Q: Delayed vs other coking processes in Indian refineries Which coking process is most widely used in Indian oil refineries for residue upgrading?

Introduction / Context: Coking converts vacuum residue into lighter products and petroleum coke. Process selection depends on feed quality, product slate, and capital considerations. Understanding which process is dominant locally aids context for plant operations and exams. Given Data / Assumptions: Indian refinery configuration commonly includes thermal conversion for heavy residues. We compare delayed, flexi-, fluid, and contact coking. Concept / Approach: Delayed coking is the industry workhorse worldwide, including in India, due to its relative simplicity, flexibility to handle diverse residues, and ability to produce marketable needle/sponge coke and valuable naphtha/gasoil. Fluid and flexicoking are specialized and less common, and contact coking is not typical in modern large-scale refineries. Step-by-Step Solution: Identify dominant residue upgrading route → delayed coking drums downstream of a coker heater.Note widespread adoption in Indian complexes to manage high CCR, high asphaltene crudes.Conclude delayed coking is the correct choice. Verification / Alternative check: Public refinery configuration data and project reports show multiple delayed cokers commissioned or planned across India, confirming prevalence. Why Other Options Are Wrong: Flexi-/fluid coking: Less common, higher complexity; specific licensors and fewer installations. Contact coking: Obsolete/rarely used industrially for large modern refineries. Common Pitfalls: Confusing fluid coking with fluid catalytic cracking; FCC is for VGO, not vacuum residue thermal coking. Final Answer: delayed

Q: Safe storage of petroleum products Tanks used to store inflammable petroleum products should be painted with which color to minimize heat absorption and reduce vapor losses?

Introduction / Context: Aboveground storage tanks (ASTs) for volatile petroleum products are exposed to sunlight. Surface color affects solar heat gain, which in turn impacts internal temperature, vapor pressure, breathing losses, and safety margins against overpressure. Given Data / Assumptions: Products are inflammable (e.g., gasoline, naphtha, kerosene). Ambient outdoor installation with solar exposure. Color choice influences thermal loading. Concept / Approach: Lighter colors reflect solar radiation more effectively, lowering tank skin temperature. White has the highest reflectance among common paints. This reduces product heating, vapor generation, and emissions, and helps keep internal pressure and breathing losses lower. Step-by-Step Solution: Goal: minimize heat absorption and vapor losses.Choose high-reflectance color → white.Therefore, paint tanks white for safety and emissions control. Verification / Alternative check: Industry practices and many codes recommend light/white paints for gasoline tanks. Emissions studies confirm lower vapor losses with white coatings versus darker ones. Why Other Options Are Wrong: Black: Maximizes solar absorption; increases temperature and vapor pressure. Red/Yellow: Often used for identification or safety markings, not for minimizing heat absorption on large tank surfaces. Common Pitfalls: Confusing color-coding for pipelines/labels with thermal management of large tank shells; for heat control, reflectance dominates. Final Answer: white

Question 1

Diesel quality index: What is a typical cetane number value for diesel fuel used in heavy-duty trucks under normal specifications?

Accepted Answer

Introduction / Context: Cetane number is the key ignition quality parameter for diesel fuels in compression-ignition engines. It indicates readiness of autoignition and affects cold starting, noise, and combustion smoothness in heavy-duty trucks and buses. Given Data / Assumptions: On-road diesel specifications in many regions target cetane number around the high 40s to low 50s. Engines are designed to operate efficiently without excessive ignition delay at these values. Very low or very high cetane numbers are atypical for general truck diesel supply. Concept / Approach: A cetane number near 50 balances ignition quality, emissions, and refining economics. Too low a cetane causes long ignition delay and knock-like diesel knock; extremely high cetane is not commonly required and may reduce the natural mixing time that assists soot oxidation. Step-by-Step Solution: Identify typical market range: about 45 to 55.Select a representative value for trucks: 50.Reject unrealistic values: 14 is extremely low, 85 is specialized, 35 is low for modern diesel. Verification / Alternative check: Standards such as EN 590 and ASTM D975 require minimum cetane index or number often near 51 or 40–45 minimum depending on grade; practical supply for trucks often centers near 50. Why Other Options Are Wrong: 14 / 35: Too low, would cause poor starting and harsh operation. 85: Not typical for commercial truck diesel; such high values are uncommon and unnecessary. Common Pitfalls: Confusing octane (gasoline) with cetane (diesel); assuming higher is always better regardless of engine design. Final Answer: 50

Question 2

For which liquid is the pour point numerically equal to the freezing point under standard tests, making both limits coincide?

