Production, separation and applications of phenolic-rich bio-oil--a review

Environmentally Friendly Synthesis of Highly Substituted Phenols Using Enallenoates and Grignard Reagents

We developed an efficient and environmentally friendly methodology for selectively synthesizing highly substituted phenols using readily available enallenoates and Grignard reagents. This method consistently yields good to excellent results across over 60 examples, demonstrating the substrate scope and the exploration of phenol product derivatization, further extending the method's utility.

Aromatics production from relay catalytic pyrolysis of cow manure using Ru/C and ZSM-5 dual catalysts synthesized from coal gasification fine slag

Resource utilization of solid waste can aid in gradual substitution of fossil fuels while achieving waste recycling. In this study, residual carbon and ash slag from the coal gasification fine slag were separated by froth flotation, and then was used to prepare Ru/C and ZSM-5 dual catalysts with carbon-rich and ash-rich components as raw materials, respectively. The performance of two catalysts for catalytic upgrading of volatiles from pyrolysis of cow manure (CM) to produce light aromatic hydrocarbons was systematically investigated. The direct pyrolysis products of CM mainly included alcohols, ketones, ethers, and other oxygen-containing compounds. When ZSM-5 was used as the catalyst, the yield of monocyclic aromatic hydrocarbons (MAHs) increased significantly due to the better catalytic cracking and aromatization abilities of ZSM-5 catalyst. However, the yield of phenols in the pyrolysis products improved when Ru/C was used as the catalyst due to the cleavage effect of Ru/C on the C-O bond. When Ru/C and ZSM-5 were used as dual catalysts in relay catalytic pyrolysis of volatiles, the increase in MAHs yield in the pyrolysis product was higher than the total increase obtained under Ru/C and ZSM-5 single catalysis. The possible pathways for the generation of MAHs from CM under Ru/C and ZSM-5 relay catalytic pyrolysis were revealed by the pyrolysis experiment performed on model compounds.

Depolymerization of lignin: Recent progress towards value-added chemicals and biohydrogen production

The need for alternative sources of energy became increasingly urgent as demand for energy and the use of fossil fuels both soared. When processed into aromatic compounds, lignin can be utilized as an alternative to fossil fuels, however, lignin's complex structure and recalcitrance make depolymerization impractical. This article presented an overview of the most recent advances in lignin conversion, including process technology, catalyst advancement, and case study-based end products. In addition to the three established methods (thermochemical, biochemical, and catalytic depolymerization), a lignin-first strategy was presented. Depolymerizing different forms of lignin into smaller phenolic molecules has been suggested using homogeneous and heterogeneous catalysts for oxidation or reduction. Limitations and future prospects of lignin depolymerization have been discussed which suggests that solar-driven catalytic depolymerization through photocatalysts including quantum dots offers a unique pathway to obtain the highly catalytic conversion of lignin.

Characterization of slow pyrolysis products from three different cashew wastes

A huge amount of waste is generated by the cashew processing industries. This study aims to valorise these cashew wastes generated at different levels while processing cashew nuts in factories. The feedstocks include cashew skin, cashew shell and cashew shell de-oiled cake. Slow pyrolysis of these three different cashew wastes was performed at varying temperatures (300-500℃) at a heating rate of 10℃/min in a lab scale glass-tubular reactor under inert atmosphere of nitrogen with flow rate of 50 ml/min. The total bio-oil yield for cashew skin and the de-oiled shell cake was 37.1 and 48.6 wt% at 400℃ and 450℃, respectively. However, the maximum bio-oil yield obtained for cashew shell waste was 54.9 wt% at 500℃. The bio-oil was analysed using GC-MS, FTIR, and NMR. Along with the various functionalities observed in bio-oil through GC-MS, phenolics were observed to have maximum area% for all the feedstocks at all temperatures. At all the slow pyrolysis temperatures, cashew skin led to more biochar yield (40 wt%) as compared to cashew de-oiled cake (26 wt%) and cashew shell waste (22 wt%). Biochar was characterized by various analytical tools such as XRD, FTIR, Proximate analyser, CHNS, Py-GC/MS and SEM. Characterization of biochar revealed its carbonaceous and amorphous nature along with porosity.

Hydrodeoxygenation of Bio-Oil over an Enhanced Interfacial Catalysis of Microemulsions Stabilized by Amphiphilic Solid Particles

Bio-oil emulsions were stabilized using coconut shell coke, modified amphiphilic graphene oxide, and hydrophobic nano-fumed silica as solid emulsifiers. The effects of different particles on the stability of bio-oil emulsions were discussed. Over 21 days, the average droplet size of raw bio-oil increased by 64.78%, while that of bio-oil Pickering emulsion stabilized by three particles only changed within 20%. The bio-oil Pickering emulsion stabilized by Ni/SiO2 was then used for catalytic hydrodeoxygenation. It was found that the bio-oil undergoes polymerization during catalytic hydrogenation. For raw bio-oil hydrodeoxygenation, the polymerization reaction was little affected by the temperature below 200 °C, but when the temperature raised to 250 °C, it was greatly accelerated. However, the polymerization of monocyclic aromatic compounds in the reaction process was partially inhibited under the bio-oil Pickering emulsion system. Additionally, a GC-MS analysis was performed on raw bio-oil and hydrodeoxygenated bio-oil to compare the change in GC-MS-detectable components after hydrodeoxygenation at 200 °C. The results showed that the Pickering emulsion catalytic system greatly promoted the hydrodeoxygenation of phenolic compounds in bio-oil, with most monocyclic phenolic compounds detected by GC-MS converting to near 100%.

Green Phenolic Resins from Oil Palm Empty Fruit Bunch (EFB) Phenolated Lignin and Bio-Oil as Phenol Substitutes for Bonding Plywood

Lignin is a natural biopolymer with a complex three-dimensional network and it is rich in phenol, making it a good candidate for the production of bio-based polyphenol material. This study attempts to characterize the properties of green phenol-formaldehyde (PF) resins produced through phenol substitution by the phenolated lignin (PL) and bio-oil (BO), extracted from oil palm empty fruit bunch black liquor. Mixtures of PF with varied substitution rates of PL and BO were prepared by heating a mixture of phenol-phenol substitute with 30 wt.% NaOH and 80% formaldehyde solution at 94 °C for 15 min. After that, the temperature was reduced to 80 °C before the remaining 20% formaldehyde solution was added. The reaction was carried out by heating the mixture to 94 °C once more, holding it for 25 min, and then rapidly lowering the temperature to 60 °C, to produce the PL-PF or BO-PF resins. The modified resins were then tested for pH, viscosity, solid content, FTIR, and TGA. Results revealed that the substitution of 5% PL into PF resins is enough to improve its physical properties. The PL-PF resin production process was also deemed environmentally beneficial, as it met 7 of the 8 Green Chemistry Principle evaluation criteria.

Optimization Study on Microwave-Assisted Hydrothermal Liquefaction of Malaysian Macroalgae Chaetomorpha sp. for Phenolic-Rich Bio-Oil Production

There are several methods of biomass conversion, including hydrothermal liquefaction (HTL). The implementation of microwave technology in the HTL process is still new, especially on the conversion of marine biomass into bio-crude. In this work, the macroalgae Chaetomorpha sp. was used as the biomass feedstock to produce phenolic-rich bio-oil through microwave-assisted HTL. Chaetomorpha sp. was abundantly found in Malaysia, creating a green tides issue. By utilizing these algae, the green tide issue can be solved and value-added bio-oil is obtained. However, bio-oil from macroalgae has a relatively low heating value, restricting its fuel application. Therefore, it is suggested to be used for bio-polymer synthesis, including bio-based phenol formaldehyde. In this study, the effect of different parameters, such as reaction temperature, preloaded pressure, water-to-algal biomass ratio, and holding time, on both the bio-oil yield and phenolic yield was evaluated. Folin–Ciocalteu method was introduced as the phenolic determination method and the optimal conditions were located by using Response Surface Methodology (RSM). As a results, an optimal biodiesel yield and phenolic yield of 21.47 wt% and 19.22 wt% Gallic Acid Equivalent was obtained at a reaction temperature of 226 °C, 42 bar preloaded pressure and 30:1 water-to-algal biomass ratio after 79 min. Sensitivity analysis also concluded that the water-to-algal biomass ratio is the most influential factor, followed by the preloaded pressure. The FTIR spectrum of the bio-oil produced indicated the presence of different functional group of compounds. In short, Chaetomorpha sp. has been successfully converted into valuable bio-oil through microwave-assisted HTL.

Fractional Condensation of Fast Pyrolysis Bio-Oil to Improve Biocrude Quality towards Alternative Fuels Production

Fast pyrolysis of biomass is a well-known opportunity for sustainable alternative fuel production for transport and energy. However, bio-oils from biomass pyrolysis are viscous, acidic bio-crudes that need further steps of upgrading before being used either as fuels or chemicals. A process that is complementary to bio-oil hydrotreatment or co-processing consists of optimizing and tuning the upstream condensation steps of fast pyrolysis to separate and concentrate selected classes of compounds. This can be implemented by varying the condensation temperatures in a multi-step condensation unit. In this study, fractional condensation of fast pyrolysis vapors from pinewood has been applied to a bubbling fluidized bed reactor of 1 kg h−1 feed. The reactor was operated at 500 °C and connected to a downstream interchangeable condensation unit. Tests were performed using two different condensing layouts: (1) a series of two spray condensers and a tube-in-tube water-jacketed condenser, referred to as an intensive cooler; (2) an electrostatic precipitator and the intensive cooler. Using the first configuration, which is the focus of this study, high boiling point compounds—such as sugars and lignin-derived oligomers—were condensed at higher temperatures in the first stage (100–170 °C), while water-soluble lighter compounds and most of the water was condensed at lower temperatures and thus largely removed from the bio-oil. In the first two condensing stages, the bio-oil water content remained below 7% in mass (and therefore, the oil’s high calorific content reached 22 MJ kg−1) while achieving about 43% liquid yield, compared to 55% from the single-step condensation runs. Results were finally elaborated to perform a preliminary energy assessment of the whole system toward the potential upscaling of this fractional condensation approach. The proposed layout showed a significant potential for the upstream condensation step, simplifying the downstream upgrading stages for alternative fuel production from fast pyrolysis bio-oil.

Upcycling agro-industrial blueberry waste into platform chemicals and structured materials for application in marine environments

Blueberry pruning waste (BPw), sourced as residues from agroforestry operations in Chile, was used to produce added-value products, including platform chemicals and materials. BPw fractionation was implemented using biobased solvents (γ-valerolactone, GVL) and pyrolysis (500 °C), yielding solid fractions that are rich in phenols and antioxidants. The liquid fraction was found to be enriched in sugars, acids, and amides. Alongside, filaments and 3D-printed meshes were produced via wet spinning and Direct-Ink-Writing (DIW), respectively. For the latter purpose, BPw was dissolved in an ionic liquid, 1-ethyl-3-methylimidazolium acetate ([emim][OAc]), and regenerated into lignocellulose filaments with highly aligned nanofibrils (wide-angle X-ray scattering) that simultaneously showed extensibility (wet strain as high as 39%). BPw-derived lignocellulose filaments showed a tenacity (up to 2.3 cN dtex^-1) that is comparable to that of rayon fibers and showed low light reflectance (R _ES factor <3%). Meanwhile, DIW of the respective gels led to meshes with up to 60% wet stretchability. The LCF and meshes were demonstrated to have reliable performance in marine environments. As a demonstration, we show the prospects of replacing plastic cords and other materials used to restore coral reefs on the coast of Mexico.

Aging Behaviors of Phenol-Formaldehyde Resin Modified by Bio-Oil under Five Aging Conditions

The bio-oil phenol-formaldehyde (BPF) resin, prepared by using bio-oil as a substitute for phenol, has similar bonding strength but lower price to phenol-formaldehyde (PF) resin. As a common adhesive for outdoor wood, the aging performance of BPF resin is particularly important. The variations in mass, bonding strength, microstructure, atomic composition, and chemical structure of BPF resin under five aging conditions (heat treatment, water immersion, UV exposure, hydrothermal treatment, and weatherometer treatment) were characterized by scanning electron microscope, X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy, respectively. Compared under five aging conditions, after aging 960 h, the mass loss of plywood and film was largest under hydrothermal treatment; the bonding strength of plywood, the surface roughness, and O/C ratio of the resin film changed most obviously under weatherometer treatment. FT-IR analysis showed that the decreased degree of peak intensity on CH₂ and C–O–C characteristic peaks of BPF resin were weaker under water immersion, hydrothermal treatment, and weatherometer treatment than those of PF resin. The comparison of data between BPF and PF resins after aging 960 h showed that adding bio-oil could obviously weaken the aging effect of water but slightly enhance that of heat. The results could provide a basis for the aging resistance modification of BPF resin.

Pomegranate seed polyphenol-based nanosheets as an efficient inhibitor of amyloid fibril assembly and cytotoxicity of HEWL

Poor water solubility and low bioavailability are considered as two main factors restricting therapeutic applications of natural polyphenols in relation to various disorders including amyloid-related diseases. Among various strategies developed to overcome these limitations, nanonization has attracted considerable attention. Herein, we compared the potency of bulk and nano forms of the polyphenolic fraction of pomegranate seed (PFPS) for modulating Hen Egg White Lysozyme (HEWL) amyloid fibril formation. Prepared PFPS nanosheets using direct oxidative pyrolysis were characterized by employing a range of spectroscopic and microscopic techniques. We found that the nano form can inhibit the assembly process and disintegrate preformed fibrils of HEWL much more effective than the bulk form of PFPS. Moreover, MTT-based cell viability and hemolysis assays showed the capacity of both bulk and nano forms of PFPS in attenuating HEWL amyloid fibril-induced toxicity, where the nano form was more effective. On the basis of thioflavin T results, a delay in the initiation of amyloid fibril assembly of HEWL appears to be the mechanism of action of PFPS nanosheets. We suggest that the improved efficiency of PFPS nanosheets in modulating the HEWL fibrillation process may be attributed to their increased surface area in accord with the surface-assistance model. Our results may present polyphenol-based nanosheets as a powerful approach for drug design against amyloid-related diseases.

PFPS nanosheets modulate the amyloid fibrillation of HEWL much more effective than the bulk form of PFPS. Based on the thioflavin T results, a delay in the initiation of the assembly process appears to be the mechanism of action of PFPS nanosheets.

Bio-Oil: The Next-Generation Source of Chemicals

Bio-oil, although rich in chemical species, is primarily used as fuel oil, due to its greater calorific power when compared to the biomass from which it is made. The incomplete understanding of how to explore its chemical potential as a source of value-added chemicals and, therefore, a supply of intermediary chemical species is due to the diverse composition of bio-oil. Being biomass-based, making it subject to composition changes, bio-oil is obtained via different processes, the two most common being fast pyrolysis and hydrothermal liquefaction. Different methods result in different bio-oil compositions even from the same original biomass. Understanding which biomass source and process results in a particular chemical makeup is of interest to those concerned with the refinement or direct application in chemical reactions of bio-oil. This paper presents a summary of published bio-oil production methods, origin biomass, and the resulting composition.

Lignocellulosic biomass-based pyrolysis: A comprehensive review

The efficacious application of lignocellulosic biomass for the new valuable chemicals generation curbs the excessive dependency on fossil fuels. Among the various techniques available, pyrolysis has garnered much attention for conversion of lignocellulosic biomass (encompasses cellulose, hemicellulose and lignin components) into product of solid, liquid and gases by thermal decomposition in an efficient manner. Pyrolysis conversion mechanism can be outlined as formation of char, depolymerisation, fragmentation and other secondary reactions. This paper gives a deep insight about the pyrolytic behavior of the lignocellulosic components accompanied by its by-products. Also several parameters such as reaction environment, temperature, residence time and heating rate which has a great impact on the pyrolysis process are also elucidated in a detailed manner. In addition the environmental and economical facet of lignocellulosic biomass pyrolysis for commercialization at industrial scale is critically analyzed. This article also illustrates the prevailing challenges and inhibition in implementing lignocellulosic biomass based pyrolysis with possible solution.

