New sight on the lignin torrefaction pretreatment: Relevance between the evolution of chemical structure and the properties of torrefied gaseous, liquid, and solid products

Insight into volatile-char interaction mechanisms of biomass torrefaction based on three major components

Volatile-char interaction is an important phenomenon in biomass thermal conversion process, which significantly contributes to the decomposition, deoxygenation and upgrading of biomass. However, the deep insight into volatile-char interaction mechanisms between hemicellulose, cellulose and lignin is currently unclear. In this work, above mechanism was studied through systematic single-/bi-component torrefactions and the follow-up char analysis. Results demonstrate that only hemicellulose volatile and cellulose char interaction exists during torrefaction at 250 °C, causing over 19.9 wt% of mass loss and 27.3 wt% of O removal for cellulose. This volatile-char interaction causes significant depolymerization and amorphization of cellulose by hydrolysis, acid hydrolysis and esterification reactions. The depolymerized and amorphous cellulose partly thermally decomposes to dehydrated sugars and aromatic compounds through dehydroxylation and aromatization reactions. A volatile-char interaction mechanism model is thus developed. This work provides theoretical insight into biomass thermal conversion and provides basis for the development of new thermochemical method.

Properties of Table Tennis Blade from Sorghum Bagasse Particleboard Bonded with Maleic Acid Adhesive at Different Pressing Temperatures and Times

This physical and mechanical properties of a table tennis blade made from sorghum bagasse particleboard (TTBSB-particleboard) bonded maleic acid adhesive was investigated under pressing temperature and time variations. The TTBSB-particleboard was produced via a two-stage process in this study. A pressing temperature of 170-200 °C was used to prepare the first stage for 10 min. Following this, the second stage of the TTBSB-particleboard was produced with a different pressing time of 5-20 min. The TTBSB-particleboard had a specified target density of 0.6 g/cm³ and a size of 30 cm × 30 cm × 0.6 cm, respectively. For references concerning the tested quality of TTBSB-particleboard, the JIS A 5908-2003 standard has been used. For comparison, the commercial blades of Yuguan Wooden 1011 and Donic Original Carbo Speed were tested under the same conditions. The quality of the TTBSB-particleboard was successfully enhanced by increasing the pressing temperature (170 to 200 °C) and time (5 to 20 min). As a result, the pressing condition of 200 °C and 20 min were effective in this study. The TTBSB-particleboard in this study has a greater weight than the commercial blades of Yuguan and Donic. However, the TTBSB-particleboard in this study had a ball rebound comparable to that of the Donic blade.

A rational and feasible approach to the co-management of condensates from biomass torrefaction and carbon-rich fly ash from fluidized-bed coal gasification

This study explored a promising approach to the co-management of torrefaction condensates (TCs) from biomass and carbon-rich fly ash (FA) derived from an industrial fluidized-bed coal gasifier. TC was a low-quality liquid product consisting mostly of water and a small amount of organic acids and other oxygenated organics. FA was the ultra-fine particulates with high carbon content (40-70%) and some extreme characteristics such as ultra-low volatiles, low reactivity, and high ignition temperature. The blending of FA and TC induced most of the organic components in TC to be chemically or physically adsorbed by FA, accounting for 3-13 wt% of the resultant mixtures of FA and TC (FATCs) and 11-33 wt% of the TCs. The acidic components in TC dissolved locally aggregated Ca minerals in FA, resulting in more evenly dispersed Ca on the surface of FA as an in-situ catalyst. As a result, FATCs exhibited a many-fold improvement in CO2 gasification reactivity compared to FA. And the syngas evolution rate of FATC gasification in steam-oxygen atmosphere was also remarkably elevated. In addition to the promoting effect on gasification, the combustion performance of FATCs was also greatly improved. Specifically, the ignition and burnout temperatures of FATCs were 46.5-68.5 °C and 12.4-31.7 °C lower than those of raw FA, respectively. The lower activation energy also demonstrated the higher reactivity of FATC gasification and combustion.

Life-cycle assessment of pyrolysis processes for sustainable production of biochar from agro-residues

Net carbon management of agro-residues has been an important pathway for reducing the environmental burdens of agricultural production. Converting agro-residues into biochar through pyrolysis is a prominent management strategy for achieving carbon neutrality in a circular economy, meeting both environmental and social concerns. Based on the latest studies, this study critically analyzes the life cycle assessment (LCA) of biochar production from different agro-residues and compares typical technologies for biochar production. Although a direct comparison of results is not always feasible due to different functional units and system boundaries, the net carbon sequestration potential of biochar technology is remarkably promising. By pyrolyzing agro-residues, biochar can be effectively produced and customized as: (i) alternative energy source, (ii) soil amendment, and (iii) activated carbon substitution. The combination of life cycle assessment and circular economy modelling is encouraged to achieve greener and sustainable biochar production.

