Liquefaction of Biomass and Upgrading of Bio-Oil: A Review

Hydrothermal liquefaction: Exploring biomass/plastic synergies and pathways for enhanced biofuel production

The worsening environmental conditions, diminishing fossil fuel reserves, and increasing waste accumulation have redirected the attention of researchers and scientists towards the exploration of sustainable and non-exhaustive energy sources, as well as waste mitigation techniques. Among the various thermochemical technologies producing biofuels, hydrothermal liquefaction stands out as an effective technique for the simultaneous waste valorization and the production of sustainable biofuels. Under optimal conditions, hydrothermal liquefaction converts 70-80 % of feedstock energy into bio-oil, representing approximately 30-50 % of the feedstock's original mass. The review meticulously discusses and summarizes the process and reaction mechanism along with the influence of various factors on the hydrothermal liquefaction process, including the types of feedstocks (lignocellulosic biomass and plastic waste), operating conditions (temperature, residence time, pressure, substrate-to-water ratio, particle size, and heating rate), and catalyst types. According to the data documented in existing literature, the preferred temperature and residence time for attaining maximum bio-oil yields are reported to be within the range of 260-340 °C and 10-30 min for biomass, and 300-425 °C and 15-30 min for plastics. This review highlights the critical challenges in developing and scaling up the HTL process, proposing potential solutions to enhance feedstock conversion into value-added products. Additionally, it emphasizes the significance of understanding the chemical composition and synergistic interactions between lignocellulosic biomass and plastic waste to optimize product yields and enhance the overall process efficiency. Moreover, it discusses the different products of the hydrothermal liquefaction process-bio-oil, biochar, aqueous phase, and gaseous fraction-and their potential applications, while proposing techniques to upgrade the quality of biocrude.

Catalytic Transformation of Biomass into Sustainable Carbocycles: Recent Advances, Prospects, and Challenges

Organic compounds bearing one or more carbocycles in their molecular structure have a discernible presence in all major classes of organic products of industrial significance. However, sourcing carbocyclic compounds from exhaustible, anthropogenic carbon (e. g., petroleum) raises serious concerns about sustainability in the chemical industries. This review discusses recent advances in the renewable synthesis of carbocyclic compounds from biomass components following catalytic pathways. The mechanistic insights, process optimizations, green metrics, and alternative synthetic strategies of carbocyclic compounds have been detailed. Moreover, the renewable syntheses of carbocycles have been assessed against their existing synthetic routes from petroleum for better perspectives on their sustainability and technological preparedness. This work will assist the researchers in acquiring updated information on the sustainable synthesis of carbocyclic compounds from various biomass components, comprehending the research gaps, and developing superior synthetic processes for their commercial production.

Synthesis of palladium-decorated defective tungsten oxide heterostructures with enhanced photothermal catalytic activity for hydrodeoxygenation of vanillin

The selective hydrodeoxygenation (HDO) of sustainable lignocellulosic biomass plays a pivotal role in the conversion of biomass into high-value fuels and chemicals. Nevertheless, HDO for biomass upgrading always demands high temperatures and high hydrogen (H2) pressure. Photothermal catalysis has been recognized as an effective approach for boosting chemical reactions under mild conditions while maintaining superior selectivity. Herein, we report the design of palladium-decorated defective tungsten oxide (Pd/WO3-x) catalysts with enhanced photothermal catalytic performances for the efficient HDO of vanillin. Pd/WO3-x nanoflowers have been synthesized through a solvothermal/in-situ reduction two-step strategy, and they exhibit notable photoabsorption in a wide range (200-1100 nm), high photothermal conversion and efficient charge separation efficiency. Under simulated sunlight irradiation (0.3 W cm-2), Pd/WO3-x exhibits a maximum vanillin conversion up to 86.8 % with a 2-methoxy-4-methylphenol (MMP) selectivity of 100 %, which is obviously higher than that (vanillin conversion = 33.1 %, MMP selectivity = 100 %) in the oil bath at the same temperature. Such higher conversion efficiency and selectivity under sunlight should result from the synergistic integration of hot electrons and photothermal heating, both of which are derived from localized surface plasmon resonance (LSPR) in WO3-x. Importantly, Pd/WO3-x catalyst demonstrates good stability and high selectivity to MMP even after 5 cycles. This work may offer a novel viewpoint on the advancement of photothermal catalysts and the realization of photothermal catalytic biomass conversion under mild conditions.

