Chloride removal Catalytic Reformer - Chloride Guard Options Activated Aluminas Surface Chemistry of aluminas Chloride Related Problems Caused by Alumina Chloride Related Problems HCl Removal Mechanisms Activated Aluminas Undesirable Side Reactions Green Oil formation Friedel-Crafts Alkylation Scholl Reaction Organic Chloride Formation R-Cl Formation Mechanism Chemisorption vs Chemical Reaction Key Operational and Design Considerations

1. GBH ENTERPRISES, LTD
C2PT Catalyst Process Technology
By Gerard B Hawkins
Managing Director
VULCAN Chloride Guard Technology

2. Chloride removal
A number of fixed-bed adsorbents / absorbents
have been proposed by various suppliers:
• Activated Aluminas
• Promoted Activated Aluminas
• Calcium Oxide, SodaLime, Molecular sieves
• PURASPECTM
• VULCAN Series Chloride Guards

3. REFORMATE
LPG
RECYCLE
GAS
MAKE GAS
OFF
GAS
NAPHTHA
FEED
VGP CRT-3000

4. Activated Aluminas
These are formed initially from aluminium tri-hydrate and are heated
to about 500oC in a flash calciner to form an amorphous type alumina.
The temperature activating step is used to form the special high surface
area necessary for chemisorption reactions to occur.
The surface area of the ‘gamma type’ phase is about 300-350 m2/g . This
very high surface area makes it an ideal surface to promote adsorption
reactions. Unfortunately, these high surface area aluminas are acidic in
nature ( Lewis acid sites) and although the relative acidity of the sites are
considered to be of medium strength, the high surface area ensures that
the number and density of Lewis acid sites on the surface is very high.
It is the presence of the large number of Lewis Acid sites that promote the
unwanted side-reactions to occur.

5. Al Al Al Al Al Al
O O O O
OH O O O
+ +
--
e
-
Can accept an electron Can donate an electron
Lewis Acid Lewis Basic site
H+ Cl- is a polar molecule and the chloride ion reacts
with the Lewis acid surface sites and liberates H2

6. ◦ Incomplete removal of HCl leads to corrosion &
ammonium chloride fouling
◦ Formation of organo-chloride gives
fouling/corrosion/poisoning in downstream units.
◦ Green oil formation creates problems with pipes, valves
and flanges.
◦ Short lives lead to frequent change-outs

7.  Catalyst Poisoning
 Downstream Corrosion
 Ammonium Chloride Fouling
◦ recycle compressors/export gas compressor
◦ stabiliser column
◦ heat exchangers
 Product Specifications

8.  Increased Maintenance Costs
◦ washing stabilizer column
◦ compressor maintenance
◦ replacing corroded pipes & equipment
 Loss of Hydrogen Source
◦ Severe problems could take unit off line
◦ Loss of production in downstream units
 Poisoning of Downstream Catalysts
◦ eg. Ni catalysts, Cu/Zn catalysts

9. 1. Activated aluminas remove HCl by adsorption.
The HCl has a high dipole moment and is attracted to the polar sites on the alumina
surface where it is chemisorbed ( partially dissociated).There is some evidence to
suggest that some stronger bonds are actually formed.
2. Promoted activated aluminas contain a small quantity of basic metal oxide. The
promoter will chemically react with the HCl. This reaction is faster than adsorption and is
the dominant reaction until the promoter is exhausted. Once this stage is reached,
additional chloride removal is by chemisorption but this increases the acidity of the alumina
surface.
3. HCl Transformation occurs when the inlet HCl is transformed into organic chloride
species that are not retained by the bed and exit the reactor with the carrier stream. This
occurs over acidic aluminas and is accelerated in the presence of adsorbed HCl,
adsorbed H2O and unsaturated hydrocarbons. Evidence suggests that organo-chloride
formation occurs in the top layers.

10. (I) Al2O3 + 6HCl 2AlCl3 + 3H2O
(ii) 2NaAlO4 + 2HCl Al2O3 + 2NaCl + H20
Reactions (I) and (ii) are the principal mechanisms by which chloride is adsorbed
from the stream. It has been demonstrated that the presence of moisture
increases the chloride capacity although whether due to a capacity or merely a
rate effect is not clear.
For traditional aluminas the rate limiting step is likely to be some form of
solid state diffusion into the structure.

11. Unwanted Side Reactions Occurring Across Alumina
a) Organic Chlorides
R = + HCI RCI
b) Green Oils
R1
= + R2
= H+ R1R2

12. Green Oil is formed by the reaction of organic chlorides with
aromatic compounds such as benzene and other unsaturated
hydrocarbons – this reaction is well known in organic chemistry
(Freidel Crafts) and is catalysed by highly acidic surface sites on
alumina.
C6H6 + RCl C6H5R + HCl
C6H5R + RCl C6H5R-R + HCl
Hence long chain polymeric compounds are produced of such
high molecular weight that the precipitate out causing fouling and
blockage.

13. In the case of alumina adsorbents, various condensation and polymerisation reactions are
catalysed by anhydrous AlCl3.The high molecular weight polymers block pores and deposit
‘gums’ or ‘green oil’. The gums act to form lumps of agglomerated adsorbent which reduce
capacity due to channelling of gas flow. The formation of complex organic chlorides , some
of which are volatile, is also promoted byAlCl3, resulting in chloride loss from the adsorber
and corrosion or poisoning problems.
Aromatics + Anhydrous AlCl3 dark red / orange complexes
polymeric tars
Naphthenes + Anhydrous AlCl3 orange complexes and tar
Example: A sample of liquid drained from a vessel was tested and
found to be:
87% hydrocarbon boiling below 200 C and 13% polymeric naphthenes and aromatics
unable to be distilled as the material is “pitch” like, setting solid on cooling.

14. Addition of halogens to alkenes involves attack by positive
halogen to form an intermediate carbonium ion. The loosely held
pi electrons of an alkene make it more reactive.
The less reactive benzene molecule needs the assistance of a
Lewis acid . More reactive aromatic molecules ( those whose pi
electrons are more available, phenols, furans etc..) can react with
halogens in the absence of a Lewis acid.
Naphthenes are very prone to di & polyalkylation reactions
leading to polymeric long chain structures.

15. R-Cl + AlCl3 AlCl4- + R +
H
R+ + C6H6 C6H5
+
R
H
C6H5
+ + AlCl4
- C6H5R + HCl + AlCl3
R
Friedel-Crafts reaction is an electrophilic substitution with AlCl3 acting
as a Lewis acid.
Slow
Fast
C6H5R-R

16. Other chemical reactions may occur in the presence of AlCl3.The coupling
of two aromatic molecules by treatment with a Lewis Acid and a proton
acid is called the Scholl reaction.
CH
H+
AlCl3
This type of intramolecular reaction can also occur with
activated aluminas

17. In normal operation there will be trace amounts of unsaturated
hydrocarbons in reformer reactor product that will go into both the
offgas and reformate streams. For example, in hydrogen gas ex-
catalytic reformers the concentration of ‘unsaturates’ varies from 400
ppmv to 1000 ppmv.
These unsaturated hydrocarbons will react with HCl when promoted
by an acid catalyst . These organo-chlorides can therefore be formed
across activated aluminas. These organo-chloride species are not
removed by the alumina and exit the bed in the product stream. If the
off-gas stream supplies H2 to hydrotreating or hydrocracking units,
these organo-chlorides will be hydrogenated to HCl and initiate
corrosion problems and catalyst deactivation.

