Question 1

Waxes in petroleum products – behavior and removal Which statement correctly describes the behavior of waxes naturally present in many petroleum products?

Accepted Answer

Introduction / Context: Paraffinic waxes (n-alkanes of higher carbon number) naturally occur in many crude-derived products. Their low-temperature behavior critically affects pour point, filter plugging, and fuel operability in cold climates. Given Data / Assumptions: Products considered: lube distillates, diesel/kerosene cuts, and wax-bearing fuels. We seek the statement that best reflects real behavior and standard refinery practice. Normal pressure simple distillation is assumed unless otherwise stated. Concept / Approach: Waxes are soluble at sufficiently high temperature but crystallise as temperature drops, forming networks that raise viscosity dramatically and can gel the fluid. Refineries remove wax primarily by solvent dewaxing (e.g., MEK/toluene) or catalytic dewaxing—not by simple distillation—because wax components overlap the boiling range of base oils and are difficult to separate by distillation alone. Step-by-Step Solution: Recognise that decreasing temperature yields wax crystal formation.Connect this to increased viscosity, poor pumpability, and high pour point.Identify that the correct descriptive statement is “They crystallise out at low temperature.” Verification / Alternative check: Cold-flow property tests (pour point, CFPP) and dewaxing process literature confirm wax crystallisation behavior. Why Other Options Are Wrong: Separated by distillation: Not practical due to overlapping boiling ranges; dewaxing is used. Not soluble: They are soluble when hot; insolubility only appears as crystals at low temperature. Decrease viscosity: Opposite; wax raises viscosity and can gel the product. Common Pitfalls: Assuming wax is always solid regardless of temperature; solubility is temperature dependent. Final Answer: They crystallise out at low temperature.

Question 2

Lubricating oil formulation basics: Why are paraffinic hydrocarbons considered desirable in automotive and industrial lubricating oils? They provide a comparatively high value of which key property?

Accepted Answer

Introduction: Lubricating oils must maintain an adequate lubricating film across a wide temperature range. One of the most critical bulk properties is viscosity index (VI), which indicates how sensitively an oil’s viscosity changes with temperature. The question asks why paraffinic hydrocarbons are especially valued in base oils. Given Data / Assumptions: Lube oils operate from cold start conditions to elevated operating temperatures. Base oil composition (paraffinic vs naphthenic/aromatic) strongly influences VI, volatility, oxidation stability, and low-temperature flow. We compare broad families rather than single molecules. Concept / Approach: Paraffinic base stocks typically display a higher viscosity index than naphthenic or aromatic stocks. A higher VI means viscosity changes less per degree of temperature shift, helping the oil keep an adequate film at high temperature without being excessively thick when cold. While additives (e.g., viscosity index improvers) further enhance behaviour, the native VI of the base oil sets a strong foundation for performance. Step-by-Step Solution: Relate composition to property: paraffinic → naturally higher VI.Connect higher VI to service benefits: steadier viscosity across temperature swing.Select the property most directly associated with paraffinic desirability: viscosity index. Verification / Alternative check: Handbooks show Group I/II/III paraffinic base oils with VI commonly above comparable naphthenic stocks; high-VI blends reduce the need for thickening at high temperature and improve fuel economy. Why Other Options Are Wrong: Viscosity: Absolute viscosity depends on grade; paraffinic chemistry does not inherently imply “higher” viscosity. Smoke point: Relevant to kerosene/jet fuels, not lube oil selection. Pour point: Paraffins can crystallise; pour point is improved via dewaxing and additives, not inherently “high.” Ash content: Determined by metallic additives/contaminants, not by paraffin content. Common Pitfalls: Confusing viscosity (a value at one temperature) with viscosity index (temperature sensitivity of viscosity). Final Answer: Viscosity index

Question 3

Illuminating kerosene quality: As the molecular weight (ring size/condensation) of aromatics in kerosene increases, how does its smoking tendency in wick or lamp burners change?

Accepted Answer

Introduction: Smoking tendency is a key measure for illuminating kerosene and aviation kerosene (smoke point). Heavier, more condensed aromatics tend to produce soot and smoke during diffusion flame combustion. The question probes how increasing aromatic molecular weight affects smoking behaviour. Given Data / Assumptions: Fuel: kerosene-range hydrocarbons. Change: increasing molecular weight/condensation of aromatics (more rings, higher boiling point). Context: wick/lamps and combustors where smoke point matters. Concept / Approach: Aromatics favour soot formation due to ring structures and lower hydrogen-to-carbon ratio. As molecular weight and ring condensation increase (e.g., polynuclear aromatics), soot precursors increase, causing more smoke and a lower measured smoke point. Therefore, greater aromatic molecular weight worsens smoke characteristics. Step-by-Step Solution: Link aromatic structure to soot propensity.Recognise that heavier aromatics → more sooting → more smoke.Choose the trend: smoking tendency increases. Verification / Alternative check: Standard kerosene specifications emphasise smoke point; higher heavy-aromatic content correlates with lower smoke point (i.e., worse smoking tendency). Why Other Options Are Wrong: Decreases/Remains same/Unpredictable/Vanishing: Contradict established combustion trends for aromatic-rich fuels. Common Pitfalls: Assuming higher molecular weight always improves combustion; for aromatics, it typically increases sooting. Final Answer: Increases

Question 4

Aviation/jet fuel handling: The Water Separometer Index, Modified (WSIM) reported for a petrofuel primarily indicates which behaviour?

Accepted Answer

Introduction: Water management is critical for aviation turbine fuel and other light distillates. The Water Separometer Index, Modified (WSIM) is a standard test result used to indicate how well a fuel will shed dispersed water when passed through coalescer/separator elements. Given Data / Assumptions: Fuel contains trace surfactants and additives that can affect water coalescence. WSIM is not a direct ppm water measurement but a performance index. Higher WSIM generally indicates better water separation. Concept / Approach: WSIM represents the fuel’s ability to release water in a filter-separator. Surfactants and certain additives can stabilise water-in-fuel emulsions, decreasing coalescence and lowering WSIM. Thus, WSIM is used operationally to judge whether a fuel will separate water efficiently through airport filtration systems. Step-by-Step Solution: Clarify what WSIM is (index, not water ppm).Identify the behaviour measured: separation/coalescence of dispersed water.Select the option that states “water separation characteristics.” Verification / Alternative check: Fuel quality manuals use WSIM as a gate for acceptability before aircraft fuelling; poor WSIM prompts additional treatment or filtration. Why Other Options Are Wrong: Emulsification tendency only: Related but WSIM covers separation performance through coalescers. Water content: Determined by Karl Fischer or other methods, not WSIM. Absorbing capacity/Cloud point: Different properties/tests entirely. Common Pitfalls: Assuming WSIM equals water content; it is a separability index. Final Answer: Water separation characteristics (coalescence through filters)

Question 5

Kerosene specification insight: A good-quality illuminating kerosene should exhibit which characteristic with respect to its smoke point?

Accepted Answer

Introduction: Smoke point is a standard lamp-based test that indicates the sooting tendency of kerosene. Higher smoke point correlates with cleaner, brighter burning and fewer deposits in lamps and combustors. This question asks which attribute defines “good” kerosene for illumination. Given Data / Assumptions: Kerosene is used in lamps and sometimes aviation; low soot is desirable. Aromatics lower smoke point; paraffinic content tends to raise it. Concept / Approach: Good kerosene should resist smoking; hence it should have a high smoke point. This usually coincides with lower heavy-aromatic content. Specifications often set minimum smoke point values to ensure satisfactory performance. Step-by-Step Solution: Link composition to smoke: more aromatics → lower smoke point.Define quality target: “high” smoke point equals better quality.Choose the correct characteristic accordingly. Verification / Alternative check: Product specs list minimum smoke point values; batches below spec are reprocessed or blended down. Why Other Options Are Wrong: Low smoke point: Indicates poor burning. High aromatics / low paraffins: Typically worsen smoke point. High olefins: Not a kerosene quality target; may harm stability. Common Pitfalls: Confusing density or energy content with smoke quality—smoke is primarily a sooting/combustion behaviour metric. Final Answer: High smoke point

Question 6

Diesel ignition quality trend: Among the hydrocarbon families listed, which generally shows the lowest cetane number (poorest ignition quality) in compression-ignition engines?

