Mass transfer‐limited wet oxidation of phenol

Catalytic wet oxidation carried out in a continual three‐phase trickle‐bed reactor contributes to the sustainability of chemical technology. It was found that the hydrodynamics and the mass‐transfer of reactants could have a significant impact on the performance of the trickle‐bed reactor. An aqueous phenol oxidation was tested at different temperatures and liquid feed rates and the activities of both the CuO‐supported catalyst and the extruded active carbon were compared. To avoid the impact of liquid maldistribution, a bed of catalyst particles diluted with fine glass spheres was also used. Rate‐limited conditions of both liquid‐ and gas‐phase presented reactants were determined. Under the conditions of gas component transfer limitation, a better wetting of the diluted catalyst bed can lead to a worsening in the reactor performance due to the lower overall reaction rates. © 2001 Society of Chemical Industry     

Solar gasification of carbonaceous waste feedstocks in a packed‐bed reactor—Dynamic modeling and experimental validation

Thermochemical gasification of carbonaceous waste feedstocks (specifically: scrap tire powder, industrial sludge, and sewage sludge) for high‐quality syngas production is numerically modeled and experimentally validated using concentrated solar process heat. The solar reactor consists of two cavities separated by a radiant emitter, with the upper one serving as the solar radiative absorber and the lower one containing the reacting packed bed. The reactor is modeled by considering combined heat transfer coupled to the reaction kinetics, driven by the applied solar flux at the reactor's aperture. Model validation is accomplished in terms of converted mass, reactor temperatures, efficiency, and solar upgrade based on experiments with an 8‐kW reactor subjected to solar fluxes up to 2560 suns and packed bed temperatures up to 1490 K. The transient operation of a 200‐kW pilot‐scale reactor for gasifying industrial sludge is simulated for a solar day, yielding a maximum solar‐to‐fuel energy conversion efficiency of 89%. © 2011 American Institute of Chemical Engineers AIChE J, 2011     

Catalytic wet air oxidation of phenol using active carbon: performance of discontinuous and continuous reactors

Catalytic wet air oxidation (CWAO) of an aqueous phenol solution using active carbon (AC) as catalytic material was compared for a slurry and trickle bed reactor. Semi‐batchwise experiments were carried out in a slurry reactor in the absence of external and internal mass transfer. Trickle‐bed runs were conducted under the same conditions of temperature and pressure. Experimental results from the slurry reactor study showed that the phenol removal rate significantly increased with temperature and phenol concentration, whereas partial oxygen pressure had little effect. Thus, at conditions of 160 °C and 0.71 MPa of oxygen partial pressure, almost complete phenol elimination was achieved within 2 h for an initial phenol concentration of 2.5 g dm^?3. Under the same conditions of temperature and pressure, the slurry reactor performed at much higher initial rates with respect to phenol removal than the trickle bed reactor, both for a fresh active carbon and an aged active carbon, previously used for 50 h in the trickle bed reactor, but mineralisation was found to be much lower in the slurry reactor. Mass transfer limitations, ineffective catalyst wetting or preferential flow in the trickle bed alone cannot explain the drastic difference in the phenol removal rate. It is likely that the slurry system also greatly favours the formation of condensation polymers followed by their irreversible adsorption onto the AC surface, thereby progressively preventing the phenol molecules to be oxidised. Thus, the application of this type of reactor in CWAO has to be seriously questioned when aiming at complete mineralisation of phenol. Furthermore, any kinetic study of phenol oxidation conducted in a batch slurry reactor may not be useful for the design and scale‐up of a continuous trickle bed reactor. © 2001 Society of Chemical Industry     

