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Close to 80% of hydrogen is currently produced through emissions-intensive natural gas reforming and coal gasification, with almost all the rest being by-product hydrogen produced in facilities designed for other products. To significantly contribute to the clean energy transition, it is critical to develop low-carbon hydrogen production routes that can replace current production and at the same time expand production capacity to meet new demands. The two main low-carbon production routes are Steam Methane Reforming coupled with CCUS (blue H2) or water electrolysis (green H2); however, a new path based on methane pyrolysis is becoming more and more interesting in the last years. This process involves producing H2 with solid carbon instead of CO2 (turquoise H2). The aim of this article is to present a new scheme for Hydrogen production through the cracking of methane using renewable energy. The process is based on a molten metal reactor where the main reaction takes place inside the liquid bath: the molten metal bath in fact enhances heat transfer and can facilitate carbon removal. A techno-economic assessment for distributed H2 is analysed and reported. Finally, methane cracking performances are compared to conventional H2 production processes. [ABSTRACT FROM AUTHOR]

Up to 80% of hydrogen production is currently carried out through CO2 emission-intensive natural gas reforming and coal gasification. Water-splitting electrolysis using renewable energy (green H2) is the only process that does not emit greenhouses gases, but it is a quite energy-demanding process. To significantly contribute to the clean energy transition, it is critical that low-carbon hydrogen production routes that can replace current production methods and can expand production capacity to meet new demands are developed. A new path, alternative to steam reforming coupled with CCS (blue H2) that is based on methane cracking, in which H2 production is associated with solid carbon instead of CO2 (turquoise H2), has received increasing attention recent years. The reaction takes place inside the liquid bath, a molten metal reactor. The aim of this article is to model the main kinetic mechanisms involved in the methane cracking reaction with molten metals. The model developed was validated using experimental data produced by the University of La Sapienza. Finally, such a model was used to scale up the reactor architecture. [ABSTRACT FROM AUTHOR]

Methane Cracking represents one of the most promising routes to CO2-free hydrogen production. The methane decomposition reaction is typically carried out in fixed or fluidized catalytic beds, where the metal catalyst is supported on porous ceramic particles. By proper choice of the metal catalyst, the catalytic reaction environment allows to obtain sizeable reaction rates at operating temperatures as low as 700°C. Besides, in solid catalytic beds, the catalyst is swiftly deactivated due to the massive (i.e. stoichiometric) deposition of the solid carbon product. One way to bypass carbon deposition is to use a molten metal bath (which may or may not contain catalytic metal components) as a reaction environment, where methane bubbles are introduced at the bottom of the bath and are progressively converted as they rise through the liquid metal. The key point of this process is that, owing to a large density difference between the solid carbon phase and the molten metal, the solid product of the reaction floats on top of the liquid metal and can be thus mechanically skimmed. In this article, we develop an analytical approach to the estimate of the bath height, which constitutes one of the most critical design parameters of the process. Specifically, based on the observation that in practical applications the reacting bubble is in the kinetics-controlled regime, we obtain the conversion vs time solution for a bubble of given initial size. On the assumption of ideal gaseous mixture behaviour, the knowledge of the conversion curves allows to estimate the bubble diameter as a function of time during the rise of the bubble through the molten metal. This piece of information is then post-processed to obtain the bubble motion as a function of time. The elimination of the time parameter between the two solutions allows to construct a conversion-height map for different diameters of the bubbles. [ABSTRACT FROM AUTHOR]

