Polyethylene from Ethanol
Introduction – Polyethylene
Polyethylene (PE) is a polymer of long chains of the monomer ethylene (IUPAC name "ethene"). 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 types are high-density PE (HDPE; plastic # 2) and low-density PE (LDPE; plastic # 4). Polyethylene is not biodegradable, therefore significant environmental issues are associated with its use. Recycling of PE is relatively straightforward. 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 in 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 of PE allows for widespread use in storage applications. PE is also useful as a material for digital fabrication.
Polyethylene – the current situation
Almost all PE today is derived from petroleum. In a very energy-intensive process, 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, high pressures and often toxic organic solvents. Clearly not an ideal situation.
Polyethylene from ethanol
Ethene is a very simple two-carbon organic molecule (C2H4) that does not have to be derived from petroleum. In fact, it can easily be produced from ethanol in a dehydration reaction. This has been known for many decades, but was not cost-competitive at low oil prices. Recently, a Brazilan-Japanese joint venture announced the "Green Polyethylene Project", with sugarcane as the feedstock. Commercial-scale introduction of this "BIO-polyethylene" is planned for 2011. We welcome PE to the club of bioplastics and believe that small-scale production from ethanol can be made practical.
Possible use in carbon sequestration
If renewable energy is used in the polymerization step, bio-PE could even be considered a carbon-negative plastic. Recently, wood-HDPE or bamboo-HDPE composite materials have become popular, combining good structural properties with durability. Taking this idea further, a form of carbon sequestration can be proposed, in which completely dry biomass is stored above ground. Plastic sheets are then used to limit moisture, preventing biodegradation ("plastic-enabled carbon landfill").
Links
Wikipedia entry on polyethylene [1]
Wikipedia entry on High-density polyethylene (HDPE) [2]
Wikipedia entry on Low-density polyethylene (LDPE) [3]
Patents: Production of [4] and process for obtaining [5] ethylene from ethanol
News: Brazilian company to make renewable polyethylene [6]
Collaboration Discussions
Given the availability of patents, are they expired? Can someone research the patents to the point of proposing a rigorous procedure for producing a test batch of bio-polyethylene, with the hope of scaleup for small-scale production?