Question 1

Paraffin waxes are commercially graded using a key specification relevant to product performance and end use. Select the standard parameter used for grading: specific gravity, melting point, viscosity, or penetration number.

Accepted Answer

Introduction / Context: Paraffin waxes find use in packaging, candles, coatings, and cosmetics. Grading ensures the right wax is selected for thermal and mechanical performance in the application environment. Given Data / Assumptions: End-use demands focus on softening and thermal behavior. Multiple properties can be measured, but one is primary for grading. Industry naming often references this key property. Concept / Approach: Melting point (or congealing point) is the primary grading metric for paraffin waxes because it directly dictates handling temperatures, set time, and stability in service. While oil content and needle penetration are specified for quality control, the commercial “grade” usually centers on melting point (e.g., 58–60°C wax). Step-by-Step Solution: 1) Identify application-critical performance: thermal softening behavior.2) Recognize commercial labels (e.g., 54–56°C, 58–60°C).3) Choose melting point as the grading parameter. Verification / Alternative check: Supplier datasheets and standards commonly list melting range as the headline grade with auxiliary specs for oil content and penetration. Why Other Options Are Wrong: Specific gravity/viscosity: measured but not the grading headline.Penetration number: quality attribute, not the primary grading criterion. Common Pitfalls: Confusing general QC parameters with the commercial grade label. Final Answer: Melting point

Question 2

Explain why high-boiling fractions such as atmospheric residue are distilled under vacuum at comparatively low temperatures: at elevated temperatures, which undesired phenomenon tends to predominate?

Accepted Answer

Introduction / Context: Very heavy crude fractions cannot be distilled at atmospheric pressure without exposing them to extreme temperatures. Refiners employ vacuum distillation to lower boiling points and protect product quality and equipment. Given Data / Assumptions: Feed: atmospheric residue/high-boiling components. Objective: separate into vacuum gas oils and residue safely. Concern: avoid thermal degradation at high temperatures. Concept / Approach: At sufficiently high temperatures and residence times, large hydrocarbon molecules undergo thermal cracking, producing lighter gases and coke precursors. Vacuum operation reduces required temperatures, limiting the rate of these reactions and preserving desired yields and properties. Step-by-Step Solution: 1) Recognize heavy fractions need high T to vaporize at 1 atm.2) High T promotes bond scission → thermal cracking and subsequent coke formation.3) Apply vacuum to depress boiling points and minimize cracking. Verification / Alternative check: Process design literature states vacuum distillation is chosen to avoid thermal cracking that would occur at atmospheric pressures for these boiling ranges. Why Other Options Are Wrong: Gum formation/discoloration: minor compared with fundamental cracking kinetics.Coking: often a consequence of severe thermal cracking; the primary initiating phenomenon is thermal cracking itself. Common Pitfalls: Using “coking” as the primary reason; while coke is a severe outcome, the underlying driver is thermal cracking which vacuum aims to suppress. Final Answer: Thermal cracking

Question 3

Fuel additives and antiknock quality: Tetraethyl lead (TEL) was historically added to petrol (gasoline) to raise its octane number. Identify the best reason with respect to TEL’s intrinsic antiknock strength and blending effectiveness under standard…

Accepted Answer

Introduction / Context: Octane number indicates a gasoline’s resistance to knock in spark-ignition engines. Tetraethyl lead (TEL) was widely used in legacy fuels as a powerful antiknock additive. This question checks conceptual recall of why TEL was so effective in raising octane ratings. Given Data / Assumptions: Context is historical/technical (pre-unleaded regulations). Octane number scale is based on iso-octane (100) and n-heptane (0) reference fuels. We focus on TEL’s antiknock potency as a blending component. Concept / Approach: TEL provides free-radical scavenging in the end-gas region, suppressing pre-ignition/autoignition kinetics. It exhibits an extraordinarily high blending octane value (commonly treated as greater than 100 on the RON scale), meaning very small dosages markedly increase the pool octane of gasoline. Step-by-Step Solution: 1) Recall the octane scale anchors and the meaning of “antiknock.”2) Recognize that TEL’s effectiveness corresponds to a very high equivalent octane strength.3) Therefore, characterizing TEL as “more than 100” on the octane scale best explains its potency. Verification / Alternative check: Historical refinery practice and engine test data show significant octane uplift with a few milliliters of TEL per gallon, consistent with an effective octane value above 100 as a blender. Why Other Options Are Wrong: (b) “Around 100” understates the exceptionally strong blending effect.(c) “Between 50 and 100” cannot justify the large observed uplift at low treat rates.(d) “Less than 25” contradicts TEL’s known potency.(e) TEL is not merely a scavenger; lead scavengers (e.g., ethylene dibromide) were separate additives. Common Pitfalls: Confusing the base fuel’s octane with the additive’s blending octane; the question targets the latter. Final Answer: more than 100

