The application of membrane reactor technology in hydrogen production using S–I thermochemical process: A roadmap

i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y 3 7 ( 2 0 1 2 ) 3 6 1 2 e3 6 2 0

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The application of membrane reactor technology in hydrogen production using SeI thermochemical process: A roadmap Soumitra Kar*, R.C. Bindal, S. Prabhakar, P.K. Tewari Desalination Division, Bhabha Atomic Research Centre, Mumbai 400085, India

article info

abstract

Article history:

Thermochemical cycle using water as raw material and nuclear/renewable energies as

Received 7 February 2011

sources of energy is believed to be a safe, stable and sustainable route of hydrogen

Received in revised form

production. Amongst the well-studied thermochemical cycles, the sulfureiodine (SeI)

23 March 2011

cycle is capable of achieving an energy efficiency of 50%, making it one of the most efficient

Accepted 24 March 2011

cycles among all water-splitting processes.

Available online 6 May 2011 Keywords: Hydrogen SeI thermochemical cycle

The SI cycle is characterized by three basic reactions as shown below.

1. I2 þ SO2 þ 2H2O / 2HIx þ H2SO4 (120  C) 2. 2H2SO4 / 2SO2 þ 2H2O þ O2 (830  C) 3. 2HIx / I2 þ H2 (450  C)

Membrane reactor The third section, that is the HIx (HI þ I2 þ H2O) processing section, is the most intricate step in terms of the process efficiency as it has got the lowest overall rate and very complicated separations. In order to overcome the low efficiency due to the poor equilibrium decomposition of HI, ongoing research is dedicated toward development of a hydrogen-permselective membrane reactor. Proper identification of suitable membranes and introduction of membrane reactor is proposed to improve the efficiency of the overall cycle and make hydrogen production more economical. The experimental procedure has already been optimized toward development of an asymmetric silica membrane. The authors presently intend to use the membrane in the form of a packed bed membrane reactor for the enhancement of equilibrium decomposition of HI. The present paper discusses the challenges and intricacies associated toward development of a membrane reactor which can be applied in highly corrosive environment like HI under a high temperature of about 500  C. Copyright ª 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

1.

Introduction

SeI thermochemical process is one of the promising processes of hydrogen production amongst all the alternatives available

keeping in view the predicted thermochemical efficiency and its ability to couple it to high temperature nuclear reactor [1e6]. The high reaction temperature environment and the chemicals associated in the SeI cycle pose a very corrosive

* Corresponding author. E-mail address: [email protected] (S. Kar). 0360-3199/$ e see front matter Copyright ª 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ijhydene.2011.03.170

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Reactants

Reactor

Separator

Products

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The present paper discusses in brief the fundamentals of membrane reactor technology and tries to draw attention toward the challenges associated with making this membrane reactor technology viable in a chemical processing stream like that of SeI cycle.

Reactants recycle

Fig. 1 e A conventional membrane reactor system. (Sanchez & Tsotsis, reproduced with permission from Wiley-VCH Verlag GmbH & Co. KGaA.)

working environment. Effective realization of a safe hydrogen production plant requires careful selection and optimization of materials involved within each section of SeI cycle. The specific requirements are obtained from process flow sheet for the individual section and the associated processing steps. There are three ongoing material research areas that are believed to be important for the eventual success of the SeI cycle [7]. First and foremost is the development of construction materials that can handle the corrosive environment for the lifetime of the process equipment, especially heat exchangers, boilers, and reactors. The next two important areas involve gas-permeable membranes and catalyst development. Proper identification of suitable membranes and reaction catalysts is proposed to improve the efficiency of the overall cycle and make hydrogen production more economical. In order to achieve a desirable phase separation of HI and H2SO4, the excess addition of iodine causes serious problem during processing of 3rd section, that is the HIx processing section [8]. In addition, the equilibrium-limited decomposition of HI restricts the realization of overall efficiency of the cycle. Researchers have proposed that employment of electroelectrodialysis [9] followed by membrane reactor can help realization of predicted thermal efficiency. For a process to qualify as a membrane reactor system, it must not simply combine a membrane separation unit with a chemical reactor, it must integrally couple them in such a fashion that a synergy is created between the two units, resulting in enhanced performance in terms of selectivity and yield. Often the membrane separation module and reactor are physically combined into the same unit. Such combination promises to result in a process, which is more compact and less capital intensive, and with substantial savings in processing costs [10]. Extensive research is being carried out in BARC by various groups of researchers addressing various critical issues associated with production of hydrogen by thermochemical splitting of water by SeI process. In this context, authors are engaged in the development of membrane-based processes applicable to HIx processing stream.

