Hayato Nakajima

Preliminary process analysis for the closed cycle operation of the iodine-sulfur thermochemical hydrogen production process

Abstract In the iodine–sulfur thermochemical hydrogen production process, a separation characteristic of 2-liquid phase (H2SO4 phase and HIx phase) in the separator at 0°C was measured. Two-phase separation began to occur at about 0.32 of I2 molar fraction and over. The separation characteristic became better with the increase in iodine concentration in the solution. The effect of flow rate variations of HI solution and I2 solution from the HIx distillation column on the process was evaluated. The flow rate increase in HI solution from the distillation column did not have a large effect on the flow rate of HI solution fed to the distillation column from the separator. The decreasing flow rate of I2 solution from the distillation column decreased the flow rate of I2 solution fed to the distillation column from the separator. The variation of I2 molar fraction in the H2SO4 phase in the separator was sensitive to the variation in flow rate of both solutions from the distillation column. The tolerance level of the variation was investigated by considering I2 solubility, 2-liquid phase disappearance and SO2 reaction amount.

A nickel-iodine-sulfur process for hydrogen production

Abstract A thermochemical hydrogen production process which consists of the following reactions containing nickel, iodine and sulfur (NIS process) was studied. (1.1) So 2 (aq.)+I 2 (aq.)+2H 2 O(1)→2H 2 SO 4 (aq.) (1.2) 2HI(aq.)+H 2 SO 4 (aq.)+2Ni(c)→NiI 2 +NiSO 4 (aq.)+2H 2 (g) (2) NiI 2 (c)→NI(c)+I 2 (g) (3.1) NiSO 4 (c)→NiO(c)+SO 3 (g) (3.2) SO 3 (g)→SO 2 (g)+ 1 2 O 2 (g) (4) NiO(c)+H 2 (g)→Ni(c)+H 2 O(g) This process is an improved iodine-sulfur process, and is characterized by the separation of the products of reaction (1.2) by solvent extraction, and by the absence of hydrogen or water in the high temperature reactions (3.2), (3.1) and (2). Experimental results of the main unit operations are described. The energy balance of the process is estimated, based on a simplified flow-sheet. A conceptual plant flow-sheet is discussed in connection with a VHTR.

Development of high temperature structural materials for the HTGR

Abstract In accordance with the HTGR program in Japan, a series of R&D for high temperature structural materials in particular with respect to the HTTR design code has been performed in JAERI for more than 20 years. This paper introduces R&D results of the pressure retaining low alloy steel 2 1/4Cr-1Mo and the high temperature structural alloys Hastelloy XR and Ni-Cr-W superalloy for the design code together with some fruits of recent studies.

Potential of carbon dioxide radiolysis for hydrogen production

Abstract Carbon dioxide radiolysis was investigated theoretically and experimentally, and its potential for use in hydrogen production was examined. Elementary processes in the physical, physicochemical and chemical stages of carbon dioxide radiolysis were examined from a viewpoint of energy conversion efficiency from radiation to chemical energy. The energy conversion efficiency in the physical stage was ca 70%, and in the physicochemical stage ca 40%. The back reaction in carbon dioxide radiolysis reduces product yields and lowers the energy conversion efficiency, and should be suppressed. Effects of additives, high absorbed doses and fission fragment irradiation were studied experimentally.

Study of catalytic reduction of methanol for methane-methanol thermochemical hydrogen production cycles

Abstract Methanol was found to be reduced to methane by hydriodic acid solution containing platinum ions. The reaction was considered to proceed sequentially from methanol to methyl iodide and then to methane. Platinum ion acts as a catalyst in the methane formation. In the presence of iodine, the reaction was greatly suppressed and the reaction rate was almost independent of temperature. Methane-methanol thermochemical hydrogen production cycles utilizing the reaction are discussed.

Laboratory scale demonstration of CIS process

Abstract For the purpose of demonstrating the chemical practicability of CIS Process, a closed loop demonstration apparatus was constructed and operated. The loop consists of four key reactions of six reactions in CIS Process. Methanol was converted to methane and oxygen by the apparatus with conversions of 63–80%. 12 cyclic operations were successfully carried out with no serious troubles. Indications of side reactions, deposition of carbon-like compounds and formation of sulfur-like precipitates, were recognized.

Study on Thermochemical Iodine-Sulfur Cycle at JAERI

Japan Atomic Energy Research Institute (JAERI) has been conducting an R&D on thermochemical water-splitting processes of Iodine-Sulfur family, which is a promising candidate of heat-utilization process of High Temperature Gas-cooled Reactors. Present activity at JAERI covers the following three subjects, (a) closed-loop operation technique for stable and continuous hydrogen production by e.g. suppressing possible side reactions, (b) process improvement in terms of thermal efficiency of hydrogen production utilizing membrane technologies, and (c) selection of materials for constructing the large-scale plant mainly focusing on corrosion resistance in the representative process environments. Recent progress on these studies is briefly described.© 2004 ASME

Coupling of thermochemical hydrogen production processes with an HTGR

Abstract The rates of hydrogen production by the two thermochemical processes we proposed were estimated when they were coupled with an HTGR. Also, the sensitivities of the hydrogen production rate to the highest reaction temperature and to the highest secondary helium temperature were investigated for each process. On those temperatures, the hydrogen production rate is strongly dependent, because of the relatively large requirement of the process heat at the high temperature region.

Reaction of methanol with hydriodic acid as a step of the CIS process

Abstract The reaction of methanol with hydriodic acid to produce methyl iodide was studied as a step of the CIS Process. The yield of methyl iodide increased with increasing iodine concentration. Following methyl iodide formation and activity decrease of hydriodic acid, dimethyl ether was formed by the reaction of methyl iodide and methanol. The dimethyl ether formation was accelerated by iodine. The co-existence of iodine and sulfuric acid caused no other side reactions. The separation of methyl iodide from the reaction mixture by distillation was discussed briefly.

Ions in carbon dioxide at an atmospheric pressure—II. Effect of CO and O2 addition

Abstract The formation and the subsequent reactions of positive and negative ions were observed by a TRAPI in an atmospheric pressure carbon dioxide added with small amounts of carbon monoxide and oxygen. A relatively stable ion of (44 × n)+ (n ≥ 2) having a different reactivity from that of (CO2)+n was found to be one of major ionic species in this gas system. This species was tentatively assigned as [O2(CO)2]+ (CO2)n-2. A new reaction sequence of positive ions is proposed which can be operative in the radiolysis of carbon dioxide at 1 atm.