Pyrolysis/gasification of pine sawdust biomass briquettes under carbon dioxide atmosphere: Study on carbon dioxide reduction (utilization) and biochar briquettes physicochemical properties

Recent advances in organic waste pyrolysis and gasification in a CO2 environment to value-added products

The persistent combustion of fossil fuels has resulted in a widespread greenhouse effect attributable to the continual elevation of carbon dioxide (CO2) levels in the atmosphere. Recent research indicates that utilizing CO2 as a pyrolysis gasification medium diminishes CO2 emissions and concurrently augments the value of the resultant pyrolysis gasification products. This paper reviews recent advancements in the pyrolysis gasification of organic solid wastes under a CO2 atmosphere. Meanwhile, the mechanisms of CO2 influence in the pyrolysis and gasification processes were also discussed. In comparison to noble gases, CO2 exhibits reactivity with char at≥710 °C, resulting in additional mass loss of the sample. In addition, CO2 was able to increase the specific surface area and stability of biochar and reduce biooil toxicity by lowering the content of cyclic compounds in the biooil, while CO2 was able to react with GPRs with some volatile products (e.g., light hydrocarbons) to increase biogas yield. Finally, CO2 also prevents catalyst deactivation by reducing secondary coke formation. We also recommend directing future attention toward utilizing unpurified CO2 in pyrolysis and gasification. This review aims to expand the utilization of CO2 and advocate for applying pyrolysis gasification products.

Energetic, bio-oil, biochar, and ash performances of co-pyrolysis-gasification of textile dyeing sludge and Chinese medicine residues in response to K2CO3, atmosphere type, blend ratio, and temperature

Hazardous waste stream needs to be managed so as not to exceed stock- and rate-limited properties of its recipient ecosystems. The co-pyrolysis of Chinese medicine residue (CMR) and textile dyeing sludge (TDS) and its bio-oil, biochar, and ash quality and quantity were characterized as a function of the immersion of K2CO3, atmosphere type, blend ratio, and temperature. Compared to the mono-pyrolysis of TDS, its co-pyrolysis performance with CMR (the comprehensive performance index (CPI)) significantly improved by 33.9% in the N2 atmosphere and 33.2% in the CO2 atmosphere. The impregnation catalyzed the co-pyrolysis at 370°C, reduced its activation energy by 77.3 kJ/mol in the N2 atmosphere and 134.6 kJ/mol in the CO2 atmosphere, and enriched the degree of coke gasification by 44.25% in the CO2 atmosphere. The impregnation increased the decomposition rate of the co-pyrolysis by weakening the bond energy of fatty side chains and bridge bonds, its catalytic and secondary products, and its bio-oil yield by 66.19%. Its bio-oils mainly contained olefins, aromatic structural substances, and alcohols. The immersion of K2CO3 improved the aromaticity of the co-pyrolytic biochars and reduced the contact between K and Si which made it convenient for Mg to react with SiO2 to form magnesium-silicate. The co-pyrolytic biochar surfaces mainly included -OH, -CH2, C=C, and Si-O-Si. The main phases in the co-pyrolytic ash included Ca5(PO4)3(OH), Al2O3, and magnesium-silicate.

Study on the effects of carbon dioxide atmosphere on the production of biochar derived from slow pyrolysis of organic agro-urban waste

Slow pyrolysis, a widely recognized thermochemical technique, is employed to produce biochar usually under inert atmospheres. Recently, there is a growing interest in utilizing CO2 as a carrier gas during pyrolysis as an alternative to inert atmospheres, aiming to modify the resulting pyrolytic products and make them suitable for different applications. This study investigated and compared the impact of CO2 atmosphere with N2 on pyrolysis of food waste, rice husk, and grape tree branches waste via slow pyrolysis at temperatures of 400, 500, and 600 °C at 5 and 15 °C/min for 1 h, to evaluate biochar production and its properties. The results demonstrate that CO2 atmosphere increased the biochar yield for all feedstocks and significantly influenced the physicochemical properties of biochar. Compared to N2, CO2-derived biochar exhibited less volatile matter, higher carbon content, lower O/H and O/C molar ratios and enhanced textural properties. This study highlighted the potential of utilizing CO2 for biochar production and tailoring biochar properties for specific applications and the findings contribute to the establishment of sustainable and efficient waste management systems and the production of value-added biochar products.

