Higher Heating Value Research Articles

Catalytic solvothermal liquefaction of kitchen waste over iron-based catalysts addition and two-step method to produce high-quality fuels

The disposal of kitchen waste (KW) is a wide concern because of its high moisture content, foul odor, and low energy density. Solvothermal liquefaction (STL) can directly convert KW to bio-oil without pre-drying. This study investigated the effect of iron-based catalysts (Fe, Fe2O3, and Fe3O4) and a catalytic two-step method on bio-oil production, heteroatom distributions (N and S), and pollutant decompositions during STL of KW. From the comparison of three iron-based catalysts, the catalysis of metallic Fe significantly enhanced the bio-oil yield and quality, resulting in the highest yield (52.30 %) and a high heating value (35.86 MJ/kg) of bio-oil. Meanwhile, metallic Fe noticeably increased the fraction of lighter molecules in bio-oil to 71.30 %. During the catalytic two-step method process, the nitrogen and sulfur in the raw material were primarily transferred to the aqueous phase in the form of NH4+ and SO42-. The introduction of iron-based catalysts significantly promoted the esterification and reduction reactions. The bio-oil exhibited the highest ester content (77.96 %) when Fe3O4 was present while adding metallic Fe catalyst resulted in the highest hydrocarbon content of 28.16 %. Finally, a potential reaction pathway and mechanism of the catalytic STL of KW were proposed and discussed comprehensively. This study validates the use of iron-based catalysts and a two-step method to improve the yield and quality of bio-oil. This method reduces heteroatom content through associated hydrogenation and reduction reactions, demonstrating its potential for upgrading bio-oil into high-quality fuel.

Comparative study of the thermo‐catalytic reforming of agricultural and forest residue and advanced characterization of final products in a cold climate

AbstractGlobal agricultural and forest residues hold promise for renewable fuel production through thermo‐catalytic reforming (TCR). Limited data exists on TCR outcomes for regions known for cold conditions like Canada. This study used a 2 kg h−1 TCR unit for the intermediate pyrolysis/reforming of agricultural (wheat straw pellet, WSP) and forest (softwood pellet, SWP) residues. Maximum bio‐oil yields were 8.43% for wheat straw pellets and 7.99% for softwood pellets at 400 and 500°C reactor and reformer temperatures. Feedstock, bio‐oil, and biochar properties were analyzed through proximate and ultimate analysis. At 550°C reactor and 700°C reforming temperatures, 70.73% of the wheat straw pellet‐based gas yield contained 36.11 vol.% H2 and 11.08 vol.% CH4, giving a higher heating value (HHV) of 12.54 MJ kg−1. A high concentration of CH4 (22.02 vol.%) in the softwood pellet‐based gas gave an HHV of 17.94 MJ kg−1. The low viscosity (3.9 mPa · s−1) and total acid number (7.3 mg KOH g−1) wheat straw pellet‐based bio‐oil had an O/C molar ratio of 0.09 and an HHV of 35.80 MJ kg−1. The 400/600°C reactor/reformer temperatures gave the lowest area percentage of mono‐aromatic (16 vol.%) and polycyclic aromatic (11.20 vol.%) compounds in the softwood pellet bio‐oil. The O/C molar ratio (0.5–0.6) in softwood pellet biochar elevated the higher heating value from 32.37 to 34.57 MJ kg−1. The study results guide optimal TCR unit operation in cold climates like Canada with local feedstocks, emphasizing its notable hydrogen production over bio‐oil and biochar.

