Acid gas adsorption on zeolite SSZ ‐13: Equilibrium and dynamic behavior for natural gas applications

Improved Synthesis of Hollow Fiber SSZ-13 Zeolite Membranes for High-Pressure CO2/CH4 Separation

High-silica CHA zeolite membranes are highly desired for natural gas upgrading because of their separation performance in combination with superior mechanical and chemical stability. However, the narrow synthesis condition range significantly constrains scale-up preparation. Herein, we propose a facile interzeolite conversion approach using the FAU zeolite to prepare SSZ-13 zeolite seeds, featuring a shorter induction and a longer crystallization period of the membrane synthesis on hollow fiber substrates. The membrane thickness was constant at ~3 μm over a wide span of synthesis time (24-96 h), while the selectivity (separation efficiency) was easily improved by extending the synthesis time without compromising permeance (throughput). At 0.2 MPa feed pressure and 303 K, the membranes showed an average CO2 permeance of (5.2±0.5)×10-7 mol m-2 s-1 Pa-1 (1530 GPU), with an average CO2/CH4 mixture selectivity of 143±7. Minimal defects ensure a high selectivity of 126 with a CO2 permeation flux of 0.4 mol m-2 s-1 at 6.1 MPa feed pressure, far surpassing requirements for industrial applications. The feasibility for successful scale-up of our approach was further demonstrated by the batch synthesis of 40 cm-long hollow fiber SSZ-13 zeolite membranes exhibiting CO2/CH4 mixture selectivity up to 400 (0.2 MPa feed pressure and 303 K) without using sweep gas.

Recent Attempts on the Removal of H2S from Various Gas Mixtures Using Zeolites and Waste-Based Adsorbents

Natural gas, biogas, and refinery gas all include H2S, which has adverse effects not only on the environment and human health but also on the equipment and catalysts that are employed in the relevant processes. H2S is removed from the aforementioned gases using a variety of techniques in order to fulfill the necessary sales criteria and for reasons of safety. The adsorption method stands out among various other approaches due to its straightforward operation, high level of efficiency, and low overall cost. This technique makes use of a variety of adsorbents, such as metal-organic frameworks (MOFs), activated carbon, and zeolites. The use of zeolite-based adsorbents is by far the most common of these various types. This is due to the specific properties of zeolite-based adsorbents, which include a high adsorption capacity, the ability to be regenerated, a high temperature stability, a diversity of types, the possibility of modification, high efficiency, and low cost. In addition, research is being done on adsorbents that are made from inexpensive raw materials in order to remove H2S. This article focuses on zeolites, zeolite modifications, and wastes as an adsorbent for the removal of H2S, all of which have been investigated fruitfully in recent years, as well as the promising applications of zeolites.

Technologies for Deep Biogas Purification and Use in Zero-Emission Fuel Cells Systems

A proper exploitation of biogas is key to recovering energy from biowaste in the framework of a circular economy and environmental sustainability of the energy sector. The main obstacle to widespread and efficient utilization of biogas is posed by some trace compounds (mainly sulfides and siloxanes), which can have a detrimental effect on downstream gas users (e.g., combustion engines, fuel cells, upgrading, and grid injection). Several purification technologies have been designed throughout the years. The following work reviews the main commercially available technologies along with the new concepts of cryogenic separation. This analysis aims to define a summary of the main technological aspects of the clean-up and upgrading technologies. Therefore, the work highlights which benefits and criticalities can emerge according to the intended final biogas application, and how they can be mitigated according to boundary conditions specific to the plant site (e.g., freshwater availability in WWTPs or energy recovery).

H2O and H2S adsorption by assistance of a heterogeneous carbon-boron-nitrogen nanocage: Computational study

A model of heterogeneous carbon-boron-nitrogen (C-B-N) nanocage was investigated in this work for adsorbing H2O and H2S substances. To achieve this goal, quantum chemical calculations were performed to obtain optimized configurations of substances towards the surface of nanocage. The calculations yielded three possible configurations for relaxing each of substances towards the surface. Formation of acid-base interactions between vacant orbitals of boron atom and full orbitals of each of oxygen and sulfur atoms yielded the strongest complexes of substance-nanocage in comparison with orientation of substances through their hydrogen atoms towards the surface of nanocage. As a consequence, formations of interacting H2O@C-B-N and H2S@C-B-N complexes were achievable, in which mechanism of action showed different strengths for the obtained complexes. Variations of molecular orbital features and corresponding energy gap and Fermi energy for the models before/after adsorption could help for detection of adsorbed substance through a sensor function. And finally, such C-B-N nanocage showed benefit of providing activated surface for efficient adsorption of each of H2O and H2S substance with possibility of differential adsorption regarding the strength of complex formations.