Uses of sulfuric acid

The fertilizer market is the largest single user for sulfuric acid.

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 non-ferrous materials and in the recovery of copper, nickel, and zinc from low-grade ores.

Petroleum industry uses acid as a catalyst for various reactions.

Acid strengthsAssociated end uses

PercentH2SO4 Uses

35.67 Storage batteries, electric utilities

62.18

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

106.75

109.00 Explosives

111.25

113.50

114.63

Reagent manufacture, organic sulfonations,blending with weaker acids

Surfactants, nitrations, hydrofluoric acid

Normal superphosphate and other fertilizers

About 220 million tonnes of sulfuric acid are produced/consumed per year.

World production of sulfuric acid, % by region (January 2012)

Sulfuric acid

Sulfuric acid is made from SO2, O2 and water.

SO2 comes from:• burning molten elemental sulfur with dry air• smelting and roasting metal sulfide minerals• decomposing contaminated (spent) sulfuric acid catalyst

Sulfur burning is far and away the largest source.

SO2 in the gas is made into sulfuric acid by• catalytically oxidizing it to SO3• reacting this SO3 with the H2O(ℓ) in 98.5 mass% H2SO4(ℓ),

1.5 mass% H2O(ℓ)

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, 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).

Lead chamber and tower processes

Industrial sulfuric acid production began in the eighteenth century with the burning of sulfur in the presence of KNO3 and steam.

This developed into the lead chamber and tower processes—which used nitrogen oxides to form an aqueous catalyst for SO2 oxidation.

4 NO(g) + O2(g) + 2 H2O(l) 4 HNO2(l)4 HNO2(l) + 2 SO2(g) 2 H2SO4(aq) + 4 NO(g)

The overall acid making reaction with this catalyst was:

SO2 + 0.5O2 + H2O H2SO4NOHSO4 catalyst

The lead chamber and tower processes were used in the twentieth century.

Unfortunately, their H2SO4 strength was limited to below about 70 mass% H2SO4. Above 70% H2SO4, the product acid contained stable nitrosyl hydrogen sulfate which made it unsuitable for many purposes.

Contact processThree Step Process

1) S + O2 SO2 2) SO2 + 1/2O2 SO3 3) SO3 + H2O H2SO4

Plant

Drying

H2O + H2SO4 H2SO4.H2O

To avoid:(a) accidental formation of H2SO4 by the reaction of H2O(g) with the

SO3 product of catalytic SO2 oxidation(b) condensation of the H2SO4(ℓ) in cool flues and heat exchangers(c) corrosion.

FLEXERAMIC® structured packing

Oxidation of Sulfur

Air

93% H2SO4

Sulfur

10-12% SO2

Steam

Water

Primary Generation of SO2

-79% Combustion of Sulfur

-9% Recovery from Metallurgic Processes

- 5% Regeneration of Spent Acids

Process:

- Air drying tower with acid

- Sulfur is injected into burner

- Reaction Temperature 2000°F

- Exothermic reaction must be cooled

- Steam recovered

1) S (l) S(g)2) S (g) + O2 (g) SO2 (g)

Oxidation of Sulfur Dioxide

Contact Process:

-Vanadium pentoxide catalyst

- Exothermic Reaction

- Multiple Steps with cooling in between

- Double absorption

- Heat integration

Gas Cooling

SO3 Gas

SO2 Gas

SO2 (g) + 1/2O2 (g) SO3 (g) H = –99 kJ.mol-1

Lechatelier principle is usually taken into account in deciding how to optimize the equilibrium. This states that when an equilibration system is subjected to stress, the system will tend to adjust itself in such a way that part of the stress is relieved.

Maximizing SO3

• Removal of heat – a decrease in temperature will favor the formation of SO3 since this is an exothermic process

• Increased oxygen concentration• Removal of SO3 (as in the case of the double

absorption process)• Raised system pressure• Selection of the catalyst to reduce the working

temperature (equilibrium)• Increased reaction time

Oxidation of Sulfur Dioxide

Because of the large effect temperature plays on the reaction, multiple catalyst layers are used, with cooling between each step.

Additionally, as the partial pressure of SO3 increases, further reaction is limited.

This is overcome by removing the SO3 after the third stage to drive the reaction to completion.

Gas Cooling

SO3 Gas

SO3 Gas

SO2 Gas

93% H2SO4

SO2 Gas•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

Oxidation of sulfur dioxide

Absorption

Catalytic oxidation’s SO3 product is made into H2SO4(ℓ) by contacting catalytic oxidation’s exit gas with strong sulfuric acid. The reaction is:

SO3 + H2O H2SO4

H2SO4(ℓ) is not made by reacting SO3(g) with pure H2O(ℓ). This is because Reaction is so exothermic that the product of the reactionwould be hot H2SO4 vapor—which is difficult and expensive to condense.

Efficiency of the absorption

• The H2SO4 concentration of the absorbing liquid (98.5-99.5%)

• The range of temperature of the liquid (normally 70°C-120°C)

• The technique of the distribution of acid• The raw gas humidity (mist passes the absorption

equipment)• The mist filter• The temperature of incoming gas• The co-current or counter-current character of the gas

stream in the absorbing liquid

Single absorption contact sulfuric acid plant

1.6 O2/SO2 ratio to the converter

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)

%H2SO4 = 100 + 18/80 * % oleum

20% oleum is equivalent to 104.5% H2SO4

Double absorption contact sulfuric acid plant

0.5 O2/SO2 ratio to the converter

98.5% sulfuric acid in an absorption tower to remove sulfur trioxide (SO3)

Double absorption plants are more complex, more difficult to start-up and operate in compliance within emission regulations

Double absorption contact sulfuric acid plant

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 corrosionConcentration of the acidTemperature of serviceSpeed of flow in pipes and equipmentAlloy element make-up

Recent developments

The three main recent developments in sulfuric acid making have been:

• improved materials of construction, specifically more corrosion-resistant materials

• improved SO2 oxidation catalyst, specifically V, Cs, K, Na, S, O, SiO2 catalyst with low activation temperatures

• improved techniques for recovering the heat from reactions (process intensification)