Study On Kinetics And Bleaching Process Of Ozone Bleaching Of Low Consistency Pulp

Recently,ozone has been considered as an effective agent for the bleaching of chemical pulp and an alternative bleaching choice to conventional chlorine-contained methods so as to decrease environmental pollutions.Nowadays,the researches and utilizations of ozone in pulp bleaching are mainly focused on the bleaching of high and medium consistency pulp,and there is a few reports regarding to low consistency pulp bleaching.A new automatic reaction equipment system was introduced into our laboratory to study the process of low consistency pulp bleaching with high concentration ozone.Based on the kinetics study of high and medium consistency pulp bleaching with ozone,the reacting rate of low consistency pulp bleaching with ozone was studied in terms of mass transfer.Comparing with the efficiency of different consistency pulp bleaching with ozone,it showed that the efficiency didn't matter with the initial consistency of pulp.Some potential factors such as consistency of pulp,dosage of ozone,pH,concentration of ozone,initial Kappa value of pulp,reacting time and stirring speed were studied,the optimum conditions were obtained as follows:Consistency of pulp:3%;Dosage of ozone:1.0%o.d.p;pH:2;Concentration of ozone:120g/Nm³;Initial Kappa value of pulp:13;Reacting time:30min.;Stirring speed:800r/min.The former listed conditions resulted in brightness:69.2%ISO;viscosity:658mL·g^–1;final kappa value:8.1.Meanwhile,the effects of different additives to protect the carbohydrate from degradation were tested.The selectivity of ozone bleaching were significantly improved when the assistant agent V was introduced into the bleaching system.The brightness and viscosity of bleached pulp was increased by 2.4%ISO and 72 mL/g respectively.According to the characteristics of flax pulp,the bleaching sequence OZEP was suggested.We could get the bleached pulp with brightness:86.0%ISO and viscosity:664mL/g after OZEP sequence.Comparing OZEP bleaching sequence with CEH/ECF bleaching sequences,OZEP were obviously decreased in terms of COD_cr,BOD₅ and Chromaticity.Analyzing the proportions of pentose,carboxyl group and crystallinity of cellulose in the bleached pulp for high consistency as well as low consistency pulp bleaching with ozone,It showed that the degradation of carbohydrates was alleviated to some extent in the low consistency pulp other than high consistency pulp.It was found that the number of carboxyl group obviously decreased and the crystallinity of cellulose relatively increased.It indicated that the degradation of carbohydrate was held down to a relatively larger degree during the process of bleaching with ozone when the assistant agent V was added.At the same time,some instrumental analysis methods such as microscope,scanning electron microscopy?SEM?and fiber quality analyzer were used to test the difference of fiber morphological character between before and after bleaching.It confirmed the conclusion which was got through chemical analysis methods.