Study On The New ECF Bleaching Technology Of Wheat Straw Soda-AQ Pulp

Scientifically and rationally use of grasses fiber raw material for pulping and papermaking is one of the most effective ways to slove the problem of shortage of paper making raw material,simultaneously,is also an important research subject related to the sustainable development of pulp and paper industry in our country.In this thesis,Soda-AQ wheat straw pulp was selected as raw material.The relationship between oxygen delignification of wheat straw pulp yield and Kappa number were studied,moreover,oxygen delignification was improved.The EpDP Light-ECF bleaching technology for wheat straw pulp was developed.The conditions of alkaline extraction(Ep)as the first stage for Light-ECF bleaching were systematically discussed.Then,the bleaching effect of three kinds bleaching sequences(EpDP,ODP and D0EpD1)were Compared.Which all of these,to a certain extent,will offer practical significance and application value in reducing environmental pollution load,besides in improving the pulp yield and quality.The results of the oxygen delignification of Soda-AQ wheat straw showed that the Kapper number down to the same level after oxygen delignification,the higher Kappa number of wheat straw pulp get the higher gotta rate(cooking plus oxygen delignification yield).Generally,we can get better delignification selectivity for wheat straw pulp by oxygen delignification with low temperature and long time.The results of the hydrogen peroxide reinforced alkaline extraction(Ep)with high pH value of wheat straw pulp process conditions showed that both the rose of temperature and the dosage of H2O2 has great impact on the delignification selectivity and brightness of alkaline extraction pulp.Appropriate extension of time can get lower Kappa number and higher viscosity pulp,but contribute little to the improvement of brightness.With the increasing charge of NaOH,the deligninification effect of Ep pulp was significantly enhanced.Eventually,the optimal conditions of the alkaline extraction which was the first stage for the Light-ECF bleaching as follows:pulp concentration 10%,temperature 85?,time 180 min,H2O2 dosage 0.5%,NaOH dosage 3.0%.In this condition,Kappa number of wheat straw pulp was 10.5,lignin removal rate was 29.05%,the brightness was 41.0%ISO,and the viscosity was maintained at 1167 mL/g.Both the sequences of EpDP,ODP and DOEpD1 can make the final wheat straw pulp bleached to more than 80%ISO.Among them,the bleaching sequence of EpDP(ClO2 1.0%dosage at D stage and H2O2 dosage 2.5%at P stage)can make the final wheat straw pulp bleached to more than 85%ISO.In the mean time,EpDP caused less damage to bleached pulp viscosity.Under experimental conditions,when the three different bleaching sequences bleach to the same brightness level,the EpDP bleached pulp got the highest viscosity,and the AOX content of the.bleaching waste liquor is lower.The AOX occurrence of waste liquor both the D stage and P stage were only 0.28 kg.t-1 pulp when the pulp brightness up to 85.6%ISO.