Hydrothermal Liquefaction of Biomass as One of the Most Promising Alternatives for the Synthesis of Advanced Liquid Biofuels: A Review

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.

Chromium-based metal-organic framework, MIL-101 (Cr), assisted hydrothermal pretreatment of teff (Eragrostis tef) straw biomass

Teff (Eragrostis tef) is a staple crop and holds the biggest share of grains cultivated area in Ethiopia, consequently, a large quantity of Teff straw is produced. The Teff straw was pretreated for the first time with Chromium-based Metal-Organic Framework, MIL-101(Cr), assisted hydrothermal method at temperatures ranging from 160 to 240 °C for 1/2, 1, or 2 h time independently. With an increase of pretreatment severity, the yield of total reducing sugar (TRS) was increased until reaching maximum (185 mg g-1). The identified optimum hydrothermal pretreatment condition, (180 °C and 1 h), had a feature of higher TRS yield and lower furfural concentration. The morphological analysis showed that treated Teff straw had degraded structure, higher surface area, and distorted bundles than native Teff straws. This study insight into MOFs' application in lignocellulose biomass processing, and optimizing the pretreatment condition of Teff straw biomass.

A concise review on waste biomass valorization through thermochemical conversion

Due to an increase in industrialization and urbanization, massive amounts of solid waste biomass are speedily accumulating in our environment, which poses several adverse effects on habitat and human health thus becoming a matter of discussion in the environmental community. With reference to the circular economy, continuous efforts have been put forward for setting up an organised management approach in combination with an efficient treatment technique for increasing the profitable utilization of solid waste. This review aims to provide a systematic discussion on the recent thermochemical technologies employed for converting waste biomass generated from different sources into valuable products like biochar, bio-oil, heat, energy and syngas. The article further focuses on a few important aspects of thermochemical conversion of waste biomass to useful products like technical factors affecting thermochemical processes, applications of by-products of thermochemical conversion, and biological pretreatment of waste biomass. The review assists interesting recent and scientific trends for boosting up the systematic management and valorization of solid waste through low-cost, efficient, environment-friendly and sustainable technologies.

Non-fuel applications of bio-oil for sustainability in management of bioresources

Biomass valorization by thermochemical conversion method is a promising and intriguing pathway due to the flexibility of utilizing a diverse group of biomass and biowastes, specific product delivery mechanism through manipulation of process parameters, and wide applicability of the products. Pyrolysis has been viewed as an effective valorization technique to transform biowastes into pyrolytic oil, solid char, and syngas. Syngas is generally fed to the pyrolysis process to generate heat necessary for the pyrolysis process to sustain. Pyrolysis may also be a subsidiary component in a biorefinery system where it draws feedstocks from refinery process residues or the side streams of the refinery operation. In recent times, pyrolysis products have been under intense research for their usability and diverse applicability. Bio-oil's rich chemical makeup has promising potential to be used as an advanced biofuel and is considered as a storehouse of diverse chemical species ranging from green solvents to bioactive chemicals. The current review provides a state of knowledge on non-fuel uses of bio-oil and concludes that the pyrolysis process and products could be a part of the future bioeconomy if designed in a manner that biowastes are transformed into value-added products which replace products of petroleum origin.

Sustainable Materials Containing Biochar Particles: A Review

The conversion of polymer waste, food waste, and biomasses through thermochemical decomposition to fuels, syngas, and solid phase, named char/biochar particles, gives a second life to these waste materials, and this process has been widely investigated in the last two decades. The main thermochemical decomposition processes that have been explored are slow, fast, and flash pyrolysis, torrefaction, gasification, and hydrothermal liquefaction, which produce char/biochar particles that differ in their chemical and physical properties, i.e., their carbon-content, CHNOS compositions, porosity, and adsorption ability. Currently, the main proposed applications of the char/biochar particles are in the agricultural sector as fertilizers for soil retirement and water treatment, as well as use as high adsorption particles. Therefore, according to recently published papers, char/biochar particles could be successfully considered for the formulation of sustainable polymer and biopolymer-based composites. Additionally, in the last decade, these particles have also been proposed as suitable fillers for asphalts. Based on these findings, the current review gives a critical overview that highlights the advantages in using these novel particles as suitable additives and fillers, and at the same time, it shows some drawbacks in their use. Adding char/biochar particles in polymers and biopolymers significantly increases their elastic modulus, tensile strength, and flame and oxygen resistance, although composite ductility is significantly penalized. Unfortunately, due to the dark color of the char/biochar particles, all composites show brown-black coloration, and this issue limits the applications.

