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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 ;