High purity hydrogen production through CO2 sorption-enhanced butanol steam reforming over sodium zirconate-based hybrid material

High-purity hydrogen (H 2 ) is commercially produced by steam reforming (SR), a conventional process involving several sequential steps including carbon dioxide (CO 2 ) separation. In contrast, sorption-enhanced steam reforming (SESR), a next-generation process, does the same, more efficiently and more economically, in a single step by following a strategy of employing a suitable in situ CO 2 sorbent and reforming catalyst in a single material called bifunctional material. These materials outperform the physical catalyst + sorbent mixtures and provide high yield as well as high purity H 2 . In this work, we have synthesized several new bifunctional materials aiming to produce high-purity H 2 optimally via CO 2 sorption-enhanced butanol steam reforming (SEBSR). These materials contain different amounts of a CO 2 sorbent (sodium zirconate, Na 2 ZrO 3 ) and a catalyst support (alumina, Al 2 O 3 ), however, with 10 wt% active metal (Ni) loading in each case. Each material's performance was evaluated in a down-flow fixed-bed reactor. The bifunctional material with equal weight percentages of Na 2 ZrO 3 and Al 2 O 3 , designated as HM-50, outperformed other materials. The effects of process parameters (temperature, steam-to‑carbon molar ratio (S/C) and feed flow rate) on butanol conversion and H 2 purity for SEBSR over HM-50 were investigated too. Under optimal reaction conditions (700 °C temperature, 12.5 S/C and 0.6 cm 3 min −1 feed flow rate), representing a favourable combination identified through single-factor experimental screening, butanol conversion was 100% and H 2 purity was 92%. With a breakthrough time of 20 min (i.e. only H 2 , no CO 2 , came out from the reactor till 20 min), HM-50 exhibited adsorption capacity of 90% (2.13 mmol CO 2 per gram) and endured stability till 9 adsorption-desorption cycles under the optimal reaction conditions. After each reaction (adsorption process), HM-50 could be regenerated (desorption process) within 30 min at 800 °C by passing N 2 gas and steam together. A most probable reaction mechanism pointed to dehydration of butanol to ethanol, which then decomposes to CO and CH 4 , and subsequently, the sorption-enhanced steam reforming of CH 4 produces high purity H 2 . The performance of our bifunctional material (HM-50) was superior to that of other catalytic materials for SEBSR. • SESBR was investigated using hybrid materials comprising Ni, Na 2 ZrO 3 and Al 2 O 3 . • Material HM-50 with equal weight % of Na 2 ZrO 3 and Al 2 O 3 outperformed other materials. • At best reaction conditions ( T = 700 °C, S/C = 12.5 mol/mol), 92% pure H 2 was produced. • HM-50 loaded 2.13 mmol CO 2 per gram and pre-breakthrough period was 20 min. • HM-50 was stable for 9 reaction-regeneration cycles.