Occupational Hygiene in the Basic Petroleum Chemistry Oil & Gas Industry Day 1 – Section 3 Basic Petroleum Chemistry

Introduction Composition Of Crude And Petroleum Products 1. Names of hydrocarbons and their groupings into hydrocarbon types. 2. Most important physical and chemical properties of specific hydrocarbons. 3. General chemical nature of crude petroleum and the refining operations which produce the petroleum products. Names of hydrocarbons and their groupings into hydrocarbon types. Most important physical and chemical properties of specific hydrocarbons. General chemical nature of crude petroleum and the refining operations which produce the petroleum products.

PARAFFINS Formula = Cn.H(2n+2) where n = the number of Carbon atoms Crude petroleum and its products contain compounds of carbon and hydrogen. Carbon has a combining power (bonds) of 4 and hydrogen has a combining power (bond) of 1. Simplest hydrocarbon molecule contains one Carbon atom and 4 hydrogen atoms and is C1H4 known as METHANE. Natural Gas PARAFFINS Crude petroleum and its products contain predominantly compounds of carbon and hydrogen. In organic chemistry Carbon has a combining power (bonds) of 4 and hydrogen has a combining power (bond) of 1. On this basis the simplest hydrocarbon molecule contains one Carbon atom and 4 hydrogen atoms and is C1H4 known as METHANE. This is Natural Gas and can be found in gas fields and when compressed into a liquid is LNG (Liquified Natural Gas)

Methane CH4 Ethane C2H6 Propane C3H8 iso-Butane C4H10 n-Butane C4H10

OLEFINS Formula = C(n).H(2n) where n = the number of Carbon atoms BUTENE C4H8 known as Butene-1 one double linkage (bond) on Double, or even a triple linkage between carbon atoms. This type of linkage increases chemical activity.

NAPHTHENES Naphthene or cyclic structure - carbon atoms form a ring with only two linkages available for hydrogen or substation (described later). The simplest form is 3 carbons CYCLOPROPANE C3H6

Cyclohexane C6H12

AROMATICS Combination of hydrogen and carbon based on a six carbon atoms ring with an unsaturated type linkage. BENZENE C6H6 Benzene is a known carcinogen and requires special health considerations. Benzene in gasolines is generally limited to 1% or less Series of compounds known as AROMATICS AROMATICS There also exists a peculiar and specific combination of hydrogen and carbon based on a six carbon atoms ring with an unsaturated type linkage. BENZENE C6H6 Benzene is a known carcinogen and requires special health considerations. The content of Benzene in gasolines is generally limited to 1% or less for health and environmental reasons – refer to Benzene Program. This nucleus serves as a base for a complete series of compounds known as AROMATICS

Benzene C6H6 Toluene C7H8 Again substitution can occur with replacement of one or several hydrogen atoms with methyl, ethyl, propyl and other radicals. (a radical or more precisely, a ‘free radical’ is an atom, molecule, or ion that has unpaired valence electrons or an open electron shell, and therefore may be seen as having one or more "dangling" covalent bonds which needs to join with another free bond to become stable). For example methyl benzene is TOLUENE, another component of crude and a significant component of gasoline due to its high octane rating

Xylene isomers para Xylene C8H10 ortho Xylene C8H10 meta Xylene C8H10 The aromatics are more chemically active then the paraffins and cycloparaffins but less reactive then the unsaturates. Some of these aromatics have ototoxic effect - This can result in sensor neural hearing loss, dysequilibrium, or both. Either may be reversible and temporary, or irreversible and permanent. Xylene or Dimethyl Benzene comes in 3 isomer forms, ortho- (or 1,2 dimethyl benzene), meta- ( or 1,3 dimethyl benzene), and para- xylene (1,4 dimethyl benzene); all with the same formula but slightly differing properties such as boiling point, melting point, etc. Xylene isomers

Two aromatic rings can join to form Naphthalene Three aromatic rings can join to form Anthracene Two or three rings may be condensed to form naphthalene or anthracene

Four or more aromatic rings can join to form ‘Polynuclear Aromatics’ As with the other hydrocarbons these can extend the joining of the rings to form complex structures, for example C20H12 Benzo(a)pyrene which is a potential carcinogen. By contrast another isomer Benzo(e)pyrene is not considered a potential carcinogen. These multi-ring compounds are known as Polycyclic Aromatic-Hydrocarbons (PAH) or polynuclear aromatic hydrocarbons (PNA). Naphthalene is the simplest example of a PAH. These PAHs occur in oil, coal, and tar deposits, and are produced as by-products of fuel burning (whether fossil fuel or biomass). As a pollutant, they are of concern because some compounds have been identified as carcinogenic, mutagenic, and teratogenic. PAHs are also found in cooked foods. C20H12 Benzo(a)pyrene which is a potential carcinogen.

