Column Reactor Research Articles

A novel recurrence-based approach for investigating multiphase flow dynamics in bubble column reactors.

In chemical industries, multiphase flows in a bubble column reactor are frequently observed. The nonlinearity associated with bubble hydrodynamics, such as bubble-bubble and bubble-liquid interactions, gives rise to complex spatiotemporal patterns with increased gas or liquid velocities, which are extremely difficult to model and predict. In the current study, we propose a new, computationally efficient recurrence-based approach involving the angular separation between suitably defined state vectors and implement it on the experimental multiphase flow variables. The experimental dataset that consists of image frames obtained using a high-speed imaging system is generated by varying air and water flow rates in a bubble column reactor setup. The recurrence plots using the new approach are compared with those derived from conventional recurrence, considering standard benchmark problems. Further, using the recurrence plots and recurrence quantification from the new recurrence methodology, we discover a transition from a high recurrence state to a complex regime with very low recurrence for an increase in airflow rate. Determinism exhibits a rise for the decrease in airflow rate. A sharp decline in determinism and laminarity, signifying the quick shift to complex dynamics, is more prominent for spatial recurrence than temporal recurrence, indicating that the rise in airflow rate significantly impacts the spatial location of bubbles. We identify three regimes that appeared as distinct clusters in the determinism-laminarity plane. The bubbly regime, characterized by high values of determinism and laminarity, is separated by an intermediate regime from the slug flow regime, which has low determinism and laminarity.

Probing efficient microbial CO2 utilisation through metabolic and process modelling.

Acetogenic gas fermentation is increasingly studied as a promising technology to upcycle carbon-rich waste gasses. Currently the product range is limited, and production yields, rates and titres for a number of interesting products do not allow for economically viable processes. By pairing process modelling and host-agnostic metabolic modelling, we compare fermentation conditions and various products to optimise the processes. The models were then used in a simulation of an industrial-scale bubble column reactor. We find that increased temperatures favour gas transfer rates, particularly for the valuable and limiting H2 , while furthermore predicting an optimal feed composition of 9:1 mol H2 to mol CO2 . Metabolically, the increased non-growth associated maintenance requirements of thermophiles favours the formation of catabolic products. To assess the expansion of the product portfolio beyond acetate, both a product volatility analysis and a metabolic pathway model were implemented. In-situ recovery of volatile products is shown to be within range for acetone but challenging due to the extensive evaporation of water, while the direct production of more valuable compounds by acetogens is metabolically unfavourable compared to acetate and ethanol. We discuss alternative approaches to overcome these challenges to utilise acetogenic CO2 fixation to produce a wider range of carbon negative chemicals.

Deciphering the influencing mechanism of hydraulic retention time on purification performance of a mixotrophic system from the perspective of reaction kinetics.

At present, eutrophication is increasingly serious, so it is necessary to effectively reduce nitrogen and phosphorus in water bodies. In this study, a pyrite/polycaprolactone-based mixotrophic denitrification (PPMD) system using pyrite and polycaprolactone (PCL) as electron donors was developed and compared with pyrite-based autotrophic denitrification (PAD) system and PCL-based heterotrophic denitrification (PHD) system through continuous flow experiment. The removal efficiency of NO3--N (NRE) and PO43--P (PRE) and the contribution proportion of PAD in the PPMD system were significantly increased by prolonging hydraulic retention time (HRT, from 1 to 48h). When HRT was equal to 24h, the PPMD system conformed to the zero-order kinetic model, so NRE and PRE were mainly limited by the PAD process. When HRT was equal to 48h, the PPMD system met the first-order kinetic model with NRE and PRE reaching 98.9 ± 1.1% and 91.8 ± 4.5%, respectively. When HRT = 48h, the NRE and PRE by PAD system were 82.7 ± 9.1% and 88.5 ± 4.7%, respectively, but the effluent SO42- concentration was as high as 152.1 ± 13.7mg/L (the influent SO42- concentration was 49.2 ± 3.3mg/L); the NRE by PHD system was 98.5 ± 1.7%, but the PO43--P could not be removed ideally. The concentrations of NO3--N, total nitrogen, PO43--P, and SO42- in the PPMD system also showed distinct changes along the reactor column. In addition, the microbial diversity analysis showed that prolonging HRT (from 24 to 48h) increased the abundance of autotrophic denitrifying microorganisms in the PPMD system, ultimately increasing the contribution proportion of PAD.

