High temperature ammonia modification of rice husk char to enhance CO2 adsorption: influence of pre-deashing

Abstract

To enhance the CO₂ adsorption capacity of rice husk char, pre-deashing of raw materials and high temperature ammonia treatment were combined to prepare the nitrogen-enriched char in this work. Two different pre-deashing methods were compared: HCl pre-deashing and HF–HCl pre-deashing treatment. The physicochemical properties and CO₂ adsorption capacity of the prepared nitrogen-enriched chars were investigated. The experimental results show that the micropore surface area of nitrogen-enriched char derived from HF–HCl deashed rice husk (HF–HCl–N-Char) is 549.61 m² g⁻¹, much greater than the HCl deashed (HCl–N-Char) of 313.72 m² g⁻¹ and the non-deashed (N-Char) of 303.10 m² g⁻¹. The nitrogen content of HF–HCl–N-Char (3.32 wt%) is also the highest among the three types of chars, while that of HCl–N-Char is only 1.01 wt%, even less than the N-Char (1.64 wt%). In addition, at adsorption temperatures of 30 °C and 120 °C, HF–HCl–N-Char demonstrates the largest CO₂ adsorption capacity among the three types of chars, which is 85.90 mg g⁻¹ at 30 °C and 19.27 mg g⁻¹ at 120 °C, respectively. However, compared with N-Char, HCl–N-Char exhibits no obvious increase in CO₂ adsorption capacity. This indicates that HF–HCl pre-deashing improves the CO₂ adsorption capacity of nitrogen-enriched char, but HCl pre-deashing does not.