Pyrolysis of Chinese chestnut shells: Effects of temperature and Fe presence on product composition

Harnessing recalcitrant lignocellulosic biomass for enhanced biohydrogen production: Recent advances, challenges, and future perspective

Biohydrogen (Bio-H2) is widely recognized as a sustainable and environmentally friendly energy source, devoid of any detrimental impact on the environment. Lignocellulosic biomass (LB) is a readily accessible and plentiful source material that can be effectively employed as a cost-effective and sustainable substrate for Bio-H2 production. Despite the numerous challenges, the ongoing progress in LB pretreatment technology, microbial fermentation, and the integration of molecular biology techniques have the potential to enhance Bio-H2 productivity and yield. Consequently, this technology exhibits efficiency and the capacity to meet the future energy demands associated with the valorization of recalcitrant biomass. To date, several pretreatment approaches have been investigated in order to improve the digestibility of feedstock. Nevertheless, there has been a lack of comprehensive systematic studies examining the effectiveness of pretreatment methods in enhancing Bio-H2 production through dark fermentation. Additionally, there is a dearth of economic feasibility evaluations pertaining to this area of research. Thus, this review has conducted comparative studies on the technological and economic viability of current pretreatment methods. It has also examined the potential of these pretreatments in terms of carbon neutrality and circular economy principles. This review paves the way for a new opportunity to enhance Bio-H2 production with technological approaches.

Analysis of Interactions Occurring during the Pyrolysis of Lignocellulosic Biomass

This paper presents a review of the recent advances in research on the interactions between the components of lignocellulosic biomass. The literature reports on the effects of interaction between lignocellulosic biomass components, such as cellulose-lignin, lignin-hemicellulose, and hemicellulose-cellulose, were discussed. The results obtained by other researchers were analyzed from the viewpoint of the interactions between the pyrolysis products formed along with the impact effects of the organic and inorganic components present or added to the biomass with regard to the yield and composition of the pyrolysis products. Disagreements about some statements were noted along with the lack of an unequivocal opinion about the directivity of interactions occurring during biomass pyrolysis. Based on the data in the scientific literature, it was suggested that the course of the pyrolysis process of biomass blends can be appropriately directed by changes in the ratio of basic biomass components or by additions of inorganic or organic substances.

Hydrothermal recycling of carbon absorbents loaded with emerging wastewater contaminants

Adsorption using carbon materials is one of the most efficient techniques for removal of emerging contaminants such as pharmaceuticals from wastewater. However, high costs are a major hurdle for their large-scale application in areas currently under economic constraints. While most research focuses on decreasing the adsorbent price by increasing its capacity, treatment costs for exhausted adsorbents and their respective end-of-life scenarios are often neglected. Here, we assessed a novel technique for recycling of exhausted activated biochars based on hydrothermal treatment at temperatures of 160-320 °C. While a treatment temperature of 280 °C was sufficient to fully degrade all 10 evaluated pharmaceuticals in solution, when adsorbed on activated biochars certain compounds were shielded and could not be fully decomposed even at the highest treatment temperature tested. However, the use of engineered biochar doped with Fe-species successfully increased the treatment efficiency, resulting in full degradation of all 10 parent compounds at 320 °C. The proposed recycling technique showed a high carbon retention in biochar with only minor losses, making the treatment a viable candidate for environmentally sound recycling of biochars. Recycled biochars displayed potentially beneficial structural changes ranging from an increased mesoporosity to additional oxygen bearing functional groups, providing synergies for subsequent applications as part of a sequential biochar system.

Synthesis of biochar from iron-free and iron-containing microalgal biomass for the removal of pharmaceuticals from water

