Continuous Fixed-bed Reactor Research Articles

Modeling of tartrazine adsorption onto activated carbon fiber in a continuous fixed-bed reactor

A column study was carried out using activated carbon fiber for the adsorption of tartrazine from aqueous solution. The effect of flow rate and inlet tartrazine concentration on the adsorption characteristics of the activated carbon fiber at 25°C was investigated. Adams–Bohart, Thomas, and Yoon-Nelson models each were applied to the experimental data to predict the breakthrough curves, and determine the characteristics and parameters of the column’s usefulness for tartrazine adsorption. This study revealed that carbon fiber is suitable for use as an effective adsorbent to remove tartrazine from solution.

Oxidative Dehydrogenation of n-Butane Over Vanadium Magnesium Oxide Catalysts Supported on Nano-Structured MgO and ZrO2: Effect of Oxygen Capacity of the Catalyst

Vanadium-magnesium oxide catalysts supported on nano-structured MgO and ZrO2 (Mg3(VO4)2/MgO/ZrO2) were prepared by a wet impregnation method with a variation of Mg:Zr ratio (8:1, 4:1, 2:1, and 1:1). For comparison, Mg3(VO4)2/MgO and Mg3(VO4)2/ZrO2 catalysts were also prepared by a wet impregnation method. The prepared catalysts were applied to the oxidative dehydrogenation of n-butane in a continuous flow fixed-bed reactor. Mg3(VO4)2/MgO/ZrO2 (Mg:Zr = 4:1, 2:1, and 1:1) and Mg3(VO4)2/ZrO2 catalysts showed a stable catalytic activity during the whole reaction time, while Mg3(VO4)2/MgO/ZrO2 (8:1) and Mg3(VO4)2/MgO catalysts experienced a severe catalyst deactivation. Deactivation of Mg3(VO4)2/MgO/ZrO2 (8:1) and Mg3(VO4)2/MgO catalysts was due to their low oxygen mobility. Effect of oxygen capacity (the amount of oxygen in the catalyst involved in the reaction) of the supported Mg3(V04)2 catalysts on the catalytic performance in the oxidative dehydrogenation of n-butane was investigated. Experimental results revealed that oxygen capacity of the catalyst was closely related to the catalytic activity in the oxidative dehydrogenation of n-butane. A large oxygen capacity of the catalyst was favorable for obtaining a high catalytic activity in this reaction. Among the catalysts tested, Mg3(VO4)2/MgO/ZrO2 (4:1) catalyst with the largest oxygen capacity showed the best catalytic performance.

Direct oxidation of dimethyl ether to ethanol over WO3/HZSM-5 catalysts

Abstract The direct oxidation of dimethyl ether (CH 3 OCH 3 , DME) to ethanol (CH 3 CH 2 OH) was carried out over WO 3 /HZSM-5 catalysts in a continuous flow type fixed-bed reactor. The effects of different zeolite types, WO 3 loading and reaction temperature on the reaction were investigated. Our results showed that modification of HZSM-5 with 10% WO 3 significantly improved the ethanol selectivity from 0.6% to 19.7%. The surface and structure of the catalysts were characterized by NH 3 -TPD, BET, XRD and in situ FT-IR. Ethanol can be mainly synthesized from DME direct oxidation under the cooperation of trifunctional reactive sites offered by WO 3 modified HZSM-5 catalysts.

Analysis of the Syntrophic Anaerobic Digestion of Volatile Fatty Acids Using Enriched Cultures in a Fixed‐Bed Reactor

Volatile fatty acids (VFAs) are key intermediates in anaerobic digestion. Enriched acetogenic and methanogenic cultures were used for the syntrophic anaerobic digestion of VFAs in a continuous fixed-bed reactor at mesophilic conditions. The interactive effects of propionic (HPr), butyric (HBu), and acetic (HAc) acids were analyzed. Furthermore, hydraulic retention time (HRT) and methanogen-to-acetogen ratios (M/As) were investigated as the key microbiological and operating variables of VFA anaerobic degradations. Experiments were carried out based on central composite design (CCD) and results were analyzed using response surface methodology (RSM). Effluent concentrations of HPr, HBu, HAc, and biogas production rate (BPR) were directly measured as responses. The optimum conditions were found to be HPr = 1122.9 mg/L, HBu = 1792.4 mg/L, HAc = 1735.4 mg/L, HRT = 21 hours, and M/A = 2.4 (corresponding to the maximum VFA removal and BPR). The results of verification experiments and predicted values from fitted correlations were in close agreement at a 95% confidence interval.

