Petroleum Refinery Engineering — Part 1 MCQs with Explanations

Definition: The aniline point of an oil is the minimum temperature at which the oil is completely miscible with an equal volume of aniline. Purpose of test: It is used as a qualitative measure of the aromatic content in petroleum oils. Reason: Aromatic hydrocarbons mix more readily with aniline than paraffinic hydrocarbons, resulting in a lower aniline point for oils with higher aromatic content. Conversely, oils rich in paraffins have higher aniline points. Conclusion: The aniline point test gives an indication of the aromatic content of an oil — lower aniline point means higher aromatic content, and higher aniline point means lower aromatic content.

The presence of predominantly large quantities of aromatics (polynuclear) in aviation fuel is undesirable due to several reasons, leading to various negative effects on the fuel's properties and performance. These include: High pour point: Aromatics can contribute to higher pour points, which can lead to poor flow characteristics at low temperatures, affecting the fuel's ability to flow through fuel systems and into engines during cold weather conditions. Low smoke point: Aromatics tend to have lower smoke points, which can result in increased smoke production during combustion. This can lead to reduced visibility, increased emissions, and potential operational issues. Low viscosity index: Aromatics can lower the viscosity index of the fuel, which affects its ability to lubricate and provide proper protection to engine components. High self-ignition temperature: Aromatics can contribute to a higher self-ignition temperature, making the fuel more prone to autoignition, especially at high temperatures and pressures, which can lead to engine knocking and other performance problems. Considering these negative effects, the correct answer is Option D: All of the above , as all of these factors contribute to the undesirability of predominantly large quantities of aromatics in aviation fuel.

Let's break down why Paraffins are the correct answer. Understanding the Fuels: * Gasoline needs to resist "knocking" (a harmful rattling sound in the engine). Fuel's ability to resist knocking is measured by its octane number . A higher octane number is better for gasoline. * Diesel needs to ignite easily and burn smoothly after being injected into the engine. This quality is measured by its cetane number . A higher cetane number is better for diesel. * Kerosene is used for lamps, heaters, and jet fuel. It needs to burn cleanly and provide good heat. Now let's look at the options: 1. Paraffins (Option C): * For Gasoline : Straight-chain paraffins (a type of hydrocarbon) have a low octane number . This means they make gasoline more prone to knocking. So, paraffins are undesirable in gasoline . * For Diesel : Paraffins have a high cetane number . This means they help diesel fuel ignite very easily and burn efficiently, which is exactly what diesel engines need. So, paraffins are desirable in diesel . * For Kerosene : Paraffins help kerosene burn cleanly and provide good heating value , making them desirable in kerosene as well. Because paraffins are undesirable in gasoline but desirable in diesel and kerosene, this option perfectly matches the question. 2. Aromatics (Option A): * Aromatics generally have a high octane number , which means they are actually desirable in gasoline to prevent knocking. Therefore, they don't fit the "undesirable in gasoline" part of the question. 3. Mercaptans (Option B) and Naphthenic acid (Option D): * Both Mercaptans (sulfur compounds that cause bad smell and corrosion) and Naphthenic acids (corrosive compounds) are always undesirable in ALL fuels (gasoline, diesel, kerosene). They cause problems like corrosion and need to be removed during refining. They are never considered "desirable" in any of these fuels. Therefore, the only option that fits the description of being undesirable in gasoline but desirable in diesel and kerosene is Paraffins .

Fluid Catalytic Cracking (FCC) is a catalytic conversion process used to break heavy hydrocarbons into lighter fractions like gasoline and olefins. It operates without external hydrogen and may even produce a small amount of hydrogen as a byproduct . Visbreaking is a mild thermal cracking process aimed at reducing the viscosity of heavy residues. It relies solely on heat and does not involve or consume hydrogen . Propane Deasphalting is a solvent extraction process where propane separates asphalt from deasphalted oil based on solubility differences. Since it is not a chemical reaction process, hydrogen is neither required nor consumed . Processes that consume hydrogen in refineries are typically hydroprocessing units such as hydrotreating and hydrocracking. Since none of the given options fall under this category, the correct answer is none of these .

