Slurry Reactor Research Articles

In-Situ Magnetic Alignment of Tandem Semiconductor Microwire Slurries for Solar Hydrogen Generation

Technoeconomic models have consistently shown that a photoactive slurry reactor for water-splitting could offer the cheapest route to storing solar energy as hydrogen fuel. However, abundant challenges with this approach have thus far limited such particle-based reactors to prohibitively low efficiencies. Many of the weaknesses of a particulate slurry reactor system can be addressed with monolithically integrated semiconductor tandem particles, which can achieve higher photovoltages while more efficiently utilizing the solar spectrum for water-splitting. However, subcell layers in a tandem must be current-matched and thus the orientation of such particles to the illumination may affect their performance. While ideally matched complementary bandgaps are ultimately sought, the unassisted solar water-splitting in the tandem particulate form factor was first demonstrated with a TiO2/Si microwire system. Nickel hydrogen evolution catalyst was selectively deposited on one end of the wire via a photodeposition process. A proof-of-concept was then demonstrated to use an electromagnet along with the paramagnetic Ni HER catalyst to align the microwire particles in a slurry under active agitation. A simple model is used to predict the conditions under which alignment could lead to more efficient tandem particle slurry performance.

Using prototypes to enable development of commercially viable field scale contaminated site remediation processes

Soil structure was damaged from solvents and localised heating after a large fire which had potential to limit bioremediation of an industrial site. Laboratory prototypes (biopile, bioflushing, bioreactor, slurry reactor) for treating the site contamination were developed. After successful laboratory testing (96% removal of main contaminant, phenol), the bioflushing prototype was then applied in the field. Field prototype removed 95% phenol using a small scale 2000 L bioreactor. Field trial was then scaled to commercial clean-up. Intensive soil grid sampling after 600 days treatment revealed hotspots of solvents remaining as well as the heterogeneity in the subsurface, however overall concentrations were substantially decreased below the initial assessment. The process decreased initial soil phenol concentrations of approximately 500 mg/kg (pre-treatment area average) to 75 mg/kg across the most contaminated areas. Phenol toxicity increased with depth and is linked to increasing oxygen deficit. The study demonstrated the prototyping process enabling site clean-up and scaling for bioremediation at the industrial site, provided certainty for site owner on treatment elements and achieving improved environmental and commercial outcomes.

A Process Intensification Approach for CO2 Absorption Using Amino Acid Solutions and a Guanidine Compound

Environmentally friendly amino-acid salt solutions are used for the absorption of carbon dioxide from concentrated flue-gas streams via chemical absorption. Process intensification reduces operating and capital costs by combining chemical reactions and separation operations. Here, we present a new process-intensification approach that combines the CO2 capture and the amino-acid regeneration steps into a single process carried out in a slurry three-phase reactor. The absorbed CO2 precipitates as a solid carbonated guanidine compound. The cycle is completed by separation of the solid precipitate to strip the CO2 and regenerate the guanidine compound, while the liquid solution is recycled to the slurry reactor. The process was studied by modifying a model developed by the authors for a gas-liquid bubble column without the presence of the guanidine compound. The guanidine precipitation reaction was accounted for using kinetic parameters calculated by the authors in another study. The proposed model was implemented by modifying an existing computer code used for the simulation of gas-liquid bubble columns. The calculated results showed that the proposed cycle can significantly reduce energy, equipment, and operating costs and can make an important contribution to developing a competitive cost-effective large-scale process for CO2 capture.

Irradiance-Controlled Photoassisted Synthesis of Sub-Nanometre Sized Ruthenium Nanoparticles as Co-Catalyst for TiO2 in Photocatalytic Reactions.

