Biological Pretreatment Of Bagasse Low Temperature Oxygen Alkali Pulping

The problem of resources and environment is the main challenge that mankind is facing today.It is of great value that the low or non-pollution pulping methods are developed and used for non-wood fiber's pulping,and it can ease our country's demand pressure of wood fiber material.Bagasse fiber,a residual by-product aider the extraction of juice from the crushed stalks of cane sugar,is one of the most important raw materials for papermaking industry in our country.According to the theory of cleaner production,a new clean pulping method--soda-oxygen pulping combined with biological pretreatment for the pulping of bagasse was studied in this thesis.The emphasis of the research was put on soda-oxygen pulping of bagasse at low temperature,wet storage pretreatment and biological pretreatment of bagasse and its soda-oxygen pulping at low temperature.An important breakthrough was made in soda-oxygen pulping at low-temperature.It was shown that combination of biological pretreatment with soda-oxygen pulping can reach the clean,energy-saving pulping of bagasse.The main results of the study were snmarized as follows:1)Considering the final screened yield,Kappa number,brightness,viscosity and residual NaOH in the black liquor etc.,the optimal pulping conditions at low temperature can be drawn:alkali charge 23%,T_max100℃,time at T_max180 min, initial pressure of oxygen 0.6 MPa,MgSO₄ charge 0.5%,AOA-1 usage 0.5%,and depithed bagasse consistency 12%.The resultant pulp exhibited the screened yield up to 60.93%,brightness was 63.7%SBD,viscosity was 766 dm³/kg and Kappa number was 14.2)By the lab.simulation of bagasse wet storage experiment,it can be found that there existed biological factors during the storage time,and turning point of this effect was 14-20 days.During the whole process,the cellulose and holocellulose contents of the bagasse showed the trend that went up first and down afterwards,the peak values achieved by 14 days.With the pulping conditions abovementioned as 1), bagasse stored for 14 days got the optimal results were:1# upper layer of the bagasse showing screened yield 65.15%,brightness 61.7%,viscosity 796 dm³/kg and kappa number 13.3;1# lower layer of the one having screened yield 64.65%,brightness 62.6%,viscosity 832 dm³/kg,and Kappa number 14.4.2# upper layer of the bagasse giving screened yield 65.52%,brightness 60.6%,viscosity 823dm³/kg,and kappa number 15.2;2# lower layer of bagasse exhibiting screened yield 64.15%,brightness 61.6%,viscosity 831 dm³/kg and kappa number 14.0.And 3# upper layer of the bagasse displaying screened yield 63.24%,brightness 60.9%,viscosity 829 dm³/kg and kappa number 14.5;3# lower layer demonstrating screened yield 65.33%, brightness64.3%,viscosity 840 dm³/kg and kappa number 14.5.3)By the comparison of soda-oxygen pulping at 100℃for bagasse at different biological pretreatment conditions of white-rot fungi Gr-04,the best pretreatment time was 35days.Since it attained the highest deligninfication degree,as the properties of pulp were:screened yield 60.57%,viscosity 602 dm³/kg and kappa number 10.8. Furthermore,the pulping at the temperature down to 95℃still gained good pulp with screened yield 60.66%,viscosity 634 dm³/kg and kappa number 11.4.4)The structure of lignin in different typical bagasse materials and its soda-oxygen pulps had been studied by the methods of FT-IR,¹H-NMR,¹³C-NMR and GPC.The results showed that both of the wet storage and biological pretreatment performed the function of degradation of the material lignin,and the degradation degree in the biological pretreatment was much bigger.During the pulping processes at low temperature,p-hydroxyphenyl units and sypringyl units of bagasse lignin were much easier degraded than that of guaiacyl units.It provided the theoretical principle for expounding the mechanism of delignification during soda-oxygen pulping process and also gave the supports to optimize the pulping conditions.