This paper reports the results obtained in a techno-economic analysis of the Steam Methane Reforming (SMR) technology aided with solar heat, developed and demonstrated in the European FCH JU project CoMETHy: a compact membrane reformer heated with molten salt up to 550 °C allowed to simultaneously carry out methane steam reforming, water-gas-shift reaction and hydrogen separation. This reactor can be integrated with new generation Concentrating Solar Thermal (CST) systems to supply the process heat. Experimental validation of the technology has been successfully achieved in a pilot scale plant and the results recently published. In this paper, we introduce a fully-integrated scheme and operation strategies of a plant on the 1500 Nm3/h hydrogen production scale. Then, techno-economic analysis of this new solar-driven process is presented to evaluate its competitiveness. Considering a plant capacity of 1500 Nm3/h (pure hydrogen production) and today's costs for the methane feed and the CST technology, obtained Hydrogen Production Cost (HPC) are in the range of 2.8–3.3 €/kg for a "solar-hybrid" system with high capacity factor (8000 h/year operation) and 4.7 €/kg for a "solar-only" case, while HPC≅1.7 €/kg can be obtained with the conventional route under equivalent assumptions. However, a sensitivity analysis shows that the expected drop of the cost of the CST technology will bring the HPC around 2.4 €/kg for the "solar-hybrid" case and close to 3.4 €/kg for the "solar-only" case, thus making the cost of solar reforming closer to conventional SMR with CO 2 capture and with wind/solar electrolysis in the future. In the "solar-hybrid" case total CO 2 production can be reduced by 13–29% with 58–70% of produced CO 2 recovered as pure stream (at 1.3 bar); in the "solar-only" case total CO 2 production can be reduced by 52% and 100% of produced CO 2 recovered as pure stream (at 1.3 bar). However, compared to the conventional route, CO 2 avoidance costs are still relatively high (≥137 €/ton CO2) and process optimization measures required. Therefore, optimization measures have been outlined to increase the overall process efficiency and further reduce the HPC. • Solar reforming achieved using membrane reactors heated with molten salts at 550 °C. • A solar reforming plant producing 1500 Nm3/h H 2 was designed and analyzed. • Operation modes were analyzed to continuously drive 24 h the solar reforming process. • H 2 production cost from solar reforming approaches the one from conventional routes. • Reforming driven by solar heat & power allows up to 79% reduction of CO2 emissions. [ABSTRACT FROM AUTHOR]

An innovative steam reformer for hydrogen production at temperatures lower than 550 °C has been developed in the EU project CoMETHy (Compact Multifuel-Energy To Hydrogen converter). The steam reforming process has been specifically tailored and re-designed to be combined with Concentrating Solar plants using "solar salts": a low-temperature steam reforming reactor was developed, operating at temperatures up to 550 °C, much lower than the traditional process (usually > 850 °C). This result was obtained after extensive research, going from the development of basic components (catalysts and membranes) to their integration in an innovative membrane reformer heated with molten salts, where both hydrogen production and purification occur in a single stage. The reduction of process temperatures is achieved by applying advanced catalyst systems and hydrogen selective Pd-based membranes. Process heat is supplied by using a low-cost and environmentally friendly binary NaNO 3 /KNO 3 liquid mixture (60/40 w/w) as heat transfer fluid; such mixture is commonly used for the same purpose in the concentrating solar industry, so that the process can easily be coupled with concentrating solar power (CSP) plants for the supply of renewable process heat. This paper deals with the successful operation and validation of a pilot scale reactor with a nominal capacity of 2 Nm3/h of pure hydrogen from methane. The plant was operated with molten salt circulation for about 700 h, while continuous operation of the reactor was achieved for about 150 h with several switches of operating conditions such as molten salts inlet temperature, sweep steam flow rate and steam-to-carbon feed ratio. The results obtained show that the membrane reformer allows to achieve twice as high a conversion compared to a conventional reformer operating at thermodynamic equilibrium under the same conditions considered in this paper. A highly pure hydrogen permeate stream was obtained (>99.8%), while the outlet retentate stream had low CO concentration (<2%). No macroscopic signs of reactor performance loss were observed over the experimental operation period. Image 1 • A "low-temperature" steam reforming reactor, operating up to 550 °C, was developed. • Catalysts and membranes integrated in a membrane reformer heated with molten salts. • The reformer can be combined with concentrated solar systems with heat storage. • A pilot solar reformer successfully validated with >2 Nm3/h pure H 2 production. • The compact reformer allowed hydrogen production and purification in one stage. [ABSTRACT FROM AUTHOR]