Quantitative insights on de/repolymerization and deoxygenation of lignin in subcritical water

The objective of the study was to investigate alkali lignin polymerization/depolymerization pathways in subcritical water (SW) without additives. Following a SW treatment at 200, 250, 275 and 300 °C, the products were subjected to a comprehensive suite of analyses addressing the product speciation and molecular weight (MW) distribution. The MW reduction (1.4 times) in the solid products following the SW treatment indicated a surprisingly reduced impact of cross-linking/repolymerization at 300 °C and lower temperatures. This was further confirmed by thermal carbon analysis (TCA) showing a reduction in pyrolytic charring after the SW treatment. The TD-Py gas chromatography analysis of the SW treated lignin indicated that the solid residue is less oxygenated than the initial lignin (23 vs. 29% as confirmed by elemental analysis). Thus, deoxygenation rather than re-polymerization appears to be the main process route in the absence of catalysts within the temperature range considered.

Lignin-to-chemicals: Application of catalytic hydrogenolysis of lignin to produce phenols and terephthalic acid via metal-based catalysts

Lignin is the only renewable aromatic material in nature and contains a large number of oxygen-containing functional groups. High-value and green utilization of "lignin-to-chemicals" can be realized via using lignin to produce fine chemicals such as phenols and carboxylic acids, which can not only reduce the waste of lignin in the process of lignocellulosic biomass treatment, but gradually make the substitution of traditional fossil fuels come true. The hydrogenolysis process under catalysis of metal catalyst has high product selectivity and less impurity, which is suitable for the production of same type or single fine chemicals. Hydrogenolysis of lignin via metal catalysts to produce lignin oil, and further modification of functional groups (e.g. methoxyl, alkyl and hydroxyl group) of depolymerized monomers in the bio-oil to yeild phenols and terephthalic acid are reviewed, and catalytic mechanisms are briefly summarized in this paper. Finally, the problems of lignin catalytic conversion existing currently are investigated, and the future development of this field is also prospected.

Transmembrane penetration mechanism of cyclic pollutants inspected by molecular dynamics and metadynamics: the case of morpholine, phenol, 1,4-dioxane and oxane

The presence of industrially produced chemicals in water is often not monitored, while their passive transport and accumulation can cause serious damage in living cells. Molecular dynamics simulations are an effective way to understand the mechanism of the action of these pollutants. In this paper, the passive membrane transport of 1,4-dioxane, phenol, oxane and morpholine was investigated and analyzed thoroughly from structural and energetic points of view. Free energy profiles for pollutant and water penetration into the bilayer were obtained from well-tempered metadynamics (WT-MD) simulations and a mass density-based approach. It was found that all four investigated compounds can penetrate biological membranes and affect the free energy profile of water penetration. Out of the investigated species, oxane has the thermodynamically most preferred position in the bilayer center, leading to a lower free energy barrier of water molecules by 3 kJ mol-1, resulting in 5 times more water molecules in the bilayer center. The concentration dependence of free energy was tested at two different phenol concentrations using WT-MD, and it was found that the higher phenol concentration lowers the main barrier by 3 kJ mol-1. Density-based free energy calculations were found to reproduce the results of WT-MD within the limits of chemical accuracy.

Lignin and Lignin-Derived Compounds for Wood Applications-A Review

Improving the environmental performance of resins in wood treatment by using renewable chemicals has been a topic of interest for a long time. At the same time, lignin, the second most abundant biomass on earth, is produced in large scale as a side product and mainly used energetically. The use of lignin in wood adhesives or for wood modification has received a lot of scientific attention. Despite this, there are only few lignin-derived wood products commercially available. This review provides a summary of the research on lignin application in wood adhesives, as well as for wood modification. The research on the use of uncleaved lignin and of cleavage products of lignin is reviewed. Finally, the current state of the art of commercialization of lignin-derived wood products is presented.

Recent advances in the valorization of plant biomass

Plant biomass is a highly abundant renewable resource that can be converted into several types of high-value-added products, including chemicals, biofuels and advanced materials. In the last few decades, an increasing number of biomass species and processing techniques have been developed to enhance the application of plant biomass followed by the industrial application of some of the products, during which varied technologies have been successfully developed. In this review, we summarize the different sources of plant biomass, the evolving technologies for treating it, and the various products derived from plant biomass. Moreover, the challenges inherent in the valorization of plant biomass used in high-value-added products are also discussed. Overall, with the increased use of plant biomass, the development of treatment technologies, and the solution of the challenges raised during plant biomass valorization, the value-added products derived from plant biomass will become greater in number and more valuable.