Novel calcium-rich biochar synthesis and application for phosphorus and amoxicillin removal from synthetic and urban wastewater: Batch, columns, and continuous stirring tank reactors investigations

This work examines the synthesis of a novel calcium rich biochar (MB-900) and its application for phosphorus (P) and amoxicillin removal from synthetic and treated urban wastewaters under static and dynamic conditions (laboratory column and continuous stirring tank reactors (CSTRs)). Characterization techniques show that MB-900 has an enhanced structural, textural and surface chemical properties. Besides, batch adsorption tests indicate that MB-900 has important P recovery capacity in comparison with various engineered biochars available in the literature. Furthermore, under dynamic conditions, MB-900 efficiently recovers P from both synthetic solutions and real wastewater effluent. Due to a higher residence time, P recovery in CSTR mode are 94.9 and 82.3 mg g−1 for synthetic and urban wastewater, respectively. These values are 1.4, and 6.1 times higher than those obtained in column tests. Mechanism investigations shows that P recovery occurs through electrostatic interactions, complexation, and especially precipitation as hydroxyapatite. Under column and CSTR modes, AMX behaves like a conservative tracer and was not adsorbed by MB-900. Therefore, the resulting P-loaded biochar can be applied in agriculture as a slow release fertilizer without risks related to AMX adsorption/leaching by plants.

Improvement of extracellular polysaccharides production from Cordyceps militaris immobilized alginate beads in repeated-batch fermentation

Cordyceps militaris (C. militaris) is a unique medicinal fungus of the genus Cordyceps. It has high economic value due to various biological functions from the extracellular polysaccharides (EPSs) it produces. The aim of this study was to establish a mycelium-immobilization system for EPS production in a bubble column system. First, EPS production was optimized by 90.2% (from 0.72 to 1.37 g/L) using response surface methodology under an alginate-immobilized mycelium system with 6 days of cultivation. The highest EPS production was obtained (5.3 g/L) in a flask system through elongation to 15 days of cultivation. EPS production subsequently further increased to 10.42 g/L utilizing a bubble column reactor. Furthermore, the system can be reused for at least three rounds. In the EPS characteristics analysis, the produced EPSs were mainly composed of glucose and galactose. They presented strong antibacterial activity against Staphylococcus aureus. In terms of antioxidant activity, respective the EPS concentration that caused 50% scavenging of DPPH and ABTS free radicals values (IC50) were 4.65 and 7.92 mg/mL. In summary, these findings should be helpful for establishing a suitable industrial fermentation system for C. militaris and can be studied in the food and medical industries in future work.

Preliminary Evaluation of Methods for Continuous Carbon Removal from a Molten Catalyst Bubbling Methane Pyrolysis Reactor

Methane pyrolysis in molten catalyst bubble (MCB) column reactors is an emerging technology that enables the simultaneous production of hydrogen and solid carbon, together with a mechanism for separating the two coproducts. In this process, methane is dispersed as bubbles into a high temperature molten catalyst bath producing hydrogen and low-density carbon, which floats to the surface of the bath from providing a means for them to be separated. However, the removal of carbon particulates from a bubbling column reactor is technically challenging due to the corrosive nature of the molten catalysts, contamination of the product carbon with the molten catalysts, high temperatures and lack of understanding of the technology options. Four potential concepts for the removal of carbon particulate from a methane pyrolysis molten metal bubble column reactor are presented, based on the pneumatic removal of the particles or their overflow from the reactor. The concepts are evaluated using a cold prototype reactor model. To simulate the operation of a high-temperature reactor at low temperatures, the dominant dimensionless numbers are identified and matched between a reference high-temperature reactor and the developed cold prototype using water, air and hollow glass microsphere particles as the representatives of the molten catalyst, gaseous phases and solid carbon particulates, respectively. The concepts are tested in the cold prototype. High rates of particle removal are achieved, but with different tradeoffs. The applicability of each method together with their advantages and disadvantages are discussed.

