Using CO2 as an Oxidant in the Catalytic Pyrolysis of Peat Moss from the North Polar Region

Adsorption of potentially harmful elements by metal-biochar prepared via Co-pyrolysis of coffee grounds and Nano Fe(III) oxides

Nano Fe(III) oxide (FO) was used as an amendment material in CO₂-assisted pyrolysis of spent coffee grounds (SCG) and its impacts on the syngas (H₂ & CO) generation and biochar adsorptive properties were investigated. Amendment of FO led to 153 and 682% increase of H₂ and CO in pyrolytic process of SCG, respectively, which is deemed to arise from enhanced thermal cracking of hydrocarbons and oxygen transfer reaction mediated by FO. Incorporation of FO successfully created porous structure in the produced biochar. The adsorption tests revealed that the biochar exhibited bi-functional capability to remove both positively charged Cd(II) and Ni(II), and negatively charged Sb(V). The adsorption of Cd(II) and Ni(II) was hardly deteriorated in the multiple adsorption cycles, and the adsorption of Sb(V) was further enhanced through formation of surface ternary complexes. The overall results demonstrated nano Fe(III) oxide is a promising amendment material in CO₂-assisted pyrolysis of lignocellulosic biomass for enhancing syngas generation and producing functional biochar.

Environmental benefits from the use of CO2 in the thermal disposal of cigarette butts

As the global consumption of cigarettes has increased, the massive generation of cigarette butts (CBs) has led to critical environmental and health problems. Landfilling or incineration of CBs has been conventionally carried out, but such disposal protocols have suffered from the potential risks of the unwanted/uncontrolled release of leachates, carcinogens, and toxic chemicals into all environmental media. Thus, this study focuses on developing an environmentally dependable method for CB disposal. Littered CBs from filtered/electronic cigarettes were valorized into syngas (H₂/CO). To seek a greener approach for the valorization of CBs, CO₂ was intentionally considered as a reaction intermediate. Prior to multiple pyrolysis studies, the toxic chemicals in the CBs were qualitatively determined. This study experimentally proved that the toxic chemicals in CBs were detoxified/valorized into syngas. Furthermore, this work demonstrated that CO₂ was effective in thermally destroying toxic chemicals in CBs via a gas-phase reaction. The reaction features and CO₂ synergistically enhance syngas production. With the use of a supported Ni catalyst and CO₂, syngas production from the catalytic pyrolysis of CBs was greatly enhanced (approximately 4 times). Finally, the gas-phase reaction by CO₂ was reliably maintained owing to the synergistic mechanistic/reaction feature of CO₂ for coke formation prevention on the catalyst surface.

Disposal and resource utilization of waste masks: a review

Waste masks pose a serious threat to the environment, including marine plastic pollution and soil pollution risks caused by landfills since the outbreak of COVID-19. Currently, numerous effective methods regarding disposal and resource utilization of waste masks have been reported, containing physical, thermochemical, and solvent-based technologies. As for physical technologies, the mechanical properties of the mask-based materials could be enhanced and the conductivity or antibacterial activity was endowed by adding natural fibers or inorganic nanoparticles. Regarding thermochemical technologies, catalytic pyrolysis could yield considerable hydrogen, which is an eco-friendly resource, and would mitigate the energy crisis. Noticeably, the solvent-based technology, as a more convenient and efficient method, was also considered in this paper. In this way, soaking the mask directly in a specific chemical reagent changes the original structure of polypropylene and obtains multi-functional materials. The solvent-based technology is promising in the future with the researches of sustainable and universally applicable reagents. This review could provide guidance for utilizing resources of waste masks and address the issues of plastic pollution.

Carbon dioxide-mediated thermochemical conversion of banner waste using cobalt oxide catalyst as a strategy for plastic waste treatment

In this study, the effects of CO₂ thermochemical agent and a metal oxide catalyst (Co₃O₄) on thermochemical banner waste conversion were explored. The results revealed that compared to the non-catalytic conversion of banner waste under N₂ environment, the conversion under CO₂ yielded more non-condensable gases owing to an enhanced thermal cracking of volatiles. In addition, the CO and CH₄ yields at >700 °C in CO₂ increased considerably owing to the reverse water-gas shift reaction and CO₂ methanation. The CO₂ agent reduced the yields of condensables (e.g., benzoic acids, phthalic acids, esters, biphenyls, fluorenes) and decomposition residue (e.g., char and wax), which could be attributed to the enhancement of the thermal cracking of volatiles evolved during the banner waste conversion by CO₂ and the C-H and O-H bonds present in the feedstock. In addition, the Co₃O₄ catalyst promoted the decarboxylation reaction under N₂ environment, whereas it promoted the methanation and reverse water-gas shift reaction under CO₂. This indicates that compared to the non-catalytic CO₂-assisted banner waste conversion, the use of CO₂ for the conversion of banner waste in the presence of Co₃O₄ significantly increased the yields of CH₄ and CO. Furthermore, Co₃O₄ promoted the thermal cracking of polyester bond, thus decreasing the yields of long-chain chemical compounds. In addition, the simultaneous use of Co₃O₄ catalyst and CO₂ agent minimized the formation of char and wax. For all cases (N₂ versus CO₂, non-catalytic versus catalytic), an increase in temperature enhanced the total permanent gas yield and decreased the yields of condensables, char, and wax. The findings of this study revealed the importance of the synergistic use of Co₃O₄ catalyst and CO₂ agent for the plastic waste upcycling, such as banner waste.

