naphth asulfur guards

8/10/2019 Naphth Asulfur Guards

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Gerard B. HawkinsManaging Director

Naphtha Sulfur Guards


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Contents

Catalytic Reactions in Catalytic ReformingCatalytic Reforming ReactionsSulfur Related Problems

Effects of Sulfur in Catalytic ReformingReactions in Catalytic ReformingCatalytic Reforming CatalystsEffect of Sulfur on Catalytic Reforming CatalystsCatalytic Reformer EfficiencyVULCAN Sulfur GuardsVULCAN Sulfur Guards for Catalytic ReformersVULCAN Guard Installation Protects IsomerizationCatalysts


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Contents

Liquid Phase vs Gas Phase: Relative AdvantagesLiquid Phase TreatingWhich active metal is best?Thiophenes and Nickel Sulfur GuardsSulfiding mechanisms with reduced metalsThiophene adsorption on nickel

Advantages of Cu/Zn Over Nickel Sulfur Guards

Copper oxide vs NickelNickel Sulfur GuardsManganese Sulfur Guards


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There are 4 major reactions that occur during reforming.

1. Dehydrogenation of naphthenes to aromatics2. Dehydrocyclization of paraffins to aromatics3. Isomerization

4. hydrocracking


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Desirable reactions in catalytic reforming

1. Paraffins are isomerised and converted to naphthenes

2. Olefins are saturated to form paraffins which react as in (1)3. Naphthenes are converted to aromatics

Undesirable reactions in catalytic reforming

1. Dealkylation of side chains to form butane and lighter HCs2. Cracking of paraffins and naphthenes to form butane and

lighter paraffins


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Catalytic Reformers & Isomerization Units

Operational Efficiency Catalyst Poisoning Product Specifications


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Catalytic reforming catalysts are precious metal based .The active species is platinum and in most cases rheniumis combined to retard sintering of the platinum and form a

more stable catalyst which permits operation at lowerpressures.

Platinum acts as a catalytic site for hydrogenation and

dehydrogenation reactions

Chlorinated alumina provides acid sites for isomerization,cyclization and hydrocracking reactions.


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Sulfur is a temporary poison but has a detrimental effecton the catalytic reforming process.

Sulfur poisons the platinum dehydrogenation function ofthe reaction. For operation at a constant octane, orseverity, the effects are:

Decrease in C5+ reformate yield and hydrogenmakeIncreased rate of coking and hydrocracking


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The effect of Sulfur is more severe on bimetalliccatalysts and is worse for high Rhenium / LowPlatinum skewed catalysts.

Also, the effect is worse in semi-regen than modernCCRs.


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R R

+ 3H 2

Naphthene dehydrogenation, eg methyl cyclohexane to toluene

N-C 7H16 R + 4H 2

Dehydrocyclization of paraffins to aromatics

CH 3-CH 2-CH 2-CH 2-CH 2-CH 3 CH 3-CH-CH 2-CH 2-CH 3

CH 3 Isomerization

Hydrocracking

C 10 H22 + H 2 isohexane + n-Butane

X Sulfur

X Sulfur


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Catalytic Reforming Catalysts

Platinum Catalysts

Recommended when feedstock contains S< 2ppm S Usually lead reactors of fixed bed semi-regenerative or fixed-

bed cyclic reformer units

High platinum loading recommended w hen S > 2ppm

Platinum / Rhenium

Equal metal loading recommended when S< 1 ppm with atarget of 0.5 ppm

Skewed metals loadings recommended for maximum cyc lelengths and S < 0.5 ppm w ith a target of 0.2ppm


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Catalytic Reforming Catalysts

Modified Platinum / Rhenium

Recommended for increased hydrogen, C5 + and aromatics Equal metals loadings are general purpose when S < 1ppm Skewed metals when S < 0.5 ppm and recommend a Sulfur

guard upstream

Platinum / Tin

In low pressure operations, offer higher H 2 and C5 + thanabove catalysts.

Recommended for CCR units and also fixed bed cyclicdesigns

Preserves the ring compounds to increase aromatics and H 2 yields


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Effect of Sulfur on catalytic

reforming catalysts Sulfur contamination of the bi-metallic

reforming catalyst system, through theformation of a platinum sulfide speciesand ultimately leads to the presence ofsulfate, SO 4, on the catalyst duringregeneration which results in the

following:


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Effect of Sulfur on catalyticreforming catalysts

1) Sulfate promotes platinum (Pt) mobilitywhich can lead to Pt agglomeration and lossof active surface area. This ultimately resultsin a loss catalyst stability.

2) Pt crystals can not be properly re-dispersedwhilst sulfate is present on the catalystsurface.

3) Sulfate hinders the chloride pick-up ability ofthe catalyst leading to a loss in catalystactivity. A loss in yield follows.


