Q: Function of glycol in motor gasoline Glycol added to petrol primarily acts as a/an ______ agent.

Introduction / Context: In cold climates, carburetor and intake system icing can disrupt fuel–air mixing. Certain additives mitigate icing by altering water phase behavior and vaporization characteristics. Given Data / Assumptions: Additive is a glycol (e.g., ethylene or diethylene glycol derivatives). Concept / Approach: Glycols act as anti-icing agents by depressing the freezing point of water and promoting dissolution of moisture that could otherwise crystallize as ice in carburetors or throttle bodies. They are not primary anti-knock agents (which include high-octane blending components), nor are they gum inhibitors or dewaxing agents. Step-by-Step Solution: Identify icing issue → water freezing in induction.Glycol → freeze point depression and water solubilization.Select “Anti-icing.” Verification / Alternative check: Historical winter gasoline formulations include anti-icing additives (alcohols/glycols) to prevent carburetor icing. Why Other Options Are Wrong: Anti-knock relates to octane improvers. Anti-gum agents are antioxidants/detergents. Dewaxing pertains to middle distillates, not gasoline. Common Pitfalls: Assuming one additive provides all functions; modern gasolines use additive packages with distinct components for each role. Final Answer: Anti-icing

Q: Electrical desalting of crude — what type of impurities are removed? During electrical desalting, the unit primarily removes ______ impurities from crude oil.

Introduction / Context: Electrical desalters reduce salt and water content of crude before atmospheric distillation to protect equipment and catalysts. Understanding the wetting characteristics of removable impurities clarifies why the process works. Given Data / Assumptions: Crude is mixed with wash water and subjected to a high electric field. Water droplets coalesce and separate due to electrostatic forces. Concept / Approach: The process targets water-wet (oleophobic) dispersed droplets carrying dissolved inorganic salts and fine hydrophilic solids. The electric field induces droplet dipoles, coalescence, and settling, removing brine and water-wet particulates. Oil-wet (oleophilic) fines tend to remain with the oil phase and are not efficiently removed by electrostatic coalescence alone. Step-by-Step Solution: Define oleophobic vs. oleophilic with respect to crude oil.Desalter mechanism → coalescing water-wet droplets and hydrophilic fines.Select “Oleophobic (water-wet) impurities.” Verification / Alternative check: Salt removal performance correlates with effective water coalescence, underscoring that water-wet species are captured with the aqueous phase. Why Other Options Are Wrong: Oleophilic impurities do not preferentially report to the aqueous phase. Metallic particulates may be removed only if water-wet. Common Pitfalls: Under-dosing wash water or using incompatible demulsifiers reduces removal of water-wet impurities. Final Answer: Oleophobic (water-wet) impurities

Q: Wax deoiling methods Deoiling of petroleum wax is accomplished by which method(s)?

Introduction / Context: Slack wax from lube refining contains entrained oil; deoiling (dewaxing and oil removal) is needed to meet wax product specifications such as melting point, oil content, and penetration. Given Data / Assumptions: Processes considered include chilling/filtration and solvent methods. Concept / Approach: Deoiling relies on cooling to crystallize wax and reduce oil solubility, combined with solvent extraction (e.g., MEK/toluene) to selectively dissolve oil and permit filtration or centrifugation. Heating alone would dissolve wax back into oil; vacuum flashing cannot selectively remove tightly held oil in wax crystals. Therefore, practical deoiling uses cooling plus solvent extraction. Step-by-Step Solution: Identify required phase behavior: crystallize wax, dissolve oil.Cooling + solvent → effective separation.Select “Both (b) & (c).” Verification / Alternative check: Industrial deoiling flowsheets show chilling trains with solvent addition followed by filters (rotary drum, plate-and-frame) or centrifuges. Why Other Options Are Wrong: Heating reverses the separation; vacuum flashing is not selective enough. Common Pitfalls: Insufficient residence for crystal growth or wrong solvent ratio causing poor filtration rates. Final Answer: Both (b) & (c)

Q: Effect of water content on conductivity in electrical desalting In a crude–water emulsion (about 3–8% water) inside an electrical desalter, electrical conductivity ______ as the water fraction increases.

