Three-phase Slurry Reactor Research Articles

Behavior of Nanocatalysts in Fischer–Tropsch Synthesis in Various Types of Three-Phase Slurry Reactors

Behavior of Nanocatalysts in Fischer–Tropsch Synthesis in Various Types of Three-Phase Slurry Reactors

Liquefaction, cracking and hydrogenation of microalgae biomass resources to CO2 negative advanced biofuels: Mechanisms, reaction microkinetics and modelling

Deoxygenation of triglycerides is one of the crucial pathways for the production of oxygen-free hydrocarbons and biofuels that are fully compatible with conventional internal combustion engines. The one-step liquefaction and hydrotreatment of Chlorella sorokiniana microalgae was investigated in a three-phase slurry reactor. The production of diesel-like hydrocarbons was successfully accomplished over sulfide form of NiMo/Al2O3 catalyst under hydrogen atmosphere. The present work contains a comprehensive investigation of the temperature and hydrogen pressure influence on the final product composition. The highest yield of C18 and C16 (26.1% and 10.7%, respectively) was reached by increasing the reaction temperature to 350 °C and hydrogen pressure to 50 bar, while at milder conditions (200 °C and 20 bar) the products appeared only in trace concentrations. In order to obtain an accurate kinetic model, reaction mechanism was first needed to be determined based on experimentally obtained products and intermediates. A simplified reaction pathway contains liquefaction, hydrogenolysis, hydrodeoxygenation, decarboxylation and decarbonylation. The model comprises mass transfer phenomena involved in the liquefaction process, the mass transfer of hydrogen from gas to liquid phase, adsorption, desorption and surface reaction kinetics. The lowest rate constant was calculated for the microalgae conversion to triglycerides (k0 = 1.93 × 10−6 min−1), indicating slow liquefaction.

Influence of Nickel Loading on Reduced Graphene Oxide-Based Nickel Catalysts for the Hydrogenation of Carbon Dioxide to Methane

In this study, a series of novel nickel catalysts supported on reduced graphene oxide nanosheets (Ni/rGO) with Ni loadings of 10, 15 and 20 wt% were successfully synthesized via the incipient wetness impregnation method. The physicochemical properties of the catalysts and rGO support were thoroughly characterized by thermogravimetric analyser, X-ray diffraction, fourier-transform infrared spectroscopy, Raman spectroscopy, N2 adsorption-desorption, temperature programmed reduction, temperature programmed CO2 desorption and field emission scanning electron microscopy with energy dispersive X-ray spectroscopy. The properties of the catalysts are correlated to its catalytic activity for CO2 methanation which were investigated using three-phase slurry reactor at low temperature and pressure of 240 °C and 10 bar, respectively. Among the three catalysts of different Ni loading, Ni15/rGO shows the highest activity of 51% conversion of CO2 with total selectivity towards CH4. N2-physisorption and CO2-TPD analysis suggest that high catalytic performance of Ni15/rGO is attributed to the high surface area, strong basic sites and special support effect of rGO in anchoring the active metal.

Formation of Nanosized Low-Concentrated Cobalt-Containing Catalytic Dispersions for Three-Phase Fischer–Tropsch Synthesis During the Process of Hydrogen Activation

Topochemical transformations occurring during the reduction of low-concentrated catalytic dispersions used for Fischer–Tropsch synthesis in a three-phase slurry reactor are investigated. As evidenced by dynamic light scattering and transmission electron microscopy, catalyst systems containing nanoparticles with sizes of 91 and 3 nm, respectively, are formed in systems containing cobalt at concentrations of 5 and 1 wt %. After catalyst activation via the reduction of cobalt-containing particles by hydrogen, the size of the dispersed phase is 2–3 nm regardless of the content of cobalt in the suspension. The study of magnetic properties of suspension samples in situ indicates that metallic cobalt is formed during the process of catalyst activation, as confirmed by X-ray powder diffraction analysis.

