Trickle Bed Research Articles

Odor and volatile organic compounds biotreatment using compact trickle bed bioreactors (CTBB) in a wastewater treatment plant

The main aim of this study was to optimize and maximize the impacts of odor and volatile organic compounds (VOCs) biodegradation in a wastewater treatment plant utilizing a pilot-scale compact trickle bed bioreactor (CTBB). A CTBB was built and tested for its long-term performance during which gases were supplied from the tank containing semi-liquid fats, oils, and fat waste. The concentrations of pollutants ranged from 0 to 140.75 mg/m3 H2S, 0 to 2500 mg/m3 VOCs, and 0 to 21.5 mg/m3 NH3. The CTBB was tested at different gas flow rates and at two pH values for the liquid phase: pH = 7.0 and 5.0. In the liquid phase, the pollutant removal efficiency was higher at pH = 7.0 than at pH = 5.0. Overall, the removal efficiency was between 81.5 % and 99.5 % for the VOCs and 87.5 % and 98.9 % for H2S, while NH3 removals were >99 %.

Biogas upgrading in a pilot-scale trickle bed reactor – Long-term biological methanation under real application conditions

The biological methanation of H2 and CO2 in trickle bed reactors is one promising energy conversion technology for energy storage, but experiences at pilot-scale under real application conditions are still rare. Therefore, a trickle bed reactor with a reaction volume of 0.8 m3 was constructed and installed in a wastewater treatment plant to upgrade raw biogas from the local digester. The biogas H2S concentration of about200 ppm was reduced by half, but an artificial sulfur source was required to completely satisfy the sulfur demand of the methanogens. Increasing the ammonium concentration to > 400 mg/L was the most successful pH control strategy, enabling stable long-term biogas upgrading at a CH4 production of 6.1 m3/(m3RV·d) with synthetic natural gas quality (CH4 > 98%). The results of this study with a reactor operation period of nearly 450 days, including two shutdowns, represents an important step towards the necessary full-scale integration.

Modeling and experimental investigation for development of Combined Electrolysis and Catalytic Exchange process for hydrogen isotope separation

A process based on the Combined Electrolysis and Catalytic Exchange (CECE) has been developed for separation of hydrogen isotopes. Indigenously developed Platinum supported on Carbon Aerogel based hydrophobic catalyst was used for hydrogen-water isotope exchange reaction combined with hydrophilic packing in a catalytic exchange column. The exchange column has been studied in detail for various operating conditions in this study. The intrinsic kinetics for the catalytic reaction was determined through spinning basket reactor experiments, and activation energy was estimated to be 29.7 kJ/mol. The overall mass transfer co-efficient in a mixture of hydrophilic packing and hydrophobic catalyst packed bed was determined experimentally in a pilot scale counter current trickle bed reactor to be in the range of 0.15–0.25 s-1 for the proposed range of operating conditions. Individual mass transfer resistances for vapour-liquid mass transfer, external gas mass transfer and gas-solid mass transfer were estimated using widely accepted empirical correlations. Under benchmark operating conditions, the Damkohler number for the exchange column was found to be between 0.10 and 0.16, indicating a significant contribution of surface reaction to overall mass transfer resistance. The vapour liquid mass transfer was found to be fast compared to the gas-vapour reaction. Therefore, increasing hydrophobic catalyst proportion relative to hydrophilic packing was found to increase the overall mass transfer. A steady state process model has been developed to predict the performance of overall exchange process using the experimentally determined parameters. Validation of the process model was carried out using the experimental data generated on the pilot scale trickle bed reactor. Optimum operating conditions of temperature, hydrophobic catalyst to hydrophilic packing ratio, gas and liquid superficial velocities were determined.

Surrogate modelling-assisted comparison of reactor schemes for carbon dioxide removal by enhanced weathering of minerals using seawater

Reactor-based enhanced weathering of minerals represents one of the options for CO2 removal from the atmosphere to control the concentration of greenhouse gases for stabilising the climate. Earlier studies have modelled two reactor types, namely trickle-bed reactor and packed bubble column. However, their CO2 removal potential has not been compared. Building on the previous studies, this work further develops the mechanistic reactor models to enable them to consistently describe continuous weathering of minerals using seawater. Addressing the computational demands of the mechanistic models, a surrogate modelling-based optimisation procedure is developed to allow each reactor type to be rigorously optimised for minimising two competing objectives, namely energy consumption and space requirement. This has allowed the Pareto fronts of the two reactor types to be produced and compared. When applied to calcite weathering which is predominantly controlled by gas–liquid mass transfer, the packed-bubble column has been shown to consistently outperform the trickle-bed reactor, thanks to its superior mass transfer performance. However, when considering the weathering of forsterite, packed-bubble column performance is significantly worsened compared to calcite weathering, primarily because its low dissolution rate shifts the controlling mechanism of the process from gas/liquid mass transfer to solid dissolution. These results provide new insights to inform the future evaluation of reactor-based enhanced weathering schemes in terms of reactor design selection and the implication of mineral types.