The Impact of Biomass Composition Variability on the Char Features and Yields Resulted through Thermochemical Processes

This paper explores the intricate relations between biomass polymeric composition, thermochemical conversion routes, char yields and features in order to advance the knowledge on biomass conversion processes and customize them to meet specific requirements. An exhaustive characterization has been performed for three types of biomasses: (i) spruce bark, a woody primary and secondary residue from forestry and wood processing; (ii) wheat straws-agricultural waste harvest from arable and permanent cropland; and (iii) vine shoots, a woody biomass resulting from vineyard waste. Chemical (proximate and ultimate analysis), biochemical, trace elements, and thermal analyses were performed. Also, Fourier transform infrared spectroscopy, Scanning Electron Microscopy, and thermogravimetric analysis were conducted to establish the compositional and structural characteristics of feedstock. The main polymeric components influence the amount and quality of char. The high hemicellulose content recommends wheat straws as a good candidate especially for hydrothermal carbonization. Cellulose is a primary contributor to char formation during pyrolysis, suggesting that vine shoots may yield higher-quality char compared to that converted from wheat straws. It was shown that the char yield can be predicted and is strongly dependent on the polymeric composition. While in the case of spruce bark and wheat straws, lignin has a major contribution in the char formation, cellulose and secondary lignin are main contributors for vine shoots char.

Coupling hydrothermal liquefaction and anaerobic digestion for waste biomass valorization: A review in context of circular economy

In light of the substantial global production of biomass waste, effective waste management and energy recovery solutions are of paramount importance. Hydrothermal liquefaction (HTL) and anaerobic digestion (AD) have emerged as innovative techniques for converting biomass waste into valuable resources. Their integration creates a synergistic framework that mitigates inherent limitations, leading to improved efficiency, enhanced product quality, and the comprehensive utilization of biomass. This review paper investigates the integration of HTL and AD, highlighting its significance and potential benefits as well as the optimal sequencing (HTL followed by AD and AD followed by HTL). The review encompasses experimental procedures, factors influencing both sequencing options, energy recovery characterizations, final product outcomes, as well as toxicological assessments and discussions on reduction. Additionally, it delves into the transition towards a circular bioeconomy and discusses the challenges and opportunities intrinsic to these processes. The findings presented in this review offer valuable insights to shape future research in this evolving field.

Exploring hydrothermal liquefaction (HTL) of digested sewage sludge (DSS) at 5.3 L and 0.025 L bench scale using experimental design

A common perspective within the prospect of a greener future is utilising our waste materials. One waste material of which the world has abundant resources, and where we will keep having resources, is sewage sludge. This waste material is getting an increased focus, and is commonly utilised by anaerobic digestion processes for methane production. This leaves a bioresidue of digested sewage sludge (DSS). In this study, DSS is submitted to hydrothermal liquefaction (HTL) to produce bio-oil. The studied process includes upscaling as well as considering the effects of temperature, reaction medium of water or ethanol, degree of reactor filling and stirring rate. Promising results are found as high oil yields are obtained also after upscaling. The results reported here show that stirring reduces the need of high temperatures during HTL, providing energy savings that are promising for further upscaling. In addition, a total of 18 compounds are identified and semi-quantified, showing an abundance of fatty acids and fatty acid derivatives within the oil, encouraging further studies towards separation of said fatty acids for use as biodiesel.

Development of BioPolyurethane Coatings from Biomass-Derived Alkylphenol Polyols-A Green Alternative

Bio-based polyols were obtained from the thermochemical liquefaction of two biomass feedstocks, pinewood and Stipa tenacissima, with conversion rates varying between 71.9 and 79.3 wt.%, and comprehensively characterized. They exhibit phenolic and aliphatic moieties displaying hydroxyl (OH) functional groups, as confirmed by attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) and nuclear magnetic resonance spectroscopy (NMR) analysis. The biopolyols obtained were successfully employed as a green raw material to produce bio-based polyurethane (BioPU) coatings on carbon steel substrates, using, as an isocyanate source, a commercial bio-based polyisocyanate-Desmodur^® Eco N7300. The BioPU coatings were analyzed in terms of chemical structure, the extent of the reaction of the isocyanate species, thermal stability, hydrophobicity, and adhesion strength. They show moderate thermal stability at temperatures up to 100 °C, and a mild hydrophobicity, displaying contact angles between 68° and 86°. The adhesion tests reveal similar pull-off strength values (ca. 2.2 MPa) for the BioPU either prepared with pinewood and Stipa-derived biopolyols (BPUI and BPUII). Electrochemical impedance spectroscopy (EIS) measurements were carried out on the coated substrates for 60 days in 0.05 M NaCl solution. Good corrosion protection properties were achieved for the coatings, with particular emphasis on the coating prepared with the pinewood-derived polyol, which exhibited a low-frequency impedance modulus normalized for the coating thickness of 6.1 × 10¹⁰ Ω cm at the end of the 60 days test, three times higher than for coatings prepared with Stipa-derived biopolyols. The produced BioPU formulations show great potential for application as coatings, and for further modification with bio-based fillers and corrosion inhibitors.

