by Ralph Norton
Refiners have been reforming naphtha to improve its octane or to produce aromatic chemicals since the 1930s. Initially the desired chemical reactions were achieved in Thermal Reformers without the use of catalyst by simply heating the naphtha to about 540°C (1000°F) to “crack” non-aromatics out of the naphtha boiling range. This was effective but required the construction of units that were expensive to build and operate, and that produced low yields of the desired products.
The first catalytic naphtha reforming came into practice at the start of World War II. It used a bed of catalyst to improve the yields by not just cracking non-aromatics out of the naphtha but also by changing some of the non-aromatics into aromatics. The catalyst used was a single base metal oxide on an inert support. The catalyst performance declined quickly as coke deposits formed on the catalyst. After 20 to 40 minutes in operation it was necessary to take the reactor out of service to burn the coke deposits off the catalyst. To achieve a steady operation, 2 or 3 reactors were installed with one in operation at any given time and the others in some stage of purging or coke burning. This type of unit was even more expensive to build and operate than the original Thermal Reformers. However, the demand for aromatics during the war to produce explosives and aviation gasoline was high enough to justify the construction of several of these units.
With the end of the war significantly reducing the demand for explosives and aviation gasoline these first-generation catalytic reformers were shutdown. The technical, if not economical, success of these units did lead to significant research efforts by several companies to develop a more economically practical form of catalytic reforming. These efforts resulted in the startup of the first second-generation catalytic reformer in 1950.
The second-generation naphtha reforming units could operate for between 6 months to a year without needing to regenerate the catalyst. This significant increase of time between regenerations was due to the use of a much more sophisticated catalyst technology of platinum on chloride aluminum oxide. Unlike inert base in most other catalysts, the chloride alumina base does promote reactions that are critical to the success of the reformer. Maintaining the correct balance between the reactions taking place on the metal and on the chloride alumina sites is the key to good yields and long catalyst life.
The design of naphtha reforming units has continued to evolve since the 1950s as economics, catalysts, and needs have changed. The high platinum catalyst of 1950 has evolved to include two or more metals in addition to the platinum, the platinum content has been reduced to extremely low levels, and the nature of the chloride alumina base has changed. All these changes have required changes in the regeneration procedure if the best possible catalyst performance is to be achieved.
The evolution of naphtha reforming catalyst regeneration from 1950 until today
The regeneration procedure initially used for platinum containing reforming catalysts was extremely simple. It consisted of simply purging the reactor system with nitrogen, while circulating the inert gas over the hot catalyst, adding a small amount of air to the gas to burn the coke off the catalyst, and, when the coke was burned away, replacing the inert gas with hydrogen, and restarting the naphtha feed to the unit. This simple regeneration procedure worked, but the catalyst activity, stability, and reformate yield all suffered significant drops with each regeneration. The drops were enough to justify total replacement of the catalyst after only a few regenerations.
It was obvious from the poor results from this simple regeneration procedure that the chemistry and microstructure of platinum containing reforming catalysts were not well understood. Major research efforts and field tests over the next 30 years allowed much better regeneration procedures to be developed.
The key point of the improved regeneration procedure is that much more than simply burning coke off the catalyst is necessary. In addition to burning coke it is necessary to control the chloride content of the base, adjust the crystal size of the metal(s), dry the catalyst, and, while doing these things, not damage the pore structure of the base or cause corrosion in the plant.
With the knowledge that has been developed, it is possible return the catalyst activity, yields, and cycle time to very similar to that of factory fresh catalyst for many cycles. It is now rare for catalyst replacement to be necessary because of inability to regenerate it. Almost all catalyst replacement is due to contamination of the catalyst with lead, arsenic, whole crude oil, or caustic. With good regeneration procedures most catalyst replacements should be due to changing to a new type of catalyst that better fits a refiner’s needs.
What Becht can do for you?
In a time when vendors are reducing the size of their service staffs and deemphasizing the support of older fixed bed reformers, Becht can bring you the knowledge to achieve the best possible regeneration of your unit. Becht experts have experience in the development and commercially implementation of state of the are regeneration procedures. We can assist in any one or all the following ways:
- Review current procedures to ensure the best procedure possible by providing support and expert reasoning for each procedural step.
- Provide training to operators, superintendents, and engineers to refresh and reinforce their knowledge.
- Provide long-term mentoring to members of the workforce who are new to naphtha reforming.
- Be available either on site, by phone, or virtually meeting to assist with decisions and support the site during unexpected events.
- Assist with post a regeneration audit so lessons learned can be captured to make the next regeneration even better.
The bottom line is that we are here to support and train your workforce to achieve the best possible regeneration.
Becht’s 1,500-person team includes subject matter experts across 21 disciplines. Becht’s SMEs bring a wealth of industry knowledge and expertise, most with 30+ years of experience from an owner-operator perspective. We are located around the world, ensuring that assistance and guidance is just a quick phone call away. We can work collaboratively with you and your team to minimize risk, maximize efficiency, and optimize your workforce.
If you are interested in learning more about any of Becht’s expert supports, please visit us at Becht.com.