Phase equilibrium of limonene, p-cymene, indane, butylbenzene and 1,2,3-trimethylbenzene at subatmospheric conditions

Gowda, Rajesh (2018-03)

Thesis (MEng)--Stellenbosch University, 2018.

Thesis

ENGLISH SUMMARY: Waste tyre pyrolysis has long been seen as a suitable solution to the growing issue of accumulation of waste tyres in our environment. The pyrolysis of waste tyres produces three useful products, namely gas (~15 %), char (~35 %) and oil (~50 %), which can be used as fuel in various processes or as a feedstock for chemicals, one such chemical being limonene. Limonene is an extremely useful chemical and contributes to a number of industries ranging from household chemical production to aromatherapy. The extraction of this chemical from tyrederived oil (TDO) could have positive financial benefits to the waste tyre pyrolysis industry and thereby motivate the recycling of tyres through pyrolysis rather than incineration for fuel. A significant issue faced with the recovery of limonene from waste tyres however, is that a pure fraction is difficult to obtain due to fact that there are other compounds in the TDO that boil at similar temperatures to limonene itself, including p-cymene, indane, 1,2,3-trimethylbenzene and butylbenzene. Although a significant amount of literature is available on the pyrolysis process of waste tyres, not much is available on the purification of limonene from the TDO and there is a lack of data in the literature for the concerned compounds vapour-liquid equilibrium (VLE) data. This study therefore focuses on the experimental determination of the VLE data between limonene, p-cymene, indane, butylbenzene and 1,2,3-trimethylbenzene, at subatmospheric conditions. A setup in which phase equilibrium could be obtained was therefore required to be built as no setup was available for this study. Part of the capabilities required by the setup included accurate pressure measurement and control, accurate temperature measurement and disturbance-free sampling capabilities. The type of setup chosen was a vapour and liquid recirculation still that uses a Cottrell pump to achieve vapour-liquid equilibrium from a boiling feed. The VLE still was constructed using publicly available literature, after which its functional capabilities were commissioned. The experimental methodology was verified through measurement of isobaric VLE for relevant binary systems available in literature, namely ethanol/1-butanol at 101.3 kPa and n-decane/2-heptanone, n-decane/3-heptanone and n-nonane/pentanol at 40 kPa. Experiments were conducted under Argon environments at 40 kPa in an effort to reduce compound degradation. Additional compound degradation trials conducted at 40 kPa for the experimental systems, limonene/p-cymene, limonene/indane, limonene/butylbenzene, p-cymene/butylbenzene and limonene/1,2,3-trimethylbenzene/p-cymene/indane indicated a maximum operation time of 4 hours. This can be used as an indication of the maximum total residence time suitable for an industrial operation involving these compounds if operating at pressures below 40 kPa. Experimental accuracies, encompassing temperature, pressure and analysis effects, were found to be +/- 0.32 K in terms of temperature and +/- 0.0102 mole fraction in terms of composition. Pure fractions of indane and 1,2,3-trimethylbenzene could not be procured, thereby limiting the compositional range for which data could be obtained for systems including these compounds. The experimental results showed that barely any separation was present in the two binary systems, limonene/p-cymene and limonene/indane, with low relative volatilities for p-cymene and indane (relative to limonene) respectively, in the regions that separation was present. Both systems contained azeotropes – limonene/p-cymene at about 0.25 – 0.30 mole fraction limonene and ~416.2 K and limonene/indane at ~0.55 mole fraction limonene and ~415.9 K. However, only the limonene/indane azeotrope is definite due to the limonene/p-cymene system having a slightly narrower temperature range. The binary systems of limonene/butylbenzene and p-cymene/butylbenzene showed slightly better separation without the presence of azeotropes and with slightly higher relative volatilities for limonene and p-cymene (relative to butylbenzene) respectively. However, measuring this data proved difficult on the newly built still and had to be performed on the existing, additional Pilodist VLE still. This is due to there being insufficient mixing between the mixing and heating chambers of the constructed still for systems involving butylbenzene. Boiling regimes for these systems were noted to be irregular and included sudden vaporisations of the feed coinciding with drops in the measured vapour temperature of ~2 K. Furthermore, the quarternary system of limonene/1,2,3-trimethylbenzene/p-cymene/indane showed that purification of limonene from 1,2,3-trimethylebenzene would be difficult to realise on an industrial scale. All experimentally obtained data, verification and new, were found to be thermodynamically consistent according to the McDermott-Ellis consistency test. Additionally, vapour pressure data for limonene, p-cymene and butylbenzene were also obtained. Finally, the experimentally obtained phase equilibrium data were regressed with the NRTL, Wilson and UNIQUAC activity coefficient models using the Data Regression System by Aspen Plus®. The ability of the models to regress the experimental data were determined through visual comparison and descriptive statistics (AAD and AARD values). Comparisons showed that the Wilson activity coefficient model best describes the overall behaviour of the binary systems with the NRTL model proving better for that of the quarternary system. Nevertheless, all three relevant models do manage to describe the VLE behaviour fairly well. Furthermore, all the correlative models were compared with the predictive UNIFAC model, which showed that the UNIFAC model could not accurately predict the binary systems’ behaviours.

