This study investigated hydrothermal liquefaction (HTL) of polyethylene (PE) with different amounts (ranging from 1 wt% to 19 wt%) of calcium carbonate (CaCO3). The role and the fate of CaCO3 in HTL was elucidated under different reaction conditions (425-450 degrees C for 1-2 h). For PE, at 450 degrees C-2 h, the oil yield (76 % f 0.9) obtained was higher than that from 425 degrees C-1.5 h (59 % f 12). However, with higher reaction temperatures (450 degrees C) and longer reaction times (2 h), a higher gas yield (23 % f 0.5) was also achieved. The gas chromatography-mass spectrometry (GC-MS) analysis revealed that the oil product obtained with different amounts of CaCO3 exhibited a similar composition at 425 degrees C for 1.5 hand 2 h, mostly composed of paraffin and olefins with carbon numbers ranging from C7 to C17. At 450 degrees C-2 h, the oil product was predominantly aromatics for all PE samples with different amounts of CaCO3. Additionally, inductively coupled plasma optical emission spectroscopy analysis showed that over 90 % of Ca was distributed to the post-HTL aqueous products, indicating that HTL can simultaneously remove contaminants such as CaCO3 while chemically recycling PE waste into valuable products like fuels or aromatic chemicals. To understand the complex reactions during HTL of PE with varying amounts of CaCO3, the key reactions were investigated using quantum mechanical (QM) methods to elucidate possible reaction mechanisms involved.

This study conducted a techno-economic assessment of amino acid production from brewers' spent grains (BSG) using semi-continuous subcritical water hydrolysis. The process was operated at a pressure of 15 MPa, with a water flow rate of 5 mL/min, a solvent-to-feed ratio of 20 g water/g BSG, and at various temperatures (80 degrees C to 180 degrees C). The experimental results demonstrated that the amino acid yield of the single subcritical reactor (10.20 mg/g BSG) was higher compared to the two-sequential reactors (4.72 mg/g BSG). The hydrolysate obtained experimentally was composed mainly of tryptophan (215 mu g/mL), valine (64 mu g/mL), and aspartic acid (123 mu g/mL). The economic analysis revealed that the manufacturing cost of amino acids ranged from 33.66 USD/kg to 49.42 USD/kg. The implementation cost of downstream processing represents the most significant fixed capital investment, as complex unit operations are required to isolate and purify amino acids.

This study aims to elucidate the mass transfer behavior and reaction mechanisms governing the depolymerization of polyethylene (PE) during hydrothermal processing (HTP). It specifically focuses on the comparative effects of superheated steam (SHS, defined as water heated beyond its boiling point at a given pressure without undergoing condensation) and supercritical water (SCW, formed above the critical point of water) conditions on PE depolymerization, providing an unprecedented analysis of these two environments. The effects of pressure ranging from 5.5 to 23 MPa, polymer concentrations between 30-83 wt%, and temperatures of 425 and 450 degrees C. The oil, gas, and solid products obtained were analyzed by quantifying their total yields, and the chemical compositions of the oil, aqueous phase products and gas were analyzed using gas chromatography mass spectrometry (GC-MS) and gas chromatography coupled to a thermal conductivity detector (GC-TCD) respectively. The results show comparable oil yields (similar to 83 %) between reactions conducted at lower pressures with SHS and those operated at 23 MPa with SCW. Notably, the chemical composition of the oils - primarily olefins and paraffins - remained identical regardless of changes in pressure; the same was observed when increasing polymer concentration under conditions with SHS. At higher temperatures (450 degrees C), complete conversion of PE into valuable chemicals, including benzene, toluene, ethylbenzene, and xylene (BTEX) in the oil was observed. The chemical composition of the gas revealed the absence of CO2 from reactions conducted with SHS, representing a notable advantage for this technology considering CO2 and its role as a major greenhouse gas. By understanding the differences between SHS and SCW, this study provides insights into optimizing HTP for efficient PE conversion and the development of sustainable technologies for plastic waste management and resource recovery.

