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Annual Meeting

March 21-23, 2010

Sheraton and Wyndham

Phoenix, AZ

AM-10-167 The Benefits of Cat Feed Hydrotreating and 

the Impact of Feed Nitrogen on Catalyst 

Stability

Presented By:

Per Zeuthen

Haldor Topsøe

Lyngby, Denmark

Michael T. Schmidt

Haldor Topsøe

Lyngby, Denmark

Henrik W. Rasmussen

Haldor Topsøe

Houston, TX

Brian M. Moyse

Haldor Topsøe

Houston, TX
This paper has been reproduced for the author or authors as a courtesy by the National 

Petrochemical & Refiners Association. Publication of this paper does not signify that the 

contents necessarily reflect the opinions of the NPRA, its officers, directors, members, or staff. 

Requests for authorization to quote or use the contents should be addressed directly to the 

author(s)
AM-10-167

Page 1

The Benefits of Cat Feed Hydrotreating and the Impact of Feed Nitrogen

on Catalyst Stability

Per Zeuthen and Michael T. Schmidt 1

Henrik W. Rasmussen and Brian M. Moyse 2

1 Haldor Topsøe, Nymøllevej 55, 2800 Lyngby, Denmark

2 Haldor Topsøe, 17629 El Camino Real, Houston, Texas 77058, USA

Abstract

This paper deals with the objectives and constraints of pretreating feedstocks for fluid catalytic 

cracking. It will look at the chemistry involved and, based upon new insights, will consider feed 

nitrogen and its impact on the selection of catalyst type for the most stable performance. 

Currently, there is a growing need to refine heavier and tougher crude oils with an increased 

nitrogen content and other contaminants such as polyaromatics, metals, arsenic and silicon. 

Therefore, not only hydrodesulfurization (HDS) is very important, but also hydrodenitrogenation 

(HDN) has become a critical hydroprocessing reaction which provides more insight into catalyst 

stability. In the present paper, we discuss the different nitrogen compounds found in high 

nitrogen feedstocks to FCC pretreat which we have identified using gas chromatography with 

atomic emission detection (GC-AED). Our findings can be related to several studies using 

model feedstocks which show that in particular basic nitrogen-containing molecules inhibit HDS 

reactions the most. We will discuss factors that impact the catalyst stability, and finally we will 

show data from industrial units.

1 Introduction

There is a worldwide capacity of 16 MM BPD of FCC which produces about 10 MM BPD of 

gasoline. Approximately 40%, or 6.5 MM BPD, of FCC feed is currently pretreated and about 

220 of the 400 FCC complexes around the world are equipped with a pretreater. Depending on 

the feed composition and refinery flow scheme, the feedstock to the FCC can be fully or partially 

hydrotreated. Cat Feed hydrotreaters vary in size with the smallest containing only 350 cu ft of 

catalyst and the largest containing as much as 43,000 cu ft of catalyst. All, however, have the 

same objectives, namely to reduce the feed sulfur and simultaneously to remove nitrogen and 

saturate aromatics in order to maximize the profitability of the FCC.

The feedstock to these FCC pretreaters exhibits a lot of variation, but the units usually process 

feed blends of HAGO, LVGO and HVGO derived from crude distillation unit, LC-Finers, 

visbreakers, plus CGO and HCGO from cokers.
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Although it is well established that organic FCC feed nitrogen and aromatics are key parameters 

for the profitability of the FCC and that a slight additional FCC gasoline make has significant 

additional benefits for the overall economy, most of these many Cat Feed hydrotreaters are 

being operated in order to produce a certain sulfur level in the FCC feed for the longest possible 

cycle length. The reason for this is that FCC gasoline is the main source of sulfur in the gasoline 

pool, and the amount of sulfur in the FCC gasoline is closely related to the sulfur level in the 

FCC feed. A typical relationship between the sulfur concentration in the feed to the FCC and the 

sulfur in the gasoline is shown in Figure 1.

