ChemEngineering, Volume 7, Issue 3 (June 2023) – 18 articles

Replacing the conventionally used steam reforming of methane (SRM) with a process that has a smaller carbon footprint, such as dry reforming of methane (DRM), has been found to greatly improve the industry’s utilization of greenhouse gases (GHGs). In this study, we numerically modeled a DRM process in lab-scale packed and fluidized beds using the Eulerian–Lagrangian approach. The simulation results agree well with the available experimental data. Based on these validated models, we investigated the effects of temperature, inlet composition, and contact spatial time on DRM in packed beds. The impacts of the side effects on the DRM process were also examined, particularly the role the methane decomposition reaction plays in coke formation at high temperatures. It was found that the coking amount reached thermodynamic equilibrium after 900 K. Additionally, the conversion rate in the fluidized bed was found to be slightly greater than that in the packed bed under the initial fluidization regime, and less coking was observed in the fluidized bed. The simulation results show that the adopted CFD approach was reliable for modeling complex flow and reaction phenomena at different scales and regimes. Full article

High demand for energy consumption forced the exploration of renewable energy resources, and in this context, biodiesel has received intensive attention. The process of biodiesel production itself needs to be optimized in order to make it an eco-friendly and high-performance energy resource. Within this scheme, development of low-cost and reusable heterogeneous catalysts has received much attention. Mesoporous silica materials with the characteristics of having a high surface area and being modifiable, tunable, and chemical/thermally stable have emerged as potential solid support of powerful catalysts in biodiesel production. This review highlights the latest updates on mesoporous silica modifications including acidic, basic, enzyme, and bifunctional catalysts derived from varied functionalization. In addition, the future outlook for progression is also discussed in detail. Full article

This study investigated the effectiveness of immobilizing Saccharomyces cerevisiae invertase (SInv) on magnetite nanoparticles to produce fructooligosaccharides (FOSs). Based on the existing literature and accompanied by parameter estimation, a modified kinetic model was employed to represent the kinetics of sucrose hydrolysis and transfructosylation using SInv immobilized on magnetite nanoparticle surfaces. This model was utilized to simulate the performance of batch reactors for both free and immobilized enzymes. The maximum FOS concentration for the free enzyme was determined to be 123.1 mM, while the immobilized case achieved a slightly higher concentration of 125.4 mM. Furthermore, a continuous stirred-tank reactor (CSTR) model was developed for the immobilized enzyme, resulting in a maximum FOS concentration of 73.96 mM at the reactor’s outlet and a dilution rate of 14.2 h⁻¹. To examine the impact of glucose inhibition on FOS production, a glucose oxidase reaction mechanism was integrated into the fitted immobilized theoretical model. In a batch reactor, the reduction or elimination of glucose in the reactive media led to a 2.1% increase in FOS production. Immobilizing the biocatalyst enhanced the overall performance of SInv. This enzyme immobilization approach also holds the potential for coupling glucose oxidase onto functionalized nanoparticles to minimize glucose inhibition, thereby improving FOS synthesis and facilitating optimal enzyme recovery and reuse. Full article

This paper provides an overview of hydrometallurgical copper extraction studies in which liquid extraction technology has been used with four copper deposits of different compositions. The sulfuric acid consumption rate and copper extraction efficiency, which are dependent on the initial content and forms of calcium compounds and other impurities in ore samples, were calculated, and the results are presented herein. It was established that during the leaching process, silicate compounds of alkaline earth metals, in addition to calcium and magnesium carbonate compounds, would affect the levels of sulfuric acid consumption, thereby actively lowering the acidity of the environment. Moreover, these compounds could partially sorb copper ions from sulfuric acid leaching solutions. Thus, the analysis of waste ore samples showed that residual copper is mainly contained in the form of complex silicate complexes. The presence of divalent iron compounds in the composition from one of the deposits also allowed us to perform a biochemical leaching experiment with preliminary oxidation using an Acidithiobacillus ferrooxidans bacterial culture adapted to the ore composition. The use of this biochemical method in the copper leaching process resulted in a significant reduction in sulfuric acid consumption, by 40%, and a copper recovery rate of 87.2%. Full article