Synthesis of sodium gluconate by Cr2O3/Al2O3 catalyst in a three-phase stirred slurry reactor

The present work is an attempt to study the partial oxidation of glucose in a three-phase stirred slurry reactor. Glucose is oxidized to gluconic acid and subsequently to sodium gluconate on addition of sodium hydroxide. A three-phase slurry reactor was fabricated and the reaction carried out by bubbling air through the glucose solution in the presence of Cr2O3/Al2O3 catalyst, adding NaOH and hydrogen peroxide at a pH between 9 and 10. Sodium gluconate was analyzed by HPLC. The use of a three-phase slurry reactor for this reaction is found to obtain higher conversion in a shorter period of time as well as being more economical by replacing enzymes with reusable catalyst. The effect of temperature, catalyst weight on conversion with respect to glucose is reported. The maximum conversion with initial glucose concentration of 0.4 M occurs at a temperature of 60 °C, pH of 9.5, a catalyst amount of 0.35 g, an air flow rate of 30 L/s and 5 mL (20 vol%) of hydrogen peroxide.

Mechanism, ab initio calculations and microkinetics of straight-chain alcohol, ether, ester, aldehyde and carboxylic acid hydrodeoxygenation over Ni-Mo catalyst

Hydrotreatment of bio-based model compounds was investigated in a three-phase slurry reactor over pre-sulphided NiMo/γ-Al2O3 bifunctional catalyst. Experimental results were supported by comprehensive in silico studies. Mathematical microkinetic model was developed for mass transfer phenomena, adsorption, desorption and surface kinetics description, while quantum chemical calculations were performed for the proposed reaction mechanism validation. Every moiety followed the same chemical reduction sequence as its predecessor down the oxidation ladder, except of aldehyde. Experiments using hexanal as a model compound resulted in its extraordinary high concentrations in liquid phase and on the catalyst surface, which led to mutual aldol condensation. However, this reaction was not observed when aldehyde was formed as an intermediate from hexanoic acid or methyl hexanoate, due to its low concentration and high hydrogen availability which promoted further hydrogenation into hexanol. C12/C6 (aldol condensation/hydrogenation) product ratio increased with higher temperature, reflecting higher activation energy (EA) for hexanal condensation compared to negligible hydrogenation energy barrier, confirmed by density functional theory (DFT) calculations. Primary alcohols are more resistant to HDO compared to secondary counterpart (studied in previous work) over NiMo/γ-Al2O3, specifically; the activation energy of 1-hexanol deoxygenation to olefin was 43% higher compared to secondary hexanols according to microkinetic model, and 45% higher according to quantum mechanics calculations. Primary alcohols are also extensively dehydrated into ethers, which was never the case for secondary alcohols at tested reaction conditions, while aldehydes are much easier to hydrogenate than ketones, which cannot undergo CC coupling reactions.

Hydrogenolysis of Alkanes in a Three-Phase Slurry Reactor over Cobalt Fisher–Tropsch Catalysts: A New Product Distribution Model

Kinetic models are developed for the molecular-mass distribution of the products of hydrogenolysis of mixed long-chain n-alkanes experimentally studied in the three-phase slurry reactor over nanosized cobalt-containing Fischer–Tropsch catalysts. The models are based on different hypotheses pertaining to the ratios of probabilities for the cleavage of C–C bonds as a function of their position in n-alkane chains with allowance made for the occurrence of secondary transformations of products and the vapor-liquid equilibrium in the mixture of n-alkanes in a hydrogen medium. It is demonstrated that the experimentally observed features of this distribution cannot be described in terms of the known theories of C–C bond cleavage in the hydrogenolysis of long-chain alkanes (terminal methane splitting and uniform or normal distribution of product composition). The hypothesis of a regular increase in the probability of C–C bond cleavage on going from the center of the carbon chain to its ends is advanced. Calculations performed using combinations of the distribution following this hypothesis and the normal distribution make it possible to solve the problems mentioned above.