Pressure Drop and Its Reduction in Trickle Bed Using Xanthan Gum

Pressure drop is an important parameter in the design and energy requirements of the trickle bed. Pressure reduction is one of the most important techniques for reducing energy consumption in a trickle bed. The present work involves an experimental investigation on pressure drop and pressure reduction using xanthan gum as pressure reducing agent (PRA). Pressure reduction is quantified from the pressure drop data. Based on the present observations, it is found that the percentage pressure reduction increases with an increase in the concentration of PRA and it is only effective in the range of 200–600 ppm. The experimental results indicate that a maximum of 73% pressure reduction is achievable using xanthan gum (600 ppm) as PRA.

Cellular foam-based trickle-bed DBD reactor for plasma-assisted degradation of tetracycline hydrochloride

Non thermal plasma (NTP) is a promising technology for degrading organic pollutants in water/wastewater, in which the transfer of energetic species at the interface between gas discharge and liquid phase is key to improve degradation efficiency. Herein, this work shows the development of an integrated system of dielectric barrier discharge (DBD) plasma and open-cell ceramic foam (CF) for the degradation of tetracycline hydrochloride (TCH, a model antibiotic) in liquid film. Specifically, a bespoke trickle-bed DBD reactor with liquid distributor was developed to enable the formation of uniform liquid film on the surface of the hydrophilic CF strut. Due to the improved mass transfer across the thin liquid film, the trickle-bed DBD reactor with the hydrophilic CF exhibited the comparatively highest TCH removal efficiency (>80%) and energy efficiency (viz., EETCH removal of ∼0.6 g kWh−1) among the systems under investigation such as the glass bead packed DBD. The findings showed that the presence of liquid film was beneficial to the propagation of homogeneous plasma discharge in the CF bed and promoted the mass transfer of active species from plasma discharge to liquid, and thus improved the TCH degradation efficiency. Results from quenching experiments suggested that the electron induced active species (especially O2−) played the important role in degrading TCH rather than electrons.

One-Pot Synthesis of Menthol from Citral over Ni/H-β-38 Extrudates Containing Bentonite Clay Binder in Batch and Continuous Reactors

Optimization of bifunctional Ni catalysts was performed to enhance the catalytic performance in the one-pot synthesis of commercially valuable menthol from citral. The effect of nickel precursors (nitrate, chloride, acetate, and sulfate) and the addition of bentonite clay was investigated in citral transformations in a batch reactor at 70 °C and 10 bar hydrogen, demonstrating higher activity for the Ni-H-β-38-bentonite composite derived from a nickel nitrate precursor, which can be attributed to a higher surface area, optimal Brønsted to Lewis acidity and metal particle size, as well as the egg-shell distribution of Ni particles. H-β-38 impregnated with nickel nitrate, followed by calcination and reduction, was shaped with bentonite as a binder to give extrudates for exploring the citral transformations in the trickle-bed reactor at 50–70 °C and 10 bar hydrogen. The highest selectivity to the desired menthols of 45% was obtained with 70% stereoselectivity to the menthol isomer at 70 °C. The apparent activation energy for citral transformations to menthols of 18.6 kJ/mol indicated the presence of mass transfer limitations. Catalytic activity was linked with the physical-chemical properties, which were characterized by transmission electron microscopy, X-ray diffraction, temperature-programmed reduction, Fourier transform infrared spectroscopy with pyridine, N2 physisorption, and inductively coupled plasma–optical emission spectrometry methods.

