NO selective reduction by H2 (H2-SCR) has been developed as a promising technology for the emission control for H2 combustion engines. This work focused on experimentally evaluating the effect of catalyst supports by performing material characterization, followed by the development of a kinetic model that incorporated mass transfer effects. 1 wt% Pd catalysts supported on Al2O3, TiO2, BEA zeolite, and SSZ-13 zeolite were prepared and H2-SCR performance tests were performed across the temperature range of 100–300 °C, under varying H2/NO ratios and both dry and wet conditions. The Pd/TiO2 sample was found to exhibit the highest performance for NO conversion and N2 yield. Material characterization confirmed its larger Pd particle size and lower dispersion helped suppress the competing H2 oxidation reaction; the presence of reduced-state Pd promoted catalytic conversion; and the Pd/TiO2 chemical properties facilitated hydrogen spillover. In the kinetic model, reactions involving NO reduction to N2, N2O, and NH3, as well as H2 oxidation, were simulated, accurately reproducing the experimental trend and values for all the samples. NH3 formation was observed only on the Pd/TiO2-supported catalyst and was found to be independent of NO concentration. The kinetic parameters for the different samples were consistent with both the catalytic performance and material characterization results. Moreover, the study showed that external mass transfer played a crucial role by suppressing the fast hydrogen oxidation reaction, thus enhancing hydrogen availability for NO reduction.

Absorption by aqueous potassium carbonate is gaining renewed interest as a post-combustion carbon capture technology due to its benign chemistry and low regeneration duty. In this work, we present new experimental data on the absorption rate of CO<inf>2</inf> into aqueous K<inf>2</inf>CO<inf>3</inf>. We performed absorption experiments on 25 wt% K<inf>2</inf>CO<inf>3</inf> at a temperature of 313–358 K and solvent loadings up to 70%, using a thermostatted, stirred batch reactor. A stagnant film model accounting for all reactive species was used to derive the second order rate constant (k<inf>2</inf>) for the reaction between CO<inf>2</inf> and OH⁻. The role of the reaction was found to diminish with increasing solvent loading due to a decrease in the hydroxide concentration, whereas the k<inf>2</inf> was instead found to increase with the solvent loading. To explain this behavior we developed an ion-contribution model that relates k<inf>2</inf> to the ionic composition of the solvent. The model describes the experiments over the whole range of data with good accuracy. The results of this work are relevant for industrial applications of aqueous K<inf>2</inf>CO<inf>3</inf> where the absorption process is operated at high solvent loading to minimize regeneration duties.

Aqueous potassium carbonate (K₂CO₃)-based absorption processes are among the first-generation carbon capture technologies ready for large-scale deployment. The high stability of aqueous K₂CO₃ and its low regeneration energy demand present clear advantages. However, the inherently slow CO₂ uptake by aqueous K₂CO₃ remains a key limitation. We present a comprehensive study on vanadium pentoxide (V₂O₅) as a rate promoter to enhance the absorption of CO₂ in aqueous K₂CO₃. The absorption rate of CO₂ was measured over a wide range of conditions, namely V₂O₅ concentrations up to 6 wt %, solvent loadings up to 60%, and temperatures between 313 and 358 K. The rate promoter was found to significantly enhance the absorption rate across all conditions, by up to a factor of 2–3 with respect to unpromoted K₂CO₃. Analysis of vanadium speciation indicated that this enhancement arises from the reaction between CO₂ and hydrogen monovanadate (HVO₄^2–), with a rate constant that increases exponentially with ionic strength. A kinetic model incorporating this relation accurately reproduced the observed absorption rates across the experimental range. The results of this work demonstrate V₂O₅ is an effective rate promoter under conditions typical of K₂CO₃-based processes, thus enabling reductions in compression duties and associated capital costs without major process changes.

A process-scale model for pressure retarded osmosis (PRO) using a 1-dimensional representation of the spiral-wound membrane is presented. Comparing a length-averaged modeling approach with a true counter-current approach reveals that the former holds only for relatively short membrane lengths while it over-predicts the net power output for longer membranes. For a membrane line with eight spiral-wound elements in series, the length-average model over-predicted the PRO performance by 20 %. The model was further used to assess the impact of feed pre-treatment on process performance and optimal process design. Feed pre-treatment was found to be a dominant factor affecting the optimal inlet feed flow rate and the power output. Our model suggests that for a moderate to high feed pre-treatment requirement the inlet feed flow rate is close to minimum feed flow rate of the membrane module. In the absence of feed pre-treatment a power density of 143 and 284 W m−2 for CTA and TFC membranes, respectively, was found. When feed pre-treatment with 100 Wh m−3 was employed these numbers dropped to 48 and 94 W m−2.

In this paper we study the ductile breakup of tracer aggregates in an incompressible, homogeneous, and isotropic three-dimensional turbulent flow. The flow dynamics is studied by means of a direct numerical simulation, whereas the Lagrangian velocities and stress statistics along trajectories are obtained by particle tracking. We investigate the breakup dynamics under the hypothesis that aggregates are able to deform and accumulate energy. Within this framework, breakup occurs when the energy transferred to the aggregate by the flow exceeds a critical value. We contrast our predictions for ductile breakup with those obtained for brittle breakup. We observe that turbulence intermittency is crucial for the breakup of brittle aggregates, while it becomes less relevant for ductile aggregates. In the limit of highly ductile aggregates the breakup rate is dictated by the mean properties of the flow. We propose a simple model to capture this behaviour.

