Cleaner production and environmental sustainability: Analysis of the Serbian petrochemical plant

The approach proposed in this paper emphasizes the methodology of examining the possibility of increasing energy efficiency in the case of industry, such as a petrochemical complex, which is at the same time marked as the major pollutant of the environment. The improved cleaner production methodology was used based on the conditions and needs of the major Serbian petrochemical company. This paper presents results obtained by steam system optimization and modifications. The implemented measures lead to a decrease in total energy consumption by 6% and a decrease in greenhouse gas emissions by 9 t CO₂e.     

Hydrogen desorption properties of MgH2 catalysed with NaNH2

To improve hydrogen desorption properties of MgH₂, mechanical milling of MgH₂ with low concentration (2 and 5%) of NaNH₂ has been performed. Pre-milling of MgH₂ for 10 h has been done and then six samples have been synthesised with different milling times from 15 to 60 min. Microstructural characterisation has been performed using X-ray diffraction (XRD), scanning electron microscopy (SEM) and laser scattering measurements (PSD), and correlated to desorption properties examined using Differential Scanning Calorimetry (DSC) and Hydrogen Sorption Analyser (HSA). Thermal analysis shows that desorption temperatures are shifted towards lower values. It also highlights the significance of milling time and additive concentration on desorption behaviour.     

Electronic structure and charge distribution topology of MgH2 doped with 3d transition metals

Ab initio electronic structure calculations of the Mg₁₅TMH₃₂ (TM – transition metals – 6.25 at.%) systems for the entire 3d TM series have been performed using full-potential (linearized) augmented plane waves with addition of local orbitals (FP-LAPW + LO and APW + lo) as implemented in WIEN2k code and projected augmented waves (PAW) method using Abinit code. Details of bonding and mechanism of the TM impurities influence on destabilization of MgH₂ were established by investigation of changes of electronic structure after the TM impurities insertion into MgH₂ and by using the “atoms in molecules” (AIM) Bader's charge density topology analysis. The obtained trends of all calculated observables show that along the 3d series TMs accomplish different kinds of bonding with nearest and next-nearest neighbor hydrogen atoms that in general weaken related Mg–H bonds and destabilize the surrounding MgH₂ matrix.     

Calcium–Alginate–Inulin Microbeads as Carriers for Aqueous Carqueja Extract

Carqueja (Pterospartum tridentatum) is an endemic species and various bioactive compounds have been identified in its aqueous extract. The aim of this study was to protect the natural antioxidants from the aqueous extract of carqueja by encapsulation in Ca–alginate microbeads and Ca–alginate microbeads containing 10% and 20% (w/v) of inulin. The microbeads produced by electrostatic extrusion technique had an average diameter from 625 μm to 830 μm depending on the portion of inulin. The sphericity factor of the hydrogel microbeads had values between 0.014 and 0.026, while freeze dried microbeads had irregular shape, especially those with no excipient. The reduction in microbeads size after freeze drying process (expressed as shrinkage factor) ranged from 0.338 (alginate microbeads with 20% (w/v) of inulin) to 0.523 (plain alginate microbeads). The expressed radical scavenging activity against ABTS and DPPH radicals was found to be between 30% and 40% for encapsulated extract, while the fresh extract showed around 47% and 57% of radical scavenging activity for ABTS and DPPH radicals, respectively. The correlation between antioxidant activity and the total phenolic content were found to be positive (in both assay methods, DPPH and ABTS), which indicate that the addition of inulin didn't have influence on antioxidant activity. The presence of inulin reduced stiffness of the hydrogel, and protected bead structure from collapse upon freeze‐drying. Alginate–inulin beads are envisaged to be used for delivery of aqueous P. tridentatum extract in functional food products.     

Optimal dynamic management of exploitation life of the mining machinery: models with limited interval

A theoretical concept and an illustrated practical example of the limited interval dynamic model, aimed for application in optimizing the exploitation life of the mining machinery with shorter life cycle such as bulldozers, scrapers, haul trucks, excavators with one working element and smaller capacity, etc., is presented in this paper.     

