Volume 69, Issue 5

Chemical looping combustion (CLC) is a novel method of carbon capture and sequestration. It facilitates CO 2 capture by lower energy penalties compared with other methods in this category. The major challenges encountered in CLC are oxygen carrier, reactor and fuel-type selection. A proper combination of these factors is required for an efficient CLC. There have been several studies with regard to oxygen carriers applicable to these processes: novel oxygen carriers, single perovskites and potential oxygen carriers, double perovskites, have been investigated for their oxygen capture and release properties in a number of studies. Different kinds of reactors have also been proposed for use in CLC processes. This paper presents information on the materials capable of oxygen storage and release and the different kinds of reactors investigated for CLC in different studies. It has been shown that, although there are several oxygen carriers and reactors with the desired function and efficiency for CLC, there remains the need for further improvement and optimisation in both areas.

The contents of Cl, Ca, K, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, As, Se, Rb, Sr, Ba and Pb in raw coal fly ash from five Bulgarian power plants were determined by total reflection X-ray fluorescence (TXRF), using gallium as the internal standard. The samples were analysed as in slurry form in Triton TM X-114. The experimental parameters, such as grain size, concentrations of fly ash slurry and excitation time were optimised. For validation of the method, the certified reference material BCR-176R fly ash was used. The precision of the results obtained is characterised by a relative standard deviation of approximately 10 %. The resulting data confirm the suitability of TXRF for the simultaneous determination of major, minor and trace elements in coal fly ash samples. Further advantages provided by TXRF are easy sample preparation (no sample dissolution) and the small sample amount required for analysis.

An ascorbic acid (AA) amperometric sensor was fabricated based on a glassy carbon electrode (GCE) modified with a reduced graphene oxide-wrapped hierarchical TiO 2 (RGO-TiO 2 ) nanocomposite. The RGO-TiO 2 nanocomposite was synthesized via the facial wet chemical method and characterized by scanning electron microscopy and X-ray diffraction. Cyclic voltammetry and amperometric techniques were employed to investigate its electrocatalytic performance towards the AA oxidation. The combined advantages of RGO and TiO 2 provide the electrode with higher current response and lower oxidation potential compared with those of bare GCE and TiO 2 modified GCE. The proposed electrode can be used for the determination of AA in the wide concentration range from 1 to 1500 μM with the detection limit of 0.5 μM. The proposed electrode was successfully used to determine AA in vitamin C tablets and spiked fruit juice.

This paper reports a headspace analysis technique for the determination of products, i.e., cyclohexanone (CE) and cyclohexanol (CL), of phenol hydrogenation in a supercritical water reaction system (SWRS) with water removal by hydrate formation. An addition of anhydrous calcium chloride leads to water absorption resulting in crystal water; thus, the samples can be quantitatively measured without the influence of water. After achieving equilibrium at 150­°C and maintaining it for 5 min, the obtained results showed a relative standard deviation of less than 5.3 % and the recovery ranged from 93 % to 104 %. The presented method is simple and accurate for the analysis of CL, CE and phenol in samples from phenol conversion in SWRS.

A copolymer gel has been synthesized from N-vinylcaprolactam and dodecyl methacrylate in ethanol using the free radical cross-linking polymerization method. Characterizations of the gel were performed by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and thermal gravimetric analysis (TGA) techniques. Swelling behavior of the gel was investigated in heptane, toluene, and their binary mixtures with different compositions. Swelling value in toluene is higher than that in heptane and swelling value increases with the increasing initial content of toluene in the binary mixture with heptane. The swelling values are correlated by the first- and second-order differential equations, and the best model correlating the experimental results is a second-order one. Diffusion coefficients have also been calculated for heptane and toluene at each concentration by power-law and first-order equations. While the diffusion mechanism of the gel in heptane is a Fickian one, the gel swelled in toluene exhibits a non-Fickian character. Diffusion mechanisms of the gels in binary mixtures are much more complicated. Because of the higher swelling degree in toluene compared to that in heptane, selectivity of the gel in different {heptane + toluene} mixtures with selectivity close to 1 has also been taken into consideration.

The extraction of copper from sulphuric/sulphate solutions using a hollow fibre module as contactor was studied. The aldoxime Acorga M5640 was used as an extractant. The effects on the extraction rate of the flow-rates, the concentrations of copper and extractant, pH, and the presence of Na2SO4 in the feed phase were investigated. The overall mass transfer coefficient for copper extraction was calculated from the experimental data and was compared with the value evaluated by the resistance in the series model. The extraction process was found to be governed by the diffusion in the boundary aqueous layer and also by the chemical reaction. The kinetic data obtained were used to simulate the extraction of copper with the pseudo-emulsion-based hollow fibre with strip dispersion technique. The accordance between the results thus calculated and the experimental data was found to be satisfactory, particularly for dilute feed solutions.

In this work, heat transfer via the cylindrical part of the jacket in an agitated vessel has been investigated. Heat transfer coefficients were determined using the transient method based on measuring the temperature dependency of the liquid batch on time. A multistage impeller made of two impellers was used in a cylindrical vessel with dished bottom. The lower impeller was a curved blade turbine with the diameter of d = 100 mm and the upper impeller was either a pitched three-blade or pitched four-blade impeller with the diameter of d 1 = 67 mm. Three different impeller clearances in a multistage configuration, H 3 /d 1 = 1, 1.5, and 2, were used in our measurements. The vessel was equipped with two baffles. Experimental results were evaluated using the Euler’s method and nonlinear regression procedure in the Matlab ® software and they are summarized in form of Nusselt number correlations describing their dependency on the Reynolds number.

Stylophorum lasiocarpum (Oliv.) Fedde (Papaveraceae) belongs to traditional Chinese medicine herbs but there was minimal information on the content of alkaloids in this plant. Extracts from the aerial part and roots were examined by liquid chromatography with UV and mass spectrometric detection, with nineteen alkaloids identified. Changes in alkaloid content over the entire vegetation period of a one- and two-year old plant were studied. The protoberberine alkaloids, coptisine and stylopine, were found to be the main substances in extracts of the aerial part irrespective of the plant’s age and time of harvest. Variable amounts of protopine, sanguinarine, chelerythrine, chelirubine, macarpine, chelilutine and berberine were also recorded in the aerial part. The roots contained significantly larger quantities of all alkaloids than the aerial part with the levels of most alkaloids varying from May to October, peaking in the middle of the vegetation period. Coptisine was the dominant alkaloid in all samples. The antiproliferative activities of the root extract and of seven individual alkaloids were tested on A375 human malignant melanoma cells. The significant dose-dependent toxicity of the root extract was attributed largely to the quaternary benzo[c]phenanthridine alkaloids, macarpine and sanguinarine.

The designed polyurethane surfactant (PUS) was used as a macromolecular surfactant for the preparation of polyacrylate emulsion without any other surfactants and stabilizers. The resultant polymer emulsion and film properties were compared with those of the emulsion prepared with sodium dodecyl sulfate (SDS). Long shelf-life of the polymer emulsion can be achieved at proper composition. Polymer particles show core-shell and nano-scale structure with narrow distribution. Thermoanalysis results show phase separation in the polymer film, which leads to gloss decrease with the PUS content increase. Such polymer films show good water resistance and mechanical strength.

The practical synthetic preparation of glutaric acid has remained a major challenge to date. In the present study, glutaric acid was synthesised by way of one-pot diazoniation/hydrogenation of the readily available L-glutamic acid under aqueous conditions on a gram-scale with good yields. This is the first example of the deamination of the aliphatic primary amine via diazoniation and could afford a practical approach to the production of glutaric acid.

Ambroxol used as an expectorant in treating respiratory diseases was effectively prepared with a total yield of 62 %, with o-toluidine as the feedstock via successive procedures of electrophilic bromination, acetylation, radical benzylic bromination, N-alkylation and hydrolysis processes. The addition of aqueous hydrogen peroxide could enhance the utilisation of liquid bromine in the electrophilic bromination of o-toluidine, avoiding the hazardous HBr generated as a by-product. In addition, liquid bromine promoted by MnO 2 was used efficiently for the radical benzylic bromination of N-acetyl-N-(2,4-dibromo-6-methylphenyl)acetamide under mild conditions.

Acetylacetone was successfully used as a precursor of 4-aminomethylpyrazoles and 4-aminomethylisoxazoles in a two step process at ambient temperature. In the first step, acetylacetone was transformed to the corresponding hexahydropyrimidines (1,3-diazinanes) via two consecutive one-pot Mannich aminomethylations. Hexahydropyrimidines were then treated with hydrazine, phenylhydrazine, and hydroxylamine, respectively, to obtain the corresponding 4-aminomethylpyrazoles and 4-aminomethylisoxazoles in good yields. The hexahydropyrimidine ring decomposed providing the title compounds and a reasonable mechanism has been proposed.

Non-standard experimental conditions can often enhance organocatalytic reactions considerably. The current study explores the effectiveness of a range of non-standard reaction conditions for the asymmetric organocatalytic 1,3-dipolar cycloaddition of a nitrone with α,β-unsaturated aldehydes. The influence of ionic liquids, high-pressure conditions, ultrasound, microwave irradiation and ballmilling was tested as well as the flow process. Because of the low reactivity of the nitrone and unsaturated aldehydes in the 1,3-dipolar cycloaddition, cycloadducts were isolated in only moderate yields from the majority of experiments. However, high diastereo- and enantioselectivities were observed in ionic liquids under solvent-free conditions and in the flow reactor.

The phenomenon of the increase in solubility of the non-polar phenolic antioxidant - butylated hydroxytoluene (BHT) - in aqueous solutions containing β-cyclodextrin (CD) was studied. The complexation of BHT by CD was investigated using a phase solubility study. This method makes it possible to calculate the apparent formation constant for the host-guest complex. In addition, the thermodynamic properties were evaluated, revealing a spontaneous endothermic process of complex formation. Two solubility models were also used to verify their applicability to predicting the BHT concentration in solution. Those models included the modified Apelblat and Buchowski-Ksiazczak equations. In order to investigate the antioxidant properties of the BHT/CD/water ternary systems, a radical scavenging activity using a DPPH stable radical was performed. The experiments indicated that the antioxidant activity is temperature- and CD concentration-dependent. It was shown that complexation may inhibit the radical scavenging by BHT or change the scavenging stoichiometry.

The Rh(nbd)(L-proline) (nbd = 2,5-norbornadiene) catalyst was synthesised with L-proline as ligand. The achiral monomer phenylacetylene, having two hydroxyl groups and a dodecyl group (DoDHPA), was polymerised for the first time using an isolated chiral Rh(nbd)(L-proline) as catalyst to afford polymers of Mr of 28.5 × 10 4 and 36.2 × 10 4 . The resulting polymers exhibited the Cotton effect at wavelengths assignable to the main chain, indicating that the polymers adopted one-handed helical conformation. These findings suggest that the rhodium complex with chiral amine may be the true active species for helix-sense-selective polymerisation (HSSP) of DoDHPA.