Introduction / Context: Electrical desalters use an applied field across a crude–water mixture. Conductivity governs current flow, field distribution, and droplet coalescence effectiveness. Given Data / Assumptions: Water is the conductive phase; crude is essentially insulating. Water cut varies in the 3–8% range. Concept / Approach: As the dispersed water fraction increases, more conductive pathways form, raising the bulk conductivity of the emulsion. This facilitates electrostatic coalescence until excessive water leads to short-circuiting risks. Therefore, within the normal range, conductivity increases with water content. Step-by-Step Solution: Relate conduction to volume fraction of conductive phase.Higher water → higher effective conductivity.Select “Increases.” Verification / Alternative check: Desalter operation guidelines adjust voltage with water cut to maintain optimal current density and avoid arcing. Why Other Options Are Wrong: Decreasing or unchanged trends contradict the physics of two-phase conduction. Common Pitfalls: Over-watering the desalter can cause upsets; balance wash water for salt removal without electrical instability. Final Answer: Increases

Q: Refractive index of petrofuel — what does it indicate? The refractive index (n) of a petroleum fuel, defined as the ratio of light speed in air to that in the fuel, generally correlates with its ______.

Introduction / Context: Simple optical properties such as refractive index provide rapid, non-destructive indication of hydrocarbon composition. Refineries use n and derived quantities (e.g., refractivity intercept) for quality checks. Given Data / Assumptions: Comparisons among similar boiling range fuels (to avoid volatility confounding). Concept / Approach: Refractive index increases with increasing average molecular weight and with higher aromatic content (due to higher polarizability). Thus, n qualitatively indicates both. It is not a sulfur-specific metric. Consequently, the best answer is “Both a & b.” Step-by-Step Solution: Recall polarizability trends: aromatics > naphthenes > paraffins.Heavier molecules also raise n.Select combined correlation. Verification / Alternative check: Empirical correlations (e.g., refractivity intercept) relate n and density to composition and average molecular weight. Why Other Options Are Wrong: “Only” statements omit the dual dependence. “Neither” contradicts established correlations. Common Pitfalls: Comparing across very different boiling ranges; always compare within similar distillate cuts. Final Answer: Both a & b

Question 1

Standard engine for knocking tests Knocking characteristics (octane/cetane-type tests) of petrofuels are measured in a ______ engine.

Accepted Answer

Introduction / Context: Standardized test engines provide reproducible conditions to rate fuels for knock tendency (gasoline) or ignition quality (diesel). The CFR engine is the long-standing benchmark for octane and cetane-related procedures. Given Data / Assumptions: ASTM standard methods for octane number rely on variable compression CFR spark-ignition engines. Cetane number tests likewise use CFR-type diesel test engines with controlled parameters. Concept / Approach: The CFR engine provides controlled compression ratio, speed, intake temperature, and standardized reference fuels. Octane number measures knock resistance in SI engines; cetane number measures ignition delay in CI engines. Both use CFR hardware adapted for their mode, not idealized thermodynamic cycles such as Carnot or Stirling. Step-by-Step Solution: Identify the standardized hardware → CFR engine.Map to knocking/ignition quality tests.Select CFR. Verification / Alternative check: ASTM D2699/D2700 (RON/MON) and D613 (cetane) reference CFR engines explicitly. Why Other Options Are Wrong: Carnot/Stirling are theoretical cycles, not test engines. “Diesel (unstandardized)” lacks the rigor of the CFR standard apparatus. Common Pitfalls: Assuming any engine can rate fuels; standardized conditions are essential for comparable numbers. Final Answer: CFR (Co-operative Fuel Research)

Question 2

Functional representation of mercaptans (thiols) Mercaptans are represented structurally as ______ (R and R' denote alkyl groups).

Accepted Answer

Introduction / Context: Mercaptans (thiols) are odorous sulphur compounds in petroleum streams, important for odorization (e.g., LPG) and as contaminants requiring sweetening. Knowing their functional formula is foundational to understanding their reactivity and treatment. Given Data / Assumptions: R denotes an alkyl or aryl group; the functional group involves sulphur and hydrogen. Concept / Approach: Thiols have the functional group –SH attached to carbon (R–SH). This contrasts with sulfides (R–S–R′) and disulfides (R–S–S–R′). Carboxylic acids (R–COOH) and ethers (R–O–R′) are oxygen-containing, not sulfur-thiol functionalities. Step-by-Step Solution: Identify mercaptan = thiol functional group.Write general formula → R–S–H.Choose the matching option. Verification / Alternative check: Sour gas treating and Merox processes target –SH compounds; reaction schemes depict R–SH oxidation or extraction, confirming the structure. Why Other Options Are Wrong: R–S–R and R–S–R′ are thioethers (sulfides), not thiols. R–COOH and R–O–R′ are oxygenated functions. Common Pitfalls: Confusing thiols with sulfides due to shared sulfur; odor intensity and reactivity differ markedly. Final Answer: R-S-H