Dynamics of a solar thermochemical reactor for steam-reforming of methane

A nonlinear dynamic model is developed for a steam/methane-reforming reactor that uses concentrated solar radiation as the source of high-temperature process heat. The model incorporates a set of lumped-parameter reservoirs for mass and energy. For each reservoir, the unsteady mass and energy conservation equations are formulated, which couple conduction, convection, and radiation heat transfer with the temperature dependent chemical conversion. Radiative exchange, the dominant heat transfer mode at above 800 K, is solved by a band-approximation Monte Carlo technique. The dynamic model is applied to predict the transient behavior of a 400 kW prototype solar reformer in operational modes of purging, thermal testing, startup, chemical reaction, shutdown, and cyclical operation. Time constants vary between 2 s for species transport and for thermal energy transport through ceramic insulation. Validation is accomplished by comparing modeled and experimentally measured outlet gas temperatures obtained from reactor tests in a solar tower facility.     

HYDROGENATION OF 1,5-CYCLOOCTADIENE IN A TRICKLE BED REACTOR ACCOMPANIED BY PHASE TRANSITION

This paper examined the evaporation and condensation of the reaction mixture within the trickle bed reactor during 1,5-cyclooctadiene hydrogenation. The aim of study has been to formulate a mathematical model of heat and mass transfer influenced the exothermic reaction of a volatile reaction mixture apt to evaporation by the reaction heat in the system which is often accompanied by a hot spot temperature formation in the reactor followed by the enhancement of undesirable side reactions and/or catalyst deactivation. The numerical solution of the proposed model agreed quite well with the experimental temperature profiles in the trickle bed reactor.     

Optimal operation of a membrane reactor network

In this contribution, the operation of a membrane reactor network (MRN) for the oxidative coupling of methane is optimized. Therefore, three reactors, a fixed bed reactor (FBR) and two packed bed‐membrane reactors, are modeled. For the (CPBMR), a two‐dimensional (2‐D) model is presented. This model incorporates radial diffusion and thermal conduction. In addition, two 10 cm long cooling segments for the CPBMR are implemented based on the idea of a fixed cooling temperature positioned outside the reactor shell. The model is discretized using a newly developed 2‐D orthogonal collocation on finite elements with a combination of Hermite for the radial and Lagrangian polynomials for the axial coordinate. Membrane thickness, feed compositions, temperatures at the inlet and for the cooling, diameters, and the amount of inert packing in the reactors are considered as decision variables. The optimization results in C₂ yields of up to 40% with a selectivity in C₂ products of more than 60%. The MRN consisting of an additional packed‐bed membrane reactor with an alternative feeding policy and a FBR shows a lower yield than the individual CPBMR. © 2013 American Institute of Chemical Engineers AIChE J, 60: 170–180, 2014     

Heat transfer model of a solar receiver-reactor for the thermal dissociation of ZnO—Experimental validation at 10 kW and scale-up to 1 MW

A transient heat transfer model is developed for analyzing the thermal performance of a thermochemical reactor for the solar-driven dissociation of ZnO in the 1600–2136 K range. The reactor consists of a rotating cavity-receiver lined with ZnO particles that are directly exposed to concentrated solar radiation. The model couples radiation, convection, and conduction heat transfer to the reaction kinetics for a shrinking domain and simulates a transient ablation regime with semi-batch feed cycles of ZnO particles. Validation is accomplished in terms of the numerically calculated and experimentally measured temperature profiles and reaction extents for a 10 kW reactor prototype tested in a high-flux solar simulator and subjected to peak solar concentration ratios exceeding 5000 suns. Scaling-up the reactor technology to 1 MW solar thermal power input has the potential of reaching a solar-to-chemical energy conversion efficiency of 56%.     

