Trickle Bed Research Articles

Biofilm mass transfer and thermodynamic constraints shape biofilm in trickle bed reactor syngas biomethanation

Syngas (H2, CO2, CO) produced thermochemically from lignocellulosic biomass is an underexploited source for resource recovery and valorisation through its biological conversion for the production of a wide range of chemicals and fuels. Syngas biomethanation is one such promising bioconversion pathway, displaying interesting features such as high conversion efficiency and product selectivity, as methane is the sole product of the process. The biological conversion of syngas to high purity biomethane is still typically associated with a number of challenges related to the syngas composition, CO toxicity, and gas–liquid mass transfer limitations. In this work, the syngas biomethanation process carried out in trickle bed reactors was investigated at its boundary conditions to explore the limits of the process, focusing on syngas composition and mass-transfer conditions potentially limiting process performance. The process was found to be robust when exposed to CO excess, but highly sensitive to H2 excess, which caused severe inhibition even under small amounts of excess H2. This implies that biomethane purity comparable to natural gas can be achieved by addition of renewable H2, but this requires precise control to avoid process failure. Modulating the liquid recirculation rate and gas residence time allowed for a maximum methane productivity of 9.8 ± 0.5 mmol CH4 h−1 Lreactor−1 with full conversion of H2 and CO at a gas residence time of 1 h. Nevertheless, increasing the gas–liquid mass transfer with increasing liquid recirculation rate did not lead to increased methane productivity, which suggested additional rate-limiting bottlenecks in the process. Careful investigation of other factors potentially limiting the process led to the conclusion that diffusive transport of syngas components in the biofilm was the main bottleneck of the process. This diffusive limitation leads to a scenario of severe substrate scarcity in the biofilm phase that conditions the thermodynamic feasibility of the different biochemical reactions involved in syngas biomethanation. In turn, these thermodynamic constraints were found to drive the stratification of microbial groups and sequential consumption of syngas components along the height of the reactor

Capture and catalytic conversion of CO2 from marine and offshore applications – A review

Abstract This contribution examines recent advances in modeling fluid dynamics and capture/conversion of CO2 from marine and offshore applications in packed-bed columns/trickle-bed reactors subjected to static inclination, externally-induced rolling and heaving motions. Breaking the axial symmetry of the two-phase flow once the packed bed system is tilted results in a significant decrease in process performance, the extent of which is determined by the magnitude of the tilt and the column/reactor diameter. Only the conversion of CO2 from marine engine emissions on-board large cargo ships via catalytic cycloaddition of CO2 to styrene oxide in multiphase large-diameter trickle-bed reactors increases slightly with increasing reactor inclination. Under the externally induced column/reactor oscillations, CO2 capture/conversion performance shifts toward the steady-state solution of the vertical column/reactor as the asymmetry between the two inclined positions decreases. Oscillating (between two inclined symmetrical positions) and heaving packed-bed columns/trickle-bed reactors generate an oscillating performance around the steady-state solution of the vertical static position, which is driven by the amplitude and period of the angular and heaving motions via the continuous evolution of the intensity of the reverse secondary flow and by the magnitude of the reactor/column diameter. The catalytic conversion of CO2 captured from marine emissions via an integrated process coupling reverse water-gas shift reaction and methanol synthesis in a fixed-bed reactors network system shows a remarkable enhancement with the addition of H2O adsorbent to the reaction systems in the sorption-enhanced process periods.

Biodegradation of tri-butyl phosphate by Trametes versicolor and its application in a trickle bed reactor under non-sterile conditions

