Continuous flow synthesis of silicon compounds as feedstock for solar-grade silicon production

This thesis describes the key steps in the production of high purity (solar-grade) silicon from metallurgical-grade silicon for use in the production of photovoltaic cells as alternative renewable, environmentally benign and cheap energy source. The initial part of the project involves the development and optimization of a small chemical production platform system capable of producing alkoxysilanes from metallurgical-grade silicon as green precursors to solar-grade silicon production. Specifically, the main aim of the study was to synthesize trialkoxysilanes in continuous flow mode, although the synthesis on monosilane was also done in batch mode. The alkoxylation reaction was carried out in a traditional slurry phase batch reactor, packed bed flow tubular reactor and also attempted in a continuous flow falling film tubular reactor. The effect of key parameters which affect the silicon conversion and selectivity for the desired trialkoxysilane were investigated and optimized using ethanol as a reagent model. The synthesis was then extended to the other alcohols namely methanol, n-propanol and n-butanol. Copper catalysts which were tested in the alkoxylation reaction included: CuCl, Cu(OH)2, CuO and CuSO4. CuCl and Cu(OH)2 showed comparable activity in the batch mode but the former was more efficient in the packed bed flow tubular reactor. Cu(OH)2 could be used as a non-halide catalyst but its activity is limited to short reaction cycles (500 oC) resulted in a lower rate of reaction and selectivity than when slightly lower temperatures are used (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

DNA from Plant leaf Extracts: A Review for Emerging and Promising Novel Green Corrosion Inhibitors.

With growing global awareness and concern for environmental protection through the use of less hazardous and environmentally-friendly extracts of plant origin, there has been a plethora of green corrosion inhibitors research with far reaching contributions to the science of corrosion prevention and control. Attention has increasingly turned towards green corrosion inhibitors, compounds of natural origin with anti-oxidant activity towards metals and their alloys. Green inhibitors have been investigated for their corrosion and adsorption properties with good results. The findings from these research works provide evidence of the adsorption behavior of green inhibitors which was confirmed by the adsorption isotherms that were proposed. Adsorption is the first step of any surface reaction and since corrosion is a surface phenomenon the effectiveness of green corrosion inhibitors is related to their ability to adsorb on metal surfaces. This review proposes the potential of plant dna as an emerging and promising novel inhibitor for mild steel. It begins with a list of plants that have been used in studies to determine corrosion inhibition properties and moves on to establish the adsorption behavior of bio macromolecules; protein, polysaccharides (chitosan) and dna. It reviews studies and investigation of dna interaction and adsorption on inorganic surfaces before focusing on the use of salmon (fish) sperm dna and calf thymus gland dna as green corrosion inhibitors for mild steel. It concludes that plant dna is a promising candidate for green corrosion inhibitor given the similarity between the plant and animal dna structure and function, and the fact that the use of plant is more environmentally sustainable than animal-based produc

Atomic spectrometry update: Review of advances in the analysis of metals, chemicals and materials

There has been a large increase in the number of papers published that are relevant to this review over this review period. The growth in popularity of LIBS is rapid, with applications being published for most sample types. This is undoubtedly because of its capability to analyse in situ on a production line (hence saving time and money) and its minimally destructive nature meaning that both forensic and cultural heritage samples may be analysed. It also has a standoff analysis capability meaning that hazardous materials, e.g. explosives or nuclear materials, may be analysed from a safe distance. The use of mathematical algorithms in conjunction with LIBS to enable improved accuracy has proved a popular area of research. This is especially true for ferrous and non-ferrous samples. Similarly, chemometric techniques have been used with LIBS to aid in the sorting of polymers and other materials. An increase in the number of papers in the subject area of alternative fuels was noted. This was at the expense of papers describing methods for the analysis of crude oils. For nanomaterials, previous years have seen a huge number of single particle and field flow fractionation characterisations. Although several such papers are still being published, the focus seems to be switching to applications of the nanoparticles and the mechanistic aspects of how they retain or bind with other analytes. This is the latest review covering the topic of advances in the analysis of metals, chemicals and materials. It follows on from last year's review1-6 and is part of the Atomic Spectrometry Updates series