A packed‐bed solar reactor for the carbothermal zinc production – dynamic modelling and experimental validation

Integration of concentrated solar energy into the pyrometallurgical Zn production process as clean source of high‐temperature process heat could significantly reduce fossil fuels consumption and its concomitant CO₂ emissions. The solar‐driven carbothermal reduction of ZnO is investigated using a 10‐kW_th solar reactor featuring two cavities, the upper one serving as the solar absorber and the lower one containing a packed‐bed of ZnO and beech charcoal as the biogenic reducing agent. Experimentation in a high‐flux solar simulator is carried out under radiative fluxes of 2300–2890 suns, yielding a peak solar‐to‐chemical energy conversion efficiency of 18.4%. The reactor performance under variable operating conditions is analyzed via a dynamic numerical model coupling heat transfer with chemical kinetics. The model is validated by comparison to the experimental data obtained with the 10‐kW_th packed‐bed solar reactor and further applied to predict the effect of incorporating semi‐continuous feeding of reactants on the process efficiency. © 2016 American Institute of Chemical Engineers AIChE J, 62: 4586–4594, 2016     

Continuous‐Flow Di‐N‐Alkylation of 1H‐Benzimidazole in a Fixed‐Bed Reactor

A new process for a continuous‐flow di‐N‐alkylation of 1H‐benzimidazole to 1H‐benzimidazole‐3‐ium iodide by methylene iodide in the presence of potassium carbonate in a fixed‐bed reactor is presented. The synthesis was transferred from batch to continuous operation with similar yields and conversion rates. Moreover, the influence of temperature and residence time in the continuous flow setup was characterized; optimized conditions led to a doubling of yield. In addition, the continuous flow allowed for a better control of the two‐step reaction by adding an additional tube reactor after the fixed bed that further enhanced the overall performance. With this, the continuous‐flow system presented itself as superior due to higher available temperatures and a better controllability.     

Radiation Matters in Fixed‐Bed CFD Simulations

Fixed‐bed reactors often operate at elevated temperatures, where radiation can be a significant heat‐transfer mechanism. Particle‐resolved CFD models fixed‐bed reactors on a very detailed macroscopic level. In this study, the contribution of radiative heat transfer is investigated in a 500‐mm bed of 7‐hole pellets. At industrially relevant temperatures (250 – 800 °C) and with a steam‐reforming gas‐phase mixture, the S2S and DOM radiation models were applied. Neglecting radiation results in temperatures being up to 6 % lower. In this case, the main driver is surface‐to‐surface (S2S) radiation. Additional modeling recommendations are given.     

Parallel hydrogenation for the quantification of wetting efficiency and liquid–solid mass transfer in a trickle‐bed reactor

A novel method for the measurement of wetting efficiency in a trickle‐bed reactor under reaction conditions is introduced. The method exploits reaction rate differences of two first‐order liquid‐limited reactions occurring in parallel, to infer wetting efficiencies without any other knowledge of the reaction kinetics or external mass transfer characteristics. Using the hydrogenation of linear‐ and isooctenes, wetting efficiency is measured in a 50‐mm internal diameter, high‐pressure trickle‐bed reactor. Liquid–solid mass transfer coefficients are also estimated from the experimental conversion data. Measurements were performed for upflow operation and two literature‐defined boundaries of hydrodynamic multiplicity in trickle flow. Hydrodynamic multiplicity in trickle flow gave rise to as much as 10% variation in wetting efficiency, and 10–20% variation in the specific liquid–solid mass transfer coefficient. Conversions for upflow operation were significantly higher in trickle‐flow operation, because of complete wetting and better liquid–solid mass transfer characteristics. © 2010 American Institute of Chemical Engineers AIChE J, 2011.     

Trickle bed reactor diluted with fine particles and coiled tubular flow-type reactor for kinetic measurements without external effects

Gas and liquid velocities in laboratory scale trickle bed reactors are one or two orders of magnitude lower than those in commercial reactors. Then, the kinetic data may include the external effects. This shortcoming of laboratory scale trickle bed reactor can be resolved by diluting the catalyst bed with fine inert particles. The catalyst bed dilution increases dynamic liquid holdup, pressure drop, gas–liquid mass transfer coefficient. Hydrogenation of 2-phenylpropene on Pd/Al₂O₃ was performed with the trickle bed reactor diluted with fine inert particles and the coiled tubular flow-type reactor to compare the kinetics with that of the basket type batch reactor. The trickle bed reactor diluted with fine inert particles is suitable to obtain the reaction rate without external effects even if the liquid velocity is low. The coiled tubular flow-type reactor should be used at high gas velocities.     

