Method for purifying a chlorine supply

A method for purifying a chlorine supply consisting essentially of a chlorine component comprising molecular chlorine, a bromine component comprising molecular bromine and bromine monochloride, nitrogen trichloride, water, and carbon tetrachloride, in a distillation system to form purified chlorine gas having less than 20 parts by weight of the bromine component per one million parts by weight of the purified chlorine gas and to form a distillate comprising liquid chlorine and the bromine component, wherein the distillation system is fluidly connected to a vaporizer and comprises a distillation tower that has an upper end, a lower end, a and vertical axis extending through the upper and lower ends, wherein the upper end has a diameter that is greater than a diameter of the lower end, and wherein the distillation tower comprises a plurality of horizontal trays to provide a vapor-liquid interface between a vapor and a condensate, a knockback condenser disposed above the distillation tower, in fluid communication with the upper end of the distillation tower, and sharing the vertical axis with the distillation tower, and a reboiler disposed below the distillation tower and in fluid communication with the lower end of the distillation tower, wherein the reflux condenser, the reboiler, and a vapor input to the distillation tower are electronically coupled to a flow controlling device for controlling a rate of introducing the vapor into the distillation system and the method further comprises the step of controlling a rate of introducing the vapor into the distillation system through the vapor input as a function of an amount of condensate that flows from the knockback condenser into the upper end of the distillation tower and as a function of an amount of vapor formed from the reboiler, said method comprising the steps of:

• A. introducing the chlorine supply into the vaporizer;
• B. heating the chlorine supply to a temperature of from 50° C. to 120° C. in the vaporizer to form the vapor;
• C. introducing the vapor into the distillation system to provide purified chlorine gas, a distillate comprising the liquid chlorine and the bromine component, and a bottoms component comprising the nitrogen trichloride such that a rate of introducing the vapor into the distillation system is controlled as a function of an amount of condensate formed from the knockback condenser and as a function of an amount of vapor formed from the reboiler;
• D. condensing the vapor in the reflux condenser to form the condensate which flows from the reflux condenser into the upper end of the distillation tower such that the condensate interacts with the vapor at vapor-liquid contact device thereby forming the purified chlorine gas and the distillate;
• E. heating the condensate in the reboiler to a temperature of from 90° C. to 110° C.;
• and
• F. simultaneously removing the purified chlorine gas and the distillate from the distillation system.