Question 1

In gasoline stability, which hydrocarbon family tends to show the highest gum-forming tendency during storage: paraffins, naphthenes, aromatics, or diolefins?

Accepted Answer

Introduction: Gum formation in gasoline arises from oxidative polymerization of reactive unsaturates. Identifying the hydrocarbon class most prone to forming gums is essential for storage stability and additive selection. Given Data / Assumptions: Compare gum tendency among paraffins, naphthenes, aromatics, and diolefins. Ambient storage with oxygen exposure is implied. Concept / Approach: Reactivity increases with unsaturation: diolefins (dienes) > mono-olefins > aromatics ≈ naphthenes ≈ paraffins (least). Dienes readily oxidize and polymerize, generating gums. Step-by-Step Solution: 1) Rank families by unsaturation and radical stability.2) Recognize dienes (diolefins) as most reactive for gum formation.3) Select “Diolefins.” Verification / Alternative check: ASTM gum tests and textbook trends consistently show highest gum precursors in olefinic—especially diene—fractions. Why Other Options Are Wrong: Paraffins: saturated; poor gum formers.Aromatics: relatively stable ring; lower gum tendency than dienes.Naphthenes: saturated cyclics; low gum tendency. Common Pitfalls: Assuming high octane (aromatics) implies instability; octane and oxidative stability are distinct properties. Final Answer: Diolefins

Question 2

Define the aniline point and interpret what it indicates for diesel and lubricating oils with respect to aromatic content and solvency behavior.

Accepted Answer

Introduction: The aniline point is a classical petroleum test—temperature at which equal volumes of aniline and the oil are completely miscible. It is widely used for middle distillates and lubricant base stocks to infer solvency and aromaticity trends. Given Data / Assumptions: Oil types: diesel and lube base oils. Aniline point correlates inversely with aromatic content (lower aniline point → higher aromatics). Concept / Approach: Because aniline is an aromatic amine, aromatics in oil dissolve it more readily at lower temperatures. Thus, lower aniline point implies higher aromaticity/solvency; higher aniline point implies more paraffinic character. Step-by-Step Solution: 1) Define aniline point: complete miscibility temperature with aniline at equal volumes.2) Link to composition: aromatic-rich oils mix at lower T, paraffinic oils require higher T.3) Conclude it is characteristic for diesel/lubes and indicates aromatic content. Verification / Alternative check: Refining property tables relate cetane/sooting/solvency tendencies with aniline point for distillate fuels and lube stocks. Why Other Options Are Wrong: (a) alone: incomplete; it also conveys compositional insight.(b) alone: incomplete; the test is notably applied to diesel and lube oils.Neither: contradicts standard definitions and usage. Common Pitfalls: Confusing aniline point with octane/cetane directly; it is an indirect compositional/solvency indicator, not a performance index by itself. Final Answer: Both (a) and (b)

Question 3

Fuel properties check in petroleum engineering: For straight-run petrol (gasoline) as compared to methyl/ethyl alcohol fuels, identify which property is lower for petrol. Consider typical commercial grades and standard test conditions.

Accepted Answer

Introduction / Context: Straight-run petrol (gasoline) and lower alcohols (methanol and ethanol) differ markedly in several standard fuel properties used in engine and refinery practice. This question probes recognition of the property for which petrol shows a lower value when compared with methyl/ethyl alcohol, under normal commercial ranges and test methods. Given Data / Assumptions: Fuelling context: spark-ignition (SI) engines under standard test conditions. Alcohols considered: methanol and ethanol as neat fuels reference. “Straight-run petrol” refers to naphtha fraction directly from crude distillation without reforming. Concept / Approach: Octane number measures resistance to knock. Alcohols typically exhibit very high octane ratings relative to straight-run petrol. Calorific value compares energy per unit mass or volume; gasoline generally exceeds alcohols here. Specific gravity and autoignition behavior vary, but the most consistent, widely taught contrast is octane number: petrol's is lower. Step-by-Step Solution: 1) Compare octane numbers: petrol (straight-run) often ~60–80 prior to reforming; ethanol and methanol are typically > 95 in RON terms.2) Compare calorific value: petrol > alcohols (so “lower calorific value” for petrol is false).3) Compare specific gravity: gasoline ~0.72–0.78; ethanol ~0.79; relationship is not the sought "lower" property for petrol.4) Compare ignition/autoignition temperatures: differences are not the standard hallmark contrast taught for this basic identification item. Verification / Alternative check: Engine literature and refinery texts consistently teach alcohols as high-octane oxygenated fuels; straight-run naphtha requires reforming/isomerization to raise octane. This cross-checks the choice. Why Other Options Are Wrong: (a) Petrol has higher, not lower, calorific value than alcohols.(c) Petrol typically has lower specific gravity than ethanol; option claims the opposite.(d) Ignition temperature comparison is not the standard differentiator for this recall question.(e) Not applicable because one option is correct. Common Pitfalls: Learners sometimes conflate "more energy" with "higher octane." Octane is knock resistance, not energy content; alcohols are high-octane despite lower heating value. Final Answer: Lower octane number

