Adsorption of Carbonyl Sulfide on Propylamine Tethered to Porous Silica

Carbonyl sulfide (COS) reacts slowly with amines in the aqueous solutions used to absorb CO₂ from natural gas and flue gas and can also deactivate certain aqueous amines. The effects of COS on amines tethered to porous silica, however, have not been investigated before. Hence, the adsorption of COS on aminopropyl groups tethered to porous silica was studied using in situ IR spectroscopy. COS chemisorbed mainly and reversibly as propylammonium propylthiocarbamate ion pairs [R–NH­(CO)­S^– ⁺H₃N–R] under dry conditions. In addition, a small amount of another chemisorbed species formed slowly and irreversibly. Nevertheless, the CO₂ capacities of the adsorbents were fully retained after COS was desorbed

Microporous Humins Synthesized in Concentrated Sulfuric Acid Using 5‑Hydroxymethyl Furfural

A new class of highly porous organic sorbents called microporous humins is presented. These microporous humins are derived from sustainable and industrially abundant resources, have high heat of CO₂ sorption, and could potentially be useful for the separation of carbon dioxide from gas mixtures. Their synthesis involves the polymerization of 5-hydroxymethyl furfural (HMF) in concentrated sulfuric acid and treatment with diethyl ether and heat. In particular, the porosities were tuned by the heat treatment. HMF is a potential platform chemical from biorefineries and a common intermediate in carbohydrate chemistry. A high uptake of CO₂ (up to 5.27 mmol/g at 0 °C and 1 bar) and high CO₂-over-N₂ and CO₂-over-CH₄ selectivities were observed. The microporous humins were aromatic and structurally amorphous, which was shown in a multipronged approach using ¹³C nuclear magnetic resonance and Fourier transform infrared spectroscopies, elemental analysis, and wide-angle X-ray scattering

Spherical and Porous Particles of Calcium Carbonate Synthesized with Food Friendly Polymer Additives

Porous calcium carbonate particles were synthesized by adding solutions of Ca²⁺ to solutions of CO₃^2– containing polymeric additives. Under optimized conditions well-defined aggregates of the anhydrous polymorph vaterite formed. A typical sample of these micrometer-sized aggregates had a pore volume of 0.1 cm³/g, a pore width of ∼10 nm, and a specific surface area of ∼25–30 m²/ g. Only one mixing order (calcium to carbonate) allowed the formation of vaterite, which was ascribed to the buffering capacity and relatively high pH of the CO₃^2– solution. Rapid addition of the calcium chloride solution and rapid stirring promoted the formation of vaterite, due to the high supersaturation levels achieved. With xanthan gum, porous and micrometer-sized vaterite aggregates could be synthesized over a wide range of synthetic conditions. For the other food grade polymers, hydroxypropyl methylcellulose (HPMC), methylcellulose (MC), and sodium carboxyl methylcellulose, several intensive and extensive synthetic parameters had to be optimized to obtain pure vaterite and porous aggregates. HPMC and MC allowed well-defined spherical micrometer-sized particles to form. We expect that these spherical and porous particles of vaterite could be relevant to model studies as well as a controlled delivery of particularly large molecules

Role of Ion Mobility in Molecular Sieving of CO₂ over N₂ with Zeolite NaKA

Classical molecular dynamics and Grand Canonical Monte Carlo simulations are carried out for sorbates (CO₂ and N₂) in zeolite NaKA using a universal type ab initio force field. By combining the results of these simulations, we reproduce the CO₂ uptake as a function of the K⁺ content in the zeolite NaKA as measured experimentally by Liu et al. The experiment yielded an exceptionally high CO₂-over-N₂ selectivity of >200 at a specific K⁺/(K⁺ + Na⁺) ratio of 17 atom %. This high selectivity could be attributed to the nonlinear uptake dependency of the K⁺/(K⁺ + Na⁺) ratio measured for both CO₂ and N₂. Additionally, our simulations show a strong coupling between the self-diffusion of CO₂ and the site-to-site jumping rate of the extra-framework cations. These results show that this nonlinear uptake dependency of CO₂ is the result of molecular sieving. Following this, our simulations conclude that both thermodynamic and kinetic contributions must be taken into account when modeling the uptake of this and similar materials with the same functionalities

