Synthesis and regeneration of enhanced eggshell sorbents for clean coal applications

Abstract

By the year 2010, global carbon dioxide emissions will reach a staggering 31 billion metric tons per year. With much of this CO2 coming from energy production, an economical means to capture CO2 during fossil fuel conversion is critical. One of the most promising CO2 capture techniques employs a cyclic carbonation of CaO to CaCO3 and calcination of CaCO3 back to CaO. This scheme separates CO2 into a pure stream in post-combustion and pre-combustion systems for the production of electricity, hydrogen, and liquid fuels. The challenge of this method, along with the purpose of this study is to find economical, high reactivity CaCO3 sorbents. The U.S. produces approximately 190,000 tons/yr of eggshell waste, which contains around 95% CaCO3 and presents itself as an inexpensive alternative to synthetic calcium carbonate sorbents. Various acetic acid pretreatments were tested to remove the eggshell’s membrane and alter the shell’s pore structure. The CO2 capture capacity for multiple strengths and durations of acetic acid pretreatments was then measured by carbonating the samples in a thermogravimetric analyzer using a 10% CO2 stream. Finally, six strengths of acetic acid treatments were also explored to regenerate spent sorbents that had undergone a pore collapse after multiple cycles. The conducted experimentation has shown that the membrane contains highly valuable Type X collagen, as proven through proteomic analysis, which would supplement the process economics when sold. Also, it was found that a pretreatment with acetic acid facilitates the generation of a mesoporous structure, allowing the eggshell sorbent to reach higher conversions over more carbonation/calcination cycles. Finally, regeneration of spent sorbents with acetic acid solutions showed a substantial revitalization in both recyclability and carbon capture. The combined optimization of cheaper, more sustainable sorbents for clean fossil fuel conversion, as presented here, will make the implementation of such systems a much more economical and environmentally friendly solution for future energy needs.