Catalytic Hydrotreating of Middle Distillates Blends in a Fixed-bed Reactor

7/28/2019 Catalytic Hydrotreating of Middle Distillates Blends in a Fixed-bed Reactor

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Applied Catalysis A: General 207 (2001) 407420

Catalytic hydrotreating of middle distillates blends in afixed-bed pilot reactor

Gustavo Marroqun-Snchez a, Jorge Ancheyta-Jurez a,b,

a Instituto Mexicano del Petrleo, Eje Central Lzaro Crdenas 152, Mxico 07730 DF, Mexicob Instituto Politcnico Nacional, ESIQIE, Mxico 07738 DF, Mexico

Received 24 March 2000; received in revised form 12 June 2000; accepted 18 June 2000

Abstract

An experimental study was conducted in a fixed-bed pilot reactor in order to evaluate the effect of catalytic hydrotreating

on diesel quality by using feedstocks prepared with different amounts of straight run gas oil, kerosene and jet fuel streams. Ex-periments were carried out at constant reaction pressure and hydrogen-to-oil ratio of 5.3MPa and 356.2 ml ml1, respectively.

The effect of reaction temperature and liquid hourly space velocity were studied in the range of 613633 K and 1.52.0 h1,

over a commercial Ni-Mo/-Al2O3 catalyst. The experimental information showed that diesel specifications could be reached

through single stage hydrotreating of these blends at moderate hydrotreating operating conditions. 2001 Elsevier Science

B.V. All rights reserved.

Keywords: Middle distillates; Hydrodesulfurization; Hydrotreating

1. Introduction

Catalytic hydrotreating (HDT) plays an important

role in the modern oil refining industry. The HDTprocess ranks in importance with other petroleum

refining processes, such as catalytic cracking and

reforming. The uses of the HDT process include pre-

dominantly the desulfurization of middle distillates

(kerosene, diesel fuel and jet fuel).

HDT is a catalytic process in which a number of

reactions are involved, i.e. hydrogenolysis, by which

CS, CN or CC bonds are cleaved and hydro-

genation of unsaturated compounds. The reacting

conditions of the HDT process vary with the type of

feedstock; whereas light oils are easy to desulfurize,

the desulfurization of heavy oils is very difficult.

Corresponding author. Fax: +52-5-587-3967.

E-mail address: [email protected] (J. Ancheyta-Juarez).

In view of the new diesel specifications introduced

around the world (Table 1) [15], the demand for

high-quality middle distillates has grown significantly

over the past decade [6]. Gas oils deep hydrodesulfur-ization has achieved much attention since the tolerated

sulfur content in diesel fuel is being lowered more and

more.

It becomes necessary to remove sulfur from the

compounds that are the most difficult to desulfurize,

which are higher molecular weight dibenziothiopenes

(DBT) that contain side chains in positions that limit

the access of the molecule to the active sites on the

catalyst, such as 4-methyl DBT and 4,6-dimethyl DBT

[7].

Straight run gas oil (SRGO) obtained from atmo-

spheric distillation units remains the main source

of diesel fuels, and in some cases, the light cycleoil (LCO) produced in fluid catalytic cracking units

(FCC) is frequently used as HDT feedstock. The

0926-860X/01/$ see front matter 2001 Elsevier Science B.V. All rights reserved.

PII: S 0 9 2 6 - 8 6 0 X ( 0 0 ) 0 0 6 8 3 - 9


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408 G. Marroqun-S anchez, J. Ancheyta-Juarez / Applied Catalysis A: General 207 (2001) 407420

Table 1

Specifications for diesel fuels in different countriesa

Property Mexico

PEMEX (a)

US EPA

(a)

US CARB

(a)

Sweden

class I (b)

UK

(c)

Germany

(d)

Europe

(e)

Europe

(f)

Worldwide

fuels charter

API gravity >32 >30 3339 41.145.4 3841.1 >37 >36 >36 3741.1

Flash point, K >318 >327

Viscosity @ 313K, cSt 1.94.1 1.94.1 2.04.1 1.24.0

Nitrogen, wppm 10

Sulfur, wppm 500 500 500 10 50 50 (10)b


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G. Marroqun-S anchez, J. Ancheyta-Juarez / Applied Catalysis A: General 207 (2001) 407420 409

Table 2

Middle distillates and blends properties

Properties SRGO Ka JFb B-1 B-2 B-3 B-4 B-5

API gravity 33.38 40.16 47.12 41.84 39.75 38.57 37.15 36.51

Flash point, K 333 331 317 321 323 328 328 335

Viscosity @ 313 K, cSt 4.10 1.76 0.99 1.71 2.02 2.21 2.73 3.01

Nitrogen, wppm 317 47 9 103 142 179 207 227

Sulfur, wt.% 1.21 0.67 0.21 0.58 0.71 0.81 0.92 0.97Aromatics (FIA), vol.% 26.4 21.8 19.0 21.4 22.3 23.2 23.9 24.2

Aromatics (SFC), wt.% 31.70 24.60 21.04 24.36 25.90 26.85 28.29 28.37

Mono-, wt.% 14.82 17.09 20.04 18.04 17.25 16.36 16.20 15.72

Di-, wt.% 13.42 7.51 1.00 5.59 7.47 8.72 10.21 10.52

Tri-, wt.% 3.46 0.00 0.00 0.73 1.18 1.77 1.88 2.13

Cetane number 54.1 48.0 42.8 47.5 48.9 50.7 50.9 51.9

ASTM distillation, K

IBP 429 409 417 409 414 427 429 418

10 vol.% 543 474 442 452 459 471 475 497

50 vol.% 586 507 461 491 516 532 548 555

90 vol.% 619 536 483 578 599 600 606 609

FBP 637 554 504 616 624 626 630 631

a Kerosene.b

Jet fuel.

These middle distillates were derived from a

crude oil with the following properties: 29.42 API,

2.16 wt.% sulfur, 1848 wppm nitrogen, 6.25 wt.%

Ramsbottom carbon, 4.9 wt.% asphaltenes in C7, and

22 and 111 wppm of Ni and V, respectively.

It can be observed from Table 2 that the three

streams are representative middle distillates (API grav-

ity: 33.38 SRGO, 40.16 kerosene, 47.12 jet fuel).

Kerosene and jet fuel do not present aromatics with

three rings, inclusive the jet fuel has a very low content

of di-aromatics (1.0 wt.%). However, they exhibit a

higher mono-aromatics content compared to SRGO.The total aromatic content is high in SRGO because

it increases with the boiling point of the fraction.

The following blends were prepared with SRGO,

kerosene and jet fuel streams:

B-1: 20vol.% SRGO, 30vol.% kerosene and

50 vol.% jet fuel.

B-2: 33.33 vol.% SRGO, 33.33 vol.% kerosene and

33.33 vol.% jet fuel.


20 vol.% jet fuel.


20 vol.% jet fuel. B-5: 50vol.% SRGO, 50vol.% kerosene and

0 vol.% jet fuel.

The physical and chemical properties of these

blends are also shown in Table 2. They are clas-

sified in an increasing amount of heteroatoms (i.e.

0.580.97 wt.% sulfur for B-1 and B-5, respectively).

Fig. 1 shows the variation of sulfur and nitrogen

contents as a function of API gravity for the different

blends. It can be seen that the higher jet fuel content

(B-1) the higher the API gravity and hence the lower

the heteroatoms content.

2.2. HDT catalyst and presulfiding conditions

The hydrotreating catalyst used in the present study

was a Ni-Mo/-Al2O3 commercial available sample

and its properties are presented in Table 3. This cata-

lyst showed a MoO3/NiO ratio of 4.47.

After loading the catalyst, the reactor pressure was

increased from atmospheric to 6.9 MPa (30% higher

than typical reactor pressure) in order to be sure of

the airtightness of the system. This condition was kept

during 2.5 h. Once the reactor was verify to be her-

metic, the reactor pressure was decreased to 5.3 MPa.

The temperature of the reactor was increased from

ambient to 503 K at a heating rate of 30 K h1 in thepresence of hydrogen (99.8% purity) at a flow rate of

150lh1.


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Fig. 1. Sulfur and nitrogen contents as a function of API gravity.

The catalyst was in-situ presulfided with a desulfu-

rized naphtha (specific gravity of 0.752,


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Fig. 3. Isothermal reactor.

small inert particles, whereas the catalytic conversion

behavior is that of the catalyst in the actual size [9].

The reactor temperature was maintained at the de-

sired level (613, 623 or 633 K) by using a three-zone

electric furnace, which provided an isothermal tem-

perature along the active reactor section.The catalytic bed temperature was measured dur-

ing the experiments by three thermocouples lo-

cated in a thermowell mounted at the center of the

reactor.

