Three-phase Reactions Research Articles

A three-phase reactor assessment for the deployment of Liquid Organic Hydrogen Carriers (LOHCs): dybenzyltoluene and indoles mixture systems as case studies

As a result of the large increase in the production of renewable energies, energy storage and energy carrier systems are required to meet the most ambitious objectives. In this area, hydrogen stands out as one of the most powerful tools. However, its low volumetric energy density and its challenging storage conditions lead to the search for new forms of storage. Liquid organic hydrogen carriers (LOHCs) are positioned as a promising option to store hydrogen using a catalytic reversible reaction at moderate temperature. Notwithstanding, although reactor technology is the core section of the LOHC process, it has not been assessed yet. Therefore, in this work, a three-phase reactor analysis is performed including mass, heat, and momentum phenomena along with kinetics. In particular, the two most important reactors for three-phase reactions are evaluated, trickle bed and slurry. And two of the most attractive LOHCs systems, dybenzyltoluene and a mixture composed of 1,2-dimethylindole and 7-ethylindole, are considered. The influence of the operating and design variables was studied. The results show that, for hydrogenation slurry reactors, a first region may be formed where gas–liquid is the main resistance (60%–95%). It eventually ends up with a second one where kinetics becomes the controlling step. At this point, a better catalyst use is expected for the first region. Alternatively, trickle bed hydrogenation reactors are largely controlled by mass transfer over almost the whole reactor length. If the dehydrogenation process is assessed, kinetics resistance is predominant. Surrogate models are developed to optimize the reactor performance and to include the full reactor operation in futures process design analysis allowing for an effective deployment of LOHCs systems.

Hydrophobic Hollow-Structured nanocatalyst for Aqueous-Phase selective hydrogenation of Furfural: “H2 storage and Supercharging” effect

Aqueous-phase hydrogenation of furfural (FFR) to furfuryl alcohol (FOL) has environmental advantages and industrial application potential. However, the diverse hydrogenation pathways and the extremely low solubility of H2 in water limit the hydrogenation performance. Herein, a hollow-structured SiO2-supported NiCu nanocatalyst was prepared and modified with organosilane. The NiCu alloy effectively improves the selectivity of FOL. The formation of microbubbles and “H2 storage and supercharging” inside the microbubbles and hollow structures as a result of the hydrophobic modification significantly increases the H2 pressure. This unique gas–liquid-solid three-phase interface makes H2 more fully contact the active sites, and thus improves the aqueous-phase hydrogenation activity. Besides, an excellent catalytic stability is shown due to the close contact between the metals and SiO2 derived from the same precursor. This work provides a direction for the manufacture of highly efficient metal nanocatalysts for gas–liquid-solid three-phase reactions, and has latent industrial application in the field of aqueous-phase catalytic conversion of biomass.

Enhancing the efficiency of gas-liquid-solid reactions using a monolithic microhoneycomb catalyst

Monolithic catalysts have attracted attention as a substitute for particulate catalyst beds in gas-liquid-solid three-phase reactions. In this work, carbon gel monoliths with a microhoneycomb structure (carbon gel microhoneycombs, CMHs) were synthesized, and Pt particles with an average particle diameter of 3.0 nm were loaded on them in a highly dispersed state through the incipient wetness method. In addition, it was confirmed that the loaded Pt shows a high resistance to sintering. Hydrogenation of p-nitrophenol was carried out in order to evaluate the catalytic activity of Pt/CMHs in three-phase reactions. As a result, Pt/CMHs showed a high catalytic activity even at ambient temperature and normal pressure. Furthermore, the hydrogenation reaction significantly proceeded even when hydrogen was provided at the minimum flow rate required to complete the reaction. Since Pt/CMHs showed higher reaction activity than the same catalyst in the form of particles, it was concluded that the efficiency of three-phase reactions can be significantly improved by using monolithic catalysts with a microhoneycomb structure.

Spherical Murray-Type Assembly of Co-N-C Nanoparticles as a High-Performance Trifunctional Electrocatalyst.