Question 4

Gasoline pool comparison (unleaded): Among the following gasoline types, which one generally exhibits the lowest octane number before any additional upgrading or special blending?

Accepted Answer

Introduction / Context: Gasoline streams differ in octane due to how they are produced. Understanding which refinery stream starts with the lowest octane helps explain why upgrading units (reforming, isomerization) are essential in modern refineries. Given Data / Assumptions: Unleaded context; no TEL or MMT. “Straight run” means naphtha directly from atmospheric distillation. Typical FCC gasoline and reformate qualities are considered. Concept / Approach: Straight run gasoline is rich in normal paraffins and light naphthenes, giving comparatively low octane. Catalytically reformed gasoline (reformate) is rich in aromatics/isoparaffins, hence high octane. Polymer gasoline and FCC gasoline contain more branched and olefinic species, typically higher octane than straight run. Step-by-Step Solution: 1) Identify composition drivers: branching and ring structures raise octane.2) Straight run lacks extensive branching/aromatics → lowest octane.3) Reformate > FCC > polymer gasoline typically outrank straight run in octane. Verification / Alternative check: Refinery textbooks place reformate at the high end of octane and straight run at the low end, motivating upgrading steps. Why Other Options Are Wrong: (a) FCC gasoline is more branched/olefinic than straight run.(c) Reformate has among the highest octane in the pool.(d) Polymer gasoline from olefin polymerization has elevated octane.(e) Isomerate improves octane by converting normal paraffins to isoparaffins. Common Pitfalls: Assuming “cracked” gasoline is always poor quality; for octane specifically, cracked/reformed streams are superior to straight run. Final Answer: Straight run gasoline

Question 5

Asphaltic matter in crude oils: With reference to refinery practice, which statement correctly characterizes “asphalts” present in or derived from crude oils?

Accepted Answer

Introduction / Context: “Asphalts” (asphaltenes and resinous bodies) are heavy, high-boiling constituents concentrated in vacuum residues and asphaltic crudes. Their behavior affects fouling, stability, and product quality in downstream units. Given Data / Assumptions: Focus on qualitative properties used in refinery exams. Asphalts are associated with residue streams, not light distillates. Coke formation tendency is generally undesirable in cracking units. Concept / Approach: Asphalts are high molecular weight, high boiling, polyaromatic/polar species. They oxidize readily and can form carbonaceous sludge and sediments. They are not low molecular weight/light boiling (so option a is false). They are also not “desirable” in catalytic cracking; excessive asphaltenes increase coke, deactivating catalyst and reducing liquid yields (so option b is false). Therefore, the correct characterization is their oxidisability and sludge-forming tendency (option c). Step-by-Step Solution: 1) Reject (a): contradicts heavy, high-boiling nature of asphalts.2) Reject (b): coke production is a problem, not a virtue, for FCC.3) Accept (c): aligns with observed oxidation and sludge formation.4) (d) and (e) are invalid based on the above. Verification / Alternative check: Refinery operations literature highlights sludge/asphalt stability issues (e.g., storage, blending) and catalyst fouling when asphaltic feeds are excessive. Why Other Options Are Wrong: (a) Incorrect—asphalts are heavy, not light.(b) Incorrect—higher coke is detrimental to FCC operation.(d) Incorrect—since (a) and (b) fail, “all” cannot be true.(e) Incorrect—volatility is very low for asphalts. Common Pitfalls: Misreading “produce coke” as beneficial; in FCC, coke forms on catalyst and must be burned off, limiting yields. Final Answer: readily oxidisable and prone to carbonaceous sludge formation

Question 6

Crude desalting performance: After electrical desalting, the residual salt (as NaCl) content in crude oil is typically reduced to approximately what level, expressed in ptb (pounds per thousand barrels)?

