【作者】 龚为进；

【导师】 奚旦立；

【作者基本信息】 东华大学 ， 环境工程， 2009， 博士

【摘要】 针对难降解、高浓度有机废水存在的处理成本高、难生化降解、处理效率低等问题,本文提出用超临界水氧化技术来处理这一类废水。以染料废水和丙烯酸废水为研究对象,以过氧化氢为氧化剂,在新兴的蒸发壁式反应器内进行连续流反应。研究反应温度、反应压力、氧化剂用量等因素对染料废水和丙烯酸废水中有机物的降解情况,通过对实验数据的回归分析,建立了染料废水和丙烯酸废水在超临界水中氧化反应的动力学方程;分析提出了染料分子在超临界水中的氧化降解路径;同时,研究了蒸发壁式反应器在反应过程中的腐蚀以及无机盐堵塞情况,最后指出了超临界水氧化技术工业化应用存在的问题。在温度380-460℃,压力20-30MPa,氧化剂用量比n=0.6-2.0的条件下,对染料废水进行超临界水氧化处理,研究各反应因素对染料废水的COD_Cr、TN、NH₃-N和色度降解效果的影响。研究结果表明,温度的提高有利于废水中有机物COD_Cr、TN和色度的去除,并随着温度的升高而上升。温度的影响可以从两个方面来分析。首先有机污染物的氧化反应是一个不可逆的过程。温度升高,反应速率也会随之提高,最终去除率也将随之增加。其次,在压力不变的条件下,温度升高,超临界水的密度会随之降低,反应物的浓度下降,反应速率降低。温度对反应的影响是通过这两个正反效应综合起作用的。在本研究中发现,温度对超临界水氧化反应起积极的作用。在压力为25MPa,停留时间为30s,氧化剂用量比n=1.5,反应温度为460℃的条件下,废水中COD_Cr、TN、TOC和色度的去除率分别达到94.65%、58.15%、97.09%和99.80%。反应压力的升高有利于超临界水氧化反应的进行,废水中COD_Cr、TN和色度的去除率随着压力的上升而提高。压力对有机物氧化降解的影响,一方面是因为温度不变时,压力升高导致水密度的增加,从而增大了有机物和氧的浓度,使反应速率加快的缘故。另一方面,由于水密度的增加,有机污染物在反应器中氧化降解的停留时间有所增加。停留时间的增加,有利于有机污染物的氧化降解。总之,压力的影响可以归结为反应物浓度和停留时间的影响,且两者都是正效应。因此,提高压力将有利于有机污染物的氧化降解。在温度为420℃,停留时间为30s,氧化剂用量比n=1.5,压力为30MPa的条件下,废水中COD_Cr、TN、TOC和色度的去除率分别达到93.35%、66.47%、95.30%和99.80%。氧化剂量对超临界水氧化反应的影响同温度和压力因素基本相似,氧化剂量的增加有利于反应的进行,废水中COD_Cr、TN和色度的去除随着氧化剂量的增加而上升。超临界水氧化染料废水最佳的反应条件为:温度420-440℃,压力25-28MPa,氧化剂用量比n=1.2-1.6。另外,还研究了超临界水氧化反应前后染料废水的可生化性（B/C）。研究表明,经过超临界水氧化处理后染料废水的可生化性大幅度提高,而且随着处理温度的升高和COD_Cr去除率的上升,B/C越来越高,由反应前的0.12,提高到反应后的0.44。可见,超临界水氧化可以大大地改善染料废水的可生化性。在温度370-420℃,压力20-30MPa,氧化剂用量比n=0.0-3.0的条件下,对丙烯酸废水进行超临界水氧化处理,研究结果表明,温度的提高有利于废水中有机物COD_Cr和TOC的去除,并随着温度的升高而上升。当反应温度达到420℃时,COD_Cr和TOC去除率分别为99.09%和98.36%。反应温度升高导致反应过程中活化分子增加,从而提高了氧化反应速度,反应温度升高有利于有机物的去除。丙烯酸废水中COD_Cr、TOC的去除率随着压力的上升而提高。压力升高会增加反应混合物的密度,相应地也会增加反应物的浓度,导致氧化反应的速率加快,COD_Cr和TOC去除率增加。另外,反应过程中超临界反应区域随着压力的升高而延长,这样相对延长了有机物在超临界状态下的停留时间,从而导致COD_Cr和TOC去除率的增加。丙烯酸废水中COD_Cr和TOC的去除随着氧化剂量的增加而上升。氧化剂量的增加,导致反应过程中活性自由基数量的增加,从而加快了氧化反应速率,COD_Cr和TOC去除率进一步提高。超临界水氧化丙烯酸废水的最佳反应条件为:温度420℃,压力为24-26 MPa,氧化剂用量比为n=1.0-1.5。通过GC-MS技术对超临界水氧化染料废水的产物进行分析,探讨染料分子在超临界水中氧化降解路径。研究结果表明,分散红染料在超临界水中氧化降解的过程中,蒽醌先开环生成单环或多环的中间产物,然后进一步氧化降解为短链羧酸类物质,最终氧化生成CO₂和H₂O,与此同时,也存在着中间产物或自由基之间的横向反应,如偶合、水解、取代等,但这些副产物也将经苯甲酸、苯酚氧化成为最终产物CO₂和H₂O等。在动力学分析中,考虑了反应诱导时间的存在,对传统经验速率方程进行修正,对实验数据进行分析,分别得到了染料废水和丙烯酸废水超临界水氧化反应的动力学方程表达式以及反应活化能和反应诱导时间的值。染料废水的反应活化能:Ea=12.12 kJ.mol^-1,指前因子A=1.07 s^-1;反应级数:有机物:1级,氧化剂和水:0级;不同温度下诱导时间:2.03s、1.74s、1.37s、2.93s;动力学方程表达式:-d[COD]/dt=1.07exp（-12.12/RT）[COD]。丙烯酸废水的反应活化能:Ea=20.64kJ.mol^-1,指前因子A=4.97 s^-1;反应级数:有机物:1级,氧化剂和水:0级;不同温度下诱导时间:7.31s、8.43s、7.98s、4.91s;动力学方程表达式:-d[COD]/dt=4.97exp（-20.64/RT）[COD]。对反应前后作为蒸发壁的陶瓷膜内表面的SEM照片进行对比分析,分别在反应器内部装有微孔陶瓷管和不装微孔陶瓷管的情况下测定反应液相产物中Fe元素的含量,进行对比分析,结果表明,蒸发壁式反应器能有效地阻止反应过程中对反应器的腐蚀,使得反应器的使用寿命得到延长。针对目前超临界水氧化技术的研究情况,根据本文的实验为依据,提出了该技术工业化所需要解决的问题,主要有设备腐蚀、无机盐沉积、高效催化剂的开发、系统运行的稳定性等。更多还原

【Abstract】 In order to resolve problems of high cost and low destruction efficiency faced to high concentration refractory organic wastewater,supercritical water oxidation was used to treat this kind of wastewater.Dyeing wastewater and acrylic acid wastewater were adopted as research objects in transpiring wall reactor with hydrogen peroxide as oxidant.Effects of reaction temperature,reaction pressure and oxidant dosage on destruction efficiency of organic pollutants in dyeing wastewater and acrylic acid wastewater was studied.Kinetics for dyeing wastewater and acrylic acid wastewater oxidized in supercritical water were regressed from experimental data.Destruction pathway