Future renewable energy conversion requires advanced electrocatalysis technologies for hydrogen production, fuel cells, and metal-air batteries. Highly efficient trifunctional nonprecious electrocatalysts are a critical precious metal replacement for the economically viable electrocatalysis of oxygen reduction and water splitting, both of which are a triphase electrode process. Electrocatalysts with a refined porous structure and active composition beneficial for three-phase reactions are broadly pursued. Herein, a highly promising trifunctional spherical Murray assembly of Co-N-C nanoparticles was derived from low-cost Prussian blue analogues for the oxygen reduction reaction and water splitting. The Murray-type architecture with a tunable porous hierarchy for efficient mass transfer and the combination of a Co-N-C active composition are key for the improved electrocatalytic performance. Acid-leaching produced an optimized Murray-type durable and methanol-tolerant Co-N-C electrocatalyst that achieved an onset potential of 0.94 V [vs reversible hydrogen electrode (RHE)] and a half wave potential of 0.84 V (vs RHE) as well as a large diffusion-limited current density of 5.7 mA cm-2 for the oxygen reduction reaction, which is comparable to Pt/C. In addition, it displayed low onset overpotentials of ∼150 and ∼350 mV corresponding to the hydrogen evolution reaction and oxygen evolution reaction, respectively, highlighting its great potential to be used in overall water splitting with a total splitting voltage of 1.73 V. This work highlights the importance of Murray-type electrocatalysts for multiphase energy-related reactions.

Determination of mass transfer resistances in trickle bed reactors

A methodology for determining the mass transfer resistances of three-phase reactions in trickle bed reactors is presented. The hydrogenation of styrene over Pd/C was used as a case study to demonstrate the methodology. The gas-liquid mass transfer resistance was experimentally approximated by changing the palladium content of the bed while the chemical reaction resistance was calculated by using the observed chemical reaction rate constant which has been experimentally approximated in two different stirred tank reactors by hydrogenating the same compound under the same temperature and using the same solvent and active catalytic metal. The liquid-solid mass transfer resistance was calculated by subtracting the gas-liquid mass transfer resistance and the chemical reaction resistance from the overall resistance. The wetting efficiency of the bed was estimated from the experimental data and it was compared to the literature by using the dimensionless numbers of Re, Fr, Mo, Ga, We and Stk. The specific gas-liquid and liquid-solid mass transfer coefficients found in agreement with the literature.

Comprehensive model with time limited wall reaction for entrained flow gasifier

A comprehensive model with time limited wall reaction was developed for the simulation of complex gas particle molten slag three-phase reactions and flow processes in an entrained flow gasifier. Promotional conversion rate, wall reaction time and particle size/density evolution have been considered in the wall reaction model. In order to validate the proposed model, an industrial single swirling burner gasifier was simulated, and the gasifier performance, residual carbon ratio in the trapped particle and fly ash are compared with experimental measurements. The comparison results indicate that the proposed model has sufficient accuracy for entrained flow gasifier simulation. In a single swirling burner gasifier, approximately 55.4% of the coal particles fed from the swirling burner are trapped by the molten slag surface, and 22.5% of carbon in the trapped particles are converted during the wall reaction process. The detailed residence time of the trapped particle has been calculated; the average fly time of the particle before trapped is approximately 0.66s; and the average wall reaction time on the membrane wall is approximately 3.55s.

Evaluation of Presulfided NiMo/γ-Al2O3 for Hydrodeoxygenation of Microalgae Oil To Produce Green Diesel

In the present work, reduced presulfided NiMo/γ-Al2O3, the conventional hydrotreating catalyst, was evaluated for green diesel production via hydrodeoxygenation of unrefined microalgae oil in a microreactor, mimicking the single channel of a monolithic reactor. The effect of reactor inner diameter on space-time yield of hydrocarbon and microalgae oil conversion was studied first to confirm the superiority of the microreactor for three-phase reactions. Based on the external and internal mass transfer limitation analyses, a range of process conditions without mass transfer limitation was determined for catalyst evaluation. The results showed that NiMo/γ-Al2O3 is deactivated due to the accumulation of produced oxygenated intermediates in hydrodeoxygenation reaction, and its selectivity to even-numbered carbon hydrocarbon produced from hydrodehydration correlates with the catalyst activity. The catalyst activity and life can be preserved by increasing hydrogen to oil ratio, residence time, reaction temperatur...

