TECHNOLOGY FOR PRODUCING TEREPHTHALAMIDE BASED ON CHEMICAL PROCESSING OF PLASTIC WASTE

ISSN: 2582-4686 SJIF 2021-3.261,SJIF 20222.889, 2024-6.875 ResearchBib IF: 9.948 / 2024 VOLUME-5, ISSUE-12 1161 TECHNOLOGY FOR PRODUCING TEREPHTHALAMIDE BASED ON CHEMICAL PROCESSING OF PLASTIC WASTE Normurotov J.B. PhD Student, Department of Chemical Engineering, Termez State University of Engineering and Agrotechnology Ahmedov O‘.Ch. Associate professor, termiz state university [email protected] Annotation The recycling of plastic waste plays a crucial role in ensuring environmental sustainability and resource efficiency. This study presents a chemical recycling approach for synthesizing terephthalamide through the hydrolysis of polyethylene terephthalate (PET) waste followed by amidation with urea. Optimal reaction conditions were established, and the structure of the synthesized product was confirmed using IR spectroscopy and physicochemical analyses. The results demonstrate that the proposed method is environmentally friendly, cost-effective, and suitable for potential industrial implementation Keywords: plastic waste recycling, PET hydrolysis, terephthalic acid, amidation process, terephthalamide, polymer chemistry, IR spectroscopy INTRODUCTION In recent years, the volume of plastic waste has been increasing steadily. In particular, polyethylene terephthalate (PET)–based bottles, food containers, and other household products contain polymer materials that do not readily degrade in nature and can persist in the environment for up to 100 years. This leads to significant negative impacts on water bodies, soil, and air quality. Therefore, recycling plastic waste into secondary raw materials using environmentally friendly technologies is considered a promising and sustainable approach. Specifically, the polymer chains present in PET can be hydrolyzed to obtain terephthalic acid (TPA), which can subsequently be used for the chemical synthesis of various derivatives, including terephthalamide. Terephthalamide is an organic compound belonging to the amide class and is widely used as a raw material in polymer synthesis, as well as in the production of specialty plastics, coatings, and fibers. The hydrolytic degradation of PET waste can be carried out under various conditions using different hydrolyzing agents, such as sodium hydroxide (NaOH), hydrochloric acid (HCl), water, or organic solvents. As a result of this process, the PET polymer is depolymerized into its monomeric components, primarily ethylene glycol and terephthalic acid. Notably, the hydrolysis process exhibits higher efficiency when conducted under autoclave conditions at elevated temperatures and pressures. Furthermore, terephthalic acid obtained from PET waste is a highly reactive aromatic dicarboxylic acid that is well suited for chemical modification. It can be used in the synthesis of amides, esters, polyesters, and other complex compounds. Terephthalamide, in particular, is a structurally stable compound with hydrophobic properties, making it suitable for applications in the production of specialty plastics and synthetic fibers. ISSN: 2582-4686 SJIF 2021-3.261,SJIF 20222.889, 2024-6.875 ResearchBib IF: 9.948 / 2024 VOLUME-5, ISSUE-12 1162 In this study, a technology was developed for the hydrolysis of plastic waste under conditions compatible with industrial applications, followed by the synthesis of terephthalamide from the resulting terephthalic acid. Key factors such as environmental safety, reaction efficiency, raw material and energy consumption, and the simplicity of technological conditions were taken into consideration. In addition, the synthesized products were evaluated using spectroscopic and physicochemical analysis methods. This approach provides a framework for reconsidering plastic waste not as an environmental burden, but as a valuable resource and opportunity. Materials and Methods The experimental studies were carried out in the Chemical Technologies Laboratory of Termiz State University of Engineering and Agrotechnologies. The developed technology consists of two main stages. 