Accepted Answer

Introduction / Context: Salt removal is critical before crude distillation to prevent corrosion, fouling, and catalyst poisoning downstream. Electrical desalting (with wash water and electrostatic coalescence) reduces salts to low levels specified by refinery practice. Given Data / Assumptions: Salt content is reported as ptb (pounds NaCl per thousand barrels). Standard single/two-stage desalters with adequate wash ratios. Target is typical, not absolute best-case. Concept / Approach: Typical refinery acceptance targets for desalted crude are in the low single digits of ptb, often near ~3–5 ptb, depending on crude and unit limits. Hence, the closest standard value is about 3 ptb. Step-by-Step Solution: 1) Recognize that raw crude can contain tens to hundreds of ptb.2) Electrical desalting with proper wash brings salts down by orders of magnitude.3) Select the typical specification value ≈ 3 ptb. Verification / Alternative check: Desalter design and operating manuals commonly quote product salt specs around 3–5 ptb for crude fed to atmospheric distillation. Why Other Options Are Wrong: (a) 0.03 ptb is unrealistically stringent for routine operation.(c) 35 ptb is much too high post-desalting.(d) 70 ptb approximates untreated/poorly treated crude.(e) 15 ptb exceeds standard column/corrosion tolerances. Common Pitfalls: Confusing ppm in water with ptb in crude; they are different measures. Final Answer: 3

Question 7

Trend across a crude distillation column: From the overhead to the bottom of an atmospheric crude column, which properties show a progressive increase across the product cuts?

Accepted Answer

Introduction / Context: Fractionation arranges products by volatility. Understanding how key properties vary from the lightest overhead products to the heavy bottoms is foundational to refinery operations and product characterization. Given Data / Assumptions: Standard atmospheric crude distillation (no cracking in the column). Products range from gases/naphtha at top to residue at bottom. C/H ratio means atomic carbon-to-hydrogen ratio. Concept / Approach: As we move downward, the average molecular weight increases (heavier molecules), normal boiling points increase, and the carbon-to-hydrogen ratio rises as structures become more aromatic/polynuclear and less hydrogen-rich. Step-by-Step Solution: 1) Identify volatility ordering: top cuts are most volatile, lowest MW.2) Heavier fractions contain larger, less hydrogen-saturated molecules → higher MW and higher C/H.3) Therefore, boiling point, molecular weight, and C/H ratio all increase downward. Verification / Alternative check: Assay tables show systematic increases in TBP/ASTM D86 distillation temperatures, density, and Conradson carbon with cut heaviness, consistent with higher MW and C/H. Why Other Options Are Wrong: Options (a)–(c) are individually true; thus (d) correctly aggregates them.(e) Incorrect—molecular weight and C/H do not remain constant. Common Pitfalls: Confusing C/H with H/C; the former increases as streams get heavier and more aromatic. Final Answer: all (a), (b) and (c)

Question 8

Kerosene quality control: “Char value” is the mass of charred deposition on a standard wick after burning kerosene for 24 hours at a fixed rate. For good-quality kerosene, the char value should be less than approximately how many mg per kg of kerose…