Question 3

Hydrocarbon class with poorest oxidation stability

Accepted Answer

Introduction / Context: Oxidation stability affects storage gum formation, varnish, and engine deposit tendencies. Different hydrocarbon classes (paraffins, naphthenes, aromatics, olefins) vary notably in susceptibility to autoxidation. Given Data / Assumptions: Comparison is among the common classes in refinery products. Concept / Approach: Olefins contain carbon–carbon double bonds that are highly reactive toward oxygen, forming peroxides and initiating polymerization leading to gums. Saturated paraffins and naphthenes are more stable; aromatics are resonance-stabilized. Thus, olefins exhibit the poorest oxidation stability, consistent with gasoline storage concerns where unsaturates drive gum formation. Step-by-Step Solution: Relate double bond reactivity to oxidation susceptibility.Rank: olefins worst < naphthenes/paraffins < aromatics.Select “Olefins.” Verification / Alternative check: Induction period tests and gum tests show faster degradation for olefin-rich fuels. Why Other Options Are Wrong: Paraffins/naphthenes are saturated and comparatively resistant. Aromatics resist autoxidation better than olefins despite soot propensity. Common Pitfalls: Confusing oxidation stability (chemical) with smoke/soot tendency (combustion). Aromatics smoke more but oxidize slower than olefins in storage. Final Answer: Olefins

Question 4

Function of glycol in motor gasoline Glycol added to petrol primarily acts as a/an ______ agent.

Accepted Answer

Introduction / Context: In cold climates, carburetor and intake system icing can disrupt fuel–air mixing. Certain additives mitigate icing by altering water phase behavior and vaporization characteristics. Given Data / Assumptions: Additive is a glycol (e.g., ethylene or diethylene glycol derivatives). Concept / Approach: Glycols act as anti-icing agents by depressing the freezing point of water and promoting dissolution of moisture that could otherwise crystallize as ice in carburetors or throttle bodies. They are not primary anti-knock agents (which include high-octane blending components), nor are they gum inhibitors or dewaxing agents. Step-by-Step Solution: Identify icing issue → water freezing in induction.Glycol → freeze point depression and water solubilization.Select “Anti-icing.” Verification / Alternative check: Historical winter gasoline formulations include anti-icing additives (alcohols/glycols) to prevent carburetor icing. Why Other Options Are Wrong: Anti-knock relates to octane improvers. Anti-gum agents are antioxidants/detergents. Dewaxing pertains to middle distillates, not gasoline. Common Pitfalls: Assuming one additive provides all functions; modern gasolines use additive packages with distinct components for each role. Final Answer: Anti-icing

Question 5

Electrical desalting of crude — what type of impurities are removed? During electrical desalting, the unit primarily removes ______ impurities from crude oil.

Accepted Answer

Introduction / Context: Electrical desalters reduce salt and water content of crude before atmospheric distillation to protect equipment and catalysts. Understanding the wetting characteristics of removable impurities clarifies why the process works. Given Data / Assumptions: Crude is mixed with wash water and subjected to a high electric field. Water droplets coalesce and separate due to electrostatic forces. Concept / Approach: The process targets water-wet (oleophobic) dispersed droplets carrying dissolved inorganic salts and fine hydrophilic solids. The electric field induces droplet dipoles, coalescence, and settling, removing brine and water-wet particulates. Oil-wet (oleophilic) fines tend to remain with the oil phase and are not efficiently removed by electrostatic coalescence alone. Step-by-Step Solution: Define oleophobic vs. oleophilic with respect to crude oil.Desalter mechanism → coalescing water-wet droplets and hydrophilic fines.Select “Oleophobic (water-wet) impurities.” Verification / Alternative check: Salt removal performance correlates with effective water coalescence, underscoring that water-wet species are captured with the aqueous phase. Why Other Options Are Wrong: Oleophilic impurities do not preferentially report to the aqueous phase. Metallic particulates may be removed only if water-wet. Common Pitfalls: Under-dosing wash water or using incompatible demulsifiers reduces removal of water-wet impurities. Final Answer: Oleophobic (water-wet) impurities

Question 6

Wax deoiling methods Deoiling of petroleum wax is accomplished by which method(s)?

