Published December 1983
About 90% of the hydrochloric acid (HCl) produced in the United States is made as a by-product from chlorination reactions. Although HCl is normally generated in dry gaseous form, the most common method of recovery is by absorbing it in water, which produces an aqueous acid containing 28 to 35 wt% HCl (18 to 22°Be').
This review examines five options open to a by-product acid producer. SRI believes that the best option is to recover acid in dry gaseous form and reuse it directly in an oxychlorination reaction to make vinyl chloride or to make methyl chloride, or ethyl chloride. All other options are less favorable and depend on the availability of HCl markets and/or the price differential between anhydrous and dilute acids.
Of particular interest is the process alternative of recovering by-product acid directly as anhydrous acid, which normally commands a price premium over dilute acid. We have compared the economics of recovering HCl as either anhydrous acid or 31.5 wt% acid from a typical 100 million lb/yr (45,000 metric ton/yr) toluene diisocyanate (TDI) plant. The savings in phosgene use and the higher by-product acid credit for anhydrous acid tend to offset the higher capital charges associated with anhydrous acid recovery.
Anhydrous acid recovery is possible from most chlorination reactions, SRI believes that this option is economically more viable than dilute acid recovery because of the generally poor market for dilute acid.