CO2 Physisorption over an Industrial Molecular Sieve Zeolite: An Experimental and Theoretical Approach

The present work studies the adsorption of CO2 using a zeolitic industrial molecular sieve (IMS) with a high surface area. The effect of the CO2 feed concentration and the adsorption temperature in conjunction with multiple adsorption-desorption cycles was experimentally investigated. To assess the validity of the experimental results, theoretical calculations based on well-established equations were employed and the values of equilibrium, kinetic, and thermodynamic parameters are presented. Three additional column kinetic models were applied to the data obtained experimentally, in order to predict the breakthrough curves and thus facilitate process design. Results showed a negative correlation between temperature and adsorption capacity, indicating that physical adsorption takes place. Theoretical calculations revealed that the Langmuir isotherm, the Bangham kinetic model (i.e., pore diffusion is the rate-determining step), and the Thomas and Yoon-Nelson models were suitable to describe the CO2 adsorption process by the IMS. The IMS adsorbent material maintained its high CO2 adsorption capacity (>200 mg g-1) after multiple adsorption-desorption cycles, showing excellent regenerability and requiring only a mild desorption treatment (200 °C for 15 min) for regeneration.

Adsorptive Desulfurization of Condensate Contains Aromatic Compounds Using a Commercial Molecular Sieve

This study is undertaken to evaluate the potential of a commercial molecular sieve to remove diverse sulfur compounds from condensate with high aromatic on an industrial scale. For the first part of this study, the adsorbent is characterized in detail using inductively coupled plasma optical emission spectroscopy, X-ray diffraction, field-emission scanning electron microscopy, and Brunauer-Emmett-Teller analysis. For the second part, dynamic breakthrough experiments on an industrial scale are performed to assess the dynamic adsorption performance of a commercial molecular sieve. Dynamic experiments show that the adsorbent effectively removes the sulfur compound from condensate that has approximately 900 ppmw S. In more detail, this commercial molecular sieve selectively desulfurizes condensate to about 12 ppmw S, and this is achieved when the concentration of non-sulfur aromatic is greater than 15 times higher than the total sulfur. As regeneration is a crucial part of the continuous adsorption-regeneration cycling process, the final part of this study is focused on finding a desorption method to avoid a sulfur concentration peak in tail gas.

Unique Interaction between Layered Black Phosphorus and Nitrogen Dioxide

Air pollution caused by acid gases (NO₂, SO₂) or greenhouse gases (CO₂) is an urgent environmental problem. Two-dimensional nanomaterials exhibit exciting application potential in air pollution control, among which layered black phosphorus (LBP) has superior performance and is environmentally friendly. However, the current interaction mechanism of LBP with hazardous gases is contradictory to experimental observations, largely impeding development of LBP-based air pollution control nanotechnologies. Here, interaction mechanisms between LBP and hazardous gases are unveiled based on density functional theory and experiments. Results show that NO₂ is different from other gases, as it can react with unsaturated defects of LBP, resulting in oxidation of LBP and reduction of NO₂. Computational results indicate that the redox is initiated by p orbital hybridization between one oxygen atom of NO₂ and the phosphorus atom carrying a dangling single electron in a defect's center. For NO, the interaction mechanism is chemisorption on unsaturated LBP defects, whereas for SO₂, NH₃, CO₂ or CO, the interaction is dominated by van der Waals forces (57-82% of the total interaction). Experiments confirmed that NO₂ can oxidize LBP, yet other gases such as CO₂ cannot. This study provides mechanistic understanding in advance for developing novel nanotechnologies for selectively monitoring or treating gas pollutants containing NO₂.