Adsorption selectivity of CO2 over CH4, N2 and H2 in melamine\u2013resorcinol\u2013formaldehyde xerogels

Ivan A Principe,Ashleigh J Fletcher

doi:10.1007/s10450-020-00203-w

Abstract

Sorptive selectivity of melamine–resorcinol–formaldehyde xerogels, towards CO2, CH4, N2 and H2, is reported, where all systems demonstrate potential for selective adsorption of CO2 from corresponding binary gas mixtures. Selected gas mixtures represent important gas separation applications found in industry, i.e. CO2 removal from power plant flue gases (CO2–N2), sour gas sweetening (CO2–CH4), and separation of species in the water–gas shift reaction (CO2–H2). All materials tested exhibit microporous character, enhancing adsorption of small molecules, however, it is the inclusion of a nitrogen-rich material into the gel matrix that results in enhanced selectivities for these systems. Despite the porous character of the gels, under the test conditions used to simulate industrial parameters, all three balance gases, i.e. H2, N2 and CH4, showed low affinities for the xerogels, while CO2 adsorption was notably higher and increased with the inclusion and increased concentration of melamine. Ideal adsorbed solution theory was used to demonstrate significant differences in adsorption uptake, especially for CO2–CH4, and high selectivities for CO2 over N2. In all cases, selected xerogels exhibited industrially relevant adsorption timescales for CO2 over competitor gases, demonstrating the potential of these materials for the selective adsorption of CO2 from process streams.

Highlights

CO2 is considered an important pollutant species, due to its major impact within global warming and climate change (IPCC fifth assessment report: climate change 2014 synthesis report 2014)
This concentration of C O2 sits at the higher end of the range of concentrations measured within flue gases but allows more accurate determination of competitive effects given that the higher CO2 concentration will result in a smaller margin of error in the adsorption isotherm of the gas mixture
The CO2 concentration calculated with ideal adsorbed solution theory (IAST) agrees reasonably with the concentration obtained from the adsorption isotherm of the mixture, which was 9.52 × 10–4 mmol/m2; which is primarily comprised of C O2 in the adsorbed phase

Summary

Introduction

CO2 is considered an important pollutant species, due to its major impact within global warming and climate change (IPCC fifth assessment report: climate change 2014 synthesis report 2014). A third separation process to consider is that used in pre-combustion systems to remove CO2 from H2; example industries include gasification or steam reforming, where the fuel, natural gas or coal, is treated prior to combustion, creating H2 and CO, the latter being used to increase the yield of H 2 via the water–gas shift reaction, creating the by-product of C O2, up to 20% by volume, in the process It is, necessary to separate C O2 from H 2 before the stream is fed to the gas turbines, and industry again utilises scrubbing technologies to this end. It has been suggested that any sorbent used for postcombustive CO2 removal must demonstrate high adsorption capacity at low relative concentrations of CO2, while exhibiting selective adsorption in industrially relevant timescales and a low heat of regeneration (Hao et al 2013; Yang et al 2017) This last factor has been previously reported for MRF xerogels (Principe et al 2018), and this work seeks to addressed in the present study. The data obtained demonstrate the potential of these materials for multicomponent separations in a range of applications

Sample selection

Materials and synthesis

Xerogel characterization

Results and discussion

Conclusions