Insights on Cryogenic Distillation Technology for Simultaneous CO2 and H2S Removal for Sour Gas Fields

Experimental, RSM modelling, and DFT simulation of CO2 adsorption on Modified activated carbon with LiOH

This research investigates the enhancement of CO2 adsorption capacity through the use of modified activated carbon (AC) with LiOH, focusing on operational conditions and adsorbent properties. Response Surface Methodology (RSM) is employed to optimize process parameters for maximizing CO2 adsorption capacity. The study considers temperature, pressure, LiOH concentration for modification, and adsorbent weight as independent variables across five levels. Analysis of Variance reveals that LiOH concentration, adsorbent quantity, pressure, and temperature significantly influence CO2 adsorption. Optimal values for temperature (30°C), pressure (9 bar), LiOH concentration (0.5 mol/L), and adsorbent weight (0.5 g) result in a maximal CO2 adsorption capacity of 154.90 mg/g. Equilibrium adsorption capacity is utilized for modeling, with the Freundlich model proving suitable for CO2 adsorption on LiOH-AC. Kinetic modeling indicates the second-order model's suitability for temperatures of 30 °C and 50 °C, while the Elovich model fits temperatures of 70 °C and 90 °C. Thermodynamic modeling at the optimized conditions (303 K and 6 bar) yields ∆H, ∆S, and ∆G values of adsorption as 12.258 kJ/mol, - 0.017 kJ/mol·K, and - 7.031 kJ/mol, respectively. Furthermore, structural considerations of AC are discussed alongside modeling and simulation, presenting the adsorption rate of CO2 and the binding energy index based on Density Functional Theory (DFT).

Characteristics of Solidified Carbon Dioxide and Perspectives for Its Sustainable Application in Sewage Sludge Management

Appropriate management is necessary to mitigate the environmental impacts of wastewater sludge. One lesser-known technology concerns the use of solidified CO₂ for dewatering, sanitization, and digestion improvement. Solidified CO₂ is a normal byproduct of natural gas treatment processes and can also be produced by dedicated biogas upgrading technologies. The way solidified CO₂ is sourced is fully in line with the principles of the circular economy and carbon dioxide mitigation. The aim of this review is to summarize the current state of knowledge on the production and application of solid CO₂ in the pretreatment and management of sewage sludge. Using solidified CO₂ for sludge conditioning causes effective lysis of microbial cells, which destroys activated sludge flocs, promotes biomass fragmentation, facilitates efficient dispersion of molecular associations, modifies cell morphology, and denatures macromolecules. Solidified CO₂ can be used as an attractive tool to sanitize and dewater sludge and as a pretreatment technology to improve methane digestion and fermentative hydrogen production. Furthermore, it can also be incorporated into a closed CO₂ cycle of biogas production-biogas upgrading-solidified CO₂ production-sludge disintegration-digestion-biogas production. This feature not only bolsters the technology's capacity to improve the performance and cost-effectiveness of digestion processes, but can also help reduce atmospheric CO₂ emissions, a crucial advantage in terms of environment protection. This new approach to solidified CO₂ generation and application largely counteracts previous limitations, which are mainly related to the low cost-effectiveness of the production process.

Activated carbon fiber derived from wasted coal liquefaction residual for CO2 capture

Wasted coal liquefaction residual was used to synthesize activated carbon fibers (ACFs) for CO₂ capture, and the properties of the developed ACFs were optimized by adjusting the activation conditions, including the reaction temperature and soaking time. The yield, element distribution, pore structure, composition, functional group, morphology, and adsorption capacity of the as-synthesized ACFs were characterized by various apparatuses. In addition, static and dynamic adsorption experiments were conducted to investigate the adsorption capacity of CO₂ in flue gas. The results revealed that the synthesized ACFs are mainly composed of carbon, accounting for more than 90% of the total elements. The specific surface area, pore volume, and pore width distribution of the prepared ACFs were optimized by changing the activation conditions, and ACFs with a specific surface area higher than 1400 m²/g were successfully developed by activation at 950 for 3 h. The amount of micropores occupied more than 90% of the total pore volume. The pore width distribution dominated by micropores is beneficial for CO2 adsorption since the diameter of CO₂ is 0.33 nm. From FTIR and XPS analysis, it is found that the main structure of ACFs is a carbon skeleton composed of polycyclic aromatic hydrocarbons with a small number of oxygen-containing functional groups. The adsorption isotherm of ACFs for CO₂ conforms to the Langmuir model, indicating that the adsorption process of CO₂ by ACFs can be attributed to monolayer adsorption. Both the specific surface area and oxygen-containing functional groups have crucial effects on the adsorption capacity of CO₂. The dynamic adsorption experiment determined that ACFs-920-3 had the highest adsorption capacity for CO₂ in flue gas, and adsorption equilibrium was achieved after 7 min of adsorption. The adsorption process of CO₂ in flue gas by the as-synthesized ACFs fits well with the pseudosecond kinetic model. The CO₂ adsorption capacity of the obtained ACFs remained unchanged after 10 cycles of adsorption. A high-value-added route for synthesizing ACFs for CO₂ capture using CLR as a raw material was developed.

