Thermodynamic Equilibrium Analysis of Methanol Conversion to Aromatic Hydrocarbons Using SAS: A Prelude to Biomass Deoxygenation

Abstract

Deoxygenation, or removal of oxygen from oxygenates, is a reaction of paramount importance in the production of hydrocarbon fuels from biorenewable substrates. A thermodynamic equilibrium analysis gives valuable insights into the theoretical limits of desired products when a substrate is reacted under a given set of conditions. Here we report the equilibrium composition of the methanol-to-gasoline hydrocarbon system by minimizing the total Gibbs energy of the system. Minimization was performed under constrained conditions using a non-linear optimization technique available in SAS. The system was treated as a gaseous mixture of ten components: C6H6, C7H8, C8H10 (ethyl benzene), C8H10 (xylene), CH3OH, H2O, C, CO2, CO, and H2. The carbon in the equilibrium mixture was used as a measure of coke formation, which causes deactivation of catalysts that are used in aromatization reactions. The equilibrium composition of methanol was analyzed for temperatures ranging from 400°C to 1200°C and gauge pressures of 0, 5, 10, and 15 atm. It was observed that when the temperature was increased, the system changed from negative to positive, making the deoxygenation reaction less spontaneous. The positive portion of the Gibbs free energy further increased when the pressure was increased from 0 to 15 atm.