Accepted Answer

Introduction / Context: Pour point and freezing point are low-temperature properties used to describe handling limits of liquids. In petroleum products, these values differ because of complex mixtures and wax crystallization. For a pure substance like water, the behavior is simpler and the two limits coincide under standard equilibrium conditions. Given Data / Assumptions: Pour point: lowest temperature at which oil will just flow when cooled under specific test conditions. Freezing point: temperature at which a liquid becomes a solid at given pressure. Mixtures exhibit a range of solidification behavior; pure water has a sharp phase change. Concept / Approach: Petroleum fractions contain multi-component waxes and asphaltenes, so pour point depends on wax network formation and can be well above any single-component freezing point. In contrast, pure water solidifies at a fixed temperature, and the inability to flow aligns with its freezing point, making pour and freezing points effectively equal. Step-by-Step Solution: Identify which candidate is a single pure compound under test: water.Recognize that for mixtures, pour point is a flow property influenced by wax network, not a sharp freezing transition.Select water as the liquid where pour point equals freezing point. Verification / Alternative check: Standard test methods (ASTM D97 for pour point, water freezing at 0 degree C at 1 atm) confirm the equivalence for water but divergence for petroleum mixtures. Why Other Options Are Wrong: Petrol, diesel, crude: Multi-component systems with wax or light ends; pour point is an operational flow limit and does not equal a unique freezing point. Common Pitfalls: Assuming pour point is a thermodynamic property like freezing point; it is an empirical flow property highly formulation-dependent. Final Answer: Water (pure substance)

Question 3

Solvent refining: Furfural extraction is industrially used to upgrade which petroleum stream by selectively dissolving aromatics and other undesirable species?

Accepted Answer

Introduction / Context: Solvent extraction with polar solvents like furfural, phenol, or NMP is a classic refining step for improving base oil quality. The process removes aromatics and polar compounds that degrade viscosity index, oxidation stability, and color in lubricating oils. Given Data / Assumptions: Furfural is a selective solvent for aromatics at appropriate temperature and solvent-to-oil ratios. Target stream contains significant aromatic content typical of vacuum gas oil range intended for lube base stocks. Desired improvements include higher viscosity index and better thermal stability. Concept / Approach: A two-phase extraction contacts lube distillate with furfural. Aromatics preferentially partition into the solvent-rich extract, while the raffinate is enriched in paraffinic and naphthenic molecules that possess higher viscosity index and better oxidative behavior. Downstream, solvent is recovered and streams are further finished by dewaxing and hydrotreating. Step-by-Step Solution: Define objective: reduce aromatics in lube stock.Choose solvent: furfural due to selectivity for aromatics.Outcome: upgraded lube base oil properties in the raffinate phase. Verification / Alternative check: Refining schemes show furfural extraction units in lube trains prior to solvent dewaxing and hydrofinishing. Performance metrics include viscosity index gain and Conradson carbon reduction. Why Other Options Are Wrong: Naphtha: Typically reformed or hydrotreated; not extracted by furfural for octane uplift. Wax: Upgraded by deoiling and dewaxing, not aromatic extraction. Cracking feed: Quality is adjusted by hydrotreating; extraction is uncommon for FCC feed prep. Common Pitfalls: Confusing solvent extraction for aromatics with solvent dewaxing that targets high pour point paraffins; they are distinct steps. Final Answer: Lubricating oils to improve viscosity index and stability

Question 4

Aviation gasoline specifications: The octane rating assigned to aviation gasoline can reach what approximate level under performance number scales?

Accepted Answer

Introduction / Context: Aviation piston engines demand high knock resistance due to high manifold pressures, supercharging, and severe duty cycles. Aviation gasoline is therefore formulated with very high octane quality, often beyond the conventional motor gasoline scale, and uses performance numbers exceeding 100. Given Data / Assumptions: Octane scales include RON and MON for automotive fuels; aviation uses lean and rich mixture octane ratings with performance numbers. High-performance aviation gasolines historically use tetraethyl lead and optimized blending components. Engines may operate rich to manage cylinder head temperatures and detonation margins. Concept / Approach: Performance numbers extend the scale above 100 by comparing knock-limited power output of the test fuel to that of isooctane with supercharging. As a result, aviation grades such as 100/130 indicate knock ratings beyond 100 under certain mixture conditions. Step-by-Step Solution: Recognize that aviation gasolines exceed 100 in performance number.Select the option representing values above 100.Eliminate lower values typical of automotive grades. Verification / Alternative check: Fuel grade designations like 100LL confirm octane equivalence above 100 for aviation use, matching detonation resistance requirements. Why Other Options Are Wrong: Values of 79, 87, and 97 correspond to automotive fuel ranges and are insufficient for many high-output aircraft piston engines. Common Pitfalls: Confusing automotive RON with aviation performance numbers; forgetting that the aviation scale extends beyond the isooctane cap. Final Answer: >100

Question 5

API gravity trend across crude fractions: Among the listed refinery cuts, which fraction typically exhibits the highest API gravity (i.e., is the lightest)?

