Distillation/hydrotreatment

Fig. 1. Distillation—hydrotreat process, where CW = cooling water.

HDH (2) [Hydrocracking-distillation-hydrotreatment] A process for hydiotreating and hydroconverting petroleum residues. 

Hydrotreat reform hydrodealkylate. b Recycle hydrocrack hydrotreat reform hydrodealkylate. c Recycle hydrocrack gas oil recycle hydrocrack mid-distillate hydrotreat re- ... 

The above-mentioned individual improvements described cannot be simply combined, either additively or multiplicatively. As mentioned earlier, each existing distillate hydrotreater is unique in its combination of design, catalyst, feedstock, and operating conditions. While the improvements described above are probably indicative of improvements, which can be made in many cases, it is not likely that all of the improvements mentioned are applicable to any one unit the degree of improvement at one refinery could either be greater than, or less than the benefits that are indicated for another refinery. 

Figure. 7. Activation of presulfided catalyst in industrial start-up for Distillate Hydrotreater in gas-liquid mixed phase with gas recycle.

Recycle hydrocrack gas oil recycle hydrocrack mid-distillate hydrotreat reform hydrodealkylate. 

Distillation/Hydrotreatment This technology is the most recent development, as in the KTI and Mohawk processes. After pre-treatment and thin-film distillation, the base oil fraction is hydrotreated under moderate conditions. A final distillation step gives a range of base oil streams of different viscosities with process yields of up to 90-95%. 

Base oils produced by the distillation/hydrotreatment processes are of superior quality compared to the older, previously described, used lubricant recycling technologies. They can certainly be of Gp. I quality, in some cases Gp. I+, with some re-refining processors now claiming Gp. II quality standard with improved process technologies. 

The distillation/hydrotreatment process is comparatively sophisticated, capital intensive and requires skilled operation, although operating costs are not exceptionally high. It appears to be the preferred process for the re-refining of used lubricants to produce high-quality base oils which can compete with virgin base oils at the Gp. I/II level. 

Other refinery applications in which PRISM separators have been successfully used are naphtha hydrotreaters, middle distillate hydrotreaters, cat crackers, and toluene hydrodealkylation.56,57... 

Many hydrotreaters are stay-in-business investments, so it s diffieult to quantify their upgrade value, which is the value of products minus costs -labor, materials (liquid feed, hydrogen, catalysts and chemicals), utilities, maintenance, and investment amortization. In some plants, the refinery planning LP assigns equal value to treated and imtreated naphtha, and even to treated and untreated distillates. This reflects the underlying assumption that the increase in value across a hydrotreater is equal to the cost of running the unit, i.e., the upgrade value is zero. In other LPs, the NHT that pretreats catalytic reformer feed is lumped in with the reformer. Certainly, if a key naphtha or distillate hydrotreater shuts down, ihe refinery may have to run at reduced rate, but that can be said of most units. 

The improvement in vapor-liquid contact can enhance the performance of distillate hydrotreaters. As an example, in testing of an improved vapor-liquid distributor in commercial use, Haldor-Topsoe and Phillips Petroleum found that the new Topsoe Dense Pattern Flexible Distribution Tray (installed in 1996 to replace a chimney type distributor installed in 1995 in a refiney) allowed a 30% higher sulfur feed to be processed at 25°C lower temperatures, while reducing the sulfur content of the product from 500 to 350 ppmw . Albemarle estimates that an improved vapor-liquid distributor can reduce the temperature necessary to meet a 50 ppmw sulfur level by 10 °C, which in turn would increase catalyst life and allow an increase in cycle length from 10 to 18 months. Based on the above data from Haldor-Topsoe, if temperature were maintained, the final sulfur level could be reduced by 50%. Maintaining temperature should have allowed an additional reduction in sulfur of more than two-thirds. Thus, ensuring adequate vapor-liquid contact can have a major impact on final sulfur levels. 

Feedstocks for distillate hydrotreaters and/or hydro-crackers need not necessarily be metal free since these same metals are often found in hydrogenation catalysts. It is imperative, however, that they be as free as possible of carbon and asphaltic materials. If they are not, coking of the catalyst will occur more rapidly, and more frequent regeneration will be required. Product cleanliness is far more important here than in the case of catalytic cracking feedstocks. 

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