Vapour phase dehydrogenation of cyclohexane on microstructured reactors
- Authors: Mpuhlu, Batsho
- Date: 2012
- Subjects: Dehydrogenation , Cyclohexane
- Language: English
- Type: Thesis , Doctoral , DTech (Chemistry)
- Identifier: http://hdl.handle.net/10948/8661 , vital:26418
- Description: The work that is described in this thesis forms part of the research and development projects at InnoVenton: NMMU Institute of Chemical Technology in collaboration with Sasol Technologies. The broader view of the project was testing on the so-called “Small Production Platforms” (SPP’s). In particular the main aim of this study was to investigate the effect of micro-structuring on the heterogeneous catalysed, vapour-phase oxidative dehydrogenation of cyclohexane in the presence of air. Ground work studies were done to provide a proper comparison of the micro-structured reactor with a traditional fixed-bed reactor. These included evaluation of a proper vanadium pyrophosphate catalyst for the reaction, testing of reaction parameters for the oxidative dehydrogenation reaction on a fixed-bed reactor and lastly comparing the performance of the micro-structured reactor to that of the fixed-bed reactor Various vanadium pyrophosphate catalysts that were tested for activity included: bulk (VO)2P2O7, bulk (VO)2P2O7 promoted with Fe, (VO)2P2O7 supported on -Al2O3 and Fe promoted (VO)2P2O7 supported on -Al2O3. These catalysts showed significant differences in TOF, however it was not conclusive from the results whether these differences may be traced to increased activity for dehydrogenation for different catalysts since all reactions were run under conditions of oxygen deficiency. It is, however, clear that Fe promotion significantly increase activity, irrespective of the relative degrees of oxidative dehydrogenation and normal dehydrogenation. The Fe promoted catalyst was further tested for long term stability in-view of using it as the catalyst in the micro-structured reactor. These studies showed the catalyst to have a high degree of stability with minimal structural changes under the reaction conditions used. Various response surface models describing the variation in each of the cyclohexane conversion, cyclohexene selectivity, and benzene selectivity, respectively when changing reaction condition, were derived by means of multiple regression. To obtain some idea of the degree and nature of the normal dehydrogenation reaction, the amount of deficit oxygen was estimated from the measured results for cyclohexane conversion and cyclohexene and benzene selectivities. These estimated values were also modelled as described above. The regression models were used to interpret specific trends in the responses for the oxidative dehydrogenation of cyclohexane and account for the oxygen deficit in the system. The performance of a fixed bed tubular reactor (FBR) and micro-structured sandwich reactor (MSSR) were compared over an Fe promoted vanadium pyrophosphate. Reactor performance was evaluated by varying specific reaction conditions (temperature and space velocity). Subsequently the turn-over frequencies, conversion and selectivities from the two reactors were compared. The conversion achieved in the micro-structured reactor was observed to be significantly higher than that achieved in the fixed-bed reactor at all reaction parameters. This is despite the fact that the total amount of catalyst in the micro-structured reactor is approximately 5 times less than that used in the fixed bed reactor. In addition, the contact time (1/MHSV) in the micro-structured reactor is also significantly shorter than in the fixed-bed reactor.