A critical review on biochar production from pine wastes, upgradation techniques, environmental sustainability, and challenges

Pine wastes, including pine needles, cones, and wood, are abundantly produced as an agroforestry by-product globally and have shown tremendous potential for biochar production. Various thermochemical conversion technologies have exhibited promising results in converting pine wastes to biochar, displaying impressive performance. Hence, this review paper aims to investigate the possibilities and recent technological advancements for synthesizing biochar from pine waste. Furthermore, it explores techniques for enhancing the properties of biochar and its integrated applications in various fields, such as soil and water remediation, carbon sequestration, battery capacitor synthesis, and bio-coal production. Finally, the paper sheds light on the limitations of current strategies, emphasizing the need for further research and study to address the challenges in pine waste-based biochar synthesis. By promoting sustainable and effective utilization of pine wastes, this review contributes to environmental conservation and resource management.

Utilization of current pyrolysis technology to convert biomass and manure waste into biochar for soil remediation: A review

Traditional disposal of animal manures and lignocellulosic biomass is restricted by its inefficiency and sluggishness. To advance the carbon management and greenhouse gas mitigation, this review scrutinizes the effect of pyrolysis in promoting the sustainable biomass and manure disposal as well as stimulating the biochar industry development. This review has examined the advancement of pyrolysis of animal manure (AM) and lignocellulosic biomass (LB) in terms of efficiency, cost-effectiveness, and operability. In particular, the applicability of pyrolysis biochar in enhancing the crops yields via soil remediation is highlighted. Through pyrolysis, the heavy metals of animal manures are fixated in the biochar, thereby both soil contamination via leaching and heavy metal uptake by crops are minimized. Pyrolysis biochar is potentially use in soil remediation for agronomic and environmental co-benefits. Fast pyrolysis assures high bio-oil yield and revenue with better return on investment whereas slow pyrolysis has low revenue despite its minimum investment cost because of relatively low selling price of biochar. For future commercialization, both continuous reactors and catalysis can be integrated to pyrolysis to ameliorate the efficiency and economic value of pyrolysis biochar.

Evaluation of Queen Palm residues and kraft lignin in the production of biofuels using densification and slow pyrolysis technology

This study aims to enhance the energy use of two products of industry - Queen Palm residue and kraft lignin (KF) - through the combination of two technologies - briquetting and slow pyrolysis. The addition of 20% KF provided briquettes with higher physical, energy, and mechanical properties. The yields of the pyrolysis products were affected by both the pyrolysis temperature and the addition of KF. In the bio-oil, the presence of phenols, methyl phenols, and methoxy phenols was highlighted; these compounds were present in greater quantities in the treatments with KF. It is concluded that combining the briquetting and pyrolysis processes produces both energy and economic benefits because it is possible to transport lighter loads with the same amount of energy per volume. Under the briquetting conditions adopted in this study, the addition of KF as a binder is necessary because this results in briquettes with better physical, energy and mechanical properties.

Impact of Torrefaction on Fuel Properties of Aspiration Cleaning Residues

To maximise the use of biomass for energy purposes, there are various options for converting biomass to biofuels through thermochemical conversion processes, one of which is torrefaction. Higher utilisation of waste from the aspiration cleaning of grains, such as wheat or maize, could be one of the means through which the dependence on fossil fuels could be reduced in the spirit of a circular economy. In this study, the effect of torrefaction on fuel properties of agricultural residues was investigated. The tested materials were waste by-products from the aspiration cleaning of maize grains and waste from wheat. The materials were treated by torrefaction under a nitrogen atmosphere (225 °C, 250 °C, and 275 °C), over a residence time of 30 min. During the treatment, weight loss was monitored as a function of time. Proximate and elemental composition, as well as calorific values, were analysed before and after torrefaction. Torrefaction has a positive effect on the properties of the fuels in the samples studied, as shown by the results. The carbon content increased the most between temperatures of 250 °C and 275 °C, i.e., by 11.7% wt. in waste from maize. The oxygen content in the maize waste samples decreased by 38.99% wt. after torrefaction, and in wheat waste, it decreased by 37.20% wt. compared to the original. The net calorific value increased with increasing temperatures of process and reached a value of 23.56 MJ·kg^-1 at a peak temperature of 275 °C in by-products from maize. To express the influence of the treatments on combustion behaviour, stoichiometric combustion calculations were performed. Differences of up to 20% in stoichiometric combustion parameters were found between the two types of waste. A similar case was found for fuel consumption, where a difference of 19% was achieved for torrefaction at a temperature of 275 °C, which fundamentally differentiated these fuels.

