Unit 3. Hydroconversion - portal.tpu.ru

Unit 3. Hydroconversion

Assistant lecturers

Belinskaya Nataliya Sergeevna

Kirgina Maria Vladimirovna

2

Название темы

Hydroconversion

Introduction

Hydroconversion is a term used to describe all different processes in which

hydrocarbon reacts with hydrogen.

hydrotreating

hydrocracking

The term hydrotreating is used to describe the process of the removal of

sulphur, nitrogen and metal impurities in the feedstock by hydrogen in the

presence of a catalyst.

Hydrocracking is the process of catalytic cracking of feedstock to products

with lower boiling points by reacting them with hydrogen.

3


Hydroconversion. Hydrotreating

Hydrotreating

Objectives of hydrotreating

Removing impurities, such as sulphur, nitrogen and oxygen for the

control of a final product specification or for the preparation of feed for

further processing

Removal of metals, usually in a separate guard catalytic reactor when

the organo-metallic compounds are hydrogenated and decomposed,

resulting in metal deposition on the catalyst pores

Saturation of olefins and their unstable compounds

4



Role of Hydrotreating

Figure 1. Role of hydrotreating (HT) in the refinery

Meeting finished product

specification

Kerosene, gas oil and lube oil

desulphurization

Olefin saturation for stability

improvement

Nitrogen removal

De-aromatization for kerosene

to improve cetane number

Feed preparation for downstream

units

Naphtha is hydrotreated for

removal of metal and sulphur

Sulphur, metal, polyaromatics

removal from vacuum gas oil

to be used as fluid catalytic

cracking feed

Pretreatment of hydrocracking

feed to reduce sulphur,

nitrogen and aromatics

5



Hydrotreating Chemistry

Desulphurization

a. Mercaptanes: RSH + H2 → RH + H2S

b. Sulphides: R2S + 2H2 → 2RH + H2S

c. Disulphides: (RS)2 + 3H2 → 2RH + 2H2S

d. Thiophenes:

Denitrogenation

a. Pyrrole: C4H4NH + 4H2 → C4H10 + NH3

b. Pyridine: C5H5N + 5H2 → C5H12 + NH3

6




Deoxidation

a. Phenol: C6H5OH + H2 → C6H6 + H2O

b. Peroxides: C7H13OOH + 3H2 → C7H16 + 2H2O

Hydrogenation of chlorides RCl + H2 → RH + HCl

Hydrogenation of olefins C5H10 + H2 → C5H12

Hydrogenation of aromatics

C6H6 + 3H2 → Cyclohexane

Naphthalene + H2 → Tetraline

7




Hydrogenation of organo-metallic compounds and deposition of

metals

Coke formation by the chemical condensation of polynuclear radicals

8



Termodynamics of Hydrotreating

Hydrotreating reactions are highly exothermic and reversible.

Olefin hydrogenation is usually complete.

Aromatic hydrogenation reaction can reach equilibrium under certain

condition.

Hydrodesulphurization can be carried out easier than denitrogenation.

Aromatic saturation is the most difficult reaction.

9



Hydrotreating Catalysts

The hydrotreating catalyst is a porous alumina matrix impregnated

with combinations of cobalt (Co), nickel (Ni), molybdenum (Mo) and

tungsten (W).

The catalysts mainly have pores with a surface area of (200–300 m2/g).

Co-Mo

desulphurization of

straight run

petroleum fractions

Ni-Mo

is chosen when higher activity

is required for the saturation

of polynuclear aromatic

compounds or for the removal

of nitrogen and refractory

sulphur compounds

Ni-W

is chosen only when

very high activity

aromatic saturation

is required

10



Hydrotreating Catalysts

Table 1. Reactivity of hydrotreating catalysts

Cobalt–molybdenum (Co–Mo) and nickel–molybdenum (Ni–Mo)

catalysts

resist poisoning

are the most universally applied catalysts for hydrodesulphurization

of feedstocks ranging from naphtha to residue

promote both demetallization and desulphurization

11



Hydrotreating Processes

Figure 2. The main elements of a hydrotreating process

12



Naphtha Hydrotreating

Figure 3. Naphtha hydrotreating process

13



Middle Distillates Hydrotreating

Figure 4. Diesel fuel hydrotreating unit

14



Atmospheric Residue Desulphurization

Figure 5. Atmospheric residue desulphurization process

15



Operating Conditions Increasing hydrogen partial pressure improves the removal of sulphur and nitrogen

compounds and reduces coke formation.

Higher temperatures will increase the reaction rate constant and improve the kinetics.

Excessive temperatures will lead to thermal cracking and coke formation.

High space velocity results in low conversion, low hydrogen consumption and low coke

formation.

