High-Temperature Pressure Swing Adsorption Process for CO₂ Separation

This paper presents a novel pressure swing adsorption process and the development of specifically designed sorbents for the process. It is operated at high temperature (650–800 °C) using the reversible reaction of calcium oxide with CO₂, i.e., CaO + CO₂ ⇄ CaCO₃. The new process directly stores the reaction heat released from the forward reaction in the sorbent and then releases it for sorbent regeneration under reduced CO₂ partial pressure, so that the need of pure oxygen for oxy-fuel combustion is avoided. Two potential problems of the new process, namely, loss in capacity and slow and unmatched reaction rates of chemical-controlled carbonation and calcination, were discussed in detail. Three specifically designed calcium-based sorbents showed stable performance during 92 isothermal carbonation–calcination cycles at either 680 or 750 °C. The calcination rate was significantly enhanced by increasing the reaction temperature and the introduction of steam to match the reaction rate of chemical-controlled carbonation. This pressure swing adsorption process could be used for low-cost CO₂ separation using specifically designed sorbents under carefully selected operating conditions

Behavior of CaO/CuO Based Composite in a Combined Calcium and Copper Chemical Looping Process

Integration of chemical looping combustion into calcium looping is an attractive approach to solving the problem of energy requirement for the regeneration of CaO-based sorbent. In this work, the behavior of MgO supported CaO/CuO composite in the new combined process (CaCuCL) was investigated. The composite was prepared via a simple wet mixing method and measured via a thermogravimetric analyzer for its chemical performance. It appears that the component of Cu/CuO has a significant influence on the cyclic performance of CaO, which is probably caused by the “wrapping” of Cu/CuO outside, due to its low melting point. However, this negative effect can be greatly reduced by using appropriate operating conditions in the successive reactions. When tested for 68 cycles, all synthetic sorbents showed good reactivity and stability of the Cu/CuO component, although loss-in-capacity of CaO was stilled observed

Fabrication of CaO-Based Sorbents for CO₂ Capture by a Mixing Method

Three types of sorbent were fabricated using various calcium and support precursors via a simple mixing method, in order to develop highly effective, durable, and cheap CaO-based sorbents suitable for CO₂ capture. The sorption performance and morphology of the sorbents were measured in a thermogravimetric analyzer and a scanning electron microscopy, respectively. The experimental results indicate that cement is a promising low-cost support precursor for contributing to the enhancement of cyclic CO₂ sorption capacity, especially when organometallic calcium precursors were used. A sorbent (with 75% CaO content) made from calcium l-lactate hydrate and cement showed the highest CO₂ sorption capacity of 0.36 g of CO₂/g of sorbent and its capacity decreased only slightly after 70 cycles of carbonation and calcination

Extreme drought impacts have been underestimated in grasslands and shrublands globally

Climate change is increasing the frequency and severity of short-term (~1 y) drought events—the most common duration of drought—globally. Yet the impact of this intensification of drought on ecosystem functioning remains poorly resolved. This is due in part to the widely disparate approaches ecologists have employed to study drought, variation in the severity and duration of drought studied, and differences among ecosystems in vegetation, edaphic and climatic attributes that can mediate drought impacts. To overcome these problems and better identify the factors that modulate drought responses, we used a coordinated distributed experiment to quantify the impact of short-term drought on grassland and shrubland ecosystems. With a standardized approach, we imposed ~a single year of drought at 100 sites on six continents. Here we show that loss of a foundational ecosystem function—aboveground net primary production (ANPP)—was 60% greater at sites that experienced statistically extreme drought (1-in-100-y event) vs. those sites where drought was nominal (historically more common) in magnitude (35% vs. 21%, respectively). This reduction in a key carbon cycle process with a single year of extreme drought greatly exceeds previously reported losses for grasslands and shrublands. Our global experiment also revealed high variability in drought response but that relative reductions in ANPP were greater in drier ecosystems and those with fewer plant species. Overall, our results demonstrate with unprecedented rigor that the global impacts of projected increases in drought severity have been significantly underestimated and that drier and less diverse sites are likely to be most vulnerable to extreme drought