Valorization of Biomass and Industrial Wastes as Alternative Fuels for Sustainable Cement Production

The cement industry contributes around 7% of global anthropogenic carbon dioxide emissions, mainly from the combustion of fuels and limestone decomposition during clinker production. Using alternative fuels derived from wastes is a key strategy to reduce these emissions. However, alternative fuels vary in composition and heating value, so selecting appropriate ones is crucial to maintain clinker quality and manufacturing processes while minimizing environmental impact. This study evaluated various biomass and industrial wastes as potential alternative fuels, characterizing them based on proximate analysis, elemental and oxide composition, lower heating value, and bulk density. Sawdust, pecan nutshell, industrial hose waste, and plastic waste emerged as viable options as they met the suggested thresholds for heating value, chloride, moisture, and ash content. Industrial hose waste and plastic waste were most favorable with the highest heating values while meeting all the criteria. Conversely, wind blade waste, tire-derived fuel, and automotive shredder residue did not meet all the recommended criteria. Therefore, blending them with alternative and fossil fuels is necessary to preserve clinker quality and facilitate combustion. The findings of this research will serve as the basis for developing a computational model to optimize the blending of alternative fuels with fossil fuels for cement production.

Fractionation and characterization of Dunaliella microalgal biomass and extraction of carotenoids

This paper presents findings on the application of two fractionation protocols of Dunaliella microalgal biomass with the aim to separate and recover the lipid, pigment and protein fraction, leaving as “residue” the fraction that contains carbohydrates. The first protocol (LPC) is based on the initial extraction of lipids, followed by extraction of proteins, while in the second protocol (CLP), the pigments are first extracted followed by lipids extraction. With the LPC protocol the recovered lipid fraction was 34 and 32 wt%, while the recovered proteinic fraction was 46 and 50 wt% for the two samples under study, i.e. 1120 (D. granulata) and 1220 (D. minutissima). The CLP protocol led to the initial extraction of the pigment fraction with a percentage of 10–15 wt% while the subsequently recovered lipidic fraction was 16–24 wt%. The initial biomass was characterized for its moisture (<0.7 wt% for both samples), ash (approx. 45 wt% for both samples), organic matter, elemental composition and higher heating value (HHV) which was 23 and 30 MJ/kg (organic matter based-OMB). The composition of the lipid fraction was analyzed via esterification and gas chromatography (GC-FID) showing C16 and C18 as the predominant acids in the samples. The residue/carbohydrate fraction was analyzed via acid hydrolysis and analysis by high pressure liquid chromatography (HPLC) showing about 20 wt% (-OMB) content of carbohydrates. The high ash content of the biomass was found to be co-extracted during the fractionation protocols at a percentage of ≈49 % in the lipidic fraction and 45 % in the proteinic fraction. Furthermore, emphasis was given on pigment extraction and recovery using various solvents and quantification methods. Measurements of β-carotene, carotenoids, and chlorophyll content through UV and HPLC analyses is presented with chlorophyl and carotenoid content being ≈12 wt% and ≈9 wt% for samples 1120 and 1220 (-OMB). Additionally, a comparison between three solvents (THF, dichloromethane, acetone) was performed regarding their ability to extract the pigments from the microalgal biomass showing that acetone is capable of extracting pigments when concentration of the pigments is not high. The comparison of the HPLC with the UV method, suggested that UV spectroscopy is a reliable and rapid alternative for pigments determination, while HPLC enables identification and quantitative determination of specific pigments and chlorophyll species. The study provides insights for different fractionation protocols applied in two not yet fully studied Dunaliella species as well as the chlorophyl and carotenoid content.

Thermocatalytic Pyrolysis of Waste Areca Nut into Renewable Fuel and Value-Added Chemicals.

