Jones D.S.J., Pujado P.R. Handbook of Petroleum Processing
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282 CHAPTER 6
70. W. S. Letzsch, D. Dharia, and J. L. Ross, The future of catalytic cracking, NPRA Annual
Meeting, Paper AM-97-65.
71. P. R. Satbhai, J. M. H. Dirkx, R. J. Higgins, and P. D. L. Mercera, Best practices in shell
FCC units, Akzo Nobel Catalyst Seminar, 10/98, Mumbai, India.
72. J. L. Mauleon and J. B. Sigaud, Mix temperature control enhances FCC flexibility in use
of wider range of feeds, Oil and Gas Journal, 2/23/87, 52–55.
73. C. R. Marcilly and R. R. Bonifay, Catalytic cracking of resid feedstocks, The Arabian
Journal for Science and Technology, Vol 21, No. 48, 12/96.
74. J. R. Murphy, Designs for heat removal in HOC operations, Petroleum Refining Conference,
JPI, Tokyo, 10/86.
75. I. B. Cetinkaya, Plug flow vented riser, US Patent 5,449,497.
76. R. Miller, Y.-L. Yang, E. Gbordzoe, D. L. Johnson, and T. Mallo, New Developments in
FCC feed Injection and stripping technologies, NPRA Annual Meeting, Paper AM-00-08.
77. Exxon Research and Engineering Company, Flexicracking IIIR State-of-the-Art Cat
Cracking Commercial Brochure.
78. C. C. Wear and R. W. Mott, FCC catalysts can be designed and selected for optimum
performance, Oil and Gas Journal, 7/25/88, 71–79.
79. E. G. Wollaston, W. J. Haflin, W. D. Ford, and G. J. D’Souza, FCC model valuable operating
tool, Oil and Gas Journal, 9/22/75, 87–94.
80. I. A. Vasalos, E. R. Strong, C. K. R. Hsieh, and G. J. D’Souza, New cracking process
controls FCCU SOX, Oil and Gas Journal, 6/27/77, 141–148.
81. Complete combustion of CO in cracking process, Chemical Engineering, 11/24/75.
82. P. H. Barnes, Tutorial: Basic process principles of residue cat-cracking, AIChE, 1998 Spring
National Meeting, New Orleans, 3/8-12/98.
Appendix 6.1. Commercially available FCC catalysts and additives
Note: All catalysts are micro spheres with densities from 0.70 to 0.90 gm/cc Matrix
binders are silica or aluminum sols or silica-alumina. Clays and other aluminas are
added.
Feedstocks Products
GO Gas oils MDG Minimum dry gas
R Resids MLPG Maximum LPG
HN High nitrogen MG Maximum gasoline
HNR High nickel resid MLCO Maximum LCO
HR Heavy resid MBC Maximum bottoms cracking
A All MO Maximum octane
MC Minimum coke
MLY Maximum liquid yields
MOB Maximum octane—barrels
MIO Maximum Iso-Olefins
FLUID CATALYTIC CRACKING 283
Akzo-Nobel
Applications
Catalyst name Feedstocks Products Product features
Access HN, R MLY, MBC, MDG Metals tol., high stability
Advance GO, R MG, MDG, MC Metals tol., high act with octane
Aztec ALL MLCO, MDG Middle distillate maximization
Centurion R MC Max metals tol. high stability
Centurion—max HNR MC Max Ni tol., low C high stability
Cobra ALL MOB, MDG, MBC Metals tol—max. prod. value in OB mode
Conquest ALL, R, HN MG, MBC, MDG Metals tol. max conv + stability
Conquest HD ALL, R, HN MG, MBC, MDG Metals tol., reduce cat losses, opacity
Eclipse ALL, R, HN MIO, MO, MBC, MDG Maximum isomerization
Foc HR MOB Max throughput with resids
Horizon HN, R MOB, MBC High conv with resids
Vision HR MOB, MO Increase motor octane
Catalysts and Chemicals Industries Co. Ltd.
Applications
Catalyst name Feedstocks Products Product features
HMR GO, R MOB, MBC High liq. yield with minimum dry gas and coke
BLC GO, R MOB, MBC High liq. yield with minimum dry gas and coke
STW R MOB, MBC, MDG, MC Metals tol. and high stability
DCT GO, R MOB, MBC, MDG Metals tol. and high stability
ACZ HR MOB, MBC Metals tol., high stability
Davison, W. R. Grace & CO.
