【作者】 卢春兰；

【导师】 刘长厚； 徐绍平；

【作者基本信息】 大连理工大学 ， 化学工艺， 2007， 博士

【摘要】 活性炭尤其是高比表面积活性炭具有发达的微孔结构和大的吸附容量，因而在燃料气存储、气体分离、催化反应等方面具有巨大的应用潜力。近年来，对具有高比表面积和特定孔隙结构活性炭的需求越来越多。炼油厂的副产物石油焦资源丰富，价格低廉，且碳含量高，灰分、挥发份低，是生产中高档炭的优质原料。但由于石油焦是易石墨化炭，结构致密，结晶度高，缺乏活化所需要的初孔，需用大量的强碱来活化成孔，造成生产成本高，污染严重。因而从活化成孔机理的基础上优化工艺条件、降低碱的用量、控制微孔结构是石油焦基高比表面积活性炭开发研制的关键。基于此，本论文着重展开如下几方面的探索和研究：1．以辽化石油焦为原料，以KOH为活化剂制备活性炭，考察碱焦混合方式、原料粒度、载气流速、不同溶剂浸泡、干燥升温速率对活性炭性能的影响。实验结果表明：辽化石油焦是制备高比表面积活性炭的优质原料；碱焦的混合方式、原料的粒度、活化载气的流速都会影响产品性能。采用不同的溶剂对活化产物进行浸泡，得到活性炭比表面积的大小顺序为：水≈冰醋酸)乙醇)甲醇≈四氢呋喃)乙二醇)30％双氧水，说明活化后炭颗粒中钾的化合物的脱除过程对活性炭孔的形成及吸附性能有很大的影响。2．通过预炭化处理改变原料的微晶结构和表面性质，重点考察了这些变化对活化产物性质所产生的影响。在较高的预炭化温度下，随着预炭化温度的升高，石油焦中氢和氧的含量锐减，表面官能团含量也减少，微晶结构变得更加稳定，结果使活化困难，导致活性炭比表面积减少、孔径分布发生变化，中孔含量相对增大。未处理的石油焦加三倍质量的碱活化后制得活性炭比表面积为1997m²g^-1，而在相同活化条件下由经1200℃炭化后的石油焦制得活性炭比表面积仅为12m²g^-1。而较低温度下对石油焦热处理对所制得活性炭的比表面积影响很小，但使原料中石墨微晶的d₀₀₂增大，相应的活性炭的孔径也增大了。说明石油焦的表面官能团如C-O-C、C-O-H以及-CH₃、=CH₂和-CH₂CH₃等烃基基团在化学活化过程中起着十分重要的作用，且石油焦内部微晶结构对活化过程中孔的大小有影响。3．进一步对石油焦原料分别用空气、HNO₃或H₂O₂溶液进行预氧化处理，改变原料的表面性质，证明原料表面的含氧官能团是活化过程中反应的“活性点”，对活性炭孔的形成有促进作用，从而提出预氧化石油焦的活化机理模型。石油焦经过适当条件预氧化处理后，所含的表面烃基官能团显著减少，而含氧官能团明显增多，说明烃基官能团被氧化成含氧官能团，且由于氧的引入使石墨微晶层片距离有所增大。同时，预氧化处理还可以提高石油焦反应活性，降低活化反应温度。石油焦经适当的预氧化处理后活化能够制得高比表面积的活性炭，使碱的利用率提高。其中，双氧水氧化的最佳浓度为20％，碱焦比为3：1时活化制得活性炭具有高比表面积(2744m²g^-1)和较窄的孔径分布。研究表明，可以通过控制原料的“活性点”来调控活性炭比表面积和孔径分布。4．提出了较系统的KOH活化石油焦的反应机理，阐明了活化过程中孔的形成和H₂O、H₂、CH₄、CO的来源。通过考察活化过程中活性炭孔隙结构、微晶结构的变化以及氢氧化钾的转化，表明KOH先与石油焦反应转变成K₂CO₃，形成初步的孔结构，同时证明了新生成的碳酸钾对活性炭孔结构的发展起重要作用。但直接以K₂CO₃为活化剂，活化的烧失率大，得到的活性炭孔隙却不发达，表明在氢氧化钾活化过程中，在孔道内新生成的碳酸钾更容易与碳反应起活化作用，进一步发展孔隙结构。根据反应的标准Gibbs自由能，K₂CO₃（或K₂O）直接与碳反应在730℃的活化温度下难以进行，表明它们和石油焦中-CH-、-CH₂-发生反应，起活化作用。活化反应生成的单质钾对石油焦有插层及活化作用，能使活化产物的比表面积达到98 m²g^-1，XRD分析表明活化产物中有钾-石墨插层化合物的存在。5．根据活化机理中研究的结果，利用加助剂N混合提高碱的分散作用以及助剂N在高温时的活化作用，来提高活化效果。在碱焦比为3：1，活化温度为730℃，活化时间为30分钟的条件下就可以获得收率为68％，比表面积高达2532m²g^-1的活性炭；同时，活化反应中氢气产生量较大，达到38cm³g^-1min^-1，可以分离提纯氢气。从而提出一步法活化制备高比表面积活性炭的工艺。与常规方法相比，该工艺降低了生产成本，缩短生产时间，节约能源，为进一步工业化生产奠定基础。6．以制备的石油焦基活性炭为载体，负载Ni-Mo双组分的催化剂具有和商品催化剂相近的二苯并噻吩（DBT）加氢脱硫活性：反应温度为290℃时，DBT转化率大于98％，同时具有较高稳定性。制备的高比表面积石油焦基活性炭，孔径分布大多数集中在1.0～2.0nm之间，利用该样品进行储存甲烷实验表明其具有较高的储存甲烷的性能：在1.4 MPa，室温下，甲烷的质量吸附量为0.112g·g^-1。更多还原

