Experimental methods in chemical engineering: Computational fluid dynamics/finite volume method—CFD/FVM

Computational fluid dynamics (CFD) applies numerical methods to solve transport phenomena problems. These include, for example, problems related to fluid flow comprising the Navier–Stokes transport equations for either compressible or incompressible fluids, together with turbulence models and continuity equations for single and multi-component (reacting and inert) systems. The design space is first segmented into discrete volume elements (meshing). The finite volume method, the subject of this article, discretizes the equations in time and space to produce a set of non-linear algebraic expressions that are assigned to each volume element—cell. The system of equations is solved iteratively with algorithms like the semi-implicit method for pressure-linked equations (SIMPLE) and the pressure implicit splitting of operators (PISO). CFD is especially useful for testing multiple design elements because it is often faster and cheaper than experiments. The downside is that this numerical method is based on models that require validation to check their accuracy. According to a bibliometric analysis, the broad research domains in chemical engineering include: (1) dynamics and CFD-DEM, (2) fluid flow, heat transfer, and turbulence, (3) mass transfer and combustion, (4) ventilation and the environment, and (5) design and optimization. Here, we review the basic theoretical concepts of CFD and illustrate how to set up a problem in the open-source software OpenFOAM to isomerize n-butane to i-butane in a notched reactor under turbulent conditions. We simulated the problem with 1000, 4000, and 16 000 cells. According to the Richardson extrapolation, the simulation underestimates the adiabatic temperature rise by 7% with 16 000 cells.     

Hydrogen production through chemical looping using NiO/NiAl2O4 as oxygen carrier

A new autothermal route to produce hydrogen from natural gas via chemical looping technology was investigated. Tests were conducted in a micro-fixed bed reactor loaded with 200 mg of NiO/NiAl₂O₄ as oxygen carrier. Methane reacts with a nickel oxide in the absence of molecular oxygen at 800 °C for a period of time as high as 10 min. The NiO is subsequently contacted with a synthetic air stream (21% O₂ in argon) to reconstitute the surface and combust carbon deposited on the surface. Methane conversion nears completion but to minimize combustion of the hydrogen produced, the oxidation state of the carrier was maintained below 30% (where 100% represents a fully oxidized surface). Co-feeding water together with methane resulted in stable hydrogen production. Although the carbon deposition increased with time during the reduction cycle, the production rate of hydrogen remained virtually constant. A new concept is also presented where hydrogen is obtained from methane with inherent CO₂ capture in an energy neutral 3-reactors CFB process. This process combines a methane combustion step where oxygen is provided via an oxygen carrier, a steam methane reforming step catalyzed by the reduced oxygen carrier and an oxidizing step where the O-carrier is reconstituted to its original state.     

MeOH to DME in bubbling fluidized bed: Experimental and modelling

Methanol dehydration over a ZSM‐5 containing catalyst was studied in a fluidized bed reactor. At temperatures ranging from 250 to 325°C, methanol conversion varied from 30% at a contact times of 0.14 s and approached 100% of the equilibrium conversion at a contact time starting from 10 s. Sequential and parallel reactions were negligible at low temperatures while hydrocarbon formation became appreciable at 325°C. Online gas analysis by mass spectrometry provided real‐time measurements at a frequency of 4.4 Hz that allowed for fast determination of steady‐state conditions. Gas phase residence time distribution (RTD) measurements indicated that axial dispersion was essentially negligible at short contact times with a shallow bed of catalyst. With longer residence times, the flow pattern could be approximated by six continuously stirred‐tank reactors (CSTR) in series. Both the simple 1D hydrodynamic model and a detailed multi‐zone fluidized model were used to interpret the experimental data to derive a kinetic expression for the dehydration of methanol to di‐methyl ether (DME). The expression includes the reverse reaction that is most often neglected in the literature. The reaction data were best fit with the kinetics based on the 1D model. The fluidized bed is a viable reactor type for kinetic measurements of highly exothermic reactions where hotspots and radial and axial temperature gradients are problematic in fixed beds.     