Photoassisted synthesis is as a highly appealing green procedure for controlled decoration of semiconductor catalysts with co-catalyst nanoparticles, which can be carried out without the concourse of elevated temperatures, external chemical reducing agents or applied bias potential and in a simple slurry reactor. The aim of this study is to evaluate the control that such a photoassisted method can exert on the properties of ruthenium nanoparticles supported on TiO2 by means of the variation of the incident irradiance and hence of the photodeposition rate. For that purpose, different Ru/TiO2 systems with the same metal load have been prepared under varying irradiance and characterized by means of elemental analysis, transmission electron microscopy and X-ray photoelectron spectroscopy. The photocatalytic activity of the so-obtained materials has been evaluated by using the degradation of formic acid in water under UV-A light. Particles with size around or below one nanometer were obtained, depending on the irradiance employed in the synthesis, with narrow size distribution and homogeneous dispersion over the titania support. The relation between neutral and positive oxidation states of ruthenium could also be controlled by the variation of the irradiance. The obtained photocatalytic activities for formic acid oxidation were in all cases higher than that of undecorated titania, with the sample obtained with the lowest irradiation giving rise to the highest oxidation rate. According to the catalysts characterization, photocatalytic activity is influenced by both Ru size and Ru0/Ruδ+ ratio.

Highly porous Zr-MCM-48 immobilized Cu-porphyrin for photocatalytic reduction of CO2 to methanol in a slurry reactor

Highly porous Zr-MCM-48 immobilized Cu-porphyrin for photocatalytic reduction of CO2 to methanol in a slurry reactor

Control of metal-support interaction in magnetic MoS2 catalyst to enhance hydrodesulfurization performance

Studies on the metal-support interaction have been a key step for deeply understanding the catalytic behavior of hydrodesulfurization (HDS) reactions. In particular, modification of the surface hydroxyl groups on alumina can determine its surface metal species and their dispersion degrees and thus influence the reactivity of catalysts. Herein, magnetic MoS2 nanoparticles supported on thiol groups grafted alumina (Fe3O4@Al2O3-SH@MoS2) were synthesized, leading to excellent catalytic hydrodesulfurization performance in a slurry-phase reactor of 40% desulfurization efficiency and high stability of 105 h in the long-term evaluation. Density functional theory calculations and multiple catalyst characterizations demonstrated that the grafting of thiol groups not only significantly weakened the metal-support interaction by bridging the support and active phase but also inhibited the coke formation, improved the cycle performance of the catalyst. This work proves to be an effective method to adjust the metal-support interaction, leading to enhanced catalytic performance. Besides, the magnetic properties of the catalyst enable it to be separated from the reaction media quickly, which is promising to be used in slurry reactors that process heavy crude oil.

Modeling and Simulation of Hydrodynamics and Filtration in a Membrane‐Assisted Stirred Slurry Reactor

AbstractA membrane‐assisted stirred slurry reactor is developed by equipping a membrane tube into a stirred tank. Liquid‐solid flow is simulated by the Euler‐Lagrange method with filtration and particle deposition models. Acceptable predictions on the cake mass and particle deposition patterns are achieved by comparing with experimental data. The introduction of the membrane tube generates an asymmetric flow field. Shear stress on the membrane surface has a direct influence on the particle deposition. Increasing the impeller rotating speed leads to larger shear stress and mitigates the particle deposition. The cake mass is reduced by placing the membrane tube close to the impeller. The upward liquid flow pumped by the pitched‐blade impeller results in low shear stress and the vertical‐blade impeller is preferable.

Real-time investigation of the CO2 mineral carbonation reaction rate through direct aqueous route using semi-dry desulfurization slag

Mineral carbonation via alkaline solid wastes is considered an effective approach to capture and store flue gas CO2 from industries and power plants. In this study, direct mineral carbonation of semi-dry desulfurization slag (SDe-S) through an aqueous route was investigated with an online carbonation setup to measure the amount of CO2 consumed by Ca(OH)2 at atmospheric pressure in a slurry reactor. The carbonated solid and liquid products were characterized by X-ray fluorescence, X-ray diffraction and field emission scanning electron microscopy with energy dispersive X-ray spectrometry. The results show that carbonation caused the sample particle size to become more uniform. A large amount of Ca2+ was dissolved in the waste solution which could be recycled, thus increasing the utilization rate of Ca2+. The CO2 carbonation efficiency and absorption rate of SDe-S could be improved by controlling the reaction operation parameters. The optimal reaction conditions of this reactor were 100 g/L, 60 °C, 400 rpm and 300 mL/min, and the optimal reaction termination time was limited to 249 min to ensure a CO2 absorption efficiency of higher than 90 %. The carbonation process was controlled first by the film diffusion of liquid CO2, then by the chemical reaction, then by the film diffusion of liquid Ca(OH)2, and finally by the diffusion of the product layer. Experimental simulation suggests that the semi-dry desulfurization ash could achieve high CO2 absorption efficiency at atmospheric pressure and low temperature without producing any waste liquid. That is, it pretty economical and environmentally friendly.

