Case A: aiming for olefins
Choosing a light, paraffin-rich feedstock makes the steam-cracking storyline easy to read.
Terms to know before this page
Case
An exercise where you reason about one set of conditions at a time.
Pretreatment
A step that removes troublesome components before the main process.
Downstream route
The flow of where a feedstock is sent next — which unit, which use.
Tying it together with three cases
Case B: building a high-octane blendstock
The flow becomes visible: hydrotreat heavy naphtha, then send it to reforming.
Case C: lowering volatility
Even without changing the composition, nudging the cut toward the heavy side shifts the read.
When in doubt, go through the checklist
| Lens | First question |
|---|---|
| Mixture or not | Can you write one molecular formula for it? |
| Light / heavy | Is the average carbon number on the up side or the down side? |
| PNA | Is paraffin, naphthene, or aromatic the thickest? |
| Pretreatment | Do you need to drop sulphur first to protect the catalyst? |
| Downstream route | Does it fit isomerization, reforming, or steam cracking best? |
Run through this order and even unfamiliar terms stop being intimidating.
Safety and data — do not jump from course direction to real-world judgement
What this course gives you is a sense of direction — "which way it moves." Whether a real lot is safe, or whether it meets a specification, is not decided by direction. Even the same name "naphtha" hides shifts in composition when crude, cut, or pretreatment changes. So in the field, treat the course's direction as the entry to a decision, and align the conclusion with three kinds of primary documents:
| Document | What you mainly read | Relation to course direction |
|---|---|---|
| SDS (Safety Data Sheet) | Flash point, vapour pressure, exposure limits, first aid, PPE | The course's claim that "the lighter side has stricter vapour / fire management" is grounded by checking SDS values. |
| Analytical data (COA, lot analysis) | Carbon-number distribution, PNA distribution, sulphur and aromatic content | Course phrases like "light paraffin-rich" or "heavy with thick naphthenes" are translated into the lot's actual numbers. |
| Specifications / in-house standards | Use-specific tolerances, intake conditions, banned substances | Whether a stream actually fits the downstream is finally decided OK / NG by the spec. |
Order of judgement: course direction → SDS and analytical data → specifications. Do not judge "this is safe because the course said so." The final step has to be confirmed against primary sources.
What primary sources look like — illustrative samples
So that beginners can picture "what does an actual SDS or analysis look like?", here are made-up samples (dummy values). They are not real measurements — never use them as a basis for any decision.
Sample 1 — SDS (excerpt, illustrative)
| Item | Sample value (dummy) |
|---|---|
| Product name | Light naphtha (illustrative) |
| Flash point | Below −40 °C |
| Initial boiling point (IBP) | About 35 °C |
| Final boiling point (FBP) | About 95 °C |
| Vapour pressure | About 70 kPa (37.8 °C) |
| Main hazards | Flammable liquid (Category 1), skin irritation, respiratory effects from inhalation |
| First aid | If vapour is inhaled, move to fresh air. If skin contact occurs, wash with plenty of soap and water. |
Sample 2 — Analytical data (COA excerpt, illustrative)
| Analysis item | Sample value (dummy) |
|---|---|
| Density (15 °C) | 0.685 g/cm³ |
| Paraffins | 72 vol% |
| Naphthenes | 22 vol% |
| Aromatics | 6 vol% |
| Sulphur | Below 0.5 ppm |
| Carbon-number distribution | C5: 35%, C6: 45%, C7+: 20% |
Sample 3 — In-house specification (intake criteria, illustrative)
| Item | Tolerance (dummy) |
|---|---|
| Sulphur | 1 ppm or less |
| Aromatics | 10 vol% or less |
| Initial boiling point | 30 °C or above |
| Final boiling point | 100 °C or below |
The directions the course taught you — "light paraffin-rich," "heavy with thick naphthenes" — only become meaningful when matched against numbers like these. Always read the actual sheet at the end.
Consolidated exercises 1 — Reading the feedstock (Chapters 1–3)
Two questions on reading naphtha as a mixed fraction and matching light / heavy and PNA to the right downstream.
Q 7-1 — Feedstock slanted toward ethylene
Conceptually, which feedstock is closest to one slanted toward ethylene?
- Light naphtha with a large paraffin share.
- Heavy naphtha with a large naphthene share.
- Aromatic extract only.
Show answer and reasoning
Answer: A
For the "break into smaller pieces" storyline, a light, paraffin-rich feed is the clearest entry point.
Q 7-2 — Feedstock for reforming
Conceptually, which is closest to the feedstock you would feed to a reforming unit?
- Hydrotreated heavy naphtha that contains a reasonable share of naphthenes.
- LPG.
- Only water and hydrogen.
Show answer and reasoning
Answer: A
Reforming uses heavy naphtha, with sulphur removed in an upstream step as a default.
Consolidated exercises 2 — Pretreatment and reactions (Chapter 4)
Two questions on choosing among the four verbs (protect / rearrange / push / break).
Q 7-4 — Boosting C5 / C6 octane without aromatics
To improve the octane of the C5 / C6 front end without pushing up aromatics significantly, which operation is closest?
- Isomerization.
- Steam cracking.
- Desalting.
Show answer and reasoning
Answer: A
Isomerization is the typical route for raising the octane of light naphtha.
Q 7-5 — Why sulphur is removed before reforming
What is the main reason for placing sulphur removal in front of reforming?
- To protect the catalyst.
- To raise solubility in water.
- To turn everything into olefins.
Show answer and reasoning
Answer: A
Sulphur harms downstream catalysts, so it is removed first.
Consolidated exercises 3 — Safety, properties, overall summary (Chapters 2, 3, 7)
Three questions on light-side safety, the direction shifts when you move the cut, and the one-line summary of the whole course.
Q 7-3 — Handling concerns that rise on the light cut
Which handling concern tends to rise most on the light cut?
- Vapour and fire risk.
- Solid precipitation only.
- Specific gravity always exceeding 2.
Show answer and reasoning
Answer: A
The lighter the side, the higher the vapour pressure; fire and vapour management grow in importance.
Q 7-6 — Extending FBP toward the heavy side
Keeping the family ratios constant, which combination is most likely when you extend the final boiling point (FBP) toward the heavy side?
- Average carbon number rises; volatility falls.
- Average carbon number falls; volatility rises.
- Neither changes.
Show answer and reasoning
Answer: A
Pulling in more of the heavy side raises the average carbon number and lowers volatility.
Q 7-7 — Overall summary of naphtha
Which statement is the most accurate overall summary of naphtha?
- A petroleum-derived mixture whose fraction range and composition vary, with multiple downstream routes.
- Always a single pure compound, used only as a solvent.
- A complete worldwide synonym for finished gasoline.
Show answer and reasoning
Answer: A
The starting point is to treat naphtha as "a mixed fraction that varies."
Chapter 7 summary
- Separate light / heavy, PNA, pretreatment, and downstream route, then connect them at the end.
- Light, paraffin-rich streams follow the cracking storyline; heavy streams with visible naphthenes follow the reforming storyline.
- For real-world decisions always defer to the SDS, analytical data, and in-house specifications — use this course as a concept map.