Catalytic oxidation of methanol to formaldehyde: an example of kinetics with transport phenomena in a packed-bed reactor

In the present work the partial oxidation of methanol to formaldehyde has been studied as an example of strongly exothermic reaction affected by internal diffusion in order to deep the topic of mass and heat transfer in packed-bed catalytic reactors both at particle level, introducing the calculation of the effectiveness factor for complex reactions network, and at reactor level, for what concerns long range gradients of composition and temperature. The aim of the work is to stress the impact of the use of rigorous numerical methods, today possible for the high performances reached by the computers, in the solution of a simultaneous set of many differential equations that are necessary to describe completely the mentioned system. A complete mathematical model of the particle and the reactor is presented and a solution strategy is reported for the chosen reaction by considering a reliable kinetic law and evaluating related parameters from experimental data reported by the literature. Calculation results are reported for both particle internal profiles and reactor simulation. The described approach can easily be extended to many other devices and reactors geometry such as, e.g., the ones used in the field of environmental catalysis.     

Methanol oxidative dehydrogenation in a catalytic packed-bed membrane reactor: experiments and model

Methanol oxidative dehydrogenation to formaldehyde over a Fe-Mo oxide catalyst was studied experimentally in three reactor configurations: the conventional fixed-bed reactor (FBR) and the packed-bed membrane reactor (PBMR), with either methanol (PBMR-M) or oxygen (PBMR-O) as the permeating component. The kinetics of methanol and formaldehyde partial oxidation reactions were determined independently from FBR experiments. A steady state plug-flow PBMR model, utilizing these kinetics and no adjustable parameters, fit the experiments accurately. It is shown experimentally and in accordance with the model that for given overall feed conditions, the reactor performance for methanol conversion and formaldehyde yield is in the order PBMR-M < FBR < PBMR-O.     

Short-channel structured reactor: Experiments versus previous theoretical design

The study deals with the so-called short-channel structures (very short monoliths) that were introduced by Ko?odziej and ?ojewska [1] on the theoretical basis. The structures are very short so the entrance (mixing) section occupies majority of the channel length. This leads to highly enhanced heat and mass transfer, but the flow resistance is increased as well. The article presents experimental results of flow resistance, heat and mass transfer for short-channel structures of sine and triangular cross-sectional channel shape. The results presented in terms of dimensionless quantities confirmed theoretical consideration presented in [1]. The efficiencies of the structure have been derived that show the structures as more efficient when compared to classic monoliths or packed bed reactors.     

Investigation of a rotating disc reactor for acetone stripping and asymmetric transfer hydrogenation: Modelling and experiments

Asymmetric transfer hydrogenation of acetophenone with isopropanol as hydrogen donor in the presence of a homogeneous catalyst was investigated in a rotating disc reactor. Initially, acetone stripping from binary mixtures acetone-isopropanol with nitrogen as inert gas was studied, since its removal is a key issue in improving reaction performance. The reactor consisted of a stainless steel disc mounted on a horizontal shaft, accommodated in a cylindrical shell. The disc was partially immersed in the liquid phase. Its rotation generated a thin liquid film on its upper part, which could be brought in contact with a gas phase used for stripping. A mathematical model was formulated to simulate the reactor and showed good agreement with experimental data for acetone stripping. It was observed that the efficiency of acetone removal from the liquid phase increased with the gas flowrate per initial liquid volume ratio. The effect of disk rotation was found to be small when the stripping gas was introduced in the liquid bulk. The reactor model agreed well with experimental data of the asymmetric transfer hydrogenation. An advantage of the rotating disk reactor is that the hydrodynamics of the phases can be decoupled and the gas flowrate can be increased without constraints in the liquid phase, unlike conventional agitated reactors that are limited by flooding. Simulations using high stripping gas flowrate per initial liquid volume, unachievable in stirred reactors, showed significant reduction of the residence time required to achieve >99% conversion.     

