An all-purpose porous cleaner for acid gas removal and dehydration of natural gas

V. Rozyyev, C. T. Yavuz*
Chem, 3, 5, 719-721, (2017).
DOI: 10.1016/j.chempr.2017.10.014

Raw natural gas is predominantly methane (up to 95%) but also contains larger hydrocarbons such as ethane and propane, acidic gases such as H2S and CO2, and considerable amounts of water. In some reserves, H2S can reach up to 20%, and water content can be as much as 5%. CO2 in natural gas, from ppm levels up to 0.5%, is less significant but noteworthy. Natural gas treatment starts with the removal of sludge and gas condensate, followed by acid gas removal (mostly H2S) by amine scrubbing. Regenerated H2S is converted to elemental sulfur via the Claus process or sulfuric acid by the wet sulfuric acid process. Sweet (H2S and CO2-free) natural gas is then dehydrated with the use of glycols and then separated from higher alkanes.

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Sustainable nanoporous benzoxazole networks as metal-free catalysts for one-pot oxidative self-coupling of amines by air oxygen

S. Subramanian, H. A. Patel, Y. Song, C. T. Yavuz*
Adv. Sustain. Syst., 1, 1700089, (2017).
DOI: 10.1002/adsu.201700089

The development of sustainable organocatalysts with porosity, high stability, and excellent catalytic activity offers a clean and green alternative to precious metal catalysts. Here, an efficient, nanoporous, heterogeneous benzoxazole catalyst is reported for aerobic oxidative coupling of amines. A molecular design strategy is presented to functionalize primary amines to produce valuable products under one-pot, open-air reaction conditions. Unprecedented and previously unknown, the stable imine intermediate catalyzes its own formation, also known as autocatalysis, enabling a direct and favorable access to amino acids, even if the catalysts are absent. The biomimetic benzoxazole catalysts developed here provide quantitative catalytic activity over 50 cycles with favorable kinetics with no degradation. This work also marks the first use of benzoxazoles for oxidative catalytic reactions.

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Reversible water capture by a charged metal-free porous polymer

J. Byun, H. A. Patel, D. Thirion, C. T. Yavuz*
Polymer, 126, 308-313, (2017).
Invited paper for the special issue on Porous Polymers
DOI: 10.1016/j.polymer.2017.05.071

Climate change and industrial pollution threatens the availability of clean water. Although established protocols of water treatment exist, water capture by porous materials has emerged as a viable alternative to energy intensive processes. Here we introduce a new charged porous polymer that is capable of capturing and releasing water by simple humidity or temperature swings. The quaternary amines on the framework structure attract water molecules and further solvate by coordination. The porosity of the network structure also provides enough void where water can diffuse throughout the solid. Water uptake capacity of the porous polymer surpasses common desiccants like silica gel and molecular sieves, and has the potential to act as an organic desiccant in applications like electronics or food packaging.

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Selective removal of cationic micro-pollutants using disulfide-linked network structures

M. S. Atas, S. Dursun, H. Akyildiz, M. Citir, C. T. Yavuz*, M. S. Yavuz*
RSC Adv., 7, 25969-25977, (2017). Open Access
DOI: 10.1039/C7RA04775D

Micropollutants are found in all water sources, even after thorough treatments that include membrane filtration. New ones emerge as complex molecules are continuously produced and discarded after used. Treatment methods and sorbent designs are mainly based on non-specific interactions and, therefore, have been elusive. Here, we developed swellable covalent organic polymers (COP) with great affinity towards micropollutants, such as textile industry dyes. Surprisingly, only cationic dyes in aqueous solution were selectively and completely removed. Studies of the COPs surfaces led to a gating capture, where negatively charged layer attracts cationic dyes and moves them inside the swollen gel through diffusive and hydrophobic interaction of the hydrocarbon fragments. Despite its larger molecular size, crystal violet has been taken the most, 13.4 mg g−1, surpassing all competing sorbents. The maximum adsorption capacity increased from 12.4 to 14.6 mg and from 8.9 to 11.4 mg when the temperature of dye solution was increased from 20 to 70 °C. The results indicated that disulfide-linked COPs are attractive candidates for selectively eliminating cationic dyes from industrial wastewater due to exceptional swelling behaviour, low-cost and easy synthesis.