Chemical‐looping combustion process: Kinetics and mathematical modeling

Chemical Looping Combustion technology involves circulating a metal oxide between a fuel zone where methane reacts under anaerobic conditions to produce a concentrated stream of CO₂ and water and an oxygen rich environment where the metal is reoxidized. Although the needs for electrical power generation drive the process to high temperatures, lower temperatures (600–800°C) are sufficient for industrial processes such as refineries. In this paper, we investigate the transient kinetics of NiO carriers in the temperature range of 600 to 900°C in both a fixed bed microreactor (WHSV = 2‐4 g CH₄/h/g oxygen carrier) and a fluid bed reactor (WHSV = 0.014‐0.14 g CH₄/h per g oxygen carrier). Complete methane conversion is achieved in the fluid bed for several minutes. In the microreactor, the methane conversion reaches a maximum after an initial induction period of less than 10 s. Both CO₂ and H₂O yields are highest during this induction period. As the oxygen is consumed, methane conversion drops and both CO and H₂ yields increase, whereas the CO₂ and H₂O concentrations decrease. The kinetics parameter of the gas–solids reactions (reduction of NiO with CH₄, H₂, and CO) together with catalytic reactions (methane reforming, methanation, shift, and gasification) were estimated using experimental data obtained on the fixed bed microreactor. Then, the kinetic expressions were combined with a detailed hydrodynamic model to successfully simulate the comportment of the fluidized bed reactor. © 2010 American Institute of Chemical Engineers AIChE J, 2010     

Experimental methods in chemical engineering: Raman spectroscopy

When photons impinge on a substrate, most scatter with the same frequency (elastic scattering or Rayleigh dispersion) and only 10^?7 scatter with a different energy (inelastic scattering). This inelastic interaction (Raman scattering) exchanges energy in the region of molecular vibrational transitions for crystalline and amorphous materials. Raman bands in a spectra represent vibrational transitions, like infrared, however the selection rules are different. Typically, the vibrations that are intense in Raman are weak in infrared and vice versa. A remarkable feature of the Raman effect is that it is highly sensitive to nanocrystals, even below 4 nm, which are too small to generate XRD patterns. Plasmonic enhancement, like surface‐enhanced Raman spectroscopy (SERS) boost the Raman signal by 10⁴, providing single‐molecule detection capability. Glass, quartz, and sapphire are transparent to Raman effect (depending on the energy of the incident excitation radiation), which makes it ideal to examine materials under reaction conditions (in‐situ cells and operando reactors that operate over a broad range of temperature, pressures, and environments). Raman spectroscopy emerged in the 1930s; however, infrared spectrometry displaced it. With the advent of powerful lasers in the 1970s, more researchers began to apply Raman routinely. In 2019, the Web of Science indexed 20 400 articles mentioning Raman against 50 000 articles mentioning infrared. Chemical engineers apply Raman less frequently than in material science, physical chemistry, and applied physics, with 887 articles vs 6250, 3700, and 3510 for the other disciplines. A bibliometric analysis identified four research clusters centred on thin films and optics, graphene and nanocomposites, nanoparticles and SERS, and photocatalyst.     

Chemical engineering research synergies across scientific categories

Chemical engineers operate industrial plants, design reactors and equipment, manage capital projects, estimate costs, project earnings, and drive efficiency through innovation while maintaining rigorous safety standards. The undergraduate curriculum includes mathematics, physics, chemistry, mechanics, biology, and management, much of which is common with other engineering departments. 1 However, chemical engineering research is more related to chemistry. Here, we show that chemical engineers cite journals in WoS’ chemical engineering category most, followed by physical chemistry, energy & fuels, multi‐disciplinary chemistry, environmental science, and multi‐disciplinary materials science. According to a bibliometric analysis, the major research poles include materials, biotechnology, catalysis, environment, and thermodynamics. The 5 top cited journals in 2012 were Ind. Eng. Chem. Res., J. Membrane Sci., Chem. Eng. Sci., J. Hazard. Mater., and J. Catal., which are not the journals with the highest impact factors of the category. Can. J. Chem. Eng. was ranked third among the 32 classical chemical engineering journals after AIChE J. and Chem. Eng. Sci. and with respect to the ratio of the number of citations accrued until August 2017 to the number of articles they published in 2012. Chinese researchers have authored more articles than any other nation and they co‐author research most with the USA and other Pacific Rim nations. Research collaborations between nations follow linguistic, geographical, and historical traditions.

