LLDPE is produced by the addition of alpha-olefins - butene, hexene or octene - during the polymerisation of ethylene to give a resin with a similar density to LDPE but the linearity of HDPE. Solution, slurry or gas phase processes are used to make LLDPE but the licensing of low-cost gas phase technology by Union Carbide (now Univation) and later BP Chemicals (Ineos) has contributed to the popularity of this resin. Many processes can swing between LLDPE and HDPE production although many plants tend to be dedicated to one of the two resins.
In the gas phase process, ethylene with the comonomer and hydrogen are fed to the base of a fluid bed reactor into which the catalyst is injected. Polymerisation takes place at 60-100oC and 22 bar pressure. The polymer particles formed are kept in a fluidised state by the gas stream. The polymer leaves the reactor as a white powder and is sent to a degasser where unreacted olefins are removed. Advantages claimed for the gas phase route include low temperature operation and lower operating costs.
The recent introduction of metallocene catalysts enables the production of resins with narrow molecular weight distribution giving much improved physical properties. The latest generation metallocenes are said to overcome the poor processability problems and can produce resins with properties similar to high pressure LDPE. Some companies are developing non-metallocene single site catalysts for LLDPE. New catalyst systems are also allowing more effective use of comonomers to improve performance such that claims have been made of butene copolymers with the performance of traditional hexene copolymers, and similarly for hexene copolymers with octene copolymer performance.
Webinar - Understanding Polyethylene Margins
To understand the margin and cost curve analysis behind the Asian polyethylene market and the methodology of our data collection, click on the link to view and listen to the archived version of the presentation.
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Polyethylene linear low density
Price Reports
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Polyethylene linear low density
Uses and Outlook
Global demand for linear low density polyethylene (LLDPE) has been strong and growing ahead of GDP in most industrial regions of the world. Estimates put world growth rates at around 6-7%/year with North America and Europe somewhat lower, while Asia is higher. By 2004, world production of LLDPE had surpassed 16m tonnes, according to SRI Consulting.
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