RNA as a Precursor to N‑Doped Activated Carbon

Activated carbons (ACs) have applications in gas separation and power storage, and N-doped ACs in particular can be promising supercapacitors. In this context, we studied ACs produced from yeast-derived ribonucleic acid (RNA), which contains aza-aromatic bases and phosphate-linked ribose units, and is surprisingly inexpensive. The RNA was hydrothermally carbonized to produce hydrochars that were subsequently activated with CO₂, KOH, or KHCO₃ to give ACs. The ACs adsorbed up to ∼7 mmol/g at 0 °C and 1 bar and had capacitances as high as ∼300 F/g in a three-electrode cell and a 6 M KOH­(aq) electrolyte. The material that displayed the best capacitance was tested in a two-electrode cell, which displayed a specific capacitance of 181 F/g even at a current density of 10 A/g. The ACs with the highest uptake of CO₂ and the highest capacitance were those activated with KOH and KHCO₃; however, CO₂ activation is arguably less expensive and more suitable for industrialization

Activated Carbons for Water Treatment Prepared by Phosphoric Acid Activation of Hydrothermally Treated Beer Waste

Activated carbons were produced by chemical activation of hydrothermally carbonized (HTC) beer waste, with phosphoric acid as the activation agent. The activation was optimized within a full factorial design, using the outcome of 19 different experiments. Four different parameters (concentration of the acid, activation time, activation temperature, flow rate) were analyzed with respect to their influence on the median pore size. The concentration of H₃PO₄ had a strong positive effect on the median pore size. The specific surface areas of these activated carbons were ∼1000 m²/g, which compared well commercially available activated carbons. The activated carbons had mostly large pores with a size of ∼4 nm, and a significant amount of acid surface groups. Scanning electron microscopy (SEM) revealed that the morphology of the HTC beer waste changed significantly after the chemical activation. The capacity to adsorb methylene blue from aqueous solutions was 341 mg/g, for one of the activated carbons at pH 7. A Langmuir model described the uptake of the dye quite well, which suggested a homogeneous adsorption of Methylene Blue (MB)

UV–Visible and Plasmonic Nanospectroscopy of the CO₂ Adsorption Energetics in a Microporous Polymer

In the context of carbon capture and storage (CCS), micro- and mesoporous polymers have received significant attention due to their ability to selectively adsorb and separate CO₂ from gas streams. The performance of such materials is critically dependent on the isosteric heat of adsorption (<i>Q</i>_st) of CO₂ directly related to the interaction strength between CO₂ and the adsorbent. Here, we show using the microporous polymer PIM-1 as a model system that its <i>Q</i>_st can be conveniently determined by <i>in situ</i> UV–vis optical transmission spectroscopy directly applied on the adsorbent or, with higher resolution, by indirect nanoplasmonic sensing based on localized surface plasmon resonance in metal nanoparticles. Taken all together, this study provides a general blueprint for efficient <i>optical</i> screening of micro- and mesoporous polymeric materials for CCS in terms of their CO₂ adsorption energetics and kinetics

Dispersed Uniform Nanoparticles from a Macroscopic Organosilica Powder

A colloidal dispersion of uniform organosilica nanoparticles could be produced via the disassembly of the non-surfactant-templated organosilica powder nanostructured folate material (NFM-1). This unusual reaction pathway was available because the folate and silica-containing moieties in NFM-1 are held together by noncovalent interactions. No precipitation was observed from the colloidal dispersion after a week, though particle growth occurred at a solvent-dependent rate that could be described by the Lifshitz–Slyozov–Wagner equation. An organosilica film that was prepared from the colloidal dispersion adsorbed folate-binding protein from solution but adsorbed ions from a phosphate-buffered saline solution to a larger degree. To our knowledge, this is the first instance of a colloidal dispersion of organosilica nanoparticles being derived from a macroscopic material rather than from molecular precursors

