CPL 2

Petroleum Industry

Gasoline (45-50%)

What is the highest typical yield of product from crude oil refinery?

• Pyrolysis and cracking

• Reforming

• Polymerization

• Alkylation

• Isomerization

• Hydrodealkylation and Hydrogenation

• Impurity Removal

What are some several key unit operations and unit processes to transform crude oil into useful products?

n-Paraffins (Normal Alkanes)

These are straight-chain saturated hydrocarbons with the general formula CnH2n+2; they are a major fraction of petroleum crudes, especially in the C1 to C40 range, constituting up to 20% by volume of the crude.

C1 to C4 (methane to butane) 

What normal alkanes exist as gases at normal conditions?

C5 to C17 (pentane to heptadecane)

What normal alkanes exist as liquids, forming a large fraction of fuels like gasoline, diesel, and jet fuel?

C18 and heavier

What normal alkanes (heavier compounds) exist in a waxy, solid state?

Isoparaffins (Branched Alkanes)

These are branched-chain hydrocarbons, also with the formula CnH2n+2. They are desirable components, but do not occur naturally to a great extent. They must be produced through processes like alkylation, hydroforming, and isomerization. 

Isomers

compounds with the same chemical formula but different structural arrangements; such structural difference leads to varying physical properties

TRUE

TRUE OR FALSE: Isoparaffins have a higher octane number and lower boiling point than normal alkanes

TRUE

TRUE OR FALSE: As the number of C atoms increases, the number of possible isomers grows significantly.

Naphthenes (Cycloalkanes)

• These are saturated cyclic compounds with the general formula CnH2n

• They have the same formulas as olefins (alkenes) 

Aromatic or Benzene Series

• These compounds have the general formula CnH2n-6 and are present in small amounts of crude oil 

• Heavy petroleum fractions may contain polyaromatic hydrocarbons (PAHs) or polynuclear aromatics (PNAs) which consist of multiple benzene and naphthene rings fused together

Asphalts: Asphaltenes and Resins

These are complex, low-value materials consisting of colloids of asphaltenes and resins in oil

Asphaltenes

Brownish-black solids that are soluble in aromatic solvents but not in paraffins; they are composed primarily of C and H atoms, but also contain appreciable quantities of S, O and N. 

Resins

Highly adhesive, brown semi-solids with a lower molecular weight than asphaltenes but a similar chemical composition. 

Sulfur 

A particularly important heteroatom aside from N and O in petroleum crudes and refinery products which can be found in cyclic and non-cyclic compounds in the form of thiophenes, mercaptans, and sulfides 

Hydrogen sulfide (H2S)

What is the form of sulfur in a natural gas?

• Paraffin-base - low grade gasoline and waxy lubricating oils 

• Naphthene-base -  representative of most crude oils 

• Intermediate-base - produces both wax and asphalt 

Classification of crude oil based on predominant hydrocarbon content

TRUE

TRUE OR FALSE: Consumption of energy and petroleum products is an indicator of a country’s economic development level since development is an enegry-intensive process and improves incomes as well as literacy rates are is related to higher petroleum product consumption. 

Crude Petroleum Reserves

the known quantity of crude petroleum that has been identified and is available for future processing; analogous to the inventory of raw materials in other industries 

Surface Geological Methods

• The presence of volatile HCs near the surface is a strong indicator of oil formation at a deeper level

Sensitive Gas Chromatography

(Under Surface Geological Methods), this technique is used to detect very low concentrations (as low as 10-4%) of HCs in soil and air

Microbiological Analysis

(Under Surface Geological Methods), the presence of hydrocarbon-oxidizing microbiological flora in water is often evidence of HC deposits. 

Radioactive Isotopic Exchange

(Under Surface Geological Methods), A lower C-14 assay in rock deposits can indicate areas where gaseous HCs are seeping to the surface. 

• Surface Geological Methods

• Geophyiscal Methods 

2 types of crude petroleum exploration methods

Seismic Surveys 

An extensive geophysical method of exploring crude petroleum wherein shock wave patterns are measured to characterize geological strata. 

Air surveys

An extensive geophysical method where low flying planes (250-300 kph) with magnetometers are used for magnetic surveys, which can detect variations in rock types. 

Scintillation Counter

An extensive geophysical method used for radioactivity surveys to identify certain geological formations associated with oil. 

Sonic and Ultrasonic Probing

An intensive geophysical method performed during core sampling to measure rock porosity, an important factor in reservoir quality. 

Neutron Reflecting Measures

An intensive geophysical method of exploring crude petroleum wherein a scintillation detector is used to measure neutron reflections, which increase in the vicinity of hydrocarbons. 

