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Material properties of ZnO thin films prepared by spray pyrolysis

- van Heerden, Johannes Lodewikus

  • Authors: van Heerden, Johannes Lodewikus
  • Date: 2012-08-16
  • Subjects: Thin films -- Electric properties , Thin films -- Optical properties , Zinc oxide , Zinc oxide -- Electric properties , Pyrolysis , Solar cells
  • Type: Thesis
  • Identifier: uj:2583 , http://hdl.handle.net/10210/6033
  • Description: Ph.D. , In the search to improve the conversion efficiency of solar cells such as α-Si and CuInSe2 cells, attention have recently been focused on the use of transparent conducting oxides (TCO's) as window layers and top electrodes in these cells. Materials such as indium tin oxide (ITO) and fluorine-doped tin oxide (FTO) thin films were used due to their excellent electro-optical properties, but it was found that they were unstable when subjected to a hydrogen plasma (during the a-Si deposition) and that the materials reduced to their metallic forms, degrading their electrical and optical properties. Zinc oxide (ZnO), however, possess electrical and optical properties equal to ITO and FTO, but is stable in the presence of a hydrogen plasma. In this study a system for the deposition of ZnO thin films by spray pyrolysis was developed and the films successfully deposited. The films were also doped with A1C1 3 in an attempt to further improve the films' conductivities. The films were then characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), electrical measurements (Hall and four-point probe measurements) and optical analyses of the films. The films were compared with films deposited by atomic layer epitaxy (ALE) and DC sputtering. It was found that the films were crystalline with a predominantly (002) preferred orientation. The addition of Al as dopant, however, resulted in the film structure deteriorating. The SEM micrographs obtained of the films indicated films with a close-packed structure, existing of small grains and the film surface having a textured appearance. It was further found that the deposition parameters of the films influenced both the structures of the films and the morphologies and the micrographs indicated that the addition of Al as dopant resulted in the film formation being inhibited and even resulting in no proper film being deposited. It was found that the as-deposited ZnO films were resistive and that the films had to be subjected to a post-deposition annealing to decrease the film resistivity. The annealing conditions were investigated and it was found that annealing the films in hydrogen at their deposition temperature for an hour resulted in the largest decrease in the films' resistivities, typically two orders of magnitude. Studies of the substrate temperature indicated that the films had to be deposited at between 350 and 420°C and that a reduction in the substrate temperature resulted in the film resistivity increasing. Contrary to literature, it was found that the addition of Al as dopant had no beneficial influence on the electrical properties of the films and that dopant concentrations exceeding 1.0 at.% resulted in the film resistivity increasing. The films were characterized optically by analysing the transmission spectra obtained of the films, using the envelope technique. It was found that the films had transmissions exceeding 95% and that the refractive indices and optical gaps centred around 1.99 and 3.3 eV respectively. Both properties were affected by the deposition parameters. The ZnO films deposited by spray pyrolysis compared excellently with the films prepared by ALE and DC sputtering in all aspects. It is hence clear that ZnO films, with characteristics suitable for solar cell application, can be deposited by the simple and inexpensive technique of spray pyrolysis.
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Reduction of sulphur in crude tyre oil by gasliquid phase oxidative adsorption

- Tsietsi, Pilusa, Muzenda, Edison, Mukul, Shukla

  • Authors: Tsietsi, Pilusa , Muzenda, Edison , Mukul, Shukla
  • Date: 2014
  • Subjects: Fuel , Desulphurisation , Distillation , Emissions , Pyrolysis
  • Type: Article
  • Identifier: http://ujcontent.uj.ac.za8080/10210/374451 , uj:4763 , http://hdl.handle.net/10210/11872
  • Description: This study investigates the reduction of sulphur compounds in crude tyre pyrolysis oil through gas-phase adsorption over molecular sieve. Crude tyre pyrolysis oil was distilled at 300° C using a bench scale distillation set-up consisting of an electric heating mantle, glass round bottom flask and water cooled glass condenser. The glass condenser bulb was filled with steel wool and molecular sieve pellets for effective oxidation and adsorption of sulphur compounds in the vapours prior to condensation. It was observed that gas-phase adsorption improves total sulphur capture by 19.6%. Reduction in sharp pungent smell of the condensed distilled light fractions is justified by 21.7% total sulphur removal of low boiling point mercaptans and sulphides during moisture removal stage. High boiling point and large molecular size sulphur compounds in the distilled fractions can be further reduced by 3.6% using liquid phase adsorption over activated carbon black.
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Production of liquid fuels through pyrolysis of waste hydraulic oil

