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

Incre

asin

g le

ng

th

Crude oil is a mixture of HYDROCARBONS (compounds made up of carbon and hydrogen). Some examples:

Ethane

C C

HH

H

HH

H

Butane

C C

HH H

HH

H C C H

H

HH

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)– 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 (+H2)

• C produced

Crude Oil Refining

Physical Chemical

• 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

CH3CH2CH2CH3

CH3

+ 2H2

CH3CH2CH2CH3 CH3CHCH3

CH3

• 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

• 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 DistillationCrude 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)

PetrolNaphthaKerosene

Diesel

Lubricants

Bitumen

Separating Mixtures of Hydrocarbons

Decreasingtemperature

• Since different hydrocarbons have different boiling points they can be separated by distillation.

• Crude oil is heated to about 500oC in the absence of air.

• The vapors rise and cool changing to liquids at different temperatures.

Crude Oil Mixture

Crude Oil Mixture

Crude Oil Mixture

Crude Oil Mixture

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Crude Oil Mixture

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Crude Oil Mixture

Crude Oil Mixture

Crude Oil Mixture

Decreasingmelting 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, C15 - C18 such as those found in oil, to low molecular weight hydrocarbons, like C5 - C12 such as those found in gasoline.

• This is the basis of the oil refining process.• Eg. C17H36(l) C9H20(l) + C7H16(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.

C17H36(l) + H2(g) C9H20(l) + C8H18(l)

Catalytic Cracking

alkane + 400-600oC smaller alkanes + alkenes + H2

Catalytic Reforming • Essentially this is the opposite of cracking.

• Larger molecules are formed from smaller ones (naptha fraction into aromatic gasoline molecules).

• E.g., C5H12(l) + C5H12(l) C10H22(l) + H2(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 C8H18(l) + 25 O2(g) 16 CO2(g) + 18 H2O(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., C6H12O6(l) + 6 O2(g) 6 CO2(g) + 6 H2O(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 C8H18(l) + 17 O2(g) 16 CO(g) + 18 H2O(g)

• 2 C8H18(l) + 9 O2(g) 16 C(s) + 18 H2O(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.