【Abstract】 Activated carbon （AC） with high surface area is widely used in fuel gas storage, gas separation, catalysis and various chemical processes. Controlling pore size and pore size distribution are necessary for the application of AC in a specific end use. It is well known that petroleum coke （PC） is a good precursor for preparing high surface area AC because of its’ high carbon content, low volatile and ash content. However, PC is difficult to be activated due to the stable micrographitic structure and lack of the initial pores in it, so that a large amount of KOH is needed to prepare AC from PC, which brings many problems, such as high product cost, environment pollution etc. Therefore, how to optimize the process conditions, such as mild reaction temperature with lower KOH/coke ratio, and produce AC with desired porous texture based on a deeper understanding of the chemical activation mechanism is the emphasis for further research. In this dissertation, investigations were conducted as follows:First, AC is prepared from a green PC from SINOPEC Liaoyang Petrochemical Company as precursor and KOH as activating agent, the effect of different preparation conditions, such as the method for mixing KOH and coke, carrier gas flow and particle size of coke on porosity development of AC was investigated. It has been found that the dipping of activated mixtures in different solutions before washing affects the pore formation of AC greatly; indicating the elimination of the produced potassium compounds is an important step for the porosity development of AC.To investigate the effect of the changes of surface groups and micrographitic structure of the precursor on the porosity development of AC, the PC was pre-carbonized before activation. With the increase of the heat treatment temperature, the hydrogen and oxygen content, and the surface functional groups of the PC were decreased, while the micrographitic structure of it became more stable and difficult to be activated. So the BET surface area of the corresponding AC decreased. The BET surface area of the AC made from green coke at a 3:1 KOH/Coke ratio is 1997m²g^-1, while that from 1200℃treated coke is 12m²g^-1. The pre-carbonization at relative low temperature has little effect on the BET surface area of the final carbon, but it slightly widens the micropore size of the AC.The influence of pre-oxidation of the PC with oxidizing agent H₂O₂, HNO₃ or air on the development of porosity of the produced AC was analyzed in the view of the changes of the surface chemistry and the texture of the PC. The results showed that introduction of the surface oxygen groups by the pre-oxidation leads to an increase m me reactivity of the PC in chemical activation, which results in an increase in the BET surface area and the N₂ adsorption capacity of the AC. And the addition of oxygen to the graphitic microcrystallines of the precursors slightly widens the interlayer spacing. Therefore, an AC with a surface area as high as 2744 m²g^-1 and narrow pore size distribution was prepared from the coke oxidized by 20%H₂O₂ solution with a 3:1 KOH/Coke ratio. Based on the above results, it can be indicated that the surface oxygen groups of the precursor can be acted as ’active site’, which play an important role in activation.Based on above investigations, a systemic chemical activation mechanism of the PC with KOH was propposed. During the chemical activation with KOH, pores were formed by reaction of KOH with PC, and then the formed K₂CO₃ can further react with carbon, which contributes to the porosity development. However, when the carbon precursors were activated with directly added K₂CO₃, the AC yields were all very low; while the BET surface area of them were not as large as expected. It indicates that the distribution of K₂CO₃ in the formed pores of the carbon contributes to the porosity development by the reactions of K₂CO₃ with -CH-, -CH₂- in PC. XRD analysis indicated that the produced K intercalates into the lamellae of the graphitic microcrystallines of the carbon, and broadens the interlayer space, consequently further develops the porous structure. An activated coke with a BET surface area of 98 m²g^-1 was obtained from PC by activation with the produced K.Based on the proposed chemical activation mechanism, a new method to produce high surface area AC has been developed, in which additive N was used to improve the diffusion of KOH into PC and act as activation agent at the same time during the chemical activation. The AC with high solid yield of 68%, BET surface area of 2532 m²g^-1 and narrow pore size distribution can be prepared with a 3:1 KOH/Coke ratio from activation at 730℃for 30 minutes by this method.A HDS catalyst is derived from the prepared AC supported with Ni and Mo, which shows a HDS activity comparable to that of the commercial catalyst of Mo-Ni/γ-Al₂O₃. The dibenzothiophene conversion reached over 98% at 290℃. The AC with high surface area and pore size distribution between 1.0～2.0nm was used as adsorbent for methane storage, which shows an excellent methane-storing performance. Under pressure of 1.4 MPa and room temperature, the methane-storing ability of the AC reaches 0.112 g·g^-1.更多还原