Characterization of plasma catalytic decomposition of methane: role of atomic O and reaction mechanism

In this work, we investigated atmospheric pressure plasma jet (APPJ)-assisted methane oxidation over a Ni-SiO2/Al2O3 catalyst. We evaluated possible reaction mechanisms by analyzing the correlation of gas phase, surface and plasma-produced species. Plasma feed gas compositions, plasma powers, and catalyst temperatures were varied to expand the experimental parameters. Real-time Fourier-transform infrared spectroscopy (FTIR) was applied to quantify gas phase species from the reactions. The reactive incident fluxes generated by plasma were measured by molecular beam mass spectroscopy (MBMS) using an identical APPJ operating at the same conditions. A strong correlation of the quantified fluxes of plasma-produced atomic oxygen with that of CH4 consumption, and CO and CO2 formation implies that O atoms play an essential role in CH4 oxidation for the investigated conditions. With the integration of APPJ, the apparent activation energy was lowered and a synergistic effect of 30% was observed. We also performed in-situ diffuse reflectance infrared Fourier-transform spectroscopy (DRIFTS) to analyze the catalyst surface. The surface analysis showed that surface CO abundance mirrored the surface coverage of CHn at 25 oC. This suggests that CHn adsorbed on the catalyst surface as an intermediate species that was subsequently transformed into surface CO. We observed very little surface CHn absorbance at 500 oC, while a ten-fold increase of surface CO and stronger CO2 absorption were seen. This indicates that for a nickel catalyst at 500 oC, the dissociation of CH4 to CHn may be the rate-determining step in the plasma-assisted CH4 oxidation for our conditions. We also found the CO vibrational frequency changes from 2143 cm-1 for gas phase CO to 2196 cm-1 for CO on a 25 oC catalyst surface, whereas the frequency of CO on a 500 oC catalyst was 2188 cm-1. The change in CO vibrational frequency may be related to the oxidation of the catalyst.

Inverse Molecular Design of Alkoxides and Phenoxides for Aqueous Direct Air Capture of CO2

Aqueous direct air capture (DAC) is a key technology toward a carbon negative infrastructure. Developing sorbent molecules with water- and oxygen-tolerance and high CO2 binding capacity is therefore highly desired. In this work, we analyze the CO2 absorption chemistries on amines, alkoxides, and phenoxides with density functional theory (DFT) calculations and search for the optimal sorbent using an inverse molecular design strategy. The alkoxides and phenoxides are found to be more suitable for aqueous DAC than amines thanks to their water-tolerance and capture stoichiometry of 1:1 (2:1 for amines). All three molecular systems are found to obey the same linear scaling relationship (LSR) between pK_(CO_2 ) and pK_a, since both CO2 and proton are bonded to the nucleophilic binding site through a majorly σ bonding orbital. Several high-performance alkoxides are proposed from the computational screening. In contrast, phenoxides have relatively poor correlation between pK_(CO_2 ) and pK_a, showing promise for optimization. We apply genetic algorithm (GA) to search the chemical space of substituted phenoxides for the optimal sorbent. Several promising candidates that break the LSR are discovered. The most promising off-LSR candidate phenoxides feature bulky ortho substituents forcing the CO2 adduct into a perpendicular configuration with respect to the aromatic ring. In this configuration, CO2 utilizes a different molecular orbital for binding than does the proton, and the pK_(CO_2 ) and pK_a are thus decoupled. The pK_(CO_2 )-pK_a trend and off-LSR behaviors are then confirmed by experiments, validating the inverse molecular design framework. This work not only extensively studies the chemistry of the aqueous DAC, but also presents a transferrable computational workflow for understanding and optimization of other functional molecules.

Enhancing Absorption Performance of CO2 by Amine Solution through the Spiral Wired Channel in Concentric Circular Membrane Contactors

The CO2 absorption rate by using a Monoethanolamide (MEA) solution through the spiral wired channel in concentric circular membrane contactors under both concurrent-flow and countercurrent-flow operations was investigated experimentally and theoretically. The one-dimensional mathematical modeling equation developed for predicting the absorption rate and concentration distributions was solved numerically using the fourth Runge–Kutta method under various absorbent flow rate, CO2 feed flow rate and inlet CO2 concentration in the gas feed. An economical viewpoint of the spiral wired module was examined by assessing both absorption flux improvement and power consumption increment. Meanwhile, the correlated average Sherwood number to predict the mass-transfer coefficient of the CO2 absorption mechanisms in a concentric circular membrane contactor with the spiral wired annulus channel is also obtained in a generalized and simplified expression. The theoretical predictions of absorption flux improvement were validated by experimental results in good agreements. The amine solution flowing through the annulus of a concentric circular tube, which was inserted in a tight-fitting spiral wire in a small annular spacing, could enhance the CO2 absorption flux improvement due to reduction of the concentration polarization effect. A larger concentration polarization coefficient (CPC) was achieved in the countercurrent-flow operations than that in concurrent-flow operations for various operations conditions and spiral-wire pitches. The absorption flux improvement for inserting spiral wire in the concentric circular module could provide the maximum relative increment up to 46.45%.

