Vul Can Vgpcrt Chloride Guard Technology

8/10/2019 Vul Can Vgpcrt Chloride Guard Technology

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GBH ENTERPRISES, LTD

C2PT Catalyst Process Technology

By Gerard B Hawkins

Managing Director

VULCAN Chloride Guard Technology


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Chloride removal

A number of fixed-bed adsorbents / absorbentshave been proposed by various suppliers:

Activated Aluminas Promoted Activated Aluminas

Calcium Oxide, SodaLime, Molecular sieves

PURASPECTM

VULCAN Series Chloride Guards


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REFORMATE

LPG

RECYCLE

GAS

MAKE GASOFF

GAS

NAPHTHAFEED

VGP CRT-3000


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Activated Aluminas

These are formed initially from aluminium tri -hydrate and are heatedto 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 adsorpt ionreactions. 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 theunwanted side-reactions to occur.


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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


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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


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Catalyst Poisoning

Downstream Corrosion

Ammonium Chloride Fouling recycle compressors/export gas compressor

stabiliser column

heat exchangers

Product Specifications


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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


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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.


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(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.


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Unwanted Side Reactions Occurring Across Alumina

a) Organic Chlorides

R

=

+ HCI RCI

b) Green Oils

R1=+ R2 = H+ R1R2


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Green Oil is formed by the reaction of organic chlorides witharomatic 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 andblockage.


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In the case of alumina adsorbents, various condensation and polymerisation reactions arecatalysed 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.


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Addition of halogens to alkenes involves attack by positivehalogen 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.

Naphthenesare very prone to di & polyalkylation reactions leading to polymeric long chain structures.


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R-Cl + AlCl3 AlCl4-+ R +

H

R+ + C6H6 C6H5+

RH

C6H5+ +AlCl4

- C6H5R + HCl + AlCl3

R

Friedel-Crafts reaction is an electrophilic substitution with AlCl3acting

as a Lewis acid.

Slow

Fast

C6H5R-R


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Other chemical reactions may occur in the presence of AlCl3.The couplingof 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


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In normal operation there will be trace amounts of unsaturatedhydrocarbons 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 wil l react with HCl when promotedby an acid catalyst . These organo-chlorides can therefore be formed

across activated aluminas. These organo-chlor ide species are not

removed by the alumina and exit the bed in the product stream. If the

off-gas stream supplies H2to hydrotreating or hydrocracking units,

these organo-chlorides wil l be hydrogenated to HCl and init iatecorrosion problems and catalyst deactivation.


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unsaturated hydrocarbon reacts with surface hydroxyl ( acid) site

reactive carbonioum ion formedCl 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


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Make gas and stabilizer feed from catalytic reformers contains a mixture ofolefins 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 majorcomponent, broadly inl ine with equilibrium calculations. The level of

ethylene and propylene should only be about 15% of the total olefins.

The reaction to produce organic chlor ides 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.


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CH3CH2CH=CH2+ HCl CH3CH3CHClCH31-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


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Reactivity of alkenes with HCl

C=CH2 > CH3CH=CHCH3, CH3CH2CH=CH2,

CH3CH=CH2 >CH2=CH2

CH3

CH3

Stabili ty of carbonium ions:

3 > 2 > 1 > CH3+o o o


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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 highLOI on the samples. This suggested that water must have been present.


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- 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


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High Temperature VGP CRT-3000

Low Temperature Gases

VGP CRT-2000


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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

VULCAN S i Chl id G d


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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

promot ion and highly porous suppor t - do not have adsorption properties for HCl.

HCl does not exist freely or in an adsorbed or in a partially dissociated state

with in the particle or on i ts surface.

The HCl is ir reversib ly 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


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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

Chl id G d Hi t & D l t


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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


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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 andcontinuous protection

Must change bed when chloride first breaks

through


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Vul Can Vgpcrt Chloride Guard Technology

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