Supercritical extraction of biomass as an effective pretreatment step for the char yield control in pyrolysis

peer-reviewedThis work demonstrates that the coupling of supercritical carbon dioxide extraction with pyrolysis is an effective method for the removal of extractives from forestry residues and generation of solid char with different properties from the remaining solid wood fractions. Extraction of the needles and stumps shows greater yields of resin acids, terpenes, steroids and other derivatives than that of pinewood bark, cones and branches. The char yields of both non-treated and scCO2 extracted wood fractions varied from approximately 17.5 to 38.5 wt. % on dry basis at fast heating rates. The catalytic effect of extractives is significant on the yields and morphology of solid chars in fast pyrolysis and less pronounced at slow heating rates. These results are promising as they show that both the composition and location of extractives inclusions in the interior of wood particle can affect the morphology of char samples. Moreover, the impact of alkali metals on the wood devolatilization appears to be less compared to the lignocellulosic composition in slow pyrolysis. These results demonstrate that supercritical carbon dioxide extraction can be integrated in biorefinery as a pretreatment step to control the properties of pyrolysis products by varying the heating rate

Recent Advances in the Catalytic Depolymerization of Lignin towards Phenolic Chemicals : A Review

The efficient valorization of lignin could dictate the success of the 2nd generation biorefinery. Lignin, accounting for on average a third of the lignocellulosic biomass, is the most promising candidate for sustainable production of value-added phenolics. However, the structural alteration induced during lignin isolation is often depleting its potential for value-added chemicals. Recently, catalytic reductive depolymerization of lignin has appeared to be a promising and effective method for its valorization to obtain phenolic monomers. The present study systematically summarizes the far-reaching and state-of-the-art lignin valorization strategies during different stages, including conventional catalytic depolymerization of technical lignin, emerging reductive catalytic fractionation of protolignin, stabilization strategies to inhibit the undesired condensation reactions, and further catalytic upgrading of lignin-derived monomers. Finally, the potential challenges for the future researches on the efficient valorization of lignin and possible solutions are proposed

Electrical conductivity of beech sawdust using graphite catalytic coating : unlocking the microwave-assisted thermolysis efficiency of lignocellulosic biomass

The coating of the beech sawdust using a catalytic amount of graphite (as low as 0.25 wt%) allowed a step improvement in the microwave-assisted thermolysis. Results demonstrated that the pyrolysis performance was linked to an electrical conductivity threshold of the coated samples rather than a gradual increase. With as low as 0.13 mS m−1 of electrical conductivity, the 0.75 wt% graphite coated sawdust (250–500 μm) was efficiently gasified with up to 43 wt% of gas (30 wt% of carbon monoxide, 25 vol% of hydrogen). Initial particle size impacted the thermolysis performance where optimal size (250–500 μm) provided high heat homogeneity due to efficient graphite coating and low temperature gradient between the outer and inner part of the sawdust. The small initial particle size (75–250 μm) was unsuitable for microwave pyrolysis, exhibiting a too large surface area for efficient coating with 0.75 wt% of graphite which was confirmed by the absence of electrical conductivity (<0.003 mS m−1). The electrical conductivity can be used as a marker to evaluate the suitability of the sample for microwave-assisted pyrolysis. Unlike simple graphite mixing, the mechanical coating allowed more than 20-fold decrease of susceptor quantity, providing more homogeneous samples with higher reproducibility

Microwave-assisted hydrothermal selective dissolution and utilisation of hemicellulose in Phyllostachys heterocycla cv. Pubescens

A green process for the microwave-assisted hydrothermal selective dissolution and utilisation of hemicellulose in Phyllostachys heterocycla cv. Pubescens (shortened to pubescens) was developed. The process facilitated the efficient dissolution of hemicellulose at 200°C, while obtaining hemicellulose-free residue that could be further used as starting materials within many industrial processes. A variety of analytical techniques (e.g., HPLC, FT-IR, SEM, TG/TGA, Py-GC/MS, TG-IR, 13C liquid NMR, 2D HSQC NMR, and 13C CPMAS NMR analysis) were used for the analysis of the obtained liquid and solid products, which revealed that hemicellulose was completely extracted from pubescens. A solid residue left after this process consists of cellulose and lignin in a pure form and can be used for production of glucose and aromatic compounds. Interestingly, a new route to produce hemicellulose-based films that could potentially be used for food packaging was achieved. The developed approach opens avenue for a low-cost and sustainable bamboo-based biorefinery

Subtle Microwave-Induced Overheating Effects in an Industrial Demethylation Reaction and Their Direct Use in the Development of an Innovative Microwave Reactor

