Bubble Column Reactor Research Articles

Effects of SDS surface-active agents on hydrodynamics and oxygen mass transfer in a square bubble column reactor: Experimental and CFD modeling study

This work examined experimentally and numerically the effects of sodium dodecyl sulfate (SDS) surfactant agent on mass transfer coefficients kLaL and kL in a high-aspect square bubble column reactor. To this end, SDS aqueous solutions at concentrations between 5 ppm and 30 ppm were prepared. Superficial gas velocity was varied from 0.74 cm.s−1 to 9.44 cm.s−1 covering all flow regimes to analyze the interaction between different phases and the effect of liquid surface tension on gas-liquid interfaces. Experimental data indicated that the presence of the SDS in the liquid phase augmented the overall gas holdup up to 25% at a constant gas velocity (Ug = 7.3 cm.s−1) in the transition regime, which is due to the role of SDS in bubble interactions. The impact of SDS addition on the mass transfer is twofold. Firstly, it reduced kL because the SDS molecules migrate towards the bubble-liquid interface thanks to the lower O2 diffusivity in water, thus hindering the O2 transfer from one phase to the other. Secondly, it increased aL owing to the inhibition of bubbles coalescence and, therefore, the lower mean bubble size. Among these two effects, the latter is prevailing, which led to an increase in kLaL in contaminated systems. In the second part of this work, a population balance model (PBM) was coupled with a computational fluid dynamics (CFD) model based on large-eddy simulation (LES) to analyze the effect of both tap water and SDS contaminated systems on the breakage phenomena, local flow pattern, and the resulting hydrodynamics and mass transfer features in the reactor. Ultimately, experiments and numerical simulations agreed well in terms of global gas holdup and kLaL coefficient. In particular, the transition points in the case of the SDS media (except for foam formation) provided the model with adequate PBM definitions for the dispersed phase.

Enhancement of Ozonation Reaction for Efficient Removal of Phenol from Wastewater Using a Packed Bubble Column Reactor

In the ozonation process, the phenol degradation in wastewater undergoes a low mass transfer mechanism. In this study, ozonized packed bubble column reactor was designed and constructed to remove phenol. The reactor’s inner diameter and height were 150 and 8 cm, respectively. The packing height was kept constant at 1 m in accordance with the reactor hydrodynamics. The gas distributor was designed with 55 holes of 0.5 mm. The phenol removal efficiency was evaluated at ozone concentrations of 10, 15, and 20 mg/L, contact times of 15, 30, 45, 60, 75, 90, 105, and 120 min, and phenol concentrations of 3, 6, 9, 12, and 15 mg/L. The results indicated that the highest phenol removal efficiency of 100% was achieved at 30 min in presence of packing. Moreover, the use of packing improved the contact between the gas and liquid, which significantly enhanced the phenol degradation. Actually, a thin film over a packing surface enhances the mass transfer. Also, it was found that the phenol is degraded into CO2 and H2O through a series of reaction steps. Additionally, a kinetic study of a first-order reaction provided an efficient estimation of reaction parameters with a correlation factor of 0.997.

Fe-containing carbon-coated monoliths prepared by CVD in gaseous toluene abatement - parametric analysis of the Fenton process

The degradation of toluene (present in a gas stream) by the heterogeneous Fenton process was evaluated in a bubble column reactor. The process was catalyzed by macrostructured carbon-coated monoliths that were synthesized by chemical vapor deposition (CVD), which allowed carbon growth in honeycomb cordierite monoliths, while the iron (metal phase) was incorporated by adsorption. A detailed parametric study was carried out to evaluate the effect of the main variables and process operating conditions, namely channel density of the monolith, hydrogen peroxide concentration, pH and catalyst load; as process responses, the amount of toluene transferred - η, hydrogen peroxide consumption and dissolved organic carbon (DOC) concentration in the liquid phase were assessed. The maximum ratio between the toluene transferred per catalysts mass - η/W - (6.8 ×10−2 moltoluene gcat−1), with total oxidant consumption and higher intermediate compounds remaining in solution (DOC = 33 mgC dm−3), was reached when the process was performed with a monolith with a channel density of 230 cpsi, initial pH = 3.0, [catalyst] = 0.8 g dm−3, [H2O2] = 20 mmol dm−3. During all experiments, only a small amount of iron was leached from the catalyst to the liquid phase (ca. ≤1.0 wt%), proving its stability for such application; in fact, it was found that homogenous process contribution due to iron leaching towards the overall performance is ca. 10%.