Recent Natural Corrosion Inhibitors for Mild Steel: An Overview

Traditionally, reduction of corrosion has been managed by various methods including cathodic protection, process control, reduction of the metal impurity content, and application of surface treatment techniques, as well as incorporation of suitable alloys. However, the use of corrosion inhibitors has proven to be the easiest and cheapest method for corrosion protection and prevention in acidic media. These inhibitors slow down the corrosion rate and thus prevent monetary losses due to metallic corrosion on industrial vessels, equipment, or surfaces. Inorganic and organic inhibitors are toxic and costly and thus recent focus has been turned to develop environmentally benign methods for corrosion retardation. Many researchers have recently focused on corrosion prevention methods using green inhibitors for mild steel in acidic solutions to mimic industrial processes. This paper provides an overview of types of corrosion, corrosion process, and mainly recent work done on the application of natural plant extracts as corrosion inhibitors for mild steel

Integration of a Light Rail Transit with Autonomous (driverless) Vehicles

Transportation has been a key aspect of human civilisation since before the Industrial revolution. It enabled the movement of people and goods for various reasons such as social, economic or political. Transportation was initially primitive, however, as the world began to technologically advance, there has been additional modes of transport to the generic land and water modes, including air and railways. The infrastructure used by all these modes has also improved providing durable assets to the mode users. Australian transport planners are investigating the idea of Autonomous Vehicles on the current transport networks. This mainly focus on road vehicles at this stage, but has the potential to be expanded into rail, water and air transport modes. This research project identified an opportunity to investigate utilisation the upcoming technological advancement as an integral part of a Light Rail Transit so as to provide a better service to the mode users. This will also reduce the potential for network disruption as the new technology emerges or even the inevitable redundancy of some portions of the current transport networks. This research project conducted an opinion survey of the locals in Gungahlin region and simulated the existing and future transport behaviour in the local district of Gunghalin transport network. Several scenarios were simulated and involved the alteration of the Autonomous Vehicle penetration into the transport network and reported on the identified impacts on the network and vehicle attributes. The key benefits of efficiently implementing the integration of the current and emerging technology in the transportation system is the viability of utilising the current infrastructure, with some modifications to provide a better service to the system users, improving the economic, social and political benefits in the society

Mixed-metal oxide conducting polymer nanocomposites for the removal of fluoride and chromium(VI) from aqueous solution

Abstract: Water is an indispensable natural resource for sustaining life which is undoubtedly not free in all places. The chemical composition of surface or underground waters is one of the principal aspects upon which the relevancy of water for domestic, industrial or agricultural purposes hinges upon. Inorganic anions are commonly in existence in water; nonetheless, some of these including oxy-anions, are undesirable and continually accountable for the grave environmental and health problems. Such ions like arsenic (As(V)), hexavalent chromium(Cr(VI)), fluoride (F‒) phosphate (PO43‒) and nitrate (NO3‒) when in exceeding maximum limits, constitute some of the most hazardous water pollutants. Fluoride, at low a concentration of 0.8-1.5 mg/L as recommended by World Health Organisation (WHO) can prevent tooth decay and contribute to the development of strong bones, especially in young children. However, at higher concentrations it has catastrophic health effects ranging from dental related problems to debilitating skeletal fluorosis as well as affecting body parts like the muscles, brain, lungs, kidneys, thyroid, reproduction and enzymes. Its high concentration in ground water is primarily owing to the weathering of fluoride rich minerals, high ash volcanic eruptions and many anthropogenic activities. On the other hand, industrial activities such as electroplating, leather tanning, dye production, ferrochrome production, wood preservation, mining and paints manufacture have indirectly led to the discharge of Cr(VI) ions into environmental water. Cr(VI) is one of the most toxic, highly soluble and mobile anions in the environment which causes health problems in the form of dermatitis, damage to the liver, lung and skin cancer, skin irritation and internal haemorrhage. The WHO recommended level of Cr(VI) is 0.1 mg/L in surface waters and 0.05 mg/L in drinking water. Consequently, sustainable technologies have been developed to remove fluoride and Cr(VI) ions from water ranging from chemical precipitation, reverse osmosis, electrochemical methods, adsorption, membrane processes, ion exchange and phytoremediation. Among these techniques, adsorption has shown superiority, attributed to its simplicity in design, low operating costs, efficiency and reversibility. Several adsorbents have been utilised for adsorption successfully. However, some drawbacks such as high cost, low selectivity, narrow pH ranges, low adsorption capacity, slow adsorption and poor mechanical strength have been encountered with some of the adsorbent materials. Nano-metal oxides (NMOs) and conduction polymers have a better potential as adsorbents physical and chemical properties. However they have problems of agglomeration, hence low adsorption capacity and difficult to separate from aqueous media. More studies on modification and...Ph.D. (Chemistry