AFRIKAANSE OPSOMMING: Pirolise van afvalbande word lank reeds as ʼn geskikte oplossing vir die toenemende probleem van die ophoping van afvalbande in ons omgewing beskou. Die pirolise van afvalbande lewer drie bruikbare produkte, naamlik gas (~15%), sintel (~35%) en olie (~50%), wat in verskeie prosesse gebruik kan word – as brandstof of as ʼn voermateriaal vir chemiese stowwe, waarvan limoneen een is. Limoneen is ʼn uiters nuttige chemikalie wat ʼn bydrae tot verskeie nywerhede lewer, van die vervaardiging van huishoudelike chemikalieë tot aromaterapie. Die ekstraksie van hierdie chemikalie van band-afgeleide olie (BAO) kan positiewe finansiële voordele vir die afvalbandpirolisebedryf inhou en daardeur die herwinning van bande deur pirolise, eerder as die verbranding daarvan vir brandstof, motiveer. Daar is egter ʼn probleem met die herwinning van limoneen van afvalbande: dit is moeilik om ʼn suiwer fraksie te verkry omdat daar ander verbindings in die BAO is wat teen temperature soortgelyk aan limoneen kook, met inbegrip van p-simeen, indaan, 1,2,3-trimetielbenseen en butielbenseen. Alhoewel daar ʼn aansienlike hoeveelheid literatuur oor die piroliseproses van afvalbande bestaan, is daar nie veel beskikbaar oor die suiwering van limoneen vanuit BAO nie. Daar is ook ʼn gebrek aan damp-vloeistof-ewewig- (VLE-)data van die betrokke verbindings in die literatuur. Hierdie studie fokus dus op die ekperimentele bepaling van die VLE-data tussen limoneen, p-simeen, indaan, butielbenseen en 1,2,3-trimetielbenseen, teen subatmosferiese toestande. ʼn Instrumentopstelling waarin fase-ewewig verkry kon word, moes dus gebou word, aangesien daar nie ʼn opstelling vir hierdie studie beskikbaar was nie. Die nodige vermoëns van die opstelling het akkurate drukmeting en -beheer, akkurate temperatuurmeting en steuringsvrye monsterneming ingesluit. Die gekose soort opstelling was ʼn damp-en-vloeistofhersirkuleringsdistilleerder wat ʼn Cottrell-pomp gebruik om damp-vloeistof-ewewig van die kookvoer te behaal. Die VLE-distilleerder is met behulp van openlik beskikbare literatuur gebou, waarná die funksionele vermoëns daarvan in bedryf gestel is. Die eksperimentele metodologie is deur die meting van isobariese VLE vir relevante binêre stelsels in die literatuur, naamlik etanol/1-butanol teen 101.3 kPa en n-dekaan/2-heptanoon, n-dekaan/3-heptanoon en n-nonaan/pentanol teen 40 kPa, geverifieer. Eksperimente is onder argontoestande teen 40 kPa gedoen in ʼn poging om verbindingsafbreking te beperk. Bykomende verbindingsafbraakproewe vir die eksperimentele stelsels limoneen/p-simeen, limoneen/indaan, limoneen/butielbenseen, p-simeen/butielbenseen en limoneen/1,2,3-trimetielbenseen/p-simeen/indaan, wat teen 40 kPa gedoen is, het ʼn maksimum bedryfstyd van vier uur aangedui. Dit kan gebruik word as aanduiding van die maksimum totale residensietyd wat vir industriële bedryf met hierdie verbindings geskik is indien daar teen druk van minder as 40 kPa gewerk word. Eksperimentele akkuraatheid, wat temperatuur, druk