# Plant Design for the Conversion of Plastic Waste into Valuable Chemicals (Alkyl Aromatics)
## 4 Conclusions  
In this study, we have presented the design overview and estimation of design parameters for a plant aimed at converting plastic waste into useful chemicals, specifically alkyl aromatics. The major components of the plant include a batch catalytic reactor, a shell and tube heat exchanger, and a distillation column. Regarding the design of the heat exchanger, we considered various selection criteria, such as thermal and hydraulic requirements, material capability, operational maintenance, and availability. Shell and tube \begin{table}
\begin{tabular}{l l l} \hline \hline
**Feature** & **Proposed Plant Design** & **Other Pyrolysis Plants** \\ \hline Temperature & 280 \({}^{\circ}\)C & 500 \({}^{\circ}\)C or higher [21; 22; 23] \\ Yield of alkyl aromatics & High & Low–medium [24] \\ Energy efficiency & High & Low–medium [25] \\ Product quality & High & Low–medium [25] \\ Scalability & Can be scaled up & Limited scaling opportunities [26; 27; 28; 29] \\ \hline \hline \end{tabular}
\end{table} 
Table 27: Comparison of the proposed plant design with other pyrolysis plants. Figure 6: Conversion versus catalyst weight. Figure 7: Conversion versus reactor volume. heat exchangers were chosen due to their durability and high-pressure capabilities. The design considerations for the tubes in the thermal systems included different configurations, diameters, number, length, pitch, and arrangements. Tube-side calculations were performed to determine parameters such as the Prandtl number, Reynolds number, Nusselt number, and overall heat transfer coefficient. For the distillation column design, we followed a step-by-step process, including calculations of the number of plates, column diameter, liquid flow pattern, provisional plate design, weeping point, plate pressure drop, downcomer liquid backup, and column height. The Fenske-Underwood-Gilliland (FUG) method was used to calculate the minimum number of plates, and the Kirkbride method was used to determine the feed tray location. Tray type, net vapor velocity, and column area were also determined. In the design of the catalytic batch reactor, rate laws and stoichiometry calculations were employed to analyze the reactions and determine the reaction rate constants. Material and energy balances were performed for the reactor, absorption column, and distillation column. Pressure drop calculations were conducted using the Ergun equation. The results and discussions presented quantitative data, including mass flow rates, the molar flow rates, heat duties, and compositions of various components in the reactor, absorption column, and distillation column. Additionally, graphs were provided to visualize the relationship between catalyst weight and conversion rate, as well as reactor volume and conversion rate. Based on the obtained results, we conclude that the proposed plant design for the conversion of plastic waste into alkyl aromatics is highly efficient in terms of energy utilization and product quality. The use of controlled partial depolymerization at a temperature of 280 \({}^{\circ}\)C allows for a higher yield of alkyl aromatics compared to other pyrolysis plants operating at higher temperatures. Design optimization using dimensionless numbers further contributes to improved energy efficiency and product quality. Our process of converting waste plastic into alkyl aromatics offers several positive socioeconomic implications. First, it has the potential to generate employment opportunities in various sectors, such as municipal, engineering, commercial, and industrial sectors. This can have a significant impact on the local economy, particularly in Oman, where there is a high demand for alkyl aromatics and a need to address the issue of plastic waste. The cost-effectiveness of our process allows for the production of alkyl aromatics at low prices, making the project profitable and economically viable. Furthermore, the alkyl aromatics produced through our process possess several environmentally friendly characteristics.