CN104928964B - 一种减少非木浆造纸氯气漂白过程中二噁英生成的方法 - Google Patents
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Abstract
本发明涉及一种减少非木浆造纸氯气漂白过程中二噁英生成的方法。该方法包括a)最佳pH条件下漂白:非木浆水悬浮液与氯气混合,并将该混合物在温度为20℃,调节体系初始pH值至最佳pH值3,高速搅拌下漂白60min;b)最佳温度下漂白:将非木浆水悬浮液与氯气混合,并将该混合物在体系初始pH为1,调节体系温度至最佳温度30℃,高速搅拌下漂白60min。在最佳pH值和最佳温度下漂白,可有效的减少非木浆氯气漂白过程中二噁英的生成,对于制浆造纸业二噁英减排和环境保护有重要意义。
Description
技术领域
本发明涉及一种减少非木浆造纸氯气漂白过程中二噁英生成的方法。
背景技术
二噁英(PCDD/Fs)是多氯代二苯并二噁英(PCDDs)和多氯代二苯并呋喃(PCDFs)的统称。PCDD/Fs是一类毒性极强的含氯有机化学物质,其碳原子上的氢均可被氯原子取代。根据氯原子的取代数目和取代位置的不同,该类化合物可形成210种同类物,其中PCDDs有75种,PCDFs有135种。PCDD/Fs的毒性与分子中氯原子的取代数目和取代位置相关。一般认为,17种2,3,7,8位同时被氯原子取代的同类物具有毒性,其中2,3,7,8-TCDD的毒性最大。PCDD/Fs具有环境持久性、长距离迁移性、生物累积性以及高毒性。PCDD/Fs在环境介质中难于降解转化,容易长时间滞留;同时由于其具有半挥发性,能够通过大气环流作远距离迁移,甚至沉降到地球的偏远极地地区,造成全球范围的污染传播。另一方面,PCDD/Fs具有高脂溶性的特点,易在生物体内累积,并沿着食物链逐级放大,对处于最高营养级的人类的健康产生诸多危害。PCDD/Fs能够通过皮肤、粘膜、呼吸道和消化道进入人体。长期暴露在PCDD/Fs含量较高的环境中,进入人体的PCDD/Fs会蓄积在肝脏和脂肪组织中,可能会引起肝毒性、免疫毒性、内分泌毒性等,表现为皮肤痤疮、失眠头痛、肝肺功能异常、神经系统损伤等疾病,对人体健康造成严重伤害。
废物焚烧、钢铁冶炼、有色金属再生、制浆造纸、殡葬、化工领域等六大行业是我国PCDD/Fs主要的污染源头和重点控制行业。制浆造纸被认为是化学品和消耗性产品中最大的PCDD/Fs排放源。造纸行业中PCDD/Fs主要来源于含氯漂白过程,2,3,7,8-TCDD/TCDF是纸浆漂白生成PCDD/Fs的代表性产物。国家行动计划估算2004年来源于制浆和造纸行业的PCDD/Fs排放为161g TEQ。目前发达国家的纸浆结构以木浆和废纸浆为主,漂白工艺也基本淘汰污染严重的元素氯漂白而采用污染较小的无元素氯漂白(ECF)技术,并向全无氯漂白(TCF)工艺发展。结合深度蒸煮和氧脱木素等控制措施,基本解决了木浆制浆造纸过程中PCDD/Fs的排放问题。然而,基于中国人多地少的基本国情,我国造纸业的原料结构组成呈现多元化。我国是非木浆的主要生产国和使用国,并且采用非木浆造纸具有明显的社会效益,在一定时期内是不可替代的。目前我国的制浆漂白工艺仍停留在次氯酸盐单段漂白(H)或CEH多段漂白水平,这些因素决定了我国制浆造纸行业存在环境高污染、水能高消耗的问题。
我国对造纸工业过程中PCDD/Fs的研究起步较晚,所以草浆、苇浆等非木浆氯气漂白过程中PCDD/Fs的生成,排放及减排技术的报道很少。1997年,Zheng等首先考察了五个以草浆、苇浆等为原料的非木浆造纸厂含氯漂白浆中PCDD/Fs的生成情况,分析结果显示非木浆氯化产物分布模式与木浆有所不同,认为可能是因为芦苇和木材的纤维组织结构不同造成的,说明纤维组织结构对氯化反应的影响较大。2001年,Zheng等进一步对我国苇浆造纸厂CEH漂白生产线上PCDD/Fs的排放情况进行了研究。C段,E段,H段浆中PCDD/Fs的毒性当量浓度分别为10.3,12.9,9.5pg/g,漂白废水中浓度高达315.6pg/L,说明苇浆在含氯漂白过程中生成了大量的PCDD/Fs。随着履行斯德哥尔摩公约工作的深化,以草浆、苇浆为原料的非木浆制浆造纸过程中的PCDD/Fs排放问题已引起越来越多的关注。2008年,联合国环境保护署发布的减少或消除纸浆漂白过程中PCDD/Fs的最佳可行性方案指导意见中指出,用二氧化氯代替氯气漂白可以大大减少PCDD/Fs的排放,使用不含氯的漂白剂漂白基本上可以达到PCDD/Fs的零排放。然而,对于我国非木浆造纸行业以氯气和次氯酸盐漂白为主实际情况,到目前为止,还没有适合我国国情的非木浆氯气漂白过程中PCDD/Fs的减排措施。
