ferric chloride , a known chlorination and polymerization catalyst for 1 , 3 - butadiene , can nevertheless be effectively used in a packed or trayed quench tower , operating under essentially anhydrous conditions , without plugging it . essentially all bd from a crude stream of vinyl chloride , is removed within a hold - up time of 6 minutes . the speed of removal is note - worthy because less than half the stoichiometric amount of chlorine required to chlorinate the bd is used . the bd is preferentially chlorinated , the time being too short to chlorinate a substantial amount of chloroprene and monovinylacetylene . only a portion of the bd is removed by chlorination , the remainder being removed by polymerization catalyzed by 100 - 200 ppm anhydrous fecl 3 . for such speed and effectiveness without plugging the quench tower , the amount of bd in the effluent stream is required to be controlled to no more than 100 ppm , based on the weight of 1 , 2 - dichloroethane in the stream .