Once-through CO2 hydrogenation to grid-compatible synthetic natural gas over a Ru-based catalyst at atmospheric pressure

Abstract

Exploiting a homemade Ru/Al2O3 catalyst, in this work we experimentally demonstrate the feasibility of a CO2 methanation process able to reach CO2 conversion levels in excess of 98 % with a complete CH4 selectivity. Using a once-through process configuration with two isothermal tubular packed-bed reactors in series and operating at atmospheric pressure and low temperature in the presence of a highly active catalyst, we show that it is possible to produce a gas stream able to meet stringent purity thresholds required for the direct injection of the produced synthetic natural gas (SNG) into the gas grid without further purifications other than water removal. To demonstrate that this is the simplest process configuration allowing to achieve the target, three different process configurations exploiting tubular reactors are compared: a single isothermal packed-bed reactor, two isothermal packed-bed reactors operating in series at different temperatures, and two isothermal packed-bed reactors operating in series at different temperatures with intermediate water removal. The first two configurations are limited by thermodynamics at high temperature and by kinetics at low temperatures: the maximum methane concentration in the dry-products is never adequate for their direct grid-injection. The latter configuration allows to reach thermodynamic equilibrium composition at temperatures as low as 200°C and atmospheric pressure: at those condition, methane concentration as high as 98.5 % were obtained in the dry-products. The stability of the adopted catalyst is investigated for nearly 600 h in presence of concentrated H2/CO2 streams and almost complete CO2 conversion and no relevant deactivation phenomena are observed.

Topics & Concepts