Impact of Superficial Gas Velocity on Gas Holdup in a Cu-Cl Cycle Thermochemical Oxygen Bubble Column Reactor

Impact of Superficial Gas Velocity on Gas Holdup in a Cu-Cl Cycle Thermochemical Oxygen Bubble Column Reactor

Lactose hydrolysis in packed-and fluidized-bed reactors using a recombinant β-galactosidase immobilized on magnetic core-shell capsules.

The objective of this study was to develop a bioprocess for lactose hydrolysis in diverse dairy matrices, specifically skim milk and cheese whey, utilizing column reactors employing a core-shell enzymatic system featuring β-galactosidase fused to a Cellulose Binding Domain (CBD) tag (β-galactosidase-CBD). The effectiveness of reactor configurations, including ball columns and toothed columns operating in packed and fluidized-bed modes, was evaluated for catalyzing lactose hydrolysis in both skim milk and cheese whey. In a closed system, these reactors achieved lactose hydrolysis rates of approximately 50% within 5h under all evaluated conditions. Considering the scale of the bioprocess, the developed enzymatic system was capable of continuously hydrolyzing 9.6 L of skim milk while maintaining relative hydrolysis levels of approximately 50%. The biocatalyst, created by immobilizing β-galactosidase-CBD on magnetic core-shell capsules, exhibited exceptional operational stability, and the proposed bioprocess employing these column reactors showcases the potential for scalability.

Hydrodynamics of CH4-Sn molten-metal bubble columns under electromagnetic field using computational fluid dynamics

The use of molten metal bubble column reactors (MMBCRs) for CO2-free H2 production via non-oxidative CH4 pyrolysis has gained attention due to little catalyst deactivation and simple downstream processing. Maintaining a small size of bubbles is crucial to enhance CH4 decomposition rates in MMBCRs. In this study, the effect of electromagnetic field on the hydrodynamics of MMBCRs was investigated using volume-of-fluid computational fluid dynamics (VOF-CFD) coupled with a large-eddy simulation (LES) model for turbulence and a magnetohydrodynamic (MHD) model for the electromagnetic field. Hydrodynamic parameters such as the gas holdup (αG), mean bubble size (d32), and gas–liquid interfacial area (as) were obtained from the validated VOF-CFD model in the bench-scale CH4-Sn system at 900 °C. A horizontal electromagnetic field with alternating current (AC) at an electromagnetic field strength of 1.0 T promoted bubble breakup and increased as from 8.6 to 18.2 m2/m3 compared to the MMBCR without electromagnetic field.

Nanoscale zero-valent iron alleviate antibiotic resistance risk during managed aquifer recharge (MAR) by regulating denitrifying bacterial network

The frequent occurrence of antibiotics in reclaimed water is concerning, in the case of managed aquifer recharge (MAR), it inevitably hinders further water purification and accelerates the evolutionary resistance in indigenous bacteria. In this study, we constructed two column reactors and nanoscale zero-valent iron (nZVI) amendment was applied for its effects on water quality variation, microbial community succession, and antibiotic resistance genes (ARGs) dissemination, deciphered the underlying mechanism of resistance risk reduction. Results showed that nZVI was oxidized to iron oxides in the sediment column, and total effluent iron concentration was within permissible limits. nZVI enhanced NO3--N removal by 15.5% through enriching denitrifying bacteria and genes, whereas made no effects on oxacillin (OXA) removal. In addition, nZVI exhibited a pivotal impact on ARGs and plasmids decreasing. Network analysis elucidated that the diversity and richness of ARG host declined with nZVI amendment. Denitrifying bacteria play a key role in suppressing horizontal gene transfer (HGT). The underlying mechanisms of inhibited HGT included the downregulated SOS response, the inhibited Type-Ⅳ secretion system and the weakened driving force. This study afforded vital insights into ARG spread control, providing a reference for future applications of nZVI in MAR.

