A plant is required to produce 10,000 tonnes per year of anhydrous hydrogen chloride from chlorine and hydrogen.The hydrogen source is impure: 90 per cent hydrogen, balance nitrogen. The chlorine is essentially pure chlorine,supplied in rail tankers. The hydrogen and chlorine are reacted in a burner at 1.5 bar pressure.Hydrogen is supplied to the burner in 3 per cent excess over the stoichiometric amount. The conversion of chlorine isessentially 100 per cent. The gases leaving the burner are cooled in a heat exchanger. The cooled gases pass to anabsorption column where the hydrogen chloride gas is absorbed in dilute hydrochloric acid. The absorption column isdesigned to recover 99.5 per cent of the hydrogen chloride in the feed.The unreacted hydrogen and inerts pass from the absorber to a vent scrubber where any hydrogen chloride present isneutralised by contact with a dilute, aqueous solution, of sodium hydroxide. The solution is recirculated around thescrubber.The concentration of sodium hydroxide is maintained at 5 per cent by taking a purge from the recycle loopand introducing a make-up stream of 25 per cent concentration. The maximum concentration of hydrogen chloridedischarged in the gases vented from the scrubber to atmosphere must not exceed 200 ppm (parts per million) byvolume.The strong acid from the absorption column (32 per cent HCl) is fed to a stripping column where the hydrogenchloride gas is recovered from the solution by distillation. The diluted acid from the base of this column (22 per centHCl), is recycled to the absorption column. The gases from the top of the stripping column pass through a partialcondenser, where the bulk of the water vapour present is condensed and returned to the column as reflux. The gasesleaving the column will be saturated with water vapour at 40 ŽC. The hydrogen chloride gas leaving the condenser isdried by contact with concentrated sulphuric acid in a packed column. The acid is recirculated over the packing.The concentration of sulphuric acid is maintained at 70 per cent by taking a purge from the recycle loop andintroducing a make-up stream of strong acid (98 per cent H2SO4). The anhydrous hydrogen chloride product iscompressed to 5 bar and supplied as a feed to another process.