【作者】 余阳；

【导师】 周美华；

【作者基本信息】 东华大学 ， 环境工程， 2011， 博士

【摘要】 甲醛,最简单的羰基化合物,无色挥发性气体。甲醛可在木制品、油漆、绝缘材料等许多室内产品中存在,即使空气中的体积分数在10-7浓度条件下,甲醛也可导致呕吐、胸闷、呼吸困难、皮疹和过敏反应等症状,并且甲醛也被认为是潜在的致癌物质。随着生活设施的现代化,甲醛由建筑装修等方式排入室内空气中的情况逐年增加,去除室内甲醛成为了广大居民的强烈愿望,也是许多环保工作者的重要努力方向之一。目前可采用的室内甲醛控制技术有吸附法、热破坏法、吸收法、光催化法、光化学氧化法等。这其中,吸附法因为成本相对较低、操作简单等优势而应用最为广泛。但普通吸附剂在实际应用中存在吸附效果差,吸附剂饱和需脱附或更新等问题。因此,开发应用新型高效甲醛吸附材料,并在工艺上解决吸附剂饱和问题成为当前室内甲醛处理研究的重点。超细活性碳纤维(Ultra-Fine Activated Carbon Fiber,UFACF)是活性碳纤维的特殊形式。UFACF与普通活性碳纤维的最大区别在于纤维直径,其小得多的纤维直径和纤维间网孔大小使得UFACF具有比表面积大、微孔容积大、吸附速度快等优点,相对于一般吸附材料在过滤和吸附性能上都有明显的优势,是一种具有潜力的甲醛吸附材料。本课题以混合试剂法聚合制备了不同分子量的聚丙烯腈(PAN),以PAN为原料,依次采用高压静电纺丝技术、预氧化、碳化热处理技术、水蒸气活化技术制备了新型微孔吸附剂-UFACF;并以空气中甲醛为对象,研究了UFACF的甲醛吸附性能和吸附行为。由于臭氧低压汞灯技术光化学氧化技术采用非接触方式光化学氧化降解甲醛等气态有机污染物,是一种较好的甲醛处理技术,课题将UFACF吸附与光化学氧化技术结合,组成吸附-光化学氧化耦合工艺,考察研究了吸附-光化学氧化耦合作用下的甲醛处理效果。本文意在摸索和开发可以用于吸附室内甲醛的新型吸附剂UFACF,探索UFACF的制备条件和甲醛吸附应用影响因素,为UFACF的产业化提供数据和理论支持。吸附-光化学氧化耦合工艺的提出和研究可为室内甲醛乃至整个VOCs的处理方法提供新的思路。本课题主要具体研究内容包括：PAN基静电纺超细纤维毡的制备；超细纤维毡的预氧化、碳化研究；UFACF制备；UFACF甲醛静态吸附研究；UFACF甲醛动态吸附行为研究；吸附与光化学氧化耦合工艺处理甲醛研究等。在聚丙烯腈基静电纺超细纤维毡的制备研究中,采用DMSO/H2O混合溶剂法制备了5种不同分子量的PAN,并以PAN为原料,DMF为溶剂,配成纺丝溶液,通过高压静电纺丝技术制备超细纤维毡(UFFM)。研究表明：聚合制备PAN,相同单体组成和浓度、相同反应条件情况下,随着混合溶剂中水含量的增加,生成的PAN粘均分子量相应增加,其转化率也增加。而且不同分子量PAN的热重分析显示,随着PAN分子量的增加,热重曲线的剧烈失重区会越来越明显,而且剧烈失重区的失重率也呈增加的趋势；高压静电纺丝研究中发现,PAN-4和PAN-5纺丝溶液由于分子量过高而不可纺,其原因是由于PAN-4和PAN-5纺丝液浓度低,纺丝液溶剂不能及时挥发,沾有溶剂的纤维在到达收集屏前并丝造成。另外研究中还发现：较高的纺丝电压有利于纤维直径的减小,但相应的纺丝稳定性减小,导致纤维直径分布的离散度增加。超细纤维毡的预氧化、碳化研究中以静电纺制备的三种超细纤维毡(UFFM-1、UFFM-2、UFFM-3)为原料制备超细碳纤维毡,并考察相应产品性能,以确定制备UFACF的原料。其中,预氧化的目的是使线状PAN结构经环化、脱氢作用转化为耐高温的梯形结构,以便在高温碳化过程中,超细纤维能保持纤维状态。碳化目的是去除预氧化毡中的非碳元素以生成含碳量高的超细碳纤维。研究中发现：UFFM预氧化热处理后制备的超细预氧化纤维毡是吸水性较好的材料；预氧化、碳化过程复杂的化学反应使得超细纤维的结构和元素含量发生巨大变化,相应地使得纤维质量减小；通过UFCFM纤维束拉伸性能分析,原料PAN粘均分子量越高,制备出的超细碳纤维力学性能越好,由于UFFM-3经过预氧化、碳化热处理后得到的UFCFM-3质地柔软,有更好的机械强度,可作为制备UFACF的原料。超细活性碳纤维的制备研究中,以水蒸气为活化剂进行活化正交实验,并分别以电加热和微波加热两种加热方式制备出了两类UFACF (UFACF(D)、UFACF(W)),通过对活化收率、比表面积的测定,分析了两种加热方式对UFACF制备效果的影响。研究中发现：两种加热方式均能制备出高比表面积且孔径分布集中在微孔的UFACF,其中电加热法制备的UFACF(D)最大比表面积达1075.1m2/g,微波加热法制备的UFACF(W)最大比表面积达1107.4 m2/g；由于UFACF(W)采用微波碳化、微波活化法制备,在制备成本和效率上要优于电加热制备的UFACF(D)。UFACF甲醛静态吸附研究目的主要是比较两种加热方法制备出的UFACF甲醛吸附性能的差异。研究在相同湿度条件下进行,实验中不仅对UFACF(D)-7和1JFACF(W)-5两种吸附剂的甲醛吸附容量进行测定,而且还采用全自动比表面和孔径分布分析仪对两种UFACF的微孔孔径分布进行表征。研究中发现：由于有大量极微孔的存在,两种超细活性碳纤维均有较好的低浓度甲醛吸附性能,其中,相对湿度40%条件下,UFACF(D)-7的甲醛平衡吸附量达0.50mg/g,UFACF(W)-5的甲醛平衡吸附量为0.36mg/g；在比表面积和微孔孔径分布差不多的情况下,JFACF(D)-7对甲醛和水蒸气的吸附性能优于UFACF(W)-5,其原因是含氧官能团存在于UFACF(D)-7结构中。UFACF(W)-5甲醛动态吸附行为研究发现：相同初始甲醛浓度和气体流量条件下,相对湿度越大,甲醛动态吸附性能越差。其中,相对湿度70%条件下,UFACF甲醛动态平衡吸附量为0.31 mg/g,而相对湿度30%条件下,UFACF甲醛动态平衡吸附量为0.41 mg/g；相同初始甲醛浓度且相对湿度均50%条件下,气体流量越大,甲醛有效吸附量和平衡吸附量越小。其中气体流量为1.0 L/min时,甲醛平衡吸附量仅0.23 mg/g,而气体流量为0.6 L/min时,甲醛平衡吸附量达0.50mg/g。通过对Wheeler-Jonas方程的模拟和预测发现：Wheeler-Jonas方程的模拟曲线与实验值曲线在穿透时间后和饱和时间前时间段内相似程度较高,并且,预测的平衡时间和平衡吸附量也与实验值接近。但穿透时间、有效吸附量和吸附带高度等关键数据与实验值仍然有一定的差距。吸附与光化学氧化耦合工艺处理甲醛研究中发现：低压汞灯光化学氧化作用可以产生羟基自由基,吸附-光化学氧化耦合工艺去除甲醛效果要优于单一吸附工艺或单一光化学氧化工艺。如：相对湿度50%条件下,90 min时,单一光化学氧化工艺、单一吸附工艺和吸附-光化学氧化耦合工艺的甲醛去除率分别为68.8%、37.0%和95.2%；而且相对湿度对于吸附-光化学氧化耦合工艺去除甲醛有重要影响；吸附与光化学氧化耦合工艺既可减弱光化学氧化作用二次污染问题又可解决吸附剂饱和问题,是一种新型室内空气净化技术,对室内空气品质的改善有应用价值。本课题研究的创新性成果有：1)由sciencedirect文献检索发现,UFACF的制备是一个较新的研究方向,而将UFACF应用到甲醛吸附领域则鲜有报道,本课题的研究有一定领先性。2)超细碳纤维毡制备研究中,就PAN聚合物分子量大小对UFCFM产品性能的影响进行了探讨,结论可为UFCFM或碳纤维制备产品机械性能的改善提供参考。3)微波加热进行碳化和活化研究制备UFACF,此类研究较少见诸报道,研究结论对碳吸附材料活化工艺加热方式的选择有重要价值。4)在Wheeler-Jonas方程对动态甲醛吸附行为的模拟和预测研究中发现：模拟预测出的穿透时间、有效吸附量和吸附带高度等关键数据与实验值有一定的差距,这说明Wheeler-Jonas方程对UFACF气体动态吸附行为准确预测有局限性。UFACF动态吸附行为的研究可为UFACF实际应用中工作参数的确定提供参考。5)课题以“吸附与光化学氧化耦合工艺”处理甲醛,提出了吸附剂“原位脱附”和吸附质“原位降解”概念。与单一吸附或单一光化学氧化方法相比,耦合工艺有较好的甲醛处理效果,在室内空气净化领域具有应用价值。更多还原