Table 2. Process parameters for hydrotreating different feedstocks

16


Hydroconversion. Hydrocracking

Hydrocracking

Hydrocracking is a catalytic hydrogenation process

in which high molecular weight feedstock is converted and hydrogenated

to lower molecular weight products.

Hydrogenation removes impurities

in the feed such as

sulphur, nitrogen and metals.

Cracking will break bonds,

and the resulting unsaturated products

are consequently hydrogenated into

stable compounds.

17



Role of Hydrocracking

in the Refinery

Figure 6. Role of the hydrocracker in

the refinery

Hydrocracking is mainly used

to produce middle distillates of

low sulphur content such as

kerosene and diesel.

If mild hydrocracking is used, a

low sulphur fuel oil can be

produced.

18



Feed and Products

Table 3. Typical feedstock and products

FCC – fluid catalytic cracking, LCO – light gas oil, HCO – heavy gas oil

19



Hydrocracking Chemistry

Alkane hydrocracking

Hydrodealkylation

Ring opening

20



Hydrocracking Chemistry

Hydroisomerization

Polynuclear aromatics hydrocracking

21



Hydrocracking Catalysts Classification of hydrocracking catalyst

Table 4. Bifunctional catalyst strength for hydrogenation and cracking

x represents order of strength

22



Thermodynamics of Hydrocracking

Aromatic hydrogenation

Paraffin hydrocracking

Naphthenes hydrocracking

Aromatic hydrodealkylation

exothermic reactions

Careful control of the fixed bed

temperature is required.

This is usually done by

gaseous quenches in the reactor

catalyst partitioning of the bed

Table 5. Heat of reaction

23



Hydrocracking Processes

The following factors can affect operation (product quality), yield

(quantity), and the total economics of the process:

Process configuration

Catalyst type

Operating condition

One stage (once-through or recycle)

Two stages

Conversion level

Maximization of certain product

Product quality

Catalyst cycle

Partial hydrogen pressure

Liquid hourly space velocity

Feed/hydrogen recycle ratio

24



Hydrocracking Process Configuration

Figure 7. Simplified flow diagram of one-stage hydrocracking process with and without recycle

Is used for light feed with once through or recycle process

A conversion of 40–80% of the feed can be achieved

This configuration can be used to maximize a diesel product

It employs an amorphous catalyst

25




Figure 8. Conventional two-stage hydrocracker

The hydrocracking catalyst in the first stage has a high hydrogenation/acidity ratio,

causing sulphur and nitrogen removal

In the second reactor, the catalyst used is of a low hydrogenation/acidity ratio in which

naphtha production is maximized

26




Figure 9. Main reactions in two-stage hydrocracking

27



Hydrocracking Severity

1. Conventional hydrocracking

2. Mild hydrocracking the process is run at less severe operating conditions similar to desulphurization

(hydrotreating) conditions

a one-stage reactor without recycle is used in mild hydrocracking

the production of a high yield of fuel oil and savings of hydrogen

Table 6. Comparison of operating conditions of mild hydrocracking, hydrotreating and

conventional hydrocracking

28


Hydroconversion. Catalytic Dewaxing

Catalytic Dewaxing

Catalytic dewaxing is a particular hydrocracking process used to

improve cold flow properties of middle distillates and lubricants by

cracking normal paraffins.

Dewaxing can be achieved by isomerization. Isoparaffins have lower

melting points than normal paraffins.

The properties targeted for improvement are

pour point and viscosity of middle distillates and lubricants

the cloud point of diesel fuel

the freeze point of jet fuel

29


Hydroconversion. Catalytic Dewaxing

Catalytic Dewaxing

A single-stage, once through hydrocracking process can be used for

catalytic dewaxing, with or without hydrotreating, depending on the

sulphur and nitrogen content of the feedstock.

The catalytic process is carried out as a trickle bed reactor over a

bifunctional zeolite catalyst under hydrogen flow.

A non-noble metal (e.g. nickel) supported on a medium-pore zeolite,

such as ZSM-5 can be used.

30


Hydroconversion

Issues for Self-study and Revision

Fahim M.A., Sahhhaf T.A., Elkilani A.S. Fundamentals of Petroleum Refining: – First Edition. –

Elsivier. – 2010. – 485 p. Hydrotreating pp. 153-171

Hydrocracking pp. 180-192

Meyers Robert A. (ed.) Handbook of petroleum refining processes. 3-rd edition. McGraw-Hill

Professional. – 2003. – 847 p.

Isocracking-hydrocracking for superior fuels and lubes production pp. 317-336

Documents

Unit 3. Hydroconversion - portal.tpu.ru