Question 4

Domestic energy basics: Liquefied Petroleum Gas (LPG) used for household cooking primarily consists of which hydrocarbon components under standard supply blends?

Accepted Answer

Introduction / Context: LPG supplied for household cooking is a pressurized mixture of light hydrocarbons chosen for safe handling, suitable vapor pressure at ambient conditions, and clean combustion. Knowing its typical composition is standard refinery and utilities knowledge. Given Data / Assumptions: LPG refers to bottled/cylinder cooking gas for domestic use. Typical climate: ambient temperatures where cylinders can vaporize normally. Commercial blends may vary seasonally but remain within conventional propane–butane ranges. Concept / Approach: LPG is chiefly C3–C4 hydrocarbons (propane, butane, and isobutane). Methane is the main component of natural gas (piped PNG/CNG), not bottled LPG. Carbon monoxide is a toxic combustion product, not a fuel component. Step-by-Step Solution: 1) Identify LPG family: liquefied alkanes with suitable vapor pressure—propane (C3H8) and butane (C4H10).2) Exclude methane-rich options: methane is not stored as LPG in domestic cylinders.3) Confirm safety/handling rationale: C3/C4 mixtures liquefy under moderate pressure and vaporize easily for stoves. Verification / Alternative check: Cylinder labels and national fuel standards specify propane–butane mixes (ratios tuned to season for vapor pressure control). Why Other Options Are Wrong: (b) Ethane is not a principal LPG cylinder component.(c) Methane and ethane describe natural gas mixtures, not LPG.(d) Carbon monoxide is a dangerous exhaust gas, not a fuel constituent.(e) Propane plus methane is not the standard LPG formulation. Common Pitfalls: Confusing LPG with PNG/CNG; methane dominance implies pipeline or compressed natural gas, not bottled LPG. Final Answer: Propane and butane

Question 5

Tribology and lubrication testing: The standard penetration test of a grease primarily determines which property that governs its consistency and handling behavior?

Accepted Answer

Introduction / Context: Greases are semi-solid lubricants. Penetration testing is the widely used empirical method to classify a grease by its consistency. Understanding what this test measures is a core skill in tribology and maintenance engineering. Given Data / Assumptions: Standard cone penetration test conditions (e.g., worked/unworked values). Results reported as tenths of a millimeter of cone penetration. Grease types include lithium, calcium, and complex soaps among others. Concept / Approach: Penetration reflects the relative softness or hardness—i.e., consistency—of a grease. Higher penetration value means softer grease; lower value means stiffer grease. It does not directly quantify oiliness, viscosity–temperature variation, or high-temperature service limit. Step-by-Step Solution: 1) Define penetration: depth a standard cone sinks into grease under specified conditions.2) Map to property: this gauges stiffness/consistency class (e.g., NLGI grades).3) Exclude attributes not measured: lubricity, oxidation resistance, and dropping point need other tests. Verification / Alternative check: NLGI grading correlates with penetration ranges; procurement specs select grade by required stiffness rather than "oiliness." Why Other Options Are Wrong: (b) Oiliness is better inferred from base oil type/additives, not cone penetration.(c) Service temperature uses tests like dropping point/ASTM methods.(d) Viscosity–temperature behavior is tested on the base oil (e.g., ASTM D445), not via penetration.(e) Shear stability is assessed by worked penetration change after mechanical working, not by a single penetration value alone. Common Pitfalls: Equating penetration directly with load-carrying capacity; while related via application suitability, they are distinct metrics. Final Answer: Stiffness (consistency)

Question 6

Safety and odorization in LPG distribution: Mercaptans are intentionally added to liquefied petroleum gas cylinders primarily to achieve what safety function?