Pyrolytic oil is currently in its early stages of production and distribution but has the potential to grow into a significant renewable energy source. It may be processed into a variety of useful substances, including chemicals, and used for heating, transportation, and energy production. The present investigation involves the production and characterization of pyrolytic oil from areca nut husk (ANH), with and without ZSM-5. The pyrolysis experiment was conducted in a semibatch tubular reactor at 600 °C and a heating rate of 80 °C min-1 using ZSM-5 at 20 wt %. The pyrolytic oil was examined via elemental analysis, viscosity, density, moisture content, GC-MS, FTIR, higher heating value (HHV), and ash content. The analysis of kinetics verified that the activation energy rises in proportion to the conversion rate. Additionally, employing ZSM-5 in catalytic pyrolysis at 20 wt % boosted the yield of pyrolytic oil by 11% compared to thermal pyrolysis. Employing ZSM-5 at 20 wt % resulted in a decrease in viscosity, oxygen content, and density by approximately 43.40 cSt, 15.20%, and 168 MJ kg-1, respectively. Moreover, it led to an increase in higher heating value (HHV) and carbon content by 11.71 MJ kg1- and 14.06%, respectively. An FTIR study of pyrolytic oil revealed the occurrence of hydrocarbons, aromatics, phenols, alcohols, and oxygenated chemicals. Moreover, GC-MS analysis indicated a significant increase in hydrocarbons (10.31%) and a decrease in phenols (2.36%), acids (6.38%), and oxygenated compounds with the introduction of the catalyst. Consequently, it can be inferred that utilizing ZSM-5 at 20 wt % during the pyrolysis of ANH aids in enhancing both the yield and characteristics of the resulting pyrolysis oil.

Machine Learning for Characterizing Biofuels Based on Femtosecond Laser Ionization Mass Spectrometry.

A sample mixture of fatty acid methyl esters (FAMEs) was measured by femtosecond laser ionization mass spectrometry (fsLIMS) using the fifth (206 nm) and fourth (257 nm) harmonic emissions of an ytterbium (Yb) laser (1030 nm). Molecular ions were observed as the major signals in this technique, providing valuable information concerning the molecular weight and the number of double bonds in the molecule. The mass spectral data were then used as explanatory variables in machine learning based on artificial intelligence (AI) to correlate with objective variables such as the cetane number, kinematic viscosity, specific gravity, a higher heating value, an iodine value, flash point, oxidative stability index, and a cloud point measured for reference biofuel samples containing various FAMEs. The properties of biofuels, i.e., the objective variables, were evaluated from the mass spectral data obtained for unknown samples. The errors in the evaluation were a few percent when the distribution of the FAMEs in the unknown biofuel sample was similar to those of the biofuels used for machine learning. As demonstrated herein, the present approach, involving a combination of fsLIMS and AI, has the potential for use in evaluating the properties of a biofuel and then in solving of environmental issues associated with global warming.

ANN model of co-gasification process in bubbling fluidized bed: Contribution ratio analysis

Co-gasification of coal and biomass in a bubbling fluidized bed may offer an effective and economical method to partially replace coal to produce hydrogen, thereby addressing the objectives of achieving a carbon dioxide emissions peak and carbon neutrality. An Artificial neural network (ANN) model was utilized to simulate the hydrogen and other performance of co-gasification in the bubbling fluidized bed. Five types of ANN architectures were tested, including FFBP, CFBP, EFBP, LR, and NARX. Five optimization algorithms were also applied, including L-M, GA, GD, GDX, and PSO, to identify the optimal model to give a more accurate predicate the hydrogen production. The input data were derived from the ultimate analysis of the mixed coal and biomass, the proximate analyzes of mixed coal and biomass, and the operational conditions. The output data consisted of gas composition, carbon conversion, gasification efficiency, total gas yield, syngas yield, low and high heating values of the gas. The LR-PSO with 6 hidden neurons (R2 = 0.9995 and MSE = 0.1357) outperformed other ANN types and optimization algorithms. To further understand the performance of co-gasification, the influences of biomass to coal ratio, equivalence ratio, steam to carbon ratio and temperature on ratio of H2 to CO and syngas yield were predicted. The highest ratio of H2 to CO for the work of Li et al. (2010) [26], Song et al. (2013) [27] and Valdés et al. (2015) [28] were 0.7, 1.2 and 0.88, respectively. And those for syngas yield were 0.85, 1.09 and 1.55 m3/kg, respectively. To reveal the important factor on the ratio of H2 to CO, a detailed analyzed of the contribution ratio was conducted. The most critical factor affecting co-gasification performance in the work of Song et al. (2013) [27] were identified as SC ratio and temperature, which was higher than those of W and ER. The effect of SC exceeded that of T at SC ratio of 0.4, while it came to a reverse at temperature above 700 °C. These findings may serve as a valuable tool for adjusting the various factors to achieve the desired performance in the co-gasification of coal and biomass.

