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TU2 - Refining and Gas Processes > Improving straight-run naphtha octane number > Flashcards

Improving straight-run naphtha octane number Flashcards

1
Q

What is the usual RON range for light and heavy naphtha ?

A
  • Light naphtha : 60 to 80

- Heavy naphtha : 20 to 50

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2
Q

What is the process used to turn light naphtha into a good gasoline base ?

A

Catalytic isomerization (n-P -> iP)

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3
Q

What is the process used to turn heavy naphtha into a good gasoline base ?

A

Catalytic reforming (P + N -> A)

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4
Q

What are the operating conditions of a catalytic reforming unit ?

A
  • High temperature : 500°C
  • Pressure : 10-25 bar for semi-regenerative units and 3-5 bar for regenerative units
  • Pt catalyst (70 t of catalyst for 100t/h of feed)
  • Heat supply (endoT reactions)
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5
Q

What are the products of the reforming unit ?

A 
Desirable : 
- Reformate
- H2 rich gas (1.5 - 2% wt)
By product : 
- Fuel gas
- LPG
Detrimental : coke
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6
Q

What are the three main chemical reactions in the reforming unit ?

A
  • Aromatization reaction (P + N -> A)
  • Hydrocracking reaction ( long P -> short P )
  • Side reacton (coke on the catalyst)
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7
Q

What are the characterisitcs of the aromatization reactions N -> A in the reforming unit ?

A
  • H2 producer
  • very endoT
  • very quick
  • almost complete reaction
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8
Q

What are the characterisitcs of the aromatization reactions P -> A in the reforming unit ?

A
  • H2 producer
  • very endoT
  • slow
  • incomplete
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9
Q

What are the characteristics of the hydrocracking reactions in the reforming units ?

A
  • H2 consumer
  • exoT
  • slow
  • gas producer
  • positive contributor to improve octane number
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10
Q

What are the different steps leading to coke formation on the catalyst in the reforming unit ?

A
  • Aromatics are produced
  • A tend to agglomerate and form polyaromatics compounds -> coke precursors
  • these compounds cover the catalyst surface and reduce its activity
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11
Q

How do we fight coke formation in the reforming unit ?

A

The presence of H2 in large proportions prevents the aromatics from joining together to form coke = H2 blancketing

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12
Q

What is the typical H2/HC ratio in a reforming unit ?

A

From 3 to 6 depending on the technology

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13
Q

What shape does the catalyst of catalytic reforming usually take ?

A

small bars, pellets or spheres

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14
Q

How does a catalyst act ?

A
  1. The feed molecules enter the catalyst pores
  2. the molecules are adsorbed on the catalyst, react and are desorbed
  3. The new molecules exit the catalyst pores and evacuate with the effluent
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15
Q

What are the two functions on the catalyst in the reforming unit ?

A
  • an acid function changes the structure

- Pt facilitates hydrogen exchanges

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16
Q

What is a catalyst for the reforming unit made of ?

A
  • 1% wt of chlorine (acidity)
  • 0.3 % wt of Pt (metallic function)
  • alumina (porous support)
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17
Q

What is the average cost of a catalyst for the reforming unit ?

A

150 €/kg

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18
Q

What is the usual quantity of catalyst used in the reforming unit ?

A

70 t of catalyst for 100 t/h of feed

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19
Q

What are the poisons for the catalyst of the reforming unit ?

A
  • coke
  • S and N
  • water
  • metals
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20
Q

How many reactors are they in the reforming unit ?

A

3 from smallest to biggest

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21
Q

What reaction occurs in the fisrt reactor of the reforming unit ?

A

N -> A (quick and endoT reaction)

22
Q

What reaction(s) occur in te second reactor of the reforming unit ?

A
  • End of N -> A
  • P -> A
  • Hydrocracking
23
Q

What reaction(s) occur in the third reactod of the reforming unit ?

A
  • End of P -> A

- Hydrocracking

24
Q

What is the evolution of T and P between the reactors of the catalytic reforming unit ?

