Micro and micro membrane reactors for advanced applications in chemical energy conversion

Future Power Train Solutions for Long-Haul Trucks

Achieving the CO2 reduction targets for 2050 requires extensive measures being undertaken in all sectors. In contrast to energy generation, the transport sector has not yet been able to achieve a substantive reduction in CO2 emissions. Measures for the ever more pressing reduction in CO2 emissions from transportation include the increased use of electric vehicles powered by batteries or fuel cells. The use of fuel cells requires the production of hydrogen and the establishment of a corresponding hydrogen production system and associated infrastructure. Synthetic fuels made using carbon dioxide and sustainably-produced hydrogen can be used in the existing infrastructure and will reach the extant vehicle fleet in the medium term. All three options require a major expansion of the generation capacities for renewable electricity. Moreover, various options for road freight transport with light duty vehicles (LDVs) and heavy duty vehicles (HDVs) are analyzed and compared. In addition to efficiency throughout the entire value chain, well-to-wheel efficiency and also other aspects play an important role in this comparison. These include: (a) the possibility of large-scale energy storage in the sense of so-called ‘sector coupling’, which is offered only by hydrogen and synthetic energy sources; (b) the use of the existing fueling station infrastructure and the applicability of the new technology on the existing fleet; (c) fulfilling the power and range requirements of the long-distance road transport.

Latest Developments in Membrane (Bio)Reactors

The integration of membranes inside a catalytic reactor is an intensification strategy to combine separation and reaction steps in one single physical unit. In this case, a selective removal or addition of a reactant or product will occur, which can circumvent thermodynamic equilibrium and drive the system performance towards a higher product selectivity. In the case of an inorganic membrane reactor, a membrane separation is coupled with a reaction system (e.g., steam reforming, autothermal reforming, etc.), while in a membrane bioreactor a biological treatment is combined with a separation through the membranes. The objective of this article is to review the latest developments in membrane reactors in both inorganic and membrane bioreactors, followed by a report on new trends, applications, and future perspectives.

Dynamically Operated Fischer–Tropsch Synthesis in PtL—Part 2: Coping with Real PV Profiles

Climate change calls for a paradigm shift in the primary energy generation that comes with new challenges to store and transport energy. A decentralization of energy conversion can only be implemented with novel methods in process engineering. In the second part of our work, we took a deeper look into the load flexibility of microstructured Fischer–Tropsch synthesis reactors to elucidate possible limits of dynamic operation. Real data from a 10 kW photovoltaic system is used to calculate a dynamic H2 feed flow, assuming that electrolysis is capable to react on power changes accordingly. The required CO flow for synthesis could either originate from a constantly operated biomass gasification or from a direct air capture that produces CO2; the latter is assumed to be dynamically converted into synthesis gas with additional hydrogen. Thus two cases exist, the input is constantly changing in syngas ratio or flow rate. These input data were used to perform challenging experiments with the pilot scale setup. Both cases were compared. While it appeared that a fluctuating flow rate is tolerable for constant product composition, a coupled temperature-conversion relationship model was developed. It allows keeping the conversion and product distribution constant despite highly dynamic feed flow conditions.

Dynamically Operated Fischer-Tropsch Synthesis in PtL-Part 1: System Response on Intermittent Feed

Society is facing serious challenges to reduce CO2 emissions. Effective change requires the use of advanced chemical catalyst and reactor systems to utilize renewable feedstocks. One pathway to long-term energy storage is its transformation into high quality, low-emission and CO2-neutral fuels. Performance of technologies such as the Fischer-Tropsch reaction can be maximized using the inherent advantages of microstructured packed bed reactors. Advantages arise not only from high conversion and productivity, but from its capability to resolve the natural fluctuation of renewable sources. This work highlights and evaluates a system for dynamic feed gas and temperature changes in a pilot scale Fischer-Tropsch synthesis unit for up to 7 L of product per day. Dead times were determined for non-reactive and reactive mode at individual positions in the setup. Oscillating conditions were applied to investigate responses with regard to gaseous and liquid products. The system was stable at short cycle times of 8 min. Neither of the periodic changes showed negative effects on the process performance. Findings even suggest this technology’s capability for effective, small-to-medium-scale applications with periodically changing process parameters. The second part of this work focuses on the application of a real-time photovoltaics profile to the given system.