1. Hydrolysis of PET Waste to Obtain Terephthalic Acid PET-based waste materials generated from industrial use or post-consumer products were preliminarily prepared according to the following procedure: - Sorting of waste: Only transparent containers made of PET were selected. - Washing and drying: The selected PET waste was thoroughly cleaned to remove dust, impurities, and labels, followed by drying. - Shredding: The dried PET materials were mechanically crushed into fragments with a particle size of 5–10 mm. Hydrolysis Process - Reagent ratio: PET : NaOH = 1:2 (by mass) - Amount of water: 10 g of NaOH and 5 g of plastic were added to 100 mL of water - Reaction temperature: 180 °C - Pressure: atmospheric or slightly above atmospheric pressure (in a closed vessel) - Reaction time: 3 hours After completion of the reaction, the resulting solution was filtered and neutralized using hydrochloric acid (HCl). The formed solid product—terephthalic acid—was separated from the aqueous phase and dried at 45–50 °C. As a result, terephthalic acid (TPA) was obtained with a yield of 55–60%. The product appeared as a white crystalline solid, exhibiting low solubility in water but good solubility in alkaline media. For the chemical recycling of polyethylene terephthalate (PET)–based waste, a hydrolytic depolymerization method was initially selected. During this process, the ester bonds of the PET polymer were cleaved under the action of sodium hydroxide (NaOH), leading to the formation of the main product, terephthalic acid (TPA). Initial Reaction Conditions Reagent Ratio PET : NaOH = 1 : 2 (by mass) This ratio was selected to ensure complete and efficient hydrolysis of the PET polymer. The use of sodium hydroxide in excess guarantees the completion of the reaction and facilitates effective cleavage of the polymer chains. Amount of Water For every 10 g of NaOH, 100 mL of distilled water and 5 g of shredded PET were used. ISSN: 2582-4686 SJIF 2021-3.261,SJIF 20222.889, 2024-6.875 ResearchBib IF: 9.948 / 2024 VOLUME-5, ISSUE-12 1163 Water served not only as the reaction medium but also as a solvent for NaOH, ensuring the formation of a homogeneous hydrolyzing agent. The optimal solution concentration was maintained at approximately 10 wt.% NaOH. Reaction Conditions Temperature: 180 °C At this elevated temperature, the molecular mobility of the PET polymer increases, the ester groups become more reactive, and the interaction with NaOH is significantly enhanced. At temperatures below 180 °C, the reaction proceeds slowly, whereas higher temperatures may lead to degradation of the reactants. Pressure: Atmospheric or slightly above atmospheric pressure in a partially closed vessel. The process does not require high-pressure conditions; however, operating in a closed vessel increases the boiling point of the liquid phase, thereby improving reaction efficiency. Reaction time: 3 hours This duration was considered optimal to achieve complete reaction and maximum yield. Prolonged reaction times may result in a decrease in product quality. Post-Reaction Treatment After completion of the reaction, the resulting alkaline solution was first purified by filtration. The filtrate was then neutralized using hydrochloric acid (HCl) until a pH of approximately 7 was reached. During this step, sodium terephthalate decomposed, and free terephthalic acid (TPA) precipitated from the solution. The precipitated TPA was separated and dried under the following conditions: Drying temperature: 45–50 °C This temperature was selected to remove residual moisture while preserving the crystalline structure of the product. Higher temperatures could lead to thermal degradation of the material. Results Yield: 55–60% This yield indicates that although complete depolymerization of PET was not achieved under the experimental conditions, a sufficient amount of terephthalic acid was successfully obtained. The yield may be further improved by optimizing pressure, reaction time, or NaOH concentration. Product Characteristics The obtained terephthalic acid is a white crystalline organic compound with low solubility in water and good solubility in alkaline media. Owing to its aromatic structure and the presence of two carboxyl groups, it exhibits high chemical reactivity and can readily undergo various chemical modifications. Technological and Practical Significance This stage represents a key and essential technological step in converting PET waste into valuable chemical compounds. The terephthalic acid obtained through hydrolysis offers broad opportunities for further processing, including the synthesis of amides, esters, polycondensation polymers, catalysts, and other functional materials. In particular, TPA derived from PET waste serves as a highvalue raw material for the synthesis of synthetic polyamides, such as terephthalamide. 