Improvements of calcium oxide based sorbents for multiple CO2 capture cycles

Synthesis of CaO from waste shells for microwave-assisted catalytic pyrolysis of waste cooking oil to produce aromatic-rich bio-oil

Energy shortage and environmental pollution have attracted long-term attention. In this study, CaO were prepared from waste eggshell (EGC), preserved egg shell (PEC), clam shell (CLC) and crab shell (CRC), which were then compared with commercial CaO (CMC) to catalyze microwave-assisted pyrolysis of waste cooking oil (WCO) for enrichment of aromatics in bio-oil. The characterization results indicated that EGC and CLC contained 95.54% and 95.61% CaO respectively, which were higher than that of CMC (95.11%), and the pore properties of EGC were the best. In addition, the effects of CaO type and catalytic mode on pyrolysis were studied. In CaO catalytic pyrolysis, CMC and CLC in-situ catalysis produced more aromatics than ex-situ catalysis, and PEC and CRC were more conducive to aromatics formation in ex-situ condition. EGC was conducive to produce benzene, toluene and xylene (BTX) both in in-situ (19.04%) and ex-situ (20.76%) catalytic pyrolysis. In CaO/HZSM-5 catalysis, the optimal dual catalytic mode for generating monocyclic aromatic hydrocarbons (MAHs) was Mode A (CaO separated from HZSM-5 for ex-situ catalysis), and EGC/HZSM-5 performed well in benzene, toluene and xylene (BTX) production.

Mechanochemically Activated, Calcium Oxide-Based, Magnesium Oxide-Stabilized Carbon Dioxide Sorbents

Carbon dioxide capture and storage (CCS) is a promising approach to reduce anthropogenic CO2 emissions and mitigate climate change. However, the costs associated with the capture of CO2 using the currently available technology, that is, amine scrubbing, are considered prohibitive. In this context, the so-called calcium looping process, which relies on the reversible carbonation of CaO, is an attractive alternative. The main disadvantage of naturally occurring CaO-based CO2 sorbents, such as limestone, is their rapid deactivation caused by thermal sintering. Here, we report a scalable route based on wet mechanochemical activation to prepare MgO-stabilized, CaO-based CO2 sorbents. We optimized the synthesis conditions through a fundamental understanding of the underlying stabilization mechanism, and the quantity of MgO required to stabilize CaO could be reduced to as little as 15 wt %. This allowed the preparation of CO2 sorbents that exceed the CO2 uptake of the reference limestone by 200 %.

Improved CO2 adsorption capacity and cyclic stability of CaO sorbents incorporated with MgO

The CO₂ adsorption capacity of CaO sorbents with different MgO wt% (calcination temperature 800 °C, carbonation at 650 °C with 100% CO₂, and de-carbonation at 800 °C in 100% N₂).

Development Trends in Porous Adsorbents for Carbon Capture

Accumulation of greenhouse gases especially CO2 in the atmosphere leading to global warming with undesirable climate changes has been a serious global concern. Major power generation in the world is from coal based power plants. Carbon capture through pre- and post- combustion technologies with various technical options like adsorption, absorption, membrane separations, and chemical looping combustion with and without oxygen uncoupling have received considerable attention of researchers, environmentalists and the stake holders. Carbon capture from flue gases can be achieved with micro and meso porous adsorbents. This review covers carbonaceous (organic and metal organic frameworks) and noncarbonaceous (inorganic) porous adsorbents for CO2 adsorption at different process conditions and pore sizes. Focus is also given to noncarbonaceous micro and meso porous adsorbents in chemical looping combustion involving insitu CO2 capture at high temperature (>400 °C). Adsorption mechanisms, material characteristics, and synthesis methods are discussed. Attention is given to isosteric heats and characterization techniques. The options to enhance the techno-economic viability of carbon capture techniques by integrating with CO2 utilization to produce industrially important chemicals like ammonia and urea are analyzed. From the reader's perspective, for different classes of materials, each section has been summarized in the form of tables or figures to get a quick glance of the developments.

CaO-based CO2 sorbents: from fundamentals to the development of new, highly effective materials

The enormous anthropogenic emission of the greenhouse gas CO2 is most likely the main reason for climate change. Considering the continuing and indeed growing utilisation of fossil fuels for electricity generation and transportation purposes, development and implementation of processes that avoid the associated emissions of CO2 are urgently needed. CO2 capture and storage, commonly termed CCS, would be a possible mid-term solution to reduce the emissions of CO2 into the atmosphere. However, the costs associated with the currently available CO2 capture technology, that is, amine scrubbing, are prohibitively high, thus making the development of new CO2 sorbents a highly important research challenge. Indeed, CaO, readily obtained through the calcination of naturally occurring limestone, has been proposed as an alternative CO2 sorbent that could substantially reduce the costs of CO2 capture. However, one of the major drawbacks of using CaO derived from natural sources is its rapidly decreasing CO2 uptake capacity with repeated carbonation-calcination reactions. Here, we review the current understanding of fundamental aspects of the cyclic carbonation-calcination reactions of CaO such as its reversibility and kinetics. Subsequently, recent attempts to develop synthetic, CaO-based sorbents that possess high and cyclically stable CO2 uptakes are presented.