Asfaltit ve bitümlü şist piroliz ürünlerindeki azotun potansiyometrik yöntemle incelenmesi

Abstract

ASFALT İT VE BİTÜMLÜ ŞİST PİROLİZ ÜRÜNLERİNDEKİ AZOTUN POTANSİYCMETRİK YÖNTEMLE İNCELENMESİ ÖZET Petrol ürünlerinin artan fiyatları ve yetersizliği, ülkemizdeki düşük kalor i fik değerli katı yakıtların ve bitümlü şistlerin kullanımı nı ve değerlendirilmesini yeniden gündeme getirmiştir. Bu çalışmada, Silopi ve Şırnak asfaltitleri ile Göynük ve Seyitömer Bitümlü şistleri Heinze retordunda 540 C da piroliz edilmiş, katran verimleri hesaplan mış, piroliz sonucu elde edilen katranın malten kesimi silikajel ko londa alt fraksiyonlarına ayrılarak eluat verimleri hesaplanmış, ali fatik, nötral aromatik ve polar bileşiklerdeki azotun yapısı potansi- yometrik, kromatografik ve spektroskopik yöntemlerle aydınlatılmaya çalışılmıştır. Azot içeren model bileşikler nitrobenzen, klorobenzen gibi çözücülerde, susuz ortamlarda potansiyometrik yöntemlerle titre edil miş, model bileşiklerin sudaki pK değerleriyle susuz çözücülerdeki yarı nötralizasyon potansiyelleri karşılaştırılmış, 4:1 hacım oranında klorobenzen/asetikanhidrit içeren çözücü sisteminin model bileşikler, piroliz ürünleri ve malten kesimleri için potansiyel aralığını geniş lettiği saptanmıştır. Piroliz ürünlerinin malten kesimleri silikajel kolonda parafi- nik, nötral aromatik ve polar fraksiyonlarına ayrılarak, herbir frak siyonun elementer analizleri, sayıca ve ağırlıkça ortalama molekül ağırlıkları hesaplanmıştır. Piroliz ürünlerindeki ve alt fraksiyon eluatlarındaki fonksiyonel gruplar Fourier Transform Infrared Spektros- kopisiyle incelenmiş, heksan eluatlarındaki alifatik bileşenlerin tanınmasında kapiler kolon gaz krcmatografisi kullanılmıştır _ Maltenlerin benzen eluatlarına H n.m.r. yöntemi uygulanarak yapıdaki hidrojen dağılımının miktarı, 13c h.m.r. yöntemi ile de yapıdaki karbon atomlarının dağılımı ve şekli kalitatif olarak ince lenmiştir. _v-

