【作者】 赵德清；

【导师】 陈克复；

【作者基本信息】 华南理工大学 ， 制浆造纸工程， 2010， 博士

【摘要】 我国是世界非木浆的主要生产国,是世界非木材纤维造纸产量最多、经验最丰富的国家。非木浆中禾草浆所占的比例最大,约为60%~65%,禾草浆主要是指麦草浆。在新的环保要求下,AOX排放量已经成为造纸工业水污染物排放限制执行指标,元素氯漂白被禁止使用,以麦草浆为主的非木浆漂白正在加速向ECF和TCF漂白方式转变,以二氧化氯漂白为核心的无元素氯漂白技术,是近期纸浆清洁漂白领域研发和推广的重点技术之一。本论文对麦草浆二氧化氯清洁漂白技术及其机理进行了较为系统的研究,旨在为实现麦草浆ECF清洁漂白提供一定的技术支持和理论依据,促进我国麦草浆ECF漂白早日实现工业化。对麦草浆二氧化氯与氧气脱木素效率及相应的漂白流程进行了对比研究。结果表明,ClO2脱木素(D0)对木素的修饰和改性效果好于氧脱木素(O),在脱木素率不及氧脱木素及接近氧脱木素的条件下,D0段纸浆的可漂性高于O段纸浆的可漂性。在D0段和O段脱木素率相同的条件下,采用D0A/QP、D0EP漂白流程漂后纸浆白度分别比OA/QP漂白流程高11.2%ISO和10.3%ISO。D0段废液和相应D0A/QP漂白流程三段混合废水的CODCr负荷均比O段和OA/QP漂白流程混合废水的CODCr负荷轻。研究了碱抽提协同木聚糖酶处理对麦草浆二氧化氯漂白的强化作用。结果显示,木聚糖酶预处理对ClO2脱木素的改善效果不明显,无论是脱木素前预处理(XD)还是脱木素后处理(DX),ClO2脱木素效率提高不大。采用XDP和DXP漂序,与对照样相比,木聚糖酶对麦草浆ClO2漂白的助漂效果不明显,白度提高仅1.5%ISO左右。在达到略高于对照样终点白度的条件下,木聚糖酶处理可以节省H2O2用量25%～33.3%。采用XDEPP和DXEPP漂序,经H2O2强化的碱抽提EP后,木聚糖酶对麦草浆ClO2漂白的助漂效果显著增强,与对照样相比,可以提高白度4.5%ISO。同样漂序采用木聚糖酶处理可节省ClO2用量17%~20%。碱抽提协同木聚糖酶处理对麦草浆二氧化氯漂白具有较好的强化作用。采用四种不同的碱抽提方式对麦草浆二氧化氯漂白进行强化,考查了不同碱抽提方式的强化效果,并对不同ECF漂白流程进行了对比研究。结果表明:在D0ED1漂白流程中,不同碱抽提方式对D0段木素的修饰效果不同,就后续D1漂段而言,四种不同碱抽提模式下纸浆的可漂性顺序为:D0EOP>D0EP>D0EO>D0E。在D0ED1漂白流程中,D1段pH值对终点白度有显著影响,本实验条件下,麦草浆D1段漂白最佳终点pH值范围为6.0~6.5,NaOH最佳添加量为0.6%~0.8%。研究了添加醛类助剂对非木浆二氧化氯漂白的活化效果。在ClO2脱木素段添加1.0%~1.5%的甲醛助剂,可以有效的促进和改善ClO2脱木素的速率和效率。与对照样相比,ClO2脱木素(D)后和碱抽提后纸浆(DE或DEP)的卡伯值均有所降低,ClO2的实际消耗量增大,表明甲醛对ClO2脱木素有较好的活化作用。除了甲醛以外,乙醛、乙二醛、葡萄糖等醛类或醛糖也可以起到一定的活化效果。对原浆卡伯值为21.7的烧碱-蒽醌法麦草浆,在D段添加1.5%的甲醛助剂,采用DEPP漂序,可使漂白终点白度达到81.8%ISO,比对照样提高了2.5%ISO,部分强度指标有所下降。采用GC-MS气质联用仪对麦草浆ECF漂白各段废水进行定性分析,研究表明,D0段废液的污染负荷明显低于O段和EP段。漂白废液的GC-MS检测分析表明,D0段漂白废液中含有的主要污染物为对苯醌类化合物,其比例为41.9%,D0段废液中还含有少量的含氯化合物,主要以氯代丙酮和含氯芳香化合物形式存在。O段废液的主要污染物为脂肪烃类物质,比例高达51.2%,其次为芳香醛类物质,O段废液中不含苯醌类物质,这是O段废液区别于D0段废液的一个显著特征。EP段废液的主要污染物为脂肪烃和脂肪酸类物质。D1段废液的主要污染物为脂肪酸类物质,脂肪烃类物质相对较少。P段废液的主要污染物为脂肪烃和脂肪酸类物质,总含量比例为85.9%。采用酶解-弱酸解两段法对麦草浆在ECF漂白过程中各段的木素进行分离,并采用红外光谱、紫外光谱、GPC、TG、31P-NMR、1H-NMR等对木素结构及其变化进行了分析。木素的红外吸收光谱分析表明,纸浆经二氧化氯脱木素后木素中的羰基数量增多,随着漂白反应的进行,羰基数量逐渐减少,漂白终点段D1段木素中羰基吸收峰消失。通过对木素进行紫外吸收光谱分析可知,随着漂白反应的进行,280nm处苯环的特征吸收逐渐减弱,漂白终点段D1段和P段木素在280nm处的吸收峰已经消失。木素的热重分析表明,200℃之前木素的热失重现象不明显,200℃之后木素质量百分比开始迅速下降,一直保持到500℃,500℃之后失重率逐渐趋于平缓。木素的GPC分析表明,麦草浆经过ECF漂白流程D0EPD1和D0EPP漂白后,木素试样的数均分子量、重均分子量和多分散性Mw/Mn均有所下降。木素的1H-NMR谱图分析表明,木素中甲氧基质子的含量较高,仅次于脂肪族甲基和亚甲基的质子含量。麦草浆原浆木素中主要含有紫丁香基单元和愈创木基单元,也含有少量的对羟苯基单元,随着漂白反应的进行,木素中的G、S、H三种类型的结构单元比例逐渐下降,侧链上β-O-4和β-l结构中的Hα数量在漂白中逐渐减少,β-O-4的断裂和苯环脱甲基反应是漂白过程中木素大分子降解为小分子的重要反应,醚键的断裂不仅使木素大分子降解为小分子,更使木素中产生了新的游离酚羟基,增强了木素的反应性能。木素的31P-NMR定量分析表明,木素中脂肪族羟基的含量是最高的,其含量高于木素苯环上的酚羟基含量。经二氧化氯脱木素和氧脱木素后木素中的脂肪族羟基含量和总酚羟基含量均有所升高,总酚羟基含量的升高主要是由于缩合酚羟基和对羟苯基酚羟基含量的升高而引起的。经二氧化氯脱木素和氧脱木素后紫丁香基酚羟基和愈创木基酚羟基含量均有所下降,其中紫丁香基酚羟基下降的比例大于愈创木基酚羟基,表明麦草浆二氧化氯脱木素和氧脱木素过程中,主要以紫丁香基结构氧化降解为主。从羧基含量变化来看,麦草浆原浆木素中羧基含量很少,经过二氧化氯脱木素和氧脱木素后羧基含量显著增加,这是二氧化氯脱木素和氧脱木素的一个重要特征。从D0段木素和O段木素中各种羟基含量的对比来看,D0段木素和O段木素中各类羟基和羧基的含量均相差不大。更多还原

