Linyit ve asfaltit karışımlarının düşük sıcaklık pirolizi
Low temperature pyrolysis of lignite and asphaltite mixtures
- Tez No: 19313
- Danışmanlar: DOÇ.DR. AYŞE ŞENATALAR(ERDEM)
- Tez Türü: Yüksek Lisans
- Konular: Kimya Mühendisliği, Chemical Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 1991
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Belirtilmemiş.
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 66
Özet
ÖZET Bu. çalışmada, kömür ve ağır petrollerin birlikte işlenmesinde olduğu gibi, genç kömürler olan linyitler ile mineral madde içeren; petrol kökenli bir pirobitum olan asfaltitlerin sıvılaşma esnasında birbirlerini karşılıklı olarak etkileyecekleri hipotezinden yola çıkılmıştır. Bu amaçla, değişen oranlardaki homojen asfaltit-linyit karışımları, en basit sıvılaştırma yöntemi olan düşük sıcaklık pirolizine uğratılmış ve ürün verimleri izlenmiştir. Çan linyiti, Çayırhan linyiti, Keleş linyiti ve Avgamasya asfaltiti kullanılan piroliz deneyleri, 0.125-0.314 mm aralığına öğütülmüş, ağırlıkça «100 linyit, %75 linyit-%25 asfaltı' t, %50 linyit- %50 asfaltit, %75 linyit-%25 asfaltit ve XI 00 asfaltı' t içeren karışımlarla, Heinze retortunda gerçekleştirilmiştir. 4°C/dakika ısıtma hızı ile normal statik atmosferde 550°C a kadar ısıtılan sistem, bu sıcaklıkta yarım saat bekletilmiştir. Piroliz sıvısını oluşturan su ve katranı ayırmak için her karışıma iki paralel deney uygulanmıştır. İlk deneyde, Dean-Stark metoduna göre, toluen yardımıyla su tayini yapılmıştır. Katran miktarını tayin için yapılan ikinci deneyde ise, daha düşük kaynama noktalı olan diklormetan kullanılmıştır. Daha sonra katran, n-hekzan, toluen ve THF yardımıyla, sırasıyla yağ, asfalten ve preasfalten fraksiyonlarına, silikajel kolon kromatografisi ile de alifatik, aromatik ve polar kısımlarına ayrılmıştır. Sonuçta, hipotezimize uygun olarak, asfaltit-linyit karışımları arasında, pirolitik bozunmalar esnasında sinerjistik (kuvvetlendirici) bir etkileşim görülmüştür. Linyite az miktarda asfaltit eklendiğinde maksimum değerine ulaşan bu etkileşim katran veriminde ortaya çıkmıştır. Katran miktarının maksimum olduğu karışım değerinde, gaz veriminin de bir minimum gösterdiği, semikok veriminin ise azalmadığı gözlenmiştir. Katran verimi teorik karışım verimlerinin üzerine çıkarken, katran içindeki asfaltenlerin yüzdesi de artmaktadır. Dolayısıyla da söz konusu kuvvetlendirici etki, gaz verimini azaltırken, asfalten veriminin artmasını sağlamaktadır. Bu etkileşimin su buharı ve anorganik yapının katalitik etki sinden ve/veya asfaltı' tin linyit için H-verici bir çözücü gibi davranmasından kaynaklandığı düşünülmektedir. iv
Özet (Çeviri)
LOW TEMPERATURE PYROLYSIS OF LIGNITE AND ASPHALTITE MIXTURES SUMMARY Since the mid- 1970s the field of coal liquefaction has become a lively one that has evolved from“benign neglect”in early 1960s to one which an actively competitive community is involved in a wide array of scientific, technical and adminstrative activities. The ma jor objective is the development of technology that lays the founda tion for a synthetic oil industry to supplement petroleum natural sources. It was the rapid depletion of conventional light oil reser ves, which eventually forced production industry to consider alter nate sources for the production of liquid fuels. Hence, the proces ses, which depend on coal, have become more important recently. The present state of oil in the world market seems to be sett led and running at reasonable prices. However the forecasts for the future of crude oil in the world are not optimistic. It is claimed that the crude oil reserves in Middle East will diminish at a slower rate than other resources. This will cause the bargaining power of Middle Eastern Countries to increase. It is very unlikely that the world economies would be able to absorb steep petroleum price increa ses especially if it happens, in a manner which may take place as a“third energy crisis”. In case of an energy crisis Turkey will be one of the countries that will suffer because of her strong dependen ce on imported crude. We know that the routes currently being pursued are not the ul timate solution to the lowest cost production of liquids from coal. New processes will probably use inventions now only dimly perceived. Paths now being explored will appear in retrospect to the primitive approximations for accomplishing the objective of low-cost clean li quids from coal. There is no proof, unfortunately, that new lower cost routes will be found. However, the thrust of work in several areas in this field provides firm bases for potential realization of new approaches. These bases include the following: i) Chemical understanding of coal dissolution and the structure of coal itself ii) Large-scale units that prove engineering designs. iii) Engineering of equipments, subcomponent, and process steps that simplify the process schemes. iv) The large array of experienced talent now at work. vv) Catalyst