PTQ Q3 2022 Issue

cannot be changed, so the only remaining handles are tem- perature and catalyst formulation, which depend on one another. HPNA Trim technology Depending on the severity of the feedstock and hydro- cracker unit design and operation, HPNA management by optimised catalyst selection may fall short of meeting the unit conversion target throughout the cycle. For such cases, Topsoe has developed a so-called HPNA Trim technology, which cost-effectively manages HPNAs in full conversion hydrocrackers. 9 This simple process takes advantage of the heavy HPNA compounds’ extremely high boiling points. It separates hydrocracker UCO into a light and heavy fraction by distill- ing the HPNAs concentrated in the heavy liquid product. This way, it effectively reduces the required UCO bleed rate to an absolute minimum, enables the unit to operate close to true full conversion (>99%), and maximises the yield of high-value products. The process has very few pieces of equipment. This allows for a low-cost modular approach, making it suitable for easy retro t to existing hydrocracking units. Economic analyses show a very high return on investment with a typical simple payback time of half a year. By lowering the steady-state HPNA level in hydrocracker recycle oil, the proprietary HPNA Trim technology can reduce catalyst deactivation rates and extend cycle length. The technol- ogy also is being used in the design of grassroots hydro- crackers for lower pressure with lower capital investment requirements. Topsoe has a wide portfolio of grading and pretreat cat- alysts in VGO service. An optimised catalyst load was designed for the HCU considering the varying and severe nature of the feedstock. The first bed of grading catalysts consists of six catalysts having staged size, pore structure, and activity grading. This strategy of layering catalysts has shown the follow- ing benefits: Catalyst selection Grading and pretreat  It manages staged hydrogenation of highly reactive unsaturated species in the coker gas oil, mitigating hydro- gen starvation, and gum formation.  Pore structure and pore sizes in catalysts are reduced progressively through the bed. This was done to trap con- taminants of varying size distribution and mitigate pressure drop issues.  Different metal contaminants have different interactions with catalyst support and metals. For example, nickel and vanadium are found in large porphyrin structures, and the catalyst needs a pore structure wide enough to trap these molecules. Arsenic, on the other hand, is picked up by nickel, forming nickel arsenide. Different grading catalysts designed for these contaminants, strategically placed in layers, efficiently protect the bulk pretreat and hydrocrack - ing catalysts downstream. Topsoe research on pretreat catalysts during the last

Staged grading activity. Darker shade indicates higher, lighter shade indicates lower

Particulate HDM

HDS

HDN

trapping capacity

activity activity activity

Grading cat 1 tablets Grading cat 2 rings Grading cat 3 rings

Grading cat 4 quadralobes Grading cat 5 quadralobes Grading cat 6 trilobes

Table 3

forming large HPNA is the increase in entropy due to hydrogen production. Much of the prior discussion relates to reactions at equi- librium. Indeed, as shown in Figure 6, saturated and partly saturated polyring compounds dehydrogenate at high temperatures due to equilibrium. But if the equilibrium is broken by hydrocracking, especially ring opening, HPNA growth is diminished. To summarise, the key points about HPNA formation include the following: • Saturation is favoured thermodynamically by high pres- sure and low temperature •Condensation to form larger and larger HPNAs is favoured by low pressure and high temperature • At constant pressure, the removal of HPNA precursors with hydrocracking is favoured by lower temperatures. For this refinery, controlling HPNA production required careful consideration. As discussed, HPNA precursors may undergo the following reactions depending on pressure, temperature, and catalyst formulation: saturation, hydro- cracking, or condensation to form larger HPNAs. Pressure

Grading catalysts

1st gen, HyBRIM catalyst

Premium HyBRIM catalyst

Figure 9 Catalyst in pretreatment reactor

PTQ Q3 2022