The temperature profile was measured at the middle

of each experiment by a movable axial thermocouple

located inside the reactor. The greatest deviation from

the desired temperature value was about 34 K. Threetypical temperature profiles at 613, 623 and 633 K are

shown in Fig. 3. It can be observed that an increase


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in the reaction temperature increased the temperature

differential along the reactor due to the exothermicity

of the reactions.

2.4. Operating conditions in the pilot reactor

Once the catalyst sulfiding was completed, the tem-

perature of the reactor was increased to the desired

reaction temperature and the feedstock and hydrogen

were passed at the required rates.

The hydrodesulfurization of the five blends was car-

ried out at the following operating conditions: reaction

temperature of 613, 623, and 633 K, and LHSV of 1.5

and 2.0 h1.

Reaction pressure and hydrogen-to-oil ratio for all

runs were 5.3 MPa and 356.2ml ml1, respectively. It

was used pure hydrogen in a once-through mode.

Product samples were collected at 48 h intervals

after allowing a 2 h stabilization period under each set

of conditions and mass balances for each run were inthe range 1005% [10].

2.5. Analysis of products

Physical and chemical properties were determined

with the following methods:

API gravity: ASTM D-287.

Total sulfur: ASTM D-4294.

Total nitrogen: ASTM D-4629.

Flash point: ASTM D-93.

Cinematic viscosity: ASTM D-445.

Distillation curve: ASTM D-86.

Cetane number: ASTM D-613.

Aromatics content in feed and products was measured

by fluorescent indicator adsorption (FIA) (ASTM

D-1319), and by supercritical fluid chromatography

(SFC) (ASTM D-5186), which determines aromatics

distribution (mono-, di-, tri- and poly-) in wt.%.

The FIA method has been prescribed by the Envi-

ronmental Protection Agency as a standard method for

specifying aromatics in diesel fuel, which gives the

total aromatics content in vol.%, however, it does not

give breakdown of aromatics distribution.

On the other hand, the environmental legislation

about the aromatics content in diesel fuels has led to anincreased fundamental interest in the detailed nature

of aromatic fractions. In this sense, the SFC method

has been chosen by ASTM to replace the FIA method

for determination of aromatic hydrocarbons content in

diesel fuels. Besides the FIA method does not give

the aromatics distribution, it is applied only for fuels

with final boiling point (FBP) less than 588 K, and

SFC method is valid for fuels in the boiling range of

473673 K [11].

3. Results and discussion

3.1. Effect of reaction temperature and

space-velocity on diesel quality

The effect of reaction temperature on product qua-

lity at LHSV of 2.0h1, 5.3 MPa total pressure and

356.2ml ml1 hydrogen-to-oil ratio is presented in

Fig. 4 for the five HDT feedstocks.

The product quality shown the classical behav-

ior when the temperature is increased in the range613633 K, that is a decrease in sulfur, nitrogen and

aromatics, and hence an increase in cetane number.

It should be mentioned that the reversibility of the

aromatics saturation reaction was not observed in this

study, which has been reported in the literature [12]

to be at higher temperatures (>633 K at 5.3 MPa).

The effect of space velocity (LHSV) on product

quality at 633 K reaction temperature, 5.3 MPa total

pressure and 356.2ml ml1 H2/oil ratio is presented

in Fig. 5 for the five feedstocks.

A decrease in LHSV from 2.0 to 1.5 h1 resulted in

improved product quality (a reduction in sulfur, nitro-

gen and aromatics contents, and an increase in cetanenumber).

It can be observed from Figs. 4 and 5 that the five

feedstocks reach less than 380 wppm sulfur, 53 wppm

nitrogen and 21.2 vol.% aromatics, in the range of tem-

perature 613633 K and LHSV of 1.52.0 h1. Cetane

numbers were higher than 49 for all feedstocks.

Very low sulfur, nitrogen and aromatics contents

were obtained with feedstock B-1 (


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Fig. 4. Effect of reaction temperature on product sulfur, nitrogen, aromatics and cetane number at 2.0h1 LHSV, 5.3MPa total pressure

and H2/oil ratio of 356.2 ml ml1. () B-1; () B-2; () B-3; () B-4; () B-5.

increase of 3.1 units in cetane number. This behavior at

high temperature and low space-velocity is because the

aromatics saturation and cetane number improvement

require high severity for CC bond scission to take

place from naphthenes to mono-aromatic molecules.