Accepted Answer

Introduction / Context: LPG is naturally odorless. To protect users, suppliers add trace odorants—commonly mercaptans (thiols)—to create a distinctive smell. Recognizing the reason for this practice is a key safety competency. Given Data / Assumptions: Domestic cylinder use with regulators and stoves. Mercaptans added at ppm-level doses. Objective is immediate human detection without instruments. Concept / Approach: Odorization provides early warning of leaks before concentrations approach hazardous limits. It does not alter calorific value meaningfully or shrink flammability limits; the additive amount is tiny and chosen for odor potency, not energy content. Step-by-Step Solution: 1) Identify hazard: undetected LPG leaks can accumulate and ignite.2) Identify countermeasure: mercaptans impart a strong, recognizable odor at very low concentrations.3) Link to function: enables quick, human-sensed leak detection. Verification / Alternative check: Utility and refinery standards worldwide mandate odorization of otherwise odorless gases for domestic distribution to enhance safety and compliance. Why Other Options Are Wrong: (a) Cost is minimally affected; odorization is not a cost-reduction step.(b) Flammability limits are properties of the fuel–air mixture; trace odorants do not "narrow" them.(d) Calorific value increase is negligible at ppm dosing.(e) Burner flame temperature is governed by mixture and heating value, not odorant. Common Pitfalls: Assuming odorization modifies combustion quality; its purpose is detection, not performance. Final Answer: Assist in checking and detecting cylinder leakage

Question 7

Petroleum exploration terminology: A drilled petroleum well is termed a “dry well” (or “dry hole”) when its produced hydrocarbons are in what practically non-commercial condition?

Accepted Answer

Introduction / Context: In petroleum exploration and drilling, wells are evaluated by whether they can produce hydrocarbons economically. The industry term "dry well" (or "dry hole") focuses on commerciality rather than absolute absence of hydrocarbons. Given Data / Assumptions: Assessment is based on sustainable, economic flow of oil and/or gas. Minor shows or traces do not qualify as commercial production. Water production alone is considered non-commercial for oil/gas purposes. Concept / Approach: A dry well is one that does not produce oil or gas in commercial quantities. It may encounter traces of oil/gas or shows in cuttings/mud logs but lacks marketable flow rates. Therefore, statements about "no natural gas" or "only natural gas" do not by themselves define dryness; economic viability does. Step-by-Step Solution: 1) Define "dry": absence of commercial hydrocarbons, not necessarily absolute zero molecules.2) Interpret choices: "very little oil" aligns with non-commercial yield.3) Exclude choices that focus on composition rather than commerciality (no gas / only gas). Verification / Alternative check: Industry reporting and SEC/Petroleum reserves guidelines emphasize economic producibility; wells with only shows are categorized as dry/non-productive. Why Other Options Are Wrong: (b) A well could produce oil commercially without gas; "no gas" does not imply dry.(c) Gas-only wells can be highly commercial; "only natural gas" does not imply dry.(d) All three cannot simultaneously be true and do not match the economic definition.(e) Water-only with traces indicates non-commercial status, but the question asks to choose the best among given; "very little oil (not commercial)" most directly captures the standard definition. Common Pitfalls: Equating dryness with literal zero hydrocarbon content; in practice, "dry" means non-commercial output. Final Answer: It yields only very little oil (not in commercial quantity)

Question 8

Industrial uses of petroleum coke: Considering global consumption patterns, the single largest application area for petroleum coke is typically which of the following?

Accepted Answer

Introduction / Context: Petroleum coke (petcoke) is a carbon-rich by-product of heavy oil upgrading and delayed coking units. Its end uses vary by grade (fuel-grade vs. anode-grade vs. needle coke). Recognizing the dominant consumption sector is common refinery economics knowledge. Given Data / Assumptions: Anode-grade and needle coke are used for electrodes in aluminum smelting and steel EAFs. Fuel-grade petcoke is also used widely as an industrial fuel in cement and power. Question asks for the single largest "application area" in classical exam framing. Concept / Approach: Historically, a major high-value sink for suitable petcoke is carbon electrodes/anodes (especially in aluminum electrolytic cells). While fuel use is sizable, standard chemical engineering exam keys often highlight electrode/anode manufacture as the primary "maximum use" answer due to value chain significance and textbook emphasis. Step-by-Step Solution: 1) Categorize petcoke by quality: needle/anode grades vs. fuel grade.2) Map uses: electrodes/anodes consume large tonnage of higher-quality coke.3) Compare distractors: adsorption/activated carbon are niche relative to petcoke streams; iron ore reduction typically uses coke/coal blends, not petcoke as a primary reductant. Verification / Alternative check: Standard refinery and petroleum processing texts list electrode/anode manufacture as a principal market for high-quality petcoke. Why Other Options Are Wrong: (a) Adsorption refining is not a dominant use for petcoke material.(b) Petcoke can be gasified, but this is not the mainstream destination by tonnage.(d) Ironmaking primarily uses metallurgical coke from coal.(e) Activated carbon production typically uses other feedstocks; petcoke is not standard. Common Pitfalls: Confusing "fuel-grade" consumption scale with "largest single specific application"; exam convention often points to the electrode/anode segment. Final Answer: Carbon electrode and anode manufacture

