638
The Chemistry and Technology of Petroleum
Hydrogen can also be produced by partial oxidation (POX) of hydrocarbons in which the hydrocarbon is oxidized in a limited or controlled supply of oxygen:
2
4
10 195
4
2
2
298
CH O
CO H
H
Btu/lb
K
+
Æ
+
= -
D
,
The shift reaction also occurs and a mixture of carbon monoxide and carbon dioxide is produced in
addition to hydrogen. The catalyst tube materials do not limit the reaction temperatures in partial
oxidation processes and higher temperatures may be used that enhance the conversion of methane
to hydrogen. Indeed, much of the design and operation of hydrogen plants involves protecting the
reforming catalyst and the catalyst tubes because of the extreme temperatures and the sensitivity
of the catalyst. In fact, minor variations in feedstock composition or operating conditions can have
significant effects on the life of the catalyst or the reformer itself. This is particularly true of changes
in molecular weight of the feed gas, or poor distribution of heat to the catalyst tubes.
Since the high temperature takes the place of a catalyst, partial oxidation is not limited to the
lower boiling feedstocks that are required for steam reforming. Partial oxidation processes were
first considered for hydrogen production because of expected shortages of lower boiling feedstocks
and the need to have available a disposal method for higher boiling, high-sulfur streams such as
asphalt or petroleum coke.
Catalytic partial oxidation, also known as autothermal reforming, reacts oxygen with a lowboiling feedstock by passing the resulting hot mixture over a reforming catalyst. The use of a
catalyst allows the use of lower temperatures than in non-catalytic partial oxidation and causes
a reduction in oxygen demand.
The feedstock requirements for catalytic partial oxidation processes are similar to those for steam
reforming and light hydrocarbons from refinery gas to naphtha are preferred. The oxygen substitutes for
much of the steam in preventing coking and a lower steam/carbon ratio is required. In addition, because
a large excess of steam is not required, catalytic partial oxidation produces more carbon monoxide and
less hydrogen than steam reforming. Thus, the process is more suited to situations where carbon monoxide is the more desirable product such as, for example, synthesis gas for chemical feedstocks.
23.5 COMMERCIAL PROCESSES
In spite of the use of low-quality hydrogen (that contain up to 40% by volume hydrocarbon gases), a
high-purity hydrogen stream (95%–99% by volume hydrogen) is required for hydrodesulfurization,
hydrogenation, hydrocracking, and petrochemical processes. Hydrogen, produced as a by-product
of refinery processes (principally hydrogen recovery from catalytic reformer product gases), often
is not enough to meet the total refinery requirements, necessitating the manufacturing of additional
hydrogen or obtaining supply from external sources.
Catalytic reforming remains an important process used to convert low-octane naphtha into highoctane gasoline-blending components called reformate. Reforming represents the total effect of
numerous reactions such as cracking, polymerization, dehydrogenation, and isomerization taking
place simultaneously. Depending on the properties of the naphtha feedstock (as measured by the
paraffin, olefin, naphthene, and aromatic content) and catalysts used, reformate can be produced
with very high concentrations of toluene, benzene, xylene, and other aromatics useful in gasoline
blending and petrochemical processing. Hydrogen, a significant by-product, is separated from reformate for recycling and use in other processes.
A catalytic reformer comprises a reactor section and a product-recovery section. More or less standard is a feed preparation section in which, by the combination of hydrotreatment and distillation, the
feedstock is prepared to specification. Most processes use platinum as the active catalyst. Sometimes
platinum is combined with a second catalyst (bimetallic catalyst) such as rhenium or another noble metal.
There are many different commercial catalytic-reforming processes (Chapter 24) including platforming (Figure 23.3), powerforming, ultraforming, and Thermofor catalytic reforming. In the platforming
The Chemistry and Technology of Petroleum
Hydrogen can also be produced by partial oxidation (POX) of hydrocarbons in which the hydrocarbon is oxidized in a limited or controlled supply of oxygen:
2
4
10 195
4
2
2
298
CH O
CO H
H
Btu/lb
K
+
Æ
+
= -
D
,
The shift reaction also occurs and a mixture of carbon monoxide and carbon dioxide is produced in
addition to hydrogen. The catalyst tube materials do not limit the reaction temperatures in partial
oxidation processes and higher temperatures may be used that enhance the conversion of methane
to hydrogen. Indeed, much of the design and operation of hydrogen plants involves protecting the
reforming catalyst and the catalyst tubes because of the extreme temperatures and the sensitivity
of the catalyst. In fact, minor variations in feedstock composition or operating conditions can have
significant effects on the life of the catalyst or the reformer itself. This is particularly true of changes
in molecular weight of the feed gas, or poor distribution of heat to the catalyst tubes.
Since the high temperature takes the place of a catalyst, partial oxidation is not limited to the
lower boiling feedstocks that are required for steam reforming. Partial oxidation processes were
first considered for hydrogen production because of expected shortages of lower boiling feedstocks
and the need to have available a disposal method for higher boiling, high-sulfur streams such as
asphalt or petroleum coke.
Catalytic partial oxidation, also known as autothermal reforming, reacts oxygen with a lowboiling feedstock by passing the resulting hot mixture over a reforming catalyst. The use of a
catalyst allows the use of lower temperatures than in non-catalytic partial oxidation and causes
a reduction in oxygen demand.
The feedstock requirements for catalytic partial oxidation processes are similar to those for steam
reforming and light hydrocarbons from refinery gas to naphtha are preferred. The oxygen substitutes for
much of the steam in preventing coking and a lower steam/carbon ratio is required. In addition, because
a large excess of steam is not required, catalytic partial oxidation produces more carbon monoxide and
less hydrogen than steam reforming. Thus, the process is more suited to situations where carbon monoxide is the more desirable product such as, for example, synthesis gas for chemical feedstocks.
23.5 COMMERCIAL PROCESSES
In spite of the use of low-quality hydrogen (that contain up to 40% by volume hydrocarbon gases), a
high-purity hydrogen stream (95%–99% by volume hydrogen) is required for hydrodesulfurization,
hydrogenation, hydrocracking, and petrochemical processes. Hydrogen, produced as a by-product
of refinery processes (principally hydrogen recovery from catalytic reformer product gases), often
is not enough to meet the total refinery requirements, necessitating the manufacturing of additional
hydrogen or obtaining supply from external sources.
Catalytic reforming remains an important process used to convert low-octane naphtha into highoctane gasoline-blending components called reformate. Reforming represents the total effect of
numerous reactions such as cracking, polymerization, dehydrogenation, and isomerization taking
place simultaneously. Depending on the properties of the naphtha feedstock (as measured by the
paraffin, olefin, naphthene, and aromatic content) and catalysts used, reformate can be produced
with very high concentrations of toluene, benzene, xylene, and other aromatics useful in gasoline
blending and petrochemical processing. Hydrogen, a significant by-product, is separated from reformate for recycling and use in other processes.
A catalytic reformer comprises a reactor section and a product-recovery section. More or less standard is a feed preparation section in which, by the combination of hydrotreatment and distillation, the
feedstock is prepared to specification. Most processes use platinum as the active catalyst. Sometimes
platinum is combined with a second catalyst (bimetallic catalyst) such as rhenium or another noble metal.
There are many different commercial catalytic-reforming processes (Chapter 24) including platforming (Figure 23.3), powerforming, ultraforming, and Thermofor catalytic reforming. In the platforming