基于金属氢化物高温蓄热的氢热耦合传递机理

目前大多数可再生能源如太阳能具有间歇性和不稳定性的问题,因此高效蓄热技术成为了发展太阳能的一个关键途径。金属氢化物高温蓄热技术作为热化学蓄热中最有前途的方法之一,受到了人们的广泛关注。为了实现金属氢化物高温蓄热技术的工程应用,明确其氢热耦合传递机理至关重要。本研究采用数值模拟的方法,通过建立反应器的多物理场耦合模型,讨论了不同时刻下床层内部参数的分布,得到了反应锋面的形成和移动机理以及非均匀反应的形成机理;此外,结合反应器内部氢压、接触热阻和床层热阻的变化规律,明确了不同阶段下金属氢化物高温蓄热技术的控制环节;最后,依据金属氢化物高温蓄热技术的工程应用挑战,提出了相应的研究策略。     

多段滴流床中苯酚丙酮缩合反应分离新工艺

<正> 引言 双酚A(BPA)是制造聚碳酸酯、聚砜及改性酚醛树脂等的重要中间体.工业上BPA均由苯酚和丙酮在酸性催化剂作用下缩合而成.其反应式为     

Influence of ash agglomerating fluidized bed reactor scale‐up on coal gasification characteristics

To study the influence of fluidized‐bed reactor scale‐up on coal gasification characteristics, a model of the ash agglomerating fluidized‐bed reactor has been developed using an equivalent reactor network method. With the reactor network model, the scale‐up effects of a gasifier were studied in terms of the characteristics of the chemical reactions in the jet zone, the annulus dense‐phase zone and the freeboard zone. Results showed that the changes occurred in the inequality proportion of the volume of the jet zone during the reactor scale‐up. Taking into consideration the utilization of a portion of the backflow gas, the expansion of the jet zone volume and the coal particle residence time, the temperature of the jet zone was increased from 1592 to 1662 K. Also, both the annulus dense‐phase zone temperature and the freeboard zone temperature decreased, causing subsequent decrease in the carbon conversion efficiency. © 2014 American Institute of Chemical Engineers AIChE J, 60: 1821–1829, 2014     

Hydrodynamics in a pilot‐scale cocurrent trickle‐bed reactor at low gas velocities

Hydrodynamic data obtained from laboratory‐scale trickle‐beds often fail to accurately represent industrial‐scale systems with high packing aspect ratios and column‐to‐particle diameter ratios. In this study, pressure drop, liquid holdup, and flow regime transition were investigated in a pilot‐scale trickle‐bed column of 33 cm ID and 2.45 m bed height packed with 1.6 mm × 8.4 ± 1.4 mm cylindrical extrudates for air‐water mass superficial velocities of 0.0023 – 0.094 kg/m²s and 4.5 – 45 kg/m²s, respectively, at atmospheric pressure. Significant deviation was observed from pressure drop and liquid holdup correlations at low liquid flows rates, corresponding to gravity‐driven flow limit. Likewise, liquid saturation is overestimated by correlations at high liquid flow rates, owing to significantly reduced wall effects. Lastly, trickle‐to‐dispersed bubble flow and trickle‐to‐pulsing flow regime transitions are reported using a combination of visual observations and analysis of the magnitude of local pressure fluctuations within the column. © 2018 American Institute of Chemical Engineers AIChE J, 64: 2560–2569, 2018     

Simulation of biomass char gasification in a downdraft reactor for syngas production

