Fixed-bed Flow Reactor Research Articles

Transformation of sulfur compounds in two typical atmospheric residues in hydrotreating via ESI FT-ICR MS

The atmospheric residue (AR) hydrotreating (HDT) process attracts more and more attention because it provides quality feedstock for downstream catalytic cracking. The compositional analysis of feeds and products is a key step to improve our understanding of HDT process. In this study, two ARs representing a low (LSAR) and a high sulfur content (HSAR) were hydrotreated in a fixed-bed flow reactor. With increased process severity, we employed electrospray ionization (ESI) Fourier transform ion cyclotron resonance mass spectrometer (FT-ICR MS) to monitor the evolution of the sulfur families in HDT. The results suggest that although the properties and molecular composition of sulfur classes in ARs vary, the evolution of the sulfur compounds is quite similar. Further analysis indicated that the removal difficulty of S1 and S2 species was positively correlated with the number of aromatic rings.

The influence of Ba addition on thermal stability and catalytic activity of Cu-based mixed oxide

Catalytic reduction of NO by CO was studied over La2-xBaxCuO4 (x = 0.0 or 0.4) mixed oxides prepared by coprecipitation method. The catalysts were characterized by X ray diffraction (XRD), O2 temperature-programmed desorption (O2-TPD), H2 temperature-programmed reduction (H2-TPR) and X-ray absorption near edge structure (XANES). NO + CO reaction was carried out in a fixed-bed flow reactor, from room temperature to 500 °C, at atmospheric pressure. Both fresh catalysts were active for the NO + CO reaction but when were submitted to thermal aging, the barium free catalyst significantly lost its activity. The partial substitution of La by Ba enhanced the thermal stability and although the activity of the catalyst has decreased, it remains high, approaching 100 % at 500 °C. These results can be associated with reducible copper species observed by XANES in the thermal aged catalyst containing Ba.

Supported Molybdenum Carbide and Nitride Catalysts for Carbon Dioxide Hydrogenation.

Catalysts based on molybdenum carbide or nitride nanoparticles (2–5 nm) supported on titania were prepared by wet impregnation followed by a thermal treatment under alkane (methane or ethane)/hydrogen or nitrogen/hydrogen mixture, respectively. The samples were characterized by elemental analysis, volumetric adsorption of nitrogen, X-ray diffraction, and aberration-corrected transmission electron microscopy. They were evaluated for the hydrogenation of CO2 in the 2–3 MPa and 200–300°C ranges using a gas-phase flow fixed bed reactor. CO, methane, methanol, and ethane (in fraction-decreasing order) were formed on carbides, whereas CO, methanol, and methane were formed on nitrides. The carbide and nitride phase stoichiometries were tuned by varying the preparation conditions, leading to C/Mo and N/Mo atomic ratios of 0.2–1.8 and 0.5–0.7, respectively. The carbide activity increased for lower carburizing alkane concentration and temperature, i.e., lower C/Mo ratio. Enhanced carbide performances were obtained with pure anatase titania support as compared to P25 (anatase/rutile) titania or zirconia, with a methanol selectivity up to 11% at 250°C. The nitride catalysts appeared less active but reached a methanol selectivity of 16% at 250°C.

Deoxygenation of heptanoic acid to hexene over cobalt-based catalysts: A model study for α-olefin production from renewable fatty acid

Deoxygenation of heptanoic acid, a model compound, over bimetallic cobalt (Co-Pt, Co-Au, Co-Pd, Co-Ru) supported silica catalysts, was examined for α-olefin production. The catalysts were prepared by conventional impregnation of the metal precursors on silica and characterized by XRF, TEM, H2-TPR, acetic acid-TPD, and XANES. Catalytic testing was performed in a fixed-bed flow reactor under atmospheric H2 pressure. Monometallic cobalt catalysts yielded mainly 1-hexene, but rapid deactivation was observed. Incorporation of 0.5%wt secondary metal, particularly Pt, increases activity and stability under H2. A relatively higher olefin/paraffin ratio can be obtained from the reaction over 5%Co+0.5%Pt/SiO2 when compared to that with higher Pt loading. The co-impregnation method offers Co-Pt catalysts with stability higher than that prepared by the sequential impregnation method. Over cobalt-based catalysts, the deoxygenation is proposed to proceed via reduction of heptanoic acid to heptanal that is an intermediate for decarbonylation to hexene; while other side reactions are suppressed.

