Deliquescence Behavior of Sodium Borohydride and Steam

Engineering Sciences and Fundamentals
2011 AIChE Annual Meeting
AIChE Annual Meeting
October 16, 2011 - 8:00pm

Sodium borohydride as an effective, cheap and stable material for hydrogen storage has been studied widely. Despite prior studies [1-5]on the steam hydrolysis of NaBH4, the mechanism for the release of hydrogen by water vapor/ NaBH4 contact has not been well understood. Recently, Beaird et al. [2] established that the initial step in the pathway is deliquescence of water onto NaBH4, and she reported the deliquescence relative humidity (DRH) based on visual observation of the change in appearance of NaBH4 crystals during reaction. A basic study of the phase behavior during the water vapor hydrolysis reaction is necessary should the reaction pathway be exploited in for future engineering designs. Therefore, in this presentation we build on prior DRH measurements by developing a theoretical model and utilizing this, with experiments and simulation, to accurately predict the deliquescence behavior of steam on sodium borohydride. Macroscopically, we describe deliquescence in the bulk limit where the theory is well established. Microscopically, we have also used first principles density functional theory to examine the initial stages of deliquescence at the atomic level. We have performed ab initio molecular dynamics at 300 K and 350 K using a slab model of the NaBH4(001) surface covered by water. The simulations indicate that the initial stages of deliquescence happen very rapidly, with water penetrating the (001) surface on the picosecond time-scale. Deliquescence is known to initiate clearly with increasing relative humidity on reaching free energy equality between the initial (salt particle plus vapor) and final (fully dissolved solution drop plus vapor) states until deliquescence. Additional experiments utilize in situ visualization, as described by Beaird et al. [2].

[1] R. Aiello, et al., "Production of hydrogen from chemical hydrides via hydrolysis with steam," International Journal of Hydrogen Energy, vol. 24, pp. 1123-1130, 1999.

[2] A. M. Beaird, et al., "Deliquescence in the Hydrolysis of Sodium Borohydride by Water Vapor," Industrial & Engineering Chemistry Research, vol. 49, pp. 9596-9599, 2010.

[3] H. Liu, et al., "Vapor phase batch hydrolysis of NaBH4 at elevated temperature and pressure," International Journal of Hydrogen Energy, vol. In Press, Corrected Proof.

[4] E. Y. Marrero-Alfonso, et al., "Hydrolysis of sodium borohydride with steam," International Journal of Hydrogen Energy, vol. 32, pp. 4717-4722, 2007.

[5] E. Y. Marrero-Alfonso, et al., "Minimizing water utilization in hydrolysis of sodium borohydride: The role of sodium metaborate hydrates," International Journal of Hydrogen Energy, vol. 32, pp. 4723-4730, 2007.

Professional Development Hours
0.5 PDHs
You will be able to download and print a certificate for these PDH credits once the content has been viewed. If you have already viewed this content, please click here to login.
Presenter(s): 

Would you like to access this content?

No problem. You just have to complete the following steps.

You have completed 0 of 2 steps.

  1. Log in

    You must be logged in to view this content. Log in now.

  2. Purchase Technical Presentation

    You must purchase this technical presentation using one of the options below.
    If you already purchased this content recently, please click here to refresh the system's record of ownerships.

Pricing

Credits 0.5 Use credits
List Price $25.00 Buy now
AIChE Members $15.00 Buy now
AIChE Undergraduate Student Members Free Free access
AIChE Graduate Student Members $15.00 Buy now
Related Topics: