Two discrete element method/computational fluid dynamics coupling approaches are compared: One method resolves the particle shape in the fluid flow, the other one does not. Differences between these two methods with regard to the evolution of particle-based parameters (mass, temperature) are reported. A bulk of thermally thick, pyrolyzing spherical particles is taken for the numerical study.

Abstract

The combined discrete element method/computational fluid dynamics (DEM/CFD) approach allows for the description of reacting granular assemblies passed by a gas flow. Especially for thermally thick particles, the spatial resolution of the solid object volumes, their surfaces, and of the interstitial flow domain controls the quality of results while at the same time driving computational costs. To evaluate the differences between resolved and unresolved DEM/CFD approaches, pyrolysis of a bulk of spherical wood particles enclosed by a cylindrical heating surface and passed by hot nitrogen is numerically examined. The unresolved simulation is based on the averaged volume method (AVM). For the resolved simulation, the so-called blocked-off (BO) method is applied. The results show that the total mass conversion rate of solid particles into gaseous volatiles is faster when employing the resolved BO approach. The better spatial resolution of local flow field and particle surface representation leads to a more detailed prediction of convective and radiative heat transfer to the particles, but is associated with the penalty of a six-fold computing time.

A reversed liquid-to-gas contact mode in the microchannel reactor can significantly improve the carbonization method for the synthesis of high-purity mesoporous pseudo-boehmite. The transfer mass details were simulated by computational fluid dynamics. The NaAlO₂ droplets were surrounded by the CO₂ gas flow in the microchannel, which is the key to the two-phase mixing efficiency.

Abstract

Pseudo-boehmite with a high specific surface area and large pore volume was continuously synthesized in a microchannel reactor using the carbonation method. The effects of the microchannel on the prepared pseudo-boehmite, strongly present in gas-liquid mixing efficiency, were studied. In time scale, the crystallinity of pseudo-boehmite in the microchannel, without the aging process of high-temperature stirring, reaches the standard of industrial products. Besides, the fluid and mass transfer effect of the gas-liquid mixing process in the microreactor was simulated under experimental conditions in computational fluid dynamics. The result illustrated the base-liquid surround by the acid-gas model in the microreactor, which is significantly different from the batch reactor.

Niobium tungsten oxide Nb₁₄W₃O₄₄ was synthesized by hydrothermal reaction of niobium oxalate and ammonium tungstate and subsequent calcination, and the synthetic conditions and structure were optimized for its use as an anode material in lithium-ion batteries. The nearly pure phase Nb₁₄W₃O₄₄ with a particle size of 1–2 μm shows good rate performance and cycle stability with high capacity retention.

Abstract

Niobium tungsten oxide is a potential replacement for graphite in fast-charge lithium-ion batteries due to its high rate performance and high stability. Herein, Nb₁₄W₃O₄₄ anode was synthesized by hydrothermal reaction of niobium oxalate and ammonium tungstate and sequent calcination of niobium tungsten oxide precursors. Compared with the traditional solid-state method, the particle size and calcination time of Nb₁₄W₃O₄₄ obtained by the modified method are greatly reduced. Through orthogonal experiments, the optimal synthesis conditions were determined, and it was found that hydrothermal conditions have an important influence on the particle size of the final product, while the calcination temperature and time greatly affect the purity of the product and thus influence its specific capacity during cycles.

PVDF/Cu-SiO₂ (1 wt %) composite membranes showed higher hydrophilicity and a lower irreversible fouling ratio in membrane bioreactors. They showed better resistance to Escherichia coli, and membranes containing 0.5 and 1.0 wt % of Cu-SiO₂ nanoparticles were stabilized after 28 days of release testing.

Abstract

The effects of synthesized hydrophilic Cu-SiO₂ nanoparticles on the morphology and antibiofouling performance of polyvinylidene fluoride (PVDF) membranes in a membrane bioreactor system were examined. As a result, the pure water flux of the PVDF membrane increased from 47.61 to 71.93 L m⁻²h⁻¹ in the presence of 1.0 wt % Cu-SiO₂ nanoparticles. Also, the better-developed finger-like bulk pores and thicker sponge-like surface pores for the nanocomposite membranes confirmed the lower phase inversion rate. The total fouling ratio of the membranes was reduced from 53.79 % to 24.13 % in the presence of 1.0 wt % Cu-SiO₂ nanoparticles, while the flux recovery ratio increased from 54.61 % to 88.73 %. In addition, extracellular polymeric substances analysis showed lower protein and carbohydrate formed on the membrane surface for the nanocomposite membranes.

