http://vital.seals.ac.za:8080/vital/access/manager/Index en-us 5 http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:27041 Wed 12 May 2021 23:25:12 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:20846 Wed 12 May 2021 23:23:59 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:26556 Wed 12 May 2021 22:55:06 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:25942 Wed 12 May 2021 22:39:06 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:27144 Wed 12 May 2021 20:56:03 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:38669 Wed 12 May 2021 20:55:40 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:21316 Wed 12 May 2021 20:25:14 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:32585 Wed 12 May 2021 20:18:08 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:27026 Wed 12 May 2021 20:00:36 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:27135 Wed 12 May 2021 19:53:02 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:21128 Wed 12 May 2021 19:46:37 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:26966 Wed 12 May 2021 19:34:49 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:27053 Wed 12 May 2021 19:14:50 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:26370 Wed 12 May 2021 19:14:02 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:21308 Wed 12 May 2021 19:05:58 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:21307 Wed 12 May 2021 18:59:02 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:27124 Wed 12 May 2021 18:44:27 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:26946 Wed 12 May 2021 18:17:41 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:20707 Wed 12 May 2021 17:54:45 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:27126 Wed 12 May 2021 17:49:49 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:27142 Wed 12 May 2021 17:35:46 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:20613 500 oC) resulted in a lower rate of reaction and selectivity than when slightly lower temperatures are used (<350 oC) in both reactors, although much difference was noticed in the packed bed flow tubular reactor. Synthesis in the batch reactor needed longer silicon-catalyst activation time, higher pre-heating temperature and higher catalyst amounts as compare to the packed bed flow tubular reactor. Reaction temperature and alcohol flow rate influenced the reaction in both methods. The optimum reaction temperature range and alcohol flow rate was comparable in both reactors (230 to 240 oC) and 0.1mL/min respectively. The effect of alcohol R-group (C1 to C4) on the reaction revealed that conversion and selectivity generally decrease with an increase in carbon chain length in both methods. Ethanol showed highest selectivity (>95% in batch and >97% in flow) and conversion (about 88% in batch and about 64% in flow) as compared to all other alcohols studied showing that it could be the most efficient alkoxylation alcohol for this reaction. Overally, the packed bed flow tubular reactor resulted in higher selectivity to trialkoxysilanes than the batch system. Performing the reaction under pressure resulted in increased conversion but selectivity to the desire trialkoxysilane diminished. Synthesis in a continuous flow falling film tubular reactor was not successful as it resulted in very poor conversion and selectivity. Monosilane was successfully synthesized from the disproportionation of triethoxysilane using homogeneous and heterogeneous catalysts in batch mode. The results obtained from homogeneous catalysis showed that the reaction can be conducted at room temperature. The heterogeneous catalysis method resulted in slow conversion at room temperature but mild heating up to 55 oC greatly improved the reaction. Conducting the reaction under neat conditions produced comparable results to reactions which were carried out using solvents. The disproportionation reaction was best described by the first order kinetic model. The results obtained in this research indicate that the packed bed flow tubular reactor can be utilized with future modifications for continuous flow synthesis of alkoxysilanes as feedstock for the solar-grade silicon production.]]> Wed 12 May 2021 17:32:11 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:27015 Wed 12 May 2021 17:16:33 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:20357 Wed 12 May 2021 17:06:46 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:27849 Wed 12 May 2021 16:51:06 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:27046 S-NSN (12.70 mg/g) > S-TETA (4.97 mg/g). The extraction patterns on the sorbent materials were explained by considering the coordination chemistry of the ligand with [PdCl4]2ˉ and ionic interactions of [PtCl6]2ˉ and [IrCl5(H2O]ˉ. The square planar complexes, [Pd(HNSSNH)Cl2]Cl2 and [Pd(NSNH)Cl2][PdCl4]2, were isolated, analyzed by spectroscopy and single crystal X-ray, whereas evidence of the fraction of Pd(II)-TETA complex was obtained by HPLC studies. This provided proof of the inner sphere coordination mechanism as the mode of interaction of these ligands with [PdCl4]2ˉ. Trace amounts of Brˉ anions in ligands resulted in the inadvertent isolation of bromide coordinated Pd(II) NSN and NSSN complexes. The ion-pair salts of [TETAH4]4+ with [PtCl6]2ˉ, [IrCl6]3ˉ and [RhCl6]3ˉ were also isolated and characterized by microanalysis and IR to further explain the extraction patterns.]]> Wed 12 May 2021 16:29:31 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:21312 Wed 12 May 2021 16:20:28 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:27045 Wed 12 May 2021 16:10:04 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:27154 Wed 12 May 2021 16:06:46 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:27104 Wed 12 May 2021 16:01:49 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:29743 Thu 13 May 2021 16:09:25 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:20677 Thu 13 May 2021 13:21:29 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:38918 Thu 13 May 2021 08:25:28 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:27888 Thu 13 May 2021 08:19:50 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:26960 Thu 13 May 2021 07:38:12 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:26968 _D 2 suffciently large, a non-constant positive solution is generated, that is, stationary patterns emerge, depicting dispersal of species. Predators were observed to occupy habitats surrounding prey. However, super-predators were observed to alternate their habitats, from staying away from prey to invading prey habitat. In the investigation, strategies to determine ways in which the predator species could be saved from extinction and its population improved were devised, and these included isolation of the predator from the super-predator.]]