Accepted Answer

Introduction: Cetane number measures readiness to autoignite under diesel engine conditions. Molecular structure has a strong effect: straight chains ignite readily, while ringed and highly branched structures resist autoignition. Given Data / Assumptions: Families considered: n-paraffins, isoparaffins, naphthenes, aromatics, and olefins. We compare typical diesel-range components. Concept / Approach: General ordering for cetane: n-paraffins > isoparaffins ≈ naphthenes > olefins > aromatics (lowest). Aromatics have stable ring structures and lower hydrogen-to-carbon ratio, leading to longer ignition delays and lower cetane numbers. Step-by-Step Solution: Recall family order by ignition quality.Identify the lowest family: aromatics.Select “Aromatics.” Verification / Alternative check: Fuel blending practice limits aromatic content in diesel to maintain acceptable cetane number and emissions performance. Why Other Options Are Wrong: n-Paraffins: Highest cetane among common families. Isoparaffins/Naphthenes: Intermediate values. Olefins: Typically above aromatics but below paraffins/naphthenes. Common Pitfalls: Confusing gasoline octane (aromatics high) with diesel cetane (aromatics low). Final Answer: Aromatics

Question 7

Bitumen manufacture feed type: Highest-quality paving/industrial bitumen is generally produced from which crude oil family?

Accepted Answer

Introduction: Bitumen (asphalt) quality depends on the composition of the vacuum residue obtained from crude oil. Crude family (paraffinic vs naphthenic/aromatic) strongly affects asphaltene/resin balance and, hence, final bitumen properties such as penetration, softening point, and durability. Given Data / Assumptions: Feed to bitumen production is typically vacuum residue. Naphthenic (asphaltic-base) crudes yield residues richer in asphaltenes/resins appropriate for bitumen. Concept / Approach: Naphthenic/asphaltic-base crudes provide a residue with the colloidal structure desired in bitumen, facilitating target penetration grades and temperature susceptibility. Paraffinic-base residues may require more processing or may be less suitable for high-quality paving grades without blending/modification. Step-by-Step Solution: Identify crude family that yields asphaltic residues: naphthenic.Relate residue composition to bitumen performance metrics.Select “Naphthenic.” Verification / Alternative check: Refinery practice often prefers asphaltic-base (naphthenic) crudes for making premium paving bitumen. Why Other Options Are Wrong: Paraffinic/Mixed/Intermediate: May produce less suitable residues or require blending. Super-light condensate: Too light; negligible residue for bitumen. Common Pitfalls: Assuming any heavy residue makes good bitumen—colloidal balance matters. Final Answer: Naphthenic

Question 8

Typical FCC reactor conditions: Industrial catalytic cracking (e.g., FCC) commonly operates near which pressure–temperature combination?

Accepted Answer

Introduction: Catalytic cracking (especially FCC) converts heavy gas oils to gasoline and lighter products using a solid acid catalyst at elevated temperature and modest pressure. Choosing realistic operating ranges helps distinguish FCC from hydrocracking and thermal processes. Given Data / Assumptions: Atmospheric to a few atmospheres pressure in FCC riser/regen loop. Reaction temperatures roughly around 480–540°C in the riser. Concept / Approach: FCC employs short contact times at high temperature and low–moderate pressure to favour gasoline-range products while minimising overcracking and coking. Pressures above ~3–4 atm are unusual in classic FCC risers, and temperatures near 200°C or 750°C are out of range for the cracking step. Step-by-Step Solution: Eliminate unrealistic pairs (too high P, too low/high T).Recognise typical FCC regime ~2 atm and ~500°C.Select “2 atm & 500°C.” Verification / Alternative check: Process descriptions consistently cite ~1–3 atm riser pressure and ~500°C reactor outlet temperatures. Why Other Options Are Wrong: 10 atm at 500°C: More characteristic of hydroprocessing with hydrogen, not FCC. 30 atm & 200°C / 50 atm & 750°C: Out of FCC envelope. 1 atm & 350°C: Temperature too low for effective catalytic cracking. Common Pitfalls: Mixing FCC with hydrocracking conditions where high H2 pressure is used. Final Answer: 2 atm & 500°C

Question 9

Deasphalting step choice: Which solvent is most suitable for solvent deasphalting of vacuum residue to produce deasphalted oil (DAO)?

Accepted Answer

Introduction: Solvent deasphalting (SDA) separates asphaltenes from vacuum residue to yield a cleaner deasphalted oil (DAO) for further upgrading (e.g., hydrocracking, FCC). The choice of solvent controls selectivity and yield. Given Data / Assumptions: Feed: vacuum residue rich in asphaltenes/resins. Goal: maximize DAO quality while rejecting asphaltenes/metals. Concept / Approach: Light paraffinic solvents (propane, butane, pentane) dissolve maltenes while precipitating asphaltenes. Propane is the classic SDA solvent, offering good selectivity for DAO quality. MEK is used in dewaxing, not SDA. Doctor’s solution is for sweetening (H2S/mercaptans). Methanol amine is for gas treating (acid gas removal). Step-by-Step Solution: Identify SDA principle: paraffinic solvent precipitates asphaltenes.Recall standard choice: propane.Exclude unrelated solvents used in other refinery treatments. Verification / Alternative check: Refinery flowsheets list propane deasphalting units as common SDA installations. Why Other Options Are Wrong: MEK: Dewaxing solvent, not SDA. Doctor’s solution: Sweetening, not SDA. Methanol amine: Amine treating for gases, not SDA. Toluene-only: Aromatic solvent dissolves asphaltenes, defeating precipitation. Common Pitfalls: Confusing dewaxing or sweetening chemistries with SDA. Final Answer: Propane

Question 10

Vacuum column operation: Typical absolute pressure (vacuum) maintained in a vacuum distillation unit processing reduced crude is closest to which value (in mmHg)?

Accepted Answer

Introduction: Vacuum distillation lowers boiling temperatures to prevent cracking of heavy fractions. The absolute pressure in the vacuum column is a key design/operation parameter, typically expressed in mmHg (torr). The question asks for a representative operating level for reduced crude service. Given Data / Assumptions: Service: atmospheric residue to vacuum column. Target: sufficiently low pressure to cut VGO and vacuum residue without thermal degradation. Concept / Approach: Typical absolute pressures in the flash zone and upper sections are on the order of 10–40 mmHg, achieved with steam ejectors and vacuum systems. 12 mmHg sits within this normal operating window. Values near 700 mmHg approach atmospheric pressure (ineffective), while 120 mmHg is too high for deep vacuum duty; 1.2 mmHg is achievable in lab/cryogenic systems, not common for large crude vacuum towers. Step-by-Step Solution: Recall typical vacuum tower absolute pressures ≈ 10–40 mmHg.Compare options; select the one inside this range: 12 mmHg.Reject near-atmospheric (700) and excessively deep (1.2) values. Verification / Alternative check: Design texts show flash-zone pressures commonly around 20 mmHg with top pressures even lower; 12 mmHg is a representative figure. Why Other Options Are Wrong: 1.2: Overly deep, impractical for crude towers. 120: Not deep enough for reduced crude separation. 700: Essentially atmospheric; defeats purpose. 380: Partial vacuum but far above typical crude vacuum conditions. Common Pitfalls: Confusing gauge vacuum with absolute pressure; this question uses absolute mmHg. Final Answer: 12

Question 11

Meaning of cetane number: The cetane number of a diesel fuel is fundamentally a measure of its tendency toward which ignition behaviour?

Accepted Answer

Introduction: Cetane number (CN) quantifies diesel fuel ignition quality under compression ignition. Higher CN corresponds to shorter ignition delay, enabling smoother combustion, easier cold starting, and lower noise in diesel engines. Given Data / Assumptions: Reference scale: n-heptane (CN = 100) ignites very readily; isocetane/α-methylnaphthalene historically represent low-CN behaviour. Engine-based or derived methods (e.g., CFR engine, DCN) exist. Concept / Approach: Ignition delay is the time between fuel injection and the onset of combustion. Fuels with higher CN autoignite more promptly; lower CN fuels delay longer, causing rough operation. CN does not directly measure viscosity, smoke point, oxidation stability, or the distillation curve, though these properties influence other aspects of performance. Step-by-Step Solution: Relate CN definition to ignition delay: higher CN → shorter delay.Identify the property explicitly: ignition delay tendency.Choose “Ignition delay.” Verification / Alternative check: Standards (e.g., ASTM D613, EN 15195) define CN via engine/ignition delay response relative to a reference blend scale. Why Other Options Are Wrong: Smoke point/Viscosity/Oxidation stability/Distillation: Important fuel specs but not what CN measures. Common Pitfalls: Confusing gasoline octane (knock resistance) with diesel cetane (ignitability); they are opposite in implication. Final Answer: Ignition delay