The contamination of natural water bodies with pharmaceutical compounds has raised significant concerns about ecological and public health safety. In this study, biochars were synthesized from iron-free microalgal biomass (harvested by centrifugation) and iron-containing microalgal biomass (harvested by coagulation) and tested for the adsorption of ciprofloxacin (CIP) and diclofenac (DIC) from water in batch and fixed-bed column continuous studies. The physicochemical properties of synthesized biochars were analyzed using Brunauer, Emmett and Teller (BET) surface area analyzer, elemental analyzer, Fourier Transformed Infrared spectroscopy (FTIR), X-ray Diffractometer (XRD), and Scanning electron microscope with energy dispersive spectroscopy (SEM-EDS). The maximum monolayer adsorption capacities of iron-containing biochar (FBC750W) and iron-free biochar (MBC750W) based on the Langmuir model were obtained as 75.97 mg/g and 39.08 mg/g for CIP, and 40.99 mg/g and 6.77 mg/g for DIC, respectively. Comparatively, maximum monolayer adsorption capacities of commercial activated carbon (C-AC) were found to be 50.97 mg/g and 46.39 mg/g for CIP and DIC, respectively. In fixed-bed column continuous adsorption studies, the effects of flow rate (1 and 2 mL/min) and the adsorbent amount (50 and 100 mg) on adsorption performance were evaluated. Column kinetic models, such as Bohart-Adams model and Fractal-like Bohart-Adams model were examined. The adsorption mechanisms were proposed as pore filling, π-π interaction, and electrostatic interaction. Overall, the results of this study revealed that microalgal biomass, harvested with FeCl₃, can be used for the direct synthesis of iron-containing biochar for the removal of pharmaceuticals from water.

Preparation and formation mechanism of biomass-based graphite carbon catalyzed by iron nitrate under a low-temperature condition

Graphite is a widely used industrial material, which experienced a marked shortage caused by the growing demand for electrode anode material and the increased costs for raw material. Graphitic carbon from biomass is a promising approach that will result in low-cost and efficient preparation. Herein, Fe(NO₃)₃ was selected as the catalyst for pine sawdust, and the effects of temperature and iron content on the graphitization of biochar were investigated. Additionally, the formation mechanism of the graphitic crystallite structure was explored. Results showed that the formation of pyrolysis gas increased with the increase in the amount of catalyst added or pyrolysis temperature. The change in pyrolysis gas, such as H₂ and CO, was a critical auxiliary factor reflecting the conversion process. As temperature was increased from 600 °C to 800 °C, the solid products showed high graphitization and low solid yield. Graphite structure mainly formed at 700 °C because of the formation of Fe nanoparticles. The increase in the amount of catalyst could provide more reaction sites and promote the contact between Fe and C, showing that amorphous carbon is dissolved on Fe nanoparticles and precipitated into ordered graphitic carbon. On this basis, a mechanism of "carbon dissolution-precipitation" was proposed to explain the formation of graphite structure, and the whole pyrolysis process included the transformation of the iron element were analyzed.

Exploration of the Interrelationship within Biomass Pyrolysis Liquid Composition Based on Multivariate Analysis

The diverse utilization of pyrolysis liquid is closely related to its chemical compositions. Several factors affect PA compositions during the preparation. In this study, multivariate statistical analysis was conducted to assess PA compositions data obtained from published paper and experimental data. Results showed the chemical constituents were not significantly different in different feedstock materials. Acids and phenolics contents were 31.96% (CI: 25.30−38.62) and 26.50% (CI: 21.43−31.57), respectively, accounting for 58.46% (CI: 46.72−70.19) of the total relative contents. When pyrolysis temperatures range increased to above 350 °C, acids and ketones contents decreased by more than 5.2-fold and 1.53-fold, respectively, whereas phenolics content increased by more than 2.1-fold, and acetic acid content was the highest, reaching 34.16% (CI: 25.55−42.78). Correlation analysis demonstrated a significantly negative correlation between acids and phenolics (r2 = −0.43, p < 0.001) and significantly positive correlation between ketones and alcohols (r2 = 0.26, p < 0.05). The pyrolysis temperatures had a negative linear relationship with acids (slope = −0.07, r2 = 0.16, p < 0.001) and aldehydes (slope = −0.02, r2 = 0.09, p < 0.05) and positive linear relationship with phenolics (slope = 0.04, r2 = 0.07, p < 0.05). This study provides a theoretical reference of PA application.

