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A special issue of Molecules (ISSN 1420-3049). This special issue belongs to the section "Applied Chemistry".

Deadline for manuscript submissions: closed (31 October 2024) | Viewed by 9728

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Dr. Zhuozhi Wang

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Guest Editor

School of Chemical Engineering and Technology, Hebei University of Technology, Tianjin 300130, China
Interests: biomass upgradation; solid waste; thermal conversion; co-utilization; carbon-neutral fuel
Special Issues, Collections and Topics in MDPI journals

Prof. Dr. Boxiong Shen

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Guest Editor

School of Chemical Engineering & Technology, Hebei University of Technology, Tianjin 300130, China
Interests: solid waste; NOx reduction; petroleum engineering; catalyst characterization; SCR
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

The emphasis of this Special Issue, titled “Renewable Energy, Fuels and Chemicals from Biomass”, is on exploring the diverse applications of chemistry in the deriving of renewable energy, fuels, and chemicals from biomass resources.

Key themes:

Advanced biomass conversion technologies: using efficient methodologies (such as catalysis, pyrolysis, and torrefaction) to convert a variety of biomass into renewable energy, fuels, and high-value chemicals;
Biofuel synthesis: innovations in the production of renewable biofuels, including bioethanol, biodiesel, and novel bio-based fuels, and other sustainable energy;
Catalytic processes for biomass transformation: investigating catalytic pathways that can transform biomass components into valuable chemicals;
Biotechnological advancements: emphasizing the role of biotechnology in enabling sustainable biomass transformations, including enzyme engineering, the metabolic pathway, and synthetic biology applications.

We welcome researchers in this field to contribute original research, reviews, and communications that push the boundaries of our knowledge about deriving renewable energy, fuels, and chemicals from biomass. This Special Issue provides a platform for addressing challenges and presenting breakthroughs in the chemistry of biomass conversion.

Dr. Zhuozhi Wang
Prof. Dr. Boxiong Shen
Guest Editors

Manuscript Submission Information

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Molecules is an international peer-reviewed open access semimonthly journal published by MDPI.

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Keywords

biomass conversion technologies
renewable energy
biofuel synthesis
catalytic biomass transformation
bioethanol
biodiesel
green/sustainable chemistry
biotechnological applications

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Technologies for Carbon-Neutral Fuels with High Efficiency and Clean Utilization in Molecules (12 articles)

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Research

Jump to: Review

17 pages, 4405 KiB

Open AccessArticle

Density Functional Theory Study on Na⁺ and K⁺ Catalysis in the Transformation of Glucose to Fructose and HMF in Hydrothermal Environments

by Long Gao, Qihao Chen, Yanhong Wang, Deyong Che, Baizhong Sun and Shuai Guo

Molecules 2024, 29(20), 4849; https://doi.org/10.3390/molecules29204849 - 13 Oct 2024

Viewed by 627

Abstract

Hydrothermal carbonization (HTC) is an efficient method for converting biomass into biochar. Hydrochar contains catalytic components such as alkali and alkaline earth metals (AAEMs); however, the mechanisms by which highly active metals such as potassium (K) and sodium (Na) catalyze the conversion of small carbon–water compounds into hydrochar in hydrothermal environments remain unclear. In this study, glucose was used as a small molecule model, and Na⁺ and K⁺ were used as catalysts to investigate the catalytic reaction mechanism during the hydrothermal process using density functional theory (DFT). In the presence of different ions at various binding sites, glucose isomerizes into fructose, which subsequently undergoes three consecutive dehydration reactions to form 5-hydroxymethylfurfural (HMF). The results indicate that the catalytic effectiveness of Na⁺ and K⁺ in the isomerization of glucose to fructose is optimal when interacting with specific oxygen sites on glucose. For Na⁺, the interaction with the O1 and O2 oxygens provides the lowest reaction barrier of 37.16 kcal/mol. For K⁺, the most effective interactions are with the O3 and O4 oxygens and the O5 and O6 oxygens, resulting in reduced reaction barriers of 54.35 and 31.50 kcal/mol, respectively. Dehydration of fructose to HMF catalyzed by Na⁺ ions, the catalytic effectiveness at different positions is ranked as O5O6 > O1O5, whereas for K⁺, the ranking is O1O5 > O5O6. This study explores the catalytic effects of Na⁺ and K⁺ at different binding sites on the hydrothermal reactions of glucose at the atomic level, offering theoretical support for designing catalysts for the HTC of sludge. Full article

