High temperature capture of CO₂on Li₄SiO₄-based sorbents from biomass ashes

Abstract

Highly efficient Li4SiO4 (lithium orthosilicate)/biomass‐based (Li4SiO4/bio‐based) sorbents for CO2 capture at high temperature, were developed using a water pretreated waste materials (biomass ashes). Three typical biomass ashes and a water pretreated biomass ash were as raw materials for preparing the Li4SiO4/bio‐based sorbents. These raw biomass ashes and their resulting Li4SiO4/bio‐based sorbents were characterized by energy dispersive X‐ray, X‐ray diffraction, scanning electron microscopy, nitrogen adsorption, and thermogravimetry. The stability of CO2 sorption was tested through 15 carbonation/calcination cycles in a fixed bed reactor. The characteristic results showed that the high amount of metals (especially alkali metals) of biomass ashes could produce low contents of silica and further led the amorphous silica nanoparticles to more severe quartz aggregation. Moreover, these different physical properties of biomass ashes had a significant effect on the phase composition, microstructure, specific surface area, and CO2 absorption properties of their synthesized Li4SiO4/bio‐based sorbents. With the higher contents of SiO2 and the smaller particle size, its resulting sorbent using the water pretreatment biomass ashes presented the higher amount of Li4SiO4, smaller particle size and larger specific surface area. This special structure appeared to be the main reasons for increasing in CO2 capture performance and kinetic behavior as illustrated by the thermogravimetric analyses. This pretreatment Li4SiO4/bio‐based sorbent also maintained its higher capacity during the multiple cycles. It was concluded that synthesis of Li4SiO4‐based sorbents obtained from the pretreated biomass ash is a promising approach for CO2 capture at high temperature. © 2014 American Institute of Chemical Engineers Environ Prog, 34: 526–532, 2015

Optimization of Li4SiO4 synthesis conditions by a solid state method for maximum CO2 capture at high temperature

“…Table 3 reports the kinetic parameters obtained from the fitting of some isotherms (obtained at 600 o C), including R 2 values; as represented by the high R 2 values, the model accurately fitted CO2 experimental absorption isotherms. The values of k1 were one order of magnitude larger than the k2 values, indicating that the overall absorption CO2 kinetics is controlled by the lithium diffusion rate; these values are in agreement with those found in the literature 8,16 . Sample 900-5-2 exhibited the highest k1 value and this can be attributed to an increased number of sites for CO2 chemisorption because its lower crystal size.…”

“…Furthermore, contradictory results in terms of CO2 uptake for samples prepared under very similar conditions have been previously reported, as can be deduced from Table 1. For example, CO2 uptake, some values reported in the literature are surprisingly high 8 , considering that the Si source come from a biomass ash with low Si content and the active mass for CO2 capture is reduced by dilution effect (less than 50% Li4SiO4 content in all cases). Likewise, the influence of CO2 concentration on the Li4SiO4 sorbent performance has not been yet completely understood and it seems to be highly dependent on the sorbent characteristics, i.e.…”

Recent advances in lithium containing ceramic based sorbents for high-temperature CO2 capture

“…In addition to improving the CO2 sorption performance of Li4SiO4 sorbent, it is also important to lower the cost of precursors. Until now, many kinds of cheap silicon sources such as fly ash, 114,115 rice husk ash, 49,116,117 biomass ashes, 118 halloysite, 119 diatomite, 120 and vermiculite 121 have been used for the synthesis Li4SiO4-based sorbents. Generally, the Li4SiO4-based sorbents synthesized from solid wastes or cheap silicon sources exhibited similar or even higher CO2 sorption capacity and/or better cycling performance compared to the Li4SiO4 synthesized from commercial SiO2, as summarized in Table 4.…”

“…Besides rice husk ash, several other types of biomass ashes such as cotton stalk, wood dust, and rice straw have also been studied for the synthesis of Li4SiO4. Zhao et al 118 prepared highly efficient bio-based Li4SiO4 for CO2 capture at high temperatures.…”

Understanding the flue gas components on the mechanism governing CO2 adsorption on the Li4SiO4 surface

“…In later studies, identifying potential silicon sources [16,17] and Li precursors [18], emerging synthesis routes (impregnated suspension [19,20], precipitation [21], carbon templating [22,23], and sol-gel methods [24,25]), and the incorporation of hetero elements [26][27][28][29][30][31] into the Li 4 SiO 4 crystal structure have been substantially used to prepare effective Li 4 SiO 4 sorbents. Despite these improvements in capture capacity, most sorbents still suffer from slow kinetics at low CO 2 partial pressures [32].…”