【Abstract】 Formaldehyde (HCHO), one of the simplest carbonyl compounds, is colorless volatile gas. HCHO exists in many products for home use, such as wood products, paint, insulation materials. Even if the concentration of HCHO is less than 0.1ppm, it could cause vomit, chest tightness, shortness of breath, skin rashes, allergic reactions and other symptoms. Moreover, formaldehyde is a potential carcinogen. As modern living facilities and construction enter into the house, the formaldehyde concentration in indoor air is increasing year by year and exceeds the national standard. Removal of indoor formaldehyde is the strong desire of the residents, and is also one of the important research directions for environmental researcher.Currently, the technology that could be used to deal with indoor formaldehyde included adsorption, thermal destruction, absorption, photocatalysis, photochemical oxidation method, etc. Among them, adsorption is most widely used because of the relatively lower cost, simpler operation, higher removal efficiency and other advantages. The common adsorbent has poor formaldehyde adsorption capacity and need to be desorbed or replaced after work time.Thereforc, the development and application of new efficient adsorbents for indoor formaldehyde and to solve the saturated problem of adsorbent became the research focus for indoor air purification.Ultra-fine activated carbon fiber (UFACF) is a special form of carbon fiber, the biggest difference between UFACF and ordinary carbon fiber is the fiber diameter. UFACF has much smaller fiber diameter and fiber mesh. UFACF has many adsorption advantages such as large surface area, large pore volume and fast adsorption. Because the distinct advantage in filtration and adsorption, UFACF can be used as a potential adsorbent material for formaldehyde.In this paper, polyacrylonitriles (PAN) with different molecular weight were polymerized. Taking the PAN as a material, the electrospinning technology, pre-oxidation, carbonization heat treatment technology, steam activation technology were applied for the preparation of UFACF, which was a new microporous adsorbent for indoor formaldehyde removal; And taking the indoor formaldehyde as target, the formaldehyde adsorption behaviors of UFACF were studied in different conditions; In addition, through the introduction of photochemical oxidation, the effect of adsorption-photochemical oxidation coupling technology on formaldehyde removal was studied too.The research purpose of paper was to prepare the UFACF which was nice for indoor formaldehyde adsorption and find out optimization of preparation conditions of UFACF, and the influence factors for the application of formaldehyde adsorption of UFACF were investigated in the paper too. The optimization research results of preparation conditions for UFACF could be useful to the preparation of carbon adsorbent material; the influence factors for the application of formaldehyde adsorption of UFACF could provide reference for practical application of UFACF and open a new way for air purification. This paper was consisted with several parts, which included:the preparation of electrospinning UFFM from PAN; pre-oxidation and carbonization study of UFFM; study on the preparation of UFACF; formaldehyde static adsorption of UFACF; formaldehyde dynamic adsorption behavior study of UFACF; the formaldehyde remove study of adsorption-pHotochemical