【Abstract】 As one of the most experienced countries, China is the world’s major producer of non-wood pulps, whose paper production of non-wood fiber material is the largest all along. The proportion of grass weed pulp in non-wood pulps is the largest at about 60%~65%, which mainly refers to wheat straw pulp. Under the new environmental requirements, the discharge amount of absorbable organic halides (AOX), one vital crucial toxicant in paper industry, has become one forced implementation indicator. With the stern prohibition of elemental chlorine bleaching, the bleaching modes of non-wood pulp, mainly refers to wheat straw pulp currently, are being accelerated and transformed to elemental chlorine free (ECF) and totally chlorine free (TCF) bleaching methods. ECF bleaching technology based on chlorine dioxide is one of the most important technologies being studied and expanded presently. Clean chlorine dioxide bleaching technologies on wheat straw pulp and its mechanism are investigated detailedly in this paper, for the purpose of affording certain technical supports and theory bases for realizing the transform of bleaching modes from traditional CEH to ECF bleaching of wheat straw pulp, which will facilitate the industrial process of ECF clean bleaching of wheat straw pulp and even the whole non-wood pulp.The efficiency of chlorine dioxide delignification and oxygen delignification and corresponding bleaching sequences were investigated comparatively. The results indicated that effects of ClO2 delignification (D0) on the modification of residual lignin were better than that of O2 delignification (O). Under the conditions of lower than and near to the removal rate of O2 delignification, the bleachability of D0 stage pulp was superior to that of O stage pulp. With the same removal percentage of delignification, the final brightness of bleached pulp by D0A/QP sequence and D0EP sequence were 11.2 and 10.3 points higher than the ones bleached by OA/QP sequence respectively. The CODCr loads of the D0 stage filtrate and corresponding mixed effluents by three stages of D0A/QP sequence were lower than those of O stage filtrate and corresponding mixed effluents by three stages of OA/QP sequence.Enhanced chlorine dioxide bleaching of wheat straw pulp by synergetic effect of alkaline extract and xylanase treatment were investigated. Results demonstrated that the improvement of chlorine dioxide delignification with xylanase treatment was not significant. The effectiveness of chlorine dioxide delignification was not increased distinctly whether by xylanase pretreatment prior-delignification (XD) or by xylanase treatment post-delignificatiion (DX). Using XDP and DXP bleaching sequences, the aided bleaching effect of xylanase was not obvious. The final brightness was increased only as much as 1.5 points. Meanwhile, pulp treated with xylanase reduced the consumption of hydrogen peroxide by 25%-33.3%. With peroxide-reinforced extraction (EP) and using XDEPP and DXEPP bleaching sequences, the aided bleaching effectiveness of xylanase was increased significantly, with the final brightness enhanced by 4.5 points. With the same sequences, xylanase treated pulp saved the charge of chlorine dioxide up to 17%-20%, while still maintaining the final brightness at the control level.The modification effects of four kinds of alkaline extraction modes on lignin of chlorine dioxide delignified wheat straw pulps were