A novel jet-enhanced fixed tube array reactor is developed to improve CO selective methanation (CO-SMET) performance under varying operating conditions. Based on the field synergy principle for process intensification, a single jet-tube reactor configuration is first optimized via numerical simulations by adjusting the axial/circumferential jet-hole arrangements to improve flow and heat transfer characteristics. As a result, significantly higher convective heat transfer coefficient is obtained, while the maximum temperature rise is reduced by 85.0% compared to a conventional fixed-bed plug flow reactor. Next, a tube-array reactor with two-stage distributors and 19 jet tubes achieves enhanced gas distribution uniformity, exhibiting inlet velocity deviations below 0.83%. Optimal CO activity and selectivity occur at ∼2 vol.% CO and moderate velocities, while higher concentrations or temperatures favor CO₂ methanation. In the case of the inlet CO concentration of 0.1 vol.% and the reaction temperature of 473.15 K, the outlet CO concentrations range from 79 to 93 ppm, with CO selectivity up to 66.9% and negligible thermal rise (< 0.13 K), i.e. it effectively achieved desirable CO removal while suppressed hotspot due to CO₂ methanation. The proposed reactor design provides an effective approach for high-efficiency CO removal in hydrogen purification and synthetic fuel production.

In this cross-disciplinary perspective paper we focus on the relevance of process intensification (PI) for space exploration. We review past and current space-related research involving technologies from all four elementary domains of process intensification. We point out other PI technologies which have not yet been the subject of space-related research but may offer interesting new opportunities and help overcome certain challenges in space missions. Given the commonality of concepts and approaches, as well as the fact that both process intensification and space engineering address basically the same issues – equipment miniaturization and increased process efficiency, we advocate for more intensive interactions between both scientific communities to benefit from cross-fertilization and the exchange of new ideas and experiences.

This paper investigates the validity of azimuthal averaging of 3D temperature fields in the analysis of lateral heat transfer in dense particle packings. This is conducted by synthetic generation of 3D packing surrogates of spheres, cylinders and Raschig rings with tube-to-pellet diameter ratio, 3 < N < 6, using an in-house Rigid Body Dynamics packing algorithm, followed by detailed discrete pellet CFD simulations of heat transfer from wall to bed for laminar, transient and turbulent flow regimes. The CFD results of hydrodynamics and temperature fields are benchmarked against empirical correlations for pressure drop and interphase heat transfer Nusselt number, Nu, offering the best fits with correlations proposed by Eisfeld and Schnitzlein (for cylinders and spheres) and Nemec and Levec (for rings) for pressure drop, and by Gunn and Sun and coworkers for the prediction of Nu. The CFD results demonstrate that fluctuations in local temperature are completely neglected by azimuthal-averaging of 3D temperature fields over the bed volume, leading to more than 150 °C deviations from the local temperature data. Furthermore, it is found that deviations between azimuthally-averaged axial velocity profile and true local velocities are in an analogous fashion transmitted to the temperature field. This is evidenced by the coincidence of the peaks in the deviation profiles of azimuthally-averaged temperature and velocity from the local data over the bed radius. This is due to thermal disequilibrium between fluid and pellet phases which is partially omitted by the azimuthal-averaging of the 3D temperature field and basically neglected in pseudo-homogenous k_er-h_w models.

Traveling-Wave Microwave Reactor (TMR) presents a novel heterogeneous catalytic reactor concept based on a coaxial waveguide structure. In the current paper, both modeling and experimental studies of catalyst heating in the TMR are presented. The developed 3D multiphysics model was validated from the electromagnetic and heat transfer points of view. Extrudes of silicon carbide (SiC) were selected as catalyst supports and microwave absorbing media in a packed-bed configuration. The packed-bed temperature evolution was in good agreement with experimental data, with an average deviation of less than 10%. Both experimental and simulation results show that the homogeneous temperature distribution is possible in the TMR system. It is envisioned that the TMR concept may facilitate process scale-up while providing temperature homogeneity beyond the intrinsic restrictions of microwave cavity systems.