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.

A review on selective production of value-added chemicals via catalytic pyrolysis of lignocellulosic biomass

Increasing fossil fuel consumption and global warming has been driving the worldwide revolution towards renewable energy. Biomass is abundant and low-cost resource whereas it requires environmentally friendly and cost-effective conversion technique. Pyrolysis of biomass into valuable bio-oil has attracted much attention in the past decades due to its feasibility and huge commercial outlook. However, the complex chemical compositions and high water content in bio-oil greatly hinder the large-scale application and commercialization. Therefore, catalytic pyrolysis of biomass for selective production of specific chemicals will stand out as a unique pathway. This review aims to improve the understanding for the process by illustrating the chemistry of non-catalytic and catalytic pyrolysis of biomass at the temperatures ranging from 400 to 650 °C. The focus is to introduce recent progress about producing value-added hydrocarbons, phenols, anhydrosugars, and nitrogen-containing compounds from catalytic pyrolysis of biomass over zeolites, metal oxides, etc. via different reaction pathways including cracking, Diels-Alder/aromatization, ketonization/aldol condensation, and ammoniation. The potential challenges and future directions for this technique are discussed in deep.

Hydrothermal liquefaction of Chlorella pyrenoidosa and effect of emulsification on upgrading the bio-oil

This work studied the hydrothermal liquefaction of Chlorella pyrenoidosa and effect of emulsification on upgrading the bio-oil. The fuel properties and storage stability characteristics of emulsion fuels were explored. The combustion characteristic analysis showed that the ignition temperatures of emulsion fuels (139.6-151.3 °C) were lower than that of bio-oil (176.9 °C). Besides, emulsion fuels had higher comprehensive combustion indexes (7.24-14.08 × 10^-6 × min^-2 × C^-3) than bio-oil (1.51 × 10^-6 × min^-2 × C^-3), indicating that emulsion fuels had better combustion performance. The kinetic analysis showed that emulsification could effectively reduce the activation energy, resulting in less energy input for combustion. Based on chemical composition evolution during the storage process, a possible stability mechanism was proposed. The storage stability analysis indicated that the diesel-solvable fractions in bio-oil had better stability. Overall, this work provides a feasible way for bio-oil upgrading through emulsification. In addition, a better understanding of the stability property of emulsion fuel was provided.

High yield self-nitrogen-oxygen doped hydrochar derived from microalgae carbonization in bio-oil: Properties and potential applications

In this work, the high yield self-N-O doped hydrochar had been prepared through the hydrothermal carbonization of microalgae in the aqueous bio-oil. The effects of temperature, residence time and the ratio of Chlorella and bio-oil on the solid yield were investigated. The results showed that the hydrochar had excellent thermal stability and abundant nitrogen and oxide functional groups, its solid yield reached 199.33%. After activated by KOH at high temperature, the hydrochar was transformed into a porous carbon material with high nitrogen content. The porous carbon showed high CO₂ absorption of 5.57 mmol/g at 0 °C and 1 bar. It also exhibited a high specific capacitance of 216.6F/g at 0.2 A/g and a good electrochemical stability with 88% capacitance retention after consecutive 5000 cycles.

Comprehensive two-dimensional liquid chromatography-based quali-quantitative screening of aqueous phases from pyrolysis bio-oils

Pyrolysis processes are an alternative to minimize the environmental problem associated to agrifood industrial wastes. The main product resulting from these processes is a high-value liquid product, called bio-oil. Recently, the use of comprehensive two-dimensional liquid chromatography (LC × LC) has been demonstrated as a useful tool to improve the characterization of the water-soluble phases of bio-oils, considering their complexity and high water content. However, the precise composition of bio-oils from different agrifood byproducts is still unknown. In the present study, the qualitative and quantitative screening of eight aqueous phases from different biomasses, not yet reported in the literature, using LC × LC is presented. The two-dimensional approach was based on the use of two reverse phase separations. An amide column in the first dimension together with a C18 column in the second dimension were employed. Thanks to the use of diode array and mass spectrometry detection, 28 compounds were identified and quantified in the aqueous phase samples with good figures of merit. Samples showed a distinct quali-quantitative composition and a great predominance of compounds belonging to aldehydes, ketones and phenols, most of them with high polarity.