Bioupgrading of the aqueous phase of pyrolysis oil from lignocellulosic biomass: a platform for renewable chemicals and fuels from the whole fraction of biomass

Pyrolysis, a thermal decomposition without oxygen, is a promising technology for transportable liquids from whole fractions of lignocellulosic biomass. However, due to the hydrophilic products of pyrolysis, the liquid oils have undesirable physicochemical characteristics, thus requiring an additional upgrading process. Biological upgrading methods could address the drawbacks of pyrolysis by utilizing various hydrophilic compounds as carbon sources under mild conditions with low carbon footprints. Versatile chemicals, such as lipids, ethanol, and organic acids, could be produced through microbial assimilation of anhydrous sugars, organic acids, aldehydes, and phenolics in the hydrophilic fractions. The presence of various toxic compounds and the complex composition of the aqueous phase are the main challenges. In this review, the potential of bioconversion routes for upgrading the aqueous phase of pyrolysis oil is investigated with critical challenges and perspectives.

Speciation and transformation of nitrogen for swine manure thermochemical liquefaction

The nitrogen conversion mechanism of swine manure by thermochemical liquefaction with ethanol as solvent was investigated at a lower temperature range (180–300 °C). The fate of nitrogen in liquid phase products, bio-oil and biochar was evaluated by XPS, GC–MS and other methods. After thermochemical liquefaction, most of the nitrogen in swine manure was transferred to biochar (63.75%). As the temperature increased to 220 °C, the biochar-N yields decreased to 43.29%, accompanied by an increase in bio-oil-N and liquid phase product-N by 7.99% and 1.26% respectively. The results indicated that increasing the temperature could facilitate solid nitrogen structure cracking into bio-oil-N. Amines and heterocyclic nitrogen from protein peptide bond cracking and Maillard reactions made up the main nitrogen compounds in bio-oil, and high temperatures favored the further cyclization and condensation of heterocyclic nitrogen (e.g., indole, quinoline). In the case of biochar, the inorganic nitrogen disappeared at 260 °C and was obviously transformed into liquid phase products. The rising temperature promoted the polymerization of pyridine nitrogen and pyrrole nitrogen, which formed more stabilized nitrogen formation (such as quaternary nitrogen). Nitrogen conversion and possible reaction schematics during swine manure thermochemical liquefaction were explored in this study.

Next generation of polyolefin plastics: improving sustainability with existing and novel feedstock base

Abstract

In this account, we present an overview of existing and emerging olefin production technologies, comparing them from the standpoint of carbon intensity, efficiency, feedstock type and availability. Olefins are indispensable feedstock for manufacture of polyolefin plastics and other base chemicals. Current methods of olefin production are associated with significant CO2 emissions and almost entirely rely of fossil feedstock. In order to assess potential alternatives, technical and economic maturity of six principal olefin production routes are compared in this paper. Coal (brown), oil and gas (grey), biomass (green), recycled plastic (pink) as well as carbon capture and storage (purple) and carbon capture and utilization (blue) technologies are considered. We conclude that broader adoption of biomass based “green” feedstock and introduction of recycled plastic based olefins may lead to reduced carbon footprint, however adoption of best available technologies and introduction of electrocracking to existing fossil-based “grey” olefin manufacture process can be the way to achieve highest impact most rapidly. Adoption of Power-to-X approaches to olefins starting from biogenic or atmospheric CO2 and renewable H2 can lead to ultimately carbon–neutral “blue” olefins in the long term, however substantial development and additional regulatory incentives are necessary to make the solution economically viable.