Feedstocks B-4 and B-5 presented aromatics higher

than 20 vol.% at low temperature and high space veloc-

ity (613K and 2.0 h1). This result was expected since

B-4 and B-5 feeds contain high content of SRGO,

60 and 50 vol.%, respectively, which is the higher

aromatic concentration stream used for preparing the

HDT feedstocks (26.4 vol.%).The flash point and viscosity of the hydrotreated

product decreased, while API gravity increased as the

reaction temperature was increased and the LHSV was

decreased.

The values of these diesel properties changed in the

following ranges: flash point, 338365 K; viscosity,

1.932.86 cSt, and API gravity, 3842.9.

The boiling range of the hydrotreated products

presented the following ranges: IBP, 448483 K;

10 vol.%, 460506 K; 30 vol.%, 474525 K; 50 vol.%,

491544 K; 70 vol.%, 519567 K; 90 vol.%, 571600 K,

and FBP: 610625 K.

The results of the present studies reveal that hy-

drodesulfurization is considerable influenced by reac-tion temperature and space velocity, and for a given

feedstock, low-sulfur diesel fuel (500 wppm max) can


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Fig. 5. Space-velocity effect on product sulfur, nitrogen, aromatics and cetane number at 633K, 5.3MPa and H2/oil of 356.2 ml ml1. ()

B-1; () B-2; () B-3; () B-4; () B-5.

be achieved by varying one of these process para-

meters.

3.2. Aromatics distribution in diesel fuels

3.2.1. FIA and SFC methods

A plot of total aromatics as measured by FIA and

SFC methods is presented in Fig. 6. It can be observed

that aromatics calculated by SFC (in wt.%) are always

greater than those evaluated by FIA method (in vol.%).

This difference becomes higher at high aromatic

contents.A lineal relationship, which is also shown in Fig. 6,

was found between the aromatic contents evaluated

with these two methods with correlation coefficient

R2=0.97.

3.2.2. Aromatics distribution

Aromatic compounds can be divided into four cat-

egories [13]: (1) mono-aromatics, (2) di-aromatics,

(3) tri-aromatics, and (4) polycyclic aromatics or

poly-nuclear aromatics (PNA) with four or more

condensed benzene rings.

Mono-, di- and tri-aromatics are more common in

middle distillates, whereas PNA are found in the heavy

fractions [13,14]. This was confirmed in this worksince all the HDT feedstocks showed very low contents

of aromatics with three rings (Table 2).


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Fig. 6. Comparison of methods for determining percent of aromatics. () Feedstock; () hydrotreated products.

Aromatics saturation in HDT process begins with

the partial saturation of multiple-ring aromatics

as can be observed in Fig. 7 [15]. However, the

mono-aromatics content showed an increase as the

multiring compounds are saturated as can be seen in

Fig. 8, where the mono-aromatics for B-4 feedstock

had increased from 15.72 wt.% to values higher than

19 wt.%, which is mainly due to the hydrogenation of

di- and tri-aromatics, since mono-aromatics are much

less reactive than di- or tri-aromatics.

Di- and tri-aromatics presented a reduction from

10.21 and 1.88 wt.% to values smaller than 3.0 and

0.45 wt.%, respectively.This behavior confirms that mono-aromatics are sig-

nificantly more difficult to saturate, which agrees with

experiments reported in the literature with model com-

pounds that suggest that naphthalene and substituted

naphthalenes are an order of magnitude more reactive

than benzene and substituted benzenes [16].

Aromatics density in feeds and hydrotreated prod-

ucts can be calculated with aromatics content in

Fig. 7. Aromatics saturation model.

wt.% (SFC method), aromatics content in vol.% (FIA

method) and feedstock density by means of the fol-

lowing equations:

Aromaticsin wt.% (SFC)

Aromatics in vol.% (FIA)=

garomatics/goil

mlaromatics/mloil

=

garomatics

mlaromatics

mloil

goil

=

aromatics

oil(1)

aromatics = oil

Aromaticsin wt.%

Aromatics in vol.%

(2)

It should be mentioned that the evaluation of aroma-tics density with Eq. (2) depends on the accuracy of

experimental determination of total aromatics by FIA

and SFC methods. SFC method has shown good ac-

curacy and FIA method presents poor accuracy for

determining aromatics in diesel fuels. The accuracy

of FIA method for diesels having end boiling point

(EBP) higher than 588 K has not been yet determined

[11].


