【作者】 刘立恒；

【导师】 辜敏；

【作者基本信息】 重庆大学 ， 矿业工程， 2011， 博士

【摘要】 煤层气是一种非常规天然气,它的直接排放,不但造成了资源的浪费,也引起了严重的环境及安全问题。对煤层气的综合开发利用,有利于优化我国能源结构,减少大气污染和安全问题。煤层气利用的关键其主要成分甲烷和氮气的分离。变压吸附（PSA）是分离煤层气中甲烷和氮气的有效技术之一,其关键是吸附剂。而活性炭由于具有较大的孔容,能克服吸附容量的限制,且孔径较大,扩散速率较快,比较适合于煤层气的变压吸附分离。本研究以低煤阶的褐煤为原料,采用煤焦油、聚丙烯酰胺和可溶淀粉作粘结剂制备了浓缩CH₄/N₂中CH₄的活性炭吸附剂,建立了考虑资源负荷、环境负荷和产品性能的评价体系,对各种粘结剂做了选择性评价,筛选出了污染物排放少、分离性能较好、强度高的粘结剂—可溶淀粉。在综合评价的基础上,详细讨论了工艺条件,如原料预处理方式、致孔剂的添加、活化温度、升温速率、活化水用量等对活性炭分离CH₄/N₂效果的影响,指出可溶淀粉作粘结剂制备颗粒活性炭的最佳工艺为:600℃炭化1h,800℃活化2h,升温速率10℃/min,活化水用量1.9².0ml/min;当可溶淀粉用量为40g/200g（褐煤）时,按照上述工艺制备的样品变压吸附分离CH₄/N₂的效果可稳定在25³0%。对其他淀粉替代可溶淀粉作粘结剂的可行性研究显示,由于较低的污染物排放量,较高的强度和良好的分离效果,使得由磷酸酯化淀粉制备的颗粒活性炭的综合评价高于可溶淀粉样品,综合第一次评价结果,在选择制备褐煤基颗粒活性炭的粘结剂时,首先推荐磷酸酯化淀粉,其次是可溶淀粉。粘结剂的种类对活性炭的物理性质和表面化学性质具有明显的影响,对由不同粘结剂制备出的分离CH₄/N₂效果较好的样品的分析表明:GAC-ES（磷酸酯化淀粉）的堆密度、颗粒密度和强度均高于其他样品;GAC-T（可溶淀粉）具有更高的微孔孔容,样品微孔的差异主要体现在0.45⁰.6nm;GAC-C（煤焦油）和GAC-T的表面含氧官能团的相对含量高于GAC-P（聚丙烯酰胺）。另外,GAC-C、GAC-P和GAC-T的热重分析表明:GAC-C和GAC-P除了0¹00℃的明显失重过程外,分别在300℃左右和700⁸00℃还有一个明显的失重过程。粘结剂的用量对活性炭的孔结构也具有较大的影响,以由市售食用淀粉制备的样品为例的孔结构表征显示:样品孔结构参数均随着淀粉淀粉用量的增加呈先降低后增高的趋势;TS-0.2、TS-0.25和TS-0.3全孔径分布的差异主要体现在20⁵0nm、2²0nm和0.4²nm范围内。GAC-C、GAC-P和GAC-T对CO₂、CH₄和N₂的吸附性能有较大差异,这主要是由三者的孔结构和表面化学性质的差异引起的。活性炭表面酮、醛、酸、酯及酸酐类的C=O和C-O含量越高,越有利于CH₄/N₂的变压吸附分离。同时活性炭变压吸附分离CH₄/N₂效果与其微孔孔容和分布有密切关系,微孔越发达越有利于CH₄/N₂的分离;模拟结果显示,0.6nm以上的微孔均能实现CH₄/N₂的吸附分离,0.7nm的微孔最有利于CH₄/N₂的吸附分离;但数值分析结果显示,小于0.6nm的微孔也能实现CH₄/N₂的吸附分离。原因在于10-4-3模型的相关参数只与温度相关,没有考虑压力的影响,而Knudsen准则很好地解释了这一现象。更多还原

