1

M.2.1.2

R&D on Technology for Hydrotreatment of

Residual Oil of High Metal Content

(High metal residual oil hydrotreatment group) Yokohama No. 405 Laboratory � Hideshi Iki, Yoshiaki Fukui, Kazuaki Hayasaka, Yoshiaki Ishii, Hidenobu Takahashi, Saburo Miura

1. R&D Objectives

1.1 R&D Background

Among crude oils, there is atmospheric residual oil and vacuum residual oil. The metal and

sulfur conpounds of these residual oils are removed through hydrotreatment with a

residual-desulfurization unit, and the product oil thus obtained can be taken as low-sulfur heavy

oil or FCC (fluid catalytic cracker) feedstock. The residual-desulfurization unit is comprised of a

demetalization section and a desulfurization section, and catalyst matching the objectives of

each of these section is provided. In the demetalization section, it is mainly demetalization

reactions (removal of V and Ni) that take place. In the residual oils of Middle Eastern crude oil

containing a metal constituent of 100 massppm, the metal concentration is reduced to 50-30

massppm or below at the demetalization unit outlet of a regular direct desulfurization unit.

In the residual oils from heavy crude oil, which is relatively low in price, the metal content is high.

In Iranian heavy or Arabian heavy, for instance, the metal content of residual oil exceeds 200

ppm. If this residual oil undergoes hydrotreatment, it is imperative that the metal constituent be

removed adequately, especially at the demetalization section. If metal is not removed, the post

desulfurization catalyst is poisoned and desulfurization activity quickly deteriorates. Accordingly,

when residual oil of high metal content (200 massppm or more) has been treated, the metal

content of the demetalized oil must be kept at a metal concentration of 50-30 massppm or less,

the same as that of regular feedstock. In addition, a portion of the produced oil is cracked by

FCC into intermediate fraction, but if the metal content remaining in residual-desulfurized

produced oil is higher, FCC catalyst deterioration progresses, gasoline yield drops and the

amount of catalyst used increases, all of which have adverse impacts economically.

1.2 R&D Objectives

In the present R&D, the objective is to develop a demetalization catalyst, and its application

technology, which becomes the key factor in hydrotreatment of heavy residual oil of high metal

content.

Based on current catalytic performance, the target was to develop a hydrotreatment catalyst for

fixed bed whereby hydrotreatment could be implemented stably for a one-year period so that

when residual oil (Ni + V 200 massppm or above) obtained from crude oil in the Iranian heavy

class, which is of heavy metal content, is taken as the feedstock, the metal content of the

produced oil subjected to demetalization drops to 30 massppm or below.

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2. R&D Contents

In order to treat residual oil of high metal content, the performance of demetalization catalyst

loaded at a stage prior to residual-desulfurization must be improved, the cumulative permissible

metal content must be raised, and the life of the demetalization catalyst must be prolonged. In

order to clear these hurdles, the aim of the present research is to elevate demetalization activity

through optimization of pore structure and to prolong service life. R&D has thus been conducted

on catalyst production technology and on catalyst application technology.

First of all, a detailed analysis was conducted on the residual oil to become feedstock, and the

characteristics of the feedstock were determined. In addition, technology was developed for

preparation of demetalization catalysts having pores of varied diameter and configuration.

Production of these catalysts on an industrial scale was also investigated.

These developed catalysts were evaluated in a high-pressure bench-scale reactor, using

feedstock of high metal content, and the relationship between pore structure and demetalization

activity was systematically analyzed.

The developed demetalization catalyst was combined with desulfurization catalyst and carried

out a life test. Simulator was developed in order to forecast the trend in catalytic activity at high

precision.

3. R&D Results

3.1 Analysis of Residual Oil of High Metal Content

In order to determine the characteristics of crude oil of high metal content, each type of residual

oil was fractionated into asphaltene, maltene, etc., and analyzed. The distribution in molecular

weight of the asphaltene component is shown in Figure 1. Residual oil becomes heavy and of

high metal content in the sequence: A, B, C and D. The vertical axis shows the amount of

asphaltene contained. We can see that the greater the metal content in the residual oil, the

greater becomes the amount of asphaltene it contains. What is more, in residual oil of high

metal content, asphaltene of high molecular weight becomes abundant.