Predictive modeling and multi-parametric optimization of catalytic pyrolysis of disposable face mask using a combinational approach of response surface methodology and machine learning: Insights into the influence of waste-derived catalyst

The current study aims to model and optimize the catalytic pyrolysis of face masks incorporating a waste-derived catalyst to analyze the effect of process parameters (temperature, feed-to-catalyst ratio, and inert gas flow rate) on the oil yield of the process. An integrated approach of response surface methodology (R2-0.95) and machine learning (decision trees regression, R2-0.83) demonstrated a higher prediction accuracy and lower error margins. Explainable artificial intelligence tools spotlighted temperature to be the predominant parameter followed by feed-to-catalyst ratio. Experimental oil yield (13.5%) obtained at optimized parameters (516 °C temperature, 3:1 feed-to-catalyst ratio, and 163 mL/min inert gas flow rate) was compared with those predicted through response surface methodology (13.7%) and decision trees regression (13.12%), showcasing an absolute error range of 0.2–0.4 wt%. Gas chromatography-mass spectroscopy analysis of oil highlighted the presence of silica compounds that can be extracted as value-added chemicals. Further, the overall percentage of naphthene's, paraffins, and olefins in the oil were approximated to be around 40.5% based on the peak area. The presence of hydrocarbons in oil having carbon numbers predominantly in the range of gasoline and diesel as well as a high heating value of 36.56 MJ/kg demonstrated its potential to be used as a fuel. The present study demonstrates the feasibility of valorizing the face mask into energy-dense oil comparable to commercial range fuel using a spent adsorbent based catalyst.

Enhancing lignite coal quality with biomass waste in slow pyrolysis Fischer-Tropsch reactor

Coal is a non-renewable natural resource that is widely used in thermal power plants in major industrialized countries. Most of the world's coal contains a high percentage of moisture and ash and a low caloric value. The slow pyrolysis process of coal improves its quality and significantly reduces its smoke and ash. In this study, Soma Kisrakdere lignite coal in Manisa province in Turkey with some biomass wastes (peanut shells, pine cones, and olive seeds) was evaluated by applying a slow pyrolysis process using a Fischer-Tropisch reactor. Firstly, Soma Kisrakdere lignite alone, then each waste biomass was mixed with lignite coal at weight percentages of 10 %, 25 %, and 50 % to form three mixtures for each biomass waste. The process temperature was 500°C, and the temperature rate was 0.1 °C/s. The findings obtained in this study showed that with the increase of weight percentages of biomass which added from biomass waste to lignite coal, the productivity of coal (biochar) decreased and the products of tar, decomposed water, and gases increased. As for calories, its value increased with the increase in weight of the addition the waste of biomass which added where 50 % of biomass additions were the highest value of low heating value (LHV) and high heating value (HHV) and most effective than others which added to lignite coal. Among the biomass residues used, the olive seeds were the most valuable, compared with the peanut shells and pine cones.

