Preparation Of Modified Nano-Scale CaO Particles And Evaluation As A CO₂ Adsorbent At High Temperatures In Hydrogen Producing Process

Hydrogen is not only a raw material of petroleum industry and chemical industry, but also a good carrier of energy. It can be used as a clean fuel and a kind of energy of traffic tools. CO₂ adsorption enhanced steam-methane reforming process is a favorable technique to produce hydrogen with a lower cost and a simple process, and attracts hot researches. The properties of CO₂ adsorbent is the key of the application of this new process. This paper concerns the studies of the nano-scale CaO of the preparation method and properties evaluation for providing a feasibility uses of industry.Nano-scale CaCO₃ particles were surface-coated with SiO₂ using a sol-gel method and used as high temperature CO₂ adsorption premonitory material. The CO₂ adsorption capacity and carbonate-calcination cyclic using characteristics of the adsorbent samples were tested with a laboratory diameter Φ12 mm fixed bed adsorption facility. The test results show that there is an amorphous SiO₂ film on the surface of nano-size CaCO₃, the ratio of Si to Ca is 1:39. The initial and final decomposition temperatures of the samples are 595-620℃ and 800-820℃ respectively. It has a 5-20℃ increase by comparison with nano-scale CaCO₃ particles uncoated with SiO₂. The maximum CO₂ adsorption capacity of SiO₂ coated nano-scale CaCO₃ is 92.1% at a temperature of 600℃. That is 10% higher comparing with CaCO₃ particles not coated with SiO₂. After 20 runs of cyclic carbonations and calcinations, CO₂ adsorption capacity of the SiO₂ coated samples is 64.2%. XRD analytical results showed that the crystal type of nano-scale CaCO₃ has no significant changes after 20 cyclic runs.Two kinds of intermingle-modified Nano-scale CaCO₃ particles were prepared by a mechanical mixing method used as the high temperature CO₂ adsorption premonitory material. The CO₂ adsorption capacities and carbonate-calcination cyclic adsorption capacities of the sorbents were tested. The test results show that the maximum CO₂ adsorption capacity of SiO₂ intermingle-modified sorbent is 83.8% at a temperature of 600℃, and the capacity of NaY zeolite intermingle-modified sorbent is 86.4%.Both of their CO₂ adsorption capacities are inferior to the sorbent with SiO₂ surface-coated, which is 92.1%. After 20 runs of cyclic carbonations and calcinations, CO₂ adsorption capacity of the nano-size SiO₂ modified samples is 57.4% and is 62.8% of the NaY zeolite modified samples respectively.The results of the researches show that the adsorption capacity and cyclic adsorption capacity of a SiO₂ surface-coated nano-CaCO₃ and intermingle-modified nano-CaCO₃ are much better than the nano-CaCO₃ sorbent. The technique of surface-coated with SiO₂ to prepare an adsorbent will be a significant meaning to the further study.