oxidation technology.In the research for the preparation of UFFM, five kinds of PAN with different molecular weight were polymerized via DMSO/H2O mixed solvent method, and the PAN was dissolved into the spinning solution with DMF as solvent and electrospun into UFFM. The polymerization results showed that viscosity average molecular weight and conversion rate of PAN would increase with higher H2O ratio in mixed solvent in the same monomer concentration and environment conditions. From the TG analysis, dramatic weight loss zone would appear and the weight loss ratio would larger with PAN molecular weight increasing. Electrospinning results showed that the spinning solution could not be electrospun into ultra-fine fiber if the molecular weight of PAN was too high, and the higher electrospinning voltage was favorable for finer fiber diameter but cause larger dispersion of fiber diameter distribution with the electrospinning stability decreasing.UFFM-1、UFFM-2、UFFM-3 were taken as materials to prepare UFCFM in the research of pre-oxidation and carbonization, the purpose of the experiments was to determine the raw material for the preparation of UFACF. The results of the pre-oxidation experiments showed that the UFPFM could be made from UFFM after pre-oxidation process, and which was a nice steam adsorbent. In the process of pre-oxidation and carbonization, the mass of the fibers reduced, many complex chemical reactions occurred and UFFM fiber structure and element content significantly changed. From the analysis of fiber bundles tensile properties, UFCFM-3 had high mechanical strength and could be taken as the raw material for the preparation of UFACF.In the preparation research of UFACF, two kinds of UFACF (UFACF (D) and UFACF (W)) were separately made via electric heating orthogonal activation experiments and microwave heating orthogonal activation experiments. From measuring and characterization, the optimal conditions for UFACF preparation were analyzed. Where, the maximum specific surface area of UFACF (D) reached 1075.1 m2/g and the maximum specific surface area of UFACF (W) reached 1107.4 m2/g. From the pore size distribution and infrared spectra characterization of UFACF which were made from the different heating methods were explored. To be specified, the cost and efficiency of UFACF (W) preparation were advantage than UFACF (D)In the research for static formaldehyde adsorption of UFACF, the formaldehyde adsorption performance of UFACF (D)-7 and UFACF (W)-5 were tested at same relative humidity. And automatic surface area and pore size distribution analyzer was used to investigate the micropore size distribution. From the test results, both UFACF (D)-7 and UFACF (W)-5 had nice formaldehyde adsorption properties because there were a large number of ultramicropore existing in them. But in the case of similar surface area and micropore size distribution, formaldehyde adsorption performance of UFACF (D)-7 was better than UFACF (W)-5, the presence of the oxygen groups in the UFACF (D)-7 explained the reason. Where, on the condition of relative humidity 40%, formaldehyde equilibrium adsorption capacity of UFACF (D)-7 and UFACF (W)-5 was separately 0.50mg/g and 0.36mg/g.In the research for dynamic adsorption behavior of UFACF, some experiments results were get:on the condition of same initial concentration of formaldehyde and the gas flow, larger relative humidity caused worse formaldehyde adsorption performance; on