Utilisation of a multitubular reactor system for parallel screening of catalysts for ring opening of decalin in continuous mode

The activity and selectivity of Pt/Beta, Pt/Ir-Beta/alumina and Pt/Ir-Beta/silica was investigated in the ring opening of decalin at 250–350°C in the presence of hydrogen. Time on stream experiments were performed in a special tailor made reactor system for advanced screening for catalytic three-phase reactions in continuous mode to study the decalin conversion, selectivity towards ring opening products and catalyst deactivation. The results from the activity tests were correlated to the catalyst properties. Conversion of decalin was found to be the highest over the Pt/Beta catalyst, which was the most acid catalyst. However, the highest selectivity towards the ring opening products was recorded over less acidic Pt/Ir-Beta/silica catalyst at 300°C and 40bar H2. The experimental results indicated that under conditions optimised for ring opening selectivity (300°C, 40bar H2) all the tested catalysts were slightly deactivated with time on stream. However, only when the temperature was increased to 325°C severe carbon deposition on the tested catalysts were found. Based on the coke analysis mainly naphtenes and olefins caused deactivation, which lead to changed product selectivity.

Facile synthesis of hybrid graphene and carbon nanotubes as a metal-free electrocatalyst with active dual interfaces for efficient oxygen reduction reaction

We report metal-free electrocatalysts to enhance utilization of dissolved and gaseous oxygen during oxygen reduction reaction (ORR). Proper balance between hydrophobicity and hydrophilicity is achieved using reduced graphene oxide (rGO) and polyelectrolyte functionalized multiwalled carbon nanotubes (pMWNTs). In this unique architecture, both two- and three-phase reactions in ORR can be maximized with a quasi-four-electron pathway.

Laboratory test reactor for the investigation of liquid reducing agents in the selective catalytic reduction of NOx

A test reactor was designed and built for investigating liquid reducing agents in the selective catalytic reduction (SCR) process in the laboratory. The design of the experimental setup is described in detail and its performance was evaluated. Using a glass nebulizer, liquid reducing agents were sprayed directly onto a catalyst positioned in a heated glass reactor with a length of 250 mm and an internal diameter of 20.4 mm or 40 mm. Model exhaust gases were mixed from individual gas components and were heated up to 450 °C in a heat exchanger before entering the reactor. The off-gas was analyzed using two complimentary techniques, a multi-component online FTIR gas analysis and a liquid quench gas absorption setup, to detect higher molecular compounds and aerosols. Due to the versatility of construction, processes not related to SCR, but involving three-phase reactions with gases, liquids and a catalyst, can also be investigated.

Solar Thermal Power for Lunar Materials Processing

Lunar in situ resource utilization (ISRU) processes require thermal energy at various temperatures. Chemical recovery processes (pyrolysis, gas-solid reactions, gas-liquid or three-phase reactions and desorption) require thermal energy at temperatures from 1,000 K to 2,500 K . Manufacturing processes (hot liquid processing, sinter forming, composite forming, welding, etc.) can be accomplished with thermal energy at temperatures 1,200 K–1,800 K . For these materials, process applications or solar thermal power can be effectively utilized. Physical Sciences Inc. has been developing an innovative solar power system in which solar radiation is collected by the concentrator, which transfers the concentrated solar radiation to the optical waveguide transmission line made of low loss optical fiber. In this paper, we will review our work on the development of the solar thermal power system and its application to a lunar ISRU process.

Enhancement of oxygen mass transfer rate in the presence of nanosized particles

Absorption of gases into a liquid is essentially important for two- or three-phase reactions, because the diffusion of a sparingly soluble gas, like oxygen, across a gas–liquid interface generally limits the reaction rates. Using a third, dispersed phase, the mass transfer rate could be significantly increased. The question arises how the absorption rate can be described in the presence of very fine, nanometer size particles or droplets. Its mathematical model should take into account the specific properties of the nanoparticles, e.g. the Brownian motion of particles, its effect on the diffusion of the bulk phase molecules, the mass transfer rate into the nanoparticles, its dependency on the particle size, etc. The mass transfer rate of oxygen, in the presence of nanometer size, organic droplets, has been investigated both experimentally, using organic submicron n-hexadecane droplets, and theoretically. The effect of the Brownian motion of the nanoparticles as well as its effect on the diffusivity in the nanofluid has been discussed. Accordingly, the enhanced diffusion coefficient, due to the convective motion of the continuous liquid phase induced by the moving particles, has been predicted and its effect on the mass transfer enhancement has been calculated using both homogeneous and heterogeneous mathematical models. The predicted data were compared to the measured ones.

