Propane Dehydrogenation Process Research Articles

Modeling and Simulation Study of an Industrial Radial Moving Bed Reactor for Propane Dehydrogenation Process

Abstract An accurate model is required to optimize the propane dehydrogenation reaction carried out in the radial moving bed reactors (RMBR). The present study modeled the RMBR using a plug flow reactor model incorporated with kinetic models expressed in simple power-law model. Catalyst activity and coke formation were also considered. The model was solved numerically by discretizing the RMBR in axial and radial directions. The optimized kinetic parameters were then used to predict the trends of propane conversion, temperature, catalyst activity and coke content in the RMBR along axial and radial directions. It was found that the predicted activation energies of the propane dehydrogenation, propane cracking and ethylene hydrogenation were in reasonable agreement with the experimental values reported in the literature. The model developed has accurately predicted the reaction temperature profile, conversion profile and catalyst coke content. The deviations of these simulated results from the plant data were less than 5%.

Investigation of Pd-based membranes in propane dehydrogenation (PDH) processes

Pd-based membranes have potential applicability in the PDH process to selectively remove hydrogen. In the current work, H2 flux values and coke formation kinetics applying representative gaseous feed mixtures under varying operating conditions are evaluated and modelled. From these experiments, it is clear that coke formation is very likely under the operating conditions required for an integrated catalyst and membrane system, i.e. temperatures of 450–500°C and low hydrogen to propene ratios. However, coking could be limited at lower operating temperatures, and a decrease to at least 300°C, or preferably, to 250°C is required to obtain a sufficiently stable membrane operation in the conditions observed in a non-integrated sequential reactor-membrane process design. In the sequential reactor-membrane process, the effect of steam content on catalyst and membrane activity and stability were investigated. Results show that steam is required to obtain good catalyst stability, but that the amount of produced H2 is independent on steam content between 7% and 20%. A stable membrane performance is obtained at 200°C at hydrogen recovery factor (HRF) values varying from 38% to 50%. The developed model of membrane deactivation capitalizes on the observations of a critical H/C ratio beyond which the H2 flux is stable, at a given temperature, and similarly a critical temperature at a given H/C ratio that limit the coking process. The model fits these critical ratios and predicts well the temporal behaviour.

Catalytic propane dehydrogenation: Advanced strategies for the analysis and design of moving bed reactors

A moving bed reactor (MBR) is one of the most innovative reactors that are commonly used in industry nowadays. However, the modeling and optimization of the reactor have been rarely performed at conceptual design stage due to its complexity of design, and it has resulted in increased capital and operating costs of the overall chemical processes. In this work, advanced strategies were introduced to model an MBR and its regenerator mathematically, incorporating catalyst deactivation, such as coke formation. Various reactor designs and operating parameters of the MBR were optimized to increase the overall reactor performance, such as conversion or selectivity of the main products across the reactor operating period. These optimization parameters include: (1) reactant flow inside a reactor, (2) various networks of MBRs, (3) temperature of the feed stream, (4) intermediate heating or cooling duties, (5) residence time of the catalyst or velocity of catalyst flow, and (6) flow rate of the fresh make-up catalyst. The propane dehydrogenation process was used as a case study, and the results showed the possibility of significant increase of reactor performance through optimization of the above parameters. For optimization, the simulated annealing (SA) algorithm was incorporated into the reactor modeling. This approach can be easily applied to other reaction processes in industry.

Hierarchical SAPO-34 catalytic support for superior selectivity toward propylene in propane dehydrogenation process

SAPO-34 molecular sieve with tuned hierarchical structure was synthesized and used as the catalytic support for propane dehydrogenation (PDH) reaction to receive propylene with high selectivity. Synthesized material was characterized by XRD, FESEM, BET, ICP, FT-IR and TPO techniques. The Pt-Sn/SAPO-34 (hierarchical and regular ones) catalysts were prepared by impregnation method, and then the catalytic activity and selectivity of the catalysts were evaluated in PDH reaction. The results were compared with commercial Pt-Sn/γ-Al2O3 catalyst at the same operational conditions. Results revealed that hierarchical SAPO-34 based catalyst was the most efficient catalyst with superior activity and high propylene selectivity. The results suggested higher stability of the catalyst with hierarchical structure during seven hours reaction. Moreover, the impact of operational conditions was investigated on the performance of Pt-Sn/hierarchical SAPO for the temperature range of 550–650 °C, weight hourly space velocity of 4 and 8 h−1 and H2/C3 molar ratios of 0.2–0.8, at normal pressure.

