Question 1

High-octane gasoline production: Straight-run naphtha is upgraded to a high-octane petrol primarily by which catalytic process?

Accepted Answer

Introduction: Raising the octane number of straight-run naphtha is central to gasoline production. Several catalytic processes exist, but only one directly transforms naphtha into an aromatic- and isoparaffin-rich high-octane stream. Given Data / Assumptions: Feed: Straight-run naphtha. Objective: Increase octane number significantly. Concept / Approach: Catalytic reforming (often platinum-based) dehydrogenates naphthenes to aromatics and rearranges paraffins to isoparaffins, boosting research octane number (RON) and producing hydrogen as a valuable byproduct. Step-by-Step Solution: Step 1: Identify the process that increases aromatics and isoparaffins in naphtha.Step 2: Recognize this as catalytic reforming.Step 3: Select “Reforming.” Verification / Alternative check: Reforming units are standard in refineries to supply high-octane reformate for gasoline blending and hydrogen for hydrotreating. Why Other Options Are Wrong: Cracking: Breaks large molecules to smaller; not the main route for naphtha to high octane. Polymerisation: Joins light olefins; not a naphtha upgrading step. Isomerisation: Raises octane of light naphtha (C5–C6) but not to the level of reformate. Alkylation: Combines isobutane with C3–C4 olefins; feed and objective differ. Common Pitfalls: Confusing isomerisation (C5–C6) improvements with the much larger octane boost from reforming. Final Answer: Reforming

Question 2

Operating pressure in cracking units: Although high pressure tends to retard cracking, industrial units still maintain a positive pressure of about 10–15 kgf/cm^2 mainly to achieve what?

Accepted Answer

Introduction: Cracking reactions form lighter products at elevated temperatures. Pressure influences phase behaviour, secondary reactions, and coking tendency. Given Data / Assumptions: Typical operating pressure: about 10–15 kgf/cm^2. Cracking rate itself is retarded by higher pressure. Concept / Approach: Moderate positive pressure helps keep heavier material in the liquid phase, improving heat transfer and reducing the tendency to form coke on reactor surfaces. Lower gas holdup also curbs overcracking and polymerization leading to coke. Step-by-Step Solution: Step 1: Recognize that increased pressure is not to speed cracking but to manage side reactions and phase.Step 2: Identify the principal benefit: suppress coke formation.Step 3: Note the auxiliary benefit of maintaining liquid-phase contact and more stable operation. Verification / Alternative check: Industrial practice balances temperature (to achieve conversion) with pressure (to limit coking and gas make), selecting ~10–15 kgf/cm^2 as a compromise. Why Other Options Are Wrong: Increase light distillates: Pressure alone does not increase yield; temperature-severity is primary. Enhance octane directly: Octane relates to product composition, not directly to pressure setting. Reduce gum content: Gum control is more related to olefin management and treating. Raise temperature without runaway: Temperature control is independent of maintaining moderate pressure. Common Pitfalls: Assuming any operating change that stabilizes operation must also increase octane or light-end yield. Final Answer: Suppress coke formation and maintain liquid-phase operation

Question 3

In petroleum refining, what is the typical straight-run yield of diesel obtained directly from crude oil atmospheric distillation (i.e., before any cracking or conversion processes)?

Accepted Answer

Introduction: Diesel obtained directly from atmospheric (straight-run) distillation of crude oil forms a modest portion of the barrel before any conversion units like cracking or hydrocracking are applied. Knowing this typical yield helps in preliminary refinery material balance and economics. Given Data / Assumptions: Straight-run means no cracking or conversion has been performed. Typical mixed crude slate (not an extreme light or heavy crude). We are estimating a representative percentage range rather than an exact constant. Concept / Approach: The atmospheric column separates crude by boiling range. Straight-run diesel cuts (roughly 180 to 360 C range) usually emerge in the high-teens to ~20s percent by volume for many common crudes. Conversion units later boost diesel pool volumes, but those are not counted here. Step-by-Step Solution: 1) Identify product of interest: straight-run diesel only.2) Use typical refinery heuristics: SR diesel yield commonly lies around the high-teens to low-20s percent of crude.3) Compare with options and select the nearest representative percentage. Verification / Alternative check: Industry planning heuristics and refinery textbooks often cite SR diesel yields near ~15–25 percent depending on crude. A mid-teens to high-teens figure is a conservative representative choice for a generic crude mix. Why Other Options Are Wrong: 8 percent: Too low for typical mixed crudes.28 percent: More characteristic of diesel after conversion blending, not just straight-run.35 percent: Unusually high for SR alone.None of the above: Not applicable because a plausible typical value is listed. Common Pitfalls: Confusing total diesel pool (after cracking/hydrocracking) with straight-run diesel only can inflate the expected number. Crude type variability also misleads if a single fixed value is assumed. Final Answer: 18 percent

Question 4

In petroleum product testing, which instrument is specifically used to determine the colour of light petroleum fractions and refined products?

