5874
Ind. Eng. Chem. Res. 2004, 43, 5874-5879
Silica Membrane Reactor for the Thermochemical Iodine-Sulfur Process To Produce Hydrogen Mikihiro Nomura,*,† Seiji Kasahara,‡ and Shin-ichi Nakao† Department of Chemical System Engineering, Faculty of Engineering, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan, and Department of Advanced Nuclear Heat Technology, Oarai Research Establishment, Japan Atomic Energy Research Institute, Niibori 3607, Narita-cho, Oarai-machi, Higashiibaraki-gun, Ibaraki 311-1394, Japan
Silica membranes prepared by chemical vapor deposition were applied to the decomposition reaction of HI of the iodine-sulfur process in order to improve one-pass conversion of HI. Equilibrium conversion of HI is 22% at 723 K without hydrogen removal. Hydrogen was successfully extracted from the decomposition reactor using the silica membranes between 723 and 873 K. HI conversions were increased with an increase in the hydrogen extraction ratio. The maximum HI one-pass conversion was 76.4% at 873 K. The total thermal efficiency can be improved by 1% for this HI conversion by calculating the heat/mass balance of the process. The concentration profile in the reactor was evaluated by using the simple two-dimensional simulation. H2 permeances measured by the experimental method were almost the same as those of the simulation, and the membrane reactor system was found to have permeation limitations. Membranes with higher H2 permeances should be developed for the membrane reactor. Introduction Hydrogen is one of the clean energy media without carbon dioxide emission. There have been many processes investigated for an efficient hydrogen production. If nonfossil energies such as solar or nuclear energies are used for water-splitting methods for hydrogen production, no carbon dioxide will be discharged through the hydrogen energy system. There have been many thermochemical methods proposed to reduce the maximum temperature required to produce hydrogen from water using heat as an energy source. The UT-3 cycle and the iodine-sulfur (IS or SI) process are the two major water-splitting methods that have been investigated throughout the 1990s. The IS process is one of thermochemical water-splitting processes using iodine and sulfur as reaction agents, and this process has been developed by the group of General Atomics.1,2 The maximum required temperature for the process is ca. 1100 K. This process consists of three reactions.
2H2O + I2 + SO2 ) 2HI + H2SO4 (Bunsen reaction) 2HI ) H2 + I2 H2SO4 ) 1/2O2 + SO2 + H2O I2, SO2, and H2O are reacted in the Bunsen reaction, and two kinds of acids (HI and H2SO4) are obtained. HI and H2SO4 are separated using a liquid-liquid separator by adding I2 and H2O. After the separation procedures of the acids, HI and H2SO4 are decomposed at ca. 700 and 1100 K, respectively. I2 and SO2 are * To whom correspondence should be addressed. Tel. and fax: +81-3-5841-7346. E-mail:
[email protected]. † Department of Chemical System Engineering. ‡ Department of Advanced Nuclear Heat Technology.
recycled to the Bunsen reaction. In these 10 years, the IS process has been mainly developed by the group of Japan Atomic Energy Research Institute.3-16 Nakajima et al.4 reported that continuous hydrogen production at the rate of 1 LH2/h was demonstrated using the glassmade apparatus. Hydrogen was successfully obtained for 24 h by the IS process. Recently, a hydrogen production rate of 31.5 LH2/h was demonstrated for 20 h in order to investigate the control system of the total process.15 Many separation processes are, however, required for this process to recycle I2, SO2, or other chemicals. These separation processes should be improved for efficient hydrogen production. Kasahara et al.10,11 evaluated the total thermal efficiency of hydrogen production using an electro-electrodialysis (EED)8,9 and a hydrogen-permselective membrane reactor5-7 for the 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. The concentration procedures of HI after EED should be optimized in the process, while the thermal efficiency of hydrogen production increased with an increase in the HI conversion at the reactor. Equilibrium conversion of HI at 723 K is only 22%. HI, hydrogen, and I2 should be separated after the decomposition reaction of HI to recycle HI to the decomposition reactor. There are no metallic materials found to be stable under HI, hydrogen, and H2O vapor.16 Thus, a hydrogen-permselective membrane reactor to improve HI conversion had been investigated. Hwang et al.5 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. This silica membrane was stable under hydrogen, HI, and H2O vapors at 723 K for 48 h.6 However, the effects of the application of a hydrogen-permselective membrane on a HI decomposition reaction are not clear. In this paper, a silica membrane prepared by the CVD method was
10.1021/ie0497691 CCC: $27.50 © 2004 American Chemical Society Published on Web 08/04/2004
Ind. Eng. Chem. Res., Vol. 43, No. 18, 2004 5875
between 2.1 and 5.7 mL min-1. Nitrogen was also introduced into the feed at the rate of 4.7 mL min-1 in the case of the higher HI conversion conditions. The permeation side of the membrane was swept by nitrogen at 200 mL min-1. The total pressures of both sides of the membrane were the same asthe atmospheric pressure. Hydrogen concentrations in the feed and in the permeation were measured by using gas chromatography. HI and I2 were removed by liquid-nitrogen traps before introducing them into the gas chromatograph. The HI bottle was put into the draft with an autovalve shutter for stopping the bottle by a HI sensor near the membrane module. The leaking valve (0.01 MPa) was placed in the draft so as to not leak HI on the outside of the draft. Figure 1. Schematic diagram of the silica membrane reactor. MF: mass-flow controller. CT: cold trap.