Pd-Based Membranes: Overview and Perspectives

Palladium (Pd)-based membranes have received a lot of attention from both academia and industry thanks to their ability to selectively separate hydrogen from gas streams. Integration of such membranes with appropriate catalysts in membrane reactors allows for hydrogen production with CO₂ capture that can be applied in smaller bioenergy or combined heat and power (CHP) plants, as well as in large-scale power plants. Pd-based membranes are, therefore, regarded as a Key Enabling Technology (KET) to facilitate the transition towards a knowledge-based, low carbon and resource-efficient economy. This Special Issue of the journal Membranes on “Pd-based Membranes: Overview and Perspectives” contains nine peer-reviewed articles. Topics include manufacturing techniques, understanding of material phenomena, module and reactor design, novel applications, and demonstration efforts and industrial exploitation.

Intensified LOHC-Dehydrogenation Using Multi-Stage Microstructures and Pd-Based Membranes

Liquid organic hydrogen carriers (LOHC) are able to store hydrogen stably and safely in liquid form. The carrier can be loaded or unloaded with hydrogen via catalytic reactions. However, the release reaction brings certain challenges. In addition to an enormous heat requirement, the released hydrogen is contaminated by traces of evaporated LOHC and by-products. Micro process engineering offers a promising approach to meet these challenges. In this paper, a micro-structured multi-stage reactor concept with an intermediate separation of hydrogen is presented for the application of perhydro-dibenzyltoluene dehydrogenation. Each reactor stage consists of a micro-structured radial flow reactor designed for multi-phase flow of LOHC and released hydrogen. The hydrogen is separated from the reactors’ gas phase effluent via PdAg-membranes, which are integrated into a micro-structured environment. Separate experiments were carried out to describe the kinetics of the reaction and the separation ability of the membrane. A model was developed, which was fed with these data to demonstrate the influence of intermediate separation on the efficiency of LOHC dehydrogenation.

Experimental Evaluation of a Membrane Micro Channel Reactor for Liquid Phase Direct Synthesis of Hydrogen Peroxide in Continuous Flow Using Nafion® Membranes for Safe Utilization of Undiluted Reactants

In recent years, various modular micro channel reactors have been developed to overcome limitations in challenging chemical reactions. Direct synthesis of hydrogen peroxide from hydrogen and oxygen is a very interesting process in this regard. However, the complex triphasic process (gaseous reactants, reaction in liquid solvent, solid catalyst) still holds challenges regarding safety, selectivity and productivity. The membrane micro reactor system for continuous liquid phase H2O2 direct synthesis was designed to reduce safety issues by separate dosing of the gaseous reactants via a membrane into a liquid-flow channel filled with a catalyst. Productivity is increased by enhanced mass transport, attainable in micro channels and by multiple re-saturation of the liquid with the reactants over the length of the reaction channel. Lastly, selectivity is optimized by controlling the reactant distribution. The influence of crucial technical features of the design, such as micro channel geometry, were studied experimentally in relationship with varying reaction conditions such as residence time, pressure, reactant ratio and solvent flow rate. Successful continuous operation of the reactor at pressures up to 50 bars showed the feasibility of this system. During the experiments, control over the reactant ratio was found to be crucial in order to maximize product yield. Thereby, yields above 80% were achieved. The results obtained are the key elements for future development and optimization of this reactor system, which will hopefully lead to a breakthrough in decentralized H2O2 production.

Recent Developments in Compact Membrane Reactors with Hydrogen Separation

Hydrogen production and storage in small and medium scale, and chemical heat storage from renewable energy, are of great interest nowadays. Micro-membrane reactors for reforming of methane, as well as for the dehydrogenation of liquid organic hydrogen carriers (LOHCs), have been developed. The systems consist of stacked plates with integrated palladium (Pd) membranes. As an alternative to rolled and electroless plated (Pd) membranes, the development of a cost-effective method for the fabrication of Pd membranes by suspension plasma spraying is presented.