Selectivity of partial hydrogenation reactions performed in a pore-through-flow catalytic membrane reactor

The selectivity of partial hydrogenation reactions of unsaturated substrates was studied in a membrane reactor operating at 323 K and 40 bar hydrogen pressure. The reactor system was constructed as a loop of a saturation vessel and a membrane module in which the reaction mixture was resaturated with hydrogen up to 100 times. In a porous membrane made from cross-linked polyacrylic acid palladium nanoparticles were incorporated as catalysts. A well-defined residence time within the membrane was achieved due to a defined pore structure of the membrane and a convective mass flow of the reaction mixture through the membrane. The selectivity for the partially hydrogenated products was investigated as a function of the pore size of the PAA membrane and was compared to commercially available catalysts. Compared to experiments with supported catalysts (Pd/C and Pd/Al₂O₃) in a slurry and a fixed bed reactor the selectivity for the desired products could be increased by 3% (1-octyne) up to 40% (geraniol).     

Propyne hydrogenation in a continuous polymeric catalytic membrane reactor

Propyne hydrogenation was studied in a continuous polymeric catalytic membrane reactor (pCMR), both experimentally and theoretically. It was used a poly(dimethylsiloxane) (PDMS) composite membrane with an average thickness of , loaded with 5 wt% of 9 nm diameter Pd clusters. The reaction was conducted at 308 K and several feed compositions at a fixed flow rate were tested.The mathematical model proposed includes the mass balances to the retentate and permeate chambers and the mass balance and transport kinetics through the catalytic membrane. The pCMR model also considers a reaction rate equation composed of two terms: the propyne to propylene and the propylene to propane hydrogenations. The selectivity between these two reactions is described by the bicomponent adsorption of propyne and propylene obtained by the IAST model (thermodynamic selectivity). The proposed model represents quite well the experimental data regarding the flow rates and mixture compositions of the permeate and retentate streams.     

A three-phase nonequilibrium dynamic model for catalytic distillation

A detailed three-phase nonequilibrium (NEQ) dynamic model for simulating batch and continuous catalytic distillation (CD) processes has been developed. In this model, both molar and energy holdups in liquid and vapour phases are taken into account. Multicomponent mass transfer and heat transfer between vapour and liquid phases as well as between liquid and solid (catalyst) phases are described by the Maxwell-Stefan equations. The resulting differential and algebra equations in this model are implemented in gPROMS and C++. The simulation results are in good agreement with the experimental data obtained from the batch and continuous CD processes for the production of diacetone alcohol (DAA) using Amberlite IRA-900 as a catalyst. Sensitivity analysis on the mass transfer and kinetics using the three-phase NEQ dynamic model indicates that the formation of DAA is controlled by solid-liquid mass transfer, whereas the formation of mesityl oxide is kinetically controlled under the simulation conditions.     

Glucose oxidation in a three-phase stirred airlift reactor: experiments and model

The three-phase catalytic oxidation of glucose into gluconic acid is studied in a new type of reactor: a stirred internal-loop airlift reactor. The influence of oxygen flow rate and of agitation on reaction rate are experimentally checked. By means of a model, a better knowledge of the reaction kinetic order for oxygen is reached.     

Kinetics of catalytic transfer hydrogenation of soybean oil

The catalytic transfer hydrogenation of soybean oil was studied by using various concentrations of sodium formate solutions, an emulsifier and paladium on a carbon catalyst. Sodium formate concentration and addition of the emuldifier significantly affect the reaction rate because of their influence on the liquid/liquid interface. Under conditions in which diffusion effects are eliminated, all reactions carried out in diluted sodium formate solution obey first-order kinetics with respect to fatty acids. This allows control over the hydrogenation process of soybean oil, needed to obtain partially hydrogenated oil containing about 1% linolenic acid and a relatively high level of linoleic acid with no increase in the stearic acid concentration.     

