Effects of the addition of an organic polymer on the hydrolysis of sodium tetrahydroborate in batch reactors

• Published in: International journal of hydrogen energy Vol. 35; no. 20; pp. 11456 - 11469
• Main Authors: Ferreira, M.J.F., Fernandes, V.R., Gales, L., Rangel, C.M., Pinto, A.M.F.R.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01.10.2010; Elsevier
• Subjects: Alternative fuels. Production and utilization; Applied sciences; Byproducts; Crystal structure; Energy; Exact sciences and technology; Fuels; Hydrogen; Hydrogen generation, hydrogen storage, organic polymers; Hydrogen storage; Hydrolysis; Liquid phases; Reactors; Reused Ni–Ru bimetallic catalyst; Sodium; Sodium borohydride hydrolysis; Solubility; Reused Ni–Ru bimetallic catalyst; Sodium borohydride hydrolysis; Hydrogen generation, hydrogen storage, organic polymers; Costs; Hydrogen storage; Ruthenium; Hydrogen; Reused Ni-Ru bimetallic catalyst; Cellulose; Solubility; Experimental study; Dissolution; Hydroborates; Hydrolysis; Portable; Additive; Boron; Storage capacity; Stainless steel; Nickel; Yield; Kinetics; Catalyst; Hydrogen production; Crystalline structure
• ISSN: 0360-3199; 1879-3487
• DOI: 10.1016/j.ijhydene.2010.07.079

An experimental study is presented both on the generation and storage of molecular hydrogen (H 2) by small additions of an organic polymer – carboxymethyl cellulose (CMC) – to sodium borohydride (NaBH 4) through the alkaline hydrolysis, in the presence of a powdered nickel–ruthenium based catalyst reused from 274 to 282 times. The experiments were performed at 45 °C in two batch reactors with internal volumes of 0.229 L and 0.369 L, made of stainless-steel with bottom conical shape, positioned vertically. The results showed that working at moderate pressures, up to 2.7 MPa, increases slightly the H 2 dissolution in the liquid phase, enhanced by the changing of the polarity of the remained solution inside the reactor: a value of 0.182 for dimensionless H 2 solubility in the liquid phase with 0.25 wt% CMC was found, at 45 °C, based on Henry’s law. As a consequence, sodium tetrahydroxoborate, NaB(OH) 4 by-product was produced in the presence of CMC additive, showing the absence of crystalline water in its crystal structure (NaB(OH) 4 presents structural water, with boron atoms linked to four hydroxyl groups). This new finding never reported to form at < 50 °C, has a positive impact in recyclability costs of NaBO 2 back to NaBH 4 due to the elimination of two energy consuming steps in the metaborate dehydration kinetics. In fact our system of compressed hydrogen, shows that both H 2 generation rates and yields and hydrogen storage capacities can be augmented, the latter to reach ≈ 6 wt%, by adding small amounts of an organic polymer (CMC) to the classic NaBH 4 hydrolysis, performed with stoichiometric amount of water. The eventual success of this new route will depend upon developing a advantageous method of converting borates into tetrahydroborate and also finding materials (chemicals) which enhance the solubility of H 2, promoting its reversible storage in the liquid phase. We therefore attempted to show that a less Polar Organic Polymeric Solution ( lPOPS) of NaBH 4 is a suitable hydrogen carrier for portable and/or niche applications.