explored, and various corresponding ECF bleaching sequences were investigated comparatively. Results indicated that in D0ED1 bleaching sequences the modification effects of alkali extraction modes on the residue lignin of D0 stage were different. As far as the subsequent D1 stage was concerned, the bleachability order of pulps, from easiest to hardest, was D0EOP>D0EP>D0EO>D0E. It was demonstrated that in D0ED1 bleaching sequences the influence of pH value on the brightness of D1 stage was significant, the optimal final pH range was 6.0~6.5% and the optimized charge of NaOH was 0.6%~0.8% under the conditions of present experimentation.The activation effectiveness of aldehydes on chlorine dioxide bleaching of non-wood pulps was investigated. The rate and efficiency of chlorine dioxide delignification were enhanced and facilitated effectively through adding 1.0%-1.5% formaldehyde to D stage. Compared to the control, the kappa numbers both in the D stage and in DE or DEP stage were decreased somewhat, simultaneously, the actual consumption of ClO2 was increased, which demonstrated that the improvement of formaldehyde on chlorine dioxide bleaching was certain. Except for formaldehyde, a certain extent of activation effect can be obtained by adding other aldehydes or aldoses, such as acetaldehyde, glyoxal, glucose, et al. The effectiveness of formaldehyde was relevant to the initial kappa number of unbleached pulps. The higher of the initial kappa numbers of unbleached pulps, the better of activating effect of formaldehyde on D stage. By adding 1.5% formaldehyde to D stage and with DEPP bleaching sequences, the unbleached Soda-AQ wheat straw pulps with a initial kappa number of 21.7 reached a final brightness of 81.7%, 2.5 points higher than the control. Correspondingly, some physical strength properties decreased to a certain extent.Various ECF bleaching effluents were qualitative analyzed and quantitative determined using GC-MS analyzer. Results showed that the pollutant load of D0 stage was remarkably lower than that of O stage and EP stage. The analysis of bleaching filtrates by GC-MS analyzer indicated that except for including the main pollutants such as the benzoquinones with the content of 41.9% in D0 filtrate, D0 stage filtrate also contained a small portion of organic chlorine compounds, mainly in the form of chloro-acetone and chlorinated aromatic compounds. Additionally, as for O stage comprising of the main aliphatic hydrocarbons with the content of 51.2%, followed by aromatic aldehydes, there is no any content of ketone in O stage filtrate, which is a significant characteristic different to the D0 stage filtrate. The main pollutant ingredients of EP filtrate were aliphatic hydrocarbons and fatty acids, while the main pollutant types of D1 stage were fatty acids, with lower content of aliphatic hydrocarbons relatively. As with the EP stage, the main pollutant compositions of P filtrate were referred to aliphatic hydrocarbons and fatty acids with the total content of 85.9%.Using two-step methods of enzyme hydrolysis and weak