An experimental study on CO2 and butane adsorption on activated carbon

Abstract

The aim of this study is to investigate the effect of textural and surface chemical properties of activated carbon (AC) samples on their CO2 and butane adsorption capacities and adsorption behavior. In the first part of the study, the effects of surface chemistry, oxidation method, Na2CO3 impregnation and calcination temperature on selective CO2 adsorption behavior of activated carbon samples, which had been previously prepared by B. S. Çağlayan, was determined under dynamic conditions. Adsorption experiments were performed with a gravimetric analyzer and gas concentrations were analyzed with a mass spectrometer. Oxygen bearing surface groups of unimpregnated samples were determined via Temperature Programmed Surface Group Decomposition (TPSGD or TPD) deconvolutions. The results revealed that air oxidation increased the amounts of anhydrides and carbonyl/quinones whereas reduced the amounts of lactones and carboxyls. Total surface area and CO2 adsorption capacity increased with air oxidation. HNO3 oxidation had a strong influence on surface groups. Increase in the acidic carboxylic sites and reduction in the BET surface area upon HNO3 treatment, resulted in a decrease in the CO2 adsorption capacity. However, the results revealed that HNO3 oxidization has enhanced Na2CO3 dispersion more than air oxidation. This enhancement was attributed to increase in the carboxylic surface groups as well. It was discovered that Na2CO3 impregnation enhanced both reversible and irreversible CO2 adsorption. Calcination temperature, on the other hand, had no effect on the CO2 adsorption behavior up to 250 °C, however, sample calcined at 300 °C showed more superior adsorption capacity in comparison with other calcined samples. All samples showed selective CO2 adsorption behavior whereas Na2CO3 impregnated samples irreversibly adsorbed H2 and CO to a certain extent as the gases came into contact with the adsorbent. In the second part of the study, the relation between AC characteristics of commercial activated carbons (AC10, AC11 and AC12), which were provided by Ford Otosan A. Ş., and their butane adsorption capacity and characteristics were studied. For this purpose, butane adsorption isotherms were obtained at 40 °C, 70 °C and 100 °C by using a gravimetric analyzer in static mode. Oxygen bearing surface groups and total surface areas of the samples were determined via TPSGD/TPD and BET methods, respectively. Butane adsorption capacity of samples AC10, AC11 and AC12 was determined as 28.29%, 29.56% and 49.67% by weight at 1 bar and 40 °C respectively. Results revealed that there is a strong relationship between surface area and adsorption capacity. In addition, it was found out that lactone, phenol and carbonyl/quinone groups has no significant contribution on the adsorption capacity whereas, carboxyl and anhydride surface groups may have a limited positive contribution on the adsorption capacity. High correlation was obtained upon fitting Langmuir isotherm on the adsorption data showing butane adsorption on AC samples can be represented with Langmuir isotherm. The heat of adsorption was calculated as -13.2 kj/mol, -12.6 kj/mol and -16.5 kj/mol for samples AC10, AC11 and AC12 respectively from modified form of Clasius Clapeyron equation by using Langmuir constants obtained..