Abstract
A novel methylcyclohexane (MCH) dehydrogenation system driven by solar energy with a hydrogen permeation membrane (HPM) reactor is proposed in this study. It is a promising method, via this novel system, to generate pure hydrogen and store intermittent solar energy. In this research, the thermodynamic analysis of MCH dehydrogenation via the HPM reactor was conducted based on numerical simulation. The conversion rates and thermodynamic efficiencies under different temperatures (150–350 °C), permeate pressures from 0.001 to 0.5 bar, and solar irradiation in the four seasons were studied and analyzed. Under a hydrogen partial pressure difference, HPM can separate hydrogen and shift the reaction equilibrium forward for a higher conversion rate of MCH, which can reach nearly 99.7% in this system. The first-law of thermodynamic efficiency, the solar-to-fuel efficiency, and the exergy efficiency are up to 95.58%, 38.65%, and 94.22%, respectively. This study exhibits the feasibility and potential of MCH dehydrogenation via the HPM reactor driven by solar energy and provides a novel approach for solar energy storage.
Highlights
Considered as a green energy carrier, hydrogen is becoming a viable clean choice of energy storage and transportation, and it can be further utilized for power generation by fuel cells [1,2,3]
There are two main organic hydride hydrogen storage systems based on the dehydrogenation reaction: the cyclohexane (CH)–benzene (BZ) system and the methylcyclohexane (MCH)–methylbenzene (TOL) system
MCH and TOL in the MCH dehydrogenation system have lower melting points (−126 ◦ C for MCH, −95 ◦ C for TOL) than the compounds in the CH–BZ system (6.5 ◦ C for CH, 5.5 ◦ C for BZ), which means that MCH can be stably stored as a liquid at room temperature [7,8,9]
Summary
Considered as a green energy carrier, hydrogen is becoming a viable clean choice of energy storage and transportation, and it can be further utilized for power generation by fuel cells [1,2,3]. Many scholars used a hydrogen permeation membrane (HPM) to improve the conversion rate of the MCH dehydrogenation process: Jawad et al. Cholewa et al simulated MCH dehydrogenation based on a Pd membrane reactor, and they achieved an MCH conversion rate of 90% and hydrogen recovery above 80% under the conditions: 350 ◦ C, 30 bar with a permeate pressure of 3 bar [13]. In the process of MCH dehydrogenation heated by a solar trough collector, the mid/low-temperature solar energy with low energy level is converted into chemical energy, which has a relatively high energy level, and there is an improvement in the energy level, which is defined as the ratio of exergy change to enthalpy change during the energy release process [28].
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