Characterization of type III kerogen from Tyrolean shale (Hahntennjoch, Austria) based on its oxidation products

Abstract

A 29-step alkaline permanganate degradation of type III kerogen from Tyrolean (Hahntennjoch, Austria) oil shale was performed. A high yield of oxidation products was obtained (93.7 % relative to the original kerogen): 0.5 % neutrals and bases, 19.5 % ether-soluble acids and 58.9 % of precipitated (PA). A substantial amount of kerogen carbon (14.8 %) was oxidized into carbon dioxide. The organic residue remaining after the final oxidation step was 6.9 %. The PA components were further oxidized and the total yields relative to original PA were 1.0 % neutrals and bases and 59.0 % ether-soluble acids, the non-degraded residue being 29.3 %. Detailed quantitative and qualitative analysis of all oxidation products suggested the Tyrolean shale kerogen to be a heterogeneous macromolecular substance consisting of three types of structures differing in composition and susceptibility towards alkaline permanganate: the first, resistant, presumably composed of aromatic structures linked by resorcinol ethereal bonds; the second, combined in nature, the aliphatic part comprising methyl-substituents and short cross-links, both easily oxidized into CO2, water and low molecular weight acids and aromatic structures yielding aromatic diand tri-carboxylic acids as oxidation products; finally the third, composed of aliphatic cross-links and substituents, alicyclic (and/or heterocyclic) and some aromatic structures, bound into units moderately resistant towards oxidation. The overall yields of kerogen and PA oxidation products lead towards a balance between aromatic, alkane monoand dicarboxylic and alkanepolycarboxylic acids, suggesting a shift of the structure of Tyrolean shale kerogen from typical aromatic reference type III towards a heterogeneous aromatic-aliphaticalicyclic type structure.

Stupnjevitom degradacijom kerogena tirolskog škriljca pomoću alkalnog permanganata dobijeni su visoki prinosi oksidacionih proizvoda. Dobijene nerastvorne kiseline naknadno su degradovane u 8 stupnjeva. Detaljna GC-MS analiza kiselina rastvornih u etru, dobijenih degradacijom kerogena, potom intermedijarnih nerastvornih kiselina, pokazala je da je kerogen tirolskog škriljca heterogena makromolekularna supstanca i da se sastoji iz tri tipa strukture, različitog sastava i različite osetljivosti na primenjeno oksidaciono sredstvo. Prvi tip je aromatične prirode sa rezorcinolnim etarskim umreženjem, otporan prema alkalnom permanganatu. Drugi se vrlo lako oksiduje, a sastoji se od aromatičnih struktura umreženih kratkim alifatičnim nizovima i sa većim udelom metil-supstituenata. Ovaj tip strukture je pri oksidaciji dao visok prinos SO2, alifatične kiseline malih molekulskih masa i aromatične dii trikarboksilne kiseline u visokom prinosu. Treći tip strukture je srednje osetljivosti na permanganat, a sastoji se od alicikličnih i/ili heterocikličnih i aromatičnih jezgara povezanih alifatičnim nizovima srednjih dužina. Kvantitativan odnos alifatičnih, aromatičnih i alkan-polikarboksilnih kiselina u oksidacionim proizvodima pokazao je da struktura kerogena tirolskog škriljca odstupa od tipskih, dominantno aromatičnih struktura tipa III, kojima pripada po svom H/C-O/C atomskom odnosu, i da je pomerena ka heterogenim, aromatično-alifatično-alicikličnim strukturama tipa II.