Progress on modeling and design of membrane reactors for hydrogen production

This paper presents an overview of recent research carried out by the authors on the development and analysis of mathematical models describing hydrogen production in membrane reactors. The case considered is that of methane steam reforming (SR) in a reactor with the typical double pipe configuration, in which a hydrogen-permeable membrane is present on the outer wall of the innermost tube. The model developed accounts for the rate of reaction, convective and dispersive transport in the axial and radial directions, and hydrogen permeation across the membrane. Density variations with pressure and gas composition have been accounted for, leading to a full coupling of mass and momentum transport. Different geometric aspect ratios have also been studied to assess the influence of catalyst volume on the overall performance of the system. The presence of two distinct transport regimes, in which hydrogen permeation is limited either by transport within the packed bed or permeation across the membrane, has been identified, along with the operating conditions that determine their range of existence. This has allowed the development of a simplified model, valid under the hypothesis that the reaction is fast compared to transport. In the permeation-controlled regime, the permeate flow rate and recovery may be found by solving a set of two PDEs, whereas an analytical solution is available for the transport-controlled regime. The main steps and observations that have brought to the development of the simplified model are presented, along with a guide to its implementatio

Modeling Fixed Bed Membrane Reactors for Hydrogen Production through Steam Reforming Reactions: A Critical Analysis

Membrane reactors for hydrogen production have been extensively studied in the past years due to the interest in developing systems that are adequate for the decentralized production of high-purity hydrogen. Research in this field has been both experimental and theoretical. The aim of this work is two-fold. On the one hand, modeling work on membrane reactors that has been carried out in the past is presented and discussed, along with the constitutive equations used to describe the different phenomena characterizing the behavior of the system. On the other hand, an attempt is made to shed some light on the meaning and usefulness of models developed with different degrees of complexity. The motivation has been that, given the different ways and degrees in which transport models can be simplified, the process is not always straightforward and, in some cases, leads to conceptual inconsistencies that are not easily identifiable or identified

Scale Down of Reforming Processes for Hydrogen Production from Renewable Sources

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Isopropyl alcohol vapour removal from diluted gaseous stream by adsorption: Experimental results and dynamic model

The gas phase adsorption of isopropyl alcohol (IPA) onto a commercial activated carbon at 30°C was investigated under different operating conditions. Fixed-bed experiments were performed to obtain equilibrium and kinetic data for IPA adsorption. The equilibrium data were fitted by means of the Langmuir equation and isotherm parameters were determined. A dynamic, isothermal, dilute solution adsorption model, based on the linear driving force (LDF) approximation, was developed to describe the kinetic adsorption behavior. A very good agreement between experimental and model results was found when a LDF mass-transfer-rate coefficient dependent on the gas concentration was used

A tunable microfluidic device toiInvestigate the influence of fluid-dynamics on polymer nanoprecipitation

Polymer drug-embedding nanocapsules are attracting increasing attention as effective tools for the targeted delivery of pharmaceutical molecules on specific biological tissues. Besides, it is well established that an effective selectivity of the delivery dictates that the size of the carrier particles be accurately controlled, thus maintaining the size dispersion of the particle population as low as possible. To this end, microfluidics-assisted precipitation provides a promising alternative to the traditional processes in that the structure of the flow - ultimately controlling the particle size distribution - can be reliably predicted from the solution of Navier-Stokes equations in the laminar regime. Notwithstanding the great potential provided by microfluidics techniques, much about the interaction between fluid-dynamics and polymer transport and precipitation is yet to be understood. In this work, we investigate polymer precipitation in a simple cross-junction inflow-outflow microchannel, which has proven a viable benchmark to gain insight into the physics of nanoprecipitation in that the particle size distribution is sensitively dependent on the flow operating conditions. Specifically, previous experimental work by some of these authors proved that average particle size can vary by an order of magnitude for operating conditions where the solvent flow rate varies by a factor of three, while keeping the non-solvent flow rate constant. The scope of this work is to show that such sensitive dependence on operating conditions finds direct correspondence in the kinematic structure of the flow, which undergoes abrupt qualitative changes in the same range of operating conditions, provided a fully three-dimensional solution of the incompressible Navier-Stokes equation (thus retaining the inertial term in momentum balance) is afforded

How does radial convection influence the performance of membrane module for gas separation processes?