- Rapoo, O.B., Muzenda, E., Nkosi, N.P.

A comparative review of waste tyre pyrolysis, gasification and liquefaction (PGL) processes

- Muzenda, Edison

  • Authors: Muzenda, Edison
  • Date: 2014
  • Subjects: Pyrolysis , Gases - Liquefaction , Waste tyre pyrolysis , Waste tyres - Environmental aspects
  • Type: Article
  • Identifier: uj:5030 , http://hdl.handle.net/10210/13550
  • Description: This article reviews remedial waste tyre technologies as well as utilization for energy and material recovery. Application examples and scenarios are drawn from developing countries such as South Africa. Waste minimization and utilization technologies are required to address the growing waste tyre problem. Waste tyres cause a variety of environmental and health challenges as they are bulk and non-degradable. Potential solutions to address the waste tyre problem are pyrolysis, gasification and liquefaction (PGL) processes. Process conditions and potential products for each process are reviewed and discussed in this paper. An environmental impact assessment of PGL processes and potential remedial solutions are also presented. PGL processes have huge potential for business. However the success of any operation depends on several economic and environmental factors such as capital and operating costs, feed availability, permitting process and emission from these operations.
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Development of a simulation model for gasification of South African solid waste : waste tyres and agricultural residue

- Mavukwana, Athi-enkosi

  • Authors: Mavukwana, Athi-enkosi
  • Date: 2016
  • Subjects: Biomass gasification , Biomass - Combustion , Pyrolysis
  • Language: English
  • Type: Masters (Thesis)
  • Identifier: http://hdl.handle.net/10210/242836 , uj:25059
  • Description: Abstract: Biomass is a potential fuel source that can contribute significantly to South Africa’s energy needs. Direct combustion is still the most used technology to utilize biomass high heating value. However this process suffers from significant inefficiencies and therefore creates the need for alternative processes to be analyzed. The present dissertation describes the study of fluidized gasification of biomass to produce syngas using ASPEN simulation software and the thermal decomposition of agricultural residues using thermogravimetric analysis (TGA). The TGA results confirmed that the thermal decomposition of two biomass types studied occurs in three stages. The first stage is the loss of moisture, occurring between 30oC and 120oC. The second stage is the devolution stage and constitutes the highest mass loss up to 65 wt%. This stage starts at 220oC for bagasse and 200oC for corncobs. The last stage is the thermal decomposition of lignin and the degration of heavier volatiles and the formation of char. This stage starts at 375oC for bagasse and 350oC for corncobs. The process decomposition of bagasse and corncobs shows good resemblance in all stages, therefore there are no kinetic limitations for co-processing of these materials in thermochemical processes such as gasification. These results were in agreement with those published in literature. The simulation software package Aspen plus was used to model the fluidized gasification of corncobs, bagasse and waste tyres. The gasification process was modelled by decomposing the dry feed of biomass into volatile components and ash followed by partial oxidation and gasification of the volatile components assuming the gasification reactions reached chemical equilibrium. The modelled data were compared to experimental results published in literature for processes where sugarcane bagasse and other biomass with comparable ultimate composition similar to bagasse were used as feedstock. The study focused on the effect of air (ER) and steam (SBR) on the composition of syngas and the gasification temperature. The results show that the optimum conditions for gasification of corncobs were ER of 0.34-0.36 and SBR of 0.8-1, these condition corresponded to a gasification temperature of 850-890oC. An ER of 0.33 to 0.38 and SBR of 1-2 were the optimum conditions to operate the gasification of waste tyres. The optimum conditions for bagasse gasification were found to be: ER 0.15-0.2 and the temperature of 800-900oC, SBR 0.9-1. However the simulation data under-predicted the CH4 formation and slightly over-predicted the H2 formation. However the overall results were in fair agreement with experimental data reported in literature. , M.Tech. (Chemical Engineering)
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Influence of pyrolyzed sludge use as an adsorbent in removal of selected trace metals from wastewater treatment