Highly efficient Ru/MgO–Er2O3 catalysts for ammonia synthesis

This study aimed to develop a highly efficient Ru catalyst using mixed oxide support of lanthanides and MgO. Mixed oxide support of Er2O3 with MgO showed higher catalytic activity for ammonia synthesis among other lanthanides. Therefore, MgO–Er2O3 mixed oxide supports with different molar ratios of Mg/Er were prepared by the co-precipitation method. 1% Ru was deposited by the impregnation method using Ru(NO3)3 as a Ru precursor. The activity measurement for ammonia synthesis was carried out in a fixed-bed flow reactor. It was found that the catalytic activity of the Ru/MgO–Er2O3 catalyst with higher MgO content (Mg/Er = 25/1) was comparably high as that obtained for 1% Ru deposited on pure Er2O3 support under same reaction conditions. The plausible reason was attributed to the same textural properties of the mixed oxide MgO–Er2O3 supported Ru catalysts up to a Mg/Er ratio of 25/1, where Ru was selectively deposited on Er2O3.

Transition Metal Sulfides- and Noble Metal-Based Catalysts for N-Hexadecane Hydroisomerization: A Study of Poisons Tolerance

Bifunctional catalysts on the base of transition metal sulfides (CoMoS and NiWS) and platinum as noble metal were synthesized via wetness impregnation of freshly synthesized Al2O3-SAPO-11 composites, supported with favorable acidic properties. The physical-chemical properties of the prepared materials were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), low-temperature N2 adsorption and high resolution transmission electron microscopy (HR TEM) methods. Catalytic properties were studied in n-hexadecane isomerization using a fixed-bed flow reactor. The catalytic poisons tolerance of transition metal sulfides (TMS)- and Pt-catalysts has been studied for sulfur and nitrogen, with the amount of 10–100 ppm addition to feedstock. TMS-catalysts show good stability during sulfur-containing feedstock processing, whereas Pt-catalyst loses much of its isomerization activity. Nitrogen-containing compounds in the feedstock has a significant impact on the catalytic activity of both TMS and Pt-based catalysts.

THERMOCATALYTIC DEGRADATION OF POLYPROPYLENE IN PRESENCE OF ALUMINUM SILICATES

The process of thermocatalytic conversion of polypropylene into liquid hydrocarbons using amorphous aluminum silicates with aluminum content of 1.6-12.9 wt.% as catalysts was studied. The aluminum silicates were synthesized by sol-gel method using hydrolysis of tetraethoxysilane in a presence of aluminum salt at pH=9. All samples possessed acidic sites with pKa value of 3.46-5.00 and had a developed surface. Textural properties of the aluminum silicates were determined. Thermocatalytic conversion of polypropylene was carried out in a flow fixed-bed reactor with a fixed layer of the mixture of the catalyst and the reagent at a mass ratio of polymer : catalyst of 3 : 1 in argon atmosphere with a gradual rise of temperature in the range of 300 – 450 ºС. The sample of silica, which did not contain aluminum, was demonstrated to be inactive in polypropylene degradation, while other catalysts provided conversion of polypropylene into liquid products. The highest yield of liquid products was 80% for a catalyst with an aluminum content of 8.1 wt.%. According to the results of GLC saturated hydrocarbons were identified among the products for all samples. The effect of the concentration of acidic centers on the chemical and fractional composition of the target products was shown. For the studied aluminum silicates with the same pKa values, an increase in the aluminum content favored the formation of a lighter hydrocarbon fraction. For the catalyst with the highest aluminum content the n-alkanes of С5-С10 composition were identified. These products were closest to gasoline oil fraction. This provides a possibility to consider secondary polyolefins as an alternative source of motor fuels. An influence of catalyst composition on maximal temperature of polyethylene degradation was determined by differential thermal analysis.