Partial Oxidation of Ethanol to Acetaldehyde over LaMnO3-Based Perovskites: A Kinetic Study

A set of experiments was carried out in a continuous fixed-bed reactor to investigate the relative catalytic activities of LaMnO3 and LaMn0.95Pd0.05O3 for the partial oxidation of ethanol to acetaldehyde. Both catalysts were prepared by the sol–gel method. The resultant data have indicated that LaMn0.95Pd0.05O3 is more active than LaMnO3 and that acetaldehyde selectivities of both are close at around 90%. To gain an in-depth understanding of perovskite’s chemistry involved, kinetic analysis of the data has been conducted with the differential method. Accordingly, eight elementary reactions have been proposed by resorting to the Mars–van Krevelen redox cycle. Subsequently, these elementary reactions have been lumped into five steps comprising ethanol adsorption, oxygen adsorption, surface reaction, acetaldehyde desorption, and water desorption. This has rendered it possible to derive a set of rate equations based on the Langmuir–Hinshelwood–Hougen–Watson formalism. The exploration of these rate equations has revealed that surface reaction, evolving chemisorbed ethanol and oxygen, is rate-limiting. The estimated activation energies of 11.72 kcal/mol for LaMnO3 and 12.44 kcal/mol for LaMn0.95Pd0.05O3 are nearly identical; however, the pre-exponential factor of the latter is about twice the value of the former. This can be attributed to the better reducibility of Pd-promoted LaMnO3, thereby leading to greater reactivity in ethanol partial oxidation.

A general process for the cyclization of aminoalcohols to the corresponding amines over Cu–Cr–La/γ-Al2O3

A general process for the cyclization of aminoalcohols to the corresponding amines over Cu–Cr–La/γ-Al2O3 is established in a continuous fixed-bed reactor. The catalyst was characterized by XRD, XPS and NH3-TPD. The doped Cr is found to improve the copper particle dispersion. The addition of La neutralized the strong acid sites and decreased the amount of the acid sites, which facilitated the desorption of amino compounds on the surface of catalysts and inhibited the carbon deposition. Under the optimum conditions, the yields of pyrrolidine, piperidine and piperazine were 99.5, 99.5 and 98.6 %, in order, while the yields of hexahydro-1H-azepine and homopiperazine were 46.5 and 32.7 % due to the unstable seven-membered ring by the cyclization of the corresponding aminoalcohols over Cu–Cr–La/γ-Al2O3.

Tailor‐Made Mesoporous Ti‐SBA‐15 Catalysts for Oxidative Desulfurization of Refractory Aromatic Sulfur Compounds in Transport Fuel

AbstractWe propose large‐pore titanium‐containing organosilylated mesoporous silica (Ti‐SBA‐15) as a highly efficient catalyst for the oxidative desulfurization (ODS) of refractory aromatic sulfur compounds with the aim to produce ultra‐low sulfur diesel. To achieve this, we synthesized a series of mesoporous Ti‐SBA‐15 catalysts according to a new procedure. The procedure is based on the controlled grafting of titanium chelates on SBA‐15 silica at low temperatures (5 °C). This specific synthesis procedure ensured a high dispersion of the required 4‐coordinate tetrahedral Ti4+ sites located on the mesopore surface. To substantiate the influence of the titanium content and mesopore size on the ODS performance of the catalysts, the parameters were varied in the range of 0.7 to 4.7 mol % (Si/Ti) and 5.1 to 9.0 nm, respectively. The resulting Ti‐SBA‐15 catalysts were then tested in the oxidative desulfurization (ODS) of model sulfur‐containing compounds in the presence of cumene hydroperoxide (CHP) as the organic oxidant. The ODS of a real industrial diesel fuel was also carried out in a continuous fixed bed reactor with the same Ti‐SBA‐15 catalysts and CHP. The catalytic results revealed that the Ti‐SBA‐15 catalysts with the largest pore sizes (>7.3 nm) and highest Ti contents (>2.8 mol %) were highly active catalysts for ODS reactions. Moreover, the catalysts with large pores and high Ti loadings appeared to be stable for over 30 h and were far less prone to deactivation than their equivalent Ti‐SBA‐15 samples with smaller pore diameters and lower Ti contents.