Figure 1. Typical FCC feed sulfur vs. gasoline sulfur

In other words, the refinery scheme sets the sulfur requirements for the pretreater unit and once 

this is fixed, catalyst stability is of prime importance.

In addition to the sulfur requirements, there is a growing interest in processing heavy oils and 

extra heavy oils with much higher nitrogen contents. It is our experience that there has been a 

20% increase in nitrogen content of feeds to FCC units over the past 5 years. Nitrogen is a 

poison for FCC catalysts, and removal of nitrogen improves FCC performance with respect to 

conversion, gasoline yields and gasoline quality. The organic nitrogen compounds in the feed 

are removed catalytically by hydrodenitrogenation (HDN), which is generally the most difficult 

hydrotreatment reaction. 

Most of the nitrogen is present as heterocyclic compounds with multiple aromatic rings. Basic 

compounds are mainly 6-member ring nitrogen-containing compounds, e.g. quinolines, 
AM-10-167

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benzoquinolines, etc. Non-basic compounds are mainly 5-member ring compounds, e.g. 

indoles, carbazoles, etc. For ready reference, some of these chemical structures are shown in

Table 1.

Basic Non-basic

Quinoline

Boiling point: 460°F

b

c

f d

g

h

N

Indole

Boiling point: 489°F

N

H

2

3

4

5

6

7

Benzo(h)quinoline

Boiling point: 640°F

N

Carbazole

Boiling point: 671°F

N

H

1

2

3

5 4

6

7

8

Acridine

(dibenzo(b,e)pyridine 

or benzo(b)quinoline)

Boiling point: 655°F

N

1,2-Benzocarbazole

N

H

Table 1. Structures of selected organic nitrogen compounds

Typically, half the total nitrogen is concentrated in the heaviest 30% in heavy feeds (Bettati 

et al., 2005 and references therein) with carbazole compounds substituted at position 1 being 

the most abundant (Wiwel et al., 2000). The high relative concentrations of 1-substituted 

carbazoles in crudes are attributed to preferential migration of nitrogen compounds having 

sterically shielded N-centers. Di- and tri-methyl carbazoles with substitution at position 1 were 

observed to be the most dominant species.

Considerable attention has been paid to elucidate the problem of nitrogen compound inhibition 

because the effects are not only important from a process point of view, but also influence the 

development of hydroprocessing catalysts. Organic nitrogen compounds have a significantly 

negative kinetic effect (i.e are inhibitors) on hydrotreating reactions such as hydrodesulfurization 

(HDS), hydrogenolysis reactions and on hydrogenation reactions as well as playing a key role in 

the catalyst stability. The catalyst stability is due to coke depositing on the active sites. Organic 

nitrogen compounds together with polyaromatics are known as the coke precursors for which 

reason removal of the same plays a role for the catalyst stability.

Haldor Topsøe researchers have recently found another type of carbazole which exhibits an 

extremely low reactivity even in high-pressure hydrotreating:
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Figure 2. Symmetric carbazole

The symmetry of this molecule is an indication that it is very stable and therefore difficult to 

hydrotreat.

Other species are found in most feedstocks, including trace amounts of organic metal 

compounds such as vanadium, nickel and iron. These metals are typically found in levels of 0.5

– 5 ppm in total. Arsenic and silicon are also frequently present and will be dealt with below.

2 Experimental

2.1 Characterization of FCC feed and typical operating conditions from a US refiner

In this study, an extra heavy coker gas oil, XHCGO, from an US refiner was investigated. The 

feed, with properties shown in Table 2, is typically fed to the FCC pretreater in this case loaded 

with Haldor Topsøe’s NiMo/alumina catalysts, TK-561 BRIMTM/TK-559 BRIMTM. Operating 

conditions of this particular unit are presented in Table 3.

