GENERATION OF ACTIVATED CARBON FROM SPENT COFFEE GROUNDS: PROCESS OPTIMIZATION, KINETICS AND CO2 CAPTURE

Carbon dioxide capture technology is gaining popularity owing to the environmental concerns and deterioration of the climatic conditions related to atmospheric CO2 emission. Of the candidate, lignocellulose biomass samples have been considered a promising source for producing carbon-based adsorbents that can be utilized to capture recalcitrant CO2 from the post-combustion capture facility. Recently, the removal of CO2 using activated carbon (AC) has gained immense attention owing to its environmentally friendly characteristics and low cost for synthesis. Conversely, with the increasing population, the demand for coffee consumption is also accelerating. The generation of coffee residues owing to the increased consumption would increase and demand effective utilization and management. The research primarily focused on utilizing the waste generated from the coffee industries, namely spent coffee grounds (SCG) and coffee husk (CH), to evaluate their potential in synthesizing carbon-based adsorbents for CO2 removal under the post-combustion capture scenario and propose a cost-effective AC production strategy from lignocellulose-based biomass. This study focused on investigating the influence of different thermochemical conversion techniques on the physicochemical properties of biochar, followed by assessing the impact of activation parameters and the effect of deep eutectic solvent (DES) on the physicochemical characteristics of AC and the removal of CO2. Moreover, a techno-economic analysis was performed to assess the economic feasibility of biomass conversion technology used to synthesize AC. Overall, this study is divided into five research objectives with multiple sub-objectives. The first phase of this research conducted a parametric study of the conventional torrefaction technique. In this regard, SCG and CH were used as the lignocellulose-based precursor. The impact of torrefaction parameter on the physicochemical transformation of biomass was examined by varying each parameter (torrefaction temperature and reaction time) independently. The influence of torrefaction conditions on the precursors' physicochemical changes and structural transformations were analyzed using diverse analytical techniques. This is followed by evaluating the candidacy of the corresponding torrefied biomass samples towards CO2 capture performance. The physicochemical transformation of torrefied biomass samples mainly synthesized in severe torrefaction conditions (300 ℃ and 1 h) demonstrated their candidacy for CO2 removal. The equilibrium CO2 adsorption capacities of SCG-300-1 and CH-300-1 were 0.38 and 0.23 mmol/g, respectively, at 25 ℃ of column temperature and in the presence of 30 vol% CO2 in N2. Comparatively, the torrefied biomass sample derived from SCG displayed superior CO2 capture performance under a similar capture scenario than CH derived torrefied biomass sample owing to the textural properties and surface chemistry developed during the torrefaction process. The findings from phase one raised numerous research questions. For instance, is it necessary to study the thermal treatment of biomass at a temperature higher than 300 ℃ like undergoing slow pyrolysis to elevate the removal of tar from the carbon matrix and accelerate the volatilization reactions to generate biochar with enhanced textural characteristics and improved surface chemistry for superior CO2 capture performance? Furthermore, evaluating the kinetic and thermodynamic parameters before performing a high-temperature thermal treatment (slow-pyrolysis) is essential to obtain necessary information regarding the feedstock and the process parameters. Hence, phase two implemented the kinetic and thermodynamic study of the slow pyrolysis technique using SCG and CH. In this regard, the kinetic data of SCG and CH during slow pyrolysis were obtained to fit the thermogravimetric data taken using the TGA-DTG analyzer. The kinetic parameters were estimated using different iso-conversational methods followed by estimating thermodynamic parameters. In this regard, the conversion technique using SCG showed higher activity and would be efficient in terms of energy requirement as the requirement of activation energy for SCG was low (90.4-141.7 kJmol-1) compared to CH (96.0-162.1 kJmol-1). Also, SCG can be identified as a superior lignocellulose-based precursor for further valorization than CH in terms of physicochemical properties. Appropriate utilization of biochar derived from slow pyrolysis of SCG could improve the overall economics of the post-combustion CO2 capture facility. In the third phase, the impact of slow pyrolysis process parameters was assessed on biochar yield and specific surface area (SBET). Secondly, this research aimed to elucidate the correlation of pyrolysis temperature as a critical parameter with textural properties, surface composition, aromatic structure, and CO2 mitigation efficiency of SCG-derived biochar samples. The results demonstrated that biochar yield reduced with the rising pyrolysis temperature, but biochar's textural characteristics, surface functionalities and aromatic structure were positively correlated with the increasing temperature conditions. Correspondingly, the impact of pyrolysis process parameters on biochar yield complemented the findings of the second phase of this study. In this study, SCG-600 showed the highest equilibrium CO2 uptake of 2.8 mmol/g in 30 vol% of CO2 (in N2) and 30 ℃ (column temperature). It was evident that the well-developed textural characteristics and porosity, availability of basic surface functional groups, and aromatic structure of SCG-600 influenced the CO2 removal performance owing to the enhanced acid-base interactions and the presence of Vander Waals force of attraction. Treating the promising biochar sample derived from SCG at a higher temperature in the presence of a suitable activating agent becomes necessary to improve the physicochemical properties of the carbon-based adsorbent for improved CO2 capture performance. Therefore, the fourth phase's main objective was to optimize the two-stage CO2 activation process of SCG-600 using the Box-Behnken design (BBD) method. The impact of activation parameters (activation temperature, holding time, and CO2 gas flow rate) were investigated on surface area (SBET) and AC yield. In addition, the influence of thermal pre-treatment techniques (torrefaction and slow-pyrolysis) for the two-stage physical activation technique were evaluated and compared in terms of textural characteristics and CO2 adsorption performance. Further, the impact of tailoring the surface functionalities of the pristine AC sample was evaluated using deep eutectic solvent (DES) and compared with pristine AC (AC-CO2) through complementary analytical techniques. CO2 breakthrough experiments were performed under different ranges of temperatures and CO2 concentration in N2 to investigate the influence on adsorption performance and selectivity. The estimated highest equilibrium CO2 uptake for two sets of ACs (pristine and DES-treated) were 4.34 mmol/g and 5.5 mmol/g, respectively, at 25 ℃ and 15 vol % of CO2 in N2. The DES-treated AC displayed a superior adsorption capacity, selectivity, and regeneration ability due to a well-developed porous structure, morphology, and availability of a wide variety of desired functional groups that facilitated the CO2 capture process under a simulated post-combustion scenario. A comparative techno-economic assessment and sensitivity analysis were performed using different AC production scenarios from SCG. The economic viability of the AC production technique using SCG as the potential precursor was assessed based on the discounted cash flow analysis (DCFA) technique. The minimum selling price (MSP) of AC samples derived from different scenarios evaluated were US $0.15/kg,$ 0.21/kg, and $0.28/kg, respectively. Comparatively, the MSP of DES functionalized AC was lower than commercial AC (US$0.45/kg). A positive net rate of return (NRR) for all the production scenarios indicates that AC production using dried SCG is profitable from an economic point of view. The sensitivity analysis demonstrates that the feedstock cost and utility cost influence the MSP of AC production

