颗粒活性炭的制备及其PSA分离CH4/N2的性能

Preparation of the granular active carbon and its capability for separating CH_4/N_2 through adsorption

以无烟煤为原料,煤焦油为黏结剂,采用预氧化-炭化-水蒸气活化法制备了变压吸附(PSA)分离甲烷/氮气(CH_4/N_2)用的颗粒活性炭(GAC)。系统研究了炭化和活化制备条件对GAC的PSA分离效果的影响。结果表明,GAC分离CH_4/N_2是基于平衡分离效应。在炭化温度500～600℃,炭化时间1～3 h,活化温度800～950℃,活化时间2～4 h,水蒸气流速5～7 mL/min条件下制备的GAC能够将CH_4/N_2中的CH_4体积分数较原料气提高20%以上;其中,在炭化温度600℃,炭化时间2.5 h,活化温度900℃,活化时间2 h,水蒸气流速5mL/min的条件下制备的GAC能够将CH_4体积分数较原料气提高36.6%。

The present article is intended to introduce our study on the preparation of the granular active carbons （GACs） and their capability to separate CH4/N2 through pressure swing adsorption （PSA） process. As is known, granular activated carbons （GACs） can be used for separating methane and nitrogen mixture （CH4/N2）, which is involved in the separation process of methane from coal-embedded gas. GACs can be prepared by various methods. In this paper, GACs are prepared by using the so-called preoxidation-carbonization-activation technology. The first process of the preparation, that is, preoxidation and carbonization of GAC are carried out at low temperatures and then activated, whose agent is steam. Anthracite is used as a precursor and coal tar—as a binder. In this article we have investigated the effects of the GAC preparation conditions, including carbonization, activation, on its separation performance used in a PSA process consisting of five steps. The PSA results of our investigations indicate that methane concentration has gained an obvious improvement at the countercurrent depressurization and countercurrent evacuation steps in the PSA process, thus showing that the separation of CH4/N2 by means of GAC is of equilibrium separation by nature. With the increase of carbonization temperature and time, the separation behavior of GAC tends to increase at first, and then decrease. The actual influence of the activation temperature and the steam flowing rate on the separation behavior turned to be very similar to that of carbonization. However, it also seems that with the increase of activation duration, the separation behavior of GAC tends to increase. The results of our finding demonstrate that the CH4 concentration can be improved by more than 20% as compared with the feed concentration of CH4 when GAC is prepared under the proper conditions with carbonization temperature kept between 500 ℃ to 600 ℃, carbonization time being 1 h to 3 h, the activation temperature-800 ℃ to 950 ℃, the activation time between 2 h to 4 h, and the steam flowing rate—from 4 mL/min to 5 mL/min. The best GAC proves to be able prepared at the carbonization temperature of 600 ℃ for of 2.5 h, at which the CH4 concentration is likely to get enhanced to 36.6% and the activation temperature of 900 ℃ for 2 h with steam flowing rate of 5 mL/min.