ИСТИНА

Recently, expanded graphite was considered as an adsorbent for heavy-oil sorption [1,2] and was shown to be a promising one. Herein we report the correlation between expanded graphite chemical nature, porous structure and its sorption activity for water and hydrocarbons. Expanded graphite of three types was studied. The first one was prepared by exfoliation of graphite intercalation compound with nitric acid at a temperature of 900 oC (EG-1). The others were obtained by exfoliation of the product synthesized by graphite electrochemical intercalation in 60% nitric acid. The exfoliation temperatures were 350 (EG-2) and 900 (EG-3) oC. Crystalline size was determined by Scherer equation, the relative content of carbon forms was found using Raman spectrometry. Low-temperature nitrogen adsorption and reference porosimetry were used to describe porous structure of carbon materials. Dynamic contact angel technique was applied to study surface energy of expanded graphite and sorption velocity. Sorption properties were found to be depended on the way of expanded graphite preparation. The maximum sorption capacity of 80 g/g for octane and 120 g/g for motor oil was observed for chemically prepared sample EG-1 whereas the maximum sorption capacity for water and naphthalene was demonstrated by electrochemically prepared sample EG-2. The selective sorption activity toward hydrocarbons from the mixture of hydrocarbons and water was shown for all samples of expanded graphite. The total, dispersive and polar components of free surface energy of expanded graphite were measured. The polarity of the samples diminishes in a row of EG-2 (σP = 26 mN/m) >> EG-3 (σP = 3.5 mN/m) > EG 1 (σP = 0.4 mN/m). Sorption velocity for expanded graphite compressed into the pellets of different densities was measured perpendicular and parallel to compression axis. The correlation between all the measured parameters was estimated and a sorption model was proposed.