Advances in process design, techno-economic assessment and environmental aspects for hydrothermal pretreatment in the fractionation of biomass under biorefinery concept

Influence of vapothermal and hydrothermal pre-treatment on anaerobic degradability of lignocellulosic biomass

This study compares the biogas potential of solid common reed residues after undergoing vapothermal and hydrothermal pre-treatment, accompanied by a compositional and structural biomass characterization. In a pre-test series, a design of experiments approach was used to determine the influence of the initial biomass water content during vapothermal pre-treatment on the biogas yield. In the main test series, common reed was pre-treated hydrothermally (i.e., in liquid water) and vapothermally (i.e., in saturated steam) while varying temperature and residence time. The initial biomass water content significantly impacted the biogas potential, with an optimum at a value of 32 to 46 wt-%FM. In the main test series, unlike the residence time, temperature significantly impacted the subsequent anaerobic digestion. Vapothermal pre-treatment had a narrow temperature optimum while hydrothermal pre-treatment led to a biogas increase in a broader temperature range. The optimum temperature of both methods was 170 °C, where methane potentials increased by 28 % (vapothermal) and 36 % (hydrothermal) compared to the untreated sample. Considering the mass loss occurring during the pre-treatment, this increase was still 18 % for vapothermal pre-treatment, while it diminished the increase to 6 % for hydrothermal pre-treatment. Overall, vapothermal pre-treatment produced a similar amount of biogas under comparable conditions, but was less susceptible to carbon loss, and, according to an estimation of the required process energy, may offer energy savings compared to hydrothermal pre-treatment.

Tandem modification strategy on technical lignin realizing the balance of solubility and antioxidant activity in castor oil

In this study, demethylated-acylated enzymatic hydrolysis lignin (DAEHL) with excellent solubility in castor oil and antioxidant activities were prepared via the tandem modification strategy. First, iodocyclohexane simultaneously achieved β-O-4 breakage and hydrogenation, which enhanced the antioxidant activity of lignin. Furthermore, the acylation reaction by palmitoyl chloride increased the alkyl content in the lignin, which can improve the solubility of lignin in castor oil. The structural evolution of lignin showed the change in the hydroxyl group content, which induced a change in the solubility and antioxidant activity of the lignin. 1,1-diphenyl-2-picrylhydrazyl radical (DPPH), 2,2'-azinobis (3-ethylbenzothiazoline-6-sulfonic acid) ammonium salt (ABTS) radical scavenging, Fe3+ reduction capacity and oxidation induction time demonstrated the excellent antioxidant activity of the modified lignin DAEHL. In addition, the balance between antioxidant activity and solubility of lignin was realized by the tandem modification strategy. DAEHL shows good solubility over 1 wt% in castor oil. The OIT value of the castor oil was significantly increased from 162 s (pure castor oil) to 218 s with 0.3 wt% DAEHL. In addition, the wear volume of DAEHL-castor oil is only 61 % of that of castor oil. This study allows for the high-value utilization of technical lignin as a sustainable lubricant addition in castor oil. SYNOPSIS: A tandem modification strategy for technical lignin dissolving in castor oil with antioxidant activity.

Recent progress in iron and steel industry decarbonization strategies: industrial advancements and challenges

The iron and steel industry is widely acknowledged as a carbon-intensive sector, contributing significantly to greenhouse gas emissions. As the global demand and production of iron and steel continue to rise, the early implementation of low-carbon and zero-carbon strategies to expedite the decarbonization processes in the iron and steel industry is paramount for achieving the Intergovernmental Panel on Climate Change (IPCC)'s 2 ℃ climate goal. This article provides a comparative evaluation of recent low-carbon and zero-carbon strategies applied in the iron and steel industry, focusing on the fossil carbon reduction, end carbon utilization, auxiliary strategies, and international supply chain relocation. It delves into the practical manifestations, untapped possibilities, and prevailing challenges associated with these strategies' industrial implementation. Furthermore, it assesses and compares the current carbon-saving potential of the strategies within the global iron and steel industry. The results show that, despite a large industrial scale, low-carbon strategies in iron and steel have a limited emission reduction capacity of up to 55%. While zero-carbon strategies offer higher potential (95-100% reduction), they are still nascent and not widely used. Meeting the IPCC's 2 ℃ target by 2050 with current strategies alone is challenging. Hence, scaling up zero-carbon strategies quickly and expanding low-carbon ones in the long run are critical for iron and steel's carbon neutrality.