Ex-situ biological hydrogen methanation in trickle bed reactors: Integration into biogas production facilities

Biological hydrogen methanation (BHM) is a biocatalytic process for biogas upgrading. Integrating ex-situ BHM processes into biogas facilities has the advantage of using inoculum, CO2, and nutrients directly from anaerobic digestion (AD) processes to enhance CH4 productivity. This study investigated the potential of biowaste digestate as an inoculum and digested biowaste reject water as the trickling liquid and nutrient source in thermophilic trickle bed reactors (TBRs). Use of reject water improved H2 conversion efficiency to up to 99 %, thus achieving a H2 loading rate of 10.8 LH2 L Rv-1 d-1 at a gas retention time (GRT) of 1.8 h and CH4 productivity of 2.6 L LRv-1 d-1 implying that reject water contains macronutrients beneficial to enriching hydrogenotrophic methanogens. However, at high H2 loading rates, a trace element supply was necessary to stabilize process performance. Hydrogenotrophic methanogens Methanothermobacter and Methanobacterium were selectively enriched, mainly due to the increased H2 loading rate.

Preliminary gas flow experiments identify improved gas flow conditions in a pilot-scale trickle bed reactor for H2 and CO2 biological methanation

Biological methanation of H2 and CO2 is a potential energy conversion technology that can support the energy transition based on renewable sources. The methanation performance in trickle bed reactors can be improved by approaching the gas flow through the reactor towards plug flow. Through preliminary gas flow experiments without biological conversion, this study investigated operational and constructional conditions that enhance plug flow in a pilot-scale trickle bed reactor with 1 m3 gas volume. An improved gas flow was observed when the feed gas was applied in a top-to-bottom direction and when the process liquid was not trickled through the packing bed. Furthermore, the gas flow experiments identified reactor-specific properties, such as unused or dead volumes. Applying gas flow experiments prior to reactor start-up is recommended as a simple and convenient method to identify individual reactor properties and optimization potentials for higher methanation performance.

Epoxidation of light olefin mixtures with hydrogen peroxide on TS-1 in a laboratory-scale trickle bed reactor: Transient experimental study and mathematical modelling

Direct epoxidation of light olefin mixtures with hydrogen peroxide and titanium silicalite (TS-1) catalyst is interesting from a pure scientific viewpoint and it might have a considerable economic and environmental advantages. Direct epoxidation of olefin mixtures implies a significant process intensification as the separation steps of alkenes prior to the epoxidation process is avoided. Binary and ternary mixtures of ethene, propene and 1-butene were selectively epoxidized with hydrogen peroxide in the presence of TS-1 as the heterogeneous catalyst. Methanol was used as the solvent. Transient and stationary kinetic experiments were conducted in a laboratory-scale trickle bed reactor, which was operated under atmospheric pressure and isothermal conditions at 15–55 °C. The experiments were designed to investigate the kinetics of the epoxidation of light olefins at different temperatures, alkene-to-hydrogen peroxide molar ratios as well as gas and liquid residence times in the trickle bed reactor. The recorded transient responses of the reaction products confirmed that the components in the alkene mixtures are epoxidized simultaneously. The epoxide selectivity was 90 % or higher in most experiments; ring-opening products formed from the epoxides and methanol were observed as by-products. The concentration maxima of epoxides during the transient experiments were explained by accumulation of the epoxide products inside the catalyst, which resulted in partial blocking of active sites. After-treatment of the catalyst with methanol and nitrogen completely restored the initial activity. Kinetic modeling was applied, based on presumed elementary steps on the TS-1 surface to describe the behavior of the system at steady state conditions. The trickle bed reactor was described with a dynamic multiphase model, taking into account the kinetic and mass transfer effects. The numerical values of the activation energies, kinetic constants and mass transfer parameters were estimated by nonlinear regression analysis. The model gave a satisfactory description of the experimental data.

Impact of Fine Solids on Hydrotreating of Bitumen-Derived Gas Oil

Bitumen-derived gas oils that enter hydrotreaters contain fine solids such as minerals, heavy metals, and coke. The deposition of these fines will eventually restrict the flow and result in pressure buildup across the hydrotreater, which eventually necessitate the premature shutting down of the reactor system. To determine if certain types of fine particles had a greater detriment to the hydrotreating process, a series of experiments were performed by accelerated fine deposition in a trickle bed catalytic reactor under industrial conditions using bitumen-derived light gas oil. Kaolinite, montmorillonite, pyrite, and petroleum coke fines had no significant impact on the catalyst activity and catalyst deactivation toward hydrodenitrogenation (HDN), hydrodesulfurization (HDS), and hydrodearomatization. Unlike the above fines, iron(III)oxide was found to convert into FeS under hydrotreating conditions, which provided a promoting effect for HDN and HDS reactions. When comparing the trends in pressure drop across the catalyst bed, there was a delayed period during the initial fine deposition where no change in pressure drop was observed, followed by an exponential increase in pressure due to the decrease in bed porosity. The difference found between these fines was the length of this delayed period, with iron(III)oxide and petroleum coke having the longest periods of no pressure growth. From inductively coupled plasma, scanning electron microscopy with energy-dispersive spectroscopy, X-ray diffraction, and Brunauer–Emmett–Teller analysis of the fresh and spent catalysts, it was determined that the deposition of all fines occurred within the packing material in the preheating zone, with only petroleum coke and iron(III)oxide fines being found on the surface of the catalysts.

