Carbon dioxide capture from flue gas in biochar produced from spent coffee grounds: Effect of surface chemistry and porous structure

Coffee is a relevant agricultural product and one of the most consumed hot beverages globally. To assess the impact of pyrolysis temperatures (400-600 degrees C) and heating rates from 5 to 20 degrees C/min on the biochar production yields and textural characteristics, spent coffee grounds was subjected to slow-pyrolysis in a pilot-scale reactor. Further, complementary spectroscopic and textural analyses were executed to evaluate the impacts of pyrolysis temperatures on the corresponding biochar surface properties including textural characteristics, reactivity, and surface functionalities. The correlation of pyrolysis temperature with change in biochar's surface properties along with CO2 mitigation efficiency is examined. The ultimate analysis, FTIR spectroscopy, C-13 NMR spectroscopy and Raman scattering measurements confirmed an increment in the degree of aromaticity or decomposition of organic complexes in biochar. The development of basic surface functionalities after the thermal treatment was ascertained by XPS and NEXAFS analyses. Based on the surface composition and textural properties, the CO2 adsorption capacity of SCG-600 was assessed under varying adsorption temperatures at ambient pressure employing a fixed-bed reactor. In this investigation, SCG-600 showed a large CO2 uptake of 2.8 mmol/g under a typical post-combustion scenario. CO2 adsorption mechanism followed the pseudo-first-order kinetics and lower activation energy over varying investigated temperatures reveals the binding process is physical in nature. SCG-600 could be proposed as promising biochar that possesses a combination of higher surface area, well-developed microporous structure, heterogeneous and basic surface functional moieties to meet the specific requirements in dynamic CO2 adsorption.

Automated summary

This study evaluated the effects of different pyrolysis temperatures and heating rates on slow-pyrolysis of spent coffee grounds to produce biochar, as well as the impact on biochar's surface properties, reactivity, and surface functionalities. The results showed that SCG-600 has potential advantages in CO2 adsorption capacity, surface composition, and functional groups.