Energy-Related Assessment of a Hemicellulose-First Concept-Debottlenecking of a Hydrothermal Wheat Straw Biorefinery

A hemicellulose-first approach can offer advantages for biorefineries utilizing wheat straw as it combines lignocellulose fractionation and potentially higher added value from pentose-based hemicellulose. Therefore, a tailored hydrothermal concept for the production of xylooligosaccharides and xylan was investigated. The focus was on assessing the energy requirements and potential improvements based on experimental results. The wheat straw pretreatment and the downstream processing of hemicellulose hydrolysate were modeled at a scale of 30,000 tons of wheat straw dry mass per year. The results confirmed that the hydrothermal concept can be implemented in an energy-efficient manner without the need for additional auxiliaries, due to targeted process design, heat integration and a high solids loading during hydrolysis. The resulting specific energy requirements for pretreatment and hydrolysate processing are 0.28 kWh/kg and 0.13 kWh/kg of wheat straw dry mass, respectively. Compared to thermal hydrolysate processing alone, the combination of a multi-effect evaporator and pressure-driven ultrafiltration can reduce the heating and cooling energy by 29% and 44%, respectively. However, the ultrafiltration requirements (e.g., electrical energy, membrane area and costs) depend heavily on the properties of the hydrolysate and its interactions with the membrane. This work can contribute to the commercially viable ramp-up of wheat straw multi-product biorefineries.

Scots Pine Bark Extracts as Co-Hardeners of Epoxy Resins

Extracts from natural waste like bark or leaves are great sources of phytochemicals, which contain functional groups (hydroxyl, carboxylic, vinyl, allyl) attractive in terms of polymer synthesis. In this study, the synthesis of epoxy with an extract of Scots pine bark as a natural co-hardener was evaluated. Ultraviolet-visible (UV-Vis) spectroscopy was used for the identification of phytochemicals with conjugated dienes and quantification of TPC. Also, the total solid content (TSC) of representative extracts was calculated. The best extract in terms of total phenolic content (TPC) value was selected as a co-hardener and investigated using differential scanning calorimetry (DSC) for thermal effects and attenuated total reflectance Fourier transform infrared spectroscopy (ATR FTIR) for reactions between functional groups. Also, the mechanical properties (flexural modulus, flexural strength, impact strength, Shore D hardness) and density of composition were obtained for extract-based epoxy and compared to reference sample values. Results were discussed in terms of future research and improvement of compositions. Also, potential applications were proposed.

Green Process for Producing Xylooligosaccharides by Using Sequential Auto-hydrolysis and Xylanase Hydrolysis

Xylooligosaccharides (XOS), as prebiotic oligomers, are increasingly receiving attention as high value-added products produced from lignocellulosic biomass. Although the XOS contains a series of different degrees of polymerization (DP) of xylose units, DP 2 and 3 (xylobiose (X2) and xylotriose (X3)) are regarded as the main active components in food and pharmaceutical fields. Therefore, in the study, in order to achieve the maximum production of XOS with the desired DP, a combination strategy of sequential auto-hydrolysis and xylanase hydrolysis was developed with corncob as raw material. The evidences showed that the hemicellulosic xylan could be effectively decomposed into various higher DP saccharides (> 4), which were dissolved into the auto-hydrolysate; sequentially, the soluble saccharides could be rapidly hydrolyzed into XOS with desired DP by xylanase hydrolysis. Finally, a maximum XOS yield of 56.3% was achieved and the ratio of (X2 + X3)/XOS was over 80%; meanwhile, the by-products could be controlled at lower levels. Overall, this study provides solid data that support the selective and precise preparation of XOS from corncob, vigorously promoting the application of XOS as functional sugar products.

Grass lignin: biosynthesis, biological roles, and industrial applications

Lignin is a phenolic heteropolymer found in most terrestrial plants that contributes an essential role in plant growth, abiotic stress tolerance, and biotic stress resistance. Recent research in grass lignin biosynthesis has found differences compared to dicots such as Arabidopsis thaliana. For example, the prolific incorporation of hydroxycinnamic acids into grass secondary cell walls improve the structural integrity of vascular and structural elements via covalent crosslinking. Conversely, fundamental monolignol chemistry conserves the mechanisms of monolignol translocation and polymerization across the plant phylum. Emerging evidence suggests grass lignin compositions contribute to abiotic stress tolerance, and periods of biotic stress often alter cereal lignin compositions to hinder pathogenesis. This same recalcitrance also inhibits industrial valorization of plant biomass, making lignin alterations and reductions a prolific field of research. This review presents an update of grass lignin biosynthesis, translocation, and polymerization, highlights how lignified grass cell walls contribute to plant development and stress responses, and briefly addresses genetic engineering strategies that may benefit industrial applications.

Efficient co-production of reducing sugars and xylooligosaccharides via clean hydrothermal pretreatment of rape straw

Hydrothermal treatment was applied to pretreat rape straw for the efficient co-production of reducing sugars and xylooligosaccharides. It was observed that hydrothermal treatment using water as solvent and catalyst destructed the compact structure of rape straw and increased its enzymatic digestion efficiency from 24.6% to 92.0%. Xylooligosaccharide (3.3 g/L) was acquired after the treatment under 200 °C for 60 min (severity factor Log Ro = 4.7). With increasing pretreatment intensity from 3.1 to 5.4, the hemicellulose removal increased from 14.4% to 100%, and the delignification was raised from 12% to 44%. Various characterization proved that the surface morphology of treated material showed a porous shape, while the cellulose accessibility, lignin surface area and lignin hydrophobicity were greatly improved. Consequently, hydrothermal pretreatment played a vital role in the sustainable transformation of biomass to valuable biobased compounds, and had a wide range of application prospects in lignocellulosic biorefining.