Accepted Answer

Introduction / Context: Slack wax from lube refining contains entrained oil; deoiling (dewaxing and oil removal) is needed to meet wax product specifications such as melting point, oil content, and penetration. Given Data / Assumptions: Processes considered include chilling/filtration and solvent methods. Concept / Approach: Deoiling relies on cooling to crystallize wax and reduce oil solubility, combined with solvent extraction (e.g., MEK/toluene) to selectively dissolve oil and permit filtration or centrifugation. Heating alone would dissolve wax back into oil; vacuum flashing cannot selectively remove tightly held oil in wax crystals. Therefore, practical deoiling uses cooling plus solvent extraction. Step-by-Step Solution: Identify required phase behavior: crystallize wax, dissolve oil.Cooling + solvent → effective separation.Select “Both (b) & (c).” Verification / Alternative check: Industrial deoiling flowsheets show chilling trains with solvent addition followed by filters (rotary drum, plate-and-frame) or centrifuges. Why Other Options Are Wrong: Heating reverses the separation; vacuum flashing is not selective enough. Common Pitfalls: Insufficient residence for crystal growth or wrong solvent ratio causing poor filtration rates. Final Answer: Both (b) & (c)

Question 7

Effect of water content on conductivity in electrical desalting In a crude–water emulsion (about 3–8% water) inside an electrical desalter, electrical conductivity ______ as the water fraction increases.

Accepted Answer

Introduction / Context: Electrical desalters use an applied field across a crude–water mixture. Conductivity governs current flow, field distribution, and droplet coalescence effectiveness. Given Data / Assumptions: Water is the conductive phase; crude is essentially insulating. Water cut varies in the 3–8% range. Concept / Approach: As the dispersed water fraction increases, more conductive pathways form, raising the bulk conductivity of the emulsion. This facilitates electrostatic coalescence until excessive water leads to short-circuiting risks. Therefore, within the normal range, conductivity increases with water content. Step-by-Step Solution: Relate conduction to volume fraction of conductive phase.Higher water → higher effective conductivity.Select “Increases.” Verification / Alternative check: Desalter operation guidelines adjust voltage with water cut to maintain optimal current density and avoid arcing. Why Other Options Are Wrong: Decreasing or unchanged trends contradict the physics of two-phase conduction. Common Pitfalls: Over-watering the desalter can cause upsets; balance wash water for salt removal without electrical instability. Final Answer: Increases

Question 8

Refractive index of petrofuel — what does it indicate? The refractive index (n) of a petroleum fuel, defined as the ratio of light speed in air to that in the fuel, generally correlates with its ______.

Accepted Answer

Introduction / Context: Simple optical properties such as refractive index provide rapid, non-destructive indication of hydrocarbon composition. Refineries use n and derived quantities (e.g., refractivity intercept) for quality checks. Given Data / Assumptions: Comparisons among similar boiling range fuels (to avoid volatility confounding). Concept / Approach: Refractive index increases with increasing average molecular weight and with higher aromatic content (due to higher polarizability). Thus, n qualitatively indicates both. It is not a sulfur-specific metric. Consequently, the best answer is “Both a & b.” Step-by-Step Solution: Recall polarizability trends: aromatics > naphthenes > paraffins.Heavier molecules also raise n.Select combined correlation. Verification / Alternative check: Empirical correlations (e.g., refractivity intercept) relate n and density to composition and average molecular weight. Why Other Options Are Wrong: “Only” statements omit the dual dependence. “Neither” contradicts established correlations. Common Pitfalls: Comparing across very different boiling ranges; always compare within similar distillate cuts. Final Answer: Both a & b

Question 9

Wax sweating — allowable oil content To achieve efficient and satisfactory wax sweating, the upper limit of oil content in the wax should be about ______ %.

Accepted Answer

Introduction / Context: Wax sweating is a finishing step where controlled heating allows entrained oil to “sweat” out of a wax cake, improving oil content to meet specifications. Excess oil interferes with crystal networking and drainage. Given Data / Assumptions: Target is efficient sweating performance without excessive cycle time. Concept / Approach: For effective sweating, wax cakes must have limited initial oil so the crystalline structure can form a connected matrix and allow oil to drain. Industrial practice limits initial oil content to around 5% or less. Higher oil percentages hinder structure and lead to poor separation and off-spec wax. Step-by-Step Solution: Relate oil content to crystal structure strength.Apply industry guideline → ~5% maximum.Choose 5%. Verification / Alternative check: Specifications for fully refined paraffin and microcrystalline waxes show low oil content limits; process notes advise low initial oil for effective sweating. Why Other Options Are Wrong: 15–60% are far too high for efficient sweating. 2% is within spec for finished waxes, not an upper limit for initiating sweating. Common Pitfalls: Attempting to sweat wax with very high oil content instead of first deoiling by solvent/cooling methods. Final Answer: 5

Question 10

Octane quality from two-stage fluidised catalytic cracking (FCC) Gasoline produced via a two-stage FCC process typically has an octane number closest to ______.

