Question 1

Ethyl mercaptan (also called ethanethiol), commonly used as an odorant in LPG, belongs to which class of compounds?

Accepted Answer

Introduction: Ethyl mercaptan (ethanethiol) is widely recognized as the strong-smelling odorant added to otherwise odorless LPG to enable leak detection. Correctly classifying it reinforces understanding of sulfur chemistry in fuels and the need for handling precautions due to odor and corrosion potential. Given Data / Assumptions: Chemical: CH3–CH2–SH (ethanethiol). Use: odorant in LPG at low concentrations. We must identify the chemical family. Concept / Approach: “Mercaptan” is an older term for thiol compounds, which are sulfur-containing organics with the –SH functional group. Therefore, ethyl mercaptan is a sulfur compound. It is not a nitrogen compound (no –NH or amine functionality) nor an oxygenate (no –OH or ether). It is also not a halogenated hydrocarbon. Step-by-Step Solution: 1) Identify functional group: –SH indicates a thiol (mercaptan).2) Map thiols to “sulfur compounds.”3) Select “Sulphur compound.” Verification / Alternative check: Material safety data and fuel standards classify ethanethiol among sulfur odorants; similar odorants include tert-butyl mercaptan. Why Other Options Are Wrong: Nitrogen compound: Would require amine/amide functionality.Oxygenate: Implies alcohols/ethers, not present here.None/halogenated: Do not match the –SH thiol identity. Common Pitfalls: Confusing “mercaptan” terminology; despite older naming, it unequivocally denotes sulfur-containing thiols. Final Answer: Sulphur compound

Question 2

Catalytic reforming: evaluate the primary effect of increasing operating pressure in the reforming reactor, considering its influence on coke formation tendency, intrinsic reaction rates/selectivity, and the octane number of the produced gasoline (r…

Accepted Answer

Introduction / Context: Catalytic reforming (platforming) converts low-octane naphtha into high-octane reformate by dehydrogenation of naphthenes to aromatics, isomerization, and limited hydrocracking. Operating variables include temperature, pressure, hydrogen partial pressure, and space velocity. This question asks what happens when reactor pressure is increased, and which of the listed statements correctly reflects industry practice and equilibrium principles. Given Data / Assumptions: Feed: hydrotreated naphtha rich in paraffins/naphthenes. Key reactions: endothermic dehydrogenation to aromatics + H2; isomerization; mild hydrocracking. Variable of interest: higher total/partial pressure of hydrogen. Concept / Approach: Dehydrogenation and aromatization produce hydrogen; by Le Chatelier's principle, raising pressure and H2 partial pressure shifts equilibria against aromatic formation. As a result, octane number (primarily from aromatics) tends to decrease at higher pressure. Higher hydrogen partial pressure also suppresses coke formation on the catalyst surface, improving run length, not worsening coking. Apparent reaction rates for the desired endothermic dehydrogenations do not increase simply by raising pressure; severity is commonly achieved with higher temperature or lower pressure/space velocity. Step-by-Step Solution: 1) Identify desired pathway: naphthene → aromatic + H2 (endothermic, equilibrium-limited).2) Increase pressure: equilibrium shifts toward fewer moles of gas, disfavoring H2 generation and therefore aromatics formation.3) Outcome: lower aromatic yield → lower reformate octane at higher pressure.4) Coking: higher H2 partial pressure suppresses coke; so coking does not increase.5) Rate/severity: endothermic dehydrogenations are not accelerated by pressure; severity is typically raised by temperature or reduced pressure. Verification / Alternative check: Operating strategies in reformers favor lower pressures (within metallurgy/decoking constraints) to maximize octane and hydrogen yield, accepting higher coking propensity controlled by good hydrotreating and regeneration cycles. Why Other Options Are Wrong: Increases coke formation: incorrect; higher H2 suppresses coke.Increases rate/severity: not a general truth for reforming dehydrogenations.Produces higher octane: opposite of observed trend; octane typically drops as pressure rises. Common Pitfalls: Assuming that higher pressure always accelerates reactions or improves quality; for equilibrium-limited dehydrogenations, lower pressure is favorable to octane. Final Answer: None of these

Question 3

Straight-run distillation yield: estimate a typical kerosene cut percentage (by volume) obtained directly from crude oil without cracking or reforming, under conventional atmospheric distillation conditions.

Accepted Answer

Introduction / Context: In a fuels refinery, the crude distillation unit (CDU) separates crude into straight-run fractions: gases, naphtha, kerosene, diesel/gasoil, and residue. Typical yields depend on crude assay (paraffinic vs naphthenic), cut-point definitions, and plant objectives. This question asks for a representative kerosene yield from straight-run distillation only (no conversion units included). Given Data / Assumptions: Average mixed crudes with standard atmospheric cut points. Yield expressed on a typical volume percent basis. No hydrocracking or reforming contributions; strictly straight-run kerosene. Concept / Approach: Crude assays commonly show kerosene fractions in the approximate range of single digits to low teens by volume for many world crudes. While light, kerosene is narrower and smaller than total naphtha plus diesel cuts. A commonly cited reference value for general questions is about 10 percent straight-run kerosene, acknowledging that real values vary by crude type and unit targets. Step-by-Step Solution: 1) Review typical CDU product slate shares.2) Recognize kerosene is a middle distillate thinner than diesel; its window is not the dominant portion of the barrel.3) Select 10 percent as a representative, exam-appropriate straight-run yield. Verification / Alternative check: Crude assay examples and refinery planning texts often place straight-run kerosene near 8–12 percent for benchmark medium crudes, supporting a 10 percent nominal figure. Why Other Options Are Wrong: 4 percent: too low for a general typical value.18 percent or 26 percent: high for straight-run kerosene across most benchmark crudes. Common Pitfalls: Confusing total kerosene pool (including hydrocracker or coker distillates) with straight-run kerosene; the question is strictly about atmospheric distillation output. Final Answer: 10

Question 4

Elemental analysis of crude petroleum: choose the approximate mass percentage of carbon typically found in untreated crude oil samples, recognizing normal assay ranges for world crudes.

Accepted Answer

Introduction / Context: Crude petroleum is a complex mixture predominantly of hydrocarbons. Bulk elemental composition provides a fast sense of fuel properties and conversion behavior. This question focuses on the typical carbon mass percent for crude oils. Given Data / Assumptions: Representative world crudes (light to heavy). Standard ultimate analysis of untreated crude. Minor heteroatoms (S, N, O, metals) present in small percentages. Concept / Approach: Crude oils commonly exhibit carbon in the mid-80s by weight, hydrogen around the low to mid teens, and the remainder as sulphur, nitrogen, oxygen, and trace metals. While there is variation (paraffinic vs naphthenic vs aromatic), the 85 percent by mass figure is an accepted approximate benchmark for educational problems. Step-by-Step Solution: 1) Recall typical ultimate analysis ranges: C about 83–87 percent, H about 10–14 percent.2) Select the midpoint approximation for carbon.3) Choose 85 as the most defensible single value among the options. Verification / Alternative check: Published assays for benchmark crudes (e.g., Brent, WTI, Arab Light) report carbon shares in the mid-80s percent by weight with modest variation. Why Other Options Are Wrong: 65 or 75: significantly below typical ranges for crude petroleum.95: too high; would imply hydrogen and heteroatoms unrealistically low. Common Pitfalls: Assuming a single number is exact; in practice, composition depends on crude origin and assay method, but the mid-80s figure is standard for quick estimates. Final Answer: 85

Question 5

Coking feed selection: determine the most suitable feedstock for a delayed coking or fluid coking unit when the objective is to produce petroleum coke along with lighter products.

Accepted Answer

Introduction / Context: Coking is a deep-conversion thermal process used to upgrade the heaviest, most refractory fractions of crude by cracking them into lighter products (naphtha, gas oils) and solid carbon (petroleum coke). Feed selection determines yields, coke quality, and unit performance. Given Data / Assumptions: Process: delayed or fluid coking. Potential feeds: vacuum residue, light gas oil, diesel, naphtha. Goal: maximize conversion of heavy molecules and produce coke. Concept / Approach: Vacuum residue (vacuum bottoms) contains the highest boiling, polynuclear aromatic, asphaltenic, and metal-rich species that are unsuitable for distillation-based upgrading. Coking targets precisely this stream to break large molecules, reject carbon as coke, and generate usable lighter products. Lighter streams like diesel, LGO, or naphtha are not appropriate feeds for a coker and are more valuable elsewhere in the refinery. Step-by-Step Solution: 1) Identify the heaviest fraction from vacuum distillation: vacuum residue.2) Match process intent: convert residue and reject carbon as coke.3) Select vacuum residue as the ideal coker feed. Verification / Alternative check: Refinery flow schemes route VDU bottoms to delayed coking, visbreaking, resid hydrocracking, or deasphalting; among these, coking is the classic route for coke production. Why Other Options Are Wrong: Naphtha, diesel, or light gas oil: too valuable and too light for coking; poor economics and not the target for coke make. Common Pitfalls: Confusing feed suitability with temporary recycle streams; process design prioritizes the heaviest, least valuable fractions for coking. Final Answer: Vacuum residue

Question 6

Define the smoke point of kerosene precisely as used in fuel quality specifications for clean burning: identify the correct interpretation involving the flame height in a standard test lamp.