Tri-butyl phosphate (TBP) is a widely used organophosphate flame retardant. However, it is also regarded as emerging contaminant due to its various toxic effects and poor removal by conventional wastewater treatment. In present study, we investigated the degradation of TBP (10 mg/L) by the white rot fungus Trametes versicolor in both laboratory conditions and a trickle bed reactor (TBR) under non-sterile conditions. The removal yield reached 98 % after 3 days, during which the intracellular enzymatic system cytochrome P450 was involved. Four transformation products (TPs) were identified, namely dibutyl 3-hydroxybutyl phosphate, dibutyl phosphate, butyl 3-hydroxybutyl phosphate and butyl dihydrogen phosphate, which allowed us to propose a degradation pathway where hydroxylation and hydrolysis made considerable contribution. TBP treatment in the TBR with T. versicolor immobilized on wood chips operating in sequential batch mode with 10 cycles of 3 days reached average removals higher than 93 %, demonstrating the potential for practical application. Despite similar removal rates in heat-killed and abiotic controls (89 % and 97 %, respectively), global mass balance analysis indicated 86 %, 64 %, and 86 % removal by degradation in the fungal, heat-killed, and abiotic controls, respectively. Analysis of the microbial assemblage in solid phase suggested that the established bacterial populations displayed a synergistic effect with immobilized fungus. This study is the first to report on TBP degradation by T. versicolor in a TBR under non-sterile conditions, suggesting that this method could be a viable option for large-scale environmental applications.

Treatment of acidic crude palm oil using supported benzenesulfonic acid-based deep eutectic solvents in trickle bed reactor

Treatment of acidic crude palm oil using supported benzenesulfonic acid-based deep eutectic solvents in trickle bed reactor

A coupled local front reconstruction and immersed boundary method for simulating 3D multiphase flows with contact line dynamics in complex geometries

Multi-phase flows in the presence of complex solid geometries are encountered widely throughout industrial processes to intensify mass and heat transfer processes. The efficiency of these processes relies largely on the predominant fluid dynamics regime inside the reaction vessel (e.g. trickle bed, bubble column reactor). The prevailing flow structure is influenced by many factors including the nature of the fluid-solid interactions (i.e. wetting or non-wetting). Such flows are often studied using front-capturing techniques to capture the fluid-fluid interface in combination with an auxiliary model to account for fluid-solid interactions. However, these front-capturing methods have difficulties in accurately representing the interface. Therefore, we adopted a front-tracking method: the Local Front Reconstruction Method (LFRM). In this study, LFRM is coupled with the Immersed Boundary method to incorporate the no-slip boundary condition at the solid surface. The model performance is assessed using droplet spreading simulations, where the equilibrium droplet shape (i.e. radius, height, and outline), the interfacial pressure difference, and the surface tension force are compared to analytical solutions and literature data. The results show an excellent match with the analytical solutions, and additionally superior performance to state-of-the-art volume tracking models.

Carbon monoxide conversion by anaerobic microbiome in a thermophilic trickle bed reactor

Biomethanation offers a promising route for the valorization of synthesis gas, yet significant challenges arise from the limited conversion of carbon monoxide (CO). This study investigated the adaptation of an anaerobic microbiome in a continuous trickle bed reactor (TBR) with CO as the sole carbon and energy source. We evaluated reactor performance and microbial community changes under different CO loading rates and gas retention times (GRT). Optimal performance was achieved at a CO loading rate of 5.16 Nm³ m⁻³ d⁻¹ and a GRT of 60.6 min, resulting in average production rates of 0.99 Nm³ m⁻³ d⁻¹ for CH₄ and 2.55 Nm⁻³ m⁻³ d⁻¹ for CO₂, with an 88 % CO conversion rate. Microbial analysis indicated that the community was dominated by the genus Methanothermobacter, known for its ability to utilize CO as a sole substrate, followed by a co-dominance of syntrophic acetate-oxidizing bacteria Syntrophaceticus. This syntrophic relationship between Methanothermobacter and Syntrophaceticus is expected to be crucial for the efficient CO conversion process. Additionally, the study proposes a two-reactor system for converting synthesis gas to grid-quality methane.

Dynamic tank-in-series modelling and simulation of gas-liquid interaction in trickle bed reactor designed for gas fermentation

