Petroleum Size Exclusion Chromatography. Mechanisms Explaining the NMP front peak

Size Exclusion Chromatography (SEC) is abundantly used in analysis and fractionation of petroleum fractions despite numerous challenges with the techniques. Changing the eluent type amongst classical solvents in SEC normally leads to smaller changes in the elution profile of asphaltenes. Changing the eluent to N-methyl Pyrrolidone (NMP) however leads to very different chromatographic profiles. Especially the occurrence of a very early eluting peak has been severely debated in the literature without reaching a clear conclusion. NMP has particular solvent properties which target the solubility of aromatic molecules and therefore asphaltenes are only partially soluble. In order to understand the occurrence of the front peak in NMP a systematic study is undertaken by changing eluent solvents and temperature. We discuss the different mechanisms involved in SEC such as phase behavior, gel swelling, pore size, molecular size and unwanted adsorption that are all involved in the chromatographic process. To investi...