煤基高比表面积活性炭的制备及应用
文献类型：学位论文
| 作者 | 周花蕾 |
| 学位类别 | 博士 |
| 答辩日期 | 2008-06-12 |
| 授予单位 | 中国科学院过程工程研究所 |
| 授予地点 | 过程工程研究所 |
| 导师 | 陈运法 |
| 关键词 | 无烟煤 高比表面积活性炭 甲烷吸附 铬(VI) 赤泥 |
| 其他题名 | Preparation of Activated Carbon with High Specific Surface Area from Anthracite and its Application |
| 学位专业 | 化学工程 |
| 中文摘要 | 活性炭微孔发达、比表面积高、吸附能力强，是一种优良的吸附材料，广泛应用于化工、环保以及食品医药等领域。随着科学技术的飞速发展，市场对高比表面积、高性能活性炭的需求量越来越大。我国煤炭资源丰富，价格相对低廉，充分利用其价值，研究生产高比表面积、高性能的活性炭具有重要的实际意义。本文以煤为原料，研究高比表面积活性炭的制备以及在甲烷储存、水处理和离子富集中的应用，并对高比表面积活性炭的活化机理进行分析探讨。 用KOH活化法制备高比表面积活性炭。以太西无烟煤为原料，考察多种工艺因素，包括KOH与煤的比例、活化温度、活化时间、原料混合方法、活化气氛、气氛流速、升温速度、活化炉及原材料粒度等对所制备活性炭比表面积的影响。碱炭比、活化温度和活化时间是影响活性炭比表面积的重要因素；物理混合法优于浸渍混合法；活化在半封闭体系、静态空气气氛中，碱碳比为6.5、升温速率5℃/min、活化温度725℃、活化时间1h时，可制得比表面积高达4200m2•g-1的活性炭，高于目前文献中的以煤为原料制得活性炭的最高比表面积。而且这种方法不用氮气做载气，活化装置简单，并有收集金属钾的作用，从而可使生产成本大大降低，减少钾污染。原材料粒度（在80目以上）以及混合方式即研磨混合或简单搅拌混合都对活性炭的制备几乎没有影响。由所制备活性炭的吸附等温线、孔径分布以及SEM和TEM分析可知在最佳条件下制得的活性炭表面孔隙丰富，结构发达。 对活化过程进行了XRD分析、热分析以及尾气中成分的色谱分析，讨论了基于本研究中KOH对太西无烟煤的活化过程及机制。整个活化过程可分为四个阶段：第一个阶段是400℃即KOH熔融之前，主要是活化剂和原料煤中物理化学吸附水的脱除，对活性炭中孔的生成几乎没有贡献；第二个阶段是400℃到约550℃期间，主要是KOH和原料中的碳反应生成K2CO3、氢气和金属钾，这是活化过程中的主要反应，几乎持续发生在活化的整个过程；第三个阶段是550～680℃阶段，部分的KOH开始发生脱水反应，而水的存在又可以引发水煤气反应，从而也对活性炭的比表面积有着重要的贡献；第四阶段即约750℃以后，金属钾开始挥发或升华，气体在逸出的过程中，穿行于碳的微孔或碳层间，形成新的微孔。在静态的空气气氛中活化时，因为活化过程中生成的氢气逸出容器与空气发生放热反应而使活化体系温度升高，所以可使活化在较低设定温度下即得到较高比表面积的活性炭，少量的空气存在可以促进活化反应的进行；半封闭体系在高温时可以使活化过程中产生的金属钾蒸气在容器内呈半循环状态，大大促进钾的造孔作用。 用体积储气法评价了所制备的高比表面积活性炭对甲烷的吸附能力，分析了其影响因素。甲烷在活性炭上的吸附性能主要受活性炭的比表面积和孔结构两方面的影响，随着活性炭比表面积的增加，其对甲烷的吸附量增大，0.7nm以下的超微孔不适宜甲烷的吸附。本实验条件下，比表面积为3675m2/g的活性炭在298K、3.5MPa条件下，对甲烷的质量吸附量为0.216g/g。 分别用自制的高比表面积活性炭、氧化剂改性过的高比表面积活性炭，以及市场专门用于水处理的磷酸活化活性炭对六价铬进行了吸附比较，发现自制高比表面积活性炭在pH为3时，对铬有最高的吸附量及去除率，适合于酸性含铬废水的处理。其吸附等温线更符合Freundlich模型，从Langmuir模型上预测活性炭的饱和吸附量，在298K时为312mg•g-1，大大高于文献中所报导的值。热力学计算表明吸附过程是自发的、吸热的以及吸附剂对Cr(VI)具有较强的亲和力。吸附过程符合准二级动力学模型。 为了从赤泥中富集提取钪，活性炭用化学试剂改性以提高其对钪的吸附能力及选择性，发现磷酸三丁脂（TBP）改性的活性炭对钪具有很好的吸附能力和选择性。但改性过的高比表面积活性炭与市售活性炭相比，已显示不出其作为高比表面积活性炭的优势，又因其成本较高，所以在本研究中，最终选用TBP改性的市售活性炭作为富集提取钪的吸附剂。从改性活性炭的比表面积变化、红外谱图和吸附性能综合分析，TBP改性的活性炭对金属离子特别是钪离子的吸附过程中，化学吸附起着主要作用。就本研究中所用的赤泥的盐酸溶液，得到富集提取钪的最优化条件：~6.25g•L-1活性炭用量，308K的吸附温度，40min的吸附时间，可以将钪的含量提高~12倍。TBP改性的活性炭对赤泥酸溶液中钪的吸附可以用准二级动力学方程来描述。 |
| 英文摘要 | Activated carbon (AC), as an effective adsorbent, has been widely applied in chemical industry, environment protection, food and pharmaceutics industry, etc because of its abundant porous structure and high specific surface area. With the rapid development of science and technology, the demand for AC with high specific surface area is increasing very fast. There are relatively abundant sources of coals in our country. It is very valuable to product AC with high specific surface area and high performance from the coals. In this paper, the preparation and application of AC with high specific surface area in the methane adsorption, wastewater treatment and reconcentration of ions were investigated. The activation mechanism were analyzed and discussed. ACs with high specific surface area were prepared by chemical activation with KOH. Taixi anthracite was used as coal material in this study. The influence factors on activation including the weight ratio of KOH/Coal, activation temperature, activation time, mixing method of raw material and activation agent, activation atmosphere, gas flow rate, heating rate, activation furnace and particle size of materials were investigated and the optimized conditions are obtained. The weight ratio of KOH/Coal, activation temperature and activation time are important influence factors on SBET of AC. Physical mixing method is better than impregnation method. The AC with SBET of 4200m2•g-1 were obtained at 6.5 of KOH/coal weight ratio, 5℃•min-1 of heating rate, 725℃ of activation temperature and 1h of activation time when activation was in half-closed system and exposed in static air atmosphere. AC with so high specific surface area prepared from coals has not been reported in literature. More significantly, in this preparation process, no N2 is used and a simple Muffle furnace can be used as activation equipment, which will decreae the production cost. Potassium can also be collected during activation process to reduce its pollution in