JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech III PETROLEUM REFINERY ENGINEERING Previous Question Paper (August - 2022 - R18)

Crude petroleum is a complex mixture of thousands of individual chemical compounds, primarily hydrocarbons, with smaller amounts of organic compounds containing nitrogen, oxygen, and sulfur, as well as trace metallic constituents. The elemental composition typically ranges from 83-87% carbon, 10-14% hydrogen, 0.1-2% sulfur, 0.1-1.5% nitrogen, and 0.1-1.5% oxygen.

The hydrocarbon components are categorized into four main classes:

• Paraffins (Alkanes): Saturated hydrocarbons with the general formula CnH(2n+2), forming the bulk of most crude oils. They range from straight-chain (n-paraffins) to branched-chain (isoparaffins) structures.
• Naphthenes (Cycloparaffins): Saturated hydrocarbons containing one or more rings, with the general formula CnH(2n). They are major components in many crudes and contribute significantly to the liquid fraction.
• Aromatics: Unsaturated ring compounds, such as benzene and its derivatives. These provide high octane ratings in gasoline but are generally present in lower concentrations than paraffins or naphthenes.
• Asphaltics/Resins: High molecular weight, complex polycyclic structures containing heteroatoms. These are non-volatile and remain in the residue after atmospheric distillation.

Crude oil is suitable for asphalt manufacture if it contains a high concentration of heavy, high-molecular-weight hydrocarbons and polar compounds known as asphaltenes and resins. These components are essential for providing the required viscosity, ductility, and adhesive properties of asphalt.

The suitability is determined by the following factors:

• Asphaltene Content: Asphaltenes are complex, dark-brown solids that act as the structural framework of the asphalt. A crude with a higher proportion of asphaltenes is generally more suitable for producing harder, more durable asphalt grades.
• Resin-to-Asphaltene Ratio: Resins act as peptizing agents that keep asphaltenes in a stable colloidal suspension. A balanced ratio is critical to ensure the asphalt is not too brittle (low resin) or too soft (excessive resin).
• Distillation Residue: Asphalt is produced from the vacuum residue of crude oil. Crudes classified as 'asphalt-base' or 'naphthenic-base' are preferred because they yield a high volume of heavy, non-volatile residue upon distillation.
• Processing Compatibility: The crude must be amenable to vacuum distillation and subsequent air-blowing (oxidation) processes, which are used to adjust the penetration and softening point of the final asphalt product to meet industrial specifications.