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

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.

Promoting microbial utilization of phenolic substrates from bio-oil

The economic viability of the biorefinery concept is limited by the valorization of lignin. One possible method of lignin valorization is biological upgrading with aromatic-catabolic microbes. In conjunction, lignin monomers can be produced by fast pyrolysis and fractionation. However, biological upgrading of these lignin monomers is limited by low water solubility. Here, we address the problem of low water solubility with an emulsifier blend containing approximately 70 wt% Tween® 20 and 30 wt% Span® 80. Pseudomonas putida KT2440 grew to an optical density (OD600) of 1.0 ± 0.2 when supplied with 1.6 wt% emulsified phenolic monomer-rich product produced by fast pyrolysis of red oak using an emulsifier dose of 0.076 ± 0.002 g emulsifier blend per g of phenolic monomer-rich product. This approach partially mitigated the toxicity of the model phenolic monomer p-coumarate to the microbe, but not benzoate or vanillin. This study provides a proof of concept that processing of biomass-derived phenolics to increase aqueous availability can enhance microbial utilization.

Preparation and Characterization of Bio-oil Phenolic Foam Reinforced with Montmorillonite

Introducing bio-oil into phenolic foam (PF) can effectively improve the toughness of PF, but its flame retardant performance will be adversely affected and show a decrease. To offset the decrease in flame retardant performance, montmorillonite (MMT) can be added as a promising alternative to enhance the flame resistance of foams. The present work reported the effects of MMT on the chemical structure, morphological property, mechanical performance, flame resistance, and thermal stability of bio-oil phenolic foam (BPF). The Fourier transform infrared spectroscopy (FT-IR) result showed that the -OH group peaks shifted to a lower frequency after adding MMT, indicating strong hydrogen bonding between MMT and bio-oil phenolic resin (BPR) molecular chains. Additionally, when a small content of MMT (2-4 wt %) was added in the foamed composites, the microcellular structures of bio-oil phenolic foam modified by MMT (MBPFs) were more uniform and compact than that of BPF. As a result, the best performance of MBPF was obtained with the addition of 4 wt % MMT, where compressive strength and limited oxygen index (LOI) increased by 31.0% and 33.2%, respectively, and the pulverization ratio decreased by 40.6% in comparison to BPF. These tests proved that MMT can blend well with bio-oil to effectively improve the flame resistance of PF while enhancing toughness.

Study on the effect of condensing temperature of walnut shells pyrolysis vapors on the composition and properties of bio-oil

The effect of condensing temperature on composition of bio-oil obtained via fractional condensation was investigated by pyrolysis-condensation experiments of walnut shells at condensing temperatures from 290 K to 370 K. The condensing efficiency of the first stage condenser decreased from 0.59 to 0.12 with increasing temperature. Moisture of bio-oil decreased from 40% to 5%, but the C/O ratio increased from 0.50 to 1.50. Compared with contents observed at the lowest condensation temperature, the maximum content of each component increased by 50%-500%. Combined with variations in condensing efficiency and composition content, the optimum condensing temperature range for declining water in bio-oil was 340-350 K. The condensing temperature associated with the enrichment of acetic acid and furfural was 345 K. The 355 K optimum condensing temperature could be selected to achieve the maximum enrichment of guaiacol and its derivatives.

Hydrothermal liquefaction of Malaysia's algal biomass for high-quality bio-oil production

Currently, fossil materials form the majority of our energy and chemical source. Many global concerns force us to rethink about our current dependence on the fossil energy. Limiting the use of these energy sources is a key priority for most countries that pledge to reduce greenhouse gas emissions. The application of biomass, as substitute fossil resources for producing biofuels, plastics and chemicals, is a widely accepted strategy for sustainable development. Aquatic plants including algae possess competitive advantages as biomass resources compared to the terrestrial plants in this current global situation. Bio-oil production from algal biomass is technically and economically viable, cost competitive, requires no capacious lands and minimal water use and reduces atmospheric carbon dioxide. The aim of this paper is to review the potential of converting algal biomass, as an aquatic plant, into high-quality crude bio-oil through applicable processes in Malaysia. In particular, bio-based materials and fuels from algal biomass are considered as one of the reliable alternatives for clean energy. Currently, pyrolysis and hydrothermal liquefaction (HTL) are two foremost processes for bio-oil production from biomass. HTL can directly convert high-moisture algal biomass into bio-oil, whereas pyrolysis requires feedstock drying to reduce the energy consumption during the process. Microwave-assisted HTL, which can be conducted in aqueous environment, is suitable for aquatic plants and wet biomass such as algae.

