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In this comparative study, the application of response surface methodology (RSM) in predicting and optimizing the amination conditions of activated carbon adsorbent toward CO 2 adsorption was investigated. The adsorbents were prepared based on the central composite design (CCD) with three independent variables (i.e., amination temperature, amination time, and the use of pre-heat treated (HTA) or pre-oxidized (OXA) sorbent as the starting material), and the responses studied were CO 2 adsorption and desorption capacity. Two quadratic models were developed to calculate the optimum amination conditions of activated carbon that provide a compromise between the studied responses (dependent variables). From the analysis of variance (ANOVA), the temperature of ammonia treatment was found to be the most important factor; it had a positive influence on CO 2 adsorption capacity but a negative effect on desorption capacity. The optimal point indicated by numerical optimization corresponded to an OXA sorbent that had been aminated at 425 °C for 2.1 h. The activated carbon modified at optimum conditions had a CO 2 adsorption capacity of 26.47 mg/g and a CO 2 desorption capacity of 95.4%. The experimental values of the responses were in good agreement with the amounts predicted by the regression models, indicating that the developed models could adequately predict the responses from the amination variables. The stable adsorption/desorption performance of the optimal activated carbon adsorbent during cyclical operations showed its potential for practical applications.

Tailoring the surface chemistry of adsorbents, especially activated carbons, make them suitable to specific applications. Many times oxidation is the first step and greatly affects the next steps o...

There are several possible methods by which amine groups can be grafted on the surface of activated carbon (AC) to improve their capacity for CO2 adsorption. Ethylenediamine and diethylenetriamine were selected as amino compounds for anchoring on the surface of an oxidized AC. Oxidation of AC was carried out by concentrated nitric acid. For each amino compound, two “in-solvent” and “solvent-free” methods with a number of grafting times were studied. Nitrogen adsorption–desorption at 77 K and proximate and ultimate analysis were used to determine physical and chemical characteristics of the samples. Temperature-programmed (TP) CO2 adsorption test from 30°C to 120°C were performed to investigate the effect of modification on CO2 capture. The modification clearly had a negative effect on the textural characteristics of the samples, so the samples showed a less CO2 uptake at lower temperatures. However, the decrease of capture capacity with increasing temperature is to somewhat softer for amine-grafted samples, so that they have a capacity comparable to the parent sample or even more than that at elevated temperatures. This property may give the new adsorbents this opportunity to be used at flue gas temperature with a higher efficiency. CO2 capture capacity per unit surface area of all the amine-modified samples, however, was significantly improved, compared to the parent sample presenting a great influence of amino groups on the CO2 capture capacity. Moreover, the used amine compounds and grafting methods were compared in terms of adsorbent characteristics and CO2 uptake curves. Cyclic adsorption–desorption tests showed a satisfactory regeneration for the modified samples.

Activated carbon can be effectively modified for CO2 adsorption with amine groups due to their high affinity for CO2. Using approaches such as impregnation, some modifiers containing amine groups are physically adsorbed on the surface of carbon, whereas other amine groups can be directly or indirectly chemically bound to the activated carbon matrix. In the context of exploring potential techniques for grafting amine groups onto activated carbon surfaces, we herein review the literature on modifications applied to different materials and supports for a variety of applications, limited to neither activated carbon nor CO2-adsorption applications. We focus on the processes of grafting amine groups and the parameters influencing these processes. Moreover, the mechanism of CO2 adsorption involving amine groups is discussed.

A commercial granular activated carbon (GAC) was subjected to thermal treatment with ammonia for obtaining an efficient carbon dioxide (CO2) adsorbent. In general, CO2 adsorption capacity of activated carbon can be increased by introduction of basic nitrogen functionalities onto the carbon surface. In this work, the effect of oxygen surface groups before introduction of basic nitrogen functionalities to the carbon surface on CO2 adsorption capacity was investigated. For this purpose two different approaches of ammonia treatment without preliminary oxidation and amination of oxidized samples were studied. Modified carbons were characterized by elemental analysis and Fourier Transform Infrared spectroscopy (FT-IR) to study the impact of changes in surface chemistry and formation of specific surface groups on adsorption properties. The texture of the samples was characterized by conducting N2 adsorption/desorption at −196 °C. CO2 capture performance of the samples was investigated using a thermogravimetric analysis (TGA). It was found that in both modification techniques, the presence of nitrogen functionalities on carbon surface generally increased the CO2 adsorption capacity. The results indicated that oxidation followed by high temperature ammonia treatment (800 °C) considerably enhanced the CO2 uptake at higher temperatures.

The influence of surface modification of activated carbon with gaseous ammonia on adsorption properties toward carbon dioxide (CO2) was reviewed. It was apparent from the literature survey that the surface chemistry of activated carbon strongly affects the adsorption capacity. In general, CO2 adsorption capacity of activated carbon can be increased by the introduction of basic nitrogen functionalities into the carbon surface. Accordingly, in this review the impact of changes in surface chemistry and formation of specific surface groups on adsorption properties of activated carbon were studied. Two different methods, heat treatment and ammonia treatment (amination) for producing activated carbon with basic surface were compared. Amination was found to be suitable modification technique for obtaining efficient CO2 adsorbents. Finally, the common characterization methods were also mentioned.

Surface of activated carbon can be functionalized with amine groups to enhance their capacity for CO 2 adsorption. Amine functionalized solid sorbents were prepared by anchoring two types of amine compounds, namely ethylenediamine (EDA) and 2-chloroethylamine hydrochloric acid (CEA) on the surface of palm shell based activated carbon (PSAC). Samples of PSAC were first oxidized by nitric acid using three different available setups to ensure about creation of a significant amount of oxygen containing groups on the surface. At the second stage, the best oxidized sample was modified by anchoring EDA and CEA on the surface to produce a superior CO 2 adsorbent. Several quantitative and qualitative methods were used to characterize the prepared samples: Nitrogen adsorption at 77K, proximate and ultimate analysis and temperature programmed desorption (TPD). Moreover, CO 2 adsorption study was carried out using CO 2 adsorption isothermal profile at 30°C and temperature-programmed (TP) CO 2 adsorption test. All modified samples had a lower surface area than the virgin PSAC. The best modified sample presented an increase of 45% in CO 2 capture capacity at 100°C. On the other hand, on the basis of unit surface area, CO 2 capture capacity of amine modified samples was much higher, compared to the parent sample. Furthermore, the modified samples showed a less dependency of their CO 2 capacity on temperature indicating chemisorption of the adsorbate on the PSAC surface.