PONA Paraffins, Olefins, Naphthenes and Aromatics. (PONA) Petroleum chemists and engineers use PONA to describe the broad composition various refinery hydrocarbon streams (or distillation cuts or boiling ranges) and their approximate “PONA” composition. So far we have been discussing only the carbon-hydrogen compounds in four broad categories - Paraffins, Olefins, Naphthenes and Aromatics. Petroleum chemists and engineers refer to this as PONA, and it is used to describe the broad composition various refinery hydrocarbon streams (or distillation cuts or boiling ranges) and their approximate “PONA” composition. For example a crude may comprise 45% Paraffins, 0% Olefins (because they tend to react and form other compounds), 35% Naphthenes and 20% Aromatics. This allows the refinery process engineer to understand the changes in overall chemical PONA mix obtained from the various refinery processes. Summary of Product Types produced from Petroleum

Summary of Product Types from Petroleum Carbon Number Boiling Range Name Deg. C Deg. F C1-C4 <0 <30 Natural gas (LNG), Liquified Petroleum Gas (LPG) C4-C12 0-200 30-392 Gasoline, Naphtha C12-C15 200-300 392-572 Kerosene, Jet Fuel C15-C25 300-400 572-750 Gas Oil, Heating Oil, Diesel, Lube Oil >C25 >400 >750 Residuum, Asphalt (Bitumen), Paraffin Wax

Other hydrocarbon derivatives Oxygen – specifically hydroxyl group – OH produce ALCOHOLS Methane becomes Methanol Ethane becomes Ethanol (found in wines, spirits and beer) Propane becomes Propanol (or Isopropanol used in hand cleaners). Other hydrocarbon derivatives If we consider other elements beside Carbon and Hydrogen, such as Oxygen, Sulphur, Nitrogen when combined with the carbon and hydrogen we get the following broad groups Oxygen – specifically hydroxyl group – OH produce ALCOHOLS The substitution of a single hydroxyl radial for a hydrogen in an aliphatic (alkane) hydrocarbon produces an alcohol Methane becomes Methanol Ethane becomes Ethanol (found in wines, spirits and beer) Propane becomes Propanol (or Isopropanol used in hand cleaners). Here are some examples:

When the hydroxyl radical joins the aromatic ring, Benzene + OH radical we get Phenol which is both toxic and corrosive and detrimental to the finished gasoline product. With two hydroxyl groups substituted for hydrogens in the aliphatic hydrocarbon we get GLYCOLS such as Ethylene Glycol (which is used as a coolant)

Sulphur Compounds Hydrogen Sulphide H2S – a special case- Toxic Gas Aliphatic Sulphides – Mercaptans R-SH Sulphur Compounds The sulphur compounds found in petroleum and its products are with the exception of Hydrogen Sulphide H2S, are a combination of sulphur or a sulphur bearing radical with a hydrocarbon radical. Typical sulphur compounds are listed below: This gas is particularly toxic and special programs are required to deal with this hazard – refer to Hydrogen Sulphide Programme Mercaptans (Thio Alcohols)   Aliphatic sulphides Aliphatic Disulphides such as diethyl disulphide (C2H5S)2 are one of the many combinations of carbon, hydrogen and sulphur, including aliphatic polysulphides. Since sulphur compounds are usual odourous and also detrimental to the product in that they form combustion products, which are usually both odourous and environmentally unacceptable, sulphur compound removal processes are used at the refineries to produce petroleum products acceptable to the public and the environment.

Aliphatic Sulphides Aliphatic Sulphides – Mercaptans

Chemical Reactions In a Refinery Gasoline Treating Mercaptans are mixed with Caustic solution (Sodium Hydroxide NaOH) to react and produce an organic sodium sulphide which is soluble in water and removed. Gasoline Treating Here the mercaptans in the unfinished ‘sour’ (bad odour) gasoline are mixed with sodium hydroxide solution to neutralise the mercaptans into sodium salts. This process is called ‘sweetening’ .

