Akademik Veri Yönetim Sistemi
ENERGY & FUELS, cilt.19, sa.1, ss.187-199, 2005 (SCI-Expanded)
Two related propositions addressing the interpretation of size-exclusion chromatograms of heavy hydrocarbon liquids have been examined. First. that peaks observed at, the exclusion (short, retention time) limits of size exclusion chromatography (SEC) columns. when using 1-methyl-2-pyrrolidinone (NMP) as eluent, are due to aggregation brought about by sample polarity. Second, that the addition of salts such as LiBr to the NMP eluent dissipates ionic binding forces and causes the disaggregation of polar clusters. The resulting shift to longer elution times (smaller masses) is then interpreted as representing those of the disaggregated sample molecules. However, in earlier work, we observed that the addition of this salt shifted chromatograms to retention times later than the permeation limits of the analytical columns. The salt appeared to have increased surface interactions between the sample and column packing. Thus, the addition of the salt directly to the SEC eluent did not allow distinguishing, between any possible disaggregation effect and its adverse effect on the size mechanism. In this work, we have attempted to separate the two effects. The samples were fractionated by planar chromatographv (PC) using solvents with dissolved salts: LiBr or tetrabutylammonium acetate (TBAA). Any presumed disaggregation would be expected to take place during the planar chromatographic separation. The fractions were then recovered from the plates and characterized by SEC. Three coal-derived liquids were investigated. The results indicated that the salty solvents were able to mobilize more large-mass material than the solvent alone because the increased polarity of the Salty solvent was better able to displace larger molecules from the polar sites of the silica. SEC showed these fractions to be of larger apparent MM than those recovered in PC using untreated solvents. No evidence of disaggregation was found due to the use of salts.