Slurry-phase desulphurization of tyre derived oil using unsupported and supported alkaline earth metal oxides.
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Date
2021
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Abstract
The global consumption of tyres continues to increase to meet industrial, commercial, and personal transportation needs, which means that more tyres reach end-of-life. There are various methods of dealing with waste tyres, such as shredding, incineration, landfill, pyrolysis, and rethreading. The pyrolysis of waste tyres can be used to produce alternative fuels. The main waste tyre pyrolysis products are tyre pyrolysis oil, non-condensable gases and char. Due to the composition of tyres, some unwanted components end up in tyre derived oil. These unwanted components are sulphur-containing compounds, metal and metalloid impurities, and polycyclic aromatic hydrocarbons. Significant sulphur emissions such as sulphur oxides, sulphate particulate matter, and sulphur-containing compounds are released during the direct combustion of tyre derived oil. The sulphur emissions cause acid rain and environmental pollution that is harmful to human and animal health. As a result, many countries have enforced policies to minimize sulphur emissions. The study served the following purposes: (1) to identify and characterize high-value compounds within tyre derived oil to supplement existing literature for tyre derived oil as a potential replacement to conventional liquid fuels, (2) to synthesize and characterize supported alkaline earth metal oxides for desulphurization, (3) to desulphurize tyre derived oil using unsupported and supported alkaline earth metal oxides, and (4) to develop a mathematical model to describe the desulphurization results. The tyre derived oil was obtained from Mandini, a tyre pyrolysis company based in Alberton, Johannesburg. The GC-MS results showed that the tyre derived oil consists of a complex mixture of organic compounds, within the C5-C36 range. The main aromatic compounds found in the tyre derived oil were toluene (0.71 %), styrene (0.15 %), xylene (1.39 %), limonene (6.55 %), cymene (2.56 %) and benzothiazole (0.80 %). The high percentage of aromatics and naphthenic components make the tyre derived oil suitable as an alternative to conventional liquid fuels. The alkaline earth metal oxides of calcium, magnesium, and barium were chosen to desulphurize tyre derived oil. The silica-supported alkaline earth metal oxides were synthesized using the wet impregnation technique. The SEM-EDX analysis confirmed the presence of alkaline earth metal oxides on the surface of the silica particles. The untreated and treated tyre derived oil was analysed using a GC-PFDP to determine the performance of the alkaline earth metal oxides in terms of the total sulphur adsorbed. A 56.76 wt.% desulphurization was optimally achieved at a temperature of 240 oC for 30 min with a 0.0375 g/ml sorbent-to-oil ratio, using supported calcium oxide. The following sizes of silica gel were used for the invention: (1) silica gel with a 30 Å pore size and a 100-200 mesh particle size, (2) silica gel with a 60 Å pore size and a 35-60 mesh particle size, and (3) silica gel with a 150 Å pore size and a 35-60 mesh particle size. The desulphurization results, using supported alkaline earth metal oxides, suggested that pore diameter and mesh particle size do not significantly impact desulphurization for the operating conditions studied. Combining the supported alkaline earth metal oxides did not improve the desulphurization of the tyre derived oil at a temperature of 240 oC for 30 min with a 0.0125 g/ml sorbent-to-oil ratio. The balance between temperature, reaction time and sorbent-to-oil ratio provides the impetus for continued research into the combined effect of alkaline earth metal oxides for desulphurization.
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Masters Degree. University of KwaZulu-Natal, Durban.