Trickle bed reactors (TBR), historically utilized in petroleum processing and wastewater treatment, now extend their applicability in biological gas conversions, including syngas biomethanation for renewable methane production. Despite operational benefits, optimizing TBR design and scale-up demands a good understanding of the reactor's hydraulic behavior and mass transfer phenomena. This study's novelty is TBR's hydraulic characterization in respect to liquid and gas flowrates and simulation of the gas-liquid interaction by a dynamic gas-liquid transfer model. Residence time distribution (RTD) experiments in 220 mL lab- and 5000 mL pilot-scale TBRs with co-current flow of gas and liquid were conducted to determine the liquid and gas working volume and the number of tanks for a dynamic tank-in-series (TIS) model. RTD experiments revealed 2–6 tanks for varying liquid flowrate (constant gas flowrate) and 5–8 tanks for varying gas flowrate (constant liquid flowrate). A dimensionless equation, fitted to RTD experimental data, predicted the liquid working volume of a TBR at various liquid flowrates and reactor configurations. TBR simulation by TIS model considering 8 well mixed gas and liquid phase tanks connected in series, resulted in an excellent model validation with an R2 at 0.99. Finally, the model simulated the mass transfer kinetics of H2, CO, and CO2 in water under varying gas and liquid flowrates for lab- and pilot-scale TBRs. Simulation results showed increased dissolved gas concentration with higher gas flowrate (constant liquid flowrate) for both scales TBR. It was also noticeable that under constant gas flowrate, the dissolved gas concentration initially decreased (0.01 < ReL < 17), then increased (17 < ReL < 34), and again decreased (34 < ReL < 105). This behavior was the same for both scales TBR and revealed an optimum ReL value irrespective of TBR size.

Conceptual study on the intensification of gas–liquid mass transfer in trickle bed reactors by the application of strut-based and novel sheet-based periodic open cellular structures (POCS)

Rapid progress in the development of additive manufacturing technology enables the production of structured reactor internals of complex geometry. To address mass transport limitations structured internals can be used in trickle bed reactors (TBRs) as the most frequently used reactor for heterogeneously catalyzed multiphase reactions. However, reactions in TBRs are frequently limited by gas–liquid mass transfer.As periodic open cellular structures (POCS) as reactor internals were not addressed regarding g–l mass transfer yet, this contribution provides first data on gas–liquid mass transfer for different types of POCS. Therefore, desorption of dissolved oxygen in water with nitrogen gas and the two-phase pressure drop were measured. Strut-based Kelvin and diamond unit cell POCS were compared to a sphere random packed bed as a benchmark. A novel sheet-based unit cell was developed realizing meandering channels demonstrating a fivefold increase in volumetric mass transfer coefficient compared to the benchmark. To compare the performance of the setup with literature data, state of the art neural network correlations were used for comparison. This proof of concept highlights the potential of additively manufactured POCS for intensified processes in trickle bed reactors, and demonstrates their versatility in application.

Experimental characterization of dynamics of bed‐scale liquid spreading in a trickle bed

AbstractWe report measurements performed to understand the effects of gas (QG) and liquid (QL) flow rates, surface tension (σGL), liquid viscosity (μL), and particle diameter (dp) on dynamics of local liquid spreading, pressure drop, and overall liquid holdup in a pseudo‐2D trickle bed. We show that an increase in the gas‐phase inertia leads to a decrease in the lateral liquid spreading, whereas an increase in the liquid‐phase inertia leads to an increase in the lateral liquid spreading. We also show that an increase in dp causes a reduction in the lateral liquid spreading. Using dimensionless numbers (AB and We), we propose a regime map showing contributions of different forces to the local liquid spreading. We show that the interplay between the inertia and capillary forces governs the liquid distribution near the inlet, whereas the relative contribution of gravitational force increases toward the outlet. Finally, we propose a relation between AB and We for “bed‐scale” liquid spreading.

Electrocatalytic Reduction of Oxygen to Peroxide on a Microporous Carbon Layer in a Gas Diffusion Electrode: Implications for Scale-up

When coupled with renewables, the two-electron oxygen reduction reaction(O2RR) could be a valuable process to generate hydrogen peroxide (H2O2), a versatile and environmentally friendly oxidant[1]. While the electrocatalyst's nature determines the catalytic activity and selectivity (2e- vs. 4e- reduction), the O2 gas mass transport, electrolyte type (e.g., alkaline, neutral, or acidic) and its flow rate, and the electrode configuration (e.g., trickle-bed or gas diffusion (GDE) electrode) are also essential factors for scale-up[2-4]. Typically, operational current densities for O2RR are limited to less than 100 mA cm-2, which is inadequate for industrial applications. The porous gas diffusion electrode (GDE) assembly provides continuous O2 gas delivery at the catalyst/electrolyte interface by overcoming O2 mass transport limitations encountered in trickle-bed or dissolved gas (single-phase) configurations. While the GDE could enable the operation under industrially relevant current densities (i.e., > 100 mA cm-2), for two-phase flow processes, flooding imposes severe challenges in the GDE scale-up and the durability of the process. Here, we present that a microporous carbon-coated gas diffusion electrode could enable very high current density (> 500 mA cm-2) synthesis of alkaline peroxide in a flow reactor with more than 90% faradaic efficiency. The microporous carbon layer provides dual functionality, namely the catalytically active sites for the reaction and controlling the GDE flooding. In addition to the electrode design, the two-phase fluid flow dynamics and electrolyzer operation conditions are significant factors for long-term stability. Although the fluid flow effect on the trickle bed type electrolyzer has been studied [3], no study exists on the systematic investigation of the two-phase mass transfer effect in the GDE-based electrolyzer for peroxide generation with a catholyte layer. The experimental findings and mass transfer modeling highlight further improvements concerning the process scale-up.