A Machine Learning Approach to Model Oxidation of Toluene in a Bubble Column Reactor

Abstract A machine-learned (ML) subgrid-scale (SGS) modeling technique is introduced for efficient and accurate prediction of reactants and products undergoing parallel competitive reactions as seen in a bubble column. The model relies on data generated from a simple substitute problem with a small number of features. The machine-learned model corrects the errors in concentration and concentration gradients at cell faces arising from using linear interpolation and showed good accuracy for a mesh that barely covers the concentration boundary layer with minimal computational overhead. The present model, thus, offers a significant performance bonus when applied to near spherical, ellipsoid, and dimple-ellipsoidal bubbles.

Reduction of energy consumption in post-combustion carbon capture process via amine-functionalized metal-organic frameworks

In this study, CO2 capture performance of ethylenediamine-functionalized Mg-MOF-74 (EDMOF-74) suspended in 30 wt% monoethanolamine (MEA) aqueous solution is analyzed. A CO2 absorption experiment was performed in a bubble column reactor based on EDMOF-74 concentrations of 0.005, 0.01, 0.05, and 0.1 wt% for different ethylenediamine loadings. It shows that EDMOF-74/30 wt% MEA mixtures improve CO2 absorption performance by a maximum of 7.18 % as compared with the base fluid. Subsequent experiment based on large-volume feed gas reveals a less volatile CO2 absorption rate. By adding EDMOF-74 to the 30 wt% MEA aqueous solution in a cyclic CO2 absorption experiment to evaluate its industrial application, an increase in durability is indicated, which implies a reduction in energy consumption during CO2 regeneration. A feasibility study on the reduction of CO2 regeneration energy was investigated in terms of the results of cyclic experiment and the facility status of Boryeong power plant. The CO2 regeneration energy can be reduced by 13.64 %, which corresponds to a decrease of 484,233 MWht/year for 1 unit of the Boryeong power plant. The abovementioned approach is expected to compensate for the disadvantages of MEA in the industrial CO2 capture process, i.e., low CO2 capacity and high CO2 regeneration energy input.

Dynamic modeling of biological methanation for different reactor configurations: An extension of the anaerobic digestion model No. 1

In biological methanation, the methane produced by anaerobic digestion (AD) is upgraded with the addition of syngas. Several mathematical models have been developed to represent the AD process. However, the modeling of biomethanation is still under development. In this work, an extension of the anaerobic digestion model (ADM1_ME) was proposed to describe the dynamics of biomethanation. The model considered the addition of syngas flow rate (H2/CO) and the adaptation of the volumetric mass transfer coefficient for two different reactor configurations: bubble column reactor and continuous stirred tank reactor operating at mesophilic and thermophilic conditions. A sensitivity analysis using the Sobol’ and Morris methods was performed for this model, where 14 parameters were selected for model calibration. Simulation results showed an accurate fit for two experimental operating conditions from literature with a RMSE <5.15. The results showed the feasibility of the ADM1_ME to describe the biomethanation process at different operational conditions and reactor configurations.

Ant colony optimisation and fuzzy system for prediction of computational data of fluid flow in a bubble column reactor

ABSTRACT Computational data of a complex problem could be mapped and solved by artificial intelligence (AI) for postprocessing purposes and numerical time-saving. A fuzzy adaptive network as a hybrid AI system has already been used for CFD data machine learning. However, no investigation has been done for the ant colony optimisation (ACO) performance evaluation compared to the adaptive network. As a state-of-the-art method, the ACO and fuzzy system are combined and tuned to estimate the flow in a reactor. The liquid-phase velocity in the y-direction is predicted using a combination of fuzzy system and ACO in a large domain. The findings further indicate that, in addition to the CFD dataset and Navier-Stokes’s equations, employing an ant colony optimisation structure as a training technique may give an accurate approximation of two-phase flow. Furthermore, for numerical methods, a continuous link between input and output datasets may be a significant data source for the AI mechanism to train the physical process, incredibly bubbly flow. The ant colony optimisation shows a more accurate prediction than the adaptive network. As far as authors know, there are no such investigations to develop a new AI algorithm and performance analysis for fluid dynamics problems.

