Chamber process

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A.K.A. Lead chamber process. This process converts sulfur, water, and air to sulfuric acid. The maximum concentration using the chamber process is approximately 68% sulfuric acid 32% water. This is a 10-ish molar concentration with a density of 1.5-1.6. Excess water must be provided to allow full absorption of the sulfur trioxide. If the process is carried out at atmospheric pressure near room temperature, the limitation is usually the size of the container in which the burning sulfur mix, water, and air will interact. 1 m3 air at 20°C will support approximately 150g of sulfur being absorbed into 125cc of water.

Components

The Burners

  • Burn whatever sulfur compounds are available (pyrites, sulfur) and produce sulfur dioxide.
  • With a sufficiently hot pure-oxygen input stream, no fuel is needed.
  • Something to produce nitrogen dioxide is also required.

The Chamber

  • Provides a locale for the nitrogen dioxide and sulfur dioxide to intermix with water
    H2O + SO2 + NO2 H2SO4 + NO

The Guy Lussac Tower

  • Provides a way to recover the nitrogen oxides from the chamber exhaust by dissolving them in concentrated sulfuric acid.

The Glover Tower

  • Provides an exchange between SO2 from the furnace and the dissolved nitrogen oxides in the Guy Lussac tower acid.
  • In a 4-unit (burner, chamber, lussac and glover towers) plant, this is the first stage for the gasses, and the last stage for the acid.
  • The gasses (SO2 from the burners) which arrive at the top of the tower are ducted into the chamber.
  • The acid which arrives at the bottom of the tower is output to storage, usually at about 77% acid content.

Variations

  • Chamber: Simplest possible design is a burner in a chamber, no towers
  • Burner-Chamber: Separate burner and chamber works more effectively
  • Burner-Chamber-Lussac: Recycles nitrogen-oxide rich acid into the chamber
  • Burner-Glover-Chamber-Lussac: 77% acid, continuous production, low oxide losses/pollution

Methods

Chamber process

Materials

  • A closeable (but not air-tight) container lined with or made of lead or glass, preferably with a wide flat bottom on the inside
  • Sulfur and water in the indicated ratio
  • A smaller container which fits within the larger container but that is large enough to hold the sulfur while it burns
  • (optional) clean, pure glass or quartz pebbles sufficient to cover the bottom of the large container 1 pebble deep when the small container is set directly on the bottom of the large container

Process

The process is fairly simple, consisting of two phases. In the first phase we expose molten or burning sulfur to air, producing mostly SO2 and some SO3. Both are absorbed readily into water. The output of phase I is water with a substantial amount of sulfur dioxide dissolved in it. In the second phase, the solution is repeatedly warmed and aerated, allowing the dissolved dioxide component exit the water and combine with additional oxygen, slowly converting to trioxide, which is absorbed fully, producing sulfuric acid. The quartz pebbles, if included, are used to break the surface tension of the water

This version of the process is impractical for most use because Phase II may take days or weeks, depending on conditions. The nitrate chamber process (next section) can produce acid in a timeframe of hours or even minutes.

Phase I
  1. Place distilled water in the large container
  2. Place the sulfur in the small container
  3. Light the sulfur on fire
  4. Place the smaller container in the larger one
  5. (optional) Strew the quartz pebbles on the bottom of the large container, around the small container.
    Check: Their tops should rise above the surface of the water.
  6. Close the larger container
  7. Repeat
    1. Wait a few minutes for the sulfur to burn out and the temperature inside the container to drop
    2. Open the larger container carefully so as not to disturb the water within it
    3. If any sulfur floats on the surface of the water, skim it off with something made of glass or quartz
    4. If the sulfur has gone out, relight it
    5. Replace the cover on the large container
  8. Until all the sulfur has burned
Phase II
  1. Remove the smaller container
  2. Repeat
    1. Seal the larger container completely
    2. Shake the larger container vigorously
    3. Unseal the container, leaving room for oxygen to enter the container
    4. Allow it to stand for a quarter of a day
    5. Warm the container slightly
    6. Smell the liquid
  3. Until it has no odor
  4. Carefully decant the liquid (dilute sulfuric acid) at the bottom of the chamber

Nitrate chamber process

This process radically increases the speed of the dioxide→trioxide conversion, eliminating the need for the second phase entirely. It is basically Phase I above, but with 1 part of sodium- or potassium nitrate mixed into 10 parts of sulfur. The sulfur will burn longer than in the sulfur-only chamber process, partly because the saltpeter will provide oxygen to burn, but also because it won't smother itself as rapidly in fumes of sulfur dioxide.

SO2 + NO2 SO3 + NO
2 NO + O2 2 NO2 (recycled)

Materials

As above, but include:

  • 1 part by mass of nitrate for every 10 parts of sulfur

Process

  1. Place distilled water in the large container
  2. Combine the sulfur and saltpeter in the small container
  3. Light the mixture on fire
  4. Place the smaller container in the larger one
  5. Close the larger container
  6. Repeat
    1. Wait a few minutes for the mixture to burn out and the temperature inside the container to drop
    2. Open the larger container carefully so as not to disturb the water within it
    3. If any sulfur floats on the surface of the water, skim it off with something made of glass or quartz
    4. If the sulfur has gone out, relight it
    5. Replace the cover on the large container
  7. Until the mixture will no longer burn
Note: There will be a residue of sodium sulfate left in the small container, so it will not burn to emptiness.
  1. Remove the smaller container
  2. Carefully decant the liquid (dilute sulfuric acid) at the bottom of the chamber

Stochiochemistry

228g (190.5L) of (dry, 20°C) air contains 48g of oxygen. (1.5mol of O2, 3 mol of O)
32g (16cc) of sulfur contains 1 mol of S
18g (18cc) of water contains 1 mol of H2O

So...

1.5 mol O2 + 1 mol S + 1 mol H2O = 1 mol H2SO4
(228g * 0.21)g O + 32g S + 18g water = 98g H2SO4

Taking into account the maximum practical absorption (68%)

190.5L air + 32g S + 26g water = 98g(1 moles) sulfuric acid + 8g (0.44 moles) water

Example

A 1 gallon (3.8L) glass bottle is available for the production of sulfuric acid. Wanting to contain a 2x excess of air, the scale is set for 1.9L of air. This is (conveniently) .01 mol of oxygen at 20°C. Therefor 0.32g (1/6cc) of sulfur and 0.26g (1/4cc) of water are required to produce just over 1g of 68% H2SO4. For convenience sake, any amount of water may be used.

Hazards

  • Sulfur trioxide dissolution in water happens very aggressively and is strongly exothermic. Sufficient amounts of energy are released that it can vaporize the water or the acid, resulting in eruptions of hot concentrated strongly acidic mist. As with any synthesis that involves the phrase "eruptions of hot concentrated strongly acidic mist", it should be attempted only by people who know what they're doing and how to solve the problem when something goes wrong.

See Also