Compared to fossil fuels, biofuel production has been growing progressively due to much-reduced greenhouse gas emissions. Currently, bioethanol is the biggest biofuel used worldwide, and its production has been increasingly extensive. This chapter discusses different generations of bioethanol processing production, such as the first, second, third and futuristic fourth generations. Also, an overview of commercial bioethanol production shows the United States and Brazil are the countries with dominant industries, highly influenced by their national energy policies. However, the EU and China intend to increase bioethanol production driven by government support in the next few years. Then, bioethanol production is promising due to the growing expansion of countries such as China and within the EU and the demand for renewable fuels.

During the process of subcritical water hydrolysis of lignocellulosic compounds, such as brewers' spent grains, some toxic compounds can be formed due to the breakdown of the cellulose structure. These compounds are known as furanic aldehydes, and they are inhibitors of microorganisms that are used in different processes, such as fermentation and anaerobic digestion, among others. The detoxification and conditioning of these hydrolysates are required before their use in other processes that require low concentrations of toxins. One of the mechanisms that can be used to diminish those compounds is the adsorption process. For this reason, this study evaluated at-line and in-line purification strategies using different adsorbents in fixed-bed columns to remove furanic aldehydes from a model feed simulating hydrolysate from subcritical water hydrolysis. The model feed consisted of simple sugars and furanic aldehydes at appropriate concentrations. The selected adsorbents were silica-C18, hydrocarbons, and activated carbon. The results indicate that, among the adsorbents that were studied, activated carbon was the most efficient for the removal of both 5-hydroxymethylfurfural and furfural. The activated carbon removed >99% of furanic aldehydes in the experiments conducted in the at-line system. Sequential subcritical water hydrolysis followed by either at-line or in-line purification is promising for integrated inexpensive and efficient hydrolysate purification.

The global plastic market is at an all-time high and plays a major role in many sectors of daily life. Plastics, especially polyethylene (PE) and polypropylene (PP), are versatile and stable, but their durability results in a slow degradation rate, causing environmental issues. Moreover, PE and PP are commonly mixed together. Any solution to this plastic waste problem must therefore be able to handle mixed plastic streams, address impurities, and be cost-effective. Hydrothermal liquefaction (HTL) technologies have emerged as a potential solution for achieving plastic circularity at lower temperatures than traditional thermochemical conversion methods and have therefore garnered attention recently. This chapter highlights the current state-of-the-art of HTL of PE and PP into monomers, chemicals, or fuels. Discussion of non-catalytic HTL, benefits, limitations, and new techniques involving organic solvents are also included. To improve the energy efficiency of HTL, perspectives on catalytical HTL of PE and PP are presented, while new research gaps are identified.

Hydrothermal liquefaction (HTL) is an alternative process for biomass conversion with promising outcomes and environmentally-friendly prospects. However, a gap in the intermediate bioproducts was found in the hydrolysis step of HTL after a careful investigation of the current state-of-the-art. This study investigated two routes of the hydrothermal conversion of corn cob through HTL and sequential processing, i.e. subcritical water hydrolysis (SWH) + HTL. The influence of SWH (230-260 degrees C) and HTL temperatures (300-350 degrees C), and volumetric flow rate (5-10 ml min-1) were evaluated. GC-MS and FTIR analysis were performed for bio-oil characterization. Results showed that lower SWH temperatures favored glucose and furfural production, while higher temperature favored xylose and hydroxymethylfurfural (HMF). Bio-oil produced by the sequential processing exhibited a high concentration of nitrogenous and oxygenated compounds. Hydrochar produced in both routes exhibited a similar higher heating value and elemental composition, although FTIR analysis revealed different functional groups.

This review provides insights into the current research on pyrolytic bio-oil obtained from different feedstock regarding upgrading techniques and applications such as energy, fuels, chemicals, and carbon materials. Raw bio-oil is not appropriate for transportation and ignition due to undesired properties; therefore, several challenges have been reported regarding its suitable market application. For liquid biofuel production, thermochemical pathways, particularly hydrogenation and deoxygenation, must be carried out, and for chemical production, liquid solvents are mostly used via physical separation. The main issues related to downstream processes with environmental and economic assessment are also covered. The analysis indicates that the major bottlenecks for commercial applications of upgraded bio-oil are the initial stage (upgrading techniques), high production costs, and pilot scale production. Finally, future directions are addressed for the improvement of bio-oil upgrading.