This paper presents a dynamic sliding mode control (DSMC) for open-loop unstable chemical or biochemical processes with a time delay. The controller is based on the sliding mode and internal model control concepts. The proposed DSMC has an internal P/PD controller to provide systems with disturbance rejection. An identification method approximates the open-loop unstable nonlinear process to a first-order delayed unstable process (FODUP). The reduced-order model(FODUP) is used to synthesize the new controller. The performance of the controller is stable and satisfactory despite nonlinearities in the operating conditions due to set-point and process disturbance changes. In addition, the performance analysis of the control schemes was evaluated based on various indices and transient characteristics, including the integral of squared error (ISE), the total variation of control effort (TVu), the maximum overshoot (Mp), and the settling time (ts). Finally, the process output and the control action for all controllers are compared using the nonlinear process as the real plant. Full article

Lead is a highly toxic heavy metal that creates a water pollutant. It can be released from industrial processes, agricultural chemistry, and community wastes, affecting creatures and human health even at a low concentration. As a result, it is advised that lead be removed before releasing wastewater into the environment. This study synthesized three chitosan bead materials from shrimp shell wastes which were chitosan powder beads (CB), chitosan powder mixed with goethite beads (CFB), and chitosan powder beads coated with goethite (CBF) for removing lead in an aqueous solution. Their surface area, pore volumes, and pore sizes were explored according to Brunauer– Emmett–Teller, and their crystalline formations were investigated using an X-ray diffractometer. Their surface structures were studied using field emission scanning electron microscopy and a focus ion beam, and their chemical compositions were determined using an energy dispersive X-ray spectrometer. Their chemical functional groups were identified via Fourier-transform infrared spectroscopy. In addition, batch experiments were conducted to investigate the effects of several factors on removing lead, and the adsorption isotherm and kinetics were also investigated for determining their adsorption pattern and mechanism. In addition, the desorption experiments were studied to confirm their possible material reusability. The CBF demonstrated the highest surface area and smallest pore size compared with the other materials. In addition, the pore sizes of the CFB and CBF were micropores, whereas those of the CB were mesopores. All materials were semicrystalline structures, and the specific goethite peaks were observed in the CFB and CBF. All materials had spherical shapes with heterogeneous surfaces. Six chemical components of O, C, Ca, N, Cl, and Na were discovered in all materials, and Fe was only found in the CFB and CBF because of the addition of goethite. Five main chemical functional groups of N–H, O–H, C–H, C–O, and –COOH were found in all materials. The optimum conditions of the CB, CFB, and CBF for removing lead were 0.5 g, 16 h, pH 5, 0.5 g, 16 h, pH 5, and 0.4 g, 14 h, pH 5, respectively. The results of the batch experiments demonstrated that the CB, CFB, and CBF were high-efficiency adsorbents for removing lead in solution by more than 95%, whereby the CBF showed the highest lead removal of 99%. The Freundlich isotherm model and pseudo-second-order kinetic model helped to well explain their adsorption pattern and mechanism. The maximum lead adsorption capacities of the CB, CFB, and CBF were 322.58, 333.33, and 344.83 mg/g, respectively. Furthermore, all chitosan materials can be reused for more than three cycles with high lead removal by more than 94%; so, they are potential materials for application in industrial applications. Full article

The aim of the work was to assess the possibility of utilizing the waste generated in the injection molding process for the production of new products based on polyamide 6 reinforced with glass fiber. The manufactured samples were prepared with the addition of 5, 10, 15, and 100 wt.% regrind from the runner system. The impact strength, tensile strength, and hardness of injection products were obtained directly and were assessed after conditioning in distilled water for 24 h. Moreover, the structure of the tested materials was assessed using the FTIR method and their thermal properties using the DSC method. The results of the tests confirm that the addition of regrind up to 15 wt.% to virgin polyamide does not adversely affect its impact strength, tensile strength, and hardness. The water-conditioned materials showed higher values of impact strength but lower values of tensile strength and Young’s modulus at a higher elongation at break. The obtained results are important due to the assumptions of the circular economy and the minimization of the amount of waste and material losses during the injection process. Full article