Bioaugmentation by enriched hydrogenotrophic methanogens into trickle bed reactors for H2/CO2 conversion

Biomethanation represents a promising approach for biomethane production, with biofilm-based processes like trickle bed reactors (TBRs) being among the most efficient solutions. However, maintaining stable performance can be challenging, and both pure and mixed culture approaches have been applied to address this. In this study, inocula enriched with hydrogenotrophic methanogens were introduced to to TBRs as bioaugmentation strategy to assess their impacts on the process performance and microbial community dynamics. Metagenomic analysis revealed a metagenome-assembled genome belonging to the hydrogenotrophic genus Methanobacterium, which became dominant during enrichment and successfully colonized the TBR biofilm after bioaugmentation. The TBRs achieved a biogas production with > 96 % methane. The bioaugmented reactor consumed additional H2. This may be due to microbial species utilizing CO2 and H2 via various CO2 reduction pathways. Overall, implementing bioaugmentation in TBRs showed potential for establishing targeted species, although challenges remain in managing H2 consumption and optimizing microbial interactions.

Continuous biogas production and ex-situ biomethanation in a trickling bed bioreactor under mesophilic and thermophilic conditions

The utilization of biogas as a renewable energy source necessitates a reduction in its CO2 content. "Ex-situ biomethanation" is employed to convert CO2 in biogas to CH4 through hydrogenotrophic methanogens. In this study, a biogas stream (32–36 % CO2) originating from cow manure digestion was subjected to treatment in a trickle bed bioreactor (4 liters). The presence of microorganisms on the packing material was confirmed by using a 16 S rRNA test and SEM images. This study stands out by considering all four combinations of thermophilic and mesophilic conditions, monitoring the transition and steady-state phases in a two-reactor series setup. The mesophilic-thermophilic mode yielded the highest purity (92 %) with an 86 % CO2 conversion rate and an energy density of 13,870 kJ/m3. Additionally, the performance consistency was also assessed using a larger TBB (8 liters). Extending the residence time, the thermophilic-thermophilic mode yielded the highest CH4 concentration at 98 %. The 16 S rRNA results revealed that, influenced by the designated growth conditions encompassing culture media, pH, temperature, and reactor retention time, an enrichment of hydrogenotrophic methanogens occurred. Furthermore, promising results in terms of CH4 concentration and process efficiency were demonstrated by the trickled bed bioreactor employing liquid-in-gas dispersion.

The Influence of Au Loading and TiO2 Support on the Catalytic Wet Air Oxidation of Glyphosate over TiO2+Au Catalysts

This study aimed to explore the impact of varying amounts of added Au (0.5 to 2 wt.%) and the structural characteristics of anatase TiO2 supports (nanoparticles (TP, SBET = 88 m2/g) and nanorods (TR, SBET = 105 m2/g)) on the catalytic efficiency of TiO2+Au catalysts in eliminating the herbicide glyphosate from aqueous solutions via the catalytic wet air oxidation (CWAO) process. The investigation was conducted using a continuous-flow trickle-bed reactor. Regardless of the TiO2 support and the amount of Au added, the addition of Au has a positive effect on the glyphosate degradation rate. Regarding the amount of Au added, the highest catalytic activity was observed with the TP + 1% Au catalyst, which had a higher Schottky barrier (SB) than the TP + 2% Au catalyst, which helped the charge carriers in the TiO2 conduction band to increase their reduction potential by preventing them from returning to the Au. The role of glyphosate degradation product adsorption on the catalyst surface is crucial for sustaining the long-term catalytic activity of the investigated TiO2+Au materials. This was particularly evident in the case of the TR + 1% Au catalyst, which had the highest glyphosate degradation rate at the beginning of the CWAO experiment, but its catalytic activity then decreased over time due to the adsorption of glyphosate degradation products, which was favoured by the presence of strong acidic sites. In addition, the TR + 1% Au solid had the smallest average Au particle size of all analyzed materials, which were more easily deactivated by the adsorption of glyphosate degradation products. The analysis of the degradation products of glyphosate shows that the oxidation of glyphosate in the liquid phase involves the rupture of C–P and C–N bonds, as amino-methyl-phosphonic acid (AMPA), glyoxylic acid and sarcosine were detected.