Accepted Answer

Introduction / Context: API gravity is an inverse density scale widely used in petroleum production and refining. Higher API indicates lower density and lighter material. Understanding API trends across fractionation cuts helps with blending and product property control. Given Data / Assumptions: Fractions are ranked by normal boiling range: gasoline (lightest), diesel and gas oils (heavier), vacuum gas oil (heaviest among those listed). Higher boiling fractions have higher molecular weight and density. Typical API: gasoline often above 60, diesel around 30–40, gas oils lower. Concept / Approach: Atmospheric distillation separates crude into cuts. Light naphtha and gasoline-range streams have the lowest density and thus the highest API. As boiling range increases to diesel, AGO, and VGO, density rises and API falls. Step-by-Step Solution: Arrange fractions by lightness: gasoline > diesel > AGO > VGO.Highest API corresponds to lightest fraction: gasoline.Choose gasoline as correct. Verification / Alternative check: Crude assay data consistently show gasoline/naphtha cuts with the highest API gravity among distillates. Why Other Options Are Wrong: Diesel, atmospheric gas oil, vacuum gas oil: Progressively heavier, higher density, hence lower API. Common Pitfalls: Assuming API is a quality metric independent of density; it is solely a measure of relative density and does not directly indicate octane or cetane. Final Answer: Gasoline (light naphtha range)

Question 6

Safety property of petroleum products: The flash point of an oil primarily indicates which aspect of product behavior and handling risk?

Accepted Answer

Introduction / Context: Flash point is a critical safety property measured for petroleum liquids to assess ignition risk. It is defined as the lowest temperature at which a liquid generates sufficient vapor to form an ignitable mixture with air that flashes momentarily when an ignition source is applied under specified test conditions (closed cup or open cup). Given Data / Assumptions: Measured by standard methods such as ASTM D56, D93, or D92 depending on product class. Used for classification in transport regulations and for selecting safe storage temperatures. Lower flash point generally implies higher volatility and greater fire hazard. Concept / Approach: While flash point correlates with the presence of lighter ends, the core purpose of the test is safety evaluation. The temperature at which vapors ignite gives direct insight into fire and explosion hazards during routine handling, blending, or heating. Refiners also use flash point to ensure product meets specification limits for applications like kerosene and diesel. Step-by-Step Solution: Define flash point and test outcome.Relate lower flash point to higher hazard due to easier vapor formation.Select the answer emphasizing hazard indication: explosion and fire hazards. Verification / Alternative check: Material safety data sheets and transport regulations classify liquids by flash point to determine handling precautions and storage requirements, confirming its role as a hazard indicator. Why Other Options Are Wrong: Boiling point diagram: Flash point does not reveal phase diagram details. Amount of low-boiling fraction: There is correlation, but the principal use and definition target hazard assessment rather than compositional analysis. All of the above: Incorrect because part (a) is not a valid implication of flash point. Common Pitfalls: Assuming flash point equals autoignition temperature; mixing up open cup and closed cup methods and their differing values; using flash point as a direct compositional measurement. Final Answer: Explosion and fire hazards during storage and handling

Question 7

Petroleum products – assessing kerosene quality The illuminating characteristics (tendency to burn without smoke and with a steady flame) of kerosene are commonly expressed by its:

Accepted Answer

Introduction / Context: Kerosene is widely used as an illumination and heating fuel. A key quality attribute is how cleanly it burns. Refiners and users rely on standard tests to evaluate the smoke-free burning behavior, which directly impacts wick fouling, odor, and indoor air quality. Given Data / Assumptions: Kerosene is a middle-distillate petroleum fraction. We seek the standard industry measure for illuminating tendency. Comparisons with other property tests (aniline point, aromatic content) are included as distractors. Concept / Approach: The smoke point test determines the maximum flame height (in millimeters) at which a fuel burns without producing smoke under specified conditions. Higher smoke point implies fewer aromatics and better illumination quality. It is the accepted measure for evaluating kerosene's smoke-free burning behavior. Step-by-Step Solution: Identify the property that quantifies smoke-free flame height → smoke point.Recall that fuels with higher smoke points generally have lower aromatic content and better combustion behavior in lamps and burners.Conclude smoke point is the correct metric for illuminating characteristics. Verification / Alternative check: Specifications for kerosene (e.g., aviation kerosene/illumination kerosene) include minimum smoke point values, confirming its industry-standard status for illumination quality assessment. Why Other Options Are Wrong: Aniline point: Indicates aromaticity and solvency toward rubber, not direct illuminating tendency. Luminosity number: Not a standard specification metric for kerosene quality in modern practice. Aromatic content: Correlates inversely with smoke point but is not itself the practical field test for illumination quality. Common Pitfalls: Assuming high aniline point equals high smoke point; while related to composition, the smoke point test directly measures visible smoke formation and is the accepted quality indicator. Final Answer: smoke point

