造纸专业英语2.ppt

《造纸专业英语2.ppt》由会员分享，可在线阅读，更多相关《造纸专业英语2.ppt（11页珍藏版）》请在淘文阁 - 分享文档赚钱的网站上搜索。

1、Lesson 13 Pulp bleaching Bleaching is the treatment of wood and other lignocellulosic pulps with chemical agents to increase their brightness.Brightness is increased by decolorizing or dissolving the colored components in pulp,primarily lignin.Two approaches are used in the chemical bleaching of pul

2、ps.bleach v.漂白漂白lignocellulosic 木质纤维素的木质纤维素的agent 【化学化学】药剂药剂 brightness 亮度亮度decolorize vt.使脱色使脱色dissolve vt.使溶解使溶解component n.组分组分 Lesson 13 Pulp bleaching One is to almost totally remove residual lignin,which is used for bleaching of chemical pulps and leads to greater fiber-fiber bonding strength

3、in paper but weaker fibers due to the strong chemical used to decrease the length of cellulose molecules.The other approach is to utilize chemicals that selectively destroy some of the chromophoric groups in mechanical pulps,which is referred to as lignin-preserving or brightening.residual 残余的，剩余的残余

4、的，剩余的bond v 结合，使粘合结合，使粘合strength 强度强度chemical 化学药品化学药品molecule 分子分子chromophoric 发色的，发色团的发色的，发色团的group 基团，基基团，基 mechanical pulp 机械浆机械浆brightening 显白，显亮显白，显亮Lesson 13 Pulp bleaching Since lignin is a complex molecule with different linkages,the breakage of various types of bonds requires the use of di

5、fferent chemicals.Therefore,all the colored material in pulps can not be eliminated by any single chemical and bleaching is a multi-step plex 复杂的，多元的复杂的，多元的linkage 【化化】键合，成键键合，成键Lesson 13 Pulp bleaching The principal commercial bleaching chemicals consists of the oxidants:chlorine(C),oxygen(O),hypoc

6、hlorite(H),chlorine dioxide(D),hydrogen peroxide(P),and ozone(Z);the only reductant:hydrosulfite;and the only alkali:sodium hydroxide(E,or caustic extraction).oxidant 氧化剂氧化剂chlorine 氯氯oxygen 氧气氧气 hypochlorite【化化】次氯酸盐次氯酸盐chlorine dioxide 二氧化氯二氧化氯hydrogen peroxide 过氧化氢过氧化氢ozone【化化】臭氧臭氧reductant 还原剂还原剂

7、hydrosulfite【化化】亚硫酸氢盐亚硫酸氢盐alkali 碱碱 sodium hydroxide 氢氧化钠氢氧化钠caustic extraction 碱抽提碱抽提 Lesson 13 Pulp bleaching It is possible to rank each of the oxidizing chemicals for economy,selectivity,and particle bleaching,although it must be remembered that the particular conditions of use will greatly effe

8、ct on ranking.The rankings are:Economy:OCDHPZ;Selectivity:Delignification DCOZBrightening:D,PHParticle bleaching:DH,C,O,PZdelignification 脱木素作用脱木素作用Lesson 13 Pulp bleaching Because of their greater economy,chlorine and oxygen are used in the early stages of bleaching for lignin removal,but can not b

9、e used for more extensive treatment because their poor selectivity results in cellulose degradation.Chlorine dioxide,hypochlorite,and peroxide can be used in the later stage due to their selectivity and also their higher cost.Selectivity 选择性选择性degradation 降解作用降解作用Lesson 13 Pulp bleaching We can divi

10、de bleaching sequences into two parts:delignification and brightening.In the delignification part,lignin removal is the objective and kappa number is used as the principal control parameter.In the brightening part,higher brightness is the objective and brightness is the main control parameter.Oxygen

11、 can be used either before chlorination or after as an additive to the E stage(Eo).In the delignification part of the sequence,80%-85%of the residual lignin in unbleached pulp is removed.kappa number 卡伯值卡伯值parameter 参数参数chlorination【化化】氯化氯化(作用作用)additive 添加的添加的,附加的附加的;添加物添加物unbleached 未漂的未漂的Lesson 1

12、3 Pulp bleaching The brightening part of the sequence can be single stage,i.e.,H to reach 70%brightness.Or this part can be 3 or 4 stages to reach 90%brightness.Hypochlorite and chlorine dioxide are the principal bleaching agents in this part.Sequences more typical of modern mills for bleaching soft

13、wood kraft pulp are(D+C)(E+O)DED and O(D+C)(E+O)D.The most widely adopted short sequence is(D+C)(EO)D.In most cases,each bleaching stage is followed by a washing stage to remove reaction products.Lesson 13 Pulp bleaching Sulfite and hardwood kraft pulps are“easier bleaching”than softwood kraft pulps

14、.Both have lower lignin content,and the lignin residues in sulfite pulps are partially sulfonated and therefore more readily solubilized.Consequently,a somewhat simpler process can be used to achieve a comparable brightness level.sulphonate 磺酸盐，使磺化磺酸盐，使磺化solubilize v.溶解溶解Lesson 13 Pulp bleaching For

15、 mechanical pulp bleaching or pulp brightening,in order to retain the advantage of high yield,pulps must be decolored or brightened by methods that do not solubilize any appreciable amount of lignin.Commercially used chemicals for this purpose today are sodium hydrosulfite which has a reductive acti

16、on,and hydrogen peroxides which have an oxidative action.Single-stage treatments are sufficient for improving the eye appeal of newsprint-type pulps.Brightness level over 80 can often be achieved by a modern two-stage peroxide or peroxide/hydrosulfite sequence.decolor 脱色脱色appreciable 可观的可观的,可以感到的可以感到的reductive 还原性的还原性的oxidative 氧化性的氧化性的课堂练习课堂练习列出与氧有关的词列出与氧有关的词列出与氯有关的词列出与氯有关的词列出与氢（水）有关的词列出与氢（水）有关的词列出与硫有关的词列出与硫有关的词