Continuous production of biodiesel from vegetable oil using supercritical ethanol/carbon dioxide mixtures

Biodiesel production is worthy of continued study and optimization of production procedures because of its environmentally beneficial attributes and its renewable nature. Transesterification of triglycerides using supercritical ethanol on ion-exchange resin catalyst was investigated to study the ethyl ester conversion process. The reaction parameters investigated were the reaction time, pressure, temperature and molar ratio (alcohol to triglycerides), and their effect on the biodiesel formation. Addition of a co-solvent, supercritical carbon dioxide (critical point at 31°C and 7.3MPa), decreased the operating conditions maintaining a high reaction rate. The mixture ethanol/carbon dioxide used in this work was 1:3 molar ratio. The experiments were conducted at temperatures of 150–200°C, pressure from 150 to 250bar and reaction times from 2 to 10min, and molar ratios of ethanol to vegetable oil from 20 to 45. The evolution of the process was followed by gas chromatography, determining the concentration of the ethyl esters at different reaction times. Results showed that ethyl esters obtained in the continuous fixed bed reactor under supercritical conditions can achieve 80% yield of biodiesel at reaction time of 4min.

A CuZnAl-Based Hybrid Material for the Direct Synthesis of Dimethyl Ether from Syngas

A CuZnAl-based hybrid material was prepared by co-precipitation impregnation method using the active components of methanol synthesis material and pseudo-boehmite as the precursors. The as-prepared material was evaluated for the direct synthesis of dimethyl ether (DME) from syngas in a pressurized continuous flow fixed-bed reactor system. It was revealed that the hybrid material showed high activity and selectivity after an induced period, i.e. the CO conversion and DME selectivity reached as high as 81% and 67%, respectively. Moreover, it was observed that there was only slight carbon which could be eliminated rather than graphite carbon deposited on the material after run for 150 h, indicating its good stability for the direct synthesis process .

Effects of the types of zeolites on catalytic upgrading of pyrolysis wax oil

Because zeolites play an important role in an upgrading catalyst for heavy hydrocarbons in industrial refinery processes, the effects of the zeolite type on the upgrading of pyrolysis wax oil are investigated in this study. Raw pyrolysis wax oil was obtained from the pyrolysis of municipal plastic wastes in a commercial rotary kiln pyrolysis plant (Dongmyong RPF Co.). The catalystic experiments are performed for the three different types of commercial zeolites with different physicochemical properties in a continuous fixed bed reactor at 450°C for 1h as a MAT(micro-activity test) method: HZSM-5 (pure), zeolite Y (HY; pure or including 20% clay) and mordenite (HM; including 20% clay or alumina) catalysts. The highest conversion of pyrolysis wax oil into light hydrocarbons such as gas products and gasoline-range hydrocarbons is obtained for the HZSM-5 catalyst among them, and the composition of liquid products is found to become in the main aromatic components due to a shape selectivity. For the case of zeolite Y(HY), medium activity and the highest fraction of branched hydrocarbons with a high octane number, as well as a high fraction of aromatic products are shown. However, the mordenite (HM) with one-dimensional pore structure shows the lowest conversion of pyrolysis wax oil into light hydrocarbons and a very high fraction of paraffin product in the liquid product like the characteristics of raw pyrolysis wax oil.