Micropatterned Ultrathin MOF Membranes with Enhanced Molecular Sieving Property

Metal-organic frameworks (MOFs) are attractive crystalline materials for membranes due to their diverse crystalline pore structures and molecular separation properties. However, the fabrication cost is relatively high compared to conventional polymeric membranes. The concern of the cost could be eased if they are part of a value-added device, for example, as the key separation unit in a lab-on-a-chip device. This study demonstrates the feasibility of miniaturization of MOF membranes by patterning the membrane surface, a necessary step for MOF membranes to be used in compact devices. Water-stable ultrathin UiO-66 membranes with a thickness down to 250 nm on a substrate with a complex pattern were grown. The patterned membranes showed a 100 % improvement in the apparent permeation flux over conventional flat-UiO-66 membranes without compromising the molecular separation property, indicating the complexity of a surface would not be a formidable obstacle to the MOF membrane fabrication.

Production of Hydrogen by Methane Steam Reforming Coupled with Catalytic Combustion in Integrated Microchannel Reactors

This paper addresses the issues related to the rapid production of hydrogen from methane steam reforming by means of process intensification. Methane steam reforming coupled with catalytic combustion in thermally integrated microchannel reactors for the production of hydrogen was investigated numerically. The effect of the catalyst, flow arrangement, and reactor dimension was assessed to optimize the design of the system. The thermal interaction between reforming and combustion was investigated for the purpose of the rapid production of hydrogen. The importance of thermal management was discussed in detail, and a theoretical analysis was made on the transport phenomena during each of the reforming and combustion processes. The results indicated that the design of a thermally integrated system operated at millisecond contact times is feasible. The design benefits from the miniaturization of the reactors, but the improvement in catalyst performance is also required to ensure the rapid production of hydrogen, especially for the reforming process. The efficiency of heat exchange can be greatly improved by decreasing the gap distance. The flow rates should be well designed on both sides of the reactor to meet the requirements of both materials and combustion stability. The flow arrangement plays a vital role in the operation of the thermally integrated reactor, and the design in a parallel-flow heat exchanger is preferred to optimize the distribution of energy in the system. The catalyst loading is an important design parameter to optimize reactor performance and must be carefully designed. Finally, engineering maps were constructed to design thermally integrated devices with desired power, and operating windows were also determined.

Review of Supported Pd-Based Membranes Preparation by Electroless Plating for Ultra-Pure Hydrogen Production

In the last years, hydrogen has been considered as a promising energy vector for the oncoming modification of the current energy sector, mainly based on fossil fuels. Hydrogen can be produced from water with no significant pollutant emissions but in the nearest future its production from different hydrocarbon raw materials by thermochemical processes seems to be more feasible. In any case, a mixture of gaseous compounds containing hydrogen is produced, so a further purification step is needed to purify the hydrogen up to required levels accordingly to the final application, i.e., PEM fuel cells. In this mean, membrane technology is one of the available separation options, providing an efficient solution at reasonable cost. Particularly, dense palladium-based membranes have been proposed as an ideal chance in hydrogen purification due to the nearly complete hydrogen selectivity (ideally 100%), high thermal stability and mechanical resistance. Moreover, these membranes can be used in a membrane reactor, offering the possibility to combine both the chemical reaction for hydrogen production and the purification step in a unique device. There are many papers in the literature regarding the preparation of Pd-based membranes, trying to improve the properties of these materials in terms of permeability, thermal and mechanical resistance, poisoning and cost-efficiency. In this review, the most relevant advances in the preparation of supported Pd-based membranes for hydrogen production in recent years are presented. The work is mainly focused in the incorporation of the hydrogen selective layer (palladium or palladium-based alloy) by the electroless plating, since it is one of the most promising alternatives for a real industrial application of these membranes. The information is organized in different sections including: (i) a general introduction; (ii) raw commercial and modified membrane supports; (iii) metal deposition insights by electroless-plating; (iv) trends in preparation of Pd-based alloys, and, finally; (v) some essential concluding remarks in addition to futures perspectives.

Insight into the adsorption of a liquid organic hydrogen carrier, perhydro-i-dibenzyltoluene (i = m, o, p), on Pt, Pd and PtPd planar surfaces

Liquid organic hydrogen carrier (LOHC) interaction with a planar surface of a catalyst.