Optimizing Yield and Quality of Bio-Oil: A Comparative Study of Acacia tortilis and Pine Dust

We collected pine dust and Acacia tortilis samples from Zimbabwe and Botswana, respectively. We then pyrolyzed them in a bench-scale plant under varying conditions. This investigation aimed to determine an optimum temperature that will give result to maximum yield and quality of the bio-oil fraction. Our experimental results show that we obtain the maximum yield of the oil fraction at a pyrolysis temperature of 550 °C for the acacia and at 500 °C for the pine dust. Our results also show that we obtain an oil fraction with a heating value (HHV) of 36.807 MJ/kg using acacia as the feed material subject to a primary condenser temperature of 140 °C. Under the same pyrolysis temperature, we obtain an HHV value of 15.78 MJ/kg using pine dust as the raw material at a primary condenser temperature of 110 °C. The bio-oil fraction we obtain from Acacia tortilis at these condensation temperatures has an average pH value of 3.42 compared to that of 2.50 from pine dust. The specific gravity of the oil from Acacia tortilis is 1.09 compared to that of 1.00 from pine dust. We elucidated that pine dust has a higher bio-oil yield of 46.1% compared to 41.9% obtained for acacia. Although the heavy oils at condenser temperatures above 100 °C had good HHVs, the yields were low, ranging from 2.8% to 4.9% for acacia and 0.2% to 12.7% for pine dust. Our future work will entail efforts to improve the yield of the heavy oil fraction and scale up our results for trials on plant scale capacity.

Characterization of Fast Pyrolysis Bio-Oil from Hardwood and Softwood Lignin

The depletion of fossil fuel reserves and the increase of greenhouse gases (GHG) emission have led to moving towards alternative, renewable, and sustainable energy sources. Lignin is one of the significant, renewable and sustainable energy sources of biomass and pyrolysis is one of the most promising technologies that can convert lignocellulosic biomass to bio-oil. This study focuses on the production and characterization of bio-oil from hardwood and softwood lignin via pyrolysis process using a bench-scale batch reactor. In this study, a mixed solvent extraction method with different polarities was developed to fractionate different components of bio-crude oil into three fractions. The obtained fractions were characterized by using gas chromatography and mass spectrometry (GCMS). The calculated bio-oil yields from Sigma Kraft lignin and Chouka Kraft lignin were about 30.2% and 24.4%, respectively. The organic solvents, e.g., toluene, methanol, and water were evaluated for chemical extraction from bio-oil, and it was found that the efficiency of solvents is as follows: water > methanol > toluene. In both types of the bio-oil samples, phenolic compounds were found to be the most abundant chemical groups which include phenol, 2-methoxy, 2-methoxy-6-methylphenol and phenol, 4-ethyl-2-methoxy that is due to the structure and the originality of lignin, which is composed of phenyl propane units with one or two methoxy groups (O-CH3) on the aromatic ring.

Pyrolysis Products Distribution of Enzymatic Hydrolysis Lignin with/without Steam Explosion Treatment by Py-GC/MS

This paper investigated the pyrolytic behaviors of enzymatic hydrolysis lignin (EHL) and EHL treated with steam explosion (EHL-SE) by pyrolysis-gas chromatography/mass spectrometer (Py-GC/MS). It was shown that the main component of the pyrolysis products was phenolic compounds, including G-type, H-type, S-type, and C-type phenols. With different treatment methods, the proportion of units in phenolic products had changed significantly. Meanwhile, proximate, elemental, and FTIR analysis of both lignin substrates were also carried out for a further understanding of the lignin structure and composition with or without steam explosion treatment. FTIR result showed that, after steam explosion treatment, the fundamental structural framework of the lignin substrate was almost unchangeable, but the content of lignin constituent units, e.g., hydroxyl group and alkyl group, evidently changed. It was noticeable that 2-methoxy-4-vinylphenol with 11% relative content was the most predominant pyrolytic product for lignin after steam explosion treatment. Combined with the above analysis, the structural change and pyrolysis product distribution of EHL with or without steam explosion treatment could be better understood, providing more support for the multi-functional utilization of lignin.

