# 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  
In general, increasing the reaction temperature leads to an increase in the reaction rate. However, various factors, such as the composition of the gas mixture, reaction capability, volume expansion ratio, and system stability, also vary with temperature. It is important to note that higher temperatures may result in the formation of by-products, which can reduce the desired product yield. For example, at higher temperatures, vinyl may crack into methane, hydrogen, and fixed carbon, leading to the formation of polycyclic aromatic hydrocarbons (PAHs). Therefore, determining the optimum pyrolysis temperature is crucial to achieving desired results. Table 3 presents the components of the exhaust gas of the lab-scale system, which was analyzed by FTIR. The results indicate that no methyl ethyl ketone (MEK) remains in the gas phase, suggesting that MEK can be effectively decomposed with a residence time of over 1.6 s. The hydrocarbon gas components are primarily composed of methane (CH\({}_{4}\)), with respective values of 31.78%, 1.56%, and 20.66% for CH\({}_{4}\), C\({}_{2}\)H\({}_{4}\), and CO. It is noteworthy that C\({}_{2}\)H\({}_{4}\) concentration decreased over time during the long-term test, likely due to secondary decomposition reactions. This suggests that the primary cracking mechanism still occurs at lower temperatures, with reactions starting above 550 \({}^{\circ}\)C. However, the results indicate that the system reaches a steady-state condition after a few minutes of operation. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Chemical** & **Inlet** & **Outlet** & **LOD** & \\
**Compound** & **(\% mol/mol)** & **(\% mol/mol)** & **(\% mol/mol)** & **DRE** \\ \hline MEK & 57.06 & N.D. & 0.221 & \textgreater{}99.6\% \\ CH\({}_{4}\) & – & 31.78 & 0.138 & – \\ C\({}_{2}\)H\({}_{4}\) & – & 1.56 & 0.047 & – \\ C\({}_{2}\)H\({}_{6}\) & – & N.D. & 0.316 & – \\ C\({}_{2}\)H\({}_{2}\) & – & 0.07 & 0.059 & – \\ C\({}_{3}\)H\({}_{8}\) & – & N.D. & 0.174 & – \\ CO & – & 20.66 & 0.217 & – \\ CO\({}_{2}\) & – & 0.51 & 0.057 & – \\ \hline \hline \end{tabular} \(\text{LOD}=\text{``limit of detection”}\), \(\text{DRE}=1-[(\text{C}_{\text{sat}})/(\text{C}_{\text{in}})]=1-[0.221/57.06] =99.6\%\).  
\end{table} 
Table 3: The exhaust gas compositions of lab-scale system. Figure 6: The results of the calculation for (**a**) gas temperature and (**b**) gas velocity in the lab-scale cyclone-heat exchanger. Figure 7a illustrates the gas composition at different temperatures, where each temperature condition is the average of three repeated experiments. It can be observed that hydrogen concentration increases with higher temperatures, as the increased energy promotes the cracking of vinyl into hydrogen, methane, and fixed carbon [10]. Methane concentration remains relatively stable at around 40% with a slight change as the temperature increases in the range of 750-950 \({}^{\circ}\)C, as ketones decompose into methane at 550 \({}^{\circ}\)C. Theoretically, complete decomposition of MEK can be achieved at temperatures between 550-650 \({}^{\circ}\)C [23]; however, the yield rate of the undesired product, tar, cannot be ignored during these temperature regions due to the poor heat conductivity of glue. Operating at higher temperatures can result in less formation of tar. Thus, a temperature range of 750-950 \({}^{\circ}\)C is considered more appropriate as a basis for amplification in this pyrolysis case. CO concentration decreases with increasing temperature as higher energy promotes the transfer of carbon monoxide into fixed carbon. On the other hand, CO\({}_{2}\) concentration barely changes with decreasing carbon monoxide, likely due to the oxygen-containing groups on the forming carbon surfaces. In order to investigate the correlation between MEK flow rate and reactivity, both F\({}_{\text{MEK}}\) and F\({}_{\text{N2}}\) were fixed to eliminate the volume expansion effect during the tests. Table 4 displays the different flow rates at fixed temperatures.