Continuous Flow Fixed-bed Reactor Research Articles

Enhanced ozonation of nitrobenzene in water using natural iron ores: Efficiencies, mechanisms and stability

Natural minerals show potential for catalytic ozonation in industrial wastewater treatment. In this study, the efficiencies and mechanisms of two natural iron ores in catalytic ozonation processes (COPs) for aqueous nitrobenzene degradation were initially investigated. Compared with single ozonation process, the removal of TOC increased by about 60 % and 35 % in COPs with natural magnetite and pyrite, respectively. Both natural magnetite and pyrite could promote O3 decomposition to form hydroxyl radicals and 1O2. But the inner reaction pathways were different. The natural magnetite facilitated O3 decomposition through the Lewis acids and the electron transfer between Fe(II)/Fe(III) on the catalyst surface, while electron transfer was the only pathway for O3 decomposition by natural pyrite. Continuous flow fixed-bed reactor was adopted to provide better simulation of the practical operation conditions, so that the potential of engineering application could be evaluated. The natural magnetite exhibited excellent catalytic activity and stability during long period continuous operation in fixed-bed reactor. The removal of TOC maintained at 81.9 % under the optimized operating parameters of hydraulic retention time (2.84 h), O3 velocity (0.25 L min−1) and O3 concentration (30 mg L−1). HCO3− and PO43− obviously inhibited the TOC removal efficiencies through radical scavenging and surface –OH occupying. While low concentration of Cl− and SO42− showed negligible effect on the mineralization of aqueous nitrobenzene. After the continuous operation for 672 h, the removal of TOC for nitrobenzene solution in the magnetite-COP system was still stable at about 80 %. The present study demonstrated the engineering application prospect of the natural iron ores in catalytic ozonation treatment of recalcitrant chemical wastewaters.

Efficient synthesis of ethanol and propanediol from glucose via a noble metal promoted CuWO4 catalyst

Biomass is the most promising carbon feedstock for producing chemicals and fuels as substitutes for fossil resources. In this work, hydrogenolysis of glucose to ethanol (EtOH) and 1,3-propanediol (1,3-PDO) were carried out over multi-function noble metal promoted CuWO4 (0.1 wt% Ru, Pt and Pd) catalysts using a continuous-flow fixed-bed reactor. Amazingly, the Ru/CuWO4 catalyst presented the best catalytic performance with 84.3% glucose conversion, 63.2% EtOH and 21.2% 1,3-PDO selectivities over 40 h reaction. An array of characterization techniques, including XPS, Cu LMM AES, in-situ CO-DRIFTS, NH3-TPD, Py-FTIR, and operando EG-DRIFTS, were applied to reveal the nature of converting glucose into EtOH and 1,3-PDO. It is discovered that the added small amount of Ru tuned the chemical states of W and Cu, resulting in forming the highest content of W5+ and Cu0 on the Ru-promoted catalyst, which improves the glucose hydrogenolysis to EtOH. Besides, the strong Brønsted acid sites (BASs) derived from W6+ contribute to relatively high 1,3-PDO selectivity on Pt/CuWO4 catalyst.

One-step synthesis of 1,4-butanediol from maleic anhydride by gas-phase selective hydrogenation over xRe/CuZnZr catalysts

Producing 1,4-butanediol with selective hydrogenation of maleic anhydride has significant financial benefits. This work reported a “green” one-step method for preparing 1,4-butanediol from maleic anhydride in a gas-phase fixed bed continuous flow reactor over an efficient 2Re/CuZnZr catalyst for the first time. In this paper, CuZnZr composite metal oxides were synthesized using the co-precipitation technique, followed by impregnation of Re to produce xRe/CuZnZr catalysts. The study aimed to investigate the effects of including Re on the catalyst's structure and performance. The results obtained from the characterization indicate that the presence of Re in the system restricts the growth of Cu0 grains. In addition, the inclusion of Re facilitated the utilization of ZnO as an effective spacer, reducing the size and quantity of Cu species agglomerates and enhancing active metal dispersion. This phenomenon may be attributed to being the primary factor responsible for the observed enhancement in the activity of the maleic anhydride hydrogenation reaction. Meanwhile, Re facilitated the transformation of γ-butyrolactone, an intermediate resulting from the hydrogenation of maleic anhydride into 1,4-butanediol. The 2Re/CuZnZr catalyst exhibited favorable catalytic activity under the conditions of 190 °C and 6 MPa, resulting in the complete conversion of maleic anhydride and a selectivity of 85 % towards 1,4-butanediol. The catalyst showed consistent catalytic performance throughout the 200 h. The finding about the impact of Re promoter on Cu-based catalysts has the potential to yield a highly efficient catalytic system for alcohol generation.