2.

Membrane reactor

A membrane reactor is a single unit operation integrating both membrane-based separation and reaction. It can also be termed as membrane-based reactive separation. They promise to be compact and less capital intensive, and because of their promise for substantial savings in the processing costs they are the potential unit-operation candidates in industries at present time. The membrane reactor has got a tremendous role in enhancement of selectivity/yield in case of equilibrium-limited reactions. The conventional and integrated membrane reactor systems are shown in Figs. 1 and 2 below. As shown in Fig. 2 there are two different chambers, one is the retentate chamber, where the reactants are fed and the reaction often takes place, and the other one is permeate chamber. The latter is either swept by an inert gas or evacuated in order to maintain a differential pressure or concentration gradient for mass transfer between the two compartments. It is where a difficult separation problem exists, coupled to a “per-pass” conversion or selectivity or equilibrium limitation problem that the application of membrane reactors makes the best sense [11]. There are different configurations of membrane reactor that have been proposed in the literature [11] in order to combine the membrane separation module and the reactor into a single unit. Six basic types of configurations as indicated in Table 1 and as shown in Fig. 3 have been classified. The most commonly referred to reactor is the PBMR, in which the reaction function is provided by a packed bed of catalysts in contact with the membrane where the membrane itself is not catalytic. In the CMR configuration the membrane provides simultaneously the separation and reaction functions. To accomplish this, one could use either an intrinsically catalytic membrane or a membrane that has been made catalytic through activation. If the membrane used in PBMR configuration is catalytically active then the configuration is termed as PBCMR. When the packed bed is replaced by a fluidized-bed the FBMR configuration results. Finally, the PBCMR (and FBCMR) uses both a catalytic bed and a permselective membrane. In the CNMR configuration the membrane is not typically permselective and it is only used to provide a reactive surface. Membrane reactors, as against any general classification, can be classified as staged membrane reactors, membrane

Fig. 2 e An integrated membrane reactor system. (Sanchez & Tsotsis, reproduced with permission from Wiley-VCH Verlag GmbH & Co. KGaA.)

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Table 1 e Classification of membrane reactors. Acronym CMR CNMR PBMR PBCMR FBMR FBCMR

Description Catalytic membrane reactor Catalytic non-permselective membrane reactor Packed bed membrane reactor Packed bed catalytic membrane reactor Fluidized-bed membrane reactor Fluidized-bed catalytic membrane reactor

Sanchez & Tsotsis, reproduced with permission from Elsevier.

reactors with multiple feed ports, multimembrane reactors [12,13]. Researchers have carried out R&D on understanding the various ways of operating these reactors, including the means to minimize reactant loss [14,15], the use of sweep gas under concurrent or counter-current operation [16], or the use of a vacuum on the permeate side. Membrane reactors could also be classified [17e19] as reactive membrane extractors when the membrane’s function is to remove one or more products. Such action could result in increasing the equilibrium yield. Membranes could also serve as a distributor for one of the reactants. Such membrane reactors find application for consecutive and parallel reactions for a better yield of the intermediate products and they do have a potential to avoid the thermal runaway phenomena, typically associated with highly exothermic reactions. The membrane’s role in a membrane reactor could also be to improve the contact between different reactive phases; where, the membrane acts as a medium for providing the intimate contact between different reactants, which are fed separately in either side of the membrane. Multiphase reactions involving a catalyst and liquid and gaseous reactants can also be studied in reactive membrane contactors. Here, the primary advantage of the use of the membrane reactor is in decreasing the mass transfer

Fig. 3 e Different membrane reactor configurations: (1) tubeside, (2) catalytic membrane, (3) inert membrane, (4) catalyst bed, (5) shellside (a) CMR, CNMR, (b) PBMR, FBMR, (c) PBCMR, FBCMR. (Sanchez & Tsotsis, reproduced with permission from Wiley-VCH Verlag GmbH & Co. KGaA.)

limitations, frequently encountered with such reactions in slurry or trickle-bed reactors. Though there have been a lot of advances in the membrane reactor technology, still few technical/technoeconomical feasibility issues are there limiting the substantial use of the product in the industrial domain. Those issues are discussed in Section 4 of the article.

3.