applied to a HI decomposition reaction especially at higher reaction temperatures. Effects of hydrogen removal through the membrane were evaluated by the total thermal efficiency based on the heat/mass balance, and the concentration profile in the reactor was discussed by using a two-dimensional simulation. Experimental Section Silica membranes for the membrane reactor were prepared by the CVD method based on the conditions shown in the literature.5 TEOS was used as a silica source and was supplied by nitrogen bubbling at 298 K. TEOS vapor was supplied at the one side of the substrate at the rate of 350 mL min-1, and the other side was vacuumed by using a vacuum pump. The pressure of the inside of a substrate was ca. 15 Torr. The substrates of the silica membrane were an γ-alumina tube having 4 nm pores provided by Noritake Co. The effective membrane area was L 5 mm × 100 mm in length (1.6 × 10-3 m2) or 200 mm in length (3.1 × 10-3 m2). CVD was carried out at 973 K for 40 min under a nitrogen atmosphere. After the deposition, the pressures of the inside of the substrates were less than 1 Torr. Two silica membranes were used for these experimental methods. Hydrogen permeance was 3.1 × 10-8 mol s-1 m-2 Pa-1 with an effective membrane area of 1.6 × 10-3 m2 for membrane 1. The other membrane (membrane 2) was 4.0 × 10-7 mol s-1 m-2 Pa-1 with an effective membrane area of 3.1 × 10-3 m2. The hydrogen selectivity over nitrogen was over 80 for each membrane. Figure 1 shows the schematic diagram of the hydrogenpermselective membrane reactor for the HI decomposition reaction. The silica membrane prepared by the CVD method was set in the membrane module made by quartz glass of inside diameter L ) 10 mm. Active carbon catalyst (Takeda Chemical Industries, RyujoShirasagi, Osaka, Japan) was placed around the membrane. The total amounts of the carbon catalyst were 2.5 and 6.4 g for membranes 1 and 2, respectively. The catalysts were well dried under a nitrogen atmosphere at 723 K for more than 1 h before the decomposition procedures. The temperature of the module was measured by the thermocouple and was controlled by the heater. HI was introduced into the membrane module from the HI bottle provided by Mitsui Chemicals (Nagoya, Japan). The purity of HI was over 99.999%. The flow rate of HI was controlled by the flowmeter
Calculations Three kinds of calculations were carried out for the evaluation. First was the evaluation by the total thermal efficiency based on the heat/mass balance. Second was the evaluation of the hydrogen removal ratio by calculating the HI decomposition equilibrium. Third was a concentration profile calculation in the membrane reactor using a simple two-dimensional simulation. The detailed calculation procedures for the evaluation by the total thermal efficiency were described in previous papers.10,11 The evaluation was based on the heat/ mass balance of the IS process featuring a hydrogenpermselective membrane reactor and EED. HI conversion at the membrane reactor was set for the evaluation parameter. The overpotential between the electrodes at EED was set at 0.20 V.8 The HI concentration after EED was 13.5 mol kgH2O-1. The reflux rate of HI distillation was fixed at 0.5. The temperature difference at the heat exchangers was set over 10 K, and waste heat of less than 373 K was not recovered by the evaluation. The thermal efficiency was calculated by the high heat value of hydrogen (285 kJ mol-1) and the required total heat demand in the process. The effect of the hydrogen removal was evaluated by equilibrium calculations of the HI decomposition reaction. The equilibrium constant Kp at high temperature was calculated according to the extrapolation of the lowtemperature data (300-700 K).17 The total pressure for the calculation was set at 1 atm. First, HI equilibrium of the decomposition was calculated. Next, some ratio of hydrogen was removed from the system, and equilibrium was recalculated under the assumption that all I2 and hydrogen were produced by the decomposition of HI. Finally, the ratio of the amount of total hydrogen and removed hydrogen was calculated using the final compositions. The ratio of removed hydrogen and total hydrogen production was defined as hydrogen extraction. The concentration profile in the membrane reactor was calculated using a simple two-dimensional simulation to evaluate the permeation properties of the silica membrane used for the experimental method. There should be a concentration profile in the membrane module. Calculation was conducted under isothermal conditions at 1 atm. The membrane was separated into 100 cells. The sizes of the membrane and the membrane module were fixed at the sizes employed for the experimental method. Figure 2 shows the schematic diagram of the cell. F in Figure 2 shows the flow rate in the feed, and P indicates that in the permeation. Subscripts inside square brackets indicate the composition of the
5876 Ind. Eng. Chem. Res., Vol. 43, No. 18, 2004
Figure 2. Schematic diagram of the cell used for the twodimensional simulation.
