# Design of Pyrolysis Plant for Waste Methyl Ethyl Ketone from the Polarizer Manufacturing Process
## 3 Results and Discussion
### Thermal Pyrolysis Result of Lab-Scale System
The residence time was calculated by dividing the gas volume (using Equation (13)) by the reaction volume. Factors such as residence time, flow field, and heat transfer are closely related to the MEK flow rate and can significantly influence the cracking process. Figure 7b illustrates the gas compositions at different residence times. The results show that H\({}_{2}\) and C\({}_{2}\)H\({}_{4}\) exhibit opposite trends with increasing residence time. Higher residence time promotes the formation of C\({}_{2}\)H\({}_{4}\), H\({}_{2}\), CH\({}_{4}\), and CO\({}_{2}\)[24]. Additionally, CO is converted into char and CO\({}_{2}\) as residence time increases, and ultimately CO\({}_{2}\) decreases due to its reaction with char [25]. These results are consistent with the trends observed in Figure 7, indicating that residence time and operating temperature are key factors in the overall pyrolysis reaction. Figure 8 depicts the tar accumulation on the top of the heat exchanger during a long-term test (4 h of continuous operation), with MEK flow rates of 10, 20, and 30 mL/min. The results indicate that higher residence times, resulting from lower MEK flow rates, can \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Case**} & **Temperature** & **MEK Flow Rates** & **N\({}_{2}\) Flow Rate** & **Retention Time** \\  & (\({}^{\circ}\)C) & **(mL/min)** & **(L/min)** & **Retention Time** \\ \hline (a) & 900 & 10 & 0.33 & 13.96 \\ (b) & 900 & 20 & 0.65 & 6.98 \\ (c) & 900 & 30 & 1 & 4.65 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Operation parameters of varied residence time tested via experimental machine. Figure 7: The gas components under different operation conditions for (**a**) temperature and (**b**) residence time. cause a pipe bridge effect and reduce continuous operability due to the accumulation of PAH on the wall. The temperature of the cone zone is decreased with the decrease in MEK flow rate, resulting in the accumulation of tar and enhancing the adsorption of char [24]. It thus hinders the stable operation of the system. However, this adverse effect gradually improves with increasing MEK flow rates. Eventually, the operation with MEK flow rates of approximately 30 mL/min demonstrates relatively excellent performance, as shown in Figure 8c, where the surface of the top plate is covered with dry char, which can be more easily scraped off. The optimal flow rate increases the cone temperature, resulting in a more fluent pyrolysis process. Figure 9a illustrates the influence of residence time on the amount of carbon, showing a consistent trend of increased char amount from 2.12 wt% up to 8.15 wt% as the residence time increased from 4.65 to 13.96 s. The top plate view in Figure 8 shows tar flat sticks accumulated on the heat exchanger's top plate during variant operations. It was observed that longer residence time resulted in increased temperature, which was conducive to the generation of carbon and char, in line with the findings of [PERSON] [26]. However, this may not be beneficial for long-term operations. Additionally, Figure 10 shows the filters after the heat exchanger at different operating temperatures, indicating a proportional relationship between tar and char formation and oil colors, as reported by OH [27]. Figure 8: Appearance of the cyclone at MEK flow rates of (**a**) 10, (**b**) 20, and (**c**) 30 mL/min. Figure 9: (**a**) Char residual (**b**) gross heating value of gases in different residence times. The higher heating value was observed to be around 4.65 s of residence time, as shown in Figure 10b. This indicates that gas tends to convert into fixed carbon or low carbon chain gases, with a burning value of approximately 150 kcal/mole in this research, accounting for about 70% of the heating value of natural gas. However, tar formation posed a challenge to continuous operations, making the optimal temperature at the cyclone a critical factor. To estimate tar reduction through heat treatment, the TGA system was used.