Similar effect of carbon and silica catalyst support on the hydrogenation reaction rate in organic slurry reactors

This paper investigates the influence of the catalyst support type on mass transport and reaction rate for the case of hydrogenation of α-methylstyrene to cumene in a gas inducing stirred slurry reactor and in a slurry bubble column. The reaction is carried out in the presence of 3% Pd/carbon and 3% Pd/silica catalyst particles. The lyophobicity of the two catalyst supports in the cumene slurry is found to be similar. The overall rate of the hydrogenation reaction is described by the classical transport and reaction resistances-in-series model. The rate of gas-to-liquid mass transfer is somewhat larger during reaction than without reaction. This enhanced mass transfer points to particle-to-bubble adhesion as a result of the relative affinity of both catalyst supports to the gas phase. The observed reaction enhancements are similar for both Pd/carbon and Pd/silica catalyst/cumene slurries.     

Development of Fe Fischer–Tropsch catalysts for slurry bubble column reactors

The effect of two binder systems — a silica-based system and a silica–kaolin–clay–phosphate-based system — on a doubly promoted Fischer–Tropsch (FT) synthesis iron catalyst (100Fe/5Cu/4.2K) was studied. The catalysts were prepared by coprecipitation, followed by binder addition and spray drying at 270°C in a 1 m diameter, 2 m tall spray dryer. The binder silica content was varied from 0 to 20 wt.%. A catalyst with 12 wt.% binder silica was found to have the highest attrition resistance. The FT activity and selectivity of this catalyst are better than a Ruhrchemie catalyst at 270°C and 1.48 MPa. The addition of precipitated silica or kaolin to catalysts containing 10–12 wt.% binder silica decreases attrition resistance and increases methane selectivity. Based on the experience gained, a catalyst has been successfully spray dried in 500 g quantity. This catalyst showed 95% CO conversion over 125 h of testing at 270°C, 1.48 MPa, and 2 NL/g-cat/h and had less than 4% methane selectivity. Its attrition resistance was one of the highest among the catalysts tested.     

钯系催化剂加氢反应及应用开发

将钯系催化剂催化加氢反应分成 11个类型 ,分别作了简介。Pd/C催化剂已应用于蒽醌法双氧水、精对苯二甲酸及己内酰胺生产。认为我国亟待开发的技术包括间苯二胺及同系产品、对氨基苯甲醚及同系产品与对氨基酚。指出Pd/C催化剂催化加氢技术开发过程中 ,应注意解决氢气源及催化剂开发与回收利用的问题。     

Determination of mass transfer resistances of fast reactions in three‐phase mechanically agitated slurry reactors

A methodology for the determination of mass transfer resistances of fast reactions in three‐phase mechanically agitated slurry reactors under the reaction conditions is presented. The mass transfer resistances affect significantly the overall mass transfer rate, the design equation and consequently the scale up of the reactor. There is not established methodology to separate the mass transfer resistances under reaction conditions by changing catalyst loading and manipulating the process variables, pressure and agitation speed. This allows to avoid the use of different catalyst particles and give the chance to calculate the mass transfer resistances without caring about the type of catalyst. We calculate each mass transfer resistance under conditions which do not allow to neglect any of the resistances. It is shown that the level off of mass transfer rate which is developed in the plot of mass transfer rate against agitation speed plots is not enough to determine the limiting regime. The hydrogenation of styrene over Pd/C (5% catalyst content) is used as case study to demonstrate the methodology. © 2016 American Institute of Chemical Engineers AIChE J, 63: 273–282, 2017     

Agglomeration and adhesion of catalyst particles in gas–liquid reactors

The colloidal properties of catalysts present in three phase slurry reactors may affect the overall behaviour of such a reactor. In part, this may arise from the adhesion of such particles to gas bubbles, which may lead to enhancement of the G–L mass transfer [Catal. Today 48 (1999) 131]. Classical film theory based on the mass transfer models are capable of quantitatively predicting such mass transfer enhancement, but only on the basis of a priori knowledge of the degree of bubble coverage by particles. Presently, various methods are reviewed that allow the accurate experimental determination of the coverage of bubbles by particles, under both stagnant and non-stagnant conditions. The relevance of these phenomena to reactive systems will be demonstrated on the basis of mass transfer data for the hydrogenation of methyl acrylate in a slurry reactor.     