A New 3-DOF Spatial Parallel Mechanism for Milling Machines with Long X Travel

It is well known that the shape and volume of the workspace are one of the greatest weaknesses of parallel kinematic machine tools (PKM). Hexaglide and Triaglide mechanisms are examples where workspace extension is achieved by elongating one axis as a principal motion axis that is a common feature of all Cartesian machines. With the idea of principal axis of motion in mind, a new 3-DOF spatial parallel mechanism for horizontal and vertical milling machines has been developed. In comparison with similar developed mechanisms it has several advantages such as: rather regular shape of the workspace (slightly modified block) similar to serial machines; greater stiffness by nature of the struts arrangement; good force and speed ratio through the entire mechanism's workspace. The paper describes the structure of the mechanism, modelling approach and simulation on a developed vertical milling machine prototype.     

Comparative Study of Reactive Dyes Oxidation by H2O2/UV,H2O2/UV/Fe2+ and H2O2/UV/Fe° Processes

The decolorization and mineralization of two reactive dyes C.I. Reactive Blue 4 (RB 4) and C.I. Reactive Blue 268 (RB 268) were studied using various advanced oxidation processes (AOPs) such as H₂O₂/UV, H₂O₂/UV/Fe²⁺, and the H₂O₂/UV/Fe°. All processes were performed within a laboratory-scale photo-reactor setup. The experimental results were assessed in terms of absorbance (A) and total organic carbon (TOC) reduction. The main degradation products were identified by high resolution gas chromatography/high resolution mass spectrometry analyses. The results of our study demonstrated that the additions of moderate concentrations of H₂O₂ and Fe catalyst during the AOPs evidently increased the decolorization efficiencies within the first few minutes of the processing time (5–10 min) for both tested dyes, and prolonged irradiation does not necessarily significantly improve decolorization. On contrary, TOC removal rate increased with the processing time and with the addition of the catalyst from 40–50% up to 70–80% at defined experimental conditions. All the tested AOPs were very successful methods for RB 268 decolorization, having very complex structure and much higher molecular weight compared to the dye RB 4. This is important from both economic and ecological points of view.     

Novel hexamethylene diamine‐functionalized macroporous copolymer for chromium removal from aqueous solutions

Macroporous copolymers of poly[(glycidyl methacrylate)‐co ‐(ethylene glycol dimethacrylate)] (PGME ) with various crosslinker (ethylene glycol dimethacrylate) concentrations and porosity parameters and additionally functionalized with hexamethylene diamine (PGME‐HD ) were tested as potential Cr(VI ) oxyanion sorbents from aqueous solutions. Kinetics of Cr(VI ) sorption was investigated in the temperature range 298–343 K and the results were fitted to chemical reaction and particle diffusion models. The Cr(VI ) sorption obeys the pseudo‐second‐order model with definite influence of pore diffusion. A temperature rise promotes chromium removal, with a maximum experimental uptake capacity of 4.21 mmol g^?1 at 343 K for the sample with the highest amino group concentration. Equilibrium data were analysed with Langmuir, Freundlich and Temkin adsorption isotherm models. Thermodynamic parameters, i.e. Gibbs free energy (ΔG ⁰), enthalpy (ΔH ⁰) and entropy change (ΔS ⁰) and activation energy of sorption (E _a), were calculated. The Cr(VI) adsorption onto PGME‐HD was found to be spontaneous and endothermic, with increased randomness in the system. Desorption experiments show that chromium anion sorption was reversible and the PGME‐HD sample GMA 60 HD was easily regenerated with 0.1 mol L^?1 NaOH up to 90% recovery in the fourth sorption/desorption cycle. In the fifth cycle, a substantial sorption loss of 37% was observed. © 2016 Society of Chemical Industry