Cracking Reaction Fluidized Catalytic Cracker (FCC) or Thermofor Catalytic Cracker (TCC). T Catalyst ‘cracks’ or breaks longer hydrocarbon molecules into smaller fractions Produces wide range of hydrocarbons from gases through to heavy residuum Cracking Reaction This is carried out in the Fluidized Catalytic Cracker (FCC) or the older Thermofor Catalytic Cracker (TCC). The catalyst is a Silica/Alumina powder or beads and the process ‘cracks’ or breaks the longer hydrocarbon molecules into smaller fractions and as a by-product also produces gases such as hydrogen, methane and other light gases. The result is a wide range of hydrocarbons from gases through to heavy residuum – sometimes called ‘Synthetic crude’

Alkylation Reaction Reaction of two gases Isobutane with Butene/Propylene to produce Alkylate Alkylate- gasoline blend stock high octane (RON 100) used in motor gasolines & aviation gasolines. Catalyst - Sulphuric acid or Hydrofluoric acid Alkylation Reaction To react two gases using a catalyst Sulphuric acid or Hydrofluoric acid to produce Alkylate – a gasoline blend stock of high octane (RON 100) used in motor gasolines and aviation gasolines.

Isomerization Reaction Changes straight chain paraffins into isomers which have higher octane rating normal Pentane (octane 68) into Isopentane (octane 92) Gasoline blend stock Isomerization Reaction This process changes straight chain paraffins into isomers which have a higher octane rating (R+0 is Research Octane number with no alkyl lead content). In this example normal Pentane with a low octane of 68 into Isopentane with an octane of 92. This provides a blend stock for gasolines

Dehydrocyclization Reaction Changes straight chain paraffin into a ring or cyclic formation (aromatic) with increase in octane rating Normal Heptane C7H16 (octane zero) transformed into Toluene (octane 120) Valuable gasoline blend stock. Hydrogen gas produced - used in other processes. Dehydrocyclization Reaction This process uses a catalyst and temperature to treats straight chain hydrocarbons by changing the straight chain paraffin into a ring or cyclic formation (aromatic) and significantly increasing the octane rating, in this example normal Heptane C7H16 with an octane rating of zero is transformed into Toluene with an octane rating of 120 and a valuable gasoline blend stock. In the process hydrogen gas is produced which can be used in other processes.

Hydrogenation – Sulphur removal Breaking the molecule and converting the sulphur radical into hydrogen sulphide and joining the hydrogen atoms to the free linkages (bonds) Hydrogenation – Sulphur removal Many of the hydrocarbons contain Sulphur atoms which are deleterious to product performance and therefore must be removed. This is achieve by breaking the molecule and converting the sulphur radical into hydrogen sulphide and joining the hydrogen atoms to the free linkages (bonds) In this example Benz(b)thiophene C8H6S is reacted with 3 molecules of Hydrogen breaking the Sulphur cyclic ring to produce H2S gas and changing the ring into an ethyl group connected to the benzene ring. The sulphur has been removed from the molecule as H2S and a valuable gasoline component Ethyl Benzene C8H10 has been produced In the following example the mercaptans represented as R-SH are reacted with a Cobalt/Molybdenum catalyst and hydrogen to produce a light hydrocarbon and H2S gas which can be stripped out of the liquid hydrocarbon.

Sulphur Recovery Hydrogen sulphide gas is converted into elemental yellow sulphur by burning in air to convert to Sulphur Dioxide SO2 SO2 then reacted with Alumina catalyst to produce elemental sulphur. Sulphur Recovery In many of the processes hydrogen sulphide is present or generated, and this must be also processes or destroyed (by burning in a flare). This hydrogen sulphide gas can be converted into elemental yellow sulphur by burning in air to convert to Sulphur Dioxide SO2 and then reacting this with Alumina catalyst to produce elemental sulphur, which can be sold. This particular example is known as the Claus Process but other sulphur recovery processes also exist. .

Naphthene Dehydrogenation Catalyst & temperature break hydrogen from cyclic structure Cyclohexane to form Benzene and 6 Hydrogen atoms Octane increase 83 to 100+. Naphthene Dehydrogenation In the previous example Hydrogen was used to break open the Sulphur compound and added to form a new molecule. In this next example by the use of a catalyst and temperature, the hydrogen is subtracted from the cyclic structure Cyclohexane to form a benzene ring - Benzene and release 6 atoms of hydrogen. In the process changing a naphthene structure to an aromatic structure and improving the octane of the hydrocarbon from 83 to 100+.

Oxidiser Reaction - Bitumens Reacts heavy vacuum treated residuum with air to polymerise heavy hydrocarbons (heavier molecules) Produces bitumen for road making. Two hydrogen atoms stripped off and reacted with air (oxygen) to produce water (steam) Oxidiser Reaction - Bitumens This process reacts heavy vacuum treated residuum with air to polymerise the heavy hydrocarbons to produce bitumen for road making. Two hydrogen atoms are stripped off and reacted with air (oxygen) to produce water (steam) and make heavier molecules – bitumen of varies grades depending on the amount of oxidising (polymerisation)

Basic Petroleum Chemistry End of Section 3 Basic Petroleum Chemistry