A systematic study of the conventional and microwave (MW) kinetics of an industrially relevant demethylation reaction is presented. In using industrially relevant reaction conditions the dominant influence of the solvent on the MW energy dissipation is avoided. Below the boiling point, the effect of MWs on the activation energy Ea and k0 is found nonexistent. Interestingly, under reflux conditions, the microwave-heated (MWH) reaction displays very pronounced zero-order kinetics, displaying a much higher reaction rate than observed for the conventionally thermal-heated (CTH) reaction. This is related to a different gas product (methyl bromide, MeBr) removal mechanism, changing from classic nucleation into gaseous bubbles to a facilitated removal through escaping gases/vapors. Additionally, the use of MWs compensates better for the strong heat losses in this reaction, associated with the boiling of HBr/water and the loss of MeBr, than under CTH. Through modeling, MWH was shown to occur inhomogeneously around gas/liquid interfaces, resulting in localized overheating in the very near vicinity of the bubbles, overall increasing the average heating rate in the bubble vicinity vis-à-vis the bulk of the liquid. Based on these observations and findings, a novel continuous reactor concept is proposed in which the escaping MeBr and the generated HBr/water vapors are the main driving forces for circulation. This reactor concept is generic in that it offers a viable and low cost option for the use of very strong acids and the managed removal/quenching of gaseous byproducts

Synthesis and application of tuneable carbon-silica composites from the microwave pyrolysis of waste paper for selective recovery of gold from acidic solutions

Microwave pyrolysis bio-oil from waste paper and K60 silica gel has successfully been utilised to synthesise mesoporous carbon-silica composites with uniquely tuneable surface properties, where functionality and structural characteristics can be altered and even enhanced by curing at different temperatures. This temperature-dependence resulted in composites ranging from highly oxygenated polymerised bio-oil composites at 300 °C to aromatic carbonaceous materials covering the silica surface at 800 °C, making them attractive materials for gold recovery from mining wastewater. The composite materials exhibit exceptional ability and selectivity to recover gold from dilute solutions. Metal adsorption on the surface of these composites proceeded via both chemisorption and physisorption leading to the reduction of Au(iii) to Au(0), resulting in high recovery capacities for gold. Composite material prepared at 500 °C demonstrated the optimum combination of surface functionality and porosity, allowing for an adsorption capacity of 320 mg g-1 of gold and with 99.5% removal being achieved at concentrations mimicking those of real-life mine tailing wastes. All materials pioneered in this research display great potential as selective adsorbents for the recovery of gold from acidic media. This journal i

Lipid production through the single-step microwave hydrolysis of macroalgae using the oleaginous yeast Metschnikowia pulcherrima

Macroalgae (seaweeds) represent an emerging resource for food and the production of commodity and specialty chemicals. In this study, a single-step microwave process was used to depolymerise a range of macroalgae native to the United Kingdom, producing a growth medium suitable for microbial fermentation. The medium contained a range of mono- and polysaccharides as well as macro- and micronutrients that could be metabolised by the oleaginous yeast Metschnikowia pulcherrima. Among twelve macroalgae species, the brown seaweeds exhibited the highest fermentation potential, especially the kelp Saccharina latissima. Applying a portfolio of ten native M. pulcherrima strains, yeast growth kinetics, as well as production of lipids and 2-phenylethanol were examined, with productivity and growth rate being strain dependent. On the 2 L scale, 6.9 g L−1 yeast biomass – a yield of 0.14 g g−1 with respect to the supplied macroalgae – containing 37.2% (w/w) lipid was achieved through utilisation of the proteins, mono- and polysaccharides from S. latissima, with no additional enzymes. In addition, the yeast degraded a range of fermentation inhibitors released upon microwave processing at high temperatures and long holding times. As macroalgae can be cultured to food grade, this system offers a novel, potentially low-cost route to edible microbial oils as well as a renewable feedstock for oleochemicals

Polysaccharide-derived mesoporous materials (Starbon®) for sustainable separation of complex mixtures

The recovery and separation of high value and low volume extractives are a considerable challenge for the commercial realisation of zero-waste biorefineries. Using solid-phase extractions (SPE) based on sustainable sorbents is a promising method to enable efficient, green and selective separation of these complex extractive mixtures. Mesoporous carbonaceous solids derived from renewable polysaccharides are ideal stationary phases due to their tuneable functionality and surface structure. In this study, the structure-separation relationships of thirteen polysaccharide-derived mesoporous materials and two modified types as sorbents for ten naturally-occurring bioactive phenolic compounds were investigated. For the first time, a comprehensive statistical analysis of the key molecular and surface properties influencing the recovery of these species was carried out. The obtained results show the possibility of developing tailored materials for purification, separation or extraction, depending on the molecular composition of the analyte. The wide versatility and application span of these polysaccharide-derived mesoporous materials offer new sustainable and inexpensive alternatives to traditional silica-based stationary phases

Combined analytical strategies for chemical and physical characterization of tar from torrefaction of olive stone

The advance in analytical methodology is critical for progress in 1) biorefinery and 2) torrefaction product commercialization. The chemical characterisation of torrefaction liquid and concentrated tar produced by Arigna Fuels’ pyrolysis plant allowed identification of polar, volatile, non-volatile compounds, species containing organically bound sulphur and nitrogen heteroatoms. The results suggest that only combined use of ion chromatography with Fourier Transform Ion Cyclotron Resonance Mass Spectrometry, and 1H-13C HS-QC can provide comprehensive information on sugar-like material and lignin-derived compounds. Due to the technical robustness and short analysis time, Fourier Transform Ion Cyclotron Resonance Mass Spectrometer was found to be a promising tool for tar analysis containing heavy molecular compounds. Importantly from a technological standpoint, the presence of aromatic and saturated compounds in both liquid and concentrated tar samples indicated the predominance of lignin-derived compounds over products originating from cellulose and hemicellulose polymers.publishedVersio