development by experienced industrial teams. Compared to the world standards, Turkey is not rich in solid fuel resources but it contains considerable amounts of lignites, oil shales and asphaltites. Lignite is considered to be the lowest rank coal with high moisture and volatile matter contents and is considered to be of poor quality because of its low heating value. It is the solid fuel with the largest amount of reserves in Turkey, totalling to approximately 8x10= tonnes. There is a considerable amount of asphaltite reserves in South eastern Turkey, which have fairly high. bHumen content. Asphaltic minerals are generally believed to be formed by migration of petro leum followed by alteration during burial. Light fractions are lost and a variety of biodegration, oxidation and other chemical reactions occur with concomitant increase in the molecular weight and decrease in the H/C ratio.. Avgamasya asphaltite isa representative deposit of the asphal tic subtances of Southeastern Turkey, which range from asphaltite to asphaltic pyrobitumen according to their degrees of alteration. It is geochemically classified as a solid aroma tic-asphal tic oil conta ining mineral matter, derived from nearfey oil deposits. It has po tential for conversion to chemical feedstocks and transport fuels. There are two generic methods of producing liquids from coal or solid fuels in general: i. Indirect liquefaction ii. Direct liquefaction. Indirect liquefaction is the gasification of coal followed by Fischer- Tropsch synthesis. Direct liquefaction methods can be classified as below; i. Hydrogenation ii. Extraction iii. Pyrolysis. Coal liquefaction by hydrogenation and/or extraction is gene rally carried out at elevated temperature (350-490°C) and hydrogen partial pressure (10-20 MPa) in the presence of a carrier solvent. The difference lies in the use of catalysts in the former. Elevated vitemperature is required for the thermal cracking of coal in order to produce reactive fragments (free radicals); the carrier solvent, hydro gen donor or non- hydrogen donor, is needed for coal solvation and transfer of reactive hydrogen to stabilize the coal -derived free ra dicals. As a result, liquids of relatively low molecular weights and gases are produced. Coal liquefaction products are generally divided into three fractions in addition to gases, water and insoluble residue. The first fraction is the pentane or hexane solubles called oils, the second fraction is the hexane insoluble but toluene solubles, called asphaltenes, the third fraction is the toluene insolubles but tethra- hydrofuran solubles, called preasphaltenes. The molecular weights of oils, asphaltenes and preasphaltenes are respectively, 400 or less, 900 to 1000 and 1000-3000. The oils are primarily neutral with only a small amount of phenols and nitrogen compounds, the asphaltenes contain less than one functional group per molecule and preasphaltenes contain more than one functional group per molecule. The gases in clude C1-C5 hydrocarbons, carbon oxides, ammonia and hydrogen disulp- hide. The term“liquefaction”as used here encompasses“liquid”. The liquid has been rather broadly defined on the basis of solubility in various solvents, and in many cases the major“liquid”product is a solid at room temperature. The extent of liquefaction or conversion, is universally defined as follows: fconverston = maf coa1 in"maf inso1uble residue out x 100 maf coal in Several direct coal liquefaction processes, such as SRC-II, EDS, H-Coal, etc.- were developed in the 1970s to produce distillate fuels from coal. However, these processes are not economical under present conditions. One of the principle drawback of these processes, is the fact that coal, a solid, must be fed into the reactor using a recycle oil in a ratio of 2: parts to only one part of coal. The re cycle stream adds considerably to the complexity of such plants, and increases the cost of production. Co-processing, where coal is liquefied in a once through mode using a petroleum derived oil or another heavy oil slurrying media, such as heavy crudes, residual oils, etc., have potential to provide a solution to some of the difficulties encountered in the direct li quefaction of coal. Co-processing is found to be interesting and useful because of the following advantages. i) It is a convenient technique to better utilize the domestic resources of coal and heavy oil. viii i). A synergism is observed in processing of heavy-oil and coal together, the mechanism of which is not clearly understood yet. iii) Processing of heavy oil streams which usually contain me tals that act as catalyst poisons, is achieved. iv) Addition of coal seems to decrease the amount of coke for mation taking place during the processing of heavy oil at temperatu res above 350QC. v) Sulfur and nitrogen contents are observed to decrease sig nificantly in the final products. vi) Can be developed to fit into the present refinery