**4. Catalyst Properties**

The properties of the molybdenum oxide and silver oxide catalyst used in the production process are shown in Table 1. It can be observed that the conversion of the molybdenum oxide-based plant is 99% and that of the silver oxide-based plant is 85%. The life of the molybdenum oxide catalyst is 12–18 months and that of the silver oxide-based process is 3–8 months. The porosity of the molybdenum oxide catalyst is 0.7 and that of the silver oxide catalyst is 0.5.


**Table 1.** Properties of catalyst.

The life of the silver catalyst is highly dependent upon the operating conditions of the formaldehyde reactor. Silver catalysts in the formaldehyde plant are typically used for a period of a few months to a year depending on the reaction temperature and pressure [22]. Generally, sintering occurs in the silver catalyst due to reaction temperatures, which results in high pressure drop over the bed, which decreases the performance of catalyst. It is observed that the water ballast process prolongs the life of catalyst by introducing water with its associated high heat capacity that equally distributes the heat over the catalyst bed resulting in minimizing coke formation and sintering [23,24]. Our objective is the performance comparison of both processes based on the plant size, installation and utility cost, and material and energy balance.