THE INVESTIGATION OF NITROGEN CONTAINING COMPOUNDS IN PYROLYSIS PRODUCTS OF ASPHALTITE AND OIL SHALE BY NONAQUEOUS POTENT IOMETRY SUMMARY The increasing costs and shortages of petroleum products have engendered considerable interest in the utilization of low-grade fossil fuels such as oil shale, tar sands etc. Current emphasis on the development of alternate energy sources has stimulated production of synthetic fuels derived from low-grade fossil fuels. The intensive development of research carried out into liquefaction of low-grade fossil fuels observed in recent years has brought the industrial production of liquid fuels from these materials to realization. A number of asphaltic substances are found in South- Eastern Turkey is approximately about 5.2x10 tonnes. The Silopi and Şırnak reserves together comprise the major part of the asphaltite deposits which ranges from asphaltite to asphaltic pyrobitumen according to their degrees of alteration. Oil shale comprise the second largest solid fuel rezerve in Turkey alter lignites, with reserves totalling approximately 5.2x10° tonnes. The geologycal reserve of the Göynük oil shale. deposit is about 2.5x10°, whereas the Seyitömer is only about 1x10° tonnes. The asphaltite bitumens are classified as aromatic- asphaltic oil derived by alteration during migration of aromatic intermediate oils originating from open-water marine sediments laid down in an anoxic environment. The oil shale is composed of kerogen which is insoluble in conventional organic solvents, bitumen which is soluble is organic solvents, and inorganic materials oil shale deposits were formed is ancient lakes and seas by the slow deposition of organic and inorganic compounds remains from the bodies of water. The geology and organic components of oil shale varies with deposit location. All direct coal liquefaction processes produce a coal-derived liquids which contains varying amounts of maltenes, asphaltenes, and preasphaltenes. The thermal decomposition of asphaltic substances and oil shale, pyrolysis or retorting, yield liquid gaseous and solid residue. - VI-The purpose of this study is to investigate the nitrogen, containing compounds in the pyrolysis products of asphaltic substances and oil shales by nonaqueous potehtiometry, column chromatography, size exclusion chromatography, elemental analysis, infrared spectroscopy and İH, ^C n.m.r. spectroscopy. The nitrogen bases in coal and coal-derived liquids, low-grade fossil fuels and derived liquids, even though they are minor components, have not been fully charecterize< The average organic nitrogen content of naturally occuring petroleum from 153 locations is around 0.1 wt % whereas most coals, shale oils and other fossil fuels range from 0.5 to 2.0 wt % nitrogen. Knowledge of the types and quantities of nitrogen compounds in fuels is important because they significantly affect both the refining and stability behaviour of crudes and products. The presence of considerable quantities of nitrogen compounds which is found in low-grade fossil oils would cause a high emission of nitrogen oxides formed during combustion. used di is impo Whether coal-derived liquids are ultimately to be rectly as a utility fuel, or chemical feedstock, it irtant to know as much as possible about the The pyrolysis products of asphaltic substances and oil shales are complex mixtures of alkanes, non polar aromatic compounds, aromatic compounds with functional groups, and heteroaromatic compounds containing significant quantities of nitrogen and sulphur compounds. Because no single technique could give complete information on all possible compound types and because cross-checking qualitative and quantitative data using one or more independent methods is always highly desirable. Because of complex nature of pyrolysis products of asphaltic substances and oil shales, fractionation according to chemical class is required before identification of individual components can be achieved. Traditionally, separation schemes have been developed by using solvent partitioning methods and column chromatography. The chemical charecter ization of such a complex mixture requries prior separation into less complex fractions. Separation procedures have progressed from an elemantary process of separating fuels into oils ( hexan-soluble materials or maltenes) and aspaltenes (benzene-soluble materials) to sophisticated chromatographic techniques. All of the procedures separate coal-derived liquids into fractions that differ according to their chemical - vii-functionality. Silopi and Şırnak asphalite as well as Göynük and Seyitömer oil shale samples were first pyrolysed in a Heinze retort at 540 C and maintained for 30 min. ' The linear heating rates of 5K/min. were used for all pyrolysis experiments. It is noticed that the oil yield is increased at low heating rates. Pyrolysis yields for both asphaltites and oil shales exhibit a common relation between the original aromatic carbon content of the sample and the residual organic carbon after pyrolysis. The Silopi asphaltite and Göynük oil shale gave high >i 1 yields whereas Şırnak asphaltite and Seyitömer oil hale medium and liquar was separated from the pyrolysis.11. Pyrolysis products and maltenes of asphaltites and oil shales were analysed by nonaqueous potentiometry capillary column gas chromatography, fourier transform infrared spectroscopy, ultimate analysis, size exclusion chromatography, *H and *¦*£ nuclear magnetic resonance spectroscopies. This work represents the first study of its kind to use differential, nonaqueous potentiometry for the charecterization of nitrogen-types in pyrolysis products of asphaltite and oil shale in Turkey. The amount of the pyrolysis products titrated ranged from 300 mg to 800 mg. A procedure is described here for classifying nitrogen in the pyrolysis products into three different t types. The basic nitrogen ( pK ^> 2) exists primarily as heteroatomic bases of pyridine, quinoline, piperidine, alkyl-aryl amine types. Weakly basic nitrogen compounds (0<cpK <Z2) is present primarily as substituted indoles, cafeine and phenazine which only one of their multiple nitrogen is titrated. Non-basic nitrogen ( pK <T0) is present as carbazoles, some amides and substituted Indoles. In this study, a series of nitrogen containing compounds with a wide range of basicities, were examined under differential nonaqueous potentiometric titrations in nitrobenzene and chlorobenzene solvents. An approximately rectilinear correlation was found between pK (in water )and Half Neutralization Potential (HNP) values for titrations performed in both solvents. The sensitivity of the Vlll-determination is limited by the size of sample and titrant strength.. Titration and total nitrogen data alone can be used for the rapid estimation of the kinds and amounts of major compound types in pyrolysis products. These data suggest that pyridines, quinolines, acridines and one nitrogen atoms in diazo compounds can be titrated as strong bases. Infrared and titration data indicate that both of the nitrogen atoms in most diazo compounds are tertiary, when these compounds are titrated, only one of nitrogen atom is reactive, apparently formation of the salt causes the second nitrogen atom to be nonreactive. The hexane soluble portion of the pyrolysis products were separated into fractions by silica gel adsorbtion chromatography. Ultimate analysis of each fraction were performed and each fraction were also subjected to size exclusion chromatography for the determination of number average molecular weight and weight average molecular weight. Elemental analysis and fourier transform infrared spectroscopy measurements indicated that the sulphur percentage is high in the neutral aromatic fractions of asphaltites whereas the nitrogen percentage is high in the neutral aromatic fractions of oil shales. '? ~ ~ The average molecular weight of polar fraction Is high in compared to other fractions, the reason for this, polar fractions of the pyrolysis products contair. too much heteroatoms, and most of the nitroge,h and oxygen containing compounds are condensed in polar fractions. The hexane eluates of maltenes were examined by capilary column gaz chromatography, and results were compared with the previous studies. The functional groups in pyrolysis products and maltenes fractions were examined by fourier trQnsform- infrared spectroscopy. The functional groups containing nitrogen in oil shales were observed in both neutral aromatic and polar fraction eluates in chromatographic separation. Whereas `the nitrogen containing functional groups in asphaltites were mainly observed in polar fractions. The ultimate ix-analysis were also supported these observation. H NMR was employed to determine the relative amounts of aromatic (H ) protons, protons on carbon adjacent %o aromatic ringsafHa) and protons on carbon not adjacent to aromatic rings (Ho, H ) NMR derived carbon and hydrogen distributions, ultimate analysis and molecular weight data were combined to construct molecular structure representative of the pyrolysis products in benzene eluates of maltenes. Elements other than hydrogen and carbon which are present in pyrolysis products (S,N,0) are less accessible by İH NMR measurements. 13 Analysis of the aliphatic region in the C NMR spectrum of the benzene eluates of maltenes revealed the presence of seven major carbon atom types. The most intense signal (2?.7ppm)is due to methylene which is four or more carbon atoms away from the ends of long alkyl chains. The associated signals at 14.1 ppm, 22,8 ppm and are due to terminal methyl, the first methylene - ~ i J.L..1-; i._.1I...1 _i j_ - X-