ChemEngineering, Volume 5, Issue 1 (March 2021) – 14 articles

In this study, we aimed to enhance the catalytic activity of perovskite catalysts and elucidate their catalytic behavior in the oxidative coupling of methane (OCM), using alkali-added LaAlO₃ perovskite catalysts. We prepared LaAlO₃_XY (X = Li, Na, K, Y = mol %) catalysts and applied them to the OCM reaction. The results showed that the alkali-added catalysts’ activities were promoted compared to the LaAlO₃ catalyst. In this reaction, ethane was first synthesized through the dimerization of methyl radicals, which were produced from the reaction of methane and oxygen vacancy in the perovskite catalysts. The high ethylene selectivity of the alkali-added catalysts originated from their abundance of electrophilic lattice oxygen species, facilitating the selective formation of C₂ hydrocarbons from ethane. The high CO_x (carbon monoxide and carbon dioxide) selectivity of the LaAlO₃ catalyst originated from its abundance of nucleophilic lattice oxygen species, favoring the selective production of CO_x from ethane. We concluded that electrophilic lattice oxygen species play a significant role in producing ethylene. We obtained that alkali-adding could be an effective method for improving the catalytic activity of perovskite catalysts in the OCM reaction. Full article

Alkali-activated adsorbents were synthesized by mixing three different slags from the steel industry: blast furnace slag (BFS), ladle slag (LS), and Lintz–Donawitz converter slag (LD). These powdered slag-based geopolymers (GP) were used to remove nickel(II) from aqueous solutions in fixed-bed column studies. The experiments were conducted in pH 6 using a phosphate buffer with initial nickel(II) concentration of 50 mg/L. Samples were taken at time intervals of between 5 and 90 min. Three adsorption–desorption cycles were implemented with a flow rate of 5 mL/min. The geopolymers were characterized by Fourier-Transform Infrared Spectroscopy (FTIR), X-ray powder diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM), X-ray fluorescence (XRF), specific surface area measurements, and a leaching test. The data were found to describe the Thomas, Adams–Bohart, and Yoon–Nelson models well. For GP (BFS, LS), experimental adsorption capacity was 2.92 mg/g, and for GP (LD, BFS, LS), it was 1.34 mg/g. The results indicated that the produced adsorbents have the potential to be used as adsorbents for the removal of nickel(II). Full article

Economically and ecologically, the thermal decomposition of methane is a promising process for large scale hydrogen production. In this experimental study, the non-catalytic decomposition of methane in the presence of small amounts of carbon dioxide was analyzed. At large scales, natural gas or biomethane are possible feedstocks for the thermal decomposition and can obtain up to $5\%$ carbon dioxide. Gas recycling can increase the amount of secondary components even further. Experiments were conducted in a packed flow reactor at temperatures from 1250 to 1350 $\mathrm{K}$. The residence time and the amounts of carbon dioxide and hydrogen in the feed were varied. A methane conversion of up to $55.4\%$ and a carbon dioxide conversion of up to $44.1\%$ were observed. At $1300 \mathrm{K}$ the hydrogen yield was $95\%$ for a feed of methane diluted in nitrogen. If carbon dioxide was added to the feed at up to a tenth with regard to the amount of supplied methane, the hydrogen yield was reduced to $85\%$. Hydrogen in the feed decreases the reaction rate of the methane decomposition and increases the carbon dioxide conversion. Full article

The heavy-metal-free photocatalytic system, in which carbon nitride is coated on polylactic acid (PLA) as biodegradable plastic through a simple dip coating method, was used for dye decomposition under visible light irradiation. Solvent selection, solvent concentration, and the number of coatings for dip coating were investigated to optimize the conditions for loading carbon nitride on PLA. Carbon nitride cannot be coated on PLA in water, but it can be strongly coated by decomposing the surface of PLA with ethanol or chlorobenzene to promote physical adsorption and activate surface. The number of dip coatings also affected the photocatalytic decomposition ability. The photocatalytic system was able to decompose the dye continuously in the flow method, and dye (rhodamine B) was decomposed by about 50% at a residence time of 12 min (flow rate 0.350 mL/min) for 30 h. Full article

