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Plastic waste is steadily polluting oceans and environments. Even when collected, it is still predominantly dumped or incinerated for energy recovery at the cost of CO2. However, no simple solution exists to deal with marine litter (ML). Overcoming limitations in collection, and in the environmentally, technically and economically acceptable use of the collected material, is of paramount importance. Chemical recycling can contribute to the transition towards a circular economy but the high variety and contamination of real waste remains the biggest challenge. In my research more than 100 kg of actual benthic ML from the North Adriatic Sea, including polyolefins packaging and polyamides fishing nets, were successfully processed “as-is” without pretreatment and converted into standardized marine gas oil (MGO) compliant with the ISO8217 via the pyrolysis and the distillation process with 8 potential harmful emissions linked to the pyrolysis process monitored and curbed to safe levels. Approximately 45 wt% yield of raw pyrolysis oil (RPO) was obtained of which 50% (v/v) being MGO. RPO and its distillates were chemically characterized via GC-MS. For all samples, more than 30% of the detected compounds were identified. 2,4-dimethyl-1-heptene, a marker of PP pyrolysis, is the most represented peak in the chemical signature of all the marine litter samples, and it differentiates commercial and pyrolysis marine gasoil. Besides, I studied the detailed composition and the steam cracking performance of distilled pyrolysis oil fractions in the naphtha-range of ML and mixed municipal plastic waste (MPW) considered unsuitable for mechanical recycling. Advanced analytical techniques including comprehensive two-dimensional gas chromatography (GC × GC) coupled with various detectors and inductively coupled plasma – mass spectrometry (ICP-MS) was applied to characterize the feedstocks and to understand how their properties affect the steam cracking performance. Both waste-derived naphtha fractions were rich in olefins and aromatics (~70% in MPW naphtha and ~51% in ML naphtha) next to traces of nitrogen, oxygen, chlorine and metals. ICP-MS analyses showed that sodium, potassium, silicon and iron were the most crucial metals that should be removed in further upgrading steps. Steam cracking of the waste-derived naphtha fractions resulted in lower light olefin yields compared to fossil naphtha used as benchmark, due to secondary reactions of aromatics and olefins. Coke formation of ML naphtha was slightly increased compared to fossil naphtha (~50%), while that of MPW naphtha was more than ~180% higher. It was concluded that mild upgrading of the waste-derived naphtha fractions or dilution with fossil feedstocks is sufficient to provide feedstocks suitable for industrial steam cracking. Waste plastics oil (WPO) obtained from a relatively large-scale batch rotary kiln pyrolysis reactor was collected and stored for 60 months in dark at 10 °C, periodically thoroughly characterized and finally tested as the drop-in fuel in internal combustion engine. It was evaluated by investigation of combustion process and emission formation phenomena under a wide range of operating parameters. The results were compared with those obtained with diesel fuel at the same injection and gas path parameters to provide a comprehensive basis for further development of control strategies. Finally, the solid residue from the pyrolysis process was evaluated for material recovery or safe disposal, thus closing the mass balance of the whole process. Due to the great contamination of the original feedstock, stabilization of solid residue is required to attain not hazardous waste criteria, but once stabilized with Portland concrete, it could even be employed as construction material, therefore transforming a problem