Petrochemicals - 4

Natural Gas Liquids (NGLs) are hydrocarbons that condense out of natural gas during processing. Methane (CH4) is the lightest alkane and remains gaseous at standard temperature and pressure, unlike ethane, propane, and butane which can be liquefied. Therefore methane is not classified as an NGL.

Natural gas is primarily composed of methane (CH4), typically 70-90% by volume. The remaining components include ethane, propane, butane, and other gases. Option A correctly identifies methane as the major constituent. CH3OH is methanol (alcohol), C2H6 is ethane (a minor component), and "None of these" is incorrect.

Crude oil is classified into three main types based on composition: paraffin base (high paraffin wax), naphthenic/asphaltic base (high asphalt content), and mixed base (intermediate). There is no "sulphur base" classification. While crude oils can be sour (high sulfur) or sweet (low sulfur), sulfur content is a property, not a classification base.

Cracking is the petroleum refining process that breaks larger, higher molecular weight hydrocarbon molecules into smaller, lower molecular weight molecules. This is done through thermal cracking (heat) or catalytic cracking (catalysts). Isomerisation rearranges molecular structure, aromatisation creates aromatic rings, and cyclisation forms ring structures - none of these reduce molecular weight like cracking does.

Third-generation petrochemicals are the final products derived from basic petrochemicals, such as synthetic rubber, plasticisers, and resins. Natural gas is a raw fossil fuel feedstock used to produce petrochemicals, not a petrochemical product itself. Therefore, it is not considered any generation of petrochemical.

Sulfur in crude oil is commonly removed using copper oxide through processes like copper sweetening. The copper oxide reacts with sulfur compounds to form copper sulfide, effectively removing sulfur impurities. Iron oxide, zinc oxide, and magnesium oxide are not typically used for this specific desulfurization purpose.

Natural gas liquids (NGLs) are separated from methane using absorption processes, cryogenic expansion (cooling to liquefy heavier components), and fractionation towers. Magnetic processes have no application in gas-liquid separation as these methods don't differentiate based on magnetic properties in this context.

The Cotrell process uses electrical precipitation to remove water and suspended solids from crude oil. Bergius process is for coal liquefaction, while Newton's process and Berthelot process are not relevant to crude oil dehydration. The Cotrell precipitator charges water droplets which are then attracted to opposite electrodes.

Conversion processes in petroleum refining change carbon numbers (cracking), hydrogen-to-carbon ratios (reforming), and molecular structures (isomerization). However, halogen content is not typically altered in these processes as halogens are not naturally occurring components in crude oil that would be modified during conversion.

Natural gas is called 'sour gas' when it contains significant amounts of hydrogen sulfide (H₂S). The sulfur content gives it corrosive properties and a rotten egg odor. Carbon (C), phosphorus (P), and arsenic (As) are not responsible for the sour designation.

Crude oil contains trace amounts of metals including magnesium (Mg), nickel (Ni), and vanadium (V) which occur naturally in petroleum. Chromium (Cr) is not typically found in crude oil deposits. These metals can poison catalysts during refining and need to be removed.