Accepted Answer

Introduction: The colour of light petroleum products is a quality indicator and is measured using standardized instruments. Correct test method selection ensures comparable, specification-grade results. Given Data / Assumptions: Product type: light petroleum fractions (e.g., kerosene, jet, gasoline blending components). Objective: identify the correct instrument for colour determination. Concept / Approach: For light, nearly water-white petroleum products, the Saybolt colour scale and its dedicated instrument, the Saybolt chromometer, are standard. Darker products often use ASTM (D1500) colour comparators, but the question’s emphasis is on light fractions where Saybolt is conventional. Step-by-Step Solution: 1) Identify target measurement: product colour.2) Map to standard instruments: Saybolt chromometer for light product colour.3) Exclude unrelated test apparatus. Verification / Alternative check: Specifications for aviation turbine fuel and kerosene frequently reference Saybolt colour for appearance; standard lab manuals align on the Saybolt chromometer for this range. Why Other Options Are Wrong: Colour comparator: Generic term; ASTM D1500 comparators are used for darker products.Cleveland open cup apparatus: Measures flash point, not colour.None of these: Incorrect because the Saybolt chromometer is appropriate.ASTM D86 distillation unit: Used for volatility curves, not colour. Common Pitfalls: Confusing colour determination with clarity/appearance checks or with unrelated tests like flash point or distillation leads to wrong instrument selection. Final Answer: Saybolt chromometer

Question 5

Compared with thermal cracking of vacuum residue, catalytic cracking typically produces what notable difference in the gasoline (petrol) product slate and quality?

Accepted Answer

Introduction: Refineries convert heavy vacuum residues into lighter, high-value products using cracking. Catalytic cracking (e.g., FCC) is preferred over thermal cracking because of both yield and quality advantages for the gasoline pool. Given Data / Assumptions: Feed: residue of vacuum distillation. Processes compared: thermal cracking vs catalytic cracking (FCC). Focus: gasoline yield and quality outcomes. Concept / Approach: Catalytic cracking employs acidic zeolite catalysts to promote selective carbon–carbon bond scission, isomerization, and aromatization, producing more gasoline with higher octane numbers versus purely thermal routes. Step-by-Step Solution: 1) Identify target product metric: gasoline yield and quality.2) Recognize FCC selectivity: higher gasoline yield and higher octane than thermal cracking.3) Select the statement that matches these known outcomes. Verification / Alternative check: Standard refinery textbooks and FCC operating data consistently show improved gasoline make and octane with catalytic pathways compared to thermal cracking for similar feeds. Why Other Options Are Wrong: Produces lower octane number petrol: Incorrect; FCC gasoline typically has higher octane.Increases sulphur content: Not inherently true; sulphur is feed-dependent and often reduced downstream (e.g., hydrotreating).Increases gum-forming materials: Modern FCC gasoline stability is managed; the statement is misleading.Reduces LPG make by half: Not a standard rule; LPG yield depends on severity and catalyst activity. Common Pitfalls: Assuming thermal and catalytic cracking have similar selectivity; ignoring the octane benefit from isomerization/aromatization pathways in FCC. Final Answer: Gives higher yield of petrol (gasoline).

Question 6

Arrange these petroleum fractions in decreasing order of their typical boiling ranges (highest boiling first): lubricating oil, diesel, petrol (gasoline), LPG.

