Dynamic simulation programs were created in the Python programming language, to describe a laboratory scale, sub-zero distillation column, that is used to separate mixtures of tetrafluoroethylene (TFE), hexafluoropropylene (HFP) and octafluorocyclobutane (OFCB). Both the equilibrium and rate-based modelling approaches were taken, to generate a comparison between the efficiency and simulation time of both models. A physical properties data bank for the three components had to be created, as the main and many of the sub-models require physical or thermodynamic properties for evaluation. The different physical property models, found in literature, were programmed into functions that could easily return the wanted property, given a set of required inputs. The applicable mixing rules for each property type was also programmed into functions, to allow for easy retrieval. The vapour-liquid equilibrium (VLE) model used, is also one that comes from literature and is based on parameters for the three binary systems. The VLE model consists of the Peng-Robinson equation of state, that utilises the Mathias-Copeman alpha function and the Wong-Sandler mixing rules, to describe the vapour phase. The liquid phase is described by the non-random two liquid (NRTL) activity coefficient model. Furthermore, the γ-Φ VLE formulation was used to put the thermodynamic model together. These models were also written into functions to serve as simulation building blocks. Mass and energy transfer on packed sections in the rate-based model was described by the Maxwell-Stefan diffusion model. The form of this model that was utilised, is the matrix-based, exact solution of the Maxwell-Stefan equations, under the two-film theory. This model was slightly simplified by assuming that the corrective flux matrix reduces to the identity matrix- an assumption that is regularly made in distillation modelling. Emphasis was laid in documenting how the models are put together to build the simulations. Dynamic simulation algorithms rarely accompany distillation models reported in literature, or authors make use of commercial software to order the modelling equations for them. One of the objectives of the research presented here was, therefore, to report on the process developed to solve the problem. Both simulation programs delivered typical responses that can be expected of distillation systems. The actual change in the magnitude of the values, however, proved to be significantly small. The cause of this, being the large liquid molar hold-up values that were produced by the model initialisation. The feed flow rate, in comparison, is too small to bring about a significant effect when suddenly increased. This could mean that the system is not capable of reaching the steady-state produced by the initialisation (as the feed cylinder may be too small to contain the required amount of feed gas) and that the column may have to be run in a continuous dynamic state. To be sure of this, however, the model will first need to be validated against experimental data. Furthermore, the simulation programs proved to progress very slowly, particularly the simulation built around the rate-based model. A time step-size of 0.5 resulted in an integration time around 1 minute and 20 seconds for the equilibrium model, while the rate model ran for over 19 minutes, both for a timespan of 300 s. It is recommended that future research focuses on building start-up simulations for the models, to provide better initial results and to give more insight into the operation of the column. Experimental validation of the models is also important, to establish their accuracies. Finally, work has to be done to improve the simulation speeds, especially if it is required that one of the models are integrated into the column's control system. / Dissertation (MEng)--University of Pretoria, 2019. / Fluorochemical Expansion Initiative / Department of Science and Technology / Department of Trade and Industry / Chemical Engineering / MEng / Unrestricted