Natural clinoptilolite was studied to assess its performance in removing caesium and strontium ions, using both static columns and an agitated tube reactor (ATR) for process intensification. Kinetic breakthrough curves were fitted using the Thomas and Modified Dose Response (MDR) models. In the static columns, the clinoptilolite adsorption capacity (q_e) for 200 ppm ion concentrations was found to be ~171 and 16 mg/g for caesium and strontium, respectively, highlighting the poor material ability to exchange strontium. Reducing the concentration of strontium to 100 ppm, however, led to a higher strontium q_e of ~48 mg/g (close to the maximum adsorption capacity). Conversely, halving the column residence time to 15 min decreased the q_e for 100 ppm strontium solutions to 13–14 mg/g. All the kinetic breakthrough data correlated well with the maximum adsorption capacities found in previous batch studies, where, in particular, the influence of concentration on the slow uptake kinetics of strontium was evidenced. For the ATR studies, two column lengths were investigated (of 25 and 34 cm) with the clinoptilolite embedded directly into the agitator bar. The 34 cm-length system significantly outperformed the static vertical columns, where the adsorption capacity and breakthrough time were enhanced by ~30%, which was assumed to be due to the heightened kinetics from shear mixing. Critically, the increase in performance was achieved with a relative process flow rate over twice that of the static columns. Full article

In this work volume-translated Peng–Robinson group contribution equation of state was used to calculate excess enthalpies. Four model systems were selected with the purpose to compare experimental and predicted enthalpy values at different temperatures. After the calculations were performed in Matlab software, results were verified with free software tool of Dortmunder Datenbank (DDB). In a next step, the mixing process and interaction forces were described on the basis of the sign and course of enthalpy values. The endothermic behavior of three systems could be well predicted, while for the most polar system, predictions were less precise. Furthermore, the discrepancy between experimental data from the literature and predicted values was discussed to evaluate the accuracy of the selected model. Lowest mean deviations (<75 J/mol and <15% at all temperatures) could be stated for alkane/benzene mixtures, while highest deviations could be again observed for the most polar mixture. Although the magnitude of deviations was in agreement with the literature, it could be shown that the selected temperature is of major importance for the quality of predictions. Furthermore, a review of different literature values for the n-hexane/benzene system could reveal that the reliability of experimental data has to be carefully checked. Full article

Properties of emulsions such as stability, viscosity or color can be influenced by the droplet size distribution. High-pressure homogenization (HPH) is the method of choice for emulsions with a low to medium viscosity with a target mean droplet diameter of less than 1 µm. During HPH, the droplets of the emulsion are exposed to shear and extensional stresses, which cause them to break up. Ongoing work is focused on better understanding the mechanisms of droplet breakup and relevant parameters. Since the gap dimensions of the disruption unit (e.g., flat valve or orifice) are small (usually below 500 µm) and the droplet breakup also takes place on small spatial and time scales, the resolution limit of current measuring systems is reached. In addition, the high velocities impede time resolved measurements. Therefore, a five-fold and fifty-fold magnified optically accessible coaxial orifice were used in this study while maintaining the dimensionless numbers characteristic for the droplet breakup (Reynolds and Weber number, viscosity and density ratio). Three matching material systems are presented. In order to verify their similarity, the local velocity profiles of the emerging free jet were measured using both a microparticle image velocimetry (µ-PIV) and a particle image velocimetry (PIV) system. Furthermore, the influence of the outlet geometry on the velocity profiles is investigated. Similar relationships were found on all investigated scales. The areas with the highest velocity fluctuations were identified where droplets are exposed to the highest turbulent forces. The Reynolds number had no influence on the normalized velocity fluctuation field. The confinement of the jet started to influence the velocity field if the outlet channel diameter is smaller than 10 times the diameter of the orifice. In conclusion, the scaling approach offers advantages to study very fast processes on very small spatial scales in detail. The presented scaling approach also offers chances in the optimization of the geometry of the disruption unit. However, the results also show challenges of each size scale, which can come from the respective production, measurement technology or experimental design. Depending on the problem to be investigated, we recommend conducting experimental studies at different scales. Full article

Laponite is an artificial nanoclay available in large quantities and at low cost. This marterial represents an efficient and suitable way of delivering hydrophobic vital dyes without the need for chemical functionalization. Laponite is available in large quantities and at low cost, then it would be an efficient way of delivering hydrophobic vital dyes without the need for chemical functionalization. The hydrodynamic diameter of laponite extrapolated to infinite dilution indicates that this clay is completely exfoliated. Furthermore, the hydrodynamic diameter in the laponite-Indocyanine green-water ternary system, at a fixed laponite concentration (2% (m/m)) exhibits a saturation curve. It was found that the extrapolated diameter at dye zero concentration is smaller than in pure water. Absorption spectra with fixed concentration of dye exhibit a red shift of 10–13 nm. On the contrary, the spectra acquired at a constant concentration of laponite do not undergo any displacement. The deconvolution of the spectra with two Gaussian peaks allows to calculate the concentration of the monomeric and dimeric species. The results were interpreted as a synergy between the dye dimerization balance and the dye-laponite binding. Full article