A two-dimensional axial-symmetric isothermal model, based on full coupling between mass and momentum transport, has been developed to describe the separation of a binary gaseous mixture in a packed bed membrane module. Steady-state conditions have been studied. The gaseous mixture to be separated enters an annular gap between two co-axial cylinders. The inner wall of the outer cylinder is impermeable to both components, whereas a membrane, with infinite selectivity towards one of the components, is supported onto the outer wall of the inner cylinder. A radial flux of the permeating components is therefore present. The main focus was on the determination of the influence of radial convection on the performance of the separator, which has been analysed in terms of three dimensionless groups. Different transport regimes could be identified, corresponding to different values of the dimensionless groups. The impact of radial convection has been assessed by comparing model predictions with those of a fully uncoupled one-dimensional model. A discrepancy up to 20% of the recovery has been observed in industrially relevant ranges of the parameters

Power-to-methanol Process Plant Performances Under Uncertainty: Economic and Environmental Criticalities

The main goal of the current chemical and energy industry is to define innovative solutions and methodologies to meet the UE target concerning CO2 net zero emissions for 2050 or even negative in a long term perspective. In order to achieve this goal, during the last years the combined heat power and chemical (HPC) generation in chemical processes proved to be rather effective. However, although the use of renewables and bio-based materials allows to considerably reduce the processes environmental impact, their nature is characterized by uncertainties both in terms of availability and properties over the years seasons. In case these upstream deviations become relevant, the energy required to mitigate the disturbances should still be drawn by the electricity grid. In most of the countries, the electricity immitted in the grid is seldom obtained by renewable energy sources since it has the purpose to be stable and constantly available within a certain demand range. As a consequence, the process, whose initial purpose was to consume CO2, is actually a positive emission system due to the energy consumption aimed at compensating perturbations. In the light of these premises, in this research work the analysis of a power-to-methanol process under uncertainty is carried out according to the flexibility indexes based methodology proposed by Di Pretoro et al. (2019). The system is composed by an electrolysis section aimed at the production of green hydrogen and a cogeneration power plant fed by biomasses that provides CO2 for the methanol synthesis. Based on the characterization of the uncertainty related to the variable biomass nature over the year seasons and to renewable energy availability, this particular approach allows to quantify the system performances under of external perturbation in terms of costs and emissions for a given methanol demand. The obtained results provide a quantitative analysis of the power-to-methanol process behaviour and permits to synthesize the system flexibility by means of a single index and to correlate it with investment and operating costs as well as with the Greenhouse Warming Potential. This methodology enables then the decision maker to have more conscious expectations about the designed plant and could be used in further studies to adapt the system design to the expected deviation in order to have a more flexible process

Analysis on High Temperature Gasification for Conversion of RDF into Bio-Methanol

Municipal solid waste (MSW) is one of the residue materials considered as a potential source for biofuel production in the EU Renewable Energy Directive (RED), which establishes that a minimum of 10% biofuels for transport shall be used in every Member State by 2020, thus promoting advanced biofuel from waste. A high-temperature gasification technology transforms MSW into a syngas rich in hydrogen and carbon monoxide and free of tar, char and harmful compounds like dioxins appearing as a promising root for methanol production. The overall process including MSW high-temperature gasification, syngas purification and conditioning up to methanol synthesis has been modeled with Aspen Plus analyzing the influence of waste composition and operating conditions on syngas composition and methanol yield. The evaluation of CAPEX and OPEX has been carried out to obtain a cost of production (COP) estimation. The greenhouse gas (GHG) emission has also been estimated and compared with the conventional waste incineration process and methanol production. The technology assessment shows interesting results technically and economically, when compared with waste to energy processes: over 50% of incoming carbon is fixed into methanol molecule, and due to the negative cost paid for RDF disposal, the bio-methanol COP provides a reasonable industrial margin

Magnetoliposomes: envisioning new strategies for water decontamination

In this work, the inclusion of magnetic nanoparticles (MNPs) within phospholipid vesicles has been investigated as novel strategy for improving stability and reactivity of these nanoparticles and extending their potential use in the environmental field. Two phospholipids able to form liposomes characterized by different rigidity and stiffness, were used as potential carriers of MNPs. The magneto-responsive liposomes were investigated for their physicochemical and stability properties. In particular, the stability of the two systems was indirectly investigated evaluating the ability of the hybrid constructs to retain a fluorescent marker in their structure. Alterations in the permeability of the membranes were determined by the rate of the marker release from the liposomes, under both mechanical and thermal stress conditions