Linyit Ve Ayçiçek Yağının Birlikte Pirolizi

Abstract

18. yüzyılın sonlarına doğru gerçekleşmeye başlayan endüstri devrimi ile birlikte, gelişen dünyanın yaşam standartları enerji tüketiminde büyük bir artışa neden olmuştur. Günümüzde bu eğilim hızlanarak devam etmektedir. Enerji ihtiyacını karşılamak için kullanılan doğal kaynaklar sınırlıdır ve dünya nüfusunun artışına paralel olarak çok hızlı bir şekilde tüketilmektedir. Bunun yanısıra, oluşabilecek enerji temini sorununu bir anda çözebilecek teknolojik bir gelişme de bulunmamaktadır. Bu durum bilinen enerji kaynaklarının en rasyonel şekilde kullanımı ve yeni enerji kaynaklarının değerlendirilmesi gibi acil önlemlerin alınması zorunluluğunu ortaya çıkartmıştır. Endüstrileşmiş ülkelerin petrole bağımlılığının her geçen gün arttığı bilinmektedir. Enerji ihtiyacının büyük bir kısmım karşılayan ve kimya endüstrisi için hayati öneme sahip bir çok hammaddenin kaynağı olan petrol yenilenemeyen enerji kaynaklarından biri olup yeryüzünde sınırlı olarak bulunmaktadır. Bilinen miktar ve tüketim hızı gözönüne alındığında petrolün 50 yıldan daha kısa bir sürede tükenmesi beklenmektedir. Diğer yandan, enerji tüketim hızı gözönüne alındığında kömürün dünya enerji ihtiyacım 300 yıldan daha uzun bir süre karşılayabileceği öngörülmektedir. Bu durumda petrolün yerini alabilecek kaynağın kömür ve kömürden elde edilen çeşitli proses ürünlerinin olacağı açıktır. Türkiye'nin 2050-2060 yıllarına kadar linyit açısından sıkıntı duymayacağı öngörülmektedir. Ülkemiz, kömürle ilgili geleceğini daha çok linyit ve onun daha genç olan kömürleri ile yeraltı zenginlikleri üzerine kurmalıdır. Enerji gereksinim ümitlerini linyite bağlayan Türkiye'nin linyit rezervleri toplam 8.3 milyar tondur. Bu bilgiler ışığında; bu çalışmada, linyit ile ayçiçek yağı birlikte piroliz edilmek suretiyle petrol eşdeğeri sentetik yakıt üretilmesi ve sıvı ürün veriminin ve/veya ürün kalitesinin arttırılması düşünülerek düşük kaliteli linyitlerimizin değerlendirilmesi amaçlanmıştır. Elde edilen sıvı ürünün karakterizasyonu kolon kromotografisi ve GC- MS yöntemi ile belirlenmiştir.

