3. Electronic Theses and Dissertations (ETDs) - All submissions
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Item Adsorption modelling of desulphurisation of light diesel fuel using chloramine T and polymer supported imidation agent(2017) Kgorane, NomathembaIn petroleum industry, sulphur compounds are undesirable due to potential corrosions and environmental challenges associated with these compounds. Sulphur occurs in varies forms in crude oil and petroleum products such as, marcaptans, disulphide, sulphides, disulphide H2S and thiophenes. Commercial scale refineries utilises hydrodesulphurisation to reduce the sulphur content in fuels, though this technology is associated with high operating and capital cost. Extractive, adsorptive, oxidative, membrane separation and bio desulphurisation are some of the alternative technology being investigated which have proven not to be as efficient and/or cost effective as compared to hydrodesulphurisation. Adsorption desulphurisation has been effective in separation processes where the sorbate concentrations are low and this technology was used to evaluate the performance of the polymer supported imidation agent (Sodium N-chloro-polystyrene sulphonamide) as an adsorbent in diesel fuel desulphurisation. A mathematical model simulating adsorption on a fixed was developed. This model incorporates internal mass transfer assuming laminar flow, constant interstitial velocity and an isothermal system. To represent liquid solid equilibrium the Langmuir isotherm was used. The model contains partial differentiate equation that were linearised by using the Euler’s forward implicit method, this enabled simulating the model using Microsoft Excel Visual Basic. The obtained simulation results were compared against experimental data. The impact of varying parameters such as initial sulphur concentration, adsorbent bed porosity and external bed surface area per particle volume was studied in detail. Existing isotherms and kinetics were discussed by using experimental data from Fadhel’s study. It was found that the adsorbate residence time is reduced by smaller adsorbent bed porosity resulting in increased adsorption rate. By decreasing the adsorbent particle diameter and an increase in initial sulphur concentration, the breakthrough time is decreased. The experiment data agreed with the simulation results and this validate that the proposed model is applicable to study the performance of fixed bed adsorption processes under isothermal conditions, no axial mixing and constant interstitial velocities. The results from the analysed Fadhel’s data showed that the modelled light oil can be desulphurise to the Euro 5 level requirements, Sulphur <500ppm, by both Chloramine T and Synthesis PI, a complete sulphur removal was achieved using both adsorbents. The desulphurisation rate proved to be faster with Chloramine T as an adsorbent as compared to Synthesis PI. Modelled light oil adsorption obeyed the pseudo-first-order kinetics and the overall adsorption rate was controlled by the chemisorption process. The diesel fuels study by Fadhel could not be desulphurised to the Euro 5 level. The diesel fuel 1 sulphur concentration was reduced from 12 354 to 11 200ppm and diesel fuel 2 from 1 900 to 800ppm. It was observed that the rate of desulphurisation proved to be faster with diesel fuel 1 as compared to that of diesel fuel 2. The Freundlich isotherm was found to be a best fit in the adsorption of diesel fuel 1, the attained R square values was 0.881 and 0.435 for Freundlich and Langmuir, respectively. Also the obtained Langmuir separation factor, RL , of 1 confirmed the that the Langmuir adsorption was unfavourable. This implies that the adsorption rate was controlled by a physisorption process. The diesel fuel 2 desulphurisation process did not fit the studied adsorption isotherms, the attained R square values was 0.433 and 0.218 for Freundlich and Langmuir, respectively. The Langmuir separation factor confirmed in-favourability at 1 and the Freundlich adsorption strength was 6.052, which is very low as compared to that pf diesel fuel 1 at 272.41. Diesel fuel 1 adsorption reaction obeyed the pseudo-second and pseudo-first order kinetics when reacted with Chloramine T and Synthesis PI, respectively. The obtained R squared values were 0.694 and 0.999 for pseudo-second and pseudo-first order, respectively. Diesel fuel 2 obeyed the third order kinetics with both Chloramine T and Synthesis PI, with R squared values calculated at 0.889 and 0.774 for Chloramine T and Synthesis PI reaction, respectively.Item Simulation of the adsorptive desulphurisation of diesel fuel(2016) Sanyangare (Chawira), FaithThe global focus on cleaner air has seen sulphur removal processes’ gaining popularity and adsorptive desulphurisation has been identified as an effective alternative. Adsorptive desulphurisation was used to simulate and evaluate the performance of the polymer supported imidation agent (Sodium N-chloro-polystyrene sulphonamide) as an adsorbent in the desulphurisation of diesel fuel. This study involved the development of a mathematical model for the adsorption process of sulphur on the polymer supported imidation agent, based on the mass balance on a continuous fixed bed column and pseudo second order kinetics. The developed model was solved using numerical methods, and the simulation of the process carried out varying different parameters; the inlet sulphur concentration, the adsorption column bed height and the particle size (radius) of the adsorbent. The simulation showed that the adsorption capacity of the studied adsorbent increased with increase in the inlet sulphur concentration; an increase in the adsorption bed height and a decrease in the adsorbent particle size. Validation of the simulation done was carried out by comparing the simulation data with experimental data. The proposed model fit experimental data and can be used to predict the inlet concentration conditions, bed height and particle size of the adsorbent. The overall research enhances the understanding of the adsorptive desulphurisation of diesel fuel using the polymer supported imidation agent and the mathematical modelling of the process.Item The desulfurization of petroleum compounds using a polymer-supported imidation agent(2016) Matoro, Tshilidzi BenedictaThe sulfur removal methods from petroleum products have become an important research topic. Sulfur poisons the catalysts found in vehicles engines and it is also a major air pollutant (Nehlsen, 2005). Recent sulfur specifications require refineries to produce ultra-clean products (Ma et al., 2002). This work aims at exploring a batch adsorptive desulfurization technique using a polymer-supported imidation agent (PI) as an adsorbent. The test was carried out at atmospheric pressure and on two commercial diesel fuels with sulfur contents of 5200 (Case 1) and 670 (Case 2) mg/kg which resembles the feed and outlet streams from the hydrodesulfurization (HDS) reactor respectively. The adsorbent was synthesized according to the procedure described by Shiraishi et al. (2003), BET, FTIR, SEM equipped with EDS and TGA were used for charaterization of the adsorbent. The PI was successfully synthesized and its surface area was 0.5333 m2/g which was incredibly lower than that of the PI synthesized by Fadhel (2010). Hence carbon nanotubes (CNTs) were added to the solution with the aim of improving the sulfur removal efficiency of PI. The obtained results indicated that PI with CNTs yield better results than PI without CNTs. In overall, the lowest sulfur content of 3462 mg/kg (33% removal efficiency) and 26 mg/kg (96% removal efficiency) for Case 1 and Case 2 respectively were obtained. Furthermore, the adsorbents were most effective at lower mixing rates (150 – 400 rpm), longer contact time (30 – 40 hours), practically high adsorbent amount (1 g) and moderate lower temperatures (25 – 50 ºC). The Freundlich adsorption isotherm model was the best fit to the experimental data in both Case 1 and Case 2. The kinetic model that best fitted well the experimental data is the pseudo-second-order model for both Case 1 and Case 2. The kinetic rate constant for Case 2 (4.079 x 10-3g/mg.min) was greater than that for Case 1 (6.75 x 10-5g/mg.min) thus indicating that fuel with low sulfur content has a higher sorption uptake than fuel with high sulfur content. Based on the results obtained in this study, it is suggested that the adsorption of sulfur at high sulfur content fuel is not capable to be used as a complimentary method to the HDS process. On the other hand, at low sulfur content fuel, there is an opportunity for combining this method with the traditional HDS method to achieve ultra-clean fuel.