Question 8

Kerosene composition – most undesirable component for clean burning Which class of hydrocarbons is considered most undesirable in kerosene due to soot formation and low smoke point?

Accepted Answer

Introduction / Context: Kerosene quality for illumination and combustion hinges on clean burning with minimal smoke. Hydrocarbon classes influence flame chemistry, soot precursors, and ultimately the smoke point. Understanding which constituents are most detrimental guides refining and hydrotreating strategies. Given Data / Assumptions: Typical kerosene contains paraffins (normal and iso-), naphthenes (cycloalkanes), and aromatics. Objective: identify the fraction linked to higher soot formation. Smoke point is a proxy for clean burning; higher is better. Concept / Approach: Aromatics have ring structures that favor soot formation via polycyclic aromatic hydrocarbon growth. They depress smoke point and lead to luminous, smoky flames. In contrast, paraffins and naphthenes generally burn cleaner, with normal paraffins usually giving the highest smoke points among the listed classes. Step-by-Step Solution: Relate aromatic content to smoke point: more aromatics → lower smoke point → more smoke/soot.Compare to other classes: n-paraffins > i-paraffins > naphthenes > aromatics in terms of increasing smoke tendency.Therefore, aromatics are the most undesirable component for clean-burning kerosene. Verification / Alternative check: Refinery practices (hydrotreating and selective hydrocracking) aim to reduce aromatics in kerosene pool to meet smoke point specifications, confirming their undesirability for illumination use. Why Other Options Are Wrong: i-paraffins / n-paraffins: Generally high smoke points; desirable for clean combustion. Naphthenes: Intermediate behavior; less problematic than aromatics. Common Pitfalls: Equating density with poor burning; density alone is not determinant—aromatic ring structures dominate soot chemistry. Final Answer: Aromatics

Question 9

Viscosity comparison among refinery streams (same temperature) Which of the following petroleum fractions has the lowest viscosity at a given temperature?

Accepted Answer

Introduction / Context: Viscosity directly affects pumping, atomization, and processing of petroleum fractions. Lighter fractions flow more easily; heavier fractions resist flow. Identifying relative viscosity among common streams is fundamental in refinery operations and equipment sizing. Given Data / Assumptions: All streams are compared at the same temperature. Typical cuts: naphtha (light), kerosene (middle), diesel (heavier middle), lube oil (heavy). No additives or unusual compositions considered. Concept / Approach: For hydrocarbon mixtures, viscosity generally increases with average molecular weight and boiling range. Therefore, among the listed options, the lightest fraction (naphtha) exhibits the lowest viscosity at a given temperature. Step-by-Step Solution: Order by cut lightness: naphtha < kerosene < diesel < lube oil.Correlate cut order with viscosity: lighter → lower viscosity.Conclude naphtha has the lowest viscosity. Verification / Alternative check: Viscosity–temperature charts and ASTM D445 data for typical refinery streams show naphtha viscosities near water-like values at ambient, while lube oils are orders of magnitude higher. Why Other Options Are Wrong: Kerosene, diesel: Heavier than naphtha; higher viscosities. Lube oil: Intentionally high viscosity for lubrication film strength; the highest among choices. Common Pitfalls: Assuming aromatic content alone governs viscosity; cut boiling range and molecular weight distribution are primary drivers for these bulk comparisons. Final Answer: Naphtha

Question 10

Delayed vs other coking processes in Indian refineries Which coking process is most widely used in Indian oil refineries for residue upgrading?

Accepted Answer

Introduction / Context: Coking converts vacuum residue into lighter products and petroleum coke. Process selection depends on feed quality, product slate, and capital considerations. Understanding which process is dominant locally aids context for plant operations and exams. Given Data / Assumptions: Indian refinery configuration commonly includes thermal conversion for heavy residues. We compare delayed, flexi-, fluid, and contact coking. Concept / Approach: Delayed coking is the industry workhorse worldwide, including in India, due to its relative simplicity, flexibility to handle diverse residues, and ability to produce marketable needle/sponge coke and valuable naphtha/gasoil. Fluid and flexicoking are specialized and less common, and contact coking is not typical in modern large-scale refineries. Step-by-Step Solution: Identify dominant residue upgrading route → delayed coking drums downstream of a coker heater.Note widespread adoption in Indian complexes to manage high CCR, high asphaltene crudes.Conclude delayed coking is the correct choice. Verification / Alternative check: Public refinery configuration data and project reports show multiple delayed cokers commissioned or planned across India, confirming prevalence. Why Other Options Are Wrong: Flexi-/fluid coking: Less common, higher complexity; specific licensors and fewer installations. Contact coking: Obsolete/rarely used industrially for large modern refineries. Common Pitfalls: Confusing fluid coking with fluid catalytic cracking; FCC is for VGO, not vacuum residue thermal coking. Final Answer: delayed

Question 11

Safe storage of petroleum products Tanks used to store inflammable petroleum products should be painted with which color to minimize heat absorption and reduce vapor losses?

Accepted Answer

Introduction / Context: Aboveground storage tanks (ASTs) for volatile petroleum products are exposed to sunlight. Surface color affects solar heat gain, which in turn impacts internal temperature, vapor pressure, breathing losses, and safety margins against overpressure. Given Data / Assumptions: Products are inflammable (e.g., gasoline, naphtha, kerosene). Ambient outdoor installation with solar exposure. Color choice influences thermal loading. Concept / Approach: Lighter colors reflect solar radiation more effectively, lowering tank skin temperature. White has the highest reflectance among common paints. This reduces product heating, vapor generation, and emissions, and helps keep internal pressure and breathing losses lower. Step-by-Step Solution: Goal: minimize heat absorption and vapor losses.Choose high-reflectance color → white.Therefore, paint tanks white for safety and emissions control. Verification / Alternative check: Industry practices and many codes recommend light/white paints for gasoline tanks. Emissions studies confirm lower vapor losses with white coatings versus darker ones. Why Other Options Are Wrong: Black: Maximizes solar absorption; increases temperature and vapor pressure. Red/Yellow: Often used for identification or safety markings, not for minimizing heat absorption on large tank surfaces. Common Pitfalls: Confusing color-coding for pipelines/labels with thermal management of large tank shells; for heat control, reflectance dominates. Final Answer: white

Question 12

Catalytic reforming – typical catalyst system Identify the commonly used catalyst for catalytic reforming of naphtha to improve octane number and produce aromatics/hydrogen.

Accepted Answer

Introduction / Context: Catalytic reforming upgrades low-octane naphtha to high-octane reformate for gasoline blending and generates valuable hydrogen. The process relies on bifunctional catalysis to promote dehydrogenation, isomerization, and cyclization reactions. Given Data / Assumptions: Naphtha range feed, presence of paraffins and naphthenes. Desired reactions: dehydrogenation to aromatics, isomerization, hydrocracking (controlled). Commercial continuous catalyst regeneration (CCR) or semi-regenerative units. Concept / Approach: Platinum on chlorided alumina (Pt/Al2O3) is the classic reforming catalyst. Platinum provides dehydrogenation/hydrogenation sites, while acidic alumina (often promoted with chloride) provides isomerization/cyclization functionality. Other metals like rhenium may be added, but the base system is Pt/Al2O3. Step-by-Step Solution: Match process needs (bifunctional) with catalyst: metallic Pt + acidic alumina.Recognize industry-standard: Pt/Al2O3 (with promoters in some formulations).Select platinum on alumina as the correct answer. Verification / Alternative check: Licensors (e.g., UOP, Axens) specify Pt/Al2O3-based systems for reforming, corroborating the choice. Why Other Options Are Wrong: Nickel/iron: Typical for hydrogenation or ammonia synthesis, not reforming selectivity. Aluminium chloride: Lewis acid used in alkylation/polymerization, not standard reforming catalyst. Common Pitfalls: Confusing catalytic reforming with catalytic cracking; FCC uses acidic zeolites at low hydrogen partial pressure, not Pt on alumina. Final Answer: platinum on alumina

Question 13

Refining chemistry – converting normal paraffins Which refinery process converts n-paraffins to i-paraffins, thereby improving octane number?