Carbon dioxide absorption using monoethanolamine, piperazine and n-metil-2-pirolidon solvents under counter current regime in packed column reactor

In this research the carbon dioxide absorption using Monoethanolamine (MEA), Piperazine (PZ) and N-Metil-2-pirolidon (NMP) solvents and their different blends (MEA/NMP, PZ/NMP, MEA/PZ) in packed column reactor filled with Raschig rings was investigated and compared for efficient carbon dioxide absorption. The process was followed in a countercurrent regime under a liquid flow rate of 200 mL/min, gas flow rate of 2.5 L/min, and CO2 concentration of 50,000 ppm. Carbon dioxide removal efficiency (%), absorption capacity (mol CO2/mol solvent), overall mass transfer coefficient (1/min) and absorption rate (mol/l.s) were monitored. The highest obtained values for carbon dioxide removal efficiency, absorption capacity and overall mass transfer coefficient were 57.5%, 0.148 mol CO2/mol solvent and 2.178 min−1 respectivelly when 0.03 M MEA/0.07 M PZ in a hybrid system was used. It was concluded that PZ blends with MEA were successful absorbent as the organic physical solvent whereas NMP didn't show improving effect in blends with MEA on the absorption efficiency.

Active Center Size-Dependent Fenton-Like Chemistry for Sustainable Water Decontamination.

Accurately controlling catalytic activity and mechanism as well as identifying structure-activity-selectivity correlations in Fenton-like chemistry is essential for designing high-performance catalysts for sustainable water decontamination. Herein, active center size-dependent catalysts with single cobalt atoms (CoSA), atomic clusters (CoAC), and nanoparticles (CoNP) were fabricated to realize the changeover of catalytic activity and mechanism in peroxymonosulfate (PMS)-based Fenton-like chemistry. Catalytic activity and durability vary with the change in metal active center sizes. Besides, reducing the metal size from nanoparticles to single atoms significantly modulates contributions of radical and nonradical mechanisms, thus achieving selective/nonselective degradation. Density functional theory calculations reveal evolutions in catalytic mechanisms of size-dependent catalytic systems over different Gibbs free energies for reactive oxygen species generation. Single-atom site contact with PMS is preferred to induce nonradical mechanisms, while PMS dissociates and generates radicals on clusters and nanoparticles. Differences originating from reaction mechanisms endow developed systems with size-dependent selectivity and mineralization for treating actual hospital wastewater in column reactors. This work brings an in-depth understanding of metal size effects in Fenton-like chemistry and guides the design of intelligent catalysts to fulfill the demand of specific scenes for water purification.

Mass transfer enhancement and hydrodynamic performance with wire mesh coupling solid particles in bubble column reactor

It is of vital significance to investigate mass transfer enhancements for chemical engineering processes. This work focuses on investigating the coupling influence of embedding wire mesh and adding solid particles on bubble motion and gas–liquid mass transfer process in a bubble column. Particle image velocimetry (PIV) technology was employed to analyze the flow field and bubble motion behavior, and dynamic oxygen absorption technology was used to measure the gas–liquid volumetric mass transfer coefficient kLa. The effect of embedding wire mesh, adding solid particles, and wire mesh coupling solid particles on the flow characteristic and kLa were analyzed and compared. The results show that the gas–liquid interface area increases by 33% to 72% when using the wire mesh coupling solid particles strategy compared to the gas–liquid two-phase flow, which is superior to the other two strengthening methods. Compared with the system without reinforcement, kLa in the bubble column increased by 0.5–1.8 times with wire mesh coupling solid particles method, which is higher than the sum of kLa increases with inserting wire mesh and adding particles, and the coupling reinforcement mechanism for affecting gas–liquid mass transfer process was discussed to provide a new idea for enhancing gas–liquid mass transfer.