(This article belongs to the Special Issue Renewable Energy, Fuels and Chemicals from Biomass)

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21 pages, 5360 KiB

Open AccessArticle

Study on Water Wash Pretreatment and Al-Si Additives to Relieve the Sintering Behavior of Fungus Bran Combustion Ash

by Dan Wang, Yu Wang, Weinan Xiao, Shengjie Guo, Shuai Guo and Yan Zhao

Molecules 2024, 29(19), 4675; https://doi.org/10.3390/molecules29194675 - 1 Oct 2024

Viewed by 519

Abstract

This study focuses on the sintering phenomenon that easily occurs during the direct combustion of molded fuel made from fungus bran (FB). To investigate the key factors influencing sintering, experiments are designed and conducted using a muffle furnace and a high-temperature drop furnace. The experimental results show that the combustion temperature is the primary factor triggering the sintering phenomenon. To effectively mitigate this issue, this study proposes two improvement strategies: water washing pretreatment and the use of additives. The analysis shows that water washing pretreatment effectively removes K and Mg elements, with the removal rates increasing as the washing temperature and time increase. Specifically, the removal rate of K ranges from 37.68% to 55.91%, and that of Mg ranges from 33.16% to 58.52%. Water washing pretreatment also reduces the degree of sintering; at 1400 °C, the TSF (tendency to slag formation) of the fuel increases by 25–40% after pretreatment, with a greater increases observed at higher washing temperatures and longer durations. Kaolin, used as an additive, significantly raises the ash melting point of FB and alleviates sintering, while P₂O₅ exacerbates it. Increasing the proportion of kaolin does not significantly enhance the TSF of high-temperature ash, but raising the P₂O₅ content from 5% to 10% lowers the TSF by 10–20% at the corresponding temperature. Full article

(This article belongs to the Special Issue Renewable Energy, Fuels and Chemicals from Biomass)

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13 pages, 4755 KiB

Open AccessArticle

Surfactant-Assisted Regulation of WS₂/Tourmaline Microstructures for Excellent Photocatalytic Performance

by Xianku Wang, Kaibin Cui, Yuqin Zhao, Ming Hao, Liang Bian, Mingming Wang and Fei Wang

Molecules 2024, 29(19), 4555; https://doi.org/10.3390/molecules29194555 - 25 Sep 2024

Viewed by 417

Abstract

The controllable electrical and optical properties of two-dimensional tungsten disulfide (WS₂) attracted much attention in photocatalysis, but commercial development has been severely restricted by their restacking properties. Surfactant-assisted synthesis techniques can be considered as an effective option to break this bottleneck. In this work, the effect of surfactants including sodium dodecylbenzene sulfonate (SDBS), hexadecyltrimethylammonium bromide (CTAB), and polyvinylpyrrolidone (PVP) on the microstructure of WS₂/tourmaline composites prepared by coupled hydrothermal and calcination methods was explored. The WS₂ nanosheets were uniformly deposited on the tourmaline surface with the assistance of 1.0 mmol/L SDBS. Meanwhile, WS₂/Tour-SDBS exhibited the highest rhodamine B (RhB) degradation activity, which was 1.8 and 2.3 times higher than that of photocatalysts prepared with CTAB and PVP under the same conditions, respectively. This study provides a new tactic for the fabrication of high-performance WS₂-based composites. Full article

(This article belongs to the Special Issue Renewable Energy, Fuels and Chemicals from Biomass)

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14 pages, 1831 KiB

Open AccessArticle

Insights into the Synergistic Effect and Inhibition Mechanism of Composite Conditioner on Sulfur-Containing Gases during Sewage Sludge Pyrolysis

by Shan Cheng, Lianghui Chen, Shaoshuo Wang, Kehui Yao and Hong Tian

Molecules 2024, 29(17), 4110; https://doi.org/10.3390/molecules29174110 - 29 Aug 2024