Accepted Answer

Introduction / Context: Octane improvement can be achieved by altering hydrocarbon structure. Straight-chain paraffins have low octane; branching increases octane. Refineries use specific catalytic routes to rearrange molecules without major carbon number change. Given Data / Assumptions: Feed contains normal paraffins (e.g., C4–C6). Goal: increase branching to raise octane while preserving carbon number. Low-temperature catalytic processes under hydrogen are available. Concept / Approach: Isomerisation catalytically rearranges straight-chain paraffins into isoparaffins. Over bifunctional catalysts (e.g., Pt on chlorided alumina or zeolites), skeletal rearrangement proceeds with minimal cracking, significantly boosting octane in light naphtha pools. Step-by-Step Solution: Identify structural change: straight-chain → branched.Choose process that rearranges but does not add/remove carbon atoms → isomerisation.Thus, isomerisation is correct. Verification / Alternative check: Process flow diagrams for light naphtha isomerization units confirm production of isopentane/isomerized C6, improving pool octane. Why Other Options Are Wrong: Alkylation: Combines isobutane with light olefins to form higher isoparaffins; not a simple n-paraffin → i-paraffin rearrangement. Polymerisation: Joins small olefins into larger molecules; different objective. None of these: Incorrect because isomerisation is the standard route. Common Pitfalls: Confusing isomerisation (rearrangement) with cracking (carbon number change). Operating severity must avoid excessive cracking to retain yield. Final Answer: Isomerisation

Question 14

Sweetening of petroleum fractions – Doctor's treatment In the traditional Doctor's treatment process for removing mercaptans (sweetening), the key reagent in the solution is:

Accepted Answer

Introduction / Context: Mercaptans (R–SH) in petroleum streams cause odor and corrosion. The Doctor's treatment is a classic sweetening process used historically to convert mercaptans to disulfides, reducing odor and improving product quality. Given Data / Assumptions: Treatment applied to lighter petroleum fractions. Alkaline solution is used along with a lead compound and elemental sulfur. Objective is oxidation of mercaptans to disulfides. Concept / Approach: Doctor's solution consists of sodium plumbite (Na2PbO2) in sodium hydroxide. In the presence of sulfur, mercaptans are converted to disulfides (RSSR), which are less odorous and remain in the oil phase. Sodium plumbite acts as a catalyst/oxidant species in the alkaline environment. Step-by-Step Solution: Identify traditional mercaptan sweetening route → Doctor's treatment.Recall composition: sodium plumbite in NaOH with added sulfur.Select sodium plumbite as the key reagent. Verification / Alternative check: Refining texts list Doctor's solution as Na2PbO2/NaOH; modern processes use alternative catalysts to avoid lead, but the classical answer remains sodium plumbite. Why Other Options Are Wrong: Sodium hydroxide: Present as solvent/base but not the distinctive Doctor reagent. Cupric chloride / potassium isobutyrate: Not used in the Doctor process; other sweetening or extraction schemes exist. Common Pitfalls: Confusing Doctor's treatment with Merox (mercaptan oxidation using cobalt/molybdenum catalysts); the key reagent in the classical Doctor method is sodium plumbite. Final Answer: sodium plumbite

Question 15

Solvent selection for lube oil dewaxing Which of the following is an undesirable property for a solvent intended for dewaxing of lubricating oil?

Accepted Answer

Introduction / Context: Dewaxing removes high-melting paraffins from lubricating oil to improve pour point and low-temperature flow. Solvent dewaxing relies on crystallizing wax from a diluted oil–solvent mixture at low temperature and filtering the crystals. Solvent choice critically affects wax crystallization and filterability. Given Data / Assumptions: Typical dewaxing solvents: methyl ethyl ketone (MEK), toluene, methyl isobutyl ketone (MIBK), propane (for propane dewaxing). Process involves chilling to precipitate wax crystals for separation. We seek the property that is undesirable for effective wax removal. Concept / Approach: An effective dewaxing solvent should dissolve the oil well (to reduce viscosity and aid heat transfer) but should not dissolve wax at low temperature so that wax crystallizes out cleanly. Therefore, complete miscibility with oil is beneficial, while high wax solubility is detrimental because it suppresses wax crystallization and reduces removal efficiency. Step-by-Step Solution: Goal: maximize wax precipitation at low T while keeping slurry pumpable.Choose solvent attributes: good oil miscibility (desirable), low wax solubility at dewaxing temperature (desirable).Thus, high solubility of wax in the solvent is undesirable. Verification / Alternative check: Phase diagrams and solvent selection literature for MEK–toluene blends show that wax solubility drops sharply at low temperature, enabling effective crystallization; processes are designed to exploit this behavior. Why Other Options Are Wrong: Complete miscibility with oil: Desirable for viscosity reduction and uniform crystallization. Both (a) and (b) / Neither: Incorrect because only high wax solubility is undesirable. Common Pitfalls: Operating too warm or selecting a solvent blend that keeps wax in solution; both reduce filtration rates and leave residual wax, harming pour point. Final Answer: High solubility of wax in the solvent.