Characteristics of bio-oil and biochar from cotton stalk pyrolysis: Effects of torrefaction temperature and duration in an ammonia environment

In this study, nitrogen-containing chemicals and nitrogen-rich biochar were prepared using ammonia (NH₃) torrefaction pretreatment technology. The effects of temperature and duration of torrefaction on the characteristics of torrefaction and pyrolysis products were evaluated. The results indicated that when the torrefaction temperature was increased to 290 °C, the nitrogen content increased significantly from 0.98% to 6.85%. XPS analysis showed that the raw biomass mainly contained amide-N and pyrrole-N. As the torrefaction temperature and duration increased, quaternary-N formation was promoted, while amide-N, pyrrole-N, and pyridine-N were consumed. Potential nitrogen doping and transformation pathways during the ammonia torrefaction process were proposed. GC-MS analysis showed that ammonia torrefaction promoted the formation of pyridines, while reducing the content of oxygen-containing species. In addition, torrefaction duration had positive effects on the yield of nitrogen-containing chemicals.

Torrefied herb residues in nitrogen, air and oxygen atmosphere: Thermal decomposition behavior and pyrolytic products characters

The thermal decomposition behavior and pyrolytic products characters of herb residue (HR) torrefied in N₂, air and O₂ were investigated in present work. The clear gradual regularity of samples in Van Krevelen diagram exhibited the severity and some similarities of torrefaction. The activation energy (E) calculated by distributed activation energy model (DAEM) found that the E values of torrefied samples was higher than raw HR if the conversion is below 0.8. Torrefaction treatment would beneficial to increase the yield of gas but inhibit the formation of oil, and the compounds of gas and bio-oil under different torrefaction conditions are also quite different. It should be noticed that the presence of oxygen in the torrefaction atmosphere would reduce the torrefaction temperature significantly, while maintaining the severity of torrefaction and pyrolytic products distribution.

Fuel properties and combustion behaviors of fast torrefied pinewood in a heavily loaded fixed-bed reactor by superheated steam

Superheated steam (SHS) was capable of fast and uniformly torrefying heavily loaded biomass. This work detailedly investigated the torrefied biomass in terms of fuel property and combustion behavior. The reactor chamber (300 ml) was fully loaded with pinewood pellets (160 g). Overall residence times were 20, 40 and 60 min (including preheating and holding periods) under 225, 275 and 325 °C. Biomass was estimated by elements, TG, FTIR, HHV, fuel property, combustion and pyrolysis behaviors, combustion kinetics and moisture reabsorption. Holding period as short as 2 min at 325 °C with a heating rate of 15 °C‧min^-1 was found to enhance energy density by 45% and generated homogeneous coal-like products with HHV of 26.76 MJ‧kg^-1. Fixed carbon content increased to 64.84 wt%. The combustion activation energy increased to 79.66 kJ‧mol^-1. Combustion indices and behaviors indicated that torrefied biomass had benign characteristics either for co-firing or as fuel. All suggests good potential of SHS torrefaction to obtain fuel alternatives.

Precursor biosynthesis regulation of lignin, suberin and cutin

The extracellular matrix of plants can contain the hydrophobic biopolymers lignin, suberin and/or cutin, which provide mechanical strength and limit water loss and pathogen invasion. Due to their remarkable chemical resistance, these polymers have a high potential in various biotechnological applications and can replace petrol-based resources, for example, in the packing industry. However, despite the importance of these polymers, the regulation of their precursor biosynthesis is far from being fully understood. This is particularly true for suberin and cutin, which hinders efforts to engineer their formation in plants and produce customised biopolymers. This review brings attention to knowledge gaps in the current research and highlights some of the most recent findings on transcription factors that regulate lignin, suberin and cutin precursor biosynthesis. Finally, we also briefly discuss how some of the remaining knowledge gaps can be closed.