Study of the deactivation of copper-based catalysts for dehydrogenation of cyclohexanol to cyclohexanone

Catalytic dehydrogenation of cyclohexanol was carried out in the gas phase in a continuous fixed bed reactor under atmospheric pressure. Two commercial catalysts composed by copper chromite and copper zinc oxide were tested. The activity of the catalysts was evaluated at 250°C, with a weight hourly space velocity of 2.89h−1 and at times on stream (TOS) higher than 400h. A slow deactivation of the catalysts was observed during the reaction, obtaining an activity reduction of 50% at TOS=350h, but maintaining 30% conversion at these conditions. Yield higher than 97% to cyclohexanone was obtained with both catalysts, in all the range of TOS studied. The main impurity observed was phenol, obtained from dehydrogenation reaction, and cyclohexene, only obtained with the copper chromite catalysts, and derived from cyclohexanol dehydration. The results of stability and selectivity with these catalysts are better than others reported in the literature. The main causes of the activity loss are associated to the coke deposition over the copper active sites and the increase of the copper metallic crystallite size. The copper zinc oxide also presents a slight blockage of the porous structure due to coke deposition, what can also decrease the catalyst activity.

Hydroisomerization of n-Heptane over Pt-Loaded USY Zeolites. Effect of Steaming, Dealumination, and the Resulting Structure on Catalytic Properties

The hydroconversion of n-heptane was studied on five USY zeolite samples loaded with 1 wt % Pt. Experiments were performed on a continuous fixed-bed stainless steel reactor at 210-310 ??C and pressures up to 15 bar. Three in-house samples were subjected to steaming treatment, and the remaining were acid-leached from a commercial source. The study aimed to evaluate the effect of acid leaching, and its subsequent extraframework alumina (EFAL) species removal, on the performance of bifunctional USY zeolite catalysts during n-heptane transformation. Results have shown that steamed samples generate more cracked products at higher conversions when compared to acid-leached ones, more than likely due to a high presence of EFAL species. The degree of steaming played a role in decreasing cracking tendency at higher pressures, which is attributed to pore structure change and decreasing acidity. In addition, steaming resulted in a catalyst sample capable of generating isomers with blended research octane numbers close to those achieved with a robust commercial catalyst. However, poisoning experiments have shown that these two catalysts are highly sensitive to sulfur and require sulfur-free feeds in order to demonstrate their full capacities.

Upgrading of coker distillate under variable hydrotreating operating conditions

Studies on hydrotreating coker distillates, produced from a delayed coker unit were done using a commercially available CoMo/γ-Al2O3 catalyst, on which 0.2wt% P2O5 was added in order to improve its characteristics. The experimental studies were conducted in a fixed-bed continuous-reactor (cata-test unit) at temperatures (300–400°C) and total hydrogen pressure (40–65bar). These conditions have affected the feedstock characteristics and great reduction of sulfur, aromatics and boiling ranges. Other improvements were obtained in diesel index (DI) due to hydrogenation reaction of aromatics and desulfurization of its sulfur contents.

Growth of single-walled carbon nanotubes on a Co–Mo–MgO supported catalyst by the CVD of methane in a fixed bed reactor: Model setting and parameter estimation

In this work methane was decomposed to hydrogen and carbon to determine its kinetic behavior during reaction over a Co–Mo–MgO supported catalyst using the CVD (Chemical Vapor Deposition) technique. Decomposition of methane molecules was performed in a continuous fixed bed reactor to obtain data to simulate methane decomposition in a gas phase heterogeneous media. The products and reactants of reaction were analyzed by molecular sieve column followed by GC-analysis of the fractions to determine the amount of product converted or reactant consumed. The synthesis of single-walled carbon nanotubes was performed at atmospheric pressure, different temperatures and reactant concentrations. The experimental data analyzed to suggest the formula for calculation of the initial specific reaction rate of the carbon nanotubes synthesis, were fitted by several mathematical models derived from different mechanisms based on Longmuir-hinshelwood expression. The suggested mechanism according to dissociation adsorption of methane seems to explain the catalytic performance in the range of operating conditions studied. The apparent activation energy for the growth of SWNTs was estimated according to Arrhenius equation. The as grown SWNTs products were characterized by SEM, TEM and Raman spectroscopy after purification. The catalyst deactivation was found to be dependent on the time, reaction temperature and partial pressure of methane and indicated that the reaction of deactivation can be modeled by a simple apparent second order of reaction.