An Impact of the Discrete Representation of the Bubble Size Distribution Function on the Flow Structure in a Bubble Column Reactor

The purpose of the present study is to analyze the effect of different discrete representations of the continuous bubble size distribution function on the flow structure in a bubble column reactor. Poly- and monodisperse media were considered, such that the mathematical expectation of the bubble size in the polydisperse case was equal to the bubble size in the monodisperse case at the same volumetric bubble contents. For these computations the normalized variances of the velocity profiles of the carrier and the disperse phases, the volume fraction of the disperse phase, and the specific area of the interfacial surface were determined. The normalized variances were calculated from a reference scenario with a detailed resolution of the bubble size distribution function with ten bubble classes. It was shown that with increase of the average bubble sizes mono- and polydisperse approaches provide converging solutions. A modified hybrid discretization of the bubble size distribution function with four classes of bubbles was shown to predict the flow structure with normalized variance less than 5% over the entire computational domain for all monitored parameters.

Modelling of fixed bed and slurry bubble column reactors for Fischer–Tropsch synthesis

Abstract An extensive review of slurry bubble column reactor and fixed bed reactor steady state models for Fischer–Tropsch synthesis is presented in this work. Material, energy and momentum balance equations are presented here along with the relevant findings of each study for modelling purposes. For fixed bed reactor models, one-dimensional and two-dimensional models can be differentiated, with the latter being better at predicting hot spots and thermal runaways, although the computational effort required solving them is also higher. Fixed bed reactors can also be classified as pseudo-homogeneous or heterogeneous models, the former considering that all phases are in thermal and chemical equilibrium, and the latter having different profiles for the catalyst particles, generally including a pellet model. For slurry bubble column reactors, single-class and double-class bubble models can be differentiated. The double-class bubble models represent better churn-turbulent regimes at the expense of a higher computational effort.

The effect of Alcanivorax borkumensis SK2, a hydrocarbon-metabolising organism, on gas holdup in a 4-phase bubble column bioprocess.

To design bioprocesses utilising hydrocarbon-metabolising organisms (HMO) as biocatalysts, the effect of the organism on the hydrodynamics of bubble column reactor (BCR), such as gas holdup, needs to be investigated. Therefore, this study investigates the first use of an HMO, Alcanivorax borkumensis SK2, as a solid phase in the operation and hydrodynamics of a BCR. The study investigated the gas holdup in 3-phase and 4-phase systems in a BCR under ranges of superficial gas velocities (UG) from 1 to 3cm/s, hydrocarbon (chain length C13-21) concentrations (HC) of 0, 5, and 10% v/v and microbial concentrations (MC) of 0, 0.35, 0.6g/l. The results indicated that UG was the most significant parameter, as gas holdup increases linearly with increasing UG from 1 to 3cm/s. Furthermore, the addition of hydrocarbons into the air-deionized water -SK2 system showed the highest increase in the gas holdup, particularly at high UG (above 2cm/s). The solids (yeast, cornflour, and SK2) phases had differing effects on gas holdup, potentially due to the difference in surface activity. In this work, SK2 addition caused a reduction in the fluid surface tension in the bioprocess which therefore resulted in an increase in the gas holdup in BCR. This work builds upon previous investigations in optimising the hydrodynamics for bubble column hydrocarbon bioprocesses for the application of alkane bioactivation.

