The coke burning step must be carefully monitored. The combustion of coke to
carbon dioxide and water is exothermic, and the oxygen concentration must be kept
low to limit the reaction and temperature rise. Excessive temperature can cause
agglomeration of the platinum or, in more extreme cases, can cause the alumina to
change from the desired phase or crystal structure to a higher temperature phase.
The water produced in the combustion also facilitates sintering of platinum. Due to
the need to gradually burn coke, the carbon burn is usually the most timeconsuming part of a regeneration.
Coke burning is usually done in the range of 400–500
C at oxygen concentrations initially in the 1–2 mol% range. Oxygen content and temperature are often
increased during burning to ensure that all coke has been combusted. Oxygen
consumption is monitored to determine the total amount of coke combusted and
the extent of the burn.
Since platinum can agglomerate even at relatively moderate exothermic conditions, the platinum must be redispersed after the carbon burn. The temperature is first
increased to approximately 500
C, oxygen content to approximately 5–6 mol%, and
chlorine or an organic chloride that breaks down to HCl and Cl 2 is injected into the
air/nitrogen stream. Platinum oxychlorides or chlorides form that redisperse platinum
over the alumina surface, ensuring that almost all the platinum is exposed for
reaction. This also adds chloride to the alumina support to enhance its acidity.
Finally, the last step in the regeneration process is the reduction of the metals on
the catalyst and sulfiding, if necessary. This is done in a dry hydrogen atmosphere.
At the temperatures required for reduction, greater than 350
C, high moisture
levels can lead to platinum agglomeration. Since water is formed in the reduction
process as platinum oxide is reduced to platinum metal, water is drained from the
unit during reduction. The reduction hydrogen is recirculated at as high a rate as
possible in order to minimize moisture content.
Sulfiding is typically done by injection of H 2 S or an organic sulfide into the unit
at the end of reduction. Sulfiding is continued until the specified sulfur level is
reached or until sulfur is no longer adsorbed by the catalyst as detected at the outlet
of the last catalyst bed.
Reforming Process Conditions
The major process variables that affect unit performance are reactor pressure,
reactor temperature, space velocity, H 2 /HC molar ratio, and catalyst type. The
relationship between the variables and process performance is generally applicable
to SR, cyclic, and continuous regeneration modes of operation.
Pressure
The reactor pressure affects reformer yields, reactor temperature requirements, and
catalyst stability. The average pressure has been defined by the inlet pressure to the
Catalytic Reforming in Petroleum Processing
251
carbon dioxide and water is exothermic, and the oxygen concentration must be kept
low to limit the reaction and temperature rise. Excessive temperature can cause
agglomeration of the platinum or, in more extreme cases, can cause the alumina to
change from the desired phase or crystal structure to a higher temperature phase.
The water produced in the combustion also facilitates sintering of platinum. Due to
the need to gradually burn coke, the carbon burn is usually the most timeconsuming part of a regeneration.
Coke burning is usually done in the range of 400–500
C at oxygen concentrations initially in the 1–2 mol% range. Oxygen content and temperature are often
increased during burning to ensure that all coke has been combusted. Oxygen
consumption is monitored to determine the total amount of coke combusted and
the extent of the burn.
Since platinum can agglomerate even at relatively moderate exothermic conditions, the platinum must be redispersed after the carbon burn. The temperature is first
increased to approximately 500
C, oxygen content to approximately 5–6 mol%, and
chlorine or an organic chloride that breaks down to HCl and Cl 2 is injected into the
air/nitrogen stream. Platinum oxychlorides or chlorides form that redisperse platinum
over the alumina surface, ensuring that almost all the platinum is exposed for
reaction. This also adds chloride to the alumina support to enhance its acidity.
Finally, the last step in the regeneration process is the reduction of the metals on
the catalyst and sulfiding, if necessary. This is done in a dry hydrogen atmosphere.
At the temperatures required for reduction, greater than 350
C, high moisture
levels can lead to platinum agglomeration. Since water is formed in the reduction
process as platinum oxide is reduced to platinum metal, water is drained from the
unit during reduction. The reduction hydrogen is recirculated at as high a rate as
possible in order to minimize moisture content.
Sulfiding is typically done by injection of H 2 S or an organic sulfide into the unit
at the end of reduction. Sulfiding is continued until the specified sulfur level is
reached or until sulfur is no longer adsorbed by the catalyst as detected at the outlet
of the last catalyst bed.
Reforming Process Conditions
The major process variables that affect unit performance are reactor pressure,
reactor temperature, space velocity, H 2 /HC molar ratio, and catalyst type. The
relationship between the variables and process performance is generally applicable
to SR, cyclic, and continuous regeneration modes of operation.
Pressure
The reactor pressure affects reformer yields, reactor temperature requirements, and
catalyst stability. The average pressure has been defined by the inlet pressure to the
Catalytic Reforming in Petroleum Processing
251