Developing a Hybrid Neuro-Fuzzy Method to Predict Carbon Dioxide (CO2) Permeability in Mixed Matrix Membranes Containing SAPO-34 Zeolite

This study compares the predictive performance of different classes of adaptive neuro-fuzzy inference systems (ANFIS) in predicting the permeability of carbon dioxide (CO₂) in mixed matrix membrane (MMM) containing the SAPO-34 zeolite. The hybrid neuro-fuzzy technique uses the MMM chemistry, pressure, and temperature to estimate CO₂ permeability. Indeed, grid partitioning (GP), fuzzy C-means (FCM), and subtractive clustering (SC) strategies are used to divide the input space of ANFIS. Statistical analyses compare the performance of these strategies, and the spider graph technique selects the best one. As a result of the prediction of more than 100 experimental samples, the ANFIS with the subtractive clustering method shows better accuracy than the other classes. The hybrid optimization algorithm and cluster radius = 0.55 are the best hyperparameters of this ANFIS model. This neuro-fuzzy model predicts the experimental database with an absolute average relative deviation (AARD) of less than 3% and a correlation of determination higher than 0.995. Such an intelligent model is not only straightforward but also helps to find the best MMM chemistry and operating conditions to maximize CO₂ separation.

Polyoxometalate/Ionic Liquid Desulfurization System for Hydrogen Sulfide Removal from High-Temperature Gas Stream

The temperature of industrial gas containing harmful H₂S can reach hundreds of degrees. However, few processes can be used directly for H₂S removal from industrial high-temperature gas. In this work, three polyoxometalates with different central atoms ((n-Bu₄N)₃VMo₁₂O₄₀, (n-Bu₄N)₃PMo₁₂O₄₀, and (n-Bu₄N)₄[α-SiMo₁₂O₄₀]) were synthesized and dissolved in four ionic liquids (Bmim]Cl, [Bmim]HCO₃, [Bmim]Mes, or [Bmim]OAc) for H₂S removal from high-temperature (90-180 °C) gases. The result showed that (n-Bu₄N)₃VMo₁₂O₄₀/[Bmim]OAc exhibited the optimal desulfurization performance, maintaining more than 98.6% desulfurization efficiency within 10 h. The reacted desulfurization solution can be regenerated by blowing air. FT-IR and XPS results show that both the central atom V and the coordination atom Mo of the polyoxometalate are involved in the oxidation of H₂S; after the regeneration by introducing air, V(+IV) and Mo(+IV) recovered to V(+V) and Mo(+VI), respectively. Our research shows that (n-Bu₄N)₃VMo₁₂O₄₀/[Bmim]OAc is an efficient, easy-to-regenerate, and suitable high-temperature gas desulfurization solution.

Material and Process Tests of Heterogeneous Membranes Containing ZIF-8, SiO2 and POSS-Ph

Heterogeneous membranes made of a polymer matrix and containing nano-metric fillers in their structure may present improved physicochemical and process properties compared to homogeneous membranes made only of polymer materials. Membranes made of a PEBAX^®2533 block copolymer were tested with fillers such as ZIF-8, SiO₂ and POSS-Ph being dosed to them. The material analysis and process tests indicate that these nanomaterials can be used as fillers for heterogeneous membranes. Chemometric analyses determined the influence of individual fillers on selected physicochemical properties of the materials which were used to produce the membranes. For specific concentrations of these fillers, improvement in the permeability and selectivity of the membranes, or at least in one of these parameters, was achieved. The greatest increase in permeability against the homogeneous membrane was obtained for membranes containing 10 wt% ZIF-8 (for CO₂, an increase of 2.07 times; for CH₄, 2.36 times; for N₂, 3.08 times). In turn, the greatest increase in selectivity was obtained for the CO₂/CH₄ mixture for the membrane containing 5 wt% SiO₂ (1.15 times), and for the CO₂/N₂ mixture for the membrane containing 2 wt% POSS-Ph (1.21 times).

Recent Progress of SAPO-34 Zeolite Membranes for CO2 Separation: A Review

In the zeolite family, the silicoaluminophosphate (SAPO)-34 zeolite has a unique chemical structure, distinctive pore size, adsorption characteristics, as well as chemical and thermal stability, and recently, has attracted much research attention. Increasing global carbon dioxide (CO₂) emissions pose a serious environmental threat to humans, animals, plants, and the entire environment. This mini-review summarizes the role of SAPO-34 zeolite membranes, including mixed matrix membranes (MMMs) and pure SAPO-34 membranes in CO₂ separation. Specifically, this paper summarizes significant developments in SAPO-34 membranes for CO₂ removal from air and natural gas. Consideration is given to a variety of successes in SAPO-34 membranes, and future ideas are described in detail to foresee how SAPO-34 could be employed to mitigate greenhouse gas emissions. We hope that this study will serve as a detailed guide to the use of SAPO-34 membranes in industrial CO₂ separation.