Diffusion transport characteristic of carbon monoxide within calcium sulfate slit in chemical looping hydrogen production: Molecular dynamics simulation

Abstract

Chemical looping hydrogen production is a kind of technology for high-carbon energy cleaning and low-carbon utilization with great development potential, which can realize H2 production and CO2 separation at low cost. CaSO4 oxygen carrier, as the non-metal oxide oxygen carrier, is not only cheap in price and friendly to the environment, but also high in amount of oxygen carried and excellent in the thermodynamic reaction property. For the key problem of its popularization and application – low reaction rate, this paper investigated the diffusion transport characteristics of the fuel gas molecule, which was one of key microprocesses affecting the reaction rate, in the channel of CaSO4 oxygen carrier. Based on the channel of CaSO4 oxygen carrier and the slit model, the influence of the slit width, reaction temperature and coverage rate of doped element Na or Fe of oxygen carrier on the internal diffusion behavior of CaSO4 oxygen carrier was investigated by the molecular dynamics simulation. The results show: CO molecules physical adsorb on CaSO4 slit surface; Increase of the slit width will reduce the binding of CaSO4 surface on single CO molecule, but CO molecular diffusion capacity will increase first and then decrease; The temperature rises will result in the growth of CO molecular diffusion capacity, because CO molecule to be easy to diffuse to the unoccupied reaction site; After Na and Fe is loaded on CaSO4 slit surface, CO molecular diffusion capacity is greatly improved, and the diffusion coefficients of CO molecule are 27 and 28 times of pure CaSO4 slit surface, respectively. The calculation results can provide theoretical basis for the structural design and channel optimization of calcium-based oxygen carrier for chemical looping hydrogen production.