Dimethyl ether conversion to light olefins in slurry and fixed‐bed reactors: coke nature and location on Mg/ZSM‐5 catalyst

AbstractBACKGROUNDThe goal of this study was to investigate the deactivation of ZSM‐5 in the DTO process (dimethyl ether to light olefins) in a slurry reactor (SLR) in polydimethylsiloxane dispersion medium compared with its deactivation in a fixed‐bed reactor (FBR), and to unveil reasons behind the rapid deactivation of the catalyst in the SLR.RESULTSUnder suspension conditions coke formation proceeds more slowly compared with fixed‐bed conditions: The amount of coke formed under suspension conditions is less than under fixed‐bed conditions, 1.4 mg versus 1.7 mg, respectively. Also, in terms of the chemical composition the coke is lighter (xylenes and trimethylbenzenes versus С4,5,6‐substituted benzenes). Using thermogravimetric analysis and gas chromatography/mass spectrometry pyrolytic system, it was shown that the decomposition products of the dispersion medium contribute to the blocking of micropores and the rapid deactivation of the catalyst in SLR. The localization of coke in both SLR and FBR occurs primarily in the microporous channels of the zeolite (>60%). In SLR, the weight fraction of coke on the external catalyst surface was 11% higher than that on the FBR. This finding can be attributed to the blocking of micropores by decomposition products of the dispersion medium.CONCLUSIONUnder suspension conditions, сoke formation in the DTO process proceeds more slowly compared with fixed‐bed conditions. The rapid loss of catalyst activity in the SLR was related not to coke formation, but instead to the blocking of catalyst pores by products of thermal decomposition of the dispersion medium. For the same reason, in SLR the weight fraction of coke on the external surface of the catalyst was higher than that in the FBR. © 2021 Society of Chemical Industry (SCI).

Systematic Comparison of Slurry and Gas‐Phase Polymerization of Ethylene: Part I Thermodynamic Effects

AbstractThe Sanchez–Lacombe model is used to investigate the multiphase and multicomponent thermodynamic equilibrium during ethylene polymerization and ethylene/1‐hexene copolymerization in slurry and gas‐phase reactors. The simulation study focuses on the interactions among ethylene, polyethylene, hydrogen, 1‐hexene, andn‐hexane under typical polymerization conditions. When used as a diluent,n‐hexane increases the concentrations of all reactants in the amorphous polymer phase due to the cosolubility effect. Moreover,n‐hexane significantly swells the amorphous polyethylene. This means that a polyethylene particle with the same degree of crystallinity has a larger amorphous phase fraction in slurry than in gas‐phase reactors. Consequently, if the gas phase concentration is the same in both modes of polymerization, the concentration of all reactive species in semi‐crystalline polyethylene particles will be higher in slurry reactors. The thermodynamic equilibrium simulations agree with the reported experimental results and can explain why supported catalysts behave differently in slurry and gas‐phase polymerizations.

Investigation of alkaline complexant on ethanol synthesis from syngas over slurry CuZnAlOOH catalyst

A series of alkaline complexants promoted slurry CuZnAlOOH catalysts were prepared by a complete liquid-phase method. These catalysts were applied in a slurry bed reactor to selectively convert syngas into ethanol and higher alcohols (HAs). Herein, we showed that the addition of alkaline complexant remarkably enhanced both CO conversion and selectivity toward to ethanol and HAs in terms of ternary CuZnAlOOH catalyst. Besides, the formation of dimethyl ether (DME) was significantly suppressed. Interestingly, different from the traditional alkalis modified copper-based catalysts, these catalysts promoted by alkaline complexants mainly increased selectivity for ethanol, while not isobutanol. It also reduced the deactivation rate of the catalysts. These catalysts were comprehensively characterized by XRD, H2-TPR, NH3-TPD-MS, N2 adsorption, FT-IR, XPS and TEM techniques. It was found that the increase of ethanol selectivity was related to the decrease of catalyst surface acidity, while the decrease of surface Cu+/(Cu0+Cu+) was regarded to the main reason for the catalysts deactivation. This paper showed that the introduction of alkaline complexants into Cu-based catalysts exhibited the potentiality to improve the stability and the yield of ethanol in a slurry bed reactor.