Dehydration of Alcohols to Olefins Catalyzed by ZrAPSO-34 Molecular Sieve

The lower olefins (Ethylene, propylene, and butylene) are considered the key to the polymeric and petrochemical industries. Dehydration of alcohols to produce light olefins (Methanol-to-olefins reaction) over SAPO-34 molecular sieve has attractedintoigh attention. Modified SAPO-34 zeolite catalyst with Zr metal was successfully prepared under microwave irradiation using morpholine as a structure direct agent. The microwave energy power used was 800 w and the crystallization time was 200 min. The catalyst sample was characterized by XRD, SEM, EDX, BET, FTIR, and TGA analysis. XRD analysis exhibited a typical chabazite structure with high crystallinity. The analysis showed macrocrystalline particles with moderate distribution of silica in the framework structure and a low surface area of 77 m2/g. The vibration peaks of the prepared catalyst showed agreement with the SAPO-34 CHA structure. Catalyst performance towards methanol-to-olefins conversion was performed in a trickle bed reactor with temperatures of 350, 400, 450, and 500 oC at a weight hourly space velocity of 7.7 h-1. The results also reveal at a temperature of 400 oC , that the best olefins selectivity was obtained, reaching 70%, with a longer lifetime of 500 min. methanol conversion was almost 100% at all reaction temperatures. In addition, the effect of methanol concentration was investigated and the results showed that increasing of water content plays a role in increasing catalyst lifetime and preventing coke depositions in pores.

Microstructured gas-liquid-(solid) interfaces: A platform for sustainable synthesis of commodity chemicals.

Gas-liquid-solid catalytic reactions are widespread in nature and man-made technologies. Recently, the exceptional reactivity observed on (electro)sprayed microdroplets, in comparison to bulk gas-liquid systems, has attracted the attention of researchers. In this perspective, we compile possible strategies to engineer catalytically active gas-liquid-(solid) interfaces based on membrane contactors, microdroplets, micromarbles, microbubbles, and microfoams to produce commodity chemicals such as hydrogen peroxide, ammonia, and formic acid. In particular, particle-stabilized microfoams, with superior upscaling capacity, emerge as a promising and versatile platform to conceive high-performing (catalytic) gas-liquid-(solid) nanoreactors. Gas-liquid-(solid) nanoreactors could circumvent current limitations of state-of-the-art multiphase reactors (e.g., stirred tanks, trickle beds, and bubble columns) suffering from poor gas solubility and mass transfer resistances and access gas-liquid-(solid) reactors with lower cost and carbon footprint.

Advances in design of internals: Applications in conventional and process intensification units

Internals within reactors play an important role in the chemical industry, and numerous studies focus on their investigation and development. This review discusses the application of internals in both conventional and Process Intensification (PI) units, including stirred tanks, fluidized beds, bubble columns, tubular vessels, trickle beds, spinning disks, rotating packed beds, rotating fluidized beds, and microreactors. It emphasizes enhancing mass and heat transfer through internals such as baffles, packing, heat exchange elements, and wall modifications. Recurring themes include phase distribution, interfacial area, slip velocities, heat transfer, and pressure drop. While internals offer benefits, challenges such as fouling and catalyst attrition are acknowledged, yet often under-quantified. Practical aspects, including manufacturing and safety, are often overlooked. The review highlights the urgent need for comprehensive evaluations, incorporating detailed Computational Fluid Dynamics (CFD) simulations and experimental studies. Based on previous research, this work aims to provide insights into innovative reactor designs that ultimately lead to optimal efficiency and energy balance in chemical processes.