Question 9

Refining processes and thermal severity: Identify which of the following common refinery processes does not involve hydrocarbon chain cracking under its core mechanism.

Accepted Answer

Introduction / Context: Many refinery conversion processes rely on breaking heavy hydrocarbon chains into lighter molecules—thermal or catalytic cracking. Understanding which processes intrinsically crack vs. those that do not is a core refinery fundamentals skill. Given Data / Assumptions: Processes listed: coking, visbreaking, and pyrolysis. Thermal severity ranges from mild (visbreaking) to severe (coking, steam cracking). We assess the core mechanism, not ancillary steps. Concept / Approach: Coking, visbreaking, and pyrolysis are all thermal cracking processes. Therefore, none of them qualifies as "does not employ cracking." Step-by-Step Solution: 1) Coking: severe thermal cracking of resid to lighter products plus solid coke.2) Visbreaking: mild thermal cracking to reduce viscosity of resid feed.3) Pyrolysis: high-temperature cracking (e.g., steam cracking to produce olefins). Verification / Alternative check: Standard process flow diagrams and unit operation descriptions confirm cracking in all three listed processes. Why Other Options Are Wrong: (a) and (b) and (c) each explicitly use cracking.(e) Partial oxidation is a gasification route; it is not among the main options asked and is presented as a distractor only. Common Pitfalls: Confusing "visbreaking" as purely viscosity adjustment without cracking; in fact, it achieves viscosity reduction via mild cracking. Final Answer: None of these (all involve cracking)

Question 10

Volatility testing by Reid method: In the Reid vapor pressure (RVP) apparatus for petrofuels at 100°F, what is the ratio of the air (vapor) chamber volume to the liquid fuel chamber volume?

Accepted Answer

Introduction / Context: Reid vapor pressure (RVP) is a legacy yet widely referenced measure of fuel volatility. The test uses a sealed apparatus with a defined vapor-to-liquid volume ratio to standardize the partial pressure measured at 100°F (approximately 37.8°C). Given Data / Assumptions: Standard RVP test temperature: 100°F. Measurement in a closed volume with specified vapor and liquid chambers. Fuel equilibrated with its own vapor plus small air space. Concept / Approach: The Reid method specifies a vapor-to-liquid chamber volume ratio of 4:1. This ensures reproducible vaporization and pressure reading across labs and fuels. Step-by-Step Solution: 1) Identify the apparatus design: separate air (vapor) chamber and liquid chamber.2) Apply the standard: vapor space volume is four times the liquid chamber volume.3) Read the gauge pressure as the Reid vapor pressure at equilibrium. Verification / Alternative check: ASTM procedure descriptions and refinery handbooks state the 4:1 vapor-to-liquid volume ratio for the Reid bomb. Why Other Options Are Wrong: (a)–(c) Ratios 1, 2, or 3 do not match the Reid standard.(e) A 5:1 ratio is not used in the canonical Reid method. Common Pitfalls: Confusing Reid vapor pressure (legacy) with true vapor pressure (TVP); the apparatus ratio is specific to the Reid method. Final Answer: 4

Question 11

Gasoline quality and reforming chemistry: Pick the incorrect statement regarding octane behavior, reforming objectives, feed selection, and catalysts used in modern gasoline reforming.

