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Aviation is one of the sectors, within the transport industry, in respect of which engine electrification is more challenging to be applied. Therefore, it is crucial to develop and widen processes for production of aviation fuel starting from renewable sources. The "Waste to Sustainable Aviation Fuel" process fits this aim perfectly. The peculiarity and novelty of this process is the link between two worlds which usually work apart: the waste conversion sector and the petrochemical/chemical one. In this regard, the waste-to-chemical process is generally composed of different sections: high temperature gasification; syngas cleaning and cleaning; syngas purification; syngas conditioning; and final synthesis. The first section is the core of the process since it is a very flexible technology able to convert unsorted and/or non-recyclable waste into syngas, as well as demolition wood or other residual biomasses. Final synthesis can then follow two different paths: - methanol or ethanol; from both, SAF can be produced. Levelized of costs of methanol and ethanol coming from proposed process are highly competitive, thus leading to a competitive final SAF cost of production. SAF produced from methanol or ethanol coming from the proposed process are eligible for renewable content introduction in aviation sector, according to ReFuelEU directive which is under definition. Following mass balance approach, a fraction deriving from fossil carbon of waste is defined as Recycle Carbon Aviation Fuel, the other coming from biogenic carbon contained in residual materials - not food or feed related - is considered Advanced biofuel. The flexibility on feedstock related to the proposed technology allows to follow markets trends in relation to waste gate fee, residual biomasses cost, and relative market surplus recognized for advanced fraction.

Thermo-Catalytic decomposition (TCD) of methane can be regarded as a cornerstone towards the development of greenhouse gas-free processes for pure hydrogen production. Most studies of TCD focused on process schemes where the extraction of hydrogen from the gaseous CH 4 − H 2 mixture is accomplished in a unit separated from the reaction environment. In this article, we investigate numerically a different setup that involves the use of a semi-batch annular fixed-bed membrane reactor. The permeselective membrane allows to lower the reaction temperature, overcoming equilibrium limitations. The intrinsic time-dependency of the process (induced by catalyst deactivation due to massive deposition of the solid carbon product), together with spatial concentration gradients triggered by hydrogen permeation through the membrane give rise to a non-trivial dynamical behavior of the reactor. Specifically, we observe that a localized reaction front develops near the membrane at the early stage of the process. At later times, the front moves away from the membrane zone throughout the bed as larger and larger portions of the catalyst become inactive. The front thickness and dynamics are found to have a strong influence upon the overall timescales of the reaction. A dimensionless analysis of the dependence of the reactor efficiency on the pressure and on the catalyst activity (here quantified by the Damkohler number) is carried out by assuming 550 °C as a working temperature. An optimal working pressure is found at relatively high Damkohler value. Qualitatively different operating modes of the membrane reactor in different regions of the pressure-Damkohler parameter space are identified and interpreted.

Recent years have seen a growing interest in water electrolysis as a way to store renewable electric energy into chemical energy, through hydrogen production. However today the share of renewable energy is still limited and there is the need to have a continuous use of H2 for industrial chemicals applications. Firstly the paper discusses the use of electrolysis - connected to a conventional grid - for a continuous H2 production in terms of associated CO2 emissions and compares such emissions with conventional methane steam reforming (MSR). Therefore, it explores the possibility to use electrical methane steam reforming (eMSR) as a way to reduce the CO2 emissions. As a way to have zero emissions, carbon mineralization of CO2 is coupled - instead of in-situ carbon capture and storage technology (CCS) - to eMSR; associated relevant cost of production is evaluated for different scenarios. It appears that to minimize such production cost, carbonate minerals must be reused in the making of other industrial products, since the amount of carbonates generated by the process is quite significant.

Currently the production of methanol from Refuse Derived Fuel, a derived product of Municipal Solid Waste, can be deemed as an excellent example of circular economy, by representing a promising alternative both to conventional methods of waste disposal and methanol production from fossil resources. High-temperature conversion of waste in syngas is the main step of the Waste-to-Methanol process. Unfortunately, produced syngas does not directly comply with the requirements for methanol synthesis, in that syngas purification and conditioning steps are required. Moreover, waste, due to its heterogeneous nature, presents a variable composition, leading to the production of variable syngas flowrate and composition. A thermodynamic equilibrium model of gasification unit has been developed in Aspen Plus environment and applied to analyse the effects of feedstock variability; RDF composition has been characterized considering as main parameters: ash, moisture and combustible fractions, carbon to hydrogen and carbon to oxygen ratios, and Lower Heating Value. Then, a simplified simulation of downstream process has been introduced to evaluate the influence of waste composition on overall methanol production. The present study allows the identification of the main parameters affecting the syngas and, accordingly, overall process yield, consumptions and emissions.

A large amount of valuable Carbon and Hydrogen is lost in the disposal of the non-recyclable fraction of Municipal Solid Waste (MSW) – particularly unsorted waste fraction and plastics residue from mechanical recycle process. The waste-to-chemical technology allows to exploit the components entrapped in the non-recyclable waste by converting it into new chemicals. The core of waste-to-chemical technology is the gasification process, which is designed to convert waste into a valuable syngas to be used as example for methanol production. Waste to methanol schemes allow to achieve significant environmental and economic benefits, which can be further intensified within the scenario of increasing share of renewable energy.

