Question 39: What options are available for managing blend stream Reid Vapor Pressure (RVP) and pentane content during the summer blend season? Discuss operational changes in existing equipment, simple modifications, and large capital projects.

Each refinery configuration will obviously be very different, so there is never going to be a one-size-fits-all solution for managing gasoline component RVP or dealing with pentane streams. However, there are certainly many common elements that can be explored.

Question 37: What is the panel's experience in operating chlorided isomerization units, which were not designed specifically for benzene saturation, in a benzene saturation mode? How are operational parameters adjusted for the different operation?

This is a good question; because as we blend more ethanol into the gasoline pool, a lot of refineries become octane-long and RVP (Reid Vapor Pressure)-long as well. So, the incentives to isomerize are diminishing as you blend more ethanol. Within Valero, we looked at one of our isomerization units and did a project to convert it into a benzene saturation unit but without capital improvements.

Question 36: What is the panel’s experience with the latest technologies used to control the bromine index (BI) in aromatic streams, other than clay treatment? How many units are operational, and how were these justified?

The most prevalent technologies for bromine index control are clay treating and selective hydrogenation of the olefins. At Axens, we recommend the selective hydrogenation route to control the olefins and trace diolefins that may appear in your aromatic streams. Last year at the NPRA Q&A, there was a similar question about the different reactive mechanisms between clay and selective hydrogenation.

Question 34: Fresh sulfuric acid fed to an alkylation unit can contain niter (nitrosylsulfuric acid) which may lead to excessive corrosion. What is niter; what does it do; can we test for it; and how can we reduce the levels in our fresh acid?

“Niter” is actually a common term referring to the amount of NOx (nitrogen oxide) or nitrates in the sulfuric acid. It is actually generated in the sulfuric acid regeneration process. One of the first steps you go through in acid regeneration is a combustion furnace. In that combustion furnace, you can generate NOx, which is really a function of your peak flame temperature and excess oxygen: the normal NOx contributors.