Accepted Answer

Introduction / Context: Smoke point is a critical kerosene property for lamp burning and turbine fuels because it gauges the tendency to form soot. Higher smoke point indicates cleaner, smokeless flames under controlled test conditions and typically correlates with lower aromatic content. Given Data / Assumptions: Standardized test lamp and wick configuration. Measurement in millimetres of flame height. No forced draft; normal atmospheric conditions during the test. Concept / Approach: The smoke point is not a time or a temperature. It is defined as the maximum flame height (in millimetres) at which the fuel burns without producing a visible smoky plume in a standard test lamp. The parameter serves as a specification limit in aviation kerosene and illuminating kerosene to ensure clean combustion. Step-by-Step Solution: 1) Eliminate interpretations involving time or temperature; the test controls flame height.2) Recall the measurement unit: millimetres of flame height.3) Choose the definition referencing the maximum smokeless flame height in a standard lamp. Verification / Alternative check: Fuel standards list minimum smoke points (e.g., in mm) for kerosene grades and aviation turbine fuels, aligning with this definition. Why Other Options Are Wrong: Time/temperature based options: not how smoke point is specified or measured.None of these: incorrect because the correct definition is provided. Common Pitfalls: Confusing smoke point (a combustion cleanliness metric) with flash point (a safety volatility metric) or with freezing point (low-temperature operability). Final Answer: Maximum flame height in mm without smoking in a standard lamp

Question 7

Platforming (catalytic reforming) feed selection: pick the most suitable refinery stream for reforming to make high-octane reformate and hydrogen under typical Pt-based catalysts.

Accepted Answer

Introduction / Context: Catalytic reforming (platforming) upgrades naphtha-range hydrocarbons to a high-octane gasoline blendstock (reformate) and produces hydrogen for hydrotreaters. Correct feed selection is essential for desired reactions: dehydrogenation of naphthenes, isomerization of paraffins, and limited hydrocracking/aromatization. Given Data / Assumptions: Candidate feeds: naphtha, C3–C4 olefins, fuel oil, atmospheric residue. Catalysts: platinum or platinum–rhenium on chlorided alumina. Objective: octane uplift and H2 generation. Concept / Approach: Reforming targets the naphtha boiling range (roughly 70–180°C, depending on refinery practice). In this window, paraffinic and naphthenic hydrocarbons can be isomerized and dehydrogenated to aromatics, sharply increasing RON. Heavier streams (fuel oil, residue) are far outside the process envelope; light olefins are routed to alkylation or polymerization rather than reforming. Step-by-Step Solution: 1) Match process chemistry to feed carbon number (C6–C10 typical).2) Identify naphtha as the correct boiling-range feed.3) Select “Naphtha.” Verification / Alternative check: Refinery block flow diagrams universally route hydrotreated naphtha to reformers; other listed streams go to different units. Why Other Options Are Wrong: Fuel oil/residue: too heavy; cause severe coking and are processed by vacuum, cracking, or resid upgrading.C3–C4 olefins: feed for alkylation/polymerization, not reforming. Common Pitfalls: Confusing reforming (octane via aromatics) with FCC or hydrocracking that handle heavier feeds. Final Answer: Naphtha

Question 8

Interpretation of the motor gasoline boiling range: explain which performance aspects it influences among ease of starting, acceleration characteristics, and vapour-lock tendency in spark-ignition engines.

Accepted Answer

Introduction / Context: The distillation curve (boiling range) of gasoline dictates volatility across temperatures. Proper volatility balance is critical to drivability: quick starting, smooth warm-up and acceleration, and avoidance of vapour lock in hot conditions. Given Data / Assumptions: Fuel: conventional motor gasoline. Key metrics: initial boiling point, midrange volatility (T10, T50), and end point. Engine: spark-ignition with carburetion or port/direct injection. Concept / Approach: Light ends (lower boiling components) ensure rapid vaporization for easy cold starting. Mid-range volatility aids throttle response and acceleration. Excessive light ends and high RVP increase vapour lock risk in warm conditions, causing fuel pumps to vaporize fuel and starve the engine. The entire boiling range must therefore be optimized to balance these competing needs. Step-by-Step Solution: 1) Link front-end volatility to cold start quality.2) Link mid-range volatility to acceleration and drivability.3) Recognize that high volatility elevates vapour lock tendency under heat soak.4) Conclude that all three listed performance aspects are influenced. Verification / Alternative check: Standards specify seasonal volatility adjustments (e.g., RVP caps) to prevent vapour lock while still ensuring startability and acceleration. Why Other Options Are Wrong: Selecting any single aspect ignores the holistic influence of the distillation curve across operating conditions. Common Pitfalls: Overemphasizing RVP alone; the entire boiling range profile dictates drivability. Final Answer: All of (a), (b), and (c)