The cetane number is a measure of the ignition quality of diesel fuel, indicating how quickly the fuel ignites after injection into the engine. Higher cetane number means shorter ignition delay and better combustion efficiency in diesel engines. Amyl nitrate is commonly used as a cetane improver because it decomposes easily under compression, helping in faster ignition of diesel fuel . Ethyl mercaptan is mainly used as an odorant in LPG for leak detection and does not improve cetane number. Naphthenic acid is associated with corrosion issues in petroleum refining and has no role in improving cetane number. Tetraethyl lead is an anti-knock agent used in petrol (gasoline) to improve octane number, not cetane number. Therefore, Amyl nitrate is the correct additive that improves the cetane number of diesel .

In petroleum refinery engineering, the additive used for improving the cetane number of diesel is Tetraethyl lead (Option A). The cetane number is a measure of the ignition quality of diesel fuel. Higher cetane numbers indicate better ignition quality, leading to smoother engine operation, reduced noise, and lower emissions. Tetraethyl lead is one of the additives used to increase the cetane number of diesel fuel by improving its combustion characteristics. Therefore, the correct option is Option A: Tetraethyl lead .

In petroleum refinery engineering, gasoline extracted from natural gas by compression and cooling is referred to as casing head gasoline (Option C). Casing head gasoline is a type of natural gasoline obtained during the initial processing of natural gas. It is typically a mixture of hydrocarbons with relatively low octane ratings compared to other types of gasoline. Casing head gasoline is used as a fuel or as a feedstock in various chemical processes. Therefore, the correct option is Option C: Casing head .

The correct answer is B: Vacuum residue . Here's why: Coking is a process that uses heat to break down large, heavy hydrocarbon molecules into smaller, lighter ones and solid carbon (coke). Vacuum residue is the heaviest fraction remaining after vacuum distillation of crude oil. It contains the largest and most complex molecules , making it the most suitable feedstock for coking. Let's look at the other options: Naphtha, Light gas oil and Diesel are all relatively lighter fractions with smaller molecules . They do not contain enough of the heavy components required for efficient coke production. These fractions are generally used as gasoline, diesel fuel, and heating oil. Therefore, vacuum residue is the most ideal feed for coking because it maximizes coke production.

In petroleum refinery engineering, the water content in crude oil as it comes out of the oil well may be as high as 25 percent (Option D). Crude oil extracted from oil wells often contains various impurities, including water, sediments, and gases. The water content in crude oil can vary depending on factors such as the geological formation of the oil reservoir and the methods used for oil extraction. In some cases, crude oil may contain significant amounts of water, up to 25 percent or more, which needs to be separated and removed during the refining process. Therefore, the correct option is Option D: 25 .

In petroleum refinery engineering, the research octane number (RON) refers to high octane number motor fuels (Option B). The research octane number (RON) is a measure of the anti-knock properties of motor fuels. Higher RON values indicate better resistance to knocking or detonation in spark-ignition engines. Fuels with high RON values are desirable for use in high-performance engines or engines with high compression ratios, as they help prevent knocking and improve engine efficiency. Therefore, the correct option is Option B: High octane number motor fuels .

In petroleum refinery engineering, the Saybolt chromometer is used to determine the color of petroleum products. The Saybolt chromometer measures the color of petroleum products by comparing them to standard color discs under standardized lighting conditions. It provides a numerical value representing the color, which is used to assess the quality and purity of the petroleum product. Therefore, the correct option is Option B: Saybolt chromometer .

In petroleum refinery engineering, aromatics are the hydrocarbons having the poorest oxidation stability. Aromatics, such as benzene, toluene, and xylene, contain one or more benzene rings in their molecular structure. These compounds are highly reactive and prone to oxidation, which can lead to the formation of harmful by-products and degradation of the petroleum product's quality over time. Therefore, the correct option is Option D: Aromatics .

The cetane number of diesel is a measure of its ignition quality or how easily the fuel ignites under compression in a diesel engine. For diesel fuel used in trucks, the cetane number is typically around 50 , which ensures efficient combustion and engine performance. A higher cetane number indicates better ignition properties, leading to smoother engine operation and reduced emissions. Therefore, Option A: 50 is the correct answer.