Three new uranyl sulfates, [pyH](H₃O)[(UO₂)₃(SO₄)₄(H₂O)₂] (1), [pyH]₂[(UO₂)₆(SO₄)₇(H₂O)] (2), and [pyH]₂[(UO₂)₂(SO₄)₃] (3), were produced upon hydrothermal treatment and successive isothermal evaporation. 1 is monoclinic, P2₁/c, a = 14.3640(13), b = 10.0910(9), c = 18.8690(17) Å, β = 107.795(2), V = 2604.2(4) ų, R₁ = 0.038; 2 is orthorhombic, C222₁, a = 10.1992(8), b = 18.5215(14), c = 22.7187(17) Å, V = 4291.7(6) ų, R₁ = 0.030; 3 is orthorhombic, Pccn, a = 9.7998(8), b = 10.0768(8), c = 20.947(2) Å, V = 2068.5(3) ų, R₁ = 0.055. In the structures of 1 and 2, the uranium polyhedra and SO₄ tetrahedra share vertices to form ${}_{\infty }^3$[(UO₂)₃(SO₄)₄(H₂O)₂]²⁻ and ${}_{\infty }^3$[(UO₂)₆(SO₄)₇(H₂O)]²⁻ frameworks featuring channels (12.2 × 6.7 Å in 1 and 12.9 × 6.5 Å in 2), which are occupied by pyridinium cations. The structure of 3 is comprised of ${}_{\infty }^2$[(UO₂)₂(SO₄)₃]²⁻ layers linked by hydrogen bonds donated by pyridinium cations. The compounds 1–3 are formed during recrystallization processes, in which the evaporation of mother liquor leads to a stepwise loss of hydration water. Full article

In this paper we analyse static properties of mass spring models (MSMs) with the focus of modelling non crystalline materials, and explore basic improvements, which can be made to MSMs with disordered point placement. Presented techniques address the problem of high variance of MSM properties which occur due to randomised nature of point distribution. The focus is placed on tuning spring parameters in a way which would compensate for local non-uniformity of point and spring density. We demonstrate that a simple force balancing algorithm can improve properties of the MSM on a global scale, while a more detailed stress distribution analysis is needed to achieve local scale improvements. Considered MSMs are three dimensional. Full article

This paper addresses the issues of slug detection and characterization in air-water two-phase flow in a vertical pipeline. A novel non-invasive measurement technique using continuous-wave Doppler ultrasound (CWDU) and bandpass power spectral density (BPSD) is proposed for multiphase flow applications and compared with the more established gamma-ray densitometry measurement. In this work, analysis using time-frequency analysis of the CWDU is performed to infer the applicability of the BPSD method for observing the slug front and trailing bubbles in a multiphase flow. The CWDU used a piezo transmitter/receiver pair with an ultrasonic frequency of 500 kHz. Signal processing on the demodulated signal of Doppler frequency was done using the Butterworth bandpass filter on the power spectral density which reveals slugs from background bubbles. The experiments were carried out in the 2” vertical pipeline-riser at the process system engineering laboratory at Cranfield University. The 2-inch test facility used in this experiment is made up of a 54.8 mm internal diameter and 10.5 m high vertical riser connected to a 40 m long horizontal pipeline. Taylor bubbles were generated using a quick-closing air valve placed at the bottom of the riser underwater flow, with rates of 0.5 litres/s, 2 litres/s, and 4 litres/s. The CWDU spectrum of the measured signal along with the BPSD method is shown to describe the distinctive nature of the slugs. Full article

Pathogenic bacteria and other microorganisms pose a potent threat to humans by causing various infectious diseases. To control the spread of infection, different antibacterial products have been developed. However, most of them are known to be associated with health hazards, environmental pollution, complex fabrication, and/or higher cost. To address these issues, in this study, a low cost, biodegradable and human skin compatible antibacterial paper has been developed. A quaternary ammonium compound, benzalkonium chloride (BKC) has been used for paper surface treatment. The concentration of aqueous solution of BKC coated on paper was varied from 0.1 wt% to 0.2 wt%. No external binder was required for coating BKC onto paper. The efficacy of the coated paper was investigated against Staphylococcus aureus ATCC 6538 and Escherichia coli ATCC 8739 bacterial strains. This antibacterial paper is highly effective against both strains with the concentrations of BKC being within the allowable limit for cytotoxic effects. The optimum concentration of BKC coated on paper can be considered as 0.15 wt%, as nearly 100% inhibition was achieved with it against both strains. The developed antibacterial paper is suitable for being used in the industry for disinfection and food packaging purposes, and also by the public for hand sanitization. Full article