Figure 2 presents concentrations of metal content in residual oil and the state of distribution of

metal content to asphaltene. In each of the residual oils, 50 percent or more of the total metal

content is included in the asphaltene. In residual oil of high metal content, in particular, if the

metal content of produced oil is to reach the target of 30 ppm, a demetalization reaction must be

carried out from 50% or more of the asphaltene.

3

Sm

all ←

Asphaltene c

onte

nt →

Larg

e

Small ← Molecular weight → Large

Residual oil D

Residual

oil C

Residual

oil B

Residual

oil A

Meta

l (N

i +

V)

concentr

ation

(massppm

)

Metal content in residual oil

Metal content in asphaltene

Figure 1: Distribution of

Asphaltene in Residual

Oil by Molecular Weight

Figure 2: State of Metal Component

Distribution in Residual Oil

3.2 Design of Demetalization Catalyst

(a) Basic policy for catalyst design

Among the causes of a decline in activity by hydrotreatment catalyst for residual oil are

blockage of the catalytic pore inlets due to the accumulation of metal on the catalyst and

coating of active points due to the deposition of carbons. In demetalization catalyst used for

processing residual oil of high metal content, the impact of pore blockage by metal that

accumulates in the demetalization reaction is especially large, as shown in Figure 3.

Coke

Sulfur molecules included Metal molecules included Pore

Accumulated metal Active site

Catalyst support

Figure 3: Catalyst Deterioration by Metal Accumulation

To obtain a catalyst whereby such deterioration of activity is curtailed and demetalization

reaction is promoted effectively, progress is being made in the present research toward

development of catalyst having a bimodal structure in which relatively large pores (macropores)

and small pores (mesopores) are combined. Here pores 500Å or less in diameter are dubbed

“mesopores,” and pores 500Å or greater in diameter are “macropores.”

(b) Optimization of pore structure

Demetalization reactions with catalyst of different mesopore diameter were evaluated using

the same feedstock, and a basic investigation was made of the relationship between

demetalization performance and pore diameter or pore structure. Table 1 below gives

feedstock properties, and Table 2 gives bench operation conditions.

4

The properties of catalyst used in evaluation are presented in Table 3.

Table 1: Feedstock Properties Table 2: Bench Operation Conditions

Feedstock Operation conditions

Density g/cc 0.977 Reaction temperature ℃ 375

Sulfur content mass% 3.78 Pressure MPa 16.7

Metal content massppm 99 LHSV 0.56

Hydrogen-oil ratio NL/L 1,100

Table 3: Catalyst Physical Properties*

Catalyst Ａ Ｂ Ｃ

Mesopore diameter 1.00 1.18 1.16

Surface area 1.00 1.10 1.04

Ni/Mo 1.0/1.0 0.7/0.8 0.6/0.7

* Relative values of catalyst A

Respecting the produced oil obtained, a compositional analysis was performed by

hydrocarbon, and changes in composition before and after reaction were followed with

respect to resin and asphaltene, where the distribution of metal content is especially great.

Figure 4 shows the reactivity against asphaltene and against resin in each catalyst. It was

found that resin component cracking is promoted in catalysts B and C, which have large

mesopore diameters. Given this fact, it will be necessary to maintain an adequate

mesopore diameter in order to achieve the demetalization performance targeted.

Cra

ckin

g r

atio

(m

ass%

)

Resin content

Catalyst A

Catalyst B

Catalyst C

Asphaltene content

Figure 4: Cracking Ratio of Resin and Asphaltene Contents

(c) Properties of trial catalyst

Supports having each type of mesopore and macro pore, and catalysts of different metal

contents were trial produced. It was confirmed that pore diameter can be adjusted by

means of alumina preparing. It was also discovered that by changing the adjustment

conditions in a bimodal alumina system, macro pore diameter and macro pore volume can

be adjusted as shown in Figure 5.

5

Sp

ecific

po

re v

olu

me

(cc/g

)

Pore diameter (µm)

(mesopore)

(macropore)

Figure 5: Bimodal Support Pore Distribution

Among the causes of a decline in activity by hydrotreatment catalyst for residual oil are

blockage of the catalytic pore inlets due to the accumulation of metal on the catalyst and

coating of active points due to the deposition of carbons. In demetalization catalyst used for

processing residual oil of high metal content, the impact of pore blockage by metal that

accumulates in the demetalization reaction is especially large. To obtain a catalyst whereby

such deterioration of activity is curtailed and demetalization reaction is promoted effectively,

progress is being made in the present research toward development of catalyst in which

macropores and mesopores are combined.