Novel Approach and Correlation for Bubble Size Distribution in a Slurry Bubble Column Reactor Operating in the Churn–Turbulent Flow Regime

A novel approach to obtain bubble size distributions and Sauter mean bubble diameters (d32) in three-phase slurry bubble column reactors (SBCRs) is presented. This approach is based on 720 experimental runs using the dynamic gas disengagement (DGD) technique for various gas–liquid–solid systems inside a pilot-scale-SBCR (0.3 m i.d./3 m height), in a wide range of pressures (1–30 bar), temperatures (298–530 K) and solid concentrations (0–17 vol %). The bubble size distributions were obtained using an iterative energy balance algorithm based on transient experimental pressure drops and forces exerted on bubbles in the disengagement cell. Bubble size distributions were described using log-normal distribution functions and the mean and variance were determined for the DGD runs. The mean and variance were correlated as functions of the system’s physical properties and operating conditions, and were used to predict d32 values with an absolute average relative error (AARE) of 11.72%. The approach was also applie...

Metal-Containing Nanodispersions as Fischer–Tropsch Catalysts in Three-Phase Slurry Reactors

Cobalt- and iron-containing dispersions that can be used as active catalysts for Fischer–Tropsch (FT) synthesis in slurry reactors and a new modification of this process based on the use of nanoheterogeneous catalysis approaches have been discussed. Synthesis procedures for the catalytic dispersions and specific features of occurrence of FT synthesis in the presence of these catalysts have been described.

Catalytic hydrogenation and hydrodeoxygenation of lignin-derived model compound eugenol over Ru/C: Intrinsic microkinetics and transport phenomena

Heterogeneous catalytic hydrotreatment is recognized as a key valorization route of bio-based oxygenates in a bio-refinery concept. Catalytic hydrodeoxygenation (HDO) and hydrogenation of eugenol, a lignin building block model component, was investigated in silico and experimentally in a three-phase slurry reactor over the ruthenium supported on carbon (Ru/C) and by using hexadecane (HD) solvent. The influence of operating process conditions on the activity and selectivity of the transformations was determined; specifically, the temperature (225–325°C), hydrogen gas pressure (4–7MPa), catalyst loading (0–0.35wt%), eugenol loading (0–5wt%), process gas (H2 and N2), stirring speed (100–1000min−1) were varied within the listed values. Based on the detailed chromatographic, spectroscopic, microscopic, temperature-programed desorption, reduction, oxidation or physisorption analysis of solid, liquid and gas phase, a rather complex reaction-pathway network for eugenol hydrotreatment was proposed. Experimental results revealed that allyl group and benzene ring saturation was favored in comparison to competitive deoxygenation reactions, namely dehydroxylation and demethoxylation of oxygen moieties on aromatic ring. The mechanism of ketone group formation has been clarified among various proposed pathways in the literature, as it most likely proceeds via keto-enol isomerization. Precursors responsible for cyclohexane-ring contraction to substituted 5-member ring compounds were also identified and mechanism and kinetics of transformation was proposed. Intrinsic microkinetic modelling was based on the proposed network of parallel and consecutive homogeneous and catalytic reactions, and accounted the gas–liquid and liquid–solid mass transfer, adsorption and desorption kinetics and thermodynamic equilibria. Model results indicate 36- and 42-times higher demethoxylation and dehydroxylation rate constants for aromatics in comparison to corresponding oxygen-containing cycloalkanes.

Intrinsic Kinetics of Three-Phase Slurry Hydrogenation of o-Nitrocardanol to o-Aminocardanol over Raney Nickel Catalyst

The intrinsic kinetics of the hydrogenation of o-nitrocardanol (ONC) to o-aminocardanol (OAC) over Raney nickel (Ra/Ni) has been investigated with methanol as a reaction medium. The catalytic hydrogenation was carried out in an agitated three-phase slurry reactor, operating in the kinetically controlled regime. The operating conditions were varied with temperature in the range 60–90 °C, initial concentration of o-nitrocardanol in the range 5.73–14.3 mmol, hydrogen partial pressures in the range 8–20 bar, and catalyst loading in the range 0.25–0.75 g dm–3. Catalyst reusability was also examined. The reaction was found to follow first-order kinetics with respect to both hydrogen and o-nitrocardanol. The Langmuir–Hinshelwood–Hougen–Watson (LHHW) approach was used to investigate the possible mechanistic path of the reaction. It was found that the reaction proceeds through dual site molecular adsorption of reactant species with the surface reaction being the rate-controlling step. Also, the various thermodynam...

