Elsevier

Fluid Phase Equilibria

Volumes 228–229, February 2005, Pages 499-503
Fluid Phase Equilibria

Hydrogen solubility in a chemical hydrogen storage medium, aromatic hydrocarbon, cyclic hydrocarbon, and their mixture for fuel cell systems

https://doi.org/10.1016/j.fluid.2004.07.013Get rights and content

Abstract

A synthetic type apparatus was designed to measure hydrogen solubility in four pure aromatic or cyclic hydrocarbons, benzene, cyclohexane, toluene, and methylcyclohexane, and two equimolar binary mixtures, benzene + cyclohexane, and methylcyclohexane + toluene. The experimental temperature was 303.15 K, and the pressure range from 0.887 to 4.827 MPa. The hydrogen solubility increased linearly with the pressure following the Henry's law. The hydrogen solubility in benzene was smaller than that in cyclohexane. Similarly, the solubility in toluene was smaller than in methylcyclohexane. In the measurement for the mixtures, the mole ratio of benzene:cyclohexane and methylcyclohexane:toluene was set to 1:1. The hydrogen solubility in the equimolar mixtures was lower than that in pure cyclic hydrocarbon, cyclohexane or methylcyclohexane. The experimental solubility data in pure hydrocarbons were correlated with the Peng–Robinson (PR) equation of state using van der Waals one fluid mixing rule. Using binary interaction parameters in the mixing rule, the hydrogen solubility in the mixtures was predicted well.

Introduction

Hydrogen has been paid much attention as a clean energy source for fuel cell vehicles (FCV). In 1993, the Ministry of International Trade and Industry of Japan initiated a World Energy Network (WE-NET) project called New Sunshine programme. In the course of the project, several hydrogen storage systems have been proposed utilizing the following types of reactions between cyclic and aromatic hydrocarbons [1], [2]:

In the proposed system, a cyclic hydrocarbon is sent from fuel tank to a membrane reactor, and catalytically converted to hydrogen and an aromatic hydrocarbon. The aromatic hydrocarbon is then send back to the fuel tank. The stored aromatic hydrocarbon is catalytically converted again to a cyclic hydrocarbon in a refinery station. The theoretical mass content of hydrogen is 7.19 mass% for cyclohexane, and 6.16 mass% for methylcyclohexane, respectively.

Experimental data of hydrogen solubility are essential for designing these hydrogen storage systems. However, limited data are available for the solubility of hydrogen in cyclic and aromatic hydrocarbons, especially in the low temperature range. In this study, a synthetic type apparatus was constructed to measure hydrogen solubility in four pure aromatic or cyclic hydrocarbons, benzene, cyclohexane, toluene, and methylcyclohexane, and two equimolecular mixtures, benzene + cyclohexane, and methylcyclohexane + toluene at 303.15 K. The experimental solubility data in the pure hydrocarbons were correlated with the Peng–Robinson (PR) equation of state using van der Waals one fluid mixing rule. Using binary interaction parameters in the mixing rule, the hydrogen solubility was predicted for the mixtures.

Section snippets

Materials

Hydrogen was obtained from Takachiho Trading Co. Ltd., Tokyo, with the stated purity of ≥99.99 %. Benzene, cyclohexane, toluene, and methylcyclohexane were special grade reagents obtained from Wako Pure Chemical Industries Ltd., Osaka, Japan. The stated purity of benzene, cyclohexane, and toluene was ≥99.5 %, and that of methylcyclohexane was ≥98.0%. All chemicals were used without further purification.

Equipment and procedure

In this study, a synthetic type apparatus was designed to measure hydrogen solubility. Fig. 1

Results and discussion

In order to validate the reliability of the experimental data, hydrogen solubility was measured in cyclohexane, and compared with the data in the literature. Table 1 lists the experimental data of this work, and Fig. 2 shows the comparison of the experimental results for cyclohexane. Herskowitz et al. [4] measured the hydrogen solubility in cyclohexane at 303.15 K and Ronze et al. [5] measured the similar data at 304 K. As shown in the figure, the literature data of hydrogen solubility in

Conclusion

Hydrogen solubility data at 303.15 K were measured in four hydrocarbons, benzene, cyclohexane, methylcyclohexane, toluene, and two equimolar mixture, benzene + cyclohexane, and methylcyclohexane + toluene, using a synthetic type apparatus. The hydrogen solubility data in the pure hydrocarbons were correlated and those in the binary mixtures predicted using the PR equation of state.

    List of symbols

    a

    attractive parameter in PR eq. (J m3/mol2)

    b

    excluded volume parameter in PR eq. (m3/mol)

    kij

    binary parameter in mixing

Acknowledgements

The authors would like to thank Dr. T. Miyata of Osaka New Material Center, Japan for his assistance, and wish to acknowledge the Ministry of Economy, Trade and Industry, Japan, and New Energy and Industrial Technology Organization (NEDO) for financial supports of this research (No. 03001393-0).

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