Measurement of Asphaltenes Using Optical Spectroscopy on a Microfluidic Platform

We present a microfluidic apparatus and method for the measurement of asphaltene content in crude-oil samples. The measurement is based on an optical absorption technique, where it was established that asphaltene coloration correlated linearly with asphaltene weight content. The initial absorbance of the oil is measured, and asphaltenes are removed from the oil by the addition of n-alkane, leading to flocculation and subsequent filtration. The absorbance of the deasphalted oil (maltenes) is then measured, and the initial asphaltene content is revealed by the change in absorbance. The asphaltene optical densities correlated linearly with conventional weight measurement results (e.g., ASTM D6560) for 38 crude-oil samples from around the world. Sample measurement repeatability was shown to be within 2% over several months. Other aspects influencing performance of the system were evaluated, including plug dispersion, flocculation kinetics, membrane degradation, and channel clogging. The microfluidic approach described here permits asphaltene content measurement in less than 30 min as opposed to days required with traditional gravimetric techniques. This many-fold reduction in measurement time will enable more frequent characterization of crude oil samples.