5.66. The quantity of sulfuric acid used globally places it among the most plent

Question

5.66. The quantity of sulfuric acid used globally places it among the most plentiful of all commodity chemicals. In the modern chemical industry, synthesis of most sulfuric acid utilizes elemental sulfur as a feedstock. However, an alternative and historically important source of sulfuric acid was the conversion of an ore containing iron pyrites (FeS2) to sulfur oxides by roasting (burning the ore with air. The following reactions occurred in an oven (1) 2FeS2(s) HO2 (g) Fe2O3 (s) 4SO20g) (2) SO2 (g) +102 (g) SO3(g) The gases leaving the oven were fed to a catalytic converter in which most of the remaining SO2 produced was oxidized to so, Finally, the gas leaving the converter was sent to an absorption column where the SO3 was taken up by water to produce sulfuric acid (H2So4). (a) The ore fed to the oven was 90.0 wt% Fesz, and the remaining material may be considered inert. Dry air was fed to the oven in 30.0% excess of the amount required to oxidize all of the sulfur in the ore to SO3. Eighty-five percent of the Fes2 was oxidized, and 60% of the so2 produced was oxidized to so,. Leaving the roaster were (i) a gas stream containing so2. So,. O2, and N2 and (ii a solid stream containing unconverted pyrites, ferric oxide (Fe203), and the inert material. Calculate the required feed rate of air in standard cubic meters per 100 kg of ore fed to the process Also determine the molar composition and volume (SCM/100 kg ore) of the gas leaving the oven (b) The gas leaving the oven entered the catalytic converter, which operated at 1.0 atm. Reaction 2) proceeded to equilibrium, at which point the component partial pressures are related by the expression pso KP(T) The gases were first heated to 6 to accelerate the rate ofreaction, and then cooled to 400°C to 0.5 enhance SO2 conversion. The equilibrium constant KP at these two temperatures is 9 atm and 397 0.5 respectively. Calculate the equilibrium fractional conversions of SO2 at these two temperatures converter was Estimate the production rate of sulfuric acid in kg/kg ore if all of the SO3 leaving the (c) transformed to sulfuric acid. What would this value be if all the sulfur in the ore had been converted?

Explanation / Answer

a) MW of FeS2 = 119.965 g/mol

85% of ore oxidise is FeS2, hence weight of FeS2 = 85 kg

moles of FeS2 = 85000/119.965 = 708.54 moles

2 moles of FeS2 require 6 moles of O2

708.54 moles of of FeS2, requires = 6/2*708.54 = 2125.62 moles of O2

Weight of oxygen = 2125.62*32 = 68.02 kg

Weight of air = 68.02/0.21 = 323.9 kg (21% oxygen is there in air)

Since 30% extra is supplied, total air supplied = 323.9*130/100 = 421.07 kg

Volume of air = 421.07/ 1.225 = 343.73 m3

Molecular weight of SO2 = 64 g

2 moles of FeS2 requires 4 moles of SO2

708.54 moles of FeS2 requires 1417.08 moles of SO2

Weight of SO2 = 1417.08*64 = 90.69 kg

c)

60% of 1417.08 was reacted to form = 850.25 moles of SO3

Considering the reaction, 850.25 moles of SO3 produces 850.25 moles of sulphuric acid

Total sulphuric acid produced = 850.25 * 98.079 = 83.32 kg

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