Refiners discuss HF alkylation process and issues. (heavy fuel; 1991 National Petroleum Refiners Association question and answer session) (Panel Discussion)

Safety and oxygenate, OPerations made HF alkylation g hot topic of discussion at the most recent National Petroleum Refiners Association annual question and answer session on refining and petrochemical technology.

The panel of experts responded to a variety of questions regarding the mechanical, process, and safety aspects of the HF alkylation process. Among the issues discussed were mitigation techniques, removal of Oxygenates from alkylation unit feed, and amylene alkylation.

The NPRA Q&A Session was held Oct. 16-18, 1991, in Denver. For further details on this important meeting and its format, see OGJ, Mar. 16, p. 37.

Amylene alkylation

Are people alkylating C[.sub.5] olefins in HF units? What levels are being alkylateld? What are the results regarding octane, Rvp, end point, and acid soluble oil (ASO) yield?

Grant: our operating experience indicates that C[.sub.5] olefins at levels above 5% of total unit charge, treated with C[.sub.3] and C[.sub.4] olefins in conventional amine/caustic systems, will cause excessive acid soluble oil production and add consumption. The increased diolefin content of the amylene feed increases acid losses through increased ASO make.

I would like to mention a few references on this topic: the 1987 NPRA Q&A Session transcript on pages 109 and 110; and also two papers presented at the 1991 NPRA Annual meeting; AM-91-16, "Integrated Olefin Processing," by Lawrence Lew, Donald Makovec, and Martyn Pfile of Phillips Petroleum Co.; and AM-91-50, "Ultimate C[.sub.4]/C[.sub.5] Olefin Processing Scheme for Maximizing Reformulated Gasoline Production," by Pam Keefer and Ken Masters of Stratco Inc. and Jean-Luc Nocca and Jean Cosyns of Institut Francais du Petrole.

Golden: Two of our U.S. refineries alkylate C[.sub.5]S- Normally about half or less of the available C[.sub.5]S are alkylated. Driving additional material off of the fluid catalytic cracked (FCC) gasoline results in a marked increase in ASO production so that handling of it becomes difficult. The increased ASO and polymer production are due to the increased levels of diolefins and C[.sub.6] + material. By alkylating C[.sub.5]S, the Rvp of FCC gasoline is reduced, bringing about an overall reduction in pool Rvp. However, I would second Mr. Scott's earlier comment that the reduction may not be as dramatic as you would suspect.

If one third to one half of the available C[.sub.5]s are alkylated, the end point of the product alkylate win remain within specification limits. Future regulation of gasoline 90% distillation point, however, could change this. Since the octane of C[.sub.5] alkylate is not radically different from mixed C[.sub.5]s in our experience, the octane impact on the overall pool is relatively small.

With regard to increasing amylene alkylation, some loss of flexibility in blending premium gasoline may be suffered since the total alkylate octane will drop as more C[.sub.5]s are added to alkylation feed.

Fischer: Our experience confirms the previous comments. We are alkylating some C[.sub.5] olefins in one of our HF alkylation units in the order of about 5% of feed. We have not quantified the results fully yet, but we have seen a drop in octane and an increase in ASO yield.

McClung: To my knowledge, no one is actually processing pentylenes alone in an alkylation unit. I know Of one other refiner besides the ones I have already mentioned who processes C[.sub.5] olefins in conjunction with C[.sub.4]s, but I have no results for that.

Pazmanyi: We do not process C[.sub.5] olefins in our HF alkylation plant, but I have some background information from UOP.

They told me there have been several applications over the years, and there has certainly been a lot of study and preparation under way for the future C[.sub.5] amylene alkylation.

Regarding the performance, around 90 to 92 road octane can be expected from C[.sub.5], amylene alkylate with 2 to 5 psi Rvp, depending on conditions, and whether it is all or only part-for example, tertiary amyl methyl ether (TAME) raffinate-of C[.sub.5] amylenes.

Regarding how much polymer would be made, they expect that the regeneration requirement would be about 1.5 to 2 times more than for C[.sub.4] olefins.

Of course, the impact Will be lessened by being only a portion of the total unit feed.

Robert E. Davis (R.E. Davis Chemical Corp.): I would like to inject one thing for the people who are alkylating C[.sub.5], olefins in HF units. Please monitor the fluoride content of your finished product.

I think you are in for a big surprise.

Oxygenate removal

Has anyone replaced all or part of their feed drying beds with materials to remove oxygenates from MTBE operations? If so, is regeneration by any stream other than butane being considered?

Knepper. We do not have an MTBE operation; however, we have oxygenates in our Butamer feed. The oxygenates originate with the saturate feed coming into the alkylation unit. We are using Alcoa Selexsorb CD alumina in a single Butamer guard dryer that is in series with the feed dryers to keep oxygenates out of the Butamer reactors. The regeneration is with butane.

We have not quantified the performance of this material in removing oxygenates, however, we lose Butamer activity every time this guard dryer is regenerated. We will be considering additional Selexsorb in the saturate feed dryers. However, when we do that, the regenerate will have to go to storage instead of back to the olefin feed.

Williams: Southwestern Refining Co. …