Improving bio-oil properties through the fast co-pyrolysis of lignocellulosic biomass and waste tyres

Pinewood sawdust and the waste rubber from truck tyres have been co-pyrolysed in order to improve the properties of bio-oil for its integration in oil refineries. In addition, an analysis has been conducted of the effect the interactions between these two materials' pyrolysis reactions have on product yields and properties. Biomass/tyre mixing ratios of 100/0, 75/25, 50/50, 25/75 and 0/100 by weight percentage have been pyrolysed in continuous mode at 500 °C in a conical spouted bed reactor, obtaining oil yields in the 55.2-71.6 wt% range. Gaseous, oil and solid fractions have been characterised for the 50/50 biomass/tyre mixture, paying special attention to the oil fraction by determining its detailed composition, elemental analysis and calorific value. Co-processing enables the stabilization of the liquid, as the co-pyrolysis oil has a stable single phase, being composed mainly of water, aromatic hydrocarbons and phenols in concentrations of 14.5, 11.1 and 9.7 wt%, respectively. Adding tyre rubber to the biomass in the pyrolysis feed improves the oil's properties, as a liquid with higher carbon content and lower oxygen and water is obtained, even if sulphur content is also increased.

One-Pot Synthesis of Active Carbon-Supported Size-Tunable Ni2P Nanoparticle Catalysts for the Pyrolysis Bio-Oil Upgrade

Catalytic hydrodeoxygenation (HDO) over Ni₂P-based catalysts is a promising technology for the pyrolysis bio-oil upgrading. However, substantial challenges still remain in the realization of the size effect for phosphide catalysts in catalyzing this reaction, and the precise size engineering of these catalysts is difficult. In this work, the Ni₂P/active carbon (AC) catalysts with varying nickel phosphide nanoparticle sizes were one-pot prepared via the modified organic liquid chemical reaction method. The Ni₂P-based catalysts were tested for HDO of the pyrolysis oil model compound (salicylaldehyde), and the conversion of salicylaldehyde first increases and then decreases with the increase of Ni₂P nanoparticle size, demonstrating that the activity for HDO of salicylaldehyde can be controlled by using nickel phosphides of varying nanoparticle sizes. The Ni₂P-2/AC catalyst with approximately 5.49 nm Ni₂P nanoparticle size exhibited the highest activity with conversion of salicylaldehyde reaching over 99% within 180 min under 220 °C, 2 MPa H₂ pressure, and the corresponding yield toward o-cresol was over 97%.

Bio-Based Chemicals from Renewable Biomass for Integrated Biorefineries

The production of chemicals from biomass, a renewable feedstock, is highly desirable in replacing petrochemicals to make biorefineries more economical. The best approach to compete with fossil-based refineries is the upgradation of biomass in integrated biorefineries. The integrated biorefineries employed various biomass feedstocks and conversion technologies to produce biofuels and bio-based chemicals. Bio-based chemicals can help to replace a large fraction of industrial chemicals and materials from fossil resources. Biomass-derived chemicals, such as 5-hydroxymethylfurfural (5-HMF), levulinic acid, furfurals, sugar alcohols, lactic acid, succinic acid, and phenols, are considered platform chemicals. These platform chemicals can be further used for the production of a variety of important chemicals on an industrial scale. However, current industrial production relies on relatively old and inefficient strategies and low production yields, which have decreased their competitiveness with fossil-based alternatives. The aim of the presented review is to provide a survey of past and current strategies used to achieve a sustainable conversion of biomass to platform chemicals. This review provides an overview of the chemicals obtained, based on the major components of lignocellulosic biomass, sugars, and lignin. First, important platform chemicals derived from the catalytic conversion of biomass were outlined. Later, the targeted chemicals that can be potentially manufactured from the starting or platform materials were discussed in detail. Despite significant advances, however, low yields, complex multistep synthesis processes, difficulties in purification, high costs, and the deactivation of catalysts are still hurdles for large-scale competitive biorefineries. These challenges could be overcome by single-step catalytic conversions using highly efficient and selective catalysts and exploring purification and separation technologies.

Bio-oil: a versatile precursor to produce carbon nanostructures in liquid phase under mild conditions

Renewable and low-cost bio-oil can be converted to carbon nanostructures in liquid phase under mild conditions.

Two-step etherification of phenolic-oil with methanol under catalysis of alumina-supported metal salts

A two-step process for the etherification of phenolic-oil is proposed to avoid the hindering effect of alkoxyphenols on the etherification of alkylphenols.

Extraction of Phenolic Compounds from Palm Oil Processing Residues and Their Application as Antioxidants

The side streams derived from the palm oil production process, namely palm kernel cake, palm pressed fibre, palm kernel shells and empty fruit bunches, were evaluated as sources of phenolic compounds. Among these streams, kernel cake had the highest total phenolic content (in mg of gallic acid equivalents (GAE) per g of dry sample) with a value of 5.19, whereas the empty fruit bunches had the lowest value (1.79). The extraction time and liquid-to-solid ratio were investigated to optimize the phenolic extraction. Kernel cake exhibited the highest total phenolic content (5.35 mg/g) with a liquid-to-solid ratio of 40:1 during 20 min of extraction. The main phenolic compounds of the extracts deriving from all byproduct streams were also identified and quantified with HPLC-DAD. Pyrogallol, 4-hydroxybenzoic acid, gallic acid and ferulic acid were the main compounds found in kernel cake extracts. Empty fruit bunch and pressed fibre extracts were also rich in 4-hydroxybenzoic acid, while pyrogallol was the predominant compound in kernel shell extracts. All extracts showed antioxidant activity as it was indicated from the results of DPPH analysis and subsequently tested in sunflower oil aiming to prolong its shelf life. The addition of 0.8% kernel cake extract increased the induction time of sunflower oil more than 50%. According to the results obtained in this study, kernel cake extracts could be considered as a value-added co-product with a potential application as antioxidants in the food industry.

Extrapolation of phenolic compounds as multi-target agents against cancer and inflammation

Natural products acquire massive structural and chemical diversity, which cannot be coordinated by any synthetic libraries for small molecules and they are continuing to inspire novel discoveries in health sciences. We have performed the computational calculations for geometry optimization and prediction of electronic and structural properties of some plant phenolic compounds through Gaussian 09 program. Energies of molecular orbitals were computed, to mimic out the stabilities arising from charge delocalization and intramolecular interactions. This process indicated the eventual charge transfer within the molecules. The molecular docking and ADMET properties of these compounds with a novel anticancer (HER2) and anti-inflammatory (COX-2) targets revealed that two molecules were capable of inhibiting both the targets, and could be used as multi target inhibitors. Furthermore, molecular dynamics simulation studies were performed to elucidate the binding mechanism and the comparison of inhibitor's binding mode with diverse biological activities as anticancer and anti-inflammatory agents. A high-quality association was reported among quantum chemical, ADMET, docking, dynamics and MMGBSA results. Communicated By Ramaswamy H. Sarma.

Preparation and Characterization of Phenolic Foam Modified with Bio-Oil

Bio-oil was added as a substitute for phenol for the preparation of a foaming phenolic resin (PR), which aimed to reduce the brittleness and pulverization of phenolic foam (PF). The components of bio-oil, the chemical structure of bio-oil phenolic resin (BPR), and the mechanical performances, and the morphological and thermal properties of bio-oil phenolic foam (BPF) were investigated. The bio-oil contained a number of phenols and abundant substances with long-chain alkanes. The peaks of OH groups, CH₂ groups, C=O groups, and aromatic skeletal vibration on the Fourier transform infrared (FT-IR) spectrum became wider and sharper after adding bio-oil. These suggested that the bio-oil could partially replace phenol to prepare resin and had great potential for toughening resin. When the substitute rate of bio-oil to phenol (B/P substitute rate) was between 10% and 20%, the cell sizes of BPFs were smaller and more uniform than those of PF. The compressive strength and flexural strength of BPFs with a 10⁻20% B/P substitute rate increased by 10.5⁻47.4% and 25.0⁻50.5% respectively, and their pulverization ratios decreased by 14.5⁻38.6% in comparison to PF. All BPFs maintained good flame-retardant properties, thermal stability, and thermal isolation, although the limited oxygen index (LOI) and residual masses by thermogravimetric (TG) analysis of BPFs were lower and the thermal conducticity was slightly greater than those of PF. This indicated that the bio-oil could be used as a renewable toughening agent for PF.

A novel two-stage biomass gasification concept: Design and operation of a 1.5 MWth demonstration plant

To gasify the biofuel of low ash melting temperature and overcome the high content of tar in bio-gas, a novel two-stage gasification concept is proposed. This concept enables the tar-free bio-gas generated in the gasification process under thermal cracking. On that basis, a demonstration project is introduced. Rice husk acts as the feedstock for its accessibility on-site in the commissioning period. System reliability has been confirmed for the stable operation of more than 60 days. Tests have been performed under some typical operating conditions. As the results suggest, the bio-gas of 6.7 MJ/Nm³ LHV is generated with cold gas efficiency and carbon conversion of 67.5% and 87% respectively. Elementary economic evaluation of this concept is also made in accordance with the commissioning results. As a result, the annual net profit of 40.92 K USD is yielded without a subsidized price for biomass materials.

Insight into structure-reactivity relationships for the iron-catalyzed hydrotreatment of technical lignins

The viability of several technical lignins as a source for biobased platform chemicals was investigated via hydrotreatment using a cheap Fe-based limonite catalyst and without using a solvent. In general, high-quality oils (up to 29 wt% total monomers) with an average relative composition of 55% alkylphenolics and 27% aromatics were obtained. Detailed structural investigations showed that the S-G aromatic unit content of the lignins was the most important factor positively affecting overall oil yields. A second parameter was the lignocellulose processing method. Even though alkaline lignin isolation provides more recalcitrant lignins, their lower aliphaticity and methoxy group content partially limit char and gas formation. Finally, enhanced monomer yields could be obtained irrespective of the ether linkage content, and a high amount of β-O-4 linkages actually showed a slightly negative effect on monomer yields. Overall, the results demonstrate that this route is particularly suitable for processing residual lignin streams.

Aging Properties of Phenol-Formaldehyde Resin Modified by Bio-Oil Using UV Weathering

The aging properties of phenol-formaldehyde resin modified by bio-oil (BPF) were analyzed using ultraviolet (UV) weathering. The variations on bonding strength of BPF were measured, and the changes on microstructure, atomic composition and chemical structure of BPF were characterized by using a scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS) and nuclear magnetic resonance (NMR), respectively. With the increase of aging time, the bonding strength decreased gradually, the resin surface became rougher and the O/C radio of resin surface increased. However, the loss rate of bonding strength of BPFs was 9.6⁻23.0% lower than that of phenol-formaldehyde resin (PF) after aging 960 h. The aging degree of BPF surfaces was smaller in comparison to PF at the same aging time. These results showed that the bio-oil had a positive effect on the anti-aging property. Analytical results revealed that with increasing the aging time, the XPS peak area of C⁻C/C⁻H decreased, while that of C=O and O⁻C=O increased. The intensity of methylene and ether bridges in NMR analysis decreased along with increasing the intensity of aldehydes, ketones, acids and esters. These results indicated that the aging mechanism of BPF was a process of the breakage of molecular chains and formation of oxygen-containing compounds.

Production, characterization, and potential of activated biochar as adsorbent for phenolic compounds from leachates in a lumber industry site

There is growing interest in low-cost, efficient materials for the removal of organic contaminants in municipal and industrial effluents. In this study, the efficiency of biochar and activated biochar, as promising adsorbents for phenol removal, was investigated at high (up to 1500 mg L^-1) and low concentrations (0.54 mg L^-1) in synthetic and real effluents (from wood-residue deposits in Québec), respectively. The performance of both materials was then evaluated in batch adsorption experiments, which were conducted using a low solid/liquid ratio (0.1 g:100 mL) at different phenol concentrations (C₀ = 5-1500 mg L^-1), and at 20 °C. Activated biochars presented higher phenol adsorption capacity compared to biochars due to their improved textural properties, higher micropore volume, and proportion of oxygenated carbonyl groups connected to their surface. The sorption equilibrium was reached within less than 4 h for all of materials, while the Langmuir model best described their sorption process. The maximum sorption capacity of activated biochars for phenol was found to be twofold relative to biochars (303 vs. 159 mg g^-1). Results also showed that activated biochars were more effective than biochars in removing low phenol concentrations in real effluents. In addition, 95% of phenol removal was attained within 96 h (although 85% was removed after 4 h), thus reaching below the maximum authorized concentration allowed by Québec's discharge criteria (0.05 mg L^-1). These results show that activated biochars made from wood residues are promising potential adsorbent materials for the efficient treatment of phenol in synthetic and real effluents.

Catalytic Fast Pyrolysis of Biomass Impregnated with Potassium Phosphate in a Hydrogen Atmosphere for the Production of Phenol and Activated Carbon

A new technique was proposed to co-produce phenol and activated carbon (AC) from catalytic fast pyrolysis of biomass impregnated with K₃PO₄ in a hydrogen atmosphere, followed by activation of the pyrolytic solid residues. Lab-scale catalytic fast pyrolysis experiments were performed to quantitatively determine the pyrolytic product distribution, as well as to investigate the effects of several factors on the phenol production, including pyrolysis atmosphere, catalyst type, biomass type, catalytic pyrolysis temperature, and catalyst impregnation content. In addition, the pyrolytic solid residues were activated to prepare ACs with high specific surface areas. The results indicated that phenol could be obtained due to the synergistic effects of K₃PO₄ and hydrogen atmosphere, with the yield and selectivity reaching 5.3 wt% and 17.8% from catalytic fast pyrolysis of poplar wood with 8 wt% K₃PO₄ at 550°C in a hydrogen atmosphere. This technique was adaptable to different woody materials for phenol production. Moreover, gas product generated from the pyrolysis process was feasible to be recycled to provide the hydrogen atmosphere, instead of extra hydrogen supply. In addition, the pyrolytic solid residue was suitable for AC preparation, using CO₂ activation method, the specific surface area was as high as 1,605 m²/g.

Investigation on biomass nitrogen-enriched pyrolysis: Influence of temperature

Biomass (bamboo waste) nitrogen-enriched pyrolysis was carried out in a fixed bed with NH₃ atmosphere at 400-800 °C, and formation mechanism of N-containing species was explored in depth. Results showed that N-enriched pyrolysis greatly increased bio-oil and gas yields. H₂ yield increased sharply to 130 mL/g (32.93 vol%) and became the main composition at higher temperature, while CH₄ and CO yields deceased, and the lower heating value of gas reached ∼14 MJ/Nm³. For bio-oil, the content of phenols (main compositions) and N-containing species increased significantly, and the maximums reached 61.33% and 11.47%, respectively. While that of acetic acid (disappeared), O-containing species (aldehydes/ketones/furans/esters) and aromatics decreased largely accordingly. For biochar, Nitrogen content increased, and it contained abundant pyridininc-N, pyrrolic-N, quaternary-N, and pyridone-N-oxide. Possible reaction pathways of biomass N-enriched pyrolysis was proposed based on products evolution. In conclusion, biomass N-enriched pyrolysis could obtain high-valued N-containing chemical species and functional biochar.

Analytical Strategies Involved in the Detailed Componential Characterization of Biooil Produced from Lignocellulosic Biomass

Elucidation of chemical composition of biooil is essentially important to evaluate the process of lignocellulosic biomass (LCBM) conversion and its upgrading and suggest proper value-added utilization like producing fuel and feedstock for fine chemicals. Although the main components of LCBM are cellulose, hemicelluloses, and lignin, the chemicals derived from LCBM differ significantly due to the various feedstock and methods used for the decomposition. Biooil, produced from pyrolysis of LCBM, contains hundreds of organic chemicals with various classes. This review covers the methodologies used for the componential analysis of biooil, including pretreatments and instrumental analysis techniques. The use of chromatographic and spectrometric methods was highlighted, covering the conventional techniques such as gas chromatography, high performance liquid chromatography, Fourier transform infrared spectroscopy, nuclear magnetic resonance, and mass spectrometry. The combination of preseparation methods and instrumental technologies is a robust pathway for the detailed componential characterization of biooil. The organic species in biooils can be classified into alkanes, alkenes, alkynes, benzene-ring containing hydrocarbons, ethers, alcohols, phenols, aldehydes, ketones, esters, carboxylic acids, and other heteroatomic organic compounds. The recent development of high resolution mass spectrometry and multidimensional hyphenated chromatographic and spectrometric techniques has considerably elucidated the composition of biooils.

Comparative study on pyrolysis of lignocellulosic and algal biomass using pyrolysis-gas chromatography/mass spectrometry

The cornstalk and chlorella were selected as the representative of lignocelulosic and algal biomass, and the pyrolysis experiments of them were carried out using pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). The physicochemical properties of samples and the pyrolytic product distribution were presented. And then the compositional differences between the two kinds of pyrolytic products were studied, the relevant pyrolysis mechanisms were analyzed systematically. Pyrolytic vapor from lignocellulosic biomass contained more phenolic and carbonyl compounds while that from algal biomass contained more long-chain fatty acids, nitrogen-containing compounds and fewer carbonyl compounds. Maillard reaction is conducive to the conversion of carbonyl compounds to nitrogenous heterocyclic compounds with better thermal stability.

Effects of feedstock characteristics on microwave-assisted pyrolysis - A review

Microwave-assisted pyrolysis is an important approach to obtain bio-oil from biomass. Similar to conventional electrical heating pyrolysis, microwave-assisted pyrolysis is significantly affected by feedstock characteristics. However, microwave heating has its unique features which strongly depend on the physical and chemical properties of biomass feedstock. In this review, the relationships among heating, bio-oil yield, and feedstock particle size, moisture content, inorganics, and organics in microwave-assisted pyrolysis are discussed and compared with those in conventional electrical heating pyrolysis. The quantitative analysis of data reported in the literature showed a strong contrast between the conventional processes and microwave based processes. Microwave-assisted pyrolysis is a relatively new process with limited research compared with conventional electrical heating pyrolysis. The lack of understanding of some observed results warrant more and in-depth fundamental research.

Adding nickel formate in alkali lignin to increase contents of alkylphenols and aromatics during fast pyrolysis

The composition of pyrolysis vapors obtained from alkali lignin pyrolysis with the additive of nickel formate was examined using the pyrolysis gas chromatography-mass spectrometry (Py-GC/MS). Characterization of bio-chars was performed using X-ray diffraction (XRD). Results showed that the nickel formate significantly increased liquid yield, simplified the types of alkali lignin pyrolysis products and increased individual component contents. The additive of nickel formate increased contents of alkylphenols and aromatics from alkali lignin pyrolysis. With an increase in temperature, a greater amount of the relative contents can be achieved. The nickel formate was thermally decomposed to form hydrogen, resulting in hydrodeoxygenation of alkali lignin during pyrolysis. It was also found that Ni is in favor of producing alkylphenols. The analysis based on the experimental result provided evidences used to propose reaction mechanism for pyrolysis of nickel formate-assisted alkali lignin.

Kinetics of coffee industrial residue pyrolysis using distributed activation energy model and components separation of bio-oil by sequencing temperature-raising pyrolysis

This study was carried out to investigate the kinetics of coffee industrial residue (CIR) pyrolysis, the effect of pyrolysis factors on yield of bio-oil component and components separation of bio-oil. The kinetics of CIR pyrolysis was analyzed using distributed activation energy model (DAEM), based on the experiments in thermogravimetric analyzer (TGA), and it indicated that the average of activation energy (E) is 187.86kJ·mol^-1. The bio-oils were prepared from CIR pyrolysis in vacuum tube furnace, and its components were determined by gas chromatography/mass spectrometry (GC-MS). Among pyrolysis factors, pyrolysis temperature is the most influential factor on components yield of bio-oil, directly concerned with the volatilization and yield of components (palmitic acid, linoleic acid, oleic acid, octadecanoic acid and caffeine). Furthermore, a new method (sequencing temperature-raising pyrolysis) was put forward and applied to the components separation of bio-oil. Based on experiments, a solution of components separation of bio-oil was come out.

Promotion of hydrogen-rich gas and phenolic-rich bio-oil production from green macroalgae Cladophora glomerata via pyrolysis over its bio-char

Conversion of Cladophora glomerata (C. glomerata) as a Caspian Sea's green macroalgae into gaseous, liquid and solid products was carried out via pyrolysis at different temperatures to determine its potential for bio-oil and hydrogen-rich gas production for further industrial utilization. Non-catalytic tests were performed to determine the optimum condition for bio-oil production. The highest portion of bio-oil was retrieved at 500°C. The catalytic test was performed using the bio-char derived at 500°C as a catalyst. Effect of the addition of the algal bio-char on the composition of the bio-oil and also gaseous products was investigated. Pyrolysis derived bio-char was characterized by BET, FESEM and ICP method to show its surface area, porosity, and presence of inorganic metals on its surface, respectively. Phenols were increased from 8.5 to 20.76area% by the addition of bio-char. Moreover, the hydrogen concentration and hydrogen selectivity were also enhanced by the factors of 1.37, 1.59 respectively.

An experimental study on the formation of methoxyaromatics during pyrolysis of Eucalyptus pulverulenta: Yields and mechanisms

The production of bio-oil rich in methoxyaromatics during catalytic pyrolysis of Eucalyptus pulverulenta (EP) was studied using a fixed-bed reactor in the temperature range of 300-500°C and the bio-oil composition was analyzed by using a GC-MS. The results showed that the highest bio-oil yield of 38.45wt% was obtained at 400°C in the presence of Na2CO3, and the concentration of methoxyaromatics reached the maximum value of 63.4%(area) in the bio-oil. The major methoxyaromatics identified in bio-oil were guaiacol, syringol, 4-ethyl-2-methoxy phenol, and 1,2,4-trimethoxybenzene. The analysis of gaseous products indicated that CO2 was the major gas at low-temperatures and concentrations of H2 and CH4 increased with increasing pyrolysis temperature. Na2CO3 promoted the formation of methoxyaromatics, while NaOH seems to have enhanced the formation of phenolics. The mechanism of the formation of methoxyaromatics during pyrolysis of EP was proposed.

Separation of high-purity syringol and acetosyringone from rice straw-derived bio-oil by combining the basification-acidification process and column chromatography

Numerous technologies have been used to reclaim valuable chemicals from bio-oil. In this study, a combination of the basification-acidification process and column chromatography was employed for the separation of high-purity syringol and acetosyringone from rice straw-derived bio-oil. The optimal conditions for the basification-acidification process and the possible precipitation mechanism of the basification were explored. The results showed the following as the optimal conditions for the basification process: mass ratio of calcium hydroxide (Ca(OH)₂ ) to bio-oil, 2.0; reaction temperature, 70°C; and reaction time, 30 min. The results also showed that 1.6 mol of hydrochloric acid (HCl) per gram of bio-oil was optimal for the acidification. The precipitation was found to proceed via a possible mechanism involving the reaction of the phenolic compounds in the bio-oil with Ca(OH)₂ to produce a precipitate. After further separation by column chromatography, purities of 91.4 and 96.2% (from gas chromatography-mass spectrometry) were obtained for syringol and acetosyringone, respectively. Their recoveries for the whole process were 73.0 and 39.3%, respectively.

Microwave-assisted catalytic pyrolysis of lignocellulosic biomass for production of phenolic-rich bio-oil

Catalytic microwave pyrolysis of peanut shell (PT) and pine sawdust (PS) using activated carbon (AC) and lignite char (LC) for production of phenolic-rich bio-oil and nanotubes was investigated in this study. The effects of process parameters such as pyrolysis temperature and biomass/catalyst ratio on the yields and composition of pyrolysis products were investigated. Fast heating rates were achieved under microwave irradiation conditions. Gas chromatography-mass spectrometry (GC-MS) analysis of bio-oil showed that activated carbon significantly enhanced the selectivity of phenolic compounds in bio-oil. The highest phenolics content in the bio-oil (61.19 %(area)) was achieved at 300°C. The selectivity of phenolics in bio-oil was higher for PT sample compared to that of PS. The formation of nanotubes in PT biomass particles was observed for the first time in biomass microwave pyrolysis.

Production of phenol-rich bio-oil during catalytic fixed-bed and microwave pyrolysis of palm kernel shell

Catalytic fixed-bed and microwave pyrolysis of palm kernel shell using activated carbon (AC) and lignite char (LC) as catalysts and microwave receptors are investigated. The effects of process parameters including temperature and biomass:catalyst ratio on the yield and composition of pyrolysis products were studied. The addition of catalyst increased the bio-oil yield, but decreased the selectivity of phenol in fixed-bed. Catalytic microwave pyrolysis of PKS significantly enhanced the selectivity of phenol production. The highest concentration of phenol in bio-oil of 64.58 %(area) and total phenolics concentration of 71.24 %(area) were obtained at 500°C using AC. Fourier transform infrared spectroscopy (FTIR) results indicated that concentration of OH, CH, CO and CO functional groups in char samples decreased after pyrolysis. Scanning electron microscopy (SEM) analysis clearly indicated the development of liquid phase in biomass particles during microwave pyrolysis, and the mechanism is also discussed.

