System design for the conversion of olive seed wastes into activated carbon

Carbon footprint refers to the amount of greenhouse gas emissions of an individual, institution or community. Reducing the carbon footprint is important to protect environmental health. It is possible to reduce carbon emissions by using green production methods and minimizing waste. Green production is achieved through the use of nature-friendly materials, increasing energy efficiency and proper waste disposal. Correct disposal of domestic and industrial waste helps protect the environment. Separately disposing of, recycling and reusing organic waste is also important for the environment. Organic wastes are wastes generated after both domestic and industrial use, such as walnut shells, hazelnut shells, hazelnut husks, corn cobs, rice husks, tea waste, pomace, fruit juice pulp, olive seeds, sewage sludge, fallen tree leaves. Since organic wastes contain C, H, O, N and S in their structure, these wastes are used in energy production (heat, fuel, electricity). Disposal of these wastes without harming the environment is possible by recycling the waste. For this reason, many methods developed to recycle waste without harming the environment are available in the literature. One of the recycling methods in question is the production of activated carbon (AC) from organic waste. Activated carbon (AC) is an adsorbent with a strong affinity, consisting of an amorphous and very large microcrystallographic structure. The porous structure of activated carbon refers to microscopic spaces into which various molecules can enter and adsorb these molecules to its surface. Its porous structure allows activated carbon to have a large surface area. These pores can be of various sizes in the form of micro, meso and macro pores found in the internal structure of activated carbon. These various types of pores increase the ability of activated carbon to adsorb. Thanks to this feature, activated carbon can attract many organic and inorganic compounds in liquid or gas phase. This adsorption property is one of the main reasons why activated carbon is widely used in many fields such as water purification, air purification, chemical processes, industrial processes, medicine, pharmaceutical and food industries. Activated carbon is a material that can be produced from industrial wastes such as walnut shell, hazelnut shell, hazelnut husk, corn cob, rice husk, tea waste, pomace, fruit juice pulp, olive seed. Activated carbon production is carried out by passing the raw material through a process of high temperature and an inert atmosphere. In this process, the raw material is activated by physical and/or chemical activation, and activated carbon with a highly porous structure is obtained from the waste. In this way, waste is prevented from harming the nature and at the same time it is obtained from an economical source. Although activated carbon is used in almost every field in our country, there is no commercially active activated carbon production facility. Therefore, it is an important need to determine the amount and current status of biomass resources suitable foractivated carbon production in our country and to reveal the most suitable process for the production of activated carbon from these wastes. This doctoral thesis project focused on producing a product equivalent to commercial activated carbon from olive seeds (OS) by physical activation method. In the literature, OS was mostly converted into AC by being processed with chemical methods. Physical activation was preferred in this study because it is a more environmentally friendly method compared to chemical activation. An approach regarding AC production trials in a dynamic environment, with a single stage and physical activation using CO2 gas, has not been found in the accessible literature. In this context, this study offers original content with production process approaches. The parameters used are temperature, grain size, gas type, and furnace type, including static and dynamic. Optimum conditions for obtaining qualified products were determined by applying SEM, BET, XRD, FTI-R, RAMAN and elemental analysis tests to the synthesized AC. Production trials of AC produced for this purpose were carried out with the single-step production approach, which is an alternative method to traditional production methods, and also with the dynamic oven system. After the raw material was dried at 70 oC, it was ground and classified according to grain size. Carbonization and/or activation of the raw material with dimensions of 1-3 mm and 0.15 mm was carried out under nitrogen (N2) and/or carbon dioxide (CO2) gas for certain periods of time between 500 and 1000 oC. In the traditional method, the raw material (olive seed) is transformed into a char by processing it under certain temperature, time and gas flow. Then, this time, the activation phase is started by increasing the oven temperature. During the activation process, char is converted into the final product, activated carbon, under certain temperature, time and gas flow. On the other hand, single-step method refers to a method in which the raw material is treated at a single temperature and gas flow for specific periods of time. In this method, activation and carbonization are carried out simultaneously, which shortens the process time and increases efficiency. Both static and dynamic type furnaces were used in experimental studies to create optimum conditions with both methods. As a result, both traditional and single-step production methods were used in activated carbon production and optimum conditions were created by comparing the two furnace types. In this context, it has been demonstrated that activated carbons obtained by the one-step production method have improved porosity and large surface area. Surface areas of synthesized activated carbons, were obtained between 350 and 1313 m2/g. A product equivalent to commercial activated carbon was obtained in both static and dynamic type furnace systems. Qualified activated carbons were obtained from raw materials that were kept in CO2 flow for 3 hours at 800 and 900 oC. Qualified activated carbons were obtained from raw materials that were kept in CO2 flow for 3 hours at a temperature of 800 oC in a dynamic type furnace and 900 oC in a static type furnace. According to the findings, it was concluded that better surface area was obtained in the dynamic system with a lower waiting time compared to the static system. When the product qualities are examined, it is seen that a product equivalent to commercial activated carbon is obtained at lower temperatures with the dynamic system. High temperature causes organic and inorganic substances in the raw material structure to leave the structure quickly, thus causing a decrease in efficiency and the formation of voids (pores/pores) in the resulting product. However, an excessive increase in temperature caused pore collapse and a decrease in efficiency. In this study, the effect of gas type on carbonization and activation processes was determined and it was revealed that CO2 molecules adsorbed to the carbon surface at high temperatureand a certain flow, increasing the surface area of carbon. Two different sizes of olive pits were used in the experiments (0.15 mm and 1-3 mm). Experimental studies show that as the grain size of the raw material used decreases, the surface area generally increases. With the increase in temperature (up to a certain temperature), there is a significant increase in the surface area of the activated carbons obtained. Experimental studies conducted with the static system revealed that the specific surface area is larger in products with small grains (0.15 mm). For this reason, in the studies carried out with the dynamic system, experiments were continued with raw materials of 0.15 mm grain size. As a result of the tests and analyses, it was determined that N2 gas did not have a significant effect on the final product in terms of characteristics. This finding shows that the use of N2 gas in the carbonization stage does not make a significant change on the properties of this material (AC) produced by the traditional method. For this reason, only CO2 gas was used in the dynamic system. Another important outcome of the study is that a large microporosity can be achieved during the activation process with CO2. It has been evaluated that significant advantages can also be achieved in terms of production costs by using this gas. It is reported in the literature that the adsorption ability of ACs with microporosity increases and becomes a more effective adsorbent. This material (AC) is widely used in many fields such as purification of industrial waste gases, water purification, cathode material in batteries and chemical processes. In this context, one of the products obtained in this study was tested for its usability as a cathode material in Li-O2 (Li-air) batteries and a successful result was obtained. With this thesis study, a trial study was carried out on the creation of the production flow diagram of carbons (carbon black and/or activated carbons) to be produced from olive seeds and technological / industrial product cost analysis, and the thesis result was presented in a qualified manner.