HYDROTREATINGOil Refining Processes

TKP-4150 - Group AApril 8th, 2013

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Background & Basics Definition of Hydrotreating Use of hydrogen for:

Removal of heteroatoms (S, N, O). Removal of heavy metals (V, Ni). Saturation of olefins and aromatics.

No significant reduction of molecular weight.

Driving forces: Process requirements. Environmental policies. Product specifications.

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Background & Basics The Role of Hydrotreating in a Refinery

Simplified processing scheme of an oil refinery (I. Chorkendorff and J. W. Niemantsverdriet, 2003)

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Chemistry of HydrotreatingHydrodesulfurization (HDS) Sulfur: most abundant heteroatom. Removed as H2S. Simple removal reactions:

Mercaptanes

Sulfides

Disulfides

RSH + H2 RH + H2S

R2S + 2H2 2RH + H2S

(RS)2 + 3H2 2RH + 2H2S

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Chemistry of HydrotreatingHydrodesulfurization (HDS) Thiophenes are more difficult to treat:

Global reaction mechanism for hydrodesulfurization of thiophene (I. Chorkendorff and J. W. Niemantsverdriet, 2003)

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Chemistry of HydrotreatingHydrodesulfurization (HDS) Sulfur is commonly present as thiophene:

Example of sulfur types distribution as a function of distillation temperature (fraction) in Arab medium distillate (Stanislaus et al, 2010)

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Chemistry of HydrotreatingHydrodenitrogenation (HDN) Mostly found in heavy fractions. Nitrogen removed as NH3.

Amines

Pyrrole

Pyridine

Quinoline

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Chemistry of HydrotreatingHydrodeoxygenation (HDO) Low and medium boiling point fractions. Non-conventional sources. Oxygen removed as water.

Phenols

Peroxides

Naphtenicacids

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Chemistry of HydrotreatingHydrodemetallization and halides removal Most common: nickel and vanadium. Removed as metal sulfides.

Chloride and bromide present at trace levels.

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Chemistry of HydrotreatingHydrodearomatization & olefin saturation Aromatics: naphtha to gasoil boiling range. Olefins and diolefins: formed in thermal

and catalytic units.

Toluene Naphthalene

Phenanthrene

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Chemistry of HydrotreatingHydrotreating Catalysts Most common: γ-alumina base, promoted

MoS2 Co-Mo:

Preferred for HDS. Lowest hydrogenation activity. Low sensitivity to H2 consumption and operating

pressure. Ni-Mo:

Better HDN and hydrogenation performance. Higher sensitivity to H2 partial pressure.

 Topsøe catalysts for hydroprocessing of petroleum fractions (Brochure, 2009)

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Chemistry of HydrotreatingDeactivation of Hydrotreating Catalysts Temporary:

Coke formation: Defines when to regenerate

catalyst. Deposition of nitrogen and

sulfur compounds.

Irreversible: Metal deposition:

V, Ni, Pb, Fe, As, among others. Catalyst support sintering.

 Example of coke buildup on catalyst and the agglomeration from unstable dienes in feed.

(Sanghavi, K. &  Schmidt, J., 2011.)

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Thermodynamics of HydrotreatingEquilibrium & Heat of Reaction Hydrotreating reactions are

exothermic.

Increasing temperature: ↑ Kinetic rates. ↑ Metal removal.

But: ↓ Equilibrium conversion. ↑ Coke formation. Aromatic saturation maximum

activity at 385°C.

Other parameters to favor reaction: ↑ H2 partial pressure. ↓ LHSV.  Equilibrium data of selected HDS

reactions.(Fahim et al, 2010)

 A

 B

 C

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Hydrotreating ProcessesGeneral Process Description Liquid feedstock is mixed with hydrogen. Furnace preheat the mix.

Naphtha (vapor). Heavier residues: gas oil or residue (mixed-

phase). Catalytic reactor. Cooling and

separation steps: Liquids to

fractionator Gases to

treatment. Main elements of Hydrotreating Processes. (Fahim et al, 2010)

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Hydrotreating ProcessesNaphtha Hydrotreating

Naphta Hydrotreating Process. (Fahim et al, 2010)

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Hydrotreating ProcessesMiddle Distillates Hydrotreating Feedstock: kerosene, jet fuel oil, and diesel.