(d) Deterioration rate of trial-produced catalyst

With respect to bimodal trial-produced catalyst, the superiority of the trial-produced catalyst

over standard catalyst in terms of deterioration speed was verified. In order to compare

demetalization performance by temperature, corrections were made in relation to a

demetalization reaction speed at a certain temperature, taken as standard, and data were

arranged by corrected demetalization reaction temperature. The results appear in Figure 6.

In trial-produced catalyst 1, demetalization activity was low, although it was exceedingly

stable. When the magnitude of active metal was optimized, trial-produced catalyst 2 was

able to demonstrate demetalization activity close to that of the standard catalyst.

In a comparison of the deterioration speed of trial-produced catalyst 2 and the standard

catalyst, it was found that the deterioration rate of bimodal catalyst is 0.76 times that of

standard catalyst. In this way it was confirmed that, while bimodal catalyst has roughly the

same demetalization activity as standard catalyst, its deterioration rate is slow. As for

deterioration per unit magnitude of metal accumulation, the deterioration rate of catalyst 2

is 0.83 times that of standard catalyst.

6

Co

rre

ctio

n r

ea

ctio

n t

em

pe

ratu

re (

°C)

No. of Operation Days

Standard catalyst

Trial-produced catalyst 1 Trial-produced catalyst 2

Figure 6: Comparison of Deterioration Speeds of Demetalization

in Trial-Produced Catalyst

In order to confirm the state of metal accumulation on catalyst, trial-produced catalyst was

placed into a basket and loaded onto a commercial unit, which was then allowed to operate

for 1 year. The loading site was the top of the 1st bed. Upon completion of operation, the

catalyst was removed and analyzed. The trial-produced catalyst that was loaded came in

two types: (1) unimodal type, and (2) bimodal type (trial-produced catalyst 1).

From a comparison of the magnitudes of metal retained by these catalysts, it was found

that approximately 1.8 times more vanadium accumulated in bimodal type catalyst than in

unimodal catalyst.

Figure 7: EPMA Analysis of Waste Catalyst

(Left: unimodal catalyst, Right: bimodal catalyst)

Next, the states of metal accumulation were measured by EPMA (Erectron Probe Micro

Analyzer). The results appear in Figure 7. With unimodal catalyst, it was discovered that

both vanadium and nickel accumulate in greatest magnitudes at the surface of the catalyst

pellet. In bimodal catalyst, on the other hand, vanadium and nickel accumulate into the

interior of the catalyst pellet, and it was clearly demonstrated that the diffusion of heavy

molecules, including metal components, functions effectively.

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(e) Activity of trial-produced catalyst

Trial-produced catalysts were evaluated with bench-scale reactor in terms of the

relationships between demetalization performance and pore size or pore structure.

Feedstock properties and bench operational conditions are presented in Tables 4 and 5,

respectively.

Table 4: Feedstock Properties Table 5: Bench Operational

Conditions

Feedstock Operation conditions

Density g/cc 1.030 Reaction temperature ℃ 360-390

Sulfur content mass% 4.8 Pressure MPa 16.7

Metal content massppm 208 LHSV 0.56

Hydrogen-oil ratio NL/L 1,100

Using a number of parameters to represent catalyst pore structure, an attempt was made

to elucidate correlations with demetalization activity. Nevertheless, clear relationships

between demetalization activity and macropore diameter, for instance, could not be

identified.

What is more, when the relationships between these pore structure parameters and

demetalization activity were investigated, it was learned that macropore structure exerts a

great impact on demetalization performance. In other words, the greater the percentage of

macropore cubic capacity, as opposed to the pore capacity in the catalyst as a whole, the

higher the level of demetalization activity. Further investigation disclosed that, as opposed

to demetalization, there is an optimum point in the percentage of macropore volume in the

pore volume of the catalyst as a whole, as shown in Figure 8.