- Matheri, A. N., Ngila, J. C., Ntuli, F., Eloko, N. S.

A review on Botswana coal potential from a pyrolysis and gasification perspective

- Makoba, Mmoloki, Botha, Daniel Erich, Rapoo, Mpho Thabang, Szabo', Las'zlo' Zsolt, Shomana, Thapelo, Agachi, Paul Serban, Muzenda, Edison

A Review on Botswana Coal Potential from a Pyrolysis and Gasification Perspective

- Makoba, Mmoloki, Botha, Daniel Erich, Rapoo, Mpho Thabang, Szabó, László Zsolt, Shomana, Thapelo, Agachi, Paul Șerban, Muzenda, Edison

A review of experimental scope, designs and methods from intermediate-fast pyrolysis of biomass

- Charis, Gratitude, Danha, Gwiranai, Muzenda, Edison, Nkosi, Nhlanhla P.

  • Authors: Charis, Gratitude , Danha, Gwiranai , Muzenda, Edison , Nkosi, Nhlanhla P.
  • Date: 2019
  • Subjects: Experimental , Ntermediate-fast , Pyrolysis
  • Language: English
  • Type: Conference proceedings
  • Identifier: http://hdl.handle.net/10210/404768 , uj:33960 , Citation: Charis, G. et al. 2019. A review of experimental scope, designs and methods from intermediate-fast pyrolysis of biomass.
  • Description: Abstract: Intermediate and fast pyrolysis (IFP) for the recovery of bio-oil from organic matter have gained the attention of researchers in their attempt to increase the contribution of renewables into the energy mix. Current research has focused on equipment configuration and variables for higher yields of the oils; methods of upgrading the oils for compatibility with existing fuel infrastructure and engines, and various tests to characterize the products or test their applicability as fuels. This paper reviews the progress in experimental work around intermediate- fast pyrolysis (hot vapour residence~1-20s; moderate to high liquid yields) in the past twelve years. The review focuses on the experimental scope, equipment used, preparation of raw materials, experimental design and characterization of bio-oils. Experimental work covering actual applications of the oils are not covered in this review paper. The feedstocks mostly researched on in IFP were rice husks, followed by pinewood, Jatropha curcas cake and rapeseed respectively. Most IFP studies have been done on woody biomass (over 100 different feedstocks) due to their consistency, followed by agricultural residues then herbaceous energy crops. Lignocellulosics proved to be the veteran organic feedstocks (~95% of IFP) ahead of non- lignocellulosic biomass (~5%). The most applied technologies in recent years, were fluidized bed followed by the free fall reactors. For the experimental design, most papers reviewed used the simple single parameter method, while a few used the central composite rotatable design and full factorial design methods. The characterization tests mostly conducted on the oils were the pH, viscosity, Karl Fischer titration and calorific value.
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Carbon nanotubes and nanospheres: synthesis by nebulised spray pyrolysis and use in catalysis