Question 9

Chemical representation of naphthenic acids: select the most appropriate general formula for cycloaliphatic (naphthenic) monocarboxylic acids commonly found in certain crude oils.

Accepted Answer

Introduction / Context: Naphthenic acids are naturally occurring cycloaliphatic carboxylic acids in some crude oils that can cause corrosion and refining challenges. Understanding their general formula helps distinguish them from straight-chain fatty acids and from aromatic acids. Given Data / Assumptions: Naphthenes are saturated cyclic hydrocarbons. We consider monocarboxylic acid derivatives of these rings. Formulae are given in generalized C/H/O forms with O2 indicating a single -COOH group. Concept / Approach: For aliphatic (acyclic) monocarboxylic acids, a common general formula is CnH2nO2, reflecting one ring-equivalent compared with alkanes (CnH2n+2). Cycloaliphatic acids (naphthenic acids) incorporate the ring deficiency of the cycloalkane core and the carboxyl group, often represented in petroleum texts by the generalized form CnH2n-2O2. This captures the hydrogen deficiency from ring formation relative to the acyclic series. Step-by-Step Solution: 1) Start from cycloalkane baseline: CnH2n.2) Incorporate a carboxyl substituent and ring hydrogen deficiency: generalized petroleum shorthand often expressed as CnH2n-2O2.3) Select the formula option matching this conventional representation. Verification / Alternative check: Petroleum chemistry references frequently use the CnH2n-2O2 shorthand for naphthenic acids, distinguishing them from normal fatty acids (CnH2nO2) and from alkanes (CnH2n+2). Why Other Options Are Wrong: CnH2n+2O2 (with or without n ≥ 6): corresponds to saturated acyclic acids, not cycloaliphatic naphthenic acids.CnH2n+6O2 (n ≤ 6): not a recognized general series for these petroleum acids. Common Pitfalls: Confusing straight-chain fatty acids with naphthenic acids; ring formation changes hydrogen count relative to acyclic analogs. Final Answer: CnH2n-2O2

Question 10

Reid vapour pressure (RVP) significance for gasoline: identify which performance or operability issue RVP is most directly used to assess among pour point, cloud point, vapour-lock tendency, and carbon residue.

Accepted Answer

Introduction / Context: Reid vapour pressure (RVP) is a standardized measure of gasoline volatility at a specified temperature. Regulators and refiners control RVP seasonally to balance startability in cold weather with hot-fuel handling issues in warm weather. Given Data / Assumptions: Fuel: conventional gasoline. RVP measured at standard conditions (Reid method). Engine/fuel system exposed to varying ambient temperatures. Concept / Approach: Higher RVP implies more volatile fuel, which aids cold starting but increases the risk of vapour lock and evaporation losses in hot conditions. Vapour lock occurs when gasoline vaporizes in the fuel pump or lines, interrupting liquid flow and causing stalling. Therefore, RVP is directly connected to vapour-lock tendency rather than low-temperature pour/cloud points (relevant to diesel) or carbon residue (a heavy-fuel property). Step-by-Step Solution: 1) Link high RVP to high volatility and vapor formation.2) Recognize vapour lock as the primary operability concern at elevated temperatures.3) Conclude RVP indicates vapour-lock tendency. Verification / Alternative check: Seasonal gasoline specifications set upper RVP limits for summer to mitigate vapour lock and evaporative emissions while still meeting startability targets. Why Other Options Are Wrong: Pour/cloud point: properties for middle distillates and wax precipitation, not gasoline.Carbon residue: associated with heavy oils; not a gasoline volatility indicator. Common Pitfalls: Assuming higher RVP is always better; it must be optimized for climate and engine design. Final Answer: Vapour-locking tendency

Question 11

Define the diesel index used to estimate ignition quality of diesel fuels by combining API gravity with aniline point; select the correct formula form and units as commonly specified.

