Recovery of high-purity NO2 and SO2 products from iron-ore sintering flue gas by distillation: process design, optimization and analysis

Conversion of medical waste into value-added products using a novel integrated system with tail gas treatment: Process design, optimization, and thermodynamic analysis

The COVID-19 pandemic has generated substantial medical waste (MW), posing risks to society. Based on widespread MW incineration, this study proposes an integrated system with tail gas treatment to convert MW into value-added products with nearly zero emissions. Herein, steam generators and supercritical CO₂ cycles were used to recover energy from MW to produce high-temperature/pressure steam and electricity. A simple power generation cycle achieved a net electricity efficiency of 22.4% through optimization. Thermodynamic analysis revealed that the most energy and exergy loss occurred in incineration. Furthermore, a pressurized reactive distillation column purified the resultant tail gas. The effects of inlet temperature, pressure, liquid/gas ratio, and recycle ratio on the removal and conversion efficiencies of NO₂ and SO₂ were evaluated. Nearly 100% of the SO₂ and 75% of the NO₂ generated by the incineration of MW have been converted into their acid forms. Based on the proposed tail gas treatment unit, high-purity CO₂ (∼98% purity) was finally obtained.

Enhancement of NOx adsorption performance on zeolite via a facile modification strategy

Adsorption is a promising technology for simultaneously capturing nitrogen oxides (NO_x) from flue gases and recycling NO₂ as a profitable chemical, for which a robust and efficient adsorbent provides the key step for success in practical applications. This work reports the enhancement of NO_x adsorption performances with less cost of desorption energy on Cu-ZSM-5 zeolites prepared by a facile and rapid (690 s) modification method, the incipient-wetness impregnation coupled with microwave drying (IM). In comparisons to H-ZSM-5, Na-ZSM-5 and conventionally liquid-phase ion-exchanged counterparts under sub-1000 ppm NO_x feed concentrations and room temperature, the IM sample renders a record NO_x adsorption capacity (q_t,NOx) of 0.878 mmol/g from dry gas stream on zeolites, and an applicable q_t,NOx of 0.1 mmol/g from wet gas stream with a proper copper loading (2.1 wt%). The temperature programmed desorption of NO_x on the optimal IM sample saturated with NO_x from wet gas stream exhibit primary peak temperature lower than reported Cu-ZSM-5 and significant NO₂ proportion (72.6 %) in desorbed NO_x. Deeper insights into advantageous NO_x oxidative adsorption over the properly-loaded Cu-ZSM-5 in terms of diverse adsorbate states and competitiveness towards H₂O were gained, showing IM method a promising sorbent improvement strategy for practical use.

Advances in air pollution control for key industries in China during the 13th five-year plan

Industrial development is an essential foundation of the national economy, but the industry is also the largest source of air pollution, of which power plants, iron and steel, building materials, and other industries emit large amounts of pollutants. Therefore, the Chinese government has promulgated a series of stringent emission regulations, and it is against this backdrop that research into air pollution control technologies for key industrial sectors is in full swing. In particular, during the 13th Five-Year Plan, breakthroughs have been made in pollution control technology for key industrial sectors. A multi-pollutant treatment technology system of desulfurization, denitrification, and dust collection, which applies to key industries such as power plants, steel, and building materials, has been developed. High-performance materials for the treatment of different pollutants, such as denitrification catalysts and desulfurization absorbers, were developed. At the same time, multi-pollutant synergistic removal technologies for flue gas in various industries have also become a hot research topic, with important breakthroughs in the synergistic removal of NO_x, SO_x, and Hg. Due to the increasingly stringent emission standards and regulations in China, there is still a need to work on the development of multi-pollutant synergistic technologies and further research and development of synergistic abatement technologies for CO₂ to meet the requirements of ultra-low emissions in industrial sectors.

