Full Potential Conversion of Vacuum Resids

Present vacuum resid conversion processes, either coking or hydroconversion, are far from achieving their maximum conversion. With the remaining petroleum resources, on average, having a greater fraction of the vacuum resid fraction, it is imperative that new resid conversion processes or schemes be developed to approach their full potential. Coking processes are limited by degrading the higher quality fractions of the vacuum resid and by secondary cracking of volatile liquid products to form hydrocarbon gases. Therefore, coking processes can be improved by separating the higher quality fraction of the vacuum resid, such as by deasphalting, prior to coking and by doing the coking in a reactor with a short vapor phase residence time but a long resid/coke residence time. In this way the laboratory coking of Arabian Heavy vacuum resid increased the yield of nearly equal quality liquid product to 76 wt% as compared with a commercial yield of 61 wt% while reducing the coke yield to less than Conradson carbon residue.

Ebullating bed hydroconversion processes, H-Oil and LC-Fining, are limited by the formation of asphaltene sediments in the heavy oil product. This limitation can be overcome by reducing the conversion per pass and deasphalting the heavy product into deasphalted oil, resin, and asphalt fractions. The deasphalted oil is added to the vacuum gas oil product and the asphalt is a heavy, aromatic byproduct. Meanwhile, the resins are recycled for further conversion.

Once dispersed catalyst hydroconversion processes are designed to overcome their compatibility limitation by more efficiently stripping out the volatile liquid product, they can produce greater than 100 vol% liquid product. However, the economic optimum conversion is more likely at lower conversion but greatly depends on the local economics.