Innovative closed-loop thermochemical pathways for sodium borohydride as a hydrogen carrier: Process development and techno-economic-environmental assessment

Sodium borohydride (NaBH₄) is a promising hydrogen carrier, but its widespread adoption is hindered by high production costs. To address this challenge, we developed four novel NaBH₄ production processes that lower production costs by combining two NaBH₄ synthesis reactions (i.e., the Brown-Schlesinger reaction and the NaB(OCH₃)₄ reduction reaction) with two different by-products (i.e., NaOH and NaOCH₃). Additionally, a closed-loop system incorporating the recycling of NaBH₄ dehydrogenation by-products was designed to enhance the mass efficiency, while heat integration improved energy efficiency. Based on the simulation results, we evaluated the techno-economic and environmental performance of the proposed processes. The proposed closed-loop process utilizing NaB(OCH₃)₄ reduction with NaOCH₃ by-product (CB2) achieved a unit production cost of 2.18 $/kg and net CO_2eq emissions of 1.20 kgCO_2eq/kg, demonstrating a cost reduction of up to 72.2 % compared with the open-loop process. Sensitivity analysis revealed that the sodium feedstock cost was the most influential cost driver, while the NaBH₄ synthesis reaction yield and dehydrogenation by-product recycling rate also significantly impacted process economics and environmental performance. These cost reductions and favorable environmental performance establish the competitiveness of NaBH₄ as a hydrogen carrier. This study provides a benchmark for NaBH₄′s economic and environmental performance, demonstrating its viability as a hydrogen carrier.