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

Copyright © 2022 The Authors. Published by American Chemical Society. This publication is licensed under CC-BY-NC-ND 4.0.Natural Sciences and Engineering Research Council of Canada (NSERC), BioFuel Net, and Canada Research Chair (CRC)Peer ReviewedTorrefaction 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 CO2 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 CO2 molecules under a typical post-combustion scenario

Techno – Economic analysis of activated carbon production from spent coffee grounds: Comparative evaluation of different production routes

2590-1745/© 2022 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/bync-nd/4.0/).Natural Sciences and Engineering Research Council of Canada (NSERC), BioFuel Net, and Canada Research Chair (CRC)Peer ReviewedActivated carbon (AC) has gained immense popularity owing to its excellent physicochemical properties and its ability to remove carbon dioxide (CO2) from flue gas stream. This study examines the potential of spent coffee grounds (SCG) as a precursor for activated carbon (AC) production via prominent thermochemical conversion technologies. Different production routes, such as slow pyrolysis, activation, and deep eutectic solvent (DES) functionalization were compared in terms of their economic viability. Three scenarios (Scenario 1–3) involving combinations of the technologies and production routes were evaluated. Scenario 1 comprises of slow pyrolysis, CO2 activation and flue gas recycling for activation. Scenario 2 includes flue gas combustion while the third scenario comprise of flue gas combustion and DES impregnation. All processes were simulated with Aspen plus, while a detailed cash flow analysis was used to estimate the profitability parameters. The price of AC was found to be the most crucial determinant of an AC production plant’s viability and feasibility. The minimum selling price (MSP) of AC samples produced from scenarios 1,2 and 3 are U.S $0.15/kg,$0.21/kg, $0.28/kg respectively. The price of pristine AC and DES treated AC were lower than the commercially available activated carbon (U.S$0.45/kg)

Design and Synthesis of Fluorescent Carbon Dot Polymer and Deciphering Its Electronic Structure

Herein we report the one-pot synthesis of a fluorescent polymer-like material (pCD) by exploiting ruthenium-doped carbon dots (CDs) as building blocks. The unusual spectral profiles of pCDswith double-humped periodic excitation dependent photoluminescence (EDPL), and the regular changes in their corresponding average lifetime indicate the formation of high energy donor states and low energy aggregated states due to the overlap of molecular orbitals throughout the chemically switchable π-network of CDs on polymerization. To probe the electronic distribution of pCDs, we have investigated the occurrence of photoinduced electron transfer with a model electron acceptor, menadione using transient absorption technique, corroborated with low magnetic field, followed by identification of the transient radical ions generated through electron transfer. The experimentally obtained B_(1/2) value, a measure of the hyperfine interactions present in the system, indicates the presence of highly conjugated π-electron cloud in pCDs. The mechanism of formation of pCDs and the entire experimental findings have further been investigated through molecular modeling and computational modeling. The DFT calculations demonstrated probable electronic transitions from the surface moieties of pCDs to the tethered ligands

Design and Synthesis of Fluorescent Carbon Dot Polymer and Deciphering Its Electronic Structure

