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Chapter 1

Catalyst

1.1Introduction

Catalyst plays an important role in large no. of important

processes in chemical engineering especially in hydrotreating

because it is a catalytic process. As the catalyst change we can

meet any required specification and/or do treating for any

process.

The following examples will well illustrate this idea.

A new sulfur specification of gas of 50 ppm. was imposed at

the end of 00! in "apan. #owe$er most of "apanese refineries

mar%eting and distributing 50 ppm. &ulfur gas oil since April

00'( ahead of legislation. This was an ongoing process withthe "apanese refineries de$eloping strategies to produce and

mar%et sulfur )free gas oil *less than 10 ppm.+ at the end of

005.

,n -ecember 000( the .&. en$ironmental protection agency

A2 administrator signed a final rule on hea$y duty engine

and $ehicles standards and high way gas oil sulfur control.

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The final rule mandates that refineries and importers of gas oil

reduce the sulfur content to 15 ppm. at "une 003.

4n April 001 the uropean commission adopted directi$e

001( this introduced amendments to the uro standard of gas

oil and gasoline specifications. &ulfur specification of gas oil

is 50 ppm. 4n 005 and 10 ppm. in 00.

Catalyst suppliers ha$e been putting intensi$e efforts to

de$elop new catalysts to meet stringent regulations of

petroleum products.

1.2Ty!s" co#osition and structur! o$

th! us!d catalyst

1.2.1 Catalyst types

Catalysts used and de$eloped for hydrotreating include

metals oxides as shown in the table 1.1 on alumina or

alumina silica support( the shown percentages means

that there is more than one choice according to the

application we do.

The selection of Co6o / Al,'catalyst due to its highly

selecti$e( easy to generate and resistance to poisoning.

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Catalyst 7i, Co, 6o,' 8,' ,5 Al,' &i,Compositio

n

9ange :

0;1' 0;3 0;'0 0;'0 0;10 !0;5 0;!5

Ta%l! 1.1& catalyst co#osition ratios

1.2.2 Catalyst design and structure

#ydrotreating catalysts are as the common use2 either 6o or

8 promoted with Co or 7i and supported on a gamma or

rare earth oxide promoters may be added to lower the acidity

of the catalyst and / or impro$e 6o sulfidability. Addition of

is %nown to increase the acti$ity of 7i

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to concentrate pores around a particular diameter has a great

impact on hydrotreating acti$ity both start of run &,92 and as

catalyst ages. 9eactions ta%ing place in hydrotreting of gas oil

00; 533 oC2 generally requires a minimum pore si@e to

o$ercome most diffusional restrictions. ores that are larger

than necessary lend little to impro$ing diffusional

characteristics and as the pore diameters of the catalyst

increase the surface area decreases at constant pore $olume2.

Acti$ity generally with surface area and loss in pore $olume

occurs in smallest diameter pores first. #ighest acti$ity

retention is maintained if pore $olume is concentrated in $ery

narrow range of pore diameters. At the hydrotreating se$erity

to reduce sulfur in light cycle oil BC,2 to 0.05 wt. : the

performance of high acti$ity catalysts 7i6o and Co6o appear

to be equi$alent. or middle distillate fractions crude oil

containing high concentration of nitrogen reduction is

achie$ed by using a catalyst charge of 0: 7i

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'i(ur! 1.1 & Catalyst $or hydrod!#!tallation

'i(ur! 1.2

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'i(ur! 1.); *T+ *cannin( Tunn!lin( +icroscoy

'i(ur! 1.,

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'i(ur! 1.-

1.3 Catalyst roc!ssin(

1.3.1 Loading the catalyst

Boading the catalyst in the reactor is an important step because

the mass of catalyst loaded in relation to a definite reaction

$olume depends on how well pac%ed it is. ac%ing depends

not only on catalyst characteristics specific gra$ity( grain

shape and si@e2 but also on the loading method. The catalyst

must be uniformly pac%ed all throughout the $olume( both

$ertically and radially in order to pre$ent channeling. The

tighter the pac%ing( the more catalyst is required and

consequently the greater the acti$ity of the reaction $olume.

#owe$er( there is also a greater ris% of pressure loss problems.

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The two main methods of catalyst loading are the Dsoc%D

method that gi$es loose pac%ing and the DdenseD method that

usually causes an increase of 15: in pac%ing density.

1.3.2 Suliding the catalyst

The catalyst in oxide form must be acti$ated by con$erting the

hydrogenation metals from oxide form to sulfide form.The catalyst was sulfided either by #& /#mixture or using

dimethyl disulfide #'C

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together with 6o or 8( but there is another correct idea said

that 7i/6o ( Co/6o( Co/8 and 7i/w can beha$e as synergic

pairs2( wor% together or cooperate.

The bul% binary phases or these elements( 7iG&( Co&G( 6o&

and 8&are present in the unsupported catalyst but the rent

wor% pro$ide their presence in both supported and

unsupported catalysts. Although Co&Gand 7i'&ha$e been

described as a promoter of 6o&or 8&. These phases

themsel$es ha$e acti$ates which are of the same order as

6o&. The synergic pairs of acti$e sulfides gi$e enhancement

of acti$ity far greater than would be expected by simultaneous

presence of non interacting phases. The relation between the

acti$ity of these synergic pairs and the periodic trends for

binary sulfides appear by examining the a$erage heats of

formation of the sulfides of the synergic pairs. The most acti$ecatalyst has a heat of formation between '0; 50 =cal/mol.

There is a correlation between H#ffor sulfides( and are

linearly correlated with heats of adsorption of sulfur on

transition metal surface. This reflects under catalytic condition

and the optimum metal sulfur bond strength on surface of

catalyst( the elements in the periodic table can di$ided into ;