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Direct access to primary amines and particle morphology control in nanoporous CO2 sorbents

N. A. Dogan§, E. Ozdemir§, C. T. Yavuz*
ChemSusChem, 10, 2130-2134, (2017). DOI: 10.1002/cssc.201700190. §: Equal contribution

Chemical tuning of nanoporous, solid sorbents for an ideal CO₂ binding requires unhindered amine functional groups on the pore walls. Although common for soluble organics, post-synthetic reduction of nitriles in porous networks often fail due to the insufficient and irreversible metal hydride penetration. Here, we synthesized a nanoporous network with pendant nitrile groups, microsphere morphology and in large scale. The hollow microspheres were easily decorated with primary amines through in situ reduction by widely available boranes. CO₂ capture capacity of the modified sorbent was increased up to an eight times of the starting nanoporous network with a high heat of adsorption (98 kJ/mol). Surface area can be easily tuned between 1 and 354 m²/g. Average particle size (~50 µm) is also quite suitable for CO₂ capture applications where processes like fluidized bed require spheres of micron sizes.

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Selective removal of heavy metal ions by disulfide linked polymer networks

D. Ko, J. S. Lee, H. A. Patel, M. H. Jakobsen, Y. Hwang, C. T. Yavuz, H. C. B. Hansen, H. R. Andersen*
J. Hazard. Mater., 332, 140–148, (2017).
DOI: 10.1016/j.jhazmat.2017.03.007.

Heavy metal contaminated surface water is one of the oldest pollution problems, which is critical to ecosystems and human health. We devised disulfide linked polymer networks and employed as a sorbent for removing heavy metal ions from contaminated water. Although the polymer network material has a moderate surface area, it demonstrated cadmium removal efficiency equivalent to highly porous activated carbon while it showed 16 times faster sorption kinetics compared to activated carbon, owing to the high affinity of cadmium towards disulfide and thiol functionality in the polymer network. The metal sorption mechanism on polymer network was studied by sorption kinetics, effect of pH, and metal complexation. We observed that the metal ions–copper, cadmium, and zinc showed high binding affinity in polymer network, even in the presence of competing cations like calcium in water.

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Enhanced sorption cycle stability and kinetics of CO2 on lithium silicates using lithium ion channeling effect of TiO2 nanotubes

J. S. Lee, C. T. Yavuz*
Ind. Eng. Chem. Res., accepted.
DOI: 10.1021/acs.iecr.6b04918.

Lithium silicate (Li₄SiO₄) is a promising high temperature CO₂ sorbent because of its large CO₂ capacity at elevated temperatures with low materials cost. However, the conventional nonporous Li₄SiO₄ shows very poor CO₂ adsorption kinetics. Thus, a Li₄SiO₄–TiO₂ nanotubes complex was synthesized where LiOH and fumed silica would be calcined around TiO₂ nanotubes. TiO₂ nanotubes in Li4SiO4 structure functioning as open highways, lithium ions were able to channel through the bulky structure and enhance the sorption kinetics, leading the total adsorption capacity to near theoretical values. Furthermore, cyclic studies at 700 °C revealed strong stability over at least 10 cycles. These findings indicate that stability and kinetics of CO₂ sorption can be greatly improved by the nanotube composites of known adsorbents.

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Monitoring instability of linear amine impregnated UiO-66 by in-situ temperature resolved powder X-ray diffraction

Y. Song, D. Thirion, S. Subramanian, M. S. Lah, C. T. Yavuz*
Micropor. Mesopor. Mater., 243, 85-90, (2017).
DOI: 10.1016/j.micromeso.2017.02.021.