Drilling and Yields

once a potential oil field is identified, the focus shifts to efficient and economical production

Drilling

• a primary goal of production research is to make drilling faster and cheaper; this includes optimizing the spacing of holes to maximize the release of oil from a reservoir

• holes must be as deep as 5 miles

• offshore drilling is more challenging and requires new procedures and technologies 

Yields

• conservation and the efficient use of reservoir energy are crucial for achieving good yields from a field 

• they have increased over time from as low as 10% to 80% of the available reservoir hydrocarbons 

Slower Withdrawal Rates

A method in improving yield in which oil is pumped at slower rates allowing water to seep in and maintain reservoir pressure

Recycling and Repressurization

A method in improving yield in which natural gas are recycled and reinjected into the reservoir to increase pressure. 

Water, Air, or Steam Flooding

A method in improving yield wherein fluids are injected into older wells to rework them and force remaining oil toward production wells 

Enlargement of Drainage Channels

A method of increasing yield injecting HCl into limestone-bearing rock can enlarge the natural drainage channels, facilitating oil flow.

• The Gas Fraction

• Light Ends: Petrol (Gasoline) 

• Intermediate Distillates

• Heavy Distillates

• Residues and By-products

2 classification of products from typical refineries

Gas Fraction

Gaseous fractions were traditionally used as fuel; their usafe is now shifting towards the preparation of synthesis gas

Natural Gas

A gas fraction that consists largely of methane with some ethane

Light Gas

A gas fraction that has compounds like C1 and C2 separated from the distillation of crude 

Off-gas

A gas fraction produced from petroleum conversion operations at the refinery, containing gases like H2, H2S, SO2, C1 and C2

LPG

A gas fraction that is a mixture of propane and butane that is liquefied and used for domestic fuel, “winterizing” gasoline, or for making synthesis gas 

Petrol

the principal refinery product, and most chemical conversion processes in a refinery are aimed at maximizing its yield; this fuel is specifically formulated for piston engines and gas turbines to meet strict combustion requirements 

Engine Knocking

A combustion characteristic referring to the high compression in an internal combustion engine that can cause violent detonation or “knocking”. 

This occurs when some of the fuel-air mixture spontaneously ignites ahead of the flame front creating high frequency pressure waves that cause parts of the engine to vibrate and produce an audible knock. 

Antiknock Characteristics

To prevent knocking, antiknock compounds are added to gasoline to slow down the burning rate; example are lead tetraethyl and lead tetramethyl (phased out), isoparaffins, and ring unsaturates

Octane Number

An arbitrary scale and parameter used to characterize the antiknock properties of a fuel; percentage of isooctane in an n-heptane/isooctane mixture 

Engine fouling

deposits can build up in the engine

Ease of starting

how quickly the engine starts

Warm-up rate

How fast the engine reaches its optimal operating temperature

Tendency of vapor lock

The formation of vapor bubbles in the fuel lines, which can disrupt fuel flow

Evaporation losses and loss of crankcase oil

The octane scale can be extended using an arbitrary power number that is proportional to the power extracted from the engine; calculated as: 

Octane Number = 100 + (Power number -100)/3

Intermediate Distillates 

This fraction includes a variety of products used primarily for heating and as fuel in diesel engines; examples include heavy fuel oils, diesel oils, and gas oil 

Heavy Distillates

These are heavier fractions that are further processed to create specialty products (ex: mineral oil, flotation and frothing oil, waxes, lubricating oil) 

Residues 

are the non-distillable, heaviest fractions left after the distillation process (ex: lubricants, fuel oil, greases, asphalt, petroleum coke, petrolatum, road oils) 

By-products

are additional materials generated during various refining processes (ex: detergents, sulfur and derivatives, ammonia) 

• Primary refinery

• Intermediate refinery

• Complex refinery 

What are the different characteristics of refineries?

Primary refinery

the simplest type of refinery, consisting of only a distillation unit; it produces residual asphalt and sells all of its overhead products to another refinery for further processing 

Intermediate refinery

this type of refinery produces motor fuel, distillate fuels, and residuals; they are commonly found in European refineries where the demand for gasoline is low compared to heating fluids

Complex refinery

a typical, comprehensive refinery that includes numerous conversion and finishing processes in addition to distilaltion 

• Independent Operations

• Integrated Operations

What are the types of refinery design? 