Real‐Time Quantitative Operando Raman Spectroscopy of a CrOx/Al2O3 Propane Dehydrogenation Catalyst in a Pilot‐Scale Reactor

AbstractCombined operando UV/vis–Raman spectroscopy has been used to study the deactivation of CrOx/Al2O3 catalyst extrudates in a pilot scale propane dehydrogenation reactor. For this purpose, UV/vis and Raman optical fiber probes have been designed, constructed and tested. The light absorption measured by operando UV/vis spectroscopy was used to correct for the effect of catalyst darkening. This makes operando Raman spectroscopy a quantitative technique to follow the formation of coke deposits on‐line during the first hour of catalytic propane dehydrogenation process. The probe was used to study the coke deposition at the top and bottom of the reactor. Differences in the rate of coke deposition were observed, which were related to the local temperature of the catalyst bed. The chemical nature of the coke deposits formed on a catalyst extrudate, as expressed by the D1/G ratio, was independent of reaction time as well as of the position of the catalyst extrudate within the reactor bed.

Synthesis and application of ZSM-5/SAPO-34 and SAPO-34/ZSM-5 composite systems for propylene yield enhancement in propane dehydrogenation process

Two types of zeolitic composite systems with binary hierarchical structures comprising ZSM-5 and SAPO-34 molecular sieves were synthesized employing different procedures. Obtained products were served as catalytic carriers for propane dehydrogenation reaction so as to promote the physicochemical properties of ZSM-5 support, enhance the propylene yield and reduce the formation of light compounds. ZSM-5/SAPO-34 was fabricated in a series hydrothermal procedure employing pre-heated ZSM-5 suspension followed by secondary growth of SAPO-34 layer whereas SAPO-34/ZSM-5 was synthesized using tetrapropylammonium bromide exchanged-SAPO-34 crystals and pre-reacted ZSM-5 slurry in a hydrothermal one-step process. The products were characterized by XRD, FESEM, EDS, FTIR, NH3-TPD, and N2 adsorption–desorption techniques to investigate the textural and structural properties of composite architectures. The catalytic performance of the bimetallic Pt-Sn-based composites were evaluated in propane dehydrogenation reaction and compared with those of physical mixture and single ZSM-5-derived catalysts. Either of composites represented improved catalytic performance due to the synergetic effect between ZSM-5 and SAPO-34, which promoted the catalytic properties of the samples. Catalytic reactivity of the composite catalysts was strongly dependent on the synthesis method and employed zeolite/zeotype ratio. Best result was acquired for Pt–Sn-based SAPO-34/ZSM-5 (Si/Al=60) brand-new efficient composite with improved stability, boosted conversion and significant selectivity towards light olefins, propylene in particular.

Nano-MgO supported CrOx catalysts applied in propane oxidative dehydrogenation: Relationship between active chromium phases and propane reaction pathway

Propane oxidative dehydrogenation was investigated on nano-MgO supported Cr catalysts. Cr-5.0 wt.% sample exhibited the best catalytic performance with a propylene selectivity of 84.1% and propane conversion of 10.8% at 450 °C. Cr5O12 and MgCrO4 were proved to be formed, and they could be consecutively reduced as shown by temperature programmed reduction results. The impacts of different Cr phases on propane reaction pathway were also investigated. Fourier transform infrared spectroscopy reflects that Cr5O12 is favorable for the propane dehydrogenation process, while MgCrO4 would activate propane but lead to the COx outcome.

Improved catalytic performance in propane dehydrogenation of PtSn/γ-Al2O3 catalysts by doping indium

Abstract Bimetallic PtSn/γ-Al 2 O 3 catalysts promoted by doping indium(In) for propane dehydrogenation are investigated with several state-of-art characterizations such as BET, XRD, NH 3 -TPD, TEM, XPS, H 2 -TPR and TPO. The results show that the indium addition evidently improves the catalytic performances and stability of PtSn/γ-Al 2 O 3 catalysts. The NH 3 -TPD profiles verify a decrease in acidity for the supports with the addition of indium. Metallic Sn and In or PtSn alloy and PtIn alloy are detected by XPS spectra on the catalysts after reduction. The presence of indium in the PtSn/In–Al 2 O 3 catalysts not only could maintain the catalytic active and propylene selectivity, but also could suppress the hydrogenolysis reaction during propane dehydrogenation process. The high activity (conversion > 41.0%) and perfect propylene selectivity (selectivity > 96%) are obtained in propane dehydrogenation after reaction for 53 h.