Diesel Fuel Hydrotreating Unit. (Fahim et al, 2010)

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Hydrotreating ProcessesAtmospheric Residue Hydrotreating Reduce metal content:

Ni and V, from 75-90 ppmw. Reduce sulfur content:

From 5 to 0.5 wt%.

Process temperature is 370°C. To avoid coke formation, steam is fed to the

heater. Guard reactor contains 8 % of the total catalyst.

(retains 30% of V). Produces: Naphtha, Diesel, and Low Sulfur Oil.

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Hydrotreating ProcessesAtmospheric Residue Hydrotreating

Atmospheric Hydrotreating Process. (Fahim et al, 2010)

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Hydrotreating ProcessesOperating Conditions Vary due to the broad variety of applications. The most important operating conditions are:

Feedstock Naphtha

Kerosene Gas oil VGO* Residu

eTemperature °C 260-300 300-340 320-

350360-380

360-380

Hydrogen

pressure bar 5-10 15-30 15-40 40-70 120-160

partial pressure bar 10-20 20-31 26-41 50-90 90-200

consumption wt% 0.05-0.10 0.1-0.2 0.3-0.5 0.4-0.7 1.5-2.0

LHSV hr-1 4-10 2-4 1-3 1-2 0.15-0.3

H2/HC ratio std m3/m3 36-48 36-48 36-48 36-48 12-24Catalyst life years 3-10 - - - 0.5-1

Typical Process Parameters for Hydrotreating of Different Feedstocks. (Fahim et al, 2010; Speight et al, 2011)

* VGO = Vacuum gas oil

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Hydrotreating ProcessesFixed-Bed Reactor

Adiabatic reactor: To control temperature, the outflow is

quenched between reactors.

Works as a plug-flow reactor: Pressure drop and reaction rate must be

balanced.

Mechanical work over the catalyst. Attrition decreases catalyst particle size:

Reactivity is favored. Pressure drop is increased.

Fixed Bed Reactor(Ullmann’s Encyclopedia of Industrial Chemistry,

1992)

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Hydrotreating ProcessesTrickle-Bed Reactor (TBRs)

Preferred for two-phase fluids.

Multiple randomly fixed-beds in the same body.

Quenching points to control temperature.

Distributor design is a very important issue.

Trickle Bed Reactor and Examples of Distributors(Lee , 2006; Renade et al. 2011)

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Safety & Environmental IssuesByproducts, Emissions, Catalyst Handling Closed process. Hydrotreating reduces SOx and NOx emissions.

Possible risk during inspections, maintenance, regeneraton/loading/ unloading of catalyst.

Catalyst may be regenerated several times to remove coke and sulfur.

CO2 and CO are produced. Sulfur reacts to form SO2.

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HydrotreatingSelected References M. A. Fahim, T. A. Al- Sahhaf and A. S. Elkilani, Fundamentals of Petroleum Refining,

Elsevier, 2010. I. Chorkendorff and J. W. Niemantsverdriet, Concepts of Modern Catalysis and

Kinetics, Weinheim: WILEY-VCH Verlag GmbH & Co., 2003. Topsøe catalysts for hydroprocessing of petroleum fractions,

http://www.topsoe.com/business_areas/refining/~/media/PDF%20files/Refining/topsoe_hydroprocessing_catalysts_aug09.ashx; Brochure, 2009. Visited: March 26th, 2013.

A. Stanislaus, A. Marafi and M. S. Rana, "Recent advances in the science and technology of ultra low sulfur diesel (ULSD) production," Catalysis Today, no. 153, p. 1–68, 2010.

Sanghavi, K. & Schmidt, J., 2011. http://www.hydrocarbonprocessing.com/Article/2892145/Achieve-success-in-gasoline-hydrotreating.html Visited : March 26th, 2013

J. G. Speight, "Chapter 8 – Hydrotreating and Desulfurization," in The Refinery of the Future, Elsevier, 2011, p. 237–273.

S. Lee, Ed., Encyclopedia of Chemical Processing, New York: Taylor & Francis Group, LLC, 2006.

V. Ranade, R. Chaudhari and P. R. Gunjal, Reactor Engineering and Applications, Elsevier, 2011. Ullmann's Encyclopedia of Industrial Chemistry, vol. B4, VCH Publishers, 1992.

HYDROTREATINGOil Refining Processes

TKP-4150 - Group AApril 8th, 2013

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