- Full Text:
- Date Issued: 2012
- Authors: Mpuhlu, Batsho
- Date: 2012
- Subjects: Dehydrogenation , Cyclohexane
- Language: English
- Type: Thesis , Doctoral , DTech (Chemistry)
- Identifier: http://hdl.handle.net/10948/8661 , vital:26418
- Description: The work that is described in this thesis forms part of the research and development projects at InnoVenton: NMMU Institute of Chemical Technology in collaboration with Sasol Technologies. The broader view of the project was testing on the so-called “Small Production Platforms” (SPP’s). In particular the main aim of this study was to investigate the effect of micro-structuring on the heterogeneous catalysed, vapour-phase oxidative dehydrogenation of cyclohexane in the presence of air. Ground work studies were done to provide a proper comparison of the micro-structured reactor with a traditional fixed-bed reactor. These included evaluation of a proper vanadium pyrophosphate catalyst for the reaction, testing of reaction parameters for the oxidative dehydrogenation reaction on a fixed-bed reactor and lastly comparing the performance of the micro-structured reactor to that of the fixed-bed reactor Various vanadium pyrophosphate catalysts that were tested for activity included: bulk (VO)2P2O7, bulk (VO)2P2O7 promoted with Fe, (VO)2P2O7 supported on -Al2O3 and Fe promoted (VO)2P2O7 supported on -Al2O3. These catalysts showed significant differences in TOF, however it was not conclusive from the results whether these differences may be traced to increased activity for dehydrogenation for different catalysts since all reactions were run under conditions of oxygen deficiency. It is, however, clear that Fe promotion significantly increase activity, irrespective of the relative degrees of oxidative dehydrogenation and normal dehydrogenation. The Fe promoted catalyst was further tested for long term stability in-view of using it as the catalyst in the micro-structured reactor. These studies showed the catalyst to have a high degree of stability with minimal structural changes under the reaction conditions used. Various response surface models describing the variation in each of the cyclohexane conversion, cyclohexene selectivity, and benzene selectivity, respectively when changing reaction condition, were derived by means of multiple regression. To obtain some idea of the degree and nature of the normal dehydrogenation reaction, the amount of deficit oxygen was estimated from the measured results for cyclohexane conversion and cyclohexene and benzene selectivities. These estimated values were also modelled as described above. The regression models were used to interpret specific trends in the responses for the oxidative dehydrogenation of cyclohexane and account for the oxygen deficit in the system. The performance of a fixed bed tubular reactor (FBR) and micro-structured sandwich reactor (MSSR) were compared over an Fe promoted vanadium pyrophosphate. Reactor performance was evaluated by varying specific reaction conditions (temperature and space velocity). Subsequently the turn-over frequencies, conversion and selectivities from the two reactors were compared. The conversion achieved in the micro-structured reactor was observed to be significantly higher than that achieved in the fixed-bed reactor at all reaction parameters. This is despite the fact that the total amount of catalyst in the micro-structured reactor is approximately 5 times less than that used in the fixed bed reactor. In addition, the contact time (1/MHSV) in the micro-structured reactor is also significantly shorter than in the fixed-bed reactor.
- Full Text:
- Date Issued: 2012
An investigation of statistical methodologies for evaluating natural herbicides for the control of yellow nutsedge (Cyperus esculentus)
- Authors: Asquith, Ilse Bernadette
- Date: 2007
- Subjects: Chemometrics , Weeds
- Language: English
- Type: Thesis , Doctoral , DTech (Chemistry)
- Identifier: vital:10376 , Chemometrics , Weeds
- Description: The present study was undertaken with the view to evaluate methodologies based on traditional Scheffé experimental designs that study mixtures as a tool for discovery research particularly when seeking new and or improved uses of existing mixtures. For the purpose of this study, the topic of controlling the problematic weed known as Yellow Nutsedge (Cyperus esculentus L. var. esculentus) or “Geel Uintjie”, was selected on a rather ad hoc basis. Yellow Nutsedge is a troublesome perennial weed found in most agricultural countries in the world. Herbicidal control is often difficult because of the weeds’ ability to propagate via tubers, which can remain dormant for a number of years and are also resistant to most synthetic herbicide controls. As a first step the study involved the selection of a group of chemical compounds that would be used in suppressing the germination of Yellow Nutsedge tubers. Treatment with various combinations of these chemical compounds as determined by statistical experimental designs was carried out. A review of the literature, particularly literature concerned with the study of the phenomenon of allelopathy, suggested that various phenolic-D-glucopyranosides could show promise in the suppressing the germination of Yellow Nutsedge tubers. This led to the selection of this group of compounds as the target group of “active” substances for the study. Since the group of phenolic-D-glucopyranosides is quite large, and in order to keep the study to a reasonable size, only four phenolic-D-glucopyranosides were selected namely: 4-nitrophenyl-D-glucopyranoside, 4-chlorophenyl--Dglucopyranoside, arbutin and salicin. This selection was based firstly based on a particular phenolic-D-glucopyranoside being a suspected allelochemical, and secondly the ease of technical synthesis using a catalytic process. In addition to the four selected phenolic-D-glucopyranosides, their aglycones (4,nitrophenol, 4,chlorophenol, hydroquinone and salicyl alcohol) were also included as potential “active” substances in order to discern any potential activity between the phenolic-D-glucopyranosides and the aglycones. iii The selected “active substances” were combined in various combinations according to various mixture designs in such a manner that the sum of the proportions of the various actives in any one mixture was always equal to 1. The mixtures of actives were then used in various germination experiments and three experimental responses were measured namely the germination, average dry mass and length of longest