Article highlights

Value-Added Bio-carbon Production through the Slow Pyrolysis of Waste Bio-oil: Fundamental Studies on Their Structure-Property-Processing Co-relation

The present work addresses the transformation of bio-oil into valuable biocarbon through slow pyrolysis. The biocarbons produced at three different temperatures (400, 600, and 900 °C), 10 °C min^-1 heating rate, and 30 min holding time were tested for their surface morphology, thermal stability, elemental composition, functionality, particle size, and thermal and electrical conductivity. The physicochemical study of bio-oil showed substantial carbon content, higher heating value, and lower nitrogen content. Also, the Thermogravimetric analyzer-FourierTransform Infrared Spectroscopy (TGA-FTIR) study of bio-oil confirmed that the majority of gases released were hydrocarbons, carbonyl products, ethers, CO, and CO_2, with a minor percentage of water and alcohol. Overall, it was found that the pyrolysis temperature has the dominant role in the yield and properties of biocarbon. The physicochemical characterization of biocarbon showed that the higher temperature based pyrolyzed biocarbon (600 and 900 °C) improved the properties in terms of thermal stability, thermal conductivity, graphitic content, ash content, and carbon content. Furthermore, the elemental and Energy-Dispersive Spectroscopy study of biocarbon confirmed the substantial depletion in oxygen and hydrogen at a higher temperature (600 and 900 °C) than the lower temperature based pyrolyzed biocarbon (400 °C). Additionally, the purest form of the biocarbon is found at a higher temperature (900 °C) with higher thermal stability and carbon content. The study of the surface morphology of biocarbon revealed that the higher temperature (600 and 900 °C) biocarbon showed larger and harder particles than the lower temperature biocarbon (400 °C); however, the electrical conductivity of biocarbon decreased, whereas thermal conductivity increased, with an increase in the pyrolysis temperatures. Moreover, the particle size analysis of biocarbon confirmed that most of the particles were found in the range of 1 μm. The increased thermal stability, carbon content, and graphitic content and the lower ash content endorse biocarbon as an excellent feedstock for carbon-based energy storage materials.

Catalytic Pyrolysis of Lignin Model Compound (Ferulic Acid) over Alumina: Surface Complexes, Kinetics, and Mechanisms

Studies of the thermochemical properties of the important model compound of lignin-ferulic acid (FA) and its surface complexes are substantial for developing technologies for catalytic pyrolysis of renewable biomass into biofuels and lignin-derived chemicals as well as for bio-oil upgrading. In this work, the catalytic pyrolysis of ferulic acid over alumina was studied by temperature-programmed desorption mass spectrometry (TPD MS), in situ FT-IR spectroscopy, thermogravimetric analysis, and DFT calculations. We established that both the carboxyl group and the active groups (HO and CH3O) of the aromatic ring interact with the alumina surface. We calculated the kinetic parameters of formation of the main products of catalytic pyrolysis: 4-vinylguaiacol, guaiacol, hydroxybenzene, benzene, toluene, cresol, naphthalene, and PACs. Possible methods of their forming from the related surface complexes of FA are suggested.

Structure-property-performance relationships of lactic acid-based deep eutectic solvents with different hydrogen bond acceptors for corn stover pretreatment

Herein, ten types of lactic acid-based deep eutectic solvents (DESs) with differently structured hydrogen bond acceptors (HBAs) were used for corn stover pretreatment. Among the tested DESs, those composed of HBAs with short alkyl chain were more effective to remove lignin and xylan, resulting in higher enzymatic digestion of the pretreated solids than their counterparts with long alky chain. Also, functional groups of HBAs demonstrated significant effects on biomass deconstruction. In order to interpret the different pretreatment performance of the tested DESs, Kamlet-Taft solvent polarity parameters of the tested DESs were correlated to their lignocellulose pretreatment performance. It was found that hydrogen bond acidity (Kamlet-Taft α parameter) had strong positive relationships with pretreatment efficacy of the studied DESs. These findings not only clarified the structure-property-performance relationships of the DESs, but also provided novel insights into design and selection of DESs for lignocellulose pretreatment.