Methane pyrolysis rate measurement using electromagnetic levitation techniques for turquoise hydrogen production: Liquid In, Ga, Bi, Sn, and Cu as catalysts

Turquoise hydrogen production is a promising technology because hydrocarbons are pyrolyzed into hydrogen and carbon without the generation of carbon dioxide. A high-temperature bubble column reactor with molten catalytic metal is suitable for this technology. However, the production efficiency of a reactor depends on various factors. A research methodology to assess the catalytic performance of molten metal catalysts is presented by employing an electromagnetic levitation technique. The catalytic reaction rate was selectively measured, which is independent of the motion of the bubbles in the bubble column reactor. Therefore, the proposed methodology is suitable for selecting an optimum molten-metal catalyst based on its catalytic properties. The hydrogen production rate per unit area of the molten metal catalyst (rH2) was measured for Bi, Cu, Ga, In, and Sn. The highest reaction rate above 1100 °C was obtained for Bi, while the highest reaction rate below 1000 °C was obtained for Ga. The reaction rate was inversely proportional to the first ionization energy of the metals. This study provides quantitative data on methane pyrolysis via in the presence of molten pure-metal catalysts using a reliable experimental technique.

Recent Developments on the Performance of Algal Bioreactors for CO2 Removal: Focusing on the Light Intensity and Photoperiods

This work presents recent developments of algal bioreactors used for CO2 removal and the factors affecting the reactor performance. The main focus of the study is on light intensity and photoperiods. The role of algae in CO2 removal, types of algal species used in bioreactors and conventional types of bioreactors including tubular bioreactor, vertical airlift reactor, bubble column reactor, flat panel or plate reactor, stirred tank reactor and specific type bioreactors such as hollow fibre membrane and disk photobioreactors etc. are discussed in details with respect to utilization of light. The effects of light intensity, light incident, photoinhibition, light provision arrangements and photoperiod on the performance of algal bioreactors for CO2 removal are also discussed. Efficient operation of algal photobioreactors cannot be achieved without the improvement in the utilization of incident light intensity and photoperiods. The readers may find this article has a much broader significance as algae is not only limited to removal or sequestration of CO2 but also it is used in a number of commercial applications including in energy (biofuel), nutritional and food sectors.

Towards the rate limit of heterologous biotechnological reactions in recombinant cyanobacteria

BackgroundCyanobacteria have emerged as highly efficient organisms for the production of chemicals and biofuels. Yet, the productivity of the cell has been low for commercial application. Cyanobacterial photobiotransformations utilize photosynthetic electrons to form reducing equivalents, such as NADPH-to-fuel biocatalytic reactions. These photobiotransformations are a measure to which extent photosynthetic electrons can be deviated toward heterologous biotechnological processes, such as the production of biofuels. By expressing oxidoreductases, such as YqjM from Bacillus subtilis in Synechocystis sp. PCC 6803, a high specific activity was obtained in the reduction of maleimides. Here, we investigated the possibility to accelerate the NAD(P)H-consuming redox reactions by addition of carbohydrates as exogenous carbon sources such as D-Glucose under light and darkness.ResultsA 1.7-fold increase of activity (150 µmol min−1 gDCW−1) was observed upon addition of D-Glucose at an OD750 = 2.5 (DCW = 0.6 g L−1) in the biotransformation of 2-methylmaleimide. The stimulating effect of D-Glucose was also observed at higher cell densities in light and dark conditions as well as in the reduction of other substrates. No increase in both effective photosynthetic yields of Photosystem II and Photosystem I was found upon D-Glucose addition. However, we observed higher NAD(P)H fluorescence when D-Glucose was supplemented, suggesting increased glycolytic activity. Moreover, the system was scaled-up (working volume of 200 mL) in an internally illuminated Bubble Column Reactor exhibiting a 2.4-fold increase of specific activity under light-limited conditions.ConclusionsResults show that under photoautotrophic conditions at a specific activity of 90 µmol min−1 gDCW−1, the ene-reductase YqjM in Synechocystis sp. PCC 6803 is not NAD(P)H saturated, which is an indicator that an increase of the rates of heterologous electron consuming processes for catalysis and biofuel production will require funnelling further reducing power from the photosynthetic chain toward heterologous processes.

