CHE 4433: Petroleum Refining Course Intro

Petroleum Refining & Petrochemicals Course Overview

• The course code is CHE 4433.

Course Learning Objectives (LOs)

• CLO1: Describe the properties of refinery products and crude oil.
• CLO2: Differentiate between atmospheric and vacuum crude oil distillation units.
• CLO3: Describe hydro-treating, catalytic reforming, and isomerization and explain the principles used.
• CLO3: Describe the principles for coking, catalytic cracking, and hydrocracking units.
• CLO4: Discuss the properties of common lubricating oils and describe the processes for their production.
• CLO5: Describe the petrochemical industry and discuss the properties of some typical polymers.

Crude Oil Basics

• Crude oil consists of a complex hydrocarbon mixture, primarily alkanes of varying lengths.
• It is a naturally occurring liquid found in earth formations.
• Can be found in semi-solid form mixed with sand, and it is referred to as crude bitumen in Canada's Athabasca oil sands.
• Crude oils range in consistency from water to tar-like solids and vary in color from clear to black.
• Classified as paraffinic, naphthenic, or aromatic based on the predominant hydrocarbon molecules.

Major Hydrocarbons in Crude Oil

• The approximate chain length range for crude oil hydrocarbons is C5H12 to C18H38.
• Shorter hydrocarbons are considered natural gas or natural gas liquids (NGL).
• Longer-chain hydrocarbons are more viscous, and the longest form solid bitumen or asphalt.
• Elemental composition of petroleum crude oil:
  • Carbon constitutes 83-87 wt%.
  • Hydrogen constitutes 10-14 wt%.
  • Nitrogen constitutes 0.1-2 wt%.
  • Oxygen constitutes 0.1-1.5 wt%.
  • Sulfur constitutes 0.5-6 wt %.
  • Metals constitute <0.1 wt %.

Classification of Crude Oils

• The oil industry classifies crude by its origin, such as "West Texas Intermediate, WTI" or "Brent".
• Crude is classified by relative weight or viscosity, such as light, intermediate, or heavy.
• Refiners use the terms "sweet," for low sulfur content, and "sour," for high sulfur content requiring more refining.
• Crude oil assay analysis helps understand the unique molecular characteristics of crude oils in petroleum laboratories.

Brent Blend vs. WTI

• Brent blend is a light crude oil, heavier than WTI, with about 0.37% sulfur, classifying it as sweet crude (but not as sweet as WTI).
• Brent is suited for production of petrol and middle distillates is typically refined in Northwest Europe.
• Brent Crude has an API gravity of ~38.06 and a specific gravity of ~0.835.
• WTI is a light crude oil with about 0.24% sulfur and rated as sweet crude oil. It is sweeter than Brent.
• WTI is refined mostly in the Midwest and Gulf Coast regions in the U.S.
• WTI has API gravity of ~39.6 and specific gravity of ~0.827, which is lighter than Brent crude.

Hydrocarbon Chemistry

• Crude oil is a hydrocarbon molecule mix, which includes carbon and hydrogen compounds that include 1-60 carbon atoms.
• Molecule's carbon and hydrogen number and arrangement determines hydrocarbon properties.
• Hydrocarbons with up to 4 carbon atoms are gases, 5 to 19 are liquids; 20 or more are solids.

Main Hydrocarbon Types in Crude Oil

• Paraffins (Alkanes): General formula CnH2n+2, straight or branched chains (isomers). Examples are methane, ethane, propane, and butane.
• Aromatics
• Naphthenes
• Other hydrocarbons include Alkenes, Dienes, and Alkynes.

Naphthenes and Aromatics

• Naphthenes are saturated hydrocarbons in closed rings with the formula CnH2n, found in most fractions of crude oil.
• Single-ring naphthenes (monocycloparaffins) with 5-6 carbon atoms predominate. Two-ring naphthenes(dicycloparaffins) are found in heavier naphtha ends.
• Aromatics are unsaturated ring-type compounds that react readily, they have carbon atoms deficient in hydrogen. All have at least one benzene ring.