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Fig. 8. Effect of reaction temperature and LHSV on aro-

matic distribution for B-4 feedstock. () LHSV=1.5 h1; ()

LHSV=2.0h1.

Most of the hydrotreated products in this work have

EBP higher than 588 K, specially those obtained fromfeedstocks with high SRGO content. This means that

not too much faith should be put on aromatics deter-

mination by FIA method. In spite of this, FIA numbers

were used together with aromatics by SFC method and

Eq. (2) to have an idea of aromatics density. These

results are discussed in the following paragraph.

Fig. 9 shows the variation of aromatics density in

the hydrotreated products, calculated with Eq. (2), as

a function of reaction temperature and LHSV for B-1

and B-4 feedstocks. It can be observed that the den-

sity of aromatic compounds decreases as the tempera-

ture increases and the LHSV is reduced. This confirms

that part of heavy aromatics (mostly tri- and di-) arehydrogenated into lower aromatics (mono) and their

densities and hence their molecular weights are re-

duced as the severity of the hydrotreating reactions is

increased.

3.3. Comparison of hydrotreated product properties

with diesel specifications

All the hydrotreated products obtained in the pilot

plant experiments using the five feedstocks reached

the required sulfur content (500 wppm max), cetane

number (48 min), and viscosity @ 313 K (1.94.1 cSt

for Mexico and 2.04.1 for US CARB legislation),

inclusive at the less severe operating conditions (613 K

and 2.0 h1 LHSV), as can be seen in Figs. 4 and 5.

Aromatics via FIA method presented values smaller

than 21.5 vol.% for B-4 and B-5 feedstocks, and

smaller than 19.4 vol.% for B-1, B-2 and B-3 feed-

stocks.

The experimental results indicate that at identical

operating temperatures very similar sulfur, nitrogen

and aromatics contents can be obtained with differentfeedstocks by adjusting the LHSV (first two columns

of Table 4).

The same result could be obtained by operations at

the same LHSV but with an increase of the operating

temperature, of course, at the expense of catalyst cycle

length (third and fourth columns of Table 4).

In Table 4 is also shown a comparison of three

hydrotreated products (columns 4, 5 and 6) with the

CARB diesel specification. It can be observed that all

properties reached the required CARB values, except

nitrogen and aromatics contents. It should be men-

tioned that CARB is one of the strictest specifications

for diesel fuels.The Mexican and US EPA legislations (Table 1) can

be easily reached with any of the diesel products ob-

tained by using the five feedstocks reported in Table 2,

within the operating conditions of the present study.

In addition, in some cases, the space-velocity may be

increased in order to expand the plant capacity. The

possibility of increasing the reaction temperature be-

yond 633 K and of increasing hydrogenation rate is

usually limited due to thermodynamic limitations of

aromatics hydrogenation.

3.4. Effects of type of feedstock on diesel quality

The composition of the feedstock to be treated in

a HDT plant will have a significant impact on the


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Fig. 9. Effect of reaction temperature and LHSV on aromatics density. () LHSV=1.5h1; () LHSV=2.0h1; () B-1 feedstock;

( ) B-4 feedstock.

unit performance. SRGO obtained from atmospheric

distillation remains the main source of diesel fuels.

Sometimes, the LCO obtained in FCC or coker gas

oils (CGO) are fed to the hydrotreater together with

SRGO. Each feed component contains thousands of

different molecules, making each unique in its pro-

cessability. For instance, SRGO is usually the easiest

feed to process, and LCO is difficult to treat because of

its high sulfur, nitrogen and aromatics contents. These

LCO properties adversely affect the quality of the re-

sulting diesel fuel [8].

Table 4

Comparison of operating condition to reach similar heteroatoms contents with different feedstocks

Feedstock B-1 B-2 B-3 B-4 B-4 B-5 CARB

Operating conditions

Temperature, K 633 633 623 633 623 633

LHSV, h1 2.0 1.5 2.0 2.0 1.5 1.5

Product properties

API gravity 42.61 40.96 39.66 38.71 38.72 38.45 3339

Flash point, K 340 345 348 348 354 363 327 min

Viscosity @ 313 K, cSt 1.85 2.17 2.45 2.57 2.51 2.65 2.04.1

Nitrogen, wppm 3 5 14 24 26 21 10 max

Sulfur, wppm 82 90 210 207 230 190 500 maxAromatics, vol.% 16.5 16.8 18.8 19.6 19.1 18.8 10 max

Cetane number 50.0 52.6 52.0 54.8 54.6 55.6 48 min

As the end point of blending components for diesel

production increases, the complexity of the het-

eroatoms increases and hence the hydrodesulfurization

rate decrease. Thiophenes are the lightest and most

reactive molecules with an unsaturated ring. Benzoth-

iophenes are relatively easy to desulfurize. DBT are

harder to desulfurize, but the difficulty varies greatly

according to their alkyl substitution, for instance DBT

substitued at the 4- and 4,6-positions, in particular,

are among the most refractory molecules. All of these

sulfur compounds can be found in diesel fuels.


