Mar-2011

Enabling increased production of diesel

A flexible approach features developments in selective catalysts for middle distillates and less conventional production routes based on biomass

John Petri and Stuart Simpson
UOP, A Honeywell Company

Article Summary

Dieselisation of transportation fuels demand in Europe has been a significant issue for refiners since the mid- to late 1990s. Since 1995, the average European volumetric demand ratio for gasoline to high-quality transportation diesel has fallen from 1.3 to below 0.6. As the global economy recovers and growth resumes in the coming years, it is quite possible that the trend will continue, with the demand ratio potentially falling below 0.5 by 2015. Moreover, the trend towards increased dieselisation is not only associated with highway diesel production, nor is it confined solely to Europe. Worldwide demand for middle distillates is projected to increase by almost 265 million t/y over the next decade, representing about 60% of the total projected global increase in demand for all liquid petroleum-based products.¹ It is therefore more an issue of producing adequate volumes of middle distillate fuels while maintaining balanced refinery operations and, as a result, it is a challenge for refiners worldwide.

Refiners have made large investments in both process and catalyst technologies in order to balance the production of middle distillates and gasoline with the ever-changing demand ratio and fuel 
specifications. Despite these investments, production of adequate volumes of high-quality middle distillates remains a significant challenge, not least because incremental supplies of refinery intermediates for use as conversion unit feedstocks are becoming increasingly difficult to source. As a result, refining investment strategies to maximise middle distillates production need to be adapted to focus increasingly towards the following alternatives:
• Application of the most middle distillate-selective technologies available in core hydrocracking and FCC conversion flow schemes
• Selection of processing routes that produce high-quality middle distillate stocks from less conventional feeds, including biomass, gas, heavy residual fractions and coal.

Technology innovations to increase both conventional middle distillates production and provide commercial routes to green middle distillates from second-generation biomass feedstocks include:
• UOP Unicracking catalysts for maximising high-quality diesel production
• Enhancements to the UOP/Eni Ecofining Process for high cetane green diesel production and introduction of the UOP Renewable Jet Fuel Process for producing a renewable aviation fuel blend component from biologically derived feedstocks
• UOP’s alliance with Rentech provides a complete solution for processing syngas derived from biomass to high-quality green diesel. This processing route encompasses all critical steps, including gasification, CO2 removal, Fischer-Tropsch (FT) synthesis and FT wax upgrading. The wax upgrading step is critical in all FT routes to fuels, including coal-to-liquids (CTL), gas-to-liquids (GTL) and biomass-to-liquids (BTL)
• Novel catalytic solutions that improve the efficiency of FT liquids upgrading. The technology is applicable to all FT routes to diesel. This new wax upgrading technology will be discussed, and the entire UOP-Rentech processing route, from the basic feedstock to FT diesel, will be introduced.

Unicracking HC-205LT catalyst
Hydrocracking of heavy feedstocks such as vacuum gas oils (VGO), heavy coker gas oils (HCGO) and demetalised oils (DMO) is a conventional approach to increasing refinery yields of high-value middle distillate blendstocks. However, once a hydrocracker has been installed in a refinery, the only way to raise the yield performance of the unit is either to reload with higher activity, more selective catalysts or to revamp the unit for increased feed capacity (frequently also including a catalyst upgrade). As demand ratios for middle distillates to gasoline become increasingly stretched for many refineries, it can become difficult and expensive to source incremental conversion feedstocks for a revamped hydrocracker. On the other hand, reloading with a higher performance catalyst system can enable the increased production of high-quality products without any increase in feed to the unit, resulting in an economically attractive option for many refiners. In recognition of this dilemma, UOP focuses considerable development activity on continuously raising the performance of its family of Unicracking catalysts. One such development programme has resulted in the introduction of a new high-performance Unicracking catalyst, designated HC-205LT. This catalyst was developed specifically for maximum diesel production in Enhanced Two-Stage Unicracking Process units.

UOP introduced the Enhanced Two-Stage Unicracking Process in 2008.² Its innovations significantly enhance the performance of two-stage hydrocracking to achieve a substantial increase in the yield of diesel with improved product properties. Subsequently, UOP integrated the Enhanced Two-Stage Unicracking Process with residue upgrading technologies (including the Uniflex Process) for increasing the production of high-quality middle distillates.³

The basic advantage of 
the Enhanced Two-Stage Unicracking Process configuration for maximum diesel is that the second-stage cracking section operates in a clean environment almost entirely free of ammonia and hydrogen sulphide formed in the first stage. This creates an entirely different environment for the catalysts employed in each section, thus enabling the first- and second-stage catalysts to be independently optimised for highly selective cracking to the desired product range, while minimising over cracking to lighter products.

The Enhanced Two-Stage Unicracking technology is particularly beneficial in high-capacity units, where it enables economies of scale to deliver economic benefits. In addition, the enhanced technology is very efficient when processing heavier, more contaminated feedstocks to maximise high-quality diesel production. Currently, eight units have been awarded, and the first of these units is expected to start up in 2013.

The flow scheme for the 
reactor section of a two-stage Unicracking unit for maximum diesel is shown in Figure 1. The first-stage combined feed is heated and then passed to the first-stage reactor, where it is initially processed over a pretreat catalyst section, in which the fresh feed is desulphurised, denitrified and unsaturated hydrocarbons and hetero-atoms are hydrogenated. In order to produce ultra-low sulphur diesel with less than 10 ppm sulphur, the pretreat catalyst must desulphurise the feed deeply so that the inter-stage diesel-range material contains less than 15 ppm sulphur. After the pretreat catalyst, the first-stage Unicracking catalyst affects the remainder of the desired conversion for the first stage.

A typical first-stage gross conversion is between 40 and 60 lv%, depending on the cut point between the heavy diesel and unconverted oil. The first-stage reactor effluent is cooled and the net liquid is directed to the fractionation section.