Investigating the effect of hydrogen peroxide as an electron acceptor in increasing the capability of slurry photocatalytic process in dye removal.

The hydrogen peroxide role in photocatalytic degradation of an anionic azo dye, Acid Orange 7 (AO7), was investigated in a slurry reactor. Commercial ZnO nanoparticles with an average size between 10 to 30 nm were used as catalysts. Optimum conditions for different parameters, including dye concentration (10-100 mg/L), catalyst concentration (0.1-0.5 g/L), and pH (5-10), were determined first in the absence of H2O2. Changes in the COD were measured for the optimum condition. The impact of adding hydrogen peroxide at different concentrations to the system operating at optimum conditions was investigated. It was observed that 0.416 mM hydrogen peroxide increased the system's efficiency and decreased reaction time by 40 min. The reaction followed first-order kinetic. Hydrogen peroxide alone did not contribute to oxidizing the contaminant, and its positive impact was attributed to decreasing electron-hole recombination in the photocatalytic process. Not only can the hydrogen peroxide-assisted photocatalytic process decrease retention time in treatment units, but it can also result in more contaminant degradation. Therefore, it can reduce the treatment cost.

Estimation of physical properties and hydrodynamics of slurry bubble column reactor for catalytic hydrocracking of vacuum residue

Vacuum residue (VR) was subjected to catalytic hydrocracking with H2 in a pilot-scale slurry bubble column reactor (SBCR) with 0.05 m diameter and 2 m height at 425 °C and 160 bar in the homogeneous regime. The gas holdup (αG) and composition of the product classified into five pseudo-components were measured in the SBCR. The physical properties such as density, viscosity, and surface tension of VR (feed) were analyzed prior to a three-dimensional Eulerian computational fluid dynamics (CFD) simulation to predict axial and radial hydrodynamics in the SBCR. Rather than considering the hydrocracking reactions in the CFD model, a reaction-mixture model was used to predict the variation of the axial physical properties as the reaction progresses. A customized drag coefficient based on experimental data was applied to the CFD model. The value of αG predicted by the CFD model at a superficial gas velocity of 6.4 mm/s was 6.2% which is comparable to the experimental value (6.6%). The Sauter mean diameter and specific surface area were estimated to be 1.2 mm and 304 m2/m3, respectively. The proposed CFD model, which was integrated with the axial physical properties but decoupled from chemical reaction, successfully predicted the hydrodynamics of the H2-VR SBCR.

Effect of zero‐valent iron nanoparticles on the remediation of a clayish soil contaminated with γ‐hexachlorocyclohexane (lindane) in a bioelectrochemical slurry reactor

AbstractIn this research we evaluated the effect of adding zero‐valent iron nanoparticles (ZVI‐NP) to a complete mix bioelectrochemical slurry reactors (BESR) on the remediation of a clayish soil with a high content of organic matter, contaminated with lindane. Five BESR were loaded with a clayish polluted soil (100 mg lindane/kgds), known concentrations of ZVI‐NP, liquid medium, and sulphate‐reducing inoculum to give a 33% w/v soil concentration. A one‐factor experimental design was used, where the effect of nanoparticles concentration [NP] on lindane removal efficiency (ηlin) and other response variables were evaluated. The [NP] levels were 0.0 (background control with electrical connection, BCWC), 2.5 (Exp1), 5.0 (Exp2), and 7.5 gNP/kgds (Exp3). Maximum ηlin (95%) was attained in Exp2 (5 gNP/kgds). Beyond this level the ηlin slightly decreased (Exp3 with 85% ηlin.) Approximately 40%‐57% of lindane was removed in the first 24 hours during a rapid kinetics phase. No metabolites of lindane degradation were detected after 30 days of operation in all the BESR. Energy production increased with [NP]; Exp3 generated 4.3 MJ/tonneds at 30 days, whereas the other treatments produced energy between 1.6 MJ/tonneds‐1.2 MJ/tonneds. Bioelectrical energy could partially offset the requirements of BESR mixing energy. Overall performance evaluation using an ad hoc multicriteria framework indicated that BESR followed the order Exp2 > Exp3 > Exp1 ~ BCWC > ABCWOC (abiotic control without electrical connection). There was a significant, positive effect of the combined BESR and ZVI‐NP technology for the remediation of heavy soils contaminated with lindane.