N

H

4,8,9,10-Tetrahydro-cyclohepta[def]carbazole
AM-10-167

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Property Method XHCGO 

feed

Property Method VGO 

feed

S, wt% D 4294 1.66 Simulated dist. D 7213 C

N, ppm (w/w) D 4629 5988 0.5 wt% (IBP), °F 442

N basic, wt ppm HTAS 1822

H, wt% D 7171 H 10.25 5 wt%, °F 610

API D 4052 11.8 10 wt%, °F 652

20 wt%, °F 693

30 wt%, °F 721

Si, wt ppm HTAS 0.44 40 wt%, °F 748

As, wt ppb HTAS 77 50 wt%, °F 773

Aromatics total, wt% D 6591 56.57 60 wt%, °F 797

1 ring, wt% D 6591 11.95 70 wt%, °F 823

2 ring, wt% D 6591 6.03 80 wt%, °F 855

3+ ring, wt % D 6591 38.59 90 wt%, °F 903

Fe/Ni/V, wt ppm HTAS 0.5/0.5/1 99.5 wt% (FBP), °F 1076

Table 2. XHCGO feed properties

Test conditions Condition 1

Hydrogen partial pressure, psig 1600

LHSV, 1/hr 0.51

Table 3. Operating conditions

2.2 Characterization of the organic nitrogen compounds

Prior to analysis, the nitrogen-containing compounds were concentrated by using silica-based 

solid-phase extraction (500 mg Si-SPE) using a procedure similar to that described by Li et al. 

(1997). Non-polar compounds were flushed through the column whilst the polar compounds, 

including all the nitrogen-containing compounds, were trapped on the silica SPE-column. 

Gas chromatography with a nitrogen sensitive atomic emission detector (GC-AED) was used to 

obtain qualitative results for the amount and identification of the different N-compounds.

3 Results and discussion

3.1 Feed nitrogen and sulfur

The chromatogram of the XHCGO feed is shown in Figure 3. We can ascertain that very large 

amounts of carbazoles and benzocarbazoles are present in the chromatogram. Some of the 

compounds hidden in the hump may be various basic nitrogen compounds. The basic nitrogen 

compounds are not found in any distinct group of compounds as is the case for the non-basic 
AM-10-167

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compounds. There are, however, many different types of compounds with a very large number 

of individually substituted members. In the group of carbazoles, compounds substituted in the 

position 1 are the most abundant. In the chromatogram, several minor peaks of unidentified 

nitrogen-containing compounds dominate. This plot, showing the different organic species in a 

coker derived feed, is very different from what is seen in a typical SR feed where the complexity 

is even higher. Even though the number of different organic nitrogen species is much lower in a 

coker derived feed, the compound classes are the same. The reduction seen in complexity is 

probably due to the high temperature treatment of the species in the coker where the less stable 

or semi stable N compounds are altered into fewer but stable species. 

Figure 3. GC-AED nitrogen chromatogram of XHCGO FCC pretreater feed

In hydrotreating of FCC feedstock, the impact of inhibitors on the desulfurization reaction is 

considerable. Often less than 1000 wt ppm organic nitrogen are found in a simple straight-run 

feedstock, but in thermally derived feedstocks as shown in this study, as much as 3000 – 6000 

wt ppm organic nitrogen is found. Organic nitrogen has a strong negative impact on the catalyst 

performance. Together with the organic nitrogen, the polyaromatic constituents are found to be 

among the coke precursors and as such together with the operational temperature dictate the 

coke lay down and deactivation of the catalysts by coke.
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3.2 Topsøe FCC pretreatment catalysts

Since the operation of no two FCC pretreating units is the same, the catalyst loading must be 

optimized to meet the refiner’s objectives. To meet these challenges, Topsøe has developed a 

new generation of BRIMTM catalysts for FCC pretreatment:

– TK-560 BRIMTM (CoMo)

– TK-561 BRIMTM (NiMo)

– TK-562 BRIMTM (CoMo)

3.3 Catalyst stability, impact of organic nitrogen and coke formation

Catalysts prepared with the BRIMTM technology have demonstrated hitherto unmatched stability. 

Figure 4 illustrates the stability of a first-generation NiMo BRIMTM catalyst, TK-559 BRIMTM, 

operating at a total pressure of 1800 psig and an HDS of 94% and HDN of 65%.