The aim of this study is to provide a complete energy, economic and environmental analysis of a waste to chemical process that treats a feed mixture composed of Refused Derived Fuel and Plasmix, transforming it into syngas. The process was implemented in the Aspen Plus® simulation environment, where also a sensitivity analysis returning the maximum value of humidity allowable in three different scenarios of waste mixture has been carried out. Moreover, an economic analysis has been performed in which, on the basis of capital expenditure, operating costs and revenues of the plant, Net Present Value (NPV) and Internal Rate of Return (IRR) has been assessed, finding a value of 599 M€ and 28% respectively. Finally, environmental analysis has been performed; a comparison between the carbon dioxide emissions of the case “as it is now” versus “how it could be” with the waste to chemical process implemented has been carried out in which it was calculated a saving of around 581 kt/y of CO2 emitted in the atmosphere.

The energy transition toward more sustainable production systems is currently one of the most urgent goals of the worldwide community. Carbon footprint reduction within main industry sectors may be achieved by implementing carbon capture and utilization technology as well as by substituting conventional fossil feedstock with more sustainable ones. In this scenario, the circular economy model promoting the reuse of material instead of the disposal would allow for a better use of resources and energy. Wastes having a high heating value, in particular municipal solid waste, refuse-derived fuel, and plastic waste, may be considered a precious source of carbon to be used in substitution of conventional fossil sources. Through a gasification technology working under a high-temperature and pure oxygen environment, waste may be converted into a syngas rich in H2 and CO and thus suitable to work as intermediate of a new green chemistry model. Sustainable production of chemicals such as biomethanol, bioethanol, biomethane, as well as biopolymers may be achieved from waste sources once properly converted into syngas. The waste-to-chemical approach is a valid alternative to the waste-to-energy route, allowing for a reuse of carbon into a useful end product instead of downgrading to diluted CO2 discharged as flue gas. The synergy between two different industries, waste management and the chemical industry, may account for a strategic solution in line with the principles of a circular economy and is sustainable from technical and economical points of view, as shown by two case studies here analyzed.

We investigate numerically the homogenization process of a diffusive species in a mixing channel of arbitrary length downstream a microfluidic cross-junction. The channel length, λ α , necessary to achieve a prescribed level of mixedness, α , is targeted as primary quantity of interest, and its dependence on the Reynolds number, Re , on the flow ratio between the impinging currents, R, and on the Schmidt number of the solute, Sc , is analyzed. The accurate numerical solution of the mass transport equations up to values Pe = Re Sc ≃ 10 6 of the Peclet number is here made possible by a hybrid numerical approach. This approach combines a recently proposed Monte Carlo method, enforced near the impinging zone, with a pseudo-transient 2D formulation of mass transport in the mixing channel, where purely axial (Poiseuille) flow settles in. At values of the flow ratio significantly different from unity (e.g. those used in flash nanoprecipitation) a non-trivial dependence of λ α on Re is found at fixed Sc and R. This result is interpreted based on the spectral (eigenvalue/eigenfunction) structure of the 2D generalized Sturm-Liouville pure diffusion problem defined onto the cross-section of the mixing channel. Hinging on this interpretation, we show that for Sc ⩾ 10 3 the dependence of λ α on Sc at fixed Re and R can be singled out and theoretically predicted. By this property, universal ready-to-use curves yielding the mixing length for each assigned geometry can be constructed, which could be used to correlate the mixing time with other phenomena (chemical reactions, phase changes) occurring alongside the mass transport.

Mixing of a diffusing species entrained in a three-dimensional microfluidic flow-focusing cross-junction is numerically investigated at low Reynolds numbers, $$1 \le Re \le 150$$ , for a value of the Schmidt number representative of a small solute molecule in water, $$Sc = 10^3$$ . Accurate three-dimensional simulations of the steady-state incompressible Navier–Stokes equations confirm recent results reported in the literature highlighting the occurrence of different qualitative structures of the flow geometry, whose range of existence depends on Re and on the ratio, R, between the volumetric flowrates of the impinging currents. At low values of R and increasing Re, the flux tube enclosing the solute-rich stream undergoes a topological transition, from the classical flow-focused structure to a multi-branched shape. We here show that this transition causes a nonmonotonic behavior of mixing efficiency with Re at constant flow ratio. The increase in efficiency is the consequence of a progressive compression of the cross-sectional diffusional lengthscale, which provides the mechanism sustaining the transversal Fickian flux even when the Peclet number, $${Pe=Re \, Sc}$$ , characterizing mass transport, becomes higher due to the increase in Re. The quantitative assessment of mixing efficiency at the considerably high values of the Peclet number considered ( $$10^3 \le Pe \le 1.5 \times 10^5$$ ) is here made possible by a novel method of reconstruction of steady-state cross-sectional concentration maps from velocity-weighted ensemble statistics of noisy trajectories, which does away with the severe numerical diffusion shortcomings associated with classical Eulerian approaches to mass transport in complex 3d flows.