shoot. From the results of these germination studies the canonical form of the polynomial equation describing the variation in each of the three germination responses was calculated and evaluated statistically. These equations were then used to estimate the presence of, and the magnitude of synergism between the various active substances. The results from these screening experiments and their detailed statistical analysis indicated that the response surface model for the germination response contains three synergistic blends (4-nitrophenyl--D-glucopyranoside + arbutin; 4-nitrophenyl--Dglucopyranoside + hydroquinone; and 4-chlorophenyl--D-glucopyranoside + salicin) and one antagonistic blend (4-nitrophenyl--D-glucopyranoside + 4- chlorophenol--D-glucopyranoside). The response surface model for the average dry mass response contains two synergistic blends (4-nitrophenyl--Dglucopyranoside + hydroquinone; and 4-chlorophenol--D-glucopyranoside + salicin) and the same antagonistic blend as for germination response. For both germination and average dry mass responses, the most synergistic blend was found to be the combination of 4-chlorophenyl--D-glucopyranoside and salicin. Two additional tests were conducted and both confirmed the results obtained from the screening designs. These tests involved the identification of the two components responsible for the synergistic activity that resulted in the suppression of the germination of the tubers and growth of the seedlings. The experimental response measuring the longest shoot proved to be erroneous and was excluded from the statistical analysis. In summary, this study has clearly shown that statistically designed experiments based on mixture designs can be used as a powerful tool in identifying and quantifying synergistic (or antagonistic) effects of chemicals on the germination ability of plant seeds.
- Full Text:
- Date Issued: 2007
- Authors: Asquith, Ilse Bernadette
- Date: 2007
- Subjects: Chemometrics , Weeds
- Language: English
- Type: Thesis , Doctoral , DTech (Chemistry)
- Identifier: vital:10376 , Chemometrics , Weeds
- Description: The present study was undertaken with the view to evaluate methodologies based on traditional Scheffé experimental designs that study mixtures as a tool for discovery research particularly when seeking new and or improved uses of existing mixtures. For the purpose of this study, the topic of controlling the problematic weed known as Yellow Nutsedge (Cyperus esculentus L. var. esculentus) or “Geel Uintjie”, was selected on a rather ad hoc basis. Yellow Nutsedge is a troublesome perennial weed found in most agricultural countries in the world. Herbicidal control is often difficult because of the weeds’ ability to propagate via tubers, which can remain dormant for a number of years and are also resistant to most synthetic herbicide controls. As a first step the study involved the selection of a group of chemical compounds that would be used in suppressing the germination of Yellow Nutsedge tubers. Treatment with various combinations of these chemical compounds as determined by statistical experimental designs was carried out. A review of the literature, particularly literature concerned with the study of the phenomenon of allelopathy, suggested that various phenolic-D-glucopyranosides could show promise in the suppressing the germination of Yellow Nutsedge tubers. This led to the selection of this group of compounds as the target group of “active” substances for the study. Since the group of phenolic-D-glucopyranosides is quite large, and in order to keep the study to a reasonable size, only four phenolic-D-glucopyranosides were selected namely: 4-nitrophenyl-D-glucopyranoside, 4-chlorophenyl--Dglucopyranoside, arbutin and salicin. This selection was based firstly based on a particular phenolic-D-glucopyranoside being a suspected allelochemical, and secondly the ease of technical synthesis using a catalytic process. In addition to the four selected phenolic-D-glucopyranosides, their aglycones (4,nitrophenol, 4,chlorophenol, hydroquinone and salicyl alcohol) were also included as potential “active” substances in order to discern any potential activity between the phenolic-D-glucopyranosides and the aglycones. iii The selected “active substances” were combined in various combinations according to various mixture designs in such a manner that the sum of the proportions of the various actives in any one mixture was always equal to 1. The mixtures of actives were then used in various germination experiments and three experimental responses were measured namely the germination, average dry mass and length of longest shoot. From the results of these germination studies the canonical form of the polynomial equation describing the variation in each of the three germination responses was calculated and evaluated statistically. These equations were then used to estimate the presence of, and the magnitude of synergism between the various active substances. The results from these screening experiments and their detailed statistical analysis indicated that the response surface model for the germination response contains three synergistic blends (4-nitrophenyl--D-glucopyranoside + arbutin; 4-nitrophenyl--Dglucopyranoside + hydroquinone; and 4-chlorophenyl--D-glucopyranoside + salicin) and one antagonistic blend (4-nitrophenyl--D-glucopyranoside + 4- chlorophenol--D-glucopyranoside). The response surface model for the average dry mass response contains two synergistic blends (4-nitrophenyl--Dglucopyranoside + hydroquinone; and 4-chlorophenol--D-glucopyranoside + salicin) and the same antagonistic blend as for germination response. For both germination and average dry mass responses, the most synergistic blend was found to be the combination of 4-chlorophenyl--D-glucopyranoside and salicin. Two additional tests were conducted and both confirmed the results obtained from the screening designs. These tests involved the identification of the two components responsible for the synergistic activity that resulted in the suppression of the germination of the tubers and growth of the seedlings. The experimental response measuring the longest shoot proved to be erroneous and was excluded from the statistical analysis. In summary, this study has clearly shown that statistically designed experiments based on mixture designs can be used as a powerful tool in identifying and quantifying synergistic (or antagonistic) effects of chemicals on the germination ability of plant seeds.