Fast microwave-assisted pyrolysis of wastes for biofuels production - A review

Microwave-assisted pyrolysis of waste suffers from the problem that the waste generally has low microwave absorptivity thereby resulting in low heating rate and low pyrolysis temperature. In this case, fast microwave-assisted pyrolysis is proposed and developed to help the pyrolysis of waste. This study describes two methods that can be used to realize fast microwave-assisted pyrolysis of waste: (1) premixed method (wastes are mixed with microwave absorbent) and (2) non-premixed method (wastes are poured onto the heated microwave absorbent bed). Then, biofuels (bio-oil, bio-gas, and bio-char) produced from fast microwave-assisted pyrolysis of wastes are reviewed. The review results show that the yields of bio-oil, bio-gas, and bio-char obtained from fast microwave-assisted pyrolysis of wastes varied significantly in the ranges of 2-96 wt%, 2.4-86.8 wt%, and 0.3-83.2 wt%, respectively. Although the present research focused mainly on the premixed method, non-premixed/continuous fast microwave-assisted pyrolysis is still promising and challenging.

Downstream processing of lignin derived feedstock into end products

This review provides critical analysis on various downstream processes to convert lignin derived feedstock into fuels, chemicals and materials.

Experimental Evaluation of Biomass Medium-Temperature Gasification with Rice Straw as the Fuel in a Bubbling Fluidized Bed Gasifier

Our previous pilot-scale studies (Bioresource Technology 2018, 267: 102–109) preliminarily demonstrated the feasibility of performing air gasification with a novel two-stage system, including a medium-temperature bubbling fluidized bed (BFB) reactor and a high-temperature swirl-flow furnace reactor, using rice husk as the fuel. As an extension of that work, this study aims to further investigate the reaction mechanism and application prospect of this technology in the use of a more representative biomass fuel, i. e. rice straw. The operation stability, flow behaviors and reaction characteristics in the first-stage medium-temperature gasification reactor are studied in a lab-scale BFB gasifier. The effects of important operating conditions on the syngas quality, tar yield, compositions of carbon residue, and risk of agglomeration are elucidated in depth. The results have shown that an increase in the gasification temperature can promote syngas quality, gasification efficiency, and carbon conversion, but also increases the risk of agglomeration. An increase in the gasification equivalent ratio leads to positive effects on the syngas yield, carbon conversion, and tar concentration, but also has negative effects on the syngas heating value, tar yield, and especially the restrain of agglomeration. An increase in the raw material moisture content has negative influence on the gasification performance of rice straw, in terms of the gasification efficiency, carbon conversion, tar yield, and so on. However, the increase of moisture content can reduce the cost of raw material drying, and avoid the fluctuation of bed temperature, and therefore, a practical gasification system is recommended to be designed and operated under a certain conditions with moderate moisture contents.

Selective Preparation of 4-Alkylphenol from Lignin-Derived Phenols and Raw Biomass over Magnetic Co-Fe@N-Doped Carbon Catalysts

Lignin valorization to produce high-value chemicals selectively is an enormous challenge in biorefinery. In this study, 4-alkylphenol, formed by breaking the robust C_aryl -OCH₃ bonds solely with the retention of other structures in lignin-derived methoxylalkylphenols, was produced selectively over a Co₁ -Fe_0.1 @NC catalyst from real lignin oil as feedstock, which was obtained by a "lignin-first" strategy from either birch or cornstalk. A yield of 64.7 or 88.3 mol % of 4-propylphenol was obtained if birch lignin oil or eugenol was used as the substrate, respectively. The catalysts were characterized by using methods that include Brunauer-Emmett-Teller measurements, XRD, X-ray photoelectron spectroscopy, high-resolution transmission electron microscopy, high-angle annular dark-field scanning transmission electron microscopy, energy-dispersive X-ray spectroscopy, and temperature-programmed desorption with synchrotron vacuum ultraviolet photoionization mass spectrometry. The results of catalyst characterization and comparison experiments indicated that CoN_x was the main active phase for demethoxylation and hydrogenation, and the incorporation of Fe weakens the adsorption of 4-propylphenol to the catalyst, which inhibits the excessive hydrogenation of 4-propylphenol. This work shows the potential to produce high-value-added 4-alkylphenol from renewable raw biomass.