Cooking And Bleaching Processes Improvements Of Silvergrass

In this paper,silver grass was used as the raw material,and the cooking process of traditional neutral sulfite antraquinone?NS-AQ?pulping was improved,the bleaching process of the NS-AQ pulp and Soda-AQ pulp were also modified.Firstly,some improvements of cooking process were made to utilize the cooking waste liquoras chipboard adhesive directly,with guaranteed pulp quality.Secondly,in order to improve delignification selectivity,the bleaching process of NS-AQ/Soda-AQ pulp were modified,putting Ep as the first bleaching stage to replace oxygen delignification process,and their bleaching effects were compared.The optimum conditions for silver grass NS-AQ cooking were as follows:the maximum temperature was 165?,time to maximum temperature was 100 min,holding time was 120 min,sodium sulfite charge was 14%,sodium carbonate charge was 2%,AQ charge was 0.1%,and liquor ratio was 1:5.Some properties of silver grass NS-AQ pulp produced under the optimum cooking conditions were determined.The screened pulp yield was 60.63%,and its Kappa number was 17.9.The cooking waste liquor's pH value was 7.9,and its viscosity was 25.9 mPa·s.The influence of active alkali charge,H₂O₂ dosage,reaction temperature as well as reaction time of Ep stage on the bleaching effect of silver grass Soda-AQ pulp and NS-AQ pulp were also evaluated.It appeared that the delignification rate increased with the addition of NaOH,but the excess of NaOH dosage had a slight influence on delignification and bleached-pulp brightness,and also resulted in the decrease of pulp viscosity.Temperature rose was good for delignification.The delignification rate rose markedly as the temperature ranged from 65? to 75 ?.With temperature exceeding 85?,the rate of delignification leveled off and the pulp brightness varied slightly,while the pulp viscosity reduced significantly.Extension of reaction time favored delignification,but resulted in significant reduction of pulp viscosity.Increasing dosage of H₂O₂ accelerated delignification and contributed significantly to increasing brightness of pulp,while the pulp viscosity lowers tinily.The optimum parameters for Ep bleaching of Soda-AQ pulp were as follows:pulp consistency 10%,temperature 95?,NaOH dosage 2%,H₂O₂ dosage 0.5%and reaction time 120 min.Under the optimum Ep bleaching conditions,some properties of produced Soda-AQ pulp were determined to be:Kappa number 8.81,pulp viscosity 1208 mL/g,pulp brightness 41.5%ISO and the pulp yield 95.71%.The optimum parameters for Ep bleaching of NS-AQ pulp were as follows:pulp consistency 10%,temperature 85?,NaOH dosage 3%,H₂O₂ dosage 0.5%and reaction time 120 min.Under the optimum Ep bleaching conditions,some properties of produced NS-AQ pulp were determined to be:Kappa number 9.65,pulp viscosity 1281 mL/g,pulp brightness 43.2%ISO and the pulp yield 96.64%.And the pulp viscosity of NS-AQ pulp was 1100 mL/g,pulp brightness 84.5%ISO,pulp yield EpDP bleached 91.0%.Compared with oxygen delignification,Ep bleached-pulp brightness was 43.1%ISO with the same Kappa number?Kappa number 10.2?of the NS-AQ pulp,and differed slightly from oxygen delignification?43.3%ISO?.The damage to carbohydrates was small and Ep-bleached pulp viscosity was 1208 mL/g which was 28 mL/g higher than oxygen delignification.Meanwhile,the pulp yield was 96.73%,also 3.92%higher than oxygen delignification.The delignification selectivity of Ep bleaching was 13.48,which was far greater than that of oxygen delignification.In addition,under normal pressure,Ep bleaching with less equipment investment could be operated simply and conveniently.