Mapping of operating windows for methane and ethane pyrolysis in the pulsed compression reactor by experiments and modelling

Abstract

By modelling and experiments optimal operating conditions for methane (between 1000 and 3000 K, 300 bar) and ethane pyrolysis (between 800 and 3200 K, 400 bar) in the pulsed compression reactor (PCR) were evaluated. The PCR is a free piston reactor that can compress a gas from atmospheric pressure up to 600 bar in a single pulse. A differential internal energy balance was used for solving the temperature and pressure during the compression. The GERG-2008 equation of state was used to account for non-idealities. To predict the reaction products, both chemical equilibrium (EQ) and kinetic models available from literature were evaluated. The kinetic models (GRI-mech, Holmen et al., 1995 etc.) did not predict part of the experiments well. The EQ model predicts trends well. Therefore, the EQ model was used to map the operating domains. The aim is to reach a maximum concentration of products (olefins and aromatics) in the product gas and a conversion of 20% or more. For methane pyrolysis at 1600 K and 320 bar with nitrogen as diluent and an initial gas temperature of 588 K, the model analysis led to an experimentally observed factor 5.2 increase in ethylene in the outlet (1.4%mol) compared to a previous optimum point (Slotboom et al., 2021). With ethane pyrolysis 9% of ethylene was obtained at a conversion of 66% with an ethylene selectivity of 61% around 1480 K and 400 bar. Further analysis with the EQ model showed that for the thermal coupling of methane with an initial gas temperature of 773 K, conversion is possible without diluting with nitrogen. For ethane decomposition nitrogen is always needed as a diluent up to 773 K.