Creative Chemistry: Descriptive of Recent Achievements in the Chemical Industries

by Edwin E. Slosson

If a stream of nitrogen is passed over hot calcium carbide it is taken up by the carbide according to the following equation:

CaC₂ + N₂ → CaCN₂ + C
calcium carbide nitrogen calcium cyanamid carbon

Calcium cyanamid was discovered in 1895 by Caro and Franke when they were trying to work out a new process for making cyanide to use in extracting gold. It looks like stone and, under the name of lime-nitrogen, or Kalkstickstoff, or nitrolim, is sold as a fertilizer. If it is desired to get ammonia, it is treated with superheated steam. The reaction produces heat and pressure, so it is necessary to carry it on in stout autoclaves or enclosed kettles. The cyanamid is completely and quickly converted into pure ammonia and calcium carbonate, which is the same as the limestone from which carbide was made. The reaction is:

CaCN₂ + 3H₂O → CaCO₃ + 2NH₃
calcium cyanamid water calcium carbonate ammonia

Another electrical furnace method, the Serpek process, uses aluminum instead of calcium for the fixation of nitrogen. Bauxite, or impure aluminum oxide, the ordinary mineral used in the manufacture of metallic aluminum, is mixed with coal and heated in a revolving electrical furnace through which nitrogen is passing. The equation is:

Al₂O₃ + 3C + N₂ → 2AlN + 3CO
aluminum carbon nitrogen aluminum carbon
oxide nitride monoxide

Then the aluminum nitride is treated with steam under pressure, which produces ammonia and gives back the original aluminum oxide, but in a purer form than the mineral from which was made

2AlN + 3H₂O → 2NH₃ + Al₂O₃
Aluminum water ammonia aluminum oxide
nitride

The Serpek process is employed to some extent in France in connection with the aluminum industry. These are the principal processes for the fixation of nitrogen now in use, but they by no means exhaust the possibilities. For instance, Professor John C. Bucher, of Brown University, created a sensation in 1917 by announcing a new process which he had worked out with admirable completeness and which has some very attractive features. It needs no electric power or high pressure retorts or liquid air apparatus. He simply fills a twenty-foot tube with briquets made out of soda ash, iron and coke and passes producer gas through the heated tube. Producer gas contains nitrogen since it is made by passing air over hot coal. The reaction is:

2Na₂CO₃ + 4C + N₂ = 2NaCN + 3CO
sodium carbon nitrogen sodium carbon
carbonate cyanide monoxide