Gerard B. Hawkins Managing Director

Naphtha Sulfur Guards

Contents

Catalytic Reactions in Catalytic Reforming Catalytic Reforming Reactions Sulfur Related Problems Effects of Sulfur in Catalytic Reforming Reactions in Catalytic Reforming Catalytic Reforming Catalysts Effect of Sulfur on Catalytic Reforming Catalysts Catalytic Reformer Efficiency VULCAN Sulfur Guards VULCAN Sulfur Guards for Catalytic Reformers VULCAN Guard Installation Protects Isomerization Catalysts

Contents

Liquid Phase vs Gas Phase: Relative Advantages Liquid Phase Treating Which active metal is best? Thiophenes and Nickel Sulfur Guards Sulfiding mechanisms with reduced metals Thiophene adsorption on nickel Advantages of Cu/Zn Over Nickel Sulfur Guards Copper oxide vs Nickel Nickel Sulfur Guards Manganese Sulfur Guards

There are 4 major reactions that occur during reforming. 1. Dehydrogenation of naphthenes to aromatics 2. Dehydrocyclization of paraffins to aromatics 3. Isomerization 4. hydrocracking

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 HC’s 2. Cracking of paraffins and naphthenes to form butane and lighter paraffins

Catalytic Reformers & Isomerization Units ◦ Operational Efficiency ◦ Catalyst Poisoning ◦ Product Specifications

Catalytic reforming catalysts are precious metal based . The active species is platinum and in most cases rhenium is combined to retard sintering of the platinum and form a more stable catalyst which permits operation at lower pressures. Platinum acts as a catalytic site for hydrogenation and dehydrogenation reactions Chlorinated alumina provides acid sites for isomerization, cyclization and hydrocracking reactions.

Sulfur is a temporary poison but has a detrimental effect on the catalytic reforming process. Sulfur poisons the platinum dehydrogenation function of the reaction. For operation at a constant octane, or severity, the effects are:

•Decrease in C5+ reformate yield and hydrogen make •Increased rate of coking and hydrocracking

The effect of Sulfur is more severe on bimetallic catalysts and is worse for high Rhenium / Low Platinum skewed catalysts. Also, the effect is worse in ‘semi-regen’ than modern CCR’s.

R R

+ 3H2

Naphthene dehydrogenation, eg methyl cyclohexane to toluene

N-C7H16 R + 4H2

Dehydrocyclization of paraffins to aromatics

CH3-CH2-CH2-CH2-CH2-CH3 CH3-CH-CH2-CH2-CH3

CH3 Isomerization

Hydrocracking

C10H22 + H2 isohexane + n-Butane

X Sulfur

X Sulfur

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 when S > 2ppm

Platinum / Rhenium

• Equal metal loading recommended when S< 1 ppm with a target of 0.5 ppm

• Skewed metals loadings recommended for maximum cycle lengths and S < 0.5 ppm with a target of 0.2ppm

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 H2 and C5+ than above catalysts.

• Recommended for CCR units and also fixed bed cyclic designs

• Preserves the ring compounds to increase aromatics and H2 yields

Effect of Sulfur on catalytic reforming catalysts

• Sulfur contamination of the bi-metallic reforming catalyst system, through the formation of a platinum sulfide species and ultimately leads to the presence of sulfate, SO4, on the catalyst during regeneration which results in the following:

Effect of Sulfur on catalytic reforming catalysts

1) Sulfate promotes platinum (Pt) mobility which can lead to Pt agglomeration and loss of active surface area. This ultimately results in a loss catalyst stability.

2) Pt crystals can not be properly re-dispersed

whilst sulfate is present on the catalyst surface.

3) Sulfate hinders the chloride pick-up ability of

the catalyst leading to a loss in catalyst activity. A loss in yield follows.

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 vol % change

Pt only

Balanced

Skewed

Liquid or gas duty High Capacity Sharp absorption profile Effective in dry streams Easy discharge and disposal Products for H2S, mercaptans, thiophenes Applications

– catalytic reformers – isomerisation units – lube oil units – benzene saturation units

SULFUR SPECIES H2S Mercaptan Organic Sulphide Thiophene

Increasing difficulty of removal

SULFUR GUARD DESIGN Temperature H2S = no constraint Organic S = 100 to 200oC 140 to 180oC preferred

Sulphur Loading Depends on S species & temperature

LHSV <15 h-1

Typical S inlet 0.2 - 0.4 ppmw

Typical S outlet Not Detectable

GBH Enterprises offer a comprehensive range of proven absorbents for naphtha Sulfur guard duties. The active metal composition is based upon : 1. Zinc Oxide 2. Copper oxide/ zinc oxide 3. Manganese 4. Nickel GBHE will recommend the most appropriate absorbent for a particular catalytic reformer duty.