发明内容
本发明的目的在于提供一种减少非木浆造纸氯气漂白过程中二噁英生成的方法。该方法包括a)最佳pH条件下漂白:非木浆水悬浮液与氯气混合,并将该混合物在温度为20℃,调节体系初始pH值至最佳pH值3,高速搅拌下漂白60min;b)最佳温度下漂白:将非木浆水悬浮液与氯气混合,并将该混合物在体系初始pH为1,调节体系温度至最佳温度30℃,高速搅拌下漂白60min。漂白后纸浆中二噁英含量用同位素稀释高分辨气相色谱-高分辨质谱法进行测定(HRGC-HRMS)。体系初始pH或漂白温度越高,体系中以分子态存在的氯(Cl2)越少,非木浆氯气漂白生成的二噁英越少;但pH过大或温度过高,会导致非木浆纤维素的氧化降解严重,从而影响纸产品质量。所以,初始pH及漂白温度在一定范围内存在一个最佳值。在最佳pH值和温度下漂白,可有效的减少非木浆氯气漂白过程中二噁英的生成,对于制浆造纸业二噁英减排和环境保护有重要意义。
本发明提供的一种减少非木浆造纸氯气漂白过程中二噁英生成的方法。a)最佳pH条件下漂白:非木浆水悬浮液与氯气混合,并将该混合物在温度为20℃,调节体系初始pH值至最佳pH值3,高速搅拌下漂白60min。包含以下内容:
1)、非木浆水悬浮液与酸溶液及氯气混合:漂白期间,酸溶液与非木浆悬浮液及氯气混合。漂白期间,非木浆水悬浮液一直处于高速机械搅拌(800转/min)下,以达到充分混合;
2)、所述的酸溶液为12mol/L的盐酸溶液;
3)、所述的漂白中体系的温度为20℃;
4)、所述的最佳pH条件为3,此时12mol/L的盐酸溶液用量为60μL;
5)、所述的漂白时间为60min;
6)、所用非木浆为麦草纤维原料经化学处理制取的化学浆,化学浆制取方法参见图书:制浆原理与工程第三版(中国轻工业出版社)。
本发明提供的一种减少非木浆造纸氯气漂白过程中二噁英生成的方法。b)最佳温度下漂白:将非木浆水悬浮液与氯气混合,并将该混合物在体系初始pH为1,调节体系温度至最佳温度30℃,高速搅拌下漂白60min。包含以下内容:
1)、非木浆水悬浮液与酸溶液及氯气混合:漂白期间,酸溶液与非木浆悬浮液及氯气混合。漂白期间,非木浆水悬浮液一直处于高速机械搅拌(800转/min)下,以达到充分混合;
2)、所述的酸溶液为12mol/L的盐酸溶液;
3)、所述的漂白中体系初始pH值为1,12mol/L的盐酸溶液用量为7mL;
4)、所述的不同温度下漂白:最佳温度为30℃;
5)、所述的漂白时间为60min;
6)、所用非木浆为麦草纤维原料经化学处理制取的化学浆,化学浆制取方法参见图书:制浆原理与工程第三版(中国轻工业出版社)。
漂白后纸浆中二噁英含量通过同位素稀释高分辨气相色谱-高分辨质谱法(HRGC-HRMS)进行测定。
本发明的优点与积极效果为:
本发明基于在不同pH值和温度条件下对非木浆进行氯气漂白,通过分析不同pH值和温度条件下非木浆氯气漂白二噁英的生成量,得到在不影响纸浆强度和白度条件下,减少二噁英生成的最佳氯气漂白pH值和温度条件。采用本发明方法在不降低成品纸张白度的前提下可降低非木浆氯气漂白过程中二噁英的生成量,实现了在我国现有技术水平条件下非木浆造纸行业二噁英减排的目的,对于环境保护重要要意义。
附图说明
图1为不同pH条件下非木浆氯气漂白二噁英生成情况图;
图2为不同pH条件下非木浆氯气漂白2,3,7,8-TCDD/TCDF生成情况图;
图3为不同温度条件下非木浆氯气漂白二噁英生成情况图;
图4为不同温度条件下非木浆氯气漂白2,3,7,8-TCDD/TCDF生成情况图。
具体实施方式
结合附图对本发明的方法作进一步详述。
实施例1
工业制浆造纸中麦草浆采用的氯气漂白条件为氯气用量为5%(氯气质量百分含量,每千克纸浆所用氯气的量),浆浓3%(质量浓度,每升浆水悬浮液中所含纸浆的质量),时间60min,温度25℃,初始pH为2。详见(制浆造纸工艺第二版,中国轻工业出版社)