CO2 Impact on Methane Pyrolysis as a Key Issue of Using Biogas as an Educt: A Theoretical Study

Dry reforming of methane (DRM) has attracted great interest for the production of syngas and/or hydrogen in a more environmentally friendly way. It is especially advantageous in this case to use biogas—as a mixture of methane, CO2, and traces of further gases—as a feedstock replacement for natural gas. Nevertheless, industrial implementation of DRM is currently limited because of its inherent process restrictions. The biggest challenge of dry reforming is the deposition of carbon on the catalyst, known as “coking.” The focus of this theoretical study is to evaluate the feasibility of a biogas dry reforming process in a liquid metal (Sn) bubble column reactor. This technology has already been proven suitable for methane pyrolysis to obtain hydrogen, preventing issues related to reactor clogging or catalyst deactivation caused by carbon deposition. Results show that at high operating temperatures and atmospheric pressure, a product gas primarily composed of H2 and CO would be obtained. CO2 and water vapor may also be present in the final product depending on the operating conditions. The molten tin inside the reactor would, according to the presented theoretical considerations, not be affected by the formation of carbides and oxides. Additionally, the syngas composition (the H2 : CO ratio) could be adjusted by using different CH4 : CO2 feed ratios.

A novel electrolytic gas lift reactor for efficient microbial electrosynthesis of acetate from carbon dioxide

The low current density impedes the practical application of microbial electrosynthesis for CO2 fixation. Engineering the reactor design is an effective way to increase the current density, especially for H2-mediated microbial electrosynthesis reactors. The electrolytic bubble column microbial electrosynthesis reactor has shown great potential for scaling up, but the mixing and gas mass transfer still need to be enhanced to further increase the current density. Here, we introduced an inner draft tube to the bubble column to tackle the problem. The addition of draft tube resulted in a 76.6% increase in the volumetric mass transfer coefficient (kLa) of H2, a 40% increase in the maximum current density (337 A/m2) and a 72% increase in average acetate production rate (3.1 g/L/d). The computational fluid dynamics simulations showed that the addition of draft tube enhanced mixing efficiency by enabling a more ordered cyclic flow pattern and a more uniform gas/liquid distribution. These results indicate that the electro-bubble column reactor with draft tube holds great potential for industrial implementation.

Integrated Process for High Phenol Removal from Wastewater Employing a ZnO Nanocatalyst in an Ozonation Reaction in a Packed Bubble Column Reactor

The use of an ozonized bubble column reactor (OBCR) in wastewater treatment is advantageous due to its efficient mixing and mass transfer characteristics. Among all high-performance features, the ozonation reaction in a BCR undergoes a low dissolution of O3 in the reactor with a limited reaction rate. In this study, the ozonation reaction of phenol in an OBCR was tested using a ZnO nanocatalyst and alumina balls as packing material. Three concentrations of O3 were evaluated (i.e., 10, 15, and 20 ppm), and 20 ppm was found to be the optimum concentration for phenol degradation. Also, two doses (i.e., 0.05 and 0.1 g/L) of ZnO nanocatalysts were applied in the reaction mixture, with the optimal dose found to be 0.1 g/L. Accordingly, three phenol concentrations were investigated in the OBCR (i.e., 15, 20, and 25 ppm) using four treatment methods (i.e., O3 alone, O3/Al2O3, O3/ZnO nanocatalyst, and O3/Al2O3/ZnO nanocatalyst). At a contact time of 60 min and phenol concentration of 15 ppm, the removal rate was 66.2, 73.1, 74.5, and 86.8% for each treatment method, respectively. The treatment experiment that applied the O3/Al2O3/ZnO nanocatalyst produced the highest phenol conversion into CO2 and H2O in the shortest contact time for all phenol concentrations. Thus, the OBCR employed with a ZnO nanocatalyst plus packing material is a promising technology for the rapid and active removal of phenol because it enhances the number of hydroxyl radicals (•OH) generated, which ultimately increases the oxidation activity in the OBCR. Also, the results showed efficient flow characteristics in the OBCR, with channeling problems averted due to appropriate gas movement resulting from the use of packing materials. Finally, it was found that the ozonation process in an OBCR is an efficient method for phenol conversion with good economic feasibility.

