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Hydrothermal processing (e.g., hydrothermal liquefaction) is one of the most promising systems to valorize a wide range of biomass. However, a large amount of aqueous byproduct is generated, which contains high soluble concentrations of both organics and nutrients. Thus, valorization of the aqueous byproduct can be clearly beneficial for the environment and energy recovery. Various physicochemical systems have been recognized for the valorization of aqueous byproducts, such as chemical, thermochemical, and electrochemical systems. Accordingly, this article reviews the valorization of the aqueous byproduct from hydrothermal processing (mainly hydrothermal liquefaction) from several points of view, starting with the characteristics of the aqueous byproduct originating from the hydrothermal processing of diverse biomass. The recent progress in numerous physicochemical systems, including catalytic hydrothermal gasification and microbial electrolysis cells, is comprehensively demonstrated with emphasis on their combinations since integrated systems allow energy and nutrients to be recovered more environmentally and economically feasible. The fundamentals, advantages, limitations, and the most recent findings faced in the development of each physicochemical system are also elucidated. Subsequently, the new concept of systems thinking is proposed to evaluate these systems, and a systemic framework is presented to consolidate the practical applications of these systems. Consequently, this review illustrates both the future perspectives of wastewater valorization and the milestones that should be achieved in the future. [ABSTRACT FROM AUTHOR]

Abstract: Pyrolysis has been increasingly perceived as a promising technology to produce biofuel precursors (bio‐oil) from agricultural residuals; however, there is a significant quality gap between a bio‐oil and the fuels used for transportation. In this study, we autohydrolyzed pretreated sugarcane bagasse at three different conditions (180 °C–10 min, 180 °C–40 min, 200 °C–40 min), then we investigated the effect of this pretreatment on a subsequent pyrolysis stage. High‐pressure ion‐exchange chromatography (HPIC) and the 13C cross‐polarization/magic angle spinning (CP/MAS) solid‐state nuclear magnetic resonance (NMR) revealed that the autohydrolysis pretreatment significantly disrupted the hemicellulose fractions in the sugarcane bagasse and caused the breakage of lignin ether linkages in the sugarcane bagasse feedstocks. As the 31P NMR results indicated, the autohydrolysis pretreatment removed carboxylic acid groups up to 66.7 %, which could significantly address the corrosion problem of bio‐oils. Heteronuclear single quantum correlation (HSQC) analysis suggested that the autohydrolysis pretreatment effectively lowered the presence of the oxygenated aromatic compounds in the bio‐oils. Gel permeation chromatography (GPC) analysis of the bio‐oils indicated that the oils from severely pretreated sugarcane bagasse pyrolyzed at a low temperature (i.e., 400 °C) contained lower‐molecular‐weight components similar to those present gasoline products. [ABSTRACT FROM AUTHOR]

The conversion of biomass primary pyrolysis vapors over several β-zeolites with silica-to-alumina ratios (SAR) varying from 21 to 250 was carried out in a flow microreactor to investigate the effect of number of acid sites on product speciation and deactivation of the catalyst. Experiments were conducted using a horizontal fixed bed semi-batch reactor in which up to 40 discrete 50 mg boats of biomass were pyrolyzed and the vapors upgraded over 0.5 g of the catalyst. Products were measured with a molecular beam mass spectrometer (MBMS). These studies were complemented using a tandem micropyrolyzer connected to a GCMS (py-GCMS) for speciation and quantifying the products. In the py-GCMS experiments, several 0.5 mg loads of pine were pyrolyzed sequentially and the vapors upgraded over 4 mg of catalyst. In all of these experiments, real-time measurements of the products formed were conducted as the catalyst aged and deactivated during upgrading. The results from these experiments showed that: (1) fresh catalyst for β-zeolites with lower SAR (more acid sites) produced primarily aromatic hydrocarbons and olefins with no detectable oxygen-containing species; (2) a suite of oxygenated products was observed from fresh catalysts with high SAR (few acid sites), indicating that 0.5 g of these catalyst materials did not have sufficient acid sites to deoxygenate vapors produced from pyrolysis of 50 mg of pine. This suite of oxygen containing products consisted of furans, phenol and cresols. The amount of coke deposited on each catalyst and the yield of aromatic hydrocarbons increased with the number of acid sites. However, while the catalysts were active, the biomass selectivity towards coke and hydrocarbons remained essentially constant on the catalysts of varying SAR. [ABSTRACT FROM AUTHOR]

The pyrolysis behavior of corn stover and polypropylene during co-pyrolysis was studied using a tube furnace reactor. The effects of mixing ratio of corn stover and polypropylene, pyrolysis temperature, addition amount of catalyst (HZSM-5) and reaction atmosphere (N2 and CO2) on the properties of pyrolysis products were studied. The results showed that co-pyrolysis of corn stover and polypropylene can increase the yield of pyrolysis oil. When corn stover:polypropylene = 1:3, the yield of pyrolysis oil was as high as 52.1%, which was 4.5% higher than the theoretical value. With the increase of pyrolysis temperature, the yield of pyrolysis oil increased first and then decreased, and reached the optimal yield at 550 °C. The addition of catalyst (HZSM-5) reduced the proportion of oxygenates and promoted the generation of aromatic hydrocarbons. CO2 has a certain oxidation effect on the components of pyrolysis oil, which promoted the increase of oxygen-containing aromatics and the reduction of deoxy-aromatic hydrocarbons. This study identified the theoretical basis for the comprehensive utilization of plastic and biomass energy. [ABSTRACT FROM AUTHOR]

The pyrolytic behavior of several biomass components including cellulose, hemicellulose, lignin, and tannin, from two sources of waste biomass (i.e., pine bark and pine residues) were examined. Compared to the two aromatic-based components in the biomass, carbohydrates produced much less char but more gas. Surprisingly, tannin produced a significant amount of water-soluble products; further analysis indicated that tannin could produce a large amount of catechols. The first reported NMR chemical shift databases for tannin and hemicellulose pyrolysis oils were created to facilitate the HSQC analysis. Various C–H functional groups (>30 different C–H bonds) in the pyrolysis oils could be analyzed by employing HSQC-NMR. The results indicated that most of the aromatic C–H and aliphatic C–H bonds in the pyrolysis oils produced from pine bark and pine residues resulted from the lignin and tannin components. A preliminary study for a quantitative application of HSQC-NMR on the characterization of pyrolysis oil was also done in this study. Nevertheless, the concepts established in this work open up new methods to fully characterize the whole portion of pyrolysis oils produced from various biomass components, which can provide valuable information on the thermochemical mechanisms. [ABSTRACT FROM AUTHOR]