National Petrochemical & Refiners Association 1667 K Street, NW

Suite 700 Washington, DC

20006 202.457.0480 voice

202.457.0486 fax

www.npra.org Annual Meeting

March 21

- 23

, 2010 Sheraton and Wyndham
Phoenix, AZ



## AM

- 10

- 167 The B enefits of Cat Feed Hydrotreating and

the Impact of Feed N itrogen on Catalyst
S tability

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, TXThis 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

- 1 67 Page 1 The B e nefits of Cat Feed H ydrotreating and the I mpact of F eed N itrogen

on C atalyst S tability

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

ni trogen 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 mo re insight into catalyst stability. In the present paper, we discuss the different nitrogen compounds found in high nitrogen feedstocks to FCC p retreat 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 indust rial 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 a bout 220 of the 400 FCC complexes around the world are equip ped 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 c rude d istillation u nit, LC

- F iners

, vi sbreakers, plus CGO and HCGO from c okers.AM

- 10

- 1 67 Page 2 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 F CC 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 show n 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 content s . 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 r emoval of nitrogen improve s FCC performance with respect to conversion, gasoline yields and gasoline quality

. The o rganic nitrogen compounds in the feed

are removed catalytically by hydrodenitrogenation (HDN), which is generally the most difficult hydrotreatment rea ction.

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

- 1 67 Page 3 benzoquinolines, etc. Non

- basic compounds are mainly 5

- member ring com pounds, 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 Indole Boiling point: 489°F

Benzo(h)quinoline Boiling point: 640°F Carbazole Boiling point: 671°F

Acridine (dibenzo(b,e)pyridine or benzo(b)quinoline) Boiling point: 655°F 1,2

- Benzocarbazole

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 c rudes 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 kineti c 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 c atalyst stability is due to coke depositing o n the active sites

. O rganic 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:AM

- 10

- 1 67 Page 4 Figure 2 . Symmetric carbazole

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

O ther 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 e xtra h eavy c oker g as o il, 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 Topsø e’s NiMo/alumina catalyst s , TK

- 561 BRIM TM /TK

- 559 BRIM TM . Operating conditions of this particular unit are pre sented in Table 3. 

### N
H

4,8,9,10

- Tetrahydro

- cyclohepta[ def ]carbazoleAM

- 10

- 1 67 Page 5 Property Method XHCGO

feed Property Method VGO

feed S, wt% D 4294 1.66 Simulated d ist. D 7213 C N, ppm (w/w) D 4629 5988 0.5 wt% (IBP), °F 442

N b asic, 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 t otal, wt% D 6591 56.57 60 wt%, °F 797

1 r ing, wt% D 6591 11.95 70 wt%, °F 823

2 r ing, wt% D 6591 6.03 80 wt%, °F 855

3+ r ing, 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 p artial p ressure , psig 1600
LHSV , 1/hr 0.51

Table 3

. O perat ing 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 a ll the nitrogen

- containing compounds, were trapped on the silica SPE

- column.

Gas c hromatography with a n itrogen sensitive a tomic e mission detector (GC

- AED) was used to obtain qualitative results for the amount and identification of the different N

- compou nds.



### 3 Results a nd d iscussion

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

- basicAM

- 10

- 1 67 Page 6 compounds. There are, however, many different types of compounds with a very large number

of indivi dually 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, show ing 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 d ue 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 n itrogen 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 t he coke precursors and as such together with the operational temperature dictate the coke lay down and deactivation of the catalysts by coke

.AM

- 10

- 1 67 Page 7 3.2 Topsøe FCC pretreatment catalysts

Since the operation of no two FCC pretreating unit s is the same , the catalyst l oading must be optimized to meet the refiner’s objectives. To meet these challenges, Topsøe has developed a new generation of BRIM TM catalysts for FCC pretreatment:



### – TK

- 560 BRIM TM (CoMo)



### – TK

- 561 BRIM TM (NiMo)



### – TK

- 562 BRIM TM (CoMo)

3.3 Catalyst stability, impact of organic nitrogen and coke formation

Catalysts prepared with the BRIM TM technology have demonstrated hitherto unmatched stability.

F igure 4 illustrates the stability of a first

- generation NiMo BRIM TM catalyst, TK

- 559 BRIM TM

, operating at a total pressur e of 1800 psig and an HDS of 94% and HDN of 65%.

Figure 4

. Normalized HDS temperature for TK

- 559 BRIM TM

The TK

- 559 BRIM TM 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

.AM

- 10

- 1 67 Page 8 Recently, the top one

- third of the catalyst was replaced with the next generation BRIM TM
catalyst, TK

- 561 BRIM TM

.

Figure 5 . Normalized HDS temperature for TK

- 558 BRIM TM

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

TK

- 558 BRIM TM . 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 th e BRIM TM sites)

, or via the direct desulfurization route. It is also known that the hydrogenation route is strongly kine tically inhibited by nitrogen compounds and in particular by basic nitrogen species in the feed.

F rom real feed experiments on VGO it has been demonstrated that heavy organic nitrogen

containing 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, butAM

- 10

- 1 67 Page 9 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

site s) 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 de activation 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 typica l 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, onl y the direct desulfurization route is active at these conditions.

