The material of construction of other equipment in the alkali-catalyzed processes was
carbon steel. For the acid-catalyzed system, Norden (1973) recommended that stainless steel (type 316)
should be used when sulfuric acid concentrations were below 5 wt.% or above 85 wt.% and temperatures were
below the boiling point of the sulfuric acid solution. Davis et al. (2000) indicated that stainless steel 316 has
an acceptable corrosion rate (less than 0.5 mm/yr) for 5 wt.% sulfuric acid under 100 C; for a temperature between
50 and 100 C, stainless steel (alloy 20) has good corrosion-resistance for sulfuric acid less than 60 wt.%
or greater than 80 wt.%. These guidelines formed the basis for our choice of material in all the designs.