- Full Text:
- Date Issued: 2007
A commercial process development for plant food formulation using polyprotic acids from natural extracts as chelating agents
- Authors: Ndibewu, Peter Papoh
- Date: 2005
- Subjects: Chelates , Lemon juice , Liquid fertilizers
- Language: English
- Type: Thesis , Doctoral , DTech (Chemistry)
- Identifier: vital:10368 , http://hdl.handle.net/10948/153 , Chelates , Lemon juice , Liquid fertilizers
- Description: The citrus industry is one of South Africa's largest agricultural sectors in terms of export earnings with lemon fruits and juice as a trendsetter due to their high grade quality. According to growers, the Eastern Cape Province of South Africa alone produces an excess of about 10-14,000 tons of lemon juice which is presently of no economic value due to the sour taste and “bitterness”. As a result of this excess and in order to make use of the polyprotic acids naturally occurring in the lemon juice, four fertilizer nutrient mixtures are formulated, using lemon juice as base. From a conceptual scientific approach, characterization (physico-chemical and functional properties determinations) of Eureka Lemon fruit juices were undertaken, followed by smaller scale batch formulation experiments. On the basis that these lemon juice-based fertilizer mixtures are prepared following standard liquid fertilizer formulation guidelines, a field test was conducted to evaluate their potential effectiveness to influence plant growth. A growth chamber testing on tomato plants revealed high growth response (> 99.9 % certainty) potential in two of the semi-organic mixtures formulated while the organic mixture showed a relatively good growth rate as compared to the control (pure tap water). According to statistical analysis (ANOVA) comparison, two of the semi-organic mixtures performed considerably better than the two commercial samples evaluated. Potential benefits profoundly associated with these nutrient mixtures as compared to similar liquid fertilizer products on the market is that most nutrients are chelated and dissolved in solution. Also, the mixtures contain all necessary nutrients including plant growth substances required for healthier plant growth. The most important socioeconomic impact is the value addition to the technology chain in the citrus industry. The use of fluid fertilizers in significant quantities is less than twenty years old. Nevertheless, growth has been so rapid that in South Africa demand for mixed liquid fertilizer has greatly increased from 90 000 tons NPK & blended micronutrients in 1955 to more than 600 000 per annum tons today (Report 41/2003, Department of Minerals and Energy). The liquid fertilizers market is sparsely specialized with major competitors like Omnia, Kynoch and Foskor supplying more than 50 % of the market demand. Amongst the nutrient mixtures formulated, mixture one is an NPK (1-1-2) based nutrient mixture containing both secondary nutrients (0.5 % Mg & 1.0 % Ca) and seven micronutrients (0.1 % Fe, 0.05 % Cu, 0.05 % Zn, 0.05 % Mn, 0.02 % B, 0.0005 % Mo and 0.0005 % Co). The composition of this mixture offers the formula a potential to be used as a general purpose (all stages of plant growth) fertilization mixture in view of its balanced composition (containing all essential plant nutrients). Mixture two contains essentially the micronutrients and in higher concentrations (0.3 % Fe, 0.3 % Cu, 0.1 % Zn, 0.2 % Mn, 0.02 % B, 0.0005 % Mo and 0.0005 % Co) as compared to mixture one except for boron, molybdenum and cobalt. The concentration of the micronutrients contained in this mixture is adequately high which offers a potential for it to be used in supplementing nutrition in plants with critical micronutrient-deficient symptoms. Mixture three is very similar to mixture two (1.0 % Fe, 0.05 % Cu, 0.05 % Zn, 0.05 Mn, 0.05 % B, 0.0005 % Mo and 0.0005 % Co) except that the concentrations of all seven micronutrients are considerably less than those of contained in mixture two. However, the concentration of iron in this mixture is as high as 1.0 %. The mixture has a potential to be used in high iron-deficient situations. Mixture four is an organic formula with relatively low nutrient concentrations (NPK-0.02-0.02-1, 0.27 % Mg, 0.02 % Ca, 0.008 % Fe, 0.26 % Cu, 0.012 % Zn, 0.009 % Mn). Nevertheless, this mixture is appealing for organically grown crops where the use of chemicals is prohibited by standards. These lemon juice-based nutrient mixtures were further characterized and tested for stability and storability over a period of eight weeks. This study revealed no major change in the physical quality (colour, pH and “salt out” effect). The basic formulation methodology is a two-step procedure that involves filtration of the lemon juice to remove membranous materials, mixing at ambient temperature and stabilization of the nutrient mixtures. However, for the organic nutrient formula mix, filtration follows after extraction of nutrients from plant materials using the lemon juice.
