Synthesis and Comprehensive Study of Quaternary-Ammonium-Based Sorbents for Natural Gas Sweetening

The present study provides a solvent-free organic synthesis of quaternary ammonium salts: bis(2-hydroxyethyl)dimethylammonium taurate ([BHEDMA][Tau]) and bis(2-hydroxyethyl)dimethylammonium acetate ([BHEDMA][OAc]). These ionic compounds are promising materials for carbon dioxide capture processes, as mono sorbents, supplemental components in the conventional process of chemical absorption, and in the combined membrane approach for improving sorption efficiency. The synthesized compounds were characterized by 1H NMR and FT-IR spectroscopies and elemental analysis. Afterward, the sorption properties of the compounds were evaluated using the inverse gas chromatography (IGC) method, and their thermodynamic parameters were calculated in the temperature range of 303.15–333.15 K. The enthalpy change (∆sH) was less than 80 kJ·mol−1, indicated by the physical nature of sorption and also proved by FT-IR. Henry’s law constant in regard to carbon dioxide at 303.15 K was equal to 4.76 MPa for [BHEDMA][Tau], being almost 2.5 lower than for [BHEDMA][OAc] (11.55 MPa). The calculated carbon dioxide sorption capacity for [BHEDMA][Tau] and [BHEDMA][OAc] amounted to 0.58 and 0.30 mmol·g−1, respectively. The obtained parameters are comparable with the known solid sorbents and ionic liquids used for CO2 capture. However, the synthesized compounds, combining the advantages of both alkanolamines and ionic liquids, contain no fluorine in their structure and thus match the principles of environmental care.

How much can novel solid sorbents reduce the cost of post-combustion CO2 capture? A techno-economic investigation on the cost limits of pressure-vacuum swing adsorption

This paper focuses on identifying the cost limits of two single-stage pressure-vacuum swing adsorption (PVSA) cycles for post-combustion CO2 capture if the ``ideal'' zero-cost adsorbent can be discovered. Through an integrated techno-economic optimisation, we simultaneously optimise the adsorbent properties (adsorption isotherms and particle morphology) and process design variables to determine the lowest possible cost of CO2 avoided (excluding the CO2 conditioning, transport and storage) for different industrial flue gas CO2 compositions and flow rates. The CO2 avoided cost for PVSA ranges from 87.1 to 10.4 € per tonne of CO2 avoided, corresponding to CO2 feed compositions of 3.5 mol% to 30 mol%, respectively. The corresponding costs for a monoethanolamine based absorption process, using heat from a natural gas plant, are 76.8 to 54.8 EUR per tonne of CO2 avoided, respectively showing that PVSA can be attractive for flue gas streams with high CO2 compositions. The ``ideal" adsorbents needed to attain the lowest possible CO2 avoided costs have a range of CO2 affinities with close to zero N2 adsorption, demonstrating promise for adsorbent discovery and development. The need for simultaneously optimizing the particle morphology and the process conditions are emphasized.

Bi-Functional Catalyst/Sorbent for a H2-Rich Gas from Biomass Gasification

The aim of this work is to identify the effect of the CaO phase as a CO2 sorbent and mayenite (Ca12Al14O33) as a stabilizing phase in a bi-functional material for CO2 capture in biomass syngas conditioning and cleaning at high temperature. The effect of different CaO weight contents is studied (0, 56, 85, 100 wt%) in sorbents synthesized by the wet mixing method. These high temperature solid sorbents are upgraded to bi-functional compounds by the addition of 3 or 6 wt% of nickel chosen as the metal active phase. N2 adsorption, X-ray diffraction, scanning electronic microscopy, temperature-programmed reduction analyses and CO2 sorption study were performed to characterize structural, textural, reducibility and sorption properties of bi-functional materials. Finally, sorption-enhanced reforming of toluene (chosen as tar model), of methane then of methane and toluene with bi-functional compounds were performed to study the best material to improve H2 content in a syngas, provided by steam biomass gasification. If the catalytic activity on the sorption enhanced reforming of methane exhibits a fast fall-down after 10–15 min of experimental test, the reforming of toluene reaches a constant conversion of 99.9% by using bi-functional materials.