Jul-2010

Resid FCC catalyst technology for maximum distillates yield

A catalyst developed for residuum applications with high contaminant metals levels showed a reduction in bottoms, with increased LCO and naphtha production

Martin Kraus, Qi Fu and Natalie Kiser, BASF Corporation, Catalysts Division
Orson Thornton, Big West Oil

Article Summary

Recent years have brought a major shift in the world’s demand for gasoline and distillate-range (diesel) fuel products. While gasoline consumption has shown only minor increases, the demand for distillates has been very strong, mainly driven by the transportation sector, as well as higher mileage standards and the better fuel efficiency of diesel- operated cars. The outlook for 2010–2020 shows an incremental growth in diesel demand above the 2009 level at about three times higher than that of gasoline (see Figure 11).

As a result, more and more FCC units are being operated in a maximum diesel mode in order to optimise refining margins. Aside from operational optimisation, such as undercutting gasoline, lower riser temperature, slurry recycling and improvements to hardware, the catalyst has a profound impact on product distribution. If, for example, the activity of the catalyst is adjusted by lowering the riser outlet temperature or by cutting down on catalyst addition, a catalyst not optimised for distillate-mode operation could show high residual slurry yields. In the case of resid operations, cutting down on catalyst addition would result in high coke and hydrogen yields, if the catalyst does not feature an optimised metals passivation system.

In order to address customers’ demand for a highly efficient catalyst technology for maximising FCC distillate, BASF undertook a research and development programme towards the development of a new technology platform for FCC catalysts optimised for maximum distillate yield. This platform, known as Prox-SMZ (proximal stable matrix and zeolite), was first introduced in 2008 with HDXtra, a catalyst designed for distillate maximisation in vacuum gas oil (VGO) feed FCC units. In 2008, during the first commercial trial of HDXtra in the Frontier El Dorado FCC unit, the data (see Table 1) showed a significant (4%) increase in distillate yield, as well as improved bottoms cracking.

HDUltra, a distillate maximisation co-catalyst that allows for operational flexibility in terms of distillate yield, was launched later in 2009.²

In an effort to extend the Prox-SMZ family to resid feed applications with medium to high contaminant metals levels, the novel resid distillate maximisation catalyst Stamina was recently scaled up from the development stage to commercial manufacturing. This article describes development work on Stamina, as well as the first commercial evaluation of the new catalyst in the FCC unit of Big West Oil’s refinery in Salt Lake City, Utah, in the second half of 2009.

Prox-SMZ technology platform
The Prox-SMZ technology is built on two main features: the presence of an ultra-stable and coke-selective matrix; and the close proximity of an ultra-low sodium zeolite and the Prox-SMZ matrix, which are created in a single synthesis step.

Conventionally, low zeolite-to-matrix surface area ratios (Z/M ratios) are applied to maximise distillate yield by increasing the matrix surface area and by lowering the zeolite surface area. However, without further optimisation, a lower Z/M ratio results in accentuated matrix cracking with poor coke and gas selectivities. In addition, a matrix with low hydrothermal stability will show favourably low Z/M ratios in the fresh catalysts, but comparably high Z/M ratios in the equilibrium catalyst due to the preferential loss of matrix surface area.

BASF has introduced a manufacturing process that yields an advanced matrix material. The hydrothermal stability of this proprietary matrix was compared to a variety of commercially available matrix materials after 1500°F (815°C) steaming for 4–24 hours (see Figure 2). The results show that the new manufacturing process has resulted in a matrix material demonstrating improved hydrothermal stability, thereby preserving a good (low) Z/M ratio and high matrix activity even after deactivation. The combination of this matrix with an ultra-low sodium zeolite further improves the catalyst’s overall stability.

In catalytic testing, conventional high-matrix (low Z/M) catalysts were historically known to produce large amounts of coke and dry gas due to rather unselective cracking on matrix surfaces.

In order to compare the Prox-SMZ matrix to conventional matrix technologies, two typical competitive matrix materials, as well as a matrix additive, were tested in a physical blend with RE-USY zeolite (2.6 wt% rare earth oxides). The components were separately steam deactivated at 1500°F (815°C), for four hours, at 100% steam. The blend ratio was adjusted to establish a constant Z/M ratio for all blends. The blends were evaluated for cracking performance in the advanced cracking evaluation (ACE) unit at 970°F (520°C) with a partially hydrotreated European resid feed with 3.88 wt% Conradson carbon.

The test results showed the advantage of the Prox-SMZ catalyst, featuring a significantly better light/heavy cycle oil (LCO/HCO) (bottoms upgrading ratio) at constant coke compared with the other matrix materials (see Figure 3).

The second feature of the Prox-SMZ technology is that it allows for the crystallisation of Y zeolite and the formation of the Prox-SMZ matrix in a single step. The unique manufacturing process not only forms both the matrix material and zeolite in a single step; it also brings them into intimate contact. The resulting structure is illustrated in a scanning electron microscope (SEM) micrograph of the interior of a typical catalyst particle produced in the manufacturing process (Figure 4). The submicron Y zeolite crystallites are found to be in intimate contact with the Prox-SMZ matrix.

While other catalyst technologies can incorporate zeolite and matrix materials into the same catalyst particle, they do not have the capability to bring them together in such a way. The binder used to make these catalysts creates a barrier and acts as a separator between the matrix and zeolite. It is this synergy between the zeolite and matrix that leads to rapid transfer of reactant and feed molecules from zeolitic acid sites to matrix acid sites. This enhanced transfer helps to stabilise coke precursors produced by the matrix cracking, leading to higher LCO production with lower coke.

Development of Stamina catalyst
After the launch of the HDXtra catalyst for distillate maximisation in gas oil applications, and HDUltra as a distillate maximisation co- catalyst, the focus of research and development work shifted to the extension of the Prox-SMZ technology to resid applications with high contaminant metals levels. As Figure 5 shows, the goal of the project was to develop a catalyst that matched HDXtra’s high distillate yield with the low coke yield of a high-quality maximum gasoline resid catalyst, such as Flex-Tec DMS technology.