Machine learning assisted prediction of biochar yield and composition via pyrolysis of biomass

Biochar production via pyrolysis of various organic waste has potential to reduce dependence on conventional energy sources and mitigate global warming potential. Existing models for predicting biochar yield and compositions are computationally-demanding, complex, and have low accuracy for extrapolative scenarios. Here, two data-driven machine learning models based on Multi-Layer Perceptron Neural Network and Artificial Neuro-Fuzzy Inference System are developed. The data-driven models predict biochar yield and compositions for a variety of input feedstock compositions and pyrolysis process conditions. Feature importance assessment of the input dataset revealed their competitive significance for predicting biochar yield and compositions. Overall, the predictive accuracy of the models was up to 12.7% better than the Random Forest and eXtreme Gradient Boosting machine learning algorithms reported in the literature. The models developed are valuable for environmental footprint assessment of biochar production and rapid system optimization.

Experimental and DFT investigation on N-functionalized biochars for enhanced removal of Cr(VI)

In this study, N-functionalized biochars with varied structural characteristics were designed by loading poplar leaf with different amounts of urea at 1:1 and 1:3 ratios through pyrolysis method. The addition of urea significantly increased the N content of biochar and facilitated the formation of amine (-NH-, -NH₂), imine (-HCNH), benzimidazole (-C₇H₅N₂), imidazole (-C₃H₃N₂), and pyrimidine (-C₄H₃N₂) groups due to substitution reaction and Maillard reaction. The effect of pH on Cr(VI) removal suggested that decrease in solution pH favored the formation of electrostatic attraction between the protonated functional groups and HCrO₄^-. And, experimental and density functional theory study were used to probe adsorption behaviors and adsorption mechanism which N-functionalized biochars interacted with Cr(VI). The protonation energy calculations indicated that N atoms in newly formed N-containing groups were better proton acceptors. Adsorption kinetics and isotherm experiments exhibited that N-functionalized biochars had greater removal rate and removal capacity for Cr(VI). The removal rate of Cr(VI) on N-functionalized biochar was 10.5-15.5 times that of untreated biochar. Meanwhile, N-functionalized biochar of NB3 with the largest number of adsorption sites for -C₇H₅N₂, -NH₂, -OH, -C₃H₃N₂, and phthalic acid (-C₈H₅O₄) exhibited the supreme adsorption capacity for Cr(VI) through H bonds and the highest adsorption energy was -5.01 kcal/mol. These mechanistic findings on the protonation and adsorption capacity are useful for better understanding the functions of N-functionalized biochars, thereby providing a guide for their use in various environmental applications.

The Analysis of Pore Development and Formation of Surface Functional Groups in Bamboo-Based Activated Carbon during CO2 Activation

Pore development and the formation of oxygen functional groups were studied for activated carbon prepared from bamboo (Bambusa bambos) using a two-step activation with CO2, as functions of carbonization temperature and activation conditions (time and temperature). Results show that activated carbon produced from bamboo contains mostly micropores in the pore size range of 0.65 to 1.4 nm. All porous properties of activated carbons increased with the increase in the activation temperature over the range from 850 to 950 °C, but decreased in the temperature range of 950 to 1000 °C, due principally to the merging of neighboring pores. The increase in the activation time also increased the porous properties linearly from 60 to 90 min, which then dropped from 90 to 120 min. It was found that the carbonization temperature played an important role in determining the number and distribution of active sites for CO2 gasification during the activation process. Empirical equations were proposed to conveniently predict all important porous properties of the prepared activated carbons in terms of carbonization temperature and activation conditions. Oxygen functional groups formed during the carbonization and activation steps of activated carbon synthesis and their contents were dependent on the preparation conditions employed. Using Boehm's titration technique, only phenolic and carboxylic groups were detected for the acid functional groups in both the chars and activated carbons in varying amounts. Empirical correlations were also developed to estimate the total contents of the acid and basic groups in activated carbons in terms of the carbonization temperature, activation time and temperature.

