• Energy Research

Plastic nylon 66, ethylene-vinyl acetate (EVA) and polyvinyl chloride (PVC) were treated in subcritical water to produce value-added liquid chemicals and clean solid fuels. A synergistic effect was found in the co-treatment of PVC and the other two plastic polymers. Nylon 66 was totally decomposed to water-soluble oligomers with the reaction at 330 °C for 45 min. The same condition was required for the complete hydrolysis of EVA to produce acetic acid and deacetylated solid fuel. The activation energy for nylon 66 and EVA hydrolysis were 99.30 and 146.46 kJ/mol, respectively. However, a relatively low temperature (250 °C) was adequate for PVC dechlorination (efficiency >80%). The hydrochloric acid released from PVC worked as the acidic catalyst, which significantly accelerated the hydrolysis of nylon 66 and EVA, consequently more moderate reaction conditions (250 °C for 60 min) are required. Co-treatment of PVC with other polymers by subcritical water showed a great perspective.

Abstract Hydrothermal liquefaction (HTL) is a promising technology for the production of high quality bio- crude. Aim of this study is to investigate the effect of the addition of iron powder into the HTL process of oak wood biomass. Fe in HTL conditions should be oxidized by water into Fe3O4 producing H2 in situ which is responsible for the increase of bio-crude yield. Furthermore, the presence of Fe contributes to enhance bio-crude quality due to the presence of Fe3O4 which is recognized to have catalytic activity in hydrogenation reactions. Tests in presence of oxides containing Fe in higher oxidation number such as Fe3O4 and Fe2O3 were performed. The tests were conducted with water to biomass ratio of 5, in a range of temperature of 260–320 °C, the reaction time was set to 15 min and the catalysts were added in an amount of 10% with respect to the biomass weight. Highest bio-crude yields of about 40% were reached using zerovalent Fe. Tests performed in presence of Fe3O4 gave intermediate behaviour while no improvements were registered adding Fe2O3. These results confirmed the positive dual effect of Fe addition. In fact, the H/C ratio in the bio-oil increases of about 15% with respect to the reaction conducted without iron-based compounds and Gas Chromatography–Mass Spectrometry analyses showed that the presence of aliphatic compounds is improved.

Techno-economic analyses were conducted on an iron-assisted hydrothermal liquefaction (HTL) process for converting lignocellulosic biomass into gasoline, comparing two approaches for minimizing by-product streams. The primary difference between the two approaches lies in their hydrogen (H2) source for upgrading bio-crude to bio-gasoline. Scheme 1 utilizes residual water-soluble and gaseous compounds from the process to generate the H2 needed for upgrading. Scheme 2, on the other hand, converts these waste streams into heat to supply part of the required energy, while external H2 from steam methane reforming (with or without CO2 capture) or water electrolysis (green hydrogen) is used for upgrading. Both schemes use pinewood and red mud as feedstocks. Red mud, after the reduction of Fe2O3 3 to metallic iron, is employed in the HTL reactor as a hydrogen producer, enhancing both the yield and quality of the bio-crude while minimizing the H2 2 consumption in the upgrading unit. The HTL reactor was modeled based on optimal operating conditions experimentally determined while sensitivity analyses were performed on the other scheme's units to determine their optimal conditions. A Life Cycle Assessment (LCA) was also conducted to measure the environmental impact of the two scenarios. Both schemes produce 459 tonnes of gasoline equivalent per day, consuming 33 tonnes of H2. 2 . Scheme 2 achieves a minimum fuel selling price (MFSP) of $0.94 per liter of gasoline equivalent (LGE), with methane reforming and CO2 capture providing the lowest emissions (1.13 kg CO2-Eq per kg of LGE). Scheme 1 has a slightly higher MFSP of $0.96 per LGE but is more environmentally sustainable, with a LCA showing 1.11 kg CO2Eq per kg of LGE.

Gasification converts biomass into syngas; however, severe cleaning processes are necessary due to the presence of tars, particulates and contaminants. The aim of this work is to propose a cleaning method system based on tar physical adsorption coupled with the production of pure H2 via a chemical looping process. Three fixed-bed reactors with a double-layer bed (NiO/Al2O3 and Fe-based particles) working in three different steps were used. First, NiO/Al2O3 is used to adsorb tar from syngas (300 °C); then, the adsorbed tar undergoes partial oxidization by NiO/Al2O3 to produce CO and H2 used for iron oxide reduction. In the third step, the reduced iron is oxidized with steam to produce pure H2 and to restore iron oxides. A double-layer fixed-bed reactor was fed alternatively by guaiacol and as tar model compounds, air and water were used. High-thermal-stability particles 60 wt% Fe2O3/40 wt% MgO synthetized by the coprecipitation method were used as Fe-based particles in six cycle tests. The adsorption efficiency of the NiO/Al2O3 bed is 98% and the gas phase formed is able to partially reduce iron, favoring the reduction kinetics. The efficiency of the process related to the H2 production after the first cycle is 35% and the amount of CO is less than 10 ppm.