Emerging trends and advances in valorization of lignocellulosic biomass to biofuels

Sustainable technologies pave the way to address future energy demand by converting lignocellulosic biomass into fuels, carbon-neutral materials, and chemicals which might replace fossil fuels. Thermochemical and biochemical technologies are conventional methods that convert biomass into value-added products. To enhance biofuel production, the existing technologies should be upgraded using advanced processes. In this regard, the present review explores the advanced technologies of thermochemical processes such as plasma technology, hydrothermal treatment, microwave-based processing, microbial-catalyzed electrochemical systems, etc. Advanced biochemical technologies such as synthetic metabolic engineering and genomic engineering have led to the development of an effective strategy to produce biofuels. The microwave-plasma-based technique increases the biofuel conversion efficiency by 97% and the genetic engineering strains increase the sugar production by 40%, inferring that the advanced technologies enhances the efficiency. So understanding these processes leads to low-carbon technologies which can solve the global issues on energy security, the greenhouse gases emission, and global warming.

Sustainable valorization of pitaya (Hylocereus spp.) peel in a semi-continuous high-pressure hydrothermal process to recover value-added products

This study evaluated the use of a semi-continuous high-pressure hydrothermal process for the recovery of value-added products from pitaya peel. The process was carried out at 15 MPa, a water flow rate of 2 mL/min, a solvent-to-feed ratio of 60 g water/g pitaya peel, and temperatures ranging from 40 to 210 °C. The results show that extraction temperatures (between 40 and 80 °C) promoted the recovery of betacyanin (1.52 mg/g), malic acid (25.6 mg/g), and citric acid (25.98 mg/g). The major phenolic compounds obtained were p-coumaric acid (144.63 ± 0.42 µg/g), protocatechuic acid (91.43 ± 0.32 µg/g), and piperonylic acid (74.2 ± 0.31 µg/g). The hydrolysis temperatures (between 150 and 210 °C) could produce sugars (18.09 mg/g). However, the hydrolysis process at temperatures above 180 °C generated Maillard reaction products, which increased the total phenolic compounds and antioxidant activity of the hydrolysates. Finally, the use of semi-continuous high-pressure hydrothermal process can be a sustainable and promising approach for the recovery of value-added compounds from pitaya peel, advocating a circular economy approach in the agri-food industry.

The key role of pretreatment for the one-step and multi-step conversions of European lignocellulosic materials into furan compounds

Nowadays, an increased interest from the chemical industry towards the furanic compounds production, renewable molecules alternatives to fossil molecules, which can be transformed into a wide range of chemicals and biopolymers. These molecules are produced following hexose and pentose dehydration. In this context, lignocellulosic biomass, owing to its richness in carbohydrates, notably cellulose and hemicellulose, can be the starting material for monosaccharide supply to be converted into bio-based products. Nevertheless, processing biomass is essential to overcome the recalcitrance of biomass, cellulose crystallinity, and lignin crosslinked structure. The previous reports describe only the furanic compound production from monosaccharides, without considering the starting raw material from which they would be extracted, and without paying attention to raw material pretreatment for the furan production pathway, nor the mass balance of the whole process. Taking account of these shortcomings, this review focuses, firstly, on the conversion potential of different European abundant lignocellulosic matrices into 5-hydroxymethyl furfural and 2-furfural based on their chemical composition. The second line of discussion is focused on the many technological approaches reported so far for the conversion of feedstocks into furan intermediates for polymer technology but highlighting those adopting the minimum possible steps and with the lowest possible environmental impact. The focus of this review is to providing an updated discussion of the important issues relevant to bringing chemically furan derivatives into a market context within a green European context.

Ionic liquid recovery and recycling via electrodialysis in biomass processing: An economical assessment

Extravagant price and lack of high-efficiency recovery technology limited scale-up utilization of ionic liquids. Ionic liquids recovery with electrodialysis-based techniques has caught wide concern due to membrane-based characteristic. Economical assessment for electrodialysis-based ionic liquid recovery and recycling in biomass processing was performed by determining influence of equipment-related and financial-related factors with sensitivity analysis for each factor. Overall recovery cost of 1-ethyl-3-methylimidazolium acetate, choline acetate, 1-butyl-3-methylimidazolium hydrogen sulphate and 1-ethyl-3-methylimidazolium hydrogen sulfate varied within 0.75-1.96 $/Kg, 0.99-3.00 $/Kg, 1.37-2.74 $/Kg and 1.15-2.89 $/Kg when factors changed within investigated range. Fold of membrane cost, factor of membrane stack cost, factor of auxiliary equipment cost, factor of annual maintenance cost and annual interest rate of loan were positively related with recovery cost. While percentage of annual elapsed time and loan period were negatively correlated with recovery cost. Economical assessment confirmed economic efficiency of electrodialysis for ionic liquids recovery and recycling in biomass processing.