Novel insights into the enrichment of phenols from walnut shell pyrolysis loop: Torrefaction coupled fractional condensation

Enriching high-value chemicals from the pyrolysis of agricultural and forestry waste is an efficient way to achieve sustainable development and large-scale application of biomass pyrolysis. Phenols, as important chemical raw materials, spices and food additives, have attracted widespread attention. Herein, a novel technical route of torrefaction pretreatment combined with fractional condensation in pyrolysis loop was proposed to enrich the phenols in liquid products. In this study, the enrichment of phenols from the pyrolysis loop of walnut shell under the combination of torrefaction and fractional condensation was explored using a fixed-bed pyrolysis reactor equipped with a three-stage condensation system. Simultaneously, the effects of torrefaction on feedstocks were investigated through a thermogravimetric analyzer based on the characteristics of feedstocks. The results showed that the torrefaction and pyrolysis loop had a negative impact on the pyrolysis efficiency and the yield of liquid products, while the change in the condensation efficiency depended on the combined effects of torrefaction and pyrolysis loop. In addition, phenols tended to be enriched in the second condensation stage, especially phenol, o-cresol, 4-ethylphenol. Importantly, torrefaction could significantly enrich phenols in the liquid products, and the enrichment of phenols is relatively increased by 109.44% at least. Moreover, the pyrolysis loop was also beneficial to the enrichment of phenols, which was at least 90% higher than that of walnut shell. This study provided a potential route to enrich high value-added products from the pyrolysis loop of lignocellulosic biomass.

Optimization of the nitrogen and oxygen element distribution in microalgae by ammonia torrefaction pretreatment and subsequent fast pyrolysis process for the production of N-containing chemicals

In this work, ammonia (NH₃) torrefaction pretreatment (ATP) was developed to optimize the nitrogen and oxygen element distribution of microalgae via the N-doping and oxygen removal reaction, which could obviously improve the potential use of microalgae as a feedstock for the production of N-heterocyclic chemicals through fast pyrolysis technology. The nitrogen content increased from 8.3% of raw microalgae to 11.51% at 300 °C of ATP, while the oxygen content decreased from 35.96% to 21.61%, because of the Maillard reactions. In addition, the nitrogen-doping ratio and oxygen removal ratio of ATP was much higher than the conventional nitrogen torrefaction pretreatment (NTP). With the increase of ATP torrefaction temperature or the pyrolysis temperature, the relative content of the N-containing compounds increased, while the O-containing compounds decreased. For the N-heterocyclic chemicals, higher pyrolysis temperature favored the formation of pyrroles, while inhibited the formation of pyridines and indoles.

Upgrading of bio-oil via solar pyrolysis of the biomass pretreated with aqueous phase bio-oil washing, solar drying, and solar torrefaction

In this study, three types of biomass were first pretreated with an aqueous phase bio-oil instead of traditional acid washing. Then, the washed samples were pretreated with drying (100 ℃, 30 min) and torrefaction (250 ℃, 30 min) using a parabolic-trough solar receiver system. The subsequent pyrolysis was performed at 550 ℃ for 10 min using a parabolic-dish solar receiver system. Results showed that the solar energy can effectively ensure the temperature required for biomass drying, torrefaction, and pyrolysis, having thus a potential to replace the conventional electric heating or fossil fuel heating. Such a strategy combines the advantages of the independent pretreatments, i.e., leaching out of metallic species and reduction of oxygen content. Consequently, the high heating value of bio-oil increased remarkably, the generation of acids was strongly inhibited, whereas the formation of phenols and anhydrosugars was promoted. Therefore, the method proposed herein is promising for upgrading of biomass and bio-oil.

Enhancement of the production of bio-aromatics from renewable lignin by combined approach of torrefaction deoxygenation pretreatment and shape selective catalytic fast pyrolysis using metal modified zeolites

In this work, combined approach of torrefaction deoxygenation pretreatment (TDP) and shape selective catalytic fast pyrolysis (SS-CFP) using bifunctional catalyst (metal modified HZSM-5) were employed to improve the yield of bio-BTX derived from the renewable starting material of lignin. Results showed that after TDP, the oxygen element could be removed effectively. The oxygen removal efficiency reached its maximum value of 22.27% at 300 °C, resulting in markedly decrease of unnecessary oxygenates in bio-oil. Compared to parent HZSM-5, all metal modified HZSM-5 (Ga/HZSM-5, Zn/HZSM-5, and Ga-Zn/HZSM-5) promoted the formation of bio-BTX. Zn/HZSM-5 showed the highest selective yield of bio-BTX because of the enhancement deoxygenation reaction of oxygenates and the aromatization reaction of olefins. The combined approach of TDP and SS-CFP remarkably improved the selective yield of bio-BTX, reaching the maximum value of 65.19%, which was much higher than that from single approach of TDP (33.84%) and SS-CFP (47.36%).

