Pyrolysis of contaminated PS single-layer and LDPE/PET multi-layer waste plastic packaging to optimise the production of oil for fuel applications

Van der Westhuizen, Salomie (2020-03)

Thesis (MEng)--Stellenbosch University, 2020.

Thesis

ENGLISH ABSTRACT: It has been predicted that by 2050 there will be more plastic in the ocean than fish by weight. Besides the obvious environmental threat, plastic waste also poses a loss of valuable hydrocarbon-based materials. Pyrolysis has been identified as a promising technology for the recycling of waste plastics that cannot be recycled by conventional means due to their mixed and/or contaminated nature.Two such waste plastics are black PS punnets and LDPE/PET multi-layer films used to package raw meat and dry dog food respectively. However, little has been reported on the conversion of multi-layers, the influence of contamination, or the scale-up of the process to larger scale.The pyrolysis process performance has been found to be highly dependent on the composition of the feedstock and process parameters. Additionally, large-scale processing can present added difficulties. Therefore, to make pyrolysis a viable option for processing of these particular waste plastics at a large scale, it is necessary to study its optimisation and scale-up to pilot scale.The aim of this study was to convert these two waste plastics into fuel (oil/wax) products by pyrolysis. To meet this aim, the waste plastics were characterised to determine their suitability as fuel precursors and estimate the amount of contamination.The pyrolysis process was optimised in a bench scale semi-batch reactor for the yield and quality of the oil/wax. Based on optimised conversion, the process was scaled-up in a pilot semi-continuous rotary kiln reactor. Feedstock characterisation proved that the waste plastics were suitable as oil/wax fuel precursors. Contamination in PS negatively affected the characterisation. However, both volatile matter and the sum of carbon and hydrogen contents still represented more than 95wt.%. Contamination in the LDPE/PET multi-layer resulted in insignificant characterisation differences. Oil yield of 89.8-93.2wt.% was achieved during bench scale testing of the clean PS. Heavy meat juice contamination (about 16 wt.%, dry basis) decreased the oil yield by 7.3 wt.% but did not affectthe HHV. Conversion of post-consumer densified PS resulted in similar oil yield and HHV to the clean PS. Scale up to the pilot reactor resulted in lower oil yield of 82.5±1.4wt.% with HHV similar to oils obtained at bench scale in the range of 41.9-42.5 MJ/kg (comparable to gasoline). The gross energy recovered from the oil was 88±3%. Fuel characterisation indicated the oils similarity to gasoline. However, with aromatic content greater than 68 wt.%, blending with conventional fuel will be necessary to make it commercially suitable. Maximum oil/wax yield of 75.37±0.04 wt.% was achieved during bench scale testing of the clean multi-layer. Contamination decreased the oil/wax yield to 71.45±0.03wt.%, potentially due to a catalytic effect,but did not affect the HHV. Scaling up to pilot scale resulted in lower oil/wax yield of 62±12 wt.% and unaffected HHV in the range of 43.5-44.13MJ/kg (similar to diesel). This represented a gross energy recovery of 66±12%. Fuel characterisation indicated the flowable oils similarity to diesel. However, further upgrading will be necessary to make it suitable as commercial diesel.

AFRIKAANSE OPSOMMING: Dit is voorspel dat teen 2050 daar meer plastiek as visse per gewig in die oseaan gaan wees. Buiten die vanselfsprekende omgewingsbedreiging, hou plastiekafval ook ’n verlies van waardevolle koolwaterstof-gebaseerde materiale in. Pirolise is geïdentifiseer as ’n belowende tegnologie vir die herwinning van afvalplastiek wat nie herwin kan word deur konvensionele maniere nie as gevolg van hul gemengde en/of gekontamineerde aard. Twee sulke afvalplastiekstowwe is swart PS-bakkies en LDPE/PET-multilaag films wat gebruik word om rou vleis en droë hondekos, onderskeidelik, te verpak. Daar is egter min gerapporteer oor die omsetting van multilae, die invloed van kontaminasie, of die opskalering van die proses na groter skaal. Die doeltreffendheid van die pirolieseproses is gevind om hoogs afhanklik te wees van die komposisie van die voermateriaal en prosesparameters. Daarby kan grootskaalse prosessering toegevoegde moeilikheid inhou. Daarom, om pirolise ’n uitvoerbare opsie vir die prosessering van hierdie spesifieke afvalplastiekstowwe op grootskaal te maak, is dit nodig om sy optimering en opskalering na loodsskaal te bestudeer. Die doel van hierdie studie was om hierdie twee plastiekstowwe in brandstofprodukte (olie/was) deur middel van pirolise om te skakel. Om hierdie doel te bereik is afvalplastiekstowwe gekarakteriseer om hul gepastheid as brandstofvoorlopers te bepaal en die hoeveelheid kontaminasie te beraam. Die piroliseproses is geoptimeer in ’n banktoetsskaal semilotreaktor vir die opbrengs en kwaliteit van die olie/was. Gebaseer op geoptimeerde omsetting, is die proses opgeskaal in ’n loodssemi-aaneenlopende draaioondreaktor. Karakterisering van voermateriaal het bewys dat die afvalplastiekstowwe gepas was as olie/was-brandstofvoorlopers. Kontaminasie in PS het die karakterisering negatief geaffekteer. Beide vlugtige stowwe en die som van koolstof-en waterstofinhoud het egter steeds meer as 95 wt.% verteenwoordig. Kontaminasie in die LDPE/PET-multilaag het onbeduidende karakteriseringsverskille tot gevolg gehad. Olie-opbrengs van 89.8–93.2 wt.% is bereik gedurende banktoetsskaaltoetsing van die skoon PS. Swaar vleissapkontaminasie (omtrent 16 wt.%, droë basis) het die olie-opbrengs met 7.3wt.% verminder maar het nie die HHV geaffekteer nie. Omsetting van post-verbruiker gedigte PS het soortgelyke olie-opbrengste en HHV as die skoon PS tot gevolg gehad. Vergroting van skaal na die loodsreaktor het laer olie-opbrengs van 82.5±1.4 wt.% tot gevolg gehad met HHV soortgelyk aan olies verkry by banktoetsskaal in die bestek van 41.9–42.5MJ/kg (vergelykbaar met petrol). Die bruto-energie herwin uit die olie was 88±3%. Brandstof karakterisering het aangedui dat die olies soortgelyk aan petrol is. Met aromatiese inhoud groter as 68 wt.%, sal vermenging met konvensionele brandstof noodsaaklik wees om dit kommersieel geskik te maak. Maksimum olie/was-opbrengs van 75.37±0.04 wt% is bereik gedurende banktoetsskaaltoetsing van die skoon mulitlaag. Kontaminasie het die olie/wasopbrengs na 71.45±0.03 wt.% verminder, moontlik as gevolg van ’n katalitiese effek, maat het nie die HHV geaffekteer nie. Vergroting van skaal na loodsskaal het in laer olie/wasopbrengs van 62±12 wt.% gelei en ongeaffekteerde HHV in die bestek van 43.5-44.13 MJ/kg (soortgelyk aan diesel). Hierdie het ’n bruto-energieherwinning van 66±12% verteenwoordig. Brandstof karakterisering het aangedui dat die vloeibare olies soortgelyk aan diesel is. Verdere opgradering is nodig om dit gepas vir kommersiële diesel te maak.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/108216
This item appears in the following collections: