Catalyst Residence Time Research Articles

Fluid dynamics and erosion analysis in industrial naphtha reforming: A CFD-DPM simulation approach

This paper explores using Computational Fluid Dynamics-Discrete Phase Model simulation in an industrial naphtha reforming unit. It analyzes the reformer process, including the reformer, hopper, and three elbow types. Objectives encompass catalyst residence time, fluid flow, and erosion due to the catalyst in these geometries. Simulation results unveil insights, showing varying erosion rates among the elbows. The 90-degree elbow has the highest erosion rate 4.42×10−8kgm2s, followed by the 60-degree elbow3.49×10−8kgm2s, and the 45-degree elbow with lower erosion rate 2.65×10−8kgm2s. Results align with literature, emphasizing flow dynamics' role in optimization and maintenance. The study validates simulation with only 1.58% deviation from plant data, highlighting model's precision. Catalyst residence time is 1.28 s. Erosion patterns in the hopper pinpoint high-density zones as erosion-prone areas, guiding preventive measures. This research enhances continuous catalytic reformer systems' efficiency and integrity, aiding decisions for design and maintenance, ultimately improving overall process efficiency and stability.

Research on ultrafast catalytic degradation of heterocyclic compounds by the novel high entropy catalyst

Traditional refractory wastewater treatment methods have problems of low efficiency, high cost and many by-products, so it is of great significance to develop new high-efficiency refractory wastewater treatment technology. Heterogeneous catalysts were used in the catalytic ultrafast oxidation (CUFO) process to treat textile dyeing wastewater with refractory heterocyclic compounds. Composite catalysts with varying entropies were synthesized by the ultrasonic dispersion-annealing method. The high entropy catalysts exhibited superior catalytic activity and stability compared to other catalysts. Furthermore, the impact of reaction temperature (T, 350–390 °C), residence time (t, 3–17 min), oxidation coefficient (OC, 2.1–2.9), and entropy of catalyst on the COD removal were assessed. An increase in entropy of catalyst resulted in a significant enhancement of COD removal rate. At T = 390 °C and OC = 2.90, the high entropy oxides catalyst achieved the COD removal rate of 93.95 % after the 7 min reaction. Additionally, a catalytic reaction mechanism involving the CeMnCuOx solid solution heterostructure with domino catalytic ability was proposed. Overall, the results suggest that catalytic ultrafast oxidation technology is a promising option for efficiently treating refractory organic pollutants.

Green Synthesis of 3-Hydroxybutyraldehyde from Acetaldehyde Catalyzed by La-Ca-Modified MgO/Al2O3

3-hydroxybutyraldehyde (3-HBA) is mainly employed to synthesize 1,3-BDO (1,3-butanediol), which is one of the most important components in cosmetics moisturizers. In this study, a series of composite oxide catalysts were prepared by bringing alkaline earth metal Ca and rare earth metal La to the composite oxide MgO/Al2O3, which were made through the co-precipitation method. These catalysts were applied in the synthesis of 3-HBA through acetaldehyde (AcH) condensation. The structure, texture, and acidic properties of these catalysts were characterized using various characterization methods, and the effects of catalyst composition, reaction temperature, reaction pressure, and residence time on the conversion of AcH were investigated as well. The results showed that the introduction of Ca and La weakened the acidic property and enhanced the basic property, which favored the AcH condensation to synthesize 3-HBA. At a temperature of 20 °C, pressure of 200 kPa, and residence time of 70 min, 0.5%La-2.3%Ca-2MgO/Al2O3 exhibited a better catalytic activity, and the conversion of AcH reached 95.89%. The selectivity and yield of 3-HBA were 92.08% and 88.30%, respectively. The stability test indicated that the high AcH conversion could be maintained for 5 h.

Determination of Catalyst Residence Time, Heat Generation, and Monomer Conversion via Process Variables during Propylene Polymerization by a Mathematical Model

Because of the inherent complexity of a Ziegler–Natta catalyst, its performance during propylene polymerization against the particular process variables, namely, the reaction temperature and hydrogen amounts, so far remains unclear. Obviously, these process variables directly affect the catalyst residence time, monomer conversion, and heat generation. Understanding these issues is essential for those working in the field such as catalyst chemists, polymer scientists, process engineers, designers, and producer licensors. The main aim of this work is to cover the existing gap in this field by proposing a mathematical kinetics model. The modeling approach is based on the polymer moment balance technique and validated via experimental data from a lab-scale reactor. The results of this study showed that the model has achieved the defined aims properly. Two significant conclusions were obtained. Firstly, only temperature increase has a significant effect on the conversion percent increase and hydrogen has no effect on it. Secondly, hydrogen not only increases the rate of polymerization, but also raises the deactivation constant and reduces the lifetime of the catalyst.

Study of Catalyst Coke Distribution Based on Population Balance Theory: Application to Methanol to Olefins Process

A coke distribution model of catalyst particles in three‐dimensional space was developed based on population balance theory, and an analytic expression of coke distribution for zero‐dimensional time‐independent problem was deduced. The expression shows that the coke distribution is determined by the average catalyst residence time, coke deposition (or burning) rate, and coke distribution of catalyst inflow. The coke distribution model was further applied to the methanol to olefins (MTO) process. The critical factors influencing coke distribution in MTO process, as well as the effect of coke distribution on product selectivity, were investigated. Three scales of MTO fluidized bed reactor–regenerator systems, i.e., pilot‐scale, demonstration‐scale and commercial‐scale with the reactor diameter of 0.261, 1.25, and 10.5 m, respectively, were simulated. The simulated results were in good agreement with the operation data. The model could be helpful in the operation optimization and reactor design. © 2018 American Institute of Chemical Engineers AIChE J, 65: 1149–1161, 2019

Understanding substrate substituent effects to improve catalytic efficiency in the SABRE hyperpolarisation process.

The use of parahydrogen based hyperpolarisation in NMR is becoming more widespread due to the rapidly expanding range of suitable target molecules and low-cost of parahydrogen production. Hyperpolarisation via SABRE catalysis employs a metal complex to transfer polarisation from parahydrogen into a substrate whilst they are bound. In this paper we present a quantitative study of substrate-iridium ligation effects by reference to the substrates 4-chloropyridine (A), 4-pyridinecarboxaldehyde methyl hemiacetal (B), 4-methylpyridine (C) and 4-methoxypyridine (D), and evaluate the role they play in the SABRE catalysis. Substrates whose substituents enable stronger associations yield slower substrate dissociation rates (k d). A series of variable temperature studies link these exchange rates to optimal SABRE performance and reveal the critical impact of NMR relaxation times (T 1). Longer catalyst residence times are shown to result in shorter substrate T 1 values in solution as binding to iridium promotes relaxation thereby not only reducing SABRE efficiency but decreasing the overall level of achieved hyperpolarisation. Based on these data, a route to achieve more optimal SABRE performance is defined.

Study of the coke distribution in MTO fluidized bed reactor with MP‐PIC approach

AbstractThe methanol to olefins (MTO) process has received considerable interest due to its importance in transforming abundant resources such as coal, natural gas, and biomass to widely‐demanded light olefins. In the MTO process, the coke deposited on the catalyst governs the catalyst activity and product selectivity, and thus is critical to the reaction behaviour. In the industrial processes, the residence time and coke content of catalyst particles in the reactor show a certain distribution due to the continuous outflow of spent catalyst and inflow of regenerated catalyst, which need further attention. The multi‐phase particle‐in‐cell (MP‐PIC) approach was used in the current work to simulate the catalyst residence time and coke content distribution. The effect of gas‐solid flow patterns, reactor structure, and average catalyst residence time on the residence time and coke content distribution was investigated. It was found that at high superficial velocities, the coke content distributions obtained with the MP‐PIC method are consistent with the distribution deduced from the ideally mixed flow assumption of catalyst particles. The results suggested that it is possible to simulate large‐scale MTO reactors by use of the coke distribution. In particular, by incorporating an initial coke distribution, the time needed to reach steady state in the MTO reactor simulations could be greatly reduced.

Hydrogen production by catalytic partial oxidation of propane over CeO2

A kinetic experimental study of the catalytic partial oxidation of propane was performed in an isothermal “catalytic jet stirred reactor” which has the ability to modify the ratio of the catalyst surface to the gas volume. The main goal of this study was to elucidate the detailed heterogeneous-homogeneous mechanism of this reaction and explore the capacity to produce H2. The catalyst used in this study was pellets of cerium oxide CeO2. Various operating parameters were considered: temperature, residence time, contact time and amount of catalyst. A hetero-homogeneous mechanism, composed of 71 elementary steps at the catalyst surface and 937 homogeneous gas phase reactions is proposed and validated by comparison between experimental results and simulated results over a large range of temperatures (200 < T < 800 °C), residence times (2 < τ < 6 s), number of catalyst pellets (0–8). The interactions between gas phase reactions and surface reactions are discussed.

Influence of Riser Length of a Fluid Catalytic Cracking Pilot Plant on Catalyst Residence Time and Product Selectivity

The design and operation of a circulating fluid catalytic cracking (FCC) riser pilot plant is presented in the paper. Emphasis is given on the effect of riser length on feedstock conversion and coke yield. Riser lengths considered in the study were 1.46 and 9.95 m. The effect of catalyst residence time on feedstock conversion and coke yield at constant feed rate and reactor temperature (526 °C) is presented. The catalyst residence time varies with reactor volume and catalyst circulation rate. It is shown that for the same feed conversion, high catalyst circulation rates are required with the lower riser volume. Lower gasoline and lower coke yields are experimentally observed with the short riser length. A second-order kinetic model is used to correlate the variation in conversion and coke yield. Commercial results validate the pilot plant design as a useful tool for guiding commercial operations.

Catalyst Residence Time Distributions in Riser Reactors for Catalytic Fast Pyrolysis. Part 2: Pilot-Scale Simulations and Operational Parameter Study

Using the validated simulation model developed in part one of this study for biomass catalytic fast pyrolysis (CFP), we assess the functional utility of using this validated model to assist in the development of CFP processes in fluidized catalytic cracking (FCC) reactors to a commercially viable state. Specifically, we examine the effects of mass flow rates, boundary conditions (BCs), pyrolysis vapor molecular weight variation, and the impact of the chemical cracking kinetics on the catalyst residence times. The factors that had the largest impact on the catalyst residence time included the feed stock molecular weight and the degree of chemical cracking as controlled by the catalyst activity. Because FCC reactors have primarily been developed and utilized for petroleum cracking, we perform a comparison analysis of CFP with petroleum and show that the operating regimes are fundamentally different.

Predictive Model for Particle Residence Time Distributions in Riser Reactors. Part 1: Model Development and Validation

In this computational study, we model the mixing of biomass pyrolysis vapor with a solid catalyst in circulating riser reactors with a focus on the determination of solid catalyst residence time distributions (RTDs). A comprehensive set of 2D and 3D simulations were conducted for a pilot-scale riser using the Eulerian–Eulerian two-fluid modeling framework with and without subgrid-scale models for the gas–solid interaction. A validation test case was also simulated and compared to experiments, showing agreement in the pressure gradient and RTD mean and spread. For simulation cases, it was found that for accurate RTD prediction, the Johnson and Jackson partial slip solid boundary condition was required for all models, and a subgrid model is useful so that ultra high resolutions grids, which are very computationally intensive, are not required. We discovered a 2/3 scaling relation for the RTD mean and spread when comparing resolved 2D simulations to validated unresolved 3D subgrid-scale model simulations.

Application of Filtered Model for Reacting Gas–Solid Flows and Optimization in a Large-Scale Methanol-to-Olefin Fluidized-Bed Reactor

A reactor model for a methanol-to-olefin (MTO) reaction system was constructed by incorporating a filtered drag model, a filtered gas–solid heat-transfer model, and an MTO kinetic model to probe large-scale reactor behavior and explore optimization. First, the efficiency of several typical gas–solid heat-transfer models and kinetic models was evaluated by comparing predicted results with experimental data. Second, the effect of two significant operation parameters, namely, reaction temperature and water-to-methanol ratio, were studied based on the above-mentioned model. Predictions suggested an optimum catalyst residence time (∼33 min) and an average coke content (∼6.74%) of this MTO system. In addition, relatively high temperature maximized ethylene production, and the water introduced into the feed significantly attenuated coke deposition. This work is the first to conduct coarse-grid simulations by using the developed effective filtered-CFD coupled model to probe the reaction flow and explore optimizat...

A binder-free fluidizable Mo/HZSM-5 catalyst for non-oxidative methane dehydroaromatization in a dual circulating fluidized bed reactor system

This work highlights the need for a two beds type of circulating fluidized bed reactor system and a binder-free fluidizable Mo/HZSM-5 catalyst for processing non-oxidative methane dehydroaromatization. Also discussed is the process optimization by varying temperature, CH4 space velocity, the height of catalyst bed and the mean catalyst residence times in a CH4 convertor and the paired catalyst regenerator for the binder-free Mo/HZSM-5. Typical profiles of CH4 conversion and benzene yield versus time obtained under continuous catalyst regeneration mode are discussed to show the high activity and stability of the binder-free catalyst as well as its high resistance towards attrition at 1073K and continuous circulation conditions. Recommendations to obtain an advanced binder-free Mo/HZAM-5 catalyst are made in improving the coking resistance, hydrogen regeneration activity and benzene formation activity of the binder-free catalyst.