Coaxial 3D printed Al2O3 ceramic continuous-flow fixed-bed reactor with bionic core-shell structure

Continuous-flow fixed-bed reactors (CFBR) have attracted considerable attention owing to their high efficiency and low energy consumption; however, the integrated fabrication of CFBR with core-shell structures remains a great challenge at present. Herein, a facile coaxial three-dimensional (3D) printing strategy was developed for the first time to rapidly and efficiently construct a CFBR with Al2O3 powder and aluminum dihydrogen phosphate (AP) as the outer shell ink, and Al2O3 powder, AP, and polymethyl methacrylate as the inner core ink that is extruded through a customized coaxial needle. Coaxial 3D printing realizes the integral fabrication of ceramic shells and inner porous ceramic carriers. CFBR with an outer wall thickness of 1.2 mm, core diameter of 3.7 mm, and variable length were fabricated, which were enabled with excellent catalytic properties by simply impregnating precious metal particles. The catalytic efficiencies for the reducing of 4-nitrophenol (4-NP) in the 3-cm-length Pd/CFBR, Pt/CFBR, and Ag/CFBR were found 96.9 %, 97.4 %, and 93 % after 10 min, respectively. Combining integrated fabrication, rapid prototyping, and complex architecture formation, coaxial 3D printing provides a novel strategy for directly integrating multifunctional CFBR.

Structure-reactivity relations in Cu/ZrO2 catalysed glycerol dehydration to acetol in continuous flow system

The selective dehydration of glycerol to hydroxyacetone (acetol) was studied in a continuous flow fixed-bed reactor with CuO supported on monoclinic (m-) or tetragonal (t-) ZrO2 nanoparticles. Catalysts were characterised...

Continuous liquid-phase alkylation of lignocellulose-derived phenolics and cyclopentanol under large space velocity for efficient synthesis of high-performance biofuel

It is significant to efficiently and feasibly produce high-performance jet fuel from renewable biomass. We reported here that lignin-derived phenolics can be alkylated by cellulose-derived cyclopentanol in a continuous-flow fixed-bed reactor packed with HUSY zeolite without the use of solvents. Under nitrogen pressure, the liquid-phase reaction was achieved. Among the investigated zeolites with different structures and SiO2/Al2O3, HUSY-150 exhibited excellent catalytic performance and stability. By adjusting reaction conditions, almost complete conversion of cyclopentanol was achieved, as well as high phenol conversion (∼70 %), and high polycyclic product selectivity (>95 %) over HUSY-150. Afterwards, we extended the range of feedstock from phenol to other phenolics (guaiacol, 2,6-dimethoxyphenol, and lignin oil surrogates), and even at a high LHSV (liquid hourly space velocity) of 36 mL/(gcat·h), HUSY-150 maintained robust catalytic activity. This study demonstrates a feasible and effective method for producing high-performance jet fuel blends using lignocellulose-derived compounds.

Cu-Ni bimetallic nanoparticles anchored on halloysite nanotubes for the environmental remediation

Hereby, we report the synthesis of CuNi bimetallic nanoparticles (NPs)-decorated halloysite nanotubes (CuNi/HNTs) for the catalytic reduction of 4-nitroaniline (4-NA) and rhodamine B (RhB) dye in an aqueous medium at room temperature. In this work, CuNi/HNTs composites with different wt% of CuNi NPs were synthesized and characterized by various techniques such as SEM, EDS, XRD, TEM and XPS. The TEM characterization confirmed that the CuNi bimetallic NPs (∼ 11 nm) were successfully anchored onto the outer surface of HNTs. Among the prepared catalysts, Cu0.75Ni0.25/HNTs catalyst displayed highest catalytic activity in the reduction of 4-NA to its corresponding amino derivative in the presence of NaBH4 with a maximum conversion efficiency of >99% and an apparent rate constant kapp of 0.152 s−1 within 30 s of reaction time. Notably, even after 15 cycles of catalytic reduction of 4-NA and RhB, there was no apparent deactivation of the catalytic activity of the Cu0.75Ni0.25/HNTs catalyst, demonstrating the excellent catalytic reusability and stability. The presence of CuNi NPs with low Ni content enhanced the catalytic activity due to the synergetic effect. Moreover, the continuous flow fixed bed reactor designed with Cu0.75Ni0.25/HNTs catalyst exhibited the potential application for the reduction of 4-NA and RhB dye under mild reaction conditions. Furthermore, the present catalytic system could be applicable for the treatment of various wastewater effluents.