Dynamic Adsorption/Desorption of NOx on MFI Zeolites: Effects of Relative Humidity and Si/Al Ratio

Adsorption is a potential technology that is expected to meet NO_x ultra-low emission standards and achieve the recovery of NO₂. In this study, the adsorption/desorption behavior of NO_x with competitive gases (e.g., H₂O(g) and CO₂) was studied on MFI zeolites with different Si/Al ratios and under different relative humidity (0~90% RH). Sample characterization of self-synthesizing zeolites was conducted by means of X-ray diffraction, Ar adsorption-desorption, and field emission scanning electron microscopy. The results showed that low-silica HZSM-5(35) showed the highest NO_x adsorption capacity of 297.8 μmol/g (RH = 0) and 35.4 μmol/g (RH = 90%) compared to that of other adsorbents, and the efficiency loss factor of NO_x adsorption capacity at 90%RH ranged from 85.3% to 88.1%. A water-resistance strategy was proposed for NO_x multicomponent competitive adsorption combined with dynamic breakthrough tests and static water vapor adsorption. The presence of 14% O₂ and lower adsorption temperature (25 °C) favored NO_x adsorption, while higher CO₂ concentrations (~10.5%) had less effect. The roll-up factor (η) was positively correlated with lower Si/Al ratios and higher H₂O(g) concentrations. Unlike Silicalite-1, HZSM-5(35) exhibited an acceptable industrial desorption temperature window of NO₂ (255~265 °C). This paper aims to provide a theoretical guideline for the rational selection of NO_x adsorbents for practical applications.

Condensation Separation of NO2 with Dimerization Reaction in the Presence of Noncondensable Gas: Critical Assessment and Model Development

Pure nitrogen dioxide (NO₂) has significant economic value and is widely used in many fields, for which condensation technology plays an important role in separation and purification. However, developing cost-effective NO₂ condensers remains challenging due to the lack of precise theoretical guidelines and comprehensive understanding of NO₂ condensation process. In this work, NO₂ condensation at various inlet surface subcoolings, mole fractions of noncondensable gas (NCG), and Re numbers was studied with a visualization experimental system. The influential rules of each parameter on heat transfer coefficients (HTCs) and the NO₂ condensate state as the coexistence of droplet, streamlet and film were revealed. A substantial underestimation of experimental data by the classical heat and mass transfer analogy (HMTA) model was quantified. The large discrepancy was found to originate from the uniqueness in heat transfer, mass transfer, and condensate state caused by NO₂ dimerization during condensation. A modified HMTA model was developed considering the release heat of dimerization reaction and the promotion of mass transfer by an increased NO₂ concentration gradient within the diffusion layer which contribute to improvements of HTCs by ∼6 and ∼49%, respectively. The correction of liquid film roughness regarding potential heterogeneity of dimerization was proposed as a function of the key parameters, contributing to the improvement of HTCs by ∼150%. An accurate theoretical formula for HTCs prediction within an error of ±25% was finally derived, providing the key step for success in practical applications.

Separation of SO2 and NO2 with the Zeolite Membrane: Molecular Simulation Insights into the Advantageous NO2 Dimerization Effect

NO₂ and SO₂, as valuable chemical feedstock, are worth being recycled from flue gases. The separation of NO₂ and SO₂ is a key process step to enable practical deployment. This work proposes SO₂ separation from NO₂ using chabazite zeolite (SSZ-13) membranes and provides insights into the feasibility and advantages of this process using molecular simulation. Grand canonical ensemble Monte Carlo and equilibrium molecular dynamics methods were respectively adopted to simulate the adsorption equilibria and diffusion of SO₂, NO₂, and N₂O₄ on SSZ-13 at varying Si/Al (1, 5, 11, 71, +∞), temperatures (248-348 K), and pressures (0-100 kPa). The adsorption capacity and affinity (SO₂ > N₂O₄ > NO₂) demonstrated strong competitive adsorption of SO₂ based on dual-site interactions and significant reduction in NO₂ adsorption due to dimerization in the ternary gas mixture. The simulated order of diffusivity (NO₂ > SO₂ > N₂O₄) on SSZ-13 demonstrated rapid transport of NO₂, strong temperature dependence of SO₂ diffusion, and the impermeability of SSZ-13 to N₂O₄. The membrane permeability of each component was simulated, rendering a SO₂/NO₂ membrane separation factor of 26.34 which is much higher than adsorption equilibrium (6.9) and kinetic (2.2) counterparts. The key role of NO₂-N₂O₄ dimerization in molecular sieving of SO₂ from NO₂ was addressed, providing a facile membrane separation strategy at room temperature.