Lee A. Stevens

Impact of Water Coadsorption for Carbon Dioxide Capture in Microporous Polymer Sorbents

Alcohol-containing polymer networks synthesized by Friedel-Crafts alkylation have surface areas of up to 1015 m(2)/g. Both racemic and chiral microporous binaphthol (BINOL) networks can be produced by a simple, one-step route. The BINOL networks show higher CO(2) capture capacities than their naphthol counterparts under idealized, dry conditions. In the presence of water vapor, however, these BINOL networks adsorb less CO(2) than more hydrophobic analogues, suggesting that idealized measurements may give a poor indication of performance under more realistic carbon capture conditions.

Materials challenges for the development of solid sorbents for post-combustion carbon capture

In an effort to reduce the energy penalty and cost associated with state-of-the-art carbon capture technologies, a range of 2nd and 3rd generation CO2 capture technologies are being developed. One of these technologies, based on solid sorbents for the gas separation in carbon capture, has the potential to significantly reduce the energy penalty and avoid some of the problems associated with the current technologies. However to realise this potential, two main developments are required: new porous materials and new plant integration processes. This application note describes the performance requirements and challenges associated with the development of functional materials for this application. We describe the key challenges for materials development and the requirements in terms of operating conditions, gas composition, stability, and lifetime to make solid sorbents a viable large scale CO2 capture process. Examples of potential future research and breakthrough materials currently being developed are also discussed.

Swellable, Water- and Acid-Tolerant Polymer Sponges for Chemoselective Carbon Dioxide Capture

To impact carbon emissions, new materials for carbon capture must be inexpensive, robust, and able to adsorb CO2 specifically from a mixture of other gases. In particular, materials must be tolerant to the water vapor and to the acidic impurities that are present in gas streams produced by using fossil fuels to generate electricity. We show that a porous organic polymer has excellent CO2 capacity and high CO2 selectivity under conditions relevant to precombustion CO2 capture. Unlike polar adsorbents, such as zeolite 13x and the metal-organic framework, HKUST-1, the CO2 adsorption capacity for the hydrophobic polymer is hardly affected by the adsorption of water vapor. The polymer is even stable to boiling in concentrated acid for extended periods, a property that is matched by few microporous adsorbents. The polymer adsorbs CO2 in a different way from rigid materials by physical swelling, much as a sponge adsorbs water. This gives rise to a higher CO2 capacities and much better CO2 selectivity than for other water-tolerant, nonswellable frameworks, such as activated carbon and ZIF-8. The polymer has superior function as a selective gas adsorbent, even though its constituent monomers are very simple organic feedstocks, as would be required for materials preparation on the large industrial scales required for carbon capture.

Instant MOFs: continuous synthesis of metal-organic frameworks by rapid solvent mixing.

A continuous flow reactor allows the preparation of porous metal-organic framework materials with crystallisation induced by rapid mixing of streams of preheated water and solutions of reagents in organic solvent: this gives high volume production (132 g h(-1)) with crystallite size of the products from nanoscale to micron.

‘Dry bases’: carbon dioxide capture using alkaline dry water

An alkaline form of ‘dry water’—a ‘dry base’—is prepared by the high-speed mixing of aqueous solutions of metal carbonates or organic amines with hydrophobic silica nanoparticles. Despite being mostly water, the dry base looks and flows like a powder, and adsorbs CO2 rapidly without any mixing because of its high surface-to-volume ratio. Unlike normal aqueous base solutions, dry bases can be non-corrosive because they do not readily wet surfaces.

Insights into the influence of the cooling profile on the reconstitution times of amorphous lyophilized protein formulations

Lyophilized protein formulations must be reconstituted back into solution prior to patient administration and in this regard long reconstitution times are not ideal. The factors that govern reconstitution time remain poorly understood. The aim of this research was to understand the influence of the lyophilization cooling profile (including annealing) on the resulting cake structure and reconstitution time. Three protein formulations (BSA 50mg/ml, BSA 200mg/ml and IgG1 40mg/ml, all in 7% w/v sucrose) were investigated after cooling at either 0.5°C/min, or quench cooling with liquid nitrogen with/without annealing. Significantly longer reconstitution times were observed for the lower protein concentration formulations following quench cool. Porosity measurements found concomitant increases in the surface area of the porous cake structure but a reduction in total pore volume. We propose that slow reconstitution results from either closed pores or small pores impeding the penetration of water into the lyophilized cake.