Influence of Densification on the Pyrolytic Behavior of Agricultural Biomass Waste and the Characteristics of Pyrolysis Products

TG/FT-IR techniques, UV-spectroscopy, microwave extraction, XRD and SEM were used to study how densification of the three types of agricultural biomass wastes (wheat straw, soft wood, and sunflower husk) changes the composition and structure of their pyrolysis products. It was determined that densification changes the composition of volatile products of pyrolysis at the temperature of 420 °C: sunflower husk emits 4.9 times less saturated and unsaturated hydrocarbons and 1.9 times less compounds with carbonyl group; soft wood emits 1.8 times more saturated and unsaturated hydrocarbons and compounds with carbonyl groups and 1.3 times more alcohols and phenols; and wheat straw emits 2 times more compounds with carbonyl groups. These changes are probably caused by the differences in interaction of formed volatiles with the surface of chars. These differences can be caused by distinct places of cumulation of inorganic components in the densified samples. In the densified char, the inorganics cumulate on the surface of sunflower husk whereas for wheat straw they cumulate inside the sample. In the case of soft wood, the inorganics cumulate both inside and on the surface. The decreased contribution of hydrocarbons in volatiles can be connected with the morphology of nano-particles formed in inorganics.

Feedstock doping using iron rich waste increases the pyrolysis gas yield and adsorption performance of magnetic biochar for emerging contaminants

Magnetic carbons can significantly lower the costs of wastewater treatment due to easy separation of the adsorbent. However, current production techniques often involve the use of chlorinated or sulfonated Fe precursors with an inherent potential for secondary pollution. In this study, ochre, an iron-rich waste stream was investigated as a sustainable Fe source to produce magnetic activated biochar from two agricultural feedstocks, softwood and wheat straw. Fe doping resulted in significant shifts in pyrolysis yield distribution with increased gas yields (+50%) and gas energy content (+40%) lowering the energy costs for production. Physical activation transformed ochre to magnetite/maghemite resulting in activated magnetic biochars and led to a 4-fold increase in the adsorption capacities for two common micropollutants - caffeine and fluconazole. The results show that Fe doping not only benefits the adsorbent properties but also the production process, leading the way to sustainable carbon adsorbents.

Modification on biochars for applications: A research update

Biochars are the solid product of biomass under pyrolysis or gasification treatment, whose wholesale prices are lower than commercial activated carbons and other fine materials now in use. The employment of biochars as a renewable resource for field applications, if feasible, would gain apparent economic niche. Modification using physical or chemical protocol to revise the surface properties of biochar for reaching enhanced performances of target application has attracted great research interests. This article provided an overview of biochar application, particularly with the respect to the use of modified biochar as preferred soil amendment, adsorbent, electrochemical material, anaerobic digestion promotor, and catalyst. Based on literature works the current research trends and the prospects and research needs were outlined.

Chestnut-Derived Activated Carbon as a Prospective Material for Energy Storage

In this work, we present the preparation and characterization of biomass-derived activated carbon (AC) in view of its application as electrode material for electrochemical capacitors. Porous carbons are prepared by pyrolysis of chestnut seeds and subsequent activation of the obtained biochar. We investigate here two activation methods, namely, physical by CO2 and chemical using KOH. Morphology, structure and specific surface area (SSA) of synthesized activated carbons are investigated by Brunauer-Emmett-Teller (BET) technique and scanning electron microscopy (SEM). Electrochemical studies show a clear dependence between the activation method (influencing porosity and SSA of AC) and electric capacitance values as well as rate capability of investigated electrodes. It is shown that well-developed porosity and high surface area, achieved by the chemical activation process, result in outstanding electrochemical performance of the chestnut-derived porous carbons.

Synergetic effect of magnesium citrate and temperature on the product characteristics of waste lotus seedpod pyrolysis

To understand the synergetic effect of magnesium citrate (MC) and temperature on biomass pyrolysis, co-pyrolysis of lotus seedpod (LS) and MC was carried out in a fixed bed reactor. With the addition of MC, CO2 become the dominate composition in gas (55.83-90.75 vol%). And with temperature increasing, the main components in bio-oil converted from carboxylic acid to phenols and aromatics. Meanwhile, the mesoporous carbon was formed, with the BET specific surface area up to 514.66 m2/g, and pore diameter mainly focused at 3-8 nm. For the catalytic effect, the secondary cracking of pyrolytic volatiles (acetic acid and anhydrosugar) was inhibited, therefore the gas releasing was inhibited below 550 °C. However, at higher temperature, MgO catalysts favored the reduction of acids and deoxygenation via ketonization and aldol condensation reactions. The formed MgO as a template and the catalysis of MgO during co-pyrolysis contributed to the mesoporous structure of solid char.