Abstract
Dimethyl ether has received great interest since it is considered as an environmentally-friendly chemical and can be utilized in a wide range of applications. DME is mainly used as aerosol propellant and intermediate in oil industry. It is also used as clean fuel in power generation and diesel engines. DME is produced directly from synthesis gas and indirectly via methanol dehydration over commercial γ-Al2O3 pellets. The methanol dehydration process has a low conversion which is limited by the thermodynamic equilibrium leading to a large recycle stream and size equipment. In addition, the presence of water in the feed with methanol reduces the equilibrium conversion that can be attained. An inter-stage membrane for water removal can overcome the thermodynamic limitations related to the conventional process.
In this study, two adiabatic reactor stages with inter-stage hydrophilic ceramic membrane for water removal were considered for the synthesis of DME via methanol dehydration. A commercial conventional process was simulated using Aspen-Plus ™ for an annual plant capacity of 50,000 metric tons and a 99.5 wt. % purity of DME product. A modified process for DME synthesis using water-selective alumina-silica composite membrane was developed and simulated. A parametric study was conducted to show the effect of inlet temperature on the reactor conversion which can be increased to 93 % using the inter-stage membrane. The high temperature reactor effluent was used to preheat methanol feed. The modified process shows potentials to reduce both energy and equipment size which leads to a lower process cost for DME production.