Figure 4. Normalized HDS temperature for TK-559 BRIMTM

The TK-559 BRIMTM has been used in this unit for two consecutive cycles. The first cycle was 

3 years, which was 1 year longer than any of the previous cycles. The current cycle shown in 

Figure 4 was after a skim after 850 days to extend the cycle for an additional 2-3 years. 

Normalized Weighted Average Bed Temperature

TK-559BRIMTM in FCC Pretreat Service

600

625

650

675

700

725

750

775

800

0 100 200 300 400 500 600 700 800 900 1000 1100

Run Days Normalized WABT HDS (°F)

Deactivation Rate: ~0.7 °F/month

Skimming of the 

top 1/3 of the 

catalyst volume.
AM-10-167

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Recently, the top one-third of the catalyst was replaced with the next generation BRIMTM

catalyst, TK-561 BRIMTM.

Figure 5. Normalized HDS temperature for TK-558 BRIMTM

The data in Figure 5 is from a low pressure FCC pretreat unit using our CoMo BRIMTM catalyst 

TK-558 BRIMTM. This unit operates at an LHSV of 1.5 and a hydrogen partial pressure of only 

525 psig.

It has been well established that conversion of organic sulfur and nitrogen species can proceed 

both via the fast hydrogenation route (using the BRIMTM sites), or via the direct desulfurization 

route. It is also known that the hydrogenation route is strongly kinetically inhibited by nitrogen 

compounds and in particular by basic nitrogen species in the feed. 

From real feed experiments on VGO it has been demonstrated that heavy organic nitrogencontaining compounds are the major inhibitors to the hydrogenation functionality during HDS 

(Hidalgo-Vivas et al., 2003) and thus a detrimental effect to the hydrogenation step in the 

hydrodesulfurization, hydrocracking and saturation of other molecules is to be expected.

In VGO hydrotreating, the presence of inhibitors to the desulfurization reaction is most often 

considerable, even with only 700 ppm nitrogen and about 8 wt% polyaromatics in the feed, but 
AM-10-167

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in this particular XHCGO, the content of nitrogen is as high as 6000 ppm and the content of 

PNA’s is more than 35 wt%. These species are also known as coke precursors. Some of the 

catalyst deactivation is due to coke depositing on the active sites, and since coke formation 

proceeds via coke precursors with high π-electron density, these hydrogenation sites (the BRIM

sites) are more susceptible to this form of deactivation. During the run, the operating 

temperature is raised to compensate for the deactivation of the catalyst, which results in an 

unfavorable shift in the equilibrium of the hydrogenation reactions and the deactivation will 

increase.

Even in severe VGO services where product sulfur requirements are 200-300 ppm sulfur, the 

concentration of inhibitors in the product can still be high due to the low reactivity of these 

species. It is thus clear that under typical FCC pretreatment conditions due to the high 

concentration of nitrogen species, the fast hydrogenation route is heavily impaired by adsorbed 

organic nitrogen species and aromatics and thus exhibits a very low reaction rate. For all 

practical purposes, only the direct desulfurization route is active at these conditions.

With the fundamental knowledge and understanding of the hydrogenation functionality and 

development of the BRIMTM preparation technology, BRIMTM catalysts not only have a very high 

activity due to the carrier developments and high dispersion of the active metals, but also a 

controlled ratio between the direct sulfur extraction sites and the hydrogenation sites. With the 

BRIMTM technology and the most recent generation of BRIMTM catalysts, not only the BRIMTM

site hydrogenation activity, but also the number of sites for the direct desulfurization is 

enhanced. This insight makes this technology very suitable for hydrotreating applications over a 

wide pressure range and different feeds.

For a given catalyst using primarily the hydrogenation route for desulfurization and with less 

direct desulfurization sites, the apparent performance will drop dramatically, whereas the 

performance deterioration for catalysts such as the Topsøe BRIMTM VGO catalysts with a very 

high activity for the direct route will be less affected by the VGO feed contaminants. 