Question 16

In petroleum refining terminology, what does the “stabilization” of gasoline (petrol) specifically aim to achieve in order to make the product safer to store and ship?

Accepted Answer

Introduction: Gasoline stabilization is a routine finishing step in refineries before storage and distribution. The primary purpose is to make the product safe and consistent by controlling the tendency to form excessive vapour, which can cause operational issues like vapour lock and increase flammability risk. Understanding what “stabilization” actually removes helps distinguish it from other quality-improving treatments such as oxidation stability improvement or lead susceptibility modification. Given Data / Assumptions: Product: motor gasoline (petrol). Operation occurs after initial fractionation/blending. Stabilization is carried out in a stabilizer column or flash system. Concept / Approach: Stabilization reduces the Reid Vapour Pressure (RVP) by flashing off and stripping dissolved gases and the most volatile hydrocarbons (C3–C4 range and lighter). This decreases vapour formation at ambient conditions and improves handling safety. It is different from adding antioxidants (oxidation stability) or octane enhancement measures; those are separate treatments. Step-by-Step Solution: Define stabilization goal: reduce excessive volatility for storage and transport safety.Identify method: remove dissolved gases and very light ends via flashing/stripping in a stabilizer column.Result: lower RVP, fewer vapour emissions, reduced vapour-lock risk. Verification / Alternative check: Material balance around a stabilizer shows light ends leaving overhead (fuel gas/LPG), with stabilized gasoline withdrawn from the bottom at a specified RVP suitable for marketing or further blending. Why Other Options Are Wrong: Increasing oxidation stability: relevant to gum formation control but not the definition of stabilization. Improving lead susceptibility: legacy octane-upgrading concept, unrelated to stabilization. Increasing vapour pressure: opposite of the stabilization objective. Common Pitfalls: Confusing stabilizer service with debutanizer/depropanizer units; while similar, the goal here is finished product RVP control, not pure LPG recovery alone. Final Answer: Removal of dissolved gases and very light ends from it

Question 17

Refinery furnace selection: which heater type is most commonly used to raise crude oil temperature before it enters the atmospheric fractionation tower?

Accepted Answer

Introduction: Before crude oil enters the atmospheric distillation column, it must be heated to near its flash zone temperature to vaporize distillable fractions. The equipment choice impacts fuel efficiency, coking tendency, and run length. This question focuses on the standard refinery practice for front-end heating of crude feeds. Given Data / Assumptions: Service: preheating crude oil to 320–380°C (typical range) before fractionation. Large throughputs and continuous operation. Fuel firing with heat recovery via preheat trains is common. Concept / Approach: The industry-standard unit is a pipestill fired heater (often called the crude furnace). Crude flows through tubes in radiant and convection sections, picking up heat from combustion gases. Electric immersion heaters are unsuitable for such high flow and temperature duties at scale; steam coil heaters cannot achieve the required final temperature economically for large crude rates. Step-by-Step Solution: Identify duty: bring crude to flash-zone approach temperature.Select heater capable of high, controllable outlet temperatures with good film coefficients: pipestill fired heater.Confirm practicality: widely used, compatible with heat-integration trains. Verification / Alternative check: Typical PFDs show crude preheat by heat exchangers (against product side-draws) followed by a pipestill furnace to reach the final target temperature before the atmospheric column. Why Other Options Are Wrong: Electric immersion: impractical at refinery crude rates and temperatures. Steam coils: limited approach temperature and high steam consumption. None of these: contradicts common practice. Common Pitfalls: Ignoring tube metal temperature limits and coking risk; these are handled by proper firing, residence time control, and decoking schedules in pipestill heaters. Final Answer: Pipestill fired heater (crude furnace)

Question 18

Crude assay methods: the True Boiling Point (TBP) distillation apparatus is primarily used for which refinery/lab purpose?