- Cele, Leskey Mduduzi

  • Authors: Cele, Leskey Mduduzi
  • Date: 2009-05-13T08:47:51Z
  • Subjects: Carbon , Nanotubes , Nanostructured materials , Pyrolysis , Organic compounds synthesis , Palladium catalysts , Hydrogenation , Ethylene
  • Type: Thesis
  • Identifier: uj:8370 , http://hdl.handle.net/10210/2536
  • Description: Ph.D. , This work presents a detailed study of the synthesis of carbon nanotubes and nanospheres by nebulised spray pyrolysis. This method has been used by other workers mainly for preparation of sub-micron particles and the deposition of thin films on various substrates. The effect of various synthesis parameters including the temperature, choice of the carbon source and the metal precursor as well as the carrier gas flow rate on the selectivity of the reaction and the properties of the carbon nanotubes produced was investigated. A major part of this work was devoted to a study of the effects of the addition of small quantities of oxygencontaining compounds (alcohols, esters and aldehydes) to the reaction mixture. The products were analysed using various methods including TEM, SEM, Laser- Raman spectroscopy and HRTEM. Furthermore, the possible use of carbon nanotubes and carbon nanospheres as supports for palladium in the hydrogenation of ethylene was investigated. Nebulised spray pyrolysis proved to be a suitable technique for the synthesis of well graphitized carbon nanotubes and carbon nanospheres with uniform diameters and it was demonstrated that good control of the carbon nanotube properties could be achieved by controlling the synthesis parameters. Better graphitization of the carbon nanotubes was observed at higher temperatures. Ferrocene, iron pentacarbonyl, nickelocene and cobaltocene were successfully used in carbon nanotube synthesis with the last two producing carbon nanotubes with diameters close to those on single-walled carbon nanotubes. Toluene (with and without acetylene as a supplementary carbon source), benzene, mesitylene, xylene and nhexane were successfully used to produce carbon nanotubes with a high degree of alignment while no success was achieved with ethanol. The poor yields obtained with ethanol appear to be a consequence of chemical changes in the ethanol induced by exposure to ultrasound irradiation. On the other hand, low concentrations of methyl acetate and ethyl acetate appear to enhance the production of carbon nanotubes. It was demonstrated that carbon nanotubes and nanospheres are suitable for use as supports for palladium in the hydrogenation of ethylene. Pd particles of uniform size were obtained and the conversion rates were slightly higher when the carbon nanotubes were pre-treated with a mixture of sulphuric acid and nitric acid.
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Evaluation of pyrolysis on the yield and physicochemical properties of corncob biochar

- Akintola, Ayooluwa Tomiwa

  • Authors: Akintola, Ayooluwa Tomiwa
  • Date: 2019
  • Subjects: Biochar - South Africa , Chemical engineering - South Africa , Biomass gasification - South Africa , Pyrolysis
  • Language: English
  • Type: Masters (Thesis)
  • Identifier: http://hdl.handle.net/10210/417562 , uj:35368
  • Description: Abstract: Lately, biomass, because of its abundance and sustainability has recently gained rising attention to produce various useful bio-products such as biochar. Biochar is the solid product obtained when biomass undergoes different thermochemical conversion processes. Examples of such are thermal liquefaction, gasification, and pyrolysis. Pyrolysis has, however, been reported as the most efficient for producing biochar owing to its huge biochar throughput and easy operation. The ability to effectively control its process conditions in producing biochar with desired physicochemical properties has also made pyrolysis the choicest to produce biochar. Although different feedstock has been reportedly used in its production, corncob waste has not been utilized to produce biochar in South Africa. Furthermore, most reports on the study of biochar have reported only the effect of a single or two process parameters on biochar’s yield and physicochemical characteristics. In this study, slow pyrolysis was used to produce corncob biochar from corncob waste in South Africa under the influence of three process parameters that are temperature, residence time and particle size. The temperature was varied between 300-900 ℃, residence time between 0.5-2 hrs, and particle size of 0.5-4.0 mm.The result fully validated the research hypothesis that temperature would have the mostsignificant impact on corncob biochar’s yield and physicochemical properties. Also, the influence of residence time and particle size was better understood when varied with temperature. The observations from this study would assist further research into optimization of pyrolysis process on the yield and physicochemical characteristics of corncob biochar for specific applications in South Africa. , M.Tech. (Chemical Engineering)
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