Propene - Production

Production

Propene is produced from fossil fuels—petroleum, natural gas, and, to a much lesser extent, coal. Propene is a byproduct of oil refining and natural gas processing. During oil refining, ethylene, propene, and other compounds are produced as a result of cracking larger hydrocarbon molecules to produce hydrocarbons more in demand. A major source of propene is cracking intended to produce ethylene, but it also results from refinery cracking producing other products. Propene can be separated by fractional distillation from hydrocarbon mixtures obtained from cracking and other refining processes; refinery-grade propene is about 50 to 70%.

A shift to lighter steam cracker feedstocks with relatively lower propene yields and reduced motor gasoline demand in certain areas has created an imbalance of supply and demand for propene, and on-purpose production methods are becoming increasingly significant.

On-purpose propylene production technologies include:

Olefin metathesis, also known as disproportionation, is a reversible reaction between ethylene and butenes in which double bonds are broken and then reformed to form propylene. Propylene yields of about 90 wt% are achieved. This option may also be used when there is no butene feedstock. In this case, part of the ethylene feeds an ethylene-dimerization unit that converts ethylene into butene.

Propane dehydrogenation converts propane into propylene and by-product hydrogen. The propylene from propane yield is about 85 wt%. Reaction by-products (mainly hydrogen) are usually used as fuel for the propane dehydrogenation reaction. As a result, propylene tends to be the only product, unless local demand exists for hydrogen. This route is popular in regions, such as the Middle East, where there is an abundance of propane from oil/gas operations. In this region, the propane output is expected to be capable of supplying not only domestic needs, but also the demand from China, where many PDH projects are scheduled to go on stream. However, as natural gas offerings in the USA are significantly increasing due to the rising exploitation of shale gas, propane prices are decreasing. Chemical companies are already planning to establish PDH plants in the USA to take advantage of the low price raw material, obtained from shale gas. Numerous plants dedicated to propane dehydrogenation are currently under construction around the world. There are already five licensed technologies.

Methanol-to-Olefins/Methanol-to-Propylene converts synthesis gas (syn-gas) to methanol, and then converts the methanol to ethylene and/or propylene. The process also produces water as by-product. Synthesis gas is produced from the reformation of natural gas or by the steam-induced reformation of petroleum products such as naphtha, or by gasification of coal. A large amount of methanol is required to make a world-scale ethylene and/or propylene plant.

High Severity fluid catalytic cracking (FCC) uses traditional FCC technology under severe conditions (higher catalyst-to-oil ratios, higher steam injection rates, higher temperatures, etc.) in order to maximize the amount of propylene and other light products. A high severity FCC unit is usually fed with gas oils (paraffins) and residues, and produces about 20-25 wt% propylene on feedstock together with greater volumes of motor gasoline and distillate byproducts.

Olefins Cracking includes a broad range of technologies that catalytically convert large olefins molecules (C4-C8) into mostly propylene and small amounts of ethylene.

Propene production has remained static at around 35 million tonnes (Europe and North America only) from 2000 to 2008, but it has been increasing in East Asia, most notably Singapore and China. Total world production of propene is currently about half that of ethylene.