Jet fuel range hydrocarbon synthesis through ethylene oligomerization over platelet Ni-AlSBA-15 catalyst

Converting ethylene to biojet fuel range hydrocarbons via oligomerization is an important step in biojet production from ethanol. The present study investigates the catalytic ethylene oligomerization over platelet Ni-AlSBA-15 mesoporous catalysts. The catalysts are synthesized and characterized using nitrogen adsorption–desorption isotherms, X-ray fluorescence and X-ray diffraction techniques. The catalytic performances are then evaluated in a continuous flow fixed-bed reactor under various conditions of reaction weight hourly space velocities (0.56–4.5 h−1), temperatures (150–350 °C) and pressures (1–20 bar). Experimental results demonstrate that platelet Ni-AlSBA-15 is a promising catalyst for the ethylene oligomerization to produce biojet fuel range hydrocarbons. It performs a good catalytic activity, yielding 98–99 mol% ethylene conversion and 34–42 wt% C8+ selectivity at 0.56 h−1, 275–300 °C and 20 bar. The obtained products contain mainly C4–C10 olefins with low aromatic compounds. Moreover, the catalyst exhibits good stability of the activity during long periods of operation.

Deoxygenation of esters over sulfur-free Ni–W/Al2O3 catalysts for production of biofuel components

Sulfur-free Ni–W/Al2O3 catalysts synthesized through incipient wetness impregnation technique were investigated in deoxygenation of methyl palmitate and ethyl caprate blend at 300 °C and P = 1 MPa (PH2 = 0.25 MPa) in a fixed-bed continuous flow reactor. Modification of Ni/Al2O3 catalysts by W (0.4–4.4 wt%) was found to give rise to higher both conversions of the feedstock and deoxygenation degree. In addition, this also resulted in a change in the selectivity of deoxygenation towards alkanes formed via direct hydrodeoxygenation route, compared to alkanes formed through decarboxylation/decarbonylation. Selectivity by alkanes with carbon chain length equal to those of an initial fatty acid formed via hydrodeoxygenation was found to increase with W content increasing. The synthesized catalysts were investigated by XRD, XPS, TEM, BET and H2-TPR techniques. According to XPS study of the reduced samples, tungsten was in 6+ oxidation state on the sample surface and W6+ content increased in the near-surface layer of samples with tungsten content increasing in catalysts.

Oxidative Dehydrogenation of Propane over Vanadium-Containing Faujasite Zeolite.

Oxidative dehydrogenation (ODH) of light alkanes to olefins—in particular, using vanadium-based catalysts—is a promising alternative to the dehydrogenation process. Here, we investigate how the activity of the vanadium phase in ODH is related to its dispersion in porous matrices. An attempt was made to synthesize catalysts in which vanadium was deposited on a microporous faujasite zeolite (FAU) with the hierarchical (desilicated) FAU as supports. These yielded different catalysts with varying amounts and types of vanadium phase and the porosity of the support. The phase composition of the catalysts was confirmed by X-ray diffraction (XRD); low temperature nitrogen sorption experiments resulted in their surface area and pore volumes, and reducibility was measured with a temperature-programmed reduction with a hydrogen (H2-TPR) method. The character of vanadium was studied by UV-VIS spectroscopy. The obtained samples were subjected to catalytic tests in the oxidative dehydrogenation of propane in a fixed-bed gas flow reactor with a gas chromatograph to detect subtract and reaction products at a temperature range from 400–500 °C, with varying contact times. The sample containing 6 wt% of vanadium deposited on the desilicated FAU appeared the most active. The activity was ascribed to the presence of the dispersed vanadium ions in the tetragonal coordination environment and support mesoporosity.