Biochar has gained attention as an alternative source of solid energy and for the proper disposal of agricultural biomass waste (ABW). Microwave-assisted pyrolysis (MAP) is a promising approach for the production of biochar. This review article presents the beneficial use of biochar for soil fertilization, machine learning (ML), the circular bioeconomy, and the technology readiness level. The use of machine learning techniques helps to design, predict, and optimize the process. It can also improve the accuracy and efficacy of the biochar production process, thereby reducing costs. Furthermore, the use of biochar as a soil amendment can be an attractive option for farmers. The incorporation of biochar into soil has been shown to improve soil fertility, water retention, and crop productivity. This can lead to reduced dependence on synthetic fertilizers and increased agricultural yields. The development of a biochar economy has the potential to create new job opportunities and increase the national gross domestic product (GDP). Small-scale enterprises can play a significant role in the production and distribution of biochar, providing value-added products and helping to promote sustainable agriculture. Full article

In Peru, there are more than four thousand plants with medicinal properties, including muña, which helps digestion and improves health. The way to preserve these plants is drying up. The objective of this research was to investigate the coefficient of diffusion, enthalpy, and Gibbs free energy in the drying kinetics of muña leaves. Different pretreatments were carried out on the samples (without pretreatment, as well as treated by immersion in 1% ascorbic acid and bleaching at 60 °C for 30 s), and they were dehydrated at three temperatures (40, 50, and 60 °C). The drying kinetics were modeled using eight mathematical models to represent the drying curve. The water content was reduced by the drying process. The logarithmic model was selected, as it showed the best fit to represent the drying kinetics of the muña. Activation energy values were similar between treatments (p > 0.05). The increase in temperature decreases the enthalpy and entropy and increases the Gibbs free energy with the effective diffusion coefficient. The drying kinetics allows one to determine the drying time for the storage of the product and the thermodynamic properties for the design of the equipment. Full article

Nanofiltration and reverse osmosis are used in the concentration of grape musts in winemaking. Both technologies offer an effective way to concentrate the grape musts, reducing the volume and the solids content to achieve desired characteristics in the final wine. The choice between nanofiltration and reverse osmosis depends on the specific needs of the winemaker and the desired characteristics. It is important to carefully consider the properties of the grape musts and the performance of the selected membranes to optimize the concentration process and ensure the desired outcome. Herein, we present a novel approach that allows us to choose a suitable membrane for an optimal industrial process for the concentration of musts, both in reverse osmosis and nanofiltration. The proposed method consists of combining the fitting equations of laboratory results with the balance equations on the industrial plant. Specifically, a full-scale plant has been designed and assembled with which grape musts of Trebbiano, Verdeca, Black Bombino, and White Bombino varieties have been concentrated through the selected best-performing membranes. Results of the proposed approach show that grape musts with sugar content commercially appreciated when the membranes work at high pressure can be obtained. Full article

Recently, a significant interest in eco-friendly textile products and processes has been noted among consumers and producers. In this respect, nanobubble technology is emerging as a green alternative. In this study, water-repellent cotton fabrics were produced with exhaustion and nanobubble technology (e-flow method) using a short-chain fluoropolymer. The currently most developed substituents are based on molecules with short fluorine carbon chains. The wettability, mechanical properties, air permeability and treatment durability were evaluated. The untreated and treated cotton fabrics were analyzed with ATR-FTIR (Fourier transform infrared attenuated total reflectance) and SEM (scanning electron microscopy) to reveal chemical and morphological modifications. The obtained results show that cotton samples treated with short-chain fluoropolymers, nontoxic and eco-friendly finishing chemicals, and nanobubble technology have good water repellence and good washing durability. Due to their size and structure, nanobubbles possess distinct properties that make them particularly effective at improving water quality, enhancing water treatment processes, and improving productivity in industrial applications. Nanobubbles have a strong negative surface charge that keeps them stable in liquid, prevents them from coalescing, and enables them to physically separate small particles and droplets from water, such as emulsified fats, oils, and grease. Full article

This study aims to evaluate the 3D-printed parts of different materials in terms of the achieved mechanical properties and surface characteristics. Fourteen infill patterns were employed in the 3D printing of polylactic acid (PLA), enhanced polylactic acid (PLA+), and polyethylene terephthalate glycol (PETG) materials. The printed specimens’ mechanical properties and surface characteristics were evaluated and discussed. Ultimate tensile strengths, Young’s modulus, and strain at break % were determined as mechanical properties, while average, maximum, and total height of profiles (Ra, Rz, and Rt) were measured as surface characteristics of the produced specimens. The cubic, gyroid, and concentric patterns were found to be the best infill patterns in terms of the mechanical properties of PLA, PLA+, and PETG materials, where maximum ultimate tensile strengths were recorded for these materials: 15.6250, 20.8333, and 16.5483 MPa, respectively. From the other side, the best Ra, Rz, and Rt were achieved with cross, quarter cubic, and concentric patterns of the PLA, PETG, and PLA+ materials, where the best values were (2.832 µm, 8.19 µm, and 17.53), (4.759 µm, 24.113 µm, and 35.216), and (4.234 µm, 30.136 µm, and 31.896), respectively. Full article