High-performance Cu/Mn modified ceramsite as a persulfate activator to degrade oxytetracycline in batch Erlenmeyer flask and continuous-flow fixed-bed column systems: An exploration of its practicability and non-radical mechanisms

Persulfate non-radical oxidation have excellent catalytic capability for degrading specific contaminants in complicated water environments. Nevertheless, the preparation of high-performance activators and their application in actual water treatment in continuous flow mode are still scarce and unsatisfactory. In this work, copper-, manganese-, and copper/manganese-doped ceramsites (Cu–C, Mn–C and Cu/Mn–C), successfully fabricated through a facile impregnation-calcination approach, were characterized and evaluated for their performance to activate potassium peroxydisulfate (PDS) and degrade oxytetracycline (OTC) under different pH, ceramsite dosages, and PDS dosages. Compared with Cu–C and Mn–C, Cu/Mn–C showed the highest OTC degradation rate (0.0264 min−1) via activating PDS with an OTC removal efficiency of 98.2% in 240 min at an initial OTC concentration of 40 mg/L. The removal efficiency of OTC by Cu/Mn–C only decreased to 92.8% after 5 cycles; the activating ability of the used Cu/Mn–C was almost completely recovered through 2 h of calcination at 500 °C. The results of electron paramagnetic resonance and radical quenching suggest that singlet oxygen (1O2) was unveiled to be the dominant reactive oxygen species (ROS) for contaminant degradation, originating from the regrouping of superoxide ions or reduction of active Cu/Mn sites. Synergies between Cu and Mn species to enhance ROS yield were the primary activating mechanisms. Six possible routes of OTC decomposition were inferred. Additionally, Cu/Mn–C behaved excellently in treating an actual wastewater using a continuous flow fixed-bed reactor. It is believed that this novel Cu/Mn–C/PDS system may create a fresh path to design effective and cheap metal-ceramsite hybrid activators for degrading recalcitrant contaminants in the actual application process.

Zeolites mesoporosity evaluation using the cracking of 1,3,5-triisopropylbenzene; a critical assessment

The standard faujasite Y series of Zeolyst International was tested in the catalytic cracking of 1,3,5-Triisopropylbenzene (TIPB) in a continuous-flow fixed-bed catalytic reactor. Textural properties, true density, XRD, TEM, ammonia TPD, and Brønsted acidity by the isopropylamine decomposition reaction were used to characterize the zeolites. TIPB conversion responds to the acidity available to the molecule rather than only mesoporosity. Deactivation behavior gives valuable information about accessibility. Criteria like the initial conversion or at another time are not enough for correctly ranking the catalysts; neither is the selectivity to benzene. TOF and TON are better criteria for classifying the catalysts than selectivity to a specific product like di-isomers. Zeolite CBV780 shows the highest TOF of the series, but zeolite CBV720 gives the highest TON. A good balance between acidity and mesoporosity provides the catalyst with increased activity in the TIPB cracking reaction.

Gas-phase epoxidation of Hexafluoropropene using molecular oxygen and alkali doped CuO catalyst: Mechanism and kinetics

The study investigated the partial oxidation of hexafluoropropene over CuO catalyst with molecular oxygen in a continuous flow fixed bed reactor. The catalysts were characterized using various techniques, and the results confirmed catalyst's structure-reactivity correlation. The major products were hexafluoropropene oxide (HFPO) and carbonyl fluoride, with minor trifluoroacetyl fluoride produced when the catalyst had significantly declined in primary activity. The maximum selectivity of 52.5% HFPO was obtained at 13.4% hexafluoropropene conversion at 4.5 bar and 453 K. The proposed redox mechanism kinetic model was in adequate agreement with the experimental data (R2 = 0.97 for COF2 and 0.67 for HFPO).

