Extractive desulfurisation and denitrification of pyrolysis oil from waste tyres

Uvođenjem RED II direktive promiče se upotreba goriva dobivenih iz otpada u transportnom sektoru. Takva goriva sadrže velike količine zagađivala poput sumpora, dušika i čađe. S obzirom na sve strože propise o dozvoljenoj količini sumpora u gorivu i ograničenjima konvencionalnog procesa hidrodesulfurizacije razvijaju se alternativne metode. Literaturnim istraživanjem ekstrakcijska desulfurizacija pokazala se najperspektivnijom zbog blagih uvjeta provedbe procesa te visoke učinkovitosti. Stoga, cilj ovog rada bio je iz goriva dobivenog iz otpadnih guma ukloniti sumpor i dušik ekstrakcijskom desulfurizacijom i denitirifikacijom. Kod ekstrakcije bitno je obratiti pažnju na odabir otapala. Ono mora biti selektivno te ekološki i ekonomski prihvatljivo. U tu svrhu, korištena su niskotemperaturna eutektička otapala – dva kisela, na bazi kolin klorida, i dva bazična, na bazi kalijevog karbonata, uz etilen glikol i glicerol kao donore vodikovih veza. Ekstrakcije su provođene pri relativno blagim reakcijskim uvjetima u različitim omjerima kako bi se našao optimalan omjer efikasnosti i ekonomičnosti provedbe procesa. Istraživanje je provođeno na težoj (dizelskoj) i lakšoj (benzinskoj) frakciji pirolize otpadnih guma. Praćene su koncentracije sumpora, dušika, klora, vlage te ukupna kiselost frakcija prije i poslije ekstrakcije. Cilj je bio sniziti ih na razinu prihvatljivu za njihovo umješavanje u komercijalnu dizelsku i benzinsku frakciju, a da EU standardi ostanu zadovoljeni. Na rezultate utjecali su različit sastav, stupanj onečišćenja frakcija sumporom i dušikom te svojstva otapala. Bolju ekstrakcijsku učinkovitost pokazala su bazična otapala, a najbolji rezultat dobiven je u masenom omjeru otapala i goriva 0,1. Provedena je i desulfurizacija dizelske frakcije pomoću koncentrirane sumporne kiseline u prvom stupnju i adsorbensima kalcijevim oksidom i bentonitima s pH 2-3 i pH 6-8 u drugom stupnju.Upcoming RED II directive encourages the use of advanced biofuels in the transport sector. Those fuels can contain substantial amounts of pollutants such as sulfur, nitrogen and soot. Due to the increasing fuel quality standards and conventional hydrodesulfurization and hydrodenitrification process limitations, alternative purification methods are being investigated. Current literature points to extractive desulfurization as a method of choice due to its mild operating conditions and high efficiency. The objective of this work was to remove sulfur and nitrogen from waste tire pyrolytic oil by means of extractive desulfurization and denitrification. Choosing the best solvent is very important and challenging step in the development of extraction methods. The solvent has to be selective and also ecologically and environmentally acceptable. For that purpose, several deep eutectic solvents were employed – two acidic, choline chloride based solvents and two alkaline, potassium carbonate based solvents, with ethylene glycol and glycerol as hydrogen bond donors. Experiments were conducted under mild operating conditions, with different ratios of solvent to oil in order to find the most effective and efficient process conditions. Investigation was conducted with both heavy (diesel) and light (gasoline) oil fractions. Concentrations of sulfur, nitrogen, chlorine and moisture content were measured before and after extractions, as well as total acid numbers. The goal was to purify the oil enough to make it suitable for mixing with commercial diesel and gasoline fractions to form a mixture that complies with the EU quality standards. The results show that oil composition, amount of sulfur and nitrogen and solvent properties all affect the efficiency. Alkaline solvents showed the best extraction efficiency and the most effective solvent to oil ratio was 0.1. Desulfurization of the heavier fraction was also conducted using concentrated sulfuric acid in the first step and potassium oxide and bentonite adsorbents under pH 2-3 and pH 6-8 in the second step