Liquid-phase preparation of catalysts used in slurry reactors to synthesize dimethyl ether from syngas: Effect of heat-treatment atmosphere

A CuZnAl slurry catalyst was prepared directly from a solution of metal salts by an entirely liquid-phase method. The influence of heat-treatment atmospheres with different proportions of CO₂ on the single-step synthesis of dimethyl ether (DME) from syngas was investigated and the catalysts were characterized by powder X-ray diffraction (XRD), H₂ temperature-programmed reduction (H₂-TPR), temperature-programmed desorption of ammonia (NH₃-TPD), X-ray photoelectron spectrometry (XPS) and thermogravimetry-mass spectrometry (TG-MS). Results showed that the introduction of CO₂ into the heat-treatment atmosphere made it easier to reduce the catalyst. It also adjusted the Cu⁰/Cu⁺ ratio on the catalyst surface, the CO₂ reacting with the metallic carbide there to form CO, which then reduced part of the Cu₂O to Cu. Moreover, it was concluded that the final phase structure of the catalyst and the Cu/Zn ratio on its surface depended mainly on its composition and the reaction environment and less so on the heat-treatment atmosphere. In the DME synthesis reaction, it was found that the introduction of CO₂ into the heat-treatment atmosphere restrained the water–gas shift reaction and raised the DME selectivity. An optimal amount of CO₂ in the heat-treatment atmosphere favored the increase of the DME space–time yield. The catalysts performed best when the heat-treatment atmosphere contained 50% CO₂.     

Stability of bimetallic Bi–Pd and Pb–Pd carbon-supported catalysts during their use in glyoxal oxidation

The incorporation of Bi or Pb as promoting elements in Pd-based carbon-supported catalysts drastically increases the catalytic activity in the selective oxidation of glyoxal into glyoxylic acid. Because partial dissolution of the promoter was clearly demonstrated by atomic absorption analysis of the reaction medium, experiments are performed to examine the stability of these catalysts. Dissolution tests in the presence of the individual constituents of the reaction medium (glyoxal, glyoxylate, glycolate, oxalate) were carried out in air or nitrogen to identify the factors responsible for Pb or Bi leaching. Pb- or Bi-promoted Pd/C catalysts were prepared by thermal degradation of acetate-type precursors and characterized by X-ray diffraction and X-ray photoelectron spectroscopy before and after their use in glyoxal oxidation. Promoter leaching increases with the reaction time. Monometallic Bi/C and Pb/C catalysts were found to lose smaller amounts of promoting agent than the bimetallic M–Pd/C (M=Bi, Pb) catalysts. Losses are more pronounced from Pb–Pd/C catalysts than from their Bi-based partners. Both glyoxal and glyoxylate seem to be among the main factors responsible for the promoter losses in relation to their complexing properties.     

Kinetic and mass transfer in the hydrogenation of polyunsaturated organic compounds in the presence of supported Pd catalysts

The hydrogenation of 1,5-cyclo-octadiene has been studied on well-defined Pd catalysts. The reaction is affected by internal diffusion of hydrogen into the catalyst particles. Despite this limitation, the reaction orders of the reactants have been determined. All the performed kinetic runs have been simulated and the kinetic and mass-transfer parameters giving the best fit of experimental data have been evaluated. The reaction occurs in two steps, in the first, a conjugate diene (1,3-cyclo-octene) is formed via isomerization, then, hydrogenation occurs quickly forming the monoene. The hydrogenation of the obtained cyclo-octene is relatively slow and strongly inhibited by the presence of the cyclo-octadiene. This last reaction has, therefore, been used for comparing the activities of different palladium catalysts showing an exponential behaviour of the reaction rate with the metal dispersion.     

The activity and stability of Pd/C catalysts in benzene hydrogenation

Carbon black supported Pd catalysts were prepared by an incipient wetness impregnation method and tested for benzene hydrogenation. The catalytic activity is subjected to serious deactivation. However, the deactivation is found to depend on the test procedure. When the reaction is performed under constant flow of benzene and hydrogen during a stepwise temperature-ascending-descending test sequence, no deactivation is observed. Deactivation occurs when the reaction gas is replaced by a He purge during temperature changes in the test sequence. The Pd/C catalysts prepared from different precursors show similar activation energy and similar TOF as oxide-supported Pd catalysts when deactivation is confined by applying suitable experimental procedures. EXAFS, TEM, and TGA results suggest that both Pd sintering and carbonaceous residue are responsible for the deactivation.     

