzene
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Toluene
1. Hydrodealkylation involves the thermal or catalytic reaction
of alkylated aromatics (normally methyl aromatics) with
hydrogen to produce light alkanes (normally methane) and
benzene.
• temperatures stay below 5000C to prevent metal sintering
• pressures from 2.5 to 7.0 Mpa
• Common catalysts are Group VIII metals and metal oxides, e.g., chromium
oxides, Pt, Pt oxide, on alumina
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2.Transalkylation/disporportionation involves the migration of
methyl groups among aromatic rings in the presence of hydrogen.
For example two toluene molecules produce a mixture of xylene
isomers.
• The reaction proceeds over aluminosilicate or silicoaluminophosphate
zeolites (often containing noble metal (Pt) or rare earths)
• at 400–4700C
• pressures of 1.4–3 MPa
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3.Toluene methanation is a process to convert toluene to xylenes
that has been commercialized in the last decade to a limited
extent. Methanol is reacted with excess toluene at high
temperature over acidic or zeolite catalysts to produce xylene
isomers and water.
Toluene is distilled and recycled, while the product mixture of xylene isomers must be
separated and isomerized to maximize p-xylene. Shape selective, para-enhancing
zeolites are also used here.
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Synthesis Gas
• Synthesis gas, or “syngas,” is a mixture of hydrogen
and carbon monoxide produced by the partial
oxidation of carbonaceous feedstocks.
• Syngas production involves the breaking of C–C and
C–H bonds of the raw material molecules at high
temperature via reaction with water (steam
reforming), oxygen (partial oxidation), or carbon
dioxide (carbon dioxide reforming), or combinations
therein (autothermal reforming or gasification).
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• The primary reactions in steam methane reforming (SMR),
stream hydrocarbon reforming (SHR), and carbon dioxide
reforming (CMR—not yet commercial) are endothermic, with
only the water-gas shift reaction providing heat.
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• Syngas can also be produced by partial oxidation,
typically with high purity oxygen (to avoid dilution with
large quantities of hard to separate nitrogen).
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• Gasification of solid carbonaceous raw materials
adds additional endothermic reactions of solid
carbon with steam and exothermic reactions with
oxygen.
• Methanation may also occur under appropriate
conditions.
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