Potential of genetically engineered hybrid poplar for pyrolytic production of bio-based phenolic compounds

Wild-type and two genetically engineered hybrid poplar lines were pyrolyzed in a micro-pyrolysis (Py-GC/MS) and a bench scale setup for fast and intermediate pyrolysis studies. Principal component analysis showed that the pyrolysis vapors obtained by micro-pyrolysis from wood of caffeic acid O-methyltransferase (COMT) and caffeoyl-CoA O-methyltransferase (CCoAOMT) down-regulated poplar trees differed significantly from the pyrolysis vapors obtained from non-transgenic control trees. Both fast micro-pyrolysis and intermediate pyrolysis of transgenic hybrid poplars showed that down-regulation of COMT can enhance the relative yield of guaiacyl lignin-derived products, while the relative yield of syringyl lignin-derived products was up to a factor 3 lower. This study indicates that lignin engineering via genetic modifications of genes involved in the phenylpropanoid and monolignol biosynthetic pathways can help to steer the pyrolytic production of guaiacyl and syringyl lignin-derived phenolic compounds such as guaiacol, 4-methylguaiacol, 4-ethylguaiacol, 4-vinylguaiacol, syringol, 4-vinylsyringol, and syringaldehyde present in the bio-oil.

Production and distillative recovery of valuable lignin-derived products from biocrude

High-value guaiacols isolated from biocrude produced from catalytic pyrolysis of loblolly pine with non-zeolite alumina based catalyst.

Self-sufficient redox biotransformation of lignin-related benzoic acids with Aspergillus flavus

Aromatic carboxylic acids are readily obtained from lignin in biomass processing facilities. However, efficient technologies for lignin valorization are missing. In this work, a microbial screening was conducted to find versatile biocatalysts capable of transforming several benzoic acids structurally related to lignin, employing vanillic acid as model substrate. The wild-type Aspergillus flavus growing cells exhibited exquisite selectivity towards the oxidative decarboxylation product, 2-methoxybenzene-1,4-diol. Interestingly, when assaying a set of structurally related substrates, the biocatalyst displayed the oxidative removal of the carboxyl moiety or its reduction to the primary alcohol whether electron withdrawing or donating groups were present in the aromatic ring, respectively. Additionally, A. flavus proved to be highly tolerant to vanillic acid increasing concentrations (up to 8 g/L), demonstrating its potential application in chemical synthesis. A. flavus growing cells were found to be efficient biotechnological tools to perform self-sufficient, structure-dependent redox reactions. To the best of our knowledge, this is the first report of a biocatalyst exhibiting opposite redox transformations of the carboxylic acid moiety in benzoic acid derivatives, namely oxidative decarboxylation and carboxyl reduction, in a structure-dependent fashion.

A Comparative study of microwave-induced pyrolysis of lignocellulosic and algal biomass

Microwave (MW) pyrolysis of algal and lignocellulosic biomass samples were studied using a modified domestic oven. The pyrolysis temperature was recorded continuously by inserting a thermocouple into the samples. Temperatures as high as 1170 and 1015°C were achieved for peanut shell and Chlorella vulgaris. The activation energy for MW pyrolysis was calculated by Coats-Redfern method and the values were 221.96 and 214.27kJ/mol for peanut shell and C. vulgaris, respectively. Bio-oil yields reached to 27.7wt.% and 11.0wt.% during pyrolysis of C. vulgaris and peanut shell, respectively. The bio-oil samples from pyrolysis were analyzed by a gas chromatography-mass spectrometry (GC-MS). Bio-oil from lignocellulosic biomass pyrolysis contained more phenolic compounds while that from microalgae pyrolysis contained more nitrogen-containing species. Fourier transform infrared spectroscopy (FTIR) analysis results showed that concentration of OH, CH, CO, OCH3, and CO functional groups in char samples decreased significantly after pyrolysis.