Accepted Answer

Introduction: Petroleum fractions are separated by boiling range. Ordering these fractions by decreasing boiling point reinforces understanding of atmospheric distillation cuts. Given Data / Assumptions: Fractions considered: lubricating oil, diesel, petrol (gasoline), LPG. Decreasing order requested: highest boiling first. Concept / Approach: Heavier fractions boil at higher temperatures. Lubricating oil cuts are heaviest among the list, followed by diesel, then petrol, while LPG is the lightest with the lowest boiling range. Step-by-Step Solution: 1) Identify heaviest fraction: lubricating oil (highest boiling).2) Next heavier: diesel.3) Then: petrol (gasoline).4) Lightest: LPG (lowest boiling). Verification / Alternative check: Typical boiling ranges confirm the order: lube oil > diesel > gasoline > LPG for atmospheric products. Why Other Options Are Wrong: Options b, c, d, e misplace gasoline or LPG relative to diesel and lubricating oil, contradicting distillation principles. Common Pitfalls: Confusing density with boiling range or assuming diesel boils below petrol; also mixing up LPG with light naphtha ranges. Final Answer: lubricating oil > diesel > petrol > LPG

Question 7

In gasoline (petrol) formulation, why are antioxidants added to the fuel blend?

Accepted Answer

Introduction: Gasoline stability is affected by oxidation of unsaturated components, which can form gums and deposits. Antioxidant additives interrupt radical chain reactions responsible for gum formation. Given Data / Assumptions: Fuel: gasoline (petrol). Additive: antioxidants (e.g., phenolic or amine types). Concept / Approach: Antioxidants act as radical scavengers, slowing oxidation that otherwise forms high-molecular-weight gums. This preserves storage stability and protects fuel systems. Step-by-Step Solution: 1) Identify the degradation pathway: oxidation leads to gum formation.2) Match additive function: antioxidants inhibit oxidation chain reactions.3) Conclude purpose: reduce gum formation in service and storage. Verification / Alternative check: Fuel specifications and additive supplier literature consistently associate antioxidants with improved oxidation stability and reduced gum. Why Other Options Are Wrong: Colour identification: Dye additives, not antioxidants, impart colour.Prevent icing: Anti-icing agents or alcohols address carburettor icing.Prevent lead build-up: Lead scavengers historically addressed deposits when leaded gasoline was used.Increase RVP: Volatility modifiers, not antioxidants, affect RVP. Common Pitfalls: Confusing antioxidants with detergents, metal deactivators, dyes, or volatility improvers; each addresses different performance properties. Final Answer: To minimise gum formation by inhibiting oxidation

Question 8

Aviation turbine fuel (ATF/jet fuel) has an average boiling range closest to which common refinery fraction?

Accepted Answer

Introduction: Aviation turbine fuel (jet fuel) is a middle distillate with a boiling range designed for combustion stability, safety, and operability at altitude. Its range aligns closely with kerosene cuts. Given Data / Assumptions: Product: ATF/jet fuel. Comparison set: LPG, gasoline, kerosene, diesel, lube oils. Concept / Approach: ATF specifications (e.g., freezing point, flash point, volatility) are engineered around a kerosene-range distillate, not as light as gasoline nor as heavy as diesel/lube oils. Step-by-Step Solution: 1) Place ATF within distillation ladder: mid-distillate region.2) Identify closest standard fraction: kerosene-range hydrocarbons.3) Select answer consistent with specs and practice. Verification / Alternative check: Jet-A/Jet-A1 products are essentially kerosene-type fuels; kerosene hydrocarbon distillation profiles match ATF closely. Why Other Options Are Wrong: LPG and gasoline: Too light.Diesel and lube oils: Heavier boiling ranges.Gasoline: Different volatility and octane requirements. Common Pitfalls: Equating ATF with diesel because both are middle distillates; ATF is typically lighter and more tightly specified in freezing point and smoke point compared with diesel. Final Answer: Kerosene

Question 9

Choose the correct statement about thermal cracking of petroleum hydrocarbons with respect to operating conditions and product distribution.

Accepted Answer

Introduction: Thermal cracking breaks larger hydrocarbon molecules into smaller ones by heat (and often steam dilution). Pressure, temperature, and residence time govern severity and the distribution of lighter products and olefins. Given Data / Assumptions: Process: non-catalytic thermal cracking. Variables: temperature, pressure, residence time. Focus: trend of lighter hydrocarbon yield. Concept / Approach: Lower pressure generally shifts equilibria and kinetics to favour molecule scission and suppress recombination, increasing lighter products and olefinicity at given temperature severity. Step-by-Step Solution: 1) Recognize cracking severity depends on T, P, and time.2) Lower pressure limits secondary recombination, enhancing light ends.3) Therefore, low pressure tends to increase lighter hydrocarbon yield. Verification / Alternative check: Steam cracking (extremely low partial pressure via steam dilution) is an extreme case showing high light olefin yields, illustrating the low-pressure effect. Why Other Options Are Wrong: Temperature insensitivity: False; severity is highly temperature-dependent.Residence time: Increasing time generally increases severity, not decreases it.Lower octane with greater depth: Deeper cracking usually increases olefins/aromatics that enhance octane; the statement is misleading.High pressure maximizes olefins: Opposite trend; high pressure favours recombination. Common Pitfalls: Assuming pressure only affects equipment design; in cracking, pressure materially alters radical recombination and product distribution. Final Answer: At low pressure, the yield of lighter hydrocarbons increases.