Question 12

In petroleum product finishing and purification, clay treatment (adsorptive contacting with activated clay/earth) is primarily used to remove which objectionable constituents, particularly from cracked gasoline and similar streams?

Accepted Answer

Introduction: Clay treatment is a classic adsorption-based polishing step used in petroleum refining to improve the appearance and stability of products, most notably cracked gasoline and certain kerosene fractions. Understanding what clay treatment actually removes helps avoid confusing it with entirely different unit operations such as electrical desalting or solvent dewaxing. Given Data / Assumptions: The term “clay treatment” refers to contacting product with activated clay/bleaching earth or fuller’s earth, followed by filtration. Typical applications include cracked gasoline and kerosene-range streams where colour bodies, trace gum precursors, and dissolved gases/odorous species are present. It is not a primary salt/water removal or wax-removal process. Concept / Approach: Activated clays have a high surface area and polar sites that adsorb coloured compounds (poly-aromatics, resinous species), certain sulfur-oxygen species, and other trace contaminants. In cracked gasoline, clay contacting can lighten colour and reduce objectionable odor or dissolved gas content that might otherwise impair stability or customer perception. Step-by-Step Solution: 1) Identify the adsorptive nature of clay treatment and its common targets: colour bodies and trace reactive species.2) Recognize its typical service: polishing of cracked gasoline/kerosene to improve colour and stability.3) Exclude operations that require entirely different physics/chemistry (e.g., desalting or dewaxing). Verification / Alternative check: Refinery practice distinguishes clay treating (adsorption) from electric desalting (water/salt removal), caustic washing (acidic species neutralization), and solvent dewaxing (crystallization/filtration). Vendor literature and standard manuals list “colour improvement and odor reduction” as the main benefits for gasoline-range products. Why Other Options Are Wrong: Salt removal from crude: Done by electrical desalters with dilution water.Wax removal: Achieved by solvent dewaxing (e.g., MEK–toluene) or chilling/filtration, not clays.None of these / coalescence: Do not describe adsorption polishing. Common Pitfalls: Confusing clay treatment with bleaching of edible oils or with acid/caustic treating; while analogous in concept, petroleum clay contacting has distinct targets and is not a desalting or dewaxing shortcut. Final Answer: Colour and dissolved gases from cracked gasoline

Question 13

Pick the incorrect statement about common petroleum tests and crude characterisation indices. Identify the one that is factually wrong.

Accepted Answer

Introduction: This question checks familiarity with standard petroleum test methods and indices: flash point apparatus selection (Abel, Pensky–Martens, Cleveland) and the meaning of the viscosity index (VI), as well as the UOP K/characterisation factor trend for crude types. Knowing which statements are correct versus incorrect is crucial for QA/QC and specification work. Given Data / Assumptions: Abel is commonly applied to low flash point materials (generally below about 50 °C). Pensky–Martens (closed cup) is used for mid-range flash points (above roughly 50 °C). Paraffinic crude typically has a characterisation factor greater than 12. High viscosity index (VI) means viscosity changes little with temperature. Concept / Approach: Evaluate each statement against standard definitions: the viscosity index is inversely related to viscosity’s temperature sensitivity. A high VI indicates relatively stable viscosity across temperature changes. Therefore, a statement claiming “large change of viscosity with temperature” corresponds to a low VI, not a high VI. The flash point apparatus pairings and crude paraffinic K-factor trend are standard facts. Step-by-Step Solution: a) Pensky–Martens for > 50 °C: aligns with practice.b) Paraffinic crudes having characterisation factor > 12: correct rule of thumb.c) Abel for < 50 °C: correct pairing.d) High susceptibility of viscosity to temperature ≡ low VI, so the statement is wrong.e) Cleveland (open cup) is indeed used for higher flash point materials such as lubricating oils. Verification / Alternative check: Testing standards and refinery handbooks outline these instrument ranges and the VI definition consistently; laboratory SOPs confirm the above mappings. Why Other Options Are Wrong (as choices for “incorrect”): a, b, c, e: These reflect accepted practice and definitions. Common Pitfalls: Reversing the meaning of VI (thinking high VI means large change), or confusing Abel with Pensky–Martens temperature ranges. Final Answer: An oil that shows a large change of viscosity with temperature has a high viscosity index.

