CHƯƠNG 3 xúc tác CHO QUÁ TRÌNH CHẾ BIẾN dầu mỏ

Xúc tác cho quá trình chế biến dầu mỏ


Catalytic Reforming
*Increasing the octane number of a low-octane
naphtha fraction
* the key process for obtaining benzene, toluene,
and xylenes (BTX).
Reformer Feeds
•heavy naphtha fraction
•naphtha from other sources


Reforming Catalysts
The catalysts generally used in catalytic reforming are dual
functional to provide two types of catalytic sites,
hydrogenation-dehydrogenation sites and acid sites.
The former sites are provided by platinum, which is
the best known hydrogenation-dehydrogenation catalyst
and the latter (acid sites) promote carbonium ion formation
and are provided by an alumina carrier. The two types of
sites are necessary for aromatization and isomerization
reactions.


Aromatization


Aromatization

Aromatization


Isomerisation


Isomerisation


Hydrocracking
Hydrocracking is a hydrogen-consuming reaction
that leads to higher gas production and lower liquid yield.
This reaction is favored at high temperatures and high
hydrogen partial pressure. The following represents a
hydrocracking reaction:

Bond breaking can occur at any position along the hydrocarbon
chain
Hydrocracking long-chain molecules can produce
C6, C7, and C8 hydrocarbons that are suitable for
dehydro-cyclization to aromatics.


Hydrodealkylation
Hydrodealkylation is a cracking reaction of an
aromatic side chain in presence of hydrogen. Like
hydrocracking, the reaction consumes hydrogen and is
favored at a higher hydrogen partial pressure. This
reaction is particularly important for increasing benzene
yield when methylbenzenes and ethylbenzene are

dealkylated.


Catalytic Cracking
Catalytic cracking (Cat-cracking) is a remarkably versatile and
flexible process. Its principal aim is to crack lower-value stocks
and produce higher-value light and middle distillates. The
process also produces light hydrocarbon gases, which are
important feedstocks for petrochemicals
Feeds
The feeds to catalytic cracking units vary from gas
oils to crude residues.


FCC (fluid catalytic cracking) feedstocks are often
pretreated to decrease the metallic and asphaltene
contents.
Residium fluid catalytic cracking (RFCC) has gained
wide acceptance due to a larger production of gasoline
with only small amounts of low-value products


Cracking Catalysts
Acid-treated clays were the first catalysts used in
catalytic cracking processes, but have been replaced by
synthetic amorphous silica-alumina, which is more active and
stable. Incorporating zeolites (crystalline alumina-silica) with
the silica/alumina catalyst improves selectivity towards
aromatics. These catalysts have both Lewis and Bronsted
acid sites that promote carbonium ion formation.

Bronsted acid sites



Cracking Reactions


Cracking Reactions
The most important cracking reaction, is the carbon-carbon
beta bond scission. A bond at a position beta to the
positively-charged carbon breaks heterolytically, yielding an
olefin and another carbocation.This can be represented by
the following example:



Hydrotreatment Catalysts and Reactions
Hydrodesulfurization, HDS
The catalysts should be sulfur-resistant. The cobalt-molybdenum
system supported on alumina was found to be an effective catalyst.
NiO/MoO3
and NiO/WO3


Hydrotreatment Catalysts and Reactions


Alkylation Process