Selective hydrogenation of sunflower seed oil in a three-phase catalytic membrane reactor

Continuous hydrogenation of sunflower seed oil has been carried out in a novel three-phase catalytic membrane hydrogenation reactor. The membrane reactor consisted of a membrane impregnated with Pd as the active catalyst, which provided a catalytic interface between the gas phase (H₂) and the oil. Hydrogenations were carried out at different pressures, temperatures, and selectivities, and the formation of trans isomers was monitored during the hydrogenation runs. For the three-phase catalytic membrane reactor, interfacial transport resistances and intraparticle diffusion limitations did not influence the hydrogenation reaction. Hydrogenation runs under kinetically controlled conditions showed that oleic and elaidic acid were not hydrogenated in the presence of linoleic acid. Initial formation of stearic acid was caused by direct conversion of linoleic acid into stearic acid by a shunt reaction. Furthermore, high selectivities led to high trans levels, which is in accordance with the many published data on hydrogenation of vegetable oils in slurry reactors. Finally, the catalytic membrane showed severe catalyst deactivation. Only partial recovery of the catalyst activity was possible.     

Selective hydrogenation of cyclopentadiene in a catalytic cellulose acetate hollow-fiber reactor

A catalytic membrane reactor was established with catalytic hollow fibers prepared by supporting polymer anchored palladium catalysts on the inside wall of cellulose acetate hollow fibers. The selective hydrogenation of cyclopentadiene was carried out in the catalytic membrane reactor at 40°C in two ways: (1) by hydrogen permeating into the hollow fibers, and (2) by hydrogen premixed in the gas phase.     

Pseudo-steady state method on study of xylose hydrogenation in a trickle-bed reactor

A new approach to assess the overall mass transfer coefficients in a partial wetting trickle-bed reactor was proposed and tested in hydrogenation of xylose. An effective data-acquiring procedure featured by recycling a large volume of liquid feed has been adopted after the steady state operation. Since the volume of the fresh feed taken for recycling was so large that the xylose feed concentration decreased slowly during the prolonged recycling period, the pseudo-steady state was therefore achieved. By relating outlet and inlet xylose contents in liquid flow of the reactor, the reaction results varied with xylose feed concentration were simulated. The coefficients of the two reactants, hydrogen and xylose, were correlated simultaneously with a steady state reaction model. The estimated coefficients fell in the range of trickle-bed reactors at low flow rates and manifested a partial wetting status.     

Kinetic experiments and modeling of a three-phase catalytic hydrogenation reaction in supercritical CO2

The three-phase catalytic hydrogenation of an unsaturated ketone using supercritical carbon dioxide as a solvent was studied in order to simulate the performance of a semi-industrial trickle-bed reactor. High pressure kinetic experiments were carried out in a modified internal recycle reactor of Berty type. An industrial Pd on alumina supported catalyst was used, in form of egg-shell pellets. Data were collected over the whole conversion range, allowing for a thorough inspection of the reaction rate composition dependencies. It is shown that supercritical CO₂ strongly increases the reaction rate. Experimental data sets were fit using both simple homogeneous power-law kinetics and complex heterogeneous Langmuir–Hinshelwood models: here, the estimation of liquid concentrations was performed through vapor–liquid equilibrium calculations based on an equation-of-state approach.     

2-氧代-4-苯基丁酸乙酯不对称加氢滴流床反应器模型

研究了滴流床反应器中2-氧代-4-苯基丁酸乙酯在10,11-二氢辛可尼定修饰的Pt/A l2O3作用下不对称催化加氢反应特征,实验在4个不同催化床层中进行。考虑催化剂部分润湿和静、动持液量,结合复杂的传质和反应过程,建立了不对称催化加氢滴流床反应器模型。在本征动力学研究的基础上,用模型模拟了滴流床中反应物和产物沿反应器轴向的浓度分布,并对不同操作条件下不对称加氢反应的转化率和光学收率进行了预测,与实验数据比较一致,表明此反应器模型对非均相不对称催化反应的工程化有重要的指导意义。     

