Sulfur dioxide removal: An overview of regenerative flue gas desulfurization and factors affecting desulfurization capacity and sorbent regeneration

Numerous mitigation techniques have been incorporated to capture or remove SO₂ with flue gas desulfurization (FGD) being the most common method. Regenerative FGD method is advantageous over other methods due to high desulfurization efficiency, sorbent regenerability, and reduction in waste handling. The capital costs of regenerative methods are higher than those of commonly used once-through methods simply due to the inclusion of sorbent regeneration while operational and management costs depend on the operating hours and fuel composition. Regenerable sorbents like ionic liquids, deep eutectic solvents, ammonium halide solutions, alkyl-aniline solutions, amino acid solutions, activated carbons, mesoporous silica, zeolite, and metal-organic frameworks have been reported to successfully achieve high SO₂ removal. The presence of other gases in flue gas, e.g., O₂, CO₂, NOx, and water vapor, and the reaction temperature critically affect the sorption capacity and sorbent regenerability. To obtain optimal SO₂ removal performance, other parameters such as pH, inlet SO₂ concentration, and additives need to be adequately governed. Due to its high removal capacity, easy preparation, non-toxicity, and low regeneration temperature, the use of deep eutectic solvents is highly feasible for upscale utilization. Metal-organic frameworks demonstrated highest reported SO₂ removal capacity; however, it is not yet applicable at industrial level due to its high price, weak stability, and robust formulation.

Separation Properties of Porous MoS2 Membranes Decorated with Small Molecules

Using first-principles simulations, we surveyed the interactions between porous MoS₂ monolayers in the 2H phase and 15 small molecules (H₂, O₂, H₂O, H₂S, CO, CO₂, SO₂, N₂, NO, NO₂, NH₃, HF, HCl, CH₄, and CH₃OH). Four types of molecules including H₂, O₂, H₂S, and NO₂ directly dissociate and saturate the corners of the most common S-rimmed triangular pores, while other molecules only molecularly adsorb. The trisublayered structure of a MoS₂ monolayer allows a new in-pore stable adsorption configuration in addition to the most studied above-pore adsorption configuration. Furthermore, the gas penetration pathways through the MoS₂ membranes are no longer the conventional single-peak curve with one transition state like in the case of porous graphenes but are the "M"-shaped curve featuring two transition states connected by a stable in-pore adsorption state. The irreversible pore passivation via dissociative adsorption and reversible pore decoration by molecular adsorption will lead to very different separation performances of the MoS₂ membranes, largely by changing the effective pore size. For example, the S-rimmed pores in the pore-3Mo2S membrane allow free pass of CH₄ and CO₂ molecules. If passivated by H atoms, the membrane can be used to separate gas mixtures like H₂/CH₄ and H₂/CO₂ with selectivities of 10⁹:1 and 10⁸:1, respectively. The permeance value of H₂ is estimated to be about 0.15 mol m^-2 s^-1 Pa^-1 at room temperature and 0.1 bar pressure drop across the membrane. In contrast, the medium strong adsorption of a SO₂ molecule in the center of the pore will completely block the passage of CO₂ and CH₄, whose removal only needs heating. Our work reveals the complex behaviors of porous transition metal dichalcogenides (TMDs) toward guest molecules.

Exploration of tetra-branched multiple-site SO2 capture materials

Efficient exploration of the configuration space of the reaction complexes consisting of multi-branched structures and SO₂ molecules.

Designing tri-branched multiple-site SO2 capture materials

Tri-branched species with multiple isolated reactive sites are proposed for high and uniform SO₂ capture.