Question 14

Viscosity unit conversion: approximately how many Redwood No. 1 (Redwood I) seconds correspond to a kinematic viscosity of 1 centistoke under standard comparison conditions?

Accepted Answer

Introduction: Legacy viscometers (Redwood, Saybolt, Engler) report efflux times rather than absolute SI units. Engineers often need quick, approximate conversions to the SI-based kinematic viscosity unit, the centistoke (cSt). This question tests recognition of the commonly used Redwood I to cSt correlation for low viscosities. Given Data / Assumptions: We are relating Redwood No. 1 (a low-range efflux viscometer) seconds to kinematic viscosity in centistokes. The conversion is empirical and approximate, valid over typical calibration ranges. We specifically want the Redwood I seconds for 1 cSt. Concept / Approach: Empirical charts and formulas provide approximate relationships between efflux time and kinematic viscosity. For Redwood I, a commonly used approximation yields approximately 4.08 Redwood I seconds per 1 cSt at low viscosities. While exact values depend on calibration temperature and instrument, 4.08 is a widely cited round figure for quick estimates near water-like viscosities. Step-by-Step Solution: 1) Identify the need: convert 1 cSt into an equivalent Redwood I efflux time.2) Use standard empirical correlation/lookup: 1 cSt ≈ 4.08 Redwood I seconds for low-viscosity fluids.3) Select 4.08 as the closest representative value among options. Verification / Alternative check: Conversion tables in older refinery and lubrication manuals list near this value for water-like viscosities; more precise work should reference the exact instrument's calibration curve. Why Other Options Are Wrong: 1 or 0.408: Too low versus standard tables.40.8: An order of magnitude too high for 1 cSt.2.2: Not supported by typical Redwood I correlations. Common Pitfalls: Confusing Redwood I with Saybolt Universal or mixing up temperature bases; each instrument and temperature requires its own correlation or chart. Final Answer: 4.08

Question 15

In catalytic reforming of straight-run or hydrotreated naphtha, what is a representative gasoline (reformate) liquid yield expressed as percent by weight, excluding by-product hydrogen and light gases?

Accepted Answer

Introduction: Catalytic reforming upgrades low-octane naphtha into high-octane reformate and produces hydrogen. Knowing typical reformate yield helps in refinery LP planning, hydrogen balance, and octane pool forecasting. Given Data / Assumptions: Feed: naphtha in the gasoline boiling range. Process: semi-regenerative or continuous catalyst regeneration reforming. We are asked for a representative liquid reformate yield by weight, not counting H2 and C1–C4 gases. Concept / Approach: Reforming involves dehydrogenation, isomerisation, cyclization, and dehydrocyclization. These steps generate hydrogen and some light ends (C1–C4), so the liquid reformate yield is less than 100% of feed. A typical planning value lies around the mid-80s wt%, subject to severity and feed composition. Hence, 85 wt% is a sensible representative figure. Step-by-Step Solution: 1) Recognize that reforming consumes part of the feed as light gases and H2.2) Recall planning heuristics: reformate yields ~80–90 wt% depending on severity and feed paraffinicity.3) Choose 85 as a representative middle value. Verification / Alternative check: Licensor and textbook examples often show yields near 83–88 wt% for standard severities; severe reforming for high octane typically lowers yield slightly. Why Other Options Are Wrong: 65 or 50: Too low for typical operation; would imply excessive cracking.98: Unrealistically high given H2 and light gas formation.72: Low relative to mainstream planning figures. Common Pitfalls: Assuming reforming is purely rearrangement with no yield loss; dehydrogenation and side cracking inevitably produce off-gas. Final Answer: 85

Question 16

Aniline point of high-speed diesel (HSD): choose the approximate value (in °C) most commonly cited for typical diesel fuels.