Accepted Answer

Introduction / Context: Gasoline reforming improves octane by rearranging and dehydrogenating hydrocarbons. Understanding correct vs. incorrect statements about octane trends, desired reactions, suitable feeds, and catalysts is essential in refining practice. Given Data / Assumptions: Focus on conventional process knowledge: thermal vs. catalytic reforming. Paraffinic/naphthenic naphtha ranges are typical feeds. Platinum on bifunctional supports is the standard catalyst family. Concept / Approach: Lower boiling (shorter chain) paraffins typically show higher octane than heavier normal paraffins; dehydrogenation of naphthenes to aromatics increases octane; Pt on silica-alumina (often chlorided alumina) is standard for catalytic reforming. "Dearomatised kerosene" is not an ideal thermal reforming feed; reforming targets naphtha—not kerosene—with significant naphthene content for octane uplift. Step-by-Step Solution: 1) Validate (a): octane decreases with increasing straight-chain length in normal paraffins; thus (a) is true.2) Validate (b): converting naphthenes to aromatics is a classic desired reforming reaction raising octane and producing hydrogen.3) Validate (d): platinum on acidic support is canonical for catalytic reforming.4) Evaluate feed claim (c): kerosene boiling range is too heavy; thermal reforming of kerosene is neither "most ideal" nor standard compared to naphtha feeds. Verification / Alternative check: Refining textbooks specify straight-run naphtha (naphthenic/paraffinic) as reforming feed; catalytic reforming replaced thermal reforming due to selectivity and octane gains. Why Other Options Are Wrong: (a) True — hence not the incorrect statement.(b) True — desired reaction pathway.(d) True — common catalyst base.(e) True — isomerization improves octane by increasing branching. Common Pitfalls: Confusing reforming with hydrocracking; reforming chiefly rearranges and dehydrogenates, not deep cracking of kerosene feeds. Final Answer: The most ideal feedstock for thermal reforming is dearomatised kerosene.

Question 12

Three-stage crude distillation design: In a high-pressure primary tower (first stage) of a three-stage crude oil distillation system, the typical operating pressure maintained is approximately how many kg/cm^2?

Accepted Answer

Introduction / Context: Some refinery configurations employ staged crude distillation with a high-pressure (HP) primary tower upstream of medium/low-pressure sections. Recognizing typical pressure levels aids in understanding column design, vapor–liquid traffic, and pump-around duties. Given Data / Assumptions: Three-stage crude distillation: HP primary, followed by lower-pressure sections. Nominal crude slate and standard preheat/desalting. Pressures quoted as gauge values in kg/cm^2 (approximate ranges). Concept / Approach: HP primary towers often operate at a few kg/cm^2 to suppress vaporization in upstream equipment, improve heat integration, and control flash behavior. Typical values cluster around 3 kg/cm^2 for textbook problems, with subsequent stages at progressively lower pressures toward near-atmospheric conditions. Step-by-Step Solution: 1) Relate pressure to flash zone temperature and vapor load control.2) Use canonical exam ranges: HP ~3 kg/cm^2, MP ~1.5 kg/cm^2, LP ~near-atmospheric.3) Select the closest standard option that matches common design teaching. Verification / Alternative check: Process design examples in petroleum refining courses frequently cite ~3 kg/cm^2 for HP sections, scaling with crude and column size. Why Other Options Are Wrong: (a) 1.5 kg/cm^2 is more typical of a medium-pressure or second stage.(c) 6 kg/cm^2 is higher than common textbook HP primary values for this context.(d) 12 kg/cm^2 is excessive for a distillation primary tower in this service.(e) 0.8 kg/cm^2 is too low for an HP primary stage. Common Pitfalls: Assuming all crude towers run at near-atmospheric pressure; multi-stage systems intentionally vary pressure by stage. Final Answer: 3

Question 13

Petroleum refining: What is the typical yield (by weight percent) of straight-run LPG obtained directly from crude oil distillation in a refinery?

Accepted Answer

Introduction / Context: Liquefied petroleum gas (LPG) is a light hydrocarbon mixture (mainly propane and butane) recovered in refineries from crude oil. When obtained directly from atmospheric and vacuum distillation—without cracking or reforming—it is called straight-run LPG. Understanding its typical yield helps in material balance, product slate planning, and economic evaluation of a refinery crude run. Given Data / Assumptions: Feed: untreated crude oil processed through atmospheric (and possibly vacuum) distillation only. Product of interest: straight-run LPG (C3–C4 range). We are considering typical global refinery practice with conventional crudes (no special condensate-rich case). Yield basis: weight percent of crude. Concept / Approach: Crude oil contains a spectrum of hydrocarbons. The lightest fraction yields gases and LPG. Without conversion processes (e.g., catalytic cracking, hydrocracking), the natural—or straight-run—LPG cut is modest. Industry references consistently report a low single-digit wt% for straight-run LPG across common crude types, often near 1–2 wt% depending on crude light-ends and distillation cut points. Step-by-Step Solution: Step 1: Recognize that straight-run product excludes conversion-derived LPG (no cracking).Step 2: Relate to crude assay: typical crude has limited native C3–C4 content after allowing for dissolved gases and stabilizer losses.Step 3: Typical refinery reports show ~1–2 wt% straight-run LPG; a common figure taught in petroleum exams is around 1–1.5 wt%.Step 4: Choose the option that matches the common teaching value range. Verification / Alternative check: Assays for medium crudes show LPG + dry gas as a small fraction. Where lighter condensates are processed, LPG can rise, but exam-standard “typical” values stay near ~1–1.5 wt% for straight-run only. Higher LPG yields generally require conversion units producing additional C3–C4. Why Other Options Are Wrong: 10–15: Too high for straight-run; such values imply conversion-derived LPG or very light condensate slates. 20–25: Unrealistically high without extensive cracking operations. 0.1–0.2: Too low; would underestimate normal straight-run recovery. Common Pitfalls: Confusing straight-run LPG with total refinery LPG (which can include conversion LPG). Also, mixing volume percent with weight percent or using unusual crude cases can mislead the estimate. Final Answer: 1–1.5 (weight percent)

Question 14

Petroleum products sweetening: The traditional "Doctor's solution" used for sweetening sour petroleum fractions is chemically which compound?

Accepted Answer

Introduction / Context: Many straight-run and cracked petroleum fractions contain mercaptans and other sulphur species. Sweetening converts objectionable sulphur compounds into less odorous, less corrosive, or less reactive forms. The historical “Doctor test” and “Doctor sweetening” are classic quality checks/processes in petroleum refining. Given Data / Assumptions: Question asks the composition of the traditional Doctor’s solution. Focus is on the reagent used in mercaptan sweetening tests/processes. Answer options list various sodium and lead compounds. Concept / Approach: The classical Doctor process employs a solution of sodium plumbite (Na2PbO2) in caustic. In the presence of elemental sulphur, mercaptans are oxidized to disulphides while lead sulphide forms. The associated Doctor test checks whether a petroleum sample turns “sweet” (passes) under set conditions. Step-by-Step Solution: Step 1: Recall that “Doctor’s solution” = sodium plumbite solution in alkali.Step 2: Recognize its role in converting mercaptans and indicating product sweetness.Step 3: Select the option that matches sodium plumbite. Verification / Alternative check: Standard petroleum textbooks and test methods repeatedly associate the Doctor test and process with sodium plumbite as the specific reagent in an alkaline medium. Why Other Options Are Wrong: Sodium thiosulphate: Used as a reducing/complexing agent in various chemistries, not the Doctor reagent. Sodium sulphite: A different sulphur oxy-salt; not the historical Doctor reagent. Lead sulphate: A product or precipitate type in some lead reactions, not the reagent solution itself. Common Pitfalls: Confusing the “test” name with end products or with other sulphur treatment chemistries (e.g., caustic wash alone, copper strip corrosion test). Final Answer: Sodium plumbite

Question 15

Refining separation: Which solvent is conventionally used in the deasphalting of petroleum residua to separate asphaltenes from deasphalted oil?

Accepted Answer

Introduction / Context: Deasphalting is a key residue conversion/separation step that splits heavy vacuum bottoms into deasphalted oil (DAO) and an asphaltene-rich pitch. The choice of solvent critically affects selectivity, quality of DAO, and yield of pitch. Given Data / Assumptions: Feed is a petroleum residue (e.g., vacuum bottoms). We seek the commonly used solvent in deasphalting units. Options include polar and nonpolar solvents used elsewhere in refining. Concept / Approach: Propane deasphalting (PDA) is a long-established technology. Light paraffinic solvents such as propane (and sometimes butane/pentane variants) selectively dissolve maltenes while rejecting asphaltenes. In contrast, furfural and liquid SO2 are used for extractive processes on distillates (e.g., aromatic extraction), and MEK commonly appears in dewaxing blends (often with toluene), not deasphalting. Step-by-Step Solution: Step 1: Recall PDA uses liquefied propane under pressure as the solvent.Step 2: Identify that propane’s paraffinic nature rejects asphaltenes.Step 3: Select “Propane.” Verification / Alternative check: Standard process diagrams and vendor literature universally refer to “Propane Deasphalting” for residue separation, confirming the solvent choice. Why Other Options Are Wrong: Furfural: Aromatics extraction for lube/distillate improvement, not residue deasphalting. Methyl ethyl ketone: Common in solvent dewaxing (paired with toluene), not PDA. Liquid sulphur dioxide: Historical extractive solvent for aromatics, not the residue deasphalting standard. Common Pitfalls: Mixing up extraction services (dewaxing vs deasphalting vs aromatics extraction) due to overlapping “solvent” terminology. Final Answer: Propane