2. Synthesis of Terephthalamide The obtained terephthalic acid was reacted with urea under the following conditions: Molar ratio: TPA : urea = 1 : 2 Reaction apparatus: Autoclave ISSN: 2582-4686 SJIF 2021-3.261,SJIF 20222.889, 2024-6.875 ResearchBib IF: 9.948 / 2024 VOLUME-5, ISSUE-12 1164 Reaction conditions: Temperature of 185 °C and pressure of 3–5 atm Reaction time: 3 hours Product: Terephthalamide obtained as a white amorphous or crystalline solid During the reaction, amide groups are formed, resulting in a terephthalamide molecule containing two amide functional groups. The reaction can be expressed as follows: C₆H₄(COOH)₂ + 2NH₂CONH₂ → C₆H₄(CONH₂)₂ + 2H₂O + CO₂ Analytical Methods IR Spectroscopic Analysis The synthesized terephthalamide sample was analyzed using infrared (IR) spectroscopy. Characteristic absorption bands corresponding to N–H stretching vibrations were observed in the range of 3300–3500 cm⁻¹, while absorption bands in the region of 1600–1650 cm⁻¹ were attributed to the stretching vibrations of the carbonyl (C=O) groups. These spectral features confirm the presence of amide functional groups in the synthesized compound. Figure 1. Results of IR spectroscopic analysis Physicochemical Properties - Melting point: above 300 °C - Appearance: white crystalline powder ISSN: 2582-4686 SJIF 2021-3.261,SJIF 20222.889, 2024-6.875 ResearchBib IF: 9.948 / 2024 VOLUME-5, ISSUE-12 1165 - Solubility in water: very low - pH: neutral Results and Discussion (Extended) Based on the conducted laboratory experiments, the practical and theoretical foundations for obtaining terephthalic acid through the hydrolysis of plastic waste—specifically PET bottles and food containers—were established. In this study, the hydrolysis process was carried out at a temperature of 180 °C for 3 hours in the presence of sodium hydroxide (NaOH). During the post-hydrolysis neutralization and drying stages, the product yield ranged from 55 to 60%, which can be considered a favorable result for small-scale experimental studies. The obtained terephthalic acid was subsequently reacted with urea at a temperature of 185 °C and a pressure of 3–5 atm to synthesize terephthalamide. The evolution of water and carbon dioxide during the reaction indicates that an irreversible condensation process took place. IR spectroscopic analysis revealed characteristic N–H stretching vibrations of amide groups in the range of 3300–3500 cm⁻¹, as well as carbonyl (C=O) stretching vibrations around 1650 cm⁻¹. These findings confirm the presence of amide functional groups in the synthesized product. Based on the analysis and evaluation of the results, the following key conclusions were drawn: 1. Environmental safety: Unlike incineration or landfilling, the proposed technology converts plastic waste into valuable chemical products through chemical recycling. This approach not only reduces the amount of waste but also prevents air and soil pollution. Since the main by-products of the reactions are water and CO₂, the associated toxic impact is minimal. 2. Technological simplicity and practicality: The hydrolysis and amidation reactions can be carried out using conventional laboratory equipment or small-scale industrial units. The main reagents (NaOH, HCl, and urea) are readily available on the local market, inexpensive, and easy to store. This provides a solid basis for scaling up the process to an industrial level. 3. Economic efficiency: PET waste represents an inexpensive and abundantly available raw material. Converting it into chemical products with high added value offers significant economic advantages. Terephthalamide, in particular, is widely used in the polymer industry for the synthesis of structural fibers, resins, and specialty materials, highlighting the economic feasibility of the proposed process. 4. Flexibility and future prospects: Terephthalic acid can react not only with urea but also with other amine compounds, serving as a versatile precursor for the synthesis of various amides. This opens up opportunities for producing multifunctional polymers, stabilizers, engineering plastics, and materials with potential pharmaceutical applications. Conclusion Within the scope of this study, a technology was developed for obtaining terephthalic acid from plastic waste and subsequently synthesizing terephthalamide. The physicochemical and spectroscopic analyses of the obtained products confirmed their high quality and structural integrity. The proposed technology not only contributes to solving environmental problems associated with plastic waste accumulation but also creates opportunities for the development of new industrial sectors. In future research, the application of the synthesized product in the production of polyamides, optical materials, engineering plastics, and environmentally friendly polymers will be further investigated. ISSN: 2582-4686 SJIF 2021-3.261,SJIF 20222.889, 2024-6.875 ResearchBib IF: 9.948 / 2024 VOLUME-5, ISSUE-12 1166 The results of this study are of significant practical and scientific importance, as they demonstrate an effective approach not only to managing plastic waste but also to converting it into products with high added value. Consequently, this technology may contribute to the sustainable development of the industrial sector of the Republic of Uzbekistan and to the preservation of ecological balance. References 1. Normurotov J.B., Ahmedov O‘.Ch. 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