HIx processing section

In SeI cycle, sulfuric acid cannot be separated from hydrogen iodide, by thermal means, without reversing the equilibria. This separation is readily accomplished in the presence of a large excess of iodine, with the formation of two immiscible liquid phases, a light H2SO4/H2O phase and a heavy HIx (HI/I2/ H2O) phase, which essentially poses tremendous difficulty in the successive processing of HIx stream. In Section 3 of SeI cycle, the HI phase is first concentrated by distillation and the HIeH2O distillate at azeotropic composition (13% molar in HI) is decomposed in the vapor phase according to the third reaction. HI decomposition can be accomplished by either reactive or extractive distillation. Reactive distillation is a simple one step process. HIx solution boils at temperatures approaching 300  C. Operating pressures under these conditions are in the range of 20e50 bar. On the other hand, in the process of extractive distillation, iodine separation from HIx is made effective at 120  C using H3PO4 followed by distillation of HIx and subsequent concentration of H3PO4 HIx solution is extremely corrosive. Glass was chosen as a suitable material for handling the corrosive properties of the solution, but this requires measures to operate at these high pressures. One way to do this is to place the distillation column inside a pressure vessel, and match the pressure outside the column to the pressure within. Thus, a large part of the experimental effort is directed toward the containment and control of this differential pressure system. In addition, the small diameter and close tray spacing of a laboratory-scale column makes adiabatic operation an issue [20]. On the other hand, extractive distillation suffers from a serious drawback of addition another chemical species and making the SeI cycle more complex to process further. In JAERI (Japan Atomic Energy Research Institute), the hydrogen production under closed-cycle operation has been demonstrated in laboratory-scale [21]. In JAERI’s demonstration experiment, hydrogen was produced by thermal decomposition of gaseous HI. This scheme suffered from the low equilibrium decomposition ratio of hydrogen iodide (about 20%). The low decomposition ratio led to the increase of the amounts of recycle materials (HI, I2, H2O) and therefore decreased the thermal efficiency. In order to enhance the decomposition ratio, focus was made on the application of a membrane reactor and efforts were oriented to prepare the hydrogen separation membrane based on ceramics having thermal resistance and corrosion resistance in the process environment. The total thermal efficiency of hydrogen production was evaluated [22,23] using an electro-electrodialysis (EED) and a hydrogen-permselective membrane reactor for the

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concentration and decomposition procedures of HI by calculating the heat/mass balance of the process. Process parameters and properties of the membrane for HI separation were the parameters for the evaluation. Researchers [24] claimed that the silica membrane prepared by a chemical vapor deposition (CVD) of tetraethyl orthosilicate (TEOS) was effective for the separation of hydrogen and HI. The effects of three typical membrane techniques (an electro-electrodialysis (EED), an electrochemical cell (EC), a hydrogen-permselective membrane reactor (HPMR)) were evaluated [25] on total thermal efficiency by heat/mass balance calculations based on the experimental data. The HPMR at the decomposition reaction of HI was effective to improve one pass conversion of HI to 76.4%, and the amount of recycled HI was reduced by 91.5% using this membrane technique. Fig. 4 shows the two options out of three (including the phosphoric acid extraction) practiced in the research centre. The authors are targeting the encircled area, where the pseudo azeotrope of HIx would be broken using the process of electroelectrodialysis (EED) followed by the enhancement of equilibrium decomposition of HI using a membrane reactor in-line with executions made by the researchers [26]. It is believed that EED coupled with membrane reactor can be a suitable alternative against the reactive distillation column, keeping in view corrosion issues discussed in the next section. Several works in this direction have been carried out in Idaho National Laboratory, USA [27] and University of Sheffield, UK [28].

on the membrane as a ‘black box’. Predictive models of the membrane separation processes will subsequently be developed as a design aid for the full-scale process. These models will be incorporated into ProSim to allow the entire process to be evaluated. A database will be developed to contain an in depth information on the in-house developed membranes and membrane reactor process to aid in the selection of suitable systems. It is realized that lot of challenges are associated in exploiting the potential benefits of a membrane reactor, especially when the process stream is high corroding like that of SeI cycle. The intricate steps involved are shown in the form of a flowchart (Fig. 5) and elaborated in the next section.

4.1.