Thermogravimetric Study on Peat Catalytic Pyrolysis for Potential Hydrocarbon Generation

Peat has attracted considerable interest as a potential source of alternative fuel in terms of improving hydrocarbons production and satisfying market demand. The next decade is likely to witness a raise in its exploitation. Nevertheless, the characteristics of peat pyrolysis process, via which many experts expect a considerable generation of hydrocarbons, have not been dealt with in depth. In the present study we have applied thermal analysis combined with isoconversional and model methods for clarifying the kinetic and thermodynamic aspects of the process of generating hydrocarbons from peat via pyrolysis in the absence and presence of iron tallates as a catalytic agent. The obtained results showed a positive effect of the opted catalyst on the process of peat pyrolysis. It has been shown that the catalyst is able to reduce the energy of activation of peat pyrolysis process. Moreover, the Gibbs energy, enthalpy and entropy of complex formation values have been found lower in the presence of iron tallates for all the applied isoconversional methods (Friedman and KAS). The evidence from the present study points toward the beneficial effect generated from the utilization of iron tallates in the processes of hydrocarbons generation from peat for improving energy production in the future.

Dynamic Evolution and Covariant Response Mechanism of Volatile Organic Compounds and Residual Functional Groups during the Online Pyrolysis of Coal and Biomass Fuels

Volatile organic compound (VOC) emissions from pyrolysis of widely used biomass are expected to increase significantly under the carbon neutrality target. However, the dynamic emissions and evolution mechanism of biomass-VOCs remain unclear, hindered by complex reactions and offline measurements. Here, we propose a novel covariant evolution mechanism to interpret the emission heterogeneities, sequential temperature responses, and evolved correlations of both VOCs and residual functional groups (RFGs) during corn straw (CS), wood pellet (WP), and semibituminous coal (SBC) pyrolysis. An innovative combination of online thermogravimetric-Fourier transform infrared-gas chromatography/mass spectrometry and two dimensional-correlation spectroscopy was applied. The relative percentages of CS/WP-VOCs were higher than those of SBC-VOCs, and most VOCs tended to have relatively small carbon skeletons as the average carbon oxidation state increased. With the temperature increased from low to high during CS/WP pyrolysis, the primary sequential response of VOCs (acids → phenols/esters → alcohols/ethers/aldehydes/ketones → hydrocarbons/aromatics) corresponded to the RFG response (hydroxyl groups → -CH₃/-CH₂-/-CH groups → aliphatic ethers and conjugated ketones). Compared with the relative regularity for CS/WP responses, the gas-solid products from SBC pyrolysis exhibited complex temperature-dependent responses and high oxidation-induced variability. These insights provide favorable strategies for the online monitoring system to facilitate priority removal of coal and biomass fuels-VOCs.

Functional use of CO2 to mitigate the formation of bisphenol A in catalytic pyrolysis of polycarbonate

The growing consumption of plastic materials has increased hazardous threats to all environmental media, since current plastic waste management methods release microplastics and toxic chemicals. As such, massive generation of plastic derived pollutants leads to significant public health and environmental problems. In this work, an environmentally sound method for valorization of plastic waste is suggested. In detail, pyrolysis of polycarbonate-containing plastic waste such as automotive headlight housing (AHH) was carried out using CO₂ as a co-reactant. AHH was chosen as it discharges bisphenol A (BPA) and aromatic compounds. Under CO₂ condition, emissions of BPA and its derivatives were suppressed by 14.5% due to gas phase reactions (GPRs) with CO₂. Nevertheless, reaction kinetics for GPRs was not significant. To impart the GPRs, catalytic pyrolysis was done using Ni and Co-based catalysts. During catalytic pyrolysis, syngas production was more than tenfold up comparing to pyrolysis without catalyst. The expedited GPRs over catalysts resulted in the enhanced syngas formation. Total concentration of the toxic chemicals from CO₂-assisted catalytic pyrolysis of AHH decreased by 86.1% and 66.7% over Ni and Co catalysts, comparing to those from N₂ environment.