Question 10

How do aromatics influence key fuel quality metrics in diesel, kerosene, and petrol (gasoline)? Select the correct statement.

Accepted Answer

Introduction: Aromatic content affects combustion properties differently across fuels. Understanding these trends is vital for meeting specifications and engine performance requirements. Given Data / Assumptions: Three fuels considered: diesel, kerosene, petrol (gasoline). We seek the correct directional effect of aromatics on standard quality metrics. Concept / Approach: Aromatics tend to lower diesel cetane number (poorer ignition quality), lower kerosene smoke point (more sooting), and raise gasoline octane (improved knock resistance). Step-by-Step Solution: 1) Diesel: aromatics lower cetane → statement “increase cetane” is false.2) Kerosene: aromatics lower smoke point → statement “increase smoke point” is false.3) Petrol: aromatics raise octane → statement is true. Verification / Alternative check: Fuel property tables and specs consistently document these trends; reformate rich in aromatics often boosts gasoline octane, while diesel specs limit aromatics to preserve ignition quality. Why Other Options Are Wrong: Option a: Direction is reversed for diesel.Option b: Direction is reversed for kerosene smoke point.Option d: Combines incorrect statements.Option e: Contradicts gasoline octane behaviour. Common Pitfalls: Generalizing a single effect of aromatics across all fuels; each metric responds differently because of engine and combustion mode differences (SI vs CI). Final Answer: In petrol, aromatics increase octane number.

Question 11

With reference to crude petroleum composition, which class of hydrocarbons is almost absent in native crude oils before refining?

Accepted Answer

Introduction: Crude oil is a complex natural mixture dominated by paraffins and naphthenes with varying aromatics and sulphur species. Understanding which families are naturally present guides processing expectations. Given Data / Assumptions: We consider native crude (pre-refining) composition. We identify the class nearly absent in untreated crude. Concept / Approach: Olefins (alkenes) are typically reaction products of cracking and are rarely present in significant amounts in native crude because they are less thermodynamically stable than paraffins/naphthenes over geologic timescales. Step-by-Step Solution: 1) List natural families: paraffins, naphthenes, aromatics; sulphur compounds including mercaptans may appear.2) Recognize olefins form mainly during thermal/catalytic cracking, not in the reservoir.3) Conclude olefins are almost absent in crude petroleum. Verification / Alternative check: Analytical surveys of crude oils confirm negligible olefin content; refinery olefins mainly originate downstream in cracking units and steam crackers. Why Other Options Are Wrong: Mercaptans: Frequently present in sour crudes in small to moderate amounts.Naphthenes/cycloparaffins: Common and often abundant.Paraffins: Common and often dominant. Common Pitfalls: Assuming refinery product distributions reflect reservoir composition; cracking products like olefins largely arise during processing, not in situ. Final Answer: Olefins (alkenes)

Question 12

In an electrical desalter used for crude oil, what are the typical operating pressure and temperature maintained for effective salt and water removal?