Intrinsic kinetics of Fischer–Tropsch reactions over an industrial Co–Ru/γ-Al2O3 catalyst in slurry phase reactor

The rate of Fischer–Tropsch synthesis over an industrial well-characterized Co–Ru/γ-Al₂O₃ catalyst was studied in a laboratory well mixed, continuous flow, slurry reactor under the conditions relevant to industrial operations as follows: temperature of 200–240 °C, pressure of 20–35 bar, H₂/CO feed ratio of 1.0–2.5, gas hourly space velocity of 500–1500 N cm³ g_cat^− 1 h^− 1 and conversions of 10–84% of carbon monoxide and 13–89% of hydrogen. The ranges of partial pressures of CO and H₂ have been chosen as 5–15 and 10–25 bar respectively. Five kinetic models are considered: one empirical power law model and four variations of the Langmuir–Hinshelwood–Hougen–Watson representation. All models considered incorporate a strong inhibition due to CO adsorption. The data of this study are fitted fairly well by a simple LHHW form − R_H2 + CO = ap_H2^0.988p_CO^0.508 / (1 + bp_CO^0.508)² in comparison to fits of the same data by several other representative LHHW rate forms proposed in other works. The apparent activation energy was 94–103 kJ/mol. Kinetic parameters are determined using the genetic algorithm approach (GA), followed by the Levenberg–Marquardt (LM) method to make refined optimization, and are validated by means of statistical analysis. Also, the performance of the catalyst for Fischer–Tropsch synthesis and the hydrocarbon product distributions were investigated under different reaction conditions.     

The selective hydrogenation of butyne-1,4-diol by supported palladiums: a comparative study on slurry, fixed bed, and monolith downflow bubble column reactors

The present study was carried out to asses performance of a Pd-monolith downflow bubble column (DBC) reactor, and compare it with that of the slurry and the fixed bed DBC. The selective hydrogenation of butyne-1,4-diol to cis-2-butene-1,4-diol over palladium catalyst was chosen as a model reaction. In principle, the monolith DBC allowed the reaction to take place under kinetic control regime. Comparison with DBC employing 5% Pd/C powder and 1% Pd-on-Raschig ring catalysts revealed a better performance of the monolith DBC (1% Pd loading) with advantage of smaller reaction volume and intensified reaction rate. In the monolith DBC, improved hydrogen transport was possible, as the interface between bubbles and the channel wall was very thin, thus, the length of the diffusion path was very short. In addition, the interfacial surface area at both gas–liquid and liquid–solid interface in the monolith was also very high. The reaction kinetics was well represented by the Langmuir–Hinshelwood mechanism. As an alternative to conventional three-phase reactors, the monolith DBC was simple due to its inherent characteristic operation and no specially designed device.     

Measurement and enhancement of gas-liquid mass transfer in milliliter-scale slurry reactors

Due to the limited availability of chemical reactants in the early process development of pharmaceuticals and fine chemicals, and sometimes the high-cost of catalyst, it is increasingly popular to use milliliter-scale slurry reactors with reaction volumes of 20 ml or less to screen catalyst candidates for three-phase reactions. To ensure the success of catalyst screening, it is advantageous to run reactions under kinetically controlled conditions so that the activities of different catalysts can be compared. Because catalysts with small particle sizes are used in slurry reactors, the reactions are susceptible to gas-liquid mass transfer limitations. This work presents an efficient way of enhancing gas-liquid mass transfer in milliliter-scale reactors through the use of magnetically driven agitation with complex motion. In the reactor described here, gas-liquid mass transfer coefficients can be doubled over those obtained with the agitation technique used in commercial milliliter-scale units. In addition, the reactor can achieve the top range of mass transfer coefficients obtained in a full-scale reactor. This work also presents the first measurements of gas-liquid mass transfer coefficients in milliliter-scale reactors, which are two orders-of-magnitude smaller than systems for which mass transfer coefficients have been reported earlier. Both physical and chemical absorption techniques are used.     

Racemization of (R)-(−)-10-methyl-Δ-octalin: Stereochemical requirements for double bond migration (isomerization) on metal catalysts

(R)-(−)-10-methyl-Δ¹⁽⁹⁾-octalin was synthesized in a mixture with cis- and trans-(R)-(−)-10-methyl-Δ¹⁽²⁾-octalin in a five step sequence. After removal of the cis- and trans-(R)-(−)-10-methyl-Δ¹⁽²⁾-octalins by hydrogenation over 5% Pt/C, 5% Rh/C, or 5% Pd/C, the remaining (R)-(−)-10-methyl-Δ¹⁽⁹⁾-octalin was monitored for racemization (double bond migration) during continued hydrogenation. No racemization occurs over these catalysts. However, slow racemization does occur in increasing amounts during hydrogenations over a series of 1% Pd/SiO₂ catalysts with dispersions increasing from 36%D to 84%D. The ratio of cis- to trans-9-methyldecalin changes from 1.8 over 5% Rh/C, 1.6 over 5% Pt/C, 1.1 over 5% Pd/C, to 1.0 over the 1% Pd/SiO₂ catalysts. Since double bond migration does not occur over the 5% catalysts, it cannot be used to account for differences in the ratio of cis- to trans- products. Congestion around the double bond inhibits addition, but double bond migration seems to require the allylic hydrogens to be nearly perpendicular to the planes of the double bond and the surface.     