In-depth exploration of mechanism and energy balance characteristics of an advanced continuous microwave pyrolysis coupled with carbon dioxide reforming technology to generate high-quality syngas

This study firstly coupled advanced continuous microwave pyrolysis with CO₂ reforming technology to recover syngas from cow manure and CO₂. The contribution of CO₂ to syngas, pyrolysis mechanism, and energy balance characteristics were analyzed thoroughly. The results showed that continuous microwave pyrolysis coupled with CO₂ reforming technology has superiorities over other pyrolysis methods in bio-gas generation. The bio-gas yield, syngas content, and heating value of syngas reached the maximum value of 71.02 wt%, 85.70 vol%, and 10.87 MJ/Nm³, respectively. CO₂ strengthened pyrolysis and reacted with pyrolysis products to produce high-quality syngas and reduce H₂S. Due to the limited substances that can react with CO₂ and excessive energy consumption with increasing CO₂ concentration, the utilization efficiencies of CO₂ and energy decreased from 36.31% and 27.27% to 31.16% and 24.24%, respectively. This work provides basic theory and technical support for advanced technology to recover high-quality syngas from biomass with low energy consumption.

A Thermal Study on Peat Oxidation Behavior in the Presence of an Iron-Based Catalyst

Peat is a resource used for heat and energy, particularly in countries where peat is abundant and conventional fuels are not available. Some countries have made extensive use of peat resources to produce electricity and heat in addition to light hydrocarbons. By doing so, they were able to reduce the cost of importing fossil fuels. To the best of our knowledge, there is a lack of a detailed description of the peat oxidation process in the presence of other substances. Herein, the process of peat oxidation was studied in-depth by means of thermal analysis in the presence of iron tallate acting as a catalytic agent. Differential scanning calorimetry and thermogravimetric analysis demonstrated an oil-like oxidation behavior during the combustion of the used peat. The process of peat oxidation includes two main regions: low-temperature oxidation (LTO), which occurs during the oxidation of light hydrocarbons, followed by the so-called high-temperature oxidation (HTO), which includes the oxidation of the obtained coke-like product. Moreover, the application of non-isothermal kinetics experiments based on the isoconversional and model approach principle have confirmed the role of 2% iron tallate in peat mass by improving the oxidation rate at low- and high-temperature oxidation (HTO) regions. The results obtained from this study have proven that the added catalyst improves efficiency with regards to the energy activation in the process by leading to its significant decrease from 110.8 ± 7.8 kJ/mol to 81.8 ± 7.5 kJ/mol for LTO and from 157.8 ± 19.1 kJ/mol to 137.6 ± 9.3 kJ/mol for HTO. These findings clearly confirm the improvement in the rate of the process by shifting the LTO and HTO peaks to lower regions in the presence of the catalyst. These results further emphasize the possible impact which could be generated by the application of thermally enhanced oil recovery methods on peat development and exploitation.

Strategic disposal of flood debris via CO2-assisted catalytic pyrolysis

Recent abnormal climate changes resulted in the dramatic alternation of rainfall and flood patterns in many countries. The massive generation of flood debris, a mixture of soil (sediment), biomass, plastic, metal, and various hazardous materials, poses various environmental and public health problems. This study suggests a sustainable technical platform to convert the hazardous materials into value-added products. CO₂-assisted pyrolysis was used to thermally convert flood debris into syngas (H₂ and CO). CO₂ enhanced the syngas production due to gas phase homogeneous reactions (HRs) between CO₂ and volatile hydrocarbons evolved from pyrolysis of flood debris. For improvement of HRs in line with enhancement of syngas production, additional thermal energy and earth abundant catalyst were used. In particular, Ni/SiO₂ catalyst increased more than one order of magnitude higher syngas production, comparing to non-catalytic pyrolysis. Synergistic effect of CO₂ and Ni catalyst showed nearly 50% more production of syngas in reference to catalytic pyrolysis under N₂. During flood debris pyrolysis, compositional matrix of flood debris was also determined by detecting index chemicals of waste materials that cannot be identified by naked eyes. Thus, this study confirmed that CO₂-assisted pyrolysis is a useful tool for conversion of flood debris into value-added chemicals.

