Destruction of cyanides by alkaline hydrolysis in a pipeline reactor

Free as well as organically‐bound cyanides in a waste stream have been destroyed by alkaline hydrolysis in a simple pipeline reactor. This process has been running successfully at plant scale since 1969. Kinetic analysis shows that the hydrolysis is (pseudo) first order, but with two activation energies depending on temperature: 15.5 and 10.5 kcal/gm mole, for temperatures below and above 170°C, respectively. At lower temperatures (below 170°C), the rate limiting step is destruction of free and loosely bound cyanide, and at higher temperatures, the rate limitation is cyanide release from the more resistant organic entities. Design of plant scale reactors, based on laboratory kinetic data, requires estimation of the extent of backmixing. This has been estimated successfully using literature reported values of axial diffusion coefficients for various geometries considered. Plant performance data have been found to correlate very close to the design estimates. The pipeline hydrolysis reactor offers a novel and simple solution and should be applicable to cyanide disposal problems in a number of industries.