Dantas Silvio, Struckhoff Katie Cychosz, Thommes Matthias, Neimark Alexander V
Department of Chemical and Biochemical Engineering , Rutgers, The State University of New Jersey , 98 Brett Road , Piscataway , New Jersey 08854 , United States.
Anton Paar Quantatec Inc. , 1900 Corporate Drive , Boynton Beach , Florida 33426 , United States.
Langmuir. 2019 Sep 3;35(35):11291-11298. doi: 10.1021/acs.langmuir.9b01748. Epub 2019 Aug 19.
Carbon dioxide adsorption on micro- and mesoporous carbonaceous materials in a wide range of temperatures and pressures is of great importance for the problems of gas separations, greenhouse gas capture and sequestration, enhanced hydrocarbon recovery from shales and coals, as well as for the characterization of nanoporous materials using CO as a molecular probe. We investigate the influence of temperature on CO adsorption focusing on the capillary condensation and hysteresis phenomena. We present experimental data on the adsorption of CO on CMK-3, ordered carbon with mesopores of ∼5-6 nm, at various temperatures (185-273 K) and pressures (up to 35 bars). Using Monte Carlo (MC) simulations in the grand canonical and mesocanonical ensembles, we attempt to predict the transition from reversible capillary condensation to hysteretic adsorption-desorption cycles that is experimentally observed with the decrease of temperature. We show that although the desorption at all temperatures occurs at the conditions of pore vapor-liquid equilibrium, the capillary condensation is a nucleation-driven process associated with an effective energy barrier of ∼43 kT, specific to the sample used in this work. This barrier can be overcome at the equilibrium conditions in the region of reversible condensation at temperatures higher than 240 K. At lower temperatures, the regime of developing hysteresis is observed with progressively widening hysteresis loops. The position of capillary condensation transition is estimated using the pressure dependence of the energy barrier calculated by the thermodynamic integration of the van der Waals-type continuous canonical isotherm simulated with the gauge cell MC method. These findings lay the foundation for developing kernels of CO adsorption and desorption isotherm for calculating the pore size distribution in the entire range of micropore and mesopore sizes from one high-pressure experimental isotherm.
在广泛的温度和压力范围内，二氧化碳在微孔和介孔碳质材料上的吸附对于气体分离、温室气体捕获与封存、提高页岩和煤炭中的烃采收率等问题至关重要，同时对于使用一氧化碳作为分子探针表征纳米多孔材料也很重要。我们研究温度对一氧化碳吸附的影响，重点关注毛细凝聚和滞后现象。我们展示了一氧化碳在CMK - 3（一种具有约5 - 6纳米介孔的有序碳）上在不同温度（185 - 273K）和压力（高达35巴）下的吸附实验数据。使用巨正则系综和介正则系综中的蒙特卡罗（MC）模拟，我们试图预测随着温度降低实验观察到的从可逆毛细凝聚到滞后吸附 - 解吸循环的转变。我们表明，尽管在所有温度下解吸都发生在孔气 - 液平衡条件下，但毛细凝聚是一个成核驱动的过程，与约43kT的有效能垒相关，这是这项工作中所用样品特有的。在高于240K的温度下，在可逆凝聚区域的平衡条件下可以克服这个能垒。在较低温度下，观察到滞后现象逐渐发展，滞后回线逐渐变宽。使用通过规范单元MC方法模拟的范德华型连续正则等温线的热力学积分计算的能垒对压力的依赖性来估计毛细凝聚转变的位置。这些发现为开发一氧化碳吸附和解吸等温线的内核奠定了基础，以便从一个高压实验等温线计算整个微孔和介孔尺寸范围内的孔径分布。
