Experimental and Modeling Studies of Torrefaction of Spent Coffee Grounds and Coffee Husk: Effects on Surface Chemistry and Carbon Dioxide Capture Performance

Abstract

Torrefaction of biomass is a promising thermochemical pretreatment technique used to upgrade the properties of biomass to produce solid fuel with improved fuel properties. A comparative study of the effects of torrefaction temperatures (200, 250, and 300 °C) and residence times (0.5 and 1 h) on the quality of torrefied biomass samples derived from spent coffee grounds (SCG) and coffee husk (CH) were conducted. An increase in torrefaction temperature (200–300 °C) and residence time (0.5–1 h) for CH led to an improvement in the fixed carbon content (17.9–31.8 wt %), calorific value (18.3–25 MJ/kg), and carbon content (48.5–61.2 wt %). Similarly, the fixed carbon content, calorific value, and carbon content of SCG rose by 14.6–29 wt %, 22.3–30.3 MJ/kg, and 50–69.5 wt %, respectively, with increasing temperature and residence time. Moreover, torrefaction led to an improvement in the hydrophobicity and specific surface area of CH and SCG. The H/C and O/C atomic ratios for both CH- and SCG-derived torrefied biomass samples were in the range of 0.93–1.0 and 0.19–0.20, respectively. Moreover, a significant increase in volatile compound yield was observed at temperatures between 250 and 300 °C. Maximum volatile compound yields of 11.9 and 6.2 wt % were obtained for CH and SCG, respectively. A comprehensive torrefaction model for CH and SCG developed in Aspen Plus provided information on the mass and energy flows and the overall process energy efficiency. Based on the modeling results, it was observed that with increasing torrefaction temperature to 300 °C, the mass and energy yield values of the torrefied biomass samples declined remarkably (97.3% at 250 °C to 67.5% at 300 °C for CH and 96.7% at 250 °C to 75.1% at 300 °C for SCG). The SCG-derived torrefied biomass tested for CO 2 adsorption at 25 °C had a comparatively higher adsorption capacity of 0.38 mmol/g owing to its better textural characteristics. SCG would need further thermal treatment or functionalization to tailor the surface properties to attract more CO 2 molecules under a typical post-combustion scenario.

Biochar and bio-oil fuel properties from nickel nanoparticles assisted pyrolysis of cassava peel

“…(2022) Khat stem 450 19.55 Afessa et al. (2022) Palm fibre 500 26.60 Selvarajoo and Oochit (2020) Coffee husk 300 25.00 Mukherjee et al. (2022) Citrus peels 500 25.73 Selvarajoo et al.…”

“…According to Figure 3 a, three distinct stages of weight loss were observed from the thermal decomposition pattern of the CBC at different temperatures in the range of 20–300 °C, 300–460 °C and 460–580 °C, respectively. In the first stage which occurred at a temperature up to 300 °C, weight loss was ascribed to the dehydration, removal of moisture and light volatile matter from the samples ( Mukherjee et al., 2022 ). Particularly, the observed weight loss associated with dehydration was not significant in all the samples and may be attributed to the hydrophobic nature of the biochars compared to the DCP sample.…”

“…The observed decline in mass loss trend may be linked to the attainment of thermal stability by the CBC samples at different temperatures. Generally, the thermal stability of biomass materials is achieved under severe pyrolysis conditions of higher pyrolysis temperature, higher heating rate and longer residence time ( Mukherjee et al., 2022 ). Above all, higher mass loss was recorded in stage two for biochar at a lower pyrolysis temperature and may be attributed to the presence of a large number of combustible materials in the biochar that was possibly left behind due to incomplete decomposition of lignocellulosic materials during pyrolysis ( Selvarajoo et al., 2022 ).…”

“…The significant mass loss observed at this temperature zone may be attributed to the combustion of volatile matters and is considered the active phase of the pyrolysis process (Askeland et al, 2019). Generally, the basic J o u r n a l P r e -p r o o f lignocellulosic building blocks decomposition is obtained for hemicellulose (220 to 315 °C), cellulose (325 to 400 °C) and lignin (400 to 900 °C) (Mukherjee et al, 2022). The decomposition of hemicellulose occurred in stage one, while hemicellulose, cellulose and lignin decomposed in stage two.…”

“…The observed decline in mass loss trend may be linked to the attainment of thermal stability by the CBC samples at different temperatures. Generally, the thermal stability of biomass materials is achieved under severe pyrolysis conditions of higher pyrolysis temperature, higher heating rate and longer residence time (Mukherjee et al, 2022).…”