Slo:16.8.4 Describe the fractional distillation of petroleum

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Slo:16.8.4 Describe the fractional distillation of petroleum

FRACTIONAL DISTILLATION OF PETROLEUMFractional distillation

Fractional distillation differs from distillation only in that it separates a mixture into a number of different parts, called fractions. A tall column is fitted above the mixture, with several condensers coming off at different heights. The column is hot at the bottom and cool at the top. Substances with high boiling points condense at the bottom and substances with low boiling points condense at the top. Like distillation, fractional distillation works because the different substances in the mixture have different boiling points.Fractional distillation of crude oilBecause they have different boiling points, the substances in crude oil can be separated using fractional distillation. The crude oil is evaporated and its vapors allowed to condense at different temperatures in the fractionating column. Each fraction contains hydrocarbon molecules with a similar number of carbon atoms.Oil fractionsThe diagram below summarizes the main fractions from crude oil and their uses, and the trends in properties. Note that the gases condense at the top of the column, the liquids in the middle and the solids stay at the bottom.

The main fractions include refinery gases, gasoline (petrol), naphtha, kerosene, diesel oil, fuel oil, and a residue that contains bitumen. These fractions are mainly used as fuels, although they do have other uses too.Hydrocarbons with small molecules make better fuels than hydrocarbons with large molecules because they are volatile, flow easily and are easily ignited.

EXTRACTION OF ALIMUNIUM

PROCESS OF EXTRACTION OF ALIMUNIUM:Aluminium ore is called bauxite. The bauxite is purified to yield a white powder, aluminium oxide, from which aluminium can be extracted. The extraction is done by electrolysis. But first the aluminium oxide must be made molten so that electricity can pass through it.

BAYERS PROCESSTheBayer processis the principal industrial means of refiningbauxiteto producealumina(aluminium oxide). Bauxite, the most important ore ofaluminium, contains only 3054%aluminium oxide, (alumina), Al2O3, the rest being a mixture ofsilica, variousiron oxides, andtitanium dioxide.[1]The aluminium oxide must be purified before it can be refined to aluminium metal.

FINAL STEP :ELECTROLYSISAluminium is the mostabundantmetal on Earth. Despite this, it isexpensive, largely because of the amount ofelectricityused up in the extraction process.Aluminium ore is calledbauxite. The bauxite is purified to yield a white powder, aluminium oxide, from which aluminium can be extracted.The extraction is done byelectrolysis. But first the aluminium oxide must be mademoltenso that electricity can pass through it. Aluminium oxide has a very high melting point (over 2,000C), so it would be expensive to melt it. Instead, it isdissolvedinmolten cryolite, an aluminium compound with a lower melting point than aluminium oxide. The use of cryolite reduces some of the energy costs involved in extracting aluminium.an aluminium oxide electrolysis tank is used. Both the negative electrode (cathode) and positive electrode (anode) are made ofgraphite, a form of carbon.Aluminium metalforms at the negative electrode and sinks to the bottom of the tank, where it is tapped off.Oxygenforms at the positive electrodes. This oxygen reacts with the carbon of the positive electrodes, forming carbon dioxide, and they gradually burn away. Consequently, the positive electrodes have to be replaced frequently, which adds to the cost of the process.

TEST YOURSELF:Mcqs and crqs

MCQSWhat is aluminium mainly composed of :Alimunium oxideAlimunium chlorideWhat is the process used for extraction of alimunium oxideBayers processElectrolysis

CRQS1)Define bayers process?2)Why does alimunium oxide has to be converted to molten form before electrolysis explain with reason?

MCQs on Fractional Distillation

MCQno.1In fractional distillation, a large surface area for condensation is provided througha thermometer.water bath.a fractionating column.reflux condenser.MCQno.2 What happens when crude oil is fractional distilled?Different fractions are mixed together to form oil.Sulfur is removed from the crude oil.The oil is separated into fractions of different boiling ranges by heating.Longer chain fractions are broken down into shorter chain fractions

MCQno.3 How are the hydrocarbons produced at the top of the column, different from those produced lower down?They have longer chains and lower boiling temperatures.They have shorter chains and lower boiling temperatureThey have shorter chains and higher boiling temperatures.They have longer chains and higher boiling temperatures.

CONSTRUCTED RESPONSE QUESTIONS(CRQs)ANSWERS:332

Question no. 1:Why can petrol and diesel be separated by fractional distillation?Question no. 2:What two physical processes take place in distillation?

ANSWERS OF CRQS:Qno.1:Why can petrol and diesel be separated by fractional distillation? Answer:They each have different boiling points. This is why fractional distillation work. Qno.2:What two physical processes take place in distillation? Answer:Evaporation and condensation.