CO2-assisted catalytic pyrolysis of cellulose acetate using Ni-based catalysts

Cellulose acetate (CA) is one of widely used polymers for chemical and medical applications due to its versatile physico-chemical functionalities. Although its recycle is available after a deacetylation process, the recycle process releases a huge amount of wastewater. Thus, this study investigated a direct disposal process of CA with its valorization to syngas (H₂ and CO) through pyrolysis. To construct more environmentally benign process, CO₂ was used as a co-feedstock with CA to simultaneously convert them into syngas. Pyrolysis of CA in N₂ was performed as a reference study to examine the effectiveness of CO₂ on valorization of CA. Acetic acid and methyl acetate were main volatile pyrolysates (VPs) from CA pyrolysis, and the further thermal cracking of VPs resulted in syngas and CH₄ formations under both N₂ and CO₂ conditions. To expedite syngas formations, multi-stage pyrolysis (two-stage pyrolysis) and catalytic pyrolysis were employed. With the increased thermal energy through two-stage pyrolysis, four times more production of syngas was shown, comparing to the result of a single-stage pyrolysis. With Ni catalysts, the syngas formation was the two orders of magnitude higher than the single-stage pyrolysis, and the significant enhancement of CO formation was shown in the presence of CO₂ due to combined effects of CO₂ and the Ni-based catalysts. This CO enhancement resulted from catalytically expedited gas phase reactions between CO₂ and VPs evolved from CA. In addition, the CO₂ contributed to the suppression of coke deposition on the catalyst, thereby suggesting more technical and environmental benefits of CO₂ as a reactive co-feedstock of pyrolysis in reference to N₂. Therefore, this study proved the direct and versatile technical platform to convert CA and CO₂ into syngas.

Comparative study on carbon dioxide-cofed catalytic pyrolysis of grass and woody biomass

This study investigated the mechanistic functions of CO₂ on the pyrolysis of two different biomasses to elucidate the effect of CO₂ on syngas formations during pyrolysis. To this end, CO₂-assisted pyrolysis of cellulosic biomass (barnyard grass, Echinochloa) and lignin-rich woody biomass (retinispora, Chamaecyparis obtusa) were compared. The confirmed mechanistic effectiveness of CO₂ on pyrolysis of biomass was gas phase reactions between CO₂ and volatile matters from biomass pyrolysis. Lignin-rich biomass had more CO₂ susceptibility, resulting in more enhanced CO formation via the gas phase reactions. To expedite the slow reaction rate of the gas phase reactions during biomass pyrolysis, earth-abundant catalysts (Co/SiO₂ and Ni/SiO₂) were employed for pyrolysis of two biomass substrates. With Co and Ni catalysts, the syngas formations were 2 and 3 times higher comparing to the pyrolysis of without catalyst. The cumulative formations of syngas from lignin-rich biomass was nearly doubled than that from cellulosic biomass.

Valorization of disposable COVID-19 mask through the thermo-chemical process

It becomes common to wear a disposable face mask to protect from coronavirus disease 19 (COVID-19) amid this pandemic. However, massive generations of contaminated face mask cause environmental concerns because current disposal processes (i.e., incineration and reclamation) for them release toxic chemicals. The disposable mask is made of different compounds, making it hard to be recycled. In this regard, this work suggests an environmentally benign disposal process, simultaneously achieving the production of valuable fuels from the face mask. To this end, CO2-assisted thermo-chemical process was conducted. The first part of this work determined the major chemical constituents of a disposable mask: polypropylene, polyethylene, nylon, and Fe. In the second part, pyrolysis study was employed to produce syngas and C1-2 hydrocarbons (HCs) from the disposable mask. To enhance syngas and C1-2 HCs formations, multi-stage pyrolysis was used for more C-C and C-H bonds scissions of the disposable mask. Catalytic pyrolysis over Ni/SiO2 further expedited H2 and CH4 formations due to its capability for dehydrogenation. In the presence of CO2, catalytic pyrolysis additionally produced CO, while pyrolysis in N2 did not produce it. Therefore, the thermo-chemical conversion of disposable face mask and CO2 could be an environmentally benign way to remove COVID-19 plastic waste, generating value-added products.

Mitigation of harmful chemical formation from pyrolysis of tobacco waste using CO2

Global consumption of tobacco has been continuously increasing. This results in the considerable generation of toxic waste materials from the tobacco industry and daily life. Conventional disposal methods for them (incineration and landfilling) could be a potential hazard for releasing carcinogens and toxins into our eco-system. Accordingly, an eco-friendly disposal platform for converting tobacco waste (TW) into syngas was mainly studied in this present work. To realize this, pyrolysis of two commercial cigarette products (Marlboro and HEETS (electronic cigarette)) was done under the CO2/N2 conditions. One of the main findings from the present study was that CO2 reacted with volatile matters (VMs) obtained from the thermolysis of TW through the gas phase reactions (GPRs), which provided a strategic measure to manipulate carbon rearrangement of all pyrolysates. In particular, the GPRs expedited the carbon rearrangement of harmful chemical species, converting toxic chemicals into syngas. When the fraction of VMs in TWs increased, the GPR were more effective. Therefore, the introduced eco-friendly method using CO2-mediated thermochemical process could be beneficial for energy recovery from TWs while mitigating the formations of harmful chemical species.

Industrial carbon dioxide capture and utilization: state of the art and future challenges

This review covers the sustainable development of advanced improvements in CO₂ capture and utilization.