Ammonia Synthesis at Reduced Pressure via Reactive Separation

Abstract

Ammonia is normally made at high temperature and pressure using a promoted iron catalyst. High temperatures are needed to get fast kinetics; the high pressure is used to ensure high conversion. Alternatively, ammonia can be made at high temperature but lower pressure if the product ammonia is rapidly separated. Here, we have systematically studied the effect of temperature and pressure on the rates of reaction. We then have qualitatively investigated the absorptive separation of ammonia using calcium chloride in a reaction–separation process. Rapid separation reduces the constraint of reversible reaction and enables us to obtain appropriate reaction rates at relatively lower pressure. The effect of different operating conditions—reaction temperature, pressure, absorption temperature, and gas transport—on production rates is carefully measured, and this elucidates the potential and the limits of this type of low-pressure ammonia synthesis.