A study to assess the knowledge, attitudes and beliefs of people in accepting male circumcision as a preventive method in HIV and AIDS, in Mbare and Southerton suburbs of Harare, Zimbabwe

This study explored the knowledge levels, beliefs and attitudes on male circumcision as an HIV intervention among a non-circumcising society within a country with high levels of heterosexually- transmitted infection. The study sought to gain an insight on the acceptability of male circumcision in Mbare and Southerton suburbs of Harare, Zimbabwe. A sample of 20 males who were circumcised at a health facility, 20 non- circumcised males and 20 females were reached. Three focus group discussions were held, one for non-circumcised men, one for women with circumcised partners and one for women with non-circumcised partners. Interviews were held with men circumcised at health facilities and one Key Informant (medical practitioner) from Spilhaus, Harare Hospital. Forty-seven percent of the respondents showed knowledge on the relationship between male circumcision and the prevention of HIV and AIDS. Educational attainment and different religious beliefs impact on the prevalence of male circumcision. Highly educated men sought male circumcision services more than others with secondary and primary level of education. Men who do not belong to any religion contributed the highest number of circumcised men. A significant number of women expressed that they will bring in their sons for circumcision. All most all of the circumcised men denied that male circumcision reduces sexual pleasure. A significant number of men cited stigma associated with male circumcision. Women’s role in male circumcision is seen in the preoperative and postoperative stages of male circumcision so that they provide care for the male. For men, the main predictors of circumcision preference pertained to beliefs surrounding sexual pleasure; for women, knowledge about the relationship between male circumcision status and sexually transmitted infections acquisition was the key indicator for circumcision preference. Among both sexes the main barrier to circumcision was fear of pain and death. The study thus noted that the community is not aware of the benefits of male circumcision and hence making it difficult to accept it as an HIV preventive measure. Awareness and education campaigns to increase people’s awareness on the benefits of male circumcision are needed in reducing the risk of HI

Synthesis and selective derivatization of 1,2,4-triols as a model for fluorous tagging and separation of compounds in avocado oil

M. Tech. Chemistry.While there are existing methods for the analysis and authentication of avocado oil based on the composition of the saponifiable fraction, the projected growth in the market for avocado oil as heart healthy edible oil or for use in cosmetics and pharmaceuticals may lead some producers to cheat via adulteration with inferior vegetable oils of similar fatty acid composition. Thus new methods based on the analysis of the unsaponifiable fraction could be used to complement the existing methods of detecting undesirable additives. The aim is to develop a method of selective benzoylation of 1,2-diols and 1,2,4-triols based on the Martinelli protocol

Synthesis and characterisation of Zeolites from Coal Fly Ash (CFA)

In this study, disposed coal fly ash samples from Zimbabwe were used in synthesis of zeolites. The method of direct hydrothermal treatment with sodium hydroxide at different concentrations (2, 2.5, 3.5 and 4.5 moldm-3) at a constant temperature of 100°C and activation time of 24 h was applied. Characterisation of coal fly ash and confirmation of occurrence of the zeolite material was done using XRF, XRD, FTIR, and BET techniques. The zeolite materials formed were a mixture of zeolite Na-X (NaAlSi1.1O4.2225H2O), zeolite Na-A (Na2Al2Si3.3O8.867H2O), zeolite NaP1 Na6Al6Si10O32H2O) and zeolite hydroxysodalite (Na1.08Al2Si1.68O7.441.8H2O). The variety and yield of zeolites formed depend on the concentration of sodium hydroxide used

Biosorption of zinc(II) ions from aqueous solution using msasa tree (brachystegia spiciformis) leaf powder

The purpose of this study was to explore the effectiveness of the Brachystegia spiciformis leaf powder for the removal of zinc (II) ions from aqueous solution. Batch experiments for the effect of pH, contact time, biomass dose and initial metal ion concentration were carried out in the laboratory. The adsorbent was characterized before and after biosorption of zinc ions by Fourier Transform-Infrared Spectroscopy (FT-IR). The investigation showed that the highest metal uptake was at solution pH 6, contact time of 120 mins and biomass dose of 2.0 g. The experimental data for the biosorption zinc (II) ions by Brachystegia spiciformis leaf powder was modelled to the Langmuir and Freundlich isotherms. The biosorption of zinc (II) ions fits better to the Langmuir than to the Freundlich model having correlation coefficients of 0.9902 and 0.9569 respectively. The maximum adsorption capacity Qmax was found to be 1.85 mg/g indicating the ability of the biosorbent to remove zinc from aqueous solution