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The treatment of dairy industry effluents poses a significant challenge from the environmental point of view because of its high organic load. In this work, the aqueous phase reforming of lactose was investigated as a representative model compound for the production of renewable hydrogen. The tests were conducted using two different scenarios: the first one is referred to as direct aqueous phase reforming (APR); the second one proposed a pre-hydrogenation step, followed by APR. The implementation of this reactive pretreatment allowed for minimizing the solid by-product formation with respect to the direct APR, where most of the initial carbon ended up as solid residue. The pre-hydrogenation was investigated in the range of 180–220 °C, using Ru-based catalysts. In the best scenario (using 5% Ru/C), the carbon to solid was reduced by 95%, and up to 70% of the initial carbon was converted into gaseous compounds, hence contributing to the removal of the organic content of the wastewater while producing an energy carrier. Moreover, the hydrogen selectivity increased up to 70% (with respect to 2.5% for direct APR), thanks to hindering homogeneous reaction pathways that do not lead to hydrogen production. Finally, an energetic analysis was conducted to assess the possibility of coupling the APR with the dairy industry and quantifying the percentage of energy which may be produced in situ to satisfy industrial duties. [ABSTRACT FROM AUTHOR]

Lignin‐rich stream from lignocellulosic ethanol production was converted into biocrude by continuous hydrothermal liquefaction (HTL) while hydrogen was produced by aqueous phase reforming (APR) of the HTL aqueous by‐product. The effects of Na2CO3 and NaOH were investigated both in terms of processability of the feedstock as well as yield and composition of the obtained products. A maximum biocrude yield of 27 wt% was reached in the NaOH‐catalyzed runs. A relevant amount of dissolved phenolics were detected in the co‐produced aqueous phase (AP), and removed by liquid–liquid extraction using butyl acetate or diethyl ether, preserving the APR catalyst stability and reaching an hydrogen yield up to 146 mmol H2 L−1 AP. Preliminary mass balances integrating HTL and APR showed that the hydrogen provided by APR may account for up to 46% of the hydrogen amount theoretically required for upgrading the HTL biocrude, thus significantly improving the process performance and sustainability. [ABSTRACT FROM AUTHOR]

Hydrothermal liquefaction is a promising technology for producing renewable advanced biofuels. However, some weaknesses could undermine its large-scale application, such as the significant carbon loss in the aqueous phase (AP) and the necessity of biocrude upgrading. In order to deal with these challenges, in this work the techno-economic feasibility of coupling hydrothermal liquefaction (HTL) with aqueous phase reforming (APR) was evaluated. APR is a catalytic process able to convert water-dissolved oxygenates into a hydrogen-rich gas that can be used for biocrude upgrading. Two cases were proposed, based on different lignocellulosic feedstocks: corn stover (CS) and lignin-rich stream (LRS) from cellulosic ethanol production. HTL-APR plants operating with the same mass flow (3.6 t/h) at 10 wt% solid loading were herein evaluated, resulting in an input size of 20 MW (LRS) and 16.5 MW (CS). Based on experimental and literature data, the mass and energy balances were performed; subsequently, the main equipment was designed; finally, the capital and operating costs were evaluated. The analysis showed that the minimum selling prices for the biofuel (0% internal rate of return) were 1.23 (LRS) and 1.27 €/kg (CS). The heat exchangers accounted for most of the fixed capital investment, while electricity and feedstock had the highest impact on the operating costs. The implementation of APR was particularly profitable with CS, as it produced 107% of the hydrogen required for biocrude upgrading. In this case, APR was able to significantly reduce the H 2 production cost (1.5 €/kg) making it a competitive technology compared to conventional electrolysis. [Display omitted] • A conceptual design and TEA of an HTL-APR integrated plant are performed. • APR produced the H 2 required for the corn stover HTL-derived biocrude upgrade. • Minimum biofuel selling prices are 1.23–1.27 €/kg depending on the feed. • Heat exchangers, feedstock and electricity account for 38–49% of production costs. • H 2 production cost by APR is 77% lower than by electrolysis using corn stover. [ABSTRACT FROM AUTHOR]