Microwave heating presents a potentially green alternative for energy supply to chemical and catalytic reactors as it can be based on the electricity from renewable sources. The Reverse Traveling Microwave Reactor (RTMR) is a novel heterogeneous catalytic reactor concept, based on the coaxial waveguide structure. The reactor has two microwave ports on both ends, and microwave irradiation is periodically switched between those ports to minimize the temperature gradients along the catalyst bed. In the current paper, COMSOL MULTIPHYSICS® simulation environment has been used to develop a 3D multiphysics model of the RTMR. Based on the model, operational characteristics of the reactor including electric field distribution and transient temperature profiles have been studied. Simulation results show that periodically reversed microwave irradiation improves the homogeneity of the temperature distribution inside the catalyst bed. The study provides new insights into the design and scale-up of microwave-assisted catalytic flow processes.

Microwave irradiation can intensify catalytic chemistry by selective and controlled microwave-catalytic packed-bed interaction. However, turning it to reality from laboratory to practical applications is hindered by challenges in the reactor design and scale-up. Here, we present a novel, rectangular traveling-wave microwave reactor (RTMR) and provide an easy-to-handle, 3-step design procedure of such reactor. The multiphysics model couples the electromagnetic field, heat transfer, and fluid dynamics in order to optimize the geometrical parameters and operational conditions for the microwave-assisted heterogeneous catalysis. The results show that the microwave energy input/output ports should be well-positioned and matched; otherwise, it would significantly decrease energy efficiency. In terms of microwave transmission, the RTMR presents a mix between the standing wave and the traveling-wave systems. Gas space velocity and input temperature significantly affect the temperature profile, and gas–solid temperature can present no significant difference under certain gas–solid contact.

We investigate forced convective heat transfer in packings of spheres, cylinders and Raschig rings, made of glass, steel and alumina, in relatively narrow tubes. A detailed comparison is made between resolved pellet-scale, azimuthally-averaged temperature profiles, and 2D-axially-dispersed pseudo-homogenous plug flow (2D-ADPF) predictions. The local temperature deviates significantly from azimuthally-averaged profiles, which in turn deviate from 2D-ADPF predictions. We show that the length dependency of effective heat transfer parameters is caused by thermal (non-)equilibrium between fluid and solid phases along the bed and not related to inadequate insulation of the calming section or the thermocouple's cross or an under-developed velocity and thermal field at the bed inlet. The influence of pellet shape and thermal conductivity and tube-to-pellet diameter ratio on k_er and h_w are assessed. We conclude that the models of Specchia/Baldi/Gianetto/Sicardi for all flow regimes and of Martin/Nilles for the turbulent regime are recommended for practical use for spherical particles.

Energy-efficient CH4-CO2 valorization to fuels and chemicals presents an urgent need considering the great variety of methane sources and the removal of greenhouse gases. In the present work, the microwave-assisted dry reforming of methane, DRM, has been carried out in a custom-designed rectangular mono-mode microwave applicator over several catalyst-support combinations, i.e., Pt/C, Ni/Al2O3, mechanical mixture of Ni/Al2O3-SiC and Ni/SiC. The high and steady conversions of CH4 and CO2 were obtained in the case of the mechanical mixture of Ni/Al2O3-SiC and Ni/SiC. In all the combinations investigated, the conversions reached up to 90% at a WHSV of 11,000 mL/g/h, and microwave power input of 45–60 W, at 800 °C. No significant catalyst deactivation has been observed during the 6-h operation except of Pt/C catalyst. Moreover, the microwave-assisted dry reforming of methane over Ni/SiC was shown to be an interesting, cheap process candidate, able to compete with the steam reforming.