Rationally Designed Water Enriched Nano Reactor for Stable CO2 Hydrogenation with Near 100% Ethanol Selectivity over Diatomic Palladium Active Sites

CO2 (CO) hydrogenation presents the widest route to synthesis of various valuable organic molecules, but precise carbon–carbon coupling control to targeted products along with the elimination of byproducts remains a challenge. We overcome these limitations by synthesizing a CeO2-supported dual Pd site catalyst that could actively catalyze CO2 conversion into single-product ethanol almost without C1 byproducts in a continuous-flow fixed-bed reactor. This surprising finding is derived from the observation that the synergistic catalysis between dual Pd atoms leads to extraordinary ability for the cleavage of C–O bond in *CHxOH species and the carbon–carbon coupling between *CHx and *CO species. Furthermore, the dual Pd sites could be stabilized through enriching in situ formed water in the nano reactor with a hydrophobic shell layer, thus leading to remarkably improved catalytic stability for ethanol production. As a result, the as-constructed dual Pd site catalyst exhibited superior selectivity to ethanol at 98.7%, corresponding to a productivity up to 11.6 g per gram of Pd per hour and excellent stability during the continuous test for 60 h. Our results demonstrate that multifunctional synergistic catalysis of dual active sites can break through the restriction of a reaction involving a single active site catalyst.

2nd generation PLA; Lactide formation directly from aqueous lactic acid

In order to develop a 2nd generation polylactic acid (PLA) process, lactide (LD) was synthesized directly from a commercially available 90% aqueous lactic acid (LA) solution. Experiments were conducted in an ordinary continuous flow fixed bed reactor. The reaction was carried out over various zeolites and γ-Al2O3 catalysts. Furthermore, the influence of pressure, temperature and water content in the inlet was studied. The highest LD selectivity of 98.9% was obtained using 90% LA and γ-Al2O3 as catalyst. In addition, it is concluded that LD yield increases when using highly concentrated LA oligomer with a minor amount of water. The catalysts were characterized by inductively coupled plasma atomic emission spectroscopy (ICP-AES), X-ray powder diffraction (XRD), nitrogen adsorption isotherms (BET), temperature programmed desorption of ammonia (NH3-TPD) and pyridine Fourier transformed infrared spectroscopy (Py-FTIR).

Conversion of Carbonaceous Organic Impurities (Methyldichlorosilane) in Trichlorosilane Using Weakly Basic Anion-Exchange Resin as Solid Catalyst

Trichlorosilane (SiHCl3) is an important raw material for preparing solar cells and semiconductor chips in the Siemens method. Since the boiling points of SiHCl3 and methyldichlorosilane (CH3SiHCl2) are close to each other, it is difficult to remove CH3SiHCl2 from the raw material to obtain high-purity products by traditional distillation methods. Therefore, we propose an efficient catalytic approach to convert CH3SiHCl2 to methyltrichlorosilane (CH3SiCl3) with an anion-exchange resin as the catalyst and tetrachlorosilane (SiCl4) as the Cl donor in a continuous-flow fixed bed reactor. Seven anion-exchange resins, including D201, D301, D303, 201 × 7, D301F, D315 and D380 were evaluated. The results showed that D301 resin had the best performance. Reaction conditions such as reaction temperature, reactant molar ratio and catalyst stability were investigated. The maximum conversion of CH3SiHCl2 was 60% at an optimum reaction temperature of 150 °C, n(CH3SiHCl2):n(SiCl4) = 1:3 and a liquid hourly space velocity (LHSV) of 3.0 h−1. A possible reaction mechanism is explained based on the reaction data obtained in the current work.