Measurement and enhancement of gas–liquid mass transfer in milliliter-scale slurry reactors

Due to the limited availability of chemical reactants in the early process development of pharmaceuticals and fine chemicals, and sometimes the high-cost of catalyst, it is increasingly popular to use milliliter-scale slurry reactors with reaction volumes of 20 ml or less to screen catalyst candidates for three-phase reactions. To ensure the success of catalyst screening, it is advantageous to run reactions under kinetically controlled conditions so that the activities of different catalysts can be compared. Because catalysts with small particle sizes are used in slurry reactors, the reactions are susceptible to gas–liquid mass transfer limitations. This work presents an efficient way of enhancing gas–liquid mass transfer in milliliter-scale reactors through the use of magnetically driven agitation with complex motion. In the reactor described here, gas–liquid mass transfer coefficients can be doubled over those obtained with the agitation technique used in commercial milliliter-scale units. In addition, the reactor can achieve the top range of mass transfer coefficients obtained in a full-scale reactor. This work also presents the first measurements of gas–liquid mass transfer coefficients in milliliter-scale reactors, which are two orders-of-magnitude smaller than systems for which mass transfer coefficients have been reported earlier. Both physical and chemical absorption techniques are used.

Interaction of kinetics and internal diffusion in complex catalytic three-phase reactions: Activity and selectivity in citral hydrogenation

Kinetics and mass transfer effects were studied for the complex catalytic liquid-phase hydrogenation in a semi-batch reactor, where finely dispersed and larger catalyst particles were used. Citral was used as a model molecule. The intrinsic kinetics was determined with crushed catalyst particles at 60 ∘ C and at pressures ranging from 10 to 40 bar. A kinetic model was proposed and successfully fitted to the experimental data. In order to elucidate the influence of internal diffusion on the selectivity and activity in complex reactions, citral hydrogenation was performed with larger catalyst pellets, in a pressurized autoclave equipped with a catalyst basket. As expected, the activity decreased with increasing catalyst particle size. The product distribution was shifted from the primary hydrogenation product (citronellal) to the fully hydrogenated end product (3,7-dimethyloctanol) as the catalyst particle size was increased. The concentrations of the secondary hydrogenation products were minor throughout the experiment. A complete reaction–diffusion model was developed for large pellets and complex reactions systems.

Choice of laboratory scale reactors for HDT kinetic studies or catalyst tests

Making a choice of laboratory scale reactor for kinetic studies or catalyst tests is not an easy task above all in case of three-phase reactions. In this paper, four technologies are discussed pointing up their advantages and their drawbacks. The four technologies are packed-bed reactor in downflow or upflow modes, stirred tank reactors with crushed catalyst and stirred tank reactors with catalytic basket in batch, semi-batch or continuous modes. Finally comparisons of the technologies in terms of gas–liquid and liquid–solid mass transfers are given. Using those criteria, we observe that slurry stirred tank reactors are the best systems to test crushed catalyst. Moreover, stirred tank reactors with catalytic basket equipped with gas inducing impeller are good tools to test shaped catalysts if operating conditions are favorable to operate the turbine efficiently.

Three-phase reactions in honeycombs

Hypericum olympicum L. (Hypericaceae) flowering aerial parts has been utilized in Turkish folk medicine as a remedy against inflamed skin problems.This study was designed to state the effect of H. olympicum on dermatological problems. For this purpose effect of the plant extract on the DNA strand break and matrix metalloproteinase (MMP)–9 activity of human dermal fibroblast (HDFs) cells irradiated with UVB as well as antioxidant activity potential were studied.The methanolic extract of Hypericum olympicum (HOM) was prepared by maceration at room temperature. DNA damage and increased MMP–9 activity in HDFs were induced by UVB irradiation. The cell viability was measured by water–soluble tetrazolium salt (WST)–1 assay. The effects on DNA strand break was investigated by single gel electrophoresis (commonly known as Comet assay), while MMP–9 activity was observed by gelatin zymography assay. In vitro antioxidant tests were performed to indicate the effect on reactive oxygen species (ROS). The major metabolites were identified and their concentrations were measured by high performance thin layer chromatography (HPTLC).HOM was found to recover DNA damage dose–dependently. The enzymatic activity of MMP–9 was inhibited almost 100% by the treatment of 1.5 mg/mL of the extract. It also enhanced cell proliferation in those cells, and also it was shown to possess antioxidant activity. The major metabolites of HOM were identified as chlorogenic acid and quercetin glycosides (rutin, hyperoside, isoquercitrin).Experimental studies have proven the traditional use of Hypericum olympicum in inflamed skin problems acting by inhibition of the inflammatory pathway and recovery of DNA damage induced experimentally.

