New Approach to Extend Durability of Sorbent Powders for Multicycle High Temperature CO2 Capture in Hydrogen

固体吸附剂对二氧化碳的研究是由于它们在中高温二氧化碳分离方面比液态胺、膜或低温分离技术具有潜在的优势，例如，在废生物质的蒸汽重整/气化制氢中，通过使用诸如CaO之类的吸附剂粉末来化学结合混合产物流中的二氧化碳并改变反应热力学以增加氢气产量。在与化石燃料发电厂和其他工业相结合的大规模二氧化碳捕获中也有应用。该材料工程提案解决了粉末吸附剂（如CaO）在高温应用中面临的主要问题，包括通过吸附剂增强蒸汽重整（SESR）废生物质制氢。在高温再生过程中，由于粉末床结构（致密化）的变化，二氧化碳捕集性能会下降，这阻碍了这项有前途的技术在SESR和大规模二氧化碳捕集应用中的充分利用。在bb0 ~ 800℃热处理后，会发生显著的粉末致密化，以释放二氧化碳并再生吸附剂。这会导致孔隙度和吸附剂表面积的损失，导致二氧化碳捕获性能的严重衰减。例如，近年来的发展，添加耐火间隔颗粒仅在非最佳再生条件下（例如在惰性气氛中< 850℃）才成功。在这项为期18个月的可行性研究中，将开发的粉末将利用一种新的方法来抵消致密化和表面积损失，旨在在大气条件下实现950℃（远高于现有吸附剂）的再生，而不会显著降低二氧化碳的吸收能力。新粉末的一个重要优点是，在950℃的再生过程中，将产生接近纯的二氧化碳流，产生适合与二氧化碳储存和/或利用方案集成的输出流；这与使用现有材料在较低温度下产生的混合气流形成对比。解决耐久性问题的新方法是将部分稳定氧化锆（PSZ）的超细颗粒分散在吸附剂基体中。再生后的PSZ颗粒在冷却时发生相变，导致颗粒（晶）体积增加。在周围部分烧结的吸附剂基体中产生的应变将导致微裂纹和二次应变场的发展，从而为气体的进入打开孔隙通道。因此，即使在技术上有利的高再生温度（950℃）下，后续吸附步骤中二氧化碳捕获能力的损失也将得到缓解，从而提高多循环吸附剂效率，并提高SESR中的氢气产量。还将对另一种CO2吸附剂Na2ZrO3的抗致密机制进行评估。

Research into solid adsorbents for CO2 is motivated by their potential advantages over liquid amine, membrane or cryogenic separation techniques in mid-high temperature CO2 separation, for example, in hydrogen production via steam reforming/gasification of waste biomass where production yields are increased through the use of a sorbent powder such as CaO that chemically binds the CO2 from the mixed product stream and shifts the reaction thermodynamics to increase hydrogen output. There are also applications in large scale CO2 capture involving integration with fossil fuel fired power stations, and other industries.This materials engineering based proposal addresses the major problem facing utilisation of powder sorbents such as CaO for high temperature applications, including hydrogen production by sorbent enhanced steam reforming (SESR) of waste biomass. A decay in CO2 capture performance due to changes in the structure of the powder bed (densification) during regeneration at high temperatures prevents full exploitation of this promising technology in SESR and large scale CO2 capture applications. Significant powder densification occurs after heat-treatments at > 800 C to release CO2 and regenerate the sorbent. This leads to loss of porosity and sorbent surface area, causing a serious decay in CO2 capture performance. Developments in recent years, for example, adding refractory spacer particles are only successful for non-optimal regeneration conditions (e.g. < 850 C in inert atmospheres).The powders to be developed in this 18 month feasibility study will exploit a novel means of counteracting densification and loss of surface area, aiming to achieve regeneration at 950 C (much higher than for existing sorbents) in atmospheric conditions without significant decay in CO2 sorption capacity. An important advantage of the new powders is that a near-pure CO2 stream will be generated during regeneration at 950 C, producing output streams suited to integration with CO2 storage and/or utilisation programmes; this contrasts to the mixed gas streams generated at lower temperatures using existing materials. The new approach to the durability problem is to disperse ultrafine particles of partially stabilised zirconia (PSZ) in the sorbent matrix. The PSZ particles undergo a phase transition on cooling after regeneration which results in an increase in particle (crystallite) volume. Resulting strains generated in the surrounding, partially sintered, sorbent matrix will cause microcracks and secondary strain fields to develop which will open up pore channels for ingress of gasses. Loss of CO2 capture capacity in the subsequent sorption step will thus be mitigated, even for technologically favoured high regeneration temperatures (950 C), leading to increased multi-cycle sorbent efficiency, and increased hydrogen yield in SESR. The anti-densification mechanism will also be evaluated for an alternative CO2 sorbent, Na2ZrO3.