Ambient-Pressured Acid-Catalysed Ethylene Glycol Organosolv Process: Liquefaction Structure-Activity Relationships from Model Cellulose-Lignin Mixtures to Lignocellulosic Wood Biomass

Raising the awareness of carbon dioxide emissions, climate global warming and fossil fuel depletion has renewed the transition towards a circular economy approach, starting by addressing active bio-economic precepts that all portion amounts of wood are valorised as products. This is accomplished by minimizing residues formed (preferably no waste materials), maximizing reaction productivity yields, and optimising catalysed chemical by-products. Within framework structure determination, the present work aims at drawing a parallel between the characterisation of cellulose–lignin mixture (derived system model) liquefaction and real conversion process in the acidified ethylene glycol at moderate process conditions, i.e., 150 °C, ambient atmospheric pressure and potential bio-based solvent, for 4 h. Extended-processing liquid phase is characterized considering catalyst-transformed reactant species being produced, mainly recovered lignin-based polymer, by quantitative 31P, 13C and 1H nuclear magnetic resonance (NMR) spectroscopy, as well as the size exclusion- (SEC) or high performance liquid chromatography (HPLC) separation for higher or lower molecular weight compound compositions, respectively. Such mechanistic pathway analytics help to understand the steps in mild organosolv biopolymer fractionation, which is one of the key industrial barriers preventing a more widespread manufacturing of the biomass-derived (hydroxyl, carbonyl or carboxyl) aromatic monomers or oligomers for polycarbonates, polyesters, polyamides, polyurethanes and (epoxy) resins.

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.

Valorization of Indonesian Wood Wastes through Pyrolysis: A Review

The wood processing industry produces a significant amount of wood waste. Biomass valorization through pyrolysis has the potential to increase the added value of wood wastes. Pyrolysis is an important thermochemical process that can produce solid, liquid, and gas products. This paper aims to review the pyrolysis of wood wastes from Indonesia, including teak wood (Tectona grandis), meranti (Shorea sp.), sengon (Paraserianthes falcataria (L) Nielsen), and rubberwood (Hevea brasiliensis). The review is based on an in-depth study of reliable literatures, statistical data from government agencies, and direct field observations. The results showed that pyrolysis could be a suitable process to increase the added value of wood waste. Currently, slow pyrolysis is the most feasible for Indonesia, with the main product of charcoal. The efficiency of the slow pyrolysis process can be increased by harvesting also liquid and gaseous products. The use of the main product of pyrolysis in the form of charcoal needs to be developed and diversified. Charcoal is not only used for fuel purposes but also as a potential soil improvement agent.

Upgrading of Bio-Oil Model Compounds and Bio-Crude into Biofuel by Electrocatalysis: A Review

Limited availability of fossil energy and serious environmental pollution have caused the emergence of bio-oil, which can serve as an alternative and promising green energy source. However, bio-oil generated from the rapid pyrolysis of biomass cannot be utilized immediately owing to its corrosivity, instability, and low heating value. Herein, the electrocatalytic hydrogenation (ECH) process towards bio-oil upgrading is reviewed. Specifically, the ECH integrates the advantages of mild operating conditions, no petrochemically derived hydrogen and good controllability. The influence of different factors on the conversion of bio-oil components and product selectivity in the ECH process are presented comprehensively. In addition, various reaction mechanisms are discussed in the designed ECH systems. Finally, some challenges need to be further overcome for real bio-oil reduction in the ECH process: exploration of efficient multifunctional electrocatalysts for specific bio-oil components and determination of the dominant steps in the complicated reaction path network.

Effect of Ceria Addition to Na2O-ZrO2 Catalytic Mixtures on Lignin Waste Ex-Situ Pyrolysis

Waste lignin is a potential source of renewable fuels and other chemical precursors under catalytic pyrolysis. For this purpose, four mixed metal oxide catalytic mixtures (Cat) derived from Na₂CO₃, CeO₂ and ZrO₂ were synthesised in varying compositions and utilised in a fixed bed reactor for catalytic vapour upgrading of Etek lignin pyrolysis products at 600 °C. The catalytic mixtures were analysed and characterised using XRD analysis, whilst pyrolysis products were analysed for distribution of products using FTIR, GC-MS and EA. Substantial phenolic content (20 wt%) was obtained when using equimolar catalytic mixture A (Cat_A), however the majority of these phenols were guaiacol derivatives, suggesting the catalytic mixture employed did not favour deep demethoxylation. Despite this, addition of 40–50% ceria to NaZrO₂ resulted in a remarkable reduction of coke to 4 wt%, compared to ~9 wt% of NaZrO₂. CeO₂ content higher than 50% favoured the increase in conversion of the holo-cellulose fraction, enriching the bio-oil in aldehydes, ketones and cyclopentanones. Of the catalytic mixtures studied, equimolar metal oxides content (Cat_A) appears to showcase the optimal characteristics for phenolics production and coking reduction.

