# Process of Formaldehyde and Volatile Organic Compounds' Removal from Waste Gases
## 4 Upgrading the Waste Gas Purification Process
### The Waste Gas Purification Process with Absorbers  
The procedure described in Figure 1 sufficiently reduces formaldehyde concentrations in waste gases to levels prescribed in the new EU directives. However, as seen in Table 1, approximately 280 kg of formaldehyde per year are still released after catalytic purification of waste gases. Given increasing levels of environmental concern, more formaldehyde should be removed from waste gases produced by metal oxide catalyst formaldehyde production processes. Figure 1 shows the existing catalytic process for the removal of formaldehyde from waste gases. The existing catalytic process for the removal of formaldehyde from waste gases is complemented by new flue gas cleaning technology with the implementation of a heat exchanger (EXCH4) and an absorber (ABSORB). \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Component** & **A** & **B** & **C** \\ \hline Formaldehyde & 4.4625 & –2204.13 & –30.15 \\ Water & 6.2886 & –3816.44 & –46.13 \\ Methylene glycol & 19.5527 & –6189.19 & –9.15 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Pure component vapor pressure. Figure 3: Diagram of the formaldehyde hydration chemical equilibrium constant Equation (13). Aspen Plus computer simulator does not have absorption kinetics for low concentrations of formaldehyde in water in the database, so the kinetics of formaldehyde absorption in water were added to the computer program described in Section 4.2. The results of the computer simulation shown in Figure 4 are given in Table 3, where it is evident that the concentration of formaldehyde decreased by more than five-fold. The waste gases (Figure 4) that go from heat exchanger 3 (EXCH3) to heat exchanger 4 (EXCH4) are cooled to a temperature near the dew point of the aqueous vapors present in the gases and then fed into the absorber (scrubber). In the absorber, the waste gases are rinsed with the addition of water, and FA, MG, and TVOC are absorbed in water. The waste gases go back to heat exchanger 4, where they are  
Figure 4: Computer simulation of additional waste gas treatment of metal oxide catalyst formaldehyde production processes. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Stream Name** & **Units** & **8** & **9** & **10** & **11** & **12** & **WATER** \\ \hline
**Phase** & & **VP** & **VP** & **VP** & **LP** & **VP** & **LP** \\ \hline Temperature & C & 72.30551 & 30 & 20.30396 & 21.85142 & 64.02441 & 20 \\ Pressure & bar & 1 & 1 & 1 & 1 & 1 \\ Mass Vapor & & 1 & 1 & 0.999996 & 0 & 1 & 0 \\ Fraction & & & & & & \\ Mass Liquid & & 0 & 0 & \(4.33\times 10^{-6}\) & 1 & 0 & 1 \\ Fraction & & & & & & \\ Mass Flows & kg/hr & 15,000 & 15,000 & 14,641.68 & 80,358.31 & 14,641.68 & 80,000 \\ Water & kg/hr & 400.0001 & 399.9996 & 223.4809 & 80,176.42 & 223.4811 & 80,000 \\ CO\({}_{2}\) & kg/hr & 513.0002 & 513.0002 & 441.0303 & 71.99611 & 441.0303 & 0 \\ N\({}_{2}\) & kg/hr & 13,492.01 & 13,492.01 & 13,388.47 & 103.5946 & 13,388.47 & 0 \\ Methanol & kg/hr & 0.1 & 0.1 & \(6.52\times 10^{-6}\) & 0.099935 & \(6.52\times 10^{-6}\) & 0 \\ Dimetyle & kg/hr & 0.58 & 0.58 & 0.022383 & 0.557619 & 0.022383 & 0 \\ CO & kg/hr & 0.28 & 0.28 & 0.277746 & 0.002256 & 0.277746 & 0 \\ O\({}_{2}\) & kg/hr & 594.0003 & 594.0003 & 588.3943 & 5.609134 & 588.3943 & 0 \\ Formald & kg/hr & 0.032856 & 0.032041 & 0.005188 & 0.026854 & 0.00557 & 0 \\ Methylen & kg/hr & 0.00023 & 0.001533 & 0.000642 & 0.000891 & \(3.17\times 10^{-6}\) & 0 \\ Volume Flow & m\({}^{3}\)/s & 4.26106 & 3.739237 & 3.515835 & 0.022417 & 4.039626 & 0.022271 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: The results of the computer simulation for a heat exchanger (EXCH4) and an absorber (ABSORB). heated and fed to the chimney, where they are discharged into the atmosphere. The temperature of the waste gases fed from the absorber to heat exchanger 4 can be regulated by regulating the temperature of the gases leaving heat exchanger 3, because they must be sufficiently heated so that they can be discharged into higher layers of the atmosphere.