Pure fluorocarbon gases can be sold for up to 30 USD/kg, if they were manufactured locally. Due to the absence of local demand, South Africa at present has less than 0.3 % of the fluorochemical market and most fluoro–products used in the South African industry are currently imported. The depolymerisation of waste polytetrafluoroethylene (PTFE or Teflon) filters in a nitrogen plasma reactor results in the mixture of gases which includes N2, CF4 and C3F6. An existing challenge entails the separation of these gases, which is currently attained by an energy intensive cryogenic distillation process. Both the small energy requirements as well as the small process streams required, make a membrane separation an ideal alternative to the current distillation process. Based on our research groups existing expertise in the field of zeolite membranes, it was decided to investigate the separation capability of zeolite (MFI, NaA, NaY, and hydroxysodalite) coated tubular ceramic membranes for the separation of the above mentioned gases. The separation study was subdivided into adsorption studies as well as single and binary component studies. CxFy gas adsorption on MFI zeolites. Tetrafluoromethane (CF4) and hexafluoropropylene (C3F6) were adsorbed on zeolite ZSM–5 and silicalite–1 to help explain permeation results through zeolite membranes. According to the obtained data, the separation of CF4 and C3F6 would be possible using adsorption differences. The highest ideal selectivities (~ 15) were observed at higher temperatures (373 K). While the CF4 adsorption data did not fit any isotherm, the heat of adsorption for C3F6 adsorbed on ZSM–5 and silicalite–1 was calculated as –17 and –33 kJ/mol respectively. Single gas permeation. A composite ceramic membrane consisting of a ceramic support structure, a MFI intermediate zeolite layer and a Teflon AF 2400 top layer was developed for the separation of N2, CF4 and C3F6. The adsorption properties of the Teflon AF 2400 sealing layer was investigated. A theoretical selectivity, in terms of the molar amount of gas adsorbed, of 26 in favour of the C3F6 vs CF4 was calculated, while the N2 adsorption remained below the detection limit of the instrument. While the ideal N2/CF4 and N2/C3F6 selectivities for the MFI coated support were either near or below Knudsen, it was 5 and 8 respectively for the Teflon coated support. Ideal selectivities improved to 86 and 71 for N2/CF4 and N2/C3F6 when using the composite ceramic membrane, while CF4/C3F6 ideal selectivities ranged from 0.9 to 2, with C3F6 permeating faster though the composite ceramic membrane. Zeolite based membrane separation. Inorganic membranes (?–alumina support, NaA, NaY, hydroxysodalite, MFI) and composite membranes (Teflon layered ceramic and composite ceramic membrane) were synthesized and characterized using the non–condensable gases N2, CF4 and C3F6. For the inorganic membranes either near or below Knudsen selectivities were obtained during single gas studies, while higher selectivities were obtained for the composite membranes. Subsequently, the MFI, hydroxysodalite and both composite membranes were chosen for binary mixture separation studies. The membranes exhibited binary mixture permeances in the order Teflon layered ceramic > hydroxysodalite > MFI > composite ceramic, which was comparable to the single gas permeation results. The highest separation for N2/CF4 (4) and N2/C3F6 (2.4) was obtained with the composite ceramic membrane indicating that the Teflon layer was effective in sealing non–zeolitic pore in the intermediate zeolite layer. The aim of this project was met successfully by investigating a method of fluorocarbon gas separation by zeolite based membranes using various inorganic and composite membranes with single and binary mixtures. / Thesis (Ph.D. (Chemistry))--North-West University, Potchefstroom Campus, 2012.

Pure fluorocarbon gases can be sold for up to 30 USD/kg, if they were manufactured locally. Due to the absence of local demand, South Africa at present has less than 0.3 % of the fluorochemical market and most fluoro–products used in the South African industry are currently imported. The depolymerisation of waste polytetrafluoroethylene (PTFE or Teflon) filters in a nitrogen plasma reactor results in the mixture of gases which includes N2, CF4 and C3F6. An existing challenge entails the separation of these gases, which is currently attained by an energy intensive cryogenic distillation process. Both the small energy requirements as well as the small process streams required, make a membrane separation an ideal alternative to the current distillation process. Based on our research groups existing expertise in the field of zeolite membranes, it was decided to investigate the separation capability of zeolite (MFI, NaA, NaY, and hydroxysodalite) coated tubular ceramic membranes for the separation of the above mentioned gases. The separation study was subdivided into adsorption studies as well as single and binary component studies. CxFy gas adsorption on MFI zeolites. Tetrafluoromethane (CF4) and hexafluoropropylene (C3F6) were adsorbed on zeolite ZSM–5 and silicalite–1 to help explain permeation results through zeolite membranes. According to the obtained data, the separation of CF4 and C3F6 would be possible using adsorption differences. The highest ideal selectivities (~ 15) were observed at higher temperatures (373 K). While the CF4 adsorption data did not fit any isotherm, the heat of adsorption for C3F6 adsorbed on ZSM–5 and silicalite–1 was calculated as –17 and –33 kJ/mol respectively. Single gas permeation. A composite ceramic membrane consisting of a ceramic support structure, a MFI intermediate zeolite layer and a Teflon AF 2400 top layer was developed for the separation of N2, CF4 and C3F6. The adsorption properties of the Teflon AF 2400 sealing layer was investigated. A theoretical selectivity, in terms of the molar amount of gas adsorbed, of 26 in favour of the C3F6 vs CF4 was calculated, while the N2 adsorption remained below the detection limit of the instrument. While the ideal N2/CF4 and N2/C3F6 selectivities for the MFI coated support were either near or below Knudsen, it was 5 and 8 respectively for the Teflon coated support. Ideal selectivities improved to 86 and 71 for N2/CF4 and N2/C3F6 when using the composite ceramic membrane, while CF4/C3F6 ideal selectivities ranged from 0.9 to 2, with C3F6 permeating faster though the composite ceramic membrane. Zeolite based membrane separation. Inorganic membranes (?–alumina support, NaA, NaY, hydroxysodalite, MFI) and composite membranes (Teflon layered ceramic and composite ceramic membrane) were synthesized and characterized using the non–condensable gases N2, CF4 and C3F6. For the inorganic membranes either near or below Knudsen selectivities were obtained during single gas studies, while higher selectivities were obtained for the composite membranes. Subsequently, the MFI, hydroxysodalite and both composite membranes were chosen for binary mixture separation studies. The membranes exhibited binary mixture permeances in the order Teflon layered ceramic > hydroxysodalite > MFI > composite ceramic, which was comparable to the single gas permeation results. The highest separation for N2/CF4 (4) and N2/C3F6 (2.4) was obtained with the composite ceramic membrane indicating that the Teflon layer was effective in sealing non–zeolitic pore in the intermediate zeolite layer. The aim of this project was met successfully by investigating a method of fluorocarbon gas separation by zeolite based membranes using various inorganic and composite membranes with single and binary mixtures. / Thesis (Ph.D. (Chemistry))--North-West University, Potchefstroom Campus, 2012.