Abstract The biomass conversion into more valuable fuels represents one of the most viable routes for the exploitation of this material. Hydrothermal liquefaction is currently considered one of the most efficient processes to convert wet biomass into a bio-crude, which however requires expensive upgrading treatments to be used as biofuel. The use of catalysts able to directly improve bio-crude yield and quality during the reaction is of fundamental importance to increase the overall process efficiency. Homogeneous alkaline catalysts are the most studied, but they are not recoverable at the end of the process and so cannot be reused. The use of heterogeneous catalysts allows to overcome this issue making the recovery and reuse possible, maintaining anyway high activity and selectivity in the bio-crude production. The aim of this review is to critically summarize the effect of heterogenous catalyst addition on the hydrothermal liquefaction of lignocellulosic biomass, looking specifically at the improvement in bio-crude yield and quality. On the basis of literature data about the effect of heterogeneous catalyst addition on bio-crude yield and quality in the hydrothermal liquefaction of lignocellulosic biomass, a common catalytic action was identified allowing to group the several catalysts into four classes (alkaline metal oxides, transition metals, lanthanides oxides and zeolites). The hydrodeoxygenation activity of the catalysts, their effect on bio-crude yield and quality and the operating conditions used are highlighted. The highest bio-crude yields are reported using transition metals and lanthanide oxides which are able to guarantee, at the same time, a high-quality bio-crude.

Hydrothermal liquefaction of oak wood was carried out in tubular micro reactors at different temperatures (280-330 °C), reaction times (10-30 min), and catalyst loads (10-50 wt%) using metallic Ni catalysts. For the first time, to enhance the catalytic activity of Ni particles, a coating technique producing a nanostructured surface was used, maintaining anyway the micrometric dimension of the catalyst, necessary for an easier recovery. The optimum conditions for non-catalytic liquefaction tests were determined to be 330 °C and 10 min with the bio-crude yield of 32.88%. The addition of metallic Ni catalysts (Commercial Ni powder and nanostructured surface-modified Ni particle) increased the oil yield and inhibited the char formation through hydrogenation action. Nano modified Ni catalyst resulted in a better catalytic activity in terms of bio-crude yield (36.63%), thanks to the higher surface area due to the presence of flower-like superficial nanostructures. Also, bio-crude quality resulted improved with the use of the two catalysts, with a decrease of C/H ratio and a corresponding increase of the high heating value (HHV). The magnetic recovery of the catalysts and their reusability was also investigated with good results.

Abstract Steam iron process represents a technology for H2 production based on iron redox cycles. FexOy are reduced by syngas/carbon to iron, which is subsequently oxidized by steam to produce pure H2. However, the system shows low stability. In this work, the effect of promoters (Al2O3, MgO and CeO2) on FexOy stability is investigated (10 consecutive redox cycles). Bioethanol is used as a reducing agent. The particles are synthesized by coprecipitation method, analysed by BET, XRD, SEM and tested in a fixed bed reactor (675 °C, 1 bar). Pure H2 is obtained controlling the FexOy reduction degree feeding different amounts of ethanol (4.56–1.14 mmol) until no CO is detected in oxidation. The results show that the promoters not only improve the thermal stability of FexOy but also affect its redox activity and react with iron forming spinel structures. MgO led to the highest activity and cyclability (H2 = 0.15 NL; E = 35%).

Red mud, a main waste of aluminum industry containing high amount of Fe2O3 (20–30 %), was used for the first time post-reduction as iron source in the hydrothermal liquefaction (HTL) of pinewood; aiming to maximize bio-crude yield and quality, exploiting the Fe oxidation with water to produce in-situ H2. The red mud capacity to produce H2 was investigated reducing it with the hydrochar produced through HTL at 900 °C for 3h. Red mud catalytic activity in biomass decomposition reactions, attributed to the presence of Al2O3, TiO2, SiO2 etc., was also assessed testing the as-received (FRM) and calcinated (CRM, 900 °C-3h) samples. HTL tests were performed at 330 °C for 10 min, adding an amount of red mud containing 6 wt% of Fe with respect to the biomass. The reduced red mud (RRM) demonstrated the highest activity in the conversion of biomass into high quality bio-crude (yield of 49 wt%, HHV = 30.81 MJ/kg), acting both as H2 producer and as a catalyst. Furthermore, to minimize the process wastes, the recycle of water phase (WP) and the RRM was performed for 5 consecutive runs demonstrating the feasibility of the proposed process with a considerable increase of bio-crude yield (60 wt%) and quality (HHV = 30.89 MJ/kg).