Viable Recycling of Polystyrene via Hydrothermal Liquefaction and Pyrolysis

Chemical recycling is considered one of the most sustainable solutions to limit the environmental issues related to plastic waste pollution, whereby plastic is converted into more valuable compounds when mechanical recycling is not feasible. Among the most critical fast-growing components of municipal solid waste, polystyrene represents 1/3 of the filling materials in landfills. In this work, the chemical recycling of polystyrene via two main thermochemical processes is investigated: pyrolysis and hydrothermal liquefaction (HTL). The influence of temperature (HTL: 300-360 & DEG;C and pyrolysis: 400-600 & DEG;C) and reaction time (HTL: 1-4 h; pyrolysis: 30 min) on the products obtained was studied. The obtained liquid and solid products were analyzed by using gas chromatography-mass spectrometry (GC-MS), an elemental analysis (EA), Fourier-transform infrared spectroscopy (FT-IR) and a thermogravimetric analysis (TGA). During HTL, a temperature of 360 & DEG;C and reaction time of 4 h were needed to completely decompose the polystyrene into mainly oil (83%) and water-soluble compounds (10%). The former was mainly composed of aromatics while the water phase was mainly composed of aromatics and oxygenated compounds (benzaldehyde and acetophenone). The pyrolysis led to the formation of 45% gas and 55% oil at 500 & DEG;C, and the oil was 40% styrene. Pyrolysis was thus more selective towards the recovery of the styrene monomer while the HTL can be an effective process to produce renewable aromatics

Simulation on hydrothermal liquefaction of pinewood to produce bio-crude in a zero-waste process scheme

Hydrothermal liquefaction (HTL) is one of the advanced biomass conversion technologies to produce bio-crude from wet lignocellulosic feedstocks. Hydrochar and water phase containing organics are always generated as by-products and their efficient re-use could be fundamental to decrease the whole energy consumption. Hydrogen producers like Fe are often added to the HTL reactor to maximize the bio-crude yields and quality. Furthermore, Fe can be easily recovered from the biochar at the end of the reaction and re-used, after a reduction treatment. In this work, the feasibility to produce bio-crude through HTL of pinewood in a continuous zero-waste process scheme is evaluated in an Aspen Plus® simulation. The zero- waste configuration was carried out using the water phase containing organics instead of distillate water in the HTL reactor and the hydrochar as renewable reductant of iron oxides. Experimental data were used to model the HTL (Ryield) while the iron oxide reduction and the combustion of the side streams were simulated in the Gibbs reactor (Rgibbs). Red mud, a waste stream of the Bayern process for aluminium production, containing 50 wt % of hematite (Fe2O3), was selected as low-cost iron source. The iron oxides reduction with hydrochar was performed at different temperature (400-1200 °C) to determine the optimal value (complete conversion to Fe). Based on the simulation results, hydrochar allows the complete red mud reduction at 780 °C but the separation of the carbon excess before Fe recirculation must be considered. The proposed continuous zero-waste HTL plant consumed a total energy of 5080 J s-1, mostly of it related to the HTL (4945 J s-1) and iron oxide reduction (640.2 J s-1). However, the combustion of both off gases and hydrochar excess can approximately provide the heat needed to plant (-5012 J s-1). Finally, the results demonstrated that the proposed HTL scheme might be a zero-waste process in terms of both mass and energy flows

Pure hydrogen production by steam-iron process. The synergic effect of MnO2 and Fe2O3

In the energy transition from fossil to clean fuels, hydrogen plays a key role. Proton-exchange membrane fuel cells (PEMFCs) represent the most promising hydrogen application, but they require a pure hydrogen stream (CO < 10 ppm). The steam iron process represents a technology for the production of pure H2, exploiting iron redox cycles. If renewable reducing agents are used, the process can be considered completely green. In this context, bio-ethanol can be an interesting solution that is still not thoroughly explored. In this work, the use of ethanol as a reducing agent in the steam iron process will be investigated. Ethanol, at high temperature, decomposes mainly in syngas but can also form coke, which can compromise the process effectiveness, reacting with water and producing CO together with H2. In this work, the deposition of coke is avoided by controlling the duration of the reduction step; in fact, the data demonstrated that coke deposition is significantly dependent on reduction time. Tests were carried out in a fixed bed reactor using hematite (Fe2O3) as raw iron oxide adopting several reduction times (7 minutes-25 minutes), which correspond to different amount of ethanol fed (5 mmolC2H5OH/gFe2O3-17,95 mmolC2H5OH/gFe2O3). The effect of the addition of MnO2 to increase the reduction degree of iron oxides was explored using different amount of MnO2 (10 wt% and 40 wt% with respect to Fe2O3). The tests were performed at fixed temperatures of 675°C and atmospheric pressure. The optimization of the reduction time, in the chosen operating condition, performed only with Fe2O3, shows that, feeding an amount of 5 mmolC2H5OH/gFe2O3, coke deposition is avoided and, therefore, a pure H2 stream in oxidation is obtained. The addition of MnO2 leads to increased H2 yield and process efficiency, confirming its positive effect on the reduction degree of the solid bed. A reaction pathway to demonstrate the synergic effect of Fe2O3 and MnO2 in the reduction step was proposed in this article