Viewed by 488

Abstract

Sewage sludge odorous gas release is a key barrier to resource utilization, and conditioners can mitigate the release of sulfur-containing gases. The gas release characteristics and sulfur compound distribution in pyrolysis products under both single and composite conditioning strategies of CaO, Fe₂O₃, and FeCl₃ were investigated. This study focused on the inhibition mechanisms of these conditioners on sulfur-containing gas emissions and compared the theoretical and experimental sulfur content in the products to evaluate the potential synergistic effects of the composite conditioners. The findings indicated that at 650 °C, CaO, Fe₂O₃, and FeCl₃ inhibited H₂S release by 35.8%, 23.2%, and 9.1%, respectively. Notably, the composite of CaO with FeCl₃ at temperatures ranging from 350 to 450 °C and the combination of Fe₂O₃ with FeCl₃ at 650 °C were found to exert synergistic suppression on H₂S emissions. The strongly alkaline CaO inhibited the metathesis reaction between HCl, a decomposition product of FeCl₃, and the sulfur-containing compounds within the sewage sludge, thereby exerting a synergistic suppression on the emission of H₂S. Conversely, at temperatures exceeding 550 °C, the formation of Ca-Fe compounds, such as FeCa₂O₄, appeared to diminish the sulfur-fixing capacity of the conditioners, resulting in increased H₂S emissions. For instance, the combination of CaO and FeCl₃ at 450 °C was found to synergistically reduce H₂S emissions by 56.3%, while the combination of CaO and Fe₂O₃ at 650 °C synergistically enhances the release of H₂S by 23.6%. The insights gained from this study are instrumental in optimizing the pyrolysis of sewage sludge, aiming to minimize its environmental footprint and enhance the efficiency of resource recovery. Full article

(This article belongs to the Special Issue Renewable Energy, Fuels and Chemicals from Biomass)

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18 pages, 2891 KiB

Open AccessFeature PaperArticle

Investigation of Combustion and NO/SO₂ Emission Characteristics during the Co-Combustion Process of Torrefied Biomass and Lignite

by Xu Yang, Wenkun Zhu, Zhaoming Li, Li Xu, Shujun Zhu, Jilin Tian, Zhuozhi Wang and Boxiong Shen

Molecules 2024, 29(12), 2728; https://doi.org/10.3390/molecules29122728 - 7 Jun 2024

Viewed by 837

Abstract

This paper investigates the combustion characteristics and pollutant emission patterns of the mixed combustion of lignite (L) and torrefied pine wood (TPW) under different blending ratios. Isothermal combustion experiments were conducted in a fixed bed reaction system at 800 °C, and pollutant emission concentrations were measured using a flue gas analyzer. Using scanning electron microscopy (SEM) and BET (nitrogen adsorption) experiments, it was found that torrefied pine wood (TPW) has a larger specific surface area and a more developed pore structure, which can facilitate more complete combustion of the sample. The results of the non-isothermal thermogravimetric analysis show that with the TPW blending ratio increase, the entire combustion process advances, and the ignition temperature, maximum peak temperature, and burnout temperature all show a decreasing trend. The kinetic equations of the combustion reaction process of mixed gas were calculated by Flynn–Wall–Ozawa (FWO) and Kissinger–Akahira–Sunose (KAS) kinetic equations. The results show that the blending of TPW reduces the activation energy of the combustion reaction of the mixed fuel. When the TPW blending ratio is 80%, the activation energy values of the mixed fuel are the lowest at 111.32 kJ/mol and 104.87 kJ/mol. The abundant alkali metal ions and porous structure in TPW reduce the conversion rates of N and S elements in the fuel to NO and SO₂, thus reducing the pollutant emissions from the mixed fuel. Full article

(This article belongs to the Special Issue Renewable Energy, Fuels and Chemicals from Biomass)

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15 pages, 3179 KiB

Open AccessArticle

Reactive Force Field Molecular Dynamics Investigation of NH₃ Generation Mechanism during Protein Pyrolysis Process

by Shuai Guo, Yu Wang, Shujun Zhu, Hongwei Qu, Deng Zhao, Xingcan Li and Yan Zhao

Molecules 2024, 29(9), 2016; https://doi.org/10.3390/molecules29092016 - 27 Apr 2024