Applications
Catalyst name Feedstocks Products Product features
Atlas A MBC High stability and activity
Aurora A MBC High stability and activity
GDS A MBC Selective bottoms cracking
Orion A MDG, MC Low coke, high activity
Polaris GO, R MBC Maximum bottoms conv.
Spectra A MDG, MC High activity, sel. botoms conversion
XPD GO MO, MBC Max. olefins, high activity
Vanguard GO, R MDG, MC High activity
284 CHAPTER 6
Engelhard Corp.
Applications
Catalyst name Feedstocks Products Product features
Maxol A MOB, MO Maximum C
4
olefins
Millenium GO, R MOB, MDG, MC Metals tol. low coke and dry gas
Naphtha max GO, R MG, MBC, MC Selective matrix
Naphtha max—LSG GO MG, MBC Reduce gasolines
Petromax GO, R MOB, MBC High zeolite/matrix ratio
Precision A MOB High activity
Reduxion A MO, MBC, MC Matrix acidities controlled
Syntec GO MC Low coke
Ultrium R MOB Metals tol., low coke
Vektor R MOB, MBC Max conv
Instituto Mexicano del Petr´oleo
Applications
Catalyst name Feedstocks Products Product features
IMP-FCC-05 GO MOB Gasoline selectivity
IMP-FCC-06 GO MOB
IMP-FCC-10 GO MOB, MLPG High octane, olefins
IMP-FCC-11 GO, R MOB
IMP-FCC-12 GO, R MOB Metals tol.
IMP-FCC-14 GO MG Gasoline selectivity
IMP-FCC-16 GO, R MG Gasoline selectivity
IMP-FCC-51 GO, R MOB Metals tol.
IMP-FCC-53 R MG
IMP-FCC-54 GO, R MOB
IMP-FCC-55 GO MO Olefin selectivity
Flue gas SO
x
reduction
Akzo KDSOX
CCIC PLUS 1
Davison DESOX
Englehard SoxCAT Mg based
IMP IMP-RESOX-01
Intercat Soxgetter Hydrotalcite Tech.
Flue gas NO
x
reduction
Akzo Kdnox
Grace Denox
FLUID CATALYTIC CRACKING 285
Gasoline sulfur reduction
Akzo Resolve 700, 750, 800
Davison D-Prism
RFG
Surea
Intercat LGS-150
Metals passivation
IMP IMP-ADF-01
Ondeo-nalco MVP
Nickel passivation plus Antimony
Fluidization aid
Akzo Smoothflow
Fcc additives
Bottoms cracking Comments
Akzo BCMT-100
BCMT-200 V trap
BCMT-500 Fe, V tolerance
Intercat BCA-105
Octane (Pentasil containing products)
Akzo K1000, 2000
CCIC OCTUP-3
Davison Olefins plus Moderate sieve content
Olefins extra High sieve content
Olefins max Highest sieve content
Olefins ultra
Butmax Max. butylene
Engelhard Z-2000
Z-2000 super
Z-2000 super pro
IMP
IMP-10-02
IMP-10-03
IMP-10-04 With rare earth
Intercat Isocat Moderate LPG
LGS-150 Reduce gaso. sulfur
Octamax Low LPG
Pentacat High LPG
Pentacat plus Max propylene
Pentacat-HP Max propylene
SoCat-HP High LPG
286 CHAPTER 6
Z-Cat-HP Max propylene
ZMS-B-HP Moderate LPG
ZMX-C-HP Low LPG
CO promoters
Azko KOC Pt containing
KNO
x
-DOWN Non Pt < NOX
Amber CCA-1 Pt–Pd High Act
CCA-1000 High act
CCA-350 Low act
CCA-500 Medium act
CCA-8 Pt–Pd
CCA-850 Pt
CCIC SP-IOS-60 Pt
Davison CP-3, CP-5, CP-A Varying activities
XNox
Engelhard Procat plus Pt
Procat 500, 700, 900 Pt varying activities
IMP IMP-PC-500 Pt
Intercat COP 375, 550, 850 Pt varying activities
UOP Unicat C1-3 Pt
Chapter 7
Distillate hydrocracking
Adrian Gruia (retired)*
Hydrocracking is a versatile catalytic refining process that upgrades petroleum feed-
stocks by adding hydrogen, removing impurities, and cracking to a desired boiling
range. Hydrocracking requires the conversion of a variety of types of molecules and is
characterized by the fact that the products are of significantly lower molecular weight
than the feed. Hydrocracking feeds can range from heavy vacuum gas oils and coker
gas oils to atmospheric gas oils. Products usually range from heavy diesel to light
naphtha. Hydrocrackers are designed for and run at a variety of conditions depending
on many factors such as type of feed, desired cycle length, expected product slate but
in general they will operate at the following range of conditions: liquid hourly space
velocity (LHSV)—0.5 to 2.0, H
2
circulation—5,000 to 10,000 SCFB (850–1,700
Nm
3
/m
3
), H
2PP
—1,500 to 2,000 psia (103–138 bars), and SOR temperatures ranging
between 675
◦
F and 725
◦
F (357–385
◦
C). Hydrocracking is particularly well suited
to generating products that meet or exceed all of the present tough environmental
regulations.
