Lead chamber process
Thelead chamber processwas an industrial method used to producesulfuric acidin large quantities. It has been largely supplanted by thecontact process.
In 1746 inBirmingham,England,John Roebuckbegan producingsulfuric acidinlead-lined chambers, which were stronger and less expensive and could be made much larger than theglasscontainers that had been used previously. This allowed the effective industrialization of sulfuric acid production, and with several refinements, this process remained the standard method of production for almost two centuries. The process was so robust that as late as 1946, the chamber process still accounted for 25% of sulfuric acid manufactured.[1]
History[edit]
Sulfur dioxideis introduced with steam andnitrogen dioxideinto large chambers lined with sheetleadwhere the gases are sprayed down with water andchamber acid(62–70%sulfuric acid). The sulfur dioxide and nitrogen dioxide dissolve, and over a period of approximately 30 minutes the sulfur dioxide is oxidized to sulfuric acid. The presence of nitrogen dioxide is necessary for the reaction to proceed at a reasonable rate. The process is highlyexothermic,and a major consideration of the design of the chambers was to provide a way to dissipate the heat formed in the reactions.
Early plants used very large lead-lined wooden rectangular chambers (Faulding box chambers) that were cooled by ambient air. The internal lead sheathing served to contain the corrosive sulfuric acid and to render the wooden chambers waterproof. Around the turn of the nineteenth century, such plants required about half a cubic meter of volume to process the sulfur dioxide equivalent of a kilogram of burned sulfur.[citation needed]
In the 1820s-1830s, French chemistJoseph Louis Gay-Lussac(simultaneously and likely in collaboration withWilliam Gossage) realized that it is not the bulk of liquid determining the speed of reaction but the internal area of the chamber, so he redesigned the chambers as stoneware packed masonry cylinders, which was an early example of thepacked bed.
In the 20th century, plants using Mills-Packard chambers supplanted the earlier designs. These chambers were tall tapered cylinders that were externally cooled by water flowing down the outside surface of the chamber.
Sulfur dioxide for the process was provided by burningelemental sulfuror by theroastingofsulfur-containing metal oresin a stream of air in a furnace. During the early period of manufacture,nitrogen oxideswere produced by the decomposition ofniterat high temperature in the presence of acid, but this process was gradually supplanted by the air oxidation ofammoniatonitric oxidein the presence of a catalyst. The recovery and reuse of oxides of nitrogen was an important economic consideration in the operation of a chamber process plant.
In the reaction chambers, nitric oxide reacts withoxygento produce nitrogen dioxide. Liquid from the bottom of the chambers is diluted and pumped to the top of the chamber, and sprayed downward in a fine mist. Sulfur dioxide and nitrogen dioxide are absorbed in the liquid, and react to form sulfuric acid and nitric oxide. The liberated nitric oxide is sparingly soluble in water, and returns to the gas in the chamber where it reacts with oxygen in the air to reform nitrogen dioxide. Some percentage of the nitrogen oxides is sequestered in the reaction liquor asnitrosylsulfuric acidand asnitric acid,so fresh nitric oxide must be added as the process proceeds. Later versions of chamber plants included a high-temperature Glover tower to recover the nitrogen oxides from the chamber liquor, while concentrating the chamber acid to as much as 78% H2SO4.Exhaust gases from the chambers are scrubbed by passing them into a tower, through which some of the Glover acid flows over broken tile. Nitrogen oxides are absorbed to form nitrosylsulfuric acid, which is then returned to the Glover tower to reclaim the oxides of nitrogen.
Sulfuric acid produced in the reaction chambers is limited to about 35% concentration. At higher concentrations, nitrosylsulfuric acidprecipitatesupon the lead walls in the form of 'chamber crystals', and is no longer able tocatalyzethe oxidation reactions.[2]
Chemistry[edit]
Sulfur dioxide is generated by burning elemental sulfur or by roastingpyritic orein a current of air:
- S8+ 8 O2→ 8 SO2
- 4 FeS2+ 11 O2→ 2 Fe2O3+ 8 SO2
Nitrogen oxides are produced by decomposition of niter in the presence of sulfuric acid, or by hydrolysis of nitrosylsulfuric acid:
- 2 NaNO3+ H2SO4→ Na2SO4+ H2O + NO + NO2+ O2
- 2 NOHSO4+ H2O → 2 H2SO4+ NO + NO2
In the reaction chambers, sulfur dioxide and nitrogen dioxide dissolve in the reaction liquor. Nitrogen dioxide is hydrated to producenitrous acid,which then oxidizes the sulfur dioxide to sulfuric acid and nitric oxide. The reactions are not well characterized, but it is known that nitrosylsulfuric acid is an intermediate in at least one pathway. The major overall reactions are:
- 2 NO2+ H2O → HNO2+ HNO3
- SO2(aq) + HNO3→ NOHSO4
- NOHSO4+ HNO2→ H2SO4+ NO2+ NO
- SO2(aq) + 2 HNO2→ H2SO4+ 2 NO
Nitric oxide escapes from the reaction liquor and is subsequently reoxidized by molecular oxygen to nitrogen dioxide. This is the overall rate determining step in the process:[3]
- 2 NO + O2→ 2 NO2
Nitrogen oxides are absorbed and regenerated in the process, and thus serve as acatalystfor the overall reaction:
- 2 SO2+ 2 H2O + O2→ 2 H2SO4
References[edit]
Further reading[edit]
- Derry, Thomas Kingston; Williams, Trevor I. (1993).A Short History of Technology: From the Earliest Times to A.D. 1900.New York: Dover.
- Kiefer, David M. (2001)."Sulfuric Acid: Pumping Up the Volume".American Chemical Society.Retrieved2008-04-21.