title: NH(4)OH-KOH pulping mechanisms and kinetics of rice straw.
abstract: The mechanisms and kinetics of NH(4)OH-KOH mixture pulping rice straw were studied. When aqueous ammonia was mixed with a small amount of caustic potash (ratio of 1:5), three distinct delignification phases were observed in the pulping process: a bulk delignification phase from the beginning of the cooking period to 100 degrees C, a supplementary delignification phase from 100 degrees C to 155 degrees C lasting a further 45 min, and a residual delignification phase until the end of the cooking period. There were two silica removal phases; the first phase was from the beginning of the cooking period to 100 degrees C and the second phase was from 100 degrees C to the end of the cooking period. The rate of delignification reaction was first order with respect to residual lignin and 0.3 order with respect to [OH(-)]. The silica removal was pseudo-first-order with respect to residual silica and 0.6 order with respect to [OH(-)]. The activation energies of the delignification and removal of silica reactions were 35.6 and 30.9 kJ/mol, respectively.
authors.affiliation: School of Chemical and Biomolecular Engineering, The University of Sydney, NSW 2006, Australia.
authors.forename: Guolin
authors.initials: G
authors.lastname: Huang
authors.forename: Jeffrey X
authors.initials: JX
authors.lastname: Shi
authors.forename: Tim A G
authors.initials: TA
authors.lastname: Langrish
mesh_terms: D064753:Ammonium Hydroxide; D006878:Hydroxides / Q000737:chemistry*; D007700:Kinetics; D008031:Lignin / Q000737:chemistry; D012275:Oryza; D017680:Potassium Compounds / Q000737:chemistry*; D012822:Silicon Dioxide / Q000737:chemistry; D013783:Textile Industry
chemical_list: D006878:Hydroxides; D017680:Potassium Compounds; D064753:Ammonium Hydroxide; D012822:Silicon Dioxide; D008031:Lignin; C029943:potassium hydroxide