Effect Of Phenolic/non-phenolic Structure On AOX Formation In Reaction Of Lignin With Chlorine Dioxide

During processes of chlorine dioxide bleaching,adsorbable organic halogen(AOX)is generally formed by the reaction of residual lignin of pulps with chlorine dioxide.Lignin has complex structures.Reaction paths of lignin with chlorine dioxide vary with lignin structures.And the contribution of different lignin structures to AOX formation is also quite different.Vanilly alcohol(VA)was selected as phenolic lignin model compound and veratryl alcohol(VE)was selected as non-phenolic lignin model compound in this paper.And the effect of phenolic henolic on AOX formation was studied.The results are as follows:Reaction conditions were as follow:the concentration of VA was 124.00 mmol·L-1,the molar ratio of ClO2/VA was 1,pH value was 3,the temperature was 70?.VA reacted rapidly with chlorine dioxide and AOX formation was 363.54 mg/L-1 at 2 min.The formation of AOX and the consumption of VA are mainly within 15 min.AOX formation increased with the dosage of chlorine dioxide and the concentration of VA.Chlorinated products reacted by VA withchlorine dioxide were identified by gas chromatography-mass spectrometry(GC-MS).It was found that chlorinated products were mainly chlorophenols and chlorinated biphenyls.A kinetic model for the AOX formation by the reaction of VA with chlorine dioxide under simulated chlorine dioxide bleaching conditions was established:dW/dt=73824.40·e-(899.55/T)·[H+]0.066.[ClO2]0.94·[C]0.36.And its reaction activation energy is 17220.32 J·mol-1.Reaction conditions were as follow:the concentration of VE was 124.00 mmol·L-1,the molar ratio of ClO2/VE was 1,pH value was 3,the temperature was 70?.The AOX formation reacted by VE with chlorine dioxide was 944.14 mg L-1 at 2 min,and was gradually stable after 15 min.It indicated that the reaction process was very fast.However,the AOX formation reacted by VE with chlorine dioxide was higher than that reacted by VA.And VE consumedcompletely require higher dosage of chlorine dioxide.The chlorinated products formed by the reaction of VE with chlorine dioxide were mainly chlorobenzenes with higher relative content.A kinetic model for the AOX formation was established:dW/dt=1012.05·e-(14 70/T)·[H+]0.061·[ClO2]0.85·[C]0.30.And its reaction activation energy is 281.34 J·mol-1.The lower activation energy of the reaction between VA and chlorine dioxide indicates that the non-phenolic structure is easier to react with chlorine dioxide to form AOX.In order to investigate the effect of coexistence of phenolic and non-phenolic lignin on AOX formation,the coexisted reaction of VA and VE with chlorine dioxide was studied.Reaction conditions were as follow:the total concentration of VA and VE was 124.00 mmol·L-1,the molar ratio of ClO2/lignin model compounds was 1,the molar ratio of VA/VE was 1,pH valuewas 3,the temperature was 70?.The AOX formation in coexisted reaction was higher than the total AOX formation in separated reaction.The VE consumption was also higher in coexisted reaction.The AOX formation increased with the ratio of VE if the total concentration of VA and VE remained constant.Among the chlorinated products formed by coexisted reaction,the components with higher relative content were from the reaction of VE with chlorine dioxide.Besides,new chlorinated product like 5-chlorovanillic acid,was also formed.The AOX formation kinetic model in coexisted reaction of VA and VE with chlorine dioxide was established:dW/dt=3918.32·e-(82.99/T)··[H+]0.023·[ClO2]0.96·[C]0.47.Its reaction activation energy is 1558.73J·mol-1,approximating that of VE separated reaction.