into an opportunity. Plastični odpadki vztrajno onesnažujejo oceane in okolje. Tudi če so zbrani, se jih še vedno večinoma odlaga ali sežiga za namen pridogivanje energije, pri čemer neizogibno nastaja CO2. Po drugi strani pa preproste rešitve za ravnanje z morskimi odpadki (ML) ni. Preseganje omejitev pri zbiranju ter okoljsko, tehnično in ekonomsko sprejemljivi uporabi zbranega gradiva je izjemnega pomena. Kemično recikliranje lahko prispeva k prehodu v krožno gospodarstvo, vendar velika raznolikost in onesnaženost samih odpadkov ostaja največji izziv. V moji raziskavi je bilo več kot 100 kg dejanskega bentoškega ML iz Severnega Jadranskega morja, vključno z embalažo iz poliolefinov in ribiškimi mrežami iz poliamidov, uspešno obdelanih »takšnih kot je« brez predhodne obdelave in pretvorjenih v standardizirano pomorsko plinsko olje (MGO). To je skladno z ISO8217 prek postopka pirolize in destilacije z 8 možnimi škodljivimi emisijami, povezanimi s postopkom pirolize, ki se spremljajo in omejijo na varne ravni. Dobljen je bil približno 45 ut.% izkoristek surovega piroliznega olja (RPO), od tega je 50 % (v/v) MGO. RPO in njegovi destilati so bili kemijsko karakterizirani z GC-MS. Pri vseh vzorcih je bilo identificiranih več kot 30 % zaznanih spojin. 2,4-dimetil-1-hepten, marker pirolize PP, je najbolj zastopan vrh v kemijskem podpisu vseh vzorcev morskih odpadkov in razlikuje komercialno in pirolizno morsko plinsko olje. Poleg tega sem proučeval podrobno sestavo in zmogljivost parnega krekinga frakcij destiliranega piroliznega olja v območju nafte ML in mešanih komunalnih plastičnih odpadkov (MPW), ki se štejejo za neprimerne za mehansko recikliranje. Napredne analitične tehnike, vključno z obsežno dvodimenzionalno plinsko kromatografijo (GC × GC), skupaj z različnimi detektorji in induktivno sklopljeno plazmo – masno spektrometrijo (ICP-MS), so bile uporabljene za karakterizacijo surovin in razumevanje, kako njihove lastnosti vplivajo na učinkovitost parnega krekinga. Obe frakciji nafte, pridobljeni iz odpadkov, sta bili poleg sledov dušika, kisika, klora in kovin bogati z olefini in aromati (~70 % v nafti MPW in ~51 % v nafti ML). Analize ICP-MS so pokazale, da so natrij, kalij, silicij in železo najbolj ključni elementi, ki jih je treba odstraniti v nadaljnjih korakih nadgradnje. Parni kreking frakcij nafte, pridobljene iz odpadkov, je povzročil nižje izkoristke lahkih olefinov v primerjavi s fosilno nafto, uporabljeno kot merilo, zaradi sekundarnih reakcij aromatov in olefinov. Tvorba koksa pri ML nafti je bila rahlo povečana v primerjavi s fosilno nafto (~50 %), medtem ko je bila pri MPW nafti več kot ~180 % večja. Ugotovljeno je bilo, da blago izboljšanje frakcij nafte, pridobljene iz odpadkov, ali redčenje s fosilnimi surovinami zadostuje za zagotovitev surovin, primernih za industrijski parni kreking. Odpadno plastično olje (WPO), pridobljeno iz sorazmerno obsežnega šaržnega piroliznega reaktorja z rotacijsko pečjo, je bilo zbrano in shranjeno 60 mesecev v temi pri 10 °C, občasno temeljito karakterizirano in na koncu testirano kot gorivo, ki se vstavi v motor z notranjim zgorevanjem. Ocenjen je bil s preiskavo procesa izgorevanja in pojavov nastajanja emisij v širokem razponu delovnih parametrov. Rezultati so bili primerjani s tistimi, pridobljenimi z dizelskim gorivom pri enakih parametrih vbrizgavanja, da bi zagotovili celovito podlago za nadaljnji razvoj strategij nadzora. Nazadnje je bil trdni ostanek iz procesa pirolize ovrednoten za predelavo materiala ali varno odlaganje, s čimer se je zaključila masna bilanca celotnega procesa. Zaradi velike kontaminacije prvotne surovine je potrebna stabilizacija trdnih ostankov, da se doseže merilo nenevarnega odpadka. Ko se ta stabilizira s portlandskim betonom, bi ga lahko uporabili celo kot gradbeni material, s čimer bi problem spremenili v priložnost. |