> Thu 13 May 2021 07:24:20 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:26650 Thu 13 May 2021 07:08:39 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:20766 Thu 13 May 2021 07:07:30 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:27141 Thu 13 May 2021 07:03:18 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:26925 Thu 13 May 2021 06:52:01 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:20441 Thu 13 May 2021 06:50:39 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:26558 Thu 13 May 2021 06:44:17 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:20832 Thu 13 May 2021 06:31:05 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:21175 Thu 13 May 2021 06:23:32 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:20812 Thu 13 May 2021 06:21:20 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:21141 Thu 13 May 2021 06:11:45 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:24991 Thu 13 May 2021 05:42:12 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:20975 Thu 13 May 2021 05:39:53 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:27153 Thu 13 May 2021 04:53:06 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:24719 Thu 13 May 2021 04:21:33 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:39320 0oC, and partly due to the thermodynamic equilibrium between two stereoisomers. An economically alternative process was developed, evaluated and scaled-up in a 2l reactor. The project was initiated with a specific limitation in terms of the starting material that comprised a mixture of plant sterols, which necessitated a study of the isolation and purification of the desired product from a rather complex reaction mixture. The use of silver as halide acceptor for the Koenigs-Knorr synthesis did not give statistically significant different results from the same approach but using cadmium as halide acceptor instead. However, using the direct O-glucosylation approach not only gave statistically significant higher results, but also resulted in a much more convenient procedure. Under optimum conditions, a yield of approximately 83% (isolated) of 2,3,4,6- tetra-О-acetyl-β-sitosterol-D-glucoside could be achieved, which was substantially higher than that achieved with the traditional Koenigs-Knorr methodology and above reported yields in the literature (60-80%) for direct glycosylation. Separation of 2,3,4,6-tetra-О-acetyl-β-sitosterol-D-glucoside (BSSGT) from a reaction mixture that contains 2,3,4,6-tetra-О-acetyl-campesterol-D-glucoside (CSGT), 2,3,4,6-tetra-О-acetyl campestanol-glucoside (CSSGT), and 2,3,4,6-tetra-О-acetyl-sitostanol-Dglucoside (SSGT) was investigated using column chromatography. When using silica gel particles, very good separation efficiency and product recovery could be achieved using hexane/ethyl hexane as eluent. The isolated 2,3,4,6-tetra-О-acetyl-β-sitosterol-Dglucoside was easily hydrolysed to β-sitosterol-D-glucoside in high yields (79%) using methanolic KOH. The process for the production of β-sitosterol-D-glucoside was scaled-up from the laboratory bench scale (250 cm3) to a laboratory scale of 2 l using the direct Oglycosylation method. The overall yields of the scaled reaction for β-sitosterol-D-glucoside was slightly above the literature reported values (59%, 8/92) for the KnoenigsKnorr synthesis and compares well above (62%, 0/100) the current production process (less than 20% yields). When using catalogue prices, the material costs (without recycling) for the direct Oglucosylation route is approximately 57% less for the synthesis of 1kg of β-sitosterol-Dglucoside compared to the Koenigs-Knorr route. Given further savings for recycling, the direct O-glucosylation route provides an attractive alternative route for the synthesis ofthe target compound.]]> Thu 13 May 2021 03:47:07 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:21162 Thu 13 May 2021 03:15:07 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:26561 Thu 13 May 2021 02:47:48 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:39321 Thu 13 May 2021 02:20:18 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:29742 Thu 13 May 2021 02:05:44 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:39317 Thu 13 May 2021 02:02:27 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:27106 Thu 13 May 2021 02:00:28 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:20659 Thu 13 May 2021 01:58:36 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:26961 Thu 13 May 2021 01:19:29 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:27156 Thu 13 May 2021 01:10:17 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:21782 Thu 13 May 2021 01:06:15 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:27155 90 %). Phytoplankton and MPB interactions facilitated significant night-time NH4+ and SRP effluxes, (1.5 and 0.4 mg.m-2.h-1, respectively) four days post inundation. High Silica uptake in the latter stages, was attributed to an increase in diatom abundance. Within the chambers, MPB growth was continuous whilst phytoplankton exhibited cyclical growth as the system approached dynamic equilibrium. This study demonstrated the importance of nutrient cycling in structuring aquatic food webs, and indicated the sensitivity of ephemeral wetlands to environmental perturbations.]]> Thu 13 May 2021 01:06:07 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:38571 Thu 13 May 2021 00:39:01 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:27098 Fri 03 Dec 2021 15:47:49 SAST ]]>