Accepted Answer

Introduction / Context: The char value test assesses kerosene cleanliness and tendency to form deposits during wicking combustion (e.g., lamps). Low char formation indicates better burning performance and less fouling of the wick and chimney. Given Data / Assumptions: Standard wick lamp test over a 24-hour period. Mass of char reported as mg per kg of kerosene. Seeking the conventional maximum acceptable limit for good-quality fuel. Concept / Approach: Acceptable kerosene grades exhibit very low char deposition. Practical specifications commonly cite an upper limit near 20 mg/kg. Values like 100 or 500 mg/kg would represent poor burning quality with significant deposit formation. Step-by-Step Solution: 1) Recall industry guidance for deposit control in illuminating kerosenes.2) Compare orders of magnitude: 20 mg/kg is a realistic threshold for “good.”3) Select 20 mg/kg as the best-fit limit among options. Verification / Alternative check: Historical lamp oil and illuminating kerosene specs align around this magnitude for acceptable char value. Why Other Options Are Wrong: (a) 1 mg/kg is unrealistically stringent for routine production.(c) and (d) indicate excessive deposit propensity.(e) 5 mg/kg is tighter than typical broad-market specs. Common Pitfalls: Confusing soot/char aesthetic observations with the standardized mass-based metric. Final Answer: 20

Question 9

Key cold-flow property for aviation turbine fuel: Which property is the most critical specification for a jet fuel due to the very low temperatures encountered at cruising altitude?

Accepted Answer

Introduction / Context: Aircraft routinely operate at high altitude where ambient temperatures are far below 0°C. A jet fuel must remain free-flowing and free of crystallized solids in aircraft tanks and lines to ensure safe engine operation. Given Data / Assumptions: Modern aviation turbine fuels (e.g., Jet A/Jet A-1). Long-duration cruise in cold-soak conditions. Focus on cold-flow safety rather than color or cosmetic attributes. Concept / Approach: The freezing point specifies the temperature at which solid crystals form sufficiently to endanger flow. It is the primary cold-flow limit used in jet fuel specifications. While cloud and pour points are relevant in diesel/fuel oils, jet fuel is governed most critically by freezing point for high-altitude service. Step-by-Step Solution: 1) Identify environmental stress: very low airframe/wing tank temperatures.2) Choose the property that directly ensures liquid-phase integrity at altitude: freezing point.3) Note that colour and corrosion tests do not control cold operability. Verification / Alternative check: Aviation fuel standards (e.g., Jet A-1) specify a maximum freezing point (around -47°C) as a critical requirement for safe operation. Why Other Options Are Wrong: (a) Cloud point is not the governing jet spec property.(b) Pour point is more relevant to heavier fuels and storage handling.(c) Colour is cosmetic and not performance-critical.(e) Corrosion rating is important but not the limiting cold-flow property. Common Pitfalls: Transferring diesel-fuel logic (cloud/pour point) to jet fuel without considering altitude-specific requirements. Final Answer: Freezing point

Question 10

Aviation turbine fuel — paramount specification: The single most important property that governs safe high-altitude operability of jet fuel is its:

Accepted Answer

Introduction / Context: Jet fuel must function in extreme cold during cruise. While many properties matter (flash point for handling safety, viscosity for atomization, calorific value for range), freezing point is the key limit preventing fuel solidification at altitude. Given Data / Assumptions: Aircraft wing tanks experience cold-soak temperatures well below 0°C. Fuel system reliability depends on remaining single-phase liquid. Standard commercial jet fuel specifications apply. Concept / Approach: Freezing point defines the onset of significant crystal formation; staying below this temperature ensures flow through filters, pumps, and injectors. Other properties, though important, are not typically the governing cold-limit constraint in flight. Step-by-Step Solution: 1) Identify the altitude-induced risk: low-temperature crystallization.2) Link risk to specification: freezing point controls crystal formation.3) Choose “freezing point” over viscosity, CV, flash point, or density as the paramount safety spec. Verification / Alternative check: Jet A-1 specifications cap freezing point near -47°C, highlighting its criticality for airworthiness. Why Other Options Are Wrong: (a) Viscosity matters but is not the limiting cold-flow spec.(c) Calorific value affects range, not cold operability.(d) Flash point concerns ground handling safety, not cruise cold limits.(e) Density influences energy per volume but not freezing behavior directly. Common Pitfalls: Prioritizing flash point (for storage safety) over freezing point (for in-flight safety). Final Answer: freezing point

Question 11

Catalytic reforming chemistry — undesirable pathway: Identify the reaction that is undesirable during catalytic reforming aimed at producing high-octane gasoline.