Passive acoustic emissions were detected by a new rheometric device to monitor the manufacture and rheological changes of complex fluids, live and in situ; a simplified output was then transferred to machine learning algorithms. Power-law and Herschel-Bulkley model fluids were studied on the laboratory and pilot scales. Offline rheometry was used to validate the obtained rheological properties.

Abstract

The measurement capabilities of a newly developed in-situ rheometric device based on a single passive acoustic emission sensor and machine learning algorithms were investigated. Two surfactant structured fluids demonstrating complex non-Newtonian rheology (Power-law and Herschel-Bulkley models) were examined. Furthermore, a static evaluation on the laboratory scale in comparison to dynamic processing on the pilot scale was conducted. The results indicate that the machine learning algorithms of this technology can identify, in > 90 % of scenarios, the correct type of rheology or the manufacturing process step across both scales. This identification is based on solving a classification problem using quadratic support vector machine learning algorithms, which have proven to deliver the most robust predictions across a choice of 24 different algorithms tested. Additionally, a new format of in situ rheology display was introduced, referred to as RRF™ factor.

The prospects of algae as an alternative raw source for biofuel production, various cultivation, harvesting, and conversion methodologies with merits and demerits, and the formation of bioproducts by thermochemical processes are reviewed. Technological breakthroughs like genetic engineering, synthetic biology, and nanotechnology can enhance biofuel manufacturing techniques by altering or introducing specific genes.

Abstract

The objective of this review is to interpret the usage of alternative renewable systems that is imperative for future developments on a global industrial scale. Microalgae have appeared as the most realistic source for biofuel generation due to the accumulation of lipids in most of the strains with rapid biomass expansion and greater photosynthetic efficiency than land plants. Microalgal-derived feedstocks have a broad range of commercial advantages and can be used as promising renewable fuel substitutes with zero net CO₂ emission. Important facets of algal-based biofuel production, growing and harvesting techniques, approaches to thermochemical conversion, synthesis of commodities with added value, and recent breakthroughs in the field of synthetic biology for fuel production are covered.

Shiny water drops puprle leaf. Copyright: Getty Images

The conversion of synthesis gas to a broad spectrum of products via Fischer-Tropsch reaction is one of the most important processes to solve the problem of decreasing fossil fuel resources. The effects of some operating conditions on the performance of a new kind of perovskite nanocatalyst (LaFe_0.5Mn_0.5O_{3 ±  δ} ) in a fixed-bed catalyst microreactor were investigated.

Abstract

Operating conditions and selectivity of a new perovskite nanocatalyst were studied in Fischer-Tropsch synthesis using a fixed-bed microreactor. Selectivity equations were obtained using the experimental data collected from a hydrogenation process in a fixed-bed microreactor. The operating conditions were obtained by defining the design-of-experiment scope based on response surface methodology, on 3 levels and in 15 tests. The optimum selectivity for alkenes relative to alkanes was obtained at 349.7 °C, 3.2 bar, and a H₂/CO volumetric ratio of 1. Also, the optimum selectivity for alkenes relative to the overall selectivity for other products was attained at 250 °C, 2.3 bar, and a feed volumetric ratio of 2.

Mn-based catalysts for ammonia selective catalytic reduction of NO_x exhibit good low-temperature activity but poor sulfur resistance. Doping with Sb resulted in a perforated porousness layered foam micromorphology, which promoted molecular mass transfer of the reaction gas and diffusion of the reactants/products, enhanced the catalytic activity, and increased the resistance to sulfur poisoning.

Abstract

Manganese-antimony composite oxide catalysts were prepared for use in low-temperature selective catalytic reduction of flue gas, by adopting the strategy of passivation to regulate the valence state of the active component and control catalytic activity. Activity evaluation results found that MnSb_0.36O_y delivered 80 % NO conversion in the presence of SO₂ at 200 °C, and nearly 90 % conversion at 250 °C. Doping with Sb changed the surface micromorphology, resulting in a perforated porousness layered foam with a porous structure of tens of nanometers, which was conducive to molecular mass transfer of the reaction gas. Doping with Sb regulated the valence state of the active MnO_x component, which diminished catalytic oxidation of SO₂, thus promoting catalyst stability and limiting the toxic effect of SO₂.