Application of membrane technology for purifying tyre derived oil

Tshindane, Pfano (2018-03)

Thesis (MEng)--Stellenbosch University, 2018.

Thesis

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.

AFRIKAANSE OPSOMMING: Band afkomstige olie (BAO) is „n oorvloedig verkrygbare vloeistofproduk afkomstig vanuit die pirolise van afval voertuigbande. Dit bevat „n komplekse mengsel van C6-C24 organiese verbindings van verskeie klasse soos paraffiene, olefiene, aromatiese verbindings, stikstof- en swael-bevattende verbindings sowel as geoksigineerde verbindings. BAO is „n potensiële bron van hoë markwaarde verbindings soos dl-limonien, 4-vinielsiklohekseen, tolueen, etielbenseen, xileen, en baie ander. dl-Limonien is die waardevolste verbinding in BAO. Waardevolle chemikalieë in BAO is slegs bemarkbaar in suiwerheidsgrade groter as 90% v/v. dl-Limonien, tesame met p-cymien, indaan en 1,2,4-trimetielbenseen het soortgelyke fisiese eienskappe soos kookpunt en viskositeit. Konvensionele distillasie prosedures is nie in staat om limonien te suiwer uit BAO nie weens die teenwoordigheid van hierdie limonien-soortgelyke onsuiwerhede. BAO is ook potensieel „n brandstof vir dieselenjins. Die kalorifiese waarde van BAO is al beskryf as ongeveer gelykstaande aan dié van kommersiële brandstowwe. Ander kommersiële brandstofeienskappe wat soortgelyk is aan dié van BAO sluit in vlampunt, digtheid, viskositeit, ens. Die Suid-Afrikaanse nasionale standaarde (SANS) spesifiseer dat brandstowwe „n swaelinhoud van minder as 500 ppm moet hê. Bensotiasool word algemeen gerapporteer as die volopste swaelspesie in BAO. Die suiwering van limonien vanuit BAO en die verlaging van bensotiasool in BAO is noodsaaklik in die veld van band valorisasie. Die doel van hierdie studie is die suiwering (herwinning van limonien en verlaging van bensotiasool) van BAO deur gebruik te maak van „n nuwe, groen, omgewingsvriendelike tegnologie, naamlik organiese oplosmiddel nanofiltrasie (OON). OON maak grootte-uitsluitingsgebasseerde skeiding in die afwesigheid van fase oorgange moontlik, om sodoende heelwat laer energieverbruik te verseker. Derhalwe word „n meer gunstige ekonomiese en koolstofvoetspoor verkry in vergelyking met die konvensionele skeidingsmetodes soos distillasie. Drie verskillende kommersiële OON membrane, Puramem®-280 (PM-280), STARMEM™-280 (ST-228) en Duramem®-200 (DM-200), is gebruik vir die eksperimentele werk in hierdie studie. BAO is toegelaat om deur „n membraan te dring wat aan „n doodlopende OON opstelling geïnstalleer is. Die transmembraan druk (10-40 bar), chemiese spesie konsentrasie (50-150 ppm) en oplosmiddeltipe (tolueen, 1-okteen en etanol) is gevarieer om die effek op membraan werksverrigting (vloed en uitskotverlies) te ondersoek. Daar is gevind dat suiwer chemiese spesies (limonien, p-cymien, 1,2,4-trimetielbenseen en tolueen) teen duidelik verskillende tempo‟s deur PM-280 dring in vergelyking met hul bewegingstempo‟s deur ST-228 en DM-200. Hierdie groot verskil in deurdringingstempo in die geval van PM-280 impliseer dat die membraan meer selektief is as ST-228 en DM-200. Die vloed van suiwer chemiese spesies deur PM-280 (30 bar) het gevarieer van 75 L.m-2.h-1 tot 297 L.m-2.h-1. Daar is bevind dat „n suiwer spesie se vloed deur „n membraan hoogs afhanklik is van transmembraan druk, molekulêre gewig en parameters wat die interaksie tussen die membraan en die suiwer spesie beskryf. Daar is ook gevind dat suiwer bensotiasool die membraanoppervlak van beide PM-280 en ST-228 vernietig het. Die suiwering van BAO deur PM-280 en ST-228 het gelei tot hoë BAO uitskotverliese van 88% en 100%, onderskeidelik. Konsentrasie polarisasie kan voorgestel word as „n moontlike verklaring vir die hoë BAO verliese. Negatiewe verliese, van -6% en -7%, is aangeteken met PM-280 vir limonien en bensotiasool, onderskeidelik. Negatiewe verliese impliseer dat die spesie meer gekonsentreerd is in die deurloop oplossing as in die toevoeroplossing. Vir hierdie studie beteken „n negatiewe verlies „n goeie werksverrigting by die membraan aangesien dit impliseer dat die teikenverbindinge vanuit die ru BAO onttrek word. In „n poging om die membraan werksverrigting te bevorder, is die BAO verdun met verskillende oplosmiddels (tolueen, 1-okteen en etanol). BAO/tolueen verdunning het die membraan se werksverrigting verbeter deurdat dit gelei het tot hoër negatiewe verliese deur ST-228, met onderskeidelik -10% en -98% vir limonien en bensotiasool. Die membraan se werksverrigting was egter steeds nie aanvaarbaar nie aangesien die bensotiasool persentasie verandering slegs 6.3% was. Daar is egter gevind dat die vervoer van „n verdunde BAO spesie oor die membraan baie beïnvloed is deur die interaksie tussen die membraan en die chemiese spesie. „n Spesie met „n sterk affiniteit vir die membraan het „n lae uitskotverlies getoon in vergelyking met „n spesie wat „n swak affiniteit vir die membraan het. Daar is ook gevind dat die membraan se werksverrigting nie beïnvloed is deur die konsentrasie van die BAO spesies nie. Die tegniese lewensvatbaarheid van OON vir die suiwering of fraksionering van ru BAO is nie waargeneem in hierdie studie nie. Deur vergelyking is waargeneem dat die deurbraak vir BAO swaelvermindering en limonien herwinning waarskynlik sal geskied deur distillasie prosedures.

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