Process Intensification in Pneumatically Agitated Slurry Reactors

Abstract Pneumatically agitated slurry reactors, including bubble column reactors and airlift loop reactors (ALRs), are important gas–liquid–solid multiphase reactors. These reactors have been widely applied in many processes, especially in the biological fermentation and energy chemical industry, due to their low shear stress, good mixing, perfect mass-/heat-transfer properties, and relatively low costs. To further improve the performance of slurry reactors (i.e., mixing and mass/heat transfer) and to satisfy industrial requirements (e.g., temperature control, reduction of back-mixing, and product separation), the process intensification of slurry reactors is essential. This article starts by reviewing the latest advancements in the intensification of mixing and mass/heat transfer in these two types of reactors. It then summarizes process-intensification methods for mixing and separation that allow continuous production in these slurry reactors. Process-intensification technology that integrates directional flow in an ALR with simple solid–liquid separation in a hydrocyclone is recommended for its high efficiency and low costs. This article also systematically addresses vital considerations and challenges, including flow regime discrimination, gas spargers, solid particle effects, and other concerns in slurry reactors. It introduces the progress of numerical simulation using computational fluid dynamics (CFD) for the rational design of slurry reactors and discusses difficulties in modeling. Finally, it presents conclusions and perspectives on the design of industrial slurry reactors.

Photocatalytic Porous Silica-Based Granular Media for Organic Pollutant Degradation in Industrial Waste-Streams

Photocatalytic treatment of organic contaminants in industrial wastewaters has gained interest due to their potential for effective degradation. However, photocatalytic slurry reactors are hindered by solution turbidity, dissolved salt content, and absorbance of light. Research presented here introduces the development and application of a novel, photocatalytic, porous silica-based granular media (SGM). SGM retains the cross-linked structure developed during synthesis through a combination of foaming agent addition and activation temperature. The resultant media has a high porosity of 88%, with a specific surface area of ~150 m2/gram. Photocatalytic capabilities are further enhanced as the resultant structure fixes the photocatalyst within the translucent matrix. SGM is capable of photocatalysis combined with diffusion of nucleophiles, electrophiles, and salts from pore space. The photocatalytic efficiencies of SGM at various silica contents were quantified in batch reactors using methylene blue destruction over time and cycles. Methylene blue concentrations of 10 mg/L were effectively degraded (>90%) within 40 min. This effectiveness was retained over multiple cycles and various methylene blue concentrations. SGM is a passive and cost-effective granular treatment system technology which can translate to other organic contaminants and industrial processes.

CFD simulations of stirred-tank reactors for gas-liquid and gas-liquid-solid systems using OpenFOAM®

Abstract An open-source CFD software OpenFOAM® is used to simulate two multiphase stirred-tank reactors relevant to industrial processes such as slurry polymerization and fuel production. Gas-liquid simulations are first performed in a single-impeller stirred-tank reactor, studied experimentally by Ford, J. J., T. J. Heindel, T. C. Jensen, and J. B. Drake. 2008. “X-Ray Computed Tomography of a Gas-Sparged Stirred-Tank Reactor.” Chemical Engineering Science 63: 2075–85. Three impeller rotation speeds (200, 350 and 700 rpm) with three different bubble diameters (0.5, 1.5 and 2.5 mm) are investigated. Flow patterns compared qualitatively to those from experiments. Compared to the experimental data, the simulations are in relatively good agreement for gas holdup in the reactor. The second multiphase system is a multi-impeller stirred-tank reactor, studied experimentally by Shewale, S. D., and A. B. Pandit. 2006. “Studies in Multiple Impeller Agitated Gas-Liquid Contractors.” Chemical Engineering Science 61: 486–504. Gas-liquid simulations are performed at two impeller rotation speeds (3.75 and 5.08 RPS). The simulated flow patterns agree with published pictures from the experiments. Gas-liquid-solid simulations of the multi-impeller stirred-tank reactor are also carried out at impeller rotation speed 5.08 RPS. The addition of solid particles with a volume fraction characteristic of slurry reactors changes the flow pattern significantly. The bottom Rushton turbine becomes flooded, while the upper pitched-blade downflow turbines present a radial-pumping flow pattern instead of down-pumping. Nonetheless, the solid phase has a similar flow pattern to the liquid phase, indicating that the particles modify the effective density of the fluid.