Membrane development

In the gaseous HI decomposition reaction, H2 separation membranes can play a critical role. The decomposition reaction HI / H2 þ I2 is an equilibrium reaction that has a conversion efficiency of around 22% at 450  C. One can enhance the decomposition rate by removing hydrogen from the reactor. Therefore, functional membranes that can separate hydrogen from the reactor will lead to a reduction in the amount of HI gas that needs to be recycled through the reactor. In addition, an effective separation membrane can maintain the purity of the H2 gas produced. A number of hydrogen separation membranes have been developed for many applications. Unfortunately, most of them employ metals such as Pd, PdeAg, and Zr. Since these materials have

4. Application of membrane reactor technology in SeI process (A roadmap) The authors are engaged in the assessment of the potential for membrane separations and membrane reactor technology to improve the overall thermal efficiency of the process. This involves a lab scale experimental study on a range of possible membranes and catalysts. The objective is to enable the targeting of the required separation efficiencies as a function of the process operating conditions. This will allow identification of suitable membranes for high temperature applications for incorporation into the distillation train. The initial simulations have to be carried out

electro-electrodialysis, EED

Catalytic Membrane Reactor

Fig. 4 e Options available after Bunsen section.

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Fig. 5 e Flow chart showing the roadmap/challenges associated with development of membrane reactor.

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been shown to be susceptible to corrosion in an iodine-rich environment, they are not suitable for this application. Desalination Division, BARC is associated with the development of silica-based membrane reactor for enhancement of equilibrium decomposition of HI. An attempt has been made to develop silica membrane [29] on alumina support with graded porosity using solegel processing. The process was carried out using dip-coating technique on a highly porous alumina fiberboard support. Alumina slurry was prepared under an optimized dispersion condition. The graded porous structure was formed by dipping the fiberboard (Fig. 6) in the alumina slurry and infiltrating it for varying periods of time followed by withdrawal at a constant rate of 30 cm/min. Due to the capillary action of pores present in the fiberboard, the alumina slurry got infiltrated and formed well adherent thick films of alumina (Fig. 7) with thickness varying up to 2 mm. As-grown support was sintered at 1000  C and was used as substrate for micrporous silica membranes. Conditions were optimized for sintering of the layer to improve adherence and formation of the graded composite structure without cracks (Figs. 6 and 7). Formation of silica film (with pores in the size of about 1.6 nm) on the alumina support with graded porous structure was studied using a silica sol. Silica membrane (Fig. 8) was prepared by dipping the slurry-formed-alumina-surface supported on fiberboard for 2 min in the silica sol, followed by drying/gelling and heat treatment at 600  C at a heating rate of 0.5  C/min and a soaking time of 2 h. The average pore diameter was found to be about 1.6 nm by BarreteJoynereHalenda (BJH) method. A detailed study on the surface morphology and cross-sections of monoliths and membranes (Fig. 9) were studied by scanning electron microscope. The efforts were oriented toward development of tubular membrane of 25 cm length and 1 cm OD. Fig. 10 shows the membrane in tubular configuration developed in-house. The evaluation of stability of in-house developed membranes under HIeI2 environment is in progress as per the methodology prescribed in literature [30,31].

4.2.

Catalyst development

The decomposition of HI takes place in the gaseous phase between 300 and 450  C, depending on the distillation process.

Fig. 6 e Microstructure of alumina fiberboard.

Fig. 7 e Microstructure of sintered alumina layer over alumina fiberboard.

Due to the corrosive nature of HI, and I2, only a limited number of catalysts have been evaluated in the process. Pt and Pd-based catalysts are not suitable, as they will exhibit severe corrosion if any measurable amount of moisture is present in the chemical stream. R&D on different catalyst materials is in progress. Four gamma-alumina-supported nickel catalysts were produced, characterized [32] and tested in terms of catalytic activity and stability by means of a tubular quartz reactor. It was concluded that three of the four catalysts tested demonstrated high catalytic activity, since hydrogen iodide conversion was almost coincident with the theoretical equilibrium value. On the other hand, for all the catalysts, a gradual but considerable deactivation phenomenon was observed at 500  C, while at a temperature higher than 650  C the catalytic activity was recovered. Activated carbon catalysts obtained from a variety of raw material sources and preparation methods were examined [33] for their catalytic activity to decompose HI to produce hydrogen. In general it was observed that ash content was detrimental to catalytic activity while total acid sites seemed to favor higher catalytic activity within the group of steamactivated carbons. These results suggest that activated carbon raw materials and preparation methods may have

Fig. 8 e Microstructure of silica layer.

