PHOSGENE-FREE DIMETHYL CARBONATE PRODUCTION

A novel, phosgene-free approach to producing 100 MMlb/yr of dimethyl carbonate (DMC) was designed using a two step catalytic reaction of methanol and urea to produce DMC and ammonia. The methanol and urea were mixed and heated to drive the first step of the reaction, conversion of urea to methyl carbamate (MC). The MC and methanol mixture was fed to a high pressure reactive distillation column containing the catalyst. The reactive distillation tower strips off ammonia as it is produced, forcing the reaction forward. The ammonia vapor is then sold to an adjacent plant, which uses it to produce urea. The components of the liquid stream leaving the reactive distillation tower are separated by simple distillation towers. Excess methanol and MC are recycled back to the reactive distillation tower, leaving only the purified ammonia and DMC streams as products. Several assumptions are made in the design of this process. First, due to the lack of readily-available data or binary coefficients, the interactions of DMC and MC in a vapor-liquid equilibrium environment are estimated using ASPEN Plus. Second, the exact yield of DMC is unknown under the process conditions, though the reactive distillation tower was designed in conjunction with the chosen catalyst in such a way as to guarantee a good, predictable lower bound on the production of DMC. Finally, due to the nature in which urea is mixed with methanol at high temperature and pressure, an entirely custom solids handling system is necessary to adequately mix and react the urea and methanol. As the full details of this system are not known, the design uses an approximation of the equipment and utilities required. Based on these assumptions, the design gives a DMC production scheme that is reliable, economically feasible, and environmentally neutral