The local flow structure and pressure drop in random packings of Raschig rings are analyzed using sequential Rigid Body Dynamics (RBD) method and Computational Fluid Dynamics (CFD) simulation. Tube-to-pellet diameter ratios, N, between 3 and 6 are investigated for laminar, transitional and turbulent flow regimes (5 ≤ Re_p ≤ 3,000). The computed pressure drops are in good agreement with the empirical correlation of Nemec and Levec (2005), while the Ergun equation exhibited high deviations of more than 60%, even when it is modified to explicitly account for non-sphericity of pellets. This deviation is ascribed to additional sources for eddy formation offered by Rashig rings, compared to spheres and cylinders, which cannot be counterbalanced by the usage of a higher specific surface area. The 3D results of flow structure demonstrate a large influence of packing topology on the velocity distribution: rings oriented parallel to the flow accelerate the local velocity through their axial holes, while rings oriented perpendicular to the flow provide additional space for vortex formation. The flow fields are substantially different from that found in packings of spheres and cylinders, both in terms of volume of backflow regions and velocity hotspots. This implies a higher order of local flow inhomogeneity in azimuthal and axial directions compared to spherical and cylindrical packings. Furthermore, it is found that azimuthal averaging of the 3D velocity field over the bed volume, which has been used to improve classical plug-flow pseudo-homogenous models to account for the role of tortuous velocity fields, cannot reflect the appearance of vortex regions and thereby leads to underestimation of the local axial velocity values by over 500% of the inlet velocity.

In 2015 all the United Nations (UN) member states adopted 17 sustainable development goals (UN-SDG) as part of the 2030 Agenda, which is a 15-year plan to meet ambitious targets to eradicate poverty, protect the environment, and improve the quality of life around the world. Although the global community has progressed, the pace of implementation must accelerate to reach the UN-SDG time-line. For this to happen, professionals, institutions, companies, governments and the general public must become cognizant of the challenges that our world faces and the potential technological solutions at hand, including those provided by chemical engineering. Process intensification (PI) is a recent engineering approach with demonstrated potential to significantly improve process efficiency and safety while reducing cost. It offers opportunities for attaining the UN-SDG goals in a cost-effective and timely manner. However, the pedagogical tools to educate undergraduate, graduate students, and professionals active in the field of PI lack clarity and focus. This paper sets out the state-of-the-art, main discussion points and guidelines for enhanced PI teaching, deliberated by experts in PI with either an academic or industrial background, as well as representatives from government and specialists in pedagogy gathered at the Lorentz Center (Leiden, The Netherlands) in June 2019 with the aim of uniting the efforts on education in PI and produce guidelines. In this Part 1, we discuss the societal and industrial needs for an educational strategy in the framework of PI. The terminology and background information on PI, related to educational implementation in industry and academia, are provided as a preamble to Part 2, which presents practical examples that will help educating on Process Intensification.

Microwave chemistry applications have been investigated for more than three decades. Contrary to common cavity-based microwave applicators, the traveling-wave microwave reactor has the potential to enable the process scale-up, a better coupling of microwave energy with microwave-susceptible catalysts, and consequently highly uniform microwave heating. In this work, the engineering challenges entailed with the design of a traveling-wave microwave waveguide are explained and appropriate solutions developed. A new traveling-wave microwave reactor with a coaxial waveguide structure is presented. Simulation results show that there is no standing wave generated along the structure. Furthermore, in order to keep the impedance matching and minimize the microwave reflections while the reactor is loaded with catalyst samples, new reactor's loading patterns are introduced. Simulation results showed that for the proposed method, microwave-susceptible catalytic fixed-bed could interact more efficiently with microwave energy and produce a uniform heating profile.

With renewable electricity becoming the most widespread, flexible, and accessible form of energy on Earth, electrification of chemical processes presents one of the most promising transition paths to low-carbon-footprint, environmentally-neutral manufacturing of fuels and chemicals. The current paper provides a critical perspective on the entire spectrum of chemical and catalytic reactors, in which electricity plays different roles targeting either the reaction mechanism or the thermal energy supply. Related challenges and necessary developments to address those challenges are discussed.

Achieving the United Nations sustainable development goals requires industry and society to develop tools and processes that work at all scales, enabling goods delivery, services, and technology to large conglomerates and remote regions. Process Intensification (PI) is a technological advance that promises to deliver means to reach these goals, but higher education has yet to totally embrace the program. Here, we present practical examples on how to better teach the principles of PI in the context of the Bloom’s taxonomy and summarise the current industrial use and the future demands for PI, as a continuation of the topics discussed in Part 1. In the appendices, we provide details on the existing PI courses around the world, as well as teaching activities that are showcased during these courses to aid students’ lifelong learning. The increasing number of successful commercial cases of PI highlight the importance of PI education for both students in academia and industrial staff.