A steady state, one‐dimensional computational fluid dynamics model of wood char gasification in a downdraft reactor is presented. The model is not only based on reaction kinetics and fluid flow in the porous char bed but also on equations of heat and mass conservation. An original OpenFOAM solver is used to simulate the model and the results are found to be in good agreement with published experimental data. Next, a sensitivity analysis is performed to study the influence of reactor inlet temperature and gas composition on char conversion, bed temperature profile and syngas composition. In addition, the evolution of the complex reaction mechanisms involved in mixed atmosphere gasification is investigated, and the most suitable operating parameters for controlling syngas composition are evaluated. Our simulation results provide essential knowledge for optimizing the design and operation of downdraft gasifiers to produce syngas that meets the requirements of various biofuel applications. © 2015 American Institute of Chemical Engineers AIChE J, 62: 1079–1091, 2016     

A bubbling fluidized bed solar reactor model of biomass char high temperature steam-only gasification

A two phase biomass char (biochar) steam gasification model based on the systems kinetics is developed in a bubbling fluidized bed with concentrated solar heat as source of energy. The model calculates the dynamic and steady state profiles, as well as the complex parameters of fluidized beds. This robust model is capable of predicting the temperature and concentration profiles of gases in the bubble, emulsion gas and solid phases. The Rosseland equation is used to calculate the radiative transfer within the bed. Due to the nature of the fluidized bed, the small bed thermal conductivity and bigger void between particles, there is a large temperature gradient throughout the bed, indicating that the system is highly non-isothermal. The set-up of a fluidized bed with solar irradiation in the upper side of the reactor is found to be a less efficient gasifying system in comparison with a packed bed, but could be optimized if the source of heat is changed to the bottom of the reactor. The trends and responses of the model are in good agreement with the experimental trends reported in the literature. Hydrogen is the principal product followed by carbon monoxide, the carbon dioxide production is small and the methane production is negligible.     

What is the leanest stream to sustain a nonadiabatic loop reactor: Analysis and methane combustion experiments

While previous studies experimentally demonstrated that loop reactor (LR) can be sustained with a lean feed (using ethylene combustion) and have analyzed the single‐reaction adiabatic case, this work analyzes the effects of heat loss and of reactor size to determine the leanest stream (expressed in terms of adiabatic temperature rise ΔT_lim) that will sustain the operation. For an adiabatic infinitely long reactor ΔT_lim→0 while for a finite reactor ΔT_lim scales as (1 + Pe/4)^?1 where Pe = Luρc_pf/k, and heat loss increases this limit by (β/Pe)^1/2. Thus, a good design of a LR will aim to decrease conductivity (k) and radial heat‐transfer coefficient (β) while increasing throughput (u) and reactor length. This article is also the first experimental demonstration of auto‐thermal operation in a LR for catalytic abatement of low‐concentration of methane, showing the leanest stream to be of 8000 ppm vs. 33,000 ppm in a once‐through reactor. Experimental combustion results of methane and of ethylene are compared with model predictions. © 2016 American Institute of Chemical Engineers AIChE J, 63: 2030–2042, 2017     

CO2 methanation: Optimal start‐up control of a fixed‐bed reactor for power‐to‐gas applications

Utilizing volatile renewable energy sources (e.g., solar, wind) for chemical production systems requires a deeper understanding of their dynamic operation modes. Taking the example of a methanation reactor in the context of power‐to‐gas applications, a dynamic optimization approach is used to identify control trajectories for a time optimal reactor start‐up avoiding distinct hot spot formation. For the optimization, we develop a dynamic, two‐dimensional model of a fixed‐bed tube reactor for carbon dioxide methanation which is based on the reaction scheme of the underlying exothermic Sabatier reaction mechanism. While controlling dynamic hot spot formation inside the catalyst bed, we prove the applicability of our methodology and investigate the feasibility of dynamic carbon dioxide methanation. © 2016 American Institute of Chemical Engineers AIChE J, 63: 23–31, 2017