Kathryn A. Berchtold

Greening Coal: Breakthroughs and Challenges in Carbon Capture and Storage

Like it or not, coal is here to stay, for the next few decades at least. Continued use of coal in this age of growing greenhouse gas controls will require removing carbon dioxide from the coal waste stream. We already remove toxicants such as sulfur dioxide and mercury, and the removal of CO₂ is the next step in reducing the environmental impacts of using coal as an energy source (i.e., greening coal). This paper outlines some of the complexities encountered in capturing CO₂ from coal, transporting it large distances through pipelines, and storing it safely underground.

Tuning microcavities in thermally rearranged polymer membranes for CO2 capture.

Microporous materials have a great importance in catalysis, delivery, storage and separation in terms of their performance and efficiency. Most microporous materials are comprised of inorganic frameworks, while thermally rearranged (TR) polymers are a microporous organic polymer which is tuned to optimize the cavity sizes and distribution for difficult separation applications. The sub-nano sized microcavities are controlled by in situ thermal treatment conditions which have been investigated by positron annihilation lifetime spectroscopy (PALS). The size and relative number of cavities increased from room temperature to 230 °C resulting in improvements in both permeabilities and selectivities for H(2)/CO(2) separation due to the significant increase of gas diffusion and decrease of CO(2) solubility. The highest performance of the well-tuned TR-polymer membrane was 206 Barrer for H(2) permeability and 6.2 of H(2)/CO(2) selectivity, exceeding the polymeric upper bound for gas separation membranes.

Modeling the Effects of Chain Length on the Termination Kinetics in Multivinyl Photopolymerizations

A model is presented that predicts photopolymerization kinetics over several orders of magnitude change in initiation rate. The model incorporates polymerization features that have long been assumed negligible when examining multivinyl photopolymerizations. The assumption that radical termination is chain-length-independent is relaxed by incorporating a chain-length-dependent termination (CLDT) parameter based on Random-walk theory into the kinetic model. Experiments and modeling of multivinyl free-radical photopolymerizations clearly demonstrate that CLDT is important at low conversions, where a deviation from the classical square-root relationship between polymerization rate (R p ) and initiation rate (R i ) is observed (R p R α i , α=1/2, classically). At moderate conversions, when reaction diffusion dominates termination, a transition region is observed from a chain-length-dependent to a chain-length-independent region. During this transition, long chain - long chain termination is reaction diffusion controlled while the short chain -short chain termination event remains translational and segmental diffusion controlled. The scaling exponent, α, gradually increases throughout this region until achieving the classical value, where once attained, a plateau is observed. Chain-length effects were also examined by including chain-transfer (CT) reactions into the kinetic expressions. Upon CT agent addition, a transition region is still observed; however, at low conversion, a adheres more closely to the classical predictions. Most importantly, the model clearly demonstrates a transition from a CLDT region at low conversion to reaction diffusion controlled termination region at high conversion, where chain length is unimportant.

Polymerization kinetics of HEMA/DEGDMA: using changes in initiation and chain transfer rates to explore the effects of chain-length-dependent termination.

The effect of kinetic chain length and chain transfer on the polymerization kinetics and network structure in polymerizations of loosely crosslinked 2-hydroxyethyl methacrylate/di(ethylene glycol) dimethacrylate mixtures was explored. Polymerization behavior of the monomer mixture in the presence and absence of a chain transfer agent was monitored at various initiation rates and chain transfer agent concentration levels. Dependence of the polymerization rate on the initiation rate was found to deviate from the classical square-root relationship because of chain-length-dependent termination. This effect was further confirmed by addition of a chain transfer agent. The presence of a chain transfer agent led to the formation of shorter kinetic chains, which enhanced termination and slowed the polymerization. Investigation of the polymerization kinetics after cessation of irradiation yielded kt/kp[M] values for both systems. Prior to the onset of reaction diffusion-controlled termination, the system that included a chain transfer agent exhibited much higher kt/kp[M] values than the polymerization system without added chain transfer agent. In addition, the onset of reaction diffusion-controlled termination was delayed to higher conversions in the system containing chain transfer agent. The impact of a chain transfer agent on the polymerization behavior and kinetics demonstrates that the chain-length-dependent termination phenomenon is indeed important and must be considered in kinetic modeling of loosely crosslinked systems.

Chapter 6 – H2 Selective Membranes for Precombustion Carbon Capture

Abstract Abundant fossil energy sources such as coal, biomass, and natural gas will play a dominant role in achieving energy sustainability provided advanced technologies for energy conversion from these sources in an environmentally friendly way are developed. One of the critically needed advanced technologies is carbon dioxide capture. Among known carbon separation technologies, membrane-based gas separation processes are expected to play an important role in the separation of CO2 from gaseous streams emitted by the utility industry. With no moving parts, energy conservation near thermodynamic limits, and various possible routes for integration into power generation schemes, gas separation membranes can potentially dominate the CO2 separation market. This chapter is focused on precombustion carbon capture using membranes, with detailed discussion on membrane process integration, the major membrane material classes under consideration for these separations, and their development status.