As novel hydraulic fracturing technology with directional drilling
continues to improve, shale oil will continue to be a
game-changer for North American refiners. Although credited
with many advantages, shale oil does not come without its
challenges. Suppliers and processors alike are urgently working
to adapt to the changing oil landscape. Just a few years ago,
investments were focused on processing heavy crudes. Now,
however, the industry is faced with lighter, sweeter crude
streams from shale plays.
In varying degrees at each refinery, shale oil makes up only
a percentage of the total feedstock. Present estimates put
shale oil production at 5% of total US crude demand. The
percentage could grow substantially as shale oil production
increases and refiners invest in process modifications to
handle this lighter feed.
The rapid introduction of shale oil to the refinery has come with interesting
consequences for the fluid catalytic cracking unit (FCCU). To
aid refiners in understanding the implications of shale oil, a
detailed feed analysis and cracking studies of a representative
Bakken shale oil and its fractions, compared to a typical
Mid-Continent vacuum gasoil (VGO), are provided here. These
results aid in understanding how best to optimize operations
and maximize FCC value. A key element in this optimization is
appropriate catalyst selection to overcome some of the
challenges commonly associated with processing shale oil. In
particular, the presence of iron and calcium in variable
quantities can be addressed through the application of a
catalyst with an optimized matrix and mesoporosity.
Properties of raw Bakken crude
Shale oil is highly variable. Density and other properties
can show wide variation, even within the same
field.14 For this study, a sample of raw
Bakken crude was obtained from a refinery. The crude was light
and sweet with an API gravity of 42° and a sulfur content
of 0.19 wt%. Table 1 presents the properties
of this sample, compared to published assays of Bakken, West
Texas Intermediate (WTI) and Light Louisiana Sweet (LLS) crude
The properties of the Bakken crude used in this study
closely matched those in the published assay. Similar to other
light crudes, raw Bakken crude has a low amount of FCC feed
(< 28% at 680°F+). The straight-run (SR) Bakken sample
was distilled into a 430°F− gasoline cut and a
430°F650°F light cycle oil (LCO) cut, and the
properties of these cuts were measured. The gasoline
composition and properties were analyzed via proprietary octane
calculation software based on detailed gas chromatography
analysis.6,7 The gasoline fraction from the
straight-run Bakken sample was highly paraffinic and had low
octane numbers [a research octane number (RON) of 61 and a
motor octane number (MON) of 58]. The LCO fraction had an
aniline point of 156°F and an API gravity of 37.6°,
resulting in a diesel index of 59. While the Bakken crude
sample was light and paraffinic, it also had a heavy end.
Light sweet crudes are generally easy to process, although
challenges arise when these crudes are the predominant
feedstock in refineries designed for heavier crudes. Shale
oils, like other light sweet crudes, have a much higher ratio
of 650°F− to 650°F+ material compared to
conventional crudes. Bakken shale oil has a nearly 2:1 ratio,
while typical crudes, such as Arabian Light, have ratios near
A refinery running high percentages of Bakken oil could
become overloaded with light cuts, including reformer feed and
isomerization feed, while at the same time growing short on
feed for the FCCU and the coker. Refiners running predominantly
shale oil could shut down the vacuum distillation and coker units, and
send the entire atmospheric tower bottoms (ATB) portion to the
FCCU. Many refiners would still be short on FCC feed, and some
have considered bypassing a portion of the whole shale oil
around the crude distillation unit to fill up the FCCU
Also, while the highly paraffinic Bakken ATB would crack to
high conversion, the expected low delta coke would result in
low regenerator temperatures and possible difficulty in
circulating sufficient catalyst to maintain reactor
Shale oil cracking yields
To examine the impact of shale oil on FCC yields, cracking
was performed with whole Bakken crude, a 430°F+
distillation of Bakken, a 650°F+ distillation of Bakken and
a reference sample of a typical Mid-Continent VGO. Feed
properties are presented in Table 2. Cracking
was done over an FCC catalyst in a fixed-fluidized bed advanced
cracking evaluation (ACE) test unit8 at a constant
reactor temperature of 980°F, using three catalyst-to-oil
(C/O) ratios (4, 6 and 8) for each of the feeds. The catalyst
used in the experiments was an FCC catalyst with an optimized
matrix and mesoporosity, deactivated metals-free using a cyclic
propylene steaming (CPS) protocol. Deactivated properties are
given in Table 3.
Interpolated yields at a C/O of 6 are presented in
Table 4. The whole Bakken crude resulted in
low coke and a low-octane gasoline. While the whole Bakken
crude yielded significant gasoline, much of the gasoline was
from uncracked starting material in the feed. The yields of the
430°F+ and 650°F+ distillations of the Bakken crude
were similar to those of the Mid-Continent VGO reference
sample. The 650°F+ distillation of the whole Bakken
crude had higher coke than the Mid-Continent VGO due to its
heavier end and higher Conradson carbon number.
