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Compounds from C2 compounds
(Ethylene and Acetylene)
prepared by
Dr. Deepshikha Datta
Sr Assistant Professor
Dept. of Chemical Engineering
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These starting materials are obtained from the following sources:
 Ethylene from
i) fermentation alcohol,
ii) refinery off-gases, and
iii) hydrocarbon-steam cracking
 Acetylene from
i) calcium carbide
ii) partial oxidation of petroleum fractions
iii) hydrocarbon-steam cracking
• Ethylene and Acetylene via Steam Cracking of Hydrocarbons
The steam cracking process produces ethylene/acetylene in ratio
of 0.3 to 2.0 depending on operating conditions. Propylene,
butadiene and aromatics are obtained in lesser quantities.
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Pertinent Properties of Ethane (CH2=CH2)
Mol. Wt.
28.03
M. P.
-169.40C
B. P.
-103.80C
Density
0.5699 @ -1030C
Explosive limit
Lower
3.0 vol. % in air, 2.9% in O2
29 vol. % in air, 79% in O2
Upper
Consumption Pattern
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Use in India will be predominantly for polyethylene, whereas in the U.S a more
diverse end structure has been developed.
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Possible Methods of Production
 Steam pyrolysis (cracking) of petroleum from LPG and naphtha feedstocks
 Thermal pyrolysis of ethane and/or propane-not flexible
 Dehydration of ethanol-used in India, but not competitive for large-scale
requirements in the long term
Steam Cracking of Petroleum Hydrocarbons
Quantitative Requirements
a) Basis : 1 ton of ethylene
Co-products : acetylene, propylene, butylenes, butadiene, aromatics such as
benzene, toluene, xylene heavy oil residues
a) Plant capacities : 100-600 tons/day of ethylene with current trends to much
larger units
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Process Description
The process to be detailed here is high temperature thermal reforming using
ethane, propane, butane and/or liquid naphtha. Superheated steam is mixed with
the hydrocarbon and fed through the heated coils of a pyrolysis furnace. The C2C2 feed is pyrolyzed in a separate furnace because different residence timetemperature conditions are required. The pyrolyzed gases are quenched in a
waste heat steam boiler and the scrubbed with gas oil to remove solids and
heavy hydrocarbons before sending to compressors to boost pressure to 35
atms
The compression station may also handle refinery off-gases which can be
separated in the same system. Flash vaporization removes the C1-C2 fractions
which are caustic-scrubbed to remove CO2, dried with activated alumina, and
the separated into acetylene and ethylene by a combination of absorption,
extraction, and fractionation steps. Ethane is recycled for pyrolysis and the CH4,
CO, and H2 can be further processed to obtain synthesis gas or used for fuel.
The liquid fraction from the flash chamber (C3 and higher) is split by
fractionation into a number of products. Extractive distillation is required to
separate butane-butylene and butadiene because of the close boiling point range
of the three compounds under pressure.
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Major Engineering Problems:
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Choice of process
There are numerous process modifications possible in pyrolysis of
hydrocarbons. These can be categorized as:
a)



Feed type
CH4 or natural gas-gives mainly CO, H2 and C2H2
C2, C3 – gives CO, H2 and C2H2 and C2H4
C4 and higher-gives a spectrum of products but mainly
controlled for C2H2 and C2H4
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a)







a)



Choice of pyrolysis agent
Heat only, non-catalytic –original process no longer attractive
Heat + catalyst –used in dehydrogenation of butylenes to butadiene
Heat + steam, non-catalytic –thermal reforming, also called steam cracking
Heat + steam, catalyst-catalyst reforming, used for synthesis gas preparation
Oxygen, non-catalyst-partial combustion process, used for synthesis gas and
acetylene production
Oxygen + steam, non-catalyst-modified partial combustion to give higher
yields of C2 fraction, also called steam cracking
Oxygen + steam, catalyst – oxydehydrogenation for butadiene, etc.
Choice of pyrolysis equipment
Tubular, indirect fired – used for catalyst reactions
Coiled pipe furnace- used for non-catalyst reactions in the absence of oxygen
Combustion-type burner – used for reaction where oxygen is introduced
The design of pyrolysis equipment must provide a balance between temperature,
contact time, and quench time for optimum cracking to the correct product ratio
and yield without carbon formation
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Ethanol (Synthetic)
Synthetic ethanol is made by the hydration of ethylene over a
phosphoric acid-on-celite catalyst and accounts for 18% of all
ethanol. The predominant method of ethanol manufacture, at one
time, was by fermentation of sugars: this method went out of use
in the 1930’s. However, corn fermentation is now a source of 82%
of all ethanol and is used for gasohol, a 10% alcohol: 90%
gasoline blend used for automobile fuel.
Industrial uses for ethanol are shared by synthetic and
fermentation alcohol in a 7:3 ratio and include solvents (59%) and
chemical intermediates (41%)
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Ethanol production from ethylene
In the petrochemical industry, ethanol is produced via direct and indirect
hydration of ethylene. Catalytic direct ethylene hydration was first introduced
by Shell in 1947. In this process, ethanol is produced by a reversible
exothermic reaction between ethylene and water vapor. The process consists
of three different steps including reaction, recovery and purification. The
ethylene is mixed with steam with a molar ratio of 0.6 at 250–300 °C and
70–80 bar and then passes over an acidic catalyst in a fixed bed reactor. The
water‐to‐ethylene ratio should be less than one to avoid catalyst losses. The
ethylene conversion is about 4–25 % and it is recycled. The ethanol selectivity
is 98.5 mol % . Phosphoric (V) acid coated onto a solid silicon dioxide has
been used mainly as the catalyst. Several impregnated metal phosphates
(metal: Ge, Zr, Ti, and Sn) were also studied, showing slightly higher
conversions compared with phosphoric acid on silica.
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Ethanol production from ethylene:
A simple process diagram of direct hydration of ethylene is presented in
Figure. The feed stream (ethylene and water) preheated by effluent is
heated up to 300 °C in the furnace. Thereafter, it enters into a packed bed
catalytic reactor at 70 bar. Phosphoric acid is used as catalyst and
conversion is 4–25 %. Acetaldehyde is produced as a by‐product, which can
either be sold or further hydrogenated to produce ethanol. The unreacted
reactants are separated from the outlet vapor mixture of the reactor in a high
pressure separator and then scrubbed with water to dissolve the ethanol.
The recycled vapor from the scrubber contains ethylene, and the molar ratio
of water to ethylene is maintained as 0.6:1. The bottom streams of the
scrubber and the separator are then fed to the hydrogenator, where
acetaldehyde is converted into ethanol on a nickel‐packed catalyst. In the
acetaldehyde separator column, the unreacted acetaldehyde is removed
and recycled to the hydrogenator, and the bottom stream is fed to the light
and the heavy (purifier) columns to increase the ethanol concentration 6. It
should be noted that the ethanol‐water mixture forms an azeotrope mixture
which needs special distillation techniques which eventually increase the
costs of the plant
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Ethylene Dichloride (1,2-Dichloroethane)
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This compound is of interest as it is one of the intermediates for
vinyl chloride monomer which polymerizes to polyvinyl chloride
(PVC)
1. Pertinent Properties of Ethylene Dichloride (ClCH2-CH2Cl)
Mol. Wt.
M. P.
B. P.
Density
Flash point
Ignition temperature
Explosive limit
Maximum toxicity limit
Lower
Upper
98.97
-35.30C
-83.70C
1.257 @ 200C
15.50C
4120C
6.2 vol. %
15.9 vol. %
75-100 ppm
End Use : Vinyl chloride, Antiknock agent, Solvent
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Methods of Production
Classification of Processes
•Reaction of chlorine with ethylene in liquid or vapor phase
•By-product of direct chlorination of ethane to ethyl chloride
•By-product of chlorinated hydrocarbons
Ethylene + Chlorine Reaction
Quantitative requirements
•Basis : 1 ton of C2H4Cl2 (95% yield)
Ethylene : 0.30 ton
Chlorine : 0.75 ton
Ethylene dibromide catalyst – trace
Cooling water : 48 tons
Co-products : HCl, propylene chloride, polychloethanes
•Plant capacity : 30-150 tons/day
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Process description:
Ethylene (with or without C2H6, Ch4, and H2 diluent) is mixed with chlorine and
bubbled through a liquid phase reactor. Ethylene dichloride product serves as the
reacting medium. Heat of reaction is controlled by external heat exchange and
recycle, or by coil or jacket heat transfer, to hold the reaction at 45-500C with a
pressure of 1.5-2 atms. Traces of ferric chloride or ethylene dibromide as catalyst
gives 90-95% yield with little dimer formation.
The gaseous products are cooled in two stages to strip the acid gas of ethylene
dichloride. The liquid product is alkali washed and fractionated.
Major Engineering Problems:
Process alternative
Operating the reactor above 850C provides for complete gaseous reaction. A solid
catalyst such as aluminium chloride or ferric chloride is packed in a tubular
reaction for this process variation, thus eliminating the need for recycling
ethylene dibromide. Heat control is more difficult for this modification
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Vinyl Chloride
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Pertinent Properties of Vinyl Chloride (CH2=CHCl)
Mol. Wt.
M. P.
B. P.
Density
Solubility
Flash point
Explosive limit
62.50
-153.80C
-13.810C
0.983 @ 200C
In CCl4, (C2H5)2o, and alcohols; slightly
soluble in water
770C
Lower 5 vol. %
Upper
Maximum toxicity limit
Grades
23 vol. %
500 ppm
Polymer (99% pure + inhibitors)
Consumption Pattern
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Vinyl chloride monomer is strictly an intermediate in polyvinyl
chloride production. Thus it is only in “captive production”
Methods of Production
Classification of Processes
 Ethylene dichloride thermal pyrolysis
 Acetylene-HCl reaction
 Ethylene dichloride-caustic reaction
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Ethylene Dichloride Thermal Pyrolysis
Quantitative requirements
•Basis : 1 ton of vinyl chloride (99.5% pure, 95% yield)
Ethylene dichloride
: 1.65 tons
Heating steam
: 2.0 tons
Cooling water
: 30 tons
Electricity
: 1.5 KWH
Fuel
: 5.7 Nm3
Co-product
: 0.65 ton HCl
•Plant capacities
: 30-100 tons/day
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Process Description:
Ethylene dichloride (EDC) vapour at 4 atms. is dried by silica gel
and sent to a stainless steel tubular cracking furnace. This is
externally flue gas fired and controlled at 480-5200C. The contact
surface catalyst within the tubes is pumice or charcoal. The
conversion per pass is around 50% and the ultimate yield is 9596%. Spray quenching with cold EDC prevents back-reaction.