Brief history
While the first commercial installation of a unit employing the type of technology in
use today was started up in Chevron’s Richmond CA refinery in 1960, hydrocracking
is one of the oldest hydrocarbon conversion processes. Hydrocracking technology
for coal conversion was developed in Germany as early as 1915 designed to secure
a supply of liquid fuels derived from domestic deposits of coal. The first plant for
hydrogenation of brown coal was put on stream in Leuna Germany in 1927, applying
what may be considered the first commercial hydrocracking process. Conversion
of coal to liquid fuels was a catalytic process operating at high pressures, 3000–
10,000 psig (207–690 bar) and high temperatures, 700–1000
◦
F (371–538
◦
C). Other
efforts were undertaken subsequently to develop hydrocracking technology designed
*UOP LLC.
287
288 CHAPTER 7
to convert heavy gas oils to lighter fuels. The emergent availability of Middle Eastern
crude after World War II removed the incentive to convert coal to liquid fuels, so
continuing the development of hydrocracking technology became less important.
In the mid-1950s the automobile industry started the manufacture of high-
performance cars with high-compression ratio engines that required high-octane gaso-
line. Thus catalytic cracking expanded rapidly and generated, in addition to gasoline,
large quantities of refractory cycle stock that was material that was difficult to con-
vert to gasoline and lighter products. This need to convert refractory stock to quality
gasoline was filled by hydrocracking. Furthermore, the switch of railroads from steam
to diesel engines after World War II and the introduction of commercial jet aircraft
in the late 1950s increased the demand for diesel fuel and jet fuel. The flexibility
of the newly developed hydrocracking processes made possible the production of
such fuels from heavier feedstocks. The early hydrocrackers used amorphous silica
alumina catalysts. The rapid growth of hydrocracking in the 1960s was accompa-
nied by the development of new, zeolite based hydrocracking catalysts. They showed
a significant improvement in certain performance characteristics as compared with
amorphous catalysts: higher activity, better ammonia tolerance, and higher gasoline
selectivity. While hydrocracking was used in the United States primarily in the pro-
duction of high-octane gasoline, it grew in other parts of the world, starting in the
1970s primarily for the production of middle distillates. The amorphous catalysts
remained the catalysts of choice for this application, though some ‘flexible’ catalysts
were developed that made it possible to maximize the yield of different products by
using the same catalyst but changing the operating conditions. As of the beginning
of 2001, there were more than 150 hydrocrackers operating in the world with a total
capacity in excess of 3,800,000 B/D (500,000 MT/D).
Flow schemes
Various licensors have slightly different names for their hydrocracker flow schemes,
but in general, they can be grouped into major two categories: single stage and two
stage. Table 7.1 shows the general evolution of flows schemes, generally driven by
improvements in catalysts.
Single stage once-through hydrocracking
Figure 7.1 shows a schematic of a single stage, once-through hydrocracking unit,
which is the simplest configuration for a hydrocracker. It is a variation of the single
stage hydrocracking with recycle configuration (described in “Two Stage Recycle
Hydrocracking”). The feed mixes with hydrogen and goes to the reactor. The effluent
goes to fractionation, with the unconverted material being taken out of the unit as un-
converted material. This type of unit is the lowest cost hydrocracking unit, can process
DISTILLATE HYDROCRACKING 289
Table 7.1. Evolution of hydrocracker flow schemes
Date Process scheme Reason
Early 1960s Separate hydrotreating Low activity amorphous catalysts
Mid 1960s Two-stage hydrocracking Advent of zeolitic HC catalysts
More economical scheme
Hydrocracking in 1st stage
makes a smaller 2nd stage
Late 1960s Single stage Efficient design, capacity limitation of 35,000
BPSD fresh feed for a single train
1970s and 1980s Once-through, partial
conversion
Upgraded unconverted oil for FCC or ethylene
plant feed, lube oil
heavy, high boiling feed stocks and produces high value unconverted material which
becomes feed stock for FCC units, ethylene plants or lube oil units. In general, the con-
version of the feed stock to products is 60–70 vol%, but can range as high as 90 vol%.