Direct hydrogenation of CO2 to dimethyl ether (DME) over hybrid catalysts containing CuO/ZrO2 as a metallic function and heteropolyacids as an acidic function

Dimethyl ether (DME) is considered as a substitution of diesel oil. It can be used in diesel engines because of its high cetane number (> 55). The combustion process does not generate particle matter (PM) or sulphur oxides (SOx) pollutions. One of the methods to obtain DME is direct synthesis from a CO2 and H2 mixture. On the other hand, CO2 is an attractive reagent, which is a safe and economical source of carbon. The aim of this work was to obtain DME in the direct process from the mixture CO2 and H2 in the presence of hybrid catalyst. In these catalytic the CuO/ZrO2 was selected as a metallic function. The montmorillonite K10 modified by heteropolyacids was selected as an acidic function. The catalysts were obtained by different preparation methods and contained various types of heteropolyacids. The catalysts were characterized by following methods: BET/BJH, XRD, SEM, DCS/TG, NH3-TPD and FT-IR. The direct hydrogenation of CO2 was performed in the high pressure fixed-bed flow reactor connected online with GC equipped with TCD and FID detectors. It was shown that both synthesis method of metallic function and the type of heteropolyacids have influence on the total catalytic activity of the hybrid catalyst. The acidity and thermal stability of HPAs are identified as the most important parameters having a decisive influence on the overall catalytic activity of the samples.

Hydrogen production by catalytic decomposition of methane over Fe based bi-metallic catalysts supported on CeO2–ZrO2

Methane decomposition to produce hydrogen was studied over iron based bimetallic catalysts supported on cerium-zirconium oxide in a continuous flow fixed bed reactor at 700 °C. 15 wt% Fe/CeZrO2 was prepared by wetness impregnation and the promoted Fe catalysts (15 Fe-5 Co/CeZrO2 and 15 Fe-5 Mo/CeZrO2) were prepared by co-impregnation technique. Mo promoted Fe catalyst exhibited the maximum surface area of 24.08 m2/g. X-ray diffraction studies revealed that Fe2O3, Co3O4 and MoO3 were the phases present in freshly calcined catalysts, while the reduced catalysts consisted of phases including elemental Fe, Mo and Fe–Co alloys. Both X-ray diffraction and temperature programmed reduction studies confirmed the complete reduction of metal oxide species under H2 at 700 °C. The catalytic activity of Fe/CeZrO2 was enhanced upon addition of Co and Mo as promoters. The initial hydrogen yield on 15 Fe-5 Mo/CeZrO2 was ~90% and it decreased with increase in time on stream (TOS), and finally stabilized around ~50% after 125 min of TOS. The Co promoted catalyst exhibited similar activity while the initial hydrogen yield on 15 Fe/CeZrO2 was ~83% and dropped to ~33% after 125 min of TOS. Graphitic carbon, Fe3C and Mo2C phases were observed in the XRD patterns of spent catalysts along with elemental Fe and Fe–Co alloy. It was evident from temperature programmed oxidation results that coke formation which deactivates the catalyst was dominant in 15 Fe/CeZrO2 when compared to the promoted (Co and Mo) Fe catalysts where carbon nanostructures were dominant. Both scanning electron microscopy (SEM) and transmission electron microscopy (TEM) confirmed the formation of carbon nanostructures on the surface of spent catalysts. The Fe based catalysts supported both tip and base-growth mechanisms for the growth of carbon nanostructures.

Direct Hydroxylation of Phenol to Dihydroxybenzenes by H2O2 and Fe-based Metal-Organic Framework Catalyst at Room Temperature

A semi-crystalline iron-based metal-organic framework (MOF), in particular Fe-BTC, that contained 20 wt.% Fe, was sustainably synthesized at room temperature and extensively characterized. Fe-BTC nanopowders could be used as an efficient heterogeneous catalyst for the synthesis of dihydroxybenzenes (DHBZ), from phenol with hydrogen peroxide (H2O2), as oxidant under organic solvent-free conditions. The influence of the reaction temperature, H2O2 concentration and catalyst dose were studied in the hydroxylation performance of phenol and MOF stability. Fe-BTC was active and stable (with negligible Fe leaching) at room conditions. By using intermittent dosing of H2O2, the catalytic performance resulted in a high DHBZ selectivity (65%) and yield (35%), higher than those obtained for other Fe-based MOFs that typically require reaction temperatures above 70 °C. The long-term experiments in a fixed-bed flow reactor demonstrated good Fe-BTC durability at the above conditions.