en ontledingseffek ingesluit het, was +/- 0.32 K ten opsigte van temperatuur en +/- 0.0102 molfraksie ten opsigte van samestelling. Suiwer fraksies kon nie vir indaan en 1,2,3-trimetielbenseen verkry word nie, wat die samestellingsbereik waarvoor data vir stelsels met hierdie verbindings verkry kon word, beperk. Die eksperimentele resultate het getoon dat daar nouliks enige skeiding in die twee binêre stelsels limoneen/p-simeen en limoneen/indaan was, met lae relatiewe vlugtigheid vir onderskeidelik p-simeen en indaan (relatief tot limoneen), in die gebiede waar daar skeiding was. Albei stelsels het aseotrope bevat – limoneen/p-simeen teen ~0.25 – 0.30 molfraksie limoneen en ~416.2 K en limoneen/indaan teen ~0.55 molfraksie limoneen en ~415.9 K. Slegs die limoneen/indaan-aseotroop is egter bepaal as gevolg van die feit dat die limoneen/p-simeenstelsel ʼn ietwat kleiner temperatuurbereik het. Die binêre stelsels limoneen/butielbenseen en -simeen/butielbenseen het ietwat beter skeiding getoon sonder die teenwoordigheid van aseotrope en met ietwat hoër relatiewe vlugtigheid vir onderskeidelik limoneen en p-simeen (relatief tot butielbenseen). Dit was egter moeilik om hierdie data op die nuutgeboude distilleerder te meet, so dit moes op die bestaande, bykomende Pilodist VLE-distilleerder gedoen word. Die rede hiervoor is ontoereikende vermenging tussen die meng- en verhittingskamers van die geboude distilleerder vir stelsels met butielbenseen. Daar is opgemerk dat kookregimes vir hierdie stelsels onreëlmatig was en skielike verdamping van die voer met gelyktydige afname in die gemete damptemperatuur van ~2 K ingesluit het. Voorts het die kwartenêre stelsel limoneen/1,2,3-trimetielbenseen/p-simeen/indaan getoon dat dit moeilik sou wees om limoneen op industriële skaal van 1,2,3-trimetielbenseen te suiwer. Daar is bepaal dat al die data wat eksperimenteel versamel is, sowel kontrole- as nuwe data, volgens die McDermott-Ellis-konsekwentheidstoets termodinamies konsekwent is. Daarbenewens is dampdrukdata vir limoneen, p-simeen en butielbenseen ook versamel. Laastens is regressieanalise deur middel van die dataregressiestelsel van Aspen Plus® met die NRTL-, Wilson- en UNIQUAC-aktiwiteitskoëffisiëntmodelle gedoen op die fase-ewewigsdata wat eksperimenteel verkry is. Die vermoë van die modelle om die eksperimentele data te regresseer is deur visuele vergelyking en beskrywende statistiek (absolute gemiddelde afwyking en absolute gemiddelde relatiewe afwyking) bepaal. Vergelyking het getoon dat die Wilson-aktiwiteitskoëffisiëntmodelle die algehele gedrag van die binêre stelsels die beste beskryf en dat die NRTL-model beter is in die geval van die kwartenêre stelsel. Nietemin beskryf al drie hierdie modelle die VLE-gedrag redelik goed. Verder was al die soortgelyke modelle vergelyk met die UNIFAC model, wat daarop gedui het dat die UNIFAC model nie akkuraat is in die voorspelling van ń binêre sisteem se termodinamiese optrede nie.

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