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HIGH SEVERITY OPERATION

0 0.2 0.4 0.6 0.8 1 1.2 1.4-3.5

-3

-2.5

-2

-1.5

-1

-0.5

0

Feed sulphur ppm

C5+ yield vol % change

Pt only

Balanced

Skewed

LOW SEVERITY OPERATION

0 0.2 0.4 0.6 0.8 1 1.2 1.4-3.5

-3

-2.5

-2

-1.5

-1

-0.5

0

Feed sulphur ppm

C5+ yield vo l % change

Pt only

Balanced

Skewed


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Liquid or gas dutyHigh CapacitySharp absorption profileEffective in dry streams

Easy discharge and disposalProducts for H 2S, mercaptans, thiophenes

Applications catalytic reformers

isomerisation units lube oil units benzene saturation units


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SULFUR SPECIES H2S MercaptanOrganic SulphideThiophene

Increasingdifficultyof removal

SULFUR GUARD DESIGN

Temperature H 2S = no constraintOrganic S = 100 to 200 o C140 to 180 oC preferred

Sulphur Loading Depends on S species &temperature

LHSV


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GBH Enterprises offer a comprehensive range ofproven absorbents for naphtha Sulfur guardduties.

The active metal composition is based upon :

1. Zinc Oxide2. Copper oxide/ zinc oxide3. Manganese

4. Nickel

GBHE will recommend the most appropriateabsorbent for a particular catalytic reformer duty.

VULCAN Sulfur Guards


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Selectivity varies depending on Sspecies - H2S - full removal

RSH - full removal RSR - partial removal RSSR - partial removal thiophenes - no removal

Thiophenes do not poison the guard


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REFORMATE

LPG

Key : VULCAN guard

RECYCLE GAS

MAKE GAS OFFGAS

NAPHTHAFEED


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LightNaphtha

Hydrogen

VGP-S201ReactorStripper

IsomerizationUnit

NHT

Hydro-Treater


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Liquid phase vs Gas Phase: Relative AdvantagesVapor Phase Sulfur Guards:

Advantages

- Unit treats both feed and the recycle gas, thus:

- More effective in responding to major sulfur upset.

- Faster recovery from major sulfur upsets.

- If the upset exceeds the abili ty of the guard on the first pass,the recycle gas feature results in complete removal on the secondpass.


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Vapor Phase Sulfur Guards:

Dis-advantages

- Vapor phase systems are more expensive:

- Located directly in reformer loop and operate at highertemperatures.

- Additional piping and valving to permit isolation duringregeneration of the cat reformer.

- Sulfur in the liquid feeds hits the catalyst before the recycleguard bed can take it out.

Liquid phase vs Gas Phase: Relative Advantages


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Liquid phase treating

Liquid Phase Sulfur Guards:

Advantages

- Favorable capital cost due to size and metallurgy.

- It does not impact reformer recycle compressor horse power orflow rate.

- Prevents catalyst exposure to feed sulfur on the first pass.

- Lead-Lag vessels can be readily changed on the run.


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Liquid phase treating

Liquid Phase Sulfur Guards:

Dis-advantages

- Single pass feature limits sulfur removal to H2S or RSH.

- Slower recovery from sulfur upsets.


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Experience shows that most naphtha streams containpredominantly H2S and mercaptan sulphur

Presence of th iophenes depends on naphtha source

and operation of hydrotreater

Cracked sources are more likely to contain thiophenes

For most applications a Cu/Zn product is the besttechnical and commercial choice


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Thiophenes are removed by reduced nickel

Typical thiophene pick-up is only 1-2 %w/w

Thiophenes impair the pick-up of other sulfur speciesdue to competitive absorption interference

Nickel products should be used only if:

Thiophenes are present and

Total sulfur removal is required


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Sulfiding mechanisms with

reduced metalsSulfidation mainly occurs through monolayerchemisorption of thiophene species on surfacelayers .

The thiophene is initially adsorbed in a parallelorientation and this then flips to a perpendiculararrangement on the reduced nickel surface.

Since the thiophene is unchanged during theadsorption, the coverage is l imited to a surfacemonolayer only.


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Ni Ni

S

Thiophene adsorption on nickel

Orientation

flip

Parallel vertical

approach alignment


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Higher sulfur capacity kg/m3

Absorbent not in reduced state

simpler transportation and handlingsimpler loading proceduresno cost ly reduction required

Most streams do not contain thiophenes


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Nickel is strongly recommended when thiophenicSulfur species need to be removed .

Copper oxide is recommended for the lighter lessrefractory Sulfur species due to higher absorption

capacity.

Copper oxide is generally a more

cost effective solution

Only GBHE offers both typesof proven absorbents


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Are complex S species (eg disulfides,thiophenes) present ?If so, are these at a level that will cause aproblem to the downstream process ?If so - use either: 100 % Ni-based absorbent or: a combination of Cu-based

absorbent over Ni-based as theoptimum solution


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Pre-reducedNickel

Low acidity high

surface area support

Low carbon inducing dehydrogenationcharacteristics

Surface Area> 100m2/g

A.B.D.1.0 -1.1 kg/l


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Impurity Optimum CapacitySpecies Temperature (C) %

H2S 100 16-18

RSH 150 12-14

RSSR 180 8-10

Thiophenes 200+ 0.5 - 2

Thiophene capacity s ignificantly enhanced if H2 present


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Manganese Sulfur Guards

0

5

10

15

20

25

30

Inlet 20% 40% 60% 80% OutletPercent of bed

Wt % S 100 vppm H2S in feed gas


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Manganese Sulfur guard Pre-reducedmanganese

Low acidity high

surface area support

Low carbon inducing dehydrogenationcharacteristics

Surface Area> 80m2/g

A.B.D.1.1 -1.4 kg/l


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