Sulfur Products

Ariziel Ruth D. Marquez

SULFURIC ACID

• Once called “Oil of Vitriol”

• Uses: Manufacture of fertilizers

• Manufacturing Process: Contact process – by Philips

Lead Chamber Process – only 78% H2SO4

FLOW CHART

FLOW DIAGRAM

Burner Converter Charge

Cinder

1o Air 2o Air

Burner Gas

Converter Gas

ABSORBER

Absorbing medium

Absorber Gas

Product

Equipment

I. BURNER

Charge: 1. Pure Sulfur

2. Pyrites (Sulfur Ore – FeS2)

3. Mixed Pure Sulfur and Ore

*Pure Sulfur

Reaction : S + O2 SO2 ∆H = -70920 cal/mol

S + 3/2O2 SO3 ∆H = -93900 cal/mol

Theoretical O2 is based on conversion to SO2 unless specified.

Equipment

*Pyrites - composed of FeS2 and gangue (nonvolatile,

noncombustible oxides) Reactions: 4FeS2 + 11O2 2Fe2O3 + 8SO2 ∆H = -205590 cal/mol 4FeS2 + 15O2 2Fe2O3 + 8SO3 ∆H = -251500 cal/mol

Cinder: Fe2O3, gangue, unburned FeS2, adsorbed SO2 or SO3

Primary Air as source of oxygen

Burner Gas: SO2, SO3, O2, N2

Equipment II. CONVERTER

Burner Gas: SO2, SO3, O2, N2

Secondary air if necessary.

Reaction: SO2 + 1/2O2 SO3 ∆H = -22980 cal/mol

*Factors to favor forward reaction 1. Maintain temperature at 425oC 2. Increase the concentration of SO2 and O2 3. Remove some SO3 by scrubbing

*Contact process uses catalyst to provide surface area to make the reaction effective. (V form V2O5 and Pt)

Converter Gas: SO2, SO3, O2, N2

Equipment III. ABSORBER

Converter Gas: SO2, SO3, O2, N2

Absorbing medium: Mixture of H2SO4 and water – Pure water cannot be effective because it will boil with SO2 and only fumes of the acid will be formed due to greater pressure water that SO3.

Reaction: SO3 + H2O H2SO4 ∆H = -31143 cal/mol

Negligible side reactions: SO2 + ½O2 SO3 SO2 + H2O H2SO3

Absorber Gas: SO2, O2, N2

Product: 1. 100% H2SO4 (equivalent amount of SO3 & H2O)

2. <100% H2SO4 (greater H2O than SO3)

3. >100% H2SO4 (less H2O than SO3) – Oleum (H2SO4·SO3)

Combustion of Sulfur 1. Five hundred pounds per hour of pure sulphur is burned

with 20% excess air (based on conversion to SO2). Five percent of the sulfur is oxidized to SO3 and 95% to SO2. The air is dry. Calculate the composition (in % mole) of the gas leaving the burner.

2. If the burner gas has an Orsat analysis of 16.85% SO2, 3.11% O2 and 80.04% N2, calculate the complete composition of the burner gas.

3. Pure sulphur is burned with 20% excess air based on conversion of SO3. Thirty percent of the sulfur forms SO3; the remainder forms SO2.

a. What is the analysis of the burner gas? b. The burner gas is passed through a converter. If the gases

leaving the converter have a mole fraction of oxygen of 0.043, what is the ratio of mole SO3 to mole SO2.

Combustion of Sulfur

4. 700 pounds per hour of iron pyrites containing 85% wt FeS2 and 15% gangue are charged to a burner. The cinder contains 1% S as SO3. The burner gas analysis shows a composition of 10% SO2 and 5% O2. Air used for combustion is dry. How many cubic feet of the total burner gases at 1 atm and 60oF are produced per hour?

5. A mixture of pure sulfur and of pyrites analyzing 85% FeS2 and 15% gangue is burned in a standard pyrites burner. The burner gas contains 10% SO2, 7% O2, and 83% N2 on an SO3-free basis and contains 1 mole SO3/100 mole SO3-free burner gas. The cinder contains 2% S as SO3. Calculate the percentage of FeS2 in the charge.

Material Balance @ Absorber 1. A converter gas contains 10 pound-mole SO3. If

this converter gas is allowed to pass through an absorber utilizing 80% H2SO4 as absorbing solution, calculate the weight of the product if the desired product is

a. 98% H2SO4

b. 100% H2SO4

c. 105% H2SO4 2. 250 pounds per hour of 98% H2SO4 enters an

absorption tower of a contact sulfuric acid plant. If 20% oleum is produced in this tower, how many pounds of SO3 are absorbed per hour.

Material Balance @ Absorber 3. One hundred pounds per hour of pyrites containing

90% FeS2 and 10% gangue are burned with 20% excess air based on conversion to SO3. The cinder discharged from the burner contains no sulfur. No conversion to SO3 occurs in the burner. The burner gas is passed through a converter which effects a 98% conversion of SO2 to SO3. The converter gas is passed to an absorber where all the SO3 is absorbed by 80% H2SO4 solution, which becomes 100% H2SO4 solution in the process. Calculate the following:

a. The burner gas analysis b. The converter gas analysis c. The absorber gas analysis d. The pounds of 100% H2SO4 produced per 24-h day.