Cloth catalysts for water denitrification: II. Removal of nitrates using Pd–Cu supported on glass fibers

The use of glass fibers in the form of woven cloth (GFC), as a new type of catalytic support, was studied for the reduction of aqueous nitrate solutions using a Pd/Cu–GFC catalyst. The activity (per gram Pd) and selectivity to nitrogen were found to be comparable with those found for Pd–Cu catalysts supported on the other carriers. The maximal initial removal activity was found for a catalyst with a Pd/(Pd+Cu) ratio of 0.81. The corresponding activity was 0.7 mmol min⁻¹ (g_Pd)⁻¹, and the selectivity was 97 mol% at 25°C and pH 6.5 for initial nitrate concentration of 100 mg l⁻¹. The selectivity to nitrogen declined at high conversions of nitrate and high pH.     

Hydrogenation of nitro compounds with supported platinum catalyst in supercritical carbon dioxide

Hydrogenation of a series of substituted nitro compounds such as 2-,3-,4-nitroanisole, 2-,3-,4-nitrotoluene, 2,4-dinitrobenzene and 2,4-dinitrotoluene has been studied in supercritical carbon dioxide, scCO₂ (two phases), and ethanol (three phases) with a 5 wt.% carbon supported platinum catalyst. The solubility of these compounds in scCO₂ has also been examined in the presence and absence of hydrogen. The solubility of those nitro compounds increases with increasing CO₂ pressure but decreases with the presence of hydrogen. The solubility is in the order of nitrotoluene > nitroanisole > dinitrotoluene, dinitrobenzene. Although the total conversion obtained with hydrogenation in scCO₂ is similar to that in ethanol, the selectivity to amino products is higher in the former reaction medium, indicating that scCO₂ is an ideal medium for the production of amino compounds with hydrogenation of nitro substrates using conventional supported metal catalysts.     

Study of the Characteristics of Methanol Synthesis in a Recirculation Slurry Reactor – A Novel Three‐Phase Synthesis Reactor

A process feasibility analysis on the liquid phase methanol synthesis (LPMeOH^TM) process was performed in a recirculation slurry reactor (RSR). In the three‐phase RSR system, a fine catalyst is slurried in the paraffin and this catalyst slurry is continuously recirculated through the nozzle from the slurry sector to the entrained sector by a pump. The syngas is fed concurrently with the downward flow of slurry to form the methanol product. A laboratory scale mini‐pilot plant version of a recirculation slurry reactor system was successfully designed and built to carry out process engineering research, and in addition, an identical cold model was built to measure the mass transfer coefficient in the recirculation slurry reactor. The effects of operating conditions, including temperature, pressure, gas flow rate and catalyst slurry recirculation flow rate on the productivity of methanol were studied. This experimental data helps the scale‐up and commercialization of the methanol synthesis process in recirculation slurry reactors.     

Hydrodynamics and mass transfer study of aliphatic alcohols in airlift reactors

Gas holdup and gas–liquid mass transfer coefficient were considered in an external airlift reactor. Air was sparged through some aliphatic alcohols (methanol, ethanol, n-propanol, and n-butanol) with different concentrations (0–1%, v/v). It was observed that gas holdup and mass transfer coefficient increased with increasing the number of carbons in alcohols. Furthermore, an increment in alcohols concentration increased gas holdup and mass transfer coefficient. The same behavior was observed in external and internal loop airlift reactors although gas holdup and mass transfer coefficient values were less than those of internal airlift reactor. According to the experiments, two correlations for gas holdup and mass transfer were developed.     

Synthesis and characterization of a novel solid–solid phase change luminescence material

Because of the large energy storage and small temperature variation during the phase change process, phase change materials (PCMs) are attracting increasing attention. In this study, a novel solid–solid PCM was prepared by coordinating rare earth Eu³⁺ ions to the carboxylate groups of a poly(ethylene glycol) (PEG) modified with two terephthalic acid groups. The structure and properties of the material were characterized using ¹H NMR, differential scanning calorimetry, infrared spectroscopy, gel permeation chromatograph and fluorescence spectroscopy. The coordination of Eu³⁺ with the double‐carboxylated PEG material significantly improved both the enthalpy value of the phase change material and its light‐emitting properties. This paper describes the facile synthesis and characterization of a novel phase exchange luminescent Eu–PEG material. The light‐emitting characterizations show that this modified PEG material has both good phase change properties and excellent luminescent properties. Copyright © 2010 Society of Chemical Industry