Recent progress on CO-rich syngas production via CO2 gasification of various wastes: A critical review on efficiency, challenges and outlook

Carbon monoxide (CO) is a highly valuable component of syngas which could be used to synthesize various chemicals and fuels. Conventionally, syngas is derived from fossil-based natural gas and coal which are non-renewable. To curb the problem, CO₂ gasification offers a win-win solution in which CO₂ is converted with wastes to CO, achieving carbon emission mitigation and addressing waste disposal issue simultaneously. In this review, gasification of various wastes by CO₂ with particular focus given to generation of CO-rich syngas is presented and critically discussed. This includes the effects of operating parameters (temperature, pressure and physicochemical properties of feedstocks) and advanced CO₂ gasification techniques (catalytic CO₂ gasification, CO₂ co-gasification and microwave-driven CO₂ gasification). Furthermore, associated technological challenges are highlighted and way forward in this field are proposed.

Progress in waste valorization using advanced pyrolysis techniques for hydrogen and gaseous fuel production

Hydrogen and gaseous fuel derived from wastes have opened up promising alternative pathways for the production of renewable and sustainable fuels to substitute classical fossil energy resources that cause global warming and pollution. Existing review articles focus mostly on gasification, reforming and pyrolysis processes, with limited information on particularly gaseous fuel production via pyrolysis of various waste products. This review provides an overview on the recent advanced pyrolysis technology used in hydrogen and gaseous fuel production. The key parameters to maximize the production of specific compounds were discussed. More studies are needed to optimize the process parameters and improve the understanding of reaction mechanisms and co-relationship between these advanced techniques. These advanced techniques provide novel environmentally sustainable and commercially procedures for waste-based production of hydrogen and gaseous fuels.

Carbon dioxide as a carrier gas and mixed feedstock pyrolysis decreased toxicity of sewage sludge biochar

The common use of sewage sludge (SSL)-derived biochar can be limited due to contaminants present in SSL, which may affect SSL-derived biochar toxicity. We propose the reduction of SSL-derived biochar toxicity by it co-pyrolysis with biomass and in CO₂ atmosphere. Ecotoxicity of biochars produced at 500, 600, and 700 °C from SSL and SSL with the addition of willow (at a ratio of SSL:willow - 8:2 and 6:4, w/w) in an atmosphere of N₂ or CO₂ were investigated. The toxicity of aqueous extracts derived from the biochars (Lepidium sativum - Elongation test, Vibrio fischeri - Microtox) or solid-phase toxicity (Lepidium sativum - Phytotoxkit F, Folsomia candida - Collembolan test) was also studied. SSL-derived biochar produced at N₂ atmosphere usually was toxic for all tested organisms. Co-pyrolysis of mixed feedstock reduced the toxicity of the produced biochar. In the case of biochars produced from SSL and willow under N₂ atmosphere decrease in inhibition of F. candida reproduction (from 27 to 58%) or its stimulation (from 7 to 30%) in comparison to SSL alone derived biochar, was observed. Co-pyrolysis of SSL with willow significantly reduced the toxicity of extracts the SSL-derived biochar towards L. sativum. The aqueous extracts obtained from the biochars produced at temperatures of 500 and 600 °C with willow addition were also less toxic to V. fischeri than the biochars produced from SSL alone. The change of carrier gas from N₂ to CO₂, regardless of the feedstock used, in most cases reduced toxicity or positively affected the test organisms. This was probably caused by changes in the physicochemical properties and content of contaminants in the biochars produced in an atmosphere of CO₂, compared to N₂. An exception was root growth inhibition in the solid phase tests where no significant differences were found between biochars produced in N₂ and CO₂.

Steam co-gasification of horticultural waste and sewage sludge: Product distribution, synergistic analysis and optimization

In this study, horticultural waste (HW) and sewage sludge (SS) with different mass ratios were co-gasified with steam at different temperatures to investigate the product distribution, gas synergistic interaction, and optimal design for gas products from co-gasification process. Results showed that with the increase of SS ratio in blends, the H₂ content was increased and the syngas yield was decreased. The synergistic interaction was more significant at higher temperature which promoted the H₂ production probably due to the reduction and steam oxidation of Fe species in SS during co-gasification process. The optimized highest effective gas content (82.92 vol%) was achieved with the highest HHV (11.40 MJ/m³) at the conditions of SS ratio = 0.80 and temperature of 900 °C. It indicates that steam co-gasification of HW and SS is a promising technology to produce desired syngas towards a clean and efficient waste management process.

