RHODES (Marathon Petroleum Company)

To increase cycle length on an NHT hydrotreater, the refinery needs to understand the contaminants that the reactor must handle and optimize the bed loading to maximize cycle length, as well as have the ability to handle the contaminant.

Silicon (Si) can be a big concern on NHT reactor cycle length. For the units that process coker naphtha, modification of the coker operation to minimize the injection of Si-based antifoams is key to improving cycle length. Si-based antifoams are used in the coker where the silicon will breakdown and end up in the naphtha fraction leaving the unit. Silicon can also be a factor in processing crude from various locations where Si-based antifoams are used. Understanding the amount of silicon, the bed has captured during a cycle will allow the refinery to minimize the amount of silicon traps that will be installed and maximize the use of active catalyst.

Arsenic is a strong poison for all hydrotreating catalysts. If the spent catalyst analysis shows high level of arsenic in the active catalyst bed, arsenic trap catalyst can be added into the catalyst bed to help capture arsenic and minimize the amount of arsenic that penetrates to the main bed of active catalyst. Using post-audits of the spent catalyst will help the engineers design the catalyst bed properly to protect the catalyst.

Maximizing the use of catalyst that has high surface area can increase cycle length for catalyst beds dealing with poisons. Active or regenerated catalyst typically has low surface area and can be very sensitive to poisoning, especially for Si. Regenerated catalyst typically has less surface area than the new fresh catalyst.

Finally, coking can be a concern on units that are operating at low pressure or at low hydrogen-to-hydrocarbon ratios, especially for units treating cracked naphtha or outside feeds. Therefore, maximizing the hydrogen-to-hydrocarbon ratio will help minimize coking issue.

STEVEN PHILOON (Honeywell UOP)

As a catalyst development, manufacturing, and sales business, Honeywell UOP continues to develop higher performance naphtha hydrotreating catalysts to handle our customers’ interest to run higher feed rates and utilize more difficult feeds. Moreover, we have developed next-generation catalysts that are more tolerant to contaminants in the feed, such as arsenic and silicon, along with the development of improved metals trap products to enable us to provide the most effective overall catalyst system.

For a specific unit, there is a not-always-obvious optimization with regard to the loading. There is a fixed volume that can be filled with hydrotreating catalyst, silicon or arsenic trap material, or grading/filtering material. Depending upon the operating factors that bring about the end of the cycle for a unit, the loading can be adjusted to maximize the cycle given the impact of those constraints.

RALPH WAGNER (Dorf Ketal Chemicals LLC)

Feedstock source and chemistry can have significant impact on hydrotreater catalyst performance. Phosphorous, mercury, and arsenic can reduce catalysts activity. Corrosion products, such as FeS (iron sulfide), can foul the catalyst in straight-run feedstocks. In cracked feedstocks, especially coker naphtha, unsaturated compounds may form polymers that can coke up on catalysts. Residual silica from silicone antifoam used in the delayed coker can also be detrimental. Strategies to sustain or increase cycle length targets include:

1.Implementation of a corrosion inhibition program –either by selection of materials of construction or chemical treatment or a combination of both –in the unit upstream can significantly reduce inorganic fouling. When using HTCI (high temperature corrosion inhibition) to process high TAN (total acid number) crudes, Dorf Ketal TANSCIENT™ can reduce phosphorous added to the crude by up to 80%.

2.Proactively determine metal content in the crude and develop a crude blending strategy to minimize the impact of metals. Dorf Ketal’s non-acid reactive adjunct desalter chemistry can supplement emulsion breakers fed to the desalter and remove iron and calcium to increase flexibility in the selection of crudes.

3.Implementation of a chemical treatment program containing antifoulant chemistry –which may include antioxidants, organic and/or inorganic (FeS) dispersants –has been proven successful in increasing the unit run-length.