Results of processing SR shale oil
While FCC is typically used to reduce the molecular weight
of the crude oil heavy fractions (such as VGO and ATB), in some
cases refiners are charging whole shale oil as a fraction of
the plants FCC feed. As a model case to understand the
cracking of whole crude oil in the FCC and the effect of
process conditions on yields, the whole Bakken crude described
in Table 2 was processed in a
circulating-riser FCC pilot plant at three riser outlet
temperatures: 970°F, 935°F and 900°F.
As a reference case, the Mid-Continent VGO described in
Table 2 was cracked at a riser outlet
temperature of 970°F.9 The catalyst used in the
experiments was a high-matrix FCC catalyst, deactivated
metals-free using a CPS-type protocol. Deactivated properties
are shown in Table 3.
Fig. 1 presents the yield structure of the
starting feeds and the cracked products for a riser outlet
temperature of 970°F. The Mid-Continent VGO is a typical
VGO feed with a large portion of 650°F+ material and a
small fraction of LCO-range material. When cracked, the
LCO-range material cracks to liquefied petroleum gas (LPG) and
gasoline, and the 650°F+ material cracks to the typical
distribution of LPG, gasoline and LCO, resulting in a net
increase in LCO.
1. Yield structure of starting feeds
and cracked products for SR Bakken and
The whole Bakken crude starts with large fractions of
gasoline and LCO-range material and a low amount of 650°F+
material. The amount of gasoline produced after cracking is
high since the LCO-range material cracks to predominantly
gasoline, and much of the starting gasoline is unconverted. LCO
yields are low since there is little starting 650°F+
material to crack to LCO.
For the three different reactor outlet temperatures, plots
of C/O ratio, gasoline, LCO and coke yields vs. conversion are
shown in Fig. 2. As expected, lowering the
reactor temperature increases the amount of LCO produced.
Cracking SR shale oil produces little coke and bottoms. At the
same conversion level, lowering the reactor temperature results
in slightly more gasoline yield (due to increased C/O), which
is consistent with prior research.10
2. Product yields as a function of
riser outlet temperature and feed.
At a riser outlet temperature of 970°F, the whole Bakken
feed produces more gasoline, less LCO and less coke than the
reference Mid-Continent VGO. Compared to the VGO, which
produced gasoline with a RON of 93 and a MON of 80, the SR
Bakken oil produced a paraffinic low-quality gasoline (at all
three reactor outlet temperatures) with a RON of less than 80
and a MON of less than 70.
Synthetic crude from the pilot plant runs was distilled to
recover the 430°F650°F LCO fraction. The aniline
point and API gravity of the LCO were measured to calculate the
diesel index, which is a measure of LCO quality. Fig.
3 presents data for LCO yield and quality as a
function of conversion. Increasing conversion lowers LCO
quality as a result of increased cracking of the LCO-range
paraffins to lighter hydrocarbons. As seen in prior
research,11 LCO quality follows LCO yield and did
not appear to be influenced by reactor temperature at constant
conversion. Diesel index values of the LCO produced by cracking
whole shale oil were significantly higher than those obtained
when cracking the reference Mid-Continent VGO. At a conversion
of 78 wt%, the whole Bakken sample gave an LCO with a diesel
index of 40, compared to a diesel index of 10 obtained for the
LCO produced from the Mid-Continent VGO.
3. Effect of conversion level
feed type on LCO yield and quality.
This study of the effect of operating variables shows that
whole shale oil responds to FCC operating conditions in a
similar way to conventional oils. However, the product yield
slate is substantially different in that good-quality
(high-diesel-index) LCO is produced in the FCC along with large
amounts of low-octane gasoline.
Metals in shale oil
While most shale oils are low in nickel (Ni) and vanadium
(V), they have been found to be high in inorganic solids and in
iron (Fe) and alkali metals.2,12 Table
5 presents metals analyses of whole Bakken crude, a
Bakken 650°F+ distillation, and a sample of
Also included in the table are other published metals
analyses of shale oils. While metals levels in the samples
vary, Fe and calcium (Ca) levels are generally high. Reports
from the field indicate that Bakken crude is typically low in
Ni and V, while crudes sourced from the Eagle Ford shale have
higher Ni and V levels that can vary significantly based on
To better understand the possible sources of metals in shale
oil, the sample of whole Bakken crude was filtered through an
0.8-micron filter, and the solids were recovered. Scanning
electron microscopy of the solids identified irregular micron-
and submicron-sized particles. Energy dispersive spectroscopy
maps of Fe, sulfur and Ca are shown in Fig. 4.
The Fe in the sediments is associated with sulfur.
4. Energy dispersive spectroscopy
maps of sediment in Bakken crude.