of dye molecule in supercritical water was proposed.Corrosion and inorganic salt deposition,which obstruct the industrialization of transpiring wall reactor,was investigated during the period of reaction.Dyeing wastewater was treated under supercritical water oxidation condition, temperature 380-460℃,pressure 20-30MPa,special oxidant dosage n=0.6-2.0. Effects of reaction factors on degradation efficiency of COD_Cr,TN,NH3-N and color were investigated.The result indicated that removal of COD_Cr,TN,NH3-N and color was affected positively by reaction temperature,and increased with the temperature. Effect of temperature on reaction could be explained from two aspects.Firstly, organic pollutants oxidation in supercritical water was irreversible.Reaction velocity was increased with temperature,thus the removal as well as efficiency.Secondly,the density of supercritical water was debased with increase in temperature under fixed pressure condition.Accordingly,concentration of reactants and reaction velocity reduced.Effect of temperature on reaction came from these positive and negative aspects.Positive effect of temperature on reaction was discovered in this investigation. 94.65%,58.15%,97.09%and 99.80%of COD_Cr,TN,TOC and color removal efficiency was achieved at temperature 460℃,pressure 25MPa,retention time 30s, special oxidant dosage n=1.5.Reaction pressure had positive effect on supercritical water oxidation.Removal efficiencies of COD_Cr,TN and color in wastewater were increased with pressure. Effect of pressure was due to two aspects.One,density of supercritical water increased with the pressure under fixed temperature condition,resulting in augmentation of concentration of organic compound,oxidant and reaction velocity. Two,due to increase in water density,retention time of organic pollutants was prolonged,which was favorable to oxidation destruction of organic pollutants. Summarily,pressure effect could be come down to positive effect of reactant concentration and retention time.Thus,higher pressure do favor to organic pollutants destruction.93.35%,66.47%,95.30%and 99.80%of COD_Cr,TN,TOC and color removal efficiency was achieved at temperature 420℃,pressure 30MPa,retention time 30s,oxidant dosage n=1.5.Effect of oxidant dosage on supercritical water oxidation was similar to temperature and pressure,which was positive to reaction.Removal efficiency of COD_Cr,TN and color was increased with oxidant dosage.The optimum reaction conditions for oxidation of dyeing wastewater in supercritical water were temperature 420-440℃,pressure 25-28MPa,special oxidant dosage n=1.2-1.6.Additional, biodegradability of dyeing wastewater was tested,before and after supercritical water oxidation respectively.The results indicated that B/C of dyeing wastewater was advanced greatly after treatment of supercritical water oxidation,increased with temperature and COD_Cr removal efficiency.B/C of dyeing wastewater increased form 0.12 to 0.44.Thus,biodegradability of dyeing wastewater was improved greatly by supercritical water oxidation.Acrylic acid wastewater was treated under supercritical water oxidation at temperature 370-420℃,pressure 20-30MPa,oxidant dosage n=0.0-3.0.The results indicated that COD_Cr removal efficiency was affected significantly by temperature. COD_Cr removal efficiency