The Plan Section 9.5 Crude Oil Refining Section 9.6 (very brief) on Combustion Review (if time)

9.5 Crude Oil Refining Crude oil is the petroleum that is pumped directly from the ground. It is a complex mixture of hydrocarbons with one or two carbon atoms up to a limit of ~50 carbon atoms.

Hydrocarbons & Crude Oil Longer chains mean… 1.Less ability to flow 2.Less flammable 3.Less volatile 4.Higher boiling point Increasing length Crude oil is a mixture of HYDROCARBONS (compounds made up of carbon and hydrogen). Some examples: Ethane C C H H H HH H Butane CC H H H HH H C C H H H H

Physical Processes in Refining – This is usually not useful, so it must be separated by distillation. – Classified on the basis of viscosity, hydrocarbon content & sulfur content. The less viscous, the less refining it needs. Can be separated using chemical & physical means.

Petroleum products and the ranges of hydrocarbons in each product.

Crude Oil Refining Physical Chemical Fractional distillation (fractionation) Fractional distillation – diff. bp of components allow for separation – as separation occurs the fractions are collected these are component steams – lower bp = smaller molecule – higher bp = larger molecule Cracking – larger molecules broken down with heat/catalysts – A) thermal 1900’s T & P, C (carbon/coke) – B) catalytic 1930’s uses catalyst, C – C) hydrocracking 1960’s combines catalytic & hydrogenation (+H 2 ) C produced

Crude Oil Refining PhysicalChemical Solvent extractions – solvent is added to dissolve specific components impurities, products Dewaxing – cooling to solidify a specific fraction Catalytic reforming – changing naptha (aliphatic) to aromatic (cyclic) gasoline – aromatics burn better Alkylation (isomerization) – increasing the # of branches (alkyl’s) – more branches = better burning – octane number in gas CH 3 CH 2 CH 2 CH 3 CH 3 + 2H 2 CH 3 CH 2 CH 2 CH 3 CH 3 CHCH 3 CH 3

Some types of crude oil are better for gasoline production, whereas others may be better suited for motor oil products. The raw resource is sent to be refined into different components of hydrocarbons, called a fraction. This separation can involves both physical and chemical processes.

Physical Processes in Oil Refining Crude oil is a complex mixture of thousands of compounds with various boiling points. Chemical engineers take advantage of the differences in boiling points to separate the components. This technological process is called fractional distillation or fractionation.

Fractional Distillation Set-up

Fractional Distillation of Petroleum Fractional Distillation of Petroleum Petroleum can be separated into different fractions by fractional distillation. This separation can take place because petroleum is a mixture of substances with different boiling points.

Fractional Distillation Crude oil can be separated by fractional distillation. The oil is evaporated and the hydrocarbon chains of different lengths condense at different temperatures: Fractions with low boiling points condense at the top Fractions with high boiling points condense at the bottom

Temperature increases down the column (Petroleum Gas) Petrol Naphtha Kerosene Diesel Lubricants Bitumen

Separating Mixtures of Hydrocarbons Decreasing temperature Since different hydrocarbons have different boiling points they can be separated by distillation. Crude oil is heated to about 500 o C in the absence of air. The vapors rise and cool changing to liquids at different temperatures.

Crude Oil Mixture

Decreasing melting point

Fractionation When crude oil is heated to 500°C with no air, most constituent compounds vaporize. The compounds with a higher boiling point remain as a mixture of asphalts and tars. The vaporized components of the mixture gradually cool in a metal tower. To get from one layer to the next the gas must pass through the liquid in the next tray.

Fractionation Those with higher boiling points condense in lower trays and those with lower boiling points condense in higher trays. Side streams are withdrawn at various locations along the column. These streams are called fractions. The explanation for this is based on bonding theory. Low boiling points are due to small molecules, which have fewer electrons and therefore weaker London forces compared to large molecules.

Solvent Extraction Another physical refining process, in which a solvent is added to selectively dissolve and remove an impurity or to separate some useful products from the mixture.

