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Lastdevelopmentsinpulpbleaching–OzonebleachingChemicalmodificationoffibresEFPGresearc...
Last developments in pulp bleaching – Ozone
bleaching Chemical modification of fibres EFPG research teams
2 - Why using ozone for the bleaching of chemical pulps ? Tutorial
Dominique Lachenal, Christine Chirat, Guillaume Pipon (EFPG)
Chemical pulp bleaching consists in the removal of 100% of the residual lignin left after cooking, and in the degradation of the remaining coloured groups when the lignin has gone
In both cases ozone appears to have a high efficiency. Chemistry considerations explain why the displacement ratio between ozone and chlorine dioxide is higher than1.5 in delignification (by weight). One reason relates to the higher number of electrons that ozone can exchange (on a weight basis). Another reason is due to the fact that although both ozone and chlorine dioxide participate in secondary reactions with the primary lignin oxidation products (muconic acid-type structures), ozone degrades them in smaller molecules which are soluble whereas chlorine dioxide does not. Consequently substitution of ozone for chlorine dioxide must lead to cost saving.
At the end of bleaching coloured groups are still present. These chromophores necessarily contain conjugated carbon-carbon double bonds and carbonyl groups. Again chemistry suggests that ozone must be more efficient than chlorine dioxide, since ozone is far more reactive with double bonds than chlorine dioxide.
The risk of pulp damage during ozone treatment must be taken into consideration and discussed. Contrary to chlorine dioxide, ozone may react with pulp carbohydrates. The most probable mechanism is the direct attack of molecular ozone on hemicellulose and cellulose. However several considerations indicate that in proper conditions pulp degradation must be marginal. In fact (1) lignin is far more reactive with ozone than carbohydrates and acts as a protector, (2) among carbohydrates, the amorphous and more accessible hemicelluloses should be attacked well before cellulose and (3) even if ozone molecules reach the cellulose chains, then the formation of carbonyl groups will precede the depolymerisation of cellulose.
Another concern is the effect of temperature on cellulose degradation during an ozone treatment. Nothing indicates that at moderate temperature (50-70°C), cellulose should be more degraded than at room temperature. On the contrary literature data suggest that cellulose depolymerisation would be actually less pronounced at 60°C than at 20°C.
Overall ozone possesses all the requirements to become a universal bleaching agent of chemical pulp. 展开
bleaching Chemical modification of fibres EFPG research teams
2 - Why using ozone for the bleaching of chemical pulps ? Tutorial
Dominique Lachenal, Christine Chirat, Guillaume Pipon (EFPG)
Chemical pulp bleaching consists in the removal of 100% of the residual lignin left after cooking, and in the degradation of the remaining coloured groups when the lignin has gone
In both cases ozone appears to have a high efficiency. Chemistry considerations explain why the displacement ratio between ozone and chlorine dioxide is higher than1.5 in delignification (by weight). One reason relates to the higher number of electrons that ozone can exchange (on a weight basis). Another reason is due to the fact that although both ozone and chlorine dioxide participate in secondary reactions with the primary lignin oxidation products (muconic acid-type structures), ozone degrades them in smaller molecules which are soluble whereas chlorine dioxide does not. Consequently substitution of ozone for chlorine dioxide must lead to cost saving.
At the end of bleaching coloured groups are still present. These chromophores necessarily contain conjugated carbon-carbon double bonds and carbonyl groups. Again chemistry suggests that ozone must be more efficient than chlorine dioxide, since ozone is far more reactive with double bonds than chlorine dioxide.
The risk of pulp damage during ozone treatment must be taken into consideration and discussed. Contrary to chlorine dioxide, ozone may react with pulp carbohydrates. The most probable mechanism is the direct attack of molecular ozone on hemicellulose and cellulose. However several considerations indicate that in proper conditions pulp degradation must be marginal. In fact (1) lignin is far more reactive with ozone than carbohydrates and acts as a protector, (2) among carbohydrates, the amorphous and more accessible hemicelluloses should be attacked well before cellulose and (3) even if ozone molecules reach the cellulose chains, then the formation of carbonyl groups will precede the depolymerisation of cellulose.
Another concern is the effect of temperature on cellulose degradation during an ozone treatment. Nothing indicates that at moderate temperature (50-70°C), cellulose should be more degraded than at room temperature. On the contrary literature data suggest that cellulose depolymerisation would be actually less pronounced at 60°C than at 20°C.
Overall ozone possesses all the requirements to become a universal bleaching agent of chemical pulp. 展开
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去年发展的漂白臭氧漂白化学改性纤维efpg科研队伍2-为什么用臭氧 为漂白化学纸浆? 补习米尼克lachenal,克里斯蒂chirat, 纪尧姆pipon(efpg)化学纸浆漂白包含在清除100%的残余木质素离开后烹饪 而在退化的其余有色集团当木已经在这两种情况下臭氧似乎 具有效率高. 化学因素解释为什么位移比例臭氧和二氧化氯是高than1.5木质素(按重量计算). 原因之一涉及到较多的电子,臭氧可以换(以重量计算). 另一个原因是由于这样的事实,虽然这两种臭氧和二氧化参加二次反应的 小学木质素氧化产品(muconic酸型结构), 臭氧degrades他们在小分子的水溶性,而二氧化并不. 因此替代臭氧二氧化要带头节约费用. 截至褪色有色集团仍然存在. 这些生色一定含有共轭碳-碳双键和羰基. 化学再次表明,臭氧必须更有效率比二氧化 由于臭氧是远远功与双键比二氧化氯. 风险纸浆期间损害臭氧处理,必须要加以考虑和讨论. 相反二氧化氯,臭氧可与纸浆碳水化合物. 最有可能的机制是直接攻击臭氧分子半纤维素和纤维素. 不过几个因素表明,在适当条件下纸浆退化问题必须边际. 其实(1)木质素来得反应与臭氧比碳水化合物和充当保护者 (2)碳水化合物, 非晶和更方便hemicelluloses应该攻击之前,纤维素(3)即使臭氧分子到达 纤维素链,然后形成羰基将先寡糖的纤维素. 另一项令人关切的是温度效应对纤维素进行臭氧处理. 没有任何迹象表明,在适当温度(50-70摄氏度),纤维素应该更加退化比室温. 对违反有关文献资料显示,纤维素寡糖将其实不太明显,在60°C,比在20°C 臭氧整体拥有所有的条件,成为一种普遍漂白化学纸浆.
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