Figure 5.8 places the deasphalting process in a refinery flow scheme as an intermediate process between vacuum distillation and dewaxing processes, for producing the refinery output streams as asphalt deasphalted oil (DAO), which can be directed to another separation process, dewaxing, to produce lubricating oil base stock and wax,or can be sent to conversion units such as hydrocracking to produce light and middle distillate fuels. It is important to note that the deasphalting process is an upgrading process to transform VDR into marketable products, and/or convert it to distillate fuels that command high demands.
The two objectives of the deasphalting process are:
- Produce asphalt - as final product.
- Remove asphaltenes to prevent coke, or metal buildup on catalyst in further processing of DAO.
Depending on the properties of the VDR and prevailing markets, the emphasis could be placed on one of these objectives. Remember that aromatic asphaltic crudes are more expensive to convert into distillate fuels. Such crudes could be processed readily into making high yields of asphalt and serve the asphalt market. With lighter crudes, the principal focus could be on removing the asphaltenes from VDR so that DAO produced can be used in conversion processes with a lower extent of problems caused by asphaltenes such as coke buildup, or metals buildup on catalysts in, for example, hydrotreating or hydrocracking reactions.