【Abstract】 Coal bed methane is an unconventional nature gas. Because of its planless discharge, there are many environmental and secure problems, and resources is wasted. The utilization of coal bed methane is beneficial to optimization of energy structure and decrease of atmospheric pollution and incidents in our country. The key of utilizing coal bed methane is separation of methane and nitrigen which are the main compositions of coal bed methane. Pressure swing adsorption is one of technologies that separate effectually methane and nitrogen. And adsorbent is one of the most crucial factors which influence pressure swing adsorption performance. Due to the higher pore volume, bigger pore size, faster diffusion rate and neglecting limit of loading capacity, activated carbon is more suitable for separation of coal bed methane by pressure swing adsorption.In this paper, active carbon adsorbents used for concentrating methane from CH₄/N₂ were prepared from lignite by using coal tar, tragantine and PAM as binders, respectively. A comprehensive evaluation system consisted of enviromental index, resources index and performance index is established, and used to evaluate the three binders. The results show that soluble starch is the best binders, and its advantages are low discharge of contamination and high separation effect and strength. On the basic of evaluation results, the effects of technologcial conditions, such as pretreatment methods of lignite, kinds of pore-foaming agents, activation temperature, heating rate, dosage of activation water, on separation performance are discussed. The optimized technics is carbonizing at 600℃for 1 hour, activation at 800℃for 2 hour, heating rate of 10℃/min and activation water dosage of 1.9².0ml/min. While 40g soluble starch is added in 200g lignite, the separation performances of samples prepared by optimized technics are 25³0%.The feasibility study of other starches replacing soluble starch show that duo to lower discharge of contamination, higher strength and better separation performance, sample from starch monoester phosphate is superior to soluble starch sample. In sum, starch monoester phosphate is the top-priority binder, and soluble starch is the second choice when granular activated carbon is prepared from lignite.The influence of binders kinds on physical appearance and surface chemical properties of activated carbons is enormous. The characterizations of samples from differfent binders which have the better separation performance indicate that bulk density, pellet density and strength of GAC-ES（starch monoester phosphate） are higher than other samples while GAC-T（soluble starch） has the maximal micropore volume. The difference of micropore distribution is mainly in 0.45⁰.6nm. The surface oxygen-containing functional groups relative concentrations of GAC-T and GAC-C（coal tar） are greater than GAC-P（polyacrylamide）. In addition, besides the weightlessness in 0¹00℃, GAC-T and GAC-C has another weightlessness in 300℃and 700⁸00℃, respectively.The dosages of binder are obviously influenced the pore structure of samples. Samples from commercial salep as examples, pore structure parameters are to reduce, and then to increase with the raise of salep dosage. The pore distribution difference by DFT method of TS-0.2, TS-0.25 and TS-0.3 is in 20⁵0nm, 2²0nm and 0.4²nm.Because of the differences of pore structure and surface chemical properties, adsorptive properties on CO2, CH₄ and N₂ of GAC-C, GAC-P and GAC-T are discrepant. The contents of C=O from ketone, aldehyde, organic acid, ester and estolide, and phenol C-O are greater, the separation performance of CH₄/N₂ is better. At the same time, it is advantageous to separate CH₄/N₂ that activated carbons have more micropore volume. The results of simulation by 10-4-3 model show that the micropore from 0.6nm to 2.0nm could separate CH₄/N₂, and micropore about 0.7nm is the best pore to separate CH₄/N₂. But, numerical analysis of different range micropore volumes and separation performances indicate the micropore of which pore width is less 0.6nm could also separate CH₄/N₂. The reason is that energy parameters of 10-4-3 model are only correlated with temperature,and influence of pressure is not included. However, Knudsen roles explains best the difference。更多还原