Yingchao Hu

Preparation of Novel Li4SiO4 Sorbents with Superior Performance at Low CO2 Concentration

This work produced Li4 SiO4 sorbents through an impregnated-suspension method to overcome its typical poor performance at low CO2 concentrations. A SiO2 colloidal solution and two different organic lithium precursors were selected. A bulgy surface morphology (and thus, the significantly enlarged reacting surface area) was obtained for Li4 SiO4 , which contributed to the high absorption capacity. As a result, the capacity in cyclic tests at 15 vol % CO2 was approximately 8 times higher than conventional Li4 SiO4 prepared through a solid-state reaction. The phenomenon of a progressively increasing capacity (i.e., sustainable usage) was observed over the 40 cycles investigated, and this increasing trend continued to the last cycle. Correspondingly, over the course of the multicycle absorption/ desorption processes, the sorbents evolve from lacking porosity to having a high number of micron-sized pores.

Alkali‐Doped Lithium Orthosilicate Sorbents for Carbon Dioxide Capture

New alkali-doped (Na2 CO3 and K2 CO3 ) Li4 SiO4 sorbents with excellent performance at low CO2 concentrations were synthesized. We speculate that alkali doping breaks the orderly arrangement of the Li4 SiO4 crystals, hence increasing its specific surface area and the number of pores. It was shown that 10 wt % Na2 CO3 and 5 wt % K2 CO3 are the optimal additive ratios for doped sorbents to attain the highest conversions. Moreover, under 15 vol % CO2 , the doped sorbents present clearly faster absorption rates and exhibit stable cyclic durability with impressive conversions of about 90 %, at least 20 % higher than that of non-doped Li4 SiO4 . The attained conversions are also 10 % higher than the reported highest conversion of 80 % on doped Li4 SiO4 . The performance of Li4 SiO4 is believed to be enhanced by the eutectic melt, and it is the first time that the existence of eutectic Li/Na or Li/K carbonate on doped sorbents when absorbing CO2 at high temperature is confirmed; this was done using systematical analysis combining differential scanning calorimetry with in situ powder X-ray diffraction.

Incorporation of CaO in inert solid matrix by spray drying sol mixture of precursors

Sol mixing of one soluble precursor with one insoluble precursor has been investigated to incorporate CaO in an inert solid matrix to obtain superior CaO-based sorbents for CO2 capture. However the generally used drying method in oven is a slow and high energy-consuming heating process. In this study, we investigated the application of spray-drying technique, which is a quick drying and energy saved method, to synthesize a series of CaO-based sorbents with sol mixture of calcium and inert support precursors. FSEM-EDS mapping has shown that CaO grains can be homogeneously dispersed in the inert solid support. Four synthetic CaO-based sorbents were prepared and tested under the same conditions of both pure N2 and CO2-rich calcination atmospheres and the associated surface area, morphology and grain size were also examined. Under the pure N2 calcination atmosphere, all the synthetic sorbents show a much higher CO2 capture performance than natural sorbent limestone, particularly CaO incorporated in Ca12Al14O33 exhibiting the conversion twice as high as that of limestone at the 13th cycle. However, under a CO2-rich calcination atmosphere, quicker degradation of the capture capacity was observed for these sorbents. The decay is also associated with severer sintering due to the presence of CO2, which could be proved by the larger grain size of CaO as well as smaller specific surface area of the sorbents after cycles. Nevertheless, the synthetic sorbents still perform better than natural limestone due to the presence of inert support matrix.