Hydrogen membrane reactors trap carbon dioxide
Syngas, a mixture of hydrogen (H2), carbon monoxide and carbon dioxide (CO2), is a by-product from coal and gas-fired power stations. A palladium (Pd) membrane is only permeable to H2, facilitating selective separation of this potential fuel from other syngas molecules for clean power generation. Steam condensation of the remaining stream containing mostly CO2 and steam leaves behind concentrated CO2 at high pressure. This significantly reduces the compression energy required for transport and storage. Eight partners from industry and academia joined forces in the EU-funded 'Carbon dioxide capture and hydrogen production with membranes' (CACHET II) project to optimise Pd membrane performance. Besides incorporating sulphur-resistant properties, project members also worked on scaling-up and carrying out long-term stability testing of seal and substrate technology. CACHET II members used a newly fabricated tool to specify an optimised pilot and commercial membrane module design. A reaction model was also built in, enabling the simulation tool to model the setup for an integrated water–gas–shift membrane reactor and non-integrated membrane separator. CACHET II successfully upgraded the 50 cm pure Pd membrane to 1 m using the proprietary electroless plating technique. For commercially exploitable module assembly, an innovative sealing technology was developed based on direct connection of ceramic membranes with stainless steel tubes. Improved sulphur tolerance of the membrane was achieved by developing a Pd-alloy membrane with added silver and gold. A novel copper-based high-temperature hydrogen sulphide (H2S) sorbent process enabled a 25 % reduction of energy consumption per tonne of CO2 avoided. This promises to significantly enhance the economic benefits and competitiveness of the Pd membrane in solid fuel applications. CACHET II has published seven papers with peer-reviewed journals and another five papers are currently in preparation. European and international conferences, workshops and a book titled 'Pd Membrane Technology and Applications' to be published complete the comprehensive dissemination programme. Whilst carbon capture and storage is not expected to be commercially deployed across Europe until 2020–2030, the CACHET II combination of H2 production and H2 purification for the semiconductor industry heralds the evolution of a novel industry.