Estimation of the gas hold up and flow regime of a bubble column reactor for the slurry phase hydrocracking of heavy oil

This study investigated gas hold up and flow regimes according to operating conditions (temperature, pressure, superficial gas velocity) for the design of a slurry phase hydrocracking reactor for heavy oil. Heating medium oil, vacuum residue (VR) and hydrocracking products were used in a bubble column reactor which had a diameter of 0.05 m and a height of 2.3 m. The results confirmed that the gas hold up increased and the flow regime transition point was delayed as VR was converted to a hydrocracking product (change in physical properties), and pressure also affected the flow regime transition. Using the dynamic gas disengagement method, the flow regime transition was observed in the actual hydrocracking reaction, and at the same time, it was confirmed that the hydrocracking reaction performance decreased. A VR slurry phase hydrocracking flow regime map is proposed by modifying the existing correlations, and a guide for reactor design and operation is suggested.

An optimization method for enhancement of gas–liquid mass transfer in a bubble column reactor based on the entropy generation extremum principle

In this study, an optimization method is proposed to enhance the gas–liquid mass transfer in bubble column reactor based on the entropy generation extremum principle. The mass transfer- induced entropy generation can be maximized with the increase of mass transfer rate, based on which the velocity field can be optimized. The oxygen gas–liquid mass transfer is the major rate-limiting step of the toluene emissions biodegradation process in bubble column reactor, so the entropy generation due to oxygen mass transfer is used as the objective function, and the conservation equations of the gas–liquid flow and species concentration are taken as constraints. This optimization problem is solved by the calculus of variations, the optimal liquid flow pattern is obtained and the relationship of the maximum mass transfer enhancement on viscous dissipation is revealed, which can be used to improve the design of internal structure of the bubble column reactor.

CO2-negative fuel production using low-CO2 electricity: Syngas from a combination of methane pyrolysis and dry reforming with techno-economic analysis

This work investigates the use of CO2 as a feedstock through a thermochemical approach using low-carbon electricity, in which the CO2 reforming and methane pyrolysis reactions are combined in a single electrically heated reactor (PY/DMR). The process is enabled by a molten metal catalyst which was recently reported. Kinetic data are experimentally determined for a molten Ni-In alloy and are then used to generate a process model and a techno-economic analysis. The activation energy for methane pyrolysis and dry reforming over molten Ni-In are 187 and 99 kJ/mol respectively. This results in a 236 m3 rate-limited bubble-column reactor producing 500 kta syngas. PY/DMR is compared with a dry-reforming-based technology that is combined with steam reforming (SMR/DMR), state-of-art autothermal reforming (ATR), and CO2 co-electrolysis using solid oxide electrochemical cells from both an economic and environmental standpoint. In our present-day base case, SMR/DMR is the most affordable if no decoking is required ($179.2/t), while the commercialized ATR ($193.7/t) is similar to PY/DMR ($222/t). CO2 co-electrolysis is the least affordable case ($393.2/t). A sensitivity analysis indicates that the cost of PY/DMR is the most economically competitive case when clean (carbon intensity ≤ 160 g/kWh) and affordable (≤¢2.9/kwh) electricity is used, the solid carbon is sold at over $377/t, or when abatement cost reaches $104/t-CO2eq. Both PY/DMR and co-electrolysis result in net-negative CO2 emission, after heating and fugitive emissions are accounted for. The overall carbon footprints are −0.329 kg and −1.06 kg of CO2eq/kg-syngas respectively. PY/DMR has the lowest levelized CO2 mitigation cost ($60/t).

Effect of superhydrophobic surfaces on bubble column flow dynamics

Bubbly flow in bubble column reactors promotes mixing necessary for many chemical processes. We show that if superhydrophobic-coated material is introduced into a bubble column, there can be a substantial difference in gas holdup and earlier initiation of churn-turbulent flow which can alter larger-scale mixing without a need to change the superficial gas velocity. Addition of superhydrophobic surface can also cause bubbles to (directly or indirectly assisted by the surface) escape faster to the free surface resulting in a reduced void fraction (i.e., reduced gas holdup). As the flow becomes optically opaque at few percent gas phase volume fraction, we utilize two dual plane wire mesh sensors to obtain velocity profiles and bubble size distributions, in addition to the traditional pressure and level based gas holdup measurements to calculate average phase fraction. Additionally, a custom build photon-counting dual energy threshold X-ray computed tomography system is employed to get a higher resolution measurement of the time average phase fraction non-intrusively. We report satisfactory agreement between these techniques with differences arising for understood reasons, and use the insight thus yielded to discuss the effect of superhydrophobic surfaces on bubble column flow dynamics.

Task-specific polymeric membranes to achieve high gas-liquid mass transfer

In the current study, Polyimide (P84)-based polymeric membranes were fabricated and used as spargers in the bubble column reactor (BCR) to get a high gas-liquid mass transfer (GL-MT) rate of oxygen in water. Different polymeric membranes were fabricated by incorporating polyvinyl pyrrolidone (PVP) as a porogen and a Zeolitic Imidazolate Framework (ZIF-8) to induce high porosity and hydrophobicity in the membranes. The GL-MT efficiency of membranes was evaluated by measuring the overall volumetric mass transfer coefficient (kLa) of oxygen in air. The kLa of O2 (in air) was measured by supplying the gas through a fixed membrane surface area of 11.94 cm2 at a fixed gas flow rate of 3L/min under atmospheric pressure. The results revealed that adding porogen and ZIF-8 increased the porosity of the membranes compared to the pure polymeric membranes. In comparison, the ZIF-8 (3 wt%) based membrane showed the highest porosity (80%), hydrophobicity (95° contact angle) and kLa of oxygen in air (241.2 h−1) with 78% saturation in only 60 s. ZIF-8 based membranes showed the potential to increase the amount of dissolved oxygen in BCR by reducing the bubble size, increasing the number of bubbles, and improving the hydrophobicity. The study showed that ZIF-8 based membrane diffusers are expected to produce high GL-MT in microbial syngas fermentation. To the best of our knowledge, this is the first study on the fabrication and application of polymeric membranes for GL-MT applications. Further research should be conducted under real fermentation conditions to assess the practicality of the system to support substrate utilization, microbial growth, and product formation.

Scale-up of hydrothermal processing: Liquid hot water and pilot-scale tubular steam explosion batch reactor for bioethanol production using macroalgae Sargassum spp biomass

Sargassum spp. is a biomass that can potentially use as an alternative for bioethanol production. Hydrothermal processes (liquid hot water and steam explosion pretreatment) were carried out at different operational conditions. Enzymatic hydrolysis performed a preliminary test with different ratios 1:1 and 1:2 (cellulases and hemicellulases) of enzyme loading, once selected 1:2 ratio was obtained conversion yield of 99.91% and therefore carried a scale-up in stirred bioreactor getting 95.92% saccharification yield. Pre-simultaneous saccharification and fermentation strategy was performed in a continuous stirred tank bioreactor (CSTBR), producing ethanol yield of 57.69%, and for simultaneous saccharification and fermentation strategy was performed in a bubble column reactor was 71.37% ethanol yield. The energy efficiency was analyzed in different scenarios; the best data was 30.19 (gsugar/MJ) in the bioreactor enzymatic hydrolysis process. This development allows for establishing the conditions for a third-generation biorefinery on a circular bioeconomy using Sargassum biomass.

Numerical modeling of methane pyrolysis in a bubble column of molten catalysts for clean hydrogen production

Methane pyrolysis using molten catalysts in a bubble column reactor (BCR) has recently been proposed to produce hydrogen with separable carbon particles as byproducts. In this study, a numerical model of the BCR of molten catalysts for methane pyrolysis was developed and validated using experimental data. Based on a non-isothermal 1-D simplification, continuous liquid and discrete bubble phases were considered by incorporating submodels for bubble behaviors, catalytic and homogeneous reactions, heat/mass transfer, and a submerged orifice for methane supply. The initial bubble diameter was predicted using the correlation derived from measurements. When applied to experiments with Ni(27)Bi(73) and mixtures of KCl–MnCl2, the model accurately reproduced the methane conversion at different temperatures and column heights. Furthermore, detailed information on the key phenomena was acquired, including the profiles of the bubble diameter, rise velocity, reaction rates, temperature, and gas composition. A sensitivity analysis confirmed that the uncertainties regarding the physical properties of molten catalysts had a negligible impact. A comparison of the performances of Ni(27)Bi(73) and KCl(50)MnCl2(50) under the same reaction conditions revealed a favorable influence of the catalyst density on methane conversion because of the increased pressure. The proposed model would be useful in reactor optimization and scale-up with high hydrogen productivity.