flow rates, and subscripts in and out show the inlet and outlet of the cell, respectively. At the feed side of the membrane, a mixture of HI, I2, hydrogen, and nitrogen was introduced from the former cell. The laminar film at the membrane was not counted, and the concentration profile in the cell was not considered. The residence time in the cell was calculated by the total flow rate in the cell and voids in the cell. The voids in the cell were set at 0.3 because active carbon catalyst was put in the feed side. Only hydrogen was permeated through the membrane by the partial pressure difference of hydrogen at the membrane. The effects of the permeations of the other molecules were negligible when the hydrogen/ HI selectivity of the membrane was over 100 by the literature.7 After removal of hydrogen through the membrane, equilibrium calculation was employed in the cell. The equilibrium constants were the same as those used in the former calculation.17 The calculated composition of each molecule was set at the composition of the next cell. The nitrogen flow rate in the permeation side was fixed at 200 mL min-1, which is the same as that for the experimental method, and the hydrogen compositions were calculated by the permeated hydrogen and the compositions from the former cell. The total hydrogen permeances were calculated at the last cell of the permeation side. Results and Discussion 1. Total Thermal Efficiency. Figure 3 shows the effect of HI conversion at the membrane reactor on the total thermal efficiency to produce hydrogen. The thermal efficiency was around 34%, which is lower than the maximum results (56.8%) reported in the literature.10 This is explained by the differences of the calculation parameters. In the former literature, three ideal assumptions were employed for the calculations. The first assumption was that the temperature difference at the heat exchangers was 0 K. If the temperature difference was 10 K, the thermal efficiency was 50.8%. The second assumption was that the overpotential of the EED for HI concentration was set at 0 V. The value of the overpotential through the experimental cell was 0.2 V, and the maximum thermal efficiency was calculated at 41.6% for 0.2 V of the overpotential and 10 K of the temperature difference at the heat exchangers. The last was waste heat recovery at around 400 K. The effect of waste heat recovery on the total thermal efficiency was
Figure 3. Effect of the HI conversion on the total thermal efficiency by the heat/mass evaluation of the IS process. HI concentration after EED: 13.5 mol kgH2O-1. Overvoltage at EED: 0.20 V. Reflux rate of the HI distillation: 0.5. Temperature difference at heat exchangers: 10 K.
Figure 4. Equilibrium calculation of the HI decomposition reaction by changing the ratio of extracting hydrogen.
ca. 6%. Thus, the total thermal efficiency was around 34% without these assumptions. The detailed heat/mass balance was described in the literature.10 One of the purposes for applying a membrane reactor system is to reduce the amounts of recycling agents. The thermal efficiency was sharply increased from the HI conversion at around 30%. The amount of required heat to increase the temperature of the HI vapor before the membrane reactor from HI, I2, and hydrogen mixtures can be applied when HI conversion is over 30%. Thus, no heat demands are needed from the other part of the processes. The equilibrium conversion was 22% at 723 K. For the 1% improvement of the thermal efficiency from the equilibrium condition by increasing HI conversion, HI conversion should be over 70%. Thus, the target of the HI conversion in this study was set at 70%. 2. Hydrogen Extraction Evaluation by Equilibrium Calculations. Figure 4 shows the relationship between HI conversion at the reactor and the ratio of hydrogen removal by the equilibrium calculation. There are two lines shown in the figure by changing temperatures for 723 and 873 K. These temperatures were the same as the experimental values carried out in this paper. The effect of operation temperatures on the HI decomposition reaction is little according to the difference of the two lines. The Y intercepts in Figure 4 (0 of hydrogen extraction) indicates the equilibrium conversion of the HI decomposition reaction without hydrogen
Ind. Eng. Chem. Res., Vol. 43, No. 18, 2004 5877 Table 1. HI Conversions by Changing the Reactor Temperature (1)a HI conversion temperature [K]
H2 extraction
exptl [%]
calcd [%]
723 773 823 873
0.468 0.521 0.828 0.955
32.5 35.9 43.6 51.6
27.7 30.2 43.3 61.2
a
Membrane 1. Feed: HI of 2.1 mL min-1.