Ruthenium-Loaded Halloysite Nanotubes as Mesocatalysts for Fischer-Tropsch Synthesis

Halloysite aluminosilicate nanotubes loaded with ruthenium particles were used as reactors for Fischer–Tropsch synthesis. To load ruthenium inside clay, selective modification of the external surface with ethylenediaminetetraacetic acid, urea, or acetone azine was performed. Reduction of materials in a flow of hydrogen at 400 °C resulted in catalysts loaded with 2 wt.% of 3.5 nm Ru particles, densely packed inside the tubes. Catalysts were characterized by N₂-adsorption, temperature-programmed desorption of ammonia, transmission electron microscopy, X-ray fluorescence, and X-ray diffraction analysis. We concluded that the total acidity and specific morphology of reactors were the major factors influencing activity and selectivity toward CH₄, C_2–4, and C₅₊ hydrocarbons in the Fischer–Tropsch process. Use of ethylenediaminetetraacetic acid for ruthenium binding gave a methanation catalyst with ca. 50% selectivity to methane and C_2–4. Urea-modified halloysite resulted in the Ru-nanoreactors with high selectivity to valuable C₅₊ hydrocarbons containing few olefins and a high number of heavy fractions (α = 0.87). Modification with acetone azine gave the slightly higher CO conversion rate close to 19% and highest selectivity in C₅₊ products. Using a halloysite tube with a 10–20-nm lumen decreased the diffusion limitation and helped to produce high-molecular-weight hydrocarbons. The extremely small C₂–C₄ fraction obtained from the urea- and azine-modified sample was not reachable for non-templated Ru-nanoparticles. Dense packing of Ru nanoparticles increased the contact time of olefins and their reabsorption, producing higher amounts of C₅₊ hydrocarbons. Loading of Ru inside the nanoclay increased the particle stability and prevented their aggregation under reaction conditions.

Catalytic Pyrolysis of Aliphatic Carboxylic Acids into Symmetric Ketones over Ceria-Based Catalysts: Kinetics, Isotope Effect and Mechanism

Ketonization is a promising way for upgrading bio-derived carboxylic acids from pyrolysis bio-oils, waste oils, and fats to produce high value-added chemicals and biofuels. Therefore, an understanding of its mechanism can help to carry out the catalytic pyrolysis of biomass more efficiently. Here we show that temperature-programmed desorption mass spectrometry (TPD-MS) together with linear free energy relationships (LFERs) can be used to identify catalytic pyrolysis mechanisms. We report the kinetics of the catalytic pyrolysis of deuterated acetic acid and a reaction series of linear and branched fatty acids into symmetric ketones on the surfaces of ceria-based oxides. A structure–reactivity correlation between Taft’s steric substituent constants Es* and activation energies of ketonization indicates that this reaction is the sterically controlled reaction. Surface D3-n-acetates transform into deuterated acetone isotopomers with different yield, rate, E≠, and deuterium kinetic isotope effect (DKIE). The obtained values of inverse DKIE together with the structure–reactivity correlation support a concerted mechanism over ceria-based catalysts. These results demonstrate that analysis of Taft’s correlations and using simple equation for estimation of DKIE from TPD-MS data are promising approaches for the study of catalytic pyrolysis mechanisms on a semi-quantitative level.

Effect of operating parameters on hydrothermal liquefaction of corn straw and its life cycle assessment

As the shortage of non-renewable fossil fuels, the renewable fuels should be further developed. Biomass energy has emerged the great utilization potential, and liquefaction of biomass is a typical technology. This paper studied the effect of the operation parameters on the hydrothermal liquefaction of corn straw using a batch reactor, including liquefaction temperature, initial pressure, retention time, solvent, and catalyst. The optimal liquefaction conditions for corn straw were 300 °C under 4 MPa for 15 min using the mixture of water and methanol as the solvent. After the addition of catalyst, NKC-11 catalyst showed the excellent performance, and the primary components were phenol and derivatives, alkane, furan, and the low concentration of organic acids. Lastly, the life cycle assessment on the hydrothermal liquefaction of corn straw for bio-oil production was executed. The results of LCA suggested that a net 1.31 kg of CO₂ equivalent was produced for 1 kg of bio-oil product without considering syngas, while the value changed to 13.03 kg with considering syngas. Moreover, the results of sensitivity analysis further suggested that the syngas was a key factor on the environmental impacts in the hydrothermal liquefaction of corn straw process.