Research On Energy-saving And Clean Oxygen Pulping System Of Rice Stra

Fibrous materials insufficient resources has become one of the bottlenecks affecting the sustainable development of papermaking industry of our country.It is important how reasonable to develop utilize non-wood fiber,especially the cereal straw and agricultural waste.This kind of raw material is abundant in natural resources,cheap and achieve easily.Combination of clean,energy-saving method of pulping with bleaching technique for straw pulping will be a way of sustainable development to relieve the strain on the shortage of raw materials.This thesis as a part "study on highly energy-saving clean preparation of cereal straw pulp with total oxygen pulping"supported by National Natural Science Foundations of China,mainly focus on the optimization of low-temperature alkali-oxygen pulping of rice straw,the subsequent ozone bleaching and its bleached effluent recycle in ozone bleaching process.This study is to aim at establishing the total oxygen pulping system for rice straw,in order to lay a solid foundation for its industrial application.1)Alkali-oxygen pulping of rice straw under a lower temperature was studied in this thesis.The optimized conditions were alkali charge of 18%,MgSO4 charge of 0.5%,raw material-to-liquor ratio of 1:5,pre-cooking temperature of 115℃,time at pre-cooking of 0 min,and maximum alkali-oxygen cooking temperature of 105℃ for 180min,initial oxygen pressure of 0.6MPa.The resultant pulp had screened yield of 52.06%,kappa number of 9.61,viscosity of 848 ml/g,and brightness of 51.6%.In addition,the screened yield get rid of parenchyma cells of 45.47%,kappa number of 8.59,brightness of 52.7%,and viscosity of 832ml/g.The obtained parenchyma cells had yield of 6.93%,kappa number of 9.95,brightness of 40.3%,and viscosity of 572ml/g.2)Subsequently,bleaching with ozone for alkali-oxygen rice straw pulp was investigated.The optimized ozone bleaching were carried out under pulp consistency of 50%with ozone flow of 0.5kg/(odt·min)for 10min at pH=1.5.The resultant bleached pulp had kappa number of 3.65,brightness of 70.0%,and viscosity of 768 ml/g.The effect of five additives on the ozone bleaching was compared under the optimum bleaching conditions.It was found that oxalic acid is the most effective for protecting carbohydrates in ozone bleaching.With the action of oxalic acid,the properties of the obtained pulp showed higher viscosity and selectivity.The best usage of oxalic acid of 1.5%.Compared with no additives bleached pulp,kappa number of the resulted pulp decreased by 28.22%,the brightness increased by 2.5%,viscosity dropped by 20ml/g,pulp yield increased by 1.77%,and selectivity from 6.57 to 9.95.3)Only one step of ozone bleaching has not yet made the alkali-oxygen rice straw pulp reach an expectant brightness.Two stage of ozone bleaching was shown to be able to meet the demand of the pulp with 80%brightness.The optimized ozone bleaching was that the bleaching time in first stage of ozone(Z1)and the second stage of ozone(Z2)were 10min and 5min,the dosages of oxalic acid of 1.5%and 0.5%respectively,and the rest of the conditions keep constant.It gave rise to high quality of straw pulps with brightness of 80.1%,and showed high selectivity,where the lost of the pulps in viscosity was rarely low.Additionally,clean water washing instead of acid washing treatment between the two stage of the bleaching had no negative impact on the bleached pulp,also can save drug dosage and shorten bleaching process.4)Considering that oxalic acid as well as other effective degraded fraction formed in the ozone bleaching waste liquors can used as carbohydrate protectors,the bleached effluent was recycled in the ozone bleaching.The results,through characterization of infrared spectrum(FT-IR)and the BET specific surface testing for the pulps,showed that effluent recycle had no negative effect on the properties of rice straw pulp.Therefore,the system closure of the ozone bleaching waste liquor can be achieved.The results from the study showed that the cooperation of alkali-oxygen at low-temperature with highly selectively bleached with ozone gave rise to our desiring rice straw bleached pulp with high quality.The process only related to three-step treatment in the total oxygen pulping had obvious advantages in high efficiency,energy-saving.Furthermore,the target for the system closure may be achieved with the help of the recycle of bleaching effluent,so as to realize the full-clean production of rice straw.