Chemical Glossary



para-Xylene is an aromatic compound with two methyl groups substituted onto the benzene ring at opposite positions. Para-xylene is recovered from a mixed xylenes stream by adsorption and by isomerisation of C8 aromatics. Almost all para-xylene consumed for chemicals production is used for the production of PTA and DMT, which are used in polyester production.

Petrochemical Feedstocks

Petrochemical Feedstocks are those groupings of feedstock materials that are consumed by the petrochemical industry. Conventionally these feed streams are obtained from refinery operations, however the last 20 years has seen non refinery streams, such as ethane extracted from natural gas, grow in importance as a feedstock.


Phenol is a major commodity chemical intermediate produced from cumene. Phenol is used to produce phenolic resins for wood binding and bisphenol-A for polycarbonate resins. Other engineering applications include the production of caprolactam and adipic acid, which are nylon intermediates. It can also be used directly in some medical and water treatment applications, e.g. anesthetic, disinfectant, exfoliate in cosmetic surgery, acetyl salicylic acid (aspiron) and slimicide. Phenol production is principally from the reaction of propylene and benzene to cumene, then cumene oxidation; hence phenol is classed as a propylene derivative. A white, crystalline powder at room temperature, phenol has for a long time been produced directly from coal distillation, although the volumes from this source are now small relative to propylene-based production. Phenol production is widespread globally with the exception of the Middle East, although capacity is expected to develop there also.

Phthalic Anhydride

Phthalic anhydride is an aromatics derivative produced by the oxidation of ortho-xylene. Phthalic anhydride is used to make phthalate plasticizers, which are used for PVC production. Phthalic anhydride is also used in the production of alkyd resins and unsaturated polyester resins.


Polycarbonate is a resilient engineering resin with excellent optical properties. It is commonly made from bisphenol A linked by carbonate groups (O-CO-O) in the Engineering Polymers family. Polycarbonate is an engineering resin that exhibits good strength and high clarity thus used in technical applications such as optical media and automotive applications such as transparent construction sheet, automotive headlamps, CDs and DVDs. Polycarbonates are also compounded with ABS and used in thin walled electronic applications such as mobile phones and laptop computer cases. PC faces some competition from other glass-like polymers such as PMMA and PS resin. It is stronger than PMMA and has a better light transmission characteristics than glasses.

Polyester Family

The Polyester Intermediates are the family of chemicals used in the production of the polymer polyethylene terephthalate, also known as polyester, which is used for fibre and packaging applications.

Polyethylene Terephthalate (PET) Bottle Grade

PET bottle grade is a transparent polyethylene terephthalate polymer used mainly for bottling carbonated soft drinks and mineral water. The production of PET bottle grade is by solid state polymerisation (SSP) of PET melt phase, which increases the viscosity of the polymer by vacuum treatment, but involves no other raw materials. Due to the ubiquitous usage of PET bottle grade, plants are located in all regions.

Polyethylene Terephthalate (PET) Melt Phase

PET Melt Phase is the basic, amorphous grade of PET (polyethylene terephthalate) which can be used directly for the production of polyester fibre or upgraded to PET bottle grade by solid state polymerisation (SSP). PET Melt phase is produced by the melt-phase polymerisation of terephthalic acid (from PTA or DMT) with MEG. PET melt phase plants for fibre production are increasingly concentrated in Asia, while PET melt phase plants linked to PET bottle grade operations continue to be built around the world.


Polymer is the name given to a solid that is constructed by the repeated addition of simple monomer units. The majority of petrochemical value chains end in the production of a useful polymer material, with examples including polyethylene, polystyrene and polyester.


Polyolefins is the name given to the polymers of the olefin family. By convention these are the single double bond olefins and the grouping does not contain rubber compounds that can be produced by polymerising butadiene.

Polypropylene (PP)

Polypropylene (PP) is the propylene analogue of polyethylene and is also a member of the polyolefin family. PP has a higher chemical and temperature resistance than the polyethylenes. It also has a higher toughness than HDPE and can be used in applications that experience cycling loads. PP's mechanical properties are allowing it to grow into markets that previously specified Engineering Polymers, such as under bonnet applications in the automotive industry. PP goods are commonly marked with a 5 following the recycling codes developed by the American Society of the Plastics Industry. PP is commonly produced using specialized Ziegler-Natta catalysts in slurry reactors.