VULCAN Sulfur Guards

Selectivity varies depending on S species - ◦ H2S - full removal ◦ RSH - full removal ◦ RSR - partial removal ◦ RSSR - partial removal ◦ thiophenes - no removal

Thiophenes do not “poison” the guard

REFORMATE

LPG

Key : VULCAN guard

RECYCLE GAS

MAKE GAS OFF GAS

NAPHTHA FEED

Light Naphtha

Hydrogen

VGP-S201 Reactor Stripper

Isomerization Unit

NHT

Hydro- Treater

Liquid phase vs Gas Phase: Relative Advantages

Vapor 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 ability of the guard on the first pass, the recycle gas feature results in complete removal on the second pass.

Vapor Phase Sulfur Guards: Dis-advantages - Vapor phase systems are more expensive: - Located directly in reformer loop and operate at higher temperatures. - Additional piping and valving to permit isolation during regeneration of the cat reformer. - Sulfur in the liquid feeds hits the catalyst before the recycle guard bed can take it out.

Liquid phase vs Gas Phase: Relative Advantages

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 or flow rate. - Prevents catalyst exposure to feed sulfur on the first pass. - Lead-Lag vessels can be readily changed on the run.

Liquid phase treating

Liquid Phase Sulfur Guards: Dis-advantages - Single pass feature limits sulfur removal to H2S or RSH. - Slower recovery from sulfur upsets.

Which active metal is best? Nickel is strongly recommended when thiophenic

sulfur species need to be removed .

Copper oxide is recommended for the ‘lighter’ less refractory Sulfur species due to higher absorption

capacity.

Manganese or zinc oxide is generally used for desulfurization of recycle gas in presence of

chlorides.

Copper oxide is generally the most cost effective solution

GBH Enterprises offers all types

of proven absorbents

Experience shows that most naphtha streams contain predominantly H2S and mercaptan sulphur

Presence of thiophenes 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 best

technical and commercial choice

• Thiophenes are removed by reduced nickel

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

• Thiophenes impair the pick-up of other sulfur species due to competitive absorption interference

Nickel products should be used only if: Thiophenes are present

and Total sulfur removal is required

Sulfiding mechanisms with reduced metals

Sulfidation mainly occurs through monolayer chemisorption of thiophene species on surface layers . The thiophene is initially adsorbed in a parallel orientation and this then flips to a perpendicular arrangement on the reduced nickel surface. Since the thiophene is unchanged during the adsorption, the coverage is limited to a surface monolayer only.

Ni Ni

S

Thiophene adsorption on nickel

Orientation flip

Parallel vertical approach alignment

◦ Higher sulfur capacity kg/m3 ◦ Absorbent not in reduced state

simpler transportation and handling simpler loading procedures no costly reduction required

◦ Most streams do not contain thiophenes

Nickel is strongly recommended when thiophenic Sulfur species need to be removed .

Copper oxide is recommended for the ‘lighter’ less refractory Sulfur species due to higher absorption

capacity.

Copper oxide is generally a more cost effective solution

Only GBHE offers both types

of proven absorbents

Are complex S species (eg disulfides, thiophenes) present ?

If so, are these at a level that will cause a problem to the downstream process ?

If so - use ◦ either: 100 % Ni-based absorbent ◦ or: a combination of Cu-based

absorbent over Ni-based as the optimum solution

Pre-reduced Nickel

Low acidity high surface area support

Low carbon inducing dehydrogenation characteristics

Surface Area > 100m2/g

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

Impurity Optimum Capacity Species Temperature (C) % H2S 100 16-18 RSH 150 12-14 RSSR 180 8-10 Thiophenes 200+ 0.5 - 2

Thiophene capacity significantly enhanced if H2 present

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

Manganese Sulfur guard Pre-reduced manganese

Low acidity high surface area support

Low carbon inducing dehydrogenation characteristics

Surface Area > 80m2/g

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