Accepted Answer

Introduction / Context: FCC is a primary refinery conversion unit producing high-octane gasoline rich in isoparaffins and aromatics. Two-stage or enhanced-severity FCC configurations aim for improved octane and yield profiles. Given Data / Assumptions: Octane number refers to research octane (RON) range commonly cited for FCC gasoline blends before further treating. Concept / Approach: Typical FCC gasoline exhibits high RON (low 90s) due to isomerization and aromatisation reactions over acidic zeolite catalysts. Two-stage FCC or high-severity modes can push octane further than simple cracking but not generally to the extreme upper 90s without additional reformate blending. Hence, 92 is a representative value among the options listed. Step-by-Step Solution: Recall FCC gasoline composition → high RON, moderate MON.Map two-stage severity to RON in low 90s.Select 92. Verification / Alternative check: Plant data and textbooks report FCC gasoline RON typically around 90–95 depending on severity and feed; 92 is a standard benchmark figure. Why Other Options Are Wrong: 80/87 are low for FCC gasoline. 97 is unusually high for straight-run FCC gasoline without reformate/oxygenates. Common Pitfalls: Confusing pool octane (after blending) with individual stream octane. Final Answer: 92

Question 11

Cause of gum formation in stored gasoline

Accepted Answer

Introduction / Context: Gum formation during storage degrades gasoline quality, fouls injectors/carburetors, and increases engine deposits. Understanding the mechanism informs additive selection and handling practices. Given Data / Assumptions: Stored gasoline contains trace oxygen exposure and possibly metals that catalyze reactions. Concept / Approach: Unsaturated hydrocarbons (olefins) autoxidize to peroxides, then polymerize into higher-molecular-weight species (gums). Antioxidants and metal deactivators are added to inhibit these pathways. Sulphur presence is undesirable for other reasons but is not the primary cause of gum. Aromatics tend to be oxidation-stable relative to olefins; paraffins are even more stable. Step-by-Step Solution: Identify reactive class: olefins in gasoline.Mechanism: oxidation → peroxides → polymerisation → gums.Select the correct causal statement. Verification / Alternative check: Induction period and existent gum tests correlate high-olefin blends with faster gum formation unless inhibited. Why Other Options Are Wrong: Alkylation is a refinery process, not a storage degradation route. Sulphur affects corrosion and emissions but is not the gum initiator. Aromatics and paraffins are relatively oxidation-resistant. Common Pitfalls: Confusing “gum” with soot; soot is a combustion phenomenon, not a storage polymerization issue. Final Answer: Oxidation and polymerisation of unsaturates

Question 12

Component class preference across fuels Which component class is desirable in diesel and kerosene but generally undesirable in gasoline?

Accepted Answer

Introduction / Context: Hydrocarbon classes influence ignition quality, smoke tendency, and octane rating. Diesel/kerosene require good ignition (high cetane) and clean burning, whereas gasoline requires knock resistance (high octane). Given Data / Assumptions: Paraffins include normal and isoparaffins; cetane is best for normal paraffins. Aromatics raise octane but reduce cetane and raise smoke. Concept / Approach: In diesel and kerosene, higher normal paraffin content increases cetane number and improves ignition quality; kerosene smoke point also benefits from lower aromatics. In gasoline, paraffins (especially normal) lower octane relative to aromatics and isoparaffins; thus, paraffins are comparatively undesirable in gasoline blends targeting high octane. Therefore, paraffins are the class that is desirable in diesel/kerosene but undesirable in gasoline. Step-by-Step Solution: Link paraffins → high cetane (diesel) and better smoke point (kerosene).Recognize gasoline needs high octane → aromatics/isoparaffins preferred.Select “Paraffins.” Verification / Alternative check: Fuel property charts show normal paraffins: high cetane, low octane; aromatics: low cetane, high octane; consistent with this selection. Why Other Options Are Wrong: Aromatics improve gasoline octane but harm diesel/kerosene properties. Mercaptans and acids are undesirable impurities in all fuels. Olefins cause gum and instability issues. Common Pitfalls: Failing to distinguish normal paraffins from isoparaffins; isoparaffins can aid octane more than normals but still lag aromatics for RON. Final Answer: Paraffins

Question 13

Petroleum drilling basics: A rotary oil well typically has a main boring (hole) diameter of about 20–30 cm. Approximately how deep are such commercial oil wells commonly drilled (order of magnitude in kilometres)?

