İğde çekirdeğinin piroliz kinetiğinin termogravimetrik analiz ile incelenmesi

Abstract

Son yüzyıldaki teknolojik değişmelere ve gelişmelere bağlı olarak dünyanın enerji ihtiyacı sürekli artmaktadır. Fosil enerji kaynaklarının sınırlı olması ve hızla tükenmesi alternatif enerji kaynaklarına ihtiyaç duyulmasına sebep olmuştur. Bu arayış çerçevesinde yenilenebilir enerji kaynaklarına olan ilgi artmıştır. Yenilenebilir enerji kaynakları, güneş, rüzgâr, hidrolik, dalga, jeotermal ve biyokütle olarak sınıflandırılabilir. Biyokütle enerjisi bu kaynaklar arasında oldukça büyük bir önem taşımaktadır. 1973 yılında yaşanan petrol krizi sonrası biyokütle enerjisi ile ilgili pek çok araştırma yapılmaya başlanmıştır. Günümüzde de fosil yakıt rezervlerinin azalması ve petrol fiyatlarının yüksek olması sebebiyle biyokütle önemini koruyan bir enerji kaynağı olmaya devam etmektedir. Yapısında temel olarak karbon, hidrojen ve oksijen bulunduran, kısa sürede yenilenebilen tüm bitkisel, hayvansal ve mikrobiyal kökenli maddeler biyokütle olarak tanımlanır. Biyokütleler doğrudan yakılabileceği gibi, çeşitli termokimyasal dönüşüm proseslerinden geçirilerek sıvı, katı ve gaz yakıtlarına dönüştürülerek de kullanılabilir. Bu dönüşüm proseslerinden en çok kullanılanlarından birisi pirolizdir. Biyokütlenin oksijensiz ortamda ısıl bozunma işlemi olarak tanımlanan piroliz işlemi sonucunda karbonca zengin katı ürün, yağımsı yapıda sıvı ürün ve hidrokarbonca zengin gaz ürün elde edilir.Bir biyokütle örneği olan iğde ağacı, bozulmuş toprakların kullanılabilir hale getirmesi ve erozyonu önleyici özellikleri sebebiyle önemli bir türdür. İğde, topraktaki yüksek tuzluluk, şiddetli kuraklık ve toprağın alkalinitesine karşı dayanıklılığı nedeniyle aşırı kuru alanlarda yetiştirilerek ekosistem fonksiyonlarının korunmasında önemli bir etkiye sahiptir. Bu özellikleri sebebiyle son yıllarda iğde üretiminin artırılmasına yönelik çalışmalar başlamıştır. Bu amaçla dünyada ve ülkemizde uzun zamandır bilinen ve kullanılan iğdenin ekonomik değerinin artırılması planlanmaktadır. İğde meyvesi gıda, kozmetik, kimya endüstrisinde kullanılmasının yanı sıra tıp alanında da yaygın olarak kullanılmaktadır. Bu işlemlerin sonucunda ortaya çıkan atık olan iğde çekirdekleri ise bertaraf edilmekte, yakılmakta veya sembolik rakamlarla satılmaktadır.Bu çalışma ile iğde çekirdeğinin termogravimetrik analiz yöntemiyle piroliz kinetiği çalışılmış ve kinetik parametreleri hesaplanmıştır. İğde çekirdeğinin piroliz kinetiği, üç farklı tanecik boyutunda (38-75 µm; 75-150 µm; ve 180-425 µm), azot atmosferi altında 5, 10, 20 ve 40°C/dakısıtma hızlarında, termogravimetrik analiz ile incelenmiştir. Isıl karakterizasyon işlemleri sonucunda elde edilen veriler, iğde çekirdeği numuneleri için dört ayrı bölgeye ayrılarak yorumlanmıştır. Bu bölgelerden ikisi, aktif piroliz bölgesidir ve termogravimetrik değerlendirmeler bu iki bölge temel alınarak yapılmıştır. Her bölgeye ait karakteristik sıcaklıklar belirlenmiş ve kullanılan yöntemlerde belirlenen sıcaklık aralıkları kullanılmıştır. Kinetik parametrelerin hesaplanmasında, hem modele bağlı hem de modelden bağımsız yöntemler kullanılarak her yöntemle elde edilen aktivasyon enerjileri karşılaştırmalı olarak verilmiştir. Kullanılan modele bağlı yöntemler, Coats-Redfern ve Horowitz-Metzger yöntemleri; modelden bağımsız yöntemler ise Flynn-Wall-Ozawa ve Kissinger-Akahira-Sunose yöntemleridir.

