3. DEFINITION
Synthesis gas is generally considered to be a
variable mixture of CO and H2 for the synthesis of
organic compounds.
There are cases where CO is not needed and
these specific cases are so labelled :
Ammonia synthesis gas ( 3H2 + 1N2 )
Hydrogenation of coal ( H2 only)
NOTE that all synthesis gases contain hydrogen.
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4. CONTENTS
RAW MATERIALS
CHEMICAL REACTIONS
PROPERTIES
FLOW DIAGRAM
PROCESS DESCRIPTION
ENGINEERING PROBLEMS
USES OF SYN GAS
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5. RAW MATERIALS
• REFINERY NAPHTHA OR OFF-GASES
• AIR (OPTIONAL)
• STEAM
• SMALL MAKE UP QUANTITIES OF NICKEL
AND PROMOTED IRON OXIDE CATALYST,
ETHANOLAMINES, AND AMMONICAL
CUPROUS FORMATE
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6. REACTIONS
Reforming reactions
(a) Cn
H2n+2 + nH2O nCO + (2n+1)H2
Ho
= 52 Kcal for n=1
= 238 Kcal for n=6
(b) CO + 3H2 CH4 + H2O
Ho
= -52 Kcal
Water gas shift reaction
(c) CO + 3H2 CO2 + H2 Ho
= -9.806 Kcal
7. Synthesis Gas
(various mixtures of CO/H2)
Some ( about 16%) made from coal,
but most from natural gas and oil in
the presence of steam.
-CH2- + 0.5 O2 CO + H2
∆H = -22 kcal/mol
-CH2- + H2O CO + 2H2
∆H = + 36 kcal/mol
CO/H2 ratio adjusted by varying the
amount of O2 and H2O
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8. PROPERTIES
Physical State: Gas
Appearance: Transparent colourless
pH: Not currently available.
Solubility in Water (by weight): Not determined.
Odour: Odourless
Boiling Point (760 mmHg): Not determined.
Freezing Point: Not determined.
Specific Gravity (H2O = 1): Not determined.
Vapour Pressure at 20°C: Not determined.
Vapour Density (air = 1): 0.45 - 0.57
Melting Point: Not applicable.
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10. PROCESS DESCRIPTION
The hydrocarbon feed is mixed with steam and fed to
the reforming furnace. The nickel catalyst is packed
in vertical tubes of 3-4 inches in diameter and about
20-25 feet long. Heat for the endothermic reaction is
supplied by combustion gas. The reaction
temperature must be maintained in the range of 700-
1000o
C . The process takes three alternates
depending on the end products.
For CO-H2 Synthesis Gas
The effluent reformer gas is cooled to 35o
C and
pumped to a hot potassium carbonate scrubbing
system to remove CO2
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12. For H2 gas
A water gas shift converter is used to
remove CO and form more hydrogen.
Reformer gas is quenched with steam to
give 350o
C input gas to a catalytic
converter using iron oxide catalyst
promoted with chromium oxide. A space
velocity 100-200/hr is maintained. After
scrubbing CO2, the traces of Co are
removed by methanation reaction. For
high purity hydrogen, one or two
additional stages of the shift converter,
CO2 absorber combination are added with
either ammonical cuprous formate or
molecular sieves used to remove residual
CO and CO2 down to 10 ppm or less.
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14. For NH3
synthesis gas
The correct amount of nitrogen for NH3
synthesis is added via air and the oxygen
is burned out by hydrogen in a nickel
catalysed combustion chamber inserted
immediately following the reformer.
Gases are cooled to 350o
C by a water
quench tower and then passed to shift the
converter. Except for the additional N2
which passes through, the remainder of
the process is the same as for hydrogen
preparation. 14
15. MAJOR ENGINEERING
PROBLEMS
Sulphur contamination of reforming catalyst.
Naphtha must be purified by catalytic hydrogen
treatment to remove sulphur to yield a vapour feed
of less then 5 ppm sulphur.
Design of an efficient reformer furnace to
economically supply endothermic heat of reaction.
Avoid carbon formation on catalyst by use of highly
specific catalyst ( ICI patents ).
Removal of CO and CO2 . The bulk of CO2 is
absorbed by either potassium carbonate or
monoethanolamine ( MEA ). The latter requires
more heat, but has higher driving force for
absorption giving smaller towers. 15
16. SYN GAS - USES
• Chemical feedstock - source of
CO and H2
• Production of methanol
• Synthesis of aldehydes/alcohols
from olefins via hydroformylation
• Manufacture of hydrocarbons
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