- Full Text:
- Date Issued: 2005
- Authors: Ndibewu, Peter Papoh
- Date: 2005
- Subjects: Chelates , Lemon juice , Liquid fertilizers
- Language: English
- Type: Thesis , Doctoral , DTech (Chemistry)
- Identifier: vital:10368 , http://hdl.handle.net/10948/153 , Chelates , Lemon juice , Liquid fertilizers
- Description: The citrus industry is one of South Africa's largest agricultural sectors in terms of export earnings with lemon fruits and juice as a trendsetter due to their high grade quality. According to growers, the Eastern Cape Province of South Africa alone produces an excess of about 10-14,000 tons of lemon juice which is presently of no economic value due to the sour taste and “bitterness”. As a result of this excess and in order to make use of the polyprotic acids naturally occurring in the lemon juice, four fertilizer nutrient mixtures are formulated, using lemon juice as base. From a conceptual scientific approach, characterization (physico-chemical and functional properties determinations) of Eureka Lemon fruit juices were undertaken, followed by smaller scale batch formulation experiments. On the basis that these lemon juice-based fertilizer mixtures are prepared following standard liquid fertilizer formulation guidelines, a field test was conducted to evaluate their potential effectiveness to influence plant growth. A growth chamber testing on tomato plants revealed high growth response (> 99.9 % certainty) potential in two of the semi-organic mixtures formulated while the organic mixture showed a relatively good growth rate as compared to the control (pure tap water). According to statistical analysis (ANOVA) comparison, two of the semi-organic mixtures performed considerably better than the two commercial samples evaluated. Potential benefits profoundly associated with these nutrient mixtures as compared to similar liquid fertilizer products on the market is that most nutrients are chelated and dissolved in solution. Also, the mixtures contain all necessary nutrients including plant growth substances required for healthier plant growth. The most important socioeconomic impact is the value addition to the technology chain in the citrus industry. The use of fluid fertilizers in significant quantities is less than twenty years old. Nevertheless, growth has been so rapid that in South Africa demand for mixed liquid fertilizer has greatly increased from 90 000 tons NPK & blended micronutrients in 1955 to more than 600 000 per annum tons today (Report 41/2003, Department of Minerals and Energy). The liquid fertilizers market is sparsely specialized with major competitors like Omnia, Kynoch and Foskor supplying more than 50 % of the market demand. Amongst the nutrient mixtures formulated, mixture one is an NPK (1-1-2) based nutrient mixture containing both secondary nutrients (0.5 % Mg & 1.0 % Ca) and seven micronutrients (0.1 % Fe, 0.05 % Cu, 0.05 % Zn, 0.05 % Mn, 0.02 % B, 0.0005 % Mo and 0.0005 % Co). The composition of this mixture offers the formula a potential to be used as a general purpose (all stages of plant growth) fertilization mixture in view of its balanced composition (containing all essential plant nutrients). Mixture two contains essentially the micronutrients and in higher concentrations (0.3 % Fe, 0.3 % Cu, 0.1 % Zn, 0.2 % Mn, 0.02 % B, 0.0005 % Mo and 0.0005 % Co) as compared to mixture one except for boron, molybdenum and cobalt. The concentration of the micronutrients contained in this mixture is adequately high which offers a potential for it to be used in supplementing nutrition in plants with critical micronutrient-deficient symptoms. Mixture three is very similar to mixture two (1.0 % Fe, 0.05 % Cu, 0.05 % Zn, 0.05 Mn, 0.05 % B, 0.0005 % Mo and 0.0005 % Co) except that the concentrations of all seven micronutrients are considerably less than those of contained in mixture two. However, the concentration of iron in this mixture is as high as 1.0 %. The mixture has a potential to be used in high iron-deficient situations. Mixture four is an organic formula with relatively low nutrient concentrations (NPK-0.02-0.02-1, 0.27 % Mg, 0.02 % Ca, 0.008 % Fe, 0.26 % Cu, 0.012 % Zn, 0.009 % Mn). Nevertheless, this