Accepted Answer

Introduction: Petroleum wells are drilled with relatively modest bore diameters compared to their great depths. The question asks for a realistic order-of-magnitude depth in kilometres for commercial oil wells having a main boring diameter of roughly 20–30 cm. Given Data / Assumptions: Main boring (hole) diameter: 20–30 cm. We seek the common depth range of commercial wells in km. Order-of-magnitude answer is sufficient. Concept / Approach: Commercial onshore wells frequently range from about 1 km to several kilometres in depth depending on geology, reservoir pressure, and target formation. Ultra-deep wells exist, but are not representative of typical field development wells. We therefore look for a range that reflects common practice rather than extremes. Step-by-Step Solution: Step 1: Interpret “typical” as common onshore field depths rather than record or ultra-deep cases.Step 2: Typical development wells commonly fall near 1.5–4.5 km depth.Step 3: Compare with options to find the realistic range that fits most reservoirs with 20–30 cm bore. Verification / Alternative check: Many sedimentary basins host productive formations between ~1.5 km and ~3.5 km. Shallow (0.1–0.5 km) is too small; 7.5–12.5 km or 15–20 km represent extreme or impractical depths for most fields. Why Other Options Are Wrong: 0.1 to 0.5: Too shallow for most commercial oil reservoirs. 7.5 to 12.5: Ultra-deep and atypical for routine development. 15 to 20: Unrealistic for standard oilfield practice. 0.5 to 1.0: Still too shallow for most commercial reservoirs. Common Pitfalls: Confusing record-setting “deepest wells” with normal development depths; assuming larger diameter always implies shallower depth. Final Answer: 1.5 to 4.5

Question 14

Catalytic vs thermal cracking: Which statement is incorrect regarding cracking behaviour and heat effects in petroleum refining?

Accepted Answer

Introduction: This question compares kinetic and thermal aspects of thermal and catalytic cracking. The goal is to identify the statement that does not align with established refining science. Given Data / Assumptions: Cracking can be thermal or catalytic. Iso-paraffins vs n-paraffins show different cracking tendencies. Catalyst regeneration burns coke and is exothermic. Olefins are highly reactive on acidic catalysts due to hydrogen transfer and oligomerization pathways. Concept / Approach: Acidic cracking catalysts (e.g., zeolites) lower activation energies and accelerate reactions at lower temperatures than thermal processes. Olefins are particularly reactive under catalytic conditions because of carbocation mechanisms and hydrogen transfer reactions. Step-by-Step Solution: Step 1: Check option A: Iso-paraffins (with tertiary/secondary carbons) crack more readily than n-paraffins. This is correct.Step 2: Check option B: Cracking endothermic; regeneration exothermic. Correct.Step 3: Check option C: It claims olefins decompose “slightly slower” in catalytic vs thermal cracking. This contradicts known behaviour; catalytic pathways typically accelerate olefin consumption via hydrogen transfer and oligomerization.Step 4: Option E is a true supporting fact, further contradicting C. Verification / Alternative check: Refining texts consistently note rapid olefin conversion over acidic catalysts, improving gasoline stability by reducing olefin content. Why Other Options Are Wrong: Option A: Correct relationship; not the incorrect statement. Option B: Correct heat accounting for cracking vs regeneration. Option D: Invalid because C is already incorrect. Option E: True statement about hydrogen transfer. Common Pitfalls: Assuming “faster at higher temperature” (thermal) automatically beats catalysis; overlooking the role of hydrogen transfer in catalytic systems. Final Answer: Decomposition of olefins in catalytic cracking is slightly slower than in thermal cracking.

Question 15

Petroleum product properties: Identify the single incorrect statement about specific gravity and energy content of hydrocarbon families.