air. Particle size of coal (>80mesh) and KOH has no influence on the preparation of AC, as well as mixing method such as simple stirring, grinding. Isotherms and pore size distribution of ACs high specific surface area were analyzed and their microstructures were observed with SEM and TEM. The results show that the AC with high specific surface area has aboundent and well-developed pores. With XRD analysis, thermal analysis and gas chromotagraph analysis for offgas from activation process, the activation mechanism was discussed. It is indicated that the activation process proceeded in four steps. The first was before 400℃, in which the adsorption water from materials was removed. It almost has no contribution to formation of pores. The second was during the period of 400-500℃, in which K2CO3, H2 and metal potassium were formed. It is the main activation reaction and occered almost in the whole activation process. The third was during the period of 450-680℃, in which part of KOH decomposed and H2O was formed. H2O again reacted with coal. The last was after 750℃, in which K sublimated and went through the structure of C layer, causing the formation of micropores. In the static air atmosphere, the exothermic reaction occured between H2 released from activation process and air, which improved the temperature of activation system. Therefore, ACs with high surface area can be prepared at lower programmed temperature than in N2 atmosphere. Seldom air was benefit for developing more pores. In the half-closed system, K gas formed a half-cycle inside activation container at high temperature and accelerated formation of more micropores. The methane adsorption capacity of ACs with high surface area was evaluated and the influence factors were analyzed. Both surface area and pore structure had great influence on the methane adsorption capacity. With increasing SBET of ACs, the methane adsorption capacity increased. Super-micropore below 0.7nm was not appropriate for methane adsorption. Methane adsorption capacity of 0.216g/g was obtained by the AC with SBET of 3675m2/g at 298K under 3.5MPa Compared with the adsorption performances of high specific surface area activated carbon before and after modification, and the commercial AC prepared by H3PO4 activation, the AC with high specific surface area has the highest adsorption capacity to Cr when pH is 3. The adsorption isotherms were fitted better with Freundlich than with Langmuir model. The saturated adsorption capacity can be predicted from Langmuir model and is 312mg•g-1 at 298K, which is far higher than the data in literatures. The thermodynamics investigation indicates that adsorption is spontaneous, endothermic, and the affinity between the adsorbent and adsorbate. The kinetics adsorption data was fitted by pseudo-second-order rate model. The adsorption activation enegy indicates that the adsorption of the AC with high specific surface area to Cr(VI) is cooperated by physical and chemical adsorption. To reconcentrate Sc from red mud, ACs were modified by several chemical regents to improve the adsorption capacity and selectivity to Sc. It is found that AC with high specific surface area modified by TBP shows the best adsorption performance. However, it did not performence much better than the modified commercial AC. Considering the low cost, the modified commercial AC by TBP was chosen as the adsorbent to reconcentrat Sc. The SBET, FT-IR spectra and adsorption capacity of ACs were analyzed. Chemical adsorption plays a key function for concentrating Sc3+ ion. An optimum adsorbent dosage (~6.25g/L), adsorption temperature (308K), and adsorption time (40min) were figured out for the Sc3+ solution from the red mud, in which content of Sc is improved by ~12 time. A Pseudo-second-order kinetics model was employed for describing the adsorption process of Sc3+. |
| 语种 | 中文 |
| 公开日期 | 2013-09-13 |
| 页码 | 149 |
| 源URL | [http://ir.ipe.ac.cn/handle/122111/1105]  |
| 专题 | 过程工程研究所_研究所（批量导入） |
| 推荐引用方式 GB/T 7714 | 周花蕾. 煤基高比表面积活性炭的制备及应用[D]. 过程工程研究所. 中国科学院过程工程研究所. 2008. |
入库方式： OAI收割
来源：过程工程研究所
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