Accepted Answer

Introduction: Electrical desalters remove salts and entrained water from crude before atmospheric distillation, protecting heat exchangers, furnaces, and catalysts from corrosion and fouling. Given Data / Assumptions: Device: crude electrical desalter. We seek representative operating pressure and temperature. Concept / Approach: Desalting efficiency improves with proper mixing, dilution water addition, and emulsion coalescence under an electric field. Moderate pressure and elevated temperature reduce viscosity and enhance separation without excessive vaporization. Step-by-Step Solution: 1) Select a pressure high enough to suppress flashing across heaters and maintain stable operation (about 10 kg/cm2 is common).2) Choose a temperature that lowers crude viscosity and interfacial tension (about 110–150 C is typical; 120 C is representative).3) Match to the closest option provided. Verification / Alternative check: Typical operating windows published by licensors and refiners indicate ~7–15 kg/cm2 and ~110–150 C; the 10 kg/cm2 and 120 C pair falls squarely within practice. Why Other Options Are Wrong: 1 kg/cm2 and 200 C: Too low in pressure for safe operation at that temperature.50 kg/cm2 and 250 C: Unnecessarily high; energy-intensive and atypical.10 kg/cm2 and 300 C: Excessively hot for desalting step.5 kg/cm2 and 90 C: Too cool for good viscosity reduction and separation. Common Pitfalls: Confusing upstream heater conditions with desalter internals; over-heating can worsen emulsions or risk flashing, while too low temperature reduces coalescence efficiency. Final Answer: 10 kg/cm2 and 120 C

Question 13

Classify 1,3-butadiene correctly within petroleum hydrocarbon families by identifying whether it behaves as a single-bond olefin, a di-olefin (conjugated diene), an aromatic compound, or a naphthene (cyclo-paraffin).

Accepted Answer

Introduction: Butadiene (specifically 1,3-butadiene) is a key building block in petrochemistry and polymer manufacturing. This question checks whether you can correctly classify it among common hydrocarbon families used in refining and fuels: paraffins, naphthenes, aromatics, and olefins (including diolefins). Given Data / Assumptions: Compound: 1,3-butadiene (C4H6) Context: petroleum hydrocarbon classification Compare against: naphthenes, aromatics, mono-olefins, di-olefins Concept / Approach: Hydrocarbon families are defined by bonding and ring structure. Olefins have C=C unsaturation; diolefins (dienes) contain two C=C bonds. Naphthenes are saturated cyclics. Aromatics have a conjugated ring that follows the 4n+2 rule (e.g., benzene). Step-by-Step Solution: 1) Write formula: butadiene = C4H6, indicating unsaturation.2) Identify bonds: 1,3-butadiene has two C=C bonds in conjugation.3) Conclude: it is a diene, i.e., a di-olefin; it is not cyclic (naphthene) nor aromatic. Verification / Alternative check: A quick rule: dienes have two double bonds; 1,3-positions confirm a conjugated system, still non-aromatic because there is no ring. Why Other Options Are Wrong: Naphthene: requires saturated ring; butadiene is open-chain unsaturated.Aromatic: requires planar ring with aromatic stabilization; not present here.Olefin (mono-olefin): butadiene has two C=C bonds, not one. Common Pitfalls: Confusing “conjugated” with “aromatic.” Conjugation alone does not imply aromaticity; a cyclic aromatic ring is required. Final Answer: Di-olefin (conjugated diene)

Question 14

Identify the location of India’s first crude oil refinery, referring to early petroleum history and the birthplace of refining operations within the country.

Accepted Answer

Introduction: India’s petroleum history begins in Assam, where commercial oil production and refining first took root. This question tests factual recall of that first refinery’s location. Given Data / Assumptions: We are asked for the first crude oil refinery in India. Options include several Indian locations. Concept / Approach: Use historical knowledge of Indian oil industry milestones. The earliest commercial activities and refining in India were centered in Assam in the late 19th/early 20th century. Step-by-Step Solution: 1) Recall that the pioneering oilfield developments occurred in Assam.2) Digboi is widely recognized as the site of India’s first refinery.3) Therefore, select Digboi as the correct location. Verification / Alternative check: Industry histories and standard petroleum textbooks cite Digboi (Assam) as India’s first refinery town. Why Other Options Are Wrong: Kochi: A major modern refinery hub, but not the first.Madras (Chennai): Important coastal city; not the site of the first refinery.Naharkatiya: Noted oilfield area in Assam, but the first refinery was established at Digboi. Common Pitfalls: Confusing oilfields with refinery sites, or mixing up later coastal refineries with the first historical one. Final Answer: Digboi

Question 15

Pick out the single incorrect statement regarding visbreaking, thermal cracking, catalytic cracking, and related severity/conditions in petroleum conversion processes.