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Fig. 9 e Cross-section of alumina-supported silica membrane.

played a significant role in the development of surface characteristics that eventually dictated catalyst activity and stability as well. Ceria (CeO2) was prepared [34] with different methods and at various calcinations temperatures and tested to evaluate their effect on hydrogen iodide (HI) decomposition. The results show that the CeO2 catalyst synthesized by citric-aided solegel method and calcined at low temperature (<500  C) showed more lattice defects, smaller crystallites, larger surface area and better reducibility. Lattice defects, especially the reduced surface sites, i.e., Ce3þ and oxygen vacancy, played the dominant role in surface reactions of HI decomposition. Activated charcoal is the only satisfactory catalyst found to date. However, it has been observed that iodine can be trapped inside the charcoal pores if the decomposition temperature is too low. Hence, a higher reaction temperature is required in order to maintain the reflux of iodine. Unfortunately, this can lead to accelerated corrosion. There is a need to identify a catalyst that can promote the decomposition at a lower temperature, which will be beneficial to the process. The evaluation of performance of different catalyst materials is in progress in the research center under the HIx decomposition environment.

4.3.

Membrane reactor configuration development

The idea of using membrane reactors is not new. The creation of new hydrothermally stable, and highly selective silica membranes has allowed more feasible use of membranes in

these systems to provide the full benefit of this technology. A technical and economic evaluation of the use of dense Pd membrane in methane steam reforming has been presented by the researchers [35]. An evaluation of various plant designs was presented [36] incorporating high temperature mesoporous and microporous membranes for the dry-reforming reaction of methane for hydrogen production. More recently a detailed economic feasibility study of the application of Pd membrane reactors to the water gas shift (WGS) reaction was published [37]. They also studied the effect of decreasing the membrane thickness (from 75 m down to 5 m), and increasing the membrane permeability by a factor of ten. The palladium membrane costs and the capital and operating costs decreased, but they were still higher when compared to the costs of the conventional production unit. The R&D effort in the direction of development of different configurations of membrane reactor is still new and a lot of opportunities as well as challenges are associated with each of the configurations studied till date. Coated wall catalytic films provide significant benefits over packed bed reactors, including significantly reduced pressure drop and better isothermal operation leading to increased catalyst activity [38,39]. For membrane reactors catalytic films would allow a more controlled production of hydrogen along the membrane tube profile with the possible advantage of improving catalyst activity and hydrogen permeation. It was observed [40] that by synthesizing a zeolite thin film catalyst onto a selective hollow fiber silica membrane, the reaction and separation function could be coupled very efficiently. It was reported [41] however that using thin film catalyst coatings could lead to significantly decreased catalyst stability due to increased sintering. It was found that by impregnating the catalyst particles within the membrane support they could avoid catalyst sintering while providing reaction close to the membrane surface. Balance of reaction to permeation is also an important consideration of membrane configuration [42,43]. If permeation is too low the membrane has little effect and the reactor behaves like a packed bed reactor. However, if permeation is high then excessive hydrogen is removed from the catalyst section increasing potential deactivation and coking [44]. Summarizing, it can be mentioned that the use of membranes in membrane reactor incorporates two considerations, practical and economic limits [43]. Practical limits come in to picture taking into account the relative stability of the material for the desired operation. The need for defect free, high selectivity, high permeation membranes dominates the choice of material used in membrane reactor technology [45]. Economical limits are concerned with the capital cost of such operations while scaling up and will ultimately be a deciding factor in the commercialization of this technology. Authors are working out different configurations of membrane reactor and technoeconomic feasibility analysis is in progress.

4.4.

Fig. 10 e Tubular membrane developed in-house.

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Test setup integration

A prototype membrane reactor was developed in-house. The reactor with the sweep gas, feed, product and reject lines is shown in Fig. 11. The schematic comprising of gas purification panel, mass flow controllers, high temperature furnace, gas

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end of furnace. The condenser units were put in between the membrane module and GC to take care of the iodine and unreacted HI vapors before the streams are directed to GC for composition analysis. The experiments were conducted under steady-state conditions (no change in flow rates and compositions with time). Fig. 11 e A prototype membrane reactor developed inhouse.

chromatograph (GC) etc. is shown in Fig. 12. The as-prepared silica membrane was encapsulated in a custom-made stainless steel membrane holder (Fig. 11) and sealed completely to study the permeation properties of tubular support and silica membranes over the temperature range of 30e500  C and pressure difference range of 0.2e2 bar using the experimental setup depicted in Fig. 12. Single component permeation of a series of gases, was measured by flowing a stream of each gas through the membrane after the gas being purified in the gas purification panel. Pure argon was used as sweep gas, flowing in the shellside of the permeation cell at ambient pressure. To study the hydrogen permselectivity of the membrane mixed gas stream was used. Homogeneous gas mixtures of required proportion were prepared with the help of mass flow controllers (MFC) and gas homogenizer. The pressure at the inlet of MFCs was controlled using forward electronic pressure controllers (EPC), and the system pressure was controlled using back pressure regulator kept at the post

4.5.