Methanol synthesis in a three-phase slurry reactor with ultrafine catalysts

It is shown that the effective synthesis of methanol may be performed in the presence of ultrafine catalyst systems formed by drop thermolysis in situ in a slurry reactor. Using the X-ray powder diffraction and FTIR spectroscopy data on the evolution of Cu–Zn–Al-containing catalyst dispersion during activation and catalysis, possible reasons for ultrafine catalyst deactivation are considered.

Mechanism, ab initio calculations and microkinetics of hydrogenation, hydrodeoxygenation, double bond migration and cis–trans isomerisation during hydrotreatment of C6 secondary alcohol species and ketones

Hydrotreatment of secondary hexanone and hexanol, and primary hexene species was investigated over the sulphide-form NiMo/γ-Al2O3 heterogeneous catalyst within the process temperature range 200–275°C. The mechanistic microkinetic model for a three-phase slurry reactor was developed, comprising the mass transfer flux from the dispersed gaseous H2 bubbles to liquid solvent bulk, the external convective resistance at catalytic surface interface, material lattice adsorption and desorption, and intrinsic conversion kinetics (homogeneous and catalysed). It reported the reaction rate constants and activation energies for ketones and alcohols. Intermediate alkene isomers were identified and quantified, demonstrating the same reactive selectivity regardless of the cascade reactant compound. Furthermore, the C6 olefin isomerisation studies under pressurised hydrogen and nitrogen (up to 9.5 times slower) atmospheres indicated a similar equilibrium distribution of the concentrations of 1-hexene, cis-2-hexene, trans-2-hexene, cis-3-hexene and trans-3-hexene. The position of the oxygen-containing (heteroatom) functional group on an aliphatic hydrocarbon chain exhibited only a minor kinetic effect on parallel and serial hydrogenation or de-hydroxylation steps. Quantum chemical (QC) calculations utilising density functional theory (DFT) computational framework were performed to elucidate the mechanism of hydrodeoxygenation (HDO). The competing main and side pathways were considered in calculating transition state barriers. Simulations showed a very good agreement with measured experimental data. Deoxygenation valorisation routes were examined as they are vital upon converting ligno-cellulosic biomass resources and for the production of the bio-based platform oxygenates in bio-refineries. Hexose(s), for example, are (poly)alcohols, the monomer building blocks of cellulose, which is besides lignin and hemicellulose the principal wood, grass and straw constituent.

Lab-scale experimental studies of Fischer–Tropsch kinetics in a three-phase slurry reactor under transient reaction conditions

Fluctuating electricity can be converted into hydrocarbon fuels via hydrogen as intermediate, thus replacing fossil fuels and possibly be attractive as a long-term storage in excess electricity generation situations. In this context, flexible operation of the chemical synthesis reactor may be motivated by the possibility of reducing the size of the hydrogen storage and the investment needed. The present study has the aim to identify general aspects and limitations of flexible Fischer–Tropsch reactor operation considering catalyst behavior and reactor operation in a three-phase system. In this contribution, methodology and first results of lab-scale experiments with a stirred slurry reactor are presented. Results of step-change experiments can be described by a mathematical model of the lab-scale setup, using steady-state kinetics determined in separate experiments. During periodic-change experiments, average rates of CO consumption and CH4 formation are not affected by period length. In contrast, analysis of periodic-change experiments with emphasis on hydrocarbon product distribution indicate that long chain hydrocarbon molar flows cannot follow forced oscillation as fast as methane molar flow.

A Review of Theoretical Research on Partial Parameters in Three-Phase Slurry Bubble Column Reactor

Three-phase slurry bubble column reactor owns a wide application area. This review focuses on the hydrodynamics of the reactor from the findings of published studies, which includes the flow regimes, gas holdup, bubble size and distribution and mass transfer coefficients. The factors affecting each parameter and the status of the research are discussed, and the development of slurry bubble column reactor has also been prospected. At present, the experimental data that can be used in the industrial application is not accurate, an enlargement of the reactor is still a difficult problem, it remains to be further exploring in close to real environment.