An amperometric sensor based on CaZr_0.95Sc_0.05O_3−δ (CZS) proton-conducting oxide for the measurement of hydrogen concentration in air was designed and tested. Dense CZS ceramics were fabricated through uniaxial pressing the powder synthesized by the solid-state method and sintering at 1650 °C for 2 h. The conductivity of CZS was shown to increase with increasing air humidity, which indicates the proton type of conductivity. The sensor was made from two CZS plates, one of which had a cavity was drilled to form an inner chamber, that were then pressed against each other and sealed around the perimeter to prevent gas leaking. The inner chamber of the sensor was connected with the outer atmosphere via an alumina ceramic capillary, which acted as a diffusion barrier. The sensor performance was studied in the temperature range of 600–700 °C in the mixtures of air with hydrogen. The sensor signal, or the limiting current, was found to linearly increase with the hydrogen concentration, which simplifies the sensor calibration. The sensor demonstrated a high sensitivity of ~60 μA per 1% H₂ at 700 °C, a fast response, high reproducibility, good selectivity, and long-term stability. Full article

Sewage sludge management at wastewater treatment plants is becoming a more and more challenging task. Here, an innovative integrated modeling approach is developed to investigate the optimization of a municipal wastewater treatment plant (MWWTP) by the inclusion of hydrothermal carbonization (HTC). To this aim, two alternative plant layouts have been considered: (i) a conventional activated sludge-based treatment plant, i.e., based on thickening, stabilization, conditioning, and dewatering; (ii) additional hydrothermal carbonization and integrated treatment of the spent liquor in the sludge line. An Italian MWWTP has been selected as a case study, and three different scenarios have been implemented in the process simulation software World Wide Engine for Simulation Training and Automation (WEST) by considering the effect of the different digestion times in the aerobic reactor. Then, according to the Design of Experiment (DoE) methodology applied both on simulated and experimental data, and by the use of a Python code, the desired models have been developed and compared. Finally, a Life Cycle Assessment (LCA) study has been carried out to estimate the impacts on human health, ecosystems, and resources. The integration of HTC corresponds to the generation of a valuable product (the hydrochar), whereas the conventional layout is associated with high disposal costs of the sewage sludge. According to LCA results, a sludge age of 40 days is recommended due to the lowest impacts estimated, both with and without a HTC section. This has been ascribed mainly to the electricity demand of the sludge line, which increases with the excess sludge flow rate, i.e., as the sludge age decreases. Full article

The photocatalytic degradation process and absorption kinetics of the aqueous solution of the Cibacron Brilliant Yellow 3G-P dye (Y) were investigated under UV-Vis light. Pure barium titanate BaTiO₃ (BT) and cobalt ion-substituted barium Ba_1−xCo_xTiO₃ (x = 0, …, 1) nano-compound powders (BCT) were synthesized using the sol–gel method and colloidal solution destabilization, and utilized as photocatalysts. The powder X-ray diffraction (PXRD) crystal structure analysis of the BT nanoparticles (NPs) revealed a prominent reflection corresponding to the perovskite structure. However, impurities and secondary phase distributions were qualitatively identified in the PXRD patterns for x ≥ 0.2 of cobalt substitution rate. Rietveld refinements of the PXRD data showed that the BCT nano-compound series undergoes a transition from perovskite structure to isomorphous ilmenite-type rhombohedral CoTiO₃ (CT) ceramic. The nanoparticles produced displayed robust chemical interactions, according to a Fourier transform infrared spectroscopy (FTIR) analysis. The BT and BCT nanoparticles had secondary hexagonal phases that matched the PXRD results and small aggregated, more spherically shaped particles with sizes ranging from 30 to 114 nm, according to transmission electron microscopy (TEM). Following a thorough evaluation of BCT nano-compounds with (x = 0.6), energy-dispersive X-ray (EDX) compositional elemental analysis revealed random distributions of cobalt ions. Through optical analysis of the photoluminescence spectra (PL), the electronic structure, charge carriers, defects, and energy transfer mechanisms of the compounds were examined. Due to the cobalt ions being present in the BT lattice, the UV-visible absorption spectra of BCT showed a little red-shift in the absorption curves when compared to pure BT samples. The electrical and optical characteristics of materials, such as their photon absorption coefficient, can be gathered from their UV-visible spectra. The photocatalytic reaction is brought about by the electron–hole pairs produced by this absorption. The estimated band gap energies of the examined compounds, which are in the range of 3.79 to 2.89 eV, are intriguing and require more investigation into their potential as UV photocatalysts. These nano-ceramics might be able to handle issues with pollution and impurities, such as the breakdown of organic contaminants and the production of hydrogen from water. Full article