In the electrical desalting process of crude oil, the main objective is to remove salts and other impurities by mixing the crude oil with water and applying an electric field. The typical operating conditions for this process involve maintaining a pressure of 10 kg/cm 2 and a temperature of 120°C . These conditions are optimal for the efficient separation of impurities from the crude oil. Therefore, Option A: 10 and 120 is the correct answer.

Hydrogen to carbon (H/C) ratio is higher for lighter hydrocarbon fractions and decreases as the molecular weight increases. Naphtha is a lighter petroleum fraction composed of smaller hydrocarbon molecules, so it has a higher hydrogen content relative to carbon . Gasoline is slightly heavier than naphtha and therefore has a lower H/C ratio compared to naphtha. Diesel contains longer hydrocarbon chains, resulting in a further reduced hydrogen to carbon ratio . Fuel oil is the heaviest among the options with large, complex molecules and thus has the lowest H/C ratio . Hence, naphtha has the maximum hydrogen/carbon ratio among the given options.

The grading of paraffin waxes is primarily based on their melting point . The melting point is a critical parameter because it determines the temperature at which the wax transitions from a solid to a liquid state. Different applications require paraffin waxes with specific melting points to ensure proper performance. Therefore, Option B: Melting point is the correct answer.

In petroleum refinery engineering, gasoline fraction of a crude oil will have the maximum gravity API (°API). The gravity API (°API) is a measure of the density of petroleum liquids compared to water. Higher API gravity values indicate lighter and less dense liquids. Gasoline is typically one of the lightest fractions obtained from crude oil refining processes, and therefore, it tends to have the highest API gravity among the options provided. Therefore, the correct option is Option B: Gasoline .

Option A: Diesel - Diesel is a petroleum distillate commonly used as fuel in compression-ignition engines. The aniline point of diesel is typically higher compared to naphtha or gasoline. Diesel contains fewer aromatic hydrocarbons compared to naphtha, which results in a higher aniline point. Option B: LPG - LPG (liquefied petroleum gas) consists primarily of propane and butane. It is not typically tested for aniline point as it is composed mainly of aliphatic hydrocarbons, which have lower aromatic content compared to naphtha. Option C: Naphtha - Naphtha is a petroleum fraction containing a mixture of hydrocarbons, including both aliphatic and aromatic compounds. The aniline point of naphtha is determined by the temperature at which it becomes completely miscible with an equal volume of aniline. Naphtha contains a significant amount of aromatic hydrocarbons, which contribute to its aniline point. Option D: Gasoline - Gasoline, like naphtha, is a petroleum fraction containing a mixture of hydrocarbons. It typically contains a higher proportion of light hydrocarbons and fewer aromatics compared to naphtha. Gasoline tends to have a lower aniline point compared to naphtha due to its lower aromatic content. Conclusion: Among the options provided, Option C: Naphtha is the petroleum product commonly associated with the aniline point. Naphtha contains a significant amount of aromatic hydrocarbons, which influence its aniline point. Therefore, the correct answer is Option C: Naphtha .

LPG (Liquefied Petroleum Gas) is mainly a mixture of propane and butane , and its volatility is controlled through standard specifications. The 95% evaporation temperature at 760 mm Hg (atmospheric pressure) is an important quality parameter that ensures proper vaporization and limits the presence of heavier hydrocarbons. According to standard specifications (such as ASTM/IS standards ), for commercial LPG (especially butane-rich mixtures), the 95% evaporation temperature is around 2°C . -40°C corresponds approximately to the boiling point of propane and does not represent the 95% evaporation condition of commercial LPG mixtures. Higher values like 30°C and 55°C indicate the presence of heavier components, which are undesirable in LPG. Therefore, the correct answer is 2°C .

In petroleum refinery engineering, casing head gasoline is the liquid gasoline separated from wet natural gas by compression (Option D). Casing head gasoline is obtained during the initial processing of natural gas. When natural gas is extracted from underground reservoirs, it often contains liquid hydrocarbons, including gasoline, which are separated from the gas stream by compression. This gasoline, known as casing head gasoline, is typically a mixture of hydrocarbons and is used as a fuel or as a feedstock in various chemical processes. Therefore, the correct option is Option D: Gasoline separated from wet natural gas by compression .