Independent Operations

refineries built with holding capacities between units, allowing each unit to be operated, shut down, and reconditioned independently; dominant until the early 1950s

Integrated Operations

An integrated refinery is designed with minimal “hold up” capacity between units; more cost-effective offering 20-30% investment savings because refinery maintenance requirements can be reliably scheduled

Distillation

The physical separation in petroleum industries based on differences in relative volatilities; most important of all refinery operations 

Absorption

A separation technique also based on relative volatilities; used to “scrub out” high boiling fractions from low concentration gases 

Extraction

A separation method based on the relative solubility of components in different solvents; primarily used in manufacture of lubricating oils 

Adsorption

A separation technique based on the relative adherence of components to the surface of solids; used for color removal and separation of saturates from unsaturates 

Crystallization

A separation process based on differences in freezing points; used in the preparation of waxes

Solids Handling Operations

are mechanical operations for moving and processing solid materials

Pneumatic Conveying

a solid handling operation used to transport materials like cement, catalysts, and powdered chemicals using a gas stream; originally used for grain

Bucket Elevators

A solid handling operation used for elevating powdered or granular materials to and from storage or between reaction vessels

Heat Transfer

A primary design requirement for energy conservation, with a wide use of heat exchangers

Fluid Flow

can be single-phase or two-phase; two-phase flow such as gas-solid flow is common in catalytic operations like moving bed and fluidized bed reactors 

Initial Crude Composition

The natural fraction of crude petroleum in the gasoline range is typically low, around 25-40% and its molecular structure is not ideal for modern fuel requirements

Pyrolysis and Cracking

are thermochemical conversion processes used in the petroleum industry to break down large HC molecules into smaller, more valuable ones; takes place at high temps anaerobically 

• Non-catalytic pyrolysis (thermal cracking) - selectivel can produce both small and large molecular weight compound

• Catalytic cracking 

2 main types of pyrolysis and cracking

Catalysts

are employed to reduce the required reaction temperatures and pressures, and to achieve a higher selectivity of cracking, which minimizes unwanted side reactions 

Thermal Cracking (Free Radical Theory)

The theory posits that the breakdown of HCs begins with the formation of free radicals - highly reactive particles created by the homolytic cleavage of C-C or C-H bonds

Coking

the unavoidable outcome of the complete degradation of HCs into solid carbon and hydrogen gas, represented by the reaction RH —> xC + yH2

Catalytic Cracking

a more efficient and selective refining process compared to its thermal counter part because it avoids the production of undesirable light gas fractions like C1 and C2 instead yielding a high proportion of secondary and tertiary HCs that are excellent components for modern gasoline

Feedstock Properties

A condition for pyrolysis wherein higher molecular weight feeds crack more easily but they also have greater tendency to form coke

Pressure effects

Another condition for pyrolysis and cracking wherein high pressure increases the rate of polymerization, which is often an undesirable side reaction; however it also has the benefit of increasing the overall throughput of the process

ability to function at lower temps and pressures than thermal cracking

This is the significant benefit of using catalytic cracking

rapid quenching step

In a plant setting, particularly for high temp, low contact time reactions, ______ is requried to halt the reaction and prevent the formation of undesired back or side products 

By the gradual deposition of tarry materials (coke)

How are catalysts deactivated?

By regeneration, which is an exothermic process where the coke is oxidized 

How is the deactivation of catalyst reversed?

TRUE

TRUE OR FALSE: Early fixed bed reactors were replaced by more advanced moving and fluid-bed designs where the catalyst is continuously moved between the reactor and regenerator eliminating the need for a cyclic process. 

• Catalyst to oil ratio

• Conversion

• Temperature

• Pressure

What are the key-process variables in catalytic cracking?

Fluidized bed design

Uses a liquid-like fluidization of microspheres that offer a more compact design and superior heat economy

Moving beds 

A catalytic equipment design which uses larger pellets that flow by gravity; they are simpler but less efficient with drawbacks such as higher steam requirements and poorer heat economy 

Petroleum Coking

a process to upgrade residual or heavy-end petroleum fractions by pyrolysis yielding mostly gas oils and petrol with its process variables being temp and pressure

Delayed Coking

A type of coking unit which involves heating in pipe stills, followed by coke formation in large drums that are cleaned with water jets

Fluid Bed Coking 

A type of coking unit similar to fluid bed catalytic cracking where product coke is continuously circulated and managed for particle size

Moving Bed Coking

A type of coking unit similar in design to moving bed catalytic cracking units

Reforming

a crucial refining process that aims to convert low-octane HC fractions into higher octane aromatic compounds, which are valuable components of modern gasoline 

Naphtha

The feedstock for reforming processes which refers to the HC mixtures that boil in the gasoline range (60-200 C); they are sources either as virgin, coking, or catalytic. 

Dehydrogenation 

A significant reaction type for converting valuable components to higher-octane fuels where a cycloalkane loses H atoms to form a more stable aromatic compound 

Cyclization

Another important reaction in petroleum refining where an open-chain alkane is converted into a cycloalkane

Isomerization

An important reaction in petroleum refining which plays a vital role by rearranging a cycloalkane into a more stable structural isomer, as seen when ethylcyclopentane is converted into methylcyclohexane

Hydrocracking

An important undesirable side reaction in which the paraffin chains are broken down into smaller, less useful fragments