LECTURE 10
Continuous Regenerative (moving bed) CCR Platforming UOP Process
A slight modification to the semi-regenerative process is to add an extra reactor to avoid shutting
down the whole unit during regeneration. Three reactors can be running while the forth is being
regenerated. This modified process is called the ‘‘cyclic fixed bed’’ process.
In this process, three or four reactors are installed one on the top of the other. The
schematic flow diagram of the continuous regenerative process (CCR) is shown in Figure
5.4(Martino, 2001). UOP has licensed this process under the CCR Platforming process
(Martino, 2001).
The effluent from each reactor is sent to a common furnace for heating. The catalyst
moves downwards by gravity from the first reactor (R 1) to the fourth reactor (R4).
The catalyst is sent to the regenerator to burn off the coke and then sent back to the first
reactor R1. The final product from R4 is sent to the stabilizer and gas recovery section.
The process can be operated at lower hydrogen partial pressure (PH 2 = 3 bar) compared to the
semi-generative process (PH2 = 35bar), with a reformate yield gain of nearly 10 vol%. Table 5.2
gives acomparison of the operating conditions for the three reformingprocesses.
Figure 5.3 Continuous regenerative reformer (CCR),UOP Platforming process
Material Balance in Reforming
1. Material Balance Using Empirical Correlations
2. Material Balance Using Conversion Criteria
Table 1: Reformer Correlations
Problem 1:
100 m3/h of heavy naphtha (HN) with specific gravity of 0.778 has the following
composition: A = 11.5 vol. %, N = 21.7vol. % and P = 66.8vol. % is to be
reformed to naphtha reformate of RON = 94. Calculate the yields of each product
for that reformer.
Solution:
The material balance for the reformer is presented in the following table:
2. Material Balance Using Conversion Criteria
Table 2: Naphthenes conversion to aromatics by dehydrogenation (Gary and Handwerk,
2001)
Table 3: Paraffin conversion to aromatics by dehydrocyclization (Gary and Handwerk,
2001)
Problem 2:
Heavy naphtha, which has the following detailed analysis in mol. %, is fed to a
reformer unit.
Find the composition of the products.
Final composition (mol%)
Problem 3
The following feed of 100 lbmol/h of naphtha was introduced to a reformer
Knowing that:
lnKeq = a/T +b
Keq is the equilibrium constant and T in K.
The constants a and b are given in the table above.
Assuming that the main reaction in reforming is the conversion of paraffin to the
corresponding aromatics:
Calculate the composition of reformate produced at 500 oC and 10 bar pressure.
The composition of the reformate can be calculated from the equilibrium conversions as
shown in Table 4.
Table 4.Composition of reformate produced
Isomerization of Light Naphtha
Isomerization is the process in which light straight chain paraffins of low RON (C 6, C5 and C4)
are transformed with proper catalyst into branched chains with the same carbon number and high
octane numbers.
The hydrotreated naphtha (HTN) is fractionated into heavy naphtha between 90–190 oC
(190–380 oF) which is used as a feed to the reforming unit.
Light naphtha C5 – 80 oC (C5 – 180 oF) is used as a feed to the isomerization unit.
There are two reasons for this fractionation.
1- Light hydrocarbons tend to hydrocrack in the reformer.
2- C6 hydrocarbons tend to form benzene in the reformer. Gasoline specifications require a very
low value of benzene due to its carcinogenic effect (Travers, 2001).
Thermodynamics of Isomerization
The isomerization reactions are slightly exothermic and the reactor works in the
equilibrium mode. There is no change in the number of moles and thus the reaction is not
affected by pressure change.
Better conversions are achieved at lower temperature as shown in Figure 1. Operating the
reactor at 130 oC (260 oF) will give good results.
In this figure, the degree of conversion to iso-paraffins is measured by the increase of the RON.
Paraffin recycle substantially increases the conversion (Travers, 2001).
Figure 1: Thermodynamic equilibrium with and without recycling normal paraffin (Travers,
2001)
Isomerization Reactions
Isomerization is a reversible and slightly exothermic reaction:
The conversion to iso-paraffin is not complete since the reaction is equilibrium conversion
limited. It does not depend on pressure, but it can be increased by lowering the temperature.
However operating at low temperatures will decrease the reaction rate. For this reason a very
active catalyst must be used.
Standard Isomerization Catalyst
There are two types of isomerization catalysts:
The standard Pt/chlorinated alumina with high chlorine content, which is considered quite
active.
The Pt/zeolite catalyst.
Standard Pt/chlorinated alumina with high chlorine content
This bi-functional nature catalyst in which the highly chlorinated alumina (8–15 w% Cl 2)
responsible for the acidic function of the catalyst.
The deposited Platinum (0.3–0.5 wt%) on the alumina matrix in the presence of hydrogen
will prevent coke deposition, thus ensuring high catalyst activity.
The reaction is performed at low temperature at about 130oC (266oF) to improve the
equilibrium yield and to lower chlorine elution.
The standard isomerization catalyst is sensitive to impurities such as water and sulphur
traces which will poison the catalyst and lower its activity. For this reason, the feed must be
hydrotreated before isomerization.
Limitation: The pressure of the hydrogen in the reactor will result in the elution of chlorine from
the catalyst as hydrogen chloride. For the reason, the zeolite catalyst, which is resistant to
impurities, was developed.
Zeolite Catalyst
Zeolites are crystallized silico-aluminates. Metallic particles of platinum are impregnated
on the surface of zeolites and act as hydrogen transfer centers.
The zeolite catalyst can resist impurities and does not require feed pretreatment, but it
does have lower activity and thus the reaction must be performed at a higher temperature
of 250 oC (482 oF).
A comparison of the operating conditions for the alumina and zeolite processes is shown in
Table 5.
Table 5 Comparison of operating conditions of isomerization
Isomerization Yields
The isomerate yield from light naphtha isomerization is usually very high (>97 wt%). Typical
yields are given in Table 6.
Table 6.Isomerization yield
Problem 4:
Light naphtha with a specific gravity of 0.724 is used as a feed to the isomerization unit at a rate
of 100 m3/h. Find the product composition.
Solution:
Appling the yield guidelines of Table 6, the product composition is presented in Table 6.1.
Table 6.1 Isomerization yields