Robust Bayesian optimization for flexibility analysis of expensive simulation-based models with rigorous uncertainty bounds

The performance of emerging biochemical systems rests on their potential to adapt to uncertainties quickly and accurately. Flexibility analysis is a quantitative framework for determining if a system can maintain safe and feasible operation despite uncertainty. Most available methods assume access to equation-oriented models, which can be difficult to obtain in practice. In this paper, we propose a sequential black-box flexibility analysis method, BoFlex, that overcomes this challenge by constructing probabilistic surrogate models over the joint space of uncertain and recourse variables. BoFlex is based on a special alternating confidence bound procedure, which we show finitely converges to a correct solution under mild assumptions on the unknown functions. We also establish a rigorous upper bound on the convergence rate in terms of the maximum information gain of the surrogate model. The advantages of BoFlex are demonstrated on several case studies including a heat exchanger network and a bubble column reactor.

Hydrodynamics and model of gas‐liquid flow in microbubble column reactors

AbstractMicrobubble column reactors (MBCRs) have the significant advantages of high gas holdup, large gas‐liquid interfacial area, and excellent mass transfer performance, making them attractive for applications such as hydrogenation and oxidation. However, there is still a lack of comprehensive understanding of the gas‐liquid flow behavior in MBCRs. In this work, the effects of gas and liquid superficial velocities on flow regimes, residence time distribution, and gas holdup are investigated. The gas holdup increases linearly with the increase of gas superficial velocity, even in heterogeneous regimes, ranging from 0% to 60% at gas superficial velocities of 0–25 mm/s. Additionally, the gas‐liquid interfacial areas in MBCRs are 1–2 orders of magnitude larger than those in traditional bubble column reactors. A prediction model for gas holdup is established, and the predicted values are in good agreement with the experimental values.

Eccentric bearing capacity of steel reinforced reactive powder concrete columns after high temperature exposure

The three-dimensional nonlinear finite element model of steel reinforced reactive powder concrete (SRRPC) column was created to analyze mechanical properties after high temperature. Effect of temperature on mechanical behaviors of RPC, section steel and steel bars were taken into account in model. Accuracy of the temperature distribution and the prediction of eccentric bearing capacity after high temperature was verified by comparing experimental results with numerical results. Effects of eccentricity, loading angle, RPC strength, section steel strength and steel ratio on eccentric bearing capacity after high temperature were analyzed. Findings indicate that: there are two typical failure modes of SRRPC columns after high temperature under different eccentric loads, including small and large eccentric compression failure. As eccentricity has increased, residual bearing capacity declines obviously. Increase of RPC strength will greatly increase residual bearing capacity, and improve ductility to a certain extent. Increase of section steel strength and steel ratio can improve residual bearing capacity to a certain extent. Residual bearing capacity is mostly unaffected by the loading angle. Finally, the calculation formula of normal section bearing capacity of SRRPC bias column after high temperature was established based on limit state design method, which has high accuracy and can provide reference for identifying and strengthening composite structures following fire.

Enriched microbial fuel cells; Enhancing anode fillers to purify eutrophic water

Microbial Fuel Cells (MFCs) play a crucial role in both contaminant removal and energy generation. This study focuses on developing a novel anode material composed of Poly3-hydroxybutyrate-co-3‑hydroxy, activated carbon, pyrite, and sponge iron particles. The aim is to effectively remove various pollutants, including nitrite-nitrogen, ammonium-nitrogen, nitrate-nitrogen, total inorganic nitrogen, algae, chemical oxygen demand and total phosphorus while generating bioelectricity. The MFC design involves connecting the anode carbon felt and cathode wire using externally insulated titanium, along with a fixed resistance. The anaerobic reactor column is filled with different proportions of the four particles. The results show that total inorganic nitrogen (TIN) removal rates are impressive, with 93 % in Box 2 (B2), 91 % in Box 3 (B3), 86 % in Box 1 (B1), and 66 % in Box 4 (B4). Additionally, the enhanced anode material achieved a high-power output of 959.9 mW/m3 and a current density of 6.989 A/m3. In conclusion, this study demonstrates the potential of the enriched bio-bed structure for purifying eutrophic water bodies, making it a promising method for contaminant removal and energy generation.