Modeling and control of an exothermal reaction

A generic cascade control for an exothermic catalytic hydrogenation reaction carried-out in a batch reactor has been studied using a lab-scale multi-phase reactor. The hydrogenation reaction is carried out in a three-phase slurry reactor, which is heated/cooled using oil circulating through an oil bath; additional coils are used for circulating refrigerating water. A series of tests was conducted to obtain the experimental physico-chemical parameters of the system which were then used on the modeling of the system, not only when using the controller from the oil bath but also for the study of the different control strategies. In the work we concluded that, although the system’s performance is limited by the heat exchange capacity, a gain-schedule control strategy is capable of improving the overall performance with an IAE error decrease of 40% and 20% of the overshooting temperature in relation to a single PID controller.

Using the three-way catalyst monolith reactor for reducing exhaust emissions

The monolith reactor was developed for the cleaning of exhaust gases from combustion processes, both in cars and large power plants. Nowadays, monolith reactors are increasingly being used, developed, evaluated in automotive and stationary emission control reactors such as power plants and new reactor applications such as chemical and refining processes, catalytic combustion, ozone abatement, and others. Monolith catalysts, mainstays in gas-phase automotive and environmental process applications, have found new potential in replacing three-phase slurry reactors for the production of specialty chemicals, especially when their advantages are fully utilized in recirculation loop approaches. This paper gives a general overview about monolith reactors’ benefits, fabrication, characteristics, and typical use in automotive industry. Several commercial product applications and new developments for use of monolith reactors in automotive, stationary, and chemical industry have been discussed. Different types of monolith reactor systems manufacturing, modeling, and application areas are specified with their advantages and disadvantages. Some experimental studies have been attached to compare monolith reactor types with conventional reactors.

Mathematical modeling of a slurry reactor for DME direct synthesis from syngas

In this paper, an axial dispersion mathematical model is developed to simulate a three-phase slurry bubble column reactor for direct synthesis of dimethyl ether (DME) from syngas. This large-scale reactor is modeled using mass and energy balances, catalyst sedimentation and single-bubble as well as two-bubbles class flow hydrodynamics. A comparison between the two hydrodynamic models through pilot plant experimental data from the literature shows that heterogeneous two-bubbles flow model is in better agreement with the experimental data than homogeneous single-bubble gas flow model. Also, by investigating the heterogeneous gas flow and axial dispersion model for small bubbles as well as the large bubbles and slurry (i.e. including paraffins and the catalyst) phase, the temperature profile along the reactor is obtained. A comparison between isothermal and non-isothermal reactors reveals no obvious performance difference between them. The optimum values of reactor diameter and height were obtained at 7 m and 50 m, respectively. The effects of operating variables on the axial catalyst distribution, DME productivity and CO conversion are also investigated in this research.

Direct production of dimethyl ether from synthesis gas utilizing bifunctional catalysts

In this study, direct synthesis of dimethyl ether from synthesis gas was investigated. For this purpose, H-mordenite zeolite was modified by wet impregnation of aluminum oxide onto it. The prepared catalysts were characterized by AAS, XRD and NH3-TPD analyses. Results of catalytic tests indicated that H-mordenite modified with 8 wt% aluminum oxide was an appropriate catalyst for synthesis of dimethyl ether (DME) from methanol in which methanol conversion and DME selectivity were 99.8 and 96.8%, respectively, without a noticeable change in catalyst stability. A series of bifunctional catalysts, Cu–ZnO–ZrO2/Al-modified H-mordenite, were prepared by co-precipitating sedimentation method and characterized. Synthesis of DME via direct CO hydrogenation was then evaluated in a three-phase slurry reactor. Experimental results showed that Cu–ZnO–ZrO2/Al-modified H-mordenite was a suitable catalyst for the production of dimethyl ether from synthesis gas. Ultimately, the effects of operating conditions such as temperature, pressure and feed flow rate on the process performance of the determined optimum bifunctional catalyst have been reported.

Dynamic Simulation of Gas Hydrate Formation in a Three-Phase Slurry Reactor

A dynamic hydrate formation model that incorporates growth kinetics as well as system hydrodynamics and interphase heat and mass transfer rates is presented. Supersaturation ratios and gas consumption rates were evaluated as a function of time for different gas and liquid superficial velocities. The effects of temperature and pressure were also investigated based on available kinetic information in the literature. Finally, the influence of interphase mass transfer resistance relative to kinetic resistance was also discussed.