18. • unsaturated hydrocarbon reacts with surface hydroxyl ( acid) site
• reactive carbonioum ion formed
• Cl chemisorbed to alumina surface
• carbonioum ion reacts instantly with Cl
• R-Cl formed
Al Al Al
O O
Cl O - H O - H O - H Cl
RCH2=CH RCH2CH2
+
Alumina surface
RCH2CH2Cl

19. Make gas and stabilizer feed from catalytic reformers contains a mixture of
olefins which should theoretically be present from equilibrium calculations:
Gas C2= to C4=
Liquid C4= to C8=
For typical reformate, C4= and above, the tertiary olefin is the major
component, broadly inline with equilibrium calculations. The level of
ethylene and propylene should only be about 15% of the total olefins.
The reaction to produce organic chlorides is most easily performed with
tertiary olefins due to the reactivity of the tertiary carbonium ion. Therefore,
for a mixture containing equal parts of primary, secondary and tertiary
butylene reacting with HCl, the major product is tertiary butyl chloride.

20. CH3CH2CH=CH2 + HCl CH3CH3CHClCH3
1-Butene Sec-butyl chloride
CHC=CH-CH3 + HCl CH3-C-CH2-CH3
2-Methyl-2-Butene
tert-pentyl chloride
CH3-C=CH2 + HCl CH3-C-CH3
CH3
Cl
CH3 CH3
Cl
Isobutylene
Tert-butyl chloride

21. Reactivity of alkenes with HCl
C=CH2 > CH3CH=CHCH3, CH3CH2CH=CH2,
CH3CH=CH2 >CH2=CH2
CH3
CH3
Stability of carbonium ions:
3 > 2 > 1 > CH3+
o o o

22. Leaching of components from the adsorbents can be a potential problem, leading
to both loss of chloride and contributing to fouling of the adsorbent mass.
Evidence for the mechanisms leading to leaching point to some form of
dissolution via:
AlCl3 Soluble in liquid water and organic solvent
AlCl3 + 3H2O Al(OH)3 + 3HCl
NaCl Soluble in liquid water only
Analysis of agglomerated lumps from one refinery application of their spent
activated aluminas has shown NaCl in the binding phase and unexpectedly high
LOI on the samples. This suggested that water must have been present.

23. - Enhanced chloride protection
- Proven track record in gaseous and liquid duties
- Reliable and safe operation
- Low capital cost
- Cost-effective operation
- Environmentally friendly
- No process losses
- Guaranteed solution to a problem

24.  High Temperature
◦ VGP CRT-3000
 Low Temperature Gases
◦ VGP CRT-2000

25. VULCAN Series Chloride Guards
Bi-metallic promoted
Low acidity / medium
surface area
Low ‘side-reaction’ inducing
characteristics
A.B.D.
0.60-0.80 kg/l
Theoretical capacity
32% w/w

26. VULCAN Series Chloride Guards
• New products are absorbents
– HCl removed by chemical reaction
– They have been manufactured with a reduced surface area to minimise aromatic
and hydrocarbon adsorption and its constituent components-( bi-metallic
promotion and highly porous support - do not have adsorption properties for HCl.
• HCl does not exist freely or in an adsorbed or in a partially dissociated state
within the particle or on its surface.
• The HCl is irreversibly chemically bound within the matrix.
• VULCAN Series products are not acidic and minimises / retards organic
chloride synthesis or condensation and polymerisation reactions.
• Chloride pick-up in excess of 30 % w/w in gas phase tests
• HCl removal to < 0.1 ppmv

27. Chemisorption: Alumina
MO- H+ ……... CI- H+
- Reversible
- Equilibrium loading function of T,
pHCI, pH2O
Chemical Reaction: VGP CRT 3000
Na2O + 2HCI => 2NaCI + H2O
2NaAIO4 + 2HCI => 2NaCI + H2O + AI2O3
- Irreversible
- Chloride loading constant

28. Chloride Guards - History & Development
Activated Alumina ( unpromoted) 3-5%
Activated Alumina ) (5% calcium -promoted) 5-8%
Activated Alumina ( 10% sodium promoted) 10-12 %
VGP CRT-3000 ( BIMETALLIC) 25-32%
Saturated Chloride capacity

29.  Pick-up depends on temperature, pressure,
flowrate, feed composition, inlet chloride level
 Different locations in a flow scheme will give
different expected lives
 Lead-lag gives better absorbent usage and
continuous protection
 Must change bed when chloride first breaks
through