Braskem, Brazil’s leading petrochemical producer, and Dow Chemical’s local subsidiary each have announced plans to make polyethylene, a plastic commonly used in packaging, from sugarcane-based ethanol.

The companies tout the product as far more eco-friendly than conventional polyethylene, which is made from oil-based naphtha, because its production involves dramatically lower carbon-dioxide emissions.

Though the technology to make ethanol-based polyethylene has been around for 30 years, only now do economic conditions favor putting the process to large-scale use, experts say. That’s the case in part because the local ethanol supply is growing to serve Brazil’s fast-expanding fleet of flex-fuel cars, which run on gasoline or ethanol and account for 90% of new cars produced here. Brazil is the world’s second-ranking ethanol producer after the United States and the world’s leading exporter.

Also aiding the economics of ethanol-based polyethylene are declining ethanol-production costs and rising prices for the oil needed to make naphtha.

Polyethylene made from ethanol has substantially the same chemical structure and physical properties as the naphtha-based variety. Both, while non-biodegradable, are recyclable. But only 15% of the polyethylene produced in Brazil is recycled, says Plastivida, a plastics industry association that promotes recycling. Neither Braskem nor Dow plan to recycle the so-called green polyethylene.

There are several varieties of polyethylene: linear low-density (LLDPE), which is used to make shrink wrap; low-density (LDPE), used to produce shrink wrap as well as plastic cups and plates; and high-density (HDPE), for manufacturing fruit and vegetable grocery bags as well as various types of plastic bottles.

CO2 gains cited

Braskem and Dow call ethanol-based polyethylene “green” because sugarcane captures, or sequesters, carbon dioxide (CO2) as it grows, offsetting the CO2 emissions that occur in the compound’s manufacture. Those emissions occur as ethanol is heated to convert it to ethylene gas, when tractors are used in sugarcane cultivation and as sugarcane leaves decompose.

According to Braskem, the net CO2 balance will be 2.5 kilos of CO2 captured for each kilo of green polyethylene produced. Dow, which uses a different measuring methodology, says its net CO2 balance will be 2 kilos captured for each kilo of polyethylene produced.

Braskem, Latin America’s leading polyethylene producer, will be the first to put sugarcane-based polyethylene on the market. It plans by 2009 to open a US$100 million plant that will export 80% of its 200,000-metric-ton annual output of the product. The company, which will make all three types of polyethylene using the new process, is now negotiating contracts with ethanol suppliers.

“European importers who transform polyethylene into flex-wrap and grocery sacks have told us that they are willing to pay 30% to 40% more for green polyethylene because [they] want to contribute to reducing greenhouse gas emissions,” says Antônio Morschbacker, Braskem’s manager of green polymers. “These companies also can use this green purchasing as a public relations tool.”

Dow Brasil, which makes naphtha-based polyethylene in Argentina but not Brazil, has formed a partnership with Crystalsev, Brazil’s third-ranking ethanol producer, to build a 350,000 metric-ton-per-year green LLDPE plant by 2011. Unlike Braskem’s plant, the Dow factory will be integrated, producing ethanol and polyethylene under the same roof—and alongside a Crystalsev sugarcane plantation. Dow will sell its product domestically.

Electricity from bagasse

Dow’s integrated plant will generate all the energy it needs by burning sugarcane waste, called bagasse. Braskem, meanwhile, will buy ethanol from plants that also generate energy from bagasse. Another environmental benefit of the sugarcane-based process is that it consumes less water. Vinhoto, a liquid byproduct of ethanol production, is diluted and used to fertilize and irrigate sugarcane plantations. And while sugarcane also requires other fertilizers, it does not need as much as other crops such as corn, another ethanol feedstock.

Some experts nevertheless have questions about ethanol-based polyethylene. By boosting ethanol demand, they say, it could fuel environmental pressures as sugarcane plantations consume more land. Elisabeth Grimberg of the Instituto Polis, a nonprofit that focuses on industrial pollution, notes that soot, smoke and CO2 are released when sugarcane stalks are burned to destroy leaves. And to complement vinhoto, she points out, sugarcane plantations need nitrogen and ammonia-based fertilizers, which cause CO2 emissions in their production and can exhaust the soil.

“To determine how eco-friendly ethanol-based polyethylene really is, you need to factor in all the environmental impacts,” Grimberg says. “Only then can you compare the environmental advantages of one production process over the other.”