Compressed Hydrogen Production - Speech or Presentation Example

The hydrogen generation in s exothermic reaction and is not effectively prevented by H2 partial pressure in a closed system as thermodynamic properties. In this work, we demonstrated the production of compressed H2 by the reaction between liquid NH3 and lithium hydride LiH in a closed pressure vessel, where liquid NH3 would realize better kinetic properties for the reaction with metal hydride than gaseous NHMoreore than 12 MPa H2 is obtained within several hours.

Experimental procedure involves lithium hydride (LiH) (99.4%, Alfa Aesar), Sodium hydride (NaH) (95%, Aldrich), Potassium hydride (KH) synthesized from Potassium (K) (99.95%, Aldrich,) and H2(99.99999 %), Lithium amide (LiNH2) (95%, Aldrich), Sodium amide (NaNH2) (95%, Aldrich), and Potassium amide (KNH2) synthesized from the KH and NH3(99.999 %) is used for the experiments in this case. The metal hydride MH (M= Li, Na, and K) samples are activated by milling for 10 hours under 1.0 MPa of H2 pressure using a

planetary ball mill apparatus (Fritsch, P7), where the activated MH samples are named as MH*. All the samples are handled in a glove box (Miwa MFG, MP-P60W) filled with a purified Ar (> 99.9999 %) to avoid oxidation and hydration due to water.

The H2desorption properties of MH and NH3systems are then investigated by the following process.

A weighed amount of MH or MH* is packed into a closed pressure vessel in the glove box, then 0.5 MPa NH3with immolation of NH3/MH = 1 is introduced into the vessel. After that, the reaction of MH and NH3 is allowed to proceed at room temperature for 10 minutes, 1, 12, and 24 hours under a static condition (closed system). IT estimates the reaction yield during each reaction time, the weight of the solid sample is measured before and after the reaction. The H2 absorption conditions of MNH2are examined as follows. Thermal analysis of MNH2by using differential scanning calorimetry (DSC) (TA Instruments, Q10 PDSC) installed in a glove box (Miwa MFG, DBO-1.5KP) is carried out under 0.5 MPa of H2 or Ar flow condition with a heating rate of 5 °C/minute to search the reaction temperature between MNH2and H2. From the DSC profile under H2 and Ar flow, the hydrogenation temperature is determined. After that, a weighed MNH2 is treated at the designated temperature based on the above thermal analyses for 4 hours under H2 flow condition (open system) to examine the reactivities. The sample masses before and after the experiments are measured to calculate the reaction yield. The products after the H2 desorption and absorption reaction are identified by X-ray diffraction (XRD) measurement (Rigaku, RINT-2100, CuKαradiation), where the samples are covered by a polyimide sheet (Du Pont-Toray Co., LTD., Kapton®) to protect the samples from oxidation during XRD measurements.

The salts produced by the action of ammonia on acids are known as the ammonium salts and all contain the ammonium ion (NH4+). Although ammonia is well known as a weak base, it can also act as an extremely weak acid. It is a protic substance and is capable of the formation of amides (which contain the NH2− ion). For example, Lithium dissolves in liquid ammonia to give a solution of lithium amine and hydrogen gas:

2 Li + 2 NH3 → 2 LiNH2 + H2

Schematic picture of an experimental system for a demonstration of the chemical compressor by using reactions between liquid NH3 and LiH.

Variations of inside pressure and outside temperature of the reactor during the reaction between liquid NH3 and LiH. Inset: experimental data of pressure variation and vapor pressure of NH3 in NISTXRD patterns of (a) LiH before the experiment and (b) a solid product by the reaction between liquid NH3 and LiH. 

Gas chromatogram of (a) a gaseous product by the reaction between liquid NH3 and LiH, (b) H2 or NH3 gas itself as reference.