Accepted Answer

Introduction: This question checks conceptual understanding of conversion process severity in refining: visbreaking (mild thermal), thermal cracking (severe), catalytic cracking (lower pressure/temperature than thermal), and pyrolysis/steam cracking (very severe). Given Data / Assumptions: We compare typical operating severities (T, P) and gasoline qualities. Only one statement must be incorrect after recovery. Concept / Approach: Visbreaking is designed to mildly reduce viscosity and produce limited conversion; it operates at lower severity than conventional thermal cracking. Catalytic cracking reduces required pressure (and often temperature) relative to purely thermal routes. Pyrolysis (steam cracking) is an extreme case with very high temperatures for olefin production. Step-by-Step Solution: 1) Statement (a) claims visbreaking uses higher temperature than thermal cracking. This contradicts fundamentals; visbreaking is milder.2) Statement (b) is true: pyrolysis/steam cracking is a severe thermal process at very high T.3) Statement (c) is true: catalytic gasoline exhibits higher octane and good lead response historically.4) Statement (d) is true: thermal cracking is generally more severe in T/P than catalytic routes. Verification / Alternative check: Standard refining texts list visbreaking temperatures lower than severe thermal/steam cracking and describe FCC as lower-pressure than thermal cracking. Why Other Options Are Wrong (i.e., not the incorrect one): (b) Correct: pyrolysis is severe, not mild.(c) Correct: catalytic gasolines have high octane and higher lead susceptibility historically.(d) Correct: thermal cracking typically needs higher T/P than catalytic routes. Common Pitfalls: Thinking “cracking” is uniformly severe; visbreaking is deliberately mild. Also, confusing pyrolysis severity with mild thermal steps. Final Answer: Higher temperature is employed in visbreaking than in thermal cracking.

Question 16

State the standard methods typically used to determine sulphur content in lighter versus heavier petroleum products, identifying the appropriate method for each cut.

Accepted Answer

Introduction: Sulphur determination methods in petroleum vary with boiling range and matrix. Lighter fractions are amenable to older lamp (Wickbold-type) or similar combustion methods, whereas heavier, more viscous materials require closed-vessel (bomb) combustion to ensure complete oxidation for accurate sulphur analysis. Given Data / Assumptions: Two product classes: lighter vs heavier petroleum products. Methods considered: lamp method and bomb method (closed combustion). Concept / Approach: Select the method that ensures complete combustion and reliable capture of sulphur for the given volatility/viscosity range: lamp method for light ends; bomb method for heavy stocks and residues. Step-by-Step Solution: 1) Lighter products vaporize/burn readily; lamp method suffices.2) Heavier products resist clean open combustion; use bomb method to force complete oxidation.3) Therefore, pair lamp with light products and bomb with heavy products. Verification / Alternative check: Analytical standards historically align lamp/open combustion with light distillates and closed-bomb with heavy residues for completeness and safety. Why Other Options Are Wrong: Bomb for light; lamp for heavy: mismatched to volatility/viscosity behavior.Bomb then quartz tube: not the standard pairing for heavy residues here.Quartz tube then lamp: reversed and nonstandard for the given classes. Common Pitfalls: Assuming one universal method suits all fractions; matrix drives method choice. Final Answer: Lamp method for light products; bomb method for heavy products

Question 17

In the context of gasoline formulation, identify the primary technical reason phenolic additives are used—considering effects on octane, oxidation stability (gum control), viscosity, and pour point.

Accepted Answer

Introduction: Gasoline degrades by oxidation, forming peroxides and gums that foul fuel systems. Phenolic additives (e.g., hindered phenols) are classic antioxidants used to improve storage stability and limit gum formation. Given Data / Assumptions: Gasoline base fuel prone to oxidative gum formation. Phenolic additives considered for performance. Concept / Approach: Oxidation inhibitors interrupt radical chain reactions. Phenols donate hydrogen to stabilize fuel radicals/peroxides, slowing gum formation. Octane effects are secondary; viscosity and pour point are largely unrelated in gasoline. Step-by-Step Solution: 1) Identify the dominant role of phenols: antioxidant behavior.2) Map consequences: reduced gum formation and improved storage stability.3) Conclude the correct option is antioxidant action, not pour point, viscosity, or primary octane boosting. Verification / Alternative check: Standard gasoline additive packages list phenolic antioxidants specifically for gum control and oxidation stability metrics (e.g., induction period tests). Why Other Options Are Wrong: Increase pour point: irrelevant; pour point applies to middle/heavy distillates, not to low-pour gasoline.Reduce viscosity: gasoline viscosity is already low; phenols are not viscosity modifiers.Primarily improve octane: phenols are not primary octane improvers; any octane change is incidental. Common Pitfalls: Confusing antioxidant function with octane boosters or cold-flow improvers used in diesel/lube oils. Final Answer: Act as an antioxidant (reduce gum formation)

Question 18

Name the refinery operation in which light fractions are removed from unstabilized crude or condensate to control vapor pressure and improve storage/transport safety.

