Investigation by the effects of process parameters on the production of activated carbon by chemical activation from orange pulp (Citrus sinensis L.)

Activated carbon is a material with a porous structure produced from carbon-containing raw materials. Its large surface area, large porosity, well-developed pore structure, micro and meso porosity as well as surface functional properties make it usable in many different areas. Activated carbon is a preferred adsorbent material in various industrial applications. Because of its large surface area and high pore volume, it is used for dye removal, purification of various substances (gold, air, water, etc.), recovery of solvents, removal of environmental pollutants, removal of pharmaceutical wastes from industrial wastewater, removal of heavy metals and organic compounds from aqueous solutions. In ancient times, carbon was used for many different purposes apart from its use as a fuel. Its adventure began with the change and development of needs over time, the use of activated carbon and the development of production technologies. It is known that firstly the Egyptians and Sumerians were the civilizations that used activated carbon. In the study of Hippocrates and Piliny in the field of medicine, they recommended that the water be filtered before use in order to eliminate bad taste, odor, and prevent diseases such as epilepsy, chlorosis and anthrax. The first industrial use of activated carbon was in the United Kingdom for color removal in sugar production. This study set an example for many research topics for color removal. In recent years, the formation of food waste has been described as a social, economic and environmental problem. Agriculture and livestock, post-harvest packaging, storage, processing, distribution and consumption activities waste throughout the food supply chain causes its formation. Applications of techniques aimed at the effective use of industrial food wastes have the potential to add value to these materials with low economic value. For this reason, the evaluation of food waste has gained importance in recent years. The increasing price of commercially produced activated carbons has accelerated the efforts to obtain low-cost activated carbon. Recently, there has been an increased interest in the production of activated carbon from industrial organic agricultural wastes by researchers. Orange, the most popular type of fruit in the citrus class, is a juicy and sweet fruit known as Citrus sinensis L. in Latin. Orange waste is a rich raw material for significant biotechnological transformations. Orange, one of the most grown and consumed citrus family in Turkey and in the world, is one of the most popular and useful plants in the world. Orange is widely used in the production of many products, especially orange juice. As with other citrus fruits, a large amount of peel is exposed when processing oranges into many different products. Since the peel of the orange is not consumed at home, the remaining peels from the pulp and juice are thrown into the environment as waste. Some parameters are very important when choosing the raw material to be used in the production of activated carbon. Features such as availability and easy access potential of raw materials, carbon content of raw material, amount to be supplied determine the position of the raw material in the market. Activated carbons are produced in two different ways by physical and chemical activation methods. Within the scope of the study, activated carbon was produced by using activation agent zinc chloride (ZnCl2) by chemical activation method from orange pulp (Citrus sinensis L.), which is a waste of fruit juice industry. The effects of the produced activated carbons on the process parameters were investigated. By working at different impregnation ratios (1:1, 2:1, 3:1 and 4:1) (ZnCl2/ Orange pulp) and different activation temperatures (500-900°C), the activation temperature which effects on properties such as BET surface area, pore volume and pore structure effect has been studied. The raw material impregnated with zinc chloride activation agent was carried out in the range of 500-900°C, at a heating rate of 5°C/min, under nitrogen gas (N2) flow of 200-300 cm3/min and kept at the final temperature for 2 hours. The effects of process parameters on activated carbon and raw material were determined by elemental analyzes such as activated carbon yield, BET surface area, micro and mesopore area, pore volumes, FTIR, TG/DTG, SEM. It was determined that the largest surface area was 1779.48 m2/g, obtained from activated carbon produced by mixing at 500°C at a ratio of 3:1. At the same time, it was observed that the micropore area (1383.20 m2/g) and micropore volumes (1.100 m3/g) of the activated carbon obtained in this parameter were higher than the other activated carbons. According to the results obtained, it was determined that the surface area decreased with the increase of the activation temperature. It was determined that while the carbon content increased after the activation process, the hydrogen and oxygen content decreased in general. When the changes in the moisture and ash content, volatile matter content and fixed carbon values of the activated carbons produced at different impregnation rates and activation temperatures were examined, it was observed that the moisture content decreased and the fixed carbon amount went up with the increase in the activation temperature. According to the activated carbon yield calculations, it was determined that the yield decreased with the increase of the activation temperature in activated carbons with the same impregnation ratio. It was observed that the highest yield was obtained as 21.26% from the activated carbon produced at 500°C at a ratio of 1:1. FTIR analysis was applied to orange pulp and activated carbons at different temperatures and impregnation rates. Some peaks in the orange pulp did not occur in the activated carbon. When the FTIR spectrum of the activated carbon was compared with the FTIR spectrum of the raw material, it was observed that there were changes in the functional groups. This showed that the carbonyl and aromatic groups were affected by the heat treatment. Temperature/mass loss relationship was investigated with TG/DTG analysis. With the TG/DTG curve, thermal decomposition took place in three stages and mass losses were observed. Finally, it has been determined that the selection of suitable raw materials in activated carbon production has positive effects on the process parameters. It has been observed that orange pulp, which is an industrial food waste, can be preferred in low-cost activated carbon production. It has been concluded that activated carbons can be used frequently impurity removal processes because they are good adsorbents thanks to their large surface area. The results of the experiment showed that the chemical activation method of the raw material used in the production of activated carbon was suitable for the purpose of the study. It has been observed that activated carbon with higher carbon content is obtained after the activation process with the selection of carbon containing raw materials. While the carbon content in the raw material was 45.05%, it changed between 90-93% after the activation processes at different temperatures. It was determined that this ratio increased up to 56.57% in activated carbon with the largest surface area. The efficiency of the obtained activated carbons decreased as the activation temperature increased. This is due to the weight loss that occurs as a result of the removal of volatile components with increasing temperature. The highest yield was obtained at 500°C at 1:1 impregnation ratio. While increasing impregnation rates cause an increase in surface area, it is observed that there is a decrease in the ratio of 4:1. It was observed that the micro and mesopore areas and total pore volumes decreased with increasing temperature at each impregnation rate. As the pore structure deteriorated as a result of the increase in temperature, changes were observed in these parameters. Activated carbon with the highest surface area (1779.48 m2/g) and pore volume (1,343 m3/g) was obtained at 500°C at a 3:1 impregnation ratio. When the pore size distributions were examined, it was seen that the carbons exhibited micro and mesoporous structure. The increased pore structure as a result of chemical activation was examined by taking SEM images. It was observed that the pore structure of activated carbon with a high BET surface area also expanded. Surface functional groups of activated carbons were determined by FTIR analysis. The FTIR spectra of the activated carbons differed according to the raw material due to the acid activation causing a change in the structure. It was observed that the FTIR spectra of activated carbons at different impregnation rates were similar. Experimental data of the produced activated carbon support the properties such as BET surface area and pore structure that activated carbon can be used as an adsorbent in various applications.