Green hydrogen production using doped Fe2O3 foams

This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).Hydrogen is the ideal energy vector to reduce our fossil-fuels dependency and diminish the climate change consequence. However, current production is still methane based. It is possible to produce hydrogen using bioethanol from the alcoholic fermentation of organic waste by chemical looping processes, but unfortunately current redox systems generate hydrogen with significant traces of CO. In the case of proton exchange membrane fuel cells (PEMFC), hydrogen must be highly purified to produce electricity. Here, high porosity interconnected Fe2O3 foams doped with 2 wt% Al2O3 were manufactured by the freeze-casting method, obtaining around 5.1 mmol H2 g1 sample of highly pure hydrogen (<10 ppm of CO) consuming only 3.42 mmol of ethanol on each redox cycles, with no deactivation. This result shows the possibility of using an abundant and inexpensive raw material as the iron oxide to scale-up the direct pure H2 production and facilitates its use in the automotive secto

Simulation on Hydrothermal Liquefaction of Pinewood to Produce Bio-Crude in a Zero-Waste Process Scheme

Hydrothermal liquefaction (HTL) is one of the advanced biomass conversion technologies to produce bio-crude from wet lignocellulosic feedstocks. Hydrochar and water phase containing organics are always generated as by-products and their efficient re-use could be fundamental to decrease the whole energy consumption. Hydrogen producers like Fe are often added to the HTL reactor to maximize the bio-crude yields and quality. Furthermore, Fe can be easily recovered from the biochar at the end of the reaction and re-used, after a reduction treatment. In this work, the feasibility to produce bio-crude through HTL of pinewood in a continuous zero-waste process scheme is evaluated in an Aspen Plus® simulation. The zero- waste configuration was carried out using the water phase containing organics instead of distillate water in the HTL reactor and the hydrochar as renewable reductant of iron oxides. Experimental data were used to model the HTL (Ryield) while the iron oxide reduction and the combustion of the side streams were simulated in the Gibbs reactor (Rgibbs). Red mud, a waste stream of the Bayern process for aluminium production, containing 50 wt % of hematite (Fe2O3), was selected as low-cost iron source. The iron oxides reduction with hydrochar was performed at different temperature (400-1200 °C) to determine the optimal value (complete conversion to Fe). Based on the simulation results, hydrochar allows the complete red mud reduction at 780 °C but the separation of the carbon excess before Fe recirculation must be considered. The proposed continuous zero-waste HTL plant consumed a total energy of 5080 J s-1, mostly of it related to the HTL (4945 J s-1) and iron oxide reduction (640.2 J s-1). However, the combustion of both off gases and hydrochar excess can approximately provide the heat needed to plant (-5012 J s-1). Finally, the results demonstrated that the proposed HTL scheme might be a zero-waste process in terms of both mass and energy flows

Overview of the FTU results

Since the 2018 IAEA FEC Conference, FTU operations have been devoted to several experiments covering a large range of topics, from the investigation of the behaviour of a liquid tin limiter to the runaway electrons mitigation and control and to the stabilization of tearing modes by electron cyclotron heating and by pellet injection. Other experiments have involved the spectroscopy of heavy metal ions, the electron density peaking in helium doped plasmas, the electron cyclotron assisted start-up and the electron temperature measurements in high temperature plasmas. The effectiveness of the laser induced breakdown spectroscopy system has been demonstrated and the new capabilities of the runaway electron imaging spectrometry system for in-flight runaways studies have been explored. Finally, a high resolution saddle coil array for MHD analysis and UV and SXR diamond detectors have been successfully tested on different plasma scenarios

Heterogeneous catalysts for hydrothermal liquefaction of lignocellulosic biomass. A review

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

The role of Al2O3, MgO and CeO2 addition on steam iron process stability to produce pure and renewable hydrogen

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%)

Clean syngas and hydrogen co-production by gasification and chemical looping hydrogen process using MgO-Doped Fe2O3 as redox material

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 H-2 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 degrees C); then, the adsorbed tar undergoes partial oxidization by NiO/Al2O3 to produce CO and H-2 used for iron oxide reduction. In the third step, the reduced iron is oxidized with steam to produce pure H-2 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 H-2 production after the first cycle is 35% and the amount of CO is less than 10 ppm

High thermal stability fe system to produce renewable pure hydrogen in steam iron process

The use of H2 as fuel of the future is closely linked to the development of Fuel Cells, among them Proton Exchange Membrane Fuel Cells (PEMFCs) are the most attractive. To avoid the irreversible poisoning of the platinum-based catalyst placed on the PEMFC electrodes, pure H2(CO &lt; 10 ppm) is required. Steam iron process (SIP) is a cyclical process which allows, at high temperature and low pressure, the direct production of pure H2 by redox cycles of iron. Syngas is generally used as reducing agent while steam water is used to oxidize iron and to produce pure H2. However, iron oxides powders suffer from deactivation in few redox cycles due to their low thermal stability. The aim of this study is to improve iron oxides resistance adding Al2O3 as high thermal stability material. Bioethanol is used as renewable sources of syngas to makes the process totally sustainable. To evaluate the effect of Al2O3 addition, different Fe2O3 / Al2O3 ratios were tested (40 wt%, 10 wt%, 5 and 2 wt%). The stability of the synthetized particles was evaluated with 10 redox cycles comparing the results with that of commercial Fe2O3 powders. Al2O3 does not behave as inert material in the process but it actively participates in the reduction step, catalysing coke formation due its acidity. With the sample 98 wt% Fe2O3-2 wt% Al2O3 the best performances in terms of particles stability and hydrogen purity were obtained