De

me

taliz

atio

n r

ate

(%

)

Rate of Macropore volume (%)

Figure 8: Demetalization Rate vs Ratio of Macropore Volume

(f) Improvement of trial-produced catalyst

In a catalyst system with large macro pores, catalytic strength declines. In order to

investigate catalytic strength, therefore, additions of ingredients other than alumina were

examined.

8

As a result, it was discovered, as shown in Table 6, that when additive 1 is added at a fixed

volume or greater, catalytic strength is improved. And as the addition is further increased,

its effect tops out.

Table 6: Improvement of Catalytic Strength of Alumina Carrier (Additive 1)

Carrier Additive volume Catalytic strength (kg/mm)

Ａ Zero Base

Ｂ ↓ Increasing volume ±0

Ｃ 0.2

Ｄ 0.5

Ｅ 0.5

In a comparison of trial-produced carrier A with no additive included and trial-produced

carrier D, which includes additive, there was virtually no change in pore distribution. Using

the carrier D, active metal was retained and trial-produced catalyst 3 was prepared.

As a result, it was found that in measurements of catalytic strength, trial-produced catalyst

3, to which additive 1 had been added, demonstrated an improvement in catalytic strength

by about 1.5 times as compared to the alumina-type, trial-produced catalyst 2.

Ca

taly

tic s

tre

ng

th (

Re

lative

va

lue

)

Additive 1

Additive 2

Additive 1 + 2

Trial production 2

Trial production 3

Trial production 4

Trial production 5

Figure 9: Catalytic Strength of Trial-Produced Catalyst

Similarly, the effect of additive 2 was investigated from the standpoint of improving catalytic

strength. The results appear in Figure 9. In trial-produced catalyst 4, to which additive 2

had been added, although catalytic strength was improved over that of trial-produced

catalyst 2, the effect of additive 2 was smaller than that of additive 1. With the aim of

gaining a cooperative effect from these two types of additive, trial-produced catalyst 5, to

which both additives were added, was investigated. It was discovered that catalytic

strength can be improved by up to 1.8 times by combining the two additive types. The

catalytic strength of trial-produced catalyst 5 reached a level where it could adequately

withstand use in practical equipment.

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Next, respecting optimized catalyst, a comparison was made with catalyst trial produced

thus far in terms of the distribution of metal content to maltene and asphaltene in initial

activity tests. The comparison is represented in Figure 10. It was learned that in

trial-produced catalyst 5 with additive, as compared to trial-produced catalyst thus far,

demetalization from both maltene and asphaltene is promoted and demetalization activity is

improved. Demetalization activity is even further improved in trial-produced catalyst 6, in

which the amount of additive has been optimized.

Me

tal co

nte

nt

(V +

Ni)

(m

assp

pm

)

Trial-produced catalyst

(JFY1999)

Metal content in maltene Metal content in asphaltene

Trial-produced catalyst

(JFY2000)

Trial production 5

Trial production 6

Feedstock

(JFY2001)

Figure 10: Distribution of Produced Oil Metal in Improved Catalyst

The desulfurization activity of trial-produced catalyst is represented in Figure 11. It can be

seen that the desulfurization activity of trial-produced catalysts 5 and 6 is greatly improved

over that of catalyst trial-produced thus far. Taking catalyst 2 as the standard,

desulfurization activity is improved by about 1.4 times.

De

su

lfu

riza

tio

n r

ate

(m

ass%

)

Trial production 2

Trial production 3

Trial production 4

Trial production 5

Trial production 6

Figure 11: Desulfurization Activity of Trial-Produced Catalyst

3.3 Investigation of Catalyst Application Technology

An evaluation was made of methods for combining demetalization catalyst with desulfurization

catalyst and of the performance of the direct desulfurization unit as a whole. Feedstock

properties are given in Table 7. The reaction temperature was adjusted so that the sulfur

content of produced oil becomes fixed.

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Table 7: Feedstock Properties

Feedstock (1) Feedstock (2) Feedstock (3)

Density g/cc 0.998 1.017 1.027

Sulfur content mass% 3.93 4.03 4.26

Metal content massppm 122 141 163

Respecting the combined catalyst system, Figure 12 depicts the trend in reaction

temperature, corrected so that the desulfurization rate becomes fixed. In comparison to the

conventional catalyst, the developed catalyst systems exhibit high desulfurization and high

demetalization. Moreover, the rate of deterioration in catalytic activity is slower than in

conventional catalyst, and favorable performance is demonstrated.

