Effects of temperature on methanol adsorption on functionalized graphite: Saturation of functional groups. (21st September 2018)

• Record Type: Journal Article
• Authors: Dilokekunakul, Waralee; Klomkliang, Nikom; Supasitmongkol, Somsak; Chaemchuen, Somboon; Do, D.D.; Nicholson, D.
• Is Part Of: Chemical engineering science. Volume 187(2018)
• Page Start: 16
• Page End: 26
• Publication Date: 2018-09-21
• Subjects: Methanol adsorption -- Carbon -- Isosteric heat -- Functional group -- Molecular simulation; Chemical engineering -- Periodicals; Génie chimique -- Périodiques; Chemical engineering; Periodicals; Electronic journals; 660
• DOI: 10.1016/j.ces.2018.04.063
• Languages: English
• ISSNs: 0009-2509

Abstract

Graphical abstract: Highlights: Adsorption of methanol on GTCB with two grafted hydroxyl groups was studied. Contribution heats, local density and angular distributions were analyzed. A minimum in the isosteric heat vs. loading is observed in experiment and simulation. The minimum heat is attributed to the saturation of functional groups. The minimum heat (the cusp) is more pronounced at higher temperatures. Abstract: Grand Canonical Monte Carlo simulation of methanol adsorption on a graphite model with two hydroxyl groups grafted on the surface has been carried out to investigate the effects of temperature in the range of 278–360 K. The spacing between the OH groups was chosen so that two hydrogen bonds could be formed with the first methanol molecule. In the Henry law region, the isosteric heat at zero loading is greater than the condensation heat. When the loading is increased, the isosteric heat at low temperatures decreases slightly and exhibits a shoulder, which is associated with the formation of a cluster of methanol molecules around one OH group. On further increase in loading, the adsorbate–adsorbate interactions decrease because methanol begins to adsorb on the other OH group, resulting in a sharp decrease in the isosteric heat to a minimum, at which point both OH groups are covered with methanol molecules. At higher temperatures the isosteric heat at zero loading decreases but remains higher than the condensation heat. The shoulder heat is progressively diminished with temperature because methanol molecules are distributed over the two OH groups, due to the entropic effects. Interestingly, the minimum heat still occurs when the functional groups are covered and is even more pronounced at high temperatures.