N-doping of biomass by ammonia (NH3) torrefaction pretreatment for the production of renewable N-containing chemicals by fast pyrolysis

In this work, ammonia (NH₃) torrefaction pretreatment was developed for the production of nitrogen-enriched lignocellulosic biomass and the production of N-containing chemicals via subsequent fast pyroysis process. Results showed that the content of nitrogen in biomass was significantly increased from 0.03% to 7.59% as the torrefaction temperature increased. XPS analysis showed that nitrogen-doped biomass mainly contained three types of N-containing functional groups, such as quaternary-N, pyrrolic-N, and pyridinic-N. Higher torrefaction temperature promoted the formation of pyrrolic-N, and quaternary-N, but inhibited pyridinic-N. Py-GC/MS analysis showed that higher torrefaction temperature and higher pyrolysis temperature both promoted the formation of N-containing chemicals (pyridines, pyrroles, and amines), which reached a maximum abundance of 19.89%. Amines were the dominant components in N-containing chemical fraction, accounting for 85.27% of the total chemical fraction. Lower torrefaction temperature and lower pyrolysis temperature were preferred for the production of pyridines and pyrroles.

Combined Chemical Modification of Bamboo Material Prepared Using Vinyl Acetate and Methyl Methacrylate: Dimensional Stability, Chemical Structure, and Dynamic Mechanical Properties

Acetylation and in situ polymerization are two typical chemical modifications that are used to improve the dimensional stability of bamboo. In this work, the combination of chemical modification of vinyl acetate (VA) acetylation and methyl methacrylate (MMA) in situ polymerization of bamboo was employed. Performances of the treated bamboo were evaluated in terms of dimensional stability, wettability, thermal stability, chemical structure, and dynamic mechanical properties. Results show that the performances (dimensional stability, thermal stability, and wettability) of bamboo that was prepared via the combined pretreatment of VA and MMA (VA/MMA-B) were better than those of raw bamboo, VA single-treated bamboo (VA-B), and MMA single-treated bamboo (MMA-B). According to scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) analyses, VA and MMA were mainly grafted onto the surface of the cell wall or in the bamboo cell lumen. The antiswelling efficiency and contact angle of VA/MMA-B increased to maximum values of 40.71% and 107.1°, respectively. From thermogravimetric analysis (TG/DTG curves), the highest onset decomposition temperature (277 °C) was observed in VA/MMA-B. From DMA analysis, the storage modulus (E’) of VA/MMA-B increased sharply from 15,057 Pa (untreated bamboo) to 17,909 Pa (single-treated bamboo), and the glass transition temperature was improved from 180 °C (raw bamboo) to 205 °C (single-treated bamboo).

New Perspective on Wood Thermal Modification: Relevance between the Evolution of Chemical Structure and Physical-Mechanical Properties, and Online Analysis of Release of VOCs

Thermal modification (TM) is an ecological and low-cost pretreated method to improve the dimensional stability and decay resistance of wood. This study systematically investigates the relevance between the evolution of chemical structure and the physical and mechanical properties during wood thermal modification processes. Moreover, the volatility of compounds (VOCs) was analyzed using a thermogravimetric analyzer coupled with Fourier transform infrared spectrometry (TGA-FTIR) and a pyrolizer coupled with gas chromatography/mass spectrometer (Py-GC/MS). With an increase of TM temperature, the anti-shrink efficiency and contact angle increased, while the equilibrium moisture content decreased. This result indicates that the dimensional stability improved markedly due to the reduction of hydrophilic hydroxyl (–OH). However, a slight decrease of the moduli of elasticity and of rupture was observed after TM due to the thermal degradation of hemicellulose and cellulose. Based on a TGA-FTIR analysis, the small molecular gaseous components were composed of H₂O, CH₄, CO₂, and CO, where H₂O was the dominant component with the highest absorbance intensity, i.e., 0.008 at 200 °C. Based on the Py-GC/MS analysis, the VOCs were shown to be mainly composed of acids, aldehydes, ketones, phenols, furans, alcohols, sugars, and esters, where acids were the dominant compounds, with a relative content of 37.05−42.77%.