Co

rre

ctio

n r

ea

ctio

n t

em

pe

ratu

re (

°C) Feedstock

(1) Feedstock

(2) Feedstock

(3)

Conventional catalyst system

(Service life forecast curve)

Developed catalyst system

No. of operation days

Figure 12: Trend in Correction Reaction Temperature with Each

Combination

3. 4 Development of Simulation

(a) Model outline

As for the developed simulator, in view of the fact that poisoning results from the

accumulation of metal and coke, which cause catalytic poisoning in RDS reaction,

demetalization and desulfurization sections were separated and deterioration functions

were optimized as indicated in (1) and (2) below. Simulator that predicts the service life of

demetalization catalyst was then constructed.

Desulfurization deterioration function: φS = φS (M, Cc) (1)

Demetalization deterioration function: φM = φS (M, Cc) (2)

M: Magnitude of metal (Ni + V) accumulated on catalyst

Cc: Magnitude of coke accumulated on catalyst

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Re

lative

fre

qu

en

cy f

acto

r

Calculated value

Measured value

No. of operation days

Figure 13: Forecast Values for Desulfuization Frequency Factors

vs Measurements

Using the calculated amount of metal accumulation, the desulfurization frequency factor of

the system that became diffusion determining step was calculated. Comparisons with

measurements in bench tests are presented in Figure 13. Since both results match well, it

was concluded that estimating can be made with this simulator model even in the end of

run.

(b) Developed simulator applications

The developed demetalization simulator and desulfurization simulator were combined and

used in bench tests, in which the developed demetalization catalyst and desulfurization

catalyst were combined, to evaluate life, and the trend in reaction temperature was

forecast.

Using this simulator, the results of life estimations conducted with the developed catalyst

system were taken to determine the life curve when residual oil of high metal content has

been treated. The results appear in Figure 14.

The triangular points in the figure denote bench test results, and the broken line represents

estimated life under test conditions. The solid line represents estimated life when the

feedstock metal concentration is 200 ppm. Comparisons with test results indicate that the

simulator, through optimization of parameters, can reproduce deterioration rates even in

the developed catalyst system.

From life estimations, made using the parameters with the feedstock metal concentration at

200 ppm, it is believed that operation would be possible for about 300 days, as the solid

line indicates, until the reaction upper limit temperature, which becomes a restriction in

practical equipment operation, is reached.

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Co

rre

ctio

n r

ea

ctio

n t

em

pe

ratu

re (

°C)

(Reaction upper limit) temperature

No. of operation days

Estimation curve with feedstockmetal content at 200 ppm

Figure 14: Bench Evaluations of Developed Catalyst System and

Estimation with Simulator

4. Synopsis

The physical properties of demetalization catalyst were optimized, based on an analysis of the

results of evaluations of a series of trial-produced catalysts, with a high-pressure reactor, using

feedstock of high metal content, and based on the results of analysis of compositional

ingredients (in sequence from light ingredients to saturated content, aroma content, resin

content and asphaltene content) in produced oil.

In addition, demetalization and desulfurization activities were improved by adding additive to

catalyst carrier. This is ascribed to the impact of the state of retained metal dispersion.

Manufacturing tests in commercial scale were done on developed catalyst, and the conditions

for catalyst production were certified.

In combining developed demetalization catalyst with desulfurization catalyst, the trends in

reaction temperature when residual oil has been subjected to long-term hydrotreatment were

applied to bench test results. Even in cases of combined demetalization and desulfurization

catalyst, trends in catalytic activity could be estimate to high accuracy.

From simulation studies based on life test of developed demetalization catalyst in combination

with desulfurization catalyst, it is believed that operation for 300 days with feedstock is possible

as targeted.

In the future, catalytic activity and life in combinations of demetalization catalyst with

desulfurization catalyst will have to be determined adequately, and data required for

verifications will have to be obtained. In addition, it will be confirmed that produced oil quality

and properties conform to operational standards under present conditions. And upon completion

of life test, operational data will be analyzed, as will spent catalyst, and efforts will be directed

toward improving the accuracy of the developed simulator, reflecting the characteristics of

bimodal catalyst.

Copyright 2002 Petroleum Energy Center. All rights reserved.