Ni Mg mixed metal oxides for p-type dye-sensitized solar cells

Mg Ni mixed metal oxide photocathodes have been prepared by a mixed NiCl2/MgCl2 sol-gel process. The MgO/NiO electrodes have been extensively characterized using physical and electrochemical methods. Dye-sensitized solar cells have been prepared from these films, and the higher concentrations of MgO improved the photovoltage of these devices; however, there was a notable drop in photocurrent with increasing Mg(2+). Charge extraction and XPS experiments revealed that the cause of this was a positive shift in the energy of the valence band, which decreased the driving force for electron transfer from the NiO film to the dye and, therefore, the photocurrent. In addition, increasing concentrations of MgO increases the volume of pores between 0.500 and 0.050 μm, while reducing pore volumes in the mesopore range (less than 0.050 μm) and lowering BET surface area from approximately 41 down to 30 m(2) g(-1). A MgO concentration of 5% was found to strike a balance between the increased photovoltage and decreased photocurrent, possessing a BET surface area of 35 m(2) g(-1) and a large pore volume in both the meso- and macropore range, which lead to a higher overall power conversion efficiency than NiO alone.

Hygrothermal simulation-informed design of mesoporous desiccants for optimised energy efficiency of mixed mode air conditioning systems

This paper describes an optimization technique using hygrothermal numerical modelling to determine an ideal and unknown isotherm in order to inform the design of optimised mesoporous desiccants. Their suitability for passive humidity buffering as well as their impact on energy efficiency was assessed when assisting a mixed mode air-conditioning (AC) system. Three clear stages of water vapour adsorption were found that strongly correspond to the Δw gradient when assessing the kinetics of adsorption and exchange rates for periodic moisture loads. Consistent agreement was found between the latent heat of dehumidification used by the AC system and the desiccant decay time after successive sorption loop cycles. This confirmed the materials suitability for specific applications and was found to be highly sensitive to the portion of the isotherm between φi,L − φi,U (Δw gradient), compared with full adsorption capacity (total w) when assessing total energy consumption. The experimental results of sorption kinetics appeared to be slightly underestimated between the Δw gradient and the response time to reach equilibrium moisture content (EMC). The major underestimations were found to be consistent with the kinetics of adsorption/desorption when analysing their significance based on w differences. These were largely attributed to a combination of adsorption kinetics (time-response) and adsorption/desorption hysteresis. However, this was not evident when comparing long-term experimental data and numerical estimations for water vapour sorption isotherms, since numerical model accurately predicted them. This suggests that both adsorption kinetics and the scanning curve prediction, within a hysteresis loop, are not accurately represented by current hygrothermal models and are hence a priority for future research.

Surface Bespoke Mesoporous Silica for Carbon Dioxide Adsorption

AbstractAmine functionalized mesoporous adsorbents were synthesized and evaluated for adsorption of CO2. In the present study the mesoporous silica surface was treated with a surfactant tetra-n-propyl ammonium hydroxide (TPAOH) with an aim to tailor the characteristics of mesoporous silica walls. The as synthesized adsorbents were tested for determining equilibrium adsorption capacity using 100% CO2 and diluted 15% CO2 stream at different temperatures (30, 55, and 75°C). Equilibrium CO2 adsorption capacity of TEPA modified surface-treated silica was 2.51 and 2.54  mmol/g at 75°C under 15 and 100% CO2 concentration respectively. The as-synthesized adsorbents were also tested for determining dynamic adsorption capacity using 100% CO2 and diluted (15, 50, and 75%) CO2 stream at different temperatures (30, 55, and 75°C). Dynamic CO2 adsorption capacity of TEPA modified silica was 1.67 and 4.29  mmol/g at 75°C under 15 and 100% CO2 concentration respectively. This signifies the role of surfactant treatment aff...

Step Change Adsorbents and Processes for CO2 Capture “STEPCAP

STEPCAP is a multipartner consortium project, the aim of which is to develop a targeted range of novel CO2 adsorbents for carbon capture. This research into materials and process development is essential to achieve the potential cost and efficiency benefits offered by solid sorbents capture technologies over the current state of the art processes. Firstly, this paper will discuss the key materials and process challenges associated with developing solid sorbents. This will lead into a discussion of materials development in STEPCAP which is based on a fundamental understanding of adsorption processes to design and optimise material properties and form. The development and performance of the three classes of materials under development in this study, microporous polymers, surface modified hydrotalcites, and co-doped sorbents, which offer potential for a step change increase in adsorption capacity and performance over previously developed materials will be discussed. Modified hydrotalcites such as, amine modified layered double hydroxides (LDH’s) have been synthesized via the exfoliation and grafting route. In addition, novel conjugated microporous polymers synthesized through Sonogashira-Hagihara coupling have also been investigated and have demonstrated similar capacities. Critically, due to the hydrophobic nature of some of these adsorbents, identical performance has been observed in the presence of moisture, an advantageous property for operation in the water saturated environment of flue gases. This presentation will also present data on the performance of these materials in simulated flue gases as well after simulated temperature swing regeneration cycles to assess the stability and lifetime of the sorbents.