Polystyrene (PS)

Polystyrene (PS) is a solid aromatic polymer made from the monomer styrene. A commodity polymer used largely for semi/rigid packaging applications, it can be melted at high temperature for molding or extrusion, and then resolidified. It is commonly used as insulation in building structures and packaging. Other applications include electronics housing.


Polyurethanes are made by the reaction of isocyanates (MDI and TDI) with polyols. Polyurethanes can be in the form of flexible or rigid foams, elastomers, coatings, adhesives and low molecular weight additives. MDI is typically used for rigid foams, whereas TDI is used mostly in flexible foams.

Polyvinyl Chloride (PVC)

Polyvinyl chloride (PVC) is a versatile polymer, produced by the polymerisation of VCM. PVC is almost always converted into a compound by the incorporation of additives, allowing it to be used in both rigid and flexible forms as a plastic resin. Extensively used in the construction sector, PVC has a wide variety of applications, including pipe, siding and window/door profiles, wire and cable insulation, rigid film/sheet, and flooring.


Propane is a member of the LPG (Liquified Petroleum Gases) and paraffin families, consisting of three saturated carbon atoms in a straight chain. The term liquified petroleum gas refers to its main production route as a liquified stream produced by the repressurisation of gas that separated from crude oil on extraction from underground. Propane is highly valued as a heating fuel, particularly in developing economies, and hence has a highly seasonal demand and pricing profile.

Propionaldehyde or Propanal

Propionaldehyde (or propanal) is a three-carbon aldehyde commonly produced by reacting syngas with ethylene. Its major use is in the manufacture of trimethylolethane via condensation with methanol. This is used in the manufacture of alkyd resins.


Propylene is the second member of the olefin chemical family, consisting of three hydrocarbons in a chain, linked by one double bond and one single bond. The double bond in propylene is less accessible and less reactive than that in ethylene and hence reaction conditions tend to be harsher for a given synthesis reaction. Propylene is also produced (to a lesser extent than ethylene) from the pyrolytic cracking in a steam cracker of a wide variety of hydrocarbons. Significant volumes of propylene are also produced from refinery FCC units.

Propylene Glycol

Mono, di and tri-propylene glycol are produced commercially. Monopropylene glycol (MPG) is the most widely used, and is found in cosmetics, foods, pharmaceuticals and laundry detergents, as well as substituting for monoethylene glycol in anti-freeze formulations where lower toxicity is required or chiefly to make unsaturated polyester resins used in fibreglass composites for construction applications. Most of polyester based fibreglass, however, are produced from propylene oxide. Di and tri-propylene glycol are mainly used in the production of resins and elastomers. A clear, viscous liquid at room temperature, propylene glycol is produced by the hydrolysis reaction of propylene oxide and water.

Propylene oxide

Propylene oxide is a chemical intermediate mainly used for the production of polyether polyols-which are in turn used in urethane foams, and also in production of propylene glycol, with the remainder consumed in glycol ethers. Propylene oxide is produced from propylene by two routes: mainly chlorohydrin route or to a lesser extent indirect route via hydroperoxidation of isobutane or ethylbenzene producing tertiary butyl alcohol (PO/TBA) or styrene monomer (PO/SM) as co-product respectively. Chlorohydrin route is more energy intensive, produces high by-product yield of little application, and involved chlorine waste disposal. Nevertheless, it remains economically healthy, producing 40 to 50% of PO in the United States. Some propylene oxide is also produced from cumene. Propylene oxide production is widespread outside the Middle East, although projects are now under development in the Middle East.

Purified Terephthalic Acid (PTA)

Purified terephthalic acid (PTA) is produced by the oxidation of terephthalic acid (TA) in acetic acid, and its subsequent purification, often via crystallisation. Prior to the development of the purification process, the crude TA was esterified into DMT, which could then be purified. PTA is the main ingredient in the production of PET melt phase, although much smaller volumes are used in the production of thermosetting resins and coatings. PTA production is highly capital intensive, and tends to be located close to demand centres.


Pygas is the term given to the aromatic rich stream that is extracted within a steam cracker, immediately after the feedstream has been cracked and cooled. It is extracted by washing the stream with water, and is then separated from the water phase. Pygas composition varies according to both the cracker feedstock and the severity of operation, containing valuable quantities of benzene and gasoline components.