23-Chem-B6 Petroleum Refining and Petrochemicals · Undated paper
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
National Exam 16-Chem-B6, Petroleum Refining and Petrochemicals — May 2019. 3 hours, OPEN BOOK exam (any non-communicating calculator permitted). Per the exam notes, FIVE (5) questions constitute a complete paper and only the first five as they appear in the answer book are marked; the paper as printed contains exactly five questions, all answered in full below. Questions are answered in essay format where required (clarity and organization are explicitly marked); the two calculation parts — Q1(b) blending density and Q5 distillation-sequence mass balance — follow the worked-solution format. All five questions are printed as “10 Marks”, consistent with the page-1 note that each question is of equal value.
Reference texts: Gary, Handwerk & Kaiser, Petroleum Refining: Technology and Economics, 5th ed.; Fahim, Al-Sahhaf & Elkilani, Fundamentals of Petroleum Refining; J. G. Speight, The Chemistry and Technology of Petroleum, 5th ed.; Perry's Chemical Engineers' Handbook, 9th ed. (Sec. 13, Distillation). ASTM test methods cited by number for the property definitions.
Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.
Octane number rates a gasoline's resistance to knock (auto-ignition) against primary reference fuels, where iso-octane (2,2,4-trimethylpentane) is assigned 100 and n-heptane 0. A fuel is tested in a standardized single-cylinder variable-compression CFR engine under two different protocols:
The difference is the test severity: because MON is measured under hotter, faster, more demanding conditions, $\text{MON}<\text{RON}$ for essentially all fuels, and the gap $\text{RON}-\text{MON}$ is the fuel's sensitivity. The number posted on the pump in North America is the anti-knock index, $\text{AKI}=(\text{RON}+\text{MON})/2$.
Each of the three headings below answers sub-parts (a), (b) and (c) together: the description, one example reaction, and the catalyst type.
Isomerization. Rearranges low-octane straight-chain light paraffins (n-pentane, n-hexane) into their high-octane branched isomers without changing carbon number. Example:
$$\text{n-C}_6\text{H}_{14}\;\rightleftharpoons\;\text{2,2-dimethylbutane}\quad(\text{RON}\ \sim 25\to 90+).$$
Catalyst: a bifunctional acid catalyst — platinum on chlorided alumina, or Pt on a zeolite / sulphated-zirconia acidic support — operated at low temperature (the equilibrium favours branched isomers as temperature falls).
Dehydrocyclization (the ring-forming reaction of catalytic reforming). Converts straight-chain paraffins into aromatics by simultaneous cyclization and dehydrogenation, producing very high-octane aromatic rings and hydrogen. Example:
$$\text{n-C}_7\text{H}_{16}\;\rightarrow\;\text{C}_6\text{H}_5\text{CH}_3\ (\text{toluene})+4\,\text{H}_2.$$
Catalyst: a bimetallic reforming catalyst — Pt–Re (or Pt–Sn) on chlorided alumina — which provides a metal (dehydrogenation) function and an acid (isomerization/cyclization) function.
Catalytic cracking (FCC). Cracks heavy gas oil into lighter gasoline-range molecules that are more branched, olefinic and aromatic, and therefore of much higher octane than the feed. Example:
$$\text{C}_{16}\text{H}_{34}\;\rightarrow\;\text{C}_8\text{H}_{18}\ (\text{iso-paraffin})+\text{C}_8\text{H}_{16}\ (\text{olefin}).$$
Catalyst: a solid acid — a faujasite (Y / ultrastable USY) zeolite in an amorphous silica-alumina matrix, often with a ZSM-5 octane additive.
