A Simple Technique for Surface Area Determination Through Supercritical Co2 Adsorption

Abstract

The measurement of specific surface area of porous materials has long been important in physical sciences and is currently growing in importance in applied and environmental science. Numerous systems have been developed for surface area measurement by gas adsorption. Commercial systems are available which can measure a wide range of absolute surface area with relative ease. However, their cost is often prohibitive. In this study, an inexpensive apparatus for surface area measurement has been set up to be used for measuring supercritical adsorption of CO 2 . The Ono-Kondo Lattice model was used to represent the adsorption isotherm and to determine the surface area. The results of surface area determination using CO 2 adsorption combined with OK model have been compared to the numbers obtained from nitrogen BET method. For surface area determination of zeolites and activated carbons, the new method give reasonable agreement results (within 10% deviation) compared to the results obtained from nitrogen BET method. In addition, the new method also gives more reasonable results for surface area determination of coals. As known, the nitrogen BET method gives almost zero of coals' surface area. This might due to the characteristic of the coals' structure that might be change (the pores are closed) during the cooling process in nitrogen BET method. Moreover, the new method can also be used to determine the surface area of porous materials using CO 2 adsorption data at various temperatures without sacrificing their accuracy.

Adsorption of Humic Acid onto Jordanian Kaolinite Clay: Effects of Humic Acid Concentration, pH, and Temperature

“…Probably the most widely used and studied technique for surface area determination is that of gas adsorption. The amount of gas adsorbed by a solid as a function of pressure is determined either gravimetrically or volumetrically and the surface area calculated from the adsorption isotherm models such as Langmuir [39]. A common practice in determining the surface area of porous materials is using the adsorption of nitrogen gas.…”

Gas‐in‐place calculations in shale gas reservoirs using experimental adsorption data with adsorption models

“…Although the Langmuir isotherm is commonly used in the experimental adsorption data evaluation, such as in the study of Heller & Zoback, adsorption is calculated lower than its actual value due to ignoring the volume of adsorbed gas. In this and similar studies, it was shown that the Ono‐Kondo monolayer model is useful for predicting the volume of adsorbed gas, and by using this value, absolute adsorption is calculated. For example, using the experimental adsorption data of Heller & Zoback, the absolute adsorption is calculated by applying Ono‐Kondo models.…”

“…Another advantage of Ono‐Kondo models is the prediction of the surface area of shale samples. As shown in Table , the surface area values of shale samples at 25, 50, and 75 °C are between 13.376–16.070 m 2 /g by applying the method of Sudibandriyo . Therefore, Ono‐Kondo models are capable of approximately predicting the surface area of shale samples with their experimental adsorption data.…”

“…In this study, to evaluate raw experimental adsorption data, Langmuir isotherm and Ono‐Kondo models (monolayer and three‐layer) were used. An algorithm was written for the Ono‐Kondo monolayer and three‐layer models using MATLAB to find the adsorbed phase densities at different layers, surface areas, and Ono‐Kondo model parameters. The written algorithm is checked using Sudibandriyo et al's experimental CH 4 adsorption results for BPL.…”

“…Different than the study of Hartman et al, for determining the volume of adsorbed fluid, Ono‐Kondo models were used in this study. This model was used in a few studies for the evaluation of adsorption data . None of these studies try to use the model data to predict initial gas‐in‐place amounts and adsorbed gas ratios in shale gas reservoirs by using Ono‐Kondo models.…”