Study on the Preparation of Clean Liquid Fuel by Wide Fraction High-Temperature Coal Tar Deep Hydro-Upgrading on a Pilot Plant Trickle Bed Reactor.

High-temperature coal tar contains a high content of heavy components, and the mechanism of its hydrogenation to fuel oil has not been completely revealed at present. In this work, clean environmental friendly fuel oil was obtained from wide fraction high-temperature coal tar (WHTCT) hydrotreated in a three-stage continuous pilot-scale trickle bed reactor filled with commercial catalysts. The effect of reaction temperature (345-405 °C), reaction pressure (10-18 MPa), and LHSV (0.2-0.4 h-1) on the product properties was investigated while the hydrogen/oil ratio remained constant (2000:1). Simultaneously, four lumped kinetic models were established to study the effects of reaction conditions on each component and interconversion between them. The results showed that the increase in temperature and pressure and the decrease in LHSV can effectively improve the quality of products. Under the reaction conditions of a temperature of 390 °C, a pressure of 16 MPa, an LHSV of 0.25 h-1, and a hydrogen/oil ratio of 2000:1, the S and N in the feedstocks can be reduced from 4600 and 6800 μg/g to 24.06 and 14.32 μg/g in the products, respectively. So WHTCT can be used as a suitable feed to obtain gasoline and low-freezing point diesel blending components through hydrogenation. Tail oil (TO) can easily be converted into diesel fraction (DF) and gasoline fraction (GF) with high selectivity. DF can be converted into GF only at higher temperatures, and GF hardly undergoes cracking to gas. The established kinetic model can accurately predict the content of TO, DF, GF, and gas of the products. Therefore, the results can provide a certain valuable reference for further development of industrial applications.

Modelling of gas-liquid-solid distribution in the cocurrent three-phase moving bed

The three-phase moving bed reactors (TMBRs) can supply a potential solution for the multi-phase reactions with deactivating catalysts to realize Online Catalyst Replacement (OCR). In this work, computational fluid dynamics (CFD) simulations were employed to investigate the flow behavior of each phase in a cocurrent TMBR. The Euler-Euler multi-phase flow model and two different liquid-solid force models were employed to describe the dense-phase particle flow and liquid-solid interaction, respectively. The results revealed that the solid flow rate increased due to the gas-liquid flow, but radial solids distribution had not changed significantly. The effect of gas-liquid flow on the solid volume distribution was mainly reflected in the wall and inlet region, which led to lower solid volume fraction and higher granular temperature in the local area. Meanwhile, compared with trickle beds, with the increasing gas flow rate or decreasing liquid flow rate, both the liquid holdup and flow dead zone decreased in TMBRs. With the increase in liquid flow rate, the effect of liquid migration (from the wall to the center) on the liquid distribution was weakened. Besides, due to the competition between the pressure gradient force and gas-liquid drag force, the variations of volume and velocity of each phase depended on operating conditions, which were divided into three typical ranges. The gas-liquid-solid distribution could significantly advance the understanding of flow behaviors in TMBRs, based on which the reactor development could be further promoted.

Partial Hydrogenation of FAME on Trickle Bed Reactor using Nickel Catalyst

FAME (fatty acid methyl ester) is an alternative fuel that is still limited in its application to engines because its low oxidation stability affects the quality of biodiesel storage. A solution to overcome this problem is the partial hydrogenation process in which polyunsaturated FAMEs react with hydrogen, and a catalyst breaks down unsaturated bonds which are oxidation determinants. The use of Ni/Al2O3 catalyst is more advantageous due to its lower cost and higher activity. In this research, partial hydrogenation was carried out in a trickle-bed reactor. The objective of the research is to investigate the effect of operating conditions on FAME conversion. The experimental result shows that the partial hydrogenation of polyunsaturated FAMEs in a trickle bed reactor broke down the polyunsaturated bonds (C19:2) of FAME’s into monounsaturated bonds (C19:1) and saturated bonds (C19:0). The conversion of polyunsaturated FAMEs reaches 8.93% under the inlet pressure of 0.7 MPa, the inlet temperature of 160°C, the hydrogen flowrate of 250 ml/min, the biodiesel flowrate of 0.667 ml/min, and the catalyst size of 1.5 mm.