Prospective Life Cycle Assessment of Biological Methanation in a Trickle-Bed Pilot Plant and a Potential Scale-Up

The fluctuating nature of renewable energies results in the need for sustainable storage technologies to defossilize the energy system without other negative consequences for humans and the environment. In this study, a pilot-scale trickle-bed reactor for biological methanation and various scale-up scenarios for 2024 and 2050 were investigated using life cycle assessment. A best- and worst-case scenario for technology development until 2050 was evolved using cross-consistency analysis and a morphological field, based on which the data for the ecological models were determined. The results show that the plant scale-up has a very positive effect on the ecological consequences of methanation. In the best-case scenario, the values are a factor of 23–780 lower than those of the actual plant today. A hot-spot analysis showed that electrolysis operation has an especially large impact on total emissions. The final Monte Carlo simulation shows that the technology is likely to achieve a low global warming potential with a median of 104.0 kg CO2-eq/MWh CH4 and thus can contribute to decarbonization.

Study of Hydrodynamics and Residence Time Distribution in a Trickle Bed Reactor

This study focuses on investigating the hydrodynamics using computational fluid dynamics (CFD) simulation and residence time distribution (RTD) within a trickle bed reactor (TBR). CFD simulation was performed on a packed column filled with structured packing of glass beads, while the experiments for RTD studies were conducted in a TBR filled with random packing of Raschig rings. The geometry of TBR and size of packing during CFD simulation was kept close to that of the experimental setup. CFD simulation results were obtained which predicted the flow of fluid through the TBR at different vertical planes along the column. The fluctuations of liquid velocity at various positions inside the reactor were predicted by the CFD model. RTD studies were performed for both pulse input and step input using a non-reactive tracer such as sodium hydroxide. The flowrate of water was varied from 0.6 LPH to 6 LPH for pulse input, while for step input the ratio of water to tracer flowrates was kept at 1:1, 1:2 and 2:1. This study allows us to understand how hydrodynamics and residence time distribution may have an effect on the performance of TBR.

Optimizing Power-to-Gas Technology for Efficient Renewable Energy Storage and Integration in Germany: a Review

This study explores the integration of renewable energy sources into the German power grid, with a specific focus on the application of Power-to-Gas (PtG) technology as a solution for energy storage and optimization. Amidst the growing penetration of renewables, characterized by their intermittent nature, the challenge of maintaining a stable and reliable energy supply becomes paramount. This research delves into the use of Polymer Electrolyte Membrane (PEM) electrolysis for hydrogen storage and biological methanation within the PtG process chain, aiming to enhance the efficiency of methane production and the operational performance of trickle-bed reactors. By developing an economically viable approach for PtG technology and suggesting future business models, this work contributes to the identification of the most suitable electrolysis technology for sector coupling and grid integration. The findings indicate that PtG not only offers a promising pathway for the sustainable integration of renewable energies but also underlines the need for novel, application-oriented storage solutions and the optimization of system components for better market penetration and efficiency. This research underscores the pivotal role of PtG technology in bridging the gap between renewable energy production and the existing energy infrastructure, paving the way for a more sustainable and resilient energy system in Germany.

Application of a generalized hybrid machine learning model for the prediction of H2S and VOCs removal in a compact trickle bed bioreactor (CTBB)

This study presents a generalized hybrid model for predicting H2S and VOCs removal efficiency using a machine learning model: K–NN (K - nearest neighbors) and RF (random forest). The approach adopted in this study enabled the (i) identification of odor removal efficiency (K) using a classification model, and (ii) prediction of K <100%, based on inlet concentration, time of day, pH and retention time. Global sensitivity analysis (GSA) was used to test the relationships between the inputs and outputs of the K-NN model. The results from classification model simulation showed high goodness of fit for the classification models to predict the removal of H2S and VOCs (SPEC = 0.94–0.99, SENS = 0.96–0.99). It was shown that the hybrid K-NN model applied for the “Klimzowiec” WWTP, including the pilot plant, can also be applied to the “Urbanowice” WWTP. The hybrid machine learning model enables the development of a universal system for monitoring the removal of H2S and VOCs from WWTP facilities.