PROCESS AND CATALYST INNOVATIONS IN
HYDROCRACKING TO MAXIMIZE HIGH QUALITY
DISTILLATE FUEL
Vasant Thakkar, Jill M Meister, Richard J Rossi and Li Wang
UOP LLC, a Honeywell Company
Des Plaines, Illinois, USA

INTRODUCTION
Steady worldwide economic growth continues to drive demand for transportation fuels, and in
particular, diesel. Consumption of low-sulfur, high-quality diesel is projected to grow at a faster
rate than both fuel oil and gasoline over the next 10 years. Growth in demand and stricter product
quality requirements requires increased conversion and upgrading of heavy low-quality feeds
such as vacuum gas oil, heavy coker gas oil and deasphalted oils (DAO). Hydrocracking and
hydrotreating technologies and catalyst innovations, have taken on an increasingly prominent
role in many refinery configurations. UOP’s outstanding commercial experience in delivering
hydrocracking process and catalyst technology solutions has lead to process innovations
incorporated in an enhanced two-stage UOP Unicracking™ process design, providing a
significant increase (up to 5 – 7 wt%) in distillate yields while processing difficult high-nitrogen
heavy feedstocks.
MARKET SITUATION
Refined Products Demand
The growth of refined products demand varies geographically (Figure 11). The growth rates are
slowest in the Americas, Europe and the developed countries in Asia. However, rapid economic
© 2008 UOP LLC. All rights reserved.
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development in China, India and the Middle East will help total refined products demand grow
nearly 14 million barrels per day, a 1.7% average rate, over the next 10 years. This 10-year
demand represents an average worldwide growth rate essentially the same as has been seen over
the past 10 years. It is worth noting that worldwide demand for diesel has exceeded the gasoline
demand since 2000 and that this trend is projected to continue through 2015.
Figure 1: Worldwide Refined Products Demand
35,000
Americas
1.0%
EAF
1.1%
Middle East
2.5%
China
6.1%
India
2.4%
OAP
1.0%
30,000
Total Refined Products Demand
2007: 78 million BPSD
2017: 92 million BPSD
25,000
KBPSD
20,000
15,000
10,000
5,000
0
2007 2017 2007 2017 2007 2017 2007 2017 2007 2017 2007 2017
Gasoline
Jet/Kero
Distillate
Fuel Oil
Naphtha
Other
Environmental Regulations
Motor fuel specifications have changed significantly over the past 10 to 15 years and are
continuing to evolve. The World Wide Fuel Charter Initiative is helping to set advanced
emission control requirements, and thus drive fuel qualities. Sulfur and aromatics contents are
being reduced in most developed countries and the trends are spreading to other regions. The
most notable changes govern the sulfur content of both gasoline and diesel fuel. Tier II
regulations in the U.S. have driven gasoline sulfur down to < 30 ppm. Europe has reduced sulfur
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to 50 ppm with further tightening to 10 ppm scheduled to take place later this decade. Japan
already has very low sulfur levels in its gasoline while other countries are moving in the same
direction, but most at a slower pace. The evolution of gasoline sulfur specifications is shown in
Figure 22.
Figure 2: Changing Gasoline Sulfur Standards
1000
USA
U.S. Tier 2
Sulfur, ppm
Europe
Japan
100
150
Germany
California
50
30
15
10
10
5
Automobile
Manufacturers
1
1999
2001
2003
2005
2007
Source: AM-02-36, NPRA 2002 Annual Meeting
Diesel fuel sulfur content is being reduced at a similar pace to gasoline with Germany mandating
maximum sulfur levels of 10 ppm in 2003, the U.S. mandating 15 ppm in 2006, Japan planning
to go to 10 ppm, and several other European countries voluntarily switching to 10 ppm sulfur in
diesel ahead of a 2009 deadline (Figure 3)3.
Figure 3: Changing Diesel Sulfur Standards
1000
Sulfur, ppm
USA
500
350
Europe
100
Japan
50
15
10
5
Germany
10
Automobile
Manufacturers
1
1999
2001
2003
Source: AM-02-36, NPRA 2002 Annual Meeting
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2005
2007
By the end of the decade, 80% of the world’s gasoline consumption will be ultra-low sulfur (< 50
ppm). Currently, ~65% of the world road diesel is refined to low and ultra-low sulfur diesel.
This percentage is projected to rise to approximately 75% by 2015.
UNICRACKING PROCESS FLOW SCHEMES
UOP has offered hydrocracking processes since the inception of commercial hydrocracking.
There are several Unicracking process flow schemes presently offered to meet individual
refinery needs and project objectives. The basic flow schemes considered are single-stage or
two-stage design.
Two-stage flow schemes can be employed in specific situations. UOP two-stage Unicracking
process flow schemes can be a separate hydrotreat or a two-stage Unicracking process as shown
in Figure 4. In the separate hydrotreat flow scheme the first stage provides only hydrotreating
while in the two-stage Unicracking process the first stage provides hydrotreating and partial
conversion of the feed. The second-stage of the two-stage design provides the remaining
conversion of recycle oil so that overall high conversion from the unit is achieved. These flow
schemes offer several advantages in processing heavier and highly contaminated feeds. Twostage flow schemes are economical when the throughput of the unit is relatively high.