Catalytic behavior of Co/(Nanoβ-Zeolite) bifunctional catalysts for Fischer–Tropsch reactions

Cobalt supported on Beta zeolite catalysts were prepared by impregnation of metal salts in aqueous solution and were tested for the Fischer Tropsch reaction. The support consisted of a Beta zeolite composed by crystallites of nanometric dimensions and a SiO 2/Al 2O 3 molar ratio of about 50. This support was impregnated with Co(NO 3) 2 aqueous solution using different metal loads of 7.5, 10, 15 and 20 wt% Co. These materials were characterized by X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), N 2 adsorption (BET), thermal programmed reduction (TPR) and FTIR of adsorbed pyridine (i.e., surface acid sites distribution). All the catalysts showed a significant catalytic activity for the F–T reaction from synthesis gas (CO + 2H 2), in a continuous fixed bed reactor system. The catalysts presented a bifunctional character with a maximum of activity at a specific concentration of metal and particle size. In contrast, the selectivity patterns were strongly influenced by the support acid function, which promote the formation of isoparaffins from about 220 °C, which differ with most of conventional zeolites that show a relatively low activity for isomerization at this temperature, thus indicating an effect of the small Beta zeolite crystallites size over the catalytic activity of Co/Nanoβ-Zeolite.

Evaluation of Pd−In Supported Catalysts for Water Nitrate Abatement in a Fixed-Bed Continuous Reactor

The increasing pollution of natural drinking-water sources brings about the development of new emerging technologies and processes for water remediation. In this work, the catalytic reduction of contaminated water containing nitrates (100 mg/L) was studied in a bubble column fixed-bed reactor, working at room temperature and atmospheric pressure and using hydrogen as a reducing agent. The activity and selectivity of these catalysts were evaluated under different reaction conditions (hydrogen flow, water flow, pH, acidifying agent) and verified in a stirred reactor, operating under batch conditions. On SiO2 supported catalysts, it was found that the nitrate conversion increased as the H2 flow was increased, while the N2 selectivity remained almost unaffected. On the other hand, in Al2O3 supported catalysts, an increase in H2 flow improved activity but worsened nitrogen selectivity. The best conversions and selectivity results were obtained when the feed solution was acidified with CO2. Very pronounced pH gradients or high amounts of OH− in the catalytic bed promoted nitrites and ammonium formation, provoking a notorious decrease of N2 selectivity. The highest conversion (100%) was obtained with the Al2O3 supported catalyst aged in the reaction. However, the selectivity to N2 under these conditions was 72%. On the other hand, the best selectivity to N2 was 97%, obtained with the aged SiO2 supported catalyst. In this case, the nitrate conversion was 30%. Characterization results showed that the metallic composition of the catalysts changed both after reduction and after contacting the liquid reaction media. These changes were observed by X-ray photoelectron spectroscopy (XPS) and temperature-programmed reduction (TPR). The catalysts stability was studied and discussed.

Green process technology for peroxycarboxylic acids: Estimation of kinetic and dispersion parameters aided by RTD measurements: Green synthesis of peroxycarboxylic acids

Synthesis of peroxypropionic and peroxyacetic acids from hydrogen peroxide and their carboxylic acids was carried out in a continuous fixed-bed reactor, demonstrating the concept of green process technology: biodegradable chemicals are made with the aid of heterogeneous catalysts. This reactor was constructed with several sampling locations along its length, allowing a better kinetic investigation. A profound study of the mean residence time distribution (RTD) was performed to analyze the behavior of the flow pattern at different liquid flow rates and catalyst loadings by using step and impulse methods with different tracer molecules. It was found that impulse experiments with HCl as a tracer is the most reliable method to study the RTD, because of this tracer does not interact with the catalyst. Based on the RTD study, it was demonstrated that the temperature (in the range 30–60 °C) and the catalyst distribution inside the reactor do not affect the flow pattern, but the ratio of the catalyst mass-to-liquid ratio affects the mean residence time and the liquid dispersion. Furthermore, it was shown that the presence of an axial dispersion is negligible when the average particle diameter is <1.38 mm, e.g., Péclet number exceeds 100. The kinetic study was carried out at different mean residence times (from 10 to 55 min), at different wet catalyst loadings (from 25 to 49 g) and reactor temperatures (from 30 to 60 °C). Mathematical models comprising kinetic and dispersion parameters were developed to compare the estimated parameters obtained from the continuous fixed-bed reactor with the ones obtained from a batch reactor.