Effects of biogas slurry on hydrothermal carbonization of digestate: Synergistic valorization of hydrochars and aqueous phase

In this study, livestock manure digestate (LMD) was used as feedstock for hydrothermal carbonization (HTC) at different temperature (180–260 °C) and residence time (0–4 h). Nutrient flow and distribution during the HTC process were evaluated by comparing the effects of livestock manure biogas slurry (LBS) and ultrapure water (UW) to determine the optimal reaction conditions for the synergistic production and application of hydrochars (HC) and aqueous phases (AP). Compared with UW, the HC yields derived from LBS as solvent were increased by 27.05–38.24% under the same conditions. The C content, high heating value (HHV), and energy densification of HC obtained from LMD and UW were higher than those obtained from LMD and LBS, and the ash content was lower. While, LBS circumstance improved the porosity, N content and some trace elements e.g. Ca, Fe and Mg in HC that showed excellent fertility potential. In addition, the recovery rate of K, TOC, NH4+-N, and TN concentrations in AP were significantly higher in the LBS circumstance than in UW. The results show that the addition of UW is more favorable for fuel generation, and the HC obtained from LMD and UW at 220 °C has the potential to be used as a fuel. Whereas, the addition of LBS enhanced the potential of HC and AP for agricultural applications simultaneously. It is recommended to use HC and AP obtained from LMD and LBS at 240 °C for using as fertilizer.

Renewable fuel and value-added chemicals potential of reed straw waste (RSW) by pyrolysis: Kinetics, thermodynamics, products characterization, and biochar application for malachite green removal

This study comprehensively investigates the potential of reed straw waste (RSW) for thermochemical conversion into bioenergy and value-added chemicals. The physicochemical property characterization confirmed the potential of RSW as both a renewable fuel and a source of chemical compounds. The high heating value (17.16 ± 0.20 MJ/kg), average activation energy (253.10–297.04 kJ mol−1), Gibbs free energy (153.45–158.39 kJ mol−1), and enthalpy change (248.10–292.04 kJ mol−1), underscored the significant potential of RSW for bioenergy production through pyrolysis and its compatibility for co-pyrolysis with other waste materials. Pyrolysis product analysis revealed that syngas constituted 42.25–66.48 % of the total three-phase products, with combustible components like H2, CO, and CH4 comprising 84.14–89.77 % of syngas. Bio-oil represented 18.94–35.23 % of the total three-phase products, primarily composed of phenols (30.88–46.04 %), acids (1.12–16.05 %), furans (8.84–14.46 %), ketones (9.34–16.33 %), alcohols (4.59–13.68 %), and aldehydes (5.54–11.10 %). BET and FTIR analysis of the biochar indicated that RSW biochar possessed a well-defined porous structure and abundant surface functional groups, making it capable of achieving a maximum adsorption capacity of 185.35 mg g−1 for the malachite green (MG) dye in the aquatic environment. In summary, this study holds significant implications for mitigating environmental pollution resulting from improper disposal of RSW and promoting its high-value utilization.

Safety profiling of technical lignins originating from various bioresources and conversion processes

In this work, a set of eight technical lignin samples from various botanical origins and production processes were characterized for their chemical composition, higher heating value, size distribution, dust explosion sensitivity and severity, thermal hazard characteristics and biodegradability, in further support of their sustainable use. More specifically, safety-focused parameters have been assessed in terms of consistency with relating physico-chemical properties determined for the whole set of technical lignins. The results emphasized the heterogeneity and variability of technical lignins and the subsequent need for a comprehensive characterization of new lignin feedstocks arising from novel biorefineries. Indeed, significant differences were revealed between the samples in terms of hazards sensitivity. This first comparative physico-chemical safety profiling of technical lignins could be useful for the hazard analysis and the safe design of the facilities associated with large scale valorisation of biomass residues such as lignins, targeting “zero waste” sustainable conversion of bioresources.

Industrial Two-Phase Olive Pomace Slurry-Derived Hydrochar Fuel for Energy Applications.