acid hydrolysis, various lignin were isolated from unbleached and bleached wheat straw pulp during the process of ECF bleaching, and then, lignin structure were analyzed through a serious of methods such as FT-IR, UV-VIS, GPC, TG, 31P-NMR, 1H-NMR and so on. FT-IR spectroscopy analysis showed that the carboxyl content of chlorine dioxide delignified pulp was increased, with the subsequent bleaching the carboxyl absorption gradually decreased and then disappeared in the end. UV spectrum analysis showed that with the proceeding beach the characteristic absorption peak of aromatic ring at 280nm gradually disappeared in both D1 pulp and P pulp. Thermal gravimetric (TG) analysis indicated that before 200℃the thermal weight loss of lignin was not obvious and after 200℃the loss percentage began to decline rapidly until 500℃, after 500℃the loss trends became changing flatly and mildly. GPC analysis showed that after ECF beaching sequences as D0EPD1 and D0EPP the number average molecular weight, the weight average molecular weight and polydispersity had declined to some extent.Lignin 1H-NMR analysis showed that the proton concentrations of methoxyl were relatively high, second only to that of aliphatic methyl and methylene. Lignin units of unbleached wheat straw pulp mainly included guaiacyl and syringyl units and a few amounts of p-hydroxylphenyl units. The content of three kinds of units as G, S and H types were all decreased gradually. Especially, the content ofα-proton in the structure ofβ–O-4 andβ-1 also reduced to some extent, which demonstrated that the rapture ofβ–O-4 and demethylation reaction were the main approaches by which large molecules were degraded into small ones. Moreover, the rapture of ether bonds not only degraded large lignin molecules into small ones, but also produced new phenolic hydroxyl groups, which can enhance the reactivity of lignin.31P-NMR analysis indicated that the content of aliphatic hydroxyl was higher than the ones of phenolic hydroxyl of benzene ring. After chlorine dioxide delignification and oxygen delignification the content of aliphatic hydroxyl and total phenolic hydroxyl increased somewhat, mainly due to the contribution of the rise of the content of condensed phenolic hydroxyl and p-hydroxylphenol phenolic hydroxyl. After chlorine dioxide delignification and oxygen delignification the phenolic hydroxyl content of both syringyl and guaiacyl declined to some extent, moreover, the drop percentage of the former was higher than the later, indicating that the degradation of syringyl was the principal degradation form during chlorine dioxide delignification and oxygen delignification. As for the change of carboxyl content, almost to the zero content in unbleached wheat straw pulp, the carboxyl content after ClO2 and O2 delignification were raised significantly, which was one prominent characteristic of ClO2 and O2 delignification. In terms of the comparison of hydroxyl content between D0 lignin and O lignin, the distinction of the contents of various hydroxyl and carboxyl were not significant.更多还原