This dissertation details research aimed at designing a small batch distillation column to purify tetrafluoroethylene and hexafluoropropylene from a mixture containing tetrafluoroethylene, hexafluoropropylene and octafluorocyclobutane. As no vapour-liquid equilibrium data are available for these chemicals in this mixture, new vapour-liquid equilibrium data were experimentally generated and modelled for use in the design of the batch distillation column. The data were fitted to the Peng-Robinson equation of state, utilizing the Mathias-Copeman alpha function. The model was used with the Wong- Sandler mixing rules alongside the NRTL alpha function. The model was fitted with mean relative deviations lower than 1.2 %, indicating an acceptably accurate description of the VLE data gathered by the model. The experimental data and the model also passed the thermodynamic consistency test for all the systems and isotherms. The design simulations were completed by means of the Aspen Batch Distillation, a module of the Aspen Technologies package. The results show that the optimum design for recovering high-purity products requires six equilibrium stages in the column. The batch column should consist of a still pot, also functioning as a reboiler, a packed column section and a total condenser. The total condenser and the reboiler both count as equilibrium stages. Using this design, a TFE product purity of 99.999 % is predicted with a recovery of 96 %. An HFP product purity of 99 % is predicted at a recovery of 68 %. The recovery of the HFP product can be increased, but entails a significant loss of product purity. The minimum column diameter required to achieve the flow rates suggested in the simulation is 29 mm. The column diameter was selectedas 1¼ ″ (or 31.75 mm) on the basis of the standard pipe diameters available in the industry. Pall ring packing is suggested for use in the column, with an estimated maximum HETP of 0.5 m. As there are five equilibrium stages in the column itself, the column has to be at least 2.5 m high. Copyright / Dissertation (MEng)--University of Pretoria, 2011. / Chemical Engineering / unrestricted

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Improved fabrication of poly(vinylindenefluoride)-hexafluoropropylene (PVDF-HFP) thin films is of particular interest due to the high electric coercivity found in the beta-phase structure of the thin film. We show that it is possible to obtain high-quality, beta-phase dominant PVDF-HFP thin films using a direct approach to Langmuir-Blodgett deposition without the use of annealing or additives. To improve sample quality, an automated Langmuir-Blodgett thin film deposition system was developed; a custom dipping trough was fabricated, a sample dipping mechanism was designed and constructed, and the system was automated using custom LabVIEW software. Samples were fabricated in the form of ferroelectric capacitors on substrates of glass and silicon, and implement a unique step design with a bottom electrode of copper with an aluminum wetting layer and a top electrode of gold with an aluminum wetting layer. Samples were then characterized using a custom ferroelectric measurement program implemented in LabVIEW with a Keithley picoammeter/voltage supply to confirm electric coercivity properties. Further characterization using scanning electron microscopy and atomic force microscopy confirmed the improvement in thin film fabrication over previous methods.

Indiana University-Purdue University Indianapolis (IUPUI) / Improved fabrication of poly(vinylindenefluoride)-hexafluoropropylene (PVDF-HFP) thin films is of particular interest due to the high electric coercivity found in the beta-phase structure of the thin film. We show that it is possible to obtain high-quality, beta-phase dominant PVDF-HFP thin films using a direct approach to Langmuir-Blodgett deposition without the use of annealing or additives. To improve sample quality, an automated Langmuir-Blodgett thin film deposition system was developed; a custom dipping trough was fabricated, a sample dipping mechanism was designed and constructed, and the system was automated using custom LabVIEW software. Samples were fabricated in the form of ferroelectric capacitors on substrates of glass and silicon, and implement a unique step design with a bottom electrode of copper with an aluminum wetting layer and a top electrode of gold with an aluminum wetting layer. Samples were then characterized using a custom ferroelectric measurement program implemented in LabVIEW with a Keithley picoammeter/voltage supply to confirm electric coercivity properties. Further characterization using scanning electron microscopy and atomic force microscopy confirmed the improvement in thin film fabrication over previous methods.