The use of biofuels in the transport sector is one of the strategies for its decarbonization. Here, the LCA methodology was used for the first time to assess the environmental impacts of a biorefinery where hydrothermal liquefaction (HTL) and aqueous phase reforming (APR) were integrated. This novel coupling was proposed to valorize the carbon loss in the HTL-derived aqueous phase, while simultaneously reducing the external H 2 demand during biocrude upgrading. Corn stover (residue) and lignin-rich stream (waste) were evaluated as possible lignocellulosic feedstocks. The global warming potential (GWP) was 56.1 and 58.4 g CO 2 eq/MJ biofuel , respectively. Most of the GWP was attributable to the electrolysis step in the lignin-rich stream case and to the thermal duty and platinum use in the corn stover case. Other impact categories were investigated, and an uncertainty analysis was also carried out. A sensitivity analysis on biogenic carbon, electricity/thermal energy source and alternative hydrogen supply was conducted to estimate their influence on the GWP. Finally, the two scenarios were compared with the environmental impact of fossil- and other biomass-derived fuels, also considering fuel utilization. HTL-APR allowed a 37% reduction compared to fossil diesel, further reduced to 80% with the lignin-rich stream when green energy was used. • Environmental evaluation of a biorefinery coupling HTL and APR. • Electrolysis is the most impacting factor when lignin-rich stream is used as feed. • Using decarbonized electricity would result in a 72% GWP reduction. • Thermal power is the key factor when corn stover is used as feed. • The biofuel from HTL-APR plant has 37% lower emission than fossil diesel. [ABSTRACT FROM AUTHOR]

[Display omitted] • The APR of wastewater streams close to industrial complexity has been reviewed. • Food, biodiesel and lignocellulosic processing lead to by-products valorized via APR. • The differences between real and theoretical results are highlighted and examined. • The integration with other technologies is discussed to promote benefic synergies. Wastewater is of general concern for environmental sustainability. At the industrial level, carbon-laden aqueous streams must be treated and should be valorized to reduce environmental and economic concerns. Lignocellulosic biomass processing (such as hydrolysis, pyrolysis, and hydrothermal liquefaction) results in secondary aqueous streams in which a high fraction of the initial carbon content of the biomass is virtually lost; food industry (like breweries and cheese factories) produces streams with a variety of organic load and salinity, which may complicate conventional valorization treatments; biodiesel production leads to glycerol excess in the market, which needs to be valorized. Among other alternatives, aqueous phase reforming (APR) has been proposed as a process driven at relatively mild conditions, able to convert oxygenated molecules into hydrogen. Despite its potential, APR has commonly been investigated with model compounds, and a systematic study on the possible fields of application of this technology is lacking. In the present review, the study of the available literature was focused on the valorization of complex feedstocks, such as real waste streams or synthetic mixtures, showing the outcome derived from laboratory-scale experiments. The results were critically discussed, pointing out the present limitations for the full development of this process and its application to the industrial scale. Despite the challenges of APR, its potential is noteworthy for the development of a circular low-waste economy. [ABSTRACT FROM AUTHOR]

The aqueous phase reforming (APR) is a catalytic reaction able to produce hydrogen from oxygenated compounds. The catalytic system plays a pivotal role to permit high conversion of the substrate, high selectivity towards hydrogen, and stability in the view of an industrial application. These figures of merit depend on several strategies taken by the researchers to properly design the catalyst, like the preparation method, the choice of the active metal together with possible promoters, the type of the support and so on. The available literature reports several studies where these parameters are evaluated and discussed. In this review, they were critically examined with the aim of finding correlations between the properties of the catalyst and the activity, selectivity and stability for the APR of carbon-laden water fractions. Both theoretical and experimental works have been included in the literature survey. When available, studies with the use of in-situ techniques allowed to increase the understanding of the catalytic phenomena involved in the reaction. Great attention was also reported to recently published works, so that the review could present the most up-to-date developments in the field. The most important outcomes regarding each parameter have been highlighted; moreover, the synergy among each of them has been pointed out, together with the trade-off that the researcher has to deal with in the pursuit of the optimum catalyst. [Display omitted] • The research on catalyst design for aqueous phase reforming has been reviewed. • The effect of preparation method, metal choice and support was evaluated. • Use of first-principle approaches and in-situ techniques was reported. • Challenges and perspectives for optimal catalyst system were proposed. [ABSTRACT FROM AUTHOR]