Viewed by 891

Abstract

The mechanism of ammonia formation during the pyrolysis of proteins in biomass is currently unclear. To further investigate this issue, this study employed the AMS 2023.104 software to select proteins (actual proteins) as the model compounds and the amino acids contained within them (assembled amino acids) as the comparative models. ReaxFF molecular dynamics simulations were conducted to explore the nitrogen transformation and NH₃ generation mechanisms in three-phase products (char, tar, and gas) during protein pyrolysis. The research results revealed several key findings. Regardless of whether the model compounds are actual proteins or assembled amino acids, NH₃ is the primary nitrogen-containing product during pyrolysis. However, as the temperature rises to higher levels, such as 2000 K and 2500 K, the amount of NH₃ decreases significantly in the later stages of pyrolysis, indicating that it is being converted into other nitrogen-bearing species, such as HCN and N₂. Simultaneously, we also observed significant differences between the pyrolysis processes of actual proteins and assembled amino acids. Notably, at 2000 K, the amount of NH₃ generated from the pyrolysis of assembled amino acids was twice that of actual proteins. This discrepancy mainly stems from the inherent structural differences between proteins and amino acids. In proteins, nitrogen is predominantly present in a network-like structure (NH-N), which shields it from direct external exposure, thus requiring more energy for nitrogen to participate in pyrolysis reactions, making it more difficult for NH₃ to form. Conversely, assembled amino acids can release NH₃ through a simpler deamination process, leading to a significant increase in NH₃ production during their pyrolysis. Full article

(This article belongs to the Special Issue Renewable Energy, Fuels and Chemicals from Biomass)

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18 pages, 4982 KiB

Open AccessArticle

An Optimized Method for Evaluating the Preparation of High-Quality Fuel from Various Types of Biomass through Torrefaction

by Shuai Guo, Xiaoyan Deng, Deng Zhao, Shujun Zhu, Hongwei Qu, Xingcan Li and Yan Zhao

Molecules 2024, 29(8), 1889; https://doi.org/10.3390/molecules29081889 - 21 Apr 2024

Cited by 2 | Viewed by 1479

Abstract

The pretreatment for torrefaction impacts the performance of biomass fuels and operational costs. Given their diversity, it is crucial to determine the optimal torrefaction conditions for different types of biomass. In this study, three typical solid biofuels, corn stover (CS), agaric fungus bran (AFB), and spent coffee grounds (SCGs), were prepared using fluidized bed torrefaction. The thermal stability of different fuels was extensively discussed and a novel comprehensive fuel index, “displacement level”, was analyzed. The functional groups, pore structures, and microstructural differences between the three raw materials and the optimally torrefied biochar were thoroughly characterized. Finally, the biomass fuel consumption for household heating and water supply was calculated. The results showed that the optimal torrefaction temperatures for CS, AFB, and SCGs were 240, 280, and 280 °C, respectively, with comprehensive quality rankings of the optimal torrefied biochar of AFB (260) > SCG (252) > CS (248). Additionally, the economic costs of the optimally torrefied biochar were reduced by 7.03–19.32%. The results indicated that the displacement level is an index universally applicable to the preparation of solid fuels through biomass torrefaction. AFB is the most suitable solid fuel to be upgraded through torrefaction and has the potential to replace coal. Full article

(This article belongs to the Special Issue Renewable Energy, Fuels and Chemicals from Biomass)

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17 pages, 3997 KiB

Open AccessArticle

Turn Waste Golden Tide into Treasure: Bio-Adsorbent Synthesis for CO₂ Capture with K₂FeO₄ as Catalytic Oxidative Activator

by Huijuan Ying, Chenglin Jia, Ganning Zeng and Ning Ai

Molecules 2024, 29(6), 1345; https://doi.org/10.3390/molecules29061345 - 18 Mar 2024

