Physical properties and characteristics of a solid particle highly depend on the particle shape and size. The Gas Anti Solvent (GAS) process is a recently developed process that can control the size and morphology of solid particles using supercritical fluids as an antisolvent to resrystallize desired products in solution. Though many lab-scale experiments with different choices of antisolvents exist, no study for the large-scale operation of such a system has been reported yet. This study proposes different design options of a GAS process for recrystallization of HMX (1,3,5,7-tetranitro-1,3,5,7-tetrazocane or cyclotetramethylenetetranitramine) using CO2 as an antisolvent. A detailed mathematical model for particle size distribution is integrated into the process flow sheet model. An optimal process which includes the particle size data of product and process specifications are proposed with economic evaluation and comparison of various alternative processes.