Asphalts are

ANS:C - readily oxidisable and form carbonaceous sludge.

Among the options provided, none accurately describe asphalts:

• Asphalts are typically high molecular weight compounds found in petroleum, not low molecular weight.
• They are not desirable in catalytic cracking feedstocks because they produce excessive coke, which can foul equipment and reduce efficiency.
• Asphalts are not readily oxidizable; instead, they are known for their durability and resistance to weathering.

Therefore, none of the options (a), (b), or (c) are correct descriptions of asphalts. Low molecular weight and low boiling point compounds present in petroleum refer to the lighter fractions that vaporize at lower temperatures during the refining process. Here’s an explanation:

1. Fractionation in Petroleum Refining: When crude oil is distilled in a refinery, it undergoes fractionation where it is heated to separate it into different fractions based on boiling points.
2. Lighter Fractions: The lighter fractions include gases (such as methane, ethane, propane) and liquid hydrocarbons with relatively low molecular weights and boiling points. These fractions typically include:
   • Natural Gas: Composed mainly of methane (CH4) and ethane (C2H6), which are gases at ambient temperature and pressure.
   • Gasoline: Consisting of hydrocarbons with 5 to 12 carbon atoms, which have low boiling points and are volatile.
   • Naphtha: A mixture of hydrocarbons with 5 to 10 carbon atoms, used as a feedstock in petrochemical processes.
3. Properties:
   • Low Molecular Weight: Refers to compounds with fewer carbon atoms per molecule, making them lighter in mass.
   • Low Boiling Point: These compounds have boiling points typically below 200°C, allowing them to vaporize at lower temperatures during refining.
4. Uses:
   • Fuel: Lighter fractions like gasoline and liquefied petroleum gas (LPG) are used as fuels in automotive vehicles and residential heating.
   • Feedstock: They serve as feedstocks in petrochemical processes to produce plastics, synthetic fibers, and other products.
5. Importance:
   • The separation of these lighter fractions is crucial in petroleum refining to obtain products with specific properties for various industrial and consumer applications.
   • The refining process aims to maximize the yield of valuable products like gasoline and LPG while minimizing the production of heavier, less valuable fractions like residual fuel oil and asphalt.

In summary, low molecular weight and low boiling point compounds in petroleum refer to the lighter fractions that vaporize early during distillation, providing important fuels and feedstocks for the petrochemical industry. In the context of catalytic cracking in petroleum refining, the term "desirable in catalytic cracking feedstock, because they produce coke" is somewhat misleading. Let me clarify:

1. Catalytic Cracking: Catalytic cracking is a refining process where heavier hydrocarbons, typically found in crude oil fractions such as gas oils or residual fuels, are broken down into lighter products like gasoline and diesel. This process involves using a catalyst to facilitate the chemical reactions that break large hydrocarbon molecules into smaller, more valuable ones.
2. Coke Formation: Coke formation is an undesired side reaction in catalytic cracking. It occurs when the cracking reactions produce carbonaceous deposits (coke) on the catalyst surface, which reduces the catalyst's activity and efficiency over time. This leads to the need for frequent regeneration or replacement of the catalyst.
3. Desirable Characteristics in Feedstock:
   • Low Coking Tendency: Ideally, feedstocks for catalytic cracking should have a low tendency to form coke to minimize catalyst deactivation.
   • High Yield of Valuable Products: Feedstocks should yield a high proportion of valuable products such as gasoline and light olefins (ethylene, propylene).
4. Feedstock Selection:
   • Lighter fractions, such as straight-run gasoline or light gas oils, are generally preferred as feedstocks for catalytic cracking because they contain fewer heavy components that tend to produce coke.
   • Heavy residues and asphaltic compounds, which have higher molecular weights and more complex structures, are less desirable as they are more prone to coke formation and can lead to operational issues in the cracking unit.
5. Management of Coke Formation:
   • While coke formation is inherent in catalytic cracking, refineries employ strategies to mitigate its impact. This includes catalyst regeneration techniques (such as burning off coke deposits) and careful feedstock selection to optimize process performance.

Therefore, in the context of catalytic cracking, feedstocks that are less likely to produce coke are considered more desirable because they enhance process efficiency, minimize catalyst deactivation, and maximize the yield of valuable products. The term "readily oxidizable and form carbonaceous sludge" typically describes compounds or materials that have a tendency to undergo oxidation reactions and form carbon-rich residues or deposits. Here’s an explanation:

1. Readily Oxidizable: This refers to substances that can react easily with oxygen or other oxidizing agents. Oxidation reactions involve the loss of electrons or an increase in the oxidation state of atoms in a molecule.
2. Formation of Carbonaceous Sludge: When a substance undergoes oxidation, especially if it contains carbon atoms, it can lead to the formation of carbonaceous residues or sludge. These residues are often black or dark in color and consist primarily of carbon with varying amounts of other elements depending on the original composition of the substance.
3. Examples:
   • Organic Compounds: Certain organic compounds, particularly those with unsaturated bonds or aromatic structures, can be readily oxidized under certain conditions.
   • Petroleum Products: Some fractions of crude oil or refined petroleum products, if exposed to oxygen or air for extended periods, can oxidize and form carbonaceous deposits. This includes heavy residues, tars, and some types of oils.
4. Environmental and Industrial Impact:
   • In industrial processes, the formation of carbonaceous sludge can lead to equipment fouling, reduced efficiency, and increased maintenance costs.
   • In environmental contexts, the accumulation of carbonaceous residues can impact ecosystems, especially in cases where these residues are released into soil, water, or air.
5. Prevention and Management:
   • To mitigate the formation of carbonaceous sludge, industries may use additives or treatments to stabilize products against oxidation.
   • Proper storage and handling practices, as well as the use of antioxidants or inhibitors, can help minimize oxidation and the subsequent formation of carbonaceous residues.

In summary, the term "readily oxidizable and form carbonaceous sludge" describes materials or compounds that are prone to oxidation reactions, leading to the formation of carbon-rich residues or deposits, which can have implications for both industrial processes and environmental management.