采用本发明方法不同pH条件下对麦草浆氯气漂白:浆浓及氯气用量与工业麦草浆氯气漂白相同(制浆造纸工艺第二版,中国轻工业出版社),非木浆水悬浮液(3%,20g纸浆,667mL水)与氯气混合,并将该混合物在温度为20℃,调节体系初始pH值分别为0.5,1,2,3,4,5,6,高速搅拌下漂白60min,整个漂白过程中氯气总用量为5%(1g)。在此漂白过程中所用漂白后纸浆中二噁英含量通过同位素稀释高分辨气相色谱-高分辨质谱法(HRGC-HRMS)进行测定。不同pH条件下生成的二噁英生成情况如图1所示。多氯代苯并呋喃(PCDF)在pH实验范围内,随着pH值的增大而减小,pH值达到3之后,PCDF的生成很少;多氯代苯并二噁英(PCDD)在pH为0.5和1时,生成量较大,之后其含量变化不大。从2,3,7,8-TCDD/TCDF的生成(图2)也可以看出,pH值为3时,2,3,7,8-TCDD/TCDF的生成量少。结合PCDD和PCDF的生成情况,我们认为pH为3的条件对于减少非木浆氯气漂白过程PCDD/Fs生成最佳。因为pH大于4时,非木浆纤维的氧化降解严重,会影响产品的质量。
实施例2
采用本发明方法不同温度下漂白:浆浓及氯气用量与工业麦草浆氯气漂白相同(制浆造纸工艺第二版,中国轻工业出版社),将非木浆水悬浮液(3%,20g纸浆,667mL水)与氯气混合,并将该混合物在体系初始pH为1,调节体系温度分别为20℃,30℃,40℃,50℃,60℃,70℃,高速搅拌下漂白60min,整个漂白过程中氯气总用量为5%(1g)。漂白后纸浆中二噁英含量通过同位素稀释高分辨气相色谱-高分辨质谱法(HRGC-HRMS)进行测定。不同pH条件下生成的二噁英生成情况如图3所示。30℃氯化时,PCDF的生成量较20℃显著降低,30℃到70℃之间PCDF的生成量保持平稳;但PCDD在30℃时生成量最多。再对比2,3,7,8-TCDD/TCDF的生成量,从图4可以看出,温度从20℃增加到30℃,2,3,7,8-TCDD/TCDF的生成显著降低,2,3,7,8-TCDD降低了4倍,2,3,7,8-TCDF降低了7倍。2,3,7,8-TCDD的毒性是所有PCDD中最大的,也是生成量最多的。温度过高时纤维素易发生降解,所以结合PCDD/Fs的生成以及2,3,7,8-TCDD/TCDF的生成情况,我们认为在30℃进行非木浆漂白,可以有效的减少PCDD/Fs的排放。
本发明方法包括a)最佳pH条件下漂白:非木浆水悬浮液与氯气混合,并将该混合物在温度为20℃,调节体系初始pH值至最佳pH值3,高速搅拌下漂白60min;b)最佳温度下漂白:将非木浆水悬浮液与氯气混合,并将该混合物在体系初始pH为1,调节体系温度至最佳温度30℃,高速搅拌下漂白60min。漂白后纸浆中二噁英含量用同位素稀释高分辨气相色谱-高分辨质谱法(HRGC-HRMS)进行测定。体系初始pH或漂白温度越高,体系中以分子态存在的氯(Cl2)越少,非木浆氯气漂白生成的二噁英越少;但pH过大或温度过高,会导致非木浆纤维素的氧化降解严重,从而影响纸产品质量。所以,初始pH及漂白温度在一定范围内存在一个最佳值。在最佳pH值和最佳温度下漂白,可有效的减少非木浆氯气漂白过程中二噁英的生成,对于制浆造纸业二噁英减排和环境保护有重要意义。
Claims (6)
1.一种减少非木浆造纸氯气漂白过程中二噁英生成的方法,其特征在于:
A、将非木浆水悬浮液控制在温度为15-25℃,于体系中通入氯气,用酸溶液调节体系pH值至pH值2.8-3.2,搅拌下漂白55–65min;
或B、将非木浆水悬浮液用酸溶液调节体系pH为0.8-1.2,于体系中通氯气,再调节体系温度至最佳温度28-32℃,搅拌下漂白55–65min;
所用非木浆为麦草纤维原料经化学处理制取的化学浆。
2.按照权利要求1所述的方法,其特征在于:步骤A或B中,漂白期间,酸溶液与非木浆悬浮液及氯气混合;
漂白期间,非木浆水悬浮液一直处于高速800–1000转/min的机械搅拌下,以达到充分混合。
3.按照权利要求1或2所述的方法,其特征在于:所述的酸溶液为6–12mol/L的盐酸溶液。
4.按照权利要求1所述的方法,其特征在于:
步骤A中,漂白中体系的温度为18-22℃;最佳pH值为2.9–3.0;漂白时间为58–60min;
步骤B中,漂白中体系的最佳pH值为0.9–1.1;温度为29-31℃;漂白时间为58–60min。
5.按照权利要求1所述的方法,其特征在于:所述非木浆水悬浮液所含纸浆干重的质量浓度范围为2–4%。
6.按照权利要求1所述的方法,其特征在于:所通入氯气质量范围为每千克纸浆干重的4–6%。
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