With the fundamental knowledge and understanding of the hydrogenation functionality and development of the BRIM TM preparation technology, BRIM TM catalysts not only have a very high activity due to the carrier developments and high dispersion of the active metals, but also a control led ratio between the direct sulfur extraction sites and the hydrogenation sites. With the

BRIM TM technology and the most recent generation of BRIM TM catalyst s

, not only the BRIM TM
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 BRIM TM VGO catal ysts 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 conditi ons, the hydrogenation functionality is heavily inhibited. The catalysts for FCC pretreatment such as TK

- 560 BRIM TM
(CoMo), TK

- 562 BRIM TM (CoMo) and TK

- 561 BRIM TM (NiMo) are prepared in such a way as to maximize the number of sites applicable for hydrotrea ting 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 imp act on the catalyst performance. Among such contaminants, the most often encountered are organic metals (Fe, Ni and V), silica and arsenic.AM

- 10

- 1 67 Page 10 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

– 2 0 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 req uired to

deal with such high level s 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 porphyr e nes. 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 main tain its HDS function while being exposed to a high level of contaminants, but one of the unique features of the BRIM TM technology catalysts is their robust pore system, giving a very high poison tolerance. From analysis of spent BRIM TM
VGO catalyst from a ctual 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 BRIM TM 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

. D emetallation 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

- 1 67 Page 11 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 flo w 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 unit s 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 str ong negative impact especially on HDN activity and a moderate negative impact on HDS activity. Due to the formulation and composition

, the Topsøe BRIM TM catalysts optimized for VGO services with their high porosity and surface area

, these catalysts have a very large tolerance for silicon contamination.AM

- 10

- 1 67 Page 12 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 TopTrap TM 0.34 0.26 1.45

–

TK

- 709 r ing 3.14 3.58 1.56 1.53

TK

- 711 r ing 7.48 7.30 2.67 1.62

TK

- 831 r ing 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 h eavy c oker

g as 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 crude s , in particular Russian, Venezuelan, Af rican, 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 adsorb s or reduce s 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 . R emoval of arsenic in the top of the pretreater is necessary in order to protect the main bed catalysts in theAM

- 10

- 1 67 Page 13 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 sha pe, and TK

- 47, which is a quadral obes type.

3.6 Optimum catalyst selection

The new series of BRIM TM 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 struct ures, cleaner FCC products and in particular longer operating cycles.

A high activity of the BRIM TM catalyst s 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 specification s , the increased activity of th e BRIM TM 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 NiM o (TK

- 561 BRIM TM ) and/or CoMo (TK

- 560 BRIM TM and TK

- 562

BRIM TM ) based pretreatment catalysts is dictated by the unit pressure, feed nitrogen, operating temperature and desired product properties. The CoMo based TK

- 560 BRIM TM and TK

- 562

BRIM TM catalysts wil l provide the best performance in low to moderate pressure units. Due to

the BRIM TM technology, TK

- 560 BRIM TM and TK

- 562 BRIM TM both exhibit an unmatched HDN activity that is unique for a CoMo based catalyst.

TK

- 562 BRIM TM is the catalyst of choice for th e 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 BRIM TM
catalyst exhibits equal or better H DN activity to that of the sister NiMo catalyst, TK

- 561 BRIM TM

.AM

- 10

- 1 67 Page 14 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 TK

561 BRIM TM due to its higher activity at these conditions

.



### 4 Conclusion

Topsøe has developed its next generation of BRIM TM catalyst for FCC pretreatment service. Using the BRIM TM technology, the CoMo based TK

- 560 BRIM TM and TK

- 562 BRIM TM catalysts

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

- 561

BRIM TM 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 si licon, 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 catalyst s for VGO service

, results in unmatched cycle length in FCC pretreaters

.



### 5 References

1. Bettati, A., Zeuthen, P.; Hidalgo

- Vivas, A (2005) Nitrogen tolerance of hydrocracking catalysts. In Topsøe Hydrocracking Catalyst and Technology Seminar 2005, Copenhagen

. 2. Dorbon, M.; Igniatiadis, I.; Schmitter, J.M.; A rpino, 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 High

Pressure Catalytic Hydroprocessing. Ind. Eng. Chem. Res. 30, 2021

- 2058

. 4. Hidalgo

- Vivas, A.; Knudsen, K.G.; Zeuthen, P. (2003) Kinetic modelling of VGO hydrotre atment in FCC pretreatment service. AIChE Spring Meeting, Paper T8a12a.

5. Igniatiadis, I.; Kuroki, M.; Arpino, P. (1986) Identification of ca rbazole 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 petroleum expulsion on pyrrolic nitrogen compound yields and distribution in Duver nay 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 oil s. Ind. Eng. Chem. Res. 39(2), 533

- 540

. 9. Zeuthen, P.; Knudsen, K.; Whitehurst, D.D. Organic nitrogen compounds in gas oil blends, their hydrotreated products and the importance to hydrotreatment. Catal. Today 2001, 65(2

- 4), 307

- 314

.