甲烷在MIL-101上的吸附平衡分析及充放气特性

为研制吸附储存天然气(ANG)用的金属有机框架物(MOFs),选择MIL-101(Cr)试样进行甲烷的吸附平衡与充放气实验。试样由溶剂热法合成,经测试77.15 K氮吸附数据作表征结构后,在温度293-313 K、压力0-100 k Pa和0-7 MPa条件下测试甲烷吸附平衡数据,运用亨利定律标绘和Toth方程确定甲烷在试样上的极限吸附热和绝对吸附量,比较了ClausiusClapeyron(C-C)方程和Toth势函数计算的等量吸附热。最后,在工程应用对应的流率10-30 L/min,对装填940 g试样、容积为3.2 L的适型储罐吸附床进行甲烷充放气实验。结果表明,甲烷在试样上的平均极限吸附热为23.89 k J/mol,测试范围内Toth方程预测的平均相对误差为1.06%,由C-C方程和Toth势函数确定的平均等量吸附热分别为15.51和13.56 k J/mol;在有效充放气时间内,储罐在10和30 L/min流率时的总充/放气量分别为347 L/338 L和341 L/318 L,放气率为98.3%和94.1%。工程应用应选用C-C方程确定的等量吸附热,并采取慢充/放以增大充/放气量和提高吸附床脱气率。

Adsorption equilibrium and charge/discharge characteristics of methane on MIL-101

For developing metal organic frameworks (MOFs) suitable for the storage of nature gas by adsorption, the MIL-101 (Cr) sample was synthesized by solvothermal method, with which the characterization by adsorption of nitrogen at 77.15 K and the adsorption equilibrium and charge/discharge of methane were conducted. The adsorption equilibrium data of methane on the sample were measured volumetrically at temperature range of 293-313 K within a pressure range of 0-100 kPa and 0-7 MPa, respectively. The limit isosteric heat of adsorption was determined by employing the Henry's law using the adsorption data at very low pressure region, and the absolute adsorption amounts of methane on the sample were determined via nonlinear fit of the adsorption data at high pressure range by using Toth's equation. Isosteric heats of methane adsorption were then calculated through Clausius-Clapeyron equation and Toth's potential function. The charge and discharge tests of methane were performed at a flow rate range of 10-30 L/min on a 3.2 L conformable vessel packed with samples about 940 g. The results show that the mean limit isosteric heat is 23.89 kJ/mol, and the average relative error of the result predicted by the Toth equation is about 1.06%. The mean isosteric heat of adsorption determined by Clausius-Clapeyron equation and Toth's potential function is about 15.51 kJ/mol and 13.56 kJ/mol, respectively. The results also reveal that the total amount of charge/discharge at the flow rate of 10 L/min and 30 L/min is about 347 L/338 L and 341 L/318 L, respectively, which are in correspondence with the ratios of discharge about 98.3% and 94.1%. It suggests that the isosteric heat of methane adsorption determined by Clausius-Clapeyron equation is more reasonable for practical applications, and slower charging/discharging with a smaller flow rate is beneficial to increasing the total amount of charge/discharge and the discharging of the adsorbent bed.