As discussed above, due to the large amounts of organic nitrogen and polyaromatics even in 

the product as achieved under most FCC pretreatment conditions, the hydrogenation 

functionality is heavily inhibited. The catalysts for FCC pretreatment such as TK-560 BRIMTM

(CoMo), TK-562 BRIMTM (CoMo) and TK-561 BRIMTM (NiMo) are prepared in such a way as to 

maximize the number of sites applicable for hydrotreating via the direct route which results in 

optimal stability under these severe conditions. 

3.4 Catalyst stability and metals deactivation

In addition to deactivation by coke, there are also other contaminants found in most FCC feeds 

that have a negative impact on the catalyst performance. Among such contaminants, the most 

often encountered are organic metals (Fe, Ni and V), silica and arsenic.
AM-10-167

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Most of the FCC pretreater feeds contain about 0.5 – 5.0 ppm metals (sum of Fe, Ni and V), but 

in some cases feeds with as much as 15 – 20 ppm metals are seen. Fractionation issues in the 

vacuum tower results in resid being entrained in the VGO to be processed in the FCC which can 

easily lead to these rather high levels of feed metals. A tailored catalyst system is required to 

deal with such high levels of heavy metals. A high feed metal content implies a rapid 

deactivation if not properly protected by HDM guard catalysts. Feed metals species are often in 

the form of iron, nickel and vanadium/vanadyl porphyrenes. These react with hydrogen and 

hydrogen sulfide and form metal sulfides which are trapped in the catalyst pore system 

restricting the accessibility to the catalytic active sites. A conventional HDS catalyst with a 

traditional pore system would not be able to maintain its HDS function while being exposed to a

high level of contaminants, but one of the unique features of the BRIMTM technology catalysts is 

their robust pore system, giving a very high poison tolerance. From analysis of spent BRIMTM

VGO catalyst from actual units, we have demonstrated that the catalysts are able to withstand a 

contaminant level of more than 8-10 wt% Ni+V while still providing activity for removing sulfur 

and nitrogen.

Such a high metal tolerance is one of the key parameters making the BRIMTM catalysts the most 

stable and robust catalysts in the current market. 

The Ni and V species are very large molecules, and it is thus necessary to tailor the pore size 

and structure of the demetallation (HDM) catalyst to get maximum metals pickup. Demetallation 

catalysts were originally designed for resid hydrotreater service which all operate at a very high 

pressure in the order of 2200 psi or more, and the metals content can be 200 wt ppm or more 

Ni+V. The driving force for the metals pickup is thus very different in a resid unit than in a typical 

FCC pretreat unit at the much lower pressure and 3 – 5 wt ppm metals. It is therefore necessary 

to use a different type of demetallation catalyst in an FCC pretreat unit in order to maximize the 

pickup of Ni and V. Haldor Topsøe has developed a new demetallation catalyst designated 

TK-745 for VGO service. This catalyst can pick up as much as 35 – 40 wt% Ni+V in typical VGO 

service.
AM-10-167

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Figure 6. Scan of vanadium across the diameter of a Topsøe demetallation catalyst

Figure 6 shows a vanadium scan across the diameter of our demetallation catalyst used in VGO 

service, and it clearly shows that the vanadium is evenly distributed throughout the catalyst 

particle due to optimized pore structure.

3.5 Silicon and arsenic poisoning

Silica in the VGO fraction can originate from the antifoam usage in the cokers, but today we also 

see lots of silica in SR VGO feed originating from emulsion breakers and flow improvers used in 

the upstream exploration and in pipelines. These silicon molecules which are not originating 

from antifoam are typically very large molecules, and thus, the catalyst used as silicon pickup 

guard catalyst in naphtha units and diesel units feeding coker stock will not be very effective as 

a silicon trap in VGO service. Therefore, it was necessary to modify the well-proven coker 

naphtha silicon guard catalysts to be able to handle these much larger silicon molecules present 

in the VGO feed. This new catalyst is called TK-453.