the condition of same initial concentration of formaldehyde and relative humidity, with the gas flow increasing, formaldehyde effective amount of adsorption and equilibrium adsorption were decreasing. Where, on the condition of relative humidity 70% and 30% with same gas flow rate, formaldehyde equilibrium adsorption capacity were 0.31 mg/g and 0.41 mg/g. and on the condition of gas flow rate 1.0 L/min and 0.6 L/min with relative humidity 50%, the formaldehyde equilibrium adsorption capacity were 0.23 mg/g and 0.50 mg/g. According to Wheeler-Jonas equation’ modeling and prediction for dynamic adsorption process, the simulation curves of Wheeler-Jonas equation were similarity with experimental data curve between breakthrough time and saturation time, and adsorption equilibrium time and equilibrium adsorption capacitance were close to the actual experimental data, but the breakthrough time of adsorption, the effective adsorption and adsorption band length were quite different with the actual experimental data.From the research of adsorption-photochemical oxidation coupling technology, the photooxidation of low-pressure mercury light in air could produce hydroxyl radicals, and the formaldehyde removal efficiency of adsorption-photochemical oxidation coupling technology was better than single absorption process or single photochemical oxidation process. Where, on the condition of relative humidity 50%, at 90 min, the formaldehyde removal efficiency of the single photochemical oxidation technology, the single adsorption process and the adsorption-photochemical oxidation coupling process were 68.8%,37.0% and 95.2%. Adsorption-photochemical oxidation technology was a new air purifying technology, which could solve the problem of secondary photochemical pollution and adsorbent saturation. The technology was one of directions for improving indoor air quality.The innovative research results of this paper were summarized as follows:1) With the literature search results from the sciencedirect, the preparation of UFACF was a relatively new research field, and that UFACF was applied to the adsorption of formaldehyde was rarely reported. This research projects was advanced.2) In the research of preparation of UFCFM, the influence of the PAN molecular weight to UFCFM product performance were discussed, the related analysis could provide reference for improving the mechanical properties of UFACF or carbon fiber.3) The research about the preparation of UFACF via microwave heating was rarely reported, the related experiment conclusions could be valuable for the choice of heating method of porous carbon materials preparation.4) From the Wheeler-Jonas equation simulation and prediction results about the dynamic adsorption behavior of formaldehyde, the simulated breakthrough time of adsorption, the effective adsorption and adsorption band length were quite different with the actual experimental data, which verified the wheeler-Jonas equation was limited for predicting gas dynamic adsorption behavior of UFACF. The conclusion could be useful to the adsorption applications of UFACF.5) The adsorption-photochemical oxidation coupling technology was studied in this paper. And the conception of the fixed position desorption of adsorbent and the fixed position degradation of adsorbate were proposed. From the experiment results, the coupling technology was advantage for the formaldehyde remove and had potentiality for air purification.更多还原