Enhancement of Hydrogen Separation in Plasma Membrane Reactors by Zeolite

Hydrogen is a clean energy source that does not emit carbon dioxide and is a key factor in reducing carbon dioxide emissions. Since the energy per volume of hydrogen is very small, it is necessary to liquefy hydrogen for transportation and storage. Since managing liquefied hydrogen requires a lot of energy, there is a need for an efficient hydrogen carrier. Ammonia is expected to be an attractive hydrogen carrier. It has a high hydrogen storage capacity and is very easy to handle because it liquefies readily at room temperature and 10 atm. We have developed a plasma membrane reactor (PMR) that can continuously produce pure hydrogen from ammonia by combining a pulsed plasma reactor with a hydrogen separation membrane. The PMR is a unique reactor that can simultaneously perform ammonia electro-discharge decomposition and hydrogen separation. Previous studies have shown that filling zeolites into the plasma reaction field of the PMR can dramatically improve the hydrogen separation performance. To improve the amount of produced hydrogen, it is necessary to clarify the mechanism of the improvement of hydrogen separation performance by zeolite. In this report, the difference in hydrogen separation performance when filled with different types of zeolites was investigated. By investigating the correlation between various zeolite properties and hydrogen separation enhancement characteristics, the mechanism of hydrogen separation performance enhancement by zeolites was examined.<br/>The experimental apparatus consisted of a sample gas supply system, a high-voltage pulse power supply, the Plasma membrane reactor, and a gas analysis system. Hydrogen gas (99.9%, 75% diluted by nitrogen gas) was used as the sample gas. The sample gas flow rate was controlled by a needle valve and a mass flow meter (ALICAT MS-10SLPM). The PMR consisted of a quartz tube (i.d.=38 mm, thickness=2 mm, length=400 mm) and a cylindrical high-voltage electrode with a hydrogen separation membrane (Pd/Cu 40% alloy). The grounding electrode (SUS316: length = 300 mm) was wrapped around the outside of the quartz tube. The gap length between the electrodes was 4 mm. The PMR was filled with six types of zeolites (SA-600A, 940HOD1A, 840HOD1A, 640HOD1A, 500KODAC, 330HUD1A manufactured by Tosoh Corporation). Hydrogen protonation and hydrogen separation are caused by dielectric barrier discharge (DBD) in the PMR using a high-voltage pulse power supply (Sawafuji Electric Co., Ltd.).<br/>As a result, it was confirmed that filling the PMR with various zeolites significantly increased the hydrogen permeation flow rate and extended the plasma firing area. It found that SA-600A has the highest hydrogen separation enhancement property. The surface area of SA-600A is larger than that of other zeolite samples. In the dielectric-filled DBD plasma reaction field, small streamer discharges tend to propagate along the dielectric surface; more small discharges were generated on the surface of SA-600A, which may have enhanced the protonation of hydrogen due to the higher energy density.