Effects of Pressure and the Addition of a Rejected Material from Municipal Waste Composting on the Pyrolysis of Two-Phase Olive Mill Waste

This work examines the effect of the absolute pressure (0.1 or 1.0 MPa) and the addition of a high-ash rejected material from municipal solid waste (MSW) composting (RC) on the slow pyrolysis of two-phase olive mill waste (OW). The experiments were conducted in a batch pyrolysis system using an initial mass of 750 g of feedstock. Three types of initial materials were tested: the OW alone, a mixture of OW and pure additives (5 wt % K₂CO₃ and 5 wt % CaO), and a mixture of OW and RC (10 wt %). For the OW without any additive, an increased pressure led to a market increase in the carbonization efficiency (i.e., fixed carbon yield). At atmospheric pressure, the addition of either additives (CaO + K₂CO₃) or RC led to important changes in the pyrolysis behavior as a result of the catalytic role of the alkali and alkaline earth metals (AAEMs). However, this catalytic effect, which is translated into an enhancement of the decomposition of both the hemicellulose and cellulose fractions, was not observed at 1.0 MPa. The potential stability of all of the produced biochars appeared to be very high, given the results obtained from both proximate and ultimate analyses. This high stability was confirmed by ¹³C and ¹H solid-state nuclear magnetic resonance, which showed that the carbon contained in the biochars was composed mainly or entirely of highly condensed aromatic structures. However, the highest values of stable <i>C</i> (Edinburgh stability tool) and <i>R</i>_50,<i>x</i> (recalcitrance index) were obtained for biochars produced from the OW + RC mixtures at any pressure. In summary, the addition of the rejected material from MSW composting appears to be a very cost-effective measure to obtain a potentially high-stable biochar, even at atmospheric pressure

K⁺ Exchanged Zeolite ZK‑4 as a Highly Selective Sorbent for CO₂

Adsorbents with high capacity and selectivity for adsorption of CO₂ are currently being investigated for applications in adsorption-driven separation of CO₂ from flue gas. An adsorbent with a particularly high CO₂-over-N₂ selectivity and high capacity was tested here. Zeolite ZK-4 (Si:Al ∼ 1.3:1), which had the same structure as zeolite A (LTA), showed a high CO₂ capacity of 4.85 mmol/g (273 K, 101 kPa) in its Na⁺ form. When approximately 26 at. % of the extraframework cations were exchanged for K⁺ (NaK-ZK-4), the material still adsorbed a large amount of CO₂ (4.35 mmol/g, 273 K, 101 kPa), but the N₂ uptake became negligible (<0.03 mmol/g, 273 K, 101 kPa). The majority of the CO₂ was physisorbed on zeolite ZK-4 as quantified by consecutive volumetric adsorption measurements. The rate of physisorption of CO₂ was fast, even for the highly selective sample. The molecular details of the sorption of CO₂ were revealed as well. Computer modeling (Monte Carlo, molecular dynamics simulations, and quantum chemical calculations) allowed us to partly predict the behavior of fully K⁺ exchanged zeolite K-ZK-4 upon adsorption of CO₂ and N₂ for Si:Al ratios up to 4:1. Zeolite K-ZK-4 with Si:Al ratios below 2.5:1 restricted the diffusion of CO₂ and N₂ across the cages. These simulations could not probe the delicate details of the molecular sieving of CO₂ over N₂. Still, this study indicates that zeolites NaK-ZK-4 and K-ZK-4 could be appealing adsorbents with high CO₂ uptake (∼4 mmol/g, 101 kPa, 273 K) and a kinetically enhanced CO₂-over-N₂ selectivity