Dr Khadijeh Paymooni

Spherical axial-flow membrane reactors (SMR) can be proposed as a promising alternative for conventional tubular reactors (CTR) in the catalytic naphtha reforming process. In this study, the operating conditions and design parameters of SMR are optimized via a differential evolution (DE) method to maximize the hydrogen yield, the reformate production rate, and the aromatic content of reformate (octane number). Regarding this, 26 decision variables such as the membrane thickness, catalyst mass distribution, and flow distribution of sweeping gas are optimized, and the performance of the SMR is evaluated under optimized operating conditions. The optimization results show that the operating costs can decrease sharply with a decrease in the sweeping gas streamlines' pressures where they decline from 985, 1810, and 2000 kPa in the first, the second, and the third reactors of nonoptimized SMR to 242.4, 563.1, and 796.6 kPa in optimized SMR, respectively. Moreover, the research octane number (RON) of gasoline can improve well in optimized SMR owing to the achievement of higher aromatic yield and the aromatic content of the reformate. Consequently, an optimized SMR configuration can properly address the increasing demand for high-octane gasoline. The superiority of the optimized SMR configuration to CTR can be counted as assisting the membrane concept, lower pressure drop along the reaction side, and utilizing the optimum operating conditions. © 2011 American Chemical Society.

The increasing demand for hydrogen and high octane gasoline in refineries can be addressed via utilizing alternative configurations for conventional catalytic naphtha reactors (CTR). In this regard, two case studies for a combination of isothermal and tubular membrane reactors are investigated in naphtha reforming process. The isothermal reactors are fabricated as a multi tubular reactor in a furnace. Some key parameters such as aromatic and hydrogen production rates and the aromatic content of reformate are investigated and some guidelines are proposed for the selection of a proper combination according to the desired aim of production. The simultaneous enhancement in products yield due to applying the Pd-Ag membrane layer and a slight temperature drop under an isothermal circumstance are achieved. The modeling results show that the combination of tubular membrane-isothermal-tubular membrane (MIM) reactors is a promising configuration for aromatic and hydrogen enhancement as well as achieving a desired aromatic content of the reformate.

Naphtha reforming units are of high interest for hydrogen production in refineries. In this regard, the application of membrane concept in radial-flow tubular naphtha reactors for hydrogen production is proposed. Because of the importance of the pressure drop problem in catalytic naphtha reforming units, the radial-flow reactors are proposed. A radial-flow tubular membrane reactor (RF-TMR) with the radial-flow pattern of the naphtha feed and the axial-flow pattern of the sweeping gas is proposed as an alternative configuration for conventional axial-flow tubular reactors (AF-TR). The cross-sectional area of the tubular reactor is divided into some subsections in which walls of the gaps between subsections are coated with the Pd-Ag membrane layer. A dynamic mathematical model considering radial and axial coordinates ((r, z)-coordinates) has been developed to investigate the performance of the new configuration. Results show ~300 and 11 kg/h increase in aromatic and hydrogen production rates in RF-TMR compared with AF-TR, respectively. Furthermore, smaller catalyst particles with higher efficiency can be used in RF-TMR due to a slight pressure drop. The enhancement in aromatics (octane number) and hydrogen productions owing to applying simultaneously the membrane concept and radial-flow pattern in naphtha reactors motivates the application of RF-TMR in refineries. © 2011 American Institute of Chemical Engineers (AIChE).

Hydrogen is a valuable raw material for chemical and petrochemical industry. In this regard, the operating conditions of a radial-flow tubular membrane reactor (RF-TMR) are optimized via Differential Evolution (DE) method to boost the hydrogen and aromatic yields in catalytic naphtha reforming process. In this novel configuration, the radial-flow pattern of the naphtha feed and the sweeping gas is considered in the tube and the shell sides to solve the pressure drop problem. Furthermore, the cross-section area of the tubular reactor is divided into some subsections and the gaps' wall between subsections are coated by the Pd-Ag membrane layer. The steady state and dynamic optimizations are carried out and twenty-nine decision variables such as operating pressure, membrane thickness, sweeping gas distribution and the ratio of length to diameter (LOD) are considered during the optimization process. The optimization results show 27 and 8.3kmolh-1 increase in the hydrogen and aromatic yields in optimized RF-TMR compared with conventional tubular reactor (CTR). Moreover, the new configuration is capable to be used in the radial-flow moving bed reactors, which are widely installed in refineries. © 2011 Elsevier Ltd.

Because of some disadvantages of conventional tubular reactors (CTRs), the concept of spherical membrane reactors is proposed as an alternative. In this study, it is suggested to apply hydrogen perm-selective membrane in the axial-flow spherical packed-bed naphtha reformers. The axial flow spherical packed-bed membrane reactor (AF-SPBMR) consists of two concentric spheres. The inner sphere is supposed to be a composite wall coated by a thin Pd-Ag membrane layer. Set of coupled partial differential equations are developed for the AF-SPBMR model considering the catalyst deactivation, which are solved by using orthogonal collocation method. Differential evolution optimization technique identifies some decision variables which can manipulate the input parameters to obtain the desired results. In addition to lower pressure drop, the enhancement of aromatics yield by the membrane layer in AF-SPBMR adds additional superiority to the spherical reactor performance in comparison with CTR. © 2011 American Institute of Chemical Engineers (AIChE).

In this study, a combination of isothermal and adiabatic reactors is modeled for catalytic naphtha reforming process. The performance of the proposed configuration has been investigated under an Isothermal-Adiabatic condition. In order to operate under an isothermal condition, reactors are fabricated in a furnace, consisting of multi parallel tubes. The furnace consists of two main parts, a non-reaction zone and a reaction zone. The inlet naphtha feed is preheated in the non-reaction section and the chemical reactions take place in the parallel tubes which are packed by catalysts in the reaction section. Results show a remarkable increase in the production rates of aromatic (5.72%) and light ends (8.73%) as well as a slight temperature drop under the isothermal condition by fabricating the first reactor in the furnace. The Isothermal-Adiabatic configuration properly improves the production rate of aromatics (octane number) in naphtha reforming process. © 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.

A thermally coupled membrane dual-type reactor (TCMDR) has been proposed for simultaneous hydrogen production and utilization in gas-to-liquid technology (GTL). Decalin dehydrogenation reaction is coupled with Fischer-Tropsch synthesis (FTS) reaction to improve the heat transfer between endothermic and exothermic sides. Furthermore, Pd-Ag and Hydroxy Sodalite membrane layers are assisted in TCMDR to improve the mass transfer between exothermic/endothermic side and permeation side. Some of the produced hydrogen via decalin dehydrogenation reaction is utilized in FTS reaction and the other is extracted and stored. The modeling results show 95% hydrogen production and 5% hydrogen utilization in FTS reactions in the exothermic reaction side of TCMDR configuration. The performance of TCMDR is compared with the one of conventional reactor (CR) and fluidized-bed membrane dual-type reactor (FMDR). Moreover, the gasoline yield in TCMDR increases about 17% and 29% in comparison with the one in FMDR and CR, respectively. The enhancement in gasoline and hydrogen yields demonstrates the superiority of TCMDR to the previous reactors. © 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.

In the recent years, refineries have focused on developing new ways to gain more from their asset utilization owing to increasing demand for high octane gasoline. In this regard, a thermally coupled fluidized bed naphtha reactor (TCFBNR) is proposed in this study. The first and the second reactors of a conventional catalytic naphtha reactor configuration (CR) are substituted by thermally coupled fluidized bed reactors. In this novel configuration, naphtha reforming reactions which are highly endothermic are coupled with the exothermic hydrogenation of nitrobenzene to aniline. Some drawbacks of CR such as pressure drop, internal mass transfer limitation and radial gradient of concentration and temperature are successfully solved in this novel configuration. In addition to some mentioned advantages of this novel configuration, TCFBNR configuration enhances the aromatic production rate about 20.54% and 7.13% higher than CR and TCNR, respectively. Also, the TCFBNR is capable to enhance hydrogen production rate in the shell side, the aniline flow rate in the tube section and simultaneously improves the thermal behavior of endothermic side and reduces the undesirable temperature drop. The modeling results of TCFBNR is compared with the results of CR and thermally coupled fixed-bed naphtha reactor (TCNR). These studies provide a good initial insight for some modifications and revamping of the old facilities with more efficient ones. © 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.