Accepted Answer

Introduction: Crude assay provides the foundational data for refinery planning. The True Boiling Point (TBP) distillation curve is one of the most informative characterizations, guiding cut points for naphtha, kerosene, gas oil, and residue and informing yields and qualities for downstream units. Given Data / Assumptions: TBP distillation is a laboratory method with high reflux and equilibrium-like conditions. Used on crude oils and wide boiling-range fractions. Output: temperature vs. volume percent distilled curve. Concept / Approach: TBP distillation gives a near-equilibrium boiling curve, unlike simple or ASTM D86 methods. Refiners use the TBP curve for cut planning, unit feed predictions, and property correlations. It is not intended for direct true vapour pressure measurement, and characterization factor (K) is computed from density and boiling relationships, not solely from the TBP apparatus itself. Step-by-Step Solution: Define TBP purpose: detailed distillation profile for evaluation of stocks.Connect to refinery planning: select cut points and estimate yields/qualities.Conclude: the apparatus is for evaluation of oil stocks. Verification / Alternative check: Assay reports list TBP curves and derived PNA (paraffin-naphthene-aromatic) and property correlations used in LP planning models and blend optimizations. Why Other Options Are Wrong: Characterization factor: a derived index (e.g., Watson K), not a direct TBP apparatus output. True vapour pressure: measured by separate RVP/TVP methods. None of these: incorrect, as TBP is indeed for stock evaluation. Common Pitfalls: Confusing ASTM D86/D1160 with TBP; TBP aims to approximate equilibrium distillation more closely with higher theoretical plates. Final Answer: Evaluation of oil stocks via detailed distillation curve (cut planning)

Question 19

Product treating: the Unisol process (using caustic soda with methyl alcohol) is employed for the complete removal of which impurity from gasoline?

Accepted Answer

Introduction: Gasoline “sweetening” aims to reduce odour and corrosivity by removing sulphur species, especially mercaptans. Several processes exist, but Unisol is a specific extraction-based method using caustic with alcohol to enhance solubility and mass transfer of sulphur compounds. Given Data / Assumptions: Process: Unisol (caustic soda + methyl alcohol). Feed: gasoline-range hydrocarbons. Target: specific sulphur species removal. Concept / Approach: Mercaptans (R–SH) can be extracted into an alkaline methanolic phase, forming mercaptides that preferentially partition out of the hydrocarbon phase. This differs from oxidation sweetening (e.g., Merox), where mercaptans are oxidized to disulphides. Waxes and asphalt are high–molecular weight non-volatile species irrelevant to gasoline; diolefins affect gum formation but are not the Unisol target. Step-by-Step Solution: Identify impurity: mercaptans cause odour/corrosion.Apply Unisol: extract with NaOH/methanol to remove R–SH.Result: “sweet” gasoline with lower mercaptan sulphur. Verification / Alternative check: Refinery treating schemes often show Unisol/Merox options depending on product slate and sulphur specifications. Lab tests (doctor test) confirm sweetening efficacy. Why Other Options Are Wrong: Waxes/asphalt: not present in the gasoline range; removed in other refinery steps. Diolefins: managed by hydrotreating/polymerization control, not Unisol extraction. Common Pitfalls: Confusing extraction sweetening with catalytic oxidation sweetening; selection depends on sulphur spec and economics. Final Answer: Mercaptans (sulphur compounds)

Question 20

Flash point testing of atmospheric distillation residue (heavy, high-flash petroleum fraction): which standard apparatus is appropriate?

Accepted Answer

Introduction: Flash point indicates the lowest temperature at which vapours above a liquid ignite momentarily in the presence of a flame. The correct apparatus depends on volatility: lighter products are tested in closed cups; very heavy, high-flash materials are typically tested in an open cup. Atmospheric distillation residue is a heavy fraction with very high flash point, guiding the apparatus choice. Given Data / Assumptions: Sample: atmospheric residue (long residue), very low volatility. Need: appropriate standardized method. Typical flash points: well above those of gasoline/kerosene. Concept / Approach: Cleveland Open Cup (COC) is commonly specified for heavy oils, lube stocks, and residues with high flash points, as the open configuration is more suitable for less volatile samples and aligns with historical standards for high flash materials. Pensky–Martens and Abel closed cup methods target products with lower flash points (e.g., diesel/gas oil, low-flash distillates), though PMCC is used widely for fuel oils; for very heavy residues, COC is the classical method. Step-by-Step Solution: Classify material: heavy residue → high flash point.Select test: Cleveland Open Cup aligns with heavy, high-flash fractions.Conclude: use Cleveland (open cup) apparatus. Verification / Alternative check: Refinery test plans often list COC for asphaltic residues and base oils, whereas closed cup methods are standard for middle distillates and solvents. Why Other Options Are Wrong: Pensky–Martens and Abel: better for lower flash point materials. None of these: incorrect, as COC is appropriate. Common Pitfalls: Assuming one method fits all; misapplication can under- or over-estimate flash point, affecting safety ratings and shipping classifications. Final Answer: Cleveland (open cup) apparatus

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