Accepted Answer

Introduction: The aniline point is a quick indicator of a fuel’s aromatic content and solvency. For diesel fuels, it correlates loosely (inversely) with aromaticity: higher aniline point implies more paraffinic character. Typical values help blenders and inspectors assess whether a diesel is unusually aromatic or paraffinic. Given Data / Assumptions: Fuel: high-speed diesel (HSD) in normal market ranges. Aniline point definition: minimum temperature at which equal volumes of aniline and the fuel are completely miscible. We seek a representative value rather than an extreme. Concept / Approach: Common diesel aniline points are around the range of 60–90 °C depending on crude source and processing. A textbook, rule-of-thumb figure often quoted is about 70 °C for typical HSD. Lower values would suggest unusually aromatic diesel; very high values indicate exceptionally paraffinic material. Step-by-Step Solution: 1) Recall the typical range for diesel aniline points.2) Identify 70 °C as a central, representative value.3) Select 70 °C among the choices. Verification / Alternative check: Specification references and educational tables frequently use 70 °C as an indicative value in example problems and quick-look properties. Why Other Options Are Wrong: 35: Too low for typical diesel; suggests highly aromatic character.105 or 150: Unusually high for standard HSD.20: Not realistic for diesel. Common Pitfalls: Confusing gasoline (generally not assessed by aniline point) with diesel/kerosene where the property is commonly referenced. Final Answer: 70

Question 17

Fuel handling: which of the following fuels typically does not require preheating for storage and for proper atomisation through burners under normal operating conditions?

Accepted Answer

Introduction: Different liquid fuels demand different handling strategies. Heavy fuels require heating to reduce viscosity for pumping and atomisation; lighter fuels can be pumped and atomised without preheat. Knowing which fuels need preheat prevents burner problems, poor combustion, and operational upsets. Given Data / Assumptions: Choice set spans heavy, viscous streams (tar, bitumen, PCM) and lighter middle distillates (LDO). Normal storage and burner atomisation conditions are assumed (no extreme cold). Goal: identify the fuel that does not need preheating. Concept / Approach: Viscosity governs pumpability and atomisation quality. Heavy residues (tar, bitumen, pitch-like PCM) must be heated to flow and to atomise. Even certain grades of furnace oil require moderate preheat. In contrast, light diesel oil has relatively low viscosity and can be stored and atomised at ambient temperatures in most climates without dedicated preheaters. Step-by-Step Solution: 1) Rank fuels by viscosity: tar/bitumen/PCM ≫ furnace oil > LDO.2) Apply handling rule: heavier fuels need heat; light distillates typically do not.3) Select LDO as the fuel that does not require preheating. Verification / Alternative check: Plant operating manuals specify heater setpoints for heavy fuel oil systems, while diesel burners and storage tanks are commonly unheated except in severe cold conditions. Why Other Options Are Wrong: Tar/bitumen/PCM: Very high viscosity; preheat is essential.Low-viscosity furnace oil: Often still needs mild preheat to reach atomisation viscosity. Common Pitfalls: Assuming “furnace oil” is always thin enough to avoid preheat; grade and ambient temperature matter. Final Answer: Light diesel oil (LDO)

Question 18

In a crude oil–water mixture (as encountered in desalting and production systems), bulk electrical conductivity depends on which parameters?