mixture is appealing for organically grown crops where the use of chemicals is prohibited by standards. These lemon juice-based nutrient mixtures were further characterized and tested for stability and storability over a period of eight weeks. This study revealed no major change in the physical quality (colour, pH and “salt out” effect). The basic formulation methodology is a two-step procedure that involves filtration of the lemon juice to remove membranous materials, mixing at ambient temperature and stabilization of the nutrient mixtures. However, for the organic nutrient formula mix, filtration follows after extraction of nutrients from plant materials using the lemon juice.
- Full Text:
- Date Issued: 2005
Electrochemical investigation of valve regulated lead acid batteries
- Authors: Ferg, Ernst Eduard
- Date: 2004
- Subjects: Lead acid batteries -- South Africa , Storage batteries -- South Africa , Electrochemistry -- South Africa
- Language: English
- Type: Thesis , Doctoral , DTech (Chemistry)
- Identifier: vital:10979 , http://hdl.handle.net/10948/228 , Lead acid batteries -- South Africa , Storage batteries -- South Africa , Electrochemistry -- South Africa
- Description: One of the technical advances made by the lead-acid battery industry in the field of portable power supply was the development of the valve regulated lead-acid battery (VRLA). This battery reduced the necessity for periodic servicing in terms of having to replenish the cells with distilled water. Further, this new type of battery can now be installed near sensitive electronic equipment without the danger of acid spill or dangerous fumes being emitted. In addition, longer service performance is achieved in terms of life cycle capacity, when compared to the conventional flooded type batteries. However, the new type of battery requires the manufacturing of high precision electrodes and components with low tolerances for error. In order for the manufacturers to produce such a premium product, a thorough understanding of the electrochemistry of the inner components is necessary. None of the South African lead-acid battery manufacturers are currently making VRLA batteries to supply a very competitive global market, where a large range of sizes and capabilities are available. In order to introduce the VRLA battery into such a competing market in South Africa, a niche area for its application was identified in order to establish the viability of manufacturing such a battery locally. This is done by integrating the VRLA concept into an existing battery, such as the miners cap lamp (MCL) battery. Its application is specific with well-defined performance criteria in a relatively large consumable market in the South African mining industry. The study looked at various components within a local manufacturing environment that required a better understanding and modification of the processes to build VRLA MCL batteries. This included a detailed study of the manufacturing processes of the positive electrode. The study involved the investigation of the types of grid alloys used, the type of electrode design, such as tubular or flat plate, the addition of redlead to the paste mixing process and subjecting the batteries to accelerated life cycle testing. A better understanding of the oxygen recombination cycle was also performed in order to evaluate the correct use of certain design criteria in the manufacturing process. This included the study of the pressure release valve and the type of positive electrode used. The study also looked at developing an inexpensive analytical technique to evaluate the porosity of cured and formed electrodes using a glycerol displacement method. The monitoring of the state of health (SoH) of VRLA batteries on a continuous basis is an important parameter in unique applications such as remote power supply. A device was developed to monitor the SoH of VRLA batteries on a continuous basis. The working principle of the device was tested on a MCL VRLA battery. With the development of other types of VRLA batteries for specific applications such as in stand-by power supplies, the monitoring device would then be integrated in the battery design.
