Adsorption and recovery of low concentration coal-bed methane by zeolite ZSM-5

doi:10.11949/j.issn.0438-1157.20151684

Abstract

Abstract:

As a high-silica hydrophobic material, zeolite ZSM-5 was used for the adsorption and recovery of low concentration coal-bed methane. Theoretical and experimental studies were conducted on adsorption equilibrium, adsorption kinetics and vacuum pressure swing adsorption (VPSA). Single and binary competitive adsorption equilibrium experimental data of CH₄/N₂ on zeolite ZSM-5 were measured by gravimetric method and breakthrough-curve method. The multi-site Langmuir model was used to fit the experimental data. Microporous diffusion coefficients were calculated based on the experimental data of diluted breakthrough curves and simulated results of an isothermic mathematical bi-disperse model without momentum loss. Competitive breakthrough curves of CH₄and N₂ on zeolite ZSM-5 were predicted by fixed bed adsorption models with mass, momentum and energy transfer. Effects of CH₄ concentration in feed, feed flow rate, feed time and purge/feed flow rate ratio on separation performances of ZSM-5 packed single column four-step VPSA process were investigated. It showed that ZSM-5 zeolite exhibited a relatively good selectivity for CH₄ and the diffusion in micropores was the rate determining step for both CH4 and N2 adsorption. By the process of VPSA, CH4 purity can be concentrated from 20% to 31%～41% and the recovery can be up to 93%～98%.

Key words: coal-bed methane, adsorption, methane, nitrogen, zeolite ZSM-5, VPSA

摘要：

利用高硅疏水性沸石ZSM-5吸附回收低浓度煤层气中的甲烷,对其吸附平衡、吸附动力学以及真空变压吸附分离过程进行了理论和实验研究。通过重量法和穿透曲线法测定了CH₄/N₂单组分及双组分的竞争吸附平衡数据,并采用Multisite Langmuir吸附等温线模型对其进行拟合。结合CH₄和N₂稀释穿透曲线实验数据和等温无动量损失的双分散二级孔结构扩散模型,获得CH₄和N₂在沸石ZSM-5上的微孔扩散系数。建立并求解包含质量、动量及能量传递的固定床吸附分离模型方程,预测了CH₄和N₂在沸石ZSM-5上的竞争吸附穿透曲线。进一步采用ZSM-5吸附剂填充床单柱四步真空变压吸附实验考察了进料浓度、进料流速、进料时间以及吹扫比对分离效果的影响。结果发现沸石ZSM-5对CH₄具有较好的选择性,沸石晶粒内的微孔扩散为吸附速率控制步骤,真空变压吸附工艺可将模拟煤层气中20%的CH₄提纯至31%～41%,回收率为93%～98%。

关键词: 煤层气, 吸附, 甲烷, 氮气, 沸石ZSM-5, 真空变压吸附

CLC Number:

TQ021

LIU Haiqing, WU Yijiang, YANG Ying, YANG Lin, LI Ping, YU Jianguo. Adsorption and recovery of low concentration coal-bed methane by zeolite ZSM-5[J]. CIESC Journal, 2016, 67(5): 1931-1941.

刘海庆, 吴一江, 杨颖, 杨林, 李平, 于建国. 沸石ZSM-5吸附回收低浓度煤层气中CH₄[J]. 化工学报, 2016, 67(5): 1931-1941.

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