Herein we report the one-pot synthesis of a fluorescent polymer-like material (pCD) by exploiting ruthenium-doped carbon dots (CDs) as building blocks. The unusual spectral profiles of pCDswith double-humped periodic excitation dependent photoluminescence (EDPL), and the regular changes in their corresponding average lifetime indicate the formation of high energy donor states and low energy aggregated states due to the overlap of molecular orbitals throughout the chemically switchable π-network of CDs on polymerization. To probe the electronic distribution of pCDs, we have investigated the occurrence of photoinduced electron transfer with a model electron acceptor, menadione using transient absorption technique, corroborated with low magnetic field, followed by identification of the transient radical ions generated through electron transfer. The experimentally obtained B_(1/2) value, a measure of the hyperfine interactions present in the system, indicates the presence of highly conjugated π-electron cloud in pCDs. The mechanism of formation of pCDs and the entire experimental findings have further been investigated through molecular modeling and computational modeling. The DFT calculations demonstrated probable electronic transitions from the surface moieties of pCDs to the tethered ligands

Pyrolysis kinetics and activation thermodynamic parameters of exhausted coffee residue and coffee husk using thermogravimetric analysis

Exhausted coffee residue (ECR) and coffee husk (CH) are potential feedstock for energy production through thermochemical and biochemical conversion processes. Kinetic study of ECR and CH is essential for the design and optimization of different thermochemical conversion processes. In this study, four different iso‐conversional methods were employed in the estimation of the activation energy (EA) and pre‐exponential factor (A). The methods used includes Flynn‐Wall‐Ozawa (FWO), Kissinger‐Akahira‐Sunose (KAS), Kissinger’s method, and the Friedman method. Data from the thermogravimetric/derivative thermogravimetric analysis (TGA/DTG) at varying heating rates of 5‐20°C/min in an inert environment were used in this study. It was observed that the heating rate influences the pyrolysis parameters such as peak temperature, maximum degradation rate and initial decomposition temperature. The activation energy for ECR using the FWO method was in the range of 62.3‐102.4 kJ · mol−1. Likewise, the KAS and Friedman methods yielded activation energy between 51.3‐93.3 kJ · mol−1 and 10.6‐122.7 kJ · mol−1, respectively. In addition, the activation energy calculated for CH using FWO, KAS, and Friedman methods were shown to range from 39.1‐140.6 kJ · mol−1, 27.7‐131.6 kJ · mol−1, and 24.9‐111.2 kJ · mol−1, respectively.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/168498/1/cjce24037.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/168498/2/cjce24037_am.pd

Pyrolysis kinetics and activation thermodynamic parameters of exhausted coffee residue and coffee husk using thermogravimetric analysis

Exhausted coffee residue (ECR) and coffee husk (CH) are potential feedstock for energy production through thermochemical and biochemical conversion processes. Kinetic study of ECR and CH is essential for the design and optimization of different thermochemical conversion processes. In this study, four different iso‐conversional methods were employed in the estimation of the activation energy (EA) and pre‐exponential factor (A). The methods used includes Flynn‐Wall‐Ozawa (FWO), Kissinger‐Akahira‐Sunose (KAS), Kissinger’s method, and the Friedman method. Data from the thermogravimetric/derivative thermogravimetric analysis (TGA/DTG) at varying heating rates of 5‐20°C/min in an inert environment were used in this study. It was observed that the heating rate influences the pyrolysis parameters such as peak temperature, maximum degradation rate and initial decomposition temperature. The activation energy for ECR using the FWO method was in the range of 62.3‐102.4 kJ · mol−1. Likewise, the KAS and Friedman methods yielded activation energy between 51.3‐93.3 kJ · mol−1 and 10.6‐122.7 kJ · mol−1, respectively. In addition, the activation energy calculated for CH using FWO, KAS, and Friedman methods were shown to range from 39.1‐140.6 kJ · mol−1, 27.7‐131.6 kJ · mol−1, and 24.9‐111.2 kJ · mol−1, respectively.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/168498/1/cjce24037.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/168498/2/cjce24037_am.pd

Process design, exergy, and economic assessment of a conceptual mobile autothermal methane pyrolysis unit for onsite hydrogen production

The present study proposes a conceptual mobile autothermal methane pyrolysis unit for onsite hydrogen production. Considering the shortage of hydrogen pipeline infrastructure between production plants and fuelling stations in most places where hydrogen is required, it is imperative to create alternative hydrogen production means. The design combines a catalytic plasma methane pyrolysis unit with a steam char gasification setup, combustion, and biomethanation unit for hydrogen production. The reactor design includes Ni - Br in a bubble column acting as a catalyst. Energy and exergy calculations followed by a comprehensive economic analysis were appraised to evaluate the efficiency and performance of the integrated process. The levelized cost of hydrogen (LCOH) from the conceptual design ranged from 1.3 to 1.47 U.S.$/kg, while the proposed design's net present value (NPV) was in the range of 3.76 – 4.35 M.U.S.$. Factors such as equipment purchase cost (EPC) and feedstock cost significantly influenced the NPV and LCOH. In addition, a positive NPV and lower LCOH outline the proposed design's profitability. Finally, an optimized methane conversion of 76.8 % was obtained from the study