Accepted Answer

Introduction / Context: Catalytic reforming upgrades naphtha to high-octane reformate by increasing aromatics and isoparaffins while producing hydrogen. Not all dehydrogenation/isomerization reactions are beneficial to gasoline yield and octane objectives. Given Data / Assumptions: Typical Pt/acid bifunctional catalysts. Feed: paraffinic/naphthenic naphtha boiling range. Goal: raise octane, maintain gasoline-range yield. Concept / Approach: Desired reactions include dehydrogenation of naphthenes to aromatics, isomerization of paraffins, and dehydrocyclization of suitable higher paraffins—each boosts octane and often generates hydrogen. In contrast, dehydrogenating lower paraffins tends to form light olefins/hydrogen that can over-crack or exit as gas, lowering liquid yield and not directly enhancing octane of the gasoline pool; thus it is undesirable. Step-by-Step Solution: 1) Classify reactions as octane-raising vs. yield-losing.2) Naphthene → aromatic (desired, octane up).3) Higher paraffin → cyclized/aromatic (desired, octane up).4) Lower paraffin dehydrogenation → light gas/unstable olefins (undesirable). Verification / Alternative check: Process texts emphasize minimizing C1–C4 gas make; reactions that increase light ends at the expense of C5+ liquid are detrimental. Why Other Options Are Wrong: (a) Desired: increases aromatics and octane.(c) Desired: forms high-octane rings/aromatics.(d) Desired: increases branching → higher octane.(e) Desired: essentially the same as (a) path. Common Pitfalls: Assuming “any” dehydrogenation is good; the molecular size and pathway to light ends matters. Final Answer: Dehydrogenation of lower paraffins

Question 12

Purpose of catalytic reforming: Which reaction best represents the principal desired transformation in catalytic reforming for octane improvement of naphtha?

Accepted Answer

Introduction / Context: Catalytic reforming is a key octane-boosting process that converts low-octane naphtha into high-octane reformate while generating hydrogen. The core chemistry targets molecular restructuring that elevates antiknock quality. Given Data / Assumptions: Pt-based bifunctional catalysts (metal + acid sites). Feed rich in naphthenes and normal paraffins. Objective: increase aromatics and isoparaffins content. Concept / Approach: The signature reaction is the dehydrogenation of naphthenes to aromatics (e.g., cyclohexane → benzene + H2). Aromatics and branched isoparaffins have higher octane numbers. Other listed reactions either consume hydrogen or decrease octane/liquid yield and are not the central reforming objective. Step-by-Step Solution: 1) Identify high-octane structures: aromatics and branched paraffins.2) Map to reaction: naphthene dehydrogenation directly forms aromatics and liberates H2.3) Select the reaction that most directly embodies reforming’s purpose. Verification / Alternative check: Standard reforming schematics show naphthene → aromatic + hydrogen as a headline pathway, providing both octane uplift and valuable H2 for hydrotreating. Why Other Options Are Wrong: (b) Hydrogenation is opposite of the desired dehydrogenation/aromatization.(c) Hydrocracking is a different conversion process, not the reforming focus.(d) Saturation of olefins reduces octane and is not a reforming objective.(e) HDS is performed upstream in hydrotreaters; not the main reforming reaction. Common Pitfalls: Confusing catalytic reforming with hydrocracking or hydrotreating; each has distinct goals and chemistry. Final Answer: dehydrogenation of naphthenes

Question 13

Petroleum refining – process identification In refinery history, the Thermofor (often spelled “Thermofer” in older notes) catalytic cracking unit refers to which general process type?