Porous, catalytically active ceramic membranes for gas–liquid reactions: a comparison between catalytic diffuser and forced through flow concept

Catalytically active membranes can be applied for three-phase reactions (liquid, gas and solid catalyst) and have advantages over conventional particle catalysts. Catalytically active components are deposited in the thin fine-porous membrane layer of an asymmetrical ceramic membrane. One reactant is dissolved in the liquid and diffuses through the porous structure of the membrane to the active inner surface, the other reactant is fed through the support to the catalytic layer from the other side of the membrane. Thereby, an effective contact between the two reactants and the solid catalyst is established. Under these conditions catalytically active membranes can typically be applied for hydrogenation or oxidation processes. Alternatively, if pore diffusion needs to be eliminated the dissolved reactants can be pumped through an asymmetric ceramic membrane or just a ceramic support coated with catalytically active metals. Thus, a very short contact time can be achieved. The following paper compares these two concepts—the catalytic diffuser and the forced through flow concept—and discusses their application for hydrogenation processes, like the catalytic nitrate/nitrite reduction in water and the dechlorination of chlorinated hydrocarbons. The developed catalytic membranes are not limited to these reactions, but are applicable for a number of multiphase reactions. A preparation method in order to make ceramic membranes catalytically active and different characterization methods will be described.

Palladium supported on filamentous active carbon as effective catalyst for liquid-phase hydrogenation of 2-butyne-1,4-diol to 2-butene-1,4-diol

Structured palladium catalysts suitable for three-phase reactions have been developed based on woven fabrics of active carbon fibres (ACF) as the catalytic supports. The Pd/ACF were tested in liquid-phase hydrogenation of 2-butyne-1,4-diol showing a selectivity towards 2-butene-1,4-diol up to 97% at conversions up to 80%. The catalyst multiple reuse with stable activity/selectivity in a batch reactor was also demonstrated. The reaction kinetics was studied and the main kinetic parameters were obtained. Assuming a Langmuir–Hinshelwood kinetics and a weak hydrogen adsorption a suitable kinetic model was developed consistent with the experimental data.

Preparation and characterisation aspects of carbon-coated monoliths

Carbon-coated monoliths have been prepared by dipcoating cordierite monoliths in a polymer solution and subsequent carbonisation. Parameters of preparation that were varied were viscosity of the dipcoating solution, carbon precursor and carbonisation temperature. Two different commercial polymers have been used as carbon precursors, Novolac and Furan resins. Also monoliths have been coated with slurry of such resins and a commercial mesoporous activated carbon (CP-97).The features of the final carbon that have been optimised are carbon loading, carbon layer thickness, coverage and mesoporosity. Coverage has been tested by leaching test in acid media. Both coverage and mesoporosity are considerably enhanced when the dipcoating mixture was a slurry of Furan resin and a commercial activated carbon. These features makes carbon-coated monoliths very suitable for their use as catalyst support in three-phase reactions.

Bubble Columns Staged with Structured Fibrous Catalytic Layers: Residence Time Distribution and Mass Transfer

A new reactor concept for catalyzed three-phase reactions based on the use of woven fibrous materials for bubble columns is suggested. In comparison to conventional multistage bubble columns, the trays are made from woven fibrous catalytic layers. The hydrodynamic parameters such as the residence time distribution (RTD) and the volumetric gas-liquid mass transfer coefficient k(L)a are investigated in an air/water system for different layer structures and different superficial gas (u(g0) < 60 cm/s) and liquid (u(10) < 6 cm/s) velocities. The major reactor design parameters, such as the thread diameter D, the distance between the woven threads w, and the distance between the fibrous layers b, are discussed.