A number of environmental regulations coming into force in the next few years will compel refiners to rethink their operations and future capital investments. Refiners will increasingly rely on new catalyst formulations and technologies to comply with these regulations (see related special report beginning on p. 48).
In the US, refiners are concerned with:
- Gasoline sulfur, which will have to average 30 ppm by 2005, vs. a current level of around 350 ppm.
- Diesel sulfur levels, which have to be lowered to 15 ppm by 2006.
- A possible phase-out of methyl tertiary butyl ether and an ethanol mandate.
- Driveability index.
- Diesel cetane levels.
- Mobile-source air toxics.
Outside the US (OUS), gasoline sulfur is not as important, unless the refiners are planning to export gasoline to the US. OUS economies are much more diesel-based than that of the US, which means that diesel sulfur specs are much more of a concern to those refiners. European refiners, however, have to meet stricter gasoline standards than their US counterparts; some refiners will produce 10 ppm sulfur gasoline by 2005.
The future specifications will most likely require a combination of catalyst technology and new process construction. Many refiners, however, are currently reluctant to spend significant amounts of capital on new units and are therefore looking to catalysts to help meet product specifications.
FCC unit
The FCC unit is the "heart" of most refineries and is one of the most operationally flexible units. Reformate and alkylate are virtually sulfur-free, which means that the vast majority of gasoline sulfur comes from the FCCU. It logically follows that refiners are concentrating their efforts on the FCCU to reduce product sulfur levels.
The FCCU, the primary upgrading unit in many refineries, will also help refiners make up lost octane if and when MTBE is phased out of US gasoline.
At the recent National Petrochemical & Refiners Association (NPRA) FCC seminar in Houston, the aforementioned trends as well as possible solutions were covered at a panel discussion, "The FCCU's role in meeting clean fuels objectives."
Gasoline
Refiners have a number of FCC options to deal with gasoline issues:
- Adjust operating conditions.
- Select a different feedstock.
- Use a new catalyst formulation.
- Use sulfur reduction additives.
According to one of the NPRA panelists, clean fuels from the FCCU in- volve more than just sulfur; refiners' strategies must include yield, octane, Reid vapor pressure, composition, and distillation (driveability index). All the major FCC catalyst manufacturers produce additives that help lower gasoline sulfur levels.
According to Joe McLean, product manager for refining, Engelhard Corp., using these additives can have a dilutive effect on the FCC catalyst-meaning that extra catalyst must be added along with the sulfur-reducing additive to maintain unit activity. A better solution for many refiners is to use new catalyst formulations that can reduce sulfur by as much as 50% while maintaining yield and octane.
A phase-out of MTBE will create an octane "hole." MTBE represents 11% of the US gasoline pool; an equivalent amount of octane from ethanol represents about 6% of the gasoline pool. Refiners can make up the loss in volume by using new FCC catalysts to increase yield while maintaining octane.
LCO dilemma
Refiners can also reduce gasoline sulfur by adjusting the distillation cuts in the FCC main fractionator to send more of the heavy naphtha to the light cycle oil (LCO) stream. According to McLean, the final 10% of the full-range gasoline contains 35-40% of total gasoline sulfur due to the presence of benzothiophene.
While this does lower the gasoline sulfur, it results in a gasoline yield loss and more net sulfur in the LCO. This is only a short-term solution; refiners will have to find a more permanent solution by the time the 15 ppm diesel sulfur specification transpires.
In gasoline-based economies such as the US's, refiners will try to crack the LCO as deeply as possible. Refiners in more diesel-based economies will want to operate in such a way as to increase LCO yield, but at the same time, they will have to deal with more stringent product specifications.
In either event, FCC pretreating or post-treating will definitely be a part of refiners' clean fuels strategies, a scenario that will likely force refiners to spend large amounts of capital and make some difficult decisions.
