Lecture Outline - Sulfuric Acid
- History of Manufacture Development
- Manufacture
- Oleum Production
- Heat Integration Issues / By-products
- Markets
- Usage in Caprolactam Manufacture
History of Manufacture of Sulfuric Acid
• One of the oldest industrially applied processes. Discovered by a
Persian alchemist in the tenth century.
• Saltpeter and sulfur were mixed in a glass container and burned in a
moist atmosphere. Acid was collected from the condensed vapors.
• In England, 1746, the lead chamber reactor was invented. This
invention allowed for higher production rates (<78%).
• In England, 1831, a patent was filed that described the oxidation of sulfur
dioxide over a platinum catalyst, the Contact Process. This new process
increased yields of reaction from 70 to above 95%.
• In 1913 BASF was granted a patent for the use of vanadium pentoxide
as a catalyst for the Contact Process
• By the 1930’s vanadium pentoxide was becoming the dominate catalyst
used because of insensitivities to poisons and lower cost.
• In 1960 a patent application was filed by Bayer using the so called
double-catalyst process (double absorption).
World Supply / Demand for Sulfuric Acid
(thousands of metric tons, 100% H2SO4)
250,000
200,000
150,000
100,000
50,000
0
Production
2000
1997
1994
1991
1988
1985
Annual Capacity
World Production of Sulfuric Acid
Canada
Mexico
Others
Japan
Latin
F-USSR
Europe
Africa
U.S.
Asia
0.0
5.0
10.0
15.0
Share (percent)
20.0
25.0
30.0
Manufacture
Three Step Process
1) S + O2
2) SO2 + 1/2O2
3) SO3 + H2O
SO2
SO3
H2SO4
Oxidation of Sulfur
1) S + O2
SO2
Sulfur
Steam
10-12% SO2
Water
Air
93% H2SO4
Process:
- Air drying tower with acid
Primary Generation of SO2
-79% Combustion of Sulfur
-9% Recovery from Metallurgic Processes
- 5% Regeneration of Spent Acids
- Sulfur is injected into burner
- Reaction Temperature 2000°F
- Exothermic reaction must be cooled
- Steam recovered
Oxidation of Sulfur Dioxide
Contact Process:
SO2 Gas
-Vanadium pentoxide
catalyst
Gas
Cooling
- Exothermic Rxn
- Multiple Steps with
cooling in between
- Double absorption
- Heat integration
SO3 Gas
Oxidation of Sulfur Dioxide
 Because of the large effect temperature plays on the reaction, multiple catalyst
layers had to be used with cooling between each step.
 Additionally, as the partial pressure of SO3 increases further reaction is limited.
 This was overcome by removing the SO3 after the third stage to drive the
reaction to completion.
SO2 Gas
SO2 Gas
Gas
Cooling
SO3 Gas
SO3 Gas
93% H2SO4
Oxidation of Sulfur Dioxide
• Kinetic Effects
- Oxidation of sulfur dioxide is slow and reversible
- The reaction requires a catalyst and 426.7°C temperatures
-The reaction is exothermic and sensitive to excessive heat
• Equilibrium Constant (The degree at which the reaction proceeds is temp. dependent)
log Kp = 4.956 - 4.678
T
T = absolute temp. in kelvin
Kp = equilibrium constant as a function of partial pressure of gases
Kp =
( PSO3 )
PSO2 PO2
0.5
Oxidation of Sulfur Dioxide
Temperature Profile
SO2 Gas
SO2 Gas
Gas
Cooling
SO3 Gas
510 C
75 C
430 C
200 C
SO3 Gas
125 C
93% H2SO4
Oxidation of Sulfur Dioxide
Temperature Profile
Oxidation of Sulfur Dioxide
Typical Catalyst Distribution
Catalyst
Bed
1
2
3
4
% Catalyst Conversion %
19.4
25.0
26.7
28.9
56
87
99.1
99.7
Overall Production Scheme
Oleum Production
 Sulfuric acid with additional SO3 absorbed
 20% Oleum contains 20% SO3 by weight in the oleum
 Common strengths of oleum are 20, 30, 40, 65 percent.
 To produce 20 and 30 percent oleum, only requires an additional
absorption tower.
 Oleum is used in reactions where water is excluded
SO3 + H2SO4
H2S2O7
(disulfuric acid)
Reaction By-products / Heat Integration
By-products
 57 to 64% of the energy input generates steam
 Steam energy is used to drive the turbine that supplies power to
the main air blower
 Additional steam remaining is tolled internally for other plant
operations
 SO2/SO3 is vented in small amounts and is federally regulated.
Heat Integration
 Steam is used to pre-heat and vapor from the absorption towers
used to cool
 Minimizes the cost of manufacturing to maximize the profit.
Production Considerations
 Metal corrosion is a big issue in the manufacture of sulfuric acid.
 Special alloy metals must be used to guard against excessive
corrosion.
Nickel, chromium, molybdenum, copper, an silicon are the most
important elements that enhance corrosion resistance of alloys.
 Important variables for corrosion
Concentration of the acid
Temperature of service
Speed of flow in pipes and
equipment
Alloy element make-up
Markets for Sulfuric Acid
 The fertilizer market is the largest U.S. single use for sulfuric acid and
consumes 50-65 percent of all produced.
 Second is the organic chemical industry. Production of plastics and
synthetic fibers are examples.
 Production of TiO2 consumes large quantities of sulfuric acid. TiO2 is a
white pigment used in paints and plastics.
 In the metal industry sulfuric acid is used for pickling ferrous and nonferrous materials and in the recovery of copper, nickel, and zinc from
low-grade ores.
 Finally, the petroleum industry uses acid as a catalyst for various
reactions.
Acid Strengths
Associated End Uses
Percent
H2SO4
35.67
Uses
Storage batteries, electric utilities
62.18
Normal superphosphate and other fertilizers
69.65
77.67
Normal superphosphate and other fertilizers,
isopropyl and sec-butyl alcohols
80.00
Copper leaching
93.19
Phosphoric acid, tianium dioxide, steel pickling,
regenerating ion exchange resins of utilities
98-99
Chlorine drying, alkylation, boric acid
104.50
Surfactants, nitrations, hydrofluoric acid
106.75
109.00
Explosives
111.25
113.50
114.63
Reagent manufacture, organic sulfonations,
blending with weaker acids
Usage in Caprolactam Manufacture
Production and consumption figures for caprolactam manufacture
Caprolactam Production Rate
120,000 ton/yr
H2SO4 Consumption (100% Acid)
636 kg per ton of CPL
Oleum Consumption
1300kg per ton of CPL
Ammonium Sulfate Production
312,000 ton/yr