The experimental study of effect of microwave heating time on the heavy oil properties: Prospects for heavy oil upgrading

A heavy crude oil sample from an oil field in southwest Iran was placed in a Fischer assay and heated by microwave for two-minute time steps until 14 min total heating time had elapsed. Unlike conventional heating technique (CHT), which caused light carbonic components to escape and raised C20+ components in oil samples, the value of light carbonic components increased under microwave heating technique (MHT) up to 6 min. These materials cannot escape the oil sample in MHT because the cracked components approach a superheated state, and in this study a large portion of them remained at 6 min. Moreover, in contrast to the CHT results, the C1-C20 components increased to 13.5 wt% in the analysis of cracked gases during MHT. In MHT, light components increased with heating time, and C7+ components fell. This is indicative of light components escaping after 6 min. Some components escaped as condensate. In CHT, the escape of only small amounts of condensates was observed at 12 and 14 min, while under MHT, this phenomenon started at 8 min and contained larger amounts. This phenomenon is due to secondary cracking in oil, which is created by an abrupt increase in the temperature of some components that have more capacity to absorb microwaves. The sulfur content of heavy oil in MHT tended to decrease over time, approaching 34 wt% at 14 min; in contrast, in CHT it remained constant. Sulfur was removed from the oil sample as H2S and SO2, predominantly in a gas state, but also as condensate, in increasing amounts over time. Sulfur removal from the heavy crude oil sample is highly important in the upgrading process because of its high coefficient of microwave absorption. H2S is produced from the start of MHT, but SO2 is observed only after 6 min, and then only in the produced gas. Saturation, Aromatic, Resin and Asphaltene (SARA) components analysis showed changes in the resin and asphaltene components. The amount of asphaltene components began to decline starting early in the heating process, and approached its lowest amount at 4 min (3.21 wt%). Reduction of resin components in MHT began at 8 min and reached 55% at 14 min. Asphaltenes have a high capability to absorb microwaves due to having SNO (Sulfur, Nitrogen and Oxygen) components that create hot zones in heavy oil; these hot zones enhance cracking and upgrading. Scanning electron microscopy images of asphaltene particles showed that microwaves caused some changes in the structure of these particles. Energy-dispersive spectroscopy analysis of these particles showed that SNO components under MHT declined over heating time. The results also suggest that after sulfur, nitrogen and oxygen have the highest potential to absorb microwaves.