Renewable Polyethylene

Biopolyethylene (also known as renewable polyethylene) is polyethylene made out of ethanol, which becomes ethylene after a dehydration process. It can be made from various feedstocks including sugar cane, sugar beet, and wheat grain.^[1]

The final product (polyethylene) is identical to naphta- or gas-based polyethylene, therefore maintaining the physical properties for conversion into plastics products and also maintaining its recycling properties. Polyethylene however requires specific recycling procedures which may negate its benefits over traditional plastics.

The first plant

World’s first announced ethanol-based chemical pole, totally integrated from sugarcane to polyethylene, was recently announced by The Dow Chemical Company, in conjunction with Crystalsev, a large sugar and ethanol producer in Brazil.^[2] The pole is said to be projected to produce 770 million pounds per year of renewable LLDPE (linear low-density polyethylene), will begin construction in 2008, and is slated to start production in 2011. The amount of ethanol needed to make one metric ton of polyethylene is roughly two metric tons, as dehydration takes half of the weight in water, from the sugar cane based ethanol, before converting into ethylene (C
2H
4).

Benefits

One of the main environmental benefits of this project will be the sequestration of roughly 2 kg of CO₂ per kg of polyethylene produced, which comes from the CO₂ absorbed by the sugar cane while growing, minus the CO₂ emitted through the production process. Over 1.5 billion pounds of CO₂ will be annually removed from the atmosphere, which is equivalent to the fossil emission of 1,400,000 Brazilian citizens (according to the Carbon Dioxide Information Analysis Center in 2004)^[3] or 5% of all São Paulo City CO₂ equivalent emissions (according to the São Paulo municipal green house gas emissions inventory or "Inventário de Emissões de Gases de Efeito Estufa do Município de São Paulo" in 2005). Renewable polyethylene is non-biodegradable and can be recycled in the same waste streams as traditional polyethylenes (HDPE, LDPE, LLDPE) as it is chemically identical. ^[4]

Furthermore, the pole is said to be projected to generate its own energy from the burning of the sugar cane bagasse, which will not only power the whole pole, but also will be able to sell enough energy to light up a half million people city, and will be available during the dry season, which is exactly the time when it is most needed, and the hydroelectric plants are short of water reserves.

Production

Braskem and Toyota Tsusho Corporation started joint marketing activities for producing green polyethylene from sugar cane. Braskem will build a new facility at their existing industrial unit in Triunfo, RS, Brazil with an annual production capacity of 200,000 short tons (180,000,000 kg), and will produce high-density polyethylene (HDPE) and low-density polyethylene (LDPE) from bioethanol derived from sugarcane.^[5]

References