A
  • P decreases for the circulation of gases

- T increases because we crack more and more

25
Q

What are the units at the outler of the final reactor of the catalytic reforming unit ?

A
  • Drum to recover H2 rich gas

- Stabilization column to remove LPG and fuel gas from reformate

26
Q

What is the typical RON for the reformate at the outlet of the reforming unit ?

A

98 - 102

27
Q

What is a new issue with reformate ?

A

High aromatic content -> toxicity

28
Q

What are the operating variables of the reforming unit ?

A
  • reactor inlet T

- feed flowrate

29
Q

What is the impact of the feed inlet T of the reforming unit on the yield and quality of the reformate ?

A

Higher inlet T means higher octane number but also more coke production

30
Q

What is the impact of the feed flowrate of the reforming unit on the quality of the reformate

A

Higher feedflowrate means lower residence time and therefore lower octane number

31
Q

What is the usual frequency of the catalyst regeneration for the semi-regenerative reforming unit ?

A

every 6 to 24 months

32
Q

What is the usual time for the regeneration of the catalyst in a semi-regenerative reforming unit ?

A

7 to 10 days

33
Q

What are the steps to regenerate the catalyst in a reforming unit ?

A
  1. Shut down the unit and remove HC and H2
  2. Put the reactors under N2 pressure
  3. N2 heated and circulated through furnaces and heaters
  4. Air is injected slowly and the controlled burning of the coke begins
  5. Coke burns until inlet and outlet T are the same (no more coke)
  6. The catalyst is rejuvenated (chloride + activation of Pt)
  7. N2 is removed, H2 is injected and the reactors are started up
34
Q

What are the advantages of the regenerative process of the catalytic reforming unit ?

A
  • Continuous regeneration of catalyst -> no need to stop the unit (no stop in H2 production)
  • Lower P needed (3-5 bar) because no need to protect the catalyst as much
  • H2 production doubled thanks to low pressure of H2 (Le Châtelier)
  • higher reformate yields (80 -> 90% wt)
  • the second metal in the catalyst can be used to limit HCK reaction instead of being used to limit coke production
35
Q

What is the shape of the catalyst in a regenerative reforming unit ?

A

Sphere for circulation of the catalyst

36
Q

What are the operating conditions of the isomerization unit for light naphtha ?

A
  • Tbetween 150 and 180 °C
  • P between 20 and 40 bars
  • chlorine and Pt catalyst
37
Q

What is the typical evolution of RON thanks to the isomerization unti ?

A

From 60-80 to 83-90

38
Q

What is the typical evolution of RON thanks to the reforming unit ?

A

From 20-50 to 98-102

39
Q

Why does the isomerization unit run at sol low temperatures ?

A

The isomerization units runs in the range of temperature where the catalyst has thehigher activity (150-180°C)

40
Q

Is the isomerization reaction total or equilibriated ?

A

Equilibrium reaction

41
Q

What are the characteristics of the catalyst of the isomerization unit ?

A
  • 5 to 8% wt of chlorine
  • 0.3% wt of Pt
  • alumina for porous support
42
Q

What are the main poisons of the catalyst for the isomerization unit ?

A
  • Water

- Sulfur

43
Q

Is the isomerization reaction endo or exoT ?

A

ExoT

44
Q

How many reactors are they in the isomerization unit ?

A

2 to control the T increase

45
Q

What is used to dry the feed of the isomerization unit ?

A

Molecular sieves

46
Q

What are the chemical reactions occuring in the reactors of the isomerization unit ?

A
  • nP -> iP
  • Benzene hydrogenation
  • HCK
47
Q

What are the characteristics of the 1st generation of isomerization units ?

A

No recylcling

RON 82-83

48
Q

What are the characteristics of the 2nd generation of isomerization units ?

A

Separation of nP and iP at the outlet to recycle nP

RON 85-88

49
Q

What are the characteristics of the 3rd generation of isomerization units ?

A

Separation of nP and iP with only one branching to be recycled
RON 88-90

50
Q

What are the typical LHSV and WSHV in the reforming unit?

A

Both 1-3 h-1

TU2 - Refining and Gas Processes (14 decks)

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