The present study aims to resolve the existing research gaps on olive pomace (OP) hydrochars application as a fuel by evaluating its molecular structures (FTIR and solid NMR analysis), identifying influential characteristics (Pearson correlation analysis), process optimization (response surface methodology), slagging-fouling risks (empirical indices), and combustion performance (TG-DSC analysis). The response surfaces plot for hydrothermal carbonization (HTC) of OP slurry performed in a pressure reactor under varied temperatures (180-250 °C) and residence times (2-30 min) revealed 250 °C for 30 min to be optimal conditions for producing hydrochar fuel with a higher heating value (32.20 MJ·Kg-1) and energy densification ratio (1.40). However, in terms of process efficiency and cost-effectiveness, the optimal HTC conditions for producing the hydrochar with the highest energy yield of 87.9% were 202.7 °C and 2.0 min. The molecular structure of hydrochar was mainly comprised of aromatic rings with methyl groups, alpha-C atoms of esters, and ether bond linkages of lignin fractions. The slagging and fouling risks of hydrochars were comparatively lower than those of raw OP, as indicated by low slagging and fouling indices. The Pearson correlation analysis emphasized that the enrichment of acid-insoluble lignin and extractive contents, carbon densification, and reduced ash content were the main pivotal factors for hydrochar to exhibit better biofuel characteristics for energy applications.

Hydrothermal carbonization of sugar beet pulp: optimization and characterization

In this study, the optimum hydrothermal conditions of sugar beet pulp were investigated by Response Surface Methodology (RSM) based on Central Composite Design (CCD). The hydrochar obtained from sugar beet pulp (SBP) was optimized for maximum yield and carbon content. Process conditions were chosen with reaction temperatures of 200–240 °C, residence time 60–150 min, and biomass to water ratio of 1:3–1:10. The yield and carbon content of the hydrochar varied with the process parameters. In order to obtain hydrochar with the highest yield and carbon content in optimization, the reaction temperature should be 220.74 °C, the biomass to water ratio should be 1:3, and the residence time should be 95.58 min. High heating value, energy and mass yield, and energy densification ratio of sugar beet pulp and hydrochar were also investigated. The products were characterized using FT-IR, SEM, and ultimate analysis techniques. The Coats-Redfern method was used to estimate the kinetic parameters of the combustion processes. The activation energy values of SBP and SBP-HC products were calculated as 13.88 and 11.46 kJ/mol, respectively. The kinetic data were used to determine the thermodynamic parameters (ΔH, ΔG, and ΔS). As a result, the properties of hydrochar produced from sugar beet pulp under optimum conditions have been extensively investigated and the results have shown that hydrochar has potential for use in different areas.

Insights into hydrothermal treatment of biomass blends: Assessing energy yield and ash content for biofuel enhancement.

This study explores the Hydrothermal Carbonization (HTC) treatment of lignocellulosic biomass blends, delving into the influence of several key parameters: temperature, additive nature and dosage, residence time, and biomass composition. Rapeseeds, Pinus radiata sawdust, oat husks, and pressed olive served as the studied biomasses. One hundred twenty-eight experiments were conducted to assess the effects on mass yield (MY), energy yield (EY), higher heating value (HHV), and final ash content (ASH) by a Factorial Experimental Design. The derived model equations demonstrated a robust fit to the experimental data, averaging an R2 exceeding 0.94, affirming their predictive accuracy. The observed energy yield ranged between 65% and 80%, notably with sawdust and olive blends securing EY levels surpassing 70%, while rapeseed blends exhibited the highest HHV at 25 MJ/kg. Temperature emerged as the most influential factor, resulting in an 11% decrease in MY and a substantial 2.20 MJ/kg increase in HHV. Contrastingly, blend composition and additive presence significantly impacted ASH and EY, with all blends exhibiting increased ASH in the presence of additives. Higher initial hemicellulose and aqueous extractive content in raw biomass correlated proportionally with heightened HHV.