The silicon species present in the feed adsorb strongly on the catalyst carrier and in a similar 

way to catalyst coking and slowly reduce the accessibility to the catalytic active sites. Silicon 

contamination has a strong negative impact especially on HDN activity and a moderate negative 

impact on HDS activity. Due to the formulation and composition, the Topsøe BRIMTM catalysts 

optimized for VGO services with their high porosity and surface area, these catalysts have a 

very large tolerance for silicon contamination.
AM-10-167

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Catalyst Metals Relative 

k(HDS)norm

Relative 

k(HDM)norm

Relative 

k(HDSi)norm

TK-743

1/20” QL

Ni/Mo 100 100 100

TK-453

1/20” QL

Ni/Mo 105 124 139

Table 4

Table 4 shows that TK-453 exhibits a higher activity for desulfurization, metals removal and 

silicon removal compared to previous generation TK-743 demetallation catalyst.

The following data in Table 5 shows the metals pickup from spent catalyst removed from the top 

of an FCC pretreat unit in the US.

Catalyst Ni, wt% V, wt% Fe, wt% Si, wt%

TK-25 TopTrapTM 0.34 0.26 1.45 –

TK-709 ring 3.14 3.58 1.56 1.53

TK-711 ring 7.48 7.30 2.67 1.62

TK-831 ring 7.98 7.89 2.07 1.60

TK-743 QL 8.39 8.50 2.40 1.48

TK-453 QL 8.93 9.18 1.53 1.57

Table 5

The feed to the unit from which these catalyst samples were taken is a mixture of heavy coker 

gas oil (HCGO) and HVGO (40/60% split) with a feed metals content of about 6-8 wt ppm 

Ni + V.

The table shows that even though TK-453 is protected by a layer of TK-743, it was still able to 

pick up more Ni, V and Si than TK-743 due to its optimized pore system and better 

demetallation activity.

Catalyst poisoning by arsenic is a growing problem, as more crudes, in particular Russian, 

Venezuelan, African, US West Coast and Canadian syncrudes contain significant amounts of 

arsenic. The XHCGO listed in Table 2 contains 77 ppb of arsenic, which is a significant amount. 

Arsenic is not a contaminant that adsorbs or reduces the accessibility to the active sites like

coke deposits and metals precipitation neither it is an inhibitor like organic nitrogen species, but 

it is a true catalyst poison and a very strong catalyst poison as shown in Table 6. Removal of 

arsenic in the top of the pretreater is necessary in order to protect the main bed catalysts in the 
AM-10-167

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pretreater from arsenic poisoning as well as in any of the downstream FCC processes such as 

gasoline post treaters.

Arsenic As 100

Lead Pb 10

Sodium Na 3

Metals Ni + V 3

Silicon Si 1

Table 6. Catalyst poisons in order of relative severity

Topsøe has developed two arsenic trap catalysts which have proven to be very effective in FCC 

pretreat service: TK-45, which is a high void ring shape, and TK-47, which is a quadralobes

type.

3.6 Optimum catalyst selection

The new series of BRIMTM catalysts from Topsøe will in most cases enable the refiners to meet 

the strict specifications for ultra low sulfur gasoline without post treatment. The economic benefit 

is gained from better product yield structures, cleaner FCC products and in particular longer 

operating cycles. 

A high activity of the BRIMTM catalysts in FCC pretreatment service is also of great importance 

for HDN and to the saturation of aromatic compounds, which positively affects the yield and 

quality of the gasoline produced in the FCC. With tighter fuel specifications, the increased 

activity of the BRIMTM catalysts is thus primarily utilized to achieve better product properties. 

Traditionally, NiMo catalysts have been looked upon as having a higher HDN activity for FCC 

pretreatment service and CoMo catalysts as having a higher HDS activity. A high HDN activity is 

desirable for removal of nitrogen compounds and in particular basic nitrogen compounds from 

the FCC feeds. These compounds would otherwise adversely affect the yield of the gasoline 

produced in the FCC unit.