structure and hence it provides for a smooth transition from the current refin ing technology to new coal liquefaction processes. Heavy oils or bitumens are seen to be cabaple of converting coal into soluble oil products. In almost every case, added cat alyst has shown to further increase the soluble oil yields while dec reasing the coke yields. The use of coal plus heavy oils or bitumens has brought us closer to the technical advancements that are needed for a more economical direct coal liquefaction process. The purpose of this study is to investigate the copyrolysis of three Turkish lignites (Çan, Çayırhan and Keleş lignites) with Avga- masya asphaltite. Avgamasya asphaltite, being classified as a solid nearby oil deposits, as mentioned above, was expected to show a simi lar synergism with the lignites. For this purpose, lignite and asphaltite mixtures ground to 0.125-0.315 mm were mixed thoroughly and were pyrolysed at 550°C. Mixtures containing. %1 00 lignite, %75 lignite, %50 lignite, %25 lig nite and %100 asphaltite by weight were used. Pyrolysis experiments were carried out in a Heinze retort. The temperature was controlled using a thermocouple inside the retort. The tar and aqueous liquor was collected in a liquid trap cooled by ice. A total of 40 g of sample was fed to the retort for each expe riment. The system was heated to 550°C, at a rate of 4°C/min and was held at this temperature for 30 minutes. The aqueous liquor was separated from the pyrolysis tar. For this purpose, according to Turkish standarts, the retort exit pipe and liquid trap was washed with toluene. However, since during the toluene evaporation step, some light components having boiling points lower than that of toluene, may be lost from the tar, with all blends, two parallel experiments were carried out. viiiIn the first experiment, the retort exit pipe and the liquid trap were cleaned up by toluene and the amount of water was deter mined by Dean-Stark method. After the second experiment performed in order to determine the tar yield, retort exit pipe and the liquid trap were washed with dichloromethane which has a relatively lower boiling point. After the separation of the tar from the aqueous liquor, tar was dissolved first in n-hexane to obtain the oil yield, then in to luene to obtain the asphaltene yield and finally in THF to obtain the preasphaltene yield. To separate aliphatic, aromatic and polar fractions of tar, siliea-gel column chromatoqraDhywas carried out. The asphaltene and preasphaltene contents of the tar was ob served to increase for those feed mixtures showing the strongest synergism to increase the tar yield. Silica-gel column ctromatography showed that it was mainly the neutral aromatic fraction of asphaltenes which increased as a result of this synergism. While the percentage of polar aromatic decreased. The variation of neutral and polar aromatic contents of asphaltenes with the feed ratio followed a similar trend to those of the tar and gas yields, respectively. Neutral aromatic yields were at a minimum for the range of feed mixtures giving tar yields belcw the stoichiometric line. Neutral aromatics in oils showed a similar trend for only Çayırhan and Çan lignites. Oils and asphaltenes were then separated into their aliphatic, aromatic and polar fractions by silica-gel column chromatography. A synergistic effect increasing the tar yields above the expected theoretical (stoichiometric) yields was obtained for the mixtures containing 25% by weight of asphaltite. For all three lignites used in this study, the semi coke yields were also observed to be higher than the theoretical values in the same range of asphaltite lignite ratios where the tar yields incre- IXased. In other words, the increase in the tar yields was not related to a decrease in semicoke yields, whereas feed mixtures containing 25% asphaltite and 75% lignite gave the lowest gas yields for all lignites. The variation of the total liquid yield with the ratio of feed mixture was similar to that of the tar yield. Increasing with the increase in tar yield, wheras the aliphatic fraction of oils decre ased for the same lignites in the same range. The synergism increasing the tar yields for feed mixtures containing 25% asphaltite and 75% lignite may be related to a cataly tic effect the water vapor on the inorganic constituents and/or a reactive extraction medium for the lignites provided by the asphal tite. The metals in asphaltite, such as V and Ni, may be catalyti- cally active; however their effect is expected to be seen also at the asphaltene -^> oil conversion step, hence increasing the oil content of the product. In our case, since the asphaltenic content of the tar is increasing, the asphaltite, having lower softening and solubilizati on temperatures and higher hydroaromatics content is thought to have acted as a stabilizing H-donor solvent medium for the lignites used.
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