Accepted Answer

Introduction / Context: Ignition quality of diesel is characterized directly by cetane number or indirectly by indices that correlate with composition. The diesel index is an older but still referenced empirical correlation combining density (via API gravity) and solvency/aromaticity (via aniline point) to estimate ignition quality. Given Data / Assumptions: API gravity is an inverse function of density (higher °API = lighter fuel). Aniline point reflects aromatic content/solvency (lower aniline point = higher aromatics). Diesel index formula uses specific units. Concept / Approach: The classic diesel index is defined as: Diesel Index = (°API) * (Aniline Point in °F) / 100. Lighter fuels (higher °API) and higher aniline points (more paraffinic character) increase the index, generally aligning with higher cetane quality. The index is a screening tool and does not replace measured cetane number. Step-by-Step Solution: 1) Recall unit requirements: aniline point must be in degrees Fahrenheit.2) Combine with °API by multiplication and divide by 100.3) Select the option matching this definition. Verification / Alternative check: Textbook definitions and refinery laboratory methods document the Diesel Index formula exactly in this unit system. Why Other Options Are Wrong: Using °C in the formula changes the scale and is not the standard correlation.Inverting by dividing by aniline point does not reflect the accepted definition. Common Pitfalls: Confusing Diesel Index with Cetane Index; they are related screening metrics but not identical and use different inputs. Final Answer: (°API) x (Aniline Point, °F)/100

Question 12

Fuel sulphur across refinery cuts: Among common petroleum products used in transport and heating (petrol/gasoline, kerosene/ATF-range, diesel/gasoil, and heavy fuel oil), which fraction typically contains the highest sulphur content before deep desu…

Accepted Answer

Introduction / Context: Sulphur in petroleum fuels originates from organosulphur compounds present in crude. The distribution of sulphur among product cuts depends on boiling range: heavier fractions concentrate higher-boiling sulphur species, whereas lighter products contain less and are often further hydrotreated. Understanding which product generally has the highest sulphur helps in environmental compliance and unit selection for hydrotreating. Given Data / Assumptions: Relative comparison of untreated product cuts from the same crude slate. Modern ultra-low-sulphur specifications exist, but the question targets inherent tendencies before deep desulphurisation. Products considered: petrol (gasoline), kerosene/ATF range, diesel/gasoil, and heavy fuel oil (residual). Concept / Approach: Sulphur compounds are more prevalent and higher boiling in heavier streams. During distillation, these concentrate in gasoils and especially in atmospheric/vacuum residues blended into heavy fuel oils. Lighter cuts—gasoline and kerosene—contain fewer sulphur compounds intrinsically and are routinely hydrotreated to very low levels. Therefore, heavy fuel oil typically exhibits the greatest sulphur content among listed products. Step-by-Step Solution: 1) Recognise sulphur–boiling range correlation: heavier = more sulphur.2) Order expected sulphur: fuel oil > diesel > kerosene > petrol (typical prior to deep hydrotreating).3) Select the heaviest product—fuel oil—as the one with maximum sulphur. Verification / Alternative check: Crude assays show higher sulphur numbers in bottoms/resid streams. Regulatory mandates then drive HDT/HDS severity; nonetheless, without treatment, residual fuels contain the most sulphur. Why Other Options Are Wrong: Diesel — significant sulphur possible, but generally less than residual fuels from the same crude.Petrol — intrinsically low sulphur and extensively hydrotreated.Kerosene — intermediate; aviation grades demand very low sulphur.LPG — produced by fractionation/processing with negligible sulphur after sweetening. Common Pitfalls: Assuming modern “on-spec” retail fuels reflect inherent tendencies; regulations lower sulphur across the board but do not reverse the underlying distribution without processing. Final Answer: Fuel oil (heavy oil)

Question 13

Wet natural gas processing terminology: The liquid hydrocarbon condensate obtained when wet natural gas is cooled and/or compressed (pentanes-plus stream) is commonly termed what in petroleum practice?

Accepted Answer

Introduction / Context: Natural gas from reservoirs often carries heavier hydrocarbons (C5+). When the gas is cooled and/or compressed, these heavier components condense to a liquid known in industry as condensate or natural gasoline (often called pentanes-plus). Knowing the correct terminology prevents confusion with LNG (a different product) and refined gasoline from oil refineries. Given Data / Assumptions: Feed is wet natural gas containing C2–C6+ hydrocarbons. Separation by field separators, low-temperature processing, or compression/expansion. Terminology per conventional petroleum engineering usage. Concept / Approach: The condensed liquid rich in C5+ hydrocarbons is historically termed natural gasoline. It is compositionally distinct from finished motor gasoline and from LNG. It may be stabilised to remove lighter ends before transport and blending. Step-by-Step Solution: 1) Identify process: condensation of wet gas produces a pentanes-plus liquid.2) Match to standard name: natural gasoline (not “liquid natural gas”).3) Exclude misleading phrases such as “liquefied natural gasoline,” which is not standard nomenclature. Verification / Alternative check: Gas processing texts define natural gasoline as pentanes-plus separated from natural gas streams, commonly blended into refinery naphtha/gasoline pools. Why Other Options Are Wrong: “Liquefied natural gasoline” — nonstandard term.“Liquid natural gas” — LNG is cryogenic methane-rich, not condensate.“None of these” — incorrect because a standard term exists.“Stabilised condensate” — descriptive but the commonly tested term is natural gasoline. Common Pitfalls: Confusing LNG/LPG/natural gasoline; each is distinct in composition and processing route. Final Answer: natural gasoline

Question 14

Fuel testing and composition cues: In diesel fuel quality evaluation, the aniline point is primarily used as an indicator of which type of hydrocarbon content?

Accepted Answer

Introduction / Context: The aniline point is the minimum temperature at which equal volumes of aniline and a hydrocarbon fuel are completely miscible. It serves as a proxy measure for aromaticity in middle distillates like diesel: lower aniline point implies higher aromatic content. Given Data / Assumptions: Equal-volume aniline mix used for the test. Application to diesel/gasoil-range fuels. Interpreted qualitatively rather than as an exact composition assay. Concept / Approach: Aromatics dissolve better in aniline than paraffins; therefore, fuels with more aromatics mix at lower temperatures. Conversely, paraffinic fuels show higher aniline points. Thus, aniline point is inversely related to aromatic content and is widely used for comparative assessments of diesel fuels. Step-by-Step Solution: 1) Recall definition of aniline point.2) Connect miscibility trend: high aromatics → low aniline point.3) Conclude the property inferred is aromatic content. Verification / Alternative check: Standard fuel testing references list an inverse correlation between aniline point and aromaticity for gasoils/diesels. Why Other Options Are Wrong: Paraffin — associated with higher aniline point, not lower.Olefin — test is not designed to isolate olefin content.Naphthene — contributes, but the decisive correlation is with total aromaticity.Oxygenate — not present in conventional diesel and unrelated to the aniline test. Common Pitfalls: Treating aniline point as an absolute composition measure; it is a comparative indicator affected by overall hydrocarbon family balance. Final Answer: aromatic

Question 15

Crude description by salt content: A crude oil is termed “salty” when its total dissolved salts (as NaCl) exceed approximately what mass per thousand barrels of crude?

Accepted Answer

Introduction / Context: Salt (mostly NaCl) enters crude with formation water and brine emulsions. Excess salt causes corrosion, fouling, and catalyst poisoning, so refineries classify and treat salty crudes more aggressively in desalter units. Recognising the conventional threshold helps in feed acceptance and desalter design. Given Data / Assumptions: Salt expressed as mass of NaCl per thousand barrels of crude. Rule-of-thumb threshold for “salty crude” used in exam-style questions. Units intentionally posed in kilograms per thousand barrels for comparison. Concept / Approach: Industry shorthand often flags crudes above roughly 25 kg NaCl per thousand barrels (≈ 55 lb per thousand barrels) as “salty,” indicating significant brine carryover and emulsion stability issues. While individual refineries may set different limits, this benchmark captures the conventional teaching number for classification. Step-by-Step Solution: 1) Recall common specification language (ptb or kg/MBbl).2) Convert perspective: 25 kg/MBbl ≈ 55 ptb, a clearly elevated level.3) Choose the threshold option most aligned with the teaching convention: 25. Verification / Alternative check: Desalter manuals classify feed severity using salt ranges; values near or above 25 kg/MBbl require robust wash and electrostatic treatment. Why Other Options Are Wrong: 1–15 kg/MBbl — comparatively mild to moderate; many crudes fall here after basic field separation.50 kg/MBbl — extremely high; beyond typical acceptance without intensive pre-treatment. Common Pitfalls: Mixing “ptb” (pounds per thousand barrels) with kilograms; keep units consistent when comparing limits. Final Answer: 25

Question 16

Coke formation tendencies: Choose the correct statement about coking in refinery/thermal processes considering molecular weight, pressure effects, and reaction heat.

Accepted Answer

Introduction / Context: “Coking” refers to the formation of solid carbonaceous material in thermal and catalytic processes (e.g., visbreaking, coking, FCC). It deactivates catalysts, plugs equipment, and reduces liquid yields. Understanding factors that drive coking helps in selecting severity and feed quality windows. Given Data / Assumptions: Comparison across hydrocarbon feeds from light naphtha to residua. General trends rather than unit-specific anomalies. Reaction heat refers here to net heat effects of the overall pathway to solid carbon. Concept / Approach: Heavier feeds (higher molecular weight, higher Conradson carbon/asphaltenes) contain more precursors for condensation and polyaromatic growth, thus showing stronger coking propensity. Pressure effects are complex and unit-dependent; “always enhances coke formation” is too absolute. Coking itself results from polymerisation/condensation and dehydrogenation steps; while cracking is endothermic, overall pathways to carbon are not characterised simply as exothermic in specifications. Moisture control helps but does not “eliminate” coking when heavy precursors are present. Step-by-Step Solution: 1) Compare feeds: resid > gasoils > naphtha in coking tendency.2) Link to property: higher molecular weight and asphaltenes increase condensation to coke.3) Evaluate pressure: no universal “higher pressure → more coke” rule; depends on kinetics and volatility.4) Evaluate reaction heat: oversimplified to label coking as exothermic across contexts.5) Conclude (a) is the sound general statement. Verification / Alternative check: Unit operations literature correlates coke make with feed CCR/asphaltenes and severity; heavy feeds inherently show greater coke formation under similar severities. Why Other Options Are Wrong: (b) Opposite of observed trend.(c) Overly absolute; pressure effects vary.(d) Mischaracterises complex pathways; cracking endothermy coexists with condensation sequences.(e) Drying feed reduces foaming/emulsions but not intrinsic coking propensity. Common Pitfalls: Treating a multivariate phenomenon with single-factor absolutes; always consider feed CCR, asphaltenes, and severity together. Final Answer: Coking tendency increases with increasing molecular weight.

Question 17

Diesel ignition quality improvers: Which additive is commonly used to increase the cetane number of diesel fuels (thereby shortening ignition delay in compression-ignition engines)?

Accepted Answer

Introduction / Context: Cetane number reflects how readily diesel auto-ignites under compression. Higher cetane numbers reduce ignition delay and promote smoother combustion. Chemical additives can boost cetane where base fuel quality is insufficient. Given Data / Assumptions: Focus on compression-ignition (CI) diesel engines. Consider classical improvers used at ppm–low thousands ppm dosages. Distinguish from gasoline octane improvers. Concept / Approach: Nitrate/nitrite esters (e.g., amyl nitrate, 2-ethylhexyl nitrate) act as cetane improvers by decomposing to yield radicals that facilitate low-temperature oxidation, thereby shortening ignition delay. TEL raises octane for SI engines and does not improve diesel cetane. Mercaptans are odorants; naphthenic acids are part of crude chemistry and are not cetane improvers. Step-by-Step Solution: 1) Identify additive family that raises cetane: alkyl nitrates/nitrites.2) Match example in options: amyl nitrate.3) Exclude others: TEL (octane), mercaptan (odorant), naphthenic acid (not an improver), ferrocene (organometal used occasionally in gasoline). Verification / Alternative check: Fuel additive references list 2-ethylhexyl nitrate and amyl nitrate as standard cetane improvers with strong response in poor-ignition gasoils. Why Other Options Are Wrong: Ethyl mercaptan — odorant, not a cetane improver.Naphthenic acid — corrosive species, not used to raise cetane.Tetraethyl lead — gasoline antiknock additive.Ferrocene — sometimes octane-related/combustion modifier in SI fuels, not diesel cetane booster. Common Pitfalls: Mixing octane improvers (SI) with cetane improvers (CI); they target opposite ignition behaviours. Final Answer: Amyl nitrate

Question 18

Heating value conventions: Given that petroleum fuels typically contain 12–15% hydrogen by mass, the latent heat lost with water vapour makes the gross (HHV) exceed the net (LHV) by approximately how much (kcal per kg of fuel)?

Accepted Answer

Introduction / Context: Gross (higher) heating value (HHV) includes the heat recovered if combustion water condenses to liquid; net (lower) heating value (LHV) assumes water remains as vapour and its latent heat is not recovered. The difference depends largely on the fuel hydrogen content because hydrogen combustion produces water. Given Data / Assumptions: Petroleum fuels contain roughly 12–15% hydrogen by weight. Water of combustion remains as vapour in LHV. Latent heat of vaporisation of water is the dominant contributor to HHV–LHV difference. Concept / Approach: Each kilogram of hydrogen yields 9 kg of water when fully oxidised. The latent heat associated with this water (at typical reference conditions) translates to several hundred kcal/kg of fuel. For 12–15% hydrogen fuels, the HHV–LHV gap typically falls around 600–750 kcal/kg, a standard rule-of-thumb in fuel engineering. Step-by-Step Solution: 1) Estimate water formed: 0.12–0.15 kg H per kg fuel → 1.08–1.35 kg H2O per kg fuel.2) Multiply by latent heat (order ~ latent at reference conditions) → several hundred kcal/kg fuel.3) Conclude expected difference ≈ 600–750 kcal/kg for typical petroleum fuels. Verification / Alternative check: Fuel property tables show HHV–LHV differences near this range for diesel, kerosene, and gasoline, consistent with their hydrogen content. Why Other Options Are Wrong: 250–350 — too low for 12–15% hydrogen content.1000–1500 and 2000–2500 — excessive for petroleum fuels; such gaps would imply unusually high hydrogen content or different reference conditions.100–200 — far too low. Common Pitfalls: Forgetting that HHV–LHV is fuel-dependent; natural gas (higher H fraction) shows a different gap than residual oils. Final Answer: 600–750

Question 19

Comparing typical pump grades — legacy figures: Textbook convention asks: the octane numbers of motor gasoline used in India and America are respectively taken as which of the following pairs (legacy comparison; not current market labels)?

Accepted Answer

Introduction / Context: Octane rating systems and pump labelling vary by region and era (RON vs. MON vs. AKI). Many legacy exam questions use conventional pairings to contrast "typical" octane ratings cited historically for India and America. This question follows that tradition rather than present-day pump postings. Given Data / Assumptions: Legacy textbook comparison rather than current regulatory labels. India conventionally cited with lower RON figures in older references; America often cited with higher representative numbers for premium grades. Answer reflects the exam convention. Concept / Approach: Within the conventional framing used in older petroleum MCQs, India is associated with about "87" and America with about "94" for motor gasoline octane numbers (reference grades). This should not be confused with today’s AKI labelling (e.g., 87/89/91 AKI in the U.S., roughly RON 91–98), but it matches the intended learning check in such questions. Step-by-Step Solution: 1) Recognise the legacy nature of the comparison.2) Map conventional numbers: India ≈ 87; America ≈ 94.3) Select the pair that matches this convention. Verification / Alternative check: Historic course materials often contrasted regional octane practices using these nominal values; modern specs vary by grade and method. Why Other Options Are Wrong: Reversed (94 & 87) and other pairs do not reflect the textbook convention.91 & 91 would imply identical figures, not the intended contrast. Common Pitfalls: Confusing RON with AKI; AKI is (RON + MON)/2 used on U.S. pumps today and is numerically lower than RON. Final Answer: 87 & 94

Question 20

Octane rating methods — clarify the term: In fuel testing, the Research Octane Number (RON) refers to which of the following standardised rating definitions for motor gasoline?

Accepted Answer

Introduction / Context: Octane ratings quantify knock resistance in spark-ignition engines. Two primary laboratory methods exist: Research (RON) and Motor (MON). Many exams test whether students can distinguish these and relate them to real-world labelling (e.g., AKI in North America). Given Data / Assumptions: Standardized single-cylinder CFR engine is used. Research method employs milder operating conditions; Motor method uses more severe conditions. AKI is a separate consumer label: (RON + MON) / 2. Concept / Approach: RON indicates the octane rating determined under the Research method (ASTM D2699), which uses relatively mild test parameters compared with MON (ASTM D2700). It is broadly used to characterise motor gasoline and is not limited to unleaded or aviation contexts. Step-by-Step Solution: 1) Identify the proper standard: ASTM D2699 defines RON.2) Distinguish from MON (ASTM D2700) and from AKI (consumer label).3) Select the definition that explicitly names the Research method and mild conditions. Verification / Alternative check: Fuel testing manuals tabulate both RON and MON for certification; AKI appears on retail pumps in certain regions as an average of the two lab numbers. Why Other Options Are Wrong: Motor method is MON, not RON; AKI is an average; aviation fuels use different metrics; unleaded status is unrelated to the definition of RON. Common Pitfalls: Assuming RON equals the number on American pumps; AKI is lower because it averages RON and MON. Final Answer: The octane rating measured by the Research method (ASTM D2699) under mild test conditions

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