The optimal choice between NiMo (TK-561 BRIMTM) and/or CoMo (TK-560 BRIMTM and TK-562 

BRIMTM) based pretreatment catalysts is dictated by the unit pressure, feed nitrogen, operating 

temperature and desired product properties. The CoMo based TK-560 BRIMTM and TK-562 

BRIMTM catalysts will provide the best performance in low to moderate pressure units. Due to 

the BRIMTM technology, TK-560 BRIMTM and TK-562 BRIMTM both exhibit an unmatched HDN 

activity that is unique for a CoMo based catalyst.

TK-562 BRIMTM is the catalyst of choice for the refiner who wishes to produce low sulfur 

gasoline without changing yields of gasoline or other high quality products for the longest 

possible cycle. In many low to moderate pressure applications, the Topsøe CoMo BRIMTM

catalyst exhibits equal or better HDN activity to that of the sister NiMo catalyst, TK-561 BRIMTM.
AM-10-167

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In high pressure FCC pretreatment plants and in cases where nitrogen and VGO conversion is 

the main concern due to the performance of the FCC complex, the preferred choice will be TK561 BRIMTM due to its higher activity at these conditions. 

4 Conclusion

Topsøe has developed its next generation of BRIMTM catalyst for FCC pretreatment service. 

Using the BRIMTM technology, the CoMo based TK-560 BRIMTM and TK-562 BRIMTM catalysts 

were developed for FCC pretreatment at low to moderate pressures and the NiMo, TK-561 

BRIMTM for the high pressure applications. Due to their very low sensitivity to feed inhibitors 

such as organic nitrogen and aromatics and high tolerance to feed metals and silicon, these 

catalysts show high activities and unusually high stabilities with low hydrogen consumption. 

Combining these new main bed catalysts with tailor-made demetallation and silica guard 

catalysts for VGO service, results in unmatched cycle length in FCC pretreaters. 

5 References

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catalysts. In Topsøe Hydrocracking Catalyst and Technology Seminar 2005, Copenhagen.

2. Dorbon, M.; Igniatiadis, I.; Schmitter, J.M.; Arpino, P.; Guiochon, G.; Toulhout, H.; Huc, 

A.(1984) Identification of carbazoles and benzocarbazoles in a coker gas oil and influence of 

catalytic hydrotreatment on their distribution. Fuel 63 (4), 565.

3. Girgis, M.J.; Gates, B.C. (1991) Reactivities, Reaction Networks, and Kinetics in HighPressure Catalytic Hydroprocessing. Ind. Eng. Chem. Res. 30, 2021-2058.

4. Hidalgo-Vivas, A.; Knudsen, K.G.; Zeuthen, P. (2003) Kinetic modelling of VGO 

hydrotreatment in FCC pretreatment service. AIChE Spring Meeting, Paper T8a12a.

5. Igniatiadis, I.; Kuroki, M.; Arpino, P. (1986) Identification of carbazole derivatives in a 

hydrotreated coker gas oil by gas chromatography and gas chromatography - mass 

spectrometry. J. Chromatogr. 366, 251-260.

6. Laredo, G.C.; Montesinos, A.; De los Reyes, J.A. (2004) Inhibition effects observed between 

dibenzothiophene and carbazole during the hydrotreating process. Appl. Catal. A 265 (2), 

171-183.

7. Li, M.; Yao, H.; Stasiuk, L.D.; M.G. Fowler, M.G.; Larter, S.R.(1997) Effect of maturity and 

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Formation petroleum source rocks in Alberta, Canada. Organic Geochemistry 26, 731-744.

8. Wiwel, P.; Knudsen, K.; Zeuthen, P.; Whitehurst, D. (2000) Assessing compositional 

changes of nitrogen compounds during hydrotreating of typical diesel range gas oils. Ind. 

Eng. Chem. Res. 39(2), 533-540.

9. Zeuthen, P.; Knudsen, K.; Whitehurst, D.D. Organic nitrogen compounds in gas oil blends, 

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4), 307-314.