Q&A

(2011) Question 9: What has been your experience with antimony and phosphorous poisoning on hydrotreating catalyst performance? What is the maximum level?

The effects of antimony in oil on hydrotreating catalyst have not been directly studied, but we can infer the likely impacts of antimony from a variety of information sources and past experiences.

(2011) Question 10: When replacing a noble metal catalyst with a base metal catalyst in a two-stage hydrocracking unit configuration, how can you be certain that under a low sulfur, low hydrogen sulfide environment, the second stage catalyst will remain sulfided?

A base metal sulfide catalyst will always have less, or hydrogenation compared to a noble metal catalyst. However, in certain situations where deep hydrogenation is not needed, the base metal sulfide catalyst can provide adequate hydrogenation activity. Operation with a base metal catalyst will be between 10 to 20o F higher than a noble metal catalyst, and this will shift the yield towards more thermally cracked lighter products.

(2011) Question 11: What is the minimum hydrogen sulfide required in the recycle gas for units with low sulfur feed? Do you inject sulfur compounds to maintain a minimum concentration?

It appears that in these processes the catalyst slowly loses its HDS activity. This is due to the transformation of the Molybdenum present as activator, and Nickel/Cobalt present as promoters, from their active sulfide form to the inactive metal state.

(2011) Question 12: Is there any harm adding cracked stocks too quickly after break-in following catalyst activation? What is a typical introduction rate?

On freshly activated catalysts, the surface is relatively clean (free of coke) and therefore is unusually active. This is sometimes referred to as hyperactivity. In order to maximize catalyst stability for good cycle length, it is important that the rate of coke lay down on freshly sulfided catalyst is gradually controlled. Upon completion of metals sulfiding, catalyst hyperactivity exists, but is short lived as feed processing lays initial coke on catalyst. Processing cracked stocks that contain more reactive molecules and coke precursors too early over the hyperactive catalyst can result in operability issues through cracking while accelerating the initial coke lay down on catalyst.

(2011) Question 13: What are your experiences with alternate procedures or additives to speed up the time to hydrocarbon-free a hydrotreater during cool down? What are potential downsides? Qualitatively, did the time savings justify the expense?

We have used a terpene-based product to help free hydrotreater reactor circuits of hydrocarbon in preparation for catalyst change-out. The product was effective for achieving a low level of combustibles in the reactor and in all vessels of the reactor circuit. However, in one instance, the test for entry indicated high benzene levels, and further nitrogen purging was required.

(2011) Question 14: Have you successfully dumped, screened and reloaded spent hydrotreating or hydrocracking catalyst without regeneration during a turnaround? Can you share any best practices during this operation to avoid problems on restart?

Providers of onsite screening services are typically limited in available equipment compared to offsite specialized companies. It is important to have adequate equipment to determine the particle size distribution of the screened catalyst.

(2011) Question 15: In treating kerosene, what factors play into the decision to use hydrotreating versus sweetening processes such as caustic treating?

Hydrotreating, by contrast, affects several key properties of the kerosene including smoke point, aromatic, sulfur, and nitrogen content and other properties such as oxidation stability.

(2011) Question 16: What LCO 95% distillation point do you target for optimizing ULSD production? Do you see a significant catalyst life penalty with an increased LCO cut point?

The purpose of adding more LCO is to improve the refinery’s financial performance by upgrading low value LCO to ULSD products.

(2011) Question 17: What sets the volume gain in ULSD units? How much does lowering the space velocity increase the volume gain? How much volume gain can be expected for each feed component?

Volume gain requires hydrogen consumption. Aromatic saturation reactions consume the most hydrogen, followed by olefin saturation. For same feed qualities and same LHSV, the units that make higher cetane product will have higher volume gain due to more aromatic saturation.

(2011) Question 18: What considerations are being given to include mild hydrocracking in your high pressure ULSD unit?

Due to the increasing global demand for diesel, the ability to reduce product density (increase volume gain) and blend a significant amount of heavy diesel and/or light vacuum gasoil in the ultra-low sulfur diesel pool represents a large economic advantage. These economic gains could potentially include margin increases of tens of millions of dollars per year for a refinery.

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