Accepted Answer

Introduction: The question tests understanding of how specific gravity correlates with hydrogen-to-carbon ratio and how energy content compares across hydrocarbon families (paraffins vs aromatics) on mass and volume bases. Given Data / Assumptions: Compare paraffins (alkanes) and aromatics. Relate specific gravity to C/H ratio and energy content. Assume typical petroleum-range hydrocarbons. Concept / Approach: As specific gravity increases, the average hydrogen content per carbon generally decreases (more condensed structures), increasing the C/H ratio. Energy content comparisons depend on whether we consider per unit mass or per unit volume. Step-by-Step Solution: Step 1: Option A: Higher specific gravity → higher C/H ratio (less hydrogen per carbon). This is broadly correct.Step 2: Option B: Claims aromatics have lower specific gravity than paraffins. In reality, aromatics usually have higher specific gravity than corresponding paraffins, so B is incorrect.Step 3: Option C: On a mass basis, paraffins tend to have higher heating value per kilogram than aromatics; low specific gravity correlates with higher mass-based heating value—so C is correct.Step 4: Option D: On a volume basis, higher specific gravity often translates to higher energy per litre; aromatics thus provide higher volumetric energy—so D is correct.Step 5: Option E restates the mass-basis comparison in favour of paraffins—correct. Verification / Alternative check: Fuel property tables show paraffinic streams have higher MJ/kg, whereas denser aromatic streams exhibit higher MJ/L. Why Other Options Are Wrong: Only Option B is wrong; A, C, D, and E align with standard trends. Common Pitfalls: Mixing up mass-basis and volume-basis energy content; assuming one family dominates on both metrics. Final Answer: Aromatics have lower specific gravity than corresponding paraffins.

Question 16

Natural-gas liquids: Gasoline condensed from natural gas by compression and cooling is known as which type of gasoline?

Accepted Answer

Introduction: Gas production streams can contain heavier hydrocarbons that condense as liquids under compression and cooling. The condensed gasoline-range material has a specific name in refining terminology. Given Data / Assumptions: Source: Natural gas streams. Process: Compression and cooling. Product: Gasoline-range liquid hydrocarbon mix. Concept / Approach: When separated from natural gas at the wellhead or gathering systems by pressure and temperature reduction, the gasoline-range liquid is called casing-head gasoline (a natural gasoline or condensate fraction). Step-by-Step Solution: Step 1: Identify the product obtained by condensing heavier hydrocarbons from gas.Step 2: Recall standard term: casing-head gasoline.Step 3: Match to options. Verification / Alternative check: Terminology in upstream/midstream operations distinguishes straight-run (from crude distillation), polymer gasoline (polymerization), and reformate (catalytic reforming) from this natural-gas-derived fraction. Why Other Options Are Wrong: Polymer gasoline: Produced via polymerization of olefins, not gas condensation. Unleaded gasoline: Refers to additive policy, not origin. Straight-run gasoline: From crude distillation, not gas plants. Reformate gasoline: From catalytic reforming of naphtha. Common Pitfalls: Confusing “condensate/natural gasoline” with straight-run or reformate due to overlapping boiling ranges. Final Answer: Casing-head gasoline

Question 17

Petroleum chemistry: What best describes olefins (alkenes) in the context of crude petroleum and refining?

Accepted Answer

Introduction: Olefins (alkenes) are a key class of hydrocarbons in refining reactions and gasoline quality, but their definition and typical occurrence in crude petroleum can be misunderstood. Given Data / Assumptions: We compare structural class (saturation, cyclicity). We consider whether olefins occur substantially in raw crude. Concept / Approach: Olefins are unsaturated hydrocarbons with at least one C=C double bond. They are generally acyclic (though cyclic alkenes exist), and in petroleum operations they are typically generated during thermal or catalytic cracking rather than being abundant in untreated crude. Step-by-Step Solution: Step 1: Option A calls them saturated; incorrect because olefins are unsaturated.Step 2: Option B calls them unsaturated cyclic; the prototypical olefins relevant to gasoline are acyclic, so this is not the best descriptor.Step 3: Option C claims substantial presence in crude; crude oils usually contain minimal olefins due to geologic stability factors.Step 4: Therefore, among A–C none is correct; the right choice is “None of these.” Verification / Alternative check: Refining processes (thermal/catalytic cracking, FCC) generate olefins which influence gasoline octane and stability; raw crude assays rarely report high native olefin content. Why Other Options Are Wrong: A: Saturated is wrong; olefins are unsaturated. B: Overstates cyclic forms; contextually misleading. C: Overstates crude olefin content. E: While generally true as a statement, it is not among the original A–D choices for a single-correct MCQ; thus the keyed answer remains D. Common Pitfalls: Assuming “unsaturated” automatically implies “present in crude.” Final Answer: None of these.