up to 99.09%was achieved at 420℃,respectively.More Activated molecules with higher temperature,leading to higher oxidation velocity, organic removal efficiency.Temperature had positive effect on organic pollutants removal.Removal efficiency of COD_Cr in acrylic acid wastewater was increased with pressure.The density of reaction mixture was also increased with pressure,leading to increase in concentration of reactant,reaction velocity and COD_Cr removal efficiency. Additionally,reaction zone under supercritical condition was prolonged with pressure, resulting in prolongation of retention time of organic pollutants under supercritical condition,leading to increase in COD_Cr removal efficiency.Removal efficiency of COD_Cr in acrylic acid wastewater was increased with oxidant dosage.Amount of reaction active radical was increasing with oxidant dosage, favoring reaction velocity,resulting in increase in COD_Cr removal efficiency.The optimum reaction conditions for oxidation of acrylic acid wastewater in supercritical water were considered as temperature 420℃,pressure 24-26MPa,oxidant dosage n=1.0-1.5.In order to investigate destruction pathway of dye molecule in supercritical water, reaction products of dyeing wastewater oxidized under supercritical condition was examined by GC-MS method.The results indicated that anthraquinone was decomposed to monocyclic and polycyclic intermediate hydrocarbons by means of opening-ring reaction,then destructed to short-chain carboxylates,finally oxidized to CO₂ and H₂O.Simultaneous,reactions such as coupling,hydrolyzing and substitution between intermediates and radicals were also existed.But,those by-products were oxidized to benzoic acid,phenol and final products such as H₂O,CO₂.A modified first-order rate expression was regressed from experimental data, taking into account the influence of induction time.Kinetic equation,reaction activation energy and introduction time of dyeing wastewater and acrylic acid wastewater oxidized in supercritical water were achieved.The resulting activation energy Ea was 12.12kJ.mol^-1,re-exponential factor A was 1.07s^-1,introduction time were 2.03s,1.74s,1.37s,2.93s under various temperature conditions for dyeing wastewater.Meanwhile,Ea was 12.12kJ.mol^-1,A was 4.97s^-1,introduction time were 7.31s,8.43s,7.98s,4.91s under different temperature conditions for acrylic acid wastewater.The reaction order for feed wastewater(based on COD_Cr) and oxidant were assumed to be 1 and 0 for these two kinds of wastewater.Kinetic equation for dyeing wastewater was "-d[COD]/dt=1.07exp（-12.12.64/RT）[COD]",and "-d[COD]/dt=4.97exp（-20.64/RT）[COD]" for acrylic acid wastewater. Comparison for SEM photos of ceramic tube before and after reaction was investigated.Concentration of Fe in effluent liquid samples was analyzed using method of atom absorption with and without ceramic tube as reactor.The result indicated that corrosion against reactor could be prevented effectively,and life of reactor could be prolonged using transpiring wall reactor.Aiming at present situation of supercritical water oxidation,several problems such as equipment corrosion,inorganic salt precipitation,exploitation for highly effective catalyst and stability of system for industrialization of this technology were put forward in this paper.更多还原