Waste conversion into valuable chemical products seems to be a good overcoming strategy both for the fossil fuel resources employment and for the current inefficient waste management. The main step related to the production of chemical from waste is its thermochemical conversion via gasification process. Taking into account the variable composition of waste and its high ash amount, among others, the high temperature melting gasifier is the most suitable system for ensuring the required flexibility. Indeed, besides syngas production, this system allows the melting of waste ash fraction in order to produce a vitrified and inert granular material. A simplified transient one-dimensional model of the oxidation zone including melting phenomenon could help in the understanding of process behavior. [ABSTRACT FROM AUTHOR]

Pd-based membrane reactors are strongly recognized as an effective way to boost H2 yield and natural gas (NG) conversion at low temperatures, compared to conventional steam reforming plants for hydrogen production, thereby representing a potential solution to reduce the energy penalty of such a process, while keeping the lower CO2 emissions. On the other hand, the exploitation of solar energy coupled with a membrane steam reformer can further reduce the environmental impact of these systems. On this basis, the paper deals with the design activities and experimentation carried out at a pilot level in an integrated prototype where structured catalysts and Pd-based membranes are arranged together and thermally supported by solar-heated molten salts for steam reforming reaction. [ABSTRACT FROM AUTHOR]

BACKGROUND Mixotrophic and heterotrophic growth of microalgae through biodegradation of olive mill wastewaters (OMW) is a promising strategy to improve the economic viability of microalgae production processes. However, OMW are characterized by an elevated phenols content, which makes their treatment by biological processes difficult. In this work, the influence of OMW phenols on microalgae growth was investigated by using the phenols extracted with a resin from OMW. RESULTS: OMW phenols, at 0.5 g L−1, were found to inhibit the growth of Scenedesmus sp. This inhibition was reduced by replacing an inoculum in the stationary phase with an inoculum in the exponential phase. Even with this strategy, a relevant negative effect (− 30%) on maximum cell concentration was found, which could be prevented by decreasing the phenol concentration to 0.1 g L−1. Under mixotrophic conditions, phenols reduced light penetration, limiting photosynthetic activity without significant improvement in phenols biodegradation. Under both mixotrophic and heterotrophic condition, percentage phenols removal up to 57% was achieved. CONCLUSIONS: The most promising strategy to achieve integrated microalgal cell growth and OMW phenols biodegradation is the heterotrophic cultivation with phenols concentration not greater than 0.1 g L−1 and an inoculum in exponential phase. © 2018 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Abstract: The implementation of a circular economy is a fundamental step to create a greater and more sustainable future for a better use of resources and energy. Wastes and in particular municipal solid waste represent an untapped source of carbon (and hydrogen) to produce a large range of chemicals from methane to alcohols (as methanol or ethanol) or urea. The waste to chemical process and related economics are assessed in this concept article to show the validity of such solution both from an economic point of view and from an environmental perspective considering the sensible reduction in greenhouse gas emissions with respect to conventional production from fossil fuels. [ABSTRACT FROM AUTHOR]

The waste-to-methanol (WtM) process and related economics are assessed to evidence that WtM is a valuable solution both from economic, strategic and environmental perspectives. Bio-methanol from Refuse-derived-fuels (RdF) has an estimated cost of production of about 110 €/t for a new WtM 300 t/d plant. With respect to waste-to-energy (WtE) approach, this solution allows various advantages. In considering the average market cost of methanol and the premium as biofuel, the WtM approach results in a ROI (Return of Investment) of about 29%, e.g. a payback time of about 4 years. In a hybrid scheme of integration with an existing methanol plant from natural gas, the cost of production becomes a profit even without considering the cap for bio-methanol production. The WtM process allows to produce methanol with about 40% and 30–35% reduction in greenhouse gas emissions with respect to methanol production from fossil fuels and bio-resources, respectively. [ABSTRACT FROM AUTHOR]