Table 2. HI Conversions by Changing the Reactor Temperature (2)a HI conversion temperature [K]
H2 extraction
exptl [%]
calcd [%]
723 773 823 873
0.784 0.853 0.953 0.978
47.7 46.7 65.7 76.4
39.2 43.8 59.4 69.3
Figure 5. Hydrogen-permselective membrane reactor results at 723 K.
removal. The conversion was 22% and 25% at 723 and 873 K, respectively. The HI conversion difference at 0.9 of hydrogen extraction was 4.4%, which is slightly larger than that at 0 of hydrogen extraction. The HI conversion is slightly increased with an increase in the hydrogen extraction rate until 0.8 of hydrogen extraction for both operating temperatures. On the other hand, HI conversion is sharply increased over 0.9 of hydrogen extraction. More than 0.98 of hydrogen should be extracted in order to obtain 70% of HI conversion by the equilibrium calculation. A higher operating pressure or the development of a higher hydrogen permeance membrane is required for the higher HI conversion. The experimental method was conducted at 1 atm according to the safety limitation of the apparatus. The hydrogen extraction ratio was mainly controlled by the HI flow rate in the experimental method. 3. Hydrogen Removal by the Silica Membrane Reactor. Figure 5 shows the hydrogen extraction results at 723 K by changing the HI flow rate in the feed through membrane 1 or membrane 2. These data were taken after confirming the steady state of the feed and permeation concentrations for more than 1 h. The lines in this figure were calculated based on the results in Figure 4. The HI conversion at 0 of hydrogen extraction was almost the same as the calculated line. This indicates that the hydrogen measurements were reliable for this apparatus. The HI conversion increased with increasing hydrogen extraction. The highest conversion was 61.3% by removal of 0.86 of hydrogen in the feed. However, HI conversions were slightly higher than the calculated lines. The dashed line shows the equilibrium results at Kp ) 30. From this calculation, accuracy of the equilibrium constants for HI decomposition calculated by the extrapolation at high temperatures required further discussions. To obtain higher conversion, the HI flow rate in the feed should be decreased. The smallest flow rate of HI was 2.1 mL min-1. The experimental procedure failed when a HI flow rate lower than 2.1 mL min-1 was tested. The flow rate was too small to keep plug flow in the feed, because almost all of the decomposed hydrogen was permeated through the membrane. As a result, I2 was circulated in the feed, and purple I2 vapor was found at the inlet of HI. I2 was not detected by the titration at the cold trap of the outlet of the permeation line, suggesting that the selectivity of hydrogen over HI for membranes 1 and 2 was very high. The hydrogen permeances were also stable during the experimental method. This indicates that the silica membrane prepared by a CVD method was stable at 723 K under HI decomposition conditions.
a
Membrane 2. Feed: HI of 2.1 mL min-1 + N2 of 4.7 mL min-1.