The breakup of inertial, solid aggregates in an incompressible, homogeneous and isotropic three-dimensional turbulent flow is studied by means of a direct numerical simulation, and by a Lagrangian tracking of the aggregates at varying Stokes number and fluid-to-particle density ratio. Within the point-particle approximation of the Maxey–Riley–Gatignol equations of motion, we analyze the statistics of the time series of shear and drag stresses, which are here both deemed as responsible for aggregate breakup. We observe that, regardless of the Stokes number, the shear stresses produced by the turbulent velocity gradients similarly impact the breakup statistics of inertial and neutrally buoyant aggregates, and dictate the breakup rate of loose aggregates. When the density ratio is different from unity, drag stresses become dominant and are seen to be able to cause to breakup of also the most resistant aggregates. A transition from a shear-dominated to a drag-dominated breakup regime is observed, and a power-law is seen to well describe the breakup rate of loose aggregates regardless of their inertia. The present work assesses the role of shear and drag stresses on aggregate breakup and computes breakup rates to be possibly used in population balance models.

Transport and particulate processes are ubiquitous in environmental, industrial and biological applications, often involving complex geometries and porous media. In this work we present a general population balance model for particle transport at the pore-scale, including aggregation, breakage and surface deposition. The various terms in the equations are analysed with a dimensional analysis, including a novel collision-induced breakage mechanism, and split into one- and two-particles processes. While the first are linear processes, they might both depend on local flow properties (e.g. shear). This means that the upscaling (via volume averaging and homogenisation) to a macroscopic (Darcy-scale) description requires closures assumptions. We discuss this problem and derive an effective macroscopic term for the shear-induced events, such as breakage caused by shear forces on the transported particles. We focus on breakage events as prototype for linear shear-induced events and derive upscaled breakage frequencies in periodic geometries, starting from nonlinear power-law dependence on the local fluid shear rate. Results are presented for a two-dimensional channel flow and a three dimensional regular arrangement of spheres, for arbitrarily fast (mixing-limited) events. Implications for linearised shear-induced collisions are also discussed. This work lays the foundations of a new general framework for multiscale modelling of particulate flows. 

The present work aims at investigating absorption of CO₂ into promoted and unpromoted aqueous K₂CO₃. For this we performed a series of lab experiments in a thermostated batch stirred tank gas-liquid reactor containing the solvent. The absorption of CO₂ was monitored by the decrease in the reactor pressure. To compare the different solvent blends, the experimental conditions, i.e., injection pressure, reactor temperature, stirring speed, and solvent volume were kept constant. For the interpretation of the experiments a simple absorption model is formulated based on which an apparent absorption rate is derived. Among the different rate promoters studied, we found that V₂O₅ results in a substantial increase of the absorption rate, while the use of B(OH)₃ in conjunction with V₂O₅ does not provide any tangible benefits. A semi-qualitative comparison with rate constants reported in the literature suggests that this hindering effect of B(OH)₃ is due to the lower pH of the solvent containing B(OH)₃. The solvent blends containing amine-promoters MEA and piperazine demonstrated rapid absorption. Comparison with the literature indicates that absorption in the presence of these promoters is mass transfer limited under the experimental conditions.

The aim of the work was to study the effects of neighboring particles with uniform Stefan flow in particle- fluid flows. Particle-resolved numerical simulations were carried out for particles emitting a uniform Stefan flow into the bulk fluid. The bulk fluid was uniform and isothermal. The Stefan flow volume emitted from the two particles is equal, such that it represents idealized conditions of reacting particles. Particles were located in tandem arrangement and particle distances were varied between 1.1 and 10 particle diameters (1.1 <= L/D <= 10). Three particle Reynolds numbers were considered during the simulations (Re = 2.3,7 and 14), which is similar to our previous studies. Three Stefan flow velocities were also considered during simulations to represent inward, outward, and no Stefan flow. The drag coefficient of the particles without Stefan flow showed that the results fit with previous studies on neighbor particle effects. When the particle distance is greater than 2.5 diameters (L/D > 2.5), the effects of Stefan flow and neighboring particles are independent of each other. I.e. an outward Stefan flow decreases the drag coefficient (CD) while an inward Stefan flow increases it and the upstream particle experience a higher CD than the downstream particle. When L/D <= 2.5, the effect of Stefan flow is dominant, such that equal and opposite pressure forces act on the particles, resulting in a repelling force between the two neighboring particles. The pressure force showed a large increase compared to the viscous force at these distances. The effect of Stefan flow is weakened at higher Reynolds numbers. A model was developed for the calculation of the drag coefficient. The model, which reproduce the results from the numerical simulations presented above, is a product of independent models that describe the effects of both neighboring particles and two distinguished effects of the Stefan flow.

Feed water pretreatment presents a significant issue in salinity-gradient energy production by pressure-retarded osmosis (PRO). Conventional pretreatment methods require an energy input comparable to the energy output of PRO, thus narrowing the feasibility window for power production. In this work, we investigate continuous low-dosage ozonation of the feedwater as a strategy to reduce organic membrane fouling in PRO. For this, we run laboratory experiments using humic acid, alginic acid, and natural surface water as foulants. For alginic acid and surface water, ozone at a concentration of 0.1 mg L-1substantially reduced membrane fouling and recovered the water flux of the fresh membrane. For humic acid, some residual fouling remained. Tests showed that the ozonation of humic acid leads to low-molecular-weight residues that might explain the persistent fouling. To assess the feasibility of the method, we tested the ozone compatibility of the membrane by means of Fourier transform infrared spectroscopy (FTIR) and estimated the power requirement for ozone production. FTIR showed some oxidation of the membrane material, but the membrane performance remained unaltered. The power requirement for ozonating the feed at 0.1 mg L-1is estimated to be 0.01 kWh/m3.