Ethanol production methods are expanding due to the importance of ethanol as a fuel or additive to fuels. One of these methods is converting methanol to ethanol in a three-step process. All of these steps need to deeply study and investigate to develop the process. In this research, the carbonylation of dimethyl ether to produce methyl acetate, which is the intermediate reaction of the three-step process of methanol to ethanol, has been simulated and optimized. The parameters of temperature, pressure, residence time, and feed ratio have been investigated as effective operational parameters of the process. It has been shown that the temperature and pressure of the process are more effective in the ranges of 220-280 °C and 30-50 bar, respectively. The simulation results showed a maximum point in dimethyl ether conversion in the feed ratio of 0.4-0.6, i.e., in temperature of 260 °C, residence time of 5 h, pressure of 45 bar, DME/CO/Ar = 30/67/3, and DME conversion about 22%. Also, it has been shown that increasing the residence time increases the effect of each of the above parameters. Optimization of the dimethyl ether carbonylation process has demonstrated that the combination of different ranges of the above parameters achieves the desired conversion, i.e., in pressure of 48.23 bar, temperature of 259.06 °C, residence time of 3.68 h, and dimethyl ether/feed of 0.461 vol%; conversion of dimethyl ether will be equal to 85.50%.