Effective approach to assess higher heating value of biomass from ultimate and proximate analysis

AbstractFor proper design and operation of biomass‐based energy systems, it is important to determine the higher heating value (HHV) of biomass. In this paper, two machine learning (ML) approaches, namely extra trees (ET) and least squares support vector machine (LSSVM), are used to predict the value of HHV associated with biofuels. The data required for HHV calculation, including proximate and ultimate analyses datasets, were collected from the literature. The performances of these two ML approaches for predicting biomass HHV were then compared with other smart models available in the literature. Even though the available empirical models can predict the biomass HHV with acceptable precision, it was found that our proposed ML techniques have a superior performance based on the error analysis; the proposed approaches also consider all key biomass characteristics in the developed models. In addition, the ET model proved to be slightly more accurate compared to the LSSVM model. Additionally, the developed proximate‐based ET model showed better performance compared to the ultimate‐based ET model. The most influential parameters in the developed ET models for the proximate and ultimate approaches were determined to be ash fraction and carbon fraction, respectively. Finally, it was concluded that the smart modelling techniques can be utilized as a robust and reliable alternative predictive methodology to replace direct laboratory measurement of the biomass HHV.

The Effects of Feedstock, Pyrolysis Temperature, and Residence Time on the Properties and Uses of Biochar from Broom and Gorse Wastes

Biochar (BC), which can be produced from several feedstocks, has been widely studied. However, the BC derived from highly pyrolytic shrubs, such as broom and gorse, has been less frequently used and only partially characterized. These wastes, when used for the preparation of biochar, can fix carbon and contribute to environmental conservation, helping to achieve sustainable development objectives. Eight biochars from broom and gorse were produced and fully analyzed, providing a more complete and novel description, with new insights for assessing their utilization. The aims of this study were to elucidate the effects of feedstock, pyrolysis temperature, and residence time on biochar properties and to assess the adequacy of these biochars as fuel. Elemental and proximate analyses and estimations of the lower and higher heating values were performed, and physical and chemical properties, as well as several other related energy indices, were determined. The experimental results showed that the temperature was a key factor in the properties of the biochars, while residence time was less important. The BCs obtained from the two feedstocks did not show important effects on the properties, which is consistent with the fact that they are woody legumes. These biochars had a high carbon content and were thermally stable. The BCs also had a high calorific value and suitable energetic properties. Additionally, their PAH contents were low, indicating that the use of these biochars would be safe. In conclusion, broom- and gorse-derived biochars can be considered as renewable fuels for green energy production.

Hydrothermal carbonization: Sustainable pathways for waste‐to‐energy conversion and biocoal production

AbstractHydrothermal carbonization (HTC) technology emerges as a sustainable method to convert wet biomass, including food waste and municipal solid waste into high‐energy dense biocoal. This process, conducted at temperatures ranging from 180 to 260°C and pressures of 10–50 bar, effectively transforms the organic material in wet biomass into solid, liquid, and gaseous outputs. The solid product, biocoal, possesses a high carbon concentration and heating values on par with lignite coal, presenting a cleaner alternative to traditional fossil fuels. Despite operational commercial‐scale HTC facilities globally, further adoption across various feedstocks can improve waste management and energy production. The process can achieve energy yields up to 80%, particularly at temperatures favoring the generation of secondary char with higher heating values. HTC not only aids in reducing greenhouse gas emissions through carbon sequestration in solid waste but also promotes environmental sustainability by yielding nutrient‐rich by‐products for agriculture. As a versatile and energy‐efficient solution, HTC technology is a pivotal innovation in waste‐to‐energy conversion, addressing the imperative for sustainable waste management. Other supplementary benefits are presented; they include higher employability, reduction of a nation's reliance on imported energy, and better waste control, therefore considering all pillars of sustainability. Future research should focus on optimizing process efficiency and exploring the broader applicability of HTC to various biomass feedstocks, enhancing its role in the global pursuit of sustainable energy solutions.