Adsorption capacity of phenanthrene and pyrene to engineered carbon-based adsorbents produced from sewage sludge or sewage sludge-biomass mixture in various gaseous conditions

Adsorption of phenanthrene (PHE) and pyrene (PYR) by engineered carbon-based adsorbents produced from sewage sludge in an atmosphere of nitrogen (N₂) or carbon dioxide (CO₂) at temperatures of 500, 600, and 700 °C was investigated. The addition of willow to the SSL decreased the biochar adsorption capacity. However, there was an increase in the adsorption capacity after changing N₂ to CO₂. The addition of willow to SSL and the type of carrier gas affected the mechanism of adsorption. The adsorption of PHE and PYR on the SSL-derived adsorbents produced in N₂ occurred through pore filling. The adsorption on the SSL-derived adsorbents with willow followed the mechanism of π-π electron-donor-acceptor (EDA) interactions and hydrophobic interactions. A similar mechanism was observed with regard to the biochars produced from SSL in atmosphere of CO₂. For the SSL-derived adsorbents with willow in CO₂, the adsorption mechanism was observed to vary between PHE and PYR.

Theoretical modelling of the chemical reactivity of fresh biomass chars under non-catalytic conditions

This study developed a model for the chemical reactivity of fresh biomass chars, and built a calculation equation for the char gasification rate using simple gas-solid collision theory (SCT). The effects of pore breaks, pore collapse and thermal annealing on the char reactivity were considered in the modelling. Experimental tests for six acid-washed biomass chars were performed under a CO₂ atmosphere and used a thermo-gravimetric analyzer (TGA) over the temperature range of 1073-1273 K. The results showed that the reactivity of fresh char could be predicted quantitatively by some characteristic properties of certain kind of biomass and their combined parameters. For the instability of the biomass char structure, the internal pore length and gasification temperature showed a good exponential relationship. Good agreement was achieved, and the applicability of the model was demonstrated by comparing the predicted results with experimental data.

Thermochemical conversion of cobalt-loaded spent coffee grounds for production of energy resource and environmental catalyst

Thermochemical conversion of cobalt (Co)-loaded lignin-rich spent coffee grounds (COSCG) was carried out to find the appropriate pyrolytic conditions (atmospheric gas and pyrolytic time) for syngas production (H₂ and CO) and fabricate Co-biochar catalyst (CBC) in one step. The use of CO₂ as atmospheric gas and 110-min pyrolytic time was optimal for generation of H₂ (∼1.6 mol% in non-isothermal pyrolysis for 50 min) and CO (∼4.7 mol% in isothermal pyrolysis for 60 min) during thermochemical process of COSCG. The physicochemical properties of CBC fabricated using optimized pyrolytic conditions for syngas production were scrutinized using various analytical instruments (FE-SEM, TEM, XRD, and XPS). The characterizations exhibited that the catalyst consisted of metallic Co and surface wrinkled carbon layers. As a case study, the catalytic capability of CBC was tested by reducing p-nitrophenol (PNP), and the reaction kinetics of PNP in the presence of CBC was measured from 0.04 to 0.12 s^-1.

Investigation of cracking and water availability of soil-biochar composite synthesized from invasive weed water hyacinth

Water hyacinth (WH), is one of the world's most intractable and invasive weed species. Recent studies explored the efficacy of this species as a biochar (BC) in improving soil fertility and metal adsorption. However, the soil water retention (SWR) property and crack potential of soil-WH biochar composite has still not been studied. The major objective of this study is to investigate the SWR property and corresponding crack intensity factor (CIF) for compacted soil-WH BC composites. Soil-WH BC composites at five percentages (0, 2, 5, 10 and 15) was compacted and soil parameters such as suction (ψ), water content and CIF were simultaneously monitored for 63 days (including 9 drying-wetting cycles). Results showed that soil-WH BC composite at all percentages retains more water (max. 19% and min. 6.53%) than bare soil at both saturated and drought conditions. Gradual inclusion of WH BC to soil decreases the CIF potential from 7% to 2.8%.