Upgrading 1-butanol to unsaturated, carbonyl and aromatic compounds: a new synthesis approach to produce important organic building blocks

Conversion of 1-butanol into added-value organic building blocks was achieved using fixed-bed flow reactor and Cu-based catalyst at 550 and 600 °C with and without methanol as addictive.

Influence of sulfating method on La–Ni–S2O82–/ZrO2–Al2O3 solid superacid catalyst for n-pentane isomerization

La–Ni–S2O82–/ZrO2–Al2O3 catalysts were successfully prepared by two different methods of sulfate impregnation, and the physico-chemical properties of the catalysts were characterized by X-ray diffraction, Brunauer–Emmett–Teller analysis, Fourier transform infrared spectroscopy, pyridine adsorption–infrared spectroscopy, and X-ray photoelectron spectroscopy techniques. Catalytic activities were evaluated in a fixed-bed flow reactor using n-pentane isomerization as the probe reaction. Compared with catalyst La–Ni–S2O82–/ZrO2–Al2O3-I, prepared by the traditional impregnation method, the catalyst La–Ni–S2O82–/ZrO2–Al2O3-W, prepared by the incipient-wetness impregnation method, possessed higher pore volume, pore size, sulfur content, and stronger Brønsted acid sites. The catalytic activity for La–Ni–S2O82–/ZrO2–Al2O3-W was maintained at around 56% within 3000 min with an isopentane selectivity of 88% which showed much greater stability than that of La–Ni–S2O82–/ZrO2–Al2O3-I. This can be attributed to the fact that (1) the large pore size and pore volume of La–Ni–S2O82–/ZrO2–Al2O3-W can largely suppress carbon deposition and (2) the more numerous and stronger Brønsted acid sites for La–Ni–S2O82–/ZrO2–Al2O3-W guaranteed to provide enough acid sites for isomerization during the reaction process.

Partial Oxidation of Dimethoxymethane to Syngas Over Supported Noble Metal Catalysts

Catalytic partial oxidation (PO) of dimethoxymethane (DMM) to syngas was investigated in a fixed-bed continuous flow reactor under ambient pressure and at 250–500 °C over Pt-, Rh- and Ru-supported on Ce0.75Zr0.25O2–δ catalysts. The Pt catalyst was found to be the most active and selective. It provided complete conversion of DMM to gas mixture containing ˃ 60 vol% of H2 and CO at 400 °C, GHSV = 10,000 h−1 using a reaction mixture: DMM:O2:N2 = 28.6:14.3:57.1 (vol%).

Zeolite-Based Sorbent for CO2 Capture: Preparation and Performance Evaluation.

In this work, zeolite-based sorbents were developed from gasified rice husk. CO2 capture capacity of the sorbents was examined at various temperatures and pressures employing a fixed-bed flow reactor and simulated flue gas. Various physicochemical properties such as thermal stability, pore size distribution, morphology, chemical composition, etc. of the in-house-developed materials were characterized in detail and were also compared with two commercially available zeolites. Tetra-ethylenepentamine was impregnated in the in-house-developed zeolite supports to investigate its suitability to improve the CO2 adsorption capacity. The effects of reactor pressure, temperature, Si/Al ratio, and amine loading on CO2 uptake capacity were examined. A declining trend in CO2 adsorption capacity was observed with the increase in adsorption temperature and amine loading. At 30 °C, zeolite-Y (designated as Z-Y-3, silica to alumina ratio of 2.25) sample exhibited maximum adsorption capacity, and the obtained values were around 114 and 190 mg CO2/g sorbent under atmospheric and 5 bar pressure, respectively. It was also observed that the presence of alkali metal ions influenced the adsorption capacity of the zeolites. The study inferred that the adsorbent was efficient and promising for multiple adsorption-desorption cycles without much deterioration of the capture capacity.