Regulating isomerization of gasoline-alkanes in aqueous-phase hydrodeoxygenation of sorbitol using regenerable Ni@MoOx catalysts

Aqueous-phase hydrodeoxygenation (HDO) has been regarded as an efficient biorefinery strategy for sustainable production of gasoline-alkanes from bio-polyols. However, current research focuses mainly on exploiting noble-metal HDO catalysts to acquire straight-chain C5-C6 alkanes. Herein, the aqueous-phase HDO route was firstly proposed to regulate isomerization of gasoline-alkanes in the sorbitol hydrogenolysis utilizing non-noble Mo-based catalysts in a continuous-flow fixed-bed reactor. The selective reduction removal of hydroxyl groups and isomerization of carbon chains were strongly coupled together for boosting the octane value of gasoline-alkanes over the regenerable Ni@MoOx binary catalysts derived from NiMoO4 spinel. Further characterization studies revealed that the synergism of Ni0 and MoOx played a crucial role in regulating selective dissociation of CO bonds and rearrangement of CC bonds, and suppressing excessive cleavage of CC bonds toward C1-C4 alkanes and CO/CO2. The effects of reaction parameters including reaction temperature, H2-pressure and reduction temperature were also evaluated for manipulating the product distribution between n-alkanes and isoalkanes. After optimization, a high C5-C6 yield of 87.5% with 51.7% of C5-C6 isoalkanes mainly including cycloalkanes was achieved at 280 °C under H2-pressure of 1.0 MPa over the Ni@MoOx catalyst reduced at 500 °C. This catalytic strategy could create new opportunities for producing high-quality biofuels from biomass-derived oxygenated compounds.

Catalytic hydroprocessing of waste cooking oil for the production of drop-in aviation fuel and optimization for improving jet biofuel quality in a fixed bed reactor

Waste cooking oil (WCO) is a bio-waste with significant potential for developing improved transportation fuel, specifically for the aviation industry. This work investigates the catalytic hydrocracking of WCO over commercial hydrocracking catalyst (Ni-Mo/silica-alumina) in a continuous flow fixed bed reactor to produce jet range hydrocarbons (HCs). The aim was to convert WCO into sustainable aviation and automotive fuel to get the maximum benefit from waste oil with high selectivity towards paraffins, naphthenes, minimal aromatics, and high isomerization (isomer to normal (i/n) ratio) in a single-step process using a single catalyst composition. The higher i/n ratio boosts specific energy, thermal stability and provides a low freezing point to the fuel. The results show that WCO conversion of 96.6 % with 55.6 % selectivity of jet range HCs was obtained at 420 °C temperature, 1 h−1 LHSV, 10 MPa pressure, and 2200 NLgas/Lliquid H2/oil ratio. In addition, isomer yield of 82.9 %, i/n ratio of 4.8, and selectivity of kerosene range HCs based on paraffins (43.6 %), naphthenes (8.2 %), and aromatics (3.73 %) was obtained at optimum reaction conditions. After hydroprocessing, the major fraction of heteroatoms (N = 99.9 %, S = 94.3 %, O = 99.9 %) was removed from WCO. Finally, the time on stream (TOS) study showed no deactivation of the catalyst up to 590 h, indicating the long life and stability of the catalyst, which is one of the highest lifetimes reported so far. Bio-jet fuel properties were tested according to the ASTM D-1655 standard. This research will aid in developing novel catalysts for the selective conversion of WCO into jet range HCs in a single step process.

Catalytic hydrocracking of inedible palm stearin for the production of drop-in aviation fuel and comparison with other inedible oils

This work describes the use of palm stearin oil as a feed for the catalytic hydrocracking to produce the renewable aviation kerosene and diesel using the hydrocracking catalyst in a continuous flow fixed bed reactor. The efficacy of this method is evaluated using several reaction parameters, including hydrocracking temperature, hydrogen pressure, liquid hourly space velocity (LHSV), hydrogen to feed ratio (H2/feed) and time on stream (TOS). Higher temperatures and lower LHSVs are dominant to produce kerosene with maximum selectivity of 55.7%, while lower temperatures and LHSVs favoured the diesel production with maximum of 75.4% selectivity. The isomerization reactions were promoted by higher hydrocracking temperature due to the increase in iso-paraffins. The products consist of paraffins (96.9–99.3%), naphthenes (0.1–1.86%) and aromatics (0.2–1.59%). Aromatization reactions were also taking place in the process which is a considerable benefit of this method as aromatization reactions decrease hydrogen consumption. Moderate hydrogen pressure and H2/feed ratio favour the kerosene yield. The reaction mechanistic pathway was also proposed for converting palm stearin to biofuels. Furthermore, product yield, selectivity, heteroatom removal, and double bond saturation were also explored. The stability and activity of the catalyst were studied for 600 h without observable deactivation of the catalyst.