Kinetic Modeling of Ethylene Oligomerization to High-Chain-Length Olefins Over Al-SBA-15-Supported Ni Catalyst with LiAlH4 Co-catalyst

Kinetic modeling of ethylene oligomerization was performed; an Al-SBA-15-supported Ni catalyst and LiAlH4 co-catalyst were used to produce high-chain-length olefins in a one-pot reaction. A semi-batch slurry reactor produced kinetic data at different feed flow rates and temperatures. Grouping of the kinetic and mass transfer coefficients concerning the products was introduced to estimate undetermined parameters with limited experimental data. Among the four combinatorial cases, the estimation of individual kinetic parameters and grouped mass transfer coefficients showed the lowest errors and Akaike’s information criteria. The activation energies for the formation of hexene and octene were determined to be approximately 15 and 45 kJ/mol, respectively, confirming reported values of 23.1–64.1 kJ/mol. The model showed that the formation of short-chain-length olefins accounted for the rate-determining steps, and the evaluation for the effects of operating conditions guided optimal operation; high temperature and feed flow rate maximized heavy species production, and the flow rate should be optimized to maximize light olefin production.

Development of intensified flat-plate packed-bed solar reactors for heterogeneous photocatalysis.

Solar-driven photocatalysis is a promising water-cleaning and energy-producing technology that addresses some of the most urgent engineering problems of the twenty-first century: universal access to potable water, use of renewable energy, and mitigation of CO2 emissions. In this work, we aim at improving the efficiency of solar-driven photocatalysis by studying a novel reactor design based on microfluidic principles using 3D-printable geometries. The printed reactors had a dimensional accuracy of 97%, at a cost of less than $1 per piece. They were packed with 1.0-mm glass and steel beads coated with ZnO synthesised by a sol-gel routine, resulting in a bed with 46.6% void fraction (reaction volume of ca. 840μL and equivalent flow diameter of 580μm) and a specific surface area of 3200m2m-3. Photocatalytic experiments, under sunlight-level UV-A irradiation, showed that reactors packed with steel supports had apparent reaction rates ca. 75% higher than those packed with glass supports for the degradation of an aqueous solution of acetaminophen; however, they were strongly deactivated after the first use suggesting poor fixation. Glass supports showed no measurable deactivation after three consecutive uses. The apparent first-order reaction rate constants were between 1.9 and 9.5 × 10-4s-1, ca. ten times faster than observed for conventional slurry reactors. The mass transfer was shown to be efficient (Sh > 7.7) despite the catalyst being immobilised onto fixed substrates. Finally, the proposed reactor design has the merit of a straightforward scaling out by sizing the irradiation window according to design specifications, as exemplified in the paper.

CFD-PBM investigation of the hydrodynamics in a slurry bubble column reactor with a circular gas distributor and heat exchanger tube

In this work, the effects of a circular gas distributor with the opening downward and a circular heat exchanger tube on the hydrodynamics of a pilot-scale slurry bubble column reactor were investigated by employing the CFD-PBM modeling. The simulations indicated that the circular structure of heat exchanger tube leads to a significant gas phase dispersion, inducing a stronger circulation flow of slurry. Different from the traditional perforated plates, the gas holdup profile with the circular gas distributor shows a bimodal structure in the radial direction. Moreover, the circular heat exchanger tube intensifies the bimodal distribution, resulting in a higher gas holdup in the reactor. Increasing the superficial gas velocity was beneficial in improving the whole time-averaged gas holdup. While the increase of the initial loading height of slurry has insignificant effect on the momentum transfer. In addition, proper axial height of the gas distributor is beneficial to enhance gas holdup.