Taking advantage of sulfur impurities present in commercial carbon nanofibers to generate selective palladium catalysts

Achieving high selectivity is one of the major challenges in heterogeneous catalysis, being carbon materials universally employed as catalysts support due to their so-called “inert” nature. However, due to the complexity of its intrinsic characteristics, there are still several factors to bear in mind when selecting the appropriate carbon support. In this work we demonstrate that the remaining sulfur impurities in one type of commercial carbon nanofibers (CNFs) drastically alter the catalytic properties of palladium by triggering electro-deficient active sites. Two as-received CNFs thermally processed at different severity degrees, namely PS and HHT, were used to support Pd nanoparticles through the wet impregnation technique using palladium nitrate as precursor. The proof of principle is demonstrated through two transformation reactions of biomass platform molecules: the hydrogenation of 5-hydroxymethylfurfural, performed in a batch-type reactor, and the ethanol dehydrogenation/decarbonylation reaction, carried out in a continuous flow fixed-bed reactor. In both reactions, Pd/PS was substantially more selective than its sulfur-free counterpart Pd/HHT, and one of the most selective in comparison with the state-of-the-art Pd catalysts. This finding makes available a simple, easy and green strategy to design carbon-supported Pd catalysts for selective hydrogenation and dehydrogenation reactions.

Microfluidic synthesis of fatty acid esters: Integration of dynamic combinatorial chemistry and scale effect

Integration of dynamic combinatorial chemistry and scale effect was designed to realize the efficient synthesis of bioactive compounds. Synthetic efficiency in the esterification reaction and combinatorial synthesis was significantly improved in smaller characteristic scale. Obvious increase in yield was observed when the reaction was conducted in the capillary with smaller diameters. More kinds of fatty acid esters were detected in the fixed bed flow reactor compared with the results in the flask. Based on the interaction of bioactive compounds and targets, the synthesis of compounds with high binding activity was intensified along with the dynamic shift of reaction equilibrium verified by gas chromatography. Uniform distribution of flow field would be beneficial to the mixing process, resulting in better mass transfer efficiency.

Electrochemical Upgrading of Wastes to Products- Fundamental Studies Using a Combined Experimental and Computational Approach

In recent years there has been growing interest in using electrochemical methods for hydrogenation of biomass-derived molecules for the formation of biofuels. Conventional hydrogenation processes require moderate temperatures between 433 and 678 K, pressures of 14,000 kPa, and external sources of dihydrogen for the stabilization and formation of biofuels. However, the same reaction can be performed using electrochemical reactors and much lower temperatures and pressures (293 K and 101 kPa) and with no supplied molecular hydrogen. In this work, we use a combined experimental–theoretical approach to identify atomistic features and parameters that affect the electrochemical hydrogenation (ECH) rates of different biomass organic compounds (such as aldehydes, ketones, and carboxylic acids) under ambient reaction conditions. In particular, we evaluated platinum group metals (PGM) and base-group metals (BGM) for the benzaldehyde ECH and correlated the activity with computationally-derived parameters. We then used these parameters to explain the dependence of molecule functionality on the ECH rates. The experiments were conducted using a continuous flow fixed bed reactor at room temperature and atmospheric pressure in the aqueous phase. We tested 7 metal catalysts with 12 substrates. Classical molecular dynamics simulations were performed on the metal’s most stable surfaces. The GROMACS package(83) was used for all classical molecular dynamics (MD) simulations. The results, summarized in Figure 1, indicate that the computationally-derived binding energy strongly correlates with the experimentally-derived ECH rates and hydrogen evolution reaction (HER) rates. The results suggest that Pd is the most active material for benzaldehyde ECH because it has an optimal organic reduction potential and binding energy compared to the other metals tested. However, Rh, which has a similar organic reduction potential, it is not active for benzaldehyde ECH due to the strong binding energy and high HER rates. These metrics were also used to evaluate the ECH activity of other biomass-derived molecules and we observed that the experimentally-derived parameters can be used to explain the differences in ECH activity with respect to benzaldehyde. For example, ketones such as acetophenone are not as active for ECH as benzaldehyde because of their binding energy. Figure 1