Polyethylene from Ethanol

Introduction – Polyethylene

Polyethylene (PE) is a polymer of long chains of the monomer ethylene (IUPAC name "ethylene"). It is one of the world’s most common plastics, with a wide range of uses and over 60 million tons produced worldwide every year. Several different categories exist, based mostly on density and branching. Common ones are high-density PE (HDPE, plastic # 2) and low-density PE (LDPE, plastic # 4). Polyethylene is created through polymerization of ethylene, a simple two-carbon molecule. Polyethylene is not considered biodegradable, therefore significant environmental issues are associated with its use. When disposables are involved, every effort should be made to replace PE with biodegradable alternatives. However, resistance to biodegradation can also be a desired effect with some applications. For example, geomembranes are often made of HDPE and are widely used as liners for fish ponds, constructed wetlands and biogas digesters. Excellent chemical resistance allows for widespread use in storage applications. PE can also be a useful starting material for digital fabrication.

Polyethylene – the current situation

Almost all PE today is derived from petroleum. In a process that consumes large amounts of fossil fuels, a petroleum feedstock is cracked at high temperatures. After distillation and purification in large, capital-intensive facilities, ethylene is produced. This is then polymerized to polyethylene, a process that again involves high temperatures, pressures and often toxic organic solvents. Clearly not ideal.

Polyethylene from ethanol

Ethene is a very simple organic molecule (C2H4) that does not have to be derived from petroleum. In fact, it can easily be produced from ethanol by a dehydration reaction. Recently, a Brazilan-Japanese joint venture announced the "Green Polyethylene Project", with sugarcane as the feedstock. Commercial-scale production of this "bio-polyethylene" is planned for 2011.

Links

Wikipedia entry on polyethylene [1]

Wikipedia entry on High-density polyethylene (HDPE) [2]

Wikipedia entry on Low-density polyethylene (LDPE) [3]

Patent: Production of ethylene from ethanol [4]

News: Brazilian company to make renewable polyethylene [5]