Question 16

Crude distillation practice: Why is crude oil subjected to vacuum distillation in the final stage of fractionation?

Accepted Answer

Introduction / Context: Atmospheric crude distillation separates naphtha to gas oil cuts. Heavier fractions require higher temperatures to boil, which risks cracking and coking. Vacuum distillation enables recovery of heavy distillates without excessive thermal stress. Given Data / Assumptions: Final stage uses reduced pressure (vacuum). Target products: vacuum gas oils and lube distillates. Thermal stability of heavy hydrocarbons is limited at atmospheric pressure boiling temperatures. Concept / Approach: Boiling point decreases with pressure. Operating under vacuum allows the column to vaporize high-boiling components at lower temperatures, reducing cracking/coking, preserving quality (viscosity index, color), and improving heat economy and run length. Step-by-Step Solution: Step 1: Identify thermal decomposition risk for heavy fractions at atmospheric boiling conditions.Step 2: Lower column pressure to reduce required boiling temperatures.Step 3: Conclude that vacuum operation protects heat-sensitive heavy products. Verification / Alternative check: Standard crude/vacuum unit (CDU/VDU) design texts emphasize vacuum columns for lube distillates and VGO with minimized thermal cracking and coking propensity. Why Other Options Are Wrong: Lighter products decompose more: In refineries, high-boiling material is more at risk during high-temperature exposure. Very high purity goal: Purity is not the primary reason; thermal protection is. None of these: Incorrect because there is a clear thermal sensitivity rationale. Common Pitfalls: Assuming vacuum distillation is for purity alone; confusing it with deep cut polishing or extractive operations. Final Answer: To avoid decomposition of heat-sensitive heavy products by boiling them at lower temperatures under vacuum.

Question 17

Crude column products: What name is given to the bottom product of an atmospheric crude oil distillation column?

Accepted Answer

Introduction / Context: Atmospheric distillation yields overhead gases, naphtha, kerosene, gas oils, and a high-boiling bottom stream. Standard terminology matters for communication between operations, planning, and downstream conversion units. Given Data / Assumptions: Stream is the atmospheric column bottoms. No vacuum flashing has been applied yet. Conventional refinery nomenclature is used. Concept / Approach: The atmospheric bottoms is commonly termed atmospheric residue or reduced crude (because lighter fractions have been removed). It is the typical feed to the vacuum distillation column or residue conversion units such as visbreaking, coking, or residue hydrocracking. Step-by-Step Solution: Step 1: Identify standard names: “atmospheric residue,” “reduced crude,” and sometimes “residuum.”Step 2: Choose the widely used label asked in many exams: reduced crude. Verification / Alternative check: Refinery stream maps and PFD legends frequently tag the stream as “reduced crude (AR).” Why Other Options Are Wrong: Residuum: A valid synonym in many texts, but the question expects the common exam key “reduced crude.” Asphalt: Asphalt is a product grade from further processing; not every atmospheric bottom is asphalt. Heavy ends: Informal and nonspecific; not the standard stream name. Common Pitfalls: Believing only one strict term exists; both “atmospheric residue” and “reduced crude” are accepted, but exams often key on reduced crude. Final Answer: Reduced crude

Question 18

Catalytic cracking fundamentals: Which catalyst type is characteristically used to crack heavier hydrocarbons into lighter gasoline-range molecules?

