Investigation On CO₂ Capture Performance And Pretreatment Methods Of Li₄SiO₄-based Sorbent Derived From Agricultural And Forestry Wastes

Since the Li₄SiO₄-based sorbent was proposed as a CO₂ sorbent,many scholars have done a lot of work to reduce the cost of the sorbent and promote its industrial application.The use of waste silicon sources to synthesize Li₄SiO₄-based adsorbents is undoubtedly an excellent choice.In this research,the preparation of Li₄SiO₄-based sorbent was carried out from the waste silicon source and its pretreatment method.Firstly,a typical biomass waste（bagasse）was used as a silicon source to synthesize Li₄SiO₄-based sorbent,and the pretreatment method of washing biomass ash was used for the first time,comparing with the traditional method of washing biomass.It is found that the silicon content in the ash directly determines the adsorption capacity of the sorbent.The secondary elements in the silicon sources will consume the lithium source and generate by-products during the synthesis process of the Li₄SiO₄-based sorbent,which greatly harms the adsorption performance of the sorbent.Furthermore,the element effect and mechanism of each pretreatment methods are compared.The results indicate that whether it is washed with water or acid,the sequence of calcination and washing of bagasse has the same effect on the increase of silicon content in the silicon source and has similar improvement of adsorption capacity of the synthetic sorbent.However,the cost of washing biomass ash is lower owing to fewer pretreatment reagents are used.Compared with the traditional process of washing biomass,the pretreatment method of directly washing biomass ash proposed in this article is a more economical and efficient modification of Li₄SiO₄-based sorbent method.Furthermore,the fly ash received from the biomass power plant was explored as a silicon source to prepare Li₄SiO₄-based sorbents.At the same time,two different pretreatment methods of water washing and acid washing were directly carried out on the fly ash according to the above conclusions,and then compare the effects of the two pretreatment methods on the elements of fly ash.It is found that fly ash from biomass power plant can be employed as the silicon source to produce Li₄SiO₄-based sorbent with better CO₂ sorption performance.In addition,because the combustion of biomass in power plant boilers is very complicated,most of the impurity elements in biomass exist in fly ash in the form of aluminosilicate,which cause that acid washing still has a good effect on the increase of silicon content in the fly ash.The silicon content in the fly ash after acid washing pretreatment is as high as 81.17 wt.%.The sorbent prepared by using it has a maximum sorption capacity of 0.366 g CO₂/g sorbent,which is 1.57 times the adsorption performance of the unmodified sorbent.To sum up,a joint technical route is proposed to prepare Li₄SiO₄-based adsorbent from biomass power plant fly ash and directly using it in the power plant’s own CO₂ capture system.This route can simultaneously realize the resource utilization of waste and CO₂ reduction,which is of great significance to the control of pollutants in biomass power plants.