Impregnation of activated carbons for pre- and post-combustion CO2 capture in a fixed bed pressure swing adsorption reactor: a modelling and experimental comparison

Soares dos Santos, Douglas (2019). Impregnation of activated carbons for pre- and post-combustion CO2 capture in a fixed bed pressure swing adsorption reactor: a modelling and experimental comparison. University of Birmingham. Ph.D.

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Abstract

The mitigation of greenhouse gases, such as carbon dioxide, is of timely concern in the energy sector, requiring new techniques and process options to treat acidic gases and develop solutions for capture and reuse. Solid adsorbents are potentially viable for application as the next generation carbon capture technology. Activated Carbon Norit® RB1 and Cabot Norit® R2030 were selected for this study, owing to their potentially high adsorption rates and affinity with carbon dioxide molecules. The purpose of thesis was to modify the adsorbent using chemical and amine solutions via an impregnation process to provide high adsorption capacity and performance, focusing on surface area modification and attachment of primary amine groups to improve the solid/gas interaction. Diverse characterisation techniques were used to examine and explore the essential properties and parameters of the modified adsorbents developed. Specifically, scanning electron microscopy (SEM) was used to investigate the surface morphology, thermogravimetric analysis (TGA) was applied to test the adsorption capacity with a pure CO2 flow, a high-pressure volumetric analyser (HPVA) was used to measure the gas volume adsorbed at the pre-combustion condition, producing adsorption-desorption isotherms under nitrogen and carbon dioxide binary mixtures, and the textural properties were determined by Brunauer-Emmett-Teller (BET) analysis, allowing comparison of the pore size and the volume adsorbed per sample.

The dynamic adsorption behaviour of the activated carbons (ACs) was studied in a fixed bed reactor using a carbon dioxide concentration range of 10–50% combined with a nitrogen flow. The original and modified adsorbents were tested under pre and post-combustion conditions, with the highest uptake of carbon dioxide found to be for MEA+MDEA+AMP Norit® RB1 AC II under pre-combutions and MEA (20%) Norit® RB1 AC under post-combustion conditions. The introduction of amine groups into the sample lead to the enhancement of chemisorption, while the treatment with KOH modified the surface area of the adsorbents, thereby improving uptake behaviour.

Additionally, a Pressure Swing Adsorption (PSA) model using a fixed bed reactor was developed for carbon dioxide capture at pre-combustion conditions (25oC and 25 bar) using gPROMS® ModelBuilder software [version 4.1; developed by Process System Enterprise, PSE]. A parameter estimation was executed using similar conditions as applied in the fixed bed reactor rig at the laboratory scale. Nitrogen and carbon dioxide were applied to this model taking into account the physical behaviour of the PSA unit. The estimations demonstrated an excellent approximation to the experimental breakthrough curve for both adsorbents, which also validated the model supported by the sum of squared residuals (SSR) values. Furthermore, the parameter estimation confirmed the novelty of the two amine modified adsorbents for pre-combustion carbon dioxide adsorption, due to their high potential to capture the desired gas in a binary mixture in the PSA fixed bed reactor process.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):