Aromatics (cont.)

• Naphthalenes are fused double-ring compounds.
• Polynuclears (three or more fused aromatic rings) are the most complex found in heavier crude oil fractions.

Technical Issues of Heavy Crude Oils

• Heavy crude oil is asphaltic, dense, and viscous.
• Known as naphthene-based at low paraffin wax content (<10%) or high naphthenic compounds (asphaltenes).
• Heavy oil contains over 60 carbon atoms, with high boiling point and molecular weight.
• Physical properties like viscosity affect recovery costs.
• Chemical impurities like sulfur, nitrogen, and oxygen affect refining, causing treatment and corrosion issues.
• Heavy crude oils are often discounted due to the issues.

Environmental Issues of Heavy Crude Oils

• Heavy crude oils have a more severe environmental impact as it relates to the carbon intensity when burned.
• Heavy crude oils carry more contaminants, with Orinoco extra heavy oil containing 3.5% Sulfur, Vanadium and Nickel.
• Higher carbon to hydrogen ratio releases more CO2, contributing to climate change.

Characterization of Crude Oils

• Crude oils are not easily defined, due to having hundreds of hydrocarbons which makes the exact composition unknown.
• Properties are defined by different assays. Assays uses test data to give an accurate description of crude oil quality and refinery behavior.
• The chemical and physical properties of crude oil are the basis for economic valuation, engineering design, and refinery processing.

Important Properties of Crude Oil

• Density and API Gravity
• Distillation range
• Characterization Factor
• Viscosity
• Pour point
• Carbon residue
• Impurities: Sulfur content, Salt content, Nitrogen content

Density & API Gravity (American Petroleum Institute)

• Density is the mass of oil per unit volume at 15.6°C.
• Density (ASTM D-1298, IP 160) determines the quality and sales basis.
• Laboratories use density meters to measure specific gravity.
• API gravity is a density index for crude oil or refined products.
• Formula: API gravity = (141.5/SG) – 131.5
• Crude oil's API gravity ranges from less than 10°API to over 50°API but mostly falls in the 20 to 45° API, the higher the API gravity, the lighter the crude.

API Gravity By Crude Oil Type

• Light crude oil with an API gravity higher than 31.1 °API (less than 870 kg/m3)
• Medium crude oil with an API gravity between 22.3 °API and 31.1 °API (870 to 920 kg/m3)
• Heavy crude oil with an API gravity below 22.3 °API (920 to 1000 kg/m3)
• Extra heavy crude oil with an API gravity below 10.0 °API (greater than 1000 kg/m3)
• Crude oils with low carbon, high hydrogen, and high API gravity are usually rich in paraffins and tend to yield gasoline and light petroleum VALUABLE CRUDE OIL
• High-carbon, low-hydrogen, low API gravity crudes are rich in aromatics and impurities and are LESS VALUABLE CRUDE OIL

True Boiling Point

• A full and comprehensive evaluation of crude starts with True Boiling Point Distillation
• True Boiling Point Distillation gives an indication of types of products obtained by distillation of the crude oils
• Distillation curve is a plot of boiling points (temperatures) vs % volume of distilled fractions.
• ASTM D 2887 is used to find out TBP for crude oil distillations.

ASTM Standards: Atmospheric and Vacuum Distillation

• ASTM D-86 (Atmospheric distillation) is carried out at atmospheric pressure to 300°C (572°F) to avoid breakdown.
• ASTM D-1160 (Vacuum distillation): A test at reduced pressure, of boiling temperature ranges petroleum products from the atmospheric distillation residue.

Light Hydrocarbons or Gases Analysis

• Light hydrocarbon amount in crude oils (methane to butane) included as part of a preliminary assay.
• Identification/quantification of each light component executed via GC/gas chromatography based on ASTM D-2427.