The enhanced biological methanation performance in trickle-bed reactor by different continuous hydrogen supply from nano-zero valent iron corrosion

In this paper, the hydrogen (H2) supply to trickle-bed reactor (TBR) in endogenous and exogenous ways by nano-zero-valent iron (nZVI) corrosion was indicated, in order to increase the biogas generation and methane (CH4) content from wastewater. The results showed that the nZVI corrosion H2 supply method increased the biogas generation in TBR. The daily average CH4 yields of TBR in stages 1–4 increased by 23.99 %, 35.76 %, 49.40 % and 56.13 % compared with control stage, respectively, and the highest CH4 content of 90.72 % was achieved in stage 3. The changes of enzyme concentration indicated that iron from nZVI enhanced the activities of acetate kinase and dehydrogenase, however, the activity of coenzyme F420 was lower due to the presence of homoacetogenic acetate formation that enhanced the acetoclastic methanogenesis pathway. Changes in the structure of the microbial community played an important role in the mechanism of CH4 enhancement, and the analysis of microbial abundance showed that the additions of nZVI and ferrous iron (Fe2+) changed the microbial communities, with increased abundances of hydrogenotrophic methanogens and homoacetogen.

Catalytic hydroprocessing of camelina oil/AGO mixtures over NiMoP/γ-Al2O3 catalysts

Inedible camelina oil (CSO) contains fatty acids with a high degree of unsaturation (1.8 double bonds per fatty acid on average). CSO was hydrotreated at temperatures 340–370 °C, pressures of 15–50 bar, and liquid hour space velocities (LHSVs) of 0.8–1.1 h-1 for the production of hydrocarbons that are usable as diesel components. First, hydrotreating pure CSO at 340–370 oC and low hydrogen pressures of 15–25 bar led to the formation of a mixture of n-/iso- alkanes, aromatics, and higher olefins. The presence of CC double bonds in the CSO molecule affected the progress of the side reactions and caused rapid deactivation and coking of the catalyst, especially at low hydrogen partial pressure. Hydrotreatment co-processing of polyunsaturated CSO and partially hydrogenated CSO was then done with two different gas oils or two paraffinic solvents in the range of concentration 5–20%. Co-hydrotreatment took place in a bench-scale trickle-bed reactor using commercial NiMoP/γ-Al2O3 catalysts (catalysts A and B) and a prepared catalyst, NiMoCuP/ZrO2-γ-Al2O3 (catalyst C). High triacylglyceride conversion to hydrocarbons was achieved when CSO was hydrogenated in a mixture with paraffinic solvents on NiMoP/γ-Al2O3 catalysts at hydrogen partial pressures above 30 bar and temperatures above 350 oC. CSO decarboxylation/decarbonylation reactions prevailed over hydrodeoxygenation. Hydrodeoxygenation (72%) was predominant for catalyst C with significant methanation of CO and CO2. There was a complete TAG conversion into hydrocarbons when co-processing a mixture of CSO and atmospheric gas oil at a temperature of 360 oC, LHSV of 0.8 h-1, a hydrogen pressure of 50 bar, and various ratios of hydrogen to raw material from 312 to 656 NL.L-1. The deoxygenation activity decreased in the order of catalysts C>B>A. Increasing the ratio of H2 to feed had a positive effect on the composition and properties of the liquid product. During experiments with catalyst C at 50 bar, 370 °C, and ratios of hydrogen to raw material of 293–656 NL.L-1, the cetane index increased from 46 to 58, and the polyaromatic content decreased from 12.5 to 4.4 wt%. The sulphur and nitrogen contents of the product (29.5 mg.kg-1 and 13.2 mg.kg-1) were higher than expected. In the case of catalyst C, the degree of desulphurization was lower than that of catalysts A and B.