The influence of the fluidization velocities on products yield and catalyst residence time in industrial risers

The hydrodynamic characteristic of the industrial riser used in the fluid catalytic cracking (FCC) process has been simulated. A gas–solid flow model was developed which describes a 3D industrial set-up. By combining the hydrodynamics with a reaction model the yields of the different product families were obtained with good precision. To represent the kinetic behavior, a twelve-lump model with catalyst deactivation was adopted to represent the kinetic behavior. A tracer technique for catalyst residence time, corresponding to different fluidization velocities, was also considered. The Eulerian–Eulerian approach was adopted and solved by ANSYS CFX 14.0. The results show predictions for fluidization velocities and residence time which should be adopted to get better product yields in the industrial process. The results are compared with data taken in an industrial plant. The model furnishes valuable information on the impact of the riser hydrodynamics on the product quality.

Highly selective synthesis of single-walled carbon nanotubes from methane in a coupled Downer-turbulent fluidized-bed reactor

For the synthesis of single-walled carbon nanotubes (SWCNTs) from CH4 over a Fe/MgO catalyst, we proposed a coupled Downer-turbulent fluidized-bed (TFB) reactor to enhance the selectivity and yield (or production rate) of SWCNTs. By controlling a very short catalyst residence time (1–3 s) in the Downer, only part of Fe oxides can be reduced to form Fe nano particles (NPs) available for the growth of SWCNTs. The percentage of unreduced Fe oxides increased and the yield of SWCNTs decreased accordingly with the increase of catalyst feeding rate in Downer. SWCNTs were preferentially grown on the catalyst surface and inhibited the sintering of the Fe crystallites which would be formed thereafter in the downstream TFB, evidenced by TEM, Raman and TGA. The coupled Downer-turbulent fluidized-bed reactor technology allowed higher selectivity and higher production rate of SWCNTs as compared to TFB alone.

Validation of a new set-up for continuous catalytic fast pyrolysis of biomass coupled with vapour phase upgrading

A fully controlled, continuously operated mini-plant has been designed and constructed based on auger reactor technology. Three types of biomass fast pyrolysis experiments were performed in this set-up, viz. non-catalytic, in situ catalytic fast pyrolysis and ex situ upgrading of non-catalytic fast pyrolysis vapours by means of a downstream, moving-bed catalytic reactor. Pine wood was selected as the reference biomass feedstock. The mini-plant enables variation of the catalyst loading and contact times while producing larger samples suitable for full characterization in continuous operation. Due to short catalyst residence times and the fact that the biomass fed to the reactor is always brought into contact with fresh catalyst (in case of in situ catalysis) or the pyrolysis vapours always contact with fresh catalyst in the moving bed catalytic reactor (in case of ex situ catalysis), catalyst deactivation and coking are prevented ensuring improved experimental repeatability in catalytic pyrolysis experiments. The performance of the system was verified by in- and ex situ application of a single type of heterogeneous ZSM-5 based acidic catalyst while the non-catalytic results were taken as reference. Catalytic fast pyrolysis results in more effective oxygen removal from the bio-oil in the form of water, and resulting in lower yields of the organic fraction. Moreover catalytic decarbonylation reactions gave rise to increased gas yields. With in- and ex situ catalysis, increases in the char yields were observed as well as coke deposition on the catalyst surface. GC×GC-FID and GC×GC-TOF-MS analysis of the produced bio-oils showed that the use of in- and ex situ catalysis causes conversion of high molecular weight compounds to lower ones. Disappearance of detectable sugars and aldehydes, a decrease of the yield of acids, formation of phenols, and favoured aromatics production were the other catalytic effects observed.

Transient Redox Activity of Vanadyl Pyrophosphate at Ambient and Elevated Pressure