Characterization of Crude Oils

• Crude oil classification – paraffinic, naphthenic, or aromatic at lower temperatures.
• Problems arise above 200°C, since molecules can't be classified into one group.
• Characterization factors, based on specific gravity and TBP help to characterize different crude oils.
• Two correlation groups between yield and aromaticity and paraffinicity of crude oils are: UOP Watson Characterization factor (Kw) and US Bureau of Mines Correlation index (CI)

Watson Characterization

• Formula: Kw = MABP1/3 / SG
• MABP (Mean Average Boiling Point) is the average boiling point in °R (degrees Rankine).
• SG is the specific gravity at 60° F.
• Kw is less than 10 for highly aromatic crude oils and from almost 15 for highly paraffinic crude oils
• Kw: 10.5-12.5 for highly naphtenic (cyclic) and 12.5 - 13 for highly paraffinic crude oils.
• MABP = VABP - DIFFERENTIAL
• 1. Volume average boiling point (VABP): VABP = (T20%+T50%+T80%)/3
• 2. Slope of TBP Curve: Slope = (T70%-T10%) / 60
• 3. From Figure (next page), we get Differential
• 4. MABP = VABP-DIFFERENTIAL

Kinematic Viscosity

• Viscosity is a measure of fluid's resistance to deformation under shear stress, commonly perceived as "thickness."
• Viscosity describes fluid's internal resistance to flow, a measure of fluid friction.
• Kinematic viscosity determined at 25°/100°C, measuring time for liquid volume to flow under gravity through calibrated glass capillary viscometer (ASTM D-445).
• Cost of crude oil transportation depends on kinematic viscosity.
• Light crude oils have small kinematic viscosity, then low transportation cost.

Crude Oils Behavior at Low Temperatures

• Viscosity and Pour point determinations give information about crude oil flow characteristics at low temperatures.
• Some information about the type of crude oil derived from pour point data.

Pour Point

• Pour point is the lowest oil temperature at which it will pour or flow under prescribed conditions.
• Minimum liquid temperature after which the liquid ceases to flow when decreasing the temperature.
• An easy indication of the lowest temperature at which oil is readily pumpable.
• Actual crude oils: at the pour point, the liquid phase trapped within the PARAFFIN CRYSTAL STRUCTURE.
• Paraffins are the first components to crystallize under low temperatures.

Carbon Residue

• Carbon residue is related to the asphalt content and quantity of the lubricating oil that can be valuable fractions.
• Determined by the solid residue after heating crude oil to coking temperatures (700-800°C).
• Carbon is a catalyst poison.
• Carbon residue causes rapid deactivation of catalysts, and its higher concentration means more coking.

Crude Oil Impurities

• Crude oil is dense, and contains many complex hydrocarbon molecules, also has sulfur, nitrogen, and heavy metals organic impurities.

Sulfur Compounds

• Include Hydrogen sulfide (H2S) Compounds (mercaptans, sulfides, disulfides, thiophenes etc), as well as Elemental sulfur.
• Sulfur can act as catalyst poisons, and the sulfur containing compounds may cause equipment corrosion and atmospheric pollution when burned.
• The sulfur content in crude oil varies from 0.1% to 3% weight.

Sulfur in Crude Oils

• Crude oils with less than 0.5% of sulfur are called sweet crude oil and the crude oils with more than 0.5% are called sour crude oils.
• Sour crude oils require special processing and are then less expensive than the sweet crude oils
• Combustion of a sample in oxygen to convert sulfur to sulfur dioxide, which is titrated iodometrically or detected by nondispersive infrared (D-1552) is used to evaluate the sulfur percentage.

Oxygen and Nitrogen Compounds

• Oxygen compounds, such as phenols, ketones, and carboxylic acids, occur in crude oils in varying amounts.
• Nitrogen is found in lighter fractions of crude oil, and more often in heavier fractions as non-basic compounds.
• High nitrogen content in crude oils is undesirable, as it can cause catalysts poisoning and corrosion.
• Crude oils containing nitrogen above 0.25% by weight require special processing to remove it.