Development of an in-situ H2 reduction and moderate oxidation method for 3,5-dimethylpyridine hydrogenation in trickle bed reactor

Development of an in-situ H2 reduction and moderate oxidation method for 3,5-dimethylpyridine hydrogenation in trickle bed reactor

Oak wood provides suitable nutrients for long-term continuous pesticides removal by Trametes versicolor in a pilot plant trickle bed reactor

In the Catalan area (Spain), diuron and bentazon are extensively used to control weeds and are therefore abundant in agricultural drainage. White-rot fungi have a high potential for removing these contaminants because of a potent and nonsubstrate-specific lignin-degrading enzyme system. Unfortunately, bacterial contamination hinders practical application of fungal treatment. In this study, a trickle bed reactor (TBR) containing Trametes versicolor immobilized on oak wood was used to treat spiked nonsterile agricultural wastewater. The TBR was operated for 186 days in continuous mode at different recirculation rates. The TBR exhibited stable and promising performance, with an average removal of diuron and bentazon of up to 80% and 67%, respectively, at steady state. The lignocellulosic carrier was the only carbon resource used for the immobilized biomass throughout the entire operation period and effectively suppressed bacterial growth. Adsorption of the contaminants on oak wood was also an important contribution to pesticide removal. The constructed system exhibited persistent fungal activity and high robustness to adverse impacts regarding clogging, based on pesticides removal, laccase activity, ergosterol quantity and scanning electron microscopy analysis. This study demonstrates the concept of long-term fungal treatment and paves the way to full-scale application.

Data-driven surrogate modelling and multi-variable optimization of trickle bed and packed bubble column reactors for CO2 capture via enhanced weathering

Enhanced weathering (EW) of minerals could potentially absorb atmospheric CO2 at gigaton scale per year and store it as bicarbonate and carbonate in the ocean. However, this process must be accelerated by engineered reactors, in which optimal reaction conditions maximise the CO2 capture rate and minimise the energy and water consumption. In this work, trickle beds (TBs) and packed bubble columns (PBCs), operated with fresh water and CO2 -rich flue gas, are chosen as typical chemical reactors to perform the EW-based CO2 capture. We firstly develop experimentally validated physics-based mechanistic models then generate data to train data-driven surrogate models to achieve rapid prediction of performance and multi-variable optimization. Two surrogate models, namely, response surface methodology (RSM) and extended adaptive hybrid functions (E-AHF), are developed and compared, in which the effect of five design variables on three objective functions are investigated. Results show that the R2 for the prediction of CO2 capture rate (CR) and water consumption (WC) through RSM and E-AHF is higher than 0.84. For TB reactors, in particular, the calculated R2 is higher than 0.96. The prediction accuracy of energy consumption (EC) through the RSM approach is, however, relatively poor (R2 ∼ 0.79), but is improved by using the E-AHF surrogate model, increasing to R2 ∼ 0.89. The developed data-driven surrogate model can rapidly predict the performance indicators of TB and PBC reactors without solving complex mechanistic models consisting of many partial differential equations. After optimization using the surrogate models, improvements were achieved in the objectives for TB and PBC reactors as follows: CR increased by 37.8 % and 13.1 %, EC reduced by 37.4 % and 23.8 %, and WC reduced by 12.5 % and 40.7 %, respectively.

One-Pot Synthesis of Menthol from Citral and Citronellal Over Heterogeneous Catalysts

One-pot synthesis of menthol from citronellal or citral was summarized. Both batch and continuous reactors have been recently applied. This reaction is very complex and a bifunctional catalyst exhibiting especially Lewis acid sites for cyclisation of citronellal to isopulegol are needed, while metal particles are required for its hydrogenation to menthols. Typically, too mild acidity of the catalyst and small particles do not catalyze menthol formation. Furthermore, too high acidity causes catalyst deactivation and dehydration of menthol. Very high menthol yields have been obtained in batch reactor over nobel and transition metal supported bifunctional catalysts. Shape selectivity was demonstrated for Ni-supported on Zr-modified beta zeolite, which gave high diastereoselectivity to the desired L-menthol. Recently one-pot synthesis of menthol in a trickle bed reactor has been investigated. Catalyst suffers only minor deactivation in transformation of citronellal to menthol, while more severe catalyst deactivation occurred in transforming citral to menthols. Noteworthy from the industrial point of view is that the product distribution obtained with the same catalyst under kinetic regime or under diffusional limitations differs from each other. The metal location and synthesis method of extrudates can have a major effect on the catalyst performance. Kinetic modelling of the data obtained from the trickle bed reactor considering the effectiveness factor is discussed.Graphical The results from one-pot synthesis of menthol finding applications in pharmaceuticals and fragrances from citral and its hydrogenated product, citronellal over bifunctional catalysts metal–acid are summarized. The relationship between the catalyst properties and the performance is discussed. In the continuous mode catalyst deactivation becomes apparent and in such mode of operation the product distribution might differ from those obtained in a batch reactor.