Accepted Answer

Introduction / Context: Refineries have used several catalytic cracking configurations over time. The Thermofor Catalytic Cracking (TCC) process is a classic historical design that predates modern fluid catalytic cracking (FCC). Identifying its reactor/catalyst handling style helps students contrast legacy moving-bed systems with today’s fluidised-bed FCC units. Given Data / Assumptions: The name in some texts appears as “Thermofor” or “Thermofer.” The question asks for the overall process type (how catalyst and oil contact is arranged). We consider the standard, widely taught configuration from refinery history. Concept / Approach: In moving-bed cracking, solid catalyst particles move continuously or intermittently through reactors and regenerators by gravity or mechanical means. The TCC design circulated formed catalyst pellets between reaction and regeneration—distinct from fluidised beds where catalyst behaves like a fluidized powder stream. Step-by-Step Solution: Identify TCC as an early catalytic cracking technology using formed pellets.Recall that pellets travel between reactor and regenerator under controlled movement (not fluidisation).Classify this arrangement as a moving-bed catalytic cracking process. Verification / Alternative check: Standard refining overviews depict TCC alongside Houdry fixed-bed and modern FCC fluidised-bed, explicitly labeling TCC as moving-bed. Why Other Options Are Wrong: Fixed bed: Characteristic of early Houdry units with cyclic operation, not TCC. Fluidised bed: Describes FCC, not TCC. Non-catalytic thermal unit: Cracking is catalytic in TCC. Common Pitfalls: Confusing TCC with FCC because both circulate catalyst; however, FCC uses fine powder in fluidisation, whereas TCC used moving pellets. Final Answer: Moving bed

Question 14

Fuel identification by API gravity Among petrol (gasoline), kerosene, diesel, and furnace oil, which typically has the minimum °API gravity (i.e., is the heaviest on the API scale)?

Accepted Answer

Introduction / Context: API gravity is an inverse measure of liquid density relative to water used widely in the petroleum industry. Higher °API indicates a lighter product; lower °API indicates a heavier product. Comparing common fuels helps reinforce typical property ranges. Given Data / Assumptions: Products: petrol (gasoline), kerosene, diesel, furnace oil. We seek the product with the minimum API gravity (heaviest). Typical commercial ranges are assumed. Concept / Approach: From lightest to heaviest by boiling range: gasoline > kerosene > diesel > furnace oil (residual/heavy). Since API decreases with increasing density/heaviness, furnace oil—being a residual/heavy fraction—shows the lowest API among these options. Step-by-Step Solution: Order products by typical boiling/density: gasoline (highest API) … furnace oil (lowest API).Recognize the question asks for minimum API → the heaviest material.Select furnace oil. Verification / Alternative check: Typical property tables show furnace oil/HSFO with API often well below mid-distillates. Why Other Options Are Wrong: Gasoline, kerosene, diesel: All are lighter than furnace oil and thus have higher API gravities. Common Pitfalls: Confusing API with specific gravity directly (they are related but inverse); also mixing up “minimum API” with “lowest density.” Final Answer: Furnace oil

Question 15

Edeleanu solvent extraction of kerosene In the Edeleanu process (liquid SO2 extraction at about −20 °C), which component family in kerosene is preferentially reduced to improve burning quality?

Accepted Answer

Introduction / Context: The Edeleanu process uses liquid sulphur dioxide as a selective solvent to improve kerosene quality. Lower aromatic content generally improves smoke point and combustor performance by reducing soot formation. Given Data / Assumptions: Operating temperature is near −20 °C. Feed: kerosene-range hydrocarbons. Goal: enhance burning characteristics (smokeless flame). Concept / Approach: Liquid SO2 preferentially dissolves aromatics. Extraction transfers aromatics into the solvent-rich phase, leaving a raffinate leaner in aromatics. Since aromatics correlate with lower smoke point, their reduction raises the smoke point and improves flame luminosity behavior. Step-by-Step Solution: Note that smoke/soot tendency tracks with aromatic content.Recognize that Edeleanu extraction removes aromatics selectively.Therefore, the process reduces the aromatics in kerosene. Verification / Alternative check: Classic refining texts list Edeleanu under aromatic extraction processes for kerosene/jet precursors. Why Other Options Are Wrong: Paraffins / Naphthenes: These are not the primary targets; they remain largely in the raffinate. Smoke point: Smoke point is a property, not a component family; the process raises smoke point by reducing aromatics. Common Pitfalls: Interpreting the property “smoke point” itself as the thing being extracted; in reality, component removal changes the property. Final Answer: Aromatics

Question 16

Burner handling of heavy oils What is the typical maximum viscosity for tar/PCM/fuel oil to allow easy and efficient atomisation in a conventional pressure jet burner? (Approximate equivalence: 100 Redwood I seconds ≈ 25 cSt.)