Characterization of Industrial Pt-Sn/Al2O3 Catalyst and Transient Product Formations during Propane Dehydrogenation

The major problem plaguing propane dehydrogenation process is the coke formation on the Pt-Sn/Al2O3 catalyst which leads to catalyst deactivation. Due to information paucity, the physicochemical characteristics of the commercially obtained regenerated Pt-Sn/Al2O3 catalyst (operated in moving bed reactor) and coke formation at different temperatures of reaction were discussed. The physicochemical characterization of regenerated catalyst gave a BET surface area of 104.0 m2/g with graphitic carbon content of 8.0% indicative of incomplete carbon gasification during the industrial propylene production. Effect of temperatures on coke formation was identified by studying the product yield via temperature-programmed reaction carried out at 500oC, 600oC and 700oC. It was found that ethylene was precursor to carbon laydown while propylene tends to crack into methane. Post reaction, the spent catalyst possessed relatively lower surface area and pore radius whilst exhibited higher carbon content (31.80% at 700oC) compared to the regenerated catalyst. Significantly, current studies also found that higher reaction temperatures favoured the coke formation. Consequently, the propylene yield has decreased with reaction temperature. © 2013 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0)Corrigendum/Erratum of this article at: https://doi.org/10.9767/bcrec.9.2.7136.155

The effect of oxygenate additives on the performance of Pt–Sn/γ - Al2O3 catalyst in the propane dehydrogenation process

The effect of oxygenate modifiers on the performance of Pt–Sn/γ–Al2O3 catalyst in dehydrogenation of propane was studied. Dehydrogenation reaction was carried out in a fixed-bed quartz reactor in the temperature range of 575–620 °C. Two types of oxygenate modifiers, namely water and methanol, were added to the feed. The optimum amounts of water for reaction temperatures of 575, 600 and 620 °C were 84, 120 and 140 ppm, respectively. The optimum amounts of methanol for the same reaction temperatures were 9.9, 25 and 50 ppm, respectively. Any further addition of water or methanol beyond these optimum levels resulted in a loss in activity. The addition of water or methanol led to the formation of COx at the expense of selectivity loss of propylene. The propylene yields, however, passed a maximum at the optimum amounts of added oxygenates. The addition of water and methanol in the optimum amounts resulted in a substantial reduction of coke formation as well. The improved propane conversions in the presence of optimum amounts of added water or methanol could be explained in terms of enhanced β H-elimination step in propane dehydrogenation mechanism in the presence of hydroxyl groups.

Mathematical modeling of the propane dehydrogenation process in the catalytic membrane reactor

The two-dimensional non-isothermal stationary mathematical model of the catalytic membrane reactor for the process of propane dehydrogenation has been developed. The made calculations have shown the higher efficiency of the membrane reactor in comparison with the tubular one which is achieved due to removal of hydrogen from reactionary zone through the membrane to shift the reaction equilibrium towards formation of products. The use of membrane was found to cause the propane conversion increase from 41% to 67%. The highest value of propane conversion ( X = 96%) was reached in case of additional oxidation of the removed hydrogen (conjugated dehydrogenation). The maximum value of propylene selectivity S = 98% can be as well reached in case of conjugated dehydrogenation in the membrane reactor at the reaction temperature of 500 °C. The oxidation of hydrogen in conjugated dehydrogenation process gives the increase of propylene yield from 65% (the tubular reactor) to 95%. The maximum propylene yield corresponds to T = 525 °C. It was also established that the gas space velocity in both internal and external parts of the membrane reactor is to be the one of the most important factors defining efficiency of the conjugated dehydrogenation process.

Modeling and Simulation of Coke Combustion Regeneration for Coked Cr 2O 3/Al 2O 3 Propane Dehydrogenation Catalyst

A heterogeneous model is developed for the regeneration of the Cr 2O 3/Al 2O 3 catalyst for the propane dehydrogenation process by considering the internal mass transfer and external mass/heat transfer during the coke combustion. Simulation shows that under practical operating conditions, multi-steady states exist for the catalyst pellets and the catalyst temperature is sensitive to gas temperature. However, at increased mass flow rate or lowered oxygen concentration, multi-steady states will not appear. Under the strong influences of film diffusion, the coke in the packed bed reactor will first be exhausted at the inlet, while if the film diffusion resistance is decreased, the position of first coke exhaustion moves toward the outlet of the reactor.

Repetitive control of CATOFIN process

The CATOFIN process is a propane dehydrogenation process for production of propylene. It uses multiple adiabatic fixed-bed reactors where dehydrogenation and regeneration (decoking) are performed alternatively over roughly ten minutes of period for each operation. Taking advantage of the periodic operation, the present research concerns the development of a repetitive control method to improve the operation of the CATOFIN process. The controller is designed to perform feedback action during the regeneration cycle and to run only the Kalman filter during the dehydrogenation cycle. To improve the performance while overcoming the nonlinearity of the process, a linearized time-varying process is derived from the first-law model and used for the controller design. Numerical study has shown that the proposed control system outperforms conventional feedback control methods.