In petroleum refinery engineering, the Thermofer catalytic cracking process is a fluidised bed process (Option C). Fluidised bed catalytic cracking processes involve the use of a fluidised catalyst bed where the catalyst particles are suspended and mixed with the hydrocarbon feedstock. This allows for efficient mixing and contact between the catalyst and the feedstock, promoting the cracking reactions to produce desired products such as gasoline, diesel, and other valuable hydrocarbons. Therefore, the correct option is Option C: Fluidised bed .

In petroleum refinery engineering, the order of preference for feedstock to a catalytic reformer is Virgin naphtha - coking naphtha - catalytic naphtha (Option D). Virgin naphtha: Virgin naphtha refers to the naphtha fraction obtained directly from the crude oil distillation process. It typically contains fewer impurities and is considered the highest quality naphtha for catalytic reforming. Coking naphtha: Coking naphtha is obtained as a by-product from the thermal cracking or coking process. It may contain higher levels of impurities and may have a lower quality compared to virgin naphtha. Catalytic naphtha: Catalytic naphtha is obtained from the catalytic reforming process itself. It is typically of lower quality compared to virgin naphtha and may contain more impurities. Therefore, the correct order of preference is Virgin naphtha - coking naphtha - catalytic naphtha , making Option D the correct answer.

Older crude petroleum is generally considered light and better because it has undergone natural refining processes over time. It typically gives more distillates , which are the valuable fractions obtained during refining. Additionally, older crude gives less tar , making it more desirable for refining purposes. Therefore, all the statements are true, making Option D: All of the above the correct answer.

In petroleum refinery engineering, olefins are unsaturated cyclic compounds (hydrocarbons) (Option B). Olefins, also known as alkenes, are a class of hydrocarbons containing at least one carbon-carbon double bond. They are unsaturated compounds because they contain fewer hydrogen atoms than the corresponding saturated hydrocarbons. Olefins are widely used in the petrochemical industry as feedstocks for producing various chemicals, including plastics, solvents, and synthetic fibers. Therefore, the correct option is Option B: Unsaturated cyclic compounds (hydrocarbons) .

In petroleum refinery engineering, mercaptans are almost absent in crude petroleum (Option B). Mercaptans, also known as thiols, are sulfur-containing organic compounds with the general formula R-SH, where R represents an organic group. While mercaptans can be present in refined petroleum products as contaminants, they are typically absent or present in very low concentrations in crude petroleum. Therefore, the correct option is Option B: Mercaptans .

Let's understand what an endothermic reaction means first. An endothermic reaction is a chemical reaction that absorbs heat energy from its surroundings. This means the reaction needs heat to happen. If you touch the container where an endothermic reaction is taking place, it might feel cold because it's taking heat away from your hand or the environment. Think of it like cooking: you need to supply heat for the food to cook. Now let's look at each option: Option A: Catalytic cracking Cracking is a process where large, heavy hydrocarbon molecules (like those in heavy oil) are broken down into smaller, lighter, and more valuable molecules (like gasoline). To break chemical bonds, you generally need to supply a lot of energy, usually in the form of heat. Therefore, catalytic cracking is an endothermic process , as it absorbs heat. Option B: Hydrocracking Hydrocracking is similar to catalytic cracking, but it happens in the presence of hydrogen . While breaking large molecules apart (cracking) is endothermic, the addition of hydrogen (hydrogenation) is typically a process that releases heat (exothermic) . In hydrocracking, the heat released by hydrogenation usually makes the overall reaction exothermic or slightly exothermic , meaning it generates heat rather than absorbing it. Option C: Dehydrogenation of naphthene to produce aromatic Dehydrogenation means removing hydrogen from a molecule. Naphthenes are ring-shaped saturated hydrocarbons. When you remove hydrogen from them, they can transform into aromatic compounds (like benzene or toluene), which are special ring structures with double bonds. Removing hydrogen atoms and forming these aromatic rings requires a significant input of energy (heat) . This is a very characteristic example of an endothermic reaction in petroleum refining. It absorbs a lot of heat to proceed. Option D: Catalytic polymerisation Polymerisation is the process of joining many small molecules (called monomers) together to form a much larger molecule (a polymer). When new chemical bonds are formed to create larger molecules, energy is typically released . Therefore, polymerisation reactions are generally exothermic , meaning they release heat. Conclusion: Out of the given options, both catalytic cracking (A) and dehydrogenation (C) are endothermic reactions. However, the dehydrogenation of naphthenes to aromatics is a very strongly endothermic process and is a classic example in petroleum refining that requires substantial heat input. Therefore, the correct answer is: Option C: Dehydrogenation of naphthene to produce aromatic