Table 1 shows the effects of the reaction temperature on the HI conversion for membrane 1 at 2.1 mL min-1 of HI flow rate. Pure hydrogen permeances were increased with increasing operation temperatures. The equilibrium calculations were also described by the experimental ratio of hydrogen extraction and the equilibrium at the operating temperatures. The HI conversion was improved by increasing the temperature. This might be the effect of higher hydrogen permeance at a higher permeation temperature for the silica membrane because the equilibrium difference by the temperature change is less than 5% of the HI conversions (Figure 4). The HI conversion was 51.6% by removal of 0.96 of hydrogen at 873 K. The calculated conversions were smaller until the reactor temperature was 773 K, while the experimental conversion was smaller at 873 K. This shows that hydrogen permeation is the limitation step until 773 K. I2 was circulated in the feed at 873 K under 2.1 mL min-1 of HI flow rate. However, the HI conversion was too high to keep plug flow in the feed as explained at the former section. To keep plug flow in the feed, nitrogen should be introduced in the feed especially for the higher HI conversion conditions. Table 2 shows the results using membrane 2 with HI and nitrogen as feed gases. The flow rates of HI and nitrogen in the feed were 2.1 and 5.7 mL min-1, respectively. In this case, there was no I2 vapor found at the inlet of HI, indicating that the effect of convection in the feed was not significant. HI conversions were higher than those for membrane 1, because hydrogen permeances through membrane 2 were more than 10 times larger. All of the HI conversions were similar to those of the calculated values. The small difference might be the error of the equilibrium constants evaluated by the extrapolating method. The HI conversion was 76.4% at 873 K. This conversion is over our goal to improve 1% of the total thermal efficiency as shown in Figure 3. 4. Hydrogen Permeance Estimated by a Simple Two-Dimensional Calculation. Hydrogen permeances through the silica membrane during the decomposition procedures were evaluated using a simple twodimensional simulation. Figure 6 shows hydrogen permeances measured by the pure hydrogen permeation tests (solid line) and those calculated from HI decomposition membrane reactors for membrane 1 (cf. Table 1). Calculated hydrogen permeances agree with those
5878 Ind. Eng. Chem. Res., Vol. 43, No. 18, 2004
Figure 6. Pure hydrogen permeance measurements and those calculated by the two-dimensional simulation.
Figure 8. HI conversions and hydrogen production rates as a function of the membrane length for the same membrane area.
To obtain 76.4% of HI conversion using membrane 1, 0.5 m of the membrane length was required. This is 5 times longer than that shown in Table 1. However, the hydrogen production rate from the same membrane area decreased ca. 70%. The module configuration should be optimized not only by the HI conversion but also by the total hydrogen production from one module. Conlusions
Figure 7. Concentration profiles in the membrane module.
for the pure permeation tests. This indicates that there are little interferences of HI or I2 for hydrogen permeation through the membrane. This membrane reactor is hydrogen permeation limited considering the calculation assumptions. The apparent activation energy of hydrogen permeation through membrane 1 was 24.6 kJ mol-1, which was calculated by the slope in Figure 6. This value is similar to that for the silica membranes (ca. 20 kJ mol-1) prepared by the sol-gel method.18 The experimental values and simulation results showed good agreement. Thus, the effects of the concentration profiles were discussed using the simulation results. Figure 7 shows the concentration profiles in the reactor when hydrogen permeance was set at 1.27 × 10-7 mol s-1 m-2 Pa-1. The reactor temperature was fixed at 873 K. The HI conversion was calculated at 0.516 for this condition (cf. Table 1). The x axis, L [m], indicates the length from the inlet of HI. The hydrogen concentration sharply decreased with increasing L. The hydrogen concentration was decreased by 55.2% at the half (L ) 0.05 m) of the membrane, while the ratio was only 18.6% from L ) 0.05 to 0.10 m. This shows that hydrogen removal using this type of membrane reactor is effective, especially at the entrance of the reactor. On the other hand, the HI concentration decreased by 6.7% from the inlet of the reactor to the half of the membrane and by 9.4% from the half to L ) 0.1 m. The ratio increased with an increase in the length from the inlet. Thus, the HI conversion should be improved by using a longer membrane reactor. Figure 8 shows the simulation results of the HI conversion and hydrogen production rate by changing the membrane length under a fixed membrane area of 7.1 × 10-3 m2. The membrane properties were the same as those shown in Figure 7.