Accepted Answer

Introduction: Electrical desalters and production separators rely on the electrical properties of crude–water emulsions. Understanding which variables influence conductivity helps operators optimize electric field strength, mixing, and chemical dosage for effective coalescence and salt removal. Given Data / Assumptions: A two-phase crude oil–brine system is considered. We examine macroscopic conductivity relevant to electrostatic coalescence. Parameters of interest: pH, water percentage, temperature. Concept / Approach: Conductivity is carried primarily by the aqueous phase (brine droplets). Higher water cut increases conductive pathways. Temperature affects ion mobility and viscosity, generally raising conductivity as temperature increases. pH can influence interfacial films and dissociation equilibria, subtly impacting effective conductivity and emulsion stability. Step-by-Step Solution: 1) Identify the carrier of conductivity: the brine phase in the emulsion.2) Water percentage: more brine → more continuous/connected conductive paths → higher measured conductivity.3) Temperature: higher T → increased ion mobility and reduced viscosity → higher conductivity.4) pH: affects surface-active species and ionic equilibria, influencing interfacial behavior and effective conductivity. Verification / Alternative check: Operational guidelines for electrical desalters link setpoints and field strengths to water cut and temperature; lab measurements show temperature coefficients for brine conductivity and pH effects on emulsion films. Why Other Options Are Wrong: Any single-factor choice ignores the multi-parameter nature of conductivity in emulsions.“Only salinity” is incomplete; while salinity is important, water cut, T, and pH also matter. Common Pitfalls: Assuming crude oil alone conducts; in practice, the aqueous phase dominates conductivity, and emulsions show strong dependence on water percentage and temperature. Final Answer: All (a), (b) and (c)

Question 19

Identify which of the following is not a sulphur-containing compound commonly found in crude oil and petroleum fractions.

Accepted Answer

Introduction: Crude oil contains a mix of heteroatomic species. Distinguishing sulfur- from nitrogen-containing classes is crucial for selecting hydrotreating conditions and understanding catalyst deactivation patterns. Given Data / Assumptions: We compare typical sulfur species (thiols/mercaptans, sulfides, thiophenes, sulphones) to a nitrogen heterocycle (pyrrole). Goal: pick the one that is not sulfur-bearing. Concept / Approach: Petroleum sulfur occurs as mercaptans (R–SH), sulfides (R–S–R), disulfides (R–S–S–R), thiophenic rings (aromatic sulfur), and oxidized forms such as sulphones. Pyrroles, by contrast, are five-membered nitrogen heterocycles (–NH– in the ring) and belong to nitrogen compound families, not sulfur. Step-by-Step Solution: 1) List sulfur families present in crude: mercaptans, sulfides/disulfides, thiophenes, sulphones.2) Recognize pyrrole as a nitrogen heterocycle.3) Select pyrroles as the non-sulfur compound among the options. Verification / Alternative check: Hydrotreating practice differentiates hydrodesulfurization (HDS) from hydrodenitrogenation (HDN); pyrrolic species are targeted under HDN pathways, confirming they are nitrogen, not sulfur. Why Other Options Are Wrong: Thiophenes, mercaptans, sulphones, sulfides/disulfides all contain sulfur and are routinely cited in crude assays. Common Pitfalls: Spelling variants (pyroles/pyrroles) can distract; chemically, they are nitrogen compounds. Final Answer: Pyroles (pyrroles)

Question 20

Aniline point is most relevant as a specification and screening property for which petroleum fraction among the following?

Accepted Answer

Introduction: The aniline point is used to infer aromaticity and solvency, particularly for middle distillates. It is far less meaningful for very light products like LPG or highly volatile gasoline where other measures dominate. Recognizing the fraction where aniline point has practical value aids in correct property selection. Given Data / Assumptions: Candidate fractions: LPG, naphtha/gasoline, diesel (middle distillate). Aniline point is defined by equal-volume miscibility temperature with aniline. We seek the fraction for which this property is a standard indicator. Concept / Approach: Diesel (and kerosene) specifications and blending practice often reference aniline point because it trends with aromatic content and relates to material compatibility (e.g., rubber swelling) and combustion characteristics. LPG has no such miscibility-based specification, and gasoline quality is largely governed by octane metrics rather than aniline point. Step-by-Step Solution: 1) Map fuels to relevant property sets: diesel/kerosene → aniline point; gasoline → octane; LPG → vapor pressure/composition.2) Select the fraction for which aniline point is commonly cited: diesel.3) Confirm that lighter products do not rely on this property in specifications. Verification / Alternative check: Refinery and standards references list aniline point widely for diesel and kerosene grades, while gasoline standards focus on RON/MON, distillation curve, RVP, and sulfur limits. Why Other Options Are Wrong: LPG: Compositional and vapor-pressure driven; aniline point is not used.Naphtha/gasoline: Volatility and octane dominate; aniline point is rarely applied. Common Pitfalls: Assuming every fuel uses the same property set; each fraction has distinct key performance metrics. Final Answer: Diesel

Petroleum Refinery Engineering Questions