A Comprehensive Review on Zeolite Chemistry for Catalytic Conversion of Biomass/Waste into Green Fuels

Numerous attempts have been made to produce new materials and technology for renewable energy and environmental improvements in response to global sustainable solutions stemming from fast industrial expansion and population growth. Zeolites are a group of crystalline materials having molecularly ordered micropore arrangements. Over the past few years, progress in zeolites has been observed in transforming biomass and waste into fuels. To ensure effective transition of fossil energy carriers into chemicals and fuels, zeolite catalysts play a key role; however, their function in biomass usage is more obscure. Herein, the effectiveness of zeolites has been discussed in the context of biomass transformation into valuable products. Established zeolites emphasise conversion of lignocellulosic materials into green fuels. Lewis acidic zeolites employ transition of carbohydrates into significant chemical production. Zeolites utilise several procedures, such as catalytic pyrolysis, hydrothermal liquefaction, and hydro-pyrolysis, to convert biomass and lignocelluloses. Zeolites exhibit distinctive features and encounter significant obstacles, such as mesoporosity, pore interconnectivity, and stability of zeolites in the liquid phase. In order to complete these transformations successfully, it is necessary to have a thorough understanding of the chemistry of zeolites. Hence, further examination of the technical difficulties associated with catalytic transformation in zeolites will be required. This review article highlights the reaction pathways for biomass conversion using zeolites, their challenges, and their potential utilisation. Future recommendations for zeolite-based biomass conversion are also presented.

Biorefineries: Achievements and challenges for a bio-based economy

Climate change, socioeconomical pressures, and new policy and legislation are driving a decarbonization process across industries, with a critical shift from a fossil-based economy toward a biomass-based one. This new paradigm implies not only a gradual phasing out of fossil fuels as a source of energy but also a move away from crude oil as a source of platform chemicals, polymers, drugs, solvents and many other critical materials, and consumer goods that are ubiquitous in our everyday life. If we are to achieve the United Nations' Sustainable Development Goals, crude oil must be substituted by renewable sources, and in this evolution, biorefineries arise as the critical alternative to traditional refineries for producing fuels, chemical building blocks, and materials out of non-edible biomass and biomass waste. State-of-the-art biorefineries already produce cost-competitive chemicals and materials, but other products remain challenging from the economic point of view, or their scaled-up production processes are still not sufficiently developed. In particular, lignin's depolymerization is a required milestone for the success of integrated biorefineries, and better catalysts and processes must be improved to prepare bio-based aromatic simple molecules. This review summarizes current challenges in biorefinery systems, while it suggests possible directions and goals for sustainable development in the years to come.

Understanding the Upgrading of Sewage Sludge-Derived Hydrothermal Liquefaction Biocrude via Advanced Characterization

Hydrothermal liquefaction (HTL) can thermochemically transform sewage sludge into a biocrude with high energy content, high chemical complexity, and high O and N content. The development of an efficient upgrading process for such complex feedstocks necessitates detailed knowledge of the molecular composition and the specific heteroatom-containing compounds to understand and optimize the hydrotreating reactions. In this study, we present the upgrading of sewage sludge-derived HTL biocrude via a two-stage hydrotreatment process and perform advanced chemical characterization of the feedstock, intermediate, and final upgraded products with gas chromatography-mass spectrometry (GC-MS) and Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS). We show that hydrotreatment significantly improves the quality of the oil, primarily succeeding in cracking the heavy molecules and removing the sulfur- and oxygen-containing components. FTICR-MS analysis shows that the HTL biocrude has a high concentration of fatty acid amides that readily lose their oxygen and nitrogen during hydrotreating and are converted into saturated hydrocarbons, whereas the aromatic OxNy compounds are converted into N1 and N2 classes, which are more resistant to hydrotreating. We also demonstrate that the upgraded HTL oil can be successfully blended with intermediate refinery streams, such as vacuum gas oil (VGO), for further co-processing to in-spec fuels in conventional processes. This provides an alternative route to introduce renewable carbon in existing fossil-based refineries.

High-Temperature Behavior, Oxygen Transport Properties, and Electrochemical Performance of Cu-Substituted Nd1.6Ca0.4NiO4+δ Electrode Materials

In this study, Nd1.6Ca0.4Ni1−yCuyO4+δ-based electrode materials for intermediate temperature solid oxide fuel cells (IT-SOFCs) are investigated. Materials of the series (y = 0–0.4) are obtained by pyrolysis of glycerol-nitrate compositions. The study of crystal structure and high-temperature stability in air and under low oxygen partial pressure atmospheres are performed using high-resolution neutron and in situ X-ray powder diffraction. All the samples under the study assume a structure with Bmab sp.gr. below 350 °C and with I4/mmm sp.gr. above 500 °C. A transition in the volume thermal expansion coefficient values from 7.8–9.3 to 9.1–12.0 × 10−6, K−1 is observed at approximately 400 °C in air and 500 °C in helium.The oxygen self-diffusion coefficient values, obtained using isotope exchange, monotonically decrease with the Cu content increasing, while concentration dependence of the charge carriers goes through the maximum at x = 0.2. The Nd1.6Ca0.4Ni0.8Cu0.2O4+δ electrode materialdemonstrates chemical compatibility and superior electrochemical performance in the symmetrical cells with Ce0.8Sm0.2O1.9, BaCe0.8Sm0.2O3−δ, BaCe0.8Gd0.19Cu0.1O3−δ and BaCe0.5Zr0.3Y0.1Yb0.1O3−δ solid electrolytes, potentially for application in IT-SOFCs.

A polymeric Brønsted acid ionic liquid mediated liquefaction of municipal solid waste

The rapid industrialization and population explosion continuously generate massive amounts of municipal waste. Several conventional processes are in practice for the treatment of municipal waste, but the requirement of stringent operating conditions, incomplete conversion, longer processing time and emission of toxic gases, etc., are the major associated barriers. Thus, there is an urgent requirement for a sustainable, environmentally feasible process that can process waste into energy and fuel products. In the present manuscript, polyethylenimine functionalized polymeric Bronsted acid ionic liquid (PolyE-IL) catalysts have been explored for the Catalytic Thermo Liquefaction (CTL) of organic biodegradable municipal solid waste (MSW). A series of PolyE-IL catalysts with variable counter ions were examined for CTL of MSW. Of all the tested PolyE-IL catalysts, the integration of [PEI]⁺[HSO₄]^- gave excellent MSW conversion (>85%) and yield (>80%) of liquefied products (CTL-Oil) under non-stringent reaction conditions and without any formation char and gases. The influence of reaction conditions such as catalyst concentration, reaction temperature, time, slurry concentration, and type of feedstock of conversion and yield are studied. The column adsorption and membrane separation process was integrated to facilitate the catalyst and CTL-Oil separation. A series of commercially available hydrophobic resins were tested to separate catalyst and CTL-Oil. ICT005 showed the highest adsorption efficiency of all tested resins with 35.46 mg/mL of binding capacity and K_d of 0.02159. The physicochemical properties of CTL-Oil were studied in detail by using various analytical tools, which exhibited that CTL-Oil comprises a mixture of small and large molecular weight organic compounds and has a calorific value of 4000 kcal/kg; hence it could be used for further energy and fuel applications. Thus, the reported CTL process can be beneficial to resolve both environmental and fossil fuel dependency issues simultaneously by converting MSW into CTL-Oil.