Metal Content

• Metals in crude oils come from the reservoir, recovery, transportation, and storage
• Even traces of metals can harm processes or cause corrosion and affect the quality of products.
• Trace metals are often found in crude oils in small quantities
• Test methods like Atomic Absorption Spectrometry, X-Ray fluorescence, are used to determine the amount of metals

Salts in Crude Oils

• Crude oils contain inorganic such as sodium chloride, magnesium chloride, and calcium chloride salts in suspension or dissolved in water (brine).
• Salts in crude oils come mostly from field production practices and handling to terminals/tankers.
• Most salts are dissolved with water and removed in desalters, but some can be dissolved in the crude oil itself.

Salts Content

• Accumulation of salts in stalls, heaters and exchangers lead to fouling that requires expensive clean up.
• Salts content can be determined via potentiometric titration method
• The amount of salts will determine crude oil quantity needed to consider the crude oil desalting.

Major Refinery Products by Market Demand

• LPG
• Gasoline
• Jet fuels
• Diesel fuels
• Home heating oils

LPG

• Varieties of LPG bought and sold include mixes that are primarily propane, mixes that are primarily butane, and the more common, mixes including both propane (60%) and butane (40%).
• Winter more propane, in the summer season more butane is needed.
• Propylene and butylenes usually also present in small concentration.
• A powerful odorant, ethanethiol, is added so that leaks can be detected easily

LPG Storage

• LPG are stored in large spherical tanks equipped with approved pressure relief valve on top.
• These LPG storage tanks are filled between 80%-85% of their capacity to allow expansion of the containted liquid.
• Since LPG is heavier than air it goes along floors and settles in low spots where ignition or suffocation hazards can occur if not dealt with.

Main Use of LPG

• Heating and engines

Gasoline

• Highly flammable liquid hydrocarbon mixture, derived from petroleum containing C5-C8 hydrocarbons
• Used as fuel for a combustion engine in automobiles, motorcycles, and small trucks

Octane Number

• A value indicates the resistance of a motor fuel to knock
• Based on a scale in which isooctane is 100 (minimal knock), heptane is 0 (bad knock). Gasoline pumps typically post octane number as an average of two different values, a research octane number and a motor octane rating.

Research and Motor Octane Number

• Gasoline pumps typically post octane numbers as an average of two different values: PON = (RON + MON)/2.
• Research octane number (RON) determined with test @ low speed of 600rpm (performance in cities).
• Motor octane number (MON) determined with test @ high speed of 900rpm (performance in highways).
• The octane number that is posted will be average of the two values. If RON is 98 and MON is 90, the PON comes out to be PON=94.

Motor Gasoline Characteristics

• Critical properties include:
  • RVP
  • Boiling range
  • Antiknock characteristics
  • Desirable Sulfur content ( < 300 PPM)
• RVP measures the vapor pressure exerted by a vapor of liquid and dissolved gases measured at 100° F; the RVP must meet these conditions:
  • Start: Gasoline vaporizes to provide ignitable mixture
  • restart: Gasoline doesn't to expand in injection apparatus and must let air come

Diesel Fuel

• Used for high speed engine's such as trucks and buses
• Properties: volatility, viscosity, ignition quality, sulfur content, % aromatics and cloud point
• Ignition properties expressed as CETANE NUMBER, which is comparable to gasoline octane number
• Scale indicates a fuel's tendency to knock
• Rating comparing fuel performance in engine Standard Engine is evaluated with
• • Cetane (HIGH IGNITION QUALITYCN=100)
• Alpha-Methyl-Naphthalene (LOW IGNITION QUALITY=CN=0)

Jet Fuel

• The most expensive distillate fuel used for commercial aviation and military aircraft
• Primary fraction of jet fuel blending is the kerosene fraction, from atmospheric Distillation.
• The most important characteristic is no freezing in the cold temperatures of the skies (-50 °C)

Heating Oil

• Fuel oils are N°1 and N°2
  • Fuel Oil N°1: similar to kerosene fuel with a higher pour point.
  • Fuel Oil N°2: similar to diesel fuel -Critical properties include sulfur content, pour point, distillation, and flash point
• Blended from Naphtha, Kerosene, Diesel and cracked Gas Oil.