In petroleum, the constituents responsible for ash formation are typically organometallic compounds . These compounds contain both organic (carbon-based) and metal components. During the refining process, when petroleum is subjected to high temperatures and pressure, these organometallic compounds can decompose and leave behind solid residues, forming ash. Therefore, in this context, the correct option is Option B: Organometallic compounds .

In petroleum refinery engineering, the smoke point of kerosene refers to the maximum height of flame (in mm) without causing smoking, when burnt in a standard lamp (Option C). The smoke point is an important parameter that indicates the quality of kerosene or other liquid fuels. It represents the maximum temperature at which the fuel can be burned without producing visible smoke. When the flame exceeds this height, incomplete combustion occurs, resulting in the emission of smoke. Therefore, the correct option is Option C: Maximum height of flame (in mm) without causing smoking, when burnt in a standard lamp .

In an atmospheric crude oil distillation column , crude oil is heated and separated into fractions according to their boiling ranges. The lighter fractions such as LPG, naphtha, kerosene, and gas oils vaporize and are withdrawn from different trays in the column. The material that remains at the bottom after removal of these lighter components is called Reduced crude , because it has been "reduced" in lighter volatile constituents. This bottom product is also commonly referred to as atmospheric residue , and it consists of high-boiling hydrocarbons that cannot be further distilled at atmospheric pressure without thermal cracking. Therefore, it is typically sent to a vacuum distillation unit (VDU) for further processing. Although residuum is a general term for residue, the more precise and standard term used specifically for the atmospheric column bottom product is Reduced crude .

The Abel apparatus is another commonly used instrument for determining the flash point of volatile liquids. It operates by gradually heating a sample of the liquid in a closed vessel and passing a small flame over the surface of the liquid at regular intervals. The flash point is the lowest temperature at which the vapors of the liquid ignite momentarily when exposed to the flame under specified test conditions. Therefore, the correct option is Option A: Abel apparatus .

3 is the correct answer to “Salt content (measured as sodium chloride) in electrically desalted crude oil comes down to a level of about __________ ptb (pounds per thousand barrel).”. This question is standard in competitive examination syllabi for Petroleum Refinery Engineering.

20 is the correct answer to “Char value of Kerosene is the amount of charred oil deposition on the wick obtained after burning it in a standard wick lamp at a standard rate for 24 hours. Char value of a good quality kerosene should be less than __________ mg/kg of kerosene.”. This question is standard in competitive examination syllabi for Petroleum Refinery Engineering.

85 is the correct answer to “Gasoline yield in catalytic reforming of naphtha may be about __________ percent by weight.”. This question is standard in competitive examination syllabi for Petroleum Refinery Engineering.

4.08 is the correct answer to “1 centistoke is equal to __________ Redwood I seconds.”. This question is standard in competitive examination syllabi for Petroleum Refinery Engineering.

Gasoline is the correct answer to “The main aim of cracking is to produce”. This question is standard in competitive examination syllabi for Petroleum Refinery Engineering.

Paraffinic is the correct answer to “The characterisation factor of a crude oil is calculated as 12.5. It means that; it is”. This question is standard in competitive examination syllabi for Petroleum Refinery Engineering.

Light diesel oil is the correct answer to “Which of the following does not require preheating during storage in the storage tank as well as during atomisation through burners”. This question is standard in competitive examination syllabi for Petroleum Refinery Engineering.

Aromatics is the correct answer to “Which of the following is desirable in petrol (gasoline) but undesirable in kerosene”. This question is standard in competitive examination syllabi for Petroleum Refinery Engineering.

97 is the correct answer to “Octane number of gasoline produced by two stage fluidised catalytic cracking process is”. This question is standard in competitive examination syllabi for Petroleum Refinery Engineering.

Platforming is the correct answer to “Which of the following is a non-regenerative fixed bed catalytic reforming process”. This question is standard in competitive examination syllabi for Petroleum Refinery Engineering.