Accepted Answer

Introduction / Context: Heavy fuel oils must be heated to reduce viscosity for proper atomisation in burners. Excessive viscosity produces large droplets, poor mixing with air, incomplete combustion, and smoke/soot formation. Given Data / Assumptions: Conventional pressure jet burner (not special twin-fluid/steam atomisers). Rule-of-thumb conversion: 100 Redwood I seconds ≈ 25 centistokes. We seek the practical viscosity ceiling for good atomisation. Concept / Approach: Industry practice targets a modest viscosity at the burner nozzle to balance spray quality and pump handling. A commonly taught benchmark is ~25 cSt (about 100 R1 s). Preheating lines and heaters are adjusted so the oil at the gun meets this condition. Step-by-Step Solution: Relate Redwood I seconds to centistokes using the provided equivalence.Recall burner OEM guidance clustering near 20–30 cSt for pressure atomisers.Select 25 cSt as the maximum target cited in standard guidance for “easy and efficient” atomisation. Verification / Alternative check: Combustion handbooks and burner manuals specify similar nozzle viscosity targets for heavy oils. Why Other Options Are Wrong: 5 cSt: Very low; unnecessary and can hurt pump sealing. 50 / 100 cSt: Too viscous for clean atomisation in conventional burners. Common Pitfalls: Neglecting line temperature drop—measured viscosity should be at the nozzle, not only at the heater outlet. Final Answer: 25 cSt

Question 17

Reforming process families – fixed bed variants Which among the following is classically cited as a non-regenerative fixed-bed catalytic reforming process in older refinery classifications?

Accepted Answer

Introduction / Context: Catalytic reforming converts low-octane naphtha to high-octane reformate. Historically, several branded technologies existed, differing in reactor configuration and how/when catalyst is regenerated. Given Data / Assumptions: We compare historical labels: Platforming (UOP), Hydroforming (Houdry), Thermofor catalytic reforming (moving-bed), and Hyperforming (Exxon family naming in some texts). The classification asked is “non-regenerative fixed-bed” in the legacy exam sense (i.e., not regenerated during on-stream operation). Concept / Approach: Older exam keys often describe Platforming as a fixed-bed process that, in its classical semi-regenerative configuration, runs for a cycle and is then shut down for regeneration—hence “non-regenerative” during the on-stream period. In contrast, Thermofor reforming is moving-bed continuous regeneration; Hydroforming is a fixed-bed but classically cyclic with dedicated regeneration steps; Hyperforming references continuous-regeneration lineage. Step-by-Step Solution: Identify Platforming as fixed-bed with long cycles and no on-stream regen.Recognize others either move catalyst or emphasize cyclic/continuous regeneration modes.Select Platforming for the non-regenerative fixed-bed category. Verification / Alternative check: Legacy refinery training materials frequently group Platforming under fixed-bed units that are regenerated offline at the end of a run. Why Other Options Are Wrong: Hydroforming: Historically cyclic with separate regeneration steps; not classed as “non-regenerative” in the same sense. Thermofor catalytic reforming: Moving-bed/continuous regeneration. Hyperforming: Typically associated with continuous-regeneration developments. Common Pitfalls: Equating “semi-regenerative” with “continuously regenerative.” Semi-regenerative = no on-stream regen, which older notes shorthand as “non-regenerative.” Final Answer: Platforming

Question 18

Fuel oil property prioritisation Which of the following is generally NOT considered a primary/critical property specification for fuel oil (furnace oil) in combustion service?