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Fig. 10. ASTM D-86 distillation curves for SRGO, kerosene and jet fuel.

The concentration of the most difficult to desulfu-

rize species is high in the higher boiling fractions of

diesel materials. The level of HDS difficulty increasesto the point where ring saturation reactions begin to

compete with direct sulfur removal as the preferred

mechanism for HDS. Tailoring feed components, or

diesel feed boiling range can be an effective means of

controlling the difficulty of diesel HDS [4].

Another option to achieve a high-quality diesel is

to use lighter streams, such as kerosene and jet fuel,

together with the SRGO in the feedstock to the HDT

process in order to have more easier to desulfuize sul-

fur compounds.

With respect to this latter alternative, when the

kerosene and jet fuel are blended with SRGO, a

considerable reduction in the heteroatoms contentin the HDT feedstock is observed. SRGO sulfur

and nitrogen contents are 1.21 wt.% and 317 wppm,

respectively, and, for instance, for the feedstock

having the highest amount of jet fuel (B-1), sulfur

and nitrogen contents are 0.58 wt.% and 103 wppm,

respectively.

Unfortunately, the type and concentration of the dif-

ferent sulfur compounds in the feeds used in this work

were not determined, however, as it was stated before,

easier to desulfurize compounds are found in lighter

fractions, and hence, the rate of hydrodesulfurization

increases when these streams are used together with

SRGO as HDT feedstock.In spite of this, a good idea about the complexity

of sulfur compounds can be obtained by using the

ASTM D-86 distillation curve. Fig. 10 shows the boil-

ing point curves for SRGO, kerosene and jet fuel. The

boiling ranges for each stream are: 429637 K SRGO,409554 K kerosene, and 417504 K jet fuel. Accord-

ing to this figure, jet fuel will exhibit sulfur compounds

easier to desulfurize compared to other streams, and

its blend with SRGO will also provide a HDT feed-

stock with less complex and more reactive sulfur

compounds.

3.5. Basic approaches to produce low sulfur diesel

At present, most of the world refiners are either cur-

rently producing diesel fuels with 500 wppm sulfur or

are investing aggressively to reach this level. However,

some countries require a reduction to 50 wppm or to


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unit producing 500 wppm sulfur diesel, an increase

of 2035 K will be required depending of the feed

quality [4,5]. This increase in temperature will limit

the unit cycle life to an unacceptably short time pe-

riod. This means that temperature is not an effective

solution. Hence, the long term solution will certainly

need the addition of reactor volume and quench ca-

pability or even the investment in new hydrotreating

plants.

In addition to sulfur content, future diesel will re-

quire significant reductions in aromatics, density and

boiling range together with an increase in cetane num-

ber. The optimal reaction pathways to achieve the up-

grade objectives will be feedstock dependent and will

also need to consider the best utilization of existing

refinery resources.

4. Conclusions

The effect of hydrotreating of SRGOkerosenejet

fuel blends on diesel fuel quality has been studied

in a pilot reactor over a commercial Ni-Mo/-Al2O3catalyst under typical operating conditions.

The experimental results showed that the specifica-

tions in diesel quality can be achieved through single

stage hydrotreating of these blends. The maximum sul-

fur content in diesel fuels (500 wppm) and minimum

cetane number (48) can be easily reached at moderate

hydrotreating operating conditions.

Similar heteroatom contents in the products were

observed using the five feedstocks by adjusting the

LHSV or reaction temperatures.A lineal relationship was found between SFC and

FIA methods for determining aromatic distribution.

This information was used for evaluating the aro-

matic density, which was employed to show the

partial hydrogenation of heavy aromatics into lower

aromatics.

Acknowledgements

The authors thank Instituto Mexicano del Petrleo

for its financial support.

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Catalytic Hydrotreating of Middle Distillates Blends in a Fixed-bed Reactor

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