In this study, the operating conditions of a thermally coupled membrane reactor (TCMR) in gas-to-liquid (GTL) technology are optimized via differential evolution (DE) method to maximize the hydrogen mole fraction in the endothermic side as well as the gasoline yield in the exothermic side. TCMR is designed as a double pipe reactor where highly exothermic Fischer-Tropsch synthesis (FTS) reactions in the exothermic side are coupled with decalin dehydrogenation reaction in the endothermic side. The minimum required hydrogen molar flow rate in the recycled stream is optimized to compensate a hydrogen lack at the end of the reactor in the exothermic side. The optimization results show 14.28% increase in the gasoline yield in optimized TCMR compared with conventional tubular reactor (CR). Moreover, 81.49% hydrogen is produced in the endothermic side and about 1% hydrogen is recycled to the exothermic side for utilization in FTS reactions in optimized TCMR. © 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

Due to proposing hydrogen as the main energy carrier, technologies including production, storage and utilization of hydrogen have attracted increasing attention recently. Regarding this, the feasibility of decalin as a promising hydrogen carrier is investigated in this study. The performance of decalin thermally coupled membrane reactor (DCTCMR) is compared with cyclohexane thermally coupled membrane reactor (CTCMR) for Fischer-Tropsch synthesis (FTS) in gas-to-liquid (GTL) technology. Some important parameters such as hydrogen production rate, H2 recovery yield, exothermic and endothermic temperature profiles and etc. are considered as criteria to recognize the most appropriate configuration. A comparison between the modeling results of two coupled configurations shows that DCTCMR is superior to CTCMR owing to achieving remarkably higher hydrogen production (seventeen times) compared with CTCMR. Furthermore, considerably higher H2 recovery yield (about twelve times) and faster dehydrogenation reaction rate in DCTCMR than CTCMR proposes decalin as one of the best hydrogen carriers. This study demonstrates the superiority of DCTCMR to CTCMR owing to achieving remarkably higher hydrogen production rate, H2 recovery yield and recognizing decalin as an appropriate hydrogen carrier. © 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

In this novel theoretical study, the dimensionless length of the conventional naphtha reforming reactor has been discretized into differential segments and three different cases have been investigated in this regard. In the first case, inlet temperature of each segment has been optimized via differential evolution (DE) method to obtain the optimized temperature profile along the reactors by joining the achieved inlet temperatures for each segment on the figure. Same approach has been applied in the second case in order to achieve optimum hydrogen permeation rate. In the third case, the optimum profiles of temperature and hydrogen removal have been obtained using DE optimization technique using the same approach. The objective of each optimization case is to maximize the hydrogen and aromatics production rate. As it is discussed further, unlike previous studies, application of optimum temperature and hydrogen permeation profiles simultaneously boosts hydrogen and aromatics production rate significantly. 10% and 24% enhancement in hydrogen and aromatics production rates can be achieved by applying the novel theoretical concepts in the conventional naphtha reforming process. © 2011 Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