Accepted Answer

Introduction / Context: Fuel (furnace) oils are specified for safe handling and clean combustion in industrial burners and boilers. Certain properties dominate design and compliance: viscosity (for atomisation), flash point (safety), sulphur (emissions/corrosion), pour point (low-temp flow), and calorific value. Given Data / Assumptions: Service: fuel oil for heaters/boilers/furnaces. We compare four listed properties. We ask which is not a major/primary specification. Concept / Approach: Aniline point is a solvency/aromaticity indicator widely used for kerosene/diesel/lube behaviour inference. For furnace oils, procurement and operation focus far more on viscosity, flash point, sulphur, pour point, water/sediment, and ash/vanadium—aniline point is rarely a controlling spec. Step-by-Step Solution: List common FO specs: viscosity, flash point, sulphur, pour point, CV, contaminants.Observe aniline point is not central to burner operation or compliance for FO.Choose “Aniline point.” Verification / Alternative check: Fuel oil standards (e.g., IS/ASTM grades) emphasise viscosity class, flash point, sulphur, sediment, water—rarely aniline point. Why Other Options Are Wrong: Viscosity: Critical for atomisation design and heating curves. Flash point: Safety-critical for storage/handling. Sulphur: Emissions/corrosion driver; regulatory limits apply. Common Pitfalls: Assuming properties important for middle distillates (diesel/kerosene) automatically apply to heavy fuel oils. Final Answer: Aniline point

Question 19

Thermochemistry of cracking In general refinery practice, the cracking of large hydrocarbons into smaller molecules is thermally what kind of reaction?

Accepted Answer

Introduction / Context: Cracking breaks carbon–carbon bonds to form smaller hydrocarbons (LPG, gasoline-range, etc.). Knowing whether cracking absorbs or releases heat guides reactor design, heat balance, and furnace duty planning. Given Data / Assumptions: Typical thermal/catalytic cracking conditions are considered. No unusual oxidative or hydrogenolysis side reactions are implied. Focus is on net thermal effect of cracking itself. Concept / Approach: Breaking C–C bonds requires energy input; overall, cracking is endothermic. Industrial units supply heat via furnace coils (thermal) or maintain high reactor temperature with catalyst/regenerator heat balance (e.g., FCC uses hot regenerated catalyst to supply endothermic reaction heat). Step-by-Step Solution: Recall bond dissociation: C–C scission needs energy.Recognize process designs include external/indirect heat input for cracking sections.Conclude cracking is endothermic. Verification / Alternative check: FCC heat balance explicitly shows regenerator exotherm (coke burn) supplying riser endotherm; thermal crackers rely on fired heaters. Why Other Options Are Wrong: Exothermic: Opposite of the core reaction’s heat effect. Favoured at very low temperature: Cracking requires high temperature to proceed at practical rates. None of these: Incorrect because one option is correct. Common Pitfalls: Confusing overall unit heat balance (which includes exothermic coke burn) with the intrinsic endothermicity of cracking. Final Answer: An endothermic reaction

Question 20

Reforming feed selection Which stream is generally used as the feed for catalytic reforming to produce high-octane reformate and hydrogen?

Accepted Answer

Introduction / Context: Catalytic reforming boosts octane for gasoline blending and supplies hydrogen for hydrotreating. The choice of feed determines product quality, severity, and catalyst life. Given Data / Assumptions: Standard platforming/CCR reformer conditions. Focus on mainstream refinery routing. Goal is to name the normal feedstock. Concept / Approach: Reforming targets naphtha-range molecules (C6–C8 mostly). Typical feed is straight-run or hydrotreated naphtha, not heavier distillates like AGO/VGO or residues, which are routed to FCC/hydrocracking/residue conversion instead. Step-by-Step Solution: Recall reformer chemistry (naphthenes → aromatics, paraffin isomerisation) best suits naphtha.Exclude heavy feeds (AGO/VGO/residue) that require cracking/hydrotreating pathways instead.Choose naphtha or straight-run gasoline. Verification / Alternative check: Typical refinery flow diagrams show naphtha splitter → hydrotreating → reformer → reformate + H2. Why Other Options Are Wrong: AGO/VGO: Usually to FCC/hydrocracker. Reduced crude: To vacuum distillation/thermal or residue conversion units. Common Pitfalls: Assuming “gas oil” is acceptable feed; reformers do not target those boiling ranges. Final Answer: Naphtha or straight-run gasoline

Petroleum Refinery Engineering Questions