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Figure 4: Two-Stage Unicracking Process Flow Schemes
Separate Hydrotreat
H2
H2
 Used when special product quality or
product slate requirements exist
R
 Used when special feed
considerations are present
R
F
Products
Separate
Hydrotreat
−
Large amount of product in feed
−
Very high nitrogen level in feed
Recycle Oil
Two Stage
H2
R
R
 Most cost effective for large capacity
units
 Provides high product quality and
product slate flexibility
F
Products
Two Stage
Recycle Oil
 Efficient to process difficult
feedstocks
 Low NH3 environment in second
stage
The design of hydrocracking catalyst changes depending upon the type of flow scheme
employed. The hydrocracking catalyst needs to function within the reaction environment and
severity created by the flow scheme that is chosen. As indicated in Figure 4, two-stage flow
schemes provide a unique reaction environment for the second-stage hydrocracking catalyst. The
second-stage reaction environment is cleaner and significantly boosts the cracking activity of the
catalyst.
Enhanced Two-Stage Unicracking Process
During the early years of hydrocracking, refiners were mainly interested in maximizing
production of naphtha for reforming to high octane gasoline. UOP has designed many two-stage
units for the North American market for this purpose. However with advancements in
hydrocracking catalyst technology, and the demand for maximizing distillate yields from heavier
feedstocks, two-stage design offers a cost-effective option for a larger capacity maximum
distillate unit operation. As part of continual renewal and advancement of technology, UOP has
recently advanced the two-stage Unicracking process.
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As shown in Figure 5, a typical two-stage hydrocracking design consists of the first stage that
provides hydrotreating and hydrocracking of the feed using two types of catalysts in one or two
reactors. The feed is hydrotreated and hydrocracked followed by separation of gas and liquid
effluents. The hydrocracked liquid effluent is fractionated into products and unconverted oil.
The unconverted oil is recycled to the second-stage hydrocracking reactor. The second-stage
reactor provides hydrocracking of unconverted oil so that overall conversion from the unit can be
as high as 100%.
Figure 5: Two-Stage Unicracking Flow Scheme
Reactors
Recycle gas
Scrubber
Vent Gas
Cold
Separator
Product
Separation
Flash
Drum
Hot
Separator
Butanes
Naphtha
Feed
Jet
Hot
Flash
Drum
H2
Distillate
Recycle
UCO
HPNA RM
Control
A major difference between the first and second stage hydrocracking reactor reaction
environments lies in the very low concentrations of ammonia and hydrogen sulfide in the
second-stage. The first-stage reaction environment is rich in both ammonia and hydrogen sulfide
generated by hydrodenitrogenation and hydrodesulfurization of the feed. This significantly
impacts reaction rates, particularly cracking reaction rates, leading to different product selectivity
and catalyst activity between the two-stages. The catalyst system can be optimized to obtain a
highly distillate selective overall yield structure. Optimum severity can be set for each stage to
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achieve catalyst life target with minimum catalyst volume. Overall, the two-stage design allows
optimization of conversion severity between the two stages, maximizing overall distillate
selectivity.
New advances in the two-stage Unicracking process design include several innovations in each
reaction section of the design. The pretreating section uses a high activity pretreating catalyst
that allows hydrotreating at a higher severity, providing good quality feed for the first-stage
hydrocracking section and enabling maximum first-stage selectivity to high quality distillate. The
second-stage is optimized by use of second-stage hydrocracking catalyst that is specifically
designed to take advantage of the cleaner reaction environment. The second-stage catalyst is
designed so that the cracking and metal functions are balanced. At the same time the secondstage hydrocracking severity is optimized so that maximum distillate selectivity is obtained from
the second-stage of hydrocracking.
CONCLUSIONS
Growth in demand combined with stringent quality requirements for transportation fuel make
hydrocracking a technology of choice.
Hydrocracking of heavier and highly contaminated
feedstocks require optimal technical solutions that include catalyst and flow scheme
consideration. Renewal of technology like the two-stage Unicracking process has demonstrated
significantly improved total distillate yields, 5 – 7 wt%, while processing difficult feedstocks and
producing excellent product qualities. UOP is developing process design and materials science
innovations that demonstrate our understanding of complex process reaction chemistry and the
challenges facing the industry, resulting in solutions that advance the success of our customers.
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REFERENCES
1. Purvin & Gertz Inc., “Global Petroleum Market Outlook: Prices And Margins”, Fourth
Quarter 2007 Update
2. Thakkar V. P. et al, “Innovative Hydrocracking Applications For Conversion of Heavy
Feedstocks”, AM-07-47 NPRA 2007 Annual Meeting
3. Asian Development Bank and Clean Air Initiative for Asian Cities Center, Inc., A
Roadmap for Cleaner Fuels and Vehicles in Aisa, Second Consultation Draft, December
19, 2007
UOP LLC
25 East Algonquin Road
Des Plaines, IL 60017-5017
© 2007 UOP LLC. All rights reserved.
Tel: 847.391.2000
January 2007
www.uop.com
UOP 4706B
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