The present study proposes a novel configuration of Fischer-Tropsch synthesis (FTS) reactors in which a fixed-bed water perm-selective membrane reactor is followed by a fluidized-bed hydrogen perm-selective membrane reactor. This novel concept which has been named fixed-bed membrane reactor followed by fluidized-bed membrane reactor (FMFMDR) produces gasoline from synthesis gas. The walls of the tubes of a fixed-bed reactor (water-cooled reactor) of FMFMDR configuration are coated by a high water perm-selective membrane layer. In this new configuration, two membrane reactors instead of one membrane reactor are developed for FTS reactions. In other words, two different membrane layers are used. In order to investigate the performance of FMFMDR, a one-dimensional heterogeneous model is taken into consideration. The simulation results of three schemes named fluidized-bed membrane dual-type reactor (FMDR), FMFMDR and conventional fixed-bed reactor (CR) are presented. They have been compared in terms of temperature, gasoline and CO2 yields, H2 and CO conversions and the water permeation rate through the membrane layer. Results show that the gasoline yield in FMFMDR is higher than the one in FMDR. The FMFMDR configuration not only decreases the undesired product such as CO2 but also produces more gasoline. © 2010 Elsevier Ltd.

Triethylene glycol (TEG) is one of the most important liquid desiccants in the natural gas dehydration industry. In enhanced TEG regeneration processes, liquid hydrocarbons such as toluene and isooctane are added to the stripping column of natural gas dehydration unit in order to boost water volatility and regenerate TEG to higher purity. In this study, isooctane and toluene were selected as liquid hydrocarbon solvents and the effect of these two solvents on TEG purity and the outlet water concentration from the reboiler of tray column were experimentally investigated and mathematically modeled. The vapor-liquid equilibrium calculations were performed using the NRTL activity coefficient model and ideal gas equation of state to represent the liquid and vapor phases, respectively. Moreover, a comprehensive model was used to determine the liquid molar flow rate on each tray where it changed with time and tray by tray. The impact of various concentrations of solvents and different operating conditions (total and no reflux) on the performance of the tray column was investigated. The modeling results were validated with the experimental data, and good agreement was observed between them. Results showed that the least water concentration in the reboiler and the highest TEG purity were achieved by adding 0.15 wt % isooctane under total reflux conditions. The achieved results can provide an initial insight into designing equipments in enhanced TEG regeneration processes with hydrocarbon solvent injection. © 2011 American Chemical Society.

A semi-empirical model is proposed to investigate the performance of packed columns equipped with structured packing at high pressures. The mass transfer efficiency is determined in terms of height equivalent to theoretcial plate (HETP) for empirical data of an iC4/nC4 mixture at elevated pressures. Some unexpected phenomena cause predictive models of mass transfer to be inaccurate at high pressures. The effects of the gas phase backmixing and the liquid maldistribution on the gas phase mass transfer coefficient and the effective interfacial area have been investigated in this study. The modified model is developed on the basis of the Delft model to predict the mass transfer behavior of structured packing at high pressures. The proposed model is validated by the empirical data and good agreement is observed between the empirical data and the results of the modified model. The error of HETP calculation by the modified model is less than the other models especially at moderate and high pressures. At low pressures, predicted values of different models are almost the same and they show minor errors. The difference between predicted HETP by various models increases by pressure rising. Moreover, the effect of liquid load on mass transfer in packed columns is investigated. The proposed model can predict the effect of liquid load on mass transfer performance. Proper efficiency has been obtained by the modified model for iC4/nC4 separation process in structured packed column at high pressures. © 2011 American Chemical Society.

The water dew point adjustment is one of the most important processes in all gas refineries which reduces the water content of gas to some allowable limit and separates the heavy hydrocarbons from gas. In Sarkhun gas refinery, natural gas dehydration and hydrocarbon dew point adjustment are performed by cooling method. Diethylene glycol (DEG) is injected to gas-gas heat exchanger and chiller to absorb water from wet gas and act as a freezing inhibitor. Hydrate formation in filter elements was observed in this gas refinery which has been investigated in this research. The pressure difference between slug catchers and well streams were optimized by steady state process simulation software in order to decrease the mole percentage of C6+ exited along with the outlet gas stream from slug catcher and maximize the separation of liquid hydrocarbons. The pressure difference between the slug catcher unit and well streamlines was adjusted at optimized conditions and the experimental sampling was performed during modifications. The experimental results showed a considerable decrease in the mole percentage of C6+ exited along with the outlet gas stream from slug catcher and the simulation results showed 16500 bbl/year increase in NGL production rate. Operating under optimized pressure in the dew point adjustment unit of Sarkhun gas refinery decreased the water dew point temperature to -26 °C and improved the hydrocarbon dew point temperature to -9 °C. Moreover, NGL and LPG production rates increased annually about 18672 ton and 6365 ton after modifications which results in $11million extra annual income for company. © 2011 Elsevier B.V.

Improving the octane number of the aromatics' compounds has always been an important matter in refineries and lots of investigations have been made concerning this issue. In this study, an axial-flow spherical packed-bed reactor (AF-SPBR) is considered for naphtha reforming process in the presence of catalyst deactivation. Model equations are solved by the orthogonal collocation method. The AF-SPBR results are compared with the plant data of a conventional tubular packed-bed reactor (TR). The effects of some important parameters such as pressure and temperature on aromatic and hydrogen production rates and catalyst activity have been investigated. Higher production rates of aromatics can successfully be achieved in this novel reactor. Moreover, results show the capability of flow augmentation in the proposed configuration in comparison with the TR. This study shows the superiority of AF-SPBR configuration to the conventional types. © 2009 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.

In this study, a new flow pattern (radial-flow) in a tubular reactor is proposed for the naphtha reforming process. The operating conditions of axial-flow and radial-flow tubular packed-bed reactors have been optimized by the differential evolution (DE) method. The DE optimization method has been applied to maximize hydrogen and aromatic yields in the steady-state and dynamic conditions. Some parameters, such as total pressure, the hydrogen mole fraction in the recycled stream, the length per diameter of the reactor, and the mass distributions of the catalysts, have been optimized for the steady-state conditions. Moreover, the inlet temperature of the gas at the entrance of each reactor is optimized for the unsteady-state condition to compensate for the effect of catalyst deactivation. A set of coupled partial differential equations are solved by the orthogonal collocation method. The results demonstrate that, by utilizing the optimization technique and alternating the flow pattern in conventional catalytic reformers, the aromatic and hydrogen production rates increase 3.01% and 11.50%, which can approximately satisfy the increasing demand of hydrogen and high-octane gasoline in refineries. © 2011 American Chemical Society.

One of the most important processes for controlling BTEX content in the atmosphere is reduction of BTEX emission in the stripping column of the natural gas dehydration units. An alternate approach for enhancing stripping column performance is the use of stripping agent. In this approach a volatile hydrocarbon liquid is added into the glycol regeneration system instead of stripping gas. Triethylene glycol (TEG) absorbs BTEX from natural gas in contactor and BTEX emission will occur in regenerator column. The Farrashband Gas Refinery has been simulated using a software simulator and the BTEX emission in conventional unit has been compared with new approach. Using hydrocarbon solvent decreases the environmental pollution of TEG regeneration in the natural gas process. This is an abstract of a paper presented at the 7th European Congress of Chemical Engineering-7 and 19th International Congress of Chemical and Process Engineering CHISA (Prague, Czech Republic 8/28/2010-9/1/2010).

An alternate approach for the enhancement of stripping column performance is the use of stripping agent where a volatile hydrocarbon liquid is added into the glycol regeneration system instead of stripping gas. The Farrashband Gas Refinery was simulated and triethylene glycol (TEG) purity and loss in conventional unit was examined using the alternate approach. The use of a hydrocarbon solvent enhanced TEG purity. It also reduced its loss to atmosphere. The concentration of TEG in recycle stream increased for modified natural gas dehydration processes. The stripping agent process was better than conventional process for natural gas dehydration process and TEG regeneration. However, economic estimations should also be considered. This is an abstract of a paper presented at the 7th European Congress of Chemical Engineering-7 and 19th International Congress of Chemical and Process Engineering CHISA (Prague, Czech Republic 8/28/2010-9/1/2010).