Carbon dioxide capture requires stable porous solids like zirconium based metal-organic frameworks (MOFs) in order to make sequestration efforts feasible. Because of the weak binding at low CO₂ partial pressures, oligomeric amines are commonly loaded on porous supports to maximize CO₂ capture while attempting to keep porosity for enhanced diffusion. Here we show the first temperature resolved stability study of linear-amine impregnated UiO-66 by in-situ monitoring of the PXRD pattern. Our findings show that the crystal structure shows a contraction at temperatures as low as 80 °C and deforms considerably above 120 °C, leading to significant doubts about their applicability in CO₂ capture from lean feeds. We confirm that all MOFs need to be thoroughly analyzed at least by means of PXRD at the process relevant temperatures, and reinforced before any plausible plans of application in CO₂ capture.

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EEWS 2016: Progress and Perspectives of Energy Science and Technology

J. Oh, J. W. Choi, C. T. Yavuz, S. Y. Chung, J. Y. Park, Y. Jung*
ACS Energy Lett., 2, 592–594, (2017).
DOI: 10.1021/acsenergylett.6b00640

Established in 2009, the Graduate School of EEWS (Energy, Environment, Water, and Sustainability) at the Korea Advanced Institute of Science and Technology (KAIST) is the first of its kind, an interdisciplinary department at KAIST collectively addressing with interdisciplinary approaches for the emerging and urgent issues in energy, environment, water, and natural resources of the twenty-first century for sustainable society through science, technology, and education (http://eewseng.kaist.ac.kr). Currently housing 12 research groups with diverse backgrounds in chemistry; physics; chemical, electrical, mechanical, and environmental engineering; and materials science, the EEWS is the culmination of unprecedented collaboration under the same roof with close interaction of students and faculty from unlikely backgrounds (Figure). The output in a relatively short period of time is remarkable; the collaborative research combining basic and applied disciplines of seemingly different subjects have produced many novel concepts and approaches in various energy science and technology fields that are otherwise difficult to conceive in a traditional way. In an effort to critically assess the current status of the energy research, identify major challenges, and further stimulate active interactions among the disciplines to solve the challenges, we held the first EEWS forum, “EEWS 2016: Progress and Perspectives of Energy Science and Technology”, in the KI Fusion Hall of KAIST on October 20, 2016. The meeting featured eight internationally recognized energy experts from around the world introducing their cutting-edge research covering a wide range of topics in energy materials, advanced characterization tools, and catalysis, from both experimental and theoretical viewpoints.

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Carbon Dioxide Capture Adsorbents: Chemistry and Methods, A Tutorial Review

H. A. Patel, J. Byun, C. T. Yavuz*
ChemSusChem, 10, 7, 1303-1317, (2017). DOI: 10.1002/cssc.201601545.
View PDF here

Graphical Art by Ella Marushchenko.

Excess carbon dioxide (CO₂) emissions and the inevitable consequences continuing to stimulate hard debate and awareness in both academic and public spaces, despite the clutter on understanding what really is needed to capture and store the unwanted CO₂. Capture is the most costly, nearly 70 % of the price tag on the entire carbon capture and storage (CCS) operation. In this tutorial review, we describe and evaluate CO₂ capture science and technology based on adsorbents in the context of chemistry and methods, after briefly introducing current status of CO₂ emissions. An effective sorbent design is suggested, where six checkpoints are expected to be met: cost, capacity, selectivity, stability, recyclability and fast kinetics.

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Covalent organic polymer functionalization of activated carbon surfaces through acyl chloride for environmental clean-up

P. D. Mines*, D. Thirion, B. Uthuppu, Y. Hwang, M. H. Jakobsen, H. R. Andersen, C. T. Yavuz* Chem. Eng. J., 309, 766-771, (2017). DOI: 10.1016/j.cej.2016.10.085.

Nanoporous networks of covalent organic polymers (COPs) are successfully grafted on the surfaces of activated carbons, through a series of surface modification techniques, including acyl chloride formation by thionyl chloride. Hybrid composites of activated carbon functionalized with COPs exhibit a core-shell formation of COP material grafted to the outer layers of activated carbon. This general method brings features of both COPs and porous carbons together for target-specific environmental remediation applications, which was corroborated with successful adsorption tests for organic dyes and metals.

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