Influence of Forced Carbonisation on the Binding Properties of Sludge with a High β-Belite Content

Alternative binders activated by forced carbonisation are regarded as one of the potential solutions to reducing greenhouse gas emissions, water, and energy consumption. Such binders, in particular those based on nepheline sludge (a by-product of alumina production), cured in carbon dioxide with subsequent hydration, are clinkerless building materials. The development of such binders contributes to the involvement of multi-tonnage solid industrial waste in the production cycle. This type of waste is capable of binding man-made CO2 and transforming it into stable insoluble compounds, having binder properties. The optimum technological parameters of the forced carbonisation of the nepheline slime binder was determined by the mathematical planning of the experiment. The novelty of the research is the expansion of the secondary raw material base that can bind the man-made CO2 with obtaining the construction products of appropriate quality. It was revealed that the process of active CO2 absorption by the minerals of nepheline slime is observed in the first 120 min of the forced carbonization. Immediately after carbonisation, the resulting material develops compressive strength up to 57.64 MPa, and at the subsequent hydration within 28 days this figure increases to 68.71 MPa. Calcium carbonate is the main binder that determines the high mechanical properties of the samples. During the subsequent hydration of the uncoated belite, gel-like products are formed, which additionally harden the carbonised matrix. Thus, after the forced carbonisation and the following 28 days of hardening, the material with compressive strength in the range 4.38–68.71 MPa and flexural strength of 3.1–8.9 MPa was obtained. This material was characterised by water absorption by mass in the range of 13.9–23.3% and the average density of 1640–1886 kg/m3. The softening coefficient of the material was 0.51–0.99. The results obtained enables one to consider further prospects for research in this area, in terms of the introduction of additional technological parameters to study the process of forced carbonisation of nepheline slime.

Evaluation of Capability of Some Amino Acid-based Poly (Ionic Liquid)s as Biocompatible Agent for Co2 Absorption

In this study, seven amino acid-based poly(ionic liquid)s (AAPILs) such as poly(1-butyl-3-vinylimidazolium glycinate), P[VBIm][Gly], poly (1-butyl-3-vinylimidazolium alaninate), P[VBIm][Ala], poly(1-butyl-3-vinylimidazolium valinate), P[VBIm][Val], poly(1-butyl-3-vinylimidazolium prolinate) P[VBIm][Pro], poly(1-butyl-3-vinylimidazolium hisdinate), P[VBIm][His], poly(1-butyl-3-vinylimidazolium lysinate), P[VBIm][Lys], and poly(1-butyl-3-vinylimidazolium arginate), P[VBIm][Arg] have been synthesized, characterized, and their CO2 absorption capacities were investigated using quartz crystal microbalance (QCM) at temperature range 288.15–308.15 and pressures up to 5 bar. Based on the absorption mechanism, the reaction equilibrium thermodynamic model is applied to correlating the experimental CO2 absorption capacities. The reaction equilibrium constant and Henry’s law constant were calculated to evaluate the efficiency of the AAPILs for CO2 absorption. In the investigated AAPILs, the CO2 absorption capacity was as follows: P[VBIm][Arg] > P[VBIm][Lys] > P[VBIm][His] > P[VBIm][Pro] > P[VBIm][Gly] > P[VBIm][Val] > P[VBIm][Ala]. The accessibility of available more amine groups in AAPIL with arginate anion is the main factor for the high CO2 absorption capacity. Also, chemical absorption of CO2 via carbamate formation was corroborated by FT-IR spectroscopy.

Investigation of H2S Solubility in Aqueous N- Methyldiethanolamine + Amine Functionalized UiO-66 as a nano solvent

In this paper, the experimental solubility of hydrogen sulfide in aqueous N- Methyldiethanolamine + Amine Functionalized UiO-66 (UiO-66-NH2) was studied. UiO-66-NH2 was produced using solvothermal process, and its physicochemical properties were investigated by different techniques including XRD, TGA, TEM, BET, and FTIR to realize its crystalline structure, morphology, thermal stability, and porous structure. The Zeta potential of the solution was turned out to be about 26.6 mV (millivolt), meaning that UiO-66-NH2 particles are moderately stable in aqueous 40 wt.% MDEA. The solubility of hydrogen sulfide has been carried out using the isochoric saturation / or static method in two concentration grades of 0.1 and 0.5 wt.% of UiO-66-NH2 in the aqueous solution of 40 wt.% MDEA known as nanofluid. Experimental measurements were carried out at temperatures of 303.15 through 333.15 K, and pressures up 1100 kPa. Results showed that the addition of UiO-66-NH2 nanoparticles to the MDEA solution altered the results less than 3% , while the mean value of uncertainty reported in this work is about 4% , meaning that the addition of nanoparticles do not have remarkable effect on H2S solubility. In contrast, it causes an increased capacity of CO2 absorption of that solution up to 10% .