Abstract The transient catalytic activity of vanadyl pyrophosphate (VPP) catalyst was studied at ambient and elevated pressure (4.1 bar) and a wide range of operating conditions. The range included the commercial operating conditions typical of fixed bed, fluidized bed and circulating fluidized beds (CFB) for the partial oxidation of n-butane to maleic anhydride (MA). The maleic anhydride yield improved by increasing the feed oxygen molar fraction, temperature and pressure. When the catalyst was cycled between an oxidizing (synthetic air) and a reducing environment; yield increased with an increase in the catalyst residence time in the oxidizing environment. This effect was more pronounced at higher pressure. At ambient pressure, MA selectivity varied between 50-73 % while it decreased to about 48-54 % at a pressure of 4.1 bar. A strong MA selectivity dependency on feed composition was observed when the oxidation time was in the range of actual industrial reactors (&lt; 1 minute). Selectivity data suggested that different oxygen species might be responsible for CO formation compared to other products such as CO2 and MA. Under oxidizing feed conditions (oxygen/n-butane ≥ than 3.7), an increase in n butane conversion was the main contributor to improved MA yield: n-butane conversion increased by about 70 % when the catalyst oxidation time extended from 0.3 to 10 minute. While, under fuel rich feed conditions, typical of industrial CFB operations, both MA selectivity and n-butane conversion contributed to enhancement in MA yield. Depending on the feed composition, MA selectivity increases by about 16-30 % and n butane conversion increases by about 32-55 % by extending the catalyst oxidation time. These results show the critical importance of catalyst oxidation time on reaction yield improvement especially when operating under fuel rich feed conditions. The surface adsorbed or surface lattice oxygen species were suggested to be the main responsible for n butane activation. While, the contribution of catalyst’s sub-surface lattice oxygen was believed to be very limited at fuel rich feed conditions. Under these conditions, catalyst over-reduction cannot be effectively compensated even after excessive catalyst regeneration and presence of gas phase oxygen is critical to maintain a high catalytic activity. As the reactor pressure increased to 4.1 bar, up to 60 % increase in n butane conversion accompanied by 100 % increase in oxygen conversion was observed. MA selectivity decreased by about 20 % on average but the increase in n-butane conversion resulted in an overall yield improvement of up to 30 %. Data show that the catalytic performance could be enhanced at certain combination of reactor pressure and temperature.

Modeling and simulation of polypropylene particle size distribution in industrial horizontal stirred bed reactors

AbstractThis work aims at developing a steady‐state particle size distribution (PSD) model for predicting the size distribution of polypropylene particles in the outflow streams of propylene gas‐phase horizontal stirred bed reactors (HSBR), on the one hand and investigating the effect of the catalyst residence time distribution (RTD) on the polymer PSD, on the other hand. The polymer multilayer model (PMLM) is used to describe the growth of a single particle. Knowing the PSD and RTD of a Ziegler–Natta type of catalyst and polymerization kinetics, this model allows calculating the polymer PSD of propylene polymerization in the HSBRs. The calculated polypropylene PSDs agree well with those obtained from the industrial reactors. The results reveal that both the PSD and the RTD of the catalyst affect the polymer PSD but in different manners. The effect of RTD on the PSD is less significant in the case of a nonuniform size catalyst feed. This model also allows investigating the effects of other process parameters on the polymer PSD under steady‐state conditions, including intraparticle mass‐ and heat‐transfer limitations, initial catalyst size, and polymer crystallinity. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Fluid catalytic cracking in a rotating fluidized bed in a static geometry: a CFD analysis accounting for the distribution of the catalyst coke content

Computational Fluid Dynamics is used to evaluate the use of a rotating fluidized bed in a static geometry for the catalytic cracking of gas oil. A Eulerian–Eulerian flow model is used in combination with the Kinetic Theory of Granular Flow. The catalytic cracking reactions are described by a 10-lump model. Catalyst deactivation by coke formation is included. To operate at low catalyst coke content, the catalyst residence time is small and the catalyst makes on average only a limited number of rotations in the reactor. Therefore, the catalyst bed cannot be considered well-mixed and a local distribution of the catalyst coke content is to be accounted for. The catalyst coke content distribution function has no pre-described functional form and is discretized. A continuity equation is then solved for each of the classes of catalyst with a given coke content. The impact of the strongly endothermic cracking reactions on the particle bed temperature uniformity is also studied.

Changes in Properties of PET/PC Blend by Catalyst and Time

The effects of the catalyst and residence time on poly(ethylene terephthalate)/polycarbonate blends (PET/PC) were studied. The Tg increased, while the Tm decreased with catalyst content and residence time as a consequence of exchange reactions during the processing. The extent of these reactions also influenced the crystal size of PET. Additionally, impact and tension properties were influenced by the level of transesterification reactions. The best value of impact was 89,7 ± 0,9 J · m for the PET/PC blend which contained 75 × 10−3 wt% of catalyst and 10 min of residence time, which represents a fourfold increase over the neat PET. Concerning elastic modulus, the best value was 60% higher than plain PET due to a higher amount of PC chains inserted in the PET. The melt flow index showed that the presence of PC enhanced the thermal stability of PET due to the formation of PET/PC copolymers.