A CO₂ capture technology using multi-walled carbon nanotubes with polyaspartamide surfactant

Global climate change resulting from the emission of greenhouse gases has become a widespread concern in the recent years. Carbon dioxide alone contributes roughly two-thirds to the enhanced greenhouse effect. Carbon capture and storage (CCS), an approach for mitigating potential global climate change, is widely known as a selected track towards sustainable application of fossil fuels. Technologies to separate and compress CO₂ from power plant flue gases are commercially available. Absorption, using monoethanolamine (MEA), is the most common technology applied to capture CO₂ from flue gas of fossil fuel power plants. However, the efficiency penalty induced by carbon capture within energy conversion systems poses a threat to the economic viability of these systems. The adsorption technology due to the ability to operate at moderate temperature and pressure, the increase of the capacity of CO₂ adsorption and the compliance with the environmental safety are the trickiest in the adsorbent design. The primary objective of this work was to design an adsorbent with ability of adsorbing large quantity CO₂ at efficient energy. A long chain polymer was grafted with a diamine to provide a large CO₂ anchoring site for carbamate formation, covering multiwalled carbon nanotubes (MWNTs) to enhance the surface area and pore volume. Thus, an advanced adsorbent was made after polycondensation of aspartic acid between 190°C-210°C in phosphoric acid medium and the use of dicyclohexylcarbodiimide (DCC) as the coupling agent; this resulted in long chain polysuccinimide (PSI) synthesis. A ethylenediamine (EDA) was grafted to the PSI to give a polyaspartamide (PAA), which, covering the MWNTs, has achieved an adsorbent with 100% EDA incorporation as showed 1H NMR. The chemical surface of the PAA-MWNTs showed with FTIR analysis the primary amine group and the amide group as CO₂ anchoring sites and biodegradable bonds respectively. As evaluated via BET, the low surface area and pore volume of PAA have increased by 31 and 41 times respectively with the inclusion of MWNTs (8nm). Thus, the surface area, pore volume, and pore size of the synthesized adsorbent (PAA-MWNTs) were 60.4m2/g, 0.4cm3/ respectively. Transmission electron microscope (TEM) analysis and the decrease of graphitized carbon as shown with Raman spectra have shown that the covering of MWNTs by the polymer PAA increased the diameter size from 8nm to 15nm. The TGA analysis showed a 200°C temperature limit for CO₂ adsorption using PAA-MWNTs as an adsorbent. The CO: Adsorption isotherm was completed at 25°C with the use of TGA in order to evaluate the CO₂ adsorption capacity of the adsorbents. The PAA-MWNTs showed a higher CO₂ adsorption capacity of 70gCO₂/kg compared to PAA, PSI, and MWNTs alone, where the adsorption capacity showed 46.17gCO₂/kg, 26.90gCO₂/kg, and 15.20gCO₂/kg respectively.