Deffated rice bran has potential to processing into ethanol due to its lignocellulosic composition and agricultural productivity. The composition of the pretreated deffated rice bran with Deep Eutectic Solvent was investigated aiming the production of sugars and bioproducts using subcritical water hydrolysis. Changes in the deffated rice bran composition at different pretreatment times and mixtures of deep eutectic solvent were evaluated by the derivative of thermogravimetric analysis. The pretreated deffated rice bran presented an enrichment in the content of hemicelluloses (281.0%) and delignification (59.3 %). Under the same condition of subcritical water hydrolysis (230 degrees C/R-100) the yield of fermentable sugars increased 2.20 times in the same study time interval (20 min) when comparing pretreated and untreated deffated rice bran.

The detection of analytes in complex organic matrices requires a series of analytical steps to obtain a reliable analysis. Sample preparation can be the most time-consuming, prolonged, and error-prone step, reducing the reliability of the investigation. This review aims to discuss the advantages and limitations of extracting bioactive compounds, sample preparation techniques, automation, and coupling with on-line detection. This review also evaluates all publications on this topic through a longitudinal bibliometric analysis, applying statistical and mathematical methods to analyze the trends, perspectives, and hot topics of this research area. Furthermore, state-of-the-art green extraction techniques for complex samples from vegetable matrices coupled with analysis systems are presented. Among the extraction techniques for liquid samples, solid-phase extraction was the most common for combined systems in the scientific literature. In contrast, for on-line extraction systems applied for solid samples, supercritical fluid extraction, ultrasound-assisted extraction, microwave-assisted extraction, and pressurized liquid extraction were the most frequent green extraction techniques.

Lignocellulosic biomass conversion has been researched as a potential alternative to bio-building blocks, platform chemicals, and value-added commodities due to being a renewable feedstock with lower environmental impact than fossil fuels. As food security is arguably a major challenge in the twenty-first century, researchers focus their efforts in the agricultural waste to reduce the world’s dependence on fossil fuels, while avoiding the use of human food sources and capitalizing on environmentally harmful by-products. Sub-supercritical water hydrolysis has the potential to decompose macromolecules, such as cellulose, hemicellulose, and lignin into monomeric sugars and low-molecular weight substances and valuable intermediate products for pharmaceutical, fuel, textile, and construction industry with several advantages over conventional processes; water is nontoxic and works as a solvent for a wide range of products due to the temperature effect on its characteristics (density, dielectric constant, ionic product). This review provides an overview of the state of the art in hydrolysis with sub-supercritical water in the context of recovering compounds from food processing waste and agricultural substrates.

Thermochemical processes including hydrothermal technology are gaining research interest as a potentially green method for deconstructing biomass into platform chemicals or energy carriers. Hydrothermal liquefaction (HTL) and Hydrothermal Carbonization (HTC) are advantageous because of their enhanced process performance while being environmentally friendly and technologically innovative. However, after a deep review, several works have shown a misunderstanding between HTL and HTC concepts. Therefore, this review advances understanding on the main differences and gaps found between HTL and HTC in terms of operation parameters, technical issues, and main products. Furthermore, environmental and techno-economic assessments (TEA) were presented to appraise the environmental sustainability and economic implications of these techniques. Perspectives and challenges are presented and the integration approaches of hydrothermal valorization pathways and biorefining are explored.