     

Treatment of posttraumatic stress disorder by trained lay counselors in an African refugee settlement: A randomized controlled trial.

Traumatic stress due to conflict and war causes major mental health problems in many resource-poor countries. The objective of this study was to examine whether trained lay counselors can carry out effective treatment of posttraumatic stress disorder (PTSD) in a refugee settlement. In a randomized controlled dissemination trial in Uganda with 277 Rwandan and Somalian refugees who were diagnosed with PTSD the authors investigated the effectiveness of psychotherapy administered by lay counselors. Strictly manualized narrative exposure therapy (NET) was compared with more flexible trauma counseling (TC) and a no-treatment monitoring group (MG). Fewer participants (4%) dropped out of NET treatment than TC (21%). Both active treatment groups were statistically and clinically superior to MG on PTSD symptoms and physical health but did not differ from each other. At follow-up, a PTSD diagnosis could not be established anymore in 70% of NET and 65% TC participants, whereas only 37% in MG did not meet PTSD criteria anymore. Short-term psychotherapy carried out by lay counselors with limited training can be effective to treat war-related PTSD in a refugee settlement. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Simultaneous quantitative measurement of gaseous species composition and solids volume fraction in a gas/solid flow

A novel spectroscopic method was developed to measure quantitatively and simultaneously solids volume fraction (1?ε) and gaseous species composition (Yi) in a gas/solid system. The method was comprised of an FT‐IR coupled to a fiber‐optic probe that could perform real‐time and in situ measurements of absorbance. The effect of (1?ε) and Yi on the absorbance spectra were additive and could be independently calibrated. Experiments were conducted with alkane/nitrogen mixtures and two types of particles: sand and FCC. Fuel mole fractions and (1?ε) were varied between 1.8–10.1 mol % and 0–0.45, respectively. The relative errors for Yi time‐averaged measurements were below 6% and the error increased significantly with decreasing beam intensity. A proof of concept for a novel application in fluidized beds was also completed: the fiber‐optic probe was used to measure the molar fraction of a tracer gas inside the emulsion and bubble phases during gas tracer experiments. © 2010 American Institute of Chemical Engineers AIChE J, 2010     

Regeneration studies of redox catalysts

Cited advantages of circulating fluidized bed reactors (CFB) include higher selectivity and conversion together with the ability to optimize the process conditions of each vessel independently—temperature, gas partial pressure and residence time. DuPont commercialized a CFB process to produce maleic anhydride in which a vanadium pyrophosphate (VPO) was cycled between a fast bed riser and an air fed regenerator. Together with VPO, we examined two other redox catalyst systems—MoVSb (acrylic acid from propane) and FeMoO (methanol to formaldehyde).The lattice oxygen capacity of the FeMoO catalyst was about five times higher than either the VPO or MoVSb with little adsorbed carbon but a significant quantity of chemisorbed water. Above 350 °C, carbon deposition was detected and increased with increasing temperature. Carbon deposition decreased with increasing temperature for the MoVSb system and its lattice oxygen capacity was slightly higher than for VPO. The carbon deposition pattern for VPO was the opposite of the MoVSb and increased with temperature. Based on a hydrogen and carbon mass balance during the catalyst re-oxidation treatment, the molecular composition of the adsorbed species were C₄H₆ and C₃H₃—like for the VPO and MoVSb, respectively.Based on the high lattice oxygen capacity, the formaldehyde reaction appears to be ideally suited for development in a CFB. Whereas the lattice oxygen contribution of the MoVSb is equivalent to VPO, less oxygen is required to produce acrylic acid (compared to maleic anhydride) so the incentive of developing a CFB process should be greater than for butane oxidation to maleic anhydride.