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 administrative activities. The major objective is the development of technology that lays the foundation for a synthetic oil industry to consider alternate sources for the production of liquid fuels. Hence, the processes, which depend on coal, have become more important recently. The present state of oil in the world market seems to be settled 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 increases especially if it happens, in 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 dependence on imported crude. Petroleum, coal and natural gas are at present the principles source of fuels and organic chemicals. These fossil fuels have high sulfur, nitrogen and metal content resulting in substantial amounts of SO2 and NOx being released to the atmosphere causing acid rains. These combustion of coal and crude oil also releases CO2. A continuos increase in the CO2 concentration in the atmosphere has undesirable climatic consequences through global warming by the greenhouse effect. It is estimated that, worldwide, over 20 billion metric tonnes of carbon dioxide are released into the atmosphere every year. It has been reported that significant amount of radioactive gases are also emitted during coal combustion. Moreover, research on the new energy sources not causing environmental pollution became more important with the developing environmental consciousness on the world. Because of the increase of world's population, industrialization and rapid urbanization, the reserves of fossil fuels decrease gradually. Especially, it is thought that the increase of world's population would be caused to decrease of fossil fuels in an important amount after 40-50 years. However, there is not any technological development yet to solve the problem of energy assurance as soon as possible. This situation invents the necessity of taking urgent measures from now on. The productive usage of known fuel sources and the investigation of new- renewable sources were taken very important point in that measures. Although renewable energy sources such as solar and wind energy, hydroelectric generation and biomass derived fuels, as well as alternative energy sources such as nuclear fission and fusion, have been investigated, due to environmental concerns and both technological and economic constrains, no suitable alternative non-fossil fuel energy source has been sufficiently developed to replace coal oil and gas as major energy source in the modern world. Oil, although at present the most readily useable form of fossil fuel due to its ease of transport, storage and combustion, has the smallest natural reserves, estimated at less than 50 years based on current known reserves and consumption rates. The major oil reserves are located in the Middle East a region of political instability and as a consequence long term stable supplies of crude oil can not be guaranteed, as was demonstrated during the recent gulf crisis. 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, totaling to approximately 8*109 tonnes. There are two generic methods of producing liquids from coal or solid fuels in general: 1.) Indirect liquefaction 2.) Direct liquefaction Indirect liquefaction is the gasification of coal followed by Fischer-Trorpsch synthesis. Direct liquefaction methods can be classified as below: l.)Hydrogenation 2.) Extraction 3.)Pyrolysis Coal liquefaction by hydrogenation and/or extraction is generally carried out at elevated temperature (350-490°C) and hydrogen partial pressure (10-20Mpa) in the presence of a carrier solvent. The difference lies in the use of catalysts in the former. Elevated temperature is required for the thermal cracking of coal in order to produce reactive fragments(free radicals); the carrier solvent, hydrogen donor or non-hydrogen donor is needed for coal solvation and transfer of reactive hydrogen to stabilize the coal-derived free radicals. 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 soluble called oils, the second fraction is the hexane insoluble but toluene soluble, called asphaltenes, the third fraction is the toluene insoluble but tethrahydrofuran soluble, called preasphaltenes. The molecular weights of oils, asphaltenes and preasphaltenes are respectively, 400 or less, 900-1000, 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 include C1-C5 hydrocarbons, carbon oxides, ammonia and hydrogen disulfide. 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. Co-processing, where coal is liquefied in a once through mode using a petroleum derived oil or another heavy oil slurry media, such as heavy crudes, residual oils, etc., have potential to provide a solution to some of the difficulties encountered in the direct hquefaction of coal. Co-processing is found to be interesting and useful because of the following advantages: 1.) It is a convenient technique to better utilize the domestic resources of coal and heavy oil. 2.) A synergism is observed in processing of heavy oil and coal together, the mechanism of which is not clearly understood yet. 3.) Processing of heavy oil streams which usually contain metals that act as catalyst poisons, is achieved. 4.) Addition of coal seems to decrease the amount of coke formation taking place during the processing of heavy oil at temperatures above 350°C. 5.) Sulfur and nitrogen contents are observed to decrease significantly in the final products. 6.) It can be developed to fit into the present refinery structure and hence it provides for a smooth transition from the current refining technology to new coal liquefaction processes. The purpose of this study is to investigate the copyrolysis of Göynük lignite with sunflower oil and to determine the synergetic effect between them. Göynük lignite with sunflower oil have been pyrolysed under a number of regimes and the resultant oils characterized by silicagel column chromatography, GC-MS analysis. The proximate and ultimate analysis of Göynük lignite and sunflower oil has been investigated under range of conditions using a modified Heinze retort. The results of the proximate and ultimate analysis of lignite are given in the following table. XI In all the experimental runs, the retort was heated at approximately 5°C/min to 600°C (hold time of 30 minutes). Experiments were carried out in a flowing nitrogen atmosphere. The pyrolysis tars were fractionated into n-hexane solubles and insolubles by warming the tars (lgr) in 50 ml of n-hexane then n-hexane solubles were separated into aliphatics, aromatics and polars using column adsorption chromatography. Normally, yields are expressed on a dry ash free (daf) basis to reflect the conversion of organic matter in lignite and sunflower oil. All the pyrolysis experiments were carried out in duplicate typical reparability being 2% of the total organic matter for both char and tar. Obtaining pyrolysis yields data from the measurements of condensed oil may be misleading due to the collection efficiency, separation difficulties and sample loses. The composition of Göynük lignite with sunflower oil tars are compared, which indicates that, the yields if aliphatics and aromatics decreased significantly, polars increased. The effect is more pronounced with copyrolysis, indicating that, paraffins decreased probably via dehydrogenation to olefins. Significant differences are also evidence in the n-alkane distributions. For sunflower oil pyrolysis, the proportion of lower molecular mass n-alkanes were lower compared to the Göynük lignites. GC-MS analysis of the alkanes fraction indicated that alkene concentration broadly increase with increasing sunflower oil. For example in Göynük lignite 100% pyrolysis the ratio of n- alkanes/n-alkenes was found 3.29 compared to 0.46 with sunflower oil 100%. Thus, the sunflower oil is actually promoting dehydrogenation reactions. The mass ratio of Göynük lignite to sunflower oil was varied between 1:3 (lignite: sunflower) and 3:1. The actual oil yields for the mixtures are higher up 1: 1 and then lower than those predicted. For the lignite-sunflower mixtures, the increase in oil yield are highest for 1:3 mass ratio of lignite to sunflower oil. Thus the lignite is reasonably effective in partly preventing retrogressive char forming reactions for the sunflower oil (up to mass ratio 1:1). Further information on the interactions between Xll the lignite and sunflower oil during pyrolysis can be obtain from the composition of resulting oils. The concentrations of aliphatics and aromatic decrease and the content of polars increase than those predicted from the compositions of the individual oils. This provides further evidence that the interactions between the lignite and sunflower oil go some way to limiting retrogressive char forming reactions which are probably catalyst to sunflower oil pyrolysis reactions up to 1:1 mass ratio. Under the pyrolysis conditions a synergistic effect is observed as in the modified Heinze retort for a 1:1 mixture (lignite : sunflower oil). However the oil yields for the 1:1 mixtures are similar to the predicted yields. Therefore synergism would appear to be evident only to 1 : 1 mass ratio. The results of paraffins GC-MS measurements are observed in a net dehydrogenation of the oil with increasing mass ratio of sunflower oil.