MODIFIED PULPING OF EUCALYPTUS TERETICORNIS AND LEUCAENA LEUCOCEPHALA FOR ENERGY AND CHEMICAL SAVING

Abstract

Eucalyptus tereticornis and Leucaena leucocephala are two fast-growing deciduous tropical hardwoods that were characterized for their morphological and chemical characteristics to assess their suitability for pulp production. Raw material pulping is a highly energy-intensive and pollution-generating step in the papermaking process. This study focused on combined mechanical and xylanase treatment before the kraft pulping of E. tereticornis and L. leucocephala. The objectives of the present study are as follows:  Modified pulping of eucalyptus tereticornis for improved yield and chemical saving.  Modified pulping of Leucaena leucocephala (Suu Babool) for improved yield, chemical and energy saving.  Morphological and proximate chemical studies of Eucalyptus tereticornis and Leucaena leucocephala to check their suitability and potential for production of chemical-grade pulps.  Optimization of kraft pulping process in order to reduce the kappa number prior to escalating the pulp yield of eucalyptus tereticornis and Leucaena leucocephala and effect of bio- pulping on pulp yield, optical and strength properties of pulp. The study has been presented in six chapters. The introduction was provided in chapter 1 of this thesis which mentioned Chemical compositions of different paper-making raw materials, global fiber furnish production, distribution of pulp production worldwide, Major raw materials for paper, paperboard top five paper & paperboard consuming countries and newsprint in India and distribution of paper production worldwide. Energy consumption in Indian paper mills and biopulping were also mentioned. The literature review was included in chapter 2 on the issues with the modified pulping. This chapter provided an overview of kraft pulping processes. The elimination of lignin to allow the fibers to be separated with little damage is known as chemical pulping or boiling of wood. This would be ideal if none of the fiber wall components other than lignin were removed. Existing pulping procedures, such as the kraft process, remove considerable quantities of other components, mostly hemicelluloses and some cellulose, along with lignin, in a strongly alkaline solution made primarily of OH and HS ions. Details of degradation of lignin, mechanism of peeling reactions, types of lignin and hemicelluloses linkages, mechanical treatment by Impressafiner, working principle of Impressafiner. The experimental part was discussed in chapter 3 in which the details of morphological and chemical characteristics of eucalyptus tereticornis and Leucaena leucocephala and their impact on kraft pulping. Laboratory handsheets preparation and analysis of pulp and paper properties are also mentioned. This chapter also provided fiber morphology, proximate chemical analysis and chemical characterization of E. tereticornis and L. leucocephala. Proximate chemical analysis of E. tereticornis and L. leucocephala. The cold and hot water soluble fractions in L. leucocephala were higher when compared to E. tereticornis and T. orientalis both species contained lower water-soluble fractions when compared to E. tereticornis and T. orientalis. This may have been due to a lower amount of inorganic compounds, in addition to tannin, gums, and sugars. The low water solubility indicated that fewer pulping chemicals were required to produce a high pulp yield with a low Kappa number. E. tereticornis has an average fiber length of 0.823 mm with a fiber width of 15 μm while L. leucocephala has an average fiber length of 0.964 mm with average fiber width of 25.4 mm. The Lumen diameter and cell wall thickness for E. tereticornis fibers were found to be 6.67 μm and 4.6 μm respectively and for L. leucocephala fibers these were 13.20 μm and 10.60 μm respectively. Chapter 4 included xylanase pretreatment of mechanically destructured wood chips of eucalyptus tereticornis and its effect on kraft pulping. Collection of raw material and chemical composition, xylanase pretreatment and pulping Studies was mentioned. Laboratory handsheets preparation and analysis of pulp and paper properties, results and discussion of pulping of non- destructured wood chips of eucalyptus tereticornis, pulping of destructured wood chips of eucalyptus tereticornis and pulping of destructured xylanase-treated (DXT) wood chips of eucalyptus tereticornis. Effect of mechanical and xylanase pretreatment on strength properties studies. This study focused on combined mechanical and xylanase treatment prior to the kraft pulping of E. tereticornis. A screened pulp yield of 49.1% with a Kappa number of 24.9 was obtained at the optimum cooking temperature of 160℃ without any pretreatment of the wood chips. After mechanical treatment (destructuring), a slightly higher screened pulp yield (49.4%) was obtained with a Kappa number of 24.2 at the cooking temperature of 145℃ with the same active alkali charge (15%). The optimum cooking temperature was further reduced to 140℃ for the destructured xylanase-treated wood chips. The xylanase treatment resulted in a 2% reduction in screened pulp yield due to hydrolysis of xylan. However, the Kappa number was reduced to 18.2 after xylanase pretreatment of the mechanically destructured wood chips. The combined pretreatment (destructured and xylanase treatment) of wood chips resulted in a reduction in cooking temperature by 20℃ compared to untreated wood chips. This reduction in cooking temperature can effectively reduce electrical energy requirements. Further, the combined pretreatment improved the pulp brightness by 2.0 (ISO points) and physical strength properties, which included the tensile index, tear index and burst index by 11.06%, 21.72%, and 21.79%, respectively, compared to the control. Chapter 5 covered the influence of mechanical operation on the biodelignification of Leucaena leucocephala by xylanase treatment. Fungal hyphae are unable to penetrate the core of the chips and are adhered to the surface of wood chips. In this way, enzymes secreted by the fungi are not able to hydrolyze lignin-carbohydrate linkages in the core of wood chips. Less porous structure, pore diameter, and surface area of wood chips are considered the major obstacles to biopulping. Keeping this objective in view, the surface area of wood chips of L. leucocephala can be increased by passing it through an Impressafiner. An Impressafiner compresses the chips and converts them into spongy materials. Wood chips of L. leucocephala with or without destructuring and destructured wood chips followed by enzymatic treatment were subjected to Kraft pulping at different temperatures varying from 135 to 170℃ and active alkali varying from 12-20% (as Na2O) to observe the effect of screened pulp yield and kappa number. The destructured wood chips followed by enzymatic treatment produced a pulp yield of 48.2% and kappa number 18.6. L. leucocephala without destructuring produced a pulp yield of 50.1% and kappa number 23.7. When the pulp was subjected to oxygen delignification to reduce kappa number in the vicinity of 18.6, pulp showed shrinkage by 6.64% compared to Kraft pulp of destructured wood chips followed by enzymatic treatment. Kraft pulp produced from destructured wood chips of L. leucocephala followed by enzymatic treatment showed a net saving of US$ 163.15 per digester over Kraft pulp produced without destructuring of wood chips of L. leucocephala. Moreover, the pulp obtained by destructuring followed by enzymatic treatment improved pulp brightness and physical strength properties including tensile, tear, and burst index significantly compared to pulp obtained without destructuring. The 6th chapter included the conclusion of this thesis by including the results, major achievements along with recommendations for future scope in this field.