Guozhao Ji

Spray-Dried Sodium Zirconate: A Rapid Absorption Powder for CO2 Capture with Enhanced Cyclic Stability

Abstract Improved powders for capturing CO2 at high temperatures are required for H2 production using sorption‐enhanced steam reforming. Here, we examine the relationship between particle structure and carbonation rate for two types of Na2ZrO3 powders. Hollow spray‐dried microgranules with a wall thickness of 100–300 nm corresponding to the dimensions of the primary acetate‐derived particles gave about 75 wt % theoretical CO2 conversion after a process‐relevant 5 min exposure to 15 vol % CO2. A conventional powder prepared by solid‐state reaction carbonated more slowly, achieving only 50 % conversion owing to a greater proportion of the reaction requiring bulk diffusion through the densely agglomerated particles. The hollow granular structure of the spray‐dried powder was retained postcarbonation but chemical segregation resulted in islands of an amorphous Na‐rich phase (Na2CO3) within a crystalline ZrO2 particle matrix. Despite this phase separation, the reverse reaction to re‐form Na2ZrO3 could be achieved by heating each powder to 900 °C in N2 (no dwell time). This resulted in a very stable multicycle performance in 40 cycle tests using thermogravimetric analysis for both powders. Kinetic analysis of thermogravimetric data showed the carbonation process fits an Avrami–Erofeyev 2 D nucleation and nuclei growth model, consistent with microstructural evidence of a surface‐driven transformation. Thus, we demonstrate that spray drying is a viable processing route to enhance the carbon capture performance of Na2ZrO3 powder.

Computational fluid dynamics applied to high temperature hydrogen separation membranes

This work reviews the development of computational fluid dynamics (CFD) modeling for hydrogen separation, with a focus on high temperature membranes to address industrial requirements in terms of membrane systems as contactors, or in membrane reactor arrangements. CFD modeling of membranes attracts interesting challenges as the membrane provides a discontinuity of flow, and therefore cannot be solved by the Navier-Stokes equations. To address this problem, the concept of source has been introduced to understand gas flows on both sides or domains (feed and permeate) of the membrane. This is an important solution, as the gas flow and concentrations in the permeate domain are intrinsically affected by the gas flow and concentrations in the feed domain and vice-versa. In turn, the source term will depend on the membrane used, as different membrane materials comply with different transport mechanisms, in addition to varying gas selectivity and fluxes. This work also addresses concentration polarization, a common effect in membrane systems, though its significance is dependent upon the performance of the membrane coupled with the operating conditions. Finally, CFD modeling is shifting from simplified single gas simulation to industrial gas mixtures, when the mathematical treatment becomes more complex.

Zirconia Incorporated Calcium Looping Absorbents with Superior Sintering Resistance for Carbon Dioxide Capture from In-situ or Ex-situ Processes

The sintering deactivation of Ca-based absorbents has greatly limited the application of calcium looping for either in situ or ex situ processes. In this work, a series of CaO sorbents stabilized with CaZrO3 were prepared by three different wet chemistry methods: freeze drying, spray drying and heating drying. Multi-cycle CO2 capture tests under relatively mild conditions demonstrated that the spray-dried sorbents performed best. Based on both total CO2 uptake and the deactivation rate, the optimum content of CaZrO3 was 20 wt%. Under severe conditions, the best sorbent could even retain a capacity of 0.47 g and 0.44 g CO2 per g sorbent at cycle 30 and cycle 100, respectively, which showed notable superiority over previously reported similar materials. The stabilization mechanism was explored by characterization. It was found that the introduction of CaZrO3 increased the specific surface area and the spray drying method generated a spherical structure, which could retain some pores after severe tests. Three semi-empirical equations were introduced to describe the evolution of the decay process.

Enhanced hydrogen production from thermochemical processes

To alleviate the pressing problem of greenhouse gas emissions, the development and deployment of sustainable energy technologies is necessary. One potentially viable approach for replacing fossil fuels is the development of a H2 economy. Not only can H2 be used to produce heat and electricity, it is also utilised in ammonia synthesis and hydrocracking. H2 is traditionally generated from thermochemical processes such as steam reforming of hydrocarbons and the water-gas-shift (WGS) reaction. However, these processes suffer from low H2 yields owing to their reversible nature. Removing H2 with membranes and/or extracting CO2 with solid sorbents in situ can overcome these issues by shifting the component equilibrium towards enhanced H2 production via Le Chateliers principle. This can potentially result in reduced energy consumption, smaller reactor sizes and, therefore, lower capital costs. In light of this, a significant amount of work has been conducted over the past few decades to refine these processes through the development of novel materials and complex models. Here, we critically review the most recent developments in these studies, identify possible research gaps, and offer recommendations for future research.

Membrane Separation Technology in Carbon Capture

This chapter introduces the basics of membrane technology and the application of membrane separation in carbon capture processes. A number of membranes applicable in precombustion, post-combustion or oxy-fuel combustion have been discussed. An economic comparison between conventional amine-based absorption and membrane separation demonstrates the great potential in membrane technology.