Corrosion & membrane stability studies

In distillation of HIx using membrane reactor HI / H2 þ I2 decomposition reaction is carried out in the gas phase between 300 and 450  C. The reaction environment created by HIx is extremely corrosive. In order to realize a stable, safe and functional nuclear-hydrogen production plant, the materials used to manufacture the reaction chambers, heat exchangers, and other components for HI decomposition must be carefully selected. Data from Trester and Staley [46] have shown refractory metals such as Ta and Nb and ceramic materials such as SiC and borosilicate glass to be corrosion-resistant in HIx up to 200  C, which is below the HI decomposition temperature. Since corrosion rate increases sharply with temperature, these materials and other potential candidates were re-tested [47] under extreme conditions of temperature and pressure. Immersion coupon corrosion tests were performed to screen materials selected from four classes of corrosion-resistant materials: refractory metal, reactive metal, superalloys and ceramics. Of the materials tested, only Ta and Nb-based refractory metals and ceramic mullite could stand up to the extreme environment found in HIx. Severe pitting and dissolution was observed in two different reactive

Sweep Gas to Furnace

Sweep gas to furnace

Membrane

Fig. 12 e Schematic of gas permeation setup.

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metal zirconium alloys. A nickel-based superalloy, C-276, also showed severe dissolution in HIx solution. Researchers [48] had screened a number of engineering alloys and corrosion-resistant materials in an HI/I2/6H2O gaseous environment at temperatures between 200 and 400  C. Metallic Ta, Zr, Ti, and SiC and SiN show very low corrosion rates at all temperatures. Preliminary testing of Hastelloy B and C-276 in an HI þ I2 environment in the absence of moisture was conducted [46] and it was concluded that both alloys can be used in this environment. Unlike reactions involving liquid phases, it appears that commonly available corrosion-resistant engineering alloys can be used for the HI gaseous decomposition process, but this will require more long-term testing to confirm. There are no metallic materials found to be stable under HI, hydrogen, and H2O vapor [48]. Pd-based membranes offer the greatest ideal H2 selectivity of 100% for defect-free membranes. However, Pd membranes suffer from a variety of instability issues; Pd becomes increasingly brittle in the presence of superheated steam [45], has issues with thermomechanical stability due to the phase changes of Pd during hydrogen dissolution. Silica membranes, while reporting lower selectivity from experiments, have many of the advantages of Pd membranes. Advances in solegel technology have allowed the tailoring of membranes with high quality specific pore sizes for increased permeation and selectivity [49,50]. Thus, a hydrogen-permselective membrane reactor to improve HI conversion had been investigated and it was observed that the silica membrane was stable under hydrogen, HI, and H2O vapors at 723 K for 48 h [30]. However, the effects of the application of a hydrogen-permselective membrane on an HI decomposition reaction are not entirely clear yet. On the way toward materialization of objectives, need of a defect-free high hydrogen-permselective membrane, development of proper catalyst, the way catalyst has to be impregnated onto the reactor module, development of corrosion-resistant membrane housing material, and high temperature sealants are realized and the work on each of the associated fields is in progress in the research centre.

5.

Conclusions

In the present scenario of world, where alarming issues like global warming and climate change are to be addressed, it is quite inevitable to orient the efforts toward optimization of a potential route of hydrogen production. SeI thermochemical cycle is proposed to be one of the worth-while candidates in this direction. The challenges involved in realizing the significance of SeI thermochemical cycle are well defined and sustained R&D is required to overcome those challenges. Authors here made an attempt to mention the intricacies of membrane reactor technology and have shown a roadmap to achieve the desired performance out of a membrane reactor process. It is believed that the present discussion would help in systematically organizing the research work, which should essentially lead to realization of predicted thermal efficiency of SeI cycle.

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