Hydrogen-permselective silica membranes were successfully applied to the decomposition reaction of HI in the IS process. The HI conversion was improved to 76.4% from equilibrium value (25.0%) at 873 K by extracting 97.8% of hydrogen from the reactor using the silica membrane. The total thermal efficiency to produce hydrogen can be improved ca. 1% by the effect of the membrane. The HI conversion increased with an increase in the reactor temperature due to higher hydrogen permeance at higher temperature. Hydrogen permeances through the silica membrane were the same between pure permeation tests and HI decomposition membrane reactors by the simple two-dimensional simulation, and the applied membrane reactor system was confirmed as permeation limited. The effect of the membrane reactor can be improved by developing a higher permeance membrane. Literature Cited (1) Norman, J. H.; Besenbruch, G. E.; O’Keefe, D. R. Thermochemical Water-Splitting for Hydrogen Production. GRI-80/0105, 1981. (2) Norman, J. H.; Besenbruch, G. E.; Brown, L. C.; O’Keefe, D. R.; Allen, C. L. Thermochemical Water-Splitting Cycle, BenchScale Investigations, and Process Engineering. GA-A16713, 1982. (3) Onuki, K.; Nakajima, H.; Ioka, I.; Futakawa, M.; Shimizu, S. IS process for thermochemical hydrogen production. JAERIReview 1994-006, 1994. (4) Nakajima, H.; Ikenoya, K.; Onuki, K.; Shimizu, S. ClosedCycle Continuous Hydrogen Production Test by Thermochemical IS Process. Kagaku Kogaku Ronbunshu 1998, 24, 352. (5) Hwang, G.-J.; Onuki, K.; Shimizu, S.; Ohya, H. Hydrogen separation in H2-H2O-HI gaseous mixture using the silica membrane prepared by chemical vapor deposition. J. Membr. Sci. 1999, 162, 83. (6) Hwang, G.-J.; Onuki, K.; Shimizu, S. Separation of Hydrogen from a H2-H2O-HI Gaseous Mixture Using a Silica Membrane. AIChE J. 2000, 46, 92. (7) Hwang, G.-J.; Onuki, K. Simulation Study on Catalytic Decomposition of Hydrogen Iodine in a Membrane Reactor with a Silica Membrane for the Thermochemical Water-Splitting IS Process. J. Membr. Sci. 2001, 194, 207.
Ind. Eng. Chem. Res., Vol. 43, No. 18, 2004 5879 (8) Onuki, K.; Hwang, G.-J.; Arifal; Shimizu, S. Electroelectrodialysis of hydriodic acid in the presence of iodine at elevated temperature. J. Membr. Sci. 2001, 192, 193. (9) Hwang, G.-J.; Onuki, K.; Nomura, M.; Kasahara, S.; Choi, H.-S.; Kim, J.-W. Improvement of the thermochemical watersplitting IS process by electro-electrodialysis. J. Membr. Sci. 2003, 220, 129. (10) Kasahara, S.; Hwang, G.-J.; Nakajima, H.; Choi, H.-S.; Onuki, K.; Nomura, M. Effects of the process parameters of the IS process on total thermal efficiency to produce hydrogen from water. J. Chem. Eng. Jpn. 2003, 36 (7), 887. (11) Kasahara, S.; Kubo, S.; Onuki, K.; Nomura, M. Thermal efficiency evaluation of HI synthesis/concentration procedures in the thermochemical water splitting IS process. Int. J. Hydrogen Energy 2004, 29, 579. (12) Nomura, M.; Kasahara, S.; Onuki, K. Evaluation of thermal efficiency to produce hydrogen through the IS process by thermodynamics. JAERI-Research 2002-039, 2003. (13) Nomura, M.; Ikenoya, K.; Fujiwara, S.; Nakajima, H.; Kasahara, S.; Kubo, S.; Onuki, K. Application of a membrane reactor system to the Bunsen reaction of the thermochemical water splitting IS process. Proceedings of GENES4/ANP2003, Kyoto Research Park, Kyoto, Japan, 2003; Paper 1091.
(14) Kasahara, S.; Hwang, G.-J.; Kubo, S.; Choi, H.-S.; Onuki, K.; Nomura, M. Thermal efficiency of the IS process for thermochemical hydrogen production using the HTGR. Proceedings of GENES4/ANP2003, Kyoto Research Park, Kyoto, Japan, 2003; Paper 1038. (15) Kubo, S.; Kasahara, S.; Nakajima, H.; Shimizu, S.; Ishiyama, S.; Onuki, K. R&D on water splitting IS process for hydrogen production using HTGR at JAERI. Proceedings of 2004 AIChE spring meeting, New Orleans, LA, 2004; Paper 126b. (16) Onuki, K.; Ioka, I.; Futakawa, M.; Nakajima, H.; Shimizu, S.; Tayama, I. Screening Tests on Materials of Construction for the Thermochemical IS Process. Corros. Eng. 1997, 46, 141. (17) Moore, W. J. Physical Chemistry; Tokyo Kagaku Dojin: Tokyo, Japan. (18) Nair, B. N.; Keizer, K.; Okubo, T.; Nakao, S. Evolution of pore structure in microporous silica membranes, sol-gel procedures and strategies. Adv. Mater. 1998, 10 (3), 249.
Received for review March 24, 2004 Revised manuscript received June 24, 2004 Accepted July 1, 2004 IE0497691