The economics and environmental impact of a new technology for the production of urea from municipal solid waste, particularly the residue-derived fuel (RdF) fraction, is analyzed. Estimates indicate a cost of production of approximately €135 per ton of urea (internal rate of return more than 10 %) and savings of approximately 0.113 tons of CH4 and approximately 0.78 tons of CO2 per ton of urea produced. Thus, the results show that this waste-to-urea (WtU) technology is both economically valuable and environmentally advantageous (in terms of saving resources and limiting carbon footprint) for the production of chemicals from municipal solid waste in comparison with both the production of urea with conventional technology (starting from natural gas) and the use of RdF to produce electrical energy (waste-to-energy). A further benefit is the lower environmental impact of the solid residue produced from RdF conversion. The further benefit of this technology is the possibility to realize distributed fertilizer production. [ABSTRACT FROM AUTHOR]

There are still constraints to algae-sourced biodiesel commercialization owing to the high cost and energy consumption of biomass cultivation and lipid extraction. The use of “low-cost” protic ILs based on tetramethylguanidinium and 1,8-diazabicyclo[5.4.0]undec-7-ene cations (some of them generated in situ by reaction of the corresponding bases with CO2 in the presence of methanol) for lipid extraction was assessed using Scenedesmus obliquus and compared to conventional methods. High extraction yields (up to 88% compared to conventional solvents, hexane–methanol) were obtained in most of the investigated ILs using wet microalgae (85% water). Furthermore, [HDBU][MeOCO2/HCO3] and [HTMG][MeOCO2/HCO3] resulted in the direct isolation of fatty acid methyl esters ((FAMEs)-biodiesel), formed in situ through transesterification/esterification reactions. [ABSTRACT FROM AUTHOR]

Recent research has been focused on methods to produce hydrogen. There is growing interest in the properties of hydrogen as an energy carrier and the prospects look good for hydrogen use in fuel cell applications, especially when production processes involve clean, renewable sources. Although natural gas steam reforming is the most common way to obtain hydrogen, ethanol steam reforming (ESR) may reduce the dependence on fossil fuels and cut harmful emissions. The ESR reaction is promoted at high temperatures, being strongly endothermic, but in some cases it can be performed at low temperatures, using this process as a pre-reforming step before conventional methane steam reforming (MSR). The low temperature range could reduce: the thermal duty, costs and CO formation, making the produced hydrogen capable of being fed into a fuel cell. The performances of Ni-based catalysts for ethanol steam reforming in a low temperature range (LT-ESR) were evaluated. In particular, the activity of bimetallic samples, prepared by impregnation and coprecipitation, was monitored in both diluted and concentrated feed stream conditions. By comparing bimetallic catalysts with monometallic ones prepared at different Pt or Ni loadings, it was possible to identify the most suitable sample. 3%wtPt / 10wt%Ni / CeO2 obtained by impregnation achieved the highest performances in terms of both H2 yield and durability, allowing perfect agreement with thermodynamic data. However, during stability tests, reaction plugging phenomena occurred. By changing the water-to-ethanol molar ratio from 3 to 6, a considerable increase in durability was observed. The investigation of exhaust catalysts through various characterization techniques was helpful for studying in detail possible sintering or deactivation occurrence. [ABSTRACT FROM AUTHOR]

The utilization of carbon dioxide (CO2) to produce methanol (to be used as energy vector and raw material for chemical production) in remote areas, where cheap renewable H2 could be produced from renewable sources, is a technology with a potential impact estimated to be more than 7 Gt CO2 equivalents. By using a techno-economic analysis, it is possible to evidence that methanol can be produced at competitive costs with respect to deriving energy from fossil fuels. This result, together with an analysis of the potential unexploited sources of renewable energy that are too far from users and grids, shows that the impact on the mitigation of climate change by this route is large, up to potentially 7 Gt CO2 equivalents, and at least comparable with that of carbon capture and storage (CCS). There are also advantages in terms of i) lower costs, ii) reduced impact on the environment, and iii) enhanced energy security. Further benefits are in terms of effective integration with the actual energy and chemical production value chains. The technology may be also used to store energy to solve the issue of generation intermittency present in most of the renewable energy sources. These aspects make this CO2 conversion path using renewable energy a potentially valuable approach to mitigate climate change and increase the use of renewable energy. [ABSTRACT FROM AUTHOR]