X-ray diffraction of the sediment identified the following
crystalline phases: anhydrite (Ca2SO4),
magnetite (Fe3O4) and pyrrhotite
(substoichiometric FeS). Anhydrite and pyrrhotite have been
mentioned in previous studies as being present in the Bakken
formation.13,14 Based on this analysis, it appears
that much of the iron in the Bakken crude comes from very small
particles of iron oxide and pyrrhotite.
Iron and calcium effects
Fe and Ca have negative effects on catalyst performance.
While particulate tramp Fe from rusting refinery equipment does not have a
significant detrimental effect on catalyst, finely dispersed Fe
particles in feed (either as organic compounds or as colloidal
inorganic particles) can deposit on the catalyst surface,
reducing its effectiveness.15,16
The Fe deposits combine with silica (Si), Ca, sodium (Na)
and other contaminants to form low melting temperature phases,
which collapse the pore structure of the exterior surface,
blocking feed molecules from entering the catalyst particle and
reducing conversion.17 Fe, in combination with Ca
and/or Na, has a greater negative effect on catalyst
performance than does Fe alone. The symptoms of Fe and Ca
poisoning include a loss of bottoms cracking as feed particles
are blocked from entering the catalyst particle, along with a
drop in conversion.
Catalytic solutions for FCC processing of shale oil
The variability in shale oil properties requires a catalyst
capable of process flexibility and metals tolerance. Several
catalyst design factors are important. A catalyst that cracks
deep into the bottom of the barrel increases FCC flexibility
and maximizes total distillate yield. A moderate
zeolite-to-matrix catalyst ensures that activity is not
compromised while maintaining optimal bottoms cracking. The
appropriate level of rare-earth exchange on zeolite is also a
crucial aspect in maintaining optimal coke selectivity. A
catalyst with optimized matrix and mesoporosity is a highly
effective system for the effective processing of a variety of
Catalyst design can be optimized to resist the effects of
contaminant Fe and Ca. High alumina catalysts, especially
catalysts with alumina-based binders and matrices, are best
suited to process Fe- and Ca-containing feeds because they are
more resistant to the formation of low-melting-point phases
that destroy the surface pore structure. Optimum distribution
of mesoporosity also plays a role in maintaining performance
because diffusion to active sites remains unhindered, despite
The paraffin, aromatic and porphyrin molecules in the
700°F1,000°F boiling-point fraction of FCC feed
have dynamic molecular sizes between 10 Angstroms (Å) and
30 Å.18 These molecules are too large to fit
into zeolite pores (which are typically smaller than 7.5
Å) and must first be cracked by the matrix activity of
the catalyst. For free diffusion of the
700°F1,000°F boiling-range molecules to occur,
the catalyst pore diameter needs to be 10 to 20 times the size
of the molecule, or 100 Å600
Based on these considerations, a catalyst with an optimized
alumina matrix and mesoporosity in the 100 Å600
Å range was designed.19 While two catalysts
may have similar total pore volume, their mesoporosity can vary
greatly. Table 6 compares the mesoporosity of
this optimized matrix and mesoporosity catalyst to a competing
catalyst. Note: The mercury intrusion method
measures pore sizes greater than 36 Å, so the values
represent porosity associated with the catalyst matrix only.
Micropores smaller than 100 Å are undesirable and lead to
poor coke and gas selectivity as the result of poor diffusivity
and over-cracking.15 As seen in the table, the 100
Å600 Å mesopore volume of the optimized
matrix and mesoporosity catalyst was twice that of the
The resistance of the optimized matrix and mesoporosity
catalyst to Fe and Ca poisoning was demonstrated in a
commercial application. A refinery was processing resid
feedstock high in Fe and Ca. Over time, the unit exhibited the
symptoms of Fe poisoning. As Fe nodules built up on the
catalyst surface, equilibrium catalyst activity, unit
conversion and bottoms cracking all began to suffer. The
refiner switched from a competing catalyst to one with
optimized matrix and mesoporosity.a Upon switching,
activity, bottoms cracking and coke selectivity improved, even
at higher contaminant metals levels (Fig.
5. Despite higher contaminant
the catalyst with optimized matrix and
mesoporosity improved bottoms cracking
and coke selectivity.
The shale oil boom has resulted in a renaissance in the
North American refining industry. While shale oils
are generally light, sweet and easy to crack, quality can vary
greatly, and shale-derived feeds can contain sediments with
high levels of iron and alkali metals. Catalyst formulations
with optimized matrix and mesoporosity provide the best
resistance to iron and calcium poisoning. Proper catalyst
choice allows refiners to fully exploit the opportunities of
shale oil while minimizing the detrimental impacts of
The authors thank their colleagues at Grace for their
assistance with the testing for this article. Special thanks go
to Larry Langan for his analysis of the Bakken sediment.
a Graces MIDAS FCC catalyst contains a
specialty alumina matrix and is designed to maximize the 100
Å600 Å mesoporosity optimal for
coke-selective bottoms conversion.
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