Cited by 1 | Viewed by 1017

Abstract

Converting Sargassum horneri (SH)—a harmful marine stranding that can cause golden tide—to highly porous bio-adsorbent material (via one-step catalytic oxidative pyrolysis with K₂FeO₄) can be a strategically useful method for obtaining low-cost materials suitable for CO₂ capture. In this manuscript, the behavior of different mass ratios of K₂FeO₄/SH precursor acting on the surface physicochemical properties of carbon materials are reported. The results suggest that specific surface area and total pore volume first increased to the mass ratio of K₂FeO₄/carbon precursor, then decreased. Among the samples prepared, the highest specific surface area was obtained with a K₂FeO₄/SH precursor ratio of 1:4 (25%-ASHC), and the CO₂ adsorption performance was significantly increased and faster compared with the original biochar. The fitted values of the three kinetic models showed that the double exponential model provided the best description of carbon adsorption, indicating both physical and chemical adsorption; 25%-ASHC also exhibited excellent cyclic stability. The improved CO₂ adsorption performance observed after K₂FeO₄ activation is mainly due to the increase in material porosity, specific surface area, and the enrichment of nitrogen and oxygen functional groups. Full article

(This article belongs to the Special Issue Renewable Energy, Fuels and Chemicals from Biomass)

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13 pages, 4274 KiB

Open AccessArticle

Exploring Deactivation Reasons of Biomass-Based Phosphorus-Doped Carbon as a Metal-Free Catalyst in the Catalytic Dehydroaromatization of n-Heptane

by Fei Yu, Siyuan Liu and Bo Liu

Molecules 2024, 29(6), 1288; https://doi.org/10.3390/molecules29061288 - 14 Mar 2024

Cited by 2 | Viewed by 1030

Abstract

Catalytic dehydroaromatization of n-alkanes into high-value aromatics has garnered extensive interest from both academia and industry. Our group has previously reported that phosphorus-doped carbon materials exhibit high selectivity for C-H bond activation in the dehydroaromatization of n-hexane. In this study, using n-heptane as a probe, we synthesized biomass-based phosphorus-doped carbon catalysts to investigate the impact of hydrogen heat treatment and carbon deposition on catalyst structure. Despite achieving an initial conversion of n-heptane at approximately 99.6%, with a toluene selectivity of 87.9%, the catalyst activity fell quickly. Moreover, longer hydrogen treatment time and higher hydrogen concentrations were found to accelerate catalyst deactivation. Thermogravimetric analysis (TGA) and N₂ adsorption measurements (BET) indicated that a small amount of coke deposition was not the primary cause of catalyst deactivation. Temperature-programmed desorption of ammonia gas (NH₃-TPD) revealed a significant decrease in acid-active functional groups. X-ray photoelectron spectroscopy (XPS) and solid-state ³¹P NMR spectroscopy confirmed the reduction of active central phosphorus species. These results suggest that catalyst deactivation primarily arises from the decrease in acidity and the partial reduction of phosphorus-containing groups, leading to a substantial loss of active sites. This work contributes new perspectives to understanding the properties and design improvements of metal-free carbon catalysts. Full article

(This article belongs to the Special Issue Renewable Energy, Fuels and Chemicals from Biomass)

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Review

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11 pages, 990 KiB

Open AccessReview

Release Pattern of Light Aromatic Hydrocarbons during the Biomass Roasting Process

by Yaying Zhao, Yuqing Yan, Yuhang Jiang, Yang Cao, Zhuozhi Wang, Jiapeng Li, Chenshuai Yan, Danya Wang, Lu Yuan and Guangbo Zhao

Molecules 2024, 29(6), 1188; https://doi.org/10.3390/molecules29061188 - 7 Mar 2024

Cited by 58 | Viewed by 1438

Abstract

Roasting is an important step in the pretreatment of biomass upgrading. Roasting can improve the fuel quality of biomass, reduce the O/C and H/C ratios in the biomass, and provide the biomass with a fuel quality comparable to that of lignite. Therefore, studying the structure and component evolution laws during biomass roasting treatment is important for the rational and efficient utilization of biomass. When the roasting temperature is 200–300 °C, the cellulose and hemicellulose in the biomass undergo a depolymerization reaction, releasing many monocyclic aromatic hydrocarbons with high reactivity. The proportion of monocyclic aromatic hydrocarbons in biomass roasting products can be effectively regulated by controlling the reaction temperature, residence time, catalyst, baking atmosphere, and other factors in the biomass roasting process. This paper focuses on the dissociation law of organic components in the pretreatment process of biomass roasting. Full article

(This article belongs to the Special Issue Renewable Energy, Fuels and Chemicals from Biomass)

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