Uncondensed gases are sent to a surface heat exchanger to remove
the balance of EDC and vinyl chloride.
The non-condensable containing HCl are either sent to the
acetylene-HCl process in an adjacent process area or water
scrubbed to recover HCl as muriatic acid.
The condensate is fractionated with the EDC bottoms returned for
recycle and vinyl chloride monomer taken from overhead,
stabilized and sent to storage.
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Major Engineering Problems:
Carbon formation – this occurs steadily until reaction has too
high a pressure drop, thus causing shut down and cleaning
periodically. Increasing conversion beyond 50% by longer
residence time or higher temperature increases carbon
formation and promotes polymerization of monomer
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Acetylene-HCl Reaction
Quantitative requirements
•Basis : 1 ton of vinyl chloride (99.5% pure, 97% yield)
Acetylene : 0.462 ton
Hydrogen chloride : 0.60 ton
•Plant capacities : 30-100 tons/day
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Process Description
Acetylene and dry HCl in 5-10% molar excess are vapur
blended by jet mixing in a pipe and passed through a tubular
catalyst reactor containing carbon pellets impregnated with
HgCl2. The temperature is maintained at 1600C and is gradually
raised to 2150C as the catalyst deteriorates. The effluent gases
contain vinyl chloride which is separated from unreacted
acetylene plus hydrogen chloride, these unreacted materials
being recycled.
Major Engineering Problems:
 Catalyst deterioration and replacement
 Excessive corrosion unless system is dry
 Avoiding polymerization of monomer
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Vinyl Acetate Production by Wacker process
Acetylene in liquid phase is reacted with glacial acetic acid in presence
of mercury sulfate at 60ᵒC. Alternatively in vapour phase, it is reacted
with acetic acid and at 210ᵒC over a catalyst zinc or cadmium acetate
deposited on charcoal. The exit gases are cooled at 0ᵒC, where
acetylene is separated, to be recycled. The liquid is fractionated to
separate acetate from acid. Mercuric salts did not yield high amount of
acetate, but the side product ethylidine diacetate was an important
product. Mercuric orthophosphate was found to be a superior catalyst
in this reaction. With mercuric salt of acetyl sulfuric acid, operating
below 40ᵒC, the conversion to acetate was found to be very high,
increase of temperature resulted in more of the side product.
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Vinyl Acetate Production
Ethylene Oxide
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Pertinent Properties of Ethylene Oxide
Mol. Wt.
M. P.
B. P.
Density
Flash point
Ignition temperature
Explosive limit
Lower
44.05
-111.70C
10.70C
0.896 @ 00C
-150C
4300C
3 vol. % in air
80 vol. % in air
Upper
Maximum toxicity limit
25-100 ppm
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Consumption Pattern
Principal outlet in the U.S. is for production of ethylene glycol, a
permanent antifreeze for automobile radiators. India will have very
little use for this derivative, but instead will find ethylene glycol
polyesters, non-ionic detergents, and ethanolamines useful
products derived from ethylene oxide.
Methods of Production
Classification of Processes
 Direct oxidation of ethylene
 Chlorohydrination of ethylene
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Direct oxidation of ethylene
Quantitative requirements
•Basis : 1 ton of ethylene oxide (99% purity, 70% yield)
Ethylene
: 0.92 ton
Air
: 9.0 tons
Silver
: 0.3 kg in fixed bed
: 0.7 kg in fluidized bed
Ethylene dichloride suppressor : 10-15 kg
Electricity
: 1,500 KWH
Steam
: 0.1 ton
Water
: 180 tons
•Plant capacities : 30-300 tons/day
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Process Description:
Ethylene of 95-98% purity and air are compressed separately, mixed together
giving 3-10% C2H4 volume concentration and passed over a catalyst of silver
oxide on a porous inert carrier such as alumina. A side reaction suppressing agent
such as ethylene dichloride is added to the feed to reduce the competitive
oxidation reaction to CO2 + H2O
The reaction is highly exothermic and is best carried out in a fixed bed tubular
reactor in which heat transfer salt or Dowtherm is pumped around the tube within
the shell to maintain a 250-3000C temperature. Heat is recovered in a waste-heat
steam boiler. A short residence time of 1 sec in plug flow is the design with an
ultimate yield of 60-70%.
The effluent gases from the reactor are water-washed under pressure. The
absorbed ethylene oxide is sent to a packed bed desorber-fractionator tower and
taken overhead. It still contains a large amount of water vapour plus some
impurities. This stream is compressed to 4-5 atms., and fractionated twice to
remove light ends, water, and high boiling polymers
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