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甲烷(CH4)是高效洁净的能源和化工原料,从抽采煤层气、垃圾气和油田气等气体中分离提纯CH4已受到国内外关注,加强对这些气体的综合利用,对于节能减排具有很重要的意义。这些气体中CH4含量一般较低,而且含有许多N2,由于CH4和N2的物理性质极为相似,其混合气体CH4/N2的变压吸附(PSA)分离成为分离这些气体的难点之一。PSA分离CH4/N2的关键在于吸附剂,因而对其吸附剂的研发一直受到全世界的关注。本文以褐煤为原料制备了用于PSA分离CH4/N2的粒状活性炭(GAC);研究了制备条件对GAC浓缩CH4/N2中CH4的性能、孔结构和CH4、N2的吸附性能的影响。采用的制备工艺简单,包括炭化和水蒸气物理活化两个步骤;通过实验确定了具有良好浓缩分离性能GAC的最佳制备条件。以所制备的GAC为吸附剂,采用单柱单循环五步PSA过程,能够浓缩如低浓度煤层气中的CH4。PSA实验结果表明,制备的GAC是一种新型的活性炭吸附剂,不但具有类似于炭分子筛的筛分作用,即对CH4有位阻效应,导致在减压时CH4先穿透;同时具有普通活性炭的吸附性能,即对CH4的选择吸附使得CH4在抽真空步骤得到浓缩。使用这种GAC,在PSA过程的顺向减压和抽真空两个步骤得到产品气,可将CH4/N2混合气中CH4的浓度从30%(体积分数)在顺向减压步骤提高到45%～50%(体积分数),在抽真空步骤提高到50%～60%(体积分数)。
Methane (CH4) is an efficient and clean energy and chemical raw material. The separation and purification of CH4 from the gas extracted from coal-bed methane, waste gas and oilfield gas have drawn more and more attention at home and abroad, and the comprehensive utilization of these gases is enhanced. Very important meaning. The CH4 content in these gases is generally low and contains many N2. Because the physical properties of CH4 and N2 are very similar, the pressure swing adsorption (PSA) separation of the mixed gas CH4 / N2 is one of the difficulties in separating these gases. PSA separation of CH4 / N2 key lies in the adsorbent, and thus the development of its adsorbent has been the world’s attention. In this paper, granular activated carbon (GAC) for PSA separation of CH4 / N2 was prepared from lignite. The effect of preparation conditions on the performance of CH4, the pore structure and the adsorption properties of CH4 and N2 in GAC concentrated CH4 / N2 was studied. The preparation process is simple, including two steps of carbonization and physical activation of steam. The optimal preparation conditions of GAC with good concentration and separation performance are determined experimentally. Using the prepared GAC as adsorbent, single column single cycle five-step PSA process can be used to concentrate CH4 in low concentration CBM. PSA results show that the prepared GAC is a new type of activated carbon adsorbent, which not only has the screening effect similar to that of carbon molecular sieve, ie, it has steric hindrance to CH4, which leads to CH4 penetration at the time of decompression; meanwhile, Of the adsorption performance, that is, the selective adsorption of CH4 makes CH4 concentrated in the vacuum step. Using this GAC, the product gas is obtained in two steps: forward decompression and vacuum evacuation in the PSA process. The concentration of CH4 in the CH4 / N2 mixture can be increased from 30% (volume fraction) in the forward depressurization step to 45 % ~ 50% (volume fraction), in the vacuum step up to 50% to 60% (volume fraction).