- Full Text:
- Date Issued: 2004
- Authors: Ferg, Ernst Eduard
- Date: 2004
- Subjects: Lead acid batteries -- South Africa , Storage batteries -- South Africa , Electrochemistry -- South Africa
- Language: English
- Type: Thesis , Doctoral , DTech (Chemistry)
- Identifier: vital:10979 , http://hdl.handle.net/10948/228 , Lead acid batteries -- South Africa , Storage batteries -- South Africa , Electrochemistry -- South Africa
- Description: One of the technical advances made by the lead-acid battery industry in the field of portable power supply was the development of the valve regulated lead-acid battery (VRLA). This battery reduced the necessity for periodic servicing in terms of having to replenish the cells with distilled water. Further, this new type of battery can now be installed near sensitive electronic equipment without the danger of acid spill or dangerous fumes being emitted. In addition, longer service performance is achieved in terms of life cycle capacity, when compared to the conventional flooded type batteries. However, the new type of battery requires the manufacturing of high precision electrodes and components with low tolerances for error. In order for the manufacturers to produce such a premium product, a thorough understanding of the electrochemistry of the inner components is necessary. None of the South African lead-acid battery manufacturers are currently making VRLA batteries to supply a very competitive global market, where a large range of sizes and capabilities are available. In order to introduce the VRLA battery into such a competing market in South Africa, a niche area for its application was identified in order to establish the viability of manufacturing such a battery locally. This is done by integrating the VRLA concept into an existing battery, such as the miners cap lamp (MCL) battery. Its application is specific with well-defined performance criteria in a relatively large consumable market in the South African mining industry. The study looked at various components within a local manufacturing environment that required a better understanding and modification of the processes to build VRLA MCL batteries. This included a detailed study of the manufacturing processes of the positive electrode. The study involved the investigation of the types of grid alloys used, the type of electrode design, such as tubular or flat plate, the addition of redlead to the paste mixing process and subjecting the batteries to accelerated life cycle testing. A better understanding of the oxygen recombination cycle was also performed in order to evaluate the correct use of certain design criteria in the manufacturing process. This included the study of the pressure release valve and the type of positive electrode used. The study also looked at developing an inexpensive analytical technique to evaluate the porosity of cured and formed electrodes using a glycerol displacement method. The monitoring of the state of health (SoH) of VRLA batteries on a continuous basis is an important parameter in unique applications such as remote power supply. A device was developed to monitor the SoH of VRLA batteries on a continuous basis. The working principle of the device was tested on a MCL VRLA battery. With the development of other types of VRLA batteries for specific applications such as in stand-by power supplies, the monitoring device would then be integrated in the battery design.
- Full Text:
- Date Issued: 2004
Evaluation and optimization of selected methods of arsenic removal from industrial effluent
- Authors: Rubidge, Gletwyn Robert
- Date: 2004
- Subjects: Arsenic wastes , Water -- Purification -- Arsenic removal , Sewage -- Purification
- Language: English
- Type: Thesis , Doctoral , DTech (Chemistry)
- Identifier: vital:10981 , http://hdl.handle.net/10948/230 , Arsenic wastes , Water -- Purification -- Arsenic removal , Sewage -- Purification
- Description: This research was directed at reducing arsenic levels in the effluents generated at the Canelands facility that manufactures monosodium methyl arsenate. Two effluent streams containing arsenic have to be considered, a raw water stream that is treated on site and a brine stream that is disposed of by sea outfall. Removal of arsenate from aqueous media by coagulation was investigated and models were developed describing selected variables that influence the removal of the arsenate. Three coagulant systems were investigated, namely aluminium(III) coagulation, iron(III) coagulation and binary mixtures of aluminium(III) and iron(III). Researchers have studied individual aluminium (III) sulphate and iron(III) chloride coagulation. No detailed research and modelling had, however, been carried out on the use of binary mixtures of aluminium (III) sulphate and iron (III) chloride coagulation of aqueous arsenate, nor had individual aluminium(III) sulphate and iron(III) chloride coagulation of arsenate been modelled at relatively high arsenate concentrations. The models that were generated were validated statistically and experimentally. The variables investigated in the aluminium(III) model included initial arsenate concentration, pH, polymeric flocculent concentration, aluminium(III) concentration and settling time. The variables modelled in the iron(III) coagulation were initial arsenate concentration, pH, polymeric flocculent concentration, and iron(III) to arsenic mole ratio. The modelling of the binary coagulant system included initial arsenate concentration, pH, iron (III) concentration, aluminium(III) concentration, and flocculent concentration as variables. The most efficient arsenic removal by coagulation was iron(III), followed by the binary mixture of aluminium(III) and iron(III) and the weakest coagulant was aluminium(III) sulphate. Scale-up coagulations performed on real raw water samples at a 50 litre volume showed that iron(III) was the most efficient coagulant (on a molar basis) followed closely by the binary mixture, while aluminium(III) coagulation was considerably weaker. The residual arsenic levels of the iron(III) and the binary coagulation systems met the effluent discharge criteria, but the aluminium coagulation system did not. Leaching tests showed that the iron(III) sludge was the most stable followed by the sludge of the binary mixture and the aluminium(III)-based sludge leached arsenic most readily. Settling rate studies showed that the flocs of the iron(III) coagulations settled the fastest, followed by binary mixture flocs and the aluminium flocs settled the slowest. The flocs of the binary mixture had the lowest volume, followed by the iron(III) flocs, while the aluminium(III) flocs were the most voluminous. Based on current operations of the raw water treatment plant the aluminium(III)-based coagulation is the most cost efficient. Given a relative costing of 1.00 for the aluminium(III) coagulation, the iron(III) chloride-based coagulation would be 2.67 times more expensive and the equimolar binary mixed aluminium(III)/iron(III) system would be 1.84 times the cost of aluminium(III) coagulation.
- Full Text:
- Date Issued: 2004
- Authors: Rubidge, Gletwyn Robert
- Date: 2004
- Subjects: Arsenic wastes , Water -- Purification -- Arsenic removal , Sewage -- Purification
- Language: English
- Type: Thesis , Doctoral , DTech (Chemistry)
- Identifier: vital:10981 , http://hdl.handle.net/10948/230 , Arsenic wastes , Water -- Purification -- Arsenic removal , Sewage -- Purification
- Description: This research was directed at reducing arsenic levels in the effluents generated at the Canelands facility that manufactures monosodium methyl arsenate. Two effluent streams containing arsenic have to be considered, a raw water stream that is treated on site and a brine stream that is disposed of by sea outfall. Removal of arsenate from aqueous media by coagulation was investigated and models were developed describing selected variables that influence the removal of the arsenate. Three coagulant systems were investigated, namely aluminium(III) coagulation, iron(III) coagulation and binary mixtures of aluminium(III) and iron(III). Researchers have studied individual aluminium (III) sulphate and iron(III) chloride coagulation. No detailed research and modelling had, however, been carried out on the use of binary mixtures of aluminium (III) sulphate and iron (III) chloride coagulation of aqueous arsenate, nor had individual aluminium(III) sulphate and iron(III) chloride coagulation of arsenate been modelled at relatively high arsenate concentrations. The models that were generated were validated statistically and experimentally. The variables investigated in the aluminium(III) model included initial arsenate concentration, pH, polymeric flocculent concentration, aluminium(III) concentration and settling time. The variables modelled in the iron(III) coagulation were initial arsenate concentration, pH, polymeric flocculent concentration, and iron(III) to arsenic mole ratio. The modelling of the binary coagulant system included initial arsenate concentration, pH, iron (III) concentration, aluminium(III) concentration, and flocculent concentration as variables. The most efficient arsenic removal by coagulation was iron(III), followed by the binary mixture of aluminium(III) and iron(III) and the weakest coagulant was aluminium(III) sulphate. Scale-up coagulations performed on real raw water samples at a 50 litre volume showed that iron(III) was the most efficient coagulant (on a molar basis) followed closely by the binary mixture, while aluminium(III) coagulation was considerably weaker. The residual arsenic levels of the iron(III) and the binary coagulation systems met the effluent discharge criteria, but the aluminium coagulation system did not. Leaching tests showed that the iron(III) sludge was the most stable followed by the sludge of the binary mixture and the aluminium(III)-based sludge leached arsenic most readily. Settling rate studies showed that the flocs of the iron(III) coagulations settled the fastest, followed by binary mixture flocs and the aluminium flocs settled the slowest. The flocs of the binary mixture had the lowest volume, followed by the iron(III) flocs, while the aluminium(III) flocs were the most voluminous. Based on current operations of the raw water treatment plant the aluminium(III)-based coagulation is the most cost efficient. Given a relative costing of 1.00 for the aluminium(III) coagulation, the iron(III) chloride-based coagulation would be 2.67 times more expensive and the equimolar binary mixed aluminium(III)/iron(III) system would be 1.84 times the cost of aluminium(III) coagulation.
- Full Text:
- Date Issued: 2004
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