Single stage with recycle hydrocracking
The most widely found hydrocracking unit is the single stage with recycle in which
the unconverted feed is sent back to the reactor section for further conversion.
Figure 7.2 depicts this type of unit. It is the most cost-effective design for 100% (or
near 100%) conversion and is especially used to maximize diesel product.
A more detailed flow diagram of the reactor section in a single stage hydrocracking
unit (than those shown in either Figures 7.1 and 7.2) is shown in Figure 7.3. The
fresh is passed downward through the catalyst in presence of hydrogen, after being
preheated to reaction temperature by passing it through heat exchangers and a heater.
The effluent from the reactors goes through a series of separators where hydrogen
is recovered and, together with make up hydrogen, is recycled to the reactors. The
liquid product is sent to fractionation where the final products are separated from
unconverted oil. In once-through units, the unconverted oil is sent out of the unit,
R
•F
H
2
Products
To Other Units
Feed
Figure 7.1. Single stage once-through hydrocracking unit.
290 CHAPTER 7
R
H2
Products
Recycle Oil
Feed
F
Figure 7.2. Single stage hydrocracking unit with recycle.
as previously described. In units designed to operate with recycle, the unconverted
oil combines with the fresh feed, as shown in Figure 7.3. As described in the next
section (“Chemistry”), the reaction section fulfills two functions: pre-treating and
cracking. This is shown in Figure 7.3 as separate reactors, though both functions can
be achieved in a single reactor when using amorphous catalyst. When using a pre-
treat and cracking catalyst configuration, the first catalyst (a hydrotreating catalyst)
converts organic sulfur and nitrogen from hetero compounds in the feedstock to
hydrogen sulfide and ammonia, respectively. The deleterious effect of H
2
S and NH
3
on hydrocracking catalysts is considerably less than that of the corresponding organic
hetero compounds. The hydrotreating catalyst also facilitates the hydrogenation of
aromatics. In the single stage, two-reactor configuration, the products from the first
Reactor
Separators
Reactor
Recycle Gas
Compressor
Wash Water
H.P. Hot
H.P. Cold
Flash Gas
To Fractionator
L.P. Cold
Sour Water
Makeup Compressor
To Fractionator
Recycle Oil (Fractionator Bottoms)
Fresh Feed
Hydrogen
Makeup
Figure 7.3. Typical flow diagram of reactor section of single stage hydrocracker (or first stage of a two
stage hydrocracker).
DISTILLATE HYDROCRACKING 291
R
H
2
F
Products
Recycle Oil
R
Feed
Figure 7.4. Two stage hydrocracking.
reactor are passed over a hydrocracking catalyst in the second reactor where most of
the hydrocracking takes place. The conversion occurs in the presence of NH
3
,H
2
S,
and small amounts of unconverted amounts of hetero compounds. The hydrotreating
catalyst in the first reactor is designed to convert the hetero compounds in the feed
stock. Typically, such catalysts comprise sulfided molybdenum and nickel on alumina
support. The reactor operates at temperatures varying from 570
◦
Fto800
◦
F (300–
425
◦
C) and hydrogen pressures between 1,250 and 2,500 psig (85–170 bar). Under
these conditions, in addition to heteroatom elimination, significant hydrogenation
occurs, and some cracking also takes place. The cracking reactor operates at the same
hydrogen pressures but at temperatures varying from 570 to as high as 840
◦
F (300–
450
◦
C) for amorphous hydrocracking catalysts and up to 440
◦
C (825
◦
F) for zeolite
containing catalysts.
Two stage recycle hydrocracking
The two stage hydrocracking process configuration is also widely used, especially for
large throughput units. In two stage units, the hydrotreating and some cracking takes
place in the first stage. The effluent from the first stage is separated and fractionated,
with the unconverted oil going to the second stage. The unconverted oil from the
second stage reaction section goes back to the common fractionator. A simplified
schematic of a two stage hydrocracker is shown in Figure 7.4. The catalysts in the first
stage are the same types as those used in the single stage configuration. The catalyst
in the second stage is operating in near absence of ammonia, and depending on the
particular design, in the absence or presence of hydrogen sulfide. The near absence of
NH
3
and H
2
S allows the use of either noble metal or base metal sulfide hydrocracking
catalysts.
Separate hydrotreat two stage hydrocracking
A variation of the typical two stage hydrocracking with common hydrogen circulation
loop is the separate hydrotreat hydrocracking shown in Figure 7.5 in which each stage