Three-dimensional mathematical model was developed for a rectangular TE _10n microwave heating cavity system, working at 2.45 GHz. Energy/heat, momentum equations were solved together with Maxwell's electromagnetic field equations using COMSOL MULTIPHYSICS® simulation environment. The dielectric properties, ε' and ε'', of NaY zeolite (Si/Al = 2.5) were evaluated as a function of temperature. Considering these values, the microwave heating of a porous fixed-bed made of dry NaY zeolite was simulated. Electric field distribution, axial and radial temperature profiles and temperature evolution with time were obtained. The zeolite fixed bed was heated up to 180 °C in 5 min, with 30 W power. The fixed-bed temperature evolution under non-steady state conditions showed the same trend as the one observed experimentally with only an average deviation of 10.3%. The model was used to predict microwave heating of other materials improving energy efficiency of the microwave cavity. Furthermore, the developed model was able to predict thermal runaway for zeolites.

This advanced textbook covering the fundamentals and industry applications of process intensification (PI) discusses both the theoretical and conceptual basis of the discipline. Since interdisciplinarity is a key feature of PI, the material contained in the book reaches far beyond the classical area of chemical engineering. Developments in other relevant disciplines, such as chemistry, catalysis, energy technology, applied physics, electronics and materials science, are extensively described and discussed, while maintaining a chemical engineering perspective. Divided into three major parts, the first introduces the PI principles in detail and illustrates them using practical examples. The second part is entirely devoted to fundamental approaches of PI in four domains: spatial, thermodynamic, functional and temporal. The third and final part explores the methodology for applying fundamental PI approaches in practice. As well as detailing technologies, the book focuses on safety, energy and environmental issues, giving guidance on how to incorporate PI in plant design and operation--safely, efficiently and effectively.

An optimal photon utilization is important for the economic performance of a photocatalytic reactor. However, for the desired reactor performance, it is often difficult to predict the required photon utilization. In this work, automated feedback and feedforward controllers are investigated to maintain the reactor conversion close to a desired value by adjusting the photon irradiance within a LED-based photocatalytic reactor for toluene degradation. The feedback controller was able to control the conversion during a set-point tracking experiment and was able to mitigate the effects of catalyst deactivation in an automated fashion. The feedforward controller was designed based on an empirical steady-state model to mitigate the effect of changing toluene inlet concentration and relative humidity, which were measured input disturbances. The results demonstrated that feedback and feedforward control were complementary and could mitigate the effects of disturbances effectively such that the photocatalytic reactor operated close to desired conditions at all times. The presented work is the first example of how online analytical technologies can be combined with “smart” light sources such as LEDs to implement automated process control loops that optimize photon utilization. Future work may expand on this concept by developing more advanced control strategies and exploring applications in different areas.

In this work, we report on air/N₂ gasification of a byproduct stream from an industrial fermenter in a tubular microwave plasma reactor to investigate the feasibility of the technology for organic compounds valorization, given the limited number of relevant works in the literature. In this context, an operating window regarding air/N₂/biomass flow rates and power input has been identified to enable stable and efficient operation. Up to 89% carbon conversion efficiency and 41% cold gas efficiency have been attained with syngas product composition H₂:CO:CO₂ = 41:53:6 on molar basis, fairly close to the calculated equilibrium composition values in the temperature range 973 K to 2173 K.

For many years, process intensification has been seen and considered through the prism of equipment and methods. The current review paper adds a new perspective to it and examines the role of (advanced) materials in process intensification. The discussion is illustrated with numerous examples of various types of materials that have been shown to intensify chemical and catalytic reactions, mass transfer, heat transfer, and momentum transfer processes, respectively. The role of process intensification in manufacturing of new, advanced materials is also discussed. In view of the importance of materials for process intensification, an update of the classical approach to the field of PI is postulated.