Purification

Before petroleum products can be marketed, certain impurities must be removed. The most common impurities are sulfur compounds. Apart from their foul odour, sulfur compounds are technically undesirable. In motor and aviation fuels they reduce the effectiveness of antiknock additives and interfere with the operation of exhaust-treatment systems. In diesel fuel they cause engine corrosion and complicate exhaust-treatment systems. Most crude oils contain small amounts of hydrogen sulfide, but these levels may be increased by the decomposition of heavier sulfur compounds during refinery processing. In order to minimize noxious emissions, most refinery fuel gases are desulfurized.

Other undesirable components include nitrogen compounds, which poison catalyst systems, and oxygenated compounds, which can lead to colour formation and product instability.

Exercise 3. Answer the following questions.

1. What is refinery designed for? 2. What are the main refinery processes? 3. What do crude oil distillers separate? 4. Tell about the processes after crude oil is withdrawn from storage tanks. 5. What happens with a small amount of uncondensed gas? 6. What distinguishes fractional distillation from simple distillation columns? 7. Where does unvaporized oil entering the column flow? 8. What is the difference between vacuum and fractional distillation? 9. How may bitumen be used? 10. What is the purpose of absorption? 11. What is the purpose of crystallization?

Exercise 4. Match these words with their definitions.

1. Refinery 2. Fractional distillation 3. Sidestreams 4. Bitumen 5. Absorption 6. Solvent

a) a liquid that can change a solid substance into liquid; b) plant, designed to process specific crude oils into selected products; с) process employed to recover valuable light components from the vapors that leave the top of crude-oil or process-unit fractionating columns within the refinery; d) the primary process for separating the hydrocarbon components; e) intermediate products; f) the residue remaining after vacuum distillation.

Exercise 5. Decide whether the following statements are true (T) or false (F) in relation to the information in the text or the information is not enough to make a decision (?). If you think a statement is false, change it to make it true.

1. ___ Fractional distillation units are much larger than modern crude oil distillation units employed in chemical and other industries.

2. ___ The liquid absorbs heavier constituents from the vapour and gives up lighter constituents to the vapour phase.

3. ___ In comparison with vacuum distillation fractional distillation allows for distilling heavier materials at lower temperatures.

4. ___ The separation processes are based on differences in physical properties of the components of crude oil.

5. ___ The crystallization of wax from lubricating oil fractions is essential to make oils suitable for use.

Exersice 6. Restore the order of the sentences to give the meaning to the text.