Sasongko, D., A. F. H. Luthan, and W. Wulandari. “Modified Two-Step Dimethyl Ether (DME) Synthesis Simulation from Indonesian Brown Coal”. Journal of Engineering and Technological Sciences, vol. 48, no. 3, Aug. 2016, pp. 320-33, doi:10.5614/j.eng.technol.sci.2016.48.3.6.