Hydrogen production by aqueous phase catalytic reforming of glycerine

Hydrogen is believed to be the one of the main energy carriers in the near future. In this research glycerine, which is produced in large quantities as a by-product of biodiesel process, was converted to hydrogen aiming to contribute to clean energy initiative. Conversion of glycerol to hydrogen was achieved via aqueous-phase reforming (APR) with Pt/Al2O3 catalyst. The experiments were carried out in an autoclave reactor and a continuous fixed-bed reactor. The effects of reaction temperature (160–280 °C), feed flow rate (0.05–0.5 mL/dak) and feed concentration (5–85 wt-% glycerine) on product distribution were investigated. Optimum temperature for hydrogen production with APR was determined as 230 °C. Maximum gas production rate was found at the feed flow rates around 0.1 mL/min. It was also found that hydrogen concentration in the gas product increased with decreasing glycerol concentration in the feed.

Comparative dehydrogenation of cyclohexanol to cyclohexanone with commercial copper catalysts: Catalytic activity and impurities formed

Catalytic dehydrogenation of cyclohexanol to cyclohexanone has been carried out on phase gas in a continuous fixed bed reactor under atmospheric pressure. Copper chromite and copper zinc oxide catalysts have been checked. Effect of temperature (in the range 250–290°C) and spatial time in reactor have been studied. The catalytic activity has been evaluated in terms of cyclohexanone yields and impurities from secondary reactions of dehydration and dehydrogenation of cyclohexanol have also been identified and quantified by GC/MS.Catalysts have been characterized by X-ray diffraction, temperature programmed desorption of ammonia and BET surface area measurement. High activity was confirmed by copper-based catalysts under the operating conditions, concerning the size and dispersion of the copper specie. It was also found that catalysts with alumina and chromium exhibit higher dehydration capacity, being cyclohexene the main impurity obtained. For a given cyclohexanone yield the impurities from dehydrogenation reactions showed similar trends for the three catalysts tested. Phenol was the main impurity obtained by dehydrogenation.

Study on Alumina-Supported Cobalt–Nickel Oxide Catalyst for Synthesis of Acetonitrile from Ethanol

A new alumina-supported cobalt–nickel oxide catalyst for the synthesis of acetonitrile from ethanol and ammonia was prepared by coprecipitation-kneading method. The parameters influencing the reaction were studied thoroughly and an optimized process, which is running the reaction at 380 °C under atmospheric pressure while keeping the ammonia/alcohol molar ratio of 5 and GHSV of 1,163 h−1, was obtained. Under the optimized conditions the catalyst reached its best performance when being on stream for 40 h, at which the yield of acetonitrile was 92.6%. Then the selectivity to acetonitrile decreased gradually but the yield of acetonitrile always remained higher than 81% within 720 h. The samples of the fresh and used catalyst were characterized by XRD, XPS, TEM, EDX and N2 adsorption–desorption analysis. The results revealed that carbon deposition and formation of metal carbides from the active species in the catalytic runs led to the deterioration of the catalyst. A new Co–Ni/γ-Al2O3 catalyst for the amination of ethanol to acetonitrile was studied in a continuous fixed-bed reactor and the reaction parameters were optimized. The mechanisms for the formation of acetonitrile and butyronitrile were discussed. The reasons leading to the deterioration of the catalyst were investigated through the characterization of the fresh, used and regenerated samples of the catalyst by means of XRD, XPS, TEM and N2 adsorption–desorption techniques.