Analytical evaluation of the performance of pyrolysis-gasification (Py-Gs) combination within hybrid thermochemical-biological biorefinery

Thermochemical treatments like pyrolysis and gasification, were proposed to circumvent hydrolysis bottleneck of conventional 2nd generation biorefineries. Within this big-picture, the target of this article was to establish the type and amount of bioavailable matter that can be obtained through intermediate pyrolysis of biomass followed by gasification of biochar. To establish the amount of “chemical energy” partitioned among different products’ chemical oxygen demand (COD), which is proportional to higher heating value (HHV) and often utilized for biological systems, was applied for the evaluation of thermochemical conversion of a lignocellulosic feedstock (fir wood). The most abundant product of intermediate pyrolysis was biochar, which retains from 33 % to 40 % of feedstock COD (with temperatures starting from 450 °C). The yield of water-soluble pyrolysis products (WS) slightly increases from 24 % at 450 °C to 27 % at 650 °C, whereas the yield of WI increases considerably with the same temperature. Pyrolysis temperature showed a minor effect on the composition of WS as revealed by GC-MS analysis of main compounds and size exclusion chromatography. Preliminary gasification experiments, performed at 850 °C under CO2 atmosphere, provided gasification rates for different biochars, which was equal to 0.004, 0.005, 0.006 min−1 for biochars obtained at 650, 550, and 450 °C respectively. Syngas obtained from gasification of 450 °C and 550 °C biochar was almost tar-free, whereas gasification of 650 °C biochar yielded a detectable amount of tars (0.4 %). Increasing the gasification temperature to 950 °C sharply increases the gasification rate of biochar obtained at 450 °C, allowing to obtain 55% conversion yield. Within the scope of hybrid thermochemical-biological (HTB) processes, the obtained results show that intermediate pyrolysis, when coupled with subsequent 950 °C CO2 gasification of biochar, can deliver 64% of chemical energy (by COD basis) of the lignocellulosic feedstock as bioavailable constituents, which are defined to syngas and WS based on recent biological studies. Whereas downstream fermentation can process syngas and WS materials in an effective way, such yields could surpass the holocellulose-targeted methods based on hydrolysis.

Characterization and mechanism elucidation of high-quality bio-oil production from co-pyrolysis of waste low-rank coal fines and de-oiled microalgae biomass using bimetallic (Cu-Cr) ZSM-5 catalyst

The present study provides a cleaner co-pyrolysis strategy for high-quality bio-oil production by utilizing low-cost residues such as low-rank coal (CL), de-oiled microalgae (ALG), and their blends (CLALG). The heavy metal-loaded Cu-Cr-ZSM-5 catalyst is synthesized by using ion-exchange method and investigated in the CL, ALG and CLALG pyrolysis bio-oil upgradation at different catalyst feed ratios (0.5:1, 1:1, 2:1). The synthesized catalyst was characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and brunauer-emmett-teller (BET) analysis. The synthesized catalyst is nano-crystalline of average size 7 nm. The microstructure of the synthesized catalyst shows stacked nanorods packing with connected intercrystal and intracrystal mesopores. The catalytic and non-catalytic pyrolysis of CL, ALG and CLALG are performed at 600 °C, 10 °C/min for 60 min. The non-catalytic ALG pyrolysis has shown maximum bio-oil yield (35.7%). The synergistic effect of nanorod morphology, active acid sites and excess mesoporosity of catalyst facilitates efficient deoxygenation, denitrogenation and aromatization of pyrolysis bio-oil with oxygen content from 2.1⎼3.1%, nitrogen content 3.5⎼5.1% and aromatic content 49.4⎼54.4% at catalyst feed ratio of 1:1. The maximum obtained higher heating value (HHV) of bio-oil from catalytic pyrolysis of CL (40.1 MJ/kg) followed by CLALG (38.6 MJ/kg) and ALG (36.5 MJ/kg) is very close to diesel oil with HHV (42⎼46 MJ/kg). Further, a co-pyrolysis mechanism is proposed to systematically investigate possible catalytic action sites to yield high-quality bio-oil. Thus, outcomes of the present study enrich information regarding catalyst development, catalyst feed interaction, and thermocatalytic cracking as emerging efforts towards industrial-scale upgradation of bio-oil to engine fuels.