Lignin is a raw material that can potentially be converted into valuable compounds through depolymerization reactions in addition to its use as a polymer or material. However, the chemical recalcitrance and the heterogeneous composition and structure of lignin make it challenging to establish processes that add value to this complex aromatic biopolymer. In this work, solvent fractionation was applied to obtain lignin fractions with a narrowed molecular weight and specific structural characteristics, improving its homogeneity and purity. A kraft lignin was submitted to fractionation using different ratios of acetone, ranging from 60 to 15% v/v, in aqueous mixtures. The composition, structure, and molecular weight of each fraction were studied and their potential applications were evaluated. The most water-soluble fraction has more phenolic OH, less aliphatic OH groups, and shows the lowest content of aryl-ether linkages, which is in accordance with its highest degree of condensation. On the other hand, the insoluble fraction from the mixture with 60% of acetone has the lowest molecular weight and the highest content of inorganic material. Radar plots were applied for lignin fractions evaluation and the fraction with the highest potential (IF 30:70) was submitted to alkaline oxidation with O₂. The results were compared with the products yielded from kraft lignin. An increase of about 13 and 19% was found for vanillin and syringaldehyde, respectively, when the fraction IF 30:70 was submitted to oxidation. In conclusion, the proposed fractionation process showed to be an effective method to obtain lignin fractions with specific composition and structural characteristics that could improve its potential as a source of high added-value monomeric phenolic compounds. Full article

The growth of technologies concerned with the high demand in lithium (Li) sources dictates the need for technological solutions garnering Li supplies to preserve the sustainability of the processes. The aim of this study was to use a machine learning-based search for phosphoryl-containing podandic ligands, potentially selective for lithium extraction from brine. Based on the experimental data available on the stability constant values of phosphoryl-containing organic ligands with Li${}^{+}$ and Na${}^{+}$ cations at 4:1 THF:CHCl${}_3$, candidate di-podandic ligands were proposed, for which the stability constant values (logK) with Li${}^{+}$ and Na${}^{+}$ as well as the corresponding selectivity values were evaluated using machine learning methods (ML). The modelling showed a reasonable predictive performance with the following statistical parameters: the determination coefficient R${}^2$= 0.75, 0.87 and 0.83 and root-mean-square error RMSE = 0.485, 0.449 and 0.32 were obtained for the prediction of the stability constant values with Li${}^{+}$ and Na${}^{+}$ cations and Li${}^{+}$/Na${}^{+}$ selectivity values, respectively. This ML-based analysis was complemented by the preliminary estimation of the host–guest complementarity of metal–ligand 1:1 complexes using the HostDesigner software. Full article

This study presents a new approach in the quantification of the deposited amount of impurity inside a filter cake made up of filter aid material. For this purpose, three-dimensional imaging by X-ray tomography is applied. Based on the X-ray attenuation properties, a model system consisting of kieselguhr as filter aid and barium sulphate as impurity is chosen. Due to the impurity particle size being smaller than the spatial resolution of the measuring setup, a calibration approach is necessary to gain insight into subvoxel information. A so-called phantom of similar material composition is prepared. The grey values are linearly correlated with the impurity volume fraction resulting in a calibration function, which facilitates the calculation of impurity volume fraction based on grey values measured inside the filter cake. First results are presented, showing that the approach delivers valid results for the chosen material system and reveals unexpected characteristics of the filter cake structure. Challenges in the context of the phantom approach and their influence on the obtained results are discussed. Full article