Chemical Processes in Oil Refining The two necessary chemical processes are cracking and reforming. These processes are used because there are not enough of the hydrocarbons that are in demand being produced from fractional distillation (like gasoline & diesel).

Cracking In the absence of oxygen, alkanes can be “cracked” (broken into smaller fragments) at high temperatures and in the presence of catalysts. This reduces high molecular weight hydrocarbons, C 15 - C 18 such as those found in oil, to low molecular weight hydrocarbons, like C 5 - C 12 such as those found in gasoline. This is the basis of the oil refining process. Eg.C 17 H 36(l)  C 9 H 20(l) + C 7 H 16(l) + C (s)

Cracking The story with oil refining is there are always improvements in technology. Thermal Cracking used extensively until the 1930’s produced a lot of waste solid coke. Catalytic Cracking uses catalysts and produces a lot less undesirable byproducts. Hydrocracking, yet another improvement in the 1960’s, is a combination of catalytic cracking and hydrogenation. During hydrogenation no coke is produced. C 17 H 36(l) + H 2(g)  C 9 H 20(l) + C 8 H 18(l)

Catalytic Cracking alkane o C  smaller alkanes + alkenes + H 2

Catalytic Reforming Essentially this is the opposite of cracking. Larger molecules are formed from smaller ones (naptha fraction into aromatic gasoline molecules). E.g., C 5 H 12 (l) + C 5 H 12 (l)  C 10 H 22 (l) + H 2 (g) Reforming is used to: 1. Convert low grade gasoline to higher grades. 2. Make larger hydrocarbons for synthetic lubricants.

Alkylation (Isomerization) Another way to improve the quality of gasoline is to increase the branching molecules in a process called alkylation. Also called isomerization, because it converts a molecule into a branched isomer.

Summary Catalytic Cracking: Larger molecules  smaller molecules + carbon Hydrocracking: Larger molecule + hydrogen  smaller molecules Catalytic Reforming: Aliphatic molecule  aromatic molecule + hydrogen Alkylation (Isomerization): Alphatic molecule  more branched isomer

The octane number is a description of how rapidly gasoline burns It is based on (A) n- heptane, with a number of 0, and (B) 2,2,4- trimethylpentane, with an assigned number of 100. Higher the # = the better the burn.

Case Study-Octane Number Discuss in a group.

Sulfur in Gasoline This is a huge pollution problem, because sulfur emission reduce air quality and can also lower pH of rain. Sulfur also has negative effects on the cars catalytic converter. The reduced effectiveness increases other pollutants in the air like carbon monoxide. The technology to reduce sulfur in gasoline is a process called hydrogenation or hydrotreating.

9.6 Combustion Reactions Complete Combustion Incomplete Combustion

Complete Combustion Alkanes are relatively unreactive but they burn (react with oxygen) at high temperatures to form carbon dioxide and water and to release energy (the reaction is exothermic ). In this way they can be used as fuels. Example: 2 C 8 H 18(l) + 25 O 2(g)  16 CO 2(g) + 18 H 2 O (g) + energy This is octane, the chief component of gasoline. We burn this as a fuel in our cars.

Combustion of alkanes as fuels is essentially the same as the oxidation of carbohydrate during cellular respiration in living systems. Both have the same outcomes, the release of energy to do work and the production of carbon dioxide and water. i.e., C 6 H 12 O 6 (l) + 6 O 2(g)  6 CO 2(g) + 6 H 2 O (l) + energy

Incomplete Combustion These reaction may produce carbon monoxide, and soot or any combination of carbon dioxide, carbon monoxide, and carbon (soot), in addition to water and energy. 2 C 8 H 18 (l) + 17 O 2 (g)  16 CO(g) + 18 H 2 O(g) 2 C 8 H 18 (l) + 9 O 2 (g)  16 C(s) + 18 H 2 O(g) Alcohols can be added to gasoline to reduce the carbon monoxide emissions. Alcohol is considered an oxygenator & makes combustion more complete.

Study for the Quiz tomorrow so this is Not True for You.