PTQ Q2 2025 Issue

150

5.5

VI - Old cycle VI - New cycle

4.5

120

3.5

200

400

600

800

1000

1200

Visc @ 40˚C, cSt

Days of operation

Old cycle New cycle

VI=115

VI=125

VI=135

base oil production, which is why UCO from the hydrocracker (Figure 1) is injected before the furfural extraction unit when the base oil plant operates in light and heavy neutral mode. Hydrocracker process configuration The hydrocracking unit converts VGO into middle distillate products (diesel fuel, jet fuel, and kerosene), naphtha, and LPG while simultaneously performing treating, hydrogenation, and cracking reactions. Hydrocracking is carried out at elevated temperatures and pressures in a hydrogen-rich atmosphere. The study was conducted on the refinery’s hydrocracking unit with a single-stage reactor plus recycle system. The recycle line from the fractionator bottom is normally not in operation. Consequently, UCO is not directed back to feed inlet or a sec- ondary cracking reactor for further processing. Performance comparison Topsoe has been supplying catalyst systems for the hydroc- racker for some of the cycles over the last decade of opera- tion. Production of UCO for lube base oil has been evaluated in previous cycles, but catalyst selection has focused more on other unit objectives. UCO has, therefore, not been as suita- ble for this purpose in previous cycles. Previous cycles in the hydrocracker have provided UCO with VI in the range of 100- 110, which is not significantly higher than what is achieved from the crudes normally selected for direct lube production. Proposed catalyst solution Objectives for the hydrocracking unit have changed from cycle to cycle, and the catalyst selections made by the refin - ery have reflected these changing objectives. For the 2024 cycle, a catalyst system with enhanced hydrogenation activ- ity was proposed to specifically target hydrogenation of the high boiling range of the feedstock. High hydrogenation activity results in higher aromatic saturation and opening naphthenic rings, making product fractions more paraffinic. The high UCO paraffin content results in higher VI, making it a more valuable addition to the base oil pool. Figure 2 shows the VI obtained in the 2024 cycle together with the VI obtained in previous cycles. As can be seen, the VI is significantly higher than obtained in the previous cycles using Topsoe catalyst systems. The high VI makes it a very suitable blending component in the lube base oil production. In one of the past cycles, a catalyst system with less focus Figure 2 VI obtained during a previous cycle and the 2024 cycle

on the UCO viscosity properties was installed. However, in 2024, one of the main objectives was obtaining UCO with high VI in order to use it as a component in the lube base oil production, as mentioned earlier. Comparison of UCO viscosities obtained in the two different cycles, therefore, serves as a good illustration of how the catalyst loading can be tailored to achieve certain properties. During normal operation, the feed quality to the unit changes as the crude supply to the refinery changes. Furthermore, operating conditions such as feedstock qual- ity and fractionator cut points change. These changes cause variations in UCO product quality. Heavier feedstocks with higher viscosity lead to higher viscosity UCO at the same constant conversion. Higher cut points between diesel and UCO also lead to higher viscosities of the products. Higher conversion in the unit, however, leads to lower viscosity. VI of the UCO behaves in a somewhat similar man- ner. Some feed properties and some operating conditions improve the VI. Therefore, it can be a challenge to compare the UCO quality from cycle to cycle and even from run day to run day. A good way of comparing data is to plot the viscos- ity at two different temperatures against each other. On the same plot, the corresponding viscosity at each temperature resulting in a VI of, for example, 115, 125, and 135 may be plotted as ‘iso-VI’ lines. This way, it can be clearly illustrated how different lube base oil qualities can be obtained from different catalyst systems. Alternatively, this type of plot may be used to identify the effect of different feedstocks or oper- ating scenarios. Figure 3 shows the previously mentioned viscosity plot from the two different cycles with Topsoe catalyst systems, including the ‘iso-VI’ curves. It is obvious from the plot that the catalyst system loaded in the 2024 cycle provides a sig - nificant improvement to the UCO VI compared to the Topsoe catalyst system loaded in one of the previous cycles. The refinery produces a wide range of base oils for differ - ent applications characterised by having different viscosity ranges to fit the many applications. Each base oil fraction is made up of different components that, when combined, obtain the desired properties. Target components for each base oil product, therefore, have viscosities within the speci- fication or just outside. Figure 3 Visc@100°C vs visc@40°C, illustrating the dif - ference in UCO viscosity properties from two cycles with Topsoe catalyst systems installed in the Izmir hydrocracker

PTQ Q2 2025