The growing demand for space and financial resources to manage current and new municipal solid waste (MSW) landfills has become a massive challenge for several countries. Additionally, landfills contribute to adverse environmental impacts such as pollution and CO2 (carbon dioxide) and CH4 (methane) emissions. This paper has analyzed the possibility of producing biogas from landfilled MSW. An easily degradable fraction of landfilled MSW with 8 years of landfilling was mined and subjected to chemical characterization and elemental composition analysis. The abbreviation for the study sample was called ED8 – Mined. The low values of lignin (24.5

The value of lignocellulose residues for green technologies has been growing, but biomass pretreatment is still an economic challenge. In this case study, a cost analysis of subcritical water pretreatment (SCWP) of sugarcane by‐products for ethanol production was conducted. The proposed industrial scheme is attached to a Brazilian sugarcane mill, which generates a surplus of bagasse. Seven scenarios were simulated to address the prospects of the implementation of the process in the mill. The fermentation of sugarcane bagasse hydrolysate with Scheffersomyces stipitis upgraded the ethanol yield. The fixed capital investment of the industrial process was approximately US$27 million and 35% of this was associated with the SCWP. The highest ethanol yield was obtained for the process operated with hydrolysate from sugarcane bagasse (6740.5 kg ethanol day−1), which is associated with the high hemicellulose content in the bagasse composition compared with straw. The cost difference revealed that the fixed capital investment and utilities were the largest expenses for process implementation and operation. The simulated process reached 5.45 US$ L−1 as the lowest cost of manufacturing. However, this cost is approximately 10‐fold higher than the market price for ethanol in Brazil. In conclusion, the SCWP of sugarcane straw and bagasse demands significant technical improvement before scaling up to the industrial scale for bioethanol production. © 2021 Society of Chemical Industry and John Wiley & Sons, Ltd

An economic evaluation was conducted of flavanone and sugar production from orange peel (OP) using a sequential hydrothermal process. The process was conducted at laboratory (2 x 5 L), pilot (3 x 10 L), and industrial (3 x 500 L) scales. The results demonstrate that the scale-up process decreased the cost of manufacturing (COM) with a significant increase in flavanone and sugar production. The lowest COM was of US$ 25.72/kg flavanones and US$ 1.43/kg sugars, both on an industrial scale. The predominant costs at the industrial scale (>90%) were the cost of utilities and the cost of raw materials. A low capital payback time was obtained, which decreased as return on investment and gross margin increased. A strengths, weaknesses, opportunities, and threats matrix demonstrates the relevant business topics related to the scale-up of OP processing. Thus, the current scale-up project can be considered as a promising approach to the production of flavanones and sugar from OP on an industrial scale. (c) 2020 Society of Industrial Chemistry and John Wiley & Sons Ltd

Rice husks is a residue with relevant amount of cellulose, hemicelluloses and lignin. The potential of deep eutectic solvent was investigated in rice husks pretreatment to delignification and increase in cellulose content. Sequential subcritical water hydrolysis was applied in the best pretreatment condition aiming to produce fermentable sugars. Fourier Transform Infrared Spectroscopy was used in pretreated rice husks to evaluated the increase in cellulose content at different pretreatment time (1, 2, 4 and 6 h), with choline chloride: glycerol and choline chloride: urea. The lignocellulosic composition was determined by thermogravimetric analysis. In the assay at 230 degrees C with R of 40, the highest yields of reducing sugars were obtained (49.9 +/- 2.41 g/100 g biomass) and efficiency (67.91 +/- 3.28 g sugars/100 g carbohydrates).

Hydrothermal processes are an attractive clean technology and cost-effective engineering platform for biorefineries based in the conversion of biomass to biofuels and high-value bioproducts under the basis of sustainability and circular bioeconomy. The deep and detailed knowledge of the structural changes by the severity of biomasses hydrothermal fractionation is scientifically and technological needed in order to improve processes effectiveness, reactors designs, and industrial application of the multi-scale target compounds obtained by steam explosion and liquid hot water systems. The concept of the severity factor [log(10) (R-o)] established>30 years ago, continues to be a useful index that can provide a simple descriptor of the relationship between the operational conditions for biomass fractionation in second generation of biorefineries. This review develops a deep expla-nation of the hydrothermal severity factor based in lignocellulosic biomass fractionation with emphasis in research advances, pretreatment operations and the applications of severity factor kinetic model.