Accepted Answer

Introduction / Context: Catalytic cracking is a core conversion process in refineries to transform heavier feeds into gasoline, LPG, and lighter distillates. The catalyst determines activity, selectivity, and stability under high temperature and metal/steam exposure. Given Data / Assumptions: We are referring to conventional catalytic cracking (e.g., FCC) principles. Options include materials used in other processes or as supports. Exam-style focus is on classic catalyst families. Concept / Approach: Historically, amorphous silica–alumina catalysts were used. Modern FCC catalysts are zeolite-based (Y-type) supported on silica–alumina matrices. In basic petroleum exams, “silica–alumina” is the expected umbrella answer for catalytic cracking catalysts. Step-by-Step Solution: Step 1: Recall FCC catalyst evolution from silica–alumina to zeolite on silica–alumina matrices.Step 2: Identify the canonical exam key: silica–alumina.Step 3: Select “Silica–alumina.” Verification / Alternative check: Process texts consistently describe FCC catalysts as zeolitic on silica–alumina supports—validating “silica–alumina” as the family descriptor. Why Other Options Are Wrong: Silica gel: A desiccant/adsorbent; not a cracking catalyst. Vanadium pentoxide: Typical in SOx conversion or oxidation catalysts; not FCC. Nickel: A hydrogenation/dehydrogenation metal; in FCC feed it is actually a poison that promotes dry gas formation. Common Pitfalls: Confusing supports/adsorbents with active acidic cracking catalysts; ignoring that zeolites ride on silica–alumina matrices. Final Answer: Silica–alumina

Question 19

Aniline point test: The aniline point of an oil qualitatively indicates which type of hydrocarbon content in that oil?

Accepted Answer

Introduction / Context: The aniline point is the lowest temperature at which equal volumes of aniline and a hydrocarbon mixture are completely miscible. It is widely used as an empirical indicator in fuels and lube testing to infer hydrocarbon type distribution qualitatively. Given Data / Assumptions: Aniline point is measured per standard test methods. We need to identify which hydrocarbon family correlates with the value. General trends suffice; exact numerical correlation is not required. Concept / Approach: Aromatics tend to mix more readily with aniline than paraffins. Therefore, the higher the aromatic content, the lower the aniline point; conversely, paraffinic materials have higher aniline points. Hence, the aniline point serves as a qualitative indicator of aromaticity in petroleum products. Step-by-Step Solution: Step 1: Recall the definition of aniline point.Step 2: Recognize the inverse relation: more aromatics → lower aniline point.Step 3: Conclude that the property indicates aromatic content. Verification / Alternative check: Fuel specification guides note that kerosene/jet fuels with lower aromatics typically have higher aniline points, aligning with smoke point and combustion quality trends. Why Other Options Are Wrong: Paraffin: High paraffin → high aniline point; not directly indicated as increasing with the test. Olefin: Olefinic content is not what aniline point primarily tracks. Naphthene: Cycloparaffins influence exists but the key qualitative indicator is aromaticity. Common Pitfalls: Assuming the aniline point rises with aromatics; it actually decreases with more aromatics. Final Answer: Aromatic

Question 20

Isomerisation chemistry: The isomerisation process primarily converts which hydrocarbon family into iso-paraffins to improve octane?

Accepted Answer

Introduction / Context: Isomerisation is a key octane-boosting process used to improve light naphtha quality by rearranging the carbon skeleton of hydrocarbons without changing their carbon number. Given Data / Assumptions: Target products are high-octane iso-paraffins (e.g., isopentane, isohexane). Typical feeds contain normal paraffins in C5–C6 range. Process conditions: low temperature, chlorinated alumina or zeolitic catalysts, hydrogen present to suppress coking. Concept / Approach: Normal paraffins have lower octane numbers than their branched isomers. Isomerisation increases branching (skeletal isomerization), turning n-paraffins into iso-paraffins, thereby raising octane without changing boiling range. Step-by-Step Solution: Step 1: Identify the feed family: normal paraffins.Step 2: Recognize the reaction: skeletal isomerization to iso-paraffins.Step 3: Conclude “Paraffins” is the correct family. Verification / Alternative check: Refinery flow schemes show C5/C6 isomerization units feeding into gasoline blending pools to increase Research Octane Number (RON). Why Other Options Are Wrong: Olefins: Double-bond isomerization exists but is not the primary refinery isomerisation objective for octane in light naphtha. Naphthenes: Can equilibrate among ring isomers, but octane uplift focus is on n-paraffins. None of these: Incorrect because paraffins are correct. Common Pitfalls: Confusing isomerisation with reforming (which also increases octane but via dehydrogenation/cyclization/aromatization). Final Answer: Paraffins (normal paraffins to iso-paraffins)

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