Accepted Answer

Introduction: Some crude oils and condensates contain significant light ends (C1–C4, light naphtha) that raise Reid vapor pressure (RVP). A front-end operation removes these to make the stream safer to store and ship. Given Data / Assumptions: Objective: remove light fractions to reduce vapor pressure. Context: crude/condensate handling prior to further refining. Concept / Approach: Stabilisation is a controlled flash/stripping operation that removes volatile components, lowering RVP and improving product stability for transport. It differs from conversion (visbreaking), impurity removal (sweetening), or water removal (dehydration). Step-by-Step Solution: 1) Identify the goal: reduce light ends for safe handling.2) Map the operation that achieves this goal: stabilisation.3) Conclude: select “Stabilisation.” Verification / Alternative check: Process flow diagrams show stabilizer columns upstream of storage/export for condensates and volatile crudes to meet RVP specs. Why Other Options Are Wrong: Visbreaking: conversion process to reduce viscosity of residues, not light-end removal from crude.Dehydration: removes free/emulsified water, not light hydrocarbons.Sweetening: oxidizes/removes mercaptans to improve odor/color, not primarily RVP control. Common Pitfalls: Equating “stabilisation” with general “treating”; here it specifically targets light ends and vapor pressure. Final Answer: Stabilisation

Question 19

Interpret what a higher kinematic viscosity usually indicates about a lubricating oil’s volatility and safety limits—particularly its flash and fire points.

Accepted Answer

Introduction: Viscosity correlates with molecular weight distribution and volatility in lube oils. Heavier, more viscous oils generally exhibit higher flash/fire points because fewer light, volatile components are present. Given Data / Assumptions: Property under consideration: viscosity of a lubricating oil. We relate it to flash point and fire point behavior. Concept / Approach: Flash/fire points reflect the temperature at which sufficient vapours form to ignite/sustain combustion. Lower volatility (heavier/viscous oils) requires higher temperatures to produce ignitable vapour concentrations. Step-by-Step Solution: 1) Higher viscosity implies heavier average molecules and lower volatility.2) Lower volatility raises the temperature needed to form flammable vapour.3) Hence, flash and fire points increase with viscosity, all else equal. Verification / Alternative check: Empirical data across lube grades show flash point trending upward with viscosity index/grade, barring additive anomalies. Why Other Options Are Wrong: Lower flash/fire: opposite of typical trend.Higher acid number: acidity depends on oxidation/contaminants, not viscosity per se.Higher RVP: lube oils have very low RVP; viscosity increase would not raise RVP. Common Pitfalls: Assuming any property increase implies higher reactivity/acidity; viscosity is not a direct measure of acidity. Final Answer: Higher flash point and higher fire point

Question 20

Among common refinery fuels—diesel, kerosene, petrol (gasoline), and furnace oil—identify which typically exhibits the lowest flash point (highest volatility).

Accepted Answer

Introduction: Flash point is the lowest temperature at which a liquid emits sufficient vapour to form an ignitable mixture near the surface. Lighter, more volatile fuels have lower flash points. Given Data / Assumptions: Compare diesel, kerosene, petrol, and furnace oil. Typical refinery specifications and volatility profiles apply. Concept / Approach: Volatility order: petrol (most volatile) < kerosene < diesel < furnace oil (least volatile). Therefore, petrol has the lowest flash point among the listed fuels. Step-by-Step Solution: 1) Recall boiling range/volatility hierarchy.2) Link higher volatility to lower flash point.3) Conclude petrol (gasoline) has the lowest flash point. Verification / Alternative check: Standard tables list petrol flash points well below those of kerosene/diesel/furnace oil, consistent with its light distillation range. Why Other Options Are Wrong: Diesel: heavier than kerosene/petrol; higher flash point.Kerosene: intermediate volatility; flash point above petrol.Furnace oil: heaviest listed; highest flash point. Common Pitfalls: Confusing autoignition temperature (intrinsic) with flash point (vapour formation threshold). Final Answer: Petrol (gasoline)

Petroleum Refinery Engineering Questions