Thermogravimetry Applied for Investigation of Coke Formation in Ethanol Conversion over Heteropoly Tungstate Catalysts

Thermogravimetric analysis (TGA) was used to evaluate the thermal stability and the amount of coke deposition resulting from the deactivation of catalysts during ethanol dehydration reaction in a fixed bed continuous flow reactor. In this study, a series of catalysts containing 30% of Pd doped and pure 12-tungstophosphoric acid and its insoluble Cs2.5H0.5PW12O40 salt supported on SBA-15 were prepared. The catalytic efficiency of ethanol dehydration reaction was also evaluated. Two types of coke are identified from the TPO (Temperature programmed oxidation) profiles and assigned to the coke precursor and hard coke, respectively. The results indicate that cesium salts reduced the formation of hard coke. The amount of total coke formed was significantly reduced by supporting the catalysts on mesoporous SBA-15 molecular sieves.

Vapour Phase Synthesis of 2-Methylpyridine and 4-Methylpyridine Over Potassium Salts of 12-Tungstophosphoric Acid

Vapor phase dehydrocyclization reaction of acetaldehyde and ammonia was investigated over K salts of 12-tungstophosphoric acid as catalysts in a continuous flow fixed bed reactor at 350–450℃. The yield of 2-methylpyridine and 4-methylpyridine were found to be in the range of 38.0–64.5%. The 2-methylpyridine and 4-methylpyridine are used for the preparation of insecticides, poultry drugs, cattle drugs and anti-tuberculosis drugs, veterinary analgesics etc. respectively. The reaction conditions such as temperature, contact time, and molar ratio for achieving optimal yield with respect to 2-methylpyridine and 4-methylpyridine were discussed. Catalysts were characterized through BET surface area, FT-IR, XRD and TGA. NH3-TPD studies exhibit the moderate acidity. The morphology of the catalysts was also studied by FESEM.

Cu/Zn/Zr/Ga Catalyst for Utilisation of Carbon Dioxide to Methanol—Kinetic Equations

This paper presents the kinetics of methanol synthesis from carbon dioxide and hydrogen over a Cu/Zn/Zr/Ga catalyst. Kinetic studies were carried out in a continuous-flow fixed-bed reactor in a temperature range from 433 to 513 K, pressures from 3 to 8 MPa, and GHSV from 1660 to 10,000 1/h for initial molar fractions of hydrogen from about 0.48 to 0.70, carbon dioxide from 0.05 to about 0.22, and carbon monoxide from 0 to about 0.07. Significant effects of temperature and the composition of the reaction mixture on the conversion degrees α1 and α2 were found. The Cu/Zn/Zr/Ga catalyst showed good stability over 960 h. XRD and CO2TPD characterisation were performed. Thefinally obtained results of kinetic tests were developed in the form of Langmuir–Hinshelwood kinetic equations. The numerical Levenberg–Marquardt method was used to estimate the kinetic equations. The average relative error of fitting the kinetic equations to the experimental data was 18%.

HMF hydrogenolysis over carbon-supported Ni–Cu catalysts to produce hydrogenated biofuels

Non-noble monometallic and bimetallic catalysts supported in biomass-derived carbon were tested in the 2,5-dimethylfuran (DMF) and 2,5-dimethyltetrahydrofuran (DMTHF) production from 5-hydroxymethylfurfural (HMF) hydrogenolysis using a fixed-bed continuous-flow reactor. These support and reaction system were selected in order to obtain a more sustainable catalyst development and to implement a continuous flow reaction system. The carbon-supported biomass-derived catalysts were compared with catalysts supported on commercial carbons, which were treated with acid to remove impurities. All the bimetallic catalysts exhibited high stability after 25 h-on stream, achieving DMF yields above 50% and complete HMF conversion. Biomass-derived carbon supported catalysts seems more selective toward DMF during the 8-9 h-on stream than commercial carbon supported ones. The good activity and stability of the bimetallic catalysts seems to be related to the synergistic effect between acid and metallic sites, exhibiting the most promising ones an excellent stability for 46 h on stream. Monometallic catalysts exhibited high yields, above 70%, at the beginning of the reaction. However, they suffer from partial deactivation, probably due to metal sintering. Finally, the obtained catalytic activities and selectivities toward target products are close to the reported ones for discontinuous systems, being an important aspect for its possible industrial application.