Contrasting Perspective on Asphaltene Molecular Weight. This Comment vs the Overview of A. A. Herod, K. D. Bartle, and R. Kandiyoti

Abstract

Asphaltene molecular weight (Asphaltenes, Heavy Oils and Petroleomics; Springer: New York, 2007) continues to be the subject of a longstanding debate in the literature. A paper (Energy Fuels 2007, 21, 2176−2203) recently published (referred to as HBK) claims that asphaltene molecular weights are bimodal with one component in the roughly megadalton range and a second component in the roughly 5 kDa range. These claims are in sharp contrast to results published from a variety of measurements with the overall conclusions that asphaltene molecular weights are monomodal with a most probable 750 Da (±200) with a fwhm 500–1000 Da. In this report, we provide a summary of the four molecular diffusion techniques and seven mass spectral techniques from many groups around the world that are all in accord with the 750 Da most probable mass. Moreover, here we discuss why HBK reported anomalously large asphaltene molecular weights along with the unique claim of a bimodal distribution. In particular, the size exclusion ch...