The energy needs of the world have been on the increase within the last century due to technological reforms and advancements. The rapidly depleting state of the world's limited fossil energy sources has given rise to a dependency on, and an interest in, alternative energy sources. Renewable energy sources can be broken down into categories such as solar, wind, hydraulic, wave, geothermal, and biomass. Biomass energy holds a very important place among said categories. In the wake of the 1973 oil crisis, plenty of research on biomass energy went underway and biomass energy continues to be important today, owing to the rapid depletion of fossil fuel reserves and the increase in petrol prices.Biomass is strategically significant, as it is able to be produced in many different areas and it can be transformed into vehicle fuel or electrical power. It is also harmless to the environment as well as socially and economically beneficial to communities. All vegetational, microbial or animal-sourced matter that is quickly renewable and is primarily comprised of carbon, hydrogen and oxygen can be classified as biomass.The aim of biomass transformation processes is to eliminate undesired qualities in biomass such as low energy content, low density, high moisture, and expensive transportation; and therefore allow for healthy and convenient production of chemicals and fuel.Fuel can be produced by applying thermochemical or biochemical processes onto biomass. The thermochemical processes are burning, pyrolysis, liquidization and gasification; whereas the biochemical processes are the production of energy through anaerobic digestion, and digestion via alcoholic fermentation.. Although biomass can be directly burned, it can also be transformed into liquid, solid or gas fuel using various thermochemical processes. Pyrolysis is one of the most commonly used transformation processes. Pyrolysis, defined as the thermal decay of biomass in an oxygenless environment, can yield a carbon-rich solid product, a grease-like liquid product, and a hydrocarbon-rich gas product.Waste generated in agricultural production and processing industries are very easily accessible, and this waste is transformed into solid waste through various social initiatives. The burning of this waste not only reduces its volume but also allows for energy recovery as well as economic benefits for rural communities. Biomass energy, while it makes use of the conventional infrastructure, acts as a replacement for conventional energy sources, and provides technical and economic benefits.The oleaster tree, an example to biomass, is ubiquitous and widespread in Europe, Asia and North America. It lives in all altitudes up to 3000 meters, and is typically very quick to grow and able to develop strong lateral roots. Its roots contain nodules that bind and store free nitrogen from the atmosphere and improve the soil condition.The oleaster tree is an important species for its usefulness in preventing erosion and rehabilitating spoilt land. Due to its resilience against high soil salinity, alkalinity and intense drought; it can be planted in extremely dry environments and has an important role in protecting the functionality of ecosystems. These useful qualities have led to a number of initiatives to increase oleaster production in the recent years. And thus, the aim is to increase the economic value of oleaster, which has already long been known and used in the world and in Turkey. Oleaster, in its shape, resembles the cornelian cherry, and has a mildly sour taste. It is rich in vitamins and minerals, and can be consumed fresh or in dried form. It is known to be good for intestinal and renal problems, as well as asythma and coughing. Its leaves are also consumed as tea. Oleaster is also commonly used in medicine, food, cosmetics, and chemical industries. After such processes however, the stones of the oleasters are considered waste and thrown away, burned or sold for symbolically low prices.The kinetics and burning behavior of biomass wastes must be known for the design of the burning systems. Prior to the use of fuel in energy production, its burning properties can be determined through thermo-analytical techniques such as TG and DTG which cover a wide field of application in research, development and economic evaluations.In the preparation stage of the specimen for kinetic processes, the oleaster seeds extracted from oleasters were initially dried in an atmospheric environment, and then dried in a drying oven to eliminate moisture. After waiting in the desiccator, it was ground using a mill. After the grinding, it was made into smaller particles using a porcelain mortar and mallet, and then sieved using sieves of different aperture sizes, before being categorized into different fraction intervals based on their resulting sizes. Information on its characteristics were then acquired by conducting short analyses, thermal value analysis and elemental analysis.In our work, the pyrolysis kinetics of the oleaster stone are studied using the thermogravimetric analysis method, and its kinetic parameters are calculated. The pyrolysis kinetics of the oleaster stone were examined using thermogravimetric analysis in three separate particle sizes (38-75 µm; 75-150 µm; and 180-425 µm), in nitrogenous atmosphere at heating speeds 5°C/min, 10°C/min, 20°C/min and 40°C/min.The data acquired from thermal characterization of oleaster stone specimens was interpreted in four different zones. Two of which are active pyrolysis zones, and the thermogravimetric evaluations were based primarily on those. Characteristic temperatures for each zone were determined, and the temperature intervals were taken into account accordingly.In the calculation of kinetic parameters, activation energies acquired through all methods, those that are affiliated with the model and those that are not, are provided comparatively. Methods affiliated with the model are the Coats-Redfern and the Horowitz-Metzger methods; and the model free method are the Flynn-Wall-Ozawa and the Kissinger-Akahira-Sunose methods.When model-based methods were used, there was no significant difference between the second and third active sites for each method, and no observable difference was observed when the particle size changed. In model free methods, mean activation energies were observed to decrease in the second active region, while the increase in the third active region was observed with increasing particle size. Since there is not enough literature about the effect of particle size in the study of kinetic models, this kinetic study with oleaster stone is important. For more comparable results, studies can be performed in wider particle size ranges.