Question 18

Dewaxing of petroleum products: Which of the following are common solvents used specifically for solvent dewaxing?

Accepted Answer

Introduction: Dewaxing removes high-melting waxes from lubricating oil stocks and other petroleum fractions to improve low-temperature flow properties such as pour point. Given Data / Assumptions: We focus on solvents used in the dewaxing step. Common industrial choices include ketone-based and hydrocarbon/propane systems. Concept / Approach: Solvent dewaxing relies on selective dissolution at low temperatures to precipitate wax. MEK (often with toluene or MIBK) and liquid propane are widely used. Furfural is a selective extraction solvent for aromatics, not a dewaxing solvent. Step-by-Step Solution: Step 1: Identify MEK as a classic ketone solvent for dewaxing.Step 2: Recognize propane dewaxing as an alternative process.Step 3: Exclude furfural (used in lube extraction units) and “toluene only” as incomplete. Verification / Alternative check: Process flow descriptions pair MEK with a co-solvent (often toluene) and also describe propane dewaxing units. Why Other Options Are Wrong: Furfural: Extraction solvent, not for dewaxing. Toluene only: Common co-solvent with MEK, rarely used alone as the primary dewaxing solvent. Common Pitfalls: Confusing extraction (furfural) with dewaxing; overlooking propane-based dewaxing. Final Answer: Both (b) and (c)

Question 19

Gasoline lead response: Among the listed gasoline streams, which typically shows the highest susceptibility to tetraethyl lead (TEL) octane improvement?

Accepted Answer

Introduction: “Lead susceptibility” refers to the increase in octane number achievable by adding an organo-lead antiknock such as TEL. Different gasoline streams respond differently depending on composition (paraffins, olefins, aromatics). Given Data / Assumptions: Streams considered: straight-run, reformate, FCC (catalytically cracked), polymer gasoline, natural gasoline. Legacy context where TEL usage was allowed (historical/technical). Concept / Approach: Lead response tends to be higher for olefinic and isoparaffinic streams and lower for highly aromatic reformates that already have high intrinsic octane. Step-by-Step Solution: Step 1: FCC gasoline is olefinic and responds strongly to TEL.Step 2: Reformate has high aromatics and high base octane, leaving less headroom for lead response.Step 3: Straight-run and natural gasoline show moderate to low susceptibility; polymer gasoline varies but is typically less than FCC in response. Verification / Alternative check: Textbook lead response curves show FCC gasoline with the steepest octane gain per millilitre of TEL. Why Other Options Are Wrong: Straight-run: Lower olefin content, moderate response. Reformate: Already high octane from aromatics; limited incremental response. Polymer gasoline: Less response than FCC on average. Natural gasoline: Often low octane and variable response. Common Pitfalls: Confusing “highest octane” with “highest lead susceptibility” — they are not the same. Final Answer: Catalytically cracked gasoline (FCC gasoline)

Question 20

Crude petroleum characteristics: A representative average molecular weight for crude petroleum is closest to which value?

Accepted Answer

Introduction: Crude petroleum is a complex mixture of thousands of hydrocarbons. Still, an average molecular weight can be quoted for rough engineering calculations and property correlations. Given Data / Assumptions: We seek a rough, representative average value, not the extremes for individual fractions. Concept / Approach: Whole crudes typically exhibit average molecular weights in the low hundreds; values around ~200–300 are commonly cited for representative crudes, acknowledging that light vs heavy crudes shift this number. Step-by-Step Solution: Step 1: Eliminate very small numbers like 50 (too low for whole crude).Step 2: Eliminate very large numbers like 1500 or 5000 (more typical of asphaltenes or extremely heavy fractions).Step 3: Select the mid-range choice around a few hundred, i.e., 250. Verification / Alternative check: Empirical correlations used in petroleum characterization (e.g., Watson K, density-boiling point) are consistent with average molecular weights near a few hundred for whole crude. Why Other Options Are Wrong: 50: Too low for whole crude mixtures. 1500 and 5000: Representative of heavy residues/asphaltenes, not the average of the entire crude. 100: Still low for whole crude. Common Pitfalls: Confusing the average for the whole crude with the extreme ends of the boiling range. Final Answer: 250

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