Aug-2013

Premium base oil production by the hydroprocessing route

The worldwide demand for lubricants is expected to increase by 2.6 percent annually through 20151, with Asia predicted to remain the fastest growing region.

Timothy Hilbert and Girish Chitnis, ExxonMobil Research & Engineering Company
Vasant Thakkar, Soumendra Banerjee and Jill Meister, UOP LLC, A Honeywell Company

Article Summary

Lubricant demand in the Asia pacific region is ~39 percent of the total world demand. India individually holds a major market position as the sixth largest lubricant market in the world and third in Asia. Motor vehicles are the largest market for lubricants, and growth will be led by strong gains in the developing Asian countries due to exponential growth of motor vehicles, particularly in China and India.

Engine components are subjected to enormous thermal and mechanical stresses during operation; hence lubricating oil plays an important role in internal combustion (IC) engines for increased efficiency, higher performance, trouble free operation and durability. Further, in the wake of pressures to reduce vehicle emissions and cutting edge technological developments in IC engines, the role of automotive lubricant has become vital to meeting future demands being placed on IC engine design.

Almost all the growth in lubricants today is being met by production using catalytic technology because of the demand for higher quality lube basestocks. Higher quality basestocks are usually defined in terms of higher Viscosity Index (VI). Lower viscosity reduces friction losses which the auto manufacturers utilise to improve reliability and fuel efficiency. New plants are mostly catalytic  (e.g. using hydrockracking and hydroisomerisation), while many older solvent based plants are being shut down or converted to the catalytic route. Beyond quality there are many other reasons the catalytic route for producing Lube basestock is more beneficial. In many cases, the cost of production is lower and new plants benefit from the economies of scale when building larger plants. The first catalytic based plants were introduced in the 1980s; however, at that time, the catalytic route only produced conventional basestocks (Group I). In the 1990s, hydroisomerisation was introduced to produce basestocks with higher stability. Hydroisomerisation has propagated such that a considerable amount of lube basestocks are produced in this manner.

Lube basestocks are broken into a number of categories (Groups I to IV – as shown in Figure 1). Group I typically are conventional Solvent Refined lube basestocks. Groups II and III were added to lubricant classifications in the early 1990s to represent low sulphur, low aromatic, and high Viscosity Index (VI) lubricants with good oxidative stability and soot handling. The reduction of wax content in the lubricants also improves the operating range and engine, low temperature performance via improved pour and cloud point.

Groups II and III production have increased significantly over the past 15 years at the expense of Group I production (Figure 2). Although Group I is not likely to be eliminated any time soon, the overall trend is clear, particularly in the lighter grades, because car manufacturers have specified higher qualities lubricants to operate the more sophisticated and efficient engines.

These types of lubricants (Group II and III) are almost always produced using the catalytic route. The predominant catalytic route involves a combination of hydrocracking and hydroisomerisation. The technology for hydrocracking, such as the industry-leading UOP Unicracking process, has advanced significantly over the past decades. Likewise, ExxonMobil Research and Engineering Company (EMRE) remains a leader in hydroisomerisation development; therefore an Alliance of the two companies provides substantial synergies. Figure 3 gives an overview of some of the main technology advancements both companies have introduced since the 1950s.

The catalysts used play a critical role in the economic production of the high Viscosity Index (VI) lube basestocks required by the market. The first step is hydrocracking and/or severe hydrotreating to remove sulphur and nitrogen from the feed, which are poisons to the downstream catalysts. Also important is the reduction of aromatics via both saturation and boiling range reduction due to dealkylation and ring opening which in effect raises the VI of the unconverted oil sent to the hydroisomerisation unit. The unconverted oil (UCO) from the hydrocracking unit or the product from the hydrotreating unit can be processed over the hydroisomerisation catalyst which will isomerise the n-paraffins while saturating the remaining  aromatics. EMRE’s MSDW technology is well known for this kind of chemistry and utilises the MSDW catalyst. Several generations of MSDW catalysts have developed over the years resulting in both improved stability and yield.

The UOP and EMRE Alliance mentioned above was formed in July of 2011. After one year of the Alliance, four projects are in the execution phase. One of these projects is for the production of Group III lube base oil, two projects are for fuels using the hydroisomerisation platforms, and one has elements of both. In one case, MIDW and Unicracking technologies are used to significantly improve diesel yields. In the second and third hydroisomerisation platform cases, high-cetane ULSD and high-quality kerosene that meet a very low cloud point will be produced. The combination of the Unicracking and lubes finishing technologies provides customers with the optimum route to high quality API Group III Lube basestock.

There are a large number of operating units in the world making lube basestocks. These applications span the world, but a number are concentrated in the Gulf Coast of the United States and East Asia (Figure 5). predominant routes to making Group II and III base oils (Figure 6). The route of using lube hydrocracking, MSDW, and MAXSAT technologies to produce lube base oil usually produces a Group II basestock simply because the Lube hydrocracker conversion is typically low. This route often produces heavier Lube basestocks. The second approach is with a fuels hydrocracking unit, usually operating at higher conversion and typically producing light neutral base oils with high VI.

An alternate route is to mix Group I solvent based plants with Group II catalytic approaches. In this case the extraction unit does part of the hydrocracking work by removing the poor VI components and some of the nitrogen and sulphur poisons. A significant amount of hydroconversion across a raffinate hydrocracking unit (RHC) is still needed to complete the removal of poisons and raise the VI for the MSDW process. A more detailed look at the processing steps and chemistry occurring in each step during production of the lube oil basestock using catalytic routes one or two described above are shown in Figure 7.

The feed represents a typical Arab Gulf VGO type feed. After hydrocracking, the aromatics are reduced via conversion (ring opening and dealkylation) and saturation along with sulphur and nitrogen reduction. The unconverted oil (UCO) produced by hydrocracking has high waxy VI. After the MSDW reactor, the aromatics are further saturated, the normal paraffins are isomerised for pour point reduction, and the colour is improved. A final hydrofinishing step improves the oxidative stability and colour of lube oil basestock. Dewaxed oil VI is improved throughout the process (which represents the final VI) although the waxy VI is reduced.