Heat transfer characterization of gas-liquid flows in a trickle-bed

Instantaneous local fluid-solid heat transfer coefficient (h_t) in a laboratory scale trickle-bed was measured using a constant-voltage anemometry technique. It was observed that convective heat transfer rate in the liquid-rich pulses was approximately 4 times that in gas-continuous bases for the air-water system. Time-averaged heat transfer rate was found to be positively influenced by both gas and liquid flow rates, with a stronger dependence on the latter. Heat removal efficiency, taking pressure drop penalty into account, suggested an optimum at intermediate liquid flow rate. Based on the measurements, a four-parameter heat transfer model featuring heat transfer coefficients in liquid-rich pulses (h_tp) and gas-continuous bases (h_tb), pulsing frequency and pulse fraction was developed to characterize transient h_t under various flow regimes. This model can be used in any trickle-bed reactor simulation that accounts for the dynamic interactions of catalytic reactions and heat transfer. It was found that while h_tp and h_tb correspond to liquid-solid and gas-solid heat transfer, respectively, and are determined mainly by the fluid properties, pulsing frequency and pulse fraction are the factors characterizing different flow regimes. Pulsing frequency, which can significantly impact reaction, may be tuned by selecting appropriate packing size, since smaller sizes generate higher frequency pulses. For example, a two-fold higher frequency was detected in packing as compared to that with packing. Flow regime evolution along the column axial location was identified visually, while the dispersed bubbling flow retreating to pulsing flow owing to gas bubble coalescence was evidenced by the heat transfer measurements.     

Nonlinear inferential control for an exothermic packed-bed reactor: geometric approaches

This article deals with the low-order output regulator designs for a commercial-scale packed-bed reactor. Under the static interpolation-based technique for data reconciliation mechanism, the optimum-based two-input control scheme by exploiting the secondary output information can almost attenuate measurable disturbances on the primary output. The steady-state approach not only reduces the critical hot spot and/or thermal runaway but it also dominates the desirable conversion rate in the exit. Moreover, the piece-wise iterative procedure connected with feasible programming evolution for control computation is proposed such that the flexible output regulator with the aid of the ‘intelligent’ algorithm can effectively improve the transient performance. Simulation results have shown that the non-distributed, piece-wise feedback control scheme turns out to be robust against unknown perturbations.     

Experimental studies of nitrobenzene hydrogenation in a microstructured falling film reactor

Nitrobenzene hydrogenation over palladium catalyst was performed in a microstructured falling film reactor at a range of flowrates (0.5-3 ml/min) and pressure (1-6 bar). Confocal microscopy was used to measure liquid film thickness. Comparison with film thickness prediction equations showed an overprediction of 10-30%. The k_La of this system was estimated to be 3-8 s⁻¹ with interfacial surface area per reaction volume 9000-15000 m²/m³. Conversion was found to be affected by both liquid flowrate and hydrogen pressure, and the reactor operated between the kinetic and mass transfer controlled regimes.     

硝基化物催化加氢及其催化剂开发进展

介绍了硝基化物催化加氢的优势及其催化剂的开发研究进展。硝基化物的催化加氢技术研究关键在于催化剂研究开发,主要催化剂的发展大都围绕自身的优势与不足展开,当前研究重点主要集中在进一步提高该体系催化剂的催化性能,特别是催化剂的选择性与稳定性,这也是今后进一步研究的主攻方向。     

三相浆态床汽油烯烃加氢及反应动力学

烯烃含量是考察汽油优劣的重要指标之一。实验采用三相浆态床反应器进行烯烃加氢反应,选取1-辛烯为烯烃代表物。结果表明,1-辛烯转化率随着反应温度、压力的升高而增大。1-辛烯在40～80℃,0.5～1.5 MPa的条件下,其转化率最高可达99%,90#汽油与1-辛烯混合物在80～100℃,2.0～3.0 MPa的条件下,1-辛烯转化率最高为35%,采用马夸特和改进遗传算法,根据实验数据进行参数拟合,得到汽油中1-辛烯加氢反应的动力学模型。1-辛烯和氢气的反应级数分别为0.99和1.412,反应活化能为59 255 J/mol-1。