Browsing by Author "Tshindane, Pfano"

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    Application of membrane technology for purifying tyre derived oil
    (Stellenbosch : Stellenbosch University, 2018-03) Tshindane, Pfano; Van der Gryp, Percy; Gorgens, Johann F.; Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering.
    ENGLISH SUMMARY: Tyre derived oil (TDO) is an abundant liquid product obtained after pyrolysis of waste tyre. It contains a complex mixture of C6–C24 organic compounds of various classes such as paraffins, olefins, aromatics, nitrogen and sulphur compounds as well as oxygenated compounds. TDO is a potential source of high market value compounds such as dl-limonene, 4-vinylcyclohexene, toluene, ethylbenzene, xylenes and many others. dl-limonene is the most abundant valuable chemical in TDO. Valuable chemicals in TDO are only marketable at purities greater than 90% v/v. dl-limonene together with p-Cymene, indane and 1,2,4-trimethylbenzene have similar physical properties such as boiling point and viscosity. Conventional distillation procedures fail to purify limonene from TDO because of these limonene-like impurities. TDO is also a potential fuel for diesel engines. The calorific value of TDO has been reported to be approximately equal to that of commercial fuels. Other commercial fuel properties that match that of TDO include flash point, density, viscosity etc. For fuels, the South African national standards (SANS) specifies that fuels must contain a sulphur content of less than 500 ppm. Benzothiazole is reportedly the most abundant sulphur species in TDO. The purification of limonene and the reduction of benzothiazole from TDO is vital in the field of waste tyre valorisation. The aim of this study is to investigate the purification (recovery of limonene and reduction of benzothiazole) of TDO using a novel green separation technology, namely organic solvent nanofiltration (OSN). OSN allows size-exclusion based separation with the absence of phase transitions to ensure much lower energy consumption and therefore a favourable economic and carbon footprint compared to the conventional separation methods such as distillation. Three different commercial OSN membranes, Puramem®-280 (PM-280), STARMEM™-280 (ST-228) and Duramem®-200 (DM-200), were employed for the experimental work of this study. TDO was allowed to permeate through a membrane installed to a dead-end OSN set-up. The transmembrane pressure (10-40 bar), species concentration (50-150 ppm) and feed dilution (toluene, 1-octene and ethanol) were all varied so as to investigate the effect on membrane performance (flux and rejection). It was found that pure species (Limonene, p-Cymene, 1,2,4-trimethylbenzene and toluene) permeate at distant rates through PM-280 relative to ST-228 and DM-200. The distant rates through PM-280 imply that the membrane is more selective than ST-228 and DM-200. Flux of pure species through PM-280 (30 bar) ranged from 75 L.m-2.h-1 to 297 L.m-2.h-1. Pure species flux was found to be highly dependent on transmembrane pressure, molecular weight and parameters describing the interaction between the membrane and the pure species. It was found that pure benzothiazole destroys the membrane surface of both PM-280 and ST-228. The purification of TDO through PM-280 and ST-228 resulted in high TDO rejections, 88% and 100% respectively. Concentration polarization was deduced as a possible explanation for the high TDO rejections. Negative rejections were recorded with PM-280 for limonene and benzothiazole, -6% and -7% respectively. Negative rejections imply that the species is more concentrated in the permeate than in the feed solution. For this study, a negative rejection is a good performance by the membrane since it implies that the targeted compounds are being drawn out of the crude TDO. As an effort of enhancing membrane performance, TDO was diluted with different solvents (toluene, 1-octene and ethanol). TDO/toluene dilution enhanced the membrane performance by resulting in higher negative rejections through ST-228, -10% and -98% for limonene and benzothiazole respectively. The membrane performance was still not competent since benzothiazole percent change was only 6.3%. However, it was found that the transport of diluted TDO species across the membrane is highly influenced by the interaction between the membrane and the species. A species having a strong affinity for the membrane recorded a low rejection compared to a species having a weak affinity for the membrane. It was also found that the membrane performance is unaffected by the concentration of TDO species. The technical-viability of OSN in purifying or fractionating crude TDO is unnoticed in this study. Through comparison, it was noticed that the breakthrough for TDO sulphur reduction and limonene recovery is likely to happen through distillation procedures.