[Display omitted] • Fischer-Tropsch product water was subjected to APR for hydrogen production. • Influence of temperature and time was evaluated for the conversion and selectivity. • The FT product water did not show a competitive adsorption behaviour. • The position of the OH group was found to be crucial for the product distribution. • The reuse of the catalyst did not affect the performance of the reaction. Fischer-Tropsch (FT) synthesis produces an aqueous stream containing light oxygenates as major by-product. The low carbon concentration of the organics makes its thermal recovery unprofitable. Thus, novel processes are needed to utilize this waste carbon content. In this work, the aqueous phase reforming of the wastewater obtained from a 15 kW th Fischer-Tropsch plant was explored as a promising process to produce hydrogen at mild temperatures. The FT product water was firstly characterized and afterward subjected to the reforming at different reaction temperatures and time, using a platinum catalyst supported on activated carbon. It was observed that, besides activity, the selectivity towards hydrogen was favored at higher temperatures; equally, increasing the reaction time allowed to obtain the total conversion of most molecules found in the solution, without decreasing the selectivity and reaching a plateau at 4 hours in the hydrogen productivity. In order to get more insights into the reaction mechanism and product distribution derived from the APR of FT product water, several tests were performed with single compounds, finding characteristic features. The importance of the position of the hydroxyl group in the molecule structure was highlighted, with secondary alcohols more prone to dehydrogenation pathways compared to primary alcohols. Moreover, no interference among the substrates was reported despite the mixture is constituted by several molecules: in fact, the results obtained with the real FT product water were analogous to the linear combination of the single compound tests. Finally, the reuse of the catalyst showed no appreciable deactivation phenomena. [ABSTRACT FROM AUTHOR]

[Display omitted] • The catalyst deactivation during APR of lignin-rich HTL side streams was studied. • Multi-components synthetic mixtures were used to identify the cause of deactivation. • High temperature adsorption with activated carbon increased the catalyst stability. • The solid deposit characterization showed functionalities like the original lignin. The water fraction derived from the hydrothermal liquefaction of a lignin-rich feedstock was subjected to aqueous phase reforming to produce hydrogen. Deactivation of the catalyst was observed, and it was ascribed to fouling phenomena caused by phenolic oligomers. Simple aromatics like guaiacol and phenol, as well as inorganics, were proved not to be the cause of the deactivation thanks to the use of a multi-component synthetic mixture. The influence of using activated carbon as a pretreatment was studied, leading to a strong improvement of the performance when it was carried out at high temperature. The extent of deactivation was assessed using aqueous phase reforming of glycolic acid as a model reaction test. The results were found to be correlated with the surface area of the catalyst. A thermal regeneration in inert conditions was evaluated as a mode of catalyst regeneration. While the textural properties were partially recovered, the performance of the catalyst only slightly improved. A spectroscopic analysis of the solids in the aqueous solution was carried out, highlighting the structural similarities between their nature and the lignin residue. The results obtained in this study helped to enlarge the knowledge on the aqueous phase reforming of real complex mixtures, looking at indicators of paramount importance for a possible industrial application such as the stability of the catalyst. [ABSTRACT FROM AUTHOR]

• APR of aqueous stream from lignin HTL was performed. • The study of a synthetic mixture showed competitive adsorptions. • The real mixture reported different performances according to the phenolic content. • The HTL-APR coupled configuration can reduce the H 2 need for the upgrading. Secondary streams in biorefineries need to be valorized to improve the economic and environmental sustainability of the plants. Representative model compounds of the water fraction from the hydrothermal liquefaction (HTL) of biomass were subjected to aqueous phase reforming (APR) to produce hydrogen. Carboxylic and bicarboxylic acids, hydroxyacids, alcohols, cycloketones and aromatics were identified as model compounds and tested for APR. The tests were performed with a Pt/C catalyst and the influence of the carbon concentration (0.3–1.8 wt. C%) was investigated. Typically, the increase of the concentration negatively affected the conversion of the feed toward gaseous products, without influencing the selectivity toward hydrogen production. A synthetic ternary mixture (glycolic acid, acetic acid, lactic acid) was subjected to APR to evaluate any differences in performance compared to the tests with single compounds. Indeed, glycolic acid reacted faster in the mixture than in the corresponding single compound test, while acetic acid remained almost unconverted. The influence of the reaction time, temperature and carbon concentration was also evaluated. Finally, residual water resulting from the HTL of a lignin-rich stream originating from an industrial-scale lignocellulosic ethanol process was tested for the first time, after a thorough characterization. In this framework, the stability of the catalyst was studied and found to be correlated to the presence of aromatics in the aqueous feedstock. For this reason, the influence of an extraction procedure for the selective removal of these compounds was explored, leading to an improvement in the APR performance. [ABSTRACT FROM AUTHOR]

• APR of sugars-hydrolysate from an industrial bioethanol plant was performed. • Higher reaction temperature decreased the formation of solid by-products. • A dual hydrogenation-APR configuration improved the H 2 yield of sugar solution. • Catalyst characterization confirmed the positive impact of the pre-hydrogenation. Glucose, xylose and corresponding sugar alcohols (sorbitol and xylitol) have been subjected to aqueous phase reforming for the production of hydrogen as representative compounds of hemicellulose. The aim of the investigation was to explore new valorization pathways for pentoses sugars, nowadays still not effectively exploited. A developmental platinum-based catalyst supported on carbon was used to perform the reaction in a batch system. The influence of temperature and carbon concentration were investigated in the 230–270 °C and 0.3–1.8 wt.% range, respectively. Moving towards the exploitation of a biorefinery side-stream, wheat straw hydrolysate was subjected to the same reaction conditions. A hydrogenation step was used as pre-treatment to selectively convert the sugars to their corresponding sugar alcohols, and a net hydrogen production was obtained. Deactivation phenomena were investigated during the APR of sugars reusing the catalyst after the reaction. The characterization of the spent catalysts through TGA-IR allowed to confirm the presence of superficial organic deposits responsible for the lack of the catalyst stability. [ABSTRACT FROM AUTHOR]

• Competitive adsorption in the valorization of wastewater via APR was investigated. • Combination of catalytic experiments and DFT modelling applied. • Glycolic acid significantly impedes conversion of both acetic and propionic in mixtures. • At high coverage, carboxylic acids preferentially adsorbed into dimer structures. • Adsorption strength trends found via DFT modelling reflected the experimental results. Biorefinery-derived wastewater is considered a valuable source of energy and chemicals thanks to its organic loading. However, it is constituted by different compounds which influence the performance of a catalytic valorization process. In this work, we investigated the treatment of a synthetic hydrothermal liquefaction-derived wastewater (HTL-WW) via aqueous phase reforming (APR) to obtain hydrogen. As a case study, we examined the underlying driving forces for performance differences in the APR of mono- and bi-component solutions of carboxylic acids as a model corn stover HTL-WW over Pt catalysts via a combined experimental and theoretical approach. In mono-component solutions, the conversion ranked as glycolic acid > propionic acid ≈ acetic acid, and the same was found for the hydrogen production tendency. Binary solutions of glycolic and acetic acid, with different concentration among the constituents, showed a strong inhibition of the acetic acid reactivity due to the prevalent adsorption of glycolic acid on Pt surface. The results from the APR of acetic and propionic acid solutions were less affected by such phenomena. DFT results showed that there are strong, attractive lateral interactions between carboxylic acids due to intermolecular hydrogen bonding that cause all carboxylic acids to preferentially adsorb in dimer structures. The lateral interaction strength was determined for both pure and binary mixtures of carboxylic acid dimers, with results showing that pure mixtures of carboxylic acids have stronger attractions and that glycolic acid dimers see the strongest attractions due to the added terminal hydroxyl functional group. The findings presented herein offer significant insights into the utilization of APR for industrial-like multi-component solutions, as well as for any catalytic process involving small organic compounds in an aqueous phase. [ABSTRACT FROM AUTHOR]

• Compounds representatives of biorefinery streams were tested by APR. • Several molecules were investigated for the first time. • Binary and ternary mixtures were explored to evaluate collateral effects. • Acetic acid was found as a key intermediate/by-product of APR. An extensive screening of representative molecules of a post-hydrothermal process side stream has been performed with the aim of producing a gas mixture rich in hydrogen by catalytic aqueous phase reforming. The survey enlightens possible routes of valorisation of these by-products, scarcely investigated with other processes so far. The influence of reaction temperature was studied in the 230–270 °C range, looking at both the composition of the gas phase and the characterization of the liquid products. Indeed, the information coming from the condensed phase may provide relevant insights on the components that are not easily reformed, and that should be studied